multipurpose machines using scotch yoke mechanism

Development of Multi Purpose Machine With Scotch Yoke Mechanism

CHAPTER-1 INTRODUCTION Multi-operation machine as a research area is motivated by questions that arise in industrial manufacturing, production planning, and computer control. Consider a large automotive garage with specialized shops. A car may require the following work, replace exhaust system, align wheels, and tune up. These three tasks may be carried out in any order. However, since the exhaust system, alignment, and tune-up shops are in different buildings, it is impossible to perform two tasks for a car simultaneously. When there are many cars requiring services at the three shops, it is desirable to construct a service schedule that takes the least amount of total time.

1.1 Scotch Yoke Mechanism The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.

Figure 1.1 Sectional view of Scotch yoke mechanism

Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism

Figure 1.2 Front view of Scotch Yoke Mechanism

1.2 Construction The scotch yoke mechanism is constructed with iron bars. Here the crank is made in some length and the yoke is also made using the same material. It is noted that the minimum length of the yoke should be double the length of the crank. The crank and yoke is connected with a pin. Iron bars are welded to both sides of the yoke to get the reciprocating motion. The yoke with the iron bars is fixed on the display board with the help of c clamp. Now the crank is welded to the end of the shaft of the motor. Now the pin on the crank is connected to the yoke. The pin used to connect yoke and crank is a bolt.

1.3 Working principle When the power is supplied to the 12v Dc motor, shaft and crank attached to the shaft start rotating. As the crank rotates the pin slides inside the yoke and also moves the yoke forward. When the crank rotates through in clockwise direction the yoke will get a displacement in the forward direction. The maximum displacement will be equal to the length of the crank. When the crank completes the next of rotation the yoke comes back to its initial position. For the next of rotation, yoke moves in the backward direction. When the crank completes a full rotation the yoke moves back

to the initial position. For a complete rotation of crank the yoke moves through a length equal to double the length of the crank. The displacement of the yoke can be controlled by varying the length of the crank.

Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism

CHAPTER-2 APPARATUS 2.1 Dc motors At the most basic level, electric motors exist to convert electrical energy into mechanical energy. This is done by way of two interacting magnetic fields - one stationary, and another attached to a part that can move. A number of types of electric motors exist, but most BEAM bots use DC motors1 in some form or another. DC motors have the potential for very high torque capabilities (although this is generally a function of the physical size of the motor), are easy to miniaturize, and can be "throttled" via adjusting their supply voltage. DC motors are also not only the simplest, but the oldest electric motors. The basic principles of electromagnetic induction were discovered in the early 1800's by Oersted, Gauss, and Faraday. By 1820, Hans Christian Oersted and Andre Marie Ampere had discovered that an electric current produces a magnetic field. The next 15 years saw a flurry of cross-Atlantic experimentation and innovation, leading finally to a simple DC rotary motor. A number of men were involved in the work, so proper credit for the first DC motor is really a function of just how broadly you choose to define the word "motor." A DC motor is a mechanically commutated electric motor powered from direct current (DC). The stator is stationary in space by definition and therefore so is its current. The current in the rotor is switched by the commutator to also be stationary in space. This is how the relative angle between the stator and rotor magnetic flux is maintained near 90 degrees, which generates the maximum torque. DC motors have a rotating armature winding but non-rotating armature magnetic field and a static field winding or permanent magnet. Different connections of the field and armature winding provide different inherent speed/torque regulation characteristics. The speed of a DC motor can be controlled by changing the voltage applied to the armature or by changing the field current. The introduction of variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often controlled by power electronics systems called DC drives. The introduction of DC motors to run machinery eliminated the need for local steam or internal combustion engines, and line shaft drive systems. DC motors can operate directly Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism from rechargeable batteries, providing the motive power for the first electric vehicles. Today DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines.

2.2 Principles of Operation of DC Motor In any electric motor, operation is based on simple electromagnetism. A currentcarrying conductor generates a magnetic field; when this is then placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and to the strength of the external magnetic field. As you are well aware of from playing with magnets as a kid, opposite (North and South) polarities attract, while like polarities (North and North, South and South) repel. The internal configuration of a DC motor is designed to harness the magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion. Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet or winding with a "North" polarization, while green represents a magnet or winding with a "South" polarization).

Figure 2.1 Sectional view of DC Motor Every DC motor has six basic parts: axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. In most common DC motors (and all that Beamers will see), the external magnetic field is produced by high-strength permanent magnets. The stator is the stationary part of the motor, this includes the motor casing, as well as two or more permanent magnet pole pieces. The rotors (together with the axle and attached commutator) rotate with respect to the stator. The rotor consists of windings (generally on a core), the windings being electrically connected to the commutator. The above diagram shows a common motor layout with the rotor inside the stator (field) magnets.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism The geometry of the brushes, commutator contacts, and rotor windings are such that when power is applied, the polarities of the energized winding and the stator magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. As the rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next winding. Given our example two-pole motor, the rotation reverses the direction of current through the rotor winding, leading to a "flip" of the rotor's magnetic field, driving it to continue rotating. The DC Motor or Direct Current Motor to give it its full title, is the most commonly used actuator for producing continuous movement and whose speed of rotation can easily be controlled, making them ideal for use in applications were speed control, servo type control, and/or positioning is required. A DC motor consists of two parts, a "Stator" which is the stationary part and a "Rotor" which is the rotating part. The result is that there are basically three types of DC Motor available. i.

Brushed Motor - This type of motor produces a magnetic field in a wound rotor (the part that rotates) by passing an electrical current through a commutator and carbon brush assembly, hence the term "Brushed". The stators (the stationary part) magnetic field is produced by using either a wound stator field winding or by permanent magnets. Generally brushed DC motors are cheap, small and easily controlled .

ii.

