High Backdrivability Research Articles

Backdrivable and Fully-Portable Pneumatic Back Support Exoskeleton for Lifting Assistance

To reduce the possibility of lower back pain (LBP), which is the most frequent injury in manual labor, several back support exoskeletons have been developed and implemented for lifting motion assistance. Although pneumatic power transmission is attractive due to its inherent compliance and backdrivability, the portability of the pneumatic system is highly limited due to the bulky air compressors that provide compressed air to the system. Therefore, we aimed to develop a fully-portable pneumatic back support exoskeleton by integrating all pneumatic components in the system. The compressed air consumption and generation of pneumatic system were modeled to meet design requirements. The developed exoskeleton was completely stand-alone and provides 80 Nm of maximum extension torque for 6 liftings per minute (6 l/m). The upper limit of the resistance torque was estimated to be about 2 Nm, which implies high backdrivability. Finally, lifting experiments were performed and surface electromyography (sEMG) was measured to validate the physical assistance of the developed exoskeleton system for ten subjects. Compared to the case with no exoskeleton, the back muscle activation was significantly reduced with the assistances.

Design and Control of a High-Torque and Highly Backdrivable Hybrid Soft Exoskeleton for Knee Injury Prevention During Squatting

This letter presents design and control innovations of wearable robots that tackle two barriers to widespread adoption of powered exoskeletons: restriction of human movement and versatile control of wearable co-robot systems. First, the proposed high torque density actuation comprised of our customized high-torque density motors and low ratio transmission mechanism significantly reduces the mass of the robot and produces high backdrivability. Second, we derive a biomechanics model-based control that generates assistive torque profile for versatile control of both squat and stoop lifting assistance. The control algorithm detects lifting postures using compact inertial measurement unit (IMU) sensors to generate an assistive profile that is proportional to the human joint torque produced from our model. Experimental results demonstrate that the robot exhibits low mechanical impedance (1.5 Nm backdrive torque) when it is unpowered and 0.5 Nm backdrive torque with zero-torque tracking control. Root mean square (RMS) error of torque tracking is less than 0.29 Nm (1.21% error of 24 Nm peak torque). Compared with squatting without the exoskeleton, the controller reduces 87.5%, 80% and 75% of the three knee extensor muscles (average peak EMG of 3 healthy subjects) during squat with 50% of human joint torque assistance.

Design and Validation of a Partial-Assist Knee Orthosis with Compact, Backdrivable Actuation.

This paper presents the mechatronic design and initial validation of a partial-assist knee orthosis for individuals with musculoskeletal disorders, e.g., knee osteoarthritis and lower back pain. This orthosis utilizes a quasi-direct drive actuator with a low-ratio transmission (7:1) to greatly reduce the reflected inertia for high backdrivability. To provide meaningful assistance, a custom Brushless DC (BLDC) motor is designed with encapsulated windings to improve the motor's thermal environment and thus its continuous torque output. The 2.69 kg orthosis is constructed from all custom-made components with a high package factor for lighter weight and a more compact size. The combination of compactness, backdrivability, and torque output enables the orthosis to provide partial assistance without obstructing the natural movement of the user. Several benchtop tests verify the actuator's capabilities, and a human subject experiment demonstrates reduced quadriceps muscle activation when assisted during a repetitive lifting and lowering task.

Design and Benchtop Validation of a Powered Knee-Ankle Prosthesis with High-Torque, Low-Impedance Actuators.

This paper describes the design of a powered knee- and-ankle transfemoral prosthetic leg, which implements high torque density actuators with low-reduction transmissions. The low reduction of the transmission coupled with a high-torque and low-speed motor creates an actuator with low mechanical impedance and high backdrivability. This style of actuation presents several possible benefits over modern actuation styles implemented in emerging robotic prosthetic legs. Such benefits include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, and greater potential for power regeneration. Benchtop validation experiments were conducted to verify some of these benefits. Backdrive and free-swinging knee tests confirm that both joints can be backdriven by small torques (~3 Nm). Bandwidth tests reveal that the actuator is capable of achieving frequencies required for walking and running. Lastly, open-loop impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback.

Design and control of a 3-DOF rehabilitation robot for forearm and wrist.

This paper presents a 3-DOF compact rehabilitation robot, involving mechanical structure design, control system design and gravity compensation analysis. The robot can simultaneously provide assistance for pronation/supination(P/S), flexion/extension(F/E) and adduction/abduction(A/A) joints rehabilitation training. The P/S and F/E joints are designed to be driven by cable transmission to gain a high backdrivability, and an adjustment plate is adopted to decrease the distance between the rotation axis of F/E joint of the human wrist and the robot. In addition, gravity compensation is considered to offset the impact of self-gravity on the performance of the controller. A "moving window" control strategy based on impedance control is proposed and implemented on the robot. A comparison between the "moving window" control and classical impedance control indicates that the former has more potential to stimulate the voluntary efforts of the participant, and has a less limitation moving in a fixed reference trajectory. Meanwhile, the results also validate the feasibility and safety of the wrist robot system.

