Doctoral Research on Extra Robotic Legs for Human Payload and Positioning Augmentation

The Extra Robotic Legs (XRL) system is worn by a human operator and consists of two articulated robotic legs that move with the operator to bear a heavy payload. The legs will ultimately walk, climb stairs, crouch down, and crawl with the operator while eliminating all equipment loads on the operator.

The design was driven by a need to increase the effectiveness of hazardous material emergency response personnel who are encumbered by their Personal Protective Equipment (PPE). The overarching goal of this project is to develop technology that allows workers to carry more life support equipment in order to increase their time at the job location, and to support workers who must take kneeling, crouching, and other fatiguing postures while performing tasks near the ground. Decommissioning workers, who wear heavy protection gear, in particular, require an effective solution to compensate for their physical limits and augment their capabilities, so that they can execute those fatiguing manual tasks safely, efficiently, and ergonomically.

The XRL System hopes to alleviate these issues for decommissioning work by acting as a “backpack with legs”, ensuring the human operator feels no forces from their equipment. The forces involved in the most extreme loading cases were analyzed to find an effective strategy for reducing actuator loads. Analyses reveal that the maximum torque torque is exerted during the transition from the crawling to standing mode of motion. Peak torques are significantly reduced by leveraging redundancy in force application resulting from a closed-loop kinematic chain formed by a particular posture of the XRL. In order to robustly control the XRL-robot system and maintain stability, we must achieve high-bandwidth force and position control of the legs, which in turn requires high-bandwidth force and position control of each joint in the XRL system. The power systems and actuators were designed to be near-direct-drive in order to be backdrivable while outputting significant torque, allowing for proprioceptive reactions to operator motions. A prototype was fabricated utilizing the insights gained from these analyses and initial tests of balance control while performing transitions squatting indicate the feasibility of the XRL system. Desired position, velocity, stiffness, and damping commands for all 12 motors are calculated by a whole-body coordination control program. Balance control is achieved by leveraging this interface to regulate the position of the center of mass to be over the feet. Upon successful experimental results in the laboratory, we aim to test the XRL system in industrial environments with nuclear waste management crews.



This work is sponsored by the National Science Foundation and the United States Department of Energy.