Brushless Motor - This type of motor produce a magnetic field in the rotor by using permanent magnets attached to it and commutation is achieved electronically. They are generally smaller but more expensive than conventional brushed type DC motors because they use "Hall effect" switches in the stator to produce the required stator field rotational sequence but they have better torque/speed characteristics, are more efficient and have a longer operating life than equivalent brushed types.

iii.

Servo Motor - This type of motor is basically a brushed DC motor with some form of positional feedback control connected to the rotor shaft. They are connected to and controlled by a PWM type controller and are mainly used in positional control systems and radio controlled models.

Normal DC motors have almost linear characteristics with their speed of rotation being determined by the applied DC voltage and their output torque being determined by the Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism current flowing through the motor windings. The speed of rotation of any DC motor can be varied from a few revolutions per minute (rpm) to many thousands of revolutions per minute making them suitable for electronic, automotive or robotic applications. By connecting them to gearboxes or gear-trains their output speed can be decreased while at the same time increasing the torque output of the motor at a high speed.

2.3 Brushed DC Motor A conventional brushed DC Motor consist basically of two parts, the stationary body of the motor called the Stator and the inner part which rotates producing the movement called the Rotor or "Armature" for DC machines. The motors wound stator is an electromagnet circuit which consists of electrical coils connected together in a circular configuration to produce the required North-pole then a South-pole then a North-pole etc, type stationary magnetic field system for rotation, unlike AC machines whose stator field continually rotates with the applied frequency. The current which flows within these field coils is known as the motor field current. These electromagnetic coils which form the stator field can be electrically connected in series, parallel or both together (compound) with the motors armature. A series wound DC motor has its stator field windings connected in series with the armature. Likewise, a shunt wound DC motor has its stator field windings connected in parallel with the armature as shown. 2.3.1 Series and Shunt Connected DC Motor

Figure 2.2 Series and Shunt DC Motor The rotor or armature of a DC machine consists of current carrying conductors connected together at one end to electrically isolated copper segments called the commutator.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism The commutator allows an electrical connection to be made via carbon brushes (hence the name "Brushed" motor) to an external power supply as the armature rotates. The magnetic field setup by the rotor tries to align itself with the stationary stator field causing the rotor to rotate on its axis, but cannot align itself due to commutation delays. The rotational speed of the motor is dependent on the strength of the rotors magnetic field and the more voltage that is applied to the motor the faster the rotor will rotate. By varying this applied DC voltage the rotational speed of the motor can also be varied. 2.3.2 Conventional (Brushed) DC Motor

Figure 2.3 Conventional (Brushed) DC Motor Permanent magnet (PMDC) brushed motors are generally much smaller and cheaper than their equivalent wound stator type DC motor cousins as they have no field winding. In permanent magnet DC (PMDC) motors these field coils are replaced with strong rare earth (i.e. Samarium Cobalt, or Neodymium Iron Boron) type magnets which have very high magnetic energy fields. This gives them a much better linear speed/torque characteristic than the equivalent wound motors because of the permanent and sometimes very strong magnetic field, making them more suitable for use in models, robotics and servos. Although DC brushed motors are very efficient and cheap, problems associated with the brushed DC motor is that sparking occurs under heavy load conditions between the two surfaces of the commutator and carbon brushes resulting in self generating heat, short life span and electrical noise due to sparking, which can damage any semiconductor switching Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism device such as a MOSFET or transistor. To overcome these disadvantages, Brushless DC Motors were developed.

2.4 Brushless DC Motor The brushless DC motor (BDCM) is very similar to a permanent magnet DC motor, but does not have any brushes to replace or wear out due to commutator sparking. Therefore, little heat is generated in the rotor increasing the motors life. The design of the brushless motor eliminates the need for brushes by using more complex drive circuits were the rotor magnetic field is a permanent magnet which is always in synchronization with the stator field allows for a more precise speed and torque control. Then the construction of a brushless DC motor is very similar to the AC motor making it a true synchronous motor but one disadvantage is that it is more expensive than an equivalent "brushed" motor design. The control of the brushless DC motors is very different from the normal brushed DC motor, in that it this type of motor incorporates some means to detect the rotors angular position (or magnetic poles) required to produce the feedback signals required to control the semiconductor switching devices. The most common position/pole sensor is the "Hall Effect Sensor", but some motors also use optical sensors. Using Hall Effect sensors, the polarity of the electromagnets is switched by the motor control drive circuitry. Then the motor can be easily synchronized to a digital clock signal, providing precise speed control. Brushless DC motors can be constructed to have, an external permanent magnet rotor and an internal electromagnet stator or an internal permanent magnet rotor and an external electromagnet stator. Advantages of the Brushless DC Motor compared to its “brushed” cousin are higher efficiencies, high reliability, low electrical noise, good speed control and more importantly, no brushes or commutator to wear out producing a much higher speed. However their disadvantage is that they are more expensive and more complicated to control.

2.5 DC Servo Motor DC Servo motors are used in closed loop type applications were the position of the output motor shaft is fed back to the motor control circuit. Typical positional "Feedback" devices include Resolvers, Encoders and Potentiometers as used in radio control models such as airplanes and boats etc. A servo motor generally includes a built-in gearbox for speed Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism reduction and is capable of delivering high torques directly. The output shaft of a servo motor does not rotate freely as do the shafts of DC motors because of the gearbox and feedback devices attached.

