Structural–parametric synthesis of single-loop 6R and 7R mechanisms using factorization of motion polynomials and its application in grippers

In this study, the so-called quasi-spiral motion pattern of a particular 3R (revolute) chain, which could track a quasi-spiral curve, is discovered for application in envelope gripping. Naturally, a novel perspective on the synthesis of 1-DOF (degree of freedom) single-loop 6R and 7R mechanisms is presented to implement the quasi-spiral motion pattern. In these processes, the method of factorization of the motion polynomial is used to synthesize a series of single-loop mechanisms with the motion to generate quasi-spiral curves. By employing the proposed method, numerous innovative 6R and 7R mechanisms have been developed to construct dual layers of grippers based on specific network regulations. Taking a novel 6R mechanism as an example, the forward solution of the mechanism is determined, and the relationship between different rotation angles is obtained. Then, displaying the changes in each angle during the grasping process. Finally, the novel 6R and 7R mechanisms are employed as a unit to determine the networking method and assemble new types of grippers. Grippers formed by the aforementioned 1-DOF mechanisms exhibit the characteristics of envelope grasping.