Gravity compensation and compliance based force control for auxiliarily easiness in manipulating robot arm

The objective of this paper is to present the gravity compensation and compliance based force control for auxiliarily easiness in manipulating robot arm. Haptical application of the safety-priority robot arm technique which interacts with people must reduce the gear ratio and design necessary algorithm which can provide auxiliarily easiness in moving the robot arm especially during the teach and learning mode. In this study, we discuss the effects of two aspects and propose a control algorithm to improve efficiency of carrying heavy item. Firstly, the gear ratio of motor is bounded so that robot can be more flexibly compliant while user take grip on it. However, robot manipulator control algorithms will suffer greater gravity downward pulling issue due to low gear ratio. To solve this problem of gravity compensation, we propose a method that based on the concept of vector projection to calculate a general solution which can construct a gravity model of multi-DOF robot arm. Furthermore, we define a virtual mode that is proposed to compensate the deficiency of inertia´s physical phenomenon. Secondly, we propose an approach which we call it force counterbalance control (FCC) that not only balances external load variation in addition to robot weight itself, but also keeps the property of dexterous easiness in manipulating the multi DOF robot arm. The FCC algorithm can be applied on several applications such as carrying heavy item or being auxiliarily easinese in manipulating robot arm. Our experimental result demonstrates the benefit of the proposed effect.