2.6 DC Motor Behavior At a simplistic level, using DC motors is pretty straight forward - you put power in, and get rotary motion out. Life, of course, is never this simple - there are a number of subtleties of DC motor behavior that should be accounted for in BEAMbot design. 2.6.1 High-speed output This is the simplest trait to understand and treat most DC motors run at very high output speeds (generally thousands or tens of thousands of RPM). While this is fine for some BEAM bots (say, photo poppers or solar rollers), many BEAM bots (walkers, heads) require lower speeds. 2.6.2 Back EMF Just as putting voltage across a wire in a magnetic field can generate motion, moving a wire through a magnetic field can generate voltage. This means that as a DC motor's rotor spins, it generates voltage the output voltage is known as back EMF. Because of back EMF, a spark is created at the commutator as a motor's brushes switch from contact to contact. Meanwhile, back EMF can damage sensitive circuits when a motor is stopped suddenly. 2.6.3 Noise (ripple) on power lines A number of things will cause a DC motor to put noise on its power lines: commutation noise (a function of brush / commutator design & construction), roughness in bearings (via back EMF), and gearing roughness (via back EMF, if the motor is part of a gear motor) are three big contributors. Even without these avoidable factors, any electric motor will put noise on its power lines by virtue of the fact that its current draw is not constant throughout its motion. Going back to our example two-pole motor, its current draw will be a function of the angle between its rotor coil and field magnets:

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Development of Multi Purpose Machine With Scotch Yoke Mechanism Since most small DC motors have 3 coils, the coils' current curves will overlay each other,

Added together, this ideal motor's current will then look something like this,

Reality is a bit more complex than this, as even a high-quality motor will display a current transient at each commutation transition. Since each coil has inductance (by definition) and some capacitance, there will be a surge of current as the commutator's brushes first touch a coil's contact, and another as the brushes leave the contact (here, there's a slight spark as the coil's magnetic field collapses). As a good example, consider an oscilloscope trace of the current through a Mabuchi FF-030PN motor supplied with 2 V (1ms per horizontal division, 0.05 mA per vertical division)

Figure 2.4 Current Ripple

In this case, the peak-to-peak current ripple is approximately 0.29 mA, while the average motor current is just under 31 mA. So under these conditions, the motor puts about less than 1% of current ripple onto its power lines (and as you can see from the "clean" traces, it outputs essentially no high-frequency current noise). Note that since this is a 3-pole motor, and each coil is energized in both directions over the course of a rotor rotation, one revolution

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Development of Multi Purpose Machine With Scotch Yoke Mechanism of the rotor will correspond to six of the above curves (here, 6 x 2.4 ms = 0.0144 sec, corresponding to a motor rotation rate of just fewer than 4200 RPM). Motor power ripple can wreak havoc in Nv nets by destabilizing them inadvertently. Fortunately, this can be mitigated by putting a small capacitor across the motor's power lines (you'll only be able to filter out "spikey" transients this way, though - you'll always see curves like the ones above being imposed on your power). On the flip side of this coin, motor power ripple can be put to good use - as was shown above, ripple frequency can be used to measure motor speed, and its destabilizing tendencies can be used to reverse a motor without the need for discrete "back-up" sensors 2.6.4 Characteristics of DC Motor Voltage in steady state condition

Where: 

V = input voltage



Eb = back EMF



Ia = Armature current



R = total resistance

The total resistance R is equal to Armature Resistance (Ra) + External resistance (Rph).

Figure 2.5 A: Shunt B: Series C: Compound and f = Field Coil

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Development of Multi Purpose Machine With Scotch Yoke Mechanism

2.6.5 Shunt wound motor A shunt wound motor has a high-resistance field winding connected in parallel with the armature. It responds to increased load by trying to maintain its speed and this leads to an increase in armature current. This makes it unsuitable for widely-varying loads, which may lead to overheating. 2.6.6 Series wound motor A series wound motor has a low-resistance field winding connected in series with the armature. It responds to increased load by slowing down; the current increases and the torque rises in proportional to the square of the current since the same current flows in both the armature and the field windings. If the motor is stalled, the current is limited only by the total resistance of the windings and the torque can be very high, but there is a danger of the windings becoming overheated. Series wound motors were widely used as traction motors in rail transport of every kind, but are being phased out in favor of AC induction motors supplied through solid state inverters. The counter-EMF aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant, the counter-EMF is zero and the only factor limiting the armature current is the armature resistance. Usually the armature resistance of a motor is less than 1 Ω therefore the current through the armature would be very large when the power is applied. Therefore the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-EMF. As the motor rotation builds up, the resistance is gradually cut out. The output speed torque characteristic is the most notable characteristic of series wound DC motors. The speed being almost entirely dependent on the torque required to drive the load. This suits large inertial loads as the speed will drop until the motor slowly starts to rotate & these motors have a very high stalling torque. 2.6.7 Permanent magnet motor Permanent-magnet types have some performance advantages over direct-current, excited, synchronous types, and have become predominant in fractional horsepower applications. They are smaller, lighter, more efficient and reliable than other singly fed electric machines.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field. Only recently have advances in materials technology allowed the creation of high-intensity permanent magnets, such as neodymium magnets, allowing the development of compact, high-power motors without the extra real-estate of field coils and excitation means. But as these high performance permanent magnets become more applied in electric motor or generator systems, other problems are realized. 2.6.8 Speed Control Generally, the rotational speed of a DC motor is proportional to the EMF in its coil (= the voltage applied to it minus voltage lost on its resistance), and the torque is proportional to the current. Speed control can be achieved by variable battery tapings, variable supply voltage, resistors or electronic controls. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thrusters, transistors, or, formerly, mercury arc rectifiers. In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the "ON" to "OFF" ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage "on" time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% "on" time, the average voltage at the motor will be 25 V. During the "OFF" time, the armature's inductance causes the current to continue through a diode called a "fly back diode", in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage "on" time is 100%. At 100% "on" time, the supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise. Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for petrol and small diesel engines. Series motors must never be used in Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism applications where the drive can fail (such as belt drives). As the motor accelerates, the armature (and hence field) current reduces. The reduction in field causes the motor to speed up until it destroys itself. This can also be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, the motors can reach speeds far higher than they would do under normal circumstances. This can not only cause problems for the motors themselves and the gears, but due to the differential speed between the rails and the wheels it can also cause serious damage to the rails and wheel treads as they heat and cool rapidly. Field weakening is used in some electronic controls to increase the top speed of an electric vehicle. The simplest form uses a contactor and field-weakening resistor; the electronic control monitors the motor current and switches the field weakening resistor into circuit when the motor current reduces below a preset value (this will be when the motor is at its full design speed). Once the resistor is in circuit, the motor will increase speed above its normal speed at its rated voltage. When motor current increases, the control will disconnect the resistor and low speed torque is made available. One interesting method of speed control of a DC motor is the Ward Leonard control. It is a method of controlling a DC motor (usually a shunt or compound wound) and was developed as a method of providing a speed-controlled motor from an AC supply, though it is not without its advantages in DC schemes. The AC supply is used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo. The DC output from the armature is directly connected to the armature of the DC motor (sometimes but not always of identical construction). The shunt field windings of both DC machines are independently excited through variable resistors. Extremely good speed control from standstill to full speed, and consistent torque, can be obtained by varying the generator and/or motor field current. This method of control was the de facto method from its development until it was superseded by solid state thyristor systems. It found service in almost any environment where good speed control was required, from passenger lifts through to large mine pit head winding gear and even industrial process machinery and electric cranes. Its principal disadvantage was that three machines were required to implement a scheme (five in very large installations, as the DC machines were often duplicated and controlled by a tandem variable resistor). In many applications, the motor-generator set was often left permanently running, to avoid the delays that would otherwise be caused by starting it up as required. Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism Although electronic (thyristor) controllers have replaced most small to medium WardLeonard systems, some very large ones (thousands of horsepower) remain in service. The field currents are much lower than the armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly. For example, in one installation, a 300 amp thyristor unit controls the field of the generator. The generator output current is in excess of 15,000 amperes, which would be prohibitively expensive (and inefficient) to control directly with thyristors. 2.6.9 Protection To extend a D.C. motor’s service life, protective devices and motor controllers are used to protect it from mechanical damage, excessive moisture, high dielectric stress and high temperature or thermal overloading. These protective devices

