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To overcome the limitations of a traditional soft hip exosuit directly driven by Bowden cables or winding belts at two points, in this article, we propose a new soft hip exosuit design concept based on series-wedge-structures for energy-efficient walking and running during daily activities for elderly individuals. The series-wedge-structure is designed to improve the comfort of the wearer–exosuit interface and to passively adapt to the user's body curvature, with no hindrance during movement. The design and function, including the series-wedge-structure belt, series elastic cable drive actuator, and control scheme, are described. The presented soft exosuit, which is lightweight (1.4 kg) and comfortable, provides assistive torque for hip flexion by folding series-wedge-structures driven by Bowden cables. The series-wedge-structure-based hip exosuit adopts single actuation coupled to the Bowden cable pull mechanism with a series elastic actuator to drive both hip flexions based on the out-of-phase nature of the human legs during walking and running. The exosuit performance test results show that the proposed exosuit improves the comfort of the wearer–exoskeleton interface by minimizing the shear force and maximizing the exosuit–skin interaction force contact area. Three healthy subjects walked at a fixed speed of 1.25 m/s and ran at a fixed speed of 2.2 m/s while wearing the proposed exosuit with/without assistance and without wearing the exosuit to evaluate the biomechanical and physiological effects of the proposed exosuit assistance on locomotion. The metabolic rate with exosuit assistance was reduced by 10.9% for walking and by 6.2% for running compared with not wearing the exosuit.

Although many lifting assist devices (LADs) have already been launched to the commercial market, and diverse types of LADs are under development with the recent advances in robotics technology, such LADs are not yet widely used in industrial fields. One of the main reason is the lack of versatility of fully passive type LADs and relatively high power consumption of fully active type LADs. In this study, our goal was to design a LAD that is not only more versatile than fully passive type LADs but also more energetically efficient than fully active type LADs. We analyzed the biomechanics of the lifting movement and developed a bi-articular elastic tendon mechanism based on our results. This conceptual mechanism was realized via a physical LAD operated by a series elastic actuator with a Bowden cable transmission. In this paper, we introduce our LAD and control strategy for assisting with lifting movements. Our LAD is capable of adjusting the output force behavior and assisting with lifting tasks at a low mechanical power consumption. Our preliminary testing suggests that our LAD reduces the muscle activation levels of the erector spinae and rectus abdominis muscles during a lifting task.

Few applications such as cutting shrubs and trees with prickles lead to damage to the hands while cutting it conventionally. The research has been undertaken for ease of rose plucking. A distance operated manipulator is designed and manufactured to overcome the issue of cutting roses by conventional way. The working of the tool is controlled by a lever operated mechanism. By a Bowden cable, the lever is connected to a brake caliper. The force applied by fingers at the lever is amplified at the point of application due to mechanical advantage. The end-effector consists of a gripper-cum-cutter. When the lever is operated, the stem of the rose is first gripped and then shearing of stem takes place. This unique feature of mechanism results into safe harvesting. Due to its simplest construction, it is a beneficial method. Trials have demonstrated the effective use of manipulator for rose plucking.

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.

The high energy cost of walking in individuals with cerebral palsy (CP) contributes significantly to reduced mobility and quality of life. The purpose of this study was to develop and clinically evaluate an untethered ankle exoskeleton with the ability to reduce the metabolic cost of walking in children and young adults with gait pathology from CP. We designed a battery-powered device consisting of an actuator-and-control module worn above the waist with a Bowden cable transmission used to provide torque to pulleys aligned with the ankle. Special consideration was made to minimize adding mass to the body, particularly distal portions of the lower-extremity. The exoskeleton provided plantar-flexor assistance during the mid-tolate stance phase, controlled using a real-time control algorithm and embedded sensors. We conducted a device feasibility and a pilot clinical evaluation study with five individuals with CP ages five through thirty years old. Participants completed an average of 130 minutes of exoskeleton-assisted walking practice. We observed a 19 ± 5% improvement in the metabolic cost of transport (p = 0.011) during walking with untethered exoskeleton assistance compared to how participants walked normally. These preliminary findings support the future investigation of powered ankle assistance for improving mobility in this patient population.

Wearable robots can assist motor-impaired individuals in activities of daily living, but weight is paramount for usability. Proximally placed actuators and remote actuation systems (RAS) minimize weight on users' extremities. State-of-the-art RAS employ pneumatics, hydraulics, or Bowden cables, which all have considerable limitations. Here, we present a novel Bowden-cable-based bidirectional RAS featuring high power-to-mass and power-to-volume ratios, easily accessible components, and compact mechanical design. A rack-and-pinion mechanism reduces the force transmitted through the Bowden cables, permitting use of extremely compliant sheaths. The feed-forward friction compensation model, integrated bending angle sensor, and series elastic elements ensure accurate force control across all bending angles of the Bowden cables and the user's full range of motion. As a proof-of-concept, an RAS was designed for a hand exoskeleton with a maximal output force of 150 N. With a power-to-volume and a power-to-mass ratio of 127 kW/m3 and 56 W/kg at the output, and of 2.0 kW/m3 and 1.6 W/kg for the entire system, it outperforms other state-of-the-art RAS. With the implemented speed- and current-limiting, the system operates for at least 2 h continuously. It is water- and dustproof, meeting hygienic and practical demands. Importantly, this novel system can be scaled to the requirements of various applications in wearable robotics., IEEE Robotics and Automation Letters, 3 (3), ISSN:2377-3766

