controls rebecca w. boren, ph.d. iee 437/547 introduction to human factors engineering arizona state...

Controls

Rebecca W. Boren, Ph.D.IEE 437/547Introduction to Human Factors EngineeringArizona State UniversityOctober 24, 2011

Think of as many control devices as you can and write them down.

Controls

Cameras

RemoteControls

1950 Zenith Remote Ad http://www.tvhistory.tv/Remote%20Controls.htm

Computer Input Devices

Joystick

DataHand Keyboard

Mouse

Wii

Automobile Controls

The one on the right is allhand operated.

Simple?

Designing for visibility means that just by looking, users can see the possibilities for action. Visibility is often violated in order to make things "look good“.

Complex?

Submarine controls

Multi head Shower

Onscreen Computer Controls

Onscreen Computer Control or the Real Deal?

What do these control?

Controls

Display is the perception. Seeing, hearing, or other sense

Control is the action after a decision is made.

Involves the selection and execution of responses.

Includes the feedback loop.

Model of Human Processing

Principles of Response Selection

Decision complexity

The speed with which an action can be selected is strongly influenced by the number of possible alternative actions that could be selected.

Decision complexity

Hick-Hyman Law of reaction time shows a logarithmic increase in reaction time (RT) as the number of possible stimulus-response alternatives (N) increases. Humans process information at a constant rate. RT = a + bLog2N

Hick-Hyman Law

The most efficient way to deliver a given amount of information is by a smaller number of complex decisions rather than a large number of simple decisions. An example is typing versus Morse code.

Response expectancy

We perceive rapidly and accurately that information that we expect.

We don’t expect a car

to suddenly pull in front

of us on the freeway. It

takes time to perceive

and to respond.

Response expectancy

We use the yellow caution light to help us anticipate a red light.

Compatibility

Good stimulus-response compatibility (display-control compatibility) aids in response selection.

Two sub principles: Location compatibility (mapping) Movement compatibility (moving a lever

right should move the display to the right).

Location Compatibility

Movement Compatibility

How do I turn this computer on?

Usability and Human FactorsWeb Workshop series at Monash University

How do I turn this computer on?

About 4 or 5 years ago I'd just started a new job I had a choice of using a fairly new Macintosh or a

rather old PC - I wanted to use the Mac I'd never used a Mac before And I couldn't figure out where the "ON" switch was After messing around for a long time, I accidentally

turned it on after randomly pressing a whole bunch of keys on the keyboard

I still didn't know how I'd done it, so I turned it off and tried the keys again until I realized it was the Apple key that brought the machine to life

Speed-accuracy tradeoff

Sometimes positively correlated, sometimes negatively correlated.

The first three principles result in a positive correlation. Whatever makes the response selection faster makes it less prone to error.

Principles of Speed-accuracy tradeoff

1. Good stimulus-response compatibility (display-control compatibility) aids in response selection.

2. Location compatibility (mapping)

3. Movement compatibility (moving a lever right should move the display to the right).

Speed-accuracy tradeoff

In a few cases, control devices differ in the speed-accuracy tradeoff because one induces faster, but less precise behavior or more careful but slower behavior (2nd order).

Feedback

Instantaneous or nearly instantaneous feedback is helpful.

If there is a lag of even 100 msec, an unskilled operator will have difficulty.

What kinds of feedback are helpful? Name some.

Discrete Control Activation

Physical feel. There should be some feedback as to state change: a click, beep, flashing light, change of color, etc.

Feedback lights should be redundant with another signal and should be immediate.


A toggle switch provides visual feedback, an auditory click, and a tactile snap with the sudden loss of resistance.


Size. Smaller keys are difficult for humans. In relationship to the size of large hands, it is easy to make mistakes by pressing the wrong key or two keys at once.


Confusing labeling. Key press or control activation errors also occur if the identity of a key or control is not well marked for novice users.


Well-labeled controls.

Positioning Control Device

A common human-machine task is to position an entity in space.

The positioning or pointing task is defined as “movement of a controlled entity, called a cursor, to a destination, called the target.”

Positioning Task

Movement of a controlled entity, called a cursor, to a destination, called the target.

cursor

target

Positioning Control Device

Movement time: controls typically require two different movements: movement of the hand or fingers to the

control device movement of the control device in

some direction.

Movement Time

Predicted by Fitts’ Law

MT = a + b log2(2A/W) MT is movement time A is amplitude (distance) of the movement W is width of the target (corresponds to

accuracy) log2(2A/W) is the index of difficulty (ID) a and b are constants

MT is proportional to the index of difficulty

Movement Time – Fitts’ LawMT = a + b log2(2A/W)

Fitts’ Reciprocal Tapping Task

Movement Time Examples

If the keys on a keyboard are made smaller, without the space also made proportionally smaller, then movement is more difficult.

Foot reaching a foot pedal Assembly and manipulation under a

microscope.

Device Characteristics

Direct position controls: Light pen and touch screen

Indirect position controls: Mouse, touch pad, and touch tablet.

Indirect velocity controls: Joystick and cursor keys

Direct Position Controls

Light pen and touch screen using a stylus or finger on a tablet.

Position of the human hand or finger directly corresponds to the desired location of the cursor.

Indirect Position Controls

Mouse, touch pad, and touch tablet.

