INTRODUCTION TO ERGONOMICS AND ANTHROPOMETRY

CHAPTER 1 INTRODUCTION TO ERGONOMICS AND ANTHROPOMETRY 1.1 ERGONOMICS: Ergonomics is an approach which puts human needs at the focus of designing technological systems. The name “Ergonomics” comes from the Greek word “ergon” which means work and “nomos” which means law. The core sciences from which ergonomics is drawn are: ➢ Psychology: It is concerned with human information processing and decision-making capabilities. ➢ Anatomy: The contribution of basic anatomy lies in improving physical 'fit' between people and the things they use. ➢ Engineering: it is related with designing of technical products and services by taking human characteristics into account. Ergonomics comes into everything which involves people. Work systems, sports and leisure, health and safety should all embody ergonomics principles if well designed. The aim behind having a product with ergonomic design or an ergonomic workplace is to ensure that the human working over there is safe and comfortable to be in the same position for a longer period of time. For ergonomics, human is a part of a system and must be fully integrated into it at the design stage. Human requirements are, therefore, system requirements, and can be stated in general terms as: ➢

Equipment that is usable and safe.

➢

Environment that is comfortable and appropriate with the task.

➢

Tasks those are within people’s limitations.

The implementation of ergonomics in the system design should make the system work better by eliminating aspects of systems which are undesirable, such as, ➢

Fatigue 1

➢

Accidents, injuries, and errors.

➢

User difficulties.

1.1.1 DOMAINS OF ERGONOMICS: Domains of specialization of ergonomics can be classified as follows: 1. Physical ergonomics is concerned with human anatomical, anthropometric, physiological and biomechanical characteristics. 2. Cognitive ergonomics is concerned with mental processes, such as perception, memory, reasoning, and motor response, as they affect interactions among humans and other elements of a system. 3. Organizational ergonomics is concerned with the optimization of sociotechnical systems, including their organizational structures, policies, and processes.

1.1.2 APPLICATIONS OF ERGONOMICS: Ergonomics is successfully applied in fields of: i. Aerospace ii. Product design iii. Transportation iv. Nuclear and virtual environments. v. Designing of workplaces.

1.2 ERGONOMICS IN AUTOMOBILES GOT

TO INCLUDE

POINTS from design of automobile interiors It is essential that the ergonomic input to the vehicle takes place throughout the design process. For this very purpose, most of the automobile manufacturing companies employee ergonomists. Ergonomists, usually, follow an inside out approach for the design. By following this approach, the ergonomist would get clear idea about the size, number and age of the future occupants along with their comfortable posture. This would then help the

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ergonomist to design the display and control interfaces with the knowledge of hand and eye ranges. The exterior of the vehicle would then be designed. As far as an automobile design is concerned, an ergonomist has to work on following aspects: ➢ Design of driver’s seat ➢ Design of control systems ➢ Design of hand lever and steering. Ergonomists have had to find methods of communicating ergonomic information to those who need to use it. There are a wide range of standards, guidelines and recommendations available in many areas of ergonomics that are pertinent to automotive design. The Society of Automotive Engineers (SAE) in the US has been particularly active in the generation of such Standards. The most relevant to the ergonomist are: SAE J826

H-point (ISO 6549)

SAE J1100

Seating reference point

SAE J1100

H-point travel path

SAE J1517

Driver selected seat position

SAE J941

Eyellipse (ISO 4513/BS AU 176)

SAE J1052

Driver and Passenger head position contours

SAE J287

Hand controls reach envelopes (ISO 4040/BS AU 199).

Other tools which may be used involve use of various soft wares like CAD, MANIKINS, and 2D package drawings. These MANIKINS are basically used to examine occupant accommodation. The 2D package drawings often provide the first visualizations of the proposed vehicle occupants. They are produced after the product planning stage, when the market specification has taken place and the basic parameters of the vehicle are known.

