Hyunki In

Exo-Glove: A Wearable Robot for the Hand with a Soft Tendon Routing System

Soft wearable robots are good alternatives to rigid-frame exoskeletons because they are compact and lightweight. This article describes a soft wearable hand robot called the Exo-Glove that uses a soft tendon routing system and an underactuation adaptive mechanism. The proposed system can be used to develop other types of soft wearable robots. The glove part of the system is compact and weighs 194 g. The results conducted using a healthy subject showed sufficient performance for the execution of daily life activities, namely a pinch force of 20 N, a wrap grasp force of 40 N, and a maximum grasped object size of 76 mm. The use of an underactuation mechanism enabled the grasping of objects of various shapes without active control. A subject suffering from paralysis of the hands due to a spinal cord injury was able to use the glove to grasp objects of various shapes.

Jointless structure and under-actuation mechanism for compact hand exoskeleton

It is important for a wearable robot to be compact and sufficiently light for use as an assistive device. Since human fingers are arranged in a row in dense space, the concept of traditional wearable robots using a rigid frame and a pin joint result in size and complexity problems. A structure without a conventional pin joint, called a jointless structure, has the potential to be used as a wearable robotic hand because the human skeleton and joint can replace the robots conventional structure. Another way to reduce the weight of the system is to use under-actuation. Under-actuation enables adaptive grasping with less number of actuators for robotic hands. Differential mechanisms are widely used for multi-finger under-actuation; however, they require additional working space. We propose a design with a jointless structure and a novel under-actuation mechanism to reduce the size and weight of a hand exoskeleton. Using these concepts, we developed a prototype that weighs only 80 grams. To evaluate the prototype, fingertip force and blocked force are measured. Fingertip force is the force that can be applied by the finger of the hand exoskeleton on the object surface. The fingertip force is about 18 N when actuated by a tension force of 35 N from the motor. 18 N is sufficient for simple pinch motion in daily activities. Another factor related to performance of the under-actuation mechanism is blocked force, which is a force required to stop one finger while the other finger keeps on moving. It is measured to be 0.5 N, which is sufficiently small. With these experiments, the feasibility of the new hand exoskeleton has been shown.

Development of a polymer-based tendon-driven wearable robotic hand

This paper presents the development of a polymer-based tendon-driven wearable robotic hand, Exo-Glove Poly. Unlike the previously developed Exo-Glove, a fabric-based tendon-driven wearable robotic hand, Exo-Glove Poly was developed using silicone to allow for sanitization between users in multiple-user environments such as hospitals. Exo-Glove Poly was developed to use two motors, one for the thumb and the other for the index/middle finger, and an under-actuation mechanism to grasp various objects. In order to realize Exo-Glove Poly, design features and fabrication processes were developed to permit adjustment to different hand sizes, to protect users from injury, to enable ventilation, and to embed Teflon tubes for the wire paths. The mechanical properties of Exo-Glove Poly were verified with a healthy subject through a wrap grasp experiment using a mat-type pressure sensor and an under-actuation performance experiment with a specialized test set-up. Finally, performance of the Exo-Glove Poly for grasping various shapes of object was verified, including objects needing under-actuation.

Implementation of various control algorithms for hand rehabilitation exercise using wearable robotic hand

In this paper, the control algorithms for strength exercise using wearable robotic hand are reviewed and the experimental results are analyzed and discussed. The SNU Exo-Glove is a soft exoskeleton that actuates motor function in disabled hands. This new type of device comprises a jointless simple mechanical structure and is actuated with wires. The strength exercise algorithms include isotonic, isokinetic, and impedance control exercises. An electromyography (EMG) regulation algorithm is proposed to limit the maximum level of activation of the muscles to prevent injury of the muscles and joints. The tension of the wire and the sEMG signal are analyzed to validate the effectiveness of rehabilitation with SNU Exo-Glove.

Feasibility study of a slack enabling actuator for actuating tendon-driven soft wearable robot without pretension

A soft wearable robot with a tendon drive is a promising technology that enables a wearable robot to be compact and lightweight. A soft tendon routing system was previously proposed to apply a tendon drive to a soft wearable robot. In this study, a slack enabling mechanism was proposed to increase the efficiency and guarantee the safety of the soft tendon routing system. The proposed mechanism eliminates the pre-tension of the tendons and minimizes the friction induced by the pre-tension, which causes inefficiency and a lack of safety. Furthermore, the slack enabling mechanism mechanically prevents the derailing of the tendon from the spool. In order to verify the benefits of the proposed mechanism, a prototype was built and tested on the Exo-Glove, which is a soft wearable robot for the hand. The experiment results showed that the prototype could completely remove the pre-tension, whichproposed to apply a tendon drive to a soft wearable robot. In this study, a slack enabling mechanism was proposed to increase the efficiency and guarantee the safety of the soft tendon routing system. The proposed mechanism eliminates the pre-tension of the tendons and minimizes the friction induced by the pre-tension, which causes inefficiency and a lack of safety. Furthermore, the slack enabling mechanism mechanically prevents the derailing of the tendon from the spool. In order to verify the benefits of the proposed mechanism, a prototype was built and tested on the Exo-Glove, which is a soft wearable robot for the hand. The experiment results showed that the prototype could completely remove the pre-tension, which allowed the Exo-Glove to function well with the prototype.

