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Human Control of Systems

Human Control of Systems. Tracking Tasks Human Performance Considerations Measuring Tracking & Controlling Performance System Behaviors Representing System Behaviors. Tracking/Controlling Tasks. Attributes: External input/command signal defines operator response which equals

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Human Control of Systems

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  1. Human Control of Systems • Tracking Tasks • Human Performance Considerations • Measuring Tracking & Controlling Performance • System Behaviors • Representing System Behaviors

  2. Tracking/Controlling Tasks • Attributes: • External input/command signal • defines operator response which equals • manipulating control mechanism. • Control mechanism generates an output. • Tracking Error = Input – Output • (operator requirement = null error signal)

  3. Tracking/Controlling Tasks • Main Elements: • Human Operator Intrinsic Behavior • Representation of System’s State • Operator’s Response Controls

  4. Input & Output Signals • Inputs (Targets and Courses) • Constant • Achieve and main constant heading/velocity Variable Follow curving path Chase a maneuvering butterfly Waveforms – Ramp, Step, Sinusoidal

  5. Input Waveforms • Examples: • Ramp • Constant Rate of Change • Step • Discrete Change in Value • Sinusoidal • Cyclic Changes

  6. Input & Output Signals • Outputs • Results indicated by display (cursor). • Results manifested in system behavior.

  7. Tracking/Controlling Tasks • Steps in Psychomotor Performance: • Plan • Initiate • Control • End • Check

  8. Manual Control Performance Information Processing Limits Processing Time Bandwidth Anticipation Psychological Refractory Period Limitation

  9. Limitations • Processing Time (150 – 500 ms) • Bandwidth (Maximum 2 corrections per second) • Anticipation – Required due to system time lags • Psychological Refractory Period Limitation • (Minimum 300 ms between response and next stimulus)

  10. Measuring Performance • Errors in Position • Frequency Analysis of Responses • Errors in Time and Phase

  11. Errors in Position • Constant Position Error (Mean Error) • Variable Error (Standard Deviation of the Error) • Average Absolute Error (Modulus Mean Error) • Root Mean Squared Error

  12. Pursuit & Compensatory Displays Pursuit – Displays both target & cursor movements Task = Align moving cursor with moving target Operator can observe changes in both target and cursor and determine which contributes to the error. Compensatory – Displays only one moving element Task = Align cursor with target Operator observes only absolute error and cannot determine which element movement contributes to the error.

  13. System Control Orders Position (Zero-Order) Control Rate (First-Order) Control Acceleration (Second-Order) Control Higher-Order Controls

  14. Factors Influencing Tracking Performance • Preview of Track Ahead • Type of Display (Pursuit / Compensatory) • Time Lags in Tracking • Specificity of Displayed Error • Paced vs. Self-Paced Tracking

  15. Procedures Facilitating Tracking Performance • Aiding • Predictor Displays • Quickening

  16. System Behavior • Speed/Accuracy Trade-Offs • Fitts Law Index of Movement Difficulty (ID) • ID(bits) = log2(2A/W) • A = Amplitude of intended movement • W = Width of target area • Movement Time (MT) • MT(seconds) = km + ID / cm • km = Delay Constant (Hands = 0.177 second) • cm = Information Handling Capacity (0.1 bps)

  17. Control Responsiveness • Control-Response (C/R) Ratio = Movement of Control Device / Movement of System Response Note: Previously referred to as Control-Display (C/D) Ratio Low C/R = High Sensitivity (Small Movement --- Large Response) Note: Reciprocal of C/R = System Gain

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