Unimanual and Bimanual Weight Discrimination in a Desktop Setup

Weight-perception-based fixed and variable admittance control algorithms for unimanual and bimanual lifting of objects with a power assist robotic system

Weight-perception-based fixed admittance control algorithm and variable admittance control algorithm are proposed for unimanual and bimanual lifting of objects with a power assist robotic system. To include weight perception in controls, the mass parameter for the inertial force is hypothesized as different from that for the gravitational force in the dynamics model for lifting objects with the system. For the bimanual lift, two alternative approaches of force sensor arrangements are considered: a common force sensor and two separate force sensors between object and human hands. Computational models for power assistance, excess in load forces, and manipulation efficiency and precision are derived. The fixed admittance control algorithm is evaluated in a 1-degree-of-freedom power assist robotic system. Results show that inclusion of weight perception in controls produce satisfactory performance in terms of power assistance, system kinematics and kinetics, human–robot interactions, and manipulation efficiency and precision. The fixed admittance control algorithm is then augmented to variable admittance control algorithm as a tool of active compliance to vary the admittance with inertia instead of with gravity. The evaluation shows further improvement in the performance for the variable admittance control algorithm. The evaluation also shows that bimanual lifts outperform unimanual lifts and bimanual lifts with separate force sensors outperform bimanual lifts with a common force sensor. Then, the results are proposed to develop power assist robotic systems for handling heavy objects in industries.

Charpentier's Papers of 1886 and 1891 on Weight Perception and the Size-Weight Illusion

The French physiologist Augustin Charpentier (1852–1916) published the first accounts of the size-weight illusion—the observation that if two objects differ in size but have equal mass, the smaller will feel heavier when lifted. In the current paper, translations are presented of Charpentier's much-cited 1891 paper on weight perception and the size-weight illusion, and his little-known brief 1886 paper which contains the earliest experimental data on the illusion. Charpentier explained weight illusions in terms of the sense of effort involved in lifting the object and the contrast with the expected effort. Modern research shows that people quickly adapt and use the appropriate force to pick up objects, but the illusion persists even when appropriate force is used; expectations therefore affect the perceptual system more strongly than the motor system.