Bowden cables are frequently used as remote transmissions on wearable devices because of their light weight, simplicity, and flexibility of design. However, a Bowden cable suffers from inefficiency, nonlinear backlash, and cable tension variation due to the bending of the cable housing and friction losses, leading to deteriorating force control performance, and a wearers comfort level and augmentation effectiveness. In this paper, to enhance wearable device performance and to overcome the above drawbacks, we propose a novel high-performance, cable-drive module with rolling cable transmissions (RoCT) that can efficiently transmit motion and mechanical power from an input to an output via an inner cable/rope. The RoCT is compact, modular, lightweight, extremely stiff, highly backdrivable, and is freely rotatable and translatable during manipulation. It maintains the cable tension regardless of the transmission angle between the input and output. The configuration of the proposed tethered cable-drive module, the working principle of the rolling cable transmission, and its properties, are introduced. Mechanical designs based on the working principle are also provided. Finally, as one of the applications of the proposed module, a tethered ankle exoskeleton system and its experimental results demonstrating the properties of the proposed transmission are presented.

The presence of strong magnetic fields in the magnetic resonance imaging (MRI) environment limits the integration of robotic rehabilitation systems in the MRI process. The tendency to improve imaging quality by the amplification of magnetic field strength further tightens the bidirectional compatibility constraints on MRI-compatible rehabilitation devices. We present the design, control and characterization of MRI-VisAct– a low-cost, Bowden-cable-actuated rotary series viscoelastic actuator that satisfies the bidirectional compatibility requirements to the maximum extent. Components of MRI-VisAct that are placed in the magnet room are built using nonconductive, diamagnetic MRI-compatible materials, while ferromagnetic or paramagnetic components are placed in the control room, located outside the MRI room. Power and data transmission are achieved through Bowden cables and fibre optics, respectively. This arrangement ensures that neuroimaging artefacts are minimized, while eliminating safety hazards, and device performance is not affected by the magnetic field. MRI-VisAct works under closed-loop torque control enabled through series viscoelastic actuation. MRI-VisAct is fully customizable; it can serve as a building block of higher-degrees-of-freedom MRI-compatible robotic devices.

The research and development of wearable robotic devices has been accelerated by off-board control and actuation systems. While off-board robotic actuation systems provide many benefits, the impedance at the robotic joint is often high. High joint impedance is undesirable for wearable devices like exoskeletons, as the user is unable to move their joint without actively controlled motion from the motors. We propose that the impedance can be reduced substantially in off-board robotic actuation systems by minimizing the reflected inertia from the motor. We have developed a model and optimization-based methodology for selecting a motor and set of mechanical design parameters that minimize reflected inertia. This methodology was implemented in the design of an off-board knee exoskeleton as a case study. A grey-box model was developed that incorporates biomechanical knee trajectories, an experimentally determined human-device interface stiffness model, Bowden cable stiffness and friction, and a motor model. A constrained optimization routine was developed that uses the model and a library of 157 candidate servo motors to select the actuator and mechanical design parameters that minimize reflected inertia at the exoskeleton joint. We found that 86 of the motors were able to carry out the necessary torque-velocity trajectories to achieve the prescribed exoskeleton joint torques and limb motions. The optimal motor was the Kollmorgen C133A - one of the largest in the library of candidate servo motors and required a 2.25 cm actuator pulley at the knee joint and a 17.5 cm cable sheave at the motor output. This methodology can be adapted by exoskeleton designers to develop more backdriveable exoskeletons and improve experimental capabilities. All code developed for the case study is open-source and freely available online.

Enabling individuals who are living with reduced mobility of the hand to utilize portable exoskeletons at home has the potential to deliver rehabilitation therapies with a greater intensity and relevance to activities of daily living. Various hand exoskeleton designs have been explored in the past, however, devices have remained nonportable and cumbersome for the intended users. Here we investigate a remote actuation system for wearable hand exoskeletons, which moves weight from the weakened limb to the shoulders, reducing the burden on the user and improving portability. A push-pull Bowden cable was used to transmit actuator forces from a backpack to the hand with strict attention paid to total system weight, size, and the needs of the target population. We present the design and integration of this system into a previously presented hand exoskeleton, as well as its characterization. Integration of remote actuation reduced the exoskeleton weight by 56% to 113g without adverse effects to functionality. Total actuation system weight was kept to 754g. The loss of positional accuracy inherent with Bowden cable transmissions was compensated for through closed loop positional control of the transmission output. The achieved weight reduction makes hand exoskeletons more suitable to the intended user, which will permit the study of their effectiveness in providing long duration, high intensity, and targeted rehabilitation as well as functional assistance.

Currently, wrist passive stiffness and active range of motion, two clinically relevant properties, are assessed using devices designed for rehabilitation. As a result, these devices do not have sufficient torque output and range of motion for complete wrist biomechanical assessment. To address these limitations, we are developing an actuation module specifically for assessing wrist biomechanical properties. Our device employs a serial kinematic exoskeletal architecture to directly interact with and measure wrist flexion/extension and radial/ulnar deviation. A Bowden cable-based actuation scheme, locating the motors off-board, was adopted for increased device range of motion and torque output compared with previous wrist exoskeletons. Additionally, the device was designed to incorporate a rotational elastic element at each joint, creating series elastic actuators, for accurate torque control and direct torque measurement. In this work, we present the design and demonstration of a 1-DOF module of the device, which can interact with a user’s wrist in flexion/extension, providing an important first step towards the control, evaluation, and application of the 2-DOF device.

