•·a novel cable configuration method for parallel cable-driven systems is proposed.•·the method is illustrated as feasible through force closure based on screw theory.•·the isomorphic mapping between ...cable tension space and joint space is established.•·the experiments on shoulder rehabilitation exoskeleton prototype are conducted.
Cable-driven exoskeletons play a significant role in poststroke rehabilitation. Since cables can only pull but not push, conventional parallel cable-driven exoskeletons are usually over-actuated, leading to uncertain dynamics. This paper proposes a cable configuration method utilizing the antagonistic cable pair to achieve full-actuation. The antagonistic cable pair is formed by assigning a passive impedance cable corresponding to an active driving cable. This method is illustrated as feasible through force closure analysis based on screw theory, and is implemented in a shoulder rehabilitation exoskeleton. Subsequently, the dynamics model of the exoskeleton is formulated, and the isomorphic mapping between cable tension space and joint space is established. Additionally, the elastic fluctuation absorption mechanism is presented to absorb the length fluctuation produced by the antagonistic cable pair, through the deformation of elastic elements. The continuity of cable tension is evidenced through its finite and smooth partial derivatives. Finally, the experimental results of prototype validate that the fully-actuated parallel cable-driven exoskeleton can be achieved with the proposed method.
Powered exoskeletons for people with complete paraplegia have been controlled based on predefined joint-reference trajectories. As the target users of such robots may not realize any voluntary ...movement, the human body is fully constrained and follows the movement of the powered exoskeleton joints. The predefined gait pattern, however, may or may not be adequate for every user because the gait pattern is resulting from complex interactions between the body segments and environment, as well as dynamic characteristics of the body segments. As all the persons and their body segments have different dynamic characteristics, therefore, a bespoke tuning of gait parameters is necessary in order to realize the natural gait motion, which is optimal for each user. In this article, an adaptive gait pattern adjustment method is proposed. The proposed method observes the ground contact timing, which is directly related to the adequacy of the gait pattern for the user wearing a robot. Based on the ground contact timing, the joint-reference trajectories are adjusted, which are parameterized by the trunk inclination angle. The proposed method iteratively calculates an appropriate trunk inclination angle from the information of ground contact timing. In this article, the derivation of the proposed method and its experimental verification with WalkON Suit, a powered exoskeleton, are introduced. The proposed algorithm successfully worked for two practical users with complete paraplegia, and the adapted gait patterns showed excessive performance in walking speed, oxygen consumption, palm force on crutches, etc. The results were also verified by winning both gold and bronze medals in the global competition, Cybathlon 2020, while accomplishing the best records among all the teams.
We studied the performance of a robotic orthosis designed to assist the paretic hand after stroke. It is wearable and fully user-controlled, serving two possible roles: as a therapeutic tool that ...facilitates device-mediated hand exercises to recover neuromuscular function or as an assistive device for use in everyday activities to aid functional use of the hand. We present the clinical outcomes of a pilot study designed as a feasibility test for these hypotheses. 11 chronic stroke (>2 years) patients with moderate muscle tone (Modified Ashworth Scale ≤2 in upper extremity) engaged in a month-long training protocol using the orthosis. Individuals were evaluated using standardized outcome measures, both with and without orthosis assistance. Fugl-Meyer post intervention scores without robotic assistance showed improvement focused specifically at the distal joints of the upper limb, suggesting the use of the orthosis as a rehabilitative device for the hand. Action Research Arm Test scores post intervention with robotic assistance showed that the device may serve an assistive role in grasping tasks. These results highlight the potential for wearable and user-driven robotic hand orthoses to extend the use and training of the affected upper limb after stroke.
For active AFO applications, pneumatic remote transmission has advantages in minimizing the mass and complexity of the system due to the flexibility in placing pneumatic components and providing high ...back-drivability via simple valve control. However, pneumatic systems are generally tethered to large stationary air compressors, which greatly limit the practical daily usage. In this study, we implemented a wearable custom compressor that can be worn at the trunk of the body and can generate up to 1050 kPa of pressurized air to power an unilateral active AFO for dorsiflexion (DF) assistance of drop-foot patients. In order to minimize the size and weight of the custom compressor, the compression rate of the custom compressor was optimized to the rate of consumption required to power the active AFO. The finalized system can provide a maximum assistive torque of 9.8 Nm at a functional frequency of 1 Hz and the average resistive torque during free movement was 0.03 Nm. The system was tested for five hemiplegic drop-foot patients. The proposed system showed an average improvement of 12.3° of ankle peak dorsiflexion angle during the mid to late swing phase.
