Skilful grippers

Article of 25 January 2019 

Flexible gripping

Whether it’s a tool, a telephone or a tissue, we can flexibly pick up, hold and deposit a wide variety of objects with our hands. In industry, however, there are many grippers that are matched to special tasks or workpieces. The gripper finger DHAS and the adaptive form gripper DHEF from Festo are a couple of exceptions. They skilfully pick up almost anything that comes into their gripping tools.

One gripper brings a screw, another picks up the nut, the next holds a strip. One after the other, a differently shaped workpiece needs to be grasped, and a special gripper is needed for each of them. With the gripper finger DHAS and the adaptive form gripper DHEF, things look quite different. These grippers can independently adjust to different products and shapes. They are particularly suitable for processes in which several objects with different shapes are handled.

Inspired by the fish fin – the gripper finger DHAS

Festo’s developers learned from the animal world during the development of the DHAS product. Like a fish’s tail fin, the structure with Fin Ray Effect® does not give way under lateral pressure, but bends around the pressure point instead.

Two flexible bands form the basic structure of the gripper finger. They are connected to each other via intermediate bridges. When gripping, the stable yet flexible gripper made of polyurethane easily adapts to the contour of a workpiece. A combination of two or more DHAS gripper fingers gently closes around the objects and holds them securely without damaging them. The DHAS is therefore particularly suitable for gripping sensitive objects with irregular surfaces. For example, it is used in the food industry for sorting fruit and vegetables.

The DHAS gripper finger is used in the food industry for sorting fruit and vegetables.
The DHAS gripper finger is used in the food industry for sorting fruit and vegetables.

As adaptable as a chameleon’s tongue – the adaptive form gripper DHEF

The inspiration for the adaptive form gripper DHEF comes from the chameleon. In order to catch prey, the animal lets its tongue shoot out like a rubber band. Just before the tip of its tongue reaches the insect, it retracts in the middle, while the edges continue to move forwards. This allows the tongue to adapt to the shape and size of the respective prey and firmly enclose it.

The DHEF works according to the same principle. Its central element is a silicone cap filled with slight excess pressure, modelled on the chameleon’s tongue. The deformation of the cap is controlled by a double-acting pneumatic cylinder. A piston rod is retracted and extended by ventilating the compressed air connections. The internal piston rod is connected to the tip of the silicone cap. When the rod is retracted, the cap turns inwards. This allows an object to be enclosed and gripped. Even picking up several objects, such as screws from a bowl, can be realised via a corresponding control with proportional valves.

The DHEF adaptive form gripper’s silicone cap turns inwards and encloses the object.
The DHEF adaptive form gripper’s silicone cap turns inwards and encloses the object.

From prototype to series product

In the future, individual products will be increasingly manufactured. Adaptive machines and production plants are therefore becoming increasingly important. Components like the grippers, which can adapt independently to different products and scenarios, can play an important role in the process.”

The gripper finger DHAS and the adaptive form gripper DHEF are the result of interdisciplinary research by the Bionic Learning Network. They were first designed as prototypes and then developed into series products.