Gravity Compensation Method for Whole Body-Mounted Robot With Contact Force Distribution Sensor

The emergence of sheet-type force distribution sensors has allowed direct measurement of contact force. We developed a wearable assistive robot that can directly measure contact force and investigated the gravity compensation effect of contact-force-based control. For conventional robots that do not measure the force acting between the robot and the human body (contact force) directly, a precise robot model is required for gravity compensation, which is difficult to implement in software. In the first experiment, we examined a method of gravity compensation using only joint sensors in torque-based control, which is a common conventional method, and assessed the difficulty of this method. In the next experiment, which involved one healthy subject, we confirmed that contact-force-based control has a significant gravity compensation effect without requiring a rigorous robot model. Experiments with two additional healthy subjects using the same parameters revealed that even rough parameter tuning can produce a gravity compensation effect. This letter not only proposes a simplified gravity compensator for wearable assistive robots but also demonstrates the robustness of parameter tuning in contact-force-based control under static conditions. Based on the findings of this letter, we will further study the possibility of other kinds of disturbance compensation and dynamic conditions in the future.