Effects of input shaping on manual tracking with oscillatory controlled-element dynamics

This paper examines the manual control of mechanical systems with oscillatory dynamics, and the effects of adding input shaping to suppress command-induced vibration. Behavior of the system is analyzed using concepts from manual control theory. A series of operator experiments tested tracking behavior using elements with a low-frequency (1.25 rad/s) and a high-frequency (5 rad/s) oscillatory mode. After each experimental trial, measures of subjective task difficulty and tracking performance were recorded, and frequency-domain control characteristics were computed. Results showed that the higher-frequency oscillatory mode did not significantly decrease tracking performance from the non-oscillatory case, so input shaping did not cause a significant improvement in tracking performance. However, input shaping did cause a decrease in average subjective task difficulty, and made the system closely resemble McRuer's "crossover model." For the lower-frequency case, the addition of input shaping significantly improved the tracking performance and reduced the tracking difficulty. These results demonstrate that input shaping can greatly improve the continuous tracking ability of a human-machine system in the presence of oscillatory modes.