Manipulating objects with a power assist robot in linear vertical and harmonic motion: Psychophysical-biomechanical approach to analyzing human characteristics to improve the control

This paper investigates human characteristics in terms of weight perception, load forces, motions etc. for manipulating objects with a power assist robot and proposes a novel control for the robot based on the human characteristics to improve maneuverability, safety etc. We hypothesized that weight perception due to inertia might be different from that due to gravity for manipulating objects with power-assist. A 1-DOF power assist robot was developed and simulated. Subjects manipulated objects with the robot for two types of motions: (i) linear vertical (lifting objects vertically), (ii) harmonic (objects repeatedly lifted up and lowered down).We analyzed weight perception, load forces and motions. We then introduced a novel control strategy, which was such that a virtual mass exponentially declined from a large value to a small one when the subjects manipulated the objects with the robot and the command velocity exceeded a threshold. The novel control reduced excessive load forces and accelerations and improved maneuverability, safety etc. We compared the results for linear motion to that for harmonic motion. We also demonstrated the conditions to further optimize the performances. Finally, we proposed using the findings to develop human-friendly power assist devices to manipulate heavy objects in industries that would improve productivity, worker's health and wellness. We also argued that the weight perceptual and psychophysical criteria used to control the robot would satisfy the biomechanical criteria of robot operator manipulating heavy objects, and thus we attempted to establish a trade-off between psychophysical and biomechanical criteria for manipulating objects with power-assist. © 2011 by JSME.