Synopsis Hydraulic Arm

ABSTRACT Flexible hydraulic arm is a complicated system which coupled by mechanics and hydraulics. It is widely applied in all kinds of large engineering equipments, such as concrete pump truck, bridge monitor truck, arm frame of crane, etc. The arm system of the hydraulic arm is a multi-body system with redundant freedom, strong nonlinear, coupled with rigid and flexible characters. So it is of great theoretic value and real engineering significance to study the arm system of the hydraulic arm. In this theme, the movement of flexible hydraulic arm and hydraulic cylinders are separately analyzed with flexible multi-body dynamics, and the mechanical hydraulic dynamic model of the driving system and the arm system is built with Lagrange Equation and Virtual Work Theory. And the dynamic differential equation is built with the driving force of the hydraulic cylinder as the main force. With the track programming and the optimization method, the dynamic converse problem of the arm end track is researched, so as to get the optimized rotation angle when the arm end reaches the expected point. By using the PD control theory, without decoupling and rank-decreasing, only with feedback from the hydraulic system to realize the close loop control of the arm end position, pose and movement, the relationship between the hydraulic system and the end position & pose is studied, so that the flexible distortion is reduced and the liberation is restrained. What’s more, the simulation model of the mechanical arms is built by the dynamic simulation software. The simulation result proves that the movement equation built by this way can clearly describe each dynamic character of the mechanical arms.

BACKGROUND

The basic concept used behind the operation is PASCAL’s LAW. This law states that when a pressure is applied at one point of a fluid contained in a constrained volume, then the pressure due to that force is equally transmitted to all the points of the fluid, which are acted upon by the same pressure. Using the same principle, we applied pressure to fluid in syringe which is transmitted to other end of tube which is connected to a syringe. This motion of the syringe is used to move the links or parts of the mechanism which are attached to respective syringes This hydraulic arm is designed to be a pick and place robot. A hydraulic arm is powered by fluid under pressure. Hydraulic power is widely used for robots, especially in situations where lots of power is needed. The extensive use of hydraulics is to transmit power due to the fact that properly constructed fluid power systems possess a number of favourable characteristics. They eliminate the need for complicated systems of gears, cams, and levers. Hydraulic robots use pressurized oil or water as the main working power.

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PROBLEM FORMULATION

With the advancement in technology there is something new coming out every now and then, in this process of adapting to new technologies basic simpler technologies are left out. Advanced technology requires a lot on technological and monetary help. The term basic/simpler means that even a tedious or intricate job can be with real ease only if an individual sticks to the basics. So, in this study we create a hydraulic robotic arm by reducing its cost and by using simpler materials which are easily available.

OBJECTIVES Some of the objectives of this study are mentioned below:  Eliminate the use of complicated gears, cams and levers.  Fluid is not subjected to breakage as compared to mechanical parts.  Large power can be controlled by a small orifice (Syringe).  Fluids provide wide range of motion ( Rotary and Longitudinal)

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CHAPTER 1 Introduction to fluid power Fluid power is a term which was created to include the generation, control, and application of smooth, effective power of pumped or compressed fluids (either liquids or gases) when this power is used to provide force and motion to mechanisms. This force and motion maybe in the form of pushing, pulling, rotating, regulating, or driving. Fluid power includes hydraulics, which involves liquids, and pneumatics, which involves gases. Liquids and gases are similar in many respects. The differences are pointed out in the appropriate areas of this manual. This manual presents many of the fundamental concepts in the fields of hydraulics and pneumatics. It is intended as a basic reference for all personnel of the Navy whose duties and responsibilities require them to have a knowledge of the fundamentals of fluid power. Consequently, emphasis is placed primarily on the theory of operation of typical fluid power systems and components that have applications in naval equipment. Many applications of fluid power are presented in this manual to illustrate the functions and operation of different systems and components. However, these are only representative of the many applications of fluid power in naval equipment. Individual training manuals for each rate provide information concerning the application of fluid power to specific equipment for which the rating is responsible.

1.1 History The word hydraulics is based on the Greek word for water, and originally covered the study of the physical behaviour of water at rest and in motion. Use has broadened its meaning to include the behaviour of all liquids, although it is primarily concerned with the motion of liquids. Hydraulics includes the HYDRAULIC ARM

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manner in which liquids act in tanks and pipes, deals with their properties, and explores ways to take advantage of these properties.

The time passed and the science of hydraulics kept on developing as more and more efficient ways of converting hydraulic energy into useful work were discovered. The subject of hydraulics which dealt with the physical behaviour of water at rest or in motion remained a part of civil engineering for a long time. However, after the invention of James Watt's "steam engine", there arose the need for efficient transmission of power, from the point of generation to the point of use. Step by step many types of mechanical devices such as the line shaft, gearing systems, pulleys and chains were discovered. Therefore it was thought the concept of transmitting power through fluids under pressure. This indeed was a new field of hydraulics embracing different subjects such as power transmission and control of mechanical motion, while also dealing with the characteristics of fluids under pressure. To distinguish this branch of hydraulics from water hydraulics, a new name called "Industrial hydraulics" or more commonly, "oil hydraulics" was invented. The significance behind choosing this name lies in the fact that this field of hydraulics employs oil as a medium of power transmission. Water which is considered to be practically incompressible is still used in present-day hydro technology. The term water hydraulics has since been coined for this area of engineering. Because of their superior qualities such as resistance to corrosion as well as their sliding and lubricating capacity, oils which are generally mineral-based are the preferred medium for transmission of hydraulic power.

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Fig.1

1.2 What is hydraulic power? The term hydraulic power means that it is a system of interconnected pipes carrying pressurized liquid used to transmit mechanical power from a power source, like a pump, to hydraulic equipment like lifts or motors.

Fig. 2

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1.3 How does hydraulic power work? Hydraulic power works on the principle of Pascal’s law which states that when a pressure is applied at one point of a fluid contained in a constrained volume, then the pressure due to that force is equally transmitted to all the points of the fluid.

Fig. 3 The above figure shows pick and place robotic arm by hydraulic control. Its working steps as under below:  Compressed fluid comes from the syringe.  By using syringes and pipes we control the flow of fluid and the working of different arms.  By using low RPM motor the column rotates to object.  By gaining fluid power in syringe which is placed in arm opens jaws by using hinge attachment.  Arm become down to object by gaining fluid in syringe.  Object comes between two jaws.  Arm rise up by when main syringe is pulled back by creating suction in the syringe placed near the hinge attachment.  Whole assemblies rotate by low RPM motor at right place.  Arm become down to place object at right place by using above processes HYDRAULIC ARM

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1.4 Pascal’s Law The foundation of modern hydraulics was established when Pascal discovered that pressure in a fluid acts equally in all directions. This pressure acts at right angles to the containing surfaces. If some type of pressure gauge, with an exposed face, is placed beneath the surface of a liquid (fig. 2-6) at a specific depth and pointed in different directions, the pressure will read the same. Thus, I can say that pressure in a liquid is independent of direction. Pressure due to the height of a liquid, at any level, depends on the depth of the fluid from the surface. If the exposed face of the pressure gauges, figure 2-6, is moved closer to the surface of the liquid, the indicated pressure will be less. When the depth is doubled, the indicated pressure is doubled. Thus the pressure in a liquid is directly proportional to the depth. Consider a container with vertical sides (fig. 2-7) that is 1 foot long and 1 foot wide. Let it be filled with water 1 foot deep, providing 1cubic foot of water. I learned earlier in this chapter that 1 cubic foot of water high 62.4pounds. Using this information and equation, P = F/A, I can calculate the pressure on the bottom of the container. .....................equation (1)

Since there are 144 square inches in 1 square foot

This can be stated as follows: the height of a column of water 1 foot high, having a cross-sectional area of 1 square inch, is 0.433 pound. If the depth of the column is tripled, the height of the column will be 3 x 0.433, or 1.299pounds, and the pressure at the bottom will be1.299 lb/in2 (psi), since pressure equals the force divided by the area. Thus, the pressure at any depth HYDRAULIC ARM

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in a liquid is equal to the height of the column of liquid at that depth divided by the cross-sectional area of the column at that depth. The volume of a liquid that produces the pressure is referred to as the fluid head of the liquid. The pressure of a liquid due to its fluid head is also dependent on the density of the liquid. If I let A equal any cross-sectional area of a liquid column and h equal the depth of the column, the volume becomes Ah. Using equation2-4, D = W/V, the height of the liquid above area A is equal to AhD.

