Dynamic modeling of cooperative manipulators with frictional contact at the end effectors

The kinematic and dynamic constraints of a closed kinematic chain as well as the motion equations of a cooperative robotic chain are derived in the present article. In its structure, this system employs friction to bring the end effector of cooperative arm with the common load into contact. This results in complex and time-varying constraints on the load and the end effector of cooperative arm as slip can occur on the object surface. On the contrary, one can easily change the connection loop of arms in face of obstacles. To this end, the specified objective is considered in the design of robot path and solution algorithms are defined based on the possibility of slip. The results are then used to implement the opti-mization algorithm of load distribution and calculate the dynamic load-carrying capacity. Hence, not only is the inverse dynamics studied in detail, the robot performance is evaluated in various conditions. For this purpose, the results of a cooperative robotic chain carrying a common load are compared for different values of surface friction coefficient and maximum permissible internal force. This is followed by a comparison with appropriate simulations in ANSYS. Moreover, the dynamic load-carrying capacity of the system in terms of the changes in maximum permissible internal force and the surface friction coefficient between the arm's end effector and the load is obtained. The results indicate that when appropriate conditions for the friction between end effector and load in addition to an internal force proportionate to the path are provided, the dynamic load-carrying capacity of any system can be improved. For instance, on a certain path and for the friction coefficient of 0.8 and internal force of 0.2, the dynamic load-carrying capacity of a single-arm system with grasp contact in end effector, after adding the auxiliary arm with frictional contact in end effector, reached 9.34 kg which shows an increase of 5.09 kg. (c) 2020 Elsevier Inc. All rights reserved.

Automated summary

This article derives the kinematic and dynamic constraints of a closed kinematic chain and the motion equations of a cooperative robotic chain. By using friction to bring the end effector of a cooperative arm into contact with a common load, complex constraints and solutions for slip are provided. The results show that dynamic load-carrying capacity of any system can be improved when appropriate conditions for friction and internal force are met.