1) Mechanical finger Grippers- sub-classification is based on method of actuation. 

2) Vacuum and Magnetic Grippers- sub-classification is based on type of the force-exerting elements.

3) Universal Grippers- sub-classification is inflatable fingers, soft fingers & three fingered grippers.

Mechanical Finger Grippers

Linkage Grippers: there is no cam, screw, gear. There is movement only because of links attached to input and output. There must be perfect design of mechanism such that input actuator’s motion is transformed into the gripping action at the output.

Fig 1: Linkage Grippers

Gear and Rack Grippers: movement of input due to gear motion which makes connecting links to go in motion to make gripping action at the output link.

Fig 2: Gear and Rack Grippers

Cam-actuated Grippers: reciprocating motion of the cam imparts motion to the follower, thus causing fingers to produce a grabbing action. A variety of cam profiles can be employed- constant velocity, circular arcs, harmonic curves etc.

Fig 3 Cam-actuated Grippers

Screw-driven Grippers:  operated by turning screw, in turn giving motion to connecting links and thus giving griping motion to output. Screw motion can be controlled by motor attached.

Fig 4: Screw-driven Grippers

Rope & Pulley Grippers: motor attached to the pulley makes the winding and unwinding motion of rope in turn it set gripper action into motion via connecting link.

Fig 5: Rope & Pulley Grippers

Vacuum & Magnetic Grippers

Vacuum Grippers: for non-ferrous components with flat and smooth surfaces, grippers can be built using standard vacuum cups or pads made of rubber-like materials. Not suitable for components with curved surfaces or with holes.

Fig 6: Vacuum Grippers

Magnetic Gripper: used to grip ferrous materials. Magnetic gripper uses a magnetic head to attract ferrous materials like steel plates. The magnetic head is simply constructed with a ferromagnetic core and conducting coils.

Fig 7: Magnetic Grippers

Versatile or universal Grippers

Inflatable grippers- used for picking up irregular and fragile objects without concentrated loading. In the initial position before gripping, the lever 1, are opened up, the bellows are in a compressed condition because the gas pressure in the bags,3, with the spheres is close, even a slight pressure of the object on a bag is sufficient enough to cause the bag wall to be deeply depressed and surround the object. When the degree of the surrounding is adequate the lever motion ceases, and pressure in the bags is reduced by bellows, diaphragm device pr vacuum pump, causing bags to harden without changing shape and hence gripping the object. To release the object operation is done in reverse.   

Fig 8: Inflatable Grippers

Soft Grippers: consists of multi-links and a series of pulleys actuated by a pair of wires. The soft gripper can actively conform to the periphery of objects of any shape and hold them with uniform pressure.

Fig 9: Soft Grippers

Three Fingered Grippers: the clamping movement of two-fingered type normally executes (a) beat movement (b) bite movement (c) parallel movement of the jaw. They are capable only of grasping or releasing movement.

Fig 10: Three Fingered Grippers