A host–parasite structural analysis of industrial robots

Abstract

Most driving torques in serial industrial robots are used to overcome the weight of the robot. Although actuators account for a large proportion of the total mass of a robot, they have yet to become a positive factor that enables the robot to achieve gravity balance. This study presents a host–parasite structure to reconstruct the distribution of actuators and achieve gravity balance in robots. First, based on the characteristics of tree–rattan mechanisms, a method for calculating the degrees of freedom and a symbolic representation method for the distribution of branched chains are formulated for host–parasite mechanisms. Second, a configuration analysis and optimization method for host–parasite structure-based robots and a robot prototype are presented. Finally, four host–parasite mechanisms/robots (A, B, C, and D) are compared. The results are as follows. If more parasitic branched chains are added to the yz plane, the loads along axes 2 and 3 become more balanced, which significantly increases the stiffnesses of the mechanism in the y- and z-directions ( Ky and Kz, respectively). If the additional branched chains are closer to the site of maximum deformation, the stiffness of the mechanism in the z-direction ( Kz) increases more significantly. Of the four mechanisms, mechanism D has the best overall performance. The joint torques of mechanism D along axes 2 and 3 are lower than those of mechanism A by 99.78% and 99.18%, respectively. In addition, Kx, Ky, and Kz of mechanism D are 100.56%, 336.19%, and 385.02% of those of mechanism A, respectively. Moreover, the first-order natural frequency of mechanism D is 135.94% of that of mechanism A. Host–parasitic structure is conducive to improving the performance of industrial robots.

Modeling and Analysis of the Stiffness Distribution of Host–Parasite Robots

“…Hybrid mechanisms that are composed of host and parasitic mechanisms and display H-P relationships are referred to as H-P mechanisms. [25] An H-P relationship includes two types of precedence relationship, namely, one in which a host mechanism precedes the parasitic mechanisms and one in which the parasitic branched chains of a previous level precede those of a secondary level. For an H-P mechanism that satisfies such an H-P relationship, its internal host and parasitic mechanisms can be divided in multiple ways.…”

“…For an H-P mechanism that satisfies such an H-P relationship, its internal host and parasitic mechanisms can be divided in multiple ways. Wei et al [25] proposed a new H-P palletizing robot. Figure 1 shows a three-dimensional (3D) diagram of this robot and a photograph of a prototype.…”

“…Figure 1 shows a three-dimensional (3D) diagram of this robot and a photograph of a prototype. [25] Based on the differences in geometric dimensions as well as real-world motion and stress conditions, the composition of the branched chains of the host and parasitic mechanisms of this H-P robot was adjusted in this study. The new H-P robot consists of one host branched chain (i.e., branched chain A) and six parasitic branched chains (i.e., branched chains B-G).…”

“…The host-parasite (H-P) phenomenon is ubiquitous in both the plant and animal kingdoms. [23,24] Inspired by the parasitism between trees and rattans, Wei et al [25] proposed an H-P structure that can characterize the hierarchical relationships between the DOFs of the sub-mechanisms of a mechanism. The local DOFs are modeled as H-P relationships like those in the biological world.…”

“…The local DOFs are modeled as H-P relationships like those in the biological world. A new industrial H-P robot, developed by Wei et al, [25] is able to reach gravitational equilibrium and had notably improved stiffness.…”