In recent years, the total number of physical therapists is increasing in Japan. However, it is not sufficient to nurse of patients requiring long-term care. In order to cope with the shortage of manpower, it is desirable to develop the reha- bilitation equipment. This paper describes the development of a wearable wrist rehabilitation training device using the parallel link mechanism. It is possible to train the translational and rotational motion of the wrist joint by the adop- tion of parallel links. Training of the translational motion of the wrist joint has not been discussed in existing methods. Therefore, compared to existing methods, this method can be expected to reduce the burden on the wrist joint. And it is possible to move about 60% of the wrist joint movable range of motion. This device performs repetitive training to prevent contracture of the wearer’s joints. In experiments, assumed wrist circumduction motion was trained to the six subjects. The correlation coefficient between the target trajectory and the training result was obtained and evalu- ated whether correct operation was trained. The validity of the proposed method was demonstrated. Keywords: 23rd robotics symposia, Wearable, Parallel link, Muscle and skeleton, Joint The existing training devices that use parallel links [ 4, 5] Background utilize a pneumatic cylinder as an actuator, which can be A questionnaire survey performed in 2014 by Japan’s difficult to position and is noisy because of the use of a Care Work Foundation concluded that not enough peo- pump. This study hopes to improve the ease of operation ple are working in the field of physical therapy and sim - of the device by adopting a linear servomotor. Accord- ilar occupations [1, 2]. To address this issue, efforts are ingly, we develop a wearable rehabilitation device using underway to develop training equipment to support parallel link mechanism that uses a servomotor . We and assist therapists. The existing rehabilitation equip - target the wrist joint because it is a major focus of reha- ment  is often operated using a serial link mechanism. bilitation, and the complexity of its range of motion is It tends to accumulate errors as the number of joints clear. In previous studies , the mounting position increases; hence, the serial link makes it difficult to pro - tended to be slightly misaligned because the measuring vide multiple degrees of freedom (DOF) of movement and training devices were separate, it causes a decrease in to a joint, which limits its use in joints, such as wrist training effect. In this study, we improve the equipment joints that require a high DOF of movement. To address by integrating the measuring and training devices, reduc- these issues, efforts are underway to develop rehabilita - ing the weight of the mounting part, and expanding the tion training devices that use parallel link mechanisms. range of motion. We first describe a motion experiment targeted at assumed rehabilitation training for wrist joint *Correspondence: firstname.lastname@example.org circumduction movements using the developed device, Department of Mechatronics, University of Yamanashi, 4-3-11 Takeda, and then address the effectiveness of the device based on Kofu, Yamanashi 400-8510, Japan a discussion of the experiment. Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Kitano et al. Robomech J (2018) 5:13 Page 2 of 8 60 kg). The training device used in our proposed method Methods satisfies the abovementioned conditions. Required specifications of the wrist training device Table 1 shows the maximum range of motion of the As part of this study, we develop a device that supports device and the human wrist joint. The device can train rehabilitation training for human wrist joints. Especially, approximately 60% of the movement of the wrist joint. it is assumed to be used for repetitive training to pre- However, the operation width of the device in Table 1 is vent contracture of the joint. Figure 1 shows the wrist the maximum value when operating with only a single joint comprising the radius, ulna, carpal, and metacar- rotation motion. And, when performing a compound pal bones [7–9]. The palmar/dorsi flexion and radial/ rotation motion, the range of motion decreases. Also, the ulnar deviation actions at the wrist joint are accompanied maximum range of motion decrease depending on the by deformation and translation to the palm because the mounting position. Therefore, in this experiment, train - carpal