Miniaturisable deformable grippers represent the fusion of two important research areas of the robotics laboratory, namely underactuated hands and deformable mechanisms. Based on the research we conducted recently, we were able to create a miniature gripper capable of effecting an autonomous grasp.

    The use of under-actuation allowed the actuaters to be reduced to a limited number and enabled the architecture control to be simplified. Deformable joints represent a solution to the problems of lubrification, cleaning and sterilization usually encountered with miniature joints. Thus, a combination of these technologies has led to an impressive degree of miniaturization (1 cm3 per gripper).

    Fig. 1: Miniature planar gripper made of shape memory alloy.

    Research has led to the determination of the geometry which optimizes the quality of the grasp and the selection of the geometry of the flexible joints which provides an improvement of the rigidity in directions other than those of the natural rotation axis, while maintaining the required angular range of motion.

    Several prototypes have been made through rapid prototyping so as to verify the real behaviour of the hands and the stability of the grasps.

    Fig. 2: Three-finger hand enabling a complete closing of the fingers.
    Fig. 3: Optimized under-actuation of the hand to improve the quality of grasping.

    The two prototypes in Figure 4 illustrate under-actuated fingers using blades of nitinol (51 %Ni et 49 %Ti), a superelastic alloy, as joints. This alloy allows an impressive angular range of motion (8 % of elastic deformation) to be obtained with joints of reasonable length. Moreover, in view of a future medical commercialisation, nitinol is biocompatible and responds very well to sterilization procedures normally used in the industry.

    Fig. 4: Flexible under-actuated fingers optimized by analysis of the critical parameters (A) and by artificial intelligence (B).


    A poster was prepared in 2005 on deformable grippers and can be downloaded with the PDF file below.