1.2 ANTHROPOMETRY The word Anthropometry has been derived from the Greek words “anthropos” meaning man and “metron” meaning measurement of human body. Anthropometric data are used in 3

ergonomics to specify the physical dimension of workspaces. It can be divided into two types: •

Static anthropometry

•

Dynamic anthropometry

Static anthropometry is concerned with the measurement of human subjects in rigid, standardized positions (e.g. static arm length being equivalent to its anatomical length). Static anthropometric data are used in designing equipment for the workplace where body movement is not a major variable, e.g. seat breadth, depth and height. Dynamic anthropometry is concerned with the measurement of human subjects at work or in motion (e.g. functional arm reach is a factor of the length of the upper arm, lower arm and hand, as well as the range of movement at the shoulder, elbow, wrist and fingers). Dynamic anthropometric data can be used to establish control locations using reach envelopes for the hands and feet and locations of head restraints, seat belts. For any design involving the use of anthropometric data, 4 set of constraints have to consider. They are as follows: ➢ Clearance: Clearance means provision of sufficient space around the work-place. ➢ Reach: Reach constraint refers to the ability to operate controls from a comfortable

position. ➢ Posture: Posture means the way in which the driver ➢ Strength : Strength is concerned with the application of force in operation of controls.

1.2.1 APPLICATIONS OF ANTHROPOMETRY: Anthropometric studies are used in the design of modern aircraft, preparation for cosmetic surgery, etc. When paired with ergonomics, it is used to craft office workstations, aircraft cockpits, and home furniture. Anthropometry is also used in safety design, specifically for infants and children.

1.3 ANTHROPOMETRY IN AUTOMOBILE DESIGN

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In case of automobile design, anthropometric factors are used for occupant accommodation. Various anthropometric factors have to be considered, which may include, i. Sitting height ii. Sitting eye height iii. Sitting shoulder height iv. Thigh clearance, etc. In order to establish statistical concepts that determine human variability, a large amount of data relating to various dimensions of different humans is carried out. With the help of this data a normal distribution curve is obtained.

A normal distribution is fully defined by its mean and standard deviation—if these are known any percentile may be calculated without further reference to the original measurements of individual people.

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CHAPTER 2 DESIGN OF DRIVERS SEAT Seat is an important part of car. Drivers spend great deal of time on the seat. The purpose of a seat is to provide stable bodily support in a posture that is: (i) Comfortable over a period of time; (ii) Physiologically satisfactory; (iii) Appropriate for driving. Comfort will depend upon the interaction of seat characteristics, user characteristics. Seat characteristics include seat dimensions and seat angles while user characteristics include body dimensions, body aches and pains.

2.1 Anthropometric factors related to user characteristics:

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1. 2. 3. 4. 5.

Seating height Seating eye height Sitting shoulder height Sitting elbow height Thigh clearance height 6. Popliteal height

User characteristics 1

1) Seating height: Vertical distance from the sitting surface to crown of

the head. It is used to determine overhead clearance. 2) Seating eye height: Vertical distance from the sitting surface to the

inner canthus (corner) of the eye. 3) Sitting shoulder height: Vertical distance from the seat surface to

the acromion (i.e. the bony point of the shoulder). 4) Sitting elbow height: Vertical distance from the seat surface to the

underside of the elbow. 5) Thigh clearance height: Vertical distance from the seat surface to the top of the

uncompressed soft tissue of the thigh at its thickest point, generally where it meets the abdomen. 7

6) Popliteal height: Height of underside of the knee above the bottom surface.

7. Forward reach 8. Knee height 9. Buttock popliteal height 10. Buttock knee length.

User characteristics 2

7) Forward reach: horizontal distance between back of the seat and fingertip. 8) Knee height: vertical distance between floor and top of knee. 9) Buttock popliteal height: horizontal distance between seat and underside of knee. 10)Buttock-knee length: horizontal distance between seat to front of knee.

2.2 Anthropometric factors related to seat design: 1. Seat height (H): As the height of the seat increases beyond the popliteal height of the user, pressure is felt on the underside of the thighs. Also, if the height decreases, the driver will face greater problems in sitting down and standing up and also will require greater leg room. It is therefore necessary to have proper seat height. Optimal seat depth height may be that chosen D- Seat close to the popliteal seat height.

H-Seat height A-Seat surface to bottom of backrest B- Seat surface to midpoint of lumbar curve C- Vertical height of backrest.