Fig. 4 Pressure of a liquid is independent of direction

Fig. 5—Water pressure in a 1-cubic-foot

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1.4.1 Independent of direction Since pressure is equal to the force per unit area, set A equal to 1. Then the formula pressure becomes P = h D . . . . . . . . . . Equation (2). It is essential that h and D be expressed in similar units. That is, if D is expressed in pounds per cubic foot, the value of h must be expressed in feet. If the desired pressure is to be expressed in pounds per square inch, the pressure formula, equation 2-5, becomes . . . . . . . . . . . Equation (3). Pascal was also the first to prove by experiment that the shape and volume of a container in no way alters pressure. Thus in figure2-8, if the pressure due to the height of the liquid at a point on horizontal line H is 8 psi, the pressure is 8 psi everywhere at level H in the system. Equation 2-5 also shows that the pressure is independent of the shape and volume of a container.

1.5 components of a syringe based hydraulic arm? Innovation components allow for greater alternative and innovative designs. They are not required, but are suggested to bring more engineering and innovation to the activity. Only a few innovation components are usually needed to create alternative designs, so your supply of innovation components can be used for many hydraulic arms and other activities. Here are the components that are used in this project:           

Hydraulic cylinders (Syringe with clips and mounts) Hydraulic Lines (Vinyl Tubing) Perpendicular aluminium square bar Chip board Screws Square nuts Washers Connector strips Tyres Buffers Dummy motor

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 Anything else things like the recycling bin, wood, metal, plastic, broken toys, etc.

CHAPTER 2 Forces in liquids The study of liquids is divided into two main parts:  liquids at rest (hydrostatics)  liquids in motion (hydraulics) The effects of liquids at rest can often be expressed by simple formulas. The effects of liquids in motion are more difficult to express due to frictional and other factors whose actions cannot be expressed by simple mathematics. Liquids have a definite volume but take the shape of their containing vessel. There are two additional characteristics I must explore prior to proceeding. Liquids are almost incompressible. For example, if a pressure of 100 pounds per square inch (psi) is applied to a given volume of water that is at atmospheric pressure, the volume will decrease HYDRAULIC ARM

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by only 0.03 percent. It would take a force of approximately 32 tonnes to reduce its volume by 10 percent; however, when this force is removed, the water immediately returns to its original volume. Other liquids behave in about the same manner as water. Another characteristic of a liquid is the tendency to keep its free surface level. If the surface is not level, liquids will flow in the direction which will tend to make the surface level. 2.1 Liquids at rest In studying fluids at rest, we are concerned with the transmission of force and the factors which affect the forces in liquids. Additionally, pressure in and on liquids and factors affecting pressure are of great importance. 2.2 Pressure and force The terms force and pressure are used extensively in the study of fluid power. It is essential that we distinguish between the terms. Force means a total push or pull. It is the push or pull exerted against the total area of a particular surface and is expressed in pounds or grams. Pressure means the amount of push or pull (force) applied to each unit area of the surface and is expressed in pounds per square inch (lb/in2) or grams per square centimetre (gm/cm2). Pressure maybe exerted in one direction, in several directions, or in all directions. 2.2.1 Computing Force, Pressure and Area: A formula is used in computing force, pressure, and area in fluid power systems. The formula is expressed below: F=P*A Where:  P refers to pressure,  F indicates force,  A represents area. Force equals pressure time’s area. Pressure equals force divided by area. By rearranging the formula this statement may be condensed into.

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P=

F A

Since area equals force divided by pressure, the formula is written

The figure below illustrates a memory device for recalling the different variations of this formula. Any letter in the triangle may be expressed as the product or quotient of the other two, depending on its position within the triangle. For example, to find area, consider the letter A as being set off to itself, followed by an equal sign. Now look at the other two letters. The letter F is above the letter P; therefore,

Fig. 6 NOTE: Sometimes the area may not be expressed in square units. If the surface is rectangular, you can determine its area by multiplying its length (say, in inches) by its width (also in inches). The majority of areas you will consider in these calculations are circular in shape. Either the radius or the diameter may be given, but you must know the radius in inches to find the area. The radius is onehalf the diameter. To determine the area, use the formula for finding the area of a circle. This is written A =where A is the area A=π r 2 , π is 3.1416 (3.14 or 3 1/7 for most calculations),

And r2 indicates the radius squared.

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2.3 Transmission of forces through liquids When the end of a solid bar is struck, the main force of the blow is carried straight through the bar to the other end. This happens because the bar is rigid. The direction of the blow almost entirely determines the direction of the transmitted force. 2.3.1 Fluid statics Fluid statics or Hydrostatic is the pressure exerted by a fluid at equilibrium due to the force of gravity. A fluid in this condition is known as a hydrostatic fluid. The hydrostatic pressure can be determined from a control volume analysis of an infinitesimally small cube of fluid. Since pressure is defined as the force exerted on a test area (p = F/A, with p: pressure, F: force normal to area, A: area), And the only force acting on any such small cube of fluid is the weight of the fluid column above it; hydrostatic pressure can be calculated according to the following formula:

, Where:      

p is the hydrostatic pressure (Pa), ρ is the fluid density (kg/m3), g is gravitational acceleration (m/s2), A is the test area (m2), z is the height (parallel to the direction of gravity) of the test area (m), z0 is the height of the zero reference point of the pressure (m).

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For water and other liquids, this integral can be simplified significantly for many practical applications, based on the following two assumptions: Since many liquids can be considered incompressible, a reasonably good estimation can be made from assuming a constant density throughout the liquid. (The same assumption cannot be made within a gaseous environment.) Also, since the height h of the fluid column between z and z0 is often reasonably small compared to the radius of the Earth, one can neglect the variation of g. Under these circumstances, the integral boils down to the simple formula:

Where h is the height z − z0 of the liquid column between the test volume and the zero reference point of the pressure. Note that this reference point should lie at or below the surface of the liquid. Otherwise, one has to split the integral into two (or more) terms with the constant ρliquid and ρ(z')above. For example, the absolute pressure compared to vacuum is:

Hydrostatics is about the pressures exerted by a fluid at rest. Any fluid is meant, not just water. It is usually relegated to an early chapter in Fluid Mechanics texts, since its results are widely used in that study. The study yields many useful results of its own, however, such as forces on dams, buoyancy and hydraulic actuation, and is well worth studying for such practical reasons. It is an excellent example of deductive mathematical physics, one that can be understood easily and completely from a very few fundamentals, and in which the predictions agree closely with experiment. There are few better illustrations of the use of the integral calculus, as well as the principles of ordinary statics, available to the student. A great deal can be done with only elementary mathematics. Properly adapted, the material can be

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used from the earliest introduction of school science, giving an excellent example of a quantitative science with many possibilities for hands-on experiences. The definition of a fluid deserves careful consideration. Although time is not a factor in hydrostatics, it enters in the approach to hydrostatic equilibrium. It is usually stated that a fluid is a substance that cannot resist a shearing stress, so that pressures are normal to confining surfaces. Geology has now shown us clearly that there are substances which can resist shearing forces over short time intervals, and appear to be typical solids, but which flow like liquids over long time intervals. Such materials include wax and pitch, ice, and even rock. A ball of pitch, which can be shattered by a hammer, will spread out and flow in months. Ice, a typical solid, will flow in a period of years, as shown in glaciers, and rock will flow over hundreds of years, as in convection in the mantle of the earth. Shear earthquake waves, with periods of seconds, propagate deep in the earth, though the rock there can flow like a liquid when considered over centuries. The rate of shearing may not be strictly proportional to the stress, but exists even with low stress. Viscosity may be the physical property that varies over the largest numerical range, competing with electrical resistivity. A study of hydrostatics can also include capillarity, the ideal gas laws, the velocity of sound, and hygrometry. These interesting applications will not be discussed in this article. At a beginning level, it may also be interesting to study the volumes and areas of certain shapes, or at a more advanced level, the forces exerted by heavy liquids on their containers. Hydrostatics is a very concrete science that avoids esoteric concepts and advanced mathematics. It is also much easier to demonstrate than Newtonian mechanics.

