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Abstract: A new prosthetic hand with a fixed thumb and four fingers actuated by Shape Memory Alloy (SMA) type artificial muscle has been developed in this paper. Different from typical geared motor, SMA actuator is lightweight and silent, however shows a little short stroke and small attracting force per each unit. In order to achieve enough output force and motion range of each finger, multiple SMA type artificial muscles with special device which facilitates enough length are equipped in the hand. The fundamental properties of the SMA type artificial muscle including output force and electrical response were determined experimentally and considered for the design of hand mechanism. Besides, the structure of each finger and whole system has been designed based on observation of human hand. The electrical hardware to control multiple shape memory alloy type artificial muscles has been also developed. Finally, the usefulness of the prosthetic hand has been investigated through experiments for grasping several types of objects.
Key words: Prosthetic hand, prosthetic finger, shape memory alloy, mechanism design, grasping experiment.
1. Introduction
The excellent functionality of the human hand ensures convenience and optimal performance of activities of daily living. However, the disabled who have physical disabilities of their hand experience difficulties in their works or cannot perform their tasks especially for manipulating general objects. As a useful device to support them, several types of prosthetic hands have been proposed. For example, a simple prosthetic hand just for appearance and a hook-shaped prosthetic appliance have been employed as fundamental and well-used devices [1]. However, they show very limited functionality in general.
Meanwhile, robotic hands for manipulating objects have been investigated as robotics researches for both robot and the disabled. For the design of dexterous hand mechanism, minute observation and in-depth analysis on the structure of human hand have been carried out [2-3]. Namely, mechanical structure and characteristics of human hand have been considered as a good model for design and control. However, there are differences between human and robotic system, which cause great obstacles to the design of actual robotic hand. Most of all, human hand is actuated by soft but strong actuator, i.e., muscle, which cannot be manufactured artificially with advanced technology so far. To cope with the problem, several alternatives have been proposed. Electric motor has been used as typical actuator for general robotic hand mechanism [2-4]. For abundant torque to achieve holding force, gear train with high reduction ratio is required for general motor. Thus the size of the actuators becomes large, and they cannot be installed in the hand itself. Besides, soft actuation scheme like as human muscle cannot be realized because of the lack of back-drive capability in gear train of high reduction ratio. Therefore, most of robot hands utilize tendon device to transmit the power of motor being attached in the forearm apart from hand. Some researchers utilize several types of elastic elements to improve the grasping capability of robotic finger with stiff motor-based actuation [5]. Ultrasonic motor [6] is also proposed as a candidate of actuator for hand mechanism because it has large output power for relatively small size than general DC (Direct Current) motor. However, it has been known that it has difficulties in control owing to its fundamental driving principle, which is powered by the ultrasonic vibration of its components. Besides, hydraulic and pneumatic actuators have been applied for the design of robot hand [7-9]. In this case, the system requires large and heavy power source such as an air compressor or a gas container to store the compressed air for pneumatic actuator, and pump for hydraulic actuator. Other researches related to control methodology to cooperate multiple actuators for grasping objects has been carried out [3, 5]. A method to analyze the characteristics of anthropomorphic prosthetic hands has also been proposed recently [10].
The characteristics expected of prosthetic hands are that they should be comfortable, useful for manipulating objects and lightweight. The purpose of the research is to develop a new type of prosthetic hand that could be used by individuals with a hand disability. As stated above, electric motor is generally used as actuator for conventional prosthetic or robot hands because it is easy to control the motions of prosthetic hand. However, prosthetic hand that has many motors in multiple fingers becomes heavy. So the hand system cannot be installed effectively at the end of user’s arm.
Recently, various actuators such as polymer type artificial muscle have been proposed to imitate the characteristics of human muscle. Polymer type actuator has been employed in many robots including hand and gripper. However, most of them are still far from real application because its output force is so small. One of promising actuator for robotic hand is Shape Memory Alloy (SMA) type Artificial Muscle(AM). The SMA type AM has potential for prosthetic hand design as it has a large force-to-mass ratio and therefore the hand can be lightweight. In addition, it has no gear train thus its movement is silent. Owing to those merits, SMA type AM has been utilized as actuator for robotic gripper and hand in previous researches [11]. However, the problem of weak output force is still unsettled. It comes from that the radius of driving pulley at each joint is small because SMA type AM has small output stroke. Therefore, this paper proposes a new structure of driving mechanism for large gripping force and compact design that all actuators are built in the hand itself.
