Haemin Lee

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.

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.

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.

A Novel Slack-Enabling Tendon Drive That Improves Efficiency, Size, and Safety in Soft Wearable Robots

Tendon drives are widely used in robotics. The compliance of the tendon in such drives suits them for soft robots, including soft wearable robots, but several issues impede their use. Generally, the tendon should always maintain tension to prevent derailment from the spool. However, in soft robots, tendon tension induces high friction forces owing to the absence of ball bearings. Because the kinematics of the soft robot is basically nonlinear and changed by the deformation of the structure, the kinematic difference between the soft structure and the spool causes derailment of the tendon. Moreover, continuously maintained tension in soft wearable robots causes safety issues. The linear actuator can be an option. However, the need to increase the length of the linear actuator to accommodate the excursion length of its tendon is a barrier to its use in small-scale applications. To preclude this issue, a slack-enabling actuator that employs a spool is proposed. The space efficiency of the spool enables the mechanism to be small, and a one-way clutch applies unidirectional friction force to the tendon to tighten the tendon around the spool. This paper describes the design concept for the slack-enabling mechanism, its design optimization, and system identification for force control.

Branching tendon routing: A new tendon methodology for compact transmission

In this paper, we propose a new tendon routing method using branching tendon for driving a revolute joint. Unlike conventional tendon (or wire) widely used in the tendon transmission, the branching tendon splits into sub-tendons, and the end points of the sub-tendons are located on the same link but different positions. Thus, without using any complicated and bulky mechanism, the branching tendon can transmit the tendon force through the alternative path depending on the rotating angle of the joint. Based on this concept, the design of the branching tendon with two sub-tendons is proposed. Also, an analysis of the tension transmission path of this branching tendon is performed to increase force transmitting efficiency. By applying this branching tendon, a finger joint with a compact tendon routing path was constructed. And we have verified that the branching tendon can be used to develop robotic fingers or hand prosthetics.

Design Improvement of a Polymer-Based Tendon-Driven Wearable Robotic Hand (Exo-Glove Poly)

This paper presents the design improvement of a polymer-based tendon-driven wearable robotic hand, Exo-Glove Poly. The wearability and adaptiveness are the key points to design the Exo-Glove Poly in considering the cases of practical use. Thus, magnets are embedded into the wearable part for easy donning and doffing. Also, the tendon length adjustment mechanism is designed to adapt different hand sizes by changing length of the tendons. Through these improvements, it is increased the change to practical use of the Exo-Glove Poly.

Investigation of design parameters of slack enabling actuator

Tendon drive is commonly used in various kind of machines. And, the spool is commonly used to wind and unwind the tendon because of its simplicity and compactness. However, the slack of the tendon causes the derailment of the tendon out of the spool and fails the system. In order to use the tendon drive with the spool without concerning about the derailment, the slack enabling actuator is previously proposed. In this paper, the performance criteria and the design parameters affecting the performance of the slack enabling actuator are discussed.

Control strategy of slack enabling tendon actuator for the soft wearable robot using feedback linearization

Tendon driven mechanism has been widely used in mechanical systems because of its versatility to mechanical systems requiring complex transmission. This paper proposes a control strategy of slack enabling tendon actuator using feedback linearization. The slack enabling actuator is a newly developed tendon actuator that does not fail although the tendon slacks (non-positive tension) at the outlet of the actuator which is an essential operating phase when the tendon driven is applied to the soft wearable robots. To deal with the dynamic nonlinearities of the slack enabling actuator, input-output feedback linearization was adopted and linear disturbance observer was used to estimate the output tension of the wire and reject position following error due to the external load. The results show that the estimated tension coincide with the measured tension and a proposed method have proper characteristics to control the position of the tendon while estimating the tension of the output tendon.

Trend of Soft Wearable Robotic Hand

Hand function is one of the essential functions required to perform the activities of daily living, and wearable robots that assist or recover hand functions have been consistently developed. Previously, wearable robots commonly employed conventional robotic technology such as linkage which consists of rigid links and pin joints. Recently, as the interest in soft robotics has increased, many attempts to develop a wearable robot with a soft structure have been made and are in progress in order to reduce size and weight. This paper presents the concept of a soft wearable robot composed of a soft structure by comparing it with conventional wearable robots. After that, currently developed soft wearable robots and related issues are introduced.

Preliminary study for a soft wearable knee extensor to assist physically weak people

To assist the walk of the physically weak people is important to increase their quality of life because it can expand their activity area. We present a soft wearable knee extensor, called Knee Tendon-suit, which assist the knee extension during climbing stairs. To achieve our goal, we used the tendon-driven mechanism for transmitting the actuation force and the anchor structure for transmitting the actuation force to the body. Measuring Electromyography (EMG) at the femoral muscles and the tension at the anchor, we verified performance of the Knee Tendon-suit as the first preliminary result.