sense motor fault

conditions and either annunciate an alarm to notify the operator or automatically de-energize the motor when a faulty condition occurs. For overloaded conditions, motors are protected with thermal overload relays. Bi-metal thermal overload protectors are embedded in the motor's windings and made from two dissimilar metals. They are designed such that the bimetallic strips will bend in opposite directions when a temperature set point is reached to open the control circuit and de-energize the motor. Heaters are external thermal overload protectors connected in series with the motor’s windings and mounted in the motor contactor. Solder pot heaters melt in an overload condition, which cause the motor control circuit to de-energize the motor. Bimetallic heaters function the same way as embedded bimetallic protectors. Fuses and circuit breakers are over current or short circuit protectors. Ground fault relays also provide over current protection. They monitor the electrical current between the motor’s windings and earth system ground. In motor-generators, reverse current relays prevent the battery from discharging and motorizing the generator. Since D.C. motor field loss can cause a hazardous runaway or over speed condition, loss of field relays are connected in parallel with the motor’s field to sense field current. When the field current decreases below a set point, the relay will deenergize the motor’s armature. A locked rotor condition prevents a motor from accelerating after its starting sequence has been initiated. Distance relays protect motors from locked-rotor faults. Under voltage motor protection is typically incorporated into motor controllers or starters. In addition,

motors

transformers, power

can

be

protected

conditioning

from overvoltages or

surges

equipment, MOVs, arrestors and

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with

harmonic

solation filters.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism Environmental conditions, such as dust, explosive vapors, water, and high ambient temperatures, can adversely affect the operation of a DC motor. To protect a motor from these environmental conditions, the National Electrical Manufacturers Association (NEMA) and the International Electro technical Commission (IEC) have standardized motor enclosure designs based upon the environmental protection they provide from contaminants.

2.7. DC Motor Starters The counter-Emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-Emf is zero and the only factor limiting the armature current is the armature resistance and inductance. Usually the armature resistance of a motor is less than 1 Ωtherefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices. Therefore the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation builds up, the resistance is gradually cut out. 2.7.1 Manual-starting rheostat

Figure 2.6 Manual Starting Rheostats

When electrical and DC motor technology was first developed, much of the equipment was constantly tended by an operator trained in the management of motor systems. The very first motor management systems were almost completely manual, with an attendant

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Development of Multi Purpose Machine With Scotch Yoke Mechanism starting and stopping the motors, cleaning the equipment, repairing any mechanical failures, and so forth. The first DC motor-starters were also completely manual, as shown in this image. Normally it took the operator about ten seconds to slowly advance the rheostat across the contacts to gradually increase input power up to operating speed. There were two different classes of these rheostats, one used for starting only, and one for starting and speed regulation. The starting rheostat was less expensive, but had smaller resistance elements that would burn out if required to run a motor at a constant reduced speed. This starter includes a no-voltage magnetic holding feature, which causes the rheostat to spring to the off position if power is lost, so that the motor does not later attempt to restart in the full-voltage position. It also has over current protection that trips the lever to the off position if excessive current over a set amount is detected.

2.7.2 Three-Point starter

Figure 2.7 Three Point Starters The incoming power is indicated as L1 and L2. The components within the broken lines form the three-point starter. As the name implies there are only three connections to the starter. The connections to the armature are indicated as A1 and A2. The ends of the field (excitement) coil are indicated as F1 and F2. In order to control the speed, a field rheostat is connected in series with the shunt field. One side of the line is connected to the arm of the starter (represented by an arrow in the diagram). The arm is spring-loaded so, it will return to the "Off" position when not held at any other position. i.