The paper is organized as follows: In section 2, the basic properties of SMA type AM are discussed; the mechanical design of the proposed prosthetic finger and hand is presented in sections 3-4 respectively; in section 5, conclusions and future work are addressed.
2. Properties of Shape Memory Alloy Type Artificial Muscle
The basic properties of SMA type AM used are investigated experimentally. The mechanical and electrical data through the following experiments are utilized as fundamental information for the development of a prosthetic hand.
2.1 Loading Test
Loading test to investigate the longitudinal deformation of the actuator by external force is carried out. Fig. 1 shows a test piece of SMA type AM employed in this research [12]. The length and diameter of the test piece are 200 mm and 0.15 mm respectively. Fig. 2 shows the experimental setup for the loading test. One end of the test piece is clamped at the top of the stand frame, and then its other end is loaded with forces from 4.9 × 10-2 to 3.9 × 10-1 N(increments of 4.9 × 10-2 N). The length of the test piece is compared that of un-loaded condition. The resultant relationship between length and loading force is displayed in Fig. 3.
Fig. 1 Test piece of SMA type artificial muscle named as BioMetal [12].
Fig. 2 Experimental setup for loading test.
2.2 Contraction Test
The fundamental capability of AM as an actuator is to generate pulling force due to the deformation of itself by applied electric voltage. The deformation, i.e., contraction, of the test piece by applied voltage under the condition of external force is investigated. Fig. 4 shows the resultant change of the length of the SMA type AM. Voltages ranging from 0 to 5.0 V(increments of 0.5 V) are applied to the test piece loaded by forces ranging from 9.8×10-2 to 1.372 N(increments of 9.8 × 10-2 N). Currents and deflections passing through the test piece are measured throughout the experiment. After shortening by the applied voltage, the length of the test piece becomes about 94% of the initial state. That is to say, it could be observed that the amount of deformation is about 6% of the initial length.
Fig. 3 The relation between length of AM and load force from 4.9 × 10-2 to 1.96 N.
Fig. 4 Deformation of the SMA type AM after applying the voltage of 4.0 V while the external force of 1.372 N is applied.
2.3 Relationship between Applied Voltage and Contraction of AM
In order to find out the appropriate range of input voltage to actuate the SMA type AM, the relationship between the deflection of AM and the applied voltage is investigated through experiments. Fig. 5 shows two examples of the experimental results. As shown in Fig. 5a, in the case that the loaded force is small, the deflection of SMA type AM increases when the applied voltage is changed from 1.5 to 2 V. However, in the other case that the loaded force is large, the range of input voltage to cause the deformation is changed to around 2.5 V. It means that the SMA type AM requires large value of input voltage for the generation of large output force.
3. Development of Prosthetic Finger
Based on the structure of human hand, the prosthetic finger with multiple joints is designed in this section.
Fig. 5 The relationship between the deflection of the test piece and the applied voltage while two types of external force are loaded.
3.1 Mechanism of Prosthetic Fingers
The human finger consists of three links, which are connected by three joints, i.e., the distal interpharangeal (DIP), proximal interpharangeal (PIP) and metacarpophalangeal (MP) joints as displayed in Fig. 6. The prosthetic finger developed has the same structure as human finger. The prosthetic finger is operated by two SMA type AMs. One is attached to the second link for rotation of the DIP and PIP joints. The other is attached to the third link and responsible for rotation of all joints in the finger.
The two SMA type AMs are installed inside the finger and several stoppers are used for the generation of effective torque at the joints. As a result, all three joints of the finger can be controlled by the two SMA type AMs, which allows the finger to grasp an object with irregular shape. Reversely, for opening motion of the finger, pre-loaded pulling force of the wire attached in its backside and connected to the spring in the palm of the hand works effectively.
Fig. 6 Structure of human finger and prosthetic finger.
Fig. 7 shows the motion of the prosthetic finger to grasp an object. All joints cooperate with each other for grasping motion because they are connected together by the two SMA type AM and a wire connected to reverse spring. According to the geometry of the object, motion of some joints is constrained by the contact between link and object and other free joints continue closing motion, then the shape of finger is changed for grasping resultantly.
