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Stand alone wearable power assist suit
Protective textile

Stand alone wearable power assist suit

Written by: Keijiro Yamamoto

Background:

Japan is becoming rapid aging society. There is a problem of heavy labor in nursing causing in aging society, i.e., a lumbago problem in work of holding up of heavy patient and lifting in her arms. I thought this problem to be solved as an engineer. In 1990, I decided and started to develop the machine that technically reduced the nurse's physical load to lose nurse's lumbago. It is necessary to introduce the robot so that the worker who works at nursing and the car manufacturing factory may cancel lumbago and muscular pain by heavy labor. However, it is dangerous to leave it to the robot of an autonomous type. It is necessary to bring the robot close to the user to secure the safety of the robot. The ultimate figure of this is a robot suit. That is, the robot will be worn to the body. As a result, even if the robot suit drives recklessly, the user who wore this robot suit to the body can obstruct it for oneself.


Concepts:

The basic design concepts of the power assisting suit consist of four points, i.e.


  1. An enough safety system. The controllability by the care personnel is must be assured, i.e., the assisting system consists of a master (wearer's body) and slave (suit) system in one unit.
  2. The elimination of mechanical parts in front of the suit between the patient and the care personnel. The arms and breast of the nurse could be in direct contact with the body of the patient carried in her arms. This results in good feelings between the patient and the nurse.
  3. Flexible joints using pneumatic rotary actuators using pressure cuffs to give tender touch to the joints of the care personnel. With this air bag, big power is able to be generated even by low air pressure. So, it is possible to drive with small and light air pumps which are driven by portable batteries, it was possible to become the suit of a stand alone(completely independent) type. 
  4. Assisting forces correspond with the necessary forces to the joints which are realized by a newly developed muscle hardness sensor. In addition, as a backup and fail safe system, necessary joint torque for maintaining a position is calculated from static body mechanics.


Mechanism:

The photograph of the stand alone type wearable power assisting suit and construction are shown in Fig.1. The shoulder of the arm unit can swing back and forth and side to side. The joints of the suit have double axles to extend movable area. Each unit can bend along with the bending of the arm, the waist and the leg. The joints of the elbows, waist and knees are rotated by direct drive pneumatic rotary actuators which are driven by micro air pumps applied by portable Ni-Cd batteries. Pneumatic rotary actuators using pressure cuffs give tender touch to the wearer and the maximum output force of them is limited by the maximum output pressure of micro air pump (0.1MPa). An embedded microcomputer and pump driving circuits are mounted on the back. The weight of the suit is about 32 [kg]. But, when the wearer stands upright, the entire weight of the suit can be supported by the leg units, and when the wearer bends at the waist or knee, the weights of the waist and arm units can be supported by the actuators. However, when the nursing operation is done, the wearer somewhat feel the weight of the suit.


 

The exerting muscle forces of the arms, waist and legs of the care personnel are detected by the muscle hardness sensors placed on the care personnels upper arms, on the legs above the knees and on the back above the hip. The output signals of the sensors are transmitted to the embedded microcomputer. The embedded microcomputer calculates the necessary joint torques for maintaining the position of lifting a patient and the torques are combined with the output signals of the muscle sensors to make control signals inputted into the air pump driving circuits. Then the supply of air flow to the cuff changes in accordance with the necessary joint torque. The necessary joint torques and the muscle forces driving the joints are estimated by computing the equations of body mechanics, as a function of the joint angles. The joint angles are detected by potentiometers.




Fig.1 Construction of Power Assist Suit

 


Fig.2 Sensing and Control System of Power Assist Suit


About the Author:

The author is associated with Kanagawa Institute of Technology.



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