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2.3.2 Pressure By a fluid, we have a material in mind like water or air, two very common and important fluids. Water is incompressible, while air is very compressible, but both are fluids. Water has a definite volume; air does not. Water and air have low viscosity; that is, layers of them slide very easily on one another, and they quickly assume their permanent shapes when disturbed by rapid flows. Other fluids, such as molasses, may have high viscosity and take a long time to come to equilibrium, but they are no less fluids. The coefficient of viscosity is the ratio of the shearing force to the velocity gradient. Hydrostatics deals with permanent, time-independent states of fluids, so viscosity does not appear, except as discussed in the Introduction. A fluid, therefore, is a substance that cannot exert any permanent forces tangential to a boundary. Any force that it exerts on a boundary must be normal to the boundary. Such a force is proportional to the area on which it is exerted, and is called a pressure. We can imagine any surface in a fluid as dividing the fluid into parts pressing on each other, as if it were a thin material membrane, and so think of the pressure at any point in the fluid, not just at the boundaries. In order for any small element of the fluid to be in equilibrium, the pressure must be the same in all directions (or the element would move in the direction of least pressure), and if no other forces are acting on the body of the fluid, the pressure must be the same at all neighbouring points. Therefore, in this case the pressure will be the same throughout the fluid, and the same in any direction at a point (Pascal's Principle). Pressure is expressed in units of force per unit area such as dyne/cm 2, N/cm2 (Pascal), pounds/in2 (psi) or pounds/ft2 (psf). The axiom that if a certain volume of fluid were somehow made solid, the equilibrium of forces would not be disturbed is useful in reasoning about forces in fluids.

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On earth, fluids are also subject to the force of gravity, which acts vertically downward, and has a magnitude γ = ρg per unit volume, where g is the acceleration of gravity, approximately 981 cm/s2 or 32.15 ft/s2, ρ is the density, the mass per unit volume, expressed in g/cm3, kg/m3, or slug/ft3, and γ is the specific weight, measured in lb/in3, or lb/ft3 (pcf). Gravitation is an example of a body force that disturbs the equality of pressure in a fluid. The presence of the gravitational body force causes the pressure to increase with depth, according to the equation dp = ρg dh, in order to support the water above. We call this relation the barometric equation, for when this equation is integrated, we find the variation of pressure with height or depth. If the fluid is incompressible, the equation can be integrated at once, and the pressure as a function of depth h is p = ρgh + p0. The density of water is about 1 g/cm3, or its specific weight is 62.4 pcf. We may ask what depth of water gives the normal sealevel atmospheric pressure of 14.7 psi, or 2117 psf. This is simply 2117 / 62.4 = 33.9 ft of water. This is the maximum height to which water can be raised by a suction pump, or, more correctly, can be supported by atmospheric pressure. Professor James Thomson illustrated the equality of pressure by a "curtain-ring" analogy shown in the diagram. A section of the toroid was identified, imagined to be solidified, and its equilibrium was analyzed.

Fig. 7

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The forces exerted on the curved surfaces have no component along the normal to a plane section, so the pressures at any two points of a plane must be equal, since the fluid represented by the curtain ring was in equilibrium. The right-hand part of the diagram illustrates the equality of pressures in orthogonal directions. This can be extended to any direction whatever, so Pascal's Principle is established. This demonstration is similar to the usual one using a triangular prism and considering the forces on the end and lateral faces separately. When gravity acts, the liquid assumes a free surface perpendicular to gravity, which can be proved by Thomson's method. A straight cylinder of unit crosssectional area (assumed only for ease in the arithmetic) can be used to find the increase of pressure with depth.

Fig. 8

Indeed, we see that p2 = p1 + ρgh. The upper surface of the cylinder can be placed at the free surface if desired. The pressure is now the same in any direction at a point, but is greater at points that lie deeper. From this same figure, it is easy to prove Archimedes's Principle that the buoyant force is equal to the weight of the displaced fluid, and passes through the centre of mass of this displaced fluid. Ingenious geometric arguments can be used to substitute for easier, but less transparent arguments using calculus. For example, the force on acting on one side of an inclined plane surface whose projection is AB can be found as in the diagram HYDRAULIC ARM

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at the right. O is the

point at which the prolonged

projection intersects the

free surface.

Fig. 9 The line AC' perpendicular to the plane is made equal to the depth AC of point A, and line BD' is similarly drawn equal to BD. The line OD' also passes through C', by proportionality of triangles OAC' and OAD'. Therefore, the thrust F on the plane is the weight of a prism of fluid of cross-section AC'D'B, passing through its centroid normal to plane AB. Note that the thrust is equal to the density times the area times the depth of the centre of the area, but its line of action does not pass through the centre, but below it, at the centre of thrust. The same result can be obtained with calculus by summing the pressures and the moments, of course.

2.4 Atmospheric Pressure and its Effects Suppose a vertical pipe is stood in a pool of water, and a vacuum

pump

applied to the upper end. Before we start the pump, the water levels outside and inside the pipe are equal, and the pressures on the surfaces are also equal, and equal to the atmospheric pressure. Now start the pump.

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Fig. 10 When it has sucked all the air out above the water, the pressure on the surface of the water inside the pipe is zero, and the pressure at the level of the water on the outside of the pipe is still the atmospheric pressure. Of course, there is the vapour pressure of the water to worry about if you want to be precise, but we neglect this complication in making our point. We require a column of water 33.9 ft high inside the pipe, with a vacuum above it, to balance the atmospheric pressure. Now do the same thing with liquid mercury, whose density at 0 °C is 13.5951 times that of water. The height of the column is 2.494 ft, 29.92 in, or 760.0 mm. This definition of the standard atmospheric pressure was established by Regnault in the mid-19th century. In Britain, 30 in Hg (inches of mercury) had been used previously. As a practical matter, it is convenient to measure pressure differences by measuring the height of liquid columns, a practice known as manometry. The barometer is a familiar example of this, and atmospheric pressures are traditionally given in terms of the length of a mercury column. To make a barometer, the barometric tube, closed at one end, is filled with mercury and then inverted and placed in a mercury reservoir. Corrections must be made for temperature, because the density of mercury depends on the temperature, and the brass scale expands, for capillarity if the tube is less than about 1 cm in diameter, and even slightly for altitude, since the value of g changes with altitude. The vapour pressure of mercury is only 0.001201 mmHg at 20°C, so a correction from this source is negligible. For the usual case of HYDRAULIC ARM

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a mercury column (α = 0.000181792 per °C) and a brass scale (&alpha = 0.0000184 per °C) the temperature correction is -2.74 mm at 760 mm and 20°C. Before reading the barometer scale, the mercury reservoir is raised or lowered until the surface of the mercury just touches a reference point, which is mirrored in the surface so it is easy to determine the proper position. An aneroid barometer uses a partially evacuated chamber of thin metal that expands and contracts according to the external pressure. This movement is communicated to a needle that revolves in a dial. The materials and construction are arranged to give a low temperature coefficient. The instrument must be calibrated before use, and is usually arranged to read directly in elevations. An aneroid barometer is much easier to use in field observations, such as in reconnaissance surveys. In a particular case, it would be read at the start of the day at the base camp, at various points in the vicinity, and then finally at the starting point, to determine the change in pressure with time. The height differences can be calculated from h = 60,360 log(P/p) [1 + (T + t - 64)/986) feet, where P and p are in the same units, and T, t are in °F. An absolute pressure is referred to a vacuum, while a gauge pressure is referred to the atmospheric pressure at the moment. A negative gauge pressure is a (partial) vacuum. When a vacuum is stated to be so many inches, this means the pressure below the atmospheric pressure of about 30 in. A vacuum of 25 inches is the same thing as an absolute pressure of 5 inches (of mercury). Pressures are very frequently stated in terms of the height of a fluid. If it is the same fluid whose pressure is being given, it is usually called "head," and the factor connecting the head and the pressure is the weight density ρg. In the English engineer's system, weight density is in pounds per cubic inch or cubic foot. A head of 10 ft is equivalent to a pressure of 624 psf, or 4.33 psi. It can also be considered an energy HYDRAULIC ARM

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availability of ft-lb per lb. Water with a pressure head of 10 ft can furnish the same energy as an equal amount of water raised by 10 ft. Water flowing in a pipe is subject to head loss because of friction. Take a jar and a basin of water. Fill the jar with water and invert it under the water in the basin. Now raise the jar as far as you can without allowing its mouth to come above the water surface. It is always a little surprising to see that the jar does not empty itself, but the water remains with no visible means of support. By blowing through a straw, one can put air into the jar, and as much water leaves as air enters. In fact, this is a famous method of collecting insoluble gases in the chemical laboratory, or for supplying hummingbird feeders. It is good to remind oneself of exactly the balance of forces involved. Another application of pressure is the siphon. The name is Greek for the tube that was used for drawing wine from a cask. This is a tube filled with fluid connecting two containers of fluid, normally rising higher than the water levels in the two containers, at least to pass over their rims.