This paper introduces an approach that robotizes an ankle-foot orthosis (AFO). In particular, toward post-stroke gait rehabilitation, we robotize a double-bar AFO, which is widely used in rehabilitation facilities, by newly designing a modular joint, a pneumatic actuator, and a Bowden cable force-transmission system. Our modular joint system, called the Modular Exoskeletal Joint (MEJ), has a hollow shaft for simple attachment to an AFO's pivot. We designed MEJ to compactly house an encoder that is built in a bearing in a pulley. We adopted Bowden cables to transmit contraction forces from an actuator to the MEJ. As an actuation scheme, we developed the Nested-cylinder Pneumatic Artificial Muscle (NcPAM) system. Even though PAMs are mechanically compliant and lightweight, they can still generate a large force. Therefore, they can provide an ideal actuation system for exoskeletal robots. The nested-cylinder in NcPAM houses a cable-tensioning spring to properly maintain small cable tension for passive movements and a cable stopper to connect the PAM and the cable for properly transmitting the large force generated by PAM. We show the ankle-joint trajectory tracking performances of this integrated system using iterative learning control.

Wearable robotic systems which aid or enhance human performance are the subject of substantial ongoing research efforts. Soft exosuits to assist with walking represent one class of system that leverage textiles and apparel to provide a lightweight and nonrestrictive means to interface to the lower extremity and apply assistive joint torques via a cable that applies a force across a biological joint. Current embodiments of the soft exosuit use off-the-shelf load cells attached to the distal end of a Bowden cable to measure and control the delivered force. As these systems evolve, we envision replacing all rigid components with compliant, textile-based components. Here we present a new force sensing concept suitable for exosuit applications. The approach is based on micro-machined carbon fiber composite structures encapsulated in elastomer materials as the transducer element, and high-strength, stiff textiles as the load bearing element. The transduction mechanism uses the Poisson effect in the encapsulating elastomer to create electrical contact between the carbon fiber structures. This method allows the sensor to be sensitive in tension while remaining insensitive to bending deformation. We fabricate a prototype sensor capable of detected forces up to 300 N, yet weighing just 2.15 g. The compliant nature of the materials used in fabrication allow the sensor to be flexible. The sensor output is qualitatively very repeatable, yet exhibits moderate drift at peak load. However this drift begins to stabilize over the test duration. These preliminary results demonstrate the promising potential of this sensor technology for soft exosuit systems.

In this paper, we present our cross-wire assist concept, for assisting a single joint in multiple degrees of freedom. It is comprised of four motor driven Bowden cable actuators (wires) per assisted joint, with the wires crossed over each other at the front and rear. Simulation results show that selectively actuating a subset of these wires allows torque to be generated in 6 directions, with the torque magnitude dependent on joint angle. We have built a fully wearable prototype of our assistance device for both hip joints, with 8 high-speed and independently controllable actuators each providing force up to 100 N. The prototype has a total mass of 9.3 kg, and is shown in motion capture testing to generate movement in 6 directions around the users joint, including internal and external rotation. Mobile, multi-degree of freedom assistance cross-wire system will enable assistive devices to better match human movement, allowing support and rehabilitation in tasks beyond straight line walking.

The article focuses on designed construction of the exoskeleton, which significantly reproduces the kinematic structure and the range of joint movement of the human upper limb. The exoskeleton will able to control real objects i.e. loading crane, including force feedback. The designed device, composed of seven rotary joints, is equipped with the closed loop Bowden cable conduit system with linear DC actuators. This conduit system was applied in order to significantly reduce the mass of designed construction. The article describes the proposed kinematic structure, as well as the simple dynamic analysis of the ExoArm 7-DOF. The results of the device manipulability analysis are also included in this paper.

A critical issue for Bowden-cable transmission is bending-dependent hysteresis that degrades control performance and limits the application. The relationship between input and output of the Bowden-cable varies with the changing bending angle of the cable. This paper proposes a novel method that can compensate the varying hysteresis of the Bowden-cable using an embedded auxiliary wire, called a sensing wire. The accumulated bend angle of the Bowden-cable can be estimated by measuring the displacement change of the sensing wire and the input tension of the actuation wire. The estimated bending angle of the sheath can be used to compensate the hysteresis of the Bowden-cable with a feedforward control scheme, even though it is subject to the varying shape of the Bowden-cable. The proposed system has a simple and fully embedded design inside the sheath and does not require any external shape sensor or output tension sensor, which keeps the size and complexity of the system low. The results show that the control error of output tension decreased from 4.22 N to 0.69 N when the bend angle of the Bowden-cable changes from 0° to 560°.

Hand injuries are common problems. In order to adapt to fingers of different sizes and avoid secondary injuries, a hand exoskeleton for rehabilitation is proposed. The exoskeleton is designed as a wearable device and each finger has three joints named the metacarpophalangeal (MCP) joint, the proximal interphalangeal (PIP) joint and the distal interphalangeal (DIP) joint which all employ a novel mechanism called “circuitous joint”. Adopting a symmetrical pinion and rack with a parallel sliding mechanism, the circuitous joint can cover a wide workspace of the finger and adapt to fingers of different thicknesses. And the parallel sliding mechanism ensures that the contact force between the exoskeleton and the finger is perpendicular to the finger's bone, which can minimize the secondary injuries. Moreover, the Bowden cable driving method reduces the burden on the fingers by placing the driving and control system on the forearm. Lastly, hand fitness test and contact force experiment are conducted and the results verify the rationality and effectiveness of the exoskeleton.