On the first step of the arm, full line voltage is applied across the shunt field. Since the field rheostat is normally set to minimum resistance, the speed of the motor will not be excessive; additionally, the motor will develop a large starting torque.

ii.

The starter also connects an electromagnet in series with the shunt field. It will hold the arm in position when the arm makes contact with the magnet.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism iii.

Meanwhile that voltage is applied to the shunt field, and the starting resistance limits the current to the armature.

iv.

As the motor picks up speed counter - EMF is built up; the arm is moved slowly to short.

2.7.3 Four-Point starter The four-point starter eliminates the drawback of the three-point starter. In addition to the same three points that were in use with the three-point starter, the other side of the line, L1, is the fourth point brought to the starter when the arm is moved from the "Off" position. The coil of the holding magnet is connected across the line. The holding magnet and starting resistors function identical as in the three-point starter. The possibility of accidentally opening the field circuit is quite remote. The four-point starter provides the no-voltage protection to the motor. If the power fails, the motor is disconnected from the line. 2.7.4 Energy Losses in DC Motors Losses occur when electrical energy is converted to mechanical energy (in the motor), or mechanical energy is converted to electrical energy (in the generator). For the machine to be efficient, these losses must be kept to a minimum. Some losses are electrical, others are mechanical. Electrical losses are classified as copper losses and iron losses; mechanical losses occur in overcoming the friction of various parts of the machine. Copper losses occur when electrons are forced through the copper windings of the armature and the field. These losses are proportional to the square of the current. They are sometimes called I2R losses, since they are due to the power dissipated in the form of heat in the resistance of the field and armature windings. Iron losses are subdivided in hysteresis and eddy current losses. Hysteresis losses are caused by the armature revolving in an alternating magnetic field. It, therefore, becomes magnetized first in one direction and then in the other. The residual magnetism of the iron or steel of which the armature is made causes these losses. Since the field magnets are always magnetized in one direction (dc field), they have no hysteresis losses. Eddy current losses occur because the iron core of the armature is a conductor revolving in a magnetic field. This sets up an EMF. across portions of the core, causing

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Development of Multi Purpose Machine With Scotch Yoke Mechanism currents to flow within the core. These currents heat the core and, if they become excessive, may damage the windings. As far as the output is concerned, the power consumed by eddy currents is a loss. To reduce eddy currents to a minimum, a laminated core usually is used. A laminated core is made of thin sheets of iron electrically insulated from each other. The insulation between laminations reduces eddy currents, because it is "transverse" to the direction in which these currents tend to flow. However, it has no effect on the magnetic circuit. The thinner the laminations, the more effectively this method reduces eddy current losses. 2.7.5 Advantages of DC Motor i.

Speed control over a wide range both above and below the rated speed: The attractive feature of the dc motor is that it offers the wide range of speed control both above and below the rated speeds. This can be achieved in dc shunt motors by methods such as armature control method and field control method. This is one of the main applications in which dc motors are widely used in fine speed applications such as in rolling mills and in paper mills.

ii.

High starting torque: dc series motors are termed as best suited drives for traction applications used for driving heavy loads in starting conditions. DC series motors will have a staring torque as high as 500% compared to normal operating torque. Therefore dc series motors are used in the applications such as in electric trains and cranes.

iii.

Accurate steep less speed with constant torque: Constant torque drives is one such the drives will have motor shaft torque constant over a given speed range. In such drives shaft power varies with speed.

iv.

Quick starting, stopping, reversing and acceleration

v.

Free from harmonics, reactive power consumption and many factors which make dc motors more advantageous compared to an AC induction motors.

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2.8 Drilling Machine 2.8.1Introduction Drilling machine can be defined as an instrument which is used to drill holes. Drilling machine plays an important role in mechanical workshops. The purpose of this project work is to get hold of complete information pertaining to drilling machines. A drilling machine comes in many shapes and sizes, from small hand-held power drills to bench mounted and finally floor-mounted models. Today the Industrial growth is purely depends up on latest machines; therefore the subject of drilling machines is extended too widely, because today wide varieties of drilling machines are designed for various applications. The most advanced version-drilling machine is CNC (Computer Numeric Control); it is used for drilling the PCB’s (Printed circuit boars). CNC Drilling is commonly implemented for mass production. Simple drilling machines like hand held portable drilling machines, power feed drilling machines, etc. are quite common; we can find these machines everywhere. Often these machines are used for drilling a through hole over the job; these machines cannot be used for number of machining operations for specific applications. Human force is required to drill the hole, drilling depth cannot be estimated properly, job may spoil due to human errors, and different size holes cannot be drilled without changing the drill bit. Consumes lot of time for doing repeated multiple jobs, these all are the drawbacks. To overcome all these problems, this automated drilling machine is designed which is aimed to drill the holes automatically over a job according to the drilling depth data programmed through a key board. The main concept of this machine is to drill the holes over particular jobs repeatedly at different depths, sequence is maintained. As the machine contains drill motor, the movement is controlled accurately. 2.8.2 Drill bit Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes. This article describes the types of drill bits in terms of the design of the cutter. The other end of the drill bit, the shank, is described in the drill bit shank article. Drill bits come in standard sizes, described in the drill bit sizes article. A comprehensive drill and tap size Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism chart lists metric and imperial sized drills alongside the required screw tap sizes. The term drill can refer to a drilling machine, or can refer to a drill bit for use in a drilling machine. In this article, for clarity, drill bit or bit is used throughout to refer to a bit for use in a drilling machine, and drill refers always to a drilling machine.