Fig. 11 In the diagram, the two water levels are the same, so there will be no flow. When a siphon goes below the free water levels, it is called an inverted siphon. If the levels

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in the two basins are not equal, fluid flows from the basin with the higher level into the one with the lower level, until the levels are equal. A siphon can be made by filling the tube, closing the ends, and then putting the ends under the surface on both sides. Alternatively, the tube can be placed in one fluid and filled by sucking on it. When it is full, the other end is put in place. The analysis of the siphon is easy, and should be obvious. The pressure rises or falls as described by the barometric equation through the siphon tube. There is obviously a maximum height for the siphon which is the same as the limit of the suction pump, about 34 feet. Inverted siphons (which are really not siphons at all) are sometimes used in pipelines to cross valleys. Differences in elevation are usually too great to use regular siphons to cross hills, so the fluids must be pressurized by pumps so the pressure does not fall to zero at the crests. The Quabbin Aqueduct, which supplies water to Boston, includes pumped siphons. As the level in the supply container falls, the pressure difference decreases. In some cases, one would like a source that would provide a constant pressure at the outlet of the siphon.

Fig. 12 An ingenious way to arrive at this is shown in the figure, Mariotte's Bottle. The plug must seal the air space at the top very well. A partial vacuum is created in the HYDRAULIC ARM

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air space by the fall of the water level exactly equal to the pressure difference between the surface and the end of the open tube connecting to the atmosphere. The pressure at this point is, therefore, maintained at atmospheric while water is delivered. The head available at the nozzle as shown is equal to h. This would make a good experiment to verify the relation V = √(2gh) since h and the horizontal distance reached by the jet for a given fall can both be measured easily, or the discharge from an orifice. The term "siphon" is often used in a different sense. In biology, a siphon is simply a tubular structure. A thermal siphon is a means to circulate a liquid by convection. A soda siphon is a source of carbonated water, while siphon coffee (or vacuum coffee) is made in an apparatus where the steam from boiling water pushes hot water up above the coffee and filter, and then the vacuum causes the water to descend again when the heat is removed (invented by Löff in 1830). None of these arrangements is actually a siphon in the physicist's sense. The siphon tube used in irrigation, and perhaps Thomson's siphon recorder of 1858, do use the siphon principle. The occasional spelling "syphon" is not supported by the Greek source. In some cases, especially in plumbing, siphon action is not desired, especially when it may allow dirty water to mix with clean. In these cases, vacuum breakers may be used at high points to prevent this. Siphons work because of atmospheric pressure, and would not operate in a vacuum. In the case of water, pressure reduction would eventually reach the vapour pressure and the water would boil. Mercury, which has a very low vapour pressure, would simply separate leaving a Torricellian vacuum. The siphon would be re-established if the pressure is restored. A liquid column is unstable under a negative pressure.

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Evangelista Torricelli (1608-1647), Galileo's student and secretary, a member of the Florentine Academy of Experiments, invented the mercury barometer in 1643, and brought the weight of the atmosphere to light. The mercury column was held up by the pressure of the

atmosphere,

vacui as

supposed.

Aristotle

had

not

by horror

Fig. 13 Torricelli's early death was a blow to science, but his ideas were furthered by Blaise Pascal (1623-1662). Pascal had a barometer carried up the 1465 m high Puy de Dôme, an extinct volcano in the Auvergne just west of his home of ClermontFerrand in 1648 by Périer, his brother-in-law. Pascal's experimentum crucis is one of the triumphs of early modern science. The Puy de Dôme is not the highest peak in the Massif Central--the Puy de Sancy, at 1866 m is, but it was the closest. Clermont is now the centre of the French pneumatics industry. The remarkable Otto von Guericke (1602-1686), Burgomeister of Magdeburg, Saxony, took up the cause, making the first vacuum pump, which he used in vivid demonstrations of the pressure of the atmosphere to the Imperial Diet at Regensburg in 1654. Famously, he evacuated a sphere consisting of two wellfitting hemispheres about a foot in diameter, and showed that 16 horses, 8 on each side, could not pull them apart. An original vacuum pump and hemispheres from 1663 are shown at the right (photo edited from the Deutsches Museum; see link below). He also showed that air had weight, and how much force it did require to HYDRAULIC ARM

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separate evacuated hemispheres. Then, in England, Robert Hooke (1635-1703) made a vacuum pump for Robert Boyle (1627-1691). Christian Huygens (16291695) became interested in a visit to London in 1661 and had a vacuum pump built for him. By this time, Torricelli's doctrine had triumphed over the Church's support for horror vacui. This was one of the first victories for rational physics over the illusions of experience, and is well worth consideration. Pascal demonstrated that the siphon worked by atmospheric pressure, not by horror vacui, by means of the apparatus shown at the left. The two beakers of mercury are connected by a three-way tube as

shown,

with

the

upper

branch open to the atmosphere.

Fig. 14 As the large container is filled with water, pressure on the free surfaces of the mercury in the beakers pushes mercury into the tubes. When the state shown is reached, the beakers are connected by a mercury column, and the siphon starts, emptying the upper beaker and filling the lower. The mercury has been open to the atmosphere all this time, so if there were any horror vacui, it could have flowed in at will to soothe itself. The mm of mercury is sometimes called a torr after Torricelli, and Pascal also has been honoured by a unit of pressure, a newton per square metre or 10 dyne/cm 2. A cubic centimetre of air weighs 1.293 mg under standard conditions, and a cubic HYDRAULIC ARM

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metre 1.293 kg, so air is by no means even approximately weightless, though it seems so. The weight of a sphere of air as small as 10 cm in diameter is 0.68 g, easily measurable with a chemical balance. The pressure of the atmosphere is also considerable, like being 34 ft under water, but we do not notice it. A bar is 106 dyne/cm2, very close to a standard atmosphere, which is 1.01325 bars. In meteorology, the millibar, mb, is used. 1 mb = 1.333 mmHg = 100 Pa = 1000 dyne/cm2. A kilogram-force per square centimetre is 981,000 dyne/cm2, also close to one atmosphere. In Europe, it has been considered approximately 1 atm, as in tire pressures and other engineering applications. As we have seen, in English units the atmosphere is about 14.7 psi, and this figure can be used to find other approximate equivalents. For example, 1 psi = 51.7 mmHg. In Britain, tons per square inch have been used for large pressures. The ton in this case is 2240 lb, not the American short ton. 1 tsi = 2240 psi, 1 tsf = 15.5 psi (about an atmosphere!). The fluid in question here is air, which is by no means incompressible. As we rise in the atmosphere and the pressure decreases, the air also expands. To see what happens in this case, we can make use of the ideal gas equation of state, p = ρRT/M, and assume that the temperature T is constant. Then the change of pressure in a change of altitude dh is dp = -ρg dh = -(pM/RT)gdh, or dp/p = -(Mg/RT)dh. This is a little harder to integrate than before, but the result is ln p = -Mgh/RT + C, or

ln(p/p0)

=

-Mgh/RT,

or

finally

p

=

p0exp(-Mgh/RT).