Fundamental characteristic of novel actuation system with variable viscoelastic joints and magneto-rheological clutches for human assistance

In this study, a variable viscoelastic joint system with a clutch for human assistance was proposed. The variable viscoelastic joint system comprised antagonized artificial muscles and magneto-rheological fluid brake. This system enabled the human assisting device, such as exoskeletons, to retain structural softness when compared with the existing devices driven by motor and reduction gear, which could only achieve superficial softness. In addition, a clutch system that provided high back-drivability to the wearer by structurally separating the device from the wearer was proposed. As an initial step in designing the human assisting device, a prototype with the proposed variable viscoelastic joint system for knee assistance is developed. Also, its control method was developed. Furthermore, experiments were conducted to confirm the influence of the proposed viscoelastic joint system and control method on the wearer.

High-speed and high-backdrivable actuation system considering variable-structured elastic design

This paper proposes a high-speed high-backdrivable actuator using a new actuation structure. To realize a small-sized high-torque actuator, a reduction gear is usually used. Because of the current saturation and friction effect of the actuator, the actuator has maximum values of acceleration and rotation speed. A gear with a high gear ratio reduces these two maximum values because of the presence of a reduction mechanism. The trade-off between the output torque and rotation speed exists. Consequently, it is difficult to achieve high-speed motions using a gear. Moreover, the reduction mechanism increases the friction of the motor and deteriorates its backdrivability. Therefore, in this study, a new actuation mechanism is utilized to solve such problems. The new mechanism consists of an electromagnetic clutch and elastic spring. High backdrivability and high-speed motion are achieved by releasing the clutch and transforming the elastic potential energy accumulated by the geared motor into kinetic energy, respectively. In the proposed system, the output rotation speed exceeds the maximum rotation speed obtained after it is reduced by the gear. Finally, the validity of the proposed method is verified experimentally.

可変粘弾性関節を有する膝用アシスト装置の開発と主観評価

Working population decreases because of the aging society. Therefore the workload per person increases. To solve this problem, assist suit is studied activity. This study has proposed a new actuation system with variable viscoelastic joint for an exoskeleton assist suit. This variable viscoelastic joint system is composed of antagonized artificial muscles and magneto-rheological fluid brake (MR-brake). The system enables assist suit to have structural softness and high back-drivability. This paper evaluated back-drivability of the system. So, organoleptic evaluation experiment which compares variable viscoelastic joint system to actuation system with motor and reduction gear was conducted. As a result, high back-drivability of variable viscoelastic joint system was confirmed.

電気静油圧アクチュエータのトルク効率と内部漏れ流量のモデリング

Recently, robots working in cooperation with humans are required. From the viewpoint of safety, it is necessary to perform flexible operation and accurate detection of external force. Electro hydrostatic actuators (EHAs) have mechanisms of high backdrivability. Therefore, by applying reaction force observers (RFOBs) to EHAs, it is possible to obtain force sensitivity and flexibility. Moreover, by considering nonlinear elements in EHAs, it is possible to estimate reaction force more accurately. In addition, experimental results showed an improvement of the reaction force estimation accuracy.

Design and optimization of PARTNER: a parallel actuated robotic trainer for NEuroRehabilitation.

Robotic devices are a promising and dynamic tool in the realm of post-stroke rehabilitation. Researchers are still investigating how the use of robots affects motor learning and what design characteristics best encourage recovery. We present a parallel-actuated, end-effector robot designed to provide spatial assistance for upper-limb therapy while exhibiting low impedance and high backdrivability. A gradient based optimization was performed to find an optimal design that accounted for force isotropy, mechanical advantage, workspace size, and counter-balancing. A beta prototype has been built to these specifications (low impedance and high backdrivability) and has undergone initial controller performance as well as fit and function testing. By fitting a nonlinear model to experimental frequency response data, the apparent mass, viscous friction coefficient, and dynamic dry friction coefficient were determined to be 0.242 kg, 0.114 Ns/m, and 0.894 N respectively. The robot will serve as a testing platform to investigate motor learning and evaluate the efficacy of control schemes for post-stroke movement therapy.

