15 Development of Hand Rehabilitation System Using Wire.Driven Link Mechanism for Paralysis Patients

In this chapter, we present a hand rehabilitation system for patients suffering from paralysis or contracture This system consists of two components: a hand rehabilitation machine, which moves human finger joints by using motors, and a data glove, which enables control of the movement of the finger joints attached to the rehabilitation machine. The machine is based on the arm structure type of hand rehabilitation machine; a motor indirectly moves a finger joint via a closed four-link mechanism. We used a wire-driven mechanism and a coupled mechanism for the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints. These mechanisms render the machine lightweight, resulting in a wider range of motion than that obtainable in conventional systems. The design specifications for the mechanisms and the experimental results are described in this chapter

15.1 Introduction

As the development of various technologies in medical applications becomes more rapid, machine-assisted physical rehabilitation, which requires long-term recurrent movements, is in increasing demand. For example, hand rehabilitation is an important process because hand movement is one of the most basic actions performed in daily life. Generally, hand paralysis or contracture is treated with the assistance of a physical therapist. The therapist holds and repeatedly moves the fingers affected by paralysis or contracture through the maximum range of their joint angles (Figure 15.1). A few months are usually required to improve the range through which the fingers can move. As a result, hand rehabilitation is expensive and time consuming Furthermore, the unavailability of physical therapists underscores the requirement for engineering solutions for physical rehabilitation A hand rehabilitation machine that can act as a substitute for physical therapists would be beneficial (Burger et al. 2000).

Conventional hand rehabilitation machines are categorized into two types: endoskeleton and exoskeleton. The main difference between these two types of machines is the manner in which the machine is attached to the human body With the endoskeleton type, actuators are attached directly to the skeleton and the joints are actuated by the actuators directly. With the exoskeleton type, a link mechanism is attached to the body and the joints are actuated by the actuators, which are operated by a link mechanism The endoskeleton-type machines generally use pneumatic actuators as substitutes for human muscles A pneumatic actuator consists of rubber, a tube, and an air compressor Because the drive unit (i. e., the rubber) is assembled separately, the pneumatic actuator has the advantages of high driving capability and a lightweight drive source (i.e., the air compressor; Noritsugu 2008). However, the actuator shape limits the number of places where the actuator can be attached; that is, this type of machine is not suitable for hand rehabilitation because it is difficult to attach a pneumatic actuator within the limited space available on a human finger Exoskeleton-type machines are generally heavier than endoskeleton-type machines However, the link mechanism enables the placement of the actuators anywhere on the human body Thus, exoskeleton-type machines are potentially suitable for use for any part of the human body; therefore, we used an exoskeleton-type machine for our hand rehabilitation system

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FIGURE 15.1

Rehabilitation of the injured finger.

Exoskeleton-type machines are mechanically categorized on the basis of their structure, including joint structure, arch structure, and arm structure types of machines (Figure 15.2). The joint structure type is characterized by actuators set along the fingers. It has high controllability because the actuators move the paralyzed finger joint. However, the joint structure is placed along the sides of the finger and is available for only the first, second, and fifth fingers; that is, this machine cannot be placed between fingers. Hasegawa et al. (2008) developed a power assist glove based on joint structure The glove uses motors and wire-driven mechanisms as drive sources; it is lightweight and has high drive (the grasping force of the glove is 15[N]). The third and fourth fingers, which cannot be attached to the machine, are moved by coupling them with the fifth finger. The arch structure type is characterized by an arc slider placed on the finger joint; the finger is moved by actuating the slider. Because the slider is placed on the finger, the machine can be used on all fingers (i. e., the arch structure resolves the problem faced when using the joint structure type of machine) Fu, Wang, and Wang (2008) developed a hand rehabilita-tion machine with an arch structure, and they were able to successfully control four joints in a single finger. The above-mentioned examples show that machines can possibly substitute for physical therapists because they can suitably control finger movement. A disadvantage of both the joint and arch structure type of machines is the difficulty involved in attaching them to the fingers; that is, the rotational centers of the joints of these structures should match that of the corresponding finger joint. Moreover, each finger has a different length; hence, the structure of the machine must be suitably modified for each user and different finger lenths. One of the solutions to this problem is the arm structure type of machine, which was proposed by Fu, Zhang, and Wang (2004); Kawasaki et al. (2007) developed an arm structure consisting of a closed four-link mechanism: four links (i. e., two metal links and two human finger links) and four joints (one actuated joint, two free joints, and one human finger joint). The finger joint is not directly controlled by the actuated joint. The geometry of the links indirectly controls the finger. In the closed four-link mechanism, the distance between Base 1 and Base 2 (Figure 15.2c) is adjustable because of the free joints Thus, this structure can be adjusted to suit any user without any design modification, which enhances its practical usability.