In

an isothermal atmosphere, the pressure decreases exponentially. The quantity H = RT/Mg is called the "height of the homogeneous atmosphere" or the scale height, and is about 8 km at T = 273K. This quantity gives the rough scale of the decrease of pressure with height. Of course, the real atmosphere is by no means isothermal close to the ground, but cools with height nearly linearly at about 6.5°C/km up to an altitude of about 11 km at middle latitudes, called the tropopause. Above this is a region of nearly constant temperature, the stratosphere, and then at some higher HYDRAULIC ARM

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level the atmosphere warms again to near its value at the surface. Of course, there are variations from the average values. When the temperature profile with height is known, we can find the pressure by numerical integration quite easily. The atmospheric pressure is of great importance in meteorology, since it determines the winds, which generally move at right angles to the direction of most rapid change of pressure, that is, along the isobars, which are contours of constant pressure. Certain typical weather patterns are associated with relatively high and relatively low pressures, and how they vary with time. The barometric pressure may be given in popular weather forecasts, though few people know what to do with it. If you live at a high altitude, your local weather reporter may report the pressure to be, say, 29.2 inches, but if you have a real barometer, you may well find that it is closer to 25 inches. At an elevation of 1500 m (near Denver), the atmospheric pressure is about 635 mm, and water boils at 95 °C. In fact, altitude is quite a problem in meteorology, since pressures must be measured at a common level to be meaningful. The barometric pressures quoted in the news are reduced to sea level by standard formulas, that amount to assuming that there is a column of air from your feet to sea level with a certain temperature distribution, and adding the weight of this column to the actual barometric pressure. This is only an arbitrary 'fix' and leads to some strange conclusions, such as the permanent winter highs above high plateaus that are really imaginary. 2.5 Multiplication of forces Consider the situation in figure , where the input piston is much smaller than the output piston. Assume that the area of the input piston is 2square inches. With a resistant force on the output piston a downward force of 20 pounds acting on the HYDRAULIC ARM

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input piston creates a pressure of

20 2

or 10 psi in the fluid. Although this force is

much smaller than the force applied in figures 2-9 and 2-10, the pressure is the same. This is because the force is applied to a smaller area.

Fig15.— Transmitting force through a small pipe

This pressure of 10 psi acts on all parts of the fluid container, including the bottom of the output piston. The upward force on the output piston is 200 pounds (10 pounds of pressure on each square inch). In this case, the original force has been multiplied tenfold while using the same pressure in the fluid as before. In any system with these dimensions, the ratio of output force to input force is always ten to one, regardless of the applied force. For example, if the applied force of the input piston is 50 pounds, the pressure in the system will be 25 psi. This will support a resistant force of 500 pounds on the output piston.

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Fig. 16— Multiplication of forces

The system works the same in reverse. If I change the applied force and place a 200-pound force on the output piston (fig.), making it the input piston, the output force on the input piston will be one-tenth the input force, or 20pounds. Therefore, if two pistons are used in a fluid power system, the force acting on each piston is directly proportional to its area, and the magnitude of each force is the product of the pressure and the area of each piston.

CHAPTER 3 Hydraulic fluids During the design of equipment that requires fluid power, many factors are considered in selecting the type of system to be used—hydraulic, pneumatic, or a combination of the two. Some of the factors are required speed and accuracy of operation, surrounding atmospheric conditions, economic conditions, availability of replacement fluid, required pressure level, operating temperature HYDRAULIC ARM

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range, contamination possibilities, cost of transmission lines, limitations of the equipment, lubricity, safety to the operators, and expected service life of the equipment. After the type of system has been selected, many of these same factors must be considered in selecting the fluid for the system. This chapter is devoted to hydraulic fluids. Included in it are sections on the properties and characteristics desired of hydraulic fluids; types of hydraulic fluids; hazards and safety precautions for working with, handling, and disposing of hydraulic liquids; types and control of contamination; and During the design of equipment that requires fluid power, many factors are considered in selecting the type of system to be used—hydraulic, pneumatic, or a combination of the two. Some of the factors are required speed and accuracy of operation, surrounding atmospheric conditions, economic conditions, availability of replacement fluid, required pressure level, operating temperature range, contamination possibilities, cost of transmission lines, limitations of the equipment, lubricity, safety to the operators, and expected service life of the equipment. After the type of system has been selected, many of these same factors must be considered in selecting the fluid for the system. This chapter is devoted to hydraulic fluids. Included in it are sections on the properties and characteristics desired of hydraulic fluids; types of hydraulic fluids; hazards and safety precautions for working with, handling, and disposing of hydraulic liquids; types and control of contamination; and sampling.

3.1 Properties If fluidity (the physical property of a substance that enables it to flow) and incompressibility Ire the only properties required, any liquid not too thick might be used in a hydraulic system. However, a satisfactory liquid for a particular system must possess a number of other properties. The most important properties and some characteristics are discussed in the following paragraphs. 3.1.1 Viscosity HYDRAULIC ARM

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Viscosity is one of the most important properties of hydraulic fluids. It is a measure of a fluid’s resistance to flow. A liquid, such as gasoline, which flows easily, has a low viscosity; and a liquid, such as tar, which flows slowly, has a high viscosity. The viscosity of a liquid is affected by changes in temperature and pressure. As the temperature of a liquid increases, its viscosity decreases. That is, a liquid flows more easily when it is hot than when it is cold. The viscosity of a liquid increases as the pressure on the liquid increases. A satisfactory liquid for a hydraulic system must be thick enough to give a good seal at pumps, motors, valves, and so on. These components depend on close fits for creating and maintaining pressure. Any internal leakage through these clearances results in loss of pressure, instantaneous control, and pump efficiency .Leakage losses are greater with thinner liquids (low viscosity). A liquid that is too thin will also allow rapid Layering of moving parts, or of parts that operate under heavy loads. On the other hand, if the liquid is too thick (viscosity too high),the internal friction of the liquid will cause an increase in the liquid’s flow resistance through clearances of closely fitted parts, lines, and internal passages. This results in pressure drops throughout the system, sluggish operation of the equipment, and an increase in power consumption. 3.1.1.1 Measurement of Viscosity Viscosity is normally determined by measuring the time required for a fixed volume of a fluid(at a given temperature) to flow through a calibrated orifice or capillary tube. The instruments used to measure the viscosity of a liquid are known as viscometers or viscosimeters. Several types of viscosimeters are in use today. The Say bolt viscometer, shown in figure, measures the time required, in seconds, for 60milliliters of the tested fluid at 100°F to pass through a standard orifice. The time measured is used to express the fluid’s viscosity, in Say bolt universal seconds or Say bolt furol seconds. The glass capillary viscometers, shown in figure, are examples of the second type of viscometer used. These viscometers are used measure kinematic viscosity. Like the Say bolt viscometer, the glass capillary measures the time in seconds required for the tested fluid to

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flow through the capillary. This time is multiplied by the temperature constant of the viscometer in use to provide the viscosity, expressed in centistokes. The following formulas may be used to convert centistokes (cSt units) to approximate Say bolt universal seconds (SUS units). For SUS values between 32 and 100

For SUS values greater than 100:

Figure 17— Saybolt viscometer

3.1.1.2 Viscosity Index The viscosity index of oil is a number that indicates the effect of temperature changes on the viscosity of the oil. A low viscosity index signifies relatively large change of viscosity with changes of temperature. In other words, the oil becomes extremely thin at high temperatures and extremely hick at low temperatures. On the other hand, a high viscosity index signifies relatively little change in viscosity over a HYDRAULIC ARM

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Figure 17.— Saybolt viscometer

wide temperature range. Ideal oil for most purposes is one that maintains a constant viscosity throughout temperature changes. The importance of the viscosity index can be shown easily by considering automotive lubricants. Oil having a high viscosity index resists excessive thickening when the engine is cold and, consequently, promotes rapid starting and prompt circulation; it resists excessive thinning when the motor is hot and thus provides full lubrication and prevents excessive oil consumption. Another example of the importance of the viscosity index is the need for a high viscosity index hydraulic oil for military aircraft, since hydraulic control systems may be exposed to temperatures ranging from below– 65°F at high altitudes to over 100°F on the ground. For the proper operation of the hydraulic control system, the hydraulic fluid must have a sufficiently high viscosity index to perform its functions at the extreme of the expected temperature range. Liquids with a high viscosity have a greater resistance to heat than low viscosity liquids which have been derived from the same smyce. The average hydraulic liquid has a relatively low viscosity. Fortunately, there is a wide choice of liquids available for use in the viscosity range required of hydraulic liquids. The viscosity index. Of an oil may be determined if its viscosity at any two temperatures is known. Tables, based on a large number of tests, are issued by the American Society for Testing and Materials (ASTM). These tables permit calculation of the viscosity index From known viscosities.