전기식 하지 외골격 로봇의 구동기 에너지 효율 향상을 위한 클러치 메커니즘 설계

This paper reports on the development of a roller-cam clutch mechanism. This mechanism can transfer bidirectional torque with high backdrivability, as well as increase actuation energy efficiency, in electrical exoskeleton robots. The developed mechanism was installed at the robot knee joint and unclutched during the swing phase which uses less metabolic energy, thereby functioning as a passive joint. The roller-cam clutch aimed to increase actuation energy efficiency while also producing high backdrivability by generating zero impedance for users during the swing phase. To develop the mechanism, mathematical modeling of the roller-cam clutch was conducted, with the design having more than three safety factors following optimization. Titanium (Ti-6AL-4V) material was used. Finally, modeling verification was done using ANSYS software.

A Pneumatically Driven Surgical Manipulator With a Flexible Distal Joint Capable of Force Sensing

This paper presents a novel forceps manipulator for surgical robot systems. The forceps manipulator has a highly simplified flexible distal joint, which is actuated by push–pull motions of superelastic wires. Pneumatic cylinders are employed for its driving system to realize high backdrivability of the flexible mechanism, enabling external force estimation without using a force sensor. For the kinematic description, we newly introduce a three-degree-of-freedom (DOF) continuum model considering expansion and contraction of the flexible joint, which allows three-axis force sensing on the forceps tip. We also developed a practical dynamic model, including linear-approximated elastic forces and nonlinear friction forces dependent on the joint bending angle. Effectiveness of the dynamic model is validated by open-loop control performance of the joint angles. The position control system is designed using a PID-based cascade controller with a feedforward compensator based on the dynamic model. Resolution of the joint angle control is 1 $^\circ$ , satisfying the requirement for laparoscopic surgery. An external force estimation algorithm is developed, which realizes the three-axis sensing of translational forces acting on the forceps tip. The rigid-link approximation model is also employed to treat the calculation in singular attitude, the straight position of the flexible joint. Effectiveness of the force estimator is experimentally validated using a force sensor in two cases. Estimation error is 0.37 N at maximum with a force in a radial direction, and the estimation performance using the three-DOF force estimator is much better than the one using a conventional two-DOF force estimator.

An index finger exoskeleton with series elastic actuation for rehabilitation: Design, control and performance characterization

Rehabilitation of the hands is critical for the restoration of independence in activities of daily living for individuals exhibiting disabilities of the upper extremities. There is initial evidence that robotic devices with force-control-based strategies can help in effective rehabilitation of human limbs. However, to the best of our knowledge, none of the existing hand exoskeletons allow for accurate force or torque control. In this work, we present a novel index finger exoskeleton with Bowden-cable-based series elastic actuation allowing for bidirectional torque control of the device with high backdrivability and low reflected inertia. We present exoskeleton and finger joint torque controllers along with an optimization-based offline parameter estimator. Finally, we carry out tests with the developed prototype to characterize its kinematics, dynamics, and controller performance. Results show that the device preserves the characteristics of natural motion of finger and can be controlled to achieve both exoskeleton and finger joint torque control. Finally, dynamic transparency tests show that the device can be controlled to offer minimal resistance to finger motion. Beyond the present application of the device as a hand rehabilitation exoskeleton, it has the potential to be used as a haptic device for teleoperation.

2P1-K07 サーボポンプを用いた油圧閉回路による電気-油圧アクチュエータ間のバイラテラル制御

Bilateral control is a teleoperation system enables to transmit the information about force sense. And, hydraulic actuators of high power weight ratio are often used in ultimate environments. Open loop hydraulic circuits, which are generally used, contains servo valves in the structure. But using servo valves are the cause of the low backdrivability. However, the robot can have high backdrivability using close loop hydraulic circuits with servo pumps. In this research, we use an electric actuator as a master robot and a hydraulic actuator made up of a close loop hydraulic circuit as a slave robot and bilateral control is realized.

2A2-K06 リニアアクチュエータを用いた歩行アシスト装置の開発と歩行シミュレーションによるアシスト効果の検証

This paper proposes a wearable walking assist device using a linear actuator for people who feel that walking is slightly painful in everyday life, and numerical walking simulation is conducted to evaluate the effectiveness of proposed devices, and construct an effective control method. The linear actuator intrinsically owns enough back driverbility because there is no reduction gear. Namely, it is possible to prevent tumble of a people who wears this device even if the device suddenly makes unexpected motion. This is because the people can easily resist against an output force of the actuator due to high backdrivability. A joint torque controller to assist a swing leg which is designed, and a numerical walking simulation is conducted to verify the effectiveness of assistance of the proposed device. From these simulation results, an effective feedback controller in terms of energy consumption is designed.