bones form a structure in which a bundle of small ing is carried out within the movable range of the present bones is held in place at the wrist joint. The pronation apparatus. and supination movements of the radioulnar joint also cause the radius to tilt toward the elbow and the palm to Proposed method translate. Hence, a support that includes 3 DOF of trans- This section provides an overview of the wearable parallel lation is required in addition to the 3 DOF of rotation at link-type rehabilitation device that developed. the wrist joint. The circumduction motion of the wrist joint targeted Overview of the parallel link‑type training device for rehabilitation training herein is the action of mov- The rehabilitation device developed in this study con - ing the palm in a circular motion starting from the distal sisted of a measuring device part, which measured the end of the ulna, as shown in Fig. 1 . This “circumduc - movement of the wearer’s palm, and a training device tion motion”, which is a combination of the palmar/dorsi part, which supplied translational and rotational motion flexion action and the radial/ulnar deviation action at to the wearer’s palm. Figure 2 shows the relation of the the wrist joint, is a complex operation that simultane- training device part and measuring device part. First, ously performs all the movements of the wrist joint, and the wearer’s motion is measured using measuring device has been adopted as a functional evaluation exercise for part, and the obtained motion is set as the target motion. rehabilitation training. The device must satisfy all DOF Next, by training along the target movement using a of motion of the wrist joint to train the circumduction motion in the wrist joint. Furthermore, passive rehabilita- tion training requires the ability to move the palm, which Table 1 Maximum range of motion of the device and the typically weighs approximately 500 g (the body weight- human wrist joint corrected value for the palm assuming a body weight of Human body Developed device Palmar/dorsi flexion (°) − 70 to 90 − 50 to 60 Radial/ulnar deviation action (°) − 50 to 25 − 45 to 45 Pronation and supination move- − 90 to 90 − 45 to 45 ments (°) Circumduction Metacarpals Measuring Device Training Device Hand Hand Equipment Equipment Carpals Arm Arm Equipment Wrist Joint Equipment Shaft Transfer of Motor Encoder Operation Radius Trainee Ulna Expert Integrated Training Device Fig. 1 Structure of the wrist joint Fig. 2 Relation of the training device Counter Kitano et al. Robomech J (2018) 5:13 Page 3 of 8 training device, contraction of the wrist joint can be pre- the linear encoder, and an EN02 encoder receiver module vented. Since this device can support the above transla- manufactured by Arc Device Co. was used for the coun- tional motion, it can be expected to reduce the burden on ter. The sampling time of the encoder was set to 10 ms. training. In normal rehabilitation exercises, the trainee is A 24VC150T2 lithium-ion battery made by Nissen asked to repeat the necessary actions while the therapist Chemitec Co., Ltd. was used as the power source. Table 2 provides assistance. In the training proposed herein, the lists the training device specifications. trainee first performed the actions under the instruction and assistance of the therapist. The motion was measured Calculation of the position and posture of the wrist by the measuring device. The trainee then repeatedly per - This section explains the technique for measuring wrist formed the training based on the measurement results joint motion with the device developed in this study using the training device without therapist intervention. . Figures 4 and 5 shows a model diagram of the par- Note that in the experiment described in later “Rehabili- allel links used in this study. The length of each slider is tation scenario experiment” section, the movements were measured by a linear encoder. The points in the parallel performed unassisted during the motion measurement links are named as shown in Fig. 4, and the constants and because the “trainees” were healthy subjects. variables are shown in Fig. 5. The lengths of the slider are Structure of the developed integrated training system Figure 3 shows the developed system diagram of the Table 2 Specification of the training device training device. For the training part, the system used the Installation weight 1.5 kg linear DC servomotor LM1247-120-11-C manufactured Maximum stroke speed 100 mm/s by Shinko