For the independent operation of multiple SMA type AM, namely in order to ensure that the AMs are isolated with each other, Teflon films are inserted between the AM strings in the finger mechanism. The stroke of each SMA type AM is approximately 5% of its natural length. In order to achieve the sufficient stroke of finger motion, small pulleys that lengthen the total length of each SMA type AM are built in the palm of the hand. Fig. 8 shows the first and the second finger of the prosthetic hand. Both have same structure with each other. The third and the fourth finger is operated by one SMA type AM for closing motion and one spring for reverse motion as shown in Fig. 9.
3.2 Motion Experiment of Prosthetic Finger
In order to grasp object of various geometry, the fingers should be folded according to the object’ shape naturally. The motion of finger under the condition of various constraints has been tested experimentally.
Fig. 7 Grasping motion of the prosthetic finger.
Fig. 8 First and second prosthetic fingers.
Fig. 9 The third and fourth prosthetic fingers.
Figs. 10-11 show the motion of the prosthetic finger when the first and the second finger are constrained, respectively. The authors examine the motion of the prosthetic finger when each link of the prosthetic finger is fixed. From these experiments, it can be confirmed that the prosthetic finger has the capability to grasp an object of irregular geometry.
Fig. 10 Motion of the prosthetic finger when the first and the second links are constrained.
Fig. 11 Motion of the prosthetic finger when the first link is constrained.
4. Development of Prosthetic Hand
4.1 Mechanism of Prosthetic Hand
The prosthetic hand developed in this research is displayed in Figs. 12-13. Fingers designed in the previous section are employed for the development of the prosthetic hand. The fingers are arranged based on the geometry of human hand, and the SMA type AM actuators are equipped in the palm for compactness. Two SMA type AMs are attached to the first and the second fingers in order to reinforce the grasp force. To save space, the third and fourth fingers supporting the first and the second finger are actuated by single SMA type AM, respectively. The thumb is designed as a static finger fixed to the palm. For extension of the fingers, each finger is connected via a wire to a spring positioned at the back of the hand.
As shown in Fig. 14, the dimensions used for the design of the prosthetic hand are decided based on the average data of general human hand. The mechanical frame of the prosthetic hand is made of poly-acetal material. The photograph of the prosthetic hand developed in this research is given in Fig. 15.
Fig. 12 Composition of human hand and the prosthetic hand.
Fig. 13 Side view of the prosthetic hand.
Fig. 14 Dimensions of the prosthetic hand.
Fig. 15 The prosthetic hand developed in this research.
Fig. 16 Configuration of the control system.
4.2 Control Systems
A microprocessor is used to control all fingers and interface with other system and user’s command. Fig. 16 shows the configuration of the control system for the prosthetic hand. The photograph of the hand with the developed controller is displayed in Fig. 17. In current step, a switch connected to the microprocessor is used as a simple trigger for user input. An advanced method of user interface such as voice recognition can be connected to it in the future. Actually, all AMs have different lengths because of the configuration and the geometry of the hand in both closed and open states. Particularly, the length of SMA type AM attached to the second link is different to that of the AM attached to the third link. The level of the voltage required to shorten the SMA type AM is proportional to its length. So the final length of each artificial muscle is modified by register connected to it. According to the command signal from microcomputer, the power drivers energize all actuators directly or through registers. A battery of lithium cell is also used as a portable power source for the prosthetic hand.
4.3 Experiment of Prosthetic Hand
The capability of the developed prosthetic hand to grasp objects was tested through the experiments of grasping and handling objects. The experiments of grasping various objects such as cup, ball, bottle, and pen were carried out as shown in Figs. 18-19. Through the experiments, it could be observed that the developed prosthetic hand can grasp objects of various shapes. Besides, it can handle a little weighty object. For example, the water bottle in Figs. 19-20 weighs about 500 grams. The developed prosthetic hand should be equipped at the end of user’s arm resultantly. So the system was modified as a portable type test-bed hand with built-in controller and battery. An example of experiment handling an object, i.e., a water bottle, is shown in Fig. 20.
Fig. 17 The prosthetic hand with controller.
Fig. 18 The prosthetic hand grasping a cup and a ball.
Fig. 19 The prosthetic hand grasping a bottle and a pen.
5. Conclusions
In this paper, a light and quiet prosthetic hand using SMA type AM was developed. It was designed based on the structure of human hand. And the driving mechanism of each finger was designed not only to achieve the powerful grasping force but also to rotate all joints according to object’s shape simultaneously. Its capability to grasp objects in daily environment was tested through experiments. As future work, more SMA type AMs needs to be employed to strengthen the grasping force of the prosthetic hand. It will also improve the usability of the hand and allow to be applied in actual life.
