Human Assistive Robotics

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Human Assistive Robot Design

A. Design of an assistive robot for incomplete paraplegic patients
The robot shown below is an Exoskeletal Robotic Orthosis for Walking Assistance (EROWA), which has been developed for assisting the mobility of incomplete paraplegic patients. The research topics in the design of such assistive robot systems include:
  • - a transparent actuator system that has the minimal weight, zero mechanical impedance, and high-precision in the output force,
  • - a mechanism that effectively supports the body weight without disturbing voluntary motions,
  • - an accurate and practical sensing system for measuring the dynamic state of the human body, and
  • - a robust and intelligent motion control method that stabilizes the integrated dynamics of the human body and the robot incorporating the human motion control function.

TV report (YTN News)

B. Design of an assistive robot for complete paraplegic patients

Human Assistive Control

A. Human motor control loop
Human motor control is the process by which humans use their brain/cognition to activate and coordinate the muscles and limbs involved in the performance of a motor skill. Fundamentally, it is the integration of sensory information, both about the world and the current state of the body, to determine the appropriate set of muscle forces and joint torques to generate some desired movement or action. The human motor control loop consists at least of two controllers, i.e., the cerebrum and the spinal cord, as shown in the figure below. 

Their interaction and organization are complicated, but from the viewpoint of control theory, the functions of the cerebrum and the spinal cord can be modeled as an outer-loop position feedback controller and an inner-loop force feedback loop, respectively, as shown in the following figure.

B. Fictitious gain: an approach to assist incomplete paraplegic patients
To develop a control method for robustly and intelligently assisting the incomplete paraplegic patients, a loop-shaping method can be applied to recover the impaired sensitivity of the human body system. The neuromuscular weakness can be treated as a lowered loop gain, and a fictitious filter is applied to the human motor control loop to restore the loop gain. Robust control methods can be applied for the loop shaping.


Then a feedback controller of the assistive robot is designed to realize the effect of the fictitious filter in the framework shown in the figure above. If the robot controller, C, effectively realizes the function of K, the human wearing an assistive robot may feel as if the dynamic sensitivity of his/her body is changed by the fictitious filter. In this approach, neither the recognition of the human intention nor the pre-determined joint trajectory is necessary, which is different from the conventional control methods in assistive robotics.


Simulation with exact parameters

Simulation with unknown parameters

Simulation with improved robustness

Fictitious gain method applied to elbow assistance