Electronic Co., Ltd. as the actuator and the Minimum resolution 0.01 mm MCLM-300G-S RS as the motion controller. The linear Actuator maximum acceleration 82.9 m/s DC servomotor was equipped with a Hall element and Rated thrust (total value) 21.6 N allowed length control based on PID control in combina- Standard deviation at training (angle) 0.41° tion with the controller. An MLS-12-1500-E-250 manu- Standard deviation at training (position) 0.22 mm factured by Microtek Laboratory Co., Ltd. was used for Communication(Command/Data) Power Motor Linear Motor Linear Controller Encoder Holl Element Motor Linear Motor Linear Controller Computer Encoder Holl Element Motor Linear Motor Linear Controller Encoder Holl Element Motor Linear Motor Linear Controller Encoder Holl Element Power Source DC24V Motor Linear Power Linear Motor Controller Encoder Holl Element Communication Motor Linear Linear Motor (Command/Data) Controller Encoder Holl Element Fig. 3 System chart of a developed device Kitano et al. Robomech J (2018) 5:13 Page 4 of 8 system Σ , and the order of rotation is with respect to Three-Axis the z-axis(θ ), the y-axis(θ ), and the x-axis(θ ). End Effector yaw pitch roll Rotation Bearing The points C –C of the palm equipment are defined as 1 6 p p p p T Slider C = [ C C C ] in Σ . The points C –C of the palm 1 xi yi zi p 1 6 0 0 0 0 T Sensor equipment are defined as C = [ C C C ] in Σ . 1 xi yi zi 0 The points A –A of the forearm equipment are defined 1 6 0 0 0 0 T 0 p as A = [ A A A ] in Σ . A and C are constants 1 xi yi zi 0 1 1 determined during the design process. The slider lengths A C 1 |L |–|L | are variables that depend on Q. 1 6 The palm equipment position and posture relative to the forearm equipment are calculated by iterative calcu- A 1 lation from the slider lengths (L –L ). The iterative cal - 1 6 culation is performed according to the procedure shown in Fig. 6 to maximize the accuracy of the results. In the Platform calculation, s is the differential operator, K is a propor - tional gain, Q is the current value of Q, and I(Q ) is the d d Fig. 4 Parallel-link model calculation of the inverse kinematics of the parallel links. Rehabilitation scenario experiment This section describes the rehabilitation exercise experi - θ ment performed to evaluate the effectiveness of the yaw roll developed device. Purpose of the experiment pitch We conducted an experiment based on the rehabilitation training of the circumduction motion of the wrist joint using the developed parallel link-type training device to demonstrate the effectiveness of our method. Subjects The experiment was conducted on the left hands of six male subjects aged 21–31 with no history of injury to the wrist joint (mean ± standard deviation: age 25.7 ± 4.7 years old, height 168.2 ± 10.2 cm). The pur - Fig. 5 Variables of the parallel-link model pose and content of the research were fully explained in accordance with the Declaration of Helsinki. Moreover, the subjects’ informed consent was obtained prior to the experiment. denoted by |L |, |L |, |L |, |L |, |L |, and |L |, as shown 1 2 3 4 5 6 in Fig. 5. The points O and O are at the centers of the 0 p Experimental procedure forearm equipment and the palm equipment, respec- Figure 7 shows a photograph of the training device, tively, and are the origins of the coordinate system Σ and while Fig. 8 presents the coordinate system of the train- Σ for each device. O is assumed to match the center of p 0 ing device when it is worn. Using a numerical analysis, the palm of the subject, and O is assumed to match the center of the forearm of the subject. The z-axis of each coordinate system is defined as the long axis of the palm and the forearm. The x-axis rotation angle of the coordinate system Σ is θ , the y-axis rotation angle is θ , and the z-axis roll pitch rotation angle is θ . The position and posture of the yaw 0 0 0 palm equipment are denoted by Q = [ O O O θ px py pz roll T 0 0 0 0 T θ θ ] , using O = [ O O O ] , θ , θ , and pitch yaw p px py pz roll pitch θ , where O is the coordinate of O in the coordinate yaw p p Fig. 6 Iterative calculation of the developed device Kitano et al. Robomech J (2018) 5:13 Page 5 of 8 his own wrist joint in a clockwise direction as seen from his vantage point. The changes in the length of the lin - ear encoder during the motion were measured using the Hand measuring part of the device. Three complete, consecu - Equipment tive circumduction motions were performed and meas- ured. Motion