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Seat dimensions 1

2. Seat Depth (D): The seat width should not be increased beyond the buttock popliteal height. If this happens the driver will not able to rest his back effectively without giving adequate pressure on the knees which is undesirable. 3. Backrest: The higher the backrest, more effective it is to provide rest to back while in the driving posture. Another factor such as mobility of shoulder should also be taken into account. Backrest may be differentiated into 3 types any one of which may be applicable: ➢ Low level backrest ➢ Medium level backrest ➢ High level backrest. For design of automotive seats high level backrest is preferred, since it provides support right from the lumbar to head. It is usually of the shape of the spine.

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ß: Seat angle or tilt α: Backrest angle rake angle

SEAT DIMENSIONS 2

4. Seat angle or tilt (ß): A proper seat angle should be chosen as it helps the user to maintain good contact with the backrest. Excessive angle reduces the comfort ability of the driver. For most cases it is approximately 5-10 . 5. Seat width: Distance between the hands rests of a seat. It should be some 25 mm less on either side than the maximum breadth of the hips 6. Backrest angle rake angle (α): As the backrest angle increases, a greater proportion of the weight of the trunk is supported. Increasing the angle between trunk and thighs improves lordosis. (A medical term used to describe an inward curvature of a portion of the vertebral column).

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Seat dimensions 3

7. Forward leg room: In sitting position the provision of adequate forward leg room is essential if the user is to adopt a satisfactory posture. As shown in the figure above “D” is the forward legroom, which is the total horizontal distance between buttocks and the toes, buttock-popliteal length B and foot length F sitting on a seat of height H. 7. Seat surface: The purpose of shaping or padding the seat surface is to provide an appropriate distribution of pressure beneath the buttocks. The seat surface should be more or less plane rather than shaped, although a rounded front edge is highly desirable. Covering materials should be rough to aid stability.

2.3 Seat Material: Conventional seating systems include a steel frame, with springs attached to provide support and flexibility to foam cushions. The main structure of seat backs is traditionally made of metal. This is often a tubular steel frame, with various brackets and reinforcements attached by welding or mechanical fasteners. The central section of the frame is normally closed using steel sheet, which may have contours to provide added stiffness. Some of the properties which an designer should keep in mind while selecting a material for driver’s seat are as follows: 11

1) Transmissivity: It amounts for the vibrations transmitted from the seating platform to the driver. 2) Durability: The consistency of foam characteristics during prolonged use.

3) Weight: Higher weight of seat higher will be weight of the car. 4) Ease of economy: The cost of material should be affordable as increase in this factor will cause an increase in price of the vehicle. 5) Easy to recycle: It should be environment friendly.

Traditionally steel has been the material of choice to meet stiffness and loading requirements for automotive seating applications. The use of plastics in these structural applications has been limited due to its low stiffness and strength when compared to steel. As far as foam material is considered, flexible polyurethane foam (FPF) is used, which has good reliability and flexibility. Polyurethane foam can be formulated to dampen the vibration that causes discomfort for the operator of a vehicle effectively.

Chapter 3 Design of steering and controls 3.1 Introduction-Design of steering The most common way to transmit movement by mechanical control is rotation. According to shape, different types of rotary controls can be differentiated- steerings, rotary switches, and knobs. Design, selection and arrangement of hand wheels must be considered according to the criteria of human factors and ergonomics. The dimension and position of hand wheel affect the strain to which user is subjected. Design dimensions of hand wheel must be compatible with anatomical, anthropometrical and physiological marginal human conditions.

3.1.1 Anthropometric Design Parameters The movements of flexion and extension must be considered while designing a steering. These movements occur at the wrist joint complex—that is at the ‘true’ wrist joint and at the various articulations which are present between the eight small bones of the wrist . 12

The grip used for hand wheels is power grip- in which the fingers and thumb are used to clamp the object against the palm. The thumb wraps around the back of the fingers to provide extra stability and gripping force. Thus for defining the dimensions of hand wheel various anthropometric measurements of hand has to be considered.