In recent years soft wearable exoskeletons, commonly referred to as exosuits, have been widely exploited in human assistance. Hence, a shared approach for a systematic and exhaustive control architecture is extremely important. Most of the exosuits developed so far employ a bowden cable transmission to conveniently place the actuator away from the end-effector. While having many advantages this actuation strategy presents some intrinsic limitations caused by the presence of nonlinearities, such as friction and backlash of the cables, which make it difficult to predict and control the dynamics between the device and the user. In this letter, we propose a novel hierarchical control paradigm for a cable-driven upper limb exosuits that aims at evaluating and consequently deliver the appropriate assistive torque to the user's elbow joint. The proposed control method comprises three main layers: an active impedance control which estimates the user's arm motion intention and guarantees an intuitive response of the suit to the wearer's motion; a mid-level controller which compensates for the backlash in the transmission and converts the reference arm motion to the desired position of the actuator; a low-level controller which is responsible for driving the actuation stage by compensating for the nonlinear dynamics occurring in the bowden cable to provide the desired assistive torque at the joint. Tests on healthy subjects show that wearing the exosuit reduces by $48.3\%$ the muscular effort required to lift 1 kg and that the controller is able to modulate its level of assistance to the wearer's motor ability.

This paper presents a design of gravity balanced upper limb exoskeleton used for the stroke patients to regain their motor function. Bowden cable actuators have a high power-weight ratio and can significantly reduce the mass, inertial and power consumption of the device. The gravity balancing of the device is achieved by a hybrid strategy, which uses zero free-length springs and auxiliary parallel links to locate the COM (center of mass) of the robot and keep the total potential energy of the system invariant with all configurations. The balance torques caused by the variation of body weight and height are calculated. The exoskeleton is proved to be robust with the users of different weights and heights.

The torque control of finger joints is important for effective hand rehabilitation after neural disorders such as stroke. This paper presents an approach for accurate torque control of finger joints with UT hand exoskeleton. We present 1) how we obtained an accurate kinematics model, 2) how we built the torque actuation model with Bowden cable SEA, and 3) how we controlled the torque of finger joints with the kinematic model and the Bowden cable SEA. We have validated our approach with a testbed finger and results show that the UT hand exoskeleton accurately controls the torque of finger joints.

In recent years, bowden-cable transmissions have been developed and utilized widely in many robotic applications due to advantages in durability, lightweight, safety, and flexibility. Especially, over the last decade, a substantial number of soft wearable exoskeletons using bowden cables for motion transmission have been designed for human assistance, empowerment and rehabilitation. The major advantage of soft assistive devices driven by bowden-cable transmissions is to allow decentralizing the actuation stages proximally such that their mass has the least effect on the end-effector. Besides the advantage, the main drawback of the bowden cable-driven system comes from the presence of nonlinearities such as friction and backlash hysteresis that affects their control accuracy. Hence, in this paper, we introduce a mathematical model for backlash hysteresis and propose a solution based on the nonlinear adaptive control to compensate for the backlash effect. The backlash hysteresis model and control scheme are validated first on a custom-designed test bench and then applied to control a soft exoskeleton in a preliminary human trial.

This paper presents the design and development of a single motor actuated peristaltic worm robot with three segments using a bio-inspired method of locomotion with one actuator that achieves optimised worm like peristaltic motion. Each segment consists of two solid circular disks that have a tendon connected through to the drive mechanism using a Bowden cable and a soft rubber skin that deforms under the compression of the tendon. Our hypothesis that a tuned peristaltic waveform can achieve improved performance of locomotion distance and clamping strength is proven using an initial test platform capable of demonstrating varying waveform types with multiple actuators. Three experiments were undertaken: (i) moving along a flat surface, (ii) moving through a confined tunnel (iii) moving through a confined tunnel whilst pulling a payload. Results from these experiments have identified the optimal parameters for a smart gearbox capable of achieving the same optimal peristaltic waveform signal as the more complex test platform but with only one actuator driving all three worm segments. Unlike other examples of peristaltic worm robots, this example uses a control method embedded within the mechanics of the design removing excessive number of actuators which contributes to miniaturisation, reduces power consumption and simplifies the overall design.

Myoelectric prostheses have many advantages over body-powered prostheses, yet the absence of sensory feedback in myoelectric devices is one reason body-powered devices are often preferred by amputees. While considerable progress has been made in the mechanical design and control of myoelectric prostheses, research on haptic feedback has not had a similar impact. In this study, we seek to develop a fundamental understanding of the utility of force feedback and vision in the functional operation of a body-powered upper-limb prosthesis. Using a custom body-powered prosthesis in which force feedback can be conditionally removed, we asked $ {\rm N}=10$ non-amputee participants to identify objects based on stiffness in four separate conditions with and without visual and/or force feedback. Results indicate that the combination of visual and force feedback allows for the best accuracy, followed by force feedback only, then visual feedback only. In addition, combining force feedback with visual feedback does not significantly affect identification timing compared to visual feedback alone. These findings suggest that consideration should be given to the development of force feedback displays for myoelectric prostheses that function like a Bowden cable, coupling the amputee’s control input to the resulting feedback.