Robomorphism: A Nonanthropomorphic Wearable Robot

This article describes a novel wearable robot (WR) intended to assist hip and knee flexion/ extension through series elastic actuators (SEAs). A nonanthropomorphic (NA) design was pursued to improve ergonomics while optimizing dynamic properties through a smart distribution of swinging masses. Once the anthropomorphism constraint is relaxed, the number of possible architectures becomes very high, and a methodology must be defined to point out the best options. To this purpose, a design methodology, which includes a novel approach to kinematic synthesis, topology selection, and morphological optimization, is also presented. The advantages offered by the novel architecture are demonstrated both theoretically and experimentally. In particular, the results show a low reflected inertia on the user's body, a high backdrivability, and an intrinsic tolerance to misalignments. Such advantages make the proposed robot a promising platform for the development of assistive and rehabilitation systems.

New Multi-d.o.f. Haptic Device Using a Parallel Mechanism with a Wide Rotational Working Area

A parallel mechanism is a multi-legged kinematic structure with actuators fixed on the base. In recent years, parallel mechanisms have been implemented in haptic devices due to their benefits, such as high rigidity, high output force, high accuracy and high backdrivability. Multi-d.o.f. haptic devices with rotational motion have become increasingly important as haptic applications have become diversified (e.g., in surgical training). However, typical multi-d.o.f. parallel mechanisms (e.g., Stewart platform and HEXA) have limitations on the working area for rotational motions. A multi-d.o.f. haptic device can be designed by stacking the translational and rotational mechanisms by decoupling these motions. However, this dedoupling can have an adverse effect on inertia because of the weight of the stacking mechanism. Eventually, the operability of the device deteriorates. Therefore, a parallel mechanism with both a translational and rotational multi-d.o.f. structure can effectively apply the full advantages of a parallel mechanism to a multi-d.o.f. haptic device. In this paper, a 6-d.o.f. (five active: three translations, two rotations and one passive rotation) parallel mechanism, called the D-8, is presented. In the D-8, a new redundant parallel mechanism is introduced to overcome the problem of operability.

2A2-A07 電気静油圧リンク系の力伝達構造に基づく受動的安定化制御(アクチュエータの機構と制御(2))

To achieve high backdrivability in transmission, it is an effective approach to decouple the dynamics of actuators. Electro-Hydrostatic Actuators (EHA) which is modeled as a decoupled dynamics by damping element can achieve high backdrivability. However, accurate modeling of energy loss and damping in hydraulic transmission is difficult, which requires controllers with robustness to modeling error. In this paper, we derive a model of a manipulator actuated by EHA and propose a passivity-based controller for the EHA driven manipulators. The proposed controller consists of PD control and gravity compensation based on link joint angle and velocity feedback. The whole dynamics is composed of two passive subsystems, link and pump dynamics, and asymptotic stability is given. The efficacy of the proposed controller was evaluated by experiment.

2P1-T03 冗長自由度を有する空気圧駆動鉗子マニピュレータの外力推定に関する研究(手術支援ロボティクス・メカトロニクス(2))

Laparoscopic surgery is an effective method as alternative to open surgery. Robotic manipulators with multi-DOF forceps have been reported. To ensure more intuitive and much safer manipulation, haptic sensation to operators is an indispensable function of the system. The high backdrivability of the pneumatic actuator allows the detection of external forces from pressure data and compliance control of the system without the use of force sensors. We have prototyped a model of surgical robot system, which has high performance in the estimation of external forces. In this paper, we developed a forceps manipulator with pneumatic drive having a rotating mechanism at the tip. The forceps has total 4-DOF including gripper. The redundant movement can be achieved with the 4-DOF supporting manipulator we have developed. Therefore, the forceps can improve the operability and external force estimation since the singular point can be avoided.

A cable-driven locomotor training system for restoration of gait in human SCI

A novel cable-driven robotic locomotor training system was developed to provide compliant assistance/resistance forces to the legs during treadmill training in patients with incomplete spinal cord injury (SCI). Eleven subjects with incomplete SCI were recruited to participate in two experiments to test the feasibility of the robotic gait training system. Specifically, 10 subjects participated in one experimental session to test the characteristics of the robotic gait training system and one subject participated in repeated testing sessions over 8 weeks with the robotic device to test improvements in locomotor function. Limb kinematics were recorded in one experiment to evaluate the system characteristics of the cable-driven locomotor trainer and the overground gait speed and 6min walking distance were evaluated at pre, 4 and 8 weeks post treadmill training of a single subject as well. The results indicated that the cable driven robotic gait training system improved the kinematic performance of the leg during treadmill walking and had no significant impact on the variability of lower leg trajectory, suggesting a high backdrivability of the cable system. In addition, results from a patient with incomplete SCI indicated that prolonged robotic gait training using the cable robot improved overground gait speed. Results from this study suggested that a cable driven robotic gait training system is effective in improving leg kinematic performance, yet allows variability of gait kinematics. Thus, it seems feasible to improve the locomotor function in human SCI using this cable driven robotic system, warranting testing with a larger group of patients.