Part Position Correction During Assembly According to Force and Torque Sensor Signals

The article is devoted to the issues of algorithmic support when using force-torque sensing for robotic assembly of shaft-hole type connections. The assembly system consists of an ABB IRB 140 industrial robot equipped with a Schunk GSM-P-64-E-180 pneumatic gripper and a Gamma SI-65-5 six-component force-torque sensor by ATI Industrial Automation. The robot positioning accuracy is insufficient for precision joints assembly. This can cause misalignments (linear, angular) of the parts axis when performing a technological assembly. This can lead to unwanted contact interactions. If the robot movement strategy remains unchanged, the phenomenon of jamming may occur. Therefore, it is proposed to use force-torque sensing to recognize contact interaction at assembly. The sensor is installed in front of the gripper of the assembly manipulator. The difficulty in solving this problem is that the force-torque sensor signals do not contain direct information about the position or orientation of the connected parts. To correct the robot movement it is necessary to recognize the position of the parts contact point by means of force and torque sensor signals. For this purpose, the equations of the forces - torque relationship were derived. The sensor whose parameters determine the position of the parts contact point measures force and torque values. The article considers the case of a one-point contact of the connected parts, which occurs at an unsuccessful matching. Based on a computer simulation of the process, it became possible to establish some common factors between the signs of force effects and the contact point position. The main purpose of this research is to develop an adaptive algorithm that corrects the movement of an assembly robot. The algorithm is based on the information about the forces and torques from the sensor, as well as the data on the operating element position. The use of a position-force control algorithm for robot movement will make it possible to perform a reliable assembly of precision joints. The article describes the limits on the force and torque sensor sensitivity as applied to the recognition of the part angular orientation at assembly, caused by contact interaction.