Force-Controlled Movement on Irregular Curved Surfaces for Constant-Pressure Contour-Following in Rubber Tapping Applications

Rubber tapping is a manual task whereby liquid latex is acquired from rubber trees by means of precise cuts performed by a skilled worker. This paper outlines a method of using a six-degree-of-freedom collaborative robot arm for automated rubber tapping, which attempts to create a constant force of 25 N towards the center of the tree as the end effector is moved around it in a cutting motion (semicircular helix). Internal joint torque sensors are used to sense and estimate the contact force, which is validated with an external force sensor. The results show that reduced manipulability has a negative impact on the force controller stability. Furthermore, the accuracy of the force estimation functionality is degraded when the trajectory of the robot causes the angular velocity of one or more of the joints to slow.