Fig. 20 The experiment of handling an object.
References
[1] Nagano Prefectural Rehabilitation Center, available online at: http://www.pref.nagano.jp/xsyakai/reha/reha_po/reha_poview.htm.
[2] H. Kawasaki, T. Komatsu, K. Uchiyama, Dexterous anthropomorphic robot hand with distributed tactile sensor: Gifu hand II, IEEE/ASME Transactions on Mechatronics 7 (3) (2002) 296-303.
[3] A. Jaffar, M.S. Bahari, C.Y. Low, R. Jaafar, Design and control of a multifingered anthropomorphic robotic hand, International Journal of Mechanical and Mechatronics Engineering 11 (4) (2011) 26-33.
[4] M.A. Saliba, M. Axiak, Design of a compact, dexterous robot hand with remotely located actuators and sensors, in: Proceedings of the 15th Mediterranean Conference on Control and Automation, 2007, T30-009.
[5] H. Kobayashi, R. Ozawa, Adaptive neural network control of tendon-driven mechanisms with elastic tendons, Automatica 39 (9) (2003) 1509-1519.
[6] I. Yamano, T. Maeno, Five-fingered robot hand using ultrasonic motors and elastic elements, in: Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005, pp. 2684-2689.
[7] K. Suzumori, S. Wakimoto, T. Kanda, M. Takahashi, T. Hosoya, E. Takematu, Development of power robot hand with shape adaptability using hydraulic McKibben muscles, in: Proceedings of IEEE International Conference on Robotics and Automation, 2010, pp. 1162-1168.
[8] N. Tsujiuchi, T. Koizumi, H. Komatsubara, T. Kudawara, M. Shimizu, Development of robot hand with pneumatic actuator and construct of master-slave system, in: Proceedings of 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007, pp. 3027-3030.
[9] Y. Kimura, T. Nakamura, Development of the robot hand using wire type artificial rubber muscle, JSME 11-5 (2011) 1A1-106.
[10] J.T. Belter, A.M. Dollar, Performance characteristics of anthropomorphic prosthetic hands, in: Proceedings of IEEE International Conference on Rehabilitation Robotics, 2011, pp. 921-927.
[11] S. Dilibal, R.M. Tabanli, A. Dikicioglu, Development of shape memory actuated ITU robot hand and its mine clearance compatibility, Journal of Materials Processing Technology 155-156 (2004) 1390-1394.
[12] Toki Corporation, available online at: http://www.toki.co.jp/biometal/index.php.
Key words: Prosthetic hand, prosthetic finger, shape memory alloy, mechanism design, grasping experiment.
1. Introduction
The excellent functionality of the human hand ensures convenience and optimal performance of activities of daily living. However, the disabled who have physical disabilities of their hand experience difficulties in their works or cannot perform their tasks especially for manipulating general objects. As a useful device to support them, several types of prosthetic hands have been proposed. For example, a simple prosthetic hand just for appearance and a hook-shaped prosthetic appliance have been employed as fundamental and well-used devices [1]. However, they show very limited functionality in general.
Meanwhile, robotic hands for manipulating objects have been investigated as robotics researches for both robot and the disabled. For the design of dexterous hand mechanism, minute observation and in-depth analysis on the structure of human hand have been carried out [2-3]. Namely, mechanical structure and characteristics of human hand have been considered as a good model for design and control. However, there are differences between human and robotic system, which cause great obstacles to the design of actual robotic hand. Most of all, human hand is actuated by soft but strong actuator, i.e., muscle, which cannot be manufactured artificially with advanced technology so far. To cope with the problem, several alternatives have been proposed. Electric motor has been used as typical actuator for general robotic hand mechanism [2-4]. For abundant torque to achieve holding force, gear train with high reduction ratio is required for general motor. Thus the size of the actuators becomes large, and they cannot be installed in the hand itself. Besides, soft actuation scheme like as human muscle cannot be realized because of the lack of back-drive capability in gear train of high reduction ratio. Therefore, most of robot hands utilize tendon device to transmit the power of motor being attached in the forearm apart from hand. Some researchers utilize several types of elastic elements to improve the grasping capability of robotic finger with stiff motor-based actuation [5]. Ultrasonic motor [6] is also proposed as a candidate of actuator for hand mechanism because it has large output power for relatively small size than general DC (Direct Current) motor. However, it has been known that it has difficulties in control owing to its fundamental driving principle, which is powered by the ultrasonic vibration of its components. Besides, hydraulic and pneumatic actuators have been applied for the design of robot hand [7-9]. In this case, the system requires large and heavy power source such as an air compressor or a gas container to store the compressed air for pneumatic actuator, and pump for hydraulic actuator. Other researches related to control methodology to cooperate multiple actuators for grasping objects has been carried out [3, 5]. A method to analyze the characteristics of anthropomorphic prosthetic hands has also been proposed recently [10].
