Simplified modelling and development of a bi-directionally adjustable constant-force compliant gripper

Abstract

This paper proposes the design of a wholly mechanical constant-force gripper that can accommodate the imprecise manipulation of brittle/delicate objects by the actuation. This was achieved by designing a constant-force mechanism as the jaw that allowed a constant force to be applied to the grasping objects regardless of the displacement of the mechanism. The constant-force mechanism is attached to the end effector of the gripper via a parallelogram mechanism which ensures that the jaws remain in parallel. The constant-force mechanism combines the negative stiffness of a bistable mechanism and the positive stiffness of a linear spring to generate a constant force output. By preloading the positive stiffness mechanism, the magnitude of the constant force can be adjusted to be as low as zero. The constantforce mechanism has been fully modelled and simulated using finite element analysis. A normalised force-displacement curve has been developed that allows to obtain the simplified analytical negative stiffness of the bistable mechanism. The design formulation to find the optimal configuration that produces the most constant force has been developed. Illustrated experiments prove the concept of the design although the discrepancies between finite element analysis results and testing results exist due to bistable beam manufacturing error.

Topology optimization of the compliant mechanisms considering curved beam elements using metaheuristic algorithms

“…These flexible mechanisms have broad applications in different fields such as sensor design, 1 gripper configuration, 2,3 bi-stable and multi-stable mechanisms, [4][5][6] micro-electro-mechanical systems (MEMS), 7,8 highprecision devices, 9,10 biomedical and surgery robots, 11,12 and so on. Consequently, CMs can be used in many industries, labs, and electro-mechanical equipment, although they involve some limitations about motion range and strength.…”

Design and Test of a Curved-Beam Based Compliant Gripper for Manipulations of Actively Deformable Objects

“…Compliant constant force grippers can deliver precise force output independent on complex control algorithms and structures [10] and thus are perfect candidates for handling and manipulating delicate objects with various sizes and stiffness [11], [12]. Grippers based on constant force mechanisms have been developed, where representative results include two-stage microgripper [13], bi-directionally adjustable gripper [14], force-sensing microinjector [15], apple picking actuator [16], 3D-printed gripper [17], 2-DOF gripper [18], [19], multi-mode gripper [20], [21].…”

A bistable mechanism with linear negative stiffness and large in-plane lateral stiffness: design, modeling and case studies

“…Dunning et al (2013) proposed a six degrees of freedom compliant precision stage with near constant force, which implies near zero stiffness in each direction. Hao et al (2017) designed a constant-force gripper and the constant force output of which can be adjusted to near zero by preloading the positive-stiffness mechanism. The various kinds of constant force mechanisms were developed for many different uses, such as large-stroke constant-force micro-positioning stage (Xu, 2017a), constant-force microgripper mechanism for biological micromanipulation (Xu, 2017b) and flexure-based constant-force XY precision positioning stage (Wang and Xu, 2017).…”