Wearable Power Assist Suit

1. Introduction

1.1 Background

The development of welfare machines which can meet the requirement of the elderly is now an important subject due to the rapidly aging population. The research for the robot which was aimed at supporting transfer movements of patients was begun in the 1970s, and MEL- Kong was the representative example, and an operation robot Nurcy based on the master and slave control system was developed. However, none of these show any prospects of the utility yet.

In 1990, we started to develop a Wearable Power Assist Suit, and in 1991 we fabricated a Powered Arm constructing the master and slave system in one unit by utilizing a rubber tube air actuator and sensing cuff, [ref. 1]. In 1994, we developed a Wearable Powered Suit constructed with powered arms, a powered waist, and powered legs [ref. 2], and finally in 2002, we developed a Stand Alone Type Wearable Power Assist Suit [ref. 3]. This suit was composed of newly developed air bag actuators driven by micro air pumps, newly developed muscle hardness sensors, and an embedded micro computer. The muscle hardness sensor was developed for detecting the muscle force driving joints. The micro computer was for calculation of the necessary joints torques to lift heavy objects. The calculation equations was derived by body mechanics. This suit could run continuously 20 minutes with 12 volts Ni-Cd portable batteries. The latest power assist suit can generate higher assist power, and is composed of compact body, a compact embedded micro computer, small and flat rotary sensors, and has newly designed muscle sensors which are embedded in 3-D mesh [ref. 4].

References

1.2 Basic concepts

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

  1. An enough safe system. This is assured by the controllability by the nurse, i.e., the assisting system consists of a master and slave system in one unit.
  2. The absence of mechanical parts in front of the suit. This results in good feelings between the patient and the nurse.
  3. Flexible joints using pneumatic rotary actuators using pressure cuffs. These joints give tender touch to the joints of the nurse.
  4. Assisting forces correspond with the necessary forces to the joints. This is realized by developing muscle hardness sensor which detects the muscle force driving the joints.

In addition, as a backup and fail safe system, necessary joint torque for maintaining a position is calculated from static body mechanics.

2. Mechanism

2.1 Structure

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 so that the each unit can bend with the bending of the arm, waist and leg. The joints of the elbows, waist and knees are rotated by newly developed direct drive pneumatic rotary actuators which are driven by micro air pumps applied by portable Ni-Cd batteries. An embedded microcomputer and PWM driving circuits are mounted on the back. The portable Ni-Cd batteries are attached to the legs. These units are fabricated of duralumin alloy. The weight of the suit is about 30 [kg]. 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.

The sensing and control systems of the power assisting suit are shown in Fig.2. The exerting muscle forces of the arms, waist and legs of the nurse are detected by the muscle hardness sensors placed on the nursefs upper arms (biceps brachii muscle), on the legs above the knees (rectus femoris muscle) and on the back above the hip (erector spinae muscle). The output signals of the sensors are transmitted to the embedded microcomputer.@The embedded microcomputer calculates the necessary joint torque for maintaining a position, and the necessary joint torque is combined with the output signals of the muscle sensors to make control signals inputted into the PWM driving circuits. Then the supply of air flow to the cuff changes in accordance with the necessary joint torque.

Fig 1. Side view of power assist suit

3. Controller

SOPC (System on Programmable Chip) technology was used to implement the controller of powered assisting suit. The controller consists of an APEX20K200E (200K gate) FPGA device, A/D converters, ethernet controller, two external SRAMs and EEPROM memories on a single board. This FPGA device board has 9x12 [cm] width and 2.5 [cm] height. The controller core is a 32-bit wide Nios 2.0 processor and control block module. The control block contains a 24 channel PWM (18 bit), a interface logic for A/D, FIR (Finite Impulse Response) filters and PID core (16 bit).

The control block contains 24 PWM channels (18bit), a interface logic for A/D, FIR (Finite Impulse Response) filters and PID core (16 bit). The control block is able to operate even if alone and the calculation delay of the control block is only 20 clocks (The controller runs at a clock speed of 33MHz.). The controller hardware for power assisting suit uses approximately 85% of the FPGA device.

Fig.2. Control board

4. Future Work

We are now improving the structure to make it operable in response to actual complicated care give operation, deriving a 3D physical calculation model that corresponds to these improvements, selecting a CPU that calculates at high speed, and developing a actuator capable of proving softer, smoother action.
Technical breakthrough necessary for improvement is the following,.

