Mechanical gripper mechanisms

Robot mechanical grippers and its actuating mechanisms can be classified into several methods. The first method is based on the type of finger movement. During this arrangement, the opening and closing of the fingers can be actuated by either pivoting, or linear or translational movement.

Pivoting movement:

In this motion, the rotation of fingers is concerned with the fixed pivot points of the gripper for providing open and close actions. It uses the linkage mechanism for achieving this movement.

Linear or translational movement:

During linear motion, the guide rails are used to move the fingers parallel to each other for accomplishing closing and opening. In translational movement, the fingers are maintained in a parallel orientation to each other. As like pivoting movement, it also uses the linkage mechanism for actuation.

The second method of classifying the mechanical grippers is based on the type of kinematic device used for the actuation of finger motions. It can be accomplished by anyone of these types: linkage, screw, gear and rack, rope and pulley, or cam actuation.

Linkage actuation:

The design of linkage actuation helps in finding out the conversion of gripper’s input force into the gripping force, the time taken to actuate the gripper, and the maximum capability to open the finger. It has plenty of designs for opening and closing the finger, and some of its types are shown below.

Screw actuation:

The screw-type actuated gripper consists of a screw connected with a threaded block. To rotate the screw, a motor is used along with a speed reduction device. If the screw is turned in one direction, the threaded block is moved in one direction. Similarly, the threaded block moves in the opposite direction if the screw is turned on the other direction. As the threaded block is attached with gripper, it makes the fingers to open and close.

Gear and rack actuation:

For this actuation, the gear and rack are connected with a piston, which provides linear-type movement. The two partial pinion gears are driven when the rack is moved. As it is linked with gripper, the opening and closing of fingers are accomplished.

Rope and pulley actuation:

In this actuation, a tension device is required to go up against the rope movement in the pulley. Suppose, if the pulley is activated in one direction for opening the gripper, the tension device will provide slack in the rope. Similarly, the gripper is closed by activating the pulley on the other direction.

Cam actuation:

As like linkage actuated gripper, it also has a wide range of designs for opening and closing the gripper fingers. One of its types is described shortly here. A cam actuated gripper with spring loaded follower can be used to provide open and close actions of fingers. The spring is incorporated for forcing the gripper to close if the cam is moved in one direction, while the movement of cam on the other direction causes the gripper to open. This type can be useful for holding various sizes of work parts.

Additionally, some mechanisms come under miscellaneous types. An important one is diaphragm or expandable bladder, which is inflated or deflated to open and close the fingers.

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