Tendon-driven Actuator Research Articles

A tendon-driven actuator with cantilever initiated variable stiffness used for robotic fingers

Variable stiffness actuators (VSAs) have emerged as a key actuation technology known for their bionic performance and task adaptability. However, current VSAs often exhibit relatively large sizes, making them possible for use in robotic arms and legs but less convenient for integrations into robotic hands. This paper introduces a compact design of a tendon-driven variable stiffness actuator (TVSA) based on an adjustable cantilever mechanism, which can be embedded into a robotic finger. This implementation endows the robotic finger with the independent regulation of joint position and stiffness. A concise and computationally efficient stiffness mapping model from the TVSA to the finger joints is then established, providing a theoretical foundation for the stiffness regulation of the tendon-driven fingers. A prototype of a robotic hand equipped with the presented TVSA demonstrates safe interactions with various objects of diverse shapes, weights and stiffness.

Coaxial Integrated Tendon-Driven Actuator: Design, Modeling, Control, and Performance Analysis

Coaxial Integrated Tendon-Driven Actuator: Design, Modeling, Control, and Performance Analysis

A Novel Cooling Design for an Agonistic–Antagonistic SMA Tendon-Driven Actuator

Shape memory alloys (SMAs) exhibit a unique property that undergoes deformation in response to temperature variation. This characteristic can be utilized via the application of a filiform SMA wire to tendon-driven robotic actuators for biomimetic joint movements. However, due to the inefficiencies in heat dissipation, conventional SMA tendon-driven actuators are characterized by their lower relaxation speeds than other actuators. This paper proposes a novel cooling design for an SMA tendon-driven actuator using thin-fin heat sinks based on a multi-layer wrapped SMA tendon design. In addition, the electric circuit and the controller are refined. Prototype devices are constructed to validate the performance of SMA-based actuators under PID control. The results indicate that the proposed design exceeds previous models in terms of relaxation performance by up to 5.8 times while also being able to stabilize at a target angle within 0.5 s under control.

Design of a 2DoF Ankle Exoskeleton with a Polycentric Structure and a Bi-Directional Tendon-Driven Actuator Controlled Using a PID Neural Network

Lower limb exoskeleton robots help with walking movements through mechanical force, by identifying the wearer’s walking intention. When the exoskeleton robot is lightweight and comfortable to wear, the stability of walking increases, and energy can be used efficiently. However, because it is difficult to implement the complex anatomical movements of the human body, most are designed simply. Due to this, misalignment between the human and robot movement causes the wearer to feel uncomfortable, and the stability of walking is reduced. In this paper, we developed a two degrees of freedom (2DoF) ankle exoskeleton robot with a subtalar joint and a talocrural joint, applying a four-bar linkage to realize the anatomical movement of a simple 1DoF structure mainly used for ankles. However, bidirectional tendon-driven actuators (BTDAs) do not consider the difference in a length change of both cables due to dorsiflexion (DF) and plantar flexion (PF) during walking, causing misalignment. To solve this problem, a BTDA was developed by considering the length change of both cables. Cable-driven actuators and exoskeleton robot systems create uncertainty. Accordingly, adaptive control was performed with a proportional-integral-differential neural network (PIDNN) controller to minimize system uncertainty.

A Hybrid Electromagnetic and Tendon-Driven Actuator for Minimally Invasive Surgery

Minimally invasive surgery (MIS) is a surgical technique that facilitates access to the internal tissues and organs of a patient’s body via a limited number of small incisions or natural orifice of the patients. Such a technique requires specialized slender surgical instruments with a high levels of dexterity and functionality. However, the currently available MIS instruments are rigid and could offer only limited degrees of freedom (DOFs) that hampers the surgeon’s effort to perform the required operation accurately. In this study, we have developed a hybrid electromagnetic and tendon-driven actuator as an integral part of MIS surgical instruments to provide them with optimum angulation. The design uses a novel electromagnetic structure to lock the position of individual joints, and a tendon-driven structure for the articulation of the surgical instrument. The finite element method (FEM) was utilized to predict the performance of the actuator, which was experimentally validated. Subsequently, a prototype was assembled, and corresponding kinematics analysis was presented to visualize the improvement of the developed mechanism on the functional workspace of the MIS instruments. It was concluded that the developed mechanism could offer three additional DOFs for the surgical instrument and angulation of 180° for each articulated joint.

Parameter Estimation of a Friction Model for a Tendon-sheath Mechanism

Mechanical systems using tendon-driven actuators have been widely used for bionic robot arms because not only the tendon based actuating system enables the design of robot arm to be very efficient, but also the system is very similar to the mechanism of the human body’s operation. The tendon-driven actuator, however, has a drawback caused by the friction force of the sheath. Controlling the system without considering the friction force between the sheath and the tendon could result in a failure to achieve the desired dynamic behaviors. In this study, a mathematical model was introduced to determine the friction force that is changed according to the geometrical pathway of the tendon-sheath, and the model parameters for the friction model were estimated by analyzing the data obtained from dedicated tests designed for evaluating the friction forces. Based on the results, it is possible to appropriately predict the friction force by using the information on the pathway of the tendon.

