Assistive Knee Research Articles

Shape synthesis of an assistive knee exoskeleton device to support knee joint and rehabilitate gait

Purpose: The assistive knee exoskeleton device is used for supporting the surrounding ligaments, tendons, and muscles of the injured knee joint. Various knee exoskeletons have been discussed; however, their shape synthesis is not reported. This study aims to present the shape synthesis of the assistive knee device. Moreover, four-bar linkage is used for the knee exoskeleton, in this study.Methods: Clinical biomechanical data are adapted from gait database for one gait cycle. Using the clinical gait data, position and static force analyses are performed to obtain a set of orientations and unknown forces. Simultaneously, CAD models are prepared, and the obtained forces are applied to the CAD models of the four-bar linkage knee exoskeleton. Consequently, the threshold is obtained for each component of the knee exoskeleton and the unwanted material below the threshold is removed.Results: A reduction of 45% in the peak actuating force is observed in comparison with the literature. Besides, a total reduction of 21% in the mass of four-bar knee exoskeleton is observed in contrast to the base models when shape synthesis is performed.Conclusions: An assistive knee exoskeleton is developed using the shape synthesis methodology in which four-bar linkage is used. New shapes of thigh and shank attachments are obtained. The developed knee exoskeleton can be used by persons with the injured knee for supporting the ligaments, tendons, and muscles. Besides, control technology can be implemented to make it useful for persons with monoplegia.Implications for rehabilitationAssistive knee exoskeleton devices proved to be an important tool for providing support to injured knee joints.Typically single axis joints are observed in the lower limb exoskeletons which can be replaced with linkage mechanisms to obtain the desired range of motion.In this study, four-bar linkages are used for the knee exoskeleton in which cranks and rockers are connected to the lateral and medial sides of the knee joint, for connecting shank and thigh attachments. Shape synthesis is performed on the components of four-bar exoskeleton through the evaluated reaction forces. The components are assembled to form an assistive knee exoskeleton which can be used by any person with injured knee joint.

Design and Validation of a Torque-Controllable Knee Exoskeleton for Sit-to-Stand Assistance

Individuals with poststroke hemiparesis often exhibit mobility deficits, particularly during tasks requiring high lower limb torques. The sit-to-stand transition is consistently marked by asymmetrical weight-bearing between the paretic and unaffected legs. One way to improve characteristics of stroke sit-to-stand may be to provide assistive knee extension torque with a powered exoskeleton. To perform research on the biomechanical effects of assisting sit-to-stand, a unilateral powered knee exoskeleton is required, which can accurately control torque. This paper introduces a novel series elastic actuator capable of producing the full torques and speeds required for sit-to-stand (80 Nm, 3 rad/s). It utilizes a unique transmission configuration with a series fiberglass beam spring that improves torque-control and reduces output impedance. The actuator is incorporated into a unilateral orthosis and a high-level sit-to-stand controller is implemented. A small validation study with three able-bodied subjects performing sit-to-stand is presented, demonstrating the ability to appropriately provide assistance.

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.

Design and testing of a regenerative magnetorheological actuator for assistive knee braces

In this paper, a multifunctional magneto-rheological actuator with power regeneration capability, named regenerative magnetorheological actuator (RMRA), is designed for gait assistance in the knee joint. RMRA has motor and magnetorheological (MR) brake parts working in parallel that can harvest energy through regenerative braking. This novel design provides multiple functions with good energy efficiency. The configuration and basic design of the RMRA are first introduced. Then geometrical optimization of the MR brake is conducted based on a parameterized model, and multiple factors are considered in the design objectives: braking torque, weight, and power consumption. After the optimal design is obtained, an RMRA prototype is fabricated and associated driver circuits are designed. Finally, multiple functions of the RMRA, especially three different braking modes, are modeled and tested. Experimental results of RMRA output performances in all working modes match the modeling and simulation. Assistive knee braces with the developed RMRA are promising for future applications in gait assistance and rehabilitation.

Feasibility of rehabilitation using the single-joint hybrid assistive limb to facilitate early recovery following total knee arthroplasty: A pilot study

ABSTRACTWe aimed to evaluate the feasibility of robot-assisted rehabilitation in an early postoperative setting to improve knee mobility following total knee arthroplasty (TKA). A total of 20 patients were alternatively assigned to robotassisted rehabilitation (n = 10; all women) or a control group (n = 10; 2 men and 8 women). The use of a single-joint hybrid assistive limb (HAL-SJ) in active assistive knee exercise was performed for the robot-assisted rehabilitation group while the control patients underwent conventional active assistive knee exercise. We measured the extension lag (defined as the difference between active and passive range of knee extension). We also evaluated the visual analog scale score (VAS) during active movements and active assistive movement. Concerning the extension lag, the robot-assisted rehabilitation group showed 89.4% ± 15.7% improvement (p < 0.01) while the control group showed 34.8% ± 32.1% improvement (p = 0.016). As to the VAS, the robot-assisted rehabilitation group showed 40.7% ± 23.5% improvement while the control group showed 20.4% ± 25.8% improvement (p < 0.01). The use of HAL-SJ may facilitate early recovery from knee surgery and prevent long-term complications such as quadriceps arthrogenic muscle inhibition.