Capstan brake: Passive brake for tendon-driven mechanism

Tendon-driven mechanisms are one of the most popular mechanisms for transmitting force and power from a distance. The energy efficiency of a tendon-driven system can be improved if it can maintain the actuation force while not moving, without mechanical work. This can be achieved by using a brake. A brake without an additional actuator is preferred for achieving compactness of the entire system. We present a novel passive brake mechanism - the capstan brake, which consists of a capstan, rollers, and one-way clutches. The friction between the capstan and tendon amplifies a small resisting force (originating from an inactivated motor) to gain enough brake force. Because no additional actuator is involved, no energy is consumed to generate the brake force. In addition, the one-way clutch enables the capstan to rotate in the winding direction. Therefore, the brake force is only exerted when needed, and the performance of the entire device does not decrease owing to the use of the capstan brake. The brake force of the system is limited to handling the safety issues. If the external load exceeds the maximum brake force, the brake becomes back-drivable again. The limit level can be controlled by changing the number of times the tendon is wound around the capstan. Another issue for a tendon-driven system is that the tendon escapes from a spooler when the tendon does not maintain proper tension. By implementing the rollers with the capstan brake, the tendon cannot escape from a spooler even though the tendon is not pulled by an external load in all actuating situations. The performance of the proposed brake mechanism was evaluated through several tests. The results showed that the capstan brake is suitable to be applied to the wearable robotic hand, which is one of the prospective applications of the brake. The force loss caused by the brake was negligible and the brake operated properly even though the tendon was not pulled by an external load in all actuating situations.

Investigation on the control strategy of soft wearable robotic hand with slack enabling tendon actuator

A soft wearable robot, which is an emerging type of wearable robot, can take advantage of tendon-driven mechanisms with a Bowden cable. These tendon-driven mechanisms benefits soft wearable robots because the actuator can be remotely placed and the transmission is very compact. However, it is difficult to compensate the friction along the Bowden cable which makes it hard to control. This study proposes the use of a position-based impedance controller, which is robust to the nonlinear dynamics of the system and provides compliant interaction between robot, human, and environment. Additionally, to eliminate disturbances from unexpected tension of the antagonistic wire arising from friction, this study proposes a new type of slack enabling tendon actuator. It can eliminate friction force along the antagonistic wire by actively pushing the wire while preventing derailment of the wire from the spool.

Evaluation of the antagonistic tendon driven system for SNU Exo-Glove

The tendon driven systems to control joints generally use antagonistic tendon pairs. However, while one tendon controls the joint, tension of another tendon at the opposite side acts as a resistance. Unfortunately, the resistive force cannot be eliminated when a spool is used to actuate the tendon because certain level of the tension should be maintained to prevent the escape of the tendon from the spool.

Investigation of friction characteristics of a tendon driven wearable robotic hand

Wearable robots can assist people with disabilities to perform their daily tasks. However, the size, weight and wearability are important factors in the design because it is worn by the person controlling it. Various disabilities can be assisted with wearable robot technology, from the lower to upper body. The hand is an important part of the body for the disabled to perform their daily tasks. However, compared to the arms or legs, the degree of freedom is much higher, which makes it difficult to fabricate a compact wearable robot. We propose a frameless structure and modified differential mechanism to make the wearable robot compact. For the evaluation and control, it is necessary to analyze the friction force because the mechanism we proposed delivers power through more tube than the previous tendon tube transmission. Different from the previous friction model, we consider the friction at the edge of tube ends. This paper contains the design concept of the developed wearable robotic hand and its friction characteristics.

Development and assessment of a hand assist device: GRIPIT

BackgroundAlthough various hand assist devices have been commercialized for people with paralysis, they are somewhat limited in terms of tool fixation and device attachment method. Hand exoskeleton robots allow users to grasp a wider range of tools but are heavy, complicated, and bulky owing to the presence of numerous actuators and controllers. The GRIPIT hand assist device overcomes the limitations of both conventional devices and exoskeleton robots by providing improved tool fixation and device attachment in a lightweight and compact device. GRIPIT has been designed to assist tripod grasp for people with spinal cord injury because this grasp posture is frequently used in school and offices for such activities as writing and grasping small objects.MethodsThe main development objective of GRIPIT is to assist users to grasp tools with their own hand using a lightweight, compact assistive device that is manually operated via a single wire. GRIPIT consists of only a glove, a wire, and a small structure that maintains tendon tension to permit a stable grasp. The tendon routing points are designed to apply force to the thumb, index finger, and middle finger to form a tripod grasp. A tension-maintenance structure sustains the grasp posture with appropriate tension. Following device development, four people with spinal cord injury were recruited to verify the writing performance of GRIPIT compared to the performance of a conventional penholder and handwriting. Writing was chosen as the assessment task because it requires a tripod grasp, which is one of the main performance objectives of GRIPIT.ResultsNew assessment, which includes six different writing tasks, was devised to measure writing ability from various viewpoints including both qualitative and quantitative methods, while most conventional assessments include only qualitative methods or simple time measuring assessments. Appearance, portability, difficulty of wearing, difficulty of grasping the subject, writing sensation, fatigability, and legibility were measured to assess qualitative performance while writing various words and sentences. Results showed that GRIPIT is relatively complicated to wear and use compared to a conventional assist device but has advantages for writing sensation, fatigability, and legibility because it affords sufficient grasp force during writing. Two quantitative performance factors were assessed, accuracy of writing and solidity of writing. To assess accuracy of writing, we asked subjects to draw various figures under given conditions. To assess solidity of writing, pen tip force and the angle variation of the pen were measured. Quantitative evaluation results showed that GRIPIT helps users to write accurately without pen shakes even high force is applied on the pen.ConclusionsQualitative and quantitative results were better when subjects used GRIPIT than when they used the conventional penholder, mainly because GRIPIT allowed them to exert a higher grasp force. Grasp force is important because disabled people cannot control their fingers and thus need to move their entire arm to write, while non-disabled people only need to move their fingers to write. The tension-maintenance structure developed for GRIPIT provides appropriate grasp force and moment balance on the user’s hand, but the other writing method only fixes the pen using friction force or requires the user’s arm to generate a grasp force.