Experimental study on stand-alone assistive suspension system to reduce load on small robot manipulating heavy payload

Abstract

This paper presents a single degree of freedom suspension system to assist small six degree of freedom robots manipulating heavy payload. The goal of the system is to reduce the load applied to the last link of a robot manipulating a payload that is heavier than the robot’s specified allowable load capacity. An assistive suspension system was implemented to realize vertical-only motion of the robot. A mathematical model was derived, and a proportional-integral-derivative controller with an inner velocity loop was designed. Variable parameters in the model such as friction coefficients were identified in an experiment on the voltage input and velocity output. To determine how much the assistive system reduces the load on the robot, the system was connected to the robot using an interface attached with magnets and a force sensor was fixed to the last link of the robot. In the experiment, the cable tension was measured and controlled to satisfy the design preference for the assistive system to be stand-alone, rather than relying on force sensor on the robot. The experiment was performed using various control gains under different conditions, such as the periods of input motion and payload weight. The results showed that the system could reduce 3.8 and 6.0 kg payloads on the robot to 50% and 40%, respectively.