patterns were created and passed to the training part of the device based on the acquired changes Linear DC in length, which executed the rehabilitation training for Servomotor the wearer. The palm motion during the training was measured from the measurement part of the device to perform a motion analysis. The subjects were instructed Linear to begin the training exercises in a tension-free state. Encoder In order to prevent accumulation of error by iterative calculation, it is performed the absolute position con- trol for the actuator control. Absolute position control is performed based on the initial position when device Arm mounted. Equipment Results and discussion Fig. 7 Overview of training device Results of the experiment Figure 9 shows the palm movements during each sub- ject’s rehabilitation training. The graphs show the changes in the translational and rotational motion during the training of the six subjects. For the rotational motion, the vertical axis represents posture. For the translational motion, the vertical axis represents the position. The hor - izontal axis represents time in both cases. The graph on the left represents the palm movements of each subject during the motion measurement (measured motions). The graph on the right represents the movement during training (training results). The green line in Fig. 9 shows the temporal change in measurement of θ , θ θ in roll pitch yaw order from the thinner one. Similarly, the blue line shows the temporal change during training. The orange line shows the temporal change in measurement of X, Y, Z in order from the darker one. Similarly, the red line shows Fig. 8 Relationship between model and device the temporal change during training. Discussion of the experiment the device was able to find the palm’s position (X, Y, Z) The measurement of the circumduction motion can be and posture (θ , θ , θ ) based on the length changes roll pitch yaw modeled as the combined motions of palmar/dorsi flex - in the measurements of the six linear encoders . The ion (θ ) and radial/ulnar deviation (θ ) based on the roll pitch mounting position of the training device varied depend- device structure. Focusing on temporal changes of θ roll ing on the length of the subject’s forearm. The device can and θ of all subjects in Fig. 9, it is possible to confirm pitch measure where it is mounted, and it can be adapted to periodic increase and decrease. And it can be confirmed different mounted positions. As the starting position of that the peaks of the two increase/decrease cycles are the circumduction motion, the palm, radius, and ulna deviated. Circumduction is an operation to move the were lined up side-by-side, with the palm positioned per- palm in a circular motion. By simultaneously and peri- pendicular to the body. The subject was fitted with the odically carrying out the dorsiflexion flexion motion training device at the beginning of the experiment, and and the radicular flexion motion, the motion is realized. his wrist joint was oriented in the starting position. The The measured motion is a reasonable motion. A simi - radial flexion was then applied in the direction of the lar change can be confirmed in the measurement result thumb; after which, the subject was instructed to rotate and the training result. For about 1–2 s from the start Kitano et al. Robomech J (2018) 5:13 Page 6 of 8 Fig. 9 Position and posture in training (all subjects) of motion, each subject exercises a movement differ - up the first cycle of the circumduction movements both ent from the periodic motion. This is expected to be the measuring and training, and then matching the time of radial flexion in the thumb direction which is done at the one cycle. Generally, since the correlation coefficient is start of the experiment, it is considered to be a reason- considered to have a high correlation if it is 0.7 or more, able operation. from Table 3, it can be confirmed that each movement From the experimental results, it can be confirmed that has high correlation between measuring and training. the trend of the measurement operation and the train- From results of the correlation, it was demonstrated that ing operation is consistent. In this research, in order to this device can be used to train the wearer to perform the quantitatively evaluate consistency of trends, correlation combined radial/ulnar deviation and palmar/dorsi flex - coefficients between the motions of training and measur - ion actions corresponding to a