Individuals with lower limb amputation have a high fall risk, which could be partially due to a lack of stabilizing control in conventional prostheses. Inspired by walking robots, we hypothesized ...that modulating prosthetic ankle push-off could help improve amputee balance. We developed a three-dimensional walking model, found limit cycles at two speeds, and designed state-feedback controllers that made once-per-step adjustments to ankle push-off work, fore-aft and medial-lateral foot placement, and ankle roll resistance. To assess balance, we applied increasing levels of random changes in ground height and lateral impulses until the model fell down within 100 steps. Although foot placement is known to be important for balance, we found that push-off control was at least twice as effective at recovering from both disturbances at both speeds. Push-off work affected both fore-aft and mediolateral motions, leading to good controllability, and was particularly well suited to recovery from steps up or down. Our results suggest that discrete control of ankle push-off may be more important than previously thought, and may guide the design of robotic prostheses that improve balance.
This paper presents a control approach for an overground lower limb exoskeleton that is intended to provide guidance and assistance to poorly ambulatory individuals during walking without unduly ...interfering with their ability to maintain balance. The control approach achieves these objectives by emulating a viscous flow field acting on the lower limb joints. The extent to which the control approach achieves the objectives was assessed in experiments, conducted on five healthy subjects, comparing guidance and disturbance characteristics of the velocity-based controller to a potential-field-based controller. Results show that the flow controller provides a combination of lower guidance error and lower disturbance to the user, relative to the potential-field-based controller. The paper also discusses various potentially beneficial characteristics of the flow controller, such as first-order homogeneous behavior, implicitly combined guidance and assistance behaviors, and improved directionality in error correction relative to a potential-field-based controller.
The body weight support system has been widely used to reduce the physical and psychological burden of rehabilitation walking training for patients with dyskinesia. However, it is challenging for ...current systems to reduce the weight and dynamic load of the patient simultaneously during high-performance rehabilitation training tasks. This article presents an integrated active and passive body weight support system based on a wire-driven spring-loaded parallelogram mechanism, which provides variable gravity and inertia compensation during treadmill training, depending on the patient's condition. Coupling the elastic preloaded spring with the linkage allows for greater flexibility and stability to achieve balancing conditions. As the core technology of the proposed system, the control strategy consists of three stages, the impedance-based auxiliary force generation, the quasistatic force/position conversion, and the model-based wire tension control. With the proposed controller, the effects of time delay and load inertia on the impedance performance of the system are thoroughly analyzed. The experimental results show that the system can provide effective and stable auxiliary forces with a maximum error of 5.3% and significantly reduce weight and inertia during human walking, with an average unloading error of 7.6% obtained by comparing ground reaction forces.
Highlights • We review current and new orthosis actuators against user centered requirements. • Orthosis actuator requirements must incorporate a variety of user needs. • Orthosis design requires the ...iterative input of engineers, clinicians, and users. • Researchers should develop actuators with the most readily overcome limitations. • Synergistically integrating actuator technologies can improve orthosis actuation.
An instrument for remote control of the robot by wearable brain-computer interface (BCI) is proposed for rehabilitating children with attention-deficit/hyperactivity disorder (ADHD). Augmented ...reality (AR) glasses generate flickering stimuli, and a single-channel electroencephalographic BCI detects the elicited steady-state visual evoked potentials (SSVEPs). This allows benefiting from the SSVEP robustness by leaving available the view of robot movements. Together with the lack of training, a single channel maximizes the device's wearability, fundamental for the acceptance by ADHD children. Effectively controlling the movements of a robot through a new channel enhances rehabilitation engagement and effectiveness. A case study at an accredited rehabilitation center on ten healthy adult subjects highlighted an average accuracy higher than 83%, with information transfer rate (ITR) up to 39 b/min. Preliminary further tests on four ADHD patients between six- and eight-years old provided highly positive feedback on device acceptance and attentional performance.
This article addresses a new way of generating compliant trajectories for control using movement primitives to allow physical human-robot interaction where parallel robots (PRs) are involved. PRs are ...suitable for tasks requiring precision and performance because of their robust behavior. However, two fundamental issues must be resolved to ensure safe operation: first, the force exerted on the human must be controlled and limited, and second, Type II singularities should be avoided to keep complete control of the robot. We offer a unified solution under the dynamic movement primitives (DMP) framework to tackle both tasks simultaneously. DMPs are used to get an abstract representation for movement generation and are involved in broad areas, such as imitation learning and movement recognition. For force control, we design an admittance controller intrinsically defined within the DMP structure, and subsequently, the Type II singularity evasion layer is added to the system. Both the admittance controller and the evader exploit the dynamic behavior of the DMP and its properties related to invariance and temporal coupling, and the whole system is deployed in a real PR meant for knee rehabilitation. The results show the capability of the system to perform safe rehabilitation exercises.
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