Effects of input shaping on manual control of flexible and time-delayed systems.

Objective: The objective was to study the performance of a manual tracking task with system flexibility and time delays in the input channel and to examine the effects of input shaping the human operator's commands. Background: It has long been known that low-frequency, lightly damped vibration hinders performance of a manually controlled system. Recently, input shaping has been shown to improve the performance of such systems in a compensatory-display tracking task. It is unknown if similar improvements are seen with pursuit-display tasks, or how the improvement changes when time delays are added to the system. Method: A total of 18 novice participants performed a pursuit-view tracking experiment with a spring-centered joystick. Controlled elements included an integrator, an integrator with a lightly damped flexible mode, and an input-shaped integrator with a flexible mode. The input to these controlled elements was delayed between 0 and 1 s. Tracking performance was quantified by root mean square tracking error, and subjective difficulty was quantified by ratings on a Cooper-Harper scale. Results: Performance was best with the undelayed integrator. Both time delay and flexibility degraded performance. Input shaping improved control of the flexible element, with a diminishing benefit as the time delay increased. Tracking error and subjective rating were significantly related. Some operators used a pulsive control strategy. Conclusion: Input shaping can improve the performance of a manually controlled system with flexibility, even when time delays are present. Application: This study is useful to designers of human-controlled systems, especially those with problematic flexibility and/or time delays.