3.1.2 Density and compressibility A fluid with a specific gravity of less than 1.0 is desired when height is critical, although with proper system design, a fluid with a specific gravity greater than one can be tolerated. Where avoidance of detection by military units is desired, a fluid which sinks rather than rises to the surface of the water is desirable. Fluids having a specific gravity greater than 1.0 are desired, as leaking fluid will sink, allowing HYDRAULIC ARM

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the vessel with the leak to remains undetected. Recall from that under extreme pressure a fluid may be compressed up to 7 percent of its original volume. Highly compressible fluids produce sluggish system operation. This does not present a serious problem in small, low-speed operations, but it must be considered in the operating instructions. 3.1.3 Cleanliness Cleanliness in hydraulic systems has received considerable attention recently. Some hydraulic systems, such as aerospace hydraulic systems, are extremely sensitive to contamination. Fluid cleanliness is of primary importance because contaminants can cause component malfunction, prevent proper valve seating, cause Air in components, and may increase the response time of servo valves. Fluid contaminants are discussed later. The inside of a hydraulic system can only be kept as clean as the fluid added to it. Initial fluid cleanliness can be achieved by observing stringent cleanliness requirements ( or by filtering all fluid added to the system). 3.2 Types of hydraulic fluids There have been many liquids tested for use in hydraulic systems. Currently, liquids being used include mineral oil, water, phosphate ester, water-based ethylene glycol compounds, and silicone fluids. The three most common types of hydraulic liquids are petroleum-based, synthetic fire-resistant, and water-based fire-resistant PwSH eny bthd erir ofifia -l ru ruil smac nF Bl au

y r t ae d

c

a

t st

rr i si

e e

ee s s

t t

n

a

i t

t

si ed ds

Fig. 18 3.2.1 Petroleum based fluids The most common hydraulic fluids used in shipboard systems are the petroleumbased oils. These fluids contain additives to protect the fluid from oxidation HYDRAULIC ARM

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(antioxidant), to protect system metals from corrosion (anticorrosion), to reduce tendency of the fluid to foam (foam suppressant),and to improve viscosity. Petroleum-based fluids are used in surface ships electro- hydraulic steering and deck machinery systems, submarines’ hydraulic systems, and aircraft automatic pilots, shock absorbers, brakes, control mechanisms, and other hydraulic systems using seal materials compatible with petroleum-based fluids. 3.2.2 Synthetic fire-resistant fluids Petroleum-based oils contain most of the desired properties of a hydraulic liquid. However, they are flammable under normal conditions and can become explosive when subjected to high pressures and a source of flame or high temperatures. Non flammable synthetic liquids have been developed for use in hydraulic systems where fire hazards exist.

3.2.3 Water-based fire-resistant fluids The most widely used water-based hydraulic fluids may be classified as waterglycol mixtures and water-synthetic base mixtures. The water-glycol mixture contains additives to protect it from oxidation, corrosion, and biological growth and to enhance its load-carrying capacity. There-fore, frequent checks to maintain the correct ratio of water are important. The water-based fluid used in catapult retracting engines, jet blast deflectors, and weapons elevators and handling systems conforms to MIL-H22072.The safety precautions outlined for phosphate ester fluid and the disposal of phosphate ester fluid also apply to water-based fluid conforming to MIL-H-22072. 3.3 Functions and desired properties required The primary function of a hydraulic fluid is to convey power. In use, however, there are other important functions of hydraulic fluid such as protection of the hydraulic machine components. The table below lists the major functions of a hydraulic fluid and the properties of a fluid that affect its ability to perform that function: HYDRAULIC ARM

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Function

Property 

Low compressibility (high

bulk

modulus) Medium for power transfer and control

Medium for heat transfer



Fast air release



Low foaming tendency



Low volatility



Good

thermal

capacity

and

conductivity  Sealing Medium

Lubricant

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Adequate viscosity and viscosity index



Shear stability



Viscosity for film maintenance



Low temperature fluidity



Thermal and oxidative stability



Hydrolytic stability / water tolerance



Cleanliness and filterability

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

Demulsibility



Antiwear characteristics



Corrosion control



Proper

Pump efficiency

Special function

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to

minimize

internal leakage 

High viscosity index



Fire resistance



Friction modifications



Radiation resistance



Low

Environmental impact

Functioning life

viscosity

toxicity

when

decomposed 

Biodegradability



Material compatibility

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new

or

CHAPTER 4 Components used in the fabrication of this project 4.1 Hydraulic syringes Syringes are essentially simple hydraulic systems, as they operate by moving a liquid from one place to another. The difference is that a hydraulic system uses the liquid to move another object, syringes just move the liquid. This means that syringes are the most basic form of hydraulics. A Hydraulic system is a power transmission system that uses the force of flowing liquids to transmit power. It consists of two pistons and an oil-filled pipe connecting them. A hydraulic arm is an arm that requires a hydraulic system in order to operate. A hydraulic arm is often used for heavy, repetitive manufacturing work. They handle tasks that are difficult or dangerous to human beings by transporting objects from one place to another. A hydraulic arm works with or without the use of a computer, which controls it by rotating individual step motors connected to each joint.

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Fig. 19 4.1.1 Operation Hydraulic syringe get their power from pressurized hydraulic fluid, which is typically oil or water. The hydraulic syringe consists of a cylinder barrel, in which a piston connected to a piston rod moves back and forth. The barrel is closed on one end by the cylinder bottom (also called the cap) and the other end by the cylinder head (also called the gland) where the piston rod comes out of the cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder into two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end / head end). Flanges, trunnions, clevises, Lugs are common cylinder mounting options. The piston rod also has mounting attachments to connect the cylinder to the object or machine component that it is pushing / pulling. The piston pushes the water in the other chamber back to the reservoir. If we assume that the oil enters from cap end, during extension stroke, and the oil pressure in the rod end / head end is approximately zero, the force F on the piston rod equals the pressure P in the cylinder times the piston area A:

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During the retraction stroke, if oil is pumped into the head (or gland) at the rod end and the oil from the cap end flows back to the reservoir without pressure, the fluid pressure in the rod end is (Pull Force) / (piston area - piston rod area):

Where:  P is the fluid pressure,  Fp is the pulling force,  Ap is the piston face area  Ar is the rod cross-section area. 4.1.2 Single acting vs. double acting Single acting cylinders are economical and the simplest design. Hydraulic fluid enters through a port at one end of the cylinder, which then moves the piston to extend the rod. An external force returns the piston to its normal position and forces the hydraulic fluid back through the supply tubing to the fluid reservoir. Double acting cylinders have a port at each end, supplied with hydraulic fluid for both the retraction and extension of the piston. They are used where an external force is not available to retract the piston or where high force is required in both directions of travel. A hydraulic cylinder should be used for pushing and pulling only. No bending moments or side loads should be transmitted to the piston rod or the cylinder to prevent rapid failure of the rod seals. For this reason, the ideal connection of an hydraulic cylinder is a single clevis with a spherical ball bearing. This allows the hydraulic actuator to move and allow for any misalignment between the actuator and the load it is pushing. In my project I have used Syringes working as hydraulic cylinders. HYDRAULIC ARM