Most robots have a mechanical look or are covered with plastic or metallic shells. Their actuators are stiff which gives them not only an unnatural look, but also an unnatural touch. The goal of the huggable robot Probo is to serve as robotic research platform for human–robot interaction (HRI) studies with a special focus on children. Since not only cognitive interaction, but also physical interaction is targeted a new mechatronic design must be developed. To give Probo a huggable and safe behavior a new set of actuators is developed together with a triple layered protection cover which is presented in this paper. Probo’s soft touch is introduced, on the one side by use of novel passive compliant actuators, Compliant Bowden Cable Driven Actuators (CBCDAs), and on the other side by combining custom made servo motors, Non Back Drivable Servos (NBDSs), with flexible components and materials such as springs, silicon and foam. The working principle of the novel CBCDA is extensively described, together with experiments in order to determine its level of compliance and its bandwidth.

Purpose A straight thoracic stent graft often complies poorly with the curvature of the aortic arch. We have previously reported an in vitro model of a modified stent graft that can be bent in situ after deployment to improve conformance to the aortic arch. We now report the first clinical experience with this technique in three consecutive patients. Methods Between September 2007 and August 2008, three patients were treated for different pathologies of the aortic arch with a modified thoracic stent graft that was fitted with a sliding self-locking knot and a detachable Bowden cable. Transfemoral traction on the Bowden cable enables controlled shortening of the proximal part of the stent graft at the inner curve after deployment. The stent graft is thereby directed to allow for better apposition to the aortic wall. Results The modified thoracic stent grafts were correctly orientated and deployed in all patients. Transfemoral traction on the Bowden cable successfully bent all stent grafts and improved vessel wall apposition without a residual gap on the inner curve. The Bowden cable was successfully released and withdrawn in all patients. Conclusion In situ bending of thoracic stent grafts with a sliding self-locking knot is feasible and improves proximal apposition of the device at the inner curve of the aortic arch. More data and longer follow-up are required to confirm the applicability of this technique.

Many of those who survive a stroke develop a gait disability known as stiff-knee gait (SKG). Characterized by reduced knee flexion angle during swing, people with SKG walk with poor energy efficiency and asymmetry due to the compensatory mechanisms required to clear the foot. Previous modeling studies have shown that knee flexion activity directly before the foot leaves the ground, and this should result in improved knee flexion angle during swing. The goal of this research is to physically test this hypothesis using robotic intervention. We developed a device that is capable of assisting knee flexion torque before swing but feels imperceptible (transparent) for the rest of the gait cycle. This device uses sheathed Bowden cable to control the deflection of a compliant torsional spring in a configuration known as a series elastic remote knee actuator (SERKA). In this investigation, we describe the design and evaluation of SERKA, which includes a pilot experiment on stroke subjects. SERKA could supply a substantial torque (12 N middot m) in less than 20 ms, with a maximum torque of 41 N middot m. The device resisted knee flexion imperceptibly when desired, at less than 1 N middot m rms torque during normal gait. With the remote location of the actuator, the user experiences a mass of only 1.2 kg on the knee. We found that the device was capable of increasing both peak knee flexion angle and velocity during gait in stroke subjects. Thus, the SERKA is a valid experimental device that selectively alters knee kinetics and kinematics in gait after stroke.

Purpose: To demonstrate the feasibility of a novel technique that modifies the configuration of a thoracic stent-graft after deployment to comply with the arch curvature. Technique: The principle of a Bowden cable has been applied to direct a conventional thoracic stent-graft in situ after deployment. A suture placed at the proximal inner curve of a conventional thoracic stent-graft is fitted with a sliding, self-locking knot attached to a line that runs inside a catheter through the central rod of the stent-graft. Traction applied to this line directs the endograft post deployment, which allows for better apposition to the aortic wall. Shortening the inner curve makes the stent-graft bend. The extent of bending is fully controlled by the surgeon and held in place with the sliding knot. A release mechanism allows removal of all luminal components of the mechanism. Conclusion: The described technique of directing a thoracic stent-graft in situ seems feasible and enables better apposition of the stent-graft in a glass model. It may improve the durability of thoracic stent-grafts in the aortic arch. (Less)

Bend sensors have been developed based on conductive ink, optical fiber, and electronic textiles. Each type has advantages and disadvantages in terms of performance, ease of use, and cost. This study proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. This bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable's inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The proposed sensor is not affected by a bend curvature of up to 80.0 m(-1), unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor.

Bidirectional compatibility requirements with Magnetic Resonance Imaging (MRI) have limited the adaptation of rehabilitation robots for use in MRI machines. In this paper, we present the design and control of a Bowden cable-actuated, MRI-compatible series elastic actuator (SEA) that aims to fulfil the bidirectional compatibility requirements to the maximum extend. The proposed device is built using nonconductive diamagnetic MRI compatible materials, fiber optic sensing units and a Bowden cable based actuation, such that imaging artifacts created under strong magnetic field required for neuro-imaging are minimized. In particular, utilization of Bowden-cable transmission enables the placement of the conventional non-MRI compatible control/signal processing units and electric actuators outside the MRI room. This approach not only helps avoid the MR interference caused by these parts and eliminates safety hazards within the MRI room, but also ensures that the performance of the device is not affected by the strong magnetic field, resulting in ideal bidirectional MRI compatibility. Use of a custom-built fiber optic encoder together with nonconductive leaf spring based elastic element enables torque outputs of the device to be measured and used for closed-loop torque control, rendering the system into a series elastic actuator. The proposed MRI compatible SEA is easily customizable and can be used as the building block of higher degrees of freedom MRI compatible robotic devices. Current prototype is validated to administer continuous torques up to 2 Nm with a torque control bandwidth of 1 Hz and a torque sensing resolution of 0.05 Nm.