Design and characterization of a torque-controllable actuator for knee assistance during sit-to-stand.

Individuals with post-stroke hemiparesis often have difficulty standing out of a chair. One way to potentially improve sit-to-stand is to provide knee extension assistance using a powered knee exoskeleton. An exoskeleton providing unilateral, partial assistance during sit-to-stand would need to be torque-controllable. There are no knee exoskeletons on the market suitable for conducting experiments assisting stroke patients with sit-to-stand, so to enable such experiments a research device was developed. The purpose of this report is to present the design of a novel knee exoskeleton actuator that uses a fiberglass leaf spring in series to improve torque-controllability, and present a characterization of the actuator performance. The actuator is capable of the required torque and speed for sit-to-stand, has high bandwidth (25 Hz), low output impedance at low frequencies (<;0.5 Nm), and excellent torque tracking. An orthotic brace built upon this actuator will enable an in-depth study on the biomechanical effects of providing stroke subjects with knee extension assistance during sit-to-stand.

Assessing the Relative Contributions of Active Ankle and Knee Assistance to the Walking Mechanics of Transfemoral Amputees Using a Powered Prosthesis.

Powered knee-ankle prostheses are capable of providing net-positive mechanical energy to amputees. Yet, there are limitless ways to deliver this energy throughout the gait cycle. It remains largely unknown how different combinations of active knee and ankle assistance affect the walking mechanics of transfemoral amputees. This study assessed the relative contributions of stance phase knee swing initiation, increasing ankle stiffness and powered plantarflexion as three unilateral transfemoral amputees walked overground at their self-selected walking speed. Five combinations of knee and ankle conditions were evaluated regarding the kinematics and kinetics of the amputated and intact legs using repeated measures analyses of variance. We found eliminating active knee swing initiation or powered plantarflexion was linked to increased compensations of the ipsilateral hip joint during the subsequent swing phase. The elimination of knee swing initiation or powered plantarflexion also led to reduced braking ground reaction forces of the amputated and intact legs, and influenced both sagittal and frontal plane loading of the intact knee joint. Gradually increasing prosthetic ankle stiffness influenced the shape of the prosthetic ankle plantarflexion moment, more closely mirroring the intact ankle moment. Increasing ankle stiffness also corresponded to increased prosthetic ankle power generation (despite a similar maximum stiffness value across conditions) and increased braking ground reaction forces of the amputated leg. These findings further our understanding of how to deliver assistance with powered knee-ankle prostheses and the compensations that occur when specific aspects of assistance are added/removed.

Design and control of an active knee orthosis driven by a rotary Series Elastic Actuator

Active orthosis is one of the main research topics in the field of motor recovery. This paper deals with the design and control of an active knee orthosis driven by a customized rotary Series Elastic Actuator (SEA). The proposed actuator includes a DC motor, a worm gear and a customized torsion spring. Since the elastic element is the most important component in SEA design, a finite element analysis of the spring is performed to meet the specific requirements for knee assistance. Torque and impedance control are implemented to ensure secure interaction with the patient and to enable new strategies for rehabilitation. The torque controller, cascaded with an inner motor velocity control loop, is based on H∞ criterion to achieve good system performance with relation to parametric uncertainties and external disturbances. The impedance control is implemented using a PD position controller in cascade with the torque controller, where the outer position controller determines the desired torque according to position and velocity errors and impedance parameters. A variable impedance control strategy is then implemented to show the possibility to regulate the impedance of the knee joint during walking. Experiments considering the interaction between the subject and the active orthosis are performed to evaluate the proposed controllers.