Development of Real-Time Electromyography Controlled 3D Printed Robot Hand Prototype

Developing an anthropomorphic robotic hand (ARH) has become a relevant research field due to the need to help the amputees live their life as normal people. However, the current state of research is unsatisfactory, especially in terms of structural design and the robot control method. This paper, which proposes a 3D printed ARH structure that follows the average size of an adult human hand, consists of five fingers with a tendon-driven actuator mechanism embedded in each finger structure. Besides that, the movement capability of the developed 3D printed robot hand validated by using motion capture analysis to ensure the similarity to the expected motion range in structural design is achieved. Its system functionality test was conducted in three stages: (1) muscular activity detection, (2) object detection for individual finger movement control, and (3) integration of both stages in one algorithm. Finally, an ARH was developed, which resembles human hand features, as well as a reliable system that can perform opened hand palm and some grasping postures for daily use.

A Soft Wearable Robotic Ankle-Foot-Orthosis for Post-Stroke Patients

We propose a soft robotic ankle-foot-orthosis for poststroke patients, which is inexpensive, lightweight, easy to wear, and capable of gait assistance for rehabilitation not only in the clinic but also in daily life. The device includes a 3D-printed flexible brace and an ankle support that allows natural flexion and extension of the ankle but provides support in the vertical direction preventing the structure from buckling. A bi-directional tendon-driven actuator was used for assisting both dorsiflexion and plantarflexion. The device also contains a wearable gait sensing module for measuring the leg trajectory and the foot pressures in real time for feedback control. Since the device is powered by a rechargeable battery and communicates with the main controller wirelessly, it is fully untethered, making it mobile and comfortable. Using the measured sensor data and the biomechanics of the legs, the realtime gait phase is detected, and then a gait assistance algorithm for both dorsiflexion and plantarflexion provides an accurate prediction of a control phase and timing although there are variations in the gait trajectories among individuals. As a feasibility test, the walking experiment was conducted with a post-stroke patient. The result showed improvement in both gait propulsion and foot-drop prevention.

Model predictive control for tendon-driven balloon actuator on simulation

Many pneumatic actuators have been developed to be lightweight with high output for decreasing the impact force. However, for pneumatic actuators it is difficult to maintain exact control because these actuators have constraints. In this study, we developed model predictive control (MPC) that can accommodate these constraints when applied to the pneumatic actuator we developed. As described here, we compared and evaluated the control performance using MPC and proportional–integral–derivative (PID) control with an anti-windup control system. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Model Predictive Control for Tendon-Driven Balloon Actuator under Constraints on Simulation

Many pneumatic actuators have been developed in order to be lightweight with high output for decreasing impact force. So far, a pneumatic tendon-driven balloon actuator (balloon actuator) which is compact and lightweight has been developed for a robot hand and a rehabilitation device. However, for pneumatic actuator, it is difficult to maintain exact control because these actuators have constraints. For this study, we developed a stroke control system for a balloon actuator using a constrained model predictive control (MPC) scheme that can consider constraints of the plant output. As described in this paper, we compared and evaluated the control performance using MPC and PID.

Position estimation and object collision detection of a tendon-driven actuator based on a polytopic observer synthesis

This paper proposes a multi-model based approach that estimates joint position and collision detection of a lightweight electric actuator dedicated to manipulation tasks. Taking advantage of an optimized back-drivable mechatronic design, the use of proprioceptive measures at the motor level enables the estimation of the unmeasured terminal position of the mechanical motor-to-joint transmission and force contact disturbance. A polytopic formulation is introduced based on an accurate model of the mechatronic transmission. Then, a multi-model observer-based estimator is synthesized using root-clustering for exteroceptive variables estimation without additional position/force sensor. The approach is experimentally validated with a single degree-of-freedom manipulator.

Development and control of a multifingered robotic hand using a pneumatic tendon-driven actuator

Because of the rapid aging of the Japanese population and the acute decrease in young workers in Japan, robots are anticipated for use in performing rehabilitation and daily domestic tasks for nursing and welfare services. Use in environments with humans, safety, and human affinity are particularly important robot hand characteristics. Such robot hands must have flexible movements and be lightweight. Under these circumstances, this study specifically addresses the expansion of a silicone rubber, tendon-driven actuator, which has been developed using a pneumatic balloon. A multifingered robotic hand using the actuator is developed. Moreover, a fuzzy grasping control system is applied to the proposed robotic hand. The robot hand’s development is described incorporating pneumatic balloon actuator with the softness, size, and weight of a human hand. The fuzzy grasping control system is shown to be effective for the proposed robot hand, which can grasp soft objects easily.