circumduction motion. ing were obtained. The obtained correlation coefficient is The rest of this section offers further discussion of the shown in Table 3. Since this method is aimed at prevent- effectiveness and challenges of this method. ing contractures, speed control is not performed only by Examining Fig. 9, θ changed over time in a differ - yaw setting the upper limit of the speed. For that reason, as ent manner for each subject. The circumduction motion, can be seen from experimental results, there is a time lag which rotates the palm, was achieved by a combina- between the measurement result and the training result. tion of actions of the forearm muscle group, including From past research, due to the resistance of the human the palmaris longus in the forearm. These muscles also body, a delay occurs during training, it was known that contribute to the realization of the pronation and supi- would be difficult to realize the target motion . There - nation movements; hence, it is natural to unconsciously fore, position control has priority in this study. Calcula- perform both movements at the same time. The meas - tion of the correlation coefficients was made after picking urement results from the experiment also indicated that Table 3 Correlation coefficient between measuring and training θ θ θ X Y Z roll pitch yaw A 0.96 0.99 0.99 0.99 0.99 0.96 B 0.94 1.00 0.97 0.98 0.99 0.94 C 0.96 0.99 0.99 0.99 0.99 0.82 D 0.93 0.94 0.96 0.96 0.94 0.94 E 0.98 0.98 0.99 0.98 0.99 0.94 F 0.91 0.94 0.96 0.96 0.96 0.74 Kitano et al. Robomech J (2018) 5:13 Page 7 of 8 Table 4 The operation width difference between measuring and training θ (°) θ (°) θ (°) X (mm) Y (mm) Z (mm) roll pitch yaw A − 0.1 − 0.1 − 0.8 6.0 − 1.3 − 0.4 B 1.8 3.2 4.9 − 1.0 3.2 3.1 C 2.9 3.6 6.5 4.5 1.0 1.4 D 1.4 1.8 1.8 − 1.5 3.0 − 2.3 E 4.6 0.9 2.2 − 2.2 8.2 2.1 F 4.8 1.4 6.5 − 0.7 − 1.6 − 0.5 θ varied across all subjects. A typical training device, required active participation by the subjects, while the yaw with its low DOF of movement, does not support this training was a passive exercise. As noted earlier, the cir- motion, therefore, become a burden to the wearer. cumduction motion was realized by the movement of the Hence, our method would seem to be more effective for forearm muscle group, and at that time, the wrist joint training exercises, such as the circumduction motion that was experiencing tension in the direction of the elbow. requires a high DOF of movement. However, no such tension was generated in a device such The experiment found some degree of correlation as this one that performs passive training. We suspect between θ and θ across the subjects, but almost no that the compensatory movement caused by this differ - roll pitch correlation among θ , θ , and θ because of the var- ence in tension, but this issue will be left to future work. yaw roll pitch iations in how the subjects used their muscles when per- In addition to the method to control only the trajectory forming the circumduction motion. Therefore, predicting as in this method, implementation of speed control and θ from the θ and θ values to create the motion force control will be a future subject. yaw roll pitch patterns in advance was difficult. This result suggests that methods, such as this device, which take measurements Conclusion that include θ (pronation and supination movements), This study described a developed parallel link-type wrist yaw are effective for conducting training exercises with a high joint rehabilitation device. The developed device can DOF of movement of the wrist joint. train not only three degrees of freedom of rotation but Table 4 shows the differences in the operation width also three degrees of freedom of translation in the wrist between the motion measurements and the training joint. Using the developed device, we carried out training results for each subject. The differences in the opera - assuming the circumduction motion to six subjects, and tion width were obtained by finding the maximum and measured the movement of the palm when training. We minimum widths of each movement, then calculating calculate the correlation coefficient between the train - the differences between the measured motion widths ing target and the training result, and confirmed that this and the training result widths. Examining the differences method is effective because high correlation is obtained. among the subjects, the minimum value for posture was And, the performance of this method was