The characteristics expected of prosthetic hands are that they should be comfortable, useful for manipulating objects and lightweight. The purpose of the research is to develop a new type of prosthetic hand that could be used by individuals with a hand disability. As stated above, electric motor is generally used as actuator for conventional prosthetic or robot hands because it is easy to control the motions of prosthetic hand. However, prosthetic hand that has many motors in multiple fingers becomes heavy. So the hand system cannot be installed effectively at the end of user’s arm.
Recently, various actuators such as polymer type artificial muscle have been proposed to imitate the characteristics of human muscle. Polymer type actuator has been employed in many robots including hand and gripper. However, most of them are still far from real application because its output force is so small. One of promising actuator for robotic hand is Shape Memory Alloy (SMA) type Artificial Muscle(AM). The SMA type AM has potential for prosthetic hand design as it has a large force-to-mass ratio and therefore the hand can be lightweight. In addition, it has no gear train thus its movement is silent. Owing to those merits, SMA type AM has been utilized as actuator for robotic gripper and hand in previous researches [11]. However, the problem of weak output force is still unsettled. It comes from that the radius of driving pulley at each joint is small because SMA type AM has small output stroke. Therefore, this paper proposes a new structure of driving mechanism for large gripping force and compact design that all actuators are built in the hand itself.
The paper is organized as follows: In section 2, the basic properties of SMA type AM are discussed; the mechanical design of the proposed prosthetic finger and hand is presented in sections 3-4 respectively; in section 5, conclusions and future work are addressed.
2. Properties of Shape Memory Alloy Type Artificial Muscle
The basic properties of SMA type AM used are investigated experimentally. The mechanical and electrical data through the following experiments are utilized as fundamental information for the development of a prosthetic hand.
2.1 Loading Test
Loading test to investigate the longitudinal deformation of the actuator by external force is carried out. Fig. 1 shows a test piece of SMA type AM employed in this research [12]. The length and diameter of the test piece are 200 mm and 0.15 mm respectively. Fig. 2 shows the experimental setup for the loading test. One end of the test piece is clamped at the top of the stand frame, and then its other end is loaded with forces from 4.9 × 10-2 to 3.9 × 10-1 N(increments of 4.9 × 10-2 N). The length of the test piece is compared that of un-loaded condition. The resultant relationship between length and loading force is displayed in Fig. 3.
Fig. 1 Test piece of SMA type artificial muscle named as BioMetal [12].
Fig. 2 Experimental setup for loading test.
2.2 Contraction Test
The fundamental capability of AM as an actuator is to generate pulling force due to the deformation of itself by applied electric voltage. The deformation, i.e., contraction, of the test piece by applied voltage under the condition of external force is investigated. Fig. 4 shows the resultant change of the length of the SMA type AM. Voltages ranging from 0 to 5.0 V(increments of 0.5 V) are applied to the test piece loaded by forces ranging from 9.8×10-2 to 1.372 N(increments of 9.8 × 10-2 N). Currents and deflections passing through the test piece are measured throughout the experiment. After shortening by the applied voltage, the length of the test piece becomes about 94% of the initial state. That is to say, it could be observed that the amount of deformation is about 6% of the initial length.
Fig. 3 The relation between length of AM and load force from 4.9 × 10-2 to 1.96 N.
Fig. 4 Deformation of the SMA type AM after applying the voltage of 4.0 V while the external force of 1.372 N is applied.
2.3 Relationship between Applied Voltage and Contraction of AM
In order to find out the appropriate range of input voltage to actuate the SMA type AM, the relationship between the deflection of AM and the applied voltage is investigated through experiments. Fig. 5 shows two examples of the experimental results. As shown in Fig. 5a, in the case that the loaded force is small, the deflection of SMA type AM increases when the applied voltage is changed from 1.5 to 2 V. However, in the other case that the loaded force is large, the range of input voltage to cause the deformation is changed to around 2.5 V. It means that the SMA type AM requires large value of input voltage for the generation of large output force.
