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This paper proposes a novel modular cable-driven humanoid arm with anti-parallelogram mechanisms (APMs) and Bowden cables. The lightweight arm realizes the advantage of joint independence and the rational layout of the driving units on the base. First, this paper analyzes the kinematic performance of the APM and uses the rolling motion between two ellipses to approximate a pure-circular-rolling motion. Then, a novel type of one-degree-of-freedom (1-DOF) elbow joint is proposed based on this principle, which is also applied to design the 3-DOF wrist and shoulder joints. Next, Bowden cables are used to connect the joints and their driving units to obtain a modular cable-driven arm with excellent joint independence. After that, both the forward and inverse kinematics of the entire arm are analyzed. Last, a humanoid arm prototype was developed, and the assembly velocity, joint motion performance, joint stiffness, load carrying, typical humanoid arm movements, and repeatability were tested to verify the arm performance. [ABSTRACT FROM AUTHOR]

Summary: The knee joint plays a significant role in ground clearness, which is a crucial subtask of normal walking and avoiding falls. While post-stroke survivors are often faced with muscle weakness during walking, which leads to inadequate knee flexion. The lack of ground clearance caused by inadequate knee flexion will severely impede walking, increase metabolic exertion, and increase the risk of falls. A compliant exoskeleton robot possesses more favorable edges than other rigid ones in lightweight, safety, sense of comfort, and so on. We developed a new type of soft exoskeleton robot to assist the knee joint to achieve desired movements with Bowden cable transmitting force and torque. With the agonist–antagonist driving method, like a group of muscles working, we have explored dual-motors structure to realize the knee flexion function. It has built a standard dynamic model to analyze stability and realize the control law. We have conducted simulation and prototype experiments to verify the feasibility and usefulness of our method. The results show that the device can compensate for the lack of the knee joint driving force and realize the reference movement. Finally, we concluded that our method is a desirable way, and the scheme could improve the knee flexion ability and clearing ground. [ABSTRACT FROM AUTHOR]

A parallel-wire driven system has the drawback of a narrow rotation range. To overcome this problem, this paper focuses on a 'torque wire', which consists of inner and outer wires and can transmit the inner wire rotation; the utilization of torque wires is effective in increasing the rotational range. However, significant degradation of the rotational transmission-accuracy is observed when a constant tension is applied to a torque wire. This degradation is attributed to the load in the tensile direction, which causes an increase in Coulomb friction at the sliding parts and an increase in the elastic torsion of the inner wire. Collectively defining the Coulomb friction and elastic torsion as a 'disturbance', this paper proposes a technique to suppress the disturbance and improve the rotational accuracy. This method applies a periodic change in tension to the torque wire. However, periodic tension induces lateral vibration due to parametric excitation. Thus, the amplitude and frequency of the torque wire are applied in several combinations for periodic tension as a preliminary experiment; the best combinations of amplitude/frequency with small lateral vibration are selected. The lateral vibration results are evaluated after Strutt-diagram-analysis. By using selected combinations, the usefulness of the method is experimentally confirmed. [ABSTRACT FROM AUTHOR]

The reliability of soft robotic devices will be the bottleneck that slows their commercialization. In particular, fatigue failure issues are a major concern. Thus, reliability should be taken into account from the earliest stages of development. However, to date, there have been no attempts to analyze the reliability of soft robotic devices in a systematic manner. When soft robots are employed to force transmission applications, reliability is typically a dominant issue, since soft robotic structures are constructed with soft material components; these materials have highly nonlinear properties that arise due to the large distribution in the material properties. Furthermore, reliability should be analyzed from the robot's system down to the components using domain knowledge about the system; this requires a systematic approach. This study presents a framework for reliability analysis of soft robotic devices taking into account a probability distribution that has not been considered before and examines a case study of a tendon-driven soft robot. This study focuses specifically on the (a) concept design process, (b) lifetime analysis process, and (c) design and optimization process. A life model that considers distribution is proposed using accelerated life testing based on analysis of the failure mechanism of the tendon-driven system. The tensile stress of the wire was varied during the experiment with different bend angles and output tension. The result was validated with different stress levels using a testbed to simulate an actual application. The proposed reliability analysis methodology could be applied to other soft robotic systems, such as pneumatic actuators, to improve the reliability-related properties during the robot design stage, and the life model can be used to estimate the device lifetime under various stress conditions. [ABSTRACT FROM AUTHOR]

Control of a Bowden-cable transmission requires dealing with varying frictional nonlinearity of the cable, which varies as the bend angle of the cable changes and degrades the performance of the output tension control if not compensated for. This article proposes a novel method of compensating for the changing nonlinearity of the Bowden cable. The method enables controlling the tension of a Bowden cable without directly measuring the output tension. The output tension differs from the input tension because of friction along the cable, which changes with the cable's bend angle. The bend angle can be estimated by using a Bowden-cable Angle (BoA) Sensor and the input tension of the actuation wire to compensate for the friction change. Friction compensation allows for feedforward control of the output tension of the Bowden-cable transmission despite the varying shape of the cable. The results show that the control error of the output tension decrease from 5.21 to 0.50 N when the bend angle of the Bowden cable change from 0° to 400°. The proposed control method can be fully embedded into a Bowden-cable system without redesigning the original device, minimizing the complexity and size of the actuation system. A Bowden-cable implementing the proposed control method is demonstrated with a soft wearable robotic hand. [ABSTRACT FROM AUTHOR]

