Development of new cosmetic gloves for myoelectric prosthetic hand using superelastic rubber

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Abstract

This paper reports on the design and development of new cosmetic gloves made of two different superelastic rubbers – thermoplastic styrene elastomer (TSE) and silicone rubber (TSG silicone) – and compares them with gloves made of polyvinyl chloride (PVC) for myoelectric prosthetic hands to realize a realistic appearance and flexible motion. The materials are compared in terms of their appearance, material, mechanical, and sensing properties. Appearance properties include the shape, wrinkles, fingerprints, texture, nail, and color of the hand; these properties are designed so as to produce a prosthetic hand that looks similar to a human hand. The material properties are evaluated in terms of adaptability for daily living without preventing finger motions of the powered hand by performing a tear strength test. Mechanical properties are improved by designing the thickness of the palm to grip an object. The sensing properties are essential for acquiring information about the object and the environment. The overall performance is evaluated through a material engineering test and a pick-and-place test with a powered prosthetic hand. Tear strength comparisons showed that TSE and TSG silicone could respectively withstand 5–7 and 3 times the strain that PVC could withstand before breakage. The TSE glove shows the highest stretching length before breaking and shows high flexibility even after breaking. The electric currents during EMG prosthetic hand motion showed that TSE and TSG silicone gloves successfully reduced energy consumption by around one-third for many hand movements. Flexibility test results for the maximum opening posture showed that the PVC glove greatly restricted the hand opening width. However, the differences between the cases without and with TSE gloves were very small; therefore, both cases show the same range of motion. The flexible TSE facilitated easy fitting and therefore had the lowest fitting time; in fact, it can be worn in one-third the time required for wearing PVC or TSG silicone gloves. In pick-and-place experiments, TSG silicone and TSE gloves both showed similar results for successfully grasping objects. The TSE glove is hard to break and has high elasticity; therefore, nails can be added to it. Furthermore, TSG resin is thermosetting and can be processed at room temperature, making it easy to impart conductivity. Therefore, the TSG silicone material is more suitable for implementing a sensor.

Introduction

This study develops novel cosmetic gloves using two types of superelastic rubber – thermoplastic styrene elastomer (TSE) and silicone rubber (TSG silicone) – and compares them with polyvinyl chloride (PVC) gloves for EMG prosthetic hands. This paper is a revised version of the one presented at IAS conference in 2016 [1], and it adds new ideas and results.

One of the most fundamental requirements for an artificial hand is mimicking the size, figure, color, and finger motion of a human hand. These requirements are clarified through a questionnaire survey with the study subjects. The results suggest that the subjects hope to get as realistic a hand as possible. A realistic artificial hand can be realized using a prosthetic hand with a cosmetic glove to mimic the appearance of a human hand. Realistic artificial hands have been known to exist from around 300 BC; however, such hands typically could not move [2].

An electromyogram (EMG) prosthetic hand is a powered artificial hand that has been developed for use by amputees. This hand is controlled using myoelectric signals detected in the amputee’s arm. An EMG prosthetic hand consists of a powered hand, an EMG controller, a battery, below-elbow socket, and cosmetic glove. Now, EMG prosthetic hands with five fingers that cover almost all functions of the human hand, including finger motion and wrist motion, have been developed successfully [3]. However, their total weight and size remains problematic. The attachment part on the amputee’s arm needs to support all parts of the EMG prosthetic hand system using a cylindrical socket; therefore, the system must have low weight less than 370 g [4], [5]. This requirement limits the number and weight of motors and batteries; therefore, the cosmetic glove should be designed to minimize motor power loss.

In Japan, the purchase cost of artificial hands is supported by government insurance, with 80% of upper limb amputees using artificial prostheses. In recent years, owing to government policies, it has become possible to produce a powered artificial hand even for amputees with only one hand. However, only 2% of amputees currently use a powered artificial hand [6]. This is because such hands are heavy and expensive and have an unrealistic appearance, making it difficult for users, especially women, to wear them.

In the 1960s, PVC was first used for manufacturing cosmetic gloves; a realistic appearance similar to that of a human hand could be realized using 3D copy technology based on a mold. This technology was developed to realize the natural form of the fingers and the precise texture of the skin [7]. The next step was to improve the skin color by using a silicone-based material. Toward this end, prosthetists and orthoptists established painting techniques to mimic human skin colors accurately. However, even with significant developments in powered prosthetic hand technology, emulating finger motion has remained challenging. Thus far, such technology can only recreate finger motions and handling functions [8], [9].

This paper reports the results of the development of the new cosmetic gloves made of two types of superelastic rubber materials in terms of four properties: appearance properties (shape, texture, color, and nail), material properties (durability, flexibility, and viscosity), mechanical properties (fingertip shape and dynamic viscoelasticity for grasping performance), and sensing properties (pressure sensor and vending sensor). The desired functions of the cosmetic glove and experimental results for the developed products are described. These products are designed based on existing research on prosthetics as well as new materials. Section 2 describes the design concept and requirements. Sections 3 Experimental results of functional evaluation, 4 Pick-and-Place experiment present the experimental results and evaluations, respectively.

Section snippets

Design concept and requirements

This section presents the design requirements of a cosmetic glove and proposes a design method that considers the following four aspects: (1) appearance properties (shape, texture, color, and nail), (2) material properties (durability, flexibility, and viscosity), (3) mechanical properties (fingertip shape and dynamic viscoelasticity for grasping performance), and (4) sensing properties (pressure sensor and vending sensor).