3. Development of Prosthetic Finger
Based on the structure of human hand, the prosthetic finger with multiple joints is designed in this section.
Fig. 5 The relationship between the deflection of the test piece and the applied voltage while two types of external force are loaded.
3.1 Mechanism of Prosthetic Fingers
The human finger consists of three links, which are connected by three joints, i.e., the distal interpharangeal (DIP), proximal interpharangeal (PIP) and metacarpophalangeal (MP) joints as displayed in Fig. 6. The prosthetic finger developed has the same structure as human finger. The prosthetic finger is operated by two SMA type AMs. One is attached to the second link for rotation of the DIP and PIP joints. The other is attached to the third link and responsible for rotation of all joints in the finger.
The two SMA type AMs are installed inside the finger and several stoppers are used for the generation of effective torque at the joints. As a result, all three joints of the finger can be controlled by the two SMA type AMs, which allows the finger to grasp an object with irregular shape. Reversely, for opening motion of the finger, pre-loaded pulling force of the wire attached in its backside and connected to the spring in the palm of the hand works effectively.
Fig. 6 Structure of human finger and prosthetic finger.
Fig. 7 shows the motion of the prosthetic finger to grasp an object. All joints cooperate with each other for grasping motion because they are connected together by the two SMA type AM and a wire connected to reverse spring. According to the geometry of the object, motion of some joints is constrained by the contact between link and object and other free joints continue closing motion, then the shape of finger is changed for grasping resultantly.
For the independent operation of multiple SMA type AM, namely in order to ensure that the AMs are isolated with each other, Teflon films are inserted between the AM strings in the finger mechanism. The stroke of each SMA type AM is approximately 5% of its natural length. In order to achieve the sufficient stroke of finger motion, small pulleys that lengthen the total length of each SMA type AM are built in the palm of the hand. Fig. 8 shows the first and the second finger of the prosthetic hand. Both have same structure with each other. The third and the fourth finger is operated by one SMA type AM for closing motion and one spring for reverse motion as shown in Fig. 9.
3.2 Motion Experiment of Prosthetic Finger
In order to grasp object of various geometry, the fingers should be folded according to the object’ shape naturally. The motion of finger under the condition of various constraints has been tested experimentally.
Fig. 7 Grasping motion of the prosthetic finger.
Fig. 8 First and second prosthetic fingers.
Fig. 9 The third and fourth prosthetic fingers.
Figs. 10-11 show the motion of the prosthetic finger when the first and the second finger are constrained, respectively. The authors examine the motion of the prosthetic finger when each link of the prosthetic finger is fixed. From these experiments, it can be confirmed that the prosthetic finger has the capability to grasp an object of irregular geometry.
Fig. 10 Motion of the prosthetic finger when the first and the second links are constrained.
Fig. 11 Motion of the prosthetic finger when the first link is constrained.
4. Development of Prosthetic Hand
4.1 Mechanism of Prosthetic Hand
The prosthetic hand developed in this research is displayed in Figs. 12-13. Fingers designed in the previous section are employed for the development of the prosthetic hand. The fingers are arranged based on the geometry of human hand, and the SMA type AM actuators are equipped in the palm for compactness. Two SMA type AMs are attached to the first and the second fingers in order to reinforce the grasp force. To save space, the third and fourth fingers supporting the first and the second finger are actuated by single SMA type AM, respectively. The thumb is designed as a static finger fixed to the palm. For extension of the fingers, each finger is connected via a wire to a spring positioned at the back of the hand.
As shown in Fig. 14, the dimensions used for the design of the prosthetic hand are decided based on the average data of general human hand. The mechanical frame of the prosthetic hand is made of poly-acetal material. The photograph of the prosthetic hand developed in this research is given in Fig. 15.
Fig. 12 Composition of human hand and the prosthetic hand.
Fig. 13 Side view of the prosthetic hand.
Fig. 14 Dimensions of the prosthetic hand.
Fig. 15 The prosthetic hand developed in this research.
Fig. 16 Configuration of the control system.