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FIGURE 15.2

Mechanisms of exoskeleton-type machines.

However, the closed four-link mechanism has three structural problems: (1) The finger joint has two possible configurations for an angle of the actuated joint Thus, it becomes necessary to avoid some angles of the actuated joint; that is, this mechanism limits the range of joint motion (2) The machine is heavy because the motor is placed inside the mechanism Thus, this structure is not suitable for long-term use. (3) The mechanism overloads the finger joint when the finger joint bends more than 90 degrees. This is because the free joints cannot generate rotational torque; instead, they apply shear forces to the finger joint. This, too, limits the range of the joint angle.

In this study, we developed a new hand rehabilitation machine that is based on arm structure We aimed to reduce the weight of the machine and increase the range of joint motion by using a wire-driven mechanism Furthermore, we propose a hand rehabilitation system in which fingers affected by paralysis can be moved using the proposed hand rehabilitation machine, and the finger joints can be controlled using a data glove worn on the healthy hand.

15.2 Proposed Design

15.2.1 Four-Link Mechanism with the Wire-Driven Mechanism

The arm structure type of hand rehabilitation machine uses a closed four-link mechanism, and this machine can be attached to fingers of any length. To the best of our knowledge, this is the most convenient hand rehabilitation machine available at present. Therefore, we focused on the arm structure type of machine and endeavored to improve its performance; specifically, we aimed to increase the range of joint motion and improve the control of finger movement To achieve this, we propose a design that combines the closed four-link mechanism with a wire-driven mechanism.

Our basic design is based on the arm structure type of machine (Figure 15.2c), which has three joints—one motor joint and two free joints— in the closed four-link mechanism. We substituted the motor joint with a free joint and attached three pulleys to the three free joints The pulleys are connected by two wires (Figure 15.3a); the gray line represents a flexion wire, and the black line represents an extension wire. One end of each wire is attached to Base 1, and the other end is attached to a motor. The rehabilitation machine bends the finger when the flexion wire is pulled (Figure 15.3b) and extends the finger when the extension wire is pulled (Figure 15.3c). A conceptual diagram of the rehabilitation machine is shown in Figure 15.4. The wire-driven mechanism allows spatial separation of the drive from the actuator. In this mechanism, the motor is not placed on the fingers, thereby reducing the weight of the machine on the finger. Furthermore, because the motor does not occupy space on the finger, we can add three arm structures on a finger, thus affording multiple degrees of freedom (DOFs). Therefore, it is possible to use a motor with a higher drive, which is heavier. Our proposed design is advantageous because this system would have a lighter weight, higher drive, and thus greater DOFs than do conventional machines. This mechanism can adjust to various hand sizes (Figure 15.5).

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FIGURE 15.3

Proposed design.

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FIGURE 15.4

Flexion and extension actuated by a single motor.

The combination of the wire-driven mechanism and closed four-link mechanism overcomes the limitations of the arm structure. In the original arm structure design, the motor could not rotate when the three joints were in a straight line. However, in the proposed design, all three joints can be coupled and actuated with one motor Therefore, even when the joints are in a straight line, the motor continues to rotate easily; that is, the proposed design enables a wider range of joint motion than does the original arm structure. In summary, the proposed hand rehabilitation machine is designed to be practically applicable. Its light weight will enable patients to use it for a long period. It offers multiple DOFs and high drive, which enhance the control of the fingers; this machine can therefore be used for various rehabilitation plans. To analyze the range of joint angles achievable using our proposed design, we constructed a mathematical model of the proposed machine (Figure 15.6). It consists of three pulleys, two links, and two wires. A wire runs from Base 1 to Pulley 3. Point A on Base 1 indicates the starting point of the wire, and point A on Pulley 3 indicates its end point. The length l_AB of the wire between the two pulleys is given by Equation (15.1).

