Single Servo Gripper
Here are a few experiments I have made in constructing small robot Grippers.
Single Servo Gripper
This is the simplest type of gripper. No Switches are needed to open, close or grasp an object. Two springs hold the two fingers closed. A cam on the servo (right view) pushes against two wheels to open the gripper. In the open position, the fingers close until they grasp the object or the fingers touch. The gripper closes with the strength of the two springs. Since most springs are non-linear in force, the larger the object being held, the more force is on it. The finger tips can hold thin objects and the middle section can grab larger ones.
Gearmotor gripper
This gripper uses a gearmotor (not shown) to open and close the pulley system. This complicates the whole thing as switches are needed in the open, and closed position to stop the motor in the right place. A pressure switch is also needed to stop the motor at just the right pressure on the object being grasped.
Three Finger Gripper
Here is an experiment that failed. Spectra kite string tendons pull against the springs to open the three fingers. Spectra cord is very light and strong and flexible. While it worked well and had good grip strength, the whole thing weighed too much to be practical in a small robot. Because of the leverage involved, too much weight at the end of an arm puts an enormous strain on the elbow and shoulder motors.
Gearmotor spring gripper
Here is the best compromise I have found for simple gripper technology. Springs hold it closed and spectra tendons open it by wrapping around a small pulley on a gearmotor. The tendons allow the wrist to rotate 180 degrees. Switches are needed to stop the motor when the gripper is all the way open or all the way closed. In the open position it simply closes for a timed period to grasp an object or until the closed switch goes on.
intothewind-good source for spectra kite string.
Jameco-Very nice 5-12 Volt gearmotors.
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