Mechanical Grippers

A mechanical gripper is used as an end effector in a robot for grasping the objects with its mechanically operated fingers. In industries, two fingers are enough for holding purposes. More than three fingers can also be used based on the application. As most of the fingers are of replaceable type, it can be easily removed and replaced.

A robot requires either hydraulic, electric, or pneumatic drive system to create the input power. The power produced is sent to the gripper for making the fingers react. It also allows the fingers to perform open and close actions. Most importantly, a sufficient force must be given to hold the object.

In a mechanical gripper, the holding of an object can be done by two different methods such as:

  • Using the finger pads as like the shape of the work part.
  • Using soft material finger pads.

In the first method, the contact surfaces of the fingers are designed according to the work part for achieving the estimated shape. It will help the fingers to hold the work part for some extent.

In the second method, the fingers must be capable of supplying sufficient force to hold the work part. To avoid scratches on the work part, soft type pads are fabricated on the fingers. As a result, the contact surface of the finger and co efficient of friction are improved. This method is very simple and as well as less expensive. It may cause slippage if the force applied against the work part is in the parallel direction. The slippage can be avoided by designing the gripper based on the force exerted.

nf Fg = w 1

=> co efficient of friction between the work part and fingers

nf => no. of fingers contacting

Fg => Force of the gripper

w => weight of the grasped object

The equation 1 must be changed if the weight of a work part is more than the force applied to cause the slippage.

nf Fg = w g …... 2

g => g factor

During rapid grasping operation, the work part will get twice the weight. To get rid out of it, the modified equation 1 is put forward by Engelberger. The g factor in the equation 2 is used to calculate the acceleration and gravity.

The values of g factor for several operations are given below:

  • g = 1 acceleration supplied in the opposite direction.
  • g = 2 acceleration supplied in the horizontal direction.
  • g = 3 acceleration and gravity supplied in the same direction.
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