  1. Development of actuator
    Specification
    Expansion and contraction radio:5, Critical pressure:0.25MPa, Size:50~50~100mm3
  2. Development of air pump
    Specification
    Output pressure:0.25MPa, Output flow:25 liters per minute, Size:50~50~100mm3

5. Media (excepting Japanese media)

News papers

Journals

Book

TV

Demonstrations

History and Gallery

In 1990, the development of Wearable Power Assist Suit started.


Powered Arm(1991) and Leg(1994)
(Yamamoto, K., Miyanishi, H. and Imai, M., Development of pneumatic actuator for powered arm, Proc.JHPS Autumn Meeting, (in Japanese), (1991), p.85-88, Yamamoto, K. and Hyodo, K., Powered Arm and Leg for Assisting Nurse Labor, Proc. 1st Asian Control Conf., SICE, J., (1994), p.561-564)
In 1991, we developed Powered Arm . The powered arm was composed of pneumatic actuators utilizing rubber tubes for rotating the elbow and of a cuff for sensing the movement of the arm. In 1993, we developed Powered Arm and Leg composed of the rubber tube actuators and the sensing cuffs which detect the movement of the arm and leg of the wearer.

Fig.3. Powered Arm (1991)


1st Suit (1994)
(Yamamoto, K. and Hyodo, K., Powered and Imai, M., Development of Powered Suit for Assisting Nurse Labor, Research Reports of Kanagawa Institute of Technology, Part B, Vol.20, (in Japanese), (1996), p.29-43, Yamamoto, K. Hyodo, K. and Matsuo, T., Powered Suit for Assisting Nurse Labor, Proc.3rd JHPS International Symposium, JHPS, (1996) , p.415-420)
In 1994, Powered Suit composed of the powered arms, legs, and waist having pneumatic rubber actuators was developed. The waist unit utilized link mechanisms and had a rubber tube actuator. The arms, legs and waist units were connected each other constructing a suit and attached to the wearerfs arms, legs and waist, respectively. In 1995, Powered Suit having a new pneumatic actuator using concentric sliding boxes with infinitesimal clearance was developed.

Fig.4. 1st Suit with rubber tube actuator (1994)


Fig.5. 1st Suit with sliding boxes actuator (1995)


2nd Suit (2001)
(Yamamoto, K., Hyodo, K., Ishii, M. and Matsuo, T., Development of Power Assisting Suit for Assisting Nurse Labor", JSME International Journal, 45-3, (2002) 703-711)
The power assisting suit was composed of the shoulders, the arms, the spine, the waist and the legs. The arms, waist and legs have the pneumatic rotary actuators. The pneumatic rotary actuators are constructed with pressure cuffs sandwiched between thin plates. The action of the arms, waist and legs of the nurse are sensed with the muscle hardness sensor utilizing load cell with diaphragm mounted a sensing tip. The dent of the sensing tip corresponds to the hardness of the muscle so that exerting muscle force produces electric signal.

Fig.6. 2nd Suit (2001) with cuff actuator (2001)


1st Stand Alone Suit (2002)
( YamamotoC K., IshiiC M., HyodoC K., YoshimitsuC T., and MatsuoC T., Development of Power Assisting Suit for Assisting Nurse Labor -Miniaturization of supply system to realize wearable suit-C JSME International JournalC Series CC Vol.46C No.3C(2003), pp.923-930)
We developed a stand alone wearable power assisting suit by a substantial miniaturization of the power supply and control systems using micro air pumps, portable batteries, and an embedded microcomputer. The arms, waist and legs have pneumatic rotary actuators driven directly with micro air pumps supplied by portable Ni-Cd batteries. The muscle forces are sensed with a new muscle hardness sensor utilizing a sensing tip mounted on a polymer thick film device. The embedded microcomputer calculates the necessary joint torque for maintaining a position according to the equations derived from static body mechanics using the joint angles, and the necessary joint torque is combined with the output signals of the muscle sensors to make control signals.

Fig.7. 1st Stand Alone Suit (2003)


Latest suit (2nd Stand Alone Suit) (2005)
(Ishii, M., Yamamoto, K. and Hyodo, K., A Stand-Alone Wearable Power Assist Suit -Development and Availability-, Journal of Robotics and Mechatronics, Vol.17, No.5, (2005), p.575-583.)
By further miniaturization of the power supply and control systems using micro air pumps, portable batteries, the suit became stronger and more compactly. New muscle hardness sensor utilizing a sensing tip mounted on a load cell was developed.

Fig.8. Latest Suit (2nd Stand Alone Suit) (2005)

For more information or contact us

Dr. Keijirou Yamamoto
Kanagawa Institute of Technology, Robotics and Mechatronics, Japan

Address: 1030, Shimo-Ogino, Atsugi, Kanagawa Pref.
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