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FIGURE 15.5

Adjustment of structure to various hand sizes.

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FIGURE 15.6

Schematic diagram of wire-driven mechanism.

$l_{AB} = r_{1} Θ_{1} + r_{2} Θ_{2} + r_{3} Θ_{3^{+}} \sqrt{a_{1}^{2} - (r_{1} + r_{2})^{2}} + \sqrt{a_{2}^{2} - (r_{2} + r_{3})^{2}}$ $l_{AB} = r_{1} Θ_{1} + r_{2} Θ_{2} + r_{3} Θ_{3^{+}} \sqrt{a_{1}^{2} - (r_{1} + r_{2})^{2}} + \sqrt{a_{2}^{2} - (r_{2} + r_{3})^{2}}$ (15.1)

The point (x,y) is expressed as shown in Equations (15.2) and (15.3):

$x = x_{2} + Lcos (α - Φ)$ $x = x_{2} + Lcos (α - Φ)$ (15.2)

$= a_{2} sin (Θ_{3} + Γ) - a_{2} sin (Θ_{2} - Θ_{3} - β)$ $= a_{2} sin (Θ_{3} + Γ) - a_{2} sin (Θ_{2} - Θ_{3} - β)$

$y = Lsin (α - Φ)$ $y = Lsin (α - Φ)$ (15.3)

$= h_{2} - a_{2} cos (Θ_{3} + Γ) + a_{1} cos (Θ_{2} - Θ_{3} + β)$ $= h_{2} - a_{2} cos (Θ_{3} + Γ) + a_{1} cos (Θ_{2} - Θ_{3} + β)$

L, a, ß, and y are expressed as follows:

$L = \sqrt{x_{1}^{2} + h_{1}^{2}}$ $L = \sqrt{x_{1}^{2} + h_{1}^{2}}$

$α = arctan \frac{h_{1}}{χ_{1}}$ $α = arctan \frac{h_{1}}{χ_{1}}$

$β = arccos \frac{r_{1} + r_{2}}{a_{1}}$ $β = arccos \frac{r_{1} + r_{2}}{a_{1}}$

$Γ = arccos \frac{r_{2} + r_{3}}{a_{2}}$ $Γ = arccos \frac{r_{2} + r_{3}}{a_{2}}$

The geometrical relation yields the following equation:

$Φ = π - Θ_{1} + Θ_{2} - Θ_{3}$ $Φ = π - Θ_{1} + Θ_{2} - Θ_{3}$ (15.4)

The relation between l_AB and cp is obtained by removing 9j, 0₂, and 9₃ in Equations (15.1) to (15.4); that is, the result indicates that the traction distance of the wire controls the human finger joint.

15.2.2 Coupled Mechanism for the Distal Interphalangeal and Proximal Interphalangeal Joints

Physiological studies have revealed that the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints in a human finger are actuated with the same muscles, and the movements are coupled. We used a similar coupled mechanism in our hand rehabilitation machine in order to enhance its mobility; that is, reducing the number of motors results in a lighter and smaller machine that is long lasting The conceptual design of the coupled mechanism is shown in Figure 15.7: (1) the wire-driven four-link mechanism is set on the DIP and PIP joints; (2) the wire that bends the DIP joint is connected to the wire that bends the PIP joint; and (3) the wire that extends the DIP joint is connected to the wire that extends the PIP joint Thus, both the DIP and PIP joints are both subjected to the same directional force through the connected wires, and the movements are coupled

15.3 Actual Hand Rehabilitation Machine

A computer-aided design (CAD) image and a photograph of the proposed rehabilitation machine are shown in Figures 15.8 and 15.9, respectively. The machine is designed such that there are three arm structures for the metacarpophalangeal (MP), PIP, and DIP joints. The arm structure for the MP joint is actuated with a radio control (RC) servo; the arm structures for the PIP and DIP joints are coupled using two wires so that these joints are actuated with another RC servo (i e, interference mechanism) Thus, this machine uses two RC servos to move three finger joints. The arm structure is made of two materials: the base is made of fine nylon, and the arm is made of glass epoxy. The weight of the arm structure is 51 g. We used Velcro tape to attach the arm structure to the fingers, because it is easy to attach and remove. We used the wire-driven mechanism to make the structure light. This mechanism allows the user to place the actuators on arbitrary locations. We plan to place the motor unit on the user's shoulder or the lower back of the user so that long-term usage is possible The arm struc-ture is actuated with the RC servo through two wires The wires are made of polyethylene, and they are connected to the motor through a metal spring tube A motor unit is shown in Figure 15.9. It consists of two RC servos, two pulleys, and one RC servo case with a tube attachment made of fine nylon. Its weight is 83 g. The motor is an RC servo (GWS Micro 2BBMG [Grand Wing System U. S.A. Inc., City of Industry CA, USA]; torque, 5.4 kg • cm; weight, 28 g; dimensions, 28 x 30 x 14 mm³). The specifications of the hand rehabilitation machine are listed in Table 15.1.

