The term "mechanical mirroring using controlled stiffness and actuators" ("MEMICA") denotes a developmental concept for reflecting contact forces, displacements, mechanical damping, and temperature from the hand of a remote robotic manipulator back to the hand of a human operator who controls the manipulator. The MEMICA concept is expected to result in improvements in the remote control of robots in hostile environments, and may make it possible to perform remote surgery. The concept could also be applied to providing tactile sensations of objects in computationally simulated environments ("virtual reality") and to exercise machines. The MEMICA concept could be implemented by means of various operator interfaces (e.g., joysticks, knobs, or gloves). The purpose of developing MEMICA is to enable a human operator to feel, more realistically, the stiffness, temperature, vibration, and other tactile characteristics of objects to be remotely or virtually manipulated, thereby enhancing dexterity in remote manipulation or increasing the degree of perceived realism in a simulated environment.

Figure 1. An ECS Device would resist elongation or shortening with a stiffness that would depend on the voltage applied across the electrorheological fluid flowing past the piston in the slots.

In a typical implementation of MEMICA for controlling a remote anthropomorphic robot hand, the robot hand would be equipped with actuators to generate the desired motions and forces, and would be instrumented with contact-force, temperature, and position sensors. The operator interface would be a glove instrumented with (1) mechanical actuators to reflect the displacements and the reaction (contact) forces; (2) operator-hand-action sensors, the outputs of which would be processed to generate commands for controlling the robot hand; and (3) thermoelectric heater/cooler units to provide thermal feedback from the robot hand. Thus, in a sense, the glove and the robot hand would mirror each other.

One of the major features that distinguishes the MEMICA concept from other concepts of force-reflecting robotic control is the proposed use of electrically controlled stiffness (ECS) devices at selected locations on the instrumented glove to mirror the forces of resistance to motion at the corresponding locations on the robot hand. An ECS (see Figure 1) would include a piston in a cylinder filled with an electrorheological fluid. Slots on the cylindrical piston surface would allow the liquid to flow past the piston during displacement of the piston. The slots would be lined with electrodes. The slots and electrodes would be dimensioned so that by application of voltage over a suitable range, the viscosity of the fluid, and thus the force of resistance of the piston to displacement, could be controlled over a desired range. Each finger of the glove would be equipped with ECS devices (see Figure 2) to generate reaction forces to apply the required force feedback to the operator's finger. The ECS part of the MEMICA concept is also potentially applicable to active damping of vibrations in "smart" structures.

Figure 2. ECS Devices would mirror the stiffness distribution at the corresponding locations on a remote robot finger.

While ECS devices could reflect resistance to motion, they could not actively reflect forces and displacements; that is, they could not reflect the action of something pulling or pushing on the robot hand and could not reflect vibrations. For active reflection of forces and displacements (including vibrations), it would be necessary to equip the glove with other actuators. Hydraulic, pneumatic, and shape memory alloy linear actuators have been considered for this purpose. An alternative linear actuator that might be used for this purpose would be, essentially, a motor-driven variant of a common curvature-stiffened metal tape measure.

This work was done by Yoseph Bar-Cohen and Benjamin Dolgin of Caltech and Charles Pfeiffer and Constantinos Mavroidis of Rutgers University for NASA's Jet Propulsion Laboratory.

NPO-20642


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This article first appeared in the February, 2000 issue of Motion Control Tech Briefs Magazine.

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