We propose a biomechatronics-based master/slave topology which is going to provide an Extended Physiological Proprioception (EPP)-equivalent control but without the use of a harness, cineplasty, or Bowden cable. The proposed control uses an implanted micro servo actuator. The original Bowden-cable EPP topology is compared to the proposed one and their simulation results are presented. The simulation results are encouraging since they indicate the materialization potential of the topology, both in terms of control and of low power, two essential factors in making the presence of an implant in the human body feasible. This control topology will provide a modern EPP-equivalent control scheme for upper-limb prostheses without the disadvantages of previous EPP configurations but with the control advantages of proprioceptive feedback.

Friction along the Bowden-cable transmission degenerates control performance unless it is properly compensated. Friction is produced when the bending angle of the Bowden-cable changes as the relative position of the actuator and the end-effector changes. This study proposes a method, termed loop routing, to compensate friction along the Bowden-cable. Loop routing involves making a one-round loop along the sheath that continuously maintains the sheath's bending angle at 2π regardless of the end-effector's position in 2-D space. This minimizes the bending angle change of the sheath as the end-effector translates in a 3-D workspace, which minimizes the friction change and enables feedforward friction compensation of the Bowden-cable without employing a sensor. An experiment in open-loop tension control of the Bowden-cable was conducted to evaluate the performance of the proposed method. Results show that the output tension follows the reference tension well, with an RMS error of 4.3% and a peak error of 13.3% of maximum reference.

To achieve a compact, lightweight and compliant actuator design for intrinsically safe subject-robot interactions, a Bowden cable-driven rotary series elastic actuator is proposed in this paper. To realize the zero output torque control of the proposed actuator in the presence of variable friction of the Bowden cable, a disturbance observer based torque-mode control algorithm is developed and analyzed. The effectiveness of the proposed design is verified by experiments with a human subject.

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 system dynamics approach, based on bond graphs, is presented for the analysis of prosthetic devices for a partially impaired hand. The partial impairment implies that the hand has lost one or more fingers but retains the ability of its remaining natural fingers. It is shown that the existing natural joints can be used for the actuation of prosthetic finger joints and enable performance of tasks that would not have been possible otherwise. This is a challenging task as motion has to be transmitted from the remaining natural joints to the prosthetic joints. The joint axes move with respect to each other during performance of tasks and do not have any fixed relative orientation. In this work, basic concepts for the actuation of the prosthesis required for such tasks are developed systematically. Based on these concepts, Bowden cable based joint actuation mechanisms for transmission of motion from natural joints to corresponding prosthetic joints are presented and analyzed. The analysis of dynamics of the resulting under-actuated prosthesis with joint actuation mechanism is based on bond graph models that are systematically developed. Using these models, system equations are derived and numerical simulations performed for the analysis. One- and two-joint actuated prototypes of the prosthesis have been presented and effectively demonstrate the proposed concepts.

Within the context of impedance controlled exoskeletons, common actuators have important drawbacks. Either the actuators are heavy, have a complex structure or are poor torque sources, due to gearing or heavy nonlinearity. Considering our application, an impedance controlled gait rehabilitation robot for treadmill-training, we designed an actuation system that might avoid these drawbacks. It combines a lightweight joint and a simple structure with adequate torque source quality. It consists of a servomotor, a flexible Bowden cable transmission, and a force feedback loop based on a series elastic element. A basic model was developed that is shown to describe the basic dynamics of the actuator well enough for design purpose. Further measurements show that performance is sufficient for use in a gait rehabilitation robot. The demanded force tracking bandwidths were met: 11 Hz bandwidth for the full force range (demanded 4 Hz) and 20 Hz bandwidth for smaller force range (demanded 12 Hz). The mechanical output impedance of the actuator could be reduced to hardly perceptible level. Maxima of about 0.7 Nm peaks for 4 Hz imposed motions appeared, corresponding to less than 2.5% of the maximal force output. These peaks were caused by the stick friction in the Bowden cables. Spring stiffness variation showed that both a too stiff and a too compliant spring can worsen performance. A stiff spring reduces the maximum allowable controller gain. The relatively low control gain then causes a larger effect of stick in the force output, resulting in a less smooth output in general. Low spring stiffness, on the other side, decreases the performance of the system, because saturation will occur sooner.

Persons with an upper-limb amputation who use a body-powered prosthesis typically control the prehensor through contralateral shoulder movement, which is transmitted through a Bowden cable. Increased cable tension either opens or closes the prehensor; when tension is released, some passive element, such as a spring, returns the prehensor to the default state (closed or open). In this study, we used the Southampton Hand Assessment Procedure to examine functional differences between these two types of prehensors in 29 nondisabled subjects (who used a body-powered bypass prosthesis) and 2 persons with unilateral transradial amputations (who used a conventional body-powered device). We also administered a survey to determine whether subjects preferred one prehensor or the other for specific tasks, with a long-term goal of assessing whether a prehensor that could switch between both modes would be advantageous. We found that using the voluntary closing prehensor was 1.3 s faster (p = 0.02) than using the voluntary opening prehensor, across tasks, and that there was consensus among subjects on which types of tasks they preferred to do with each prehensor type. Twenty-five subjects wanted a device that could switch between the two modes in order to perform particular tasks.