evaluated by − 0.8°, whereas the maximum value was 6.5°. Meanwhile, calculated the difference of the range of motion between for the position, the minimum value was − 2.2 mm, and training target and training result. Since the evalua- the maximum value was 8.2 mm. The minimum val - tion results, the necessity of force control is indicated, ues were negative because the movements were greater and the implementation of force control on this method during training than during the measurement. This phe - becomes a future task. The necessity of temporal agree - nomenon can be explained by the compensatory move- ment between the training target and the training result ments the subjects made to perform the training action. has been indicated, implementation of speed control is Examining the operation widths of subject A, for whom also a future subject. all movements, except in the x-axis direction, were nega- Authors’ contributions tive, greater movements during training and a relatively YK carried out the design of the wearable rehabilitation device, the systems large difference in movement in the x-axis direction were integrating, testing. TT carried out the design of device control circuit and test- ing. KY provided advice on future works and proof-reading of the paper. All found. In other words, the subject can be seen trying to authors read and approved the final manuscript. execute the training action by causing the other values to move in a manner that matched the difference in the Author details Department of Mechatronics, University of Yamanashi, 4-3-11 Takeda, Kofu, x-axis direction movement. These compensatory move - Yamanashi 400-8510, Japan. Graduate School of Engineering, Utsunomiya ments caused by the fact that the motion measurements University, 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, Japan. Kitano et al. Robomech J (2018) 5:13 Page 8 of 8 Acknowledgements 2. Kanada Y (2013) Rehabilitation, revised edn. Foundation for the Promo- This research was supported by JSPS Grant-in-Aid for Scientific Research tion of The Open University of Japan, Chiba-shi JP15K01552. 3. Fujita T, Sankai Y (2015) Development of motion control algorithm for upper limb support system based on bioelectrical signals for heavy work Competing interests over head. In: Proceedings of 2015 IEEE/SICE international symposium on The authors declare that they have no competing interests. system integration (SII2015), pp 181 4. Takaiwa M, Noritsugu T, Ito N, Sasaki D (2011) Wrist rehabilitation device Ethics approval and consent to participate using pneumatic parallel manipulator based on EMG signal. Int J Autom The experiment was approved by the Ethics Committee of Utsunomiya Uni- Technol 5(4):472–477 versity, and the committee’s directives, including the completion of consent 5. Takemura H, Onodera T, Ming D, Mizoguchi H (2012) Design and control forms, were complied with. Written informed consent was obtained from the of a wearable stewart platform-type ankle-foot assistive device. Int J Adv patient for the publication of this report and any accompanying images. Robot Syst 9:1–7 6. Kitano Y, Terashima M, Yokota K (2017) Development of wearable rehabili- tation device using the shaft motor parallel link mechanism. Contents J Publisher’s Note Jpn Soc Welf Eng 19(1):21–28 Springer Nature remains neutral with regard to jurisdictional claims in pub- 7. Kapandji IA (2005) Funktionelle anatomie der gelenke 1. obere extremi- lished maps and institutional affiliations. taet. Mosby Inc., Maryland Heights 8. Youm Y, McMurthy RY, Flatt AE, Gillespie TE (1978) Kinematics of the wrist. Received: 31 January 2018 Accepted: 16 May 2018 I. An experimental study of radial-ulnar deviation and flexion-extension. J Bone Joint Surg 60A:423–431 9. Hirano E, Imamura K (1985) Cineradiography of the wrist, orthopedics and traumatology. Kanehara & Co., Ltd., Tokyo 10. Kitano Y, Yokota K (2013) Method for measuring position and pos- ture of the shoulder skeleton using parallel links. Jpn Soc Mech Eng References C79(802):2004–2012 1. Japan’s Care Work Foundation (2016) Results of Heisei 26-year “nursing care labor survey” (survey on nursing care labor conditions in business establishments and employment actual condition of nursing workers and survey on employment awareness). http://www.kaigo -cente r.or.jp/ repor t/pdf/h28_chous a_kekka .pdf. Accessed 29 Jan 2018
ROBOMECH Journal – Springer Journals
Published: May 29, 2018
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