Development of a multi-DOF electromyography prosthetic system using the adaptive joint mechanism

A. Hernandez Arieta, R. Katoh, H. Yokoi, Y. Wenwei
2006 Applied Bionics and Biomechanics  
This paper describes an electrically powered prosthetic system controlled by electromyography (EMG) signal detected from the skin surface of the human body. The research of electrically powered prosthetic systems is divided into two main subjects. One is the design of the joint mechanism. We propose the use of an adaptive joint mechanism based on the tendon-driven architecture. This mechanism includes mechanical torque-velocity converters and a mechanism to assist the proximal joint torque by
more » ... stal actuators. The other subject is the recognition of the EMG signal. For the discrimination of many patterns and nonlinear properties of the EMG signal, we propose a controller based on a simple pattern recognition information process. The system also drives 12 servomotors to move the adaptive joint mechanism. In this paper, we show the proposed system and describe the mechanical design of the prosthetic hand. The experimental results show that the electrically powered devices can be controlled using the proposed method. 9 10 11 12 13 14 15 16 17 18 19 Key words: Q1 20 21 The development of robotics provides useful technology 22 for the medical welfare field. As an example of this, we can 23 mention the electrically powered devices that can be used 24 for support in the daily life activities, functional assistance, 25 or even functional substitution, as the case of prosthetic 26 devices. However, we still have some difficulties for the 27 practical use of these devices. One of the major challenges 28 to overcome is the acquisition of the user's intention from 29 his or her bionic signals, to provide with an appropriate 30 control signal for the device. Also, we need to consider 31 the mechanical design issues such as lightweight, small 32 size, and power supply. For the bionic signals, the elec-33 tromyography (EMG) signal can be used to control these 34 mechanical products, which reflect the muscles motion, 35 and can be acquired from the body surface. Many studies 36 have reported potential uses and difficulties for the EMG signal pattern recognition (Hudgins et al. 1993; Uchida 38 et al. 1993; Farry et al. 1996). 39 Powered prosthetic hands with multiple degrees of free-40 dom (DOF) can imitate the motions of a natural hand and 41 provide with more functionality than the body powered 42 ones (Neal 1993; Sears and Shaperman 1998; Dechev et al. 43 2001). Some products are already applied for practical use 44 in the medical area (SensorHand Technical Information 45 Booklet 2001). It is significant not only for the medical area 46 but also for robotics and mechanical engineering because 47 it could be a landmark to achieve a humanoid hand. Be-48 tween industrial robot hands and the externally powered 49 prosthetic hands (e.g., EMG controlled), there is a large 50 difference in specifications. The prosthetic devices are lim-51 ited in adequate size, weight, appearance, speed, power, 52 and control precision. To fulfill these requirements, the 53 tendon-driven mechanism has been investigated (Hirose 54 and Ma 1991; Ishikawa et al. 2000). The original paper was 55 related with our first prototype. The mechanism was im-56 proved from 10 to 12 DOF because we increase the wrist 57 movability in our new prototype. The paper description 58 was modified to follow with this improvement. We de-59 veloped a tendon-driven robot hand with 10 DOF, which 60 was later improved, adding 2 DOF to the wrist using the 61 same tendon-driven technology. This paper proposes a 62 prosthetic hand with a 12-DOF adaptive joint mechanism 107 hand opening, and wrist rotations (supination/pronation)). 108 The grasping force of the prosthetic hand should be 109 strong enough to grip a glass of water; this condition re-110 quires more than 3.5 kg/cm. Objective values of the closing 111 speed (300 mm/s) and torque are also severe for the pros-112 thetic hand. Certainly, researchers have acquired higher 113 actuation speed and grasping power, as well as more pre-114 cise controlled robot hand than the human's one (note that 115 it does not contain the planning of the hand motion). How-116 ever, these improvements in speed and torque do not come 117 without their trade-off in weight and size, making them 118 unusable in prosthetic applications. 119 On the contrary, current prosthetic hands on the mar-120 ket can achieve only the gripping force up to 100 Nm and 121 1.3 Hz as maximum open-close frequency for grasping 122 (SensorHand Technical Information Booklet 2001). The 123 power-weight ratio is a problem for the prosthetic hands, 124 because the motor is placed on the base of the hand, which, 125 368 steel, and boat fishing wire for the inner wire, due to its 369 low friction with the stainless outer wire, and its high-370 tension resistance (37 kg). The new mechanism (Fig. 13) 371 presents the same characteristics to that of the previous 372 mechanism. When the load is light, the outer wire remains 373 straight, keeping the tendon wire close to the fulcrum, re-374 sulting in low-torque-high-speed motion (Fig. 11) . When 375 the load increases, the outer wire bends, moving the ten-376 don wire away from the fulcrum, increasing the torque, 377 and reducing the actuation speed.
doi:10.1533/abbi.2005.0060 fatcat:hdtqjtgptzahrcwejd65ueui5u