EPAIA: Design, modelling and control of a novel electro-pneumatic adaptable impedance actuator

In this contribution we present the novel electro-pneumatic adaptable impedance actuator (EPAIA) consisting of a brushless DC-motor and a rotational pneumatic actuator, applied in series to the gear train. The pneumatic actuator is employed as a pneumatic torsional spring with a continuously adaptable stiffness, controlled by air inflow and pressure control. Thus, a rotary variable stiffness actuator is obtained, for which the stiffness can be expressed as a smooth nonlinear function of chamber pressures. The mechanical design furthermore utilises a planetary and a bevel gear reduction, to provide a torque amplification ratio necessary for human assistive knee joint actuation. Besides large and precise torque generation, the actuator provides a smoothly adjustable output impedance, backdrivability and a low cost, yet quality sensitive torque sensor. Following a detailed description of the mechanical design of the actuator, a dynamical model is derived using the Lagrange formalism. We propose a robust H2-torque-controller design procedure for the linearised actuator model, for which a constraint for passivity of the load transfer function is employed. The resulting controller is tested in simulations using the nonlinear validated model.

Impedance Control of a Rotary Series Elastic Actuator for Knee Rehabilitation

This paper deals with impedance control of a rotary Series Elastic Actuator designed to assist in flexion/extension of the knee joint during physical therapy. The device includes a DC motor, a worm gear and a customized torsion spring. Since the elastic element is the most important component in the actuator design, a finite element analysis is used to meet the specific requirements of knee assistance. The proposed impedance control scheme comprises three cascade controllers: an inner-loop PI velocity controller, a PI torque controller, and an outer-loop PD position controller. The impedance controller's performance is evaluated through the Frequency Response Function analysis, and experimental results demonstrate the ability of the system to reproduce impedance behavior within an amplitude and frequency range compatible for gait assistance.

보행 재활 로봇 개발을 위한 1자유도 무릎 관절 설계

One of the important issues for structural and electrical specifications in developing a robot is to determine lengths of links and motor specifications, which need to be appropriate to the purpose of robot. These issues become more critical for a gait rehabilitation robot, since a patient wears the robot. Prior to developing an entire gait rehabilitation robot, designing of a 1DOF assistive knee joint of the robot is considered in this paper. Human gait motions were used to determine an allowable range of knee joint that was rotated with a linear type actuator (ball-screw type) and links. The lengths of each link were determined by using an optimization process, minimizing the stroke of actuator and the total energy (kinetic and potential energy). Kinetic analysis was performed in order to determine maximum rotational speed and maximum torque of the motor for tracking gait trajectory properly. The prototype of 1 DOF assistive knee joint was built and examined with a impedance controller.

Preswing Knee Flexion Assistance Is Coupled With Hip Abduction in People With Stiff-Knee Gait After Stroke

Stiff-knee gait is defined as reduced knee flexion during the swing phase. It is accompanied by frontal plane compensatory movements (eg, circumduction and hip hiking) typically thought to result from reduced toe clearance. As such, we examined if knee flexion assistance before foot-off would reduce exaggerated frontal plane movements in people with stiff-knee gait after stroke. We used a robotic knee orthosis to assist knee flexion torque during the preswing phase in 9 chronic stroke subjects with stiff-knee gait on a treadmill and compared peak knee flexion, hip abduction, and pelvic obliquity angles with 5 nondisabled control subjects. Maximum knee flexion angle significantly increased in both groups, but instead of reducing gait compensations, hip abduction significantly increased during assistance in stroke subjects by 2.5 degrees , whereas no change was observed in nondisabled control subjects. No change in pelvic obliquity was observed in either group. Hip abduction increased when stroke subjects received assistive knee flexion torque at foot-off. These findings are in direct contrast to the traditional belief that pelvic obliquity combined with hip abduction is a compensatory mechanism to facilitate foot clearance during swing. Because no evidence suggested a voluntary mechanism for this behavior, we argue that these results were most likely a reflection of an altered motor template occurring after stroke.

Design, testing and control of a magnetorheological actuator for assistive kneebraces

This paper is aimed at developing a smart actuator for assistive knee braces to provideassistance to disabled or elderly people with mobility problems. A magnetorheological(MR) actuator is developed to be used in assistive knee braces to provide controllabletorque. The MR actuator can work as a brake or a clutch. When active torque is needed,the DC motor works and the MR actuator functions as a clutch to transfer the torquegenerated by the motor to the leg; when passive torque is desired, the DC motor is turnedoff and the MR actuator functions as a brake to provide controllable passive torque. Theprototype of the developed MR actuator is fabricated and experiments are carried out toinvestigate the characteristics of the MR actuator. The results show that the MR actuatoris able to provide sufficient torque needed for normal human activities. Adaptivecontrol is proposed for controlling the MR actuator. Anti-windup strategy is usedto achieve better control performance. Experiments on the MR actuator undercontrol are also performed to study the torque tracking ability of the system.

Active Assistive Knee Exerciser

Active Assistive Knee Exerciser