Development of a Gravity Compensation Module for Robotic Arm

Abstract

In this paper, we propose a gravity compensation module system for ground verification of the robot arm for space. Existing gravity compensation devices are difficult to accurately compensate for gravity due to mechanical problems. Gravity compensation of the space robot arm is very important in verifying the robot arm to be used in the actual space environment and sufficient experiments on the ground must be conducted. In addition to the existing gravity compensation method of compensating for gravity by making a mechanical device, there is also a method of making the experiment environment a microgravity environment identical to space. However, the environmental change type gravity compensation method must maintain very difficult conditions, the time to eliminate gravity is short, and a lot of costs are incurred to create the environment.

The most important point in ground verification of a space robot arm is that the influence of gravity must be quickly removed whenever and wherever desired. Although eliminating ground gravity in real time is a difficult problem, it is ideal to perform simple gravity compensation on a prototype before performing ground verification of a real space robotic arm.

To solve this problem, this paper proposes a planar gravity compensation module based on the YZ coordinate system through simulation and proposes the configuration of the gravity compensation module developed for verification on the actual ground.

First, since the length, weight, and inertia of the robot arm are required for simulation, a planar 2-link robot arm to be used in actual devices was manufactured to compensate for the gravity of the 2-link robot arm. The configuration of the motor to be used to solve the problem of the center of gravity of the robot arm and the material to be used for the robot arm are explained.

Second, to describe the force of the robot arm, the gravity compensation vector is confirmed according to Jacobian's description method. Here, the formula was solved for each Jacobian for simulation, and as a result, it was confirmed that both Jacobian technology methods resulted in the same gravity compensation vector.

Third, the gravity compensation of the two-link robot arm was confirmed using MATLAB and PyBullet simulations. Since all Jacobian description methods result in the same gravity compensation vector, the gravity compensation vector described by space Jacobian is used in this part. In this part, it is described separately when the joints of the robot arm maintain a specific angle and when the robot arm performs a specific motion.

Fourth, a planar gravity compensation module based on the actual YZ coordinate system was produced using the results obtained through simulation. The gravity compensation module includes a force control motor that compensates for the force of the gravity compensation vector and a position control motor that compensates for the direction of the gravity compensation vector. Describes the configuration and size of the device and how it is used.

As a result, the unproposed ground test module is expected to be able to be used as a ground test device regardless of location and time, and it was confirmed that the same gravity compensation vector is output regardless of how the force is described. Lastly, in future research, we aim to confirm the reduction of joint torque acting on the two-link robot arm in the same way as the simulation by conducting ground experiments on the developed gravity compensation module.