IMPORTANCE OF THESE FACTORS WID VALUS AND FOOT IMAGES JUST LIKE HAND 3. Thumb length 1. Hand length 4. Index finger length 2. Palm length. 5. Middle finger length 12. Hand breadth 6. Ring finger length 13. Hand breadth (across thumb) 7. Little finger length 9. Thumb thickness

Anthropometry Of Hand 1

10. Index finger breadth

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Anthropometry Of Hand 2

8. Thumb breadth 11. Index finger thickness 14. Hand breadth 15. Hand thickness

Anthropometry Of Hand 3

The design dimensions of the hand wheel — such as shape, material, and surface — are important factors influencing the operating effectiveness, with the characteristics performance, stress and strain of the user and safety criteria. Shape – it should be such that minimum strain on the hands is guaranteed. Surface- Surface quality should neither be so smooth as to be slippery nor be so rough as to be abrasive.

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Material-. Skin´s degree of moisture and the material´s properties such as surface roughness must be considered as unsuitable materials lead very quickly to destruction of the upper skin layer. Handwheels should facilitate two-hand control and permit rapid movements as well as accurate movements when needed. If rotations > 60° are required on a handwheel, the hands must be repositioned. The thickness diameter of the handwheel should not be less than 1.9 cm or more than 3.2 cm.

1.2

CONTROLS MANUAL

CONTROL DEVICES AND

FROM BODYSPACE There are many interactive modes that can be used to link a human response to a desired machine action. For ordinary human–machine systems, for large, slow controls requiring high levels of force the arms and legs are used with force and position feedback occurring through the hands and feet as occurs in the use of levers and foot pedals. These are known as manual controls. Manual controls can be classified according to any number of functional categories depending on the technical aspects of the machine being controlled. From an operational viewpoint, controls are classified by the nature of their machine function and by physical structure and appearance. Controls for an automobile can be classified as follows: 1) Large linear controls ➢ Foot pedals ➢ Levers. 2.) Small Linear Controls ➢ Push–Pull Knobs And Handles ➢ Push Buttons

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3.) SWITCHES ➢ Toggle ➢

Rotary

➢

Rocker

1. Foot pedals: For accelerator pedals, the resistive force should not exceed 44 N. The

recommended angle between a foot pedal and the floor varies with seat height. Recommended foot pedal stroke length varies with the type of vehicle. Larger displacements (10–18 cm) are desirable for brake pedals for safe braking especially under slippery road conditions. Foot pedals should be approximately the same width as the sole of the shoe. Pedal separation should be at least 5 cm edge to edge. Pedal shape is not a significant factor except in providing initial visual orientation. 2. Levers: They are used for shifting gears. The knob at the end of a lever is labelled to facilitate identification with a particular function. A knob in the shape of an end rounded cylinder or ball is preferable when a firm or prolonged grip is required. Recommended ends diameters are 3.2 cm for full grip.

2.) Small linear controls-push buttons: Minimum force required to operate them is 0.25kg and maximum is 2 kg. For a sloping vertical plane, buttons are preferred to be at 90° to the panel.these buttons may have built in illumination. The minimum distance throught which they should be separated from other buttons is 15mm and maximum is 22mm. The radius through which the swith gets pushed in is 50 mm. 3.) switches:

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Spring is loaded between central positions, which provides the resistance to build up then fall down. 1.2

Direction of Control Movements:

To prevent control reversal errors, it is important for controls to operate in directions that are compatible with associated display or vehicle movement. Factors to be taken into account include: 1. Location and orientation of the control relative to the operator. 2. Position of the display in relation to the control and the 3. Orientation of the operator relative to vehicle. 4. Type of action being caused by activating the control. Action desired

Control movement

Turn on

Up or press inwards.

Turn off

Down or pull outwards

Turn or move

Right,clockwise

right Turn or move

Left,anticlockwise

left

3.4 HUMAN FACTORS IN CONTROL: 3.4.1. Anthropometric Factors

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Anthropometric factors to be considered in designing manual control systems include those related to clothed body dimensions for the desired population percentile in combination with reach capabilities, working positions for operators. 3.4.2. Biomechanical Factors Biomechanical factors include strength in terms of specific force exertion capability, type of control motions required to operate controls, speed and precision of control motion required, reach capability for given control operation and effects of body acceleration upon performance. Good anthropometric design facilitates good biomechanical design. 3.4.3. Psychological Factors Psychological factors designing manual controls include those related to control location, arrangement, spacing, feedback generated, and logic as affected by interaction with the operation of other controls.

