Controls

1
Chapter 17

• Controls

2
Guideline 1

• Select the Proper Type of Control
• People impose their will on the machine through
  controls.
• The machine communicates to people through
  displays.
• Types of systems
• Open-loop
• Closed-loop

3
HumanMachine System

• Human machine system. Information flows from
  human to machine through controls. Information
  flows from machine to human through displays.
  Displays include instruments, labels, and
  accompanying printed instructions and warnings.
  The boundary between the human and the machine is
  the user interface.

Physical Environment
4
Types of Controls

• Decide discrete or continuous
• Select part of the body to implement mental
  command
• Choose mechanical interface between human body
  and machine interior
• Consider amount of human power required
• Consider errors and speed

5
Guideline 2

• Select the Proper Control Characteristics (See
  Table 17.3)
• Force
• People variables
• Muscles used
• User population
• Percentile designed for
• Control variables

6
Keys and Pushbuttons

• Keys should be non-round, concave on top, and
  consistently displaced.
• Use key interlocks.
• Feed back activation to operator.
• Use shape to indicate function.
• Avoid palm buttons.

7
Knobs

• Circular knobs depend on hand friction on
  circumference.
• Knob shape can compensate for slippery grip.
• Increasing diameter increases torque.

8
Cranks

• Provide high coefficient of friction.
• Allow grip to rotate on crank.
• Consider a sphere.

9
Hand Wheels

• For valve control, increase radius to reduce
  tangential force.
• Use recommended heights.
• Rim diameter should be 2050 mm.
• Provide legible display.
• For vehicle control, follow diameter and
  orientation recommendations.
• Consider permitting angle adjustment.

10
FootLeg Controls

• Provide greater force and free the hands.
• May be switches or pedals.
• Consider friction problems (shoe sole, dirt,
  debris).
• For continuous control, bend the ankle by
  depressing the toe.
• Consider knee switches.

11
Guideline 3

• Prevent Unintended Activation
• More severe consequences require greater
  precautions.
• Consider that operators may bypass the guard if
  it makes operation difficult.
• All equipment should have an emergency stop
  control.
• Consider two reaction times
• Human (sensing, deciding, carrying out)
• Machine

12
Methods of Reducing Accidental Activation

• Key or special tool activation (locks)
• Interlocks
• Barriers or covers
• Recessing
• Spacing
• Resistance
• Direction

13
Guideline 4

• Prevent Incorrect Identification
• Labeling
• Color
• Shape
• Size
• Mode of operation
• Location

14
Labeling

• Labels should be
• Legible
• Located properly
• Understandable

15
Color

• 8 of males, .4 of females have color perception
  problems
• Use 8 or fewer colors.
• Consider lighting requirements.
• Consider color stereotypes.
• Consider cultural differences in color
  stereotypes.

16
Shape

• Shape can be identified in the dark.
• Use up to 9 different shapes.
• Tactual shape coding is slower than color coding.
• Shapes can be a visual signal.
• Tactile signals (e.g. pimple, ridges) can help.

17
Size

• Only 2 or 3 different sizes can be
  differentiated.
• Larger sizes give mechanical advantage.
• Use larger sizes in cold environments.

18
Mode of Operation

• Consider push/pull vs. rotate vs. slide.
• Mode of operation may be a backup for
  identification methods.
• Location can identify controls and groups of
  controls.

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Guideline 5

• Make Accomplishments Equal Intentions
• Require verification of critical commands.
• Make complex sequences of actions user-friendly.
• Use more care and testing for actions with
  multiple steps.
• Check input for validity.
• For continuous controls, consider
  control/response ratio.
• Control positions often act as displays.

20
Population Stereotypes

• Engineers habit patterns may not be the users
  habit patterns.
• Stereotypes are often country-specific (light
  switches, water faucets, car blinkers).
• Consider labeling.

21
Conventional Control Movements in the United
States
22
Guideline 6

• Properly Locate and Arrange the Controls
• Foot Controls
• Avoid foot controls for standing operators.
• For continuous control, leg should fully extend
  at bottom of stroke.
• For discrete control, use one leg.
• Have straight line between pedal and back
  support.
• Comfort may be more important than force
  capability.
• Design to avoid fatigue.

23
Guideline 6 (cont.)

• Hand Controls
• Keyboards
• Manipulative controls
• Knobs
• Switches
• Force controls

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Arrangement of Controls

• Group related controls and displays together.
• Minimize layout complexity.
• Have blank space on the panel.