This paper focuses on the design, modeling, and control of a novel remote actuation, including a compact rotary series elastic actuator (SEA) and Bowden cable. This kind of remote actuation is used for an upper limb rehabilitation robot (ULRR) with four powered degrees of freedom (DOFs). The SEA mainly consists of a DC motor with planetary gearheads, inner/outer sleeves, and eight linearly translational springs. The key innovations include (1) an encoder for direct spring displacement measurement, which can be used to calculate the output torque of SEA equivalently, (2) the embedded springs can absorb the negative impact of backlash on SEA control performance, (3) and the Bowden cable enables long-distance actuation and reduces the bulky structure on the robotic joint. In modeling of this actuation, the SEA's stiffness coefficient, the dynamics of the SEA, and the force transmission of the Bowden cable are considered for computing the inputs on each powered joint of the robot. Then, both torque and impedance controllers consisting of proportional-derivative (PD) feedback, disturbance observer (DOB), and feedforward compensation terms are developed. Simulation and experimental results verify the performance of these controllers. The preliminary results show that this new kind of actuation can not only implement stable and friendly actuation over a long distance but also be customized to meet the requirements of other robotic system design. [ABSTRACT FROM AUTHOR]

Rehabilitation of the hands is critical to the recovery of functions in daily life for individuals with hand injuries. It is documented that robots with force control can help patients effectively in limb rehabilitation. However, considering the limited space of the hands, traditional torque sensors, strain beams, for example, cannot meet the need of the compact structure. Therefore, this paper presents a novel elastic torque sensor with a compact structure to realize the real-time measurement of joint torque for hand rehabilitation. We demonstrate the principle of the torque sensor by analyzing the relationship between the angle and the torque of the joint. Integrated in the exoskeleton, the torque sensor is designed with a compact structure based on the Bowden cable. Finally, we carried out experiments to show the good linearity and torque tracking performance of the sensor. Results also show that the deviation between the actual and desired values caused by the backlash characteristics of the Bowden cable. Moreover, the deviation changes in different conditions and is dependent on velocity and orientation. Therefore, an effective compensation method is proposed to reduce the deviation in the experiment. [ABSTRACT FROM AUTHOR]

Abstract: Almost universally, the effective stimulus for mammalian 9+0 primary cilia has been taken to be bending. In this article I point out that in several physiological contexts there is great advantage in detecting pressure differences across the cell wall, i.e. axially directed forces pushing fluid to and fro through the hollow cilium and its basal body beneath. The form of the cilium – a fluid-filled pipe that connects to an intricate pinwheel-shaped basal body – is well configured for detecting fluid flow. Pressure-detection calls for compressible elements within the cell, but it effectively matches form and function in a range of cases. The “pipe and pinwheel” scheme suggests that the bulbous swellings commonly found near the tip of some primary cilia are compliant, pressure-sensitive elements which act like the bulb of an eye-dropper. In looking exclusively at the bending of cilia, we might be missing aspects of a dual-stimulus system. [Copyright &y& Elsevier]

This paper describes a novel method of actuation for robotic hands. The solution employs a Bowden cable routed to each joint. The use of a Bowden cable is shown to be feasible for this purpose, even with the changing frictional forces associated with it. This method greatly simplifies the control of the hand by removing the coupling between joints, and provides for direct and accurate translation between the joints and the servo motors driving the cables. The design also allows for two degrees of freedom with the same centre of rotation to be realized in the largest knuckle of each finger; thus biological finger kinematics are more closely emulated. [ABSTRACT FROM AUTHOR]

Exoskeletons with a Bowden cable for power transmission have the advantages of a concentrated mass and flexible movement. However, their integrated motor is disturbed by the Bowden cable's friction, which limits the performance of the force loading response. In this paper, we solve this problem by designing an outer-loop feedforward-feedback proportion-differentiation controller based on an inner loop disturbance observer. Firstly, the inner loop's dynamic performance is equivalent to the designed nominal model using the proposed disturbance observer, which effectively compensates for the parameter perturbation and friction disturbance. Secondly, based on an analysis of the stability of the inner loop controller, we obtain the stability condition and discuss the influence of modeling errors on the inner loop's dynamic performance. Thirdly, to avoid excessive noise from the force sensors being introduced into the designed disturbance observer, we propose the feedforward-feedback proportion-differentiation controller based on the nominal model and pole configuration, which improves the outer loop's force loading performance. Experiments are conducted, which verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Robotic exoskeletons are a trending topic in both robotics and rehabilitation therapy. The research presented in this paper is a summary of robotic exoskeleton development and testing for a human hand, having application in motor rehabilitation treatment. The mechanical design of the robotic hand exoskeleton implements a novel asymmetric underactuated system and takes into consideration a number of advantages and disadvantages that arose in the literature in previous mechanical design, regarding hand exoskeleton design and also aspects related to the symmetric and asymmetric geometry and behavior of the biological hand. The technology used for the manufacturing and prototyping of the mechanical design is 3D printing. A comprehensive study of the exoskeleton has been done with and without the wearer's hand in the exoskeleton, where multiple feedback sources are used to determine symmetric and asymmetric behaviors related to torque, position, trajectory, and laws of motion. Observations collected during the experimental testing proved to be valuable information in the field of augmenting the human body with robotic devices. [ABSTRACT FROM AUTHOR]