Body-powered prostheses use a cable-operated system to generate forces and move prosthetic joints. However, this control system can only generate forces in one direction, so current body-powered prehensor designs allow the user either to voluntarily open or voluntarily close the tongs. Both voluntary opening (VO) and voluntary closing (VC) modes of operation have advantages for certain tasks, and many end-users desire a terminal device that can switch between the two modes. However, such a terminal device must maintain the same thumb position (i.e., point of Bowden cable attachment) and movement direction in both modes in order to avoid the need to readjust the harness after every mode switch. In this study, we demonstrate a simple design that fulfills these requirements while allowing the user to switch easily between modes. We describe the design concept, describe a rugged split-hook prototype, provide specifications (size, weight, efficiency, etc.), and present a pilot study in which five subjects with intact arms and two subjects with amputation used the VO and VC split-hook prehensor to perform the Southampton Hand Assessment Procedure. Subjects performed an average of 4 to 7 (+/- 0.2) points better when they could choose to switch between modes on a task-by-task basis than when they were constrained to using only VO or VC modes.

An innovative electric-powered glove system has been prototyped to support finger rehabilitation for people with motor impairment on their fingers after a stroke. This glove system is composed of a leather glove which has a unique actuation mechanism called an exotendon system, a muscle activity sensor is fixed on the upper forearm to detect user’s efforts during finger exercises and a controller including a microcomputer and a drive unit. An evaluation has been conducted based on A-B design of a single subject study and it has been observed that finger exercises carried out using the prototyped glove system has effectively improved the finger functionality of a stroke patient.

Robotic prostheses have the potential to significantly improve mobility for people with lower-limb amputation. Humans exhibit complex responses to mechanical interactions with these devices, however, and computational models are not yet able to predict such responses meaningfully. Experiments therefore play a critical role in development, but have been limited by the use of productlike prototypes, each requiring years of development and specialized for a narrow range of functions. Here we describe a robotic ankle‐foot prosthesis system that enables rapid exploration of a wide range of dynamical behaviors in experiments with human subjects. This emulator comprises powerful off-board motor and control hardware, a flexible Bowden cable tether, and a lightweight instrumented prosthesis, resulting in a combination of low mass worn by the human (0.96kg) and high mechatronic performance compared to prior platforms. Benchtop tests demonstrated closedloop torque bandwidth of 17Hz, peak torque of 175 Nm, and peak power of 1.0kW. Tests with an anthropomorphic pendulum “leg” demonstrated low interference from the tether, less than 1 Nm about the hip. This combination of low worn mass, high bandwidth, high torque, and unrestricted movement makes the platform exceptionally versatile. To demonstrate suitability for human experiments, we performed preliminary tests in which a subject with unilateral transtibial amputation walked on a treadmill at 1.25ms � 1 while the prosthesis behaved in various ways. These tests revealed low torque tracking error (RMS error of 2.8 Nm) and the capacity to systematically vary work production or absorption across a broad range (from � 5 to 21J per step). These results support the use of robotic emulators during early stage assessment of proposed device functionalities and for scientific study of fundamental aspects of human‐robot interaction. The design of simple, alternate end-effectors would enable studies at other joints or with additional degrees of freedom. [DOI: 10.1115/1.4026225]

A new type of wearable robot that provides a third and fourth arm for performing manipulative tasks with the wearer’s own arms is presented. These Supernumerary Robotic Limbs (SRL) work so closely with the human that he/she can potentially perceive them to be his/her own. The SRL consist of two independently acting robotic limbs that can function as either arms or legs to help the user position objects, lift weights, and maintain balance. These wearable robots are aimed to augment not only the strength and the precision of the human users, but also their range of skills and interactions with the environment. The guiding principles of the robotic design are safety, transparency and user comfort. Series viscoelastic actuators provide suitable joint torques while ensuring compliance and robust torque sensing. A Bowden cable transmission actuates the elbow joint, minimizing the robotic arms’ weight. A tuned elastic human-robot coupling ensures wearability and comfort. To quantify the mechanical advantage the SRL offers to the operator during use, joint torques generated in the human while performing static manipulation tasks have been reconstructed experimentally.© 2012 ASME

This paper presents a robot aimed to assist the shoulder movements of stroke patients during their rehabilitation process. This robot has the general form of an exoskeleton, but is characterized by an action principle on the patient no longer requiring a tedious and accurate alignment of the robot and patient's joints. It is constituted of a poly-articulated structure whose actuation is deported and transmission is ensured by Bowden cables. It manages two of the three rotational degrees of freedom (DOFs) of the shoulder. Quite light and compact, its proximal end can be rigidly fixed to the patient's back on a rucksack structure. As for its distal end, it is connected to the arm through passive joints and a splint guaranteeing the robot action principle, i.e. exert a force perpendicular to the patient's arm, whatever its configuration. This paper also presents a first prototype of this robot and some experimental results such as the arm angular excursions reached with the robot in the three joint planes.

This paper presents the comparison study of the pressure distribution analysis between wearing the transradial prosthetics with the body powered prosthetics which are focus on the transradial amputation level. The major different analysis totally depends on the amputation level, mass of both body powered prosthetics and the transradial prosthetics. The body power prosthetics involve the mechanical engineering structure of Bowden cable as the main system while transradial prosthetics used biomechatronics system as the main engineering principle. The paper briefly describes the different of pressure distribution that occur to the amputee while wearing the different approach of prosthetics hand. The data analysis of both methods using the Fscan to investigate the reliable prosthetics hand needs to be worn by the amputee.