CHAPTER 4 DESIGN OF DISPLAY PANELS 4.1 INTRODUCTION The ways in which displays can be used to support human–machine systems have multiplied. The basic aim behind the display design is that the information provided to the user should be appropriate for both user and machine system. Providing appropriate information support, in a way that is meaningful and easily interpreted, will improve the overall performance of the human–machine system. Displays may provide simple warnings or quantitative information. Most of the displays are based on the rise and fall of the needle.

4.2 CAR DASHBOARD DISPLAY A dashboard is a control panel placed in front of the driver of an automobile. A dashboard display atleast has a speedometer and a fuel gauge. In addition to these, the display

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will feature some combination of a tachometer, charging system gauge, oil pressure gauge and engine temperature gauge.

4.2.1 Speedometer: The speedometer, one of the most frequently used tools, is used to judge how fast the car is going in kp/h (kilometres per hour).

4.2.2 Fuel gauge: it gives an idea about the fuel quantity in the vehicle. It indicates full, empty & half filled tank.

4.2.3 Temperature Guage: this measures the temperature of engine coolant in degrees. It is important to monitor the temperature guage to ensure the engine is not overheating.

4.2.4 Charging System Guage: The charging system provides the electrical current to the vehicle. There are two types of gauges used to monitor charging systems: a voltmeter which measures system voltage and an ammeter which measures amperage going out of, or coming into the battery.

4.2.5 Tachometer: It measures the rpm of engine.

4.3 DESIGNING OF DISPLAYS To design an display panel, various factors have to be considered which are in relation with: 1. Design of symbols or icons for display 2. The use of words and numbers. 3. The organization of display.

4.3.1 design of symbol or icons in display: Symbols and icons are commonly used in displays to indicate system functions and to provide information from the system. Various characteristics that have to be considered while designing a symbol are as follows:

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4.3.1.1 Size: The precise size of symbols in a display is usually determined by three features: typical viewing distances, display quality, and viewing conditions. Display quality may vary in accordance with resolution, contrast, focus, and glare. Viewing conditions depend upon environmental factors such as noise, smoke or dust; they also include physiological and psychological factors such as fatigue, eye strain, and workload.

4.3.1.2 Shape: If effective contrasts in shape are used they can reduce the time it takes for users to identify appropriate information. Symbol shape can also be used to help organize displays.

4.3.2 The use of words and numbers.: Symbols often rely on visual associations and the context in which they appear for their meaning whereas words are rarely ambiguous. Words can also convey more complex meanings and ideas in a way that would be virtually impossible with symbols. Similarly, use of numbers is often the most effective way of conveying quantitative information. Various factors which are to be considered for designing words and numbers ar as follows:

4.3.2.1 Size, simplicity, and shape: As with symbols, the size of letters is largely determined by viewing distance, display quality, and viewing conditions. Font size is almost always determined via agreed international standards. Letters are usually kept as simple as possible in order to enhance legibility. Also, proper space between words and letters is to be ensured.

4.3.3 The organization of display: Good display organization is the most important determinant of whether or not users can direct their attention to the relevant information. It also plays an important part in determining how easy that information is to understand and respond to.

4.3.3.1 Configurality: 20

Configurality refers to the way in which elements within displays are arranged in order to convey information effectively. Careful attention is paid to the nature of the relationship between elements in displays in order to allow easy interpretation.

4.3.3.2 Design simplicity: In addition to the use of simple symbols and text, the simplicity of the display as a whole needs to be considered, for which following factors should be taken into account: (a) Overall density: This refers to the percentage of the total number of possible

characters or symbols which could occur in the display space. (b) Local density: This is the amount of space which is filled around a target area or

symbol. (c) Layout: this builds on consideration of grouping and considers the irregularity, or layout complexity, of functional groupings in a display.

4.3.3.3 Creating contrasts between groupings: Creating contrasts between different parts of the display layout can help users to direct their attention quickly to appropriate parts of the display. Discrimination between symbol and text clusters, or families, can also be achieved by the use of elementary features in the displays. These features include: (a) Colour (b) Size (c) Shape (d) Orientation (e) Increasing the size of critical symbol features.