Experimental results of functional evaluation

This section describes the experimental results of the functional evaluation of a cosmetic gloves made of PVC, TSE, and TSG silicone. The experiment involved four evaluations: (1) tear strength comparison, (2) fitting time comparison, (3) comparison of electric current of EMG prosthetic hand motion, and (4) flexibility comparison.

Pick-and-Place experiment

This section describes the pick-and-place (PAP) experiments conducted for comparing a prosthetic hand without a glove and hands with a PVC glove, TSE glove, and TSG silicone glove (Fig. 15(a)). The performance tests were performed by a healthy subject using the produced EMG prosthetic hand system, as shown in Fig. 15(b).

The EMG prosthetic hand system comprises a robotic hand, three EMG sensors attached on the forearm, an EMG controller that discriminates EMG signals using fast Fourier

Conclusions

For developing a superelastic cosmetic glove, this study clarified four properties of three types of rubber: appearance properties (shape, texture, color, and nail), material properties (durability, flexibility, and viscosity), mechanical properties (fingertip shape and dynamic viscoelasticity for grasping performance), and sensing properties (pressure sensor and vending sensor). The injection molding method was used for manufacturing gloves with human-like appearance for both adult and child

Acknowledgments

This research was partially supported by the Strategic Research Program for Brain Sciences, and by Adaptable and Seamless Technology Transfer Program from Japan Agency for Medical Research and Development, AMED, and also JSPS KAKENHI (grant number JP16K12951).

The authors would like to thank the EMG prosthetic hand team members: Suguru Hoshikawa, Tatsuhiro Nakamura, Jin Xiaobei, Yong Xu, Naoyuki Tani, Yuta Suzuki, Yutaro Hiyoshi, Feng Xiang, Hesong Ye, Shintaro Sakoda, Yusuke Yamanoi, Soichiro

Yoshiko Yabuki is a Ph.D. course student in the Department of Mechanical Engineering and Intelligent Systems, Graduate School of Informatics and Engineering at the University of Electro-Communications. Her current research interests include biomedical engineering and human interface of robotics.

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  • Cited by (0)

    Yoshiko Yabuki is a Ph.D. course student in the Department of Mechanical Engineering and Intelligent Systems, Graduate School of Informatics and Engineering at the University of Electro-Communications. Her current research interests include biomedical engineering and human interface of robotics.

    Kazumasa Tanahashi graduated from Chukyo University in 2004.

    In April of the same year he entered Towa Denki Company Ltd, a general trading house supplying electronic and automobile components. Since April 2009 he has worked in Tanac Co Ltd, a silicon and elastomer fabrication company.

    Yasuhiro Mouri graduated from the University of Electro-Communications in 2017 and he is currently in the first year of a master course in the Graduate School of Informatics and Engineering at the University of Electro-Communications. His current research interests lie in the haptic feedback of prosthetic arms.

    Yuta Murai graduated from the National Institute of Technology, Nara College in 2013. After graduation he worked at Takasago ltd and The University of electro-communications. He is now a doctoral course student of the university of electro-communications. His research concerns myoelectric prosthetic hands for partial hand amputation with remaining fingers function.

    Shunta Togo is an assistant professor in the Graduate School of Informatics and Engineering at the University of Electro-Communications since 2016. He received a B.E., a M.E. and a Ph.D. from Nagoya University in 2009, 2011 and 2014, respectively. He was a Japan Society for the Promotion of Science (JSPS) research fellow (DC2) in the Graduate School of Engineering, Nagoya University from 2012 to 2014. He was a JSPS research fellow (PD) in Cognitive Mechanisms Laboratories, Advanced Telecommunications Research Institute International (ATR) from 2012 to 2016. His current interests are human motor control, motor coordination, and myoelectric control device.

    Ryu Kato received a Ph.D. Degree in Engineering from The University of Tokyo in 2008. 2008–2009, Project Assistant Professor, Department of Precision Engineering, The University of Tokyo. 2009–2014, Assistant Professor, Graduate School of Informatics and Engineering, The University of Electro-communications. Currently he is Associate Professor, Division of Systems Research, Faculty of Engineering at Yokohama National University. He is a Member of the following Academic Societies: IEEE, The Robotics Society of Japan (RSJ), The Japan Society for Precision Engineering (JSPE).

    Yinlai Jiang received a Ph.D in engineering in 2008 from Kochi University of Technology, Japan. He was a research associate from 2008 to 2012, and an assistant professor from 2013 to 2014 at Kochi University of Technology. He is currently an associate professor in the Brain Science Inspired Life Support Research Center, The University of Electro-Communications. His current research interests are biological engineering, robotics, and human robot interface. He is currently a member of IEEE, The Robotic Society of Japan, Japanese Society for Medical and Biological Engineering, and Japan Society for Fuzzy Theory and Intelligent Informatics.

    Hiroshi Yokoi received Ph.D. in precision engineering from Hokkaido University in 1993. He was an engineer at Toyota Motor Corporation and he joined the Institute of Bioscience and Human Technology, AIST as the Researcher from 1993 to 1995. He was an associate professor, Faculty of Engineering at Graduate School of Hokkaido University from 1995 to 2004, and in the Department of Precision Engineering, Faculty of Engineering, the University of Tokyo from 2004 to 2009. He is currently professor of the Department of Mechanics and Intelligence at the University of Electro-Communication. His current research interests include computational intelligence in robotics, artificial life and medical engineering.

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