Prashant K. Jamwal

An Adaptive Wearable Parallel Robot for the Treatment of Ankle Injuries

This paper presents the development of a novel adaptive wearable ankle robot for the treatments of ankle sprain through physical rehabilitation. The ankle robot has a bioinspired design, devised after a careful study of the improvement opportunities in the existing ankle robots. Robot design is adaptable to subjects of varying physiological abilities and age groups. Ankle robot employs lightweight but powerful pneumatic muscle actuators (PMA) which mimics skeletal muscles in actuation. To address nonlinear characteristics of PMA, a fuzzy-based disturbance observer (FBDO) has been developed. Another instance of an adaptive fuzzy logic controller based on Mamdani inference has been developed and appended with the FBDO to compensate for the transient nature of the PMA. With the proposed control scheme, it is possible to simultaneously control four parallel actuators of the ankle robot and achieve three rotational degrees of freedom. To evaluate the robot design, the disturbance observer, and the adaptive fuzzy logic controller, experiments were performed. The ankle robot was used by a neurologically intact subject. The robot-human interaction was kept as active-passive while the robot was operated on predefined trajectories commonly adopted by the therapists. Trajectory tracking results are reported in the presence of an unpredicted human user intervention, use of compliant and nonlinear actuators, and parallel kinematic structure of the ankle robot.

Adaptive Impedance Control of a Robotic Orthosis for Gait Rehabilitation

Intervention of robotic devices in the field of physical gait therapy can help in providing repetitive, systematic, and economically viable training sessions. Interactive or assist-as-needed (AAN) gait training encourages patient voluntary participation in the robotic gait training process which may aid in rapid motor function recovery. In this paper, a lightweight robotic gait training orthosis with two actuated and four passive degrees of freedom (DOFs) is proposed. The actuated DOFs were powered by pneumatic muscle actuators. An AAN gait training paradigm based on adaptive impedance control was developed to provide interactive robotic gait training. The proposed adaptive impedance control scheme adapts the robotic assistance according to the disability level and voluntary participation of human subjects. The robotic orthosis was operated in two gait training modes, namely, inactive mode and active mode, to evaluate the performance of the proposed control scheme. The adaptive impedance control scheme was evaluated on ten neurologically intact subjects. The experimental results demonstrate that an increase in voluntary participation of human subjects resulted in a decrease of the robotic assistance and vice versa. Further clinical evaluations with neurologically impaired subjects are required to establish the