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FIGURE 15.7

Coupled mechanism for the DIP and PIP joints.

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FIGURE 15.8

CAD image of the exoskeleton of the proposed machine for one finger.

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FIGURE 15.9

Prototype of the exoskeleton for one finger.

TABLE 15.1

Specifications of Hand Rehabilitation System

Weight

Exoskeleton: 51 g

Motor unit: 83 g

Arm length

DIP: 20.0 mm

PIP: 25.0 mm

MP: 35 mm

Width

17.5 mm

15.4 Working of the Hand Rehabilitation Machine

The attachment of the hand rehabilitation machine to a hand is shown in Figure 15.9. The machine is suitably attached to the second finger (finger length, 69 mm; Figure 15.10a-1) and to the fifth finger (finger length, 58 mm; Figure 15.10b-1); after attachment, the machine can move these fingers. The time required to adjust the arm structure according to the finger length is within 1 min

The machine could successfully bend the finger joints (Figures 15.10a-2 and 15.10b-2); the ranges of motion are listed in Table 15.2. In both cases, the machine could smoothly bend the DIP joints at sufficient angles. This indicates that the coupled mechanism for DIP and PIP joints works properly. Moreover, because the pulleys on the arm structure simultaneously rotate with the wire-driven mechanism, the user feels less loading on the finger. Furthermore, the combination of the closed four-link mechanism and the wire-driven mechanism results in a one-to-one positional relationship between the motor joint and the human finger joint, which offers better control than that provided by the original arm structure

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FIGURE 15.10

Operation of the (a) index finger and (b) little finger.

TABLE 15.2

Supported Range of Motion for the Little/Index Finger Joints

	Little Finger		Index Finger
	Extension	Flexion	Extension	Flexion
MP (°)	0	85	0	85
PIP (°)	0	90	0	90
DIP (°)	0	65	0	65

15.5 Working of the Hand Rehabilitation System

Generally, hand paralysis affects only one hand. Therefore, some hand rehabilitation systems involve the use of the unaffected healthy hand This is known as self-motion control.

For example, Kawasaki et al. (2007) developed a hand rehabilitation system that acquires information about the joint angles of the healthy hand and controls the paralyzed hand with a machine by using this information

In this study, we applied the same concept to our hand rehabilitation system (Figure 15.11). The hand rehabilitation system is used in the following sequence: (1) The user wears the data glove on the healthy hand (Figure 15.12). (2) The rehabilitation machine is attached to the target finger of the affected hand. (3) The machine is calibrated for maximum flexion and extension of the finger (Figure 15.12). (4) The target finger joints are controlled by the finger joints on the data glove (i. e., mirror motion). Thus, hand rehabilitation is performed without the help of a physical therapist In addition, this system has a motion playback function that can be used without the help of a therapist

The data glove system measures the angles of the DIP and PIP joints on the index finger of the left hand. This information is fed as control input to the hand rehabilitation machine, and this input controls the angles of the DIP and PIP joints on the index finger of the right hand. The workings of the data glove system are shown in Figure 15.13: the DIP and PIP joints on the index finger of the right hand are controlled using the index finger on the left hand. Thus, the hand rehabilitation machine, which is controlled by the data glove, enables the user to achieve complex finger movements (Figure 15.14). This system greatly contributes to hand rehabilitation and can be used without the aid of a therapist In addition, because this system has a motion playback function, the user can record finger movements for a maximum of 10 seconds and play back the finger movements cyclically. Thus, long-term passive rehabilitation can be provided

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FIGURE 15.11

Control system of the hand rehabilitation system for hemiplegic patients.

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FIGURE 15.12

Data glove used for measurement of DIP and PIP joint angles.