4.2 Control Systems
A microprocessor is used to control all fingers and interface with other system and user’s command. Fig. 16 shows the configuration of the control system for the prosthetic hand. The photograph of the hand with the developed controller is displayed in Fig. 17. In current step, a switch connected to the microprocessor is used as a simple trigger for user input. An advanced method of user interface such as voice recognition can be connected to it in the future. Actually, all AMs have different lengths because of the configuration and the geometry of the hand in both closed and open states. Particularly, the length of SMA type AM attached to the second link is different to that of the AM attached to the third link. The level of the voltage required to shorten the SMA type AM is proportional to its length. So the final length of each artificial muscle is modified by register connected to it. According to the command signal from microcomputer, the power drivers energize all actuators directly or through registers. A battery of lithium cell is also used as a portable power source for the prosthetic hand.
4.3 Experiment of Prosthetic Hand
The capability of the developed prosthetic hand to grasp objects was tested through the experiments of grasping and handling objects. The experiments of grasping various objects such as cup, ball, bottle, and pen were carried out as shown in Figs. 18-19. Through the experiments, it could be observed that the developed prosthetic hand can grasp objects of various shapes. Besides, it can handle a little weighty object. For example, the water bottle in Figs. 19-20 weighs about 500 grams. The developed prosthetic hand should be equipped at the end of user’s arm resultantly. So the system was modified as a portable type test-bed hand with built-in controller and battery. An example of experiment handling an object, i.e., a water bottle, is shown in Fig. 20.
Fig. 17 The prosthetic hand with controller.
Fig. 18 The prosthetic hand grasping a cup and a ball.
Fig. 19 The prosthetic hand grasping a bottle and a pen.
5. Conclusions
In this paper, a light and quiet prosthetic hand using SMA type AM was developed. It was designed based on the structure of human hand. And the driving mechanism of each finger was designed not only to achieve the powerful grasping force but also to rotate all joints according to object’s shape simultaneously. Its capability to grasp objects in daily environment was tested through experiments. As future work, more SMA type AMs needs to be employed to strengthen the grasping force of the prosthetic hand. It will also improve the usability of the hand and allow to be applied in actual life.
Fig. 20 The experiment of handling an object.
References
[1] Nagano Prefectural Rehabilitation Center, available online at: http://www.pref.nagano.jp/xsyakai/reha/reha_po/reha_poview.htm.
[2] H. Kawasaki, T. Komatsu, K. Uchiyama, Dexterous anthropomorphic robot hand with distributed tactile sensor: Gifu hand II, IEEE/ASME Transactions on Mechatronics 7 (3) (2002) 296-303.
[3] A. Jaffar, M.S. Bahari, C.Y. Low, R. Jaafar, Design and control of a multifingered anthropomorphic robotic hand, International Journal of Mechanical and Mechatronics Engineering 11 (4) (2011) 26-33.
[4] M.A. Saliba, M. Axiak, Design of a compact, dexterous robot hand with remotely located actuators and sensors, in: Proceedings of the 15th Mediterranean Conference on Control and Automation, 2007, T30-009.
[5] H. Kobayashi, R. Ozawa, Adaptive neural network control of tendon-driven mechanisms with elastic tendons, Automatica 39 (9) (2003) 1509-1519.
[6] I. Yamano, T. Maeno, Five-fingered robot hand using ultrasonic motors and elastic elements, in: Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005, pp. 2684-2689.
[7] K. Suzumori, S. Wakimoto, T. Kanda, M. Takahashi, T. Hosoya, E. Takematu, Development of power robot hand with shape adaptability using hydraulic McKibben muscles, in: Proceedings of IEEE International Conference on Robotics and Automation, 2010, pp. 1162-1168.
[8] N. Tsujiuchi, T. Koizumi, H. Komatsubara, T. Kudawara, M. Shimizu, Development of robot hand with pneumatic actuator and construct of master-slave system, in: Proceedings of 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007, pp. 3027-3030.
[9] Y. Kimura, T. Nakamura, Development of the robot hand using wire type artificial rubber muscle, JSME 11-5 (2011) 1A1-106.
[10] J.T. Belter, A.M. Dollar, Performance characteristics of anthropomorphic prosthetic hands, in: Proceedings of IEEE International Conference on Rehabilitation Robotics, 2011, pp. 921-927.
[11] S. Dilibal, R.M. Tabanli, A. Dikicioglu, Development of shape memory actuated ITU robot hand and its mine clearance compatibility, Journal of Materials Processing Technology 155-156 (2004) 1390-1394.
[12] Toki Corporation, available online at: http://www.toki.co.jp/biometal/index.php.