Changes in the position of the limb directly correspond to changes in the position of the cursor, but on a different surface.

Indirect Velocity Controls

Joystick and cursor keys. An activation of control in

a given direction yields a velocity of cursor movement in that direction. For cursor keys the operator may repeat or hold down.

Three Types of Joysticks

Isotonic Isometric Spring-loaded

Isotonic Joystick

Typically, cursor moves as a result of movement of the joystick handle.

Handle does not move back to a neutral position.

Isometric Joystick

Cursor moves as a result of the force applied to the joystick handle.

Joystick does not move at all.

Spring-loaded Joystick

Resistance is proportional to force applied.

Displaced, but returns to a neutral position.

Offers proprioceptive and kinesthetic feedback.

This is the

preferred joystick

Usability

Feedback and gain are two important characteristics.

Feedback should be salient, visible, and immediate.

Gain is defined as the change of cursor position/change of control position.

Usability - Gain

Gain is defined as change of cursor position

change of control position If a 3 inch change in the cursor position

results from a 1 inch change in the control position, then the gain is 3.

Usability - Gain

A high gain device is one in which a small displacement of the control produces a large movement of the cursor

A low gain device aids in precision. The ideal gain is task dependent.

Choice of Control Device

For pointing and dragging, direct position devices (touch screen and light pen) may be superior.

Problems in accuracy may arise with a direct position device due to parallax errors, instability of the hand or fingers, or the imprecision of the finger area in specifying small targets.


Indirect positioning devices have greater precision and may be adjusted for gain.


Dependent on the work space environment.

Mouse takes up a lot of space. Vibration in a cab ride. Voice control difficult in a noisy

environment.


High gain devices are faster in moving to a target, but less precise (can overshoot the target).

Humans work well with a gain between 1 and 3.

Humans can adapt to a greater range of gain with experience.

Numeric Input Devices

Numerical data is usually entered by numeric keyboards or voice.

There are two styles of key pads for data entry.

Numeric Input Devices

The telephone style is the preferred method.

Voice Input

Pros: useful in time-sharing activities in which the visual and manual systems are both occupied.

Cons: cost, recognizer speed, acoustic quality, speaker dependent, noise, stress, loss of privacy, and compatibility with task.

Voice recognition is complex and still under development.

Voice Input

“How does voice input interfere with short-term memory?”

End of Part 1. Questions?

Continuous Control & Tracking

In contrast to discrete cursor movement to a target, sometimes we want to track a moving target. This requires continuous control.

Examples: bringing a fly swatter down on a moving fly, driving on a winding road.


Using a moving car as an example: the operator perceives a discrepancy or error between the desired state of the vehicle and the actual state.


The operator must turn the steering wheel to put the car back on track.


A" track” is a continuously moving dynamic target.

The Tracking Loop The basic elements of the tracking loop: e(t) = error function

of time; f(t) = force applied to the control device; u(t) = output function from the human; o(t) = system output; i(t) = position. Our goal is i(t) = o(t) and e(t) = 0. ic(t) are command inputs (changes in the target). id(t) are disturbance inputs.

Control Order

If a control is designated as zero-order, it means that the cursor controls the position of the target.

First-order means it controls the velocity of the target.

Second-order control means a change in the position of the cursor changes the acceleration of the target.

Control Order

Position Order: (zero-order). Pen across paper, marker on the white

board, moving a computer mouse to reposition a cursor on the screen.

If you hold the control still, the system output will also be still.

More precise, more human effort.

Control Order

Velocity order: first-order (rate of change of position).

Some joysticks and car radio scanners are first-order controllers.

As you hold the joystick in a direction, the velocity increases.

Can conserve human effort, but has more lag.

Control Order Acceleration order: second-order (rate of

change of velocity). Second-order control systems are rarely used

because they are hard to control (sluggish and unstable).

Think of an astronaut trying to maneuver in space by firing thrust rockets. Can get pilot-induced oscillations.

Requires a great deal of experience and effort on the part of the operator.

Control Order - Driving

Driving an automobile is a combination of first- order and second-order control systems.

The task of maintaining speed is a first-order control.

Control Order - Driving

The task of steering or lane-keeping is a second-order control.

Solutions to the Problems of Second-order Control Systems

1. Predictive displays2. Teach the tracker strategies of

anticipation. Experienced drivers look further down the road than novices do.

3. Automate to bring it to a lower-order control.

Predictive Displays

Air Traffic Predictive Display

Predictive Displays

Other issues related to controls

Instability – caused by lag somewhere in the total control loop Overcorrection due to high gain in the

system Human trying to correct too quickly

before the lagging system has had a chance to stabilize.

Other issues related to controls

Open-loop versus closed-loop systems Open-loop – no feedback – used by

experienced operators Closed-loop – feedback is valuable in

learning or fine-tuning a mental model.

Electronic Controls

Well-designed products have controls that don’t require fine fingering to operate.

The following controls are shown in descending order, from easiest (1) to most difficult (7).

1

2 3

4

Use larger muscles rather than smaller muscles.

6 5

7

Control and Display Principles are closely

related.

Standardized shape-coded knobs for US Air Force aircraft.

For transmitting discrete information

For transmitting continuous information

For transmitting cursor position information

Questions?

Resources

Tapping experiment http://ei.cs.vt.edu/~cs5724/g1/tapping.html#files

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