ECE 796/896 Human Factor Engineering

1. ECE 796/896Human Factor Engineering Chapter 11 Controls and Data entry Devices

2. Functions of Controls • Transmit control information to some device, mechanism or system. • Types of information: discrete, continuous, and cursor positioning. • Generic types of controls: identification, size, control-response ratio, resistance,lag,backlash,deadspace,and location.

4. Identification of Controls • It some cases rapid identification of a control is critical (even potentially fatal). • A coding problem, primary methods are, shape,texture,color,size,location,operational method and labels.

6. Shape Coding of Controls • Tactile sensitivity • US Air Force control knobs • Divided in three classes: • Class A: Multiple rotation • Class B: Fractional rotation • Class C: Detent Positioning

9. Texture coding of Controls • Added to shape is texture. • Experiments have shown that distinct texture are easy to select, but among version of texture selection is much less accurate.

11. Size Coding of Controls • Size is not as good as shape. • Differences less than 1/2 inch diameter and 3/8 in thickness are not desired. • It would better to combine different textures, plus diameters and thickness to allow for more distinct knobs.

13. Location Coding • Spatial coding, need to make sure devices are far enough apart so that your kinesthetic sense can select the correct one.

14. Operational Coding • Each control physically operates differently (push-pull,rotary, toggle,…) • Should avoided, need to keep things compatible.

16. Color Coding • Meaningful colors (red=stop, green=go) • Problem with dirt or low light. • Combine with size or shape to make more effective.

17. Label Coding of controls • Most common method. • If done properly, requires little or no training. • Labels take time to read. • Placed above the control so that using the control does not block reading the label.

18. Coding Methods • Use two or more coding systems to provide unique identification. • Completely redundant codes are good. • Environment is critical • Task is critical • Maintenance of the system - parts • Controls that require tight grips, should not be coded with shape points or uncomfortable shapes.

19. Control - Response Ratio • Control - response ratio (C/R) • Low C/R = high sensitivity • High C/R = low sensitivity

21. Optimium C/R Ratios • For a control knob optimum is easy to find minimizing the response time and travel times. With joysticks or levelers the curves are flat, because it works through such a short angle. There is still debate.

22. Resistance in Controls • Pure displacement control with very little resistance are called free-position or isotonic. • A pure-force or isometric control has no movement, it responds to pressure. • A combination is generally best.

23. Types of Resistance • Some type of resistance is usually desirable. • Elastic, static, coulomb friction, viscous damping, and inertia. • Elastic: Spring loaded controls, varies with displacement. • Static and coulomb friction: Resistance is maximum to initial movement. Coulomb friction is sliding friction and does not vary with speed or position.

24. Cont. • Viscous Damping: The force is a function of the speed at which the control is moved. Good for rate control. • Inertia: Varies by acceleration, has a laging affect on the initial response. • Most controls combine different resistance types.

26. More on Controls • Deadspace: The amount of movement around the null position that causes no response. • Backlash: A mechanical problem, causes a un-determined response for some area of control movement.

27. Design of Specific controls • Cranks and Handwheels: The size and placement of the wheel has a direct bearing on what aspect of operator performance is most desired.

28. Knobs for Producing torque • Control knobs are often used to apply high levels of torque to equipment. • Water facet, wood clamp … • Knob shape had no effect when the grip was good. However, when there was slipping more sides applied less torque.

31. Stick Type Controls • The length of the joystick has little effect on control performance as long as the C/R ratio (2.5-3.0). • Finger operated was best.

33. Multifunction Hand Controls • Aircraft hand controls - combine control functions. • Principles of Design: • Operator should not have to see the control to operate it. • Hand should remain in contact through out the critical operation phase. • Auxiliary controls should be able to be operated without loss of contact.

35. Foot controls • Used to control one or two functions. • Usually not desired due to other ergonomic factors. • Ankle involvement, load on the leg and position of the ankle to leg.

36. Pedal Design Considerations • In general results have been in consistent on tests.

37. Foot controls for Discrete Control action • Some studies have shown that feet could be made to more tasks and in a more sophisticated way.

39. Automobile Brake and Accelerator Pedals • Most common usage of foot controls. • Most designs have the accelerator lower than the brake pedal. However, if they are at the same level movement time is faster. • There are other factors to consider such as runaway car syndrome.

40. Data Entry Devices • Keyboards of any type are superior to other types of data entry devices. • Accuracy = data quality presented to operator. • Speed and accuracy will be greater: • Operator is familiar with the format • Text is entered upper/lower case • Long messages are broken into chunks

41. Chord vs. Sequential Keyboards • Sequential: Data entered one character at a time, most common. • Chord: A single input unit requires simultaneous activation of two or more keys. (steno, piano, mail-sorting) • Chord ones are harder to learn, one hand operation advantage.

42. Alphanumeric keys • Standard: QWERTY, because of the letter sequence on the top line. • Appears to intentionally been designed to slow data entry rate.

44. Numeric Keyboards • Two different arrangements of the numeric keyboard (keypad). • Telephone - Calculator • Telephone appears slightly faster, better accuracy.

46. Keyboard Feel • A function of: key travel, resistance characteristics, and hysteresis. • Hysteresis - To little = key bounce, to much = slower typing speed • Significant study of three designs - snap ring, elastomer,linear spring. • Preferences: least = spring, elastomer = the best in speed and errors

49. Membrane Keypads • Commonly used on electrical appliances and industrial equipment. • They have some HF issues: no key travel to sense, more force is required, the actual contact areas are hard to locate. • Improvements: audio tone, caps, and key shapes. (audio worked the best)