This paper investigates the control algorithm of an exoskeleton for hand rehabilitation, which accomplishes both active and passive rehabilitation training. In the passive mode control the PID control algorithm is executed in the velocity mode of the driver. In the active mode control, control architecture is proposed to deal with in both free space and constraint space. A resistance compensation control method is proposed to reduce the resistance in free space which is caused by the friction of the Bowden cable as well as the moment of inertial. To realize the compensation, force sensors are used to measure the force exerted by the human fingertip. A commercial driver, which could switch between the two control modes by a programmable digital switch rather than changing the physical connection manually, guarantees the realization of the required functions. The experiments are conducted to verify the proposed method, and the results show that in the active control mode, the maximum finger-exerted force with compensation is about two fifths of the force without compensation which means the resistance is greatly reduced. And in the passive mode, the maximum joint position error is about 1.2 degree, which satisfies the requirement in hand rehabilitation application. The experimental results demonstrate the validity of the proposed method.

The resistance compensation, especially the friction compensation in the Bowden cable transmission is a difficult issue to be handled. Aimed to the resistance reduction requirement in the active rehabilitative motion, a resistance compensation control method is proposed. Based on the simplified transmission model, the resistance, including the cable friction as well as the mechanical moment of inertial, is formulated. To realize the compensation, force sensors are used to measure the force exerted by the human fingertip. With the proposed algorithm, the maximum finger-exerted force is reduced to less than one third of before. The experimental result demonstrates the validity of the proposed method.

This paper presents the design and preliminary evaluation of an elastic lower-body exoskeleton (eExo). Human legs behave in a spring-like fashion while running. We selected a design that relied solely on material elasticity to store and release energy during the stance phase of running. The exoskeleton included a novel knee joint with a cam and a Bowden cable transferring energy to and from a waist-mounted extension spring. We used a friction-lock clutch controlled by hip angle via a pneumatic cylinder to release the cable during swing phase for free movement of the leg. The design also incorporated a composite leaf spring to store and release energy in the distal portion of the exoskeleton about the foot and ankle. Preliminary test data for our target subject showed that his typical leg deflection was 0.11 m with leg stiffness of 16 kN/m while running at 3.0 m/s. We used these values to set the desired stiffness (60±15% of the normal leg stiffness, or 9.6±2.4 kN/m) and deflection (0.11 m) of the exoskeleton. We created simplified multi-body and full finite element quasi-static models to achieve the desired system stiffness and validate our results, respectively. The final design model had an overall stiffness of 7.3 kN/m, which was within the desired range. We fabricated a single-leg prototype of the exo–skeleton that weighed 7.1 kg. We tested the exoskeleton stiffness quasi-statically and found a stiffness of 3.6 kN/m. While running, the exoskeleton provided ∼30% of the total leg stiffness for two subjects. Although the stiffness was lower than desired, the fabricated prototype demonstrated the ability of a quasi-passive exoskeleton to provide a significant portion of an individual’s leg stiffness while running.

A Bowden cable performance analysis, based on a Design of Experiments (DoE) is presented for orthosis applications. The need for analysing these cables is based on the construction of IKO (IKerlan's Orthosis) with five actuated degrees of freedom (DoF) to help the human arm. The aim is for an individual to be capable of lifting weight without any great effort using this exoskeleton, which should be portable and readily dressed (and, therefore, lightweight). In order to transmit the power from the actuators to the joints, Bowden cables are used due to their flexibility and light weight. Transmission performance has been analysed in terms of load loss and cable deformation in order to estimate actuator requirements and positioning accuracy. A test bench has been built to measure the cable deformation and load loss occurring between the two ends of the cable in different situations. This has been applied to cables with two different diameters and at different loads. The variables for which the effect has been analysed are weight, the angle formed by the cable at the point where it leaves the sheath, the cable flexion angle, cable length, cable flexion curvature radius and cable type.

It is the goal of this paper to present performance differences between a Direct Drive master actuator (DD) and a Bowden Cable relocated master actuator (BCD) in a typical force-feedback tele-manipulation experiment with a virtual slave. The BCD actuator is a candidate actuator for implementation in a wearable exoskeleton, in order to reduce mass and inertia on each joint of the movable structure. The BCD performance matches the one of the DD in terms of torque and position tracking in a 4 channel control. The maximum rendered contact stiffness is suitable for implementation in the ESA human arm exoskeleton, with a maximum of about 36 Nm/rad. When, instead of the DD, a relocated BCD actuator is implemented in an exoskeletons movable structure, the mechanical output power-density can be increased by more than 5 fold up to 31 mNm/cm3, with comparable performance. The specific power is then increased by more than 6 fold, to 13 Nm/kg. The Bowden Cable transmission wrapping angle alters the free movement friction only marginally by about 50 mNm only. The tracking performances are hardly affected and the contact stiffness increases with increasing wrapping angle. Transmission wrapping angles of up to 270 Deg. are tested.

This paper introduces a novel type of actuator that is investigated by ESA for force-reflection to a wearable exoskeleton. The actuator consists of a DC motor that is relocated from the joint by means of Bowden cable transmissions. The actuator shall support the development of truly ergonomic and compact wearable man-machine interfaces. Important Bowden cable transmission characteristics are discussed, which dictate a specific hardware design for such an actuator. A first prototype is shown, which was used to analyze these basic characteristics of the transmissions and to proof the overall actuation concept. A second, improved prototype is introduced, which is currently used to investigate the achievable performance as a master actuator in a master-slave control with force-feedback. Initial experimental results are presented, which show good actuator performance in a 4 channel control scheme with a slave joint. The actuator features low movement resistance in free motion and can reflect high torques during hard contact situations. High contact stability can be achieved. The actuator seems therefore well suited to be implemented into the ESA exoskeleton for space-robotic telemanipulation.