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FIGURE 15.13

Determination of the range of motion.

15.6 Conclusions and Future Works

We have developed a hand rehabilitation system for patients affected by paralysis or contracture. It consists of 2 two components: a hand rehabilita-tion machine, which moves human finger joints using motors, and a data glove, which provides control of the finger joints attached to the rehabilitation machine. The machine is based on the arm structure type of rehabilitation machine; a motor indirectly moves a finger joint via a closed four-link mechanism We have employed a wire-driven mechanism and have developed a compact design that can control all three joints (i. e., PIP, DIP, and MP joints) of a finger; the design renders the machine lightweight and offers a wider range of joint motion than conventional systems. Further, we have demonstrated the hand rehabilitation process in which the finger joints of the left hand attached to the machine are controlled by the finger joints of the right hand wearing the data glove

We intended to resolve the following issues in future studies in order to improve the practical application of our proposed system: (1) The range of motion of the machine needs to be improved because a certified hand rehabilitation machine is required to move human fingers through the following angles: 85 degrees at the MP joint, 110 degrees at the PIP joint, and 65 degrees at the DIP joint (Fu, Zhang, and Wang 2004). (2) A rehabilitation machine that can be used with all five fingers needs to be developed and its performance evaluated by testing it on actual patients. (3) A method that enables hemiplegic and paraplegic patients to control the system without the aid of therapists needs to be developed because these patients cannot achieve self-motion control

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FIGURE 15.14

Demonstration of the data glove system.

References

Burger, C. G., Lum, P. S., Shor, P. C., and Machiel Van der Loos, H. F. 2000. Development of robots for rehabilitation therapy: The Palo Alto VA/Stanford experience. Journal of Rehabilitation Research and Development, 37(6): 663-673.

Fu, Y., Wang, P., and Wang, S. 2008. Development of a multi-DOF exoskeleton based machine for injured fingers. Paper presented at the IEEE/RSJ International Conference on Intelligent Robots and Systems, Nice, France, September 22-26, 2008, 1946-1951.

Fu, Y., Zhang, F., and Wang, S. 2004. Structure types design and genetic algorithm dimension synthesis of a CPM machine for injured fingers. Paper read at the International Conference on Robotics and Biomimetics, Shenyang, China, August 22-26, 640-644.

Hasegawa, Y., Mikami, Y., Watanabe, K., and Sankai, Y. 2008. Five-fingered assistive hand with mechanical compliance of human. Paper presented at the IEEE International Conference on Robotics and Automation, Pasadena, CA, May 19-23, 2008, 718-729.

Kawasaki, H., Ito, S., Ishigure, Y., Nishimoto, Y., Aoki, T., Mouri, T., Sakaeda, H., and Abe, M. 2007. Development of a hand motion assist robot for rehabilitation therapy by self-motion control Paper presented at the IEEE 10th International Conference on Rehabilitation Robotics, 12-15 June, Noordwijk, The Netherlands, June 12-15, 2007, 234-240.

Noritsugu,T, Yamamoto, H., Sasaki, D., and Takaiwa, M 2008 Wearable power assist device for hand grasping using pneumatic artificial rubber muscle. Paper presented at the SICE Annual Conference, Sapporo, Japan, August 4-6, 2004, 420-425

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Table of Contents for
15 Development of Hand Rehabilitation System Using Wire.Driven Link Mechanism for Paralysis Patients

15

Development of Hand Rehabilitation System Using Wire-Driven Link Mechanism for Paralysis Patients

CONTENTS

15.1 Introduction

15.2 Proposed Design

15.2.1 Four-Link Mechanism with the Wire-Driven Mechanism

15.2.2 Coupled Mechanism for the Distal Interphalangeal and Proximal Interphalangeal Joints

15.3 Actual Hand Rehabilitation Machine

15.4 Working of the Hand Rehabilitation Machine

15.5 Working of the Hand Rehabilitation System

15.6 Conclusions and Future Works

References

Table of Contents for 15 Development of Hand Rehabilitation System Using Wire.Driven Link Mechanism for Paralysis Patients

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Development of Hand Rehabilitation System Using Wire-Driven Link Mechanism for Paralysis Patients

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Table of Contents for
15 Development of Hand Rehabilitation System Using Wire.Driven Link Mechanism for Paralysis Patients