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Fig. 20 4.2 Fluid lines and fittings The control and application of fluid power would be impossible without suitable means of transferring the fluid between the reservoir, the power source, and the points of application. Fluid lines are used to transfer the fluid, and fittings are used to connect the lines to the power source and the points of application. 4.2.1 Types of lines Three types of lines is used in this system are pipe (rigid), tubing (semi rigid) and hose (flexible). There are number of factors are considered while selecting the line for particular system. These factors include the type of fluid required in system pressure and the location of the system. For example, heavy pipe might be used for a large stationary fluid power system, but comparatively height height tubing must be used in aircraft and missile systems because height and space are critical factors. Flexible hose is required in installations where units must be free to move relative to each 4.3 Pipes and tubing There are three important dimensions of any tubular product—outside diameter (OD), inside diameter (ID), and wall thickness. Sizes of pipe are listed by the HYDRAULIC ARM

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nominal (or approximate) ID and the wall thickness. Sizes of tubing are listed by the actual OD and the wall thickness. 4.3.1 Selection of pipes and tubing The material, ID, and wall thickness are the three primary considerations in the selection of lines for a particular fluid power system. The ID of a line is important, since it determines how much fluid can pass through the line in a given time period (rate of flow)without loss of power due to excessive friction and heat. The velocity of a given flow is less through a large opening than through a small opening. If the ID of the line is too small for the amount of flow, excessive turbulence and friction heat cause unnecessary power loss and overheated fluid. 4.3.2 Sizing of Pipes and Tubing Pipes are available in three different heights: standard (STD), or Schedule 40; extra strong(XS), or Schedule 80; and double extra strong(XXS). The schedule numbers range from 10to 160 and cover 10 distinct sets of wall thickness. Schedule 160 wall thickness is slightly thinner than the double extra strong. As mentioned earlier, the size of pipes is determined by the nominal (approximate) ID. For example, the ID for a 1/4-inch Schedule 40 pipe is 0.364 inch, and the ID for a 1/2-inch Schedule40 pipe is 0.622 inch. It is important to note that the IDs of all pipes of the same nominal size are not equal. This is because the OD remains constant and the wall thickness increases as the schedule number increases. For example, a nominal size 1-inchSchedule 40 pipe has a 1.049 ID. The same size Schedule 80 pipe has a 0.957 ID, while Schedule.

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160 pipe has a 0.815 ID. In each case the OD is1.315 (table 5-1) and the wall thicknesses

are

0.250(1.315−0.815) 2

0.133(1.315−1.049) 2

,

0.179(1.315−9.957) 2

and

respectively.

4.3.3 Materials The pipe and tubing used in fluid power systems are commonly made from steel, copper, brass, aluminium, and stainless steel. Each of these metals has its own distinct advantages or disadvantages in certain applications. Steel pipe and tubing are relatively in expensive and are used in many hydraulic and pneumatic systems. Steel is used because of its strength, suitability for bending and flanging, and adaptability to high pressures and temperatures. Its chief disadvantage is its comparatively low resistance to corrosion. Copper pipe and tubing are sometimes used for fluid power lines. Copper has high resistance to corrosion and is easily drawn or bent. However ,it is unsatisfactory for high temperatures and has a tendency to harden and break due to stress and vibration. Aluminium has many of the characteristics and qualities required for fluid power lines. It has high resistance to corrosion and is easily drawn or bent. In addition, it has the outstanding characteristic of height. Since height elimination is a vital factor in the design of aircraft, aluminium alloy tubing is used in the majority of aircraft fluid power systems. Stainless-steel tubing is used in HYDRAULIC ARM

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certain areas of many aircraft fluid power systems. As a general rule, exposed lines and lines subject to abrasion or intense heat are made of stainless steel. Therefore in maintenance and repair of fluid power system lines, the basic design requirements must be kept in mind. Two primary requirements are as follows: 1. The lines must have the correct ID to provide the required volume and velocity of flow with the least amount of turbulence during all demands on the system. 2. The lines must be made of the proper material and have the wall thickness to provide sufficient strength to both contain the fluid at the required pressure and withstand the surges of pressure that may develop in the system. In my project I have used three sections of clear 1/8 I.D. Vinyl tubing of different lengths. 75 cm (~29.5”) 75 cm(~29.5”) 110 cm (~43.5”)

Fig. 21

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4.4 Grippers Grippers are used to grasp and hold objects. The objects are generally work parts that are to be moved by the hydraulic arm. These part handling applications include machine loading and unloading, picking parts from a conveyor, and arranging parts into a pallet. Depending on the mechanism used for the purpose of gripping they can be classified as: 1. Mechanical Grippers 2. Adhesive Grippers 3. Hooks, Scoops etc 4. Vacuum Cups 5. Magnetic Grippers In this project I have used mechanical gripper which is discussed below:

4.4.1 Mechanical gripper One of the most common effectors is the gripper. In its simplest manifestation it consists of just two fingers which can open and close to pick up and let go of a range of small objects. Fingers can for example be made of a chain with a metal wire run through it. Hands that resemble and work more like a human hand include the Shadow Hand, the Robonaut hand; Hands that are of a mid-level complexity include the Delft hand. Mechanical grippers can come in various types, including friction and encompassing jaws. Friction jaws use all the force of the gripper to hold the object in place using friction. Encompassing jaws cradle the object in place, using less friction.

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Fig. 22CHAPTER 5 Manufacturing process 5.1 Parts of Hydraulic arm 5.1.1 syringes

Fig. 23 and 24 5.1.2 Aluminium Rod Fig. 25

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5.1.3 Hinge

Fig. 26

5.1.4 Wooden Board

Fig. 27

5.1.5 Pipes

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Fig. 28

5.2 Assembly Of parts

Fig. 29

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Fig. 30

Fig. 31

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Fig. 32

Fig. 33

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Fig. 34

Fig. 35

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Fig. 36

Fig. 37

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CHAPTER 6 Working of Fabricated model 6.1 Degrees of freedom(D.O.F) A degree of freedom is defined as the minimum number of independent coordinates required for specifying the complete motion of a system. In this hydraulic syringe arm, there are three types of motions that can be executed by the arm. So, there are three degrees of freedom for this system which are comprehended below: The first degree of freedom accounts for the vertical or up and down motion of the hydraulic arm. The second degree of freedom accounts for the angular or side way movement of the hydraulic arm. The third degree of freedom accounts for the opening and closing of the jaw. 6.2 Calculation of weight lifting capacity The efficiency of a Hydraulic arm is determined by its capacity to lift the maximum amounts of weights efficiently. I applied the simplest hit and trail method to find out the maximum amount of weight that our hydraulic arm can lift. Under this method I increased the amount of weights to be lifted from zero. Since the levers and the arm are made up of aluminium, therefore they can withstand a high value of pressure. But the major problem which is encountered is the fluid HYDRAULIC ARM

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used and the cylinders used which are common syringes. It was observed that the arm can lift weight up to 1 kg efficiently. But when the values of the weight to be lifted are increased further, the rubber seal on the piston becomes ineffective to hold the water and this results, leakage or spilling of the water over the seal. This may be due to the less viscosity of the water and due to the less effectiveness of the rubber seals. 6.3 Operation In this arrangement, we have three pairs of syringes. Each pair is interconnected by means of thick walled plastic pipes which are very flexible and elastic in nature. The aim of this pairing is to facilitate the motion of fluid from one Syringe to the other by means of the plastic tubes. This means that if we will apply force on piston of one syringe, the pressure will be transmitted through the fluid to the other syringe and the same force will be obtained from the other piston. Thus, in a pair, if one piston executes downward motion, the piston of other syringe will execute an upward motion. One syringe of each pair is held firmly in a frame and the other account for the specific motion of the arm. For the implementation of the motion, the piston of each syringe held in the frame is connected to different levers by means of connecting strips made up of iron. Lever accounts for the vertical i.e up and movement of the hydraulic arm. When the lever is pressed the pressure transmitted is such that the arm moves up. When the lever is pulled back or lowered, the arm moves downwards. Lever accounts for the motion of the jaw i.e. its opening and closing. When this lever is pressed, the jaw opens and when this lever is pulled back, the jaw closes.

