Communication: Controls

Controls: Key Learning Points Type of Control Control Characteristics Unintended Activation Prevent Incorrect Identification Make Accomplishments Equal Intentions Properly Locate and Arrange the Controls

Control Definition A control is an input device on a machine that allows a human to communicate with the machine that functions with in a system.

Types of Communication Systems Open-Loop System Closed-Loop System

Type of Control: First Step Discrete control Continuous control

Type of Control: Second Step What part of the body will Implement the mental command or desired action. –Hand –Arm –Finger –Foot

Type of Control: Third Step Mechanical interface between the human body and the machine interior

Type of Control When selecting the control type, consider the potential and affects of errors.

Proper Control Characteristic Force Keys and Pushbuttons Knobs Cranks Hand Wheels Foot / Leg Controls

Proper Control Characteristic: Force People Variables –Muscles used –User population –Percentile population Control Variables –Purpose –Design

Proper Control Characteristic: Keys and Pushbutton Concave “Pimple” Consistent Spacing Consistent Displacement Key Interlocks

Used for non-critical operations A series of buttons can be used in sequence. Has only two settings, on or off Operated with the fingers or hand. Proper Control Characteristic: Pushbutton

Operated by finger or hand Can be rocked forward, backward or sideways Usually has two positions Sometimes 3 positions Proper Control Characteristic: Rocker Switch

Proper Control Characteristic: Knobs For a 35 mm diameter or length the maximum torque should be 7 N-m. An oval door knob vs a rounded knob is a good compromise for bearing surface and esthetics. eliminate sharp edges and small radii.

Proper Control Characteristic: Knobs For circular knob designs, if the rotation axis is parallel to the base of the fingers, requiring forearm rotation, increasing diameter increases the torque up to a diameter equal to the hand grip span. On average this will be around 50 mm. If the axis is perpendicular to the palm/forearm, torque increases with diameter up to about 50% of hand length, which is about 90 mm.

Proper Control Characteristic: Rotary Selector Switch Turned by hand No more than 24 settings 15 degrees between settings Increase value clockwise Decrease value counterclockwise

Proper Control Characteristic: Thumbwheel A special knob which is operated by the thumb while the fingers may be engaged in another activity. Limited range continuous adjustment

Proper Control Characteristic: Cranks Knurling is a series of small ridges or grooves on the surface or edge of a metal object, such as a thumbscrew, to aid in gripping.

Proper Control Characteristic: Hand Wheels If pushing is not required, knurls permit as much as 70% more torque than lids that are not knurled.

Proper Control Characteristic: Cranks Since the grip normally does not move within the hand, a high coefficient of friction is good. However, the grip should rotate on the crank to allow good hand-wrist orientation throughout the rotation.

Proper Control Characteristic: Hand Wheels Two hands can be used to generate greater torque. Two forces involved in using a hand wheel: –The cranking force to unlock the valve –The turning force

Proper Control Characteristic: Hand Wheels Power Steering –Wheel diameter mm. –Wheel orientation 30˚. Non-Power Steering –Wheel diameter of mm. –Wheel orientation 45˚. Grip diameter should be mm for either application.

Proper Control Characteristic: Foot / Leg Controls For continuous control it is better to bend the ankle by depressing the toe rather than depressing the heel or moving the entire leg. The range of movement at the ankle is 80˚ -115˚.

Proper Control Characteristic: Foot / Leg Controls On-off controls, such as faucets and clamping fixtures can also be activated by lateral motion of the knee and the vertical motion of the foot.

Prevent Unintended Activation Controls should be designed to prevent unintended activation.

Prevent Unintended Activation In general, all equipment should have an “emergency stop” control. In some cases equipment should turn off or stop when a control is released.

Prevent Unintended Activation Reaction times –Human Sensing Making a decision Carrying out decision –Machine Time needed to stop

Prevent Unintended Activation Have a control indicate when it has been activated with the use of position, light, sound, etc. Therefore, if it is activated accidently, the operator may be able to reverse the control.

Prevent Unintended Activation 1.Key of special tool activation (locks) 2.Interlocks 3.Barriers or covers 4.Recessing 5.Spacing 6.Resistance 7.Direction

Prevent Incorrect Identification 1.Labeling 2.Color 3.Shape 4.Size 5.Mode of operation 6.Location

Color can improve information layout. Search processes can be accelerated Informational units can be combined or separated Warning and help signals can be easier to detect. Colors can offer additional information without occupying additional space. Prevent Incorrect Identification: Color

Prevent Incorrect Identification: Location Use consistent layout to achieve good orientation for the user. The same function should be available at the same place. The same action should always produce the same result.

Prevent Incorrect Identification: Shape Shape Coding Up to nine different shapes can be used.

Make Accomplishments Equal to the Intentions Accomplish what was intended Population Stereotypes Control / Response Ratio

Location and Arrangement: Foot Controls For feet controls providing continuous power, the seated-to-pedal distance should be adjusted so the leg is fully extended an the bottom of the stroke. The crank length should be approximately 20% of leg length, that is, 10% of stature height.

Location and Arrangement: Hand Controls Keyboards Manipulative controls Force controls

Location and Arrangement: Keyboards Keyboards have two special characteristics: They are used repetitively, and they are used with both hands.

Location and Arrangement: Manipulative Controls Anthropometric 1 st percentile reach distance. Reach is to the center of the palm.

Location and Arrangement: Force Controls Standing –Waist height –Push preferred to pull –Down preferred to before Kneeling –Pull preferred to push –Up preferred to down

Communication: Controls Work Design –Chapter 15 Fitting The Task To The Human –Chapter 9 –Human-Machine Systems