4.4 Creating: Once the designer is done with all the considerations required to design the dashboard, the next step is the actual process of designing. The process of creating and evaluating the design is as follows: There a number of steps which designers typically follow when designing displays. The earliest phase of design usually consists of formulating a clear statement of requirements 21

for the display. This will include details about what should appear in the display. Prototype display designs will be created. The precise nature of the display, however, will be determined by a number of other considerations. These include the tradition and philosophy of the company for whom the display is being created, precedents created by displays of a similar nature, customer expectations, recommendations from international standards along with government requirements, and the likely costs for development.

CHAPTER 5 USE OF SOFTWARES IN ERGONOMIC DESIGN 5.1 Introduction

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Day to day technology is changing for better customer satisfaction in the Automobile sector. Due to the evolution of CAD tools, the accuracy of designs has increased. Various CAD packages like CATIA, RAMSIS, and SAMMIE CAD system are used for the ergonomic analysis of the automobile. The basic aim behind using this software is ensuring comfort and safety to the passengers. 5.2 SAMMIE CAD: The SAMMIE system is a computer based Human Modelling tool. It was developed by SAMMIE CAD Limited, which was started in 1986 by the SAMMIE system originators to continue the consultancy work of the SAMMIE Research Group, U.K. It is approved by SAE. Its capabilities make it an invaluable tool to designers working on products that are used by people. The system offers the following advantages: •

3D analysis of fit, reach, vision and posture.

•

Reduced timescale.

•

Early input of ergonomics expertise.

•

Rapid interactive design.

•

Cost effective ergonomics.

The use of this system ensures proper fit, reach, vision and posture for the user. 5.2.1 Fit: Comfort ability of user in terms of fit is ensured by this system. It can be done for various age groups using the anthropometric data. It can also create allowances for clothing and personal equipment. 5.2.2 Reach: Reach can be assessed by simply positioning hands on a certain position and accordingly reach of legs can be seen. The human model will automatically display a geometrically feasible reach posture .

5.2.3 Posture:

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The human model is displayed as a set of 18 joints and 21 straight rigid links structured hierarchically to represent the major joints and the body segments. Predicted postures can be quantified in terms of flexion/tension abduction/adduction and lateral/medial rotation at these joints. The predicted posture is clearly a function of the human model's fit, reach and vision and a poor posture will usually require modification to the size of the workstation or the layout of controls and displays. 5.2.4 Vision: Viewing angles and distances, perspective views, mirrors and reflections, and spherical aperture projections can all be assessed interactively using the SAMMIE system. A mirror modelling facility has been developed which has successfully designed mirrors for a variety of vehicles, meeting both legislative and ergonomics criteria. The focal length, convexity/concavity, size and orientation of the mirror can all be interactively adjusted to display the required field of view on the mirror surface 5.3 Specifications: SAMMIE is a data driven system allowing the user to control the anthropometry and joint movement limits of the human models from any available set of data. The system includes a number of male and female, civilian and military data sets as standard. In addition, SAMMIE allows new data sets to be created from anthropometry found in the literature. Finally, Human models can be created directly from data taken from human subjects using the standard methods. Selection of different databases and percentile values is interactive without the need for direct manipulation of the database. The human models have 23 body segments and 21 constrained joints and are capable of the full range of normal human movement. The joint movement ranges can be constrained to reflect acceptable or preferred comfort ranges inside the normal joint range or to reflect the effects of restrictive clothing or physical disability. Use of SAMMIE reduces the number of physical mock-up and prototype tests in a design program by allowing the designer to identify human-workplace interaction problems and explore a variety of design solutions in a virtual environment.

5.4 Requirements:

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SAMMIE has been solely developed for personal computers on the Windows NT /2000/XP operating systems. SAMMIE's hardware requirements are generally modest. A modern PC with Intel Processors running at 1GHz or better is sufficient. A minimum of 256MB of system RAM and a compatible graphics card with 64MB of video memory or greater are recommended. The SAMMIE system is a licensed product. The license is granted in perpetuity and enables commercial use at a single geographic site on a single Personal Computer. Pricing varies depending on the number of licenses required and whether the license is commercial or academic.

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