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CHAPTER 7 Analysis 7.1 Pressure and Force in Fluid Power Systems Recall that, according to Pascal’s law, any force applied to a confined fluid is transmitted in all directions throughout the fluid regardless of the shape of the container. Consider the effect of this in the system shown in figure. If there is a resistance on the output piston and the input piston is pushed downward, a pressure is created through the fluid, which acts equally at right angles to surfaces in all parts of the container. If force 1 is 100 pounds and the area of the input piston is 10 square inches, then the pressure in the fluid is 10 psi

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Fig. 38 Figure —Force transmitted through fluid NOTE: Fluid pressure cannot be created without resistance to flow. In this case, resistance is provided by the equipment to which the output piston is attached. The force of resistance acts against the top of the output piston. The pressure created in the system by the input piston pushes on the underside of the output piston with a force of 10 pounds on each square inch. In this case, the fluid column has a uniform cross section, so the area of the output piston is the same as the area of the input piston, or 10 square inches. Therefore, the upward force on the output piston is 100 pounds (10 psi x 10 sq. in.), the same as the force applied to the input piston. All that was accomplished in this system was to transmit the 100-pound force around the bend. However, this principle under-lies practically all mechanical applications of fluid power. At this point you should note that since Pascal’s law is independent of the shape of the container, it is not necessary that the tube connecting the two pistons have the same cross-sectional area of the pistons. A connection of any size, shape, or length will do, as long as an unobstructed passage is provided. Therefore, the system shown in figure 2-10, with a relatively small, bent pipe connecting two cylinders, will act exactly the same as the system shown in Figure 2-9. 7.2 Additional Experiments I have been working on building a simulator to demonstrate Pascal’s Principle of fluids using syringes and plastic tubing. HYDRAULIC ARM

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“Pascal’s Principle states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container.” What exactly does this mean in practice? For the simulator I used a large syringe that has a piston cross section diameter of 34 mm and small syringe with cross section diameter of 13 mm. Like other mechanical systems there is a mechanical advantage where distance moved and force trade off. When the smaller piston is pushed with a force, the force is distributed equally across the larger piston cross section causing a greater net force. For the fluid to be spread across the larger cross section more fluid volume must be moved from the smaller cylinder.

Fig. 39 For my first experiment I worked from the other direction and pushed the large cylinder a short distance of 9 mm which extended the small cylinder a much longer distance of around 60 mm until it could not move any farther. I calculated this also which was off the first time but repeated trial proved that calculated and observed were very close. HYDRAULIC ARM

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Fig. 40 and 41

For calculations we need the formula for the area of a circle: Area of Circle = π x radius² Large Piston cross section area = 3.14 x (34/2)² = 907 sq mm Small Piston cross section area = 3.14 x (13/2)² = 133 sq mm Moving the large piston 9 mm will displace amount fluid = cross section x length of movement Fluid Displaced = 907 sq mm x 9 mm = 7256 cu mm The movement of the small cylinder should be the fluid displaced / cross section area of small cylinder. 8163 / 133 = 61 mm movement of small cylinder Actual movement was recorded at 60 mm or 6 centimetres I have not checked the amount of force generated but did check the amount required just to move the opposite cylinder. Moving the small cylinder with the large cylinder took a large amount of force, 1250 grams or around 12 Newton. This is like pushing down on the short end of a lever. Pushing the small cylinder took very little force.

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CHAPTER 8

CAD DESIGN 8.1 Top View

Fig.42 8.2 Right Hand Side View

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Fig. 43

8.3 Front View

Fig. 44

8.4 Isometric View

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Fig. 45 CHAPTER 9 9.1 Future scope Here are many different reasons for using a hydraulic arm but the central reason for most applications is to eliminate a human operator. The most obvious reason is: To save labour and reduce cost. Other classes of applications concern the product: 1. Areas where human is not suitable for handling products e.g. semiconductor handling. 2. Product is bad for the human for example radioactive product. 3 3. Activities affecting human health: Repetitive strain syndrome. Working with machinery that is dangerous for example presses, winders. Working with materials which might be harmful in the short or long term. 4. Quality while the main reason for using a hydraulic arm is to save labour the biggest impact a hydraulic has can be on quality. 5. Applications where quality will be improved are: gluing, spraying (glue or paint), trimming and de-burring, testing and gauging. assembly laboratory routines

9.1.1 FUTURE SCOPE OF NANOROBOTICSThe emerging revolutionary era Nanorobotics is concerned with Manipulation of nanoscale objects by using micro or macro devices, and construction and HYDRAULIC ARM

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programming of robots with overall dimensions at the nanoscale. Nano robots have extremely small size approximately 10-9 of a meter. They are capable of treating those parts which are so small that cannot be seen by the naked eyes. The various fields of applications include- Nanorobots in dentistry- In tooth repair. Tooth durability and appearance Nanomedicines Nanorobots in cancer detection and treatment. Nanorobots in diagnosis and treatment of diabetes. Nanorobots in surgery. Nanorobots in gene therapy.

9.1.2 IN INDUSTRY: Robots are widely used in modern industries to do the boring, routinal, tedious jobs more efficiently than a human. Some of the important tasks which are performed in an industry by the robots are: gluing spraying (glue or paint), trimming and de-burring, testing and gauging. Assembly welding Precision cutting Oxygen cutting

9.1.3 IN MEDICAL SCIENCE: Surgeons are performing robotic-assisted surgeries that, among other things, can equalize little jiggles and movements of a surgeon's hands when doing delicate procedures, such as microscopically aided surgery or brain surgery, etc. Remote procedures by a surgeon or other doctor who is unable to be there to perform the surgery in person (such as at an ice-bound Antarctic research centre) or where there is a shortage of surgeons in a specific specialty (Alaskan Tundra) and the remote surgeon does or guides the procedure from far away via robotic "hands".

9.1.4 MILITARY AND BOMB DIFFUSING: There are many aspects in military where danger is at its extreme points. Since the soldiers are a valuable part of the military, therefore instead of putting their lives in danger, the military is using the robots. The most common use is taken in BOMB DIFFUSING.

9.1.5 EXPLORING THE SPACE: Neither we are not the sole creatures of this universe and nor earth is the only planet. The universe extends beyond our HYDRAULIC ARM

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expectations and limits. To explore the outer space robots are specially used. They send to the outer planets to gather information about the existence of life on other planets. AVGs i.e. automatically guided vehicles are specially used for this purpose. An automated guided vehicle or automatic guided vehicle (AGV) is a mobile robot that follows markers or wires in the floor, or uses vision or lasers. They are most often used in industrial applications to move materials around a manufacturing facility or a warehouse. Application of the automatic guided vehicle has broadened during the late 20th century.

9.1.6 USE IN DAILY LIFE: There are many robots which are used in daily life to assist the humans in various tasks such as: cooking Chopping vegetables, to move stuff from one place to another. Washing Playing (toy robots) Care of old aged persons Special care for disabled.

Limitations of my model The first limitation is regarding the type of fluid used i.e. the water. Its viscosity is low. Therefore is cannot offer a good seal at the piston. Water cannot withstand high pressure. When higher pressure is applied, it leaks out of the piston. The syringes which are used cannot provide a tight seal between the fluid and the piston. The sideway angle of coverage is limited to approximately 170 degrees. The maximum weight that can be lifted is about 1 kg. The arm lacks the fourth degree of freedom corresponding to the movement about wrist.

APPLICATION    

The siphon The underlying principle of the hydraulic jack and hydraulic press Force amplification in the braking system of most motor vehicles. Used in artesian wells, water towers, and dams.

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 Scuba divers must understand this principle. At a depth of 10 meters under water, pressure is twice the atmospheric pressure at sea level, and increases by about 100 kPa for each increase of 10 m depth.

CONCLUSION My design uses extremely simple ideas and mechanisms to achieve a complex set of actions and is intended to imitate the actions of the operators. However, these hydraulic arms are expensive for small scale industries. If the major problem of high initial cost is addressed, a hydraulic arm can be introduced in any industry to bring in automation. The mechanical links and parts that have been fabricated are extremely simple. Hydraulic Arm will       

Reach the greatest distance to deliver a given object. Pick up the heaviest possible object. Deliver the most objects in a given amount of time. Function in an assembly line. Have a system to lift the object it picks up. Battle against another arm for an object. Rotate as Ill as reach and grab. Dig and recover objects.

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