Grasping- Force Sensor for Robot Hand
A grasping-force sensor has been designed for use on a robot hand that includes
intermeshing claws that are required to remain in alignment. Like other
robotic grasping-force sensors, it relies on strain-gauge measurements of
the deflection of part of the grasping mechanism. However, the design of
the grasping-force sensor is integrated with that of the grasping mechanism
in such a way that the deflection caused by the grasping force does not
disturb the angular alignment of the claws.
The figure shows the claw assembly mounted within a supporting channel.
A motor-and-gear assembly mounted on a resilient base (not shown) moves
the claws toward or away from each other along two columns. The claws are
mounted on elastic base frames (the deflecting elements), which, in turn,
are mounted on sliding frames that move along the columns. Unlike in prior
designs, the claws can be installed, removed, or interchanged with other
end effectors without having to disassemble the actuating mechanism. The
hollow rectangular cross sections of the base frames make the frames act
similarly to parallelogram linkages when they are subjected to the grasping
force directed along their vertical (as shown in the figure) sides. The
horizontal (as shown in the figure) sides bend in the manner of cantilever
beams, while the vertical sides remain parallel. The claws and the sliding
frame, which are attached to the vertical sides, therefore remain aligned.
The distortion of the base frame causes a very small horizontal translation
of the claws toward the sliding frame, but both claws translate by the same
amount and thereby remain horizontally, translationally, as well as angularly
aligned. Even if one claw encounters an obstacle that the other does not
encounter, there is only a small horizontal misalignment, but the claws
remain angularly aligned. Two strain gauges are mounted on the outer surface
of each base frame, and two matching gauges are mounted on the sliding frame
structure on which each base frame is mounted. These gauges are connected
in a full-bridge configuration that measures the deflection along the axis
of motion of the claws toward or away from each other (the vertical axis
in the figure). The outputs of the strain-gauge bridge circuits are transmined
to the robot control computer, which converts them into indications of the
grasping force. With the help of this sensing system, the operator can feel
the initial contact between the claws and an object and modify the motions
of the robot arm, hand, and claws accordingly.
Point of Contact:
Antal Bejczy
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-4568
bejczy@telerobotics.jpl.nasa.gov
Telerobotics Program
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Maintained by: Dave Lavery
Last updated: May 10, 1996
Grasping- Force Sensor for Robot Hand