Figure 2.8 Drill Bits

2.8.3 Twist drill The twist drill bit is the type produced in largest quantity today. It drills holes in metal, plastic, and wood. The twist drill bit was invented by Steven A. Morse of East Bridgewater, Massachusetts in 1861. He received U.S. Patent 38,119 for his invention on April 7, 1863. The original method of manufacture was to cut two grooves in opposite sides of a round bar, then to twist the bar to produce the helical flutes. This gave the tool its name. Nowadays, the drill bit is usually made by rotating the bar while moving it past a grinding wheel to cut the flutes in the same manner as cutting helical gears. Tools recognizable as twist drill bits are currently produced in diameters covering a range from 0.05 mm (0.002") to 100 mm (4"). Lengths up to about 1000 mm (39") are available for use in powered hand tools. The geometry and sharpening of the cutting edges is crucial to the performance of the bit. Users often throw away small bits that become blunt, and replace them with new bits, because they are inexpensive and sharpening them well is difficult. For larger bits, special

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Development of Multi Purpose Machine With Scotch Yoke Mechanism grinding jigs are available. A special tool grinder is available for sharpening or reshaping cutting surfaces on twist drills to optimize the drill for a particular material. Manufacturers can produce special versions of the twist drill bit, varying the geometry and the materials used, to suit particular machinery and particular materials to be cut. Twist drill bits are available in the widest choice of tooling materials. However, even for industrial users, most holes are still drilled with a conventional bit of high speed steel. The most common twist drill (the one sold in general hardware stores) has a point angle of 118 degrees. This is a suitable angle for a wide array of tasks, and will not cause the uninitiated operator undue stress by wandering or digging in. A more aggressive (sharper) angle, such as 90 degrees, is suited for very soft plastics and other materials. The bit will generally be self-starting and cut very quickly. A shallower angle, such as 150 degrees, is suited for drilling steels and other tougher materials. This style bit requires a starter hole, but will not bind or suffer premature wear when a proper feed rate is used. Drills with no point angle are used in situations where a blind, flat-bottomed hole is required. These drills are very sensitive to changes in lip angle, and even a slight change can result in an inappropriately fast cutting drill bit that will suffer premature wear.The twist drill does most of the cutting with the tip of the bit. There are flutes to carry the chips up from the cutting edges to the top of the hole where they are cast off.· Some of the parts of a drill bit are diagramed below as viewed from the cutting tip of the drill,

Figure 2.9 Top view of Drill Bit

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Figure 2.10 Side View of Drill Bit Typical parameters for drill bits are, 1. Material is High Speed Steel 2. Standard Point Angle is 118° Harder materials have higher point angles; soft materials have lower point angles. The helix results in a positive cutting rake. Drill bits are typically ground (by hand) until they are the desired shape. When done grinding, the lips should be the same length and at the same angle, otherwise and oversized hole may be produced. Drill sizes are typically measured across the drill points with a micrometer.

2.9 Hacksaw Blade A hacksaw is a fine-tooth hand saw with a blade held under tension in a frame, used for cutting materials such as metal or plastics. Hand-held hacksaws consist of a metal arch with a handle, usually a pistol grip, with pins for attaching a narrow disposable blade. A screw or other mechanism is used to put the thin blade under tension. The blade can be mounted with the teeth facing toward or away from the handle, resulting in cutting action on either the push or pull stroke. On the push stroke, the arch will flex slightly, decreasing the tension on the blade, often resulting in an increased tendency of the blade to buckle and crack. Cutting on the pull stroke increases the blade tension and will result in greater control of the cut and longer blade life. Department of Mechanical Engineering, AMCEC, Bengaluru.

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Figure 2.11 Banco Hacksaw A hacksaw is a fine-tooth saw with a blade under tension in a frame, used for cutting materials Such as metal. Hand-held hacksaws consist of a metal frame with a handle, and pins for attaching a narrow disposable blade. A screw or other mechanism is used to put the thin blade under tension. A power hacksaw (or electric hacksaw) is a type of hacksaw that is powered by electric motor. Most power hacksaws are stationary machines but some portable models do exist. Stationary models usually have a mechanism to lift up the saw blade on the return stroke and some have a coolant pump to prevent the saw blade from overheating.

2.9.1 Market Potential The demand of hacksaw blade is considerably increasing day by day with the growth of Industrialization, engineering sector, real estate, and automobile sector etc. It is used in almost every Sector for cutting of materials like angle, channel, flat plates, rods and such other things. It is Also required in auto repairing shops, general repairing workshops, fitting shops, welding shops And technical institutes. Govt. Department like Railway, Defence, PWD, Postal & Telegraph and Others are one of the main users of it. In India large nos. of small enterprises are engaged in its manufacturing. By considering its demand, new production unit has great prospect. 2.9.2 Basis and Presumptions The information supplied is based on a standard type of manufacturing activity utilizing Conventional techniques of production and optimum level of performance.75% of

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Development of Multi Purpose Machine With Scotch Yoke Mechanism the envisaged capacity is taken as efficiency on single working shift of 8 hrs & 300 working days in a year. Labor and wages are required as per present circumstances. The cost in respect of land & building, machine & equipment, raw material & selling price of finished product etc are those generally obtained at the time of preparation of project profile and may vary depending upon the location, make and for variety of reasons. The interest on total capital has been assumed @ 14% p.a 2.9.3 Technical Aspects and Design Blades are available in standardized lengths, and with anywhere from three to thirtytwo teeth/inch (tpi). The blade used is based on the thickness of the material being cut, with a Minimum of three teeth in the material. Hacksaw blades are normally quite brittle, so care needs to be taken to prevent brittle fracture of the blade. Bi-metal blades are meant to minimize this risk.

