Human operators onboard moving vehicles impose unintended forces on manual control interfaces, e.g. joysticks due to vehicle accelerations in addition to the intended forces related to conscious tracking. These forces induce unintended control signals that degrade tracking performance. This phenomenon has been called vibration feedthrough or biodynamic feedthrough. Two man-machine systems are distinguished: open-loop systems, which involve controlling a piece of equipment other than the vehicle, and closed-loop systems, which involve controlling the vehicle itself. The present work focuses on joystick controlled equipment and single-axis problems.
Vibration feedthrough may degrade tracking performance in both open- and closed-loop systems, and it may result in marginally stable or unstable oscillations in closed-loop systems. The feedthrough forces can be canceled with a force-feedback joystick and a model-based cancellation controller.
Vibration feedthrough and feedthrough cancellation were first demonstrated on a system involving hardware alone. A stand-in inertia was used as a model model for the pilot’s biomechanical system. The necessary cancellation force was computed from the linearized equations of motion. Closed loop vibration feedthrough oscillations and feedthrough cancellation are demonstrated both in simulation and in experiments on a bench-top testbed and a Ride-Motion Simulator at TACOM. The results verify the cancellation concept.
Vibration feedthrough and cancellation were then investigated in man-machine systems. A human subject seated in a single-axis motion platform is asked to track a randomly moving target on a computer screen. The motion platform moved either in open-loop or closed-loop fashion, by a following position command from a filtered white noise reference signal or the joystick angle, respectively. As the preliminary test results demonstrated, the cancellation controller improved tracking performance in both open- and closed-loop tests, and it reduced oscillations in closed-loop tests.
Future work includes an extension to multiple dimensions, the analysis of the vibration modes of the human operator’s body using VICON system data, the creation of an adaptive cancellation controller.