2.9.4 Recommended Teeth per 25mm (tpi) for each material type

2.9.5 Blades Blades are available in standardized lengths, usually 10 or 12 inches for a standard hand hacksaw. "junior" hacksaws are half this size. Powered hacksaws may use large blades in a range of sizes, or small machines may use the same hand blades. The pitch of the teeth can be anywhere from fourteen to thirty-two teeth per inch (tpi) for a hand blade, with as few as three tpi for a large power hacksaw blade. The blade chosen Department of Mechanical Engineering, AMCEC, Bengaluru.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism is based on the thickness of the material being cut, with a minimum of three teeth in the material. As hacksaw teeth are so small, they are set in a "wave" set. As for other saws they are set from side to side to provide a kerfs or clearance when sawing, but the set of a hacksaw changes gradually from tooth to tooth in a smooth curve, rather than alternate teeth set left and right. Hacksaw blades are normally quite brittle, so care needs to be taken to prevent brittle fracture of the blade. Early blades were of carbon steel, now termed 'low alloy' blades, and were relatively soft and flexible. They avoided breakage, but also wore out rapidly. Except where cost is a particular concern, this type is now obsolete. 'Low alloy' blades are still the only type available for the junior hacksaw, which limits the usefulness of this otherwise popular saw. For several decades now, hacksaw blades have used high speed steel for their teeth, giving greatly improved cutting and tooth life. These blades were first available in the 'Allhard' form which cut accurately but were extremely brittle. This limited their practical use to bench work on a work piece that was firmly clamped in a vice. A softer form of high speed steel blade was also available, which wore well and resisted breakage, but was less stiff and so less accurate for precise sawing. Since the 1980s, bi-metal blades have been used to give the advantages of both forms, without risk of breakage. A strip of high speed steel along the tooth edge is electron beam welded to a softer spine. As the price of these has dropped to be comparable with the older blades, their use is now almost universal. 2.9.6 Hacksaw blade specifications The most common blade is the 12 inch or 300 mm length. Hacksaw blades have two holes near the ends for mounting them in the saw frame and the 12 inch / 300 mm dimension refers to the center to center distance between these mounting holes. 2.9.7 12 Inch Blade Hole to Hole:

11 7/8 inches / 300 mm

Overall blade length:

12 3/8 inches / 315 mm (not tightly controlled)

Mounting Hole diameter:

9/64 to 5/32 inch / 3.5 to 4 mm (not tightly controlled)

Blade Width:

7/16 to 33/64 inch / 11 to 13 mm (not tightly controlled)

Blade Thickness:

0.020 to 0.027 inches / 0.5 to 0.70 mm

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Development of Multi Purpose Machine With Scotch Yoke Mechanism The kerf produced by the blades is somewhat wider than the blade thickness due to the set of the teeth. It commonly varies between 0.030 and 0.063 inches / 0.75 and 1.6 mm depending on the pitch and set of the teeth. The 10 inch blade is also fairly common and all the above dimensions apply except for the following: Hole to Hole:

9 7/8 inches / 250 mm

Overall blade length:

10 3/8 inches / 265 mm (not tightly controlled)

A panel hacksaw eliminates the frame, so that the saw can cut into panels of sheet metal without the length of cut being restricted by the frame. Junior hacksaws are the small variant, while larger mechanical hacksaws are used to cut working pieces from bulk metal. A power hacksaw (or electric hacksaw) is a type of hacksaw that is powered either by its own electric motor or connected to a stationary engine. Most power hacksaws are stationary machines but some portable models do exist. Stationary models usually have a mechanism to lift up the saw blade on the return stroke and some have a coolant pump to prevent the saw blade from overheating. While stationary electric hacksaws are reasonably uncommon they are still produced but saws powered by stationary engines have gone out of fashion. The reason for using one is that they provide a cleaner cut than an angle grinder or other types of saw. Large, power hacksaws are sometimes used in place of a band saw for cutting metal stock to length.

2.10 Shaping Machine A shaper is a type of machine tool that uses linear relative motion between the work piece and a single-point cutting tool to machine a linear tool path. Its cut is analogous to that of a lathe, except that it is (archetypal) linear instead of helical. (Adding axes of motion can yield helical tool paths, as also done in helical planning.) A shaper is analogous to a plane, but smaller, and with the cutter riding a ram that moves above a stationary work piece, rather than the entire work piece moving beneath the cutter. The ram is moved back and forth typically by a crank inside the column; hydraulically actuated shapers also exist.

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Development of Multi Purpose Machine With Scotch Yoke Mechanism 2.10.1 Types Shapers are mainly classified as standard, draw-cut, horizontal, universal, vertical, geared, crank, hydraulic, contour and traveling head. The horizontal arrangement is the most common. Vertical shapers are generally fitted with a rotary table to enable curved surfaces to be machined (same idea as in helical planning). The vertical shaper is essentially the same thing as a slotter (slotting machine), although technically a distinction can be made if one defines a true vertical shaper as a machine whose slide can be moved from the vertical. A slotter is fixed in the vertical plane. Small shapers have been successfully made to operate by hand power. As size increases, the mass of the machine and its power requirements increase, and it becomes necessary to use a motor or other supply of mechanical power. This motor drives a mechanical arrangement (using a pinion gear, bull gear, and crank, or a chain over sprockets) or a hydraulic motor that supplies the necessary movement via hydraulic cylinders. 2.10.2 Operation A shaper operates by moving a hardened cutting tool backwards and forwards across the work piece. On the return stroke of the ram the tool is lifted clear of the work piece, reducing the cutting action to one direction only. The work piece mounts on a rigid, box-shaped table in front of the machine. The height of the table can be adjusted to suit this work piece, and the table can traverse sideways underneath the reciprocating tool, which is mounted on the ram. Table motion may be controlled manually, but is usually advanced by automatic feed mechanism acting on the feed screw. The ram slides back and forth above the work. At the front end of the ram is a vertical tool slide that may be adjusted to either side of the vertical plane along the stroke axis. This tool-slide holds the clapper box and tool post, from which the tool can be positioned to cut a straight, flat surface on the top of the work piece. The tool-slide permits feeding the tool downwards to deepen a cut. This adjustability, coupled with the use of specialized cutters and tool holders, enable the operator to cut internal and external gear tooth profiles, splines, dovetails, and keyways. The ram is adjustable for stroke and, due to the geometry of the linkage, it moves faster on the return (non-cutting) stroke than on the forward, cutting stroke. This action is via a slotted link or Whitworth link

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CHAPTER-3 FABRICATION 3.1 Frame Work

Figure 3.1 frame Specifications: Length:

68.5cm

Breadth:

18.5cm

Height:

71cm

3.2 Scotch Yoke Mechanism

Figure 3.2 Scotch Yoke Mechanism Specifications: Tube length:

85.5cm

Tube diameter:

2.5cm

Disc diameter:

14cm

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Development of Multi Purpose Machine With Scotch Yoke Mechanism Slider height:

13cm

Slider width:

5cm

Rectangular frame length: 68.5cm Rectangular frame height: 36cm 3.3 Work Table

Figure 3.3 Circular work table

Specifications: Table diameter:

7.5cm

Supporting link length:

18cm

Supporting link height:

13cm

Figure 3.4 3D view of multipurpose machine

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CHAPTER-4 4.1 Advantages  High torque output with a small cylinder size  Fewer moving parts  Smoother operation  Higher percentage of the time spent at top dead center (dwell) improving theoretical engine

efficiency of constant volume combustion cycles though actual gains have

not been demonstrated.  In an engine application, elimination of joint typically served by a wrist pin, and near elimination of piston skirt and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is eliminated. 4.2 Disadvantages  Rapid wear of the slot in the yoke caused by sliding friction and high contact pressures.  Increased heat loss during combustion due to extended dwell at top dead center offsets any constant volume combustion improvements in real engines.  Lesser percentage of the time spent at bottom dead center reducing blow down time for two stroke engines, when compared with a conventional piston and crankshaft mechanism.

4.3 Applications  This setup is most commonly used in control valve actuators in high pressure oil and gas pipelines  It has been used in various internal combustion engines, such as the Bourke engine, SyTech engine, and many hot air engines and steam engines.  It is also used in multipurpose machines and I.C engines.

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CHAPTER-5 CONCLUSION The scotch yoke mechanism is made and its advantages and disadvantages are discussed. Its motion characteristics are studied. It is concluded that this mechanism is a good choice to convert rotating motion into reciprocating motion because of fewer moving parts and smoother operation. It can be used in direct injection engines like diesel engines, hot air engines. In this project report we provide an overview of the issues concerning different aspects of multipurpose machine using scotch yoke mechanism .The project report focus on the principle of scotch yoke mechanism, type of tooling and machining parameters and process performance measure, which include cutting speed, depth of cut,material removal rate with different type of equipments which can be run simultaneously and fabricate the work piece In multipurpose machine has been presented . the presented results can help to plan the machining of work piece with expected tolerance. The following major conclusions may be drawn from the present project report. 

Multipurpose machine is derived from

turning lathe which has been a well

established industrial processes offering attractive capabilities for handling work piece of various length to be used at micro level. 

We have presented the development of multipurpose machine in various modes by which it can be actively adopted.



We have explained the various parts and components of multipurpose machine using scotch yoke mechanism.



Different types of attachments and tools which can be implemented on multipurpose machine has been discussed



We have discussed the entire time line and working chart .

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Development of Multi Purpose Machine With Scotch Yoke Mechanism The vital need for the fabrication of a multipurpose machine is significant in the much delay and time as well as energy wasted in using simple hand tools to carry out jobs. Moreover, the cost of a lathe machine is too high for an average user. Also, multipurpose machine will helps to reduce the cost and consequently increase the rate of production and craftsman’s skill. The general purpose for any project is to find solutions on a certain problems. It’s also gives main idea how the project to be completed. For this project, the problems that need to be solved are:1) Any manufacturer wants to reduce cost and time taken to complete a product but gives better quality products and increases the outputs. 2) Manufacturer tends to upgrade their machines to compete with the new machine with new technology. 3) Lathe machine cutting tool can easily break and needs to enhance its tool life.

The continuous quest to have the problems of man and his growing needs solved has led to the establishment of factories and other industries, which necessitates an intermediate technology. However, simple hand tools that were in use before are no longer efficient for mass production. Then, there comes the need for urgent attention to better and useful multipurpose machines.

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REFERENCES [1]

Mack. R., Mueller, R., Crotts, J., & Broderick, A. (2000). Perceptions, corrections and defections: implications for Scotch yoke mechanism, 10(6), 339-346.

[2]

Mattila, A.S. (2001). The effectiveness of service recovery in a multi-industry setting. The Journal of Services Marketing, 15(7), 596-583.

[3]

McDougall, G.H.G., & Levesque, T.J. (1999). Waiting for service: the effectiveness of recovery strategies. International Journal of Contemporary mechanism 11(1), 6-15.

[4]

Michel, S. (2001). Analyzing service failures and recoveries a process approach. International Journal of kinematic links, 12(1), 20-33.

[5]

Miller, J.L., Craighead, C.W., & Karwan, K.R. (2000). Service recovery: a framework and empirical Investigation. Journal of links Management, 18(4), 387400.

[6]

Six types of service scotch-Yoke mechanism and rack and pinion mechanism (Chase and Stewart, 1994)

[7]

http://ezinearticles.com/?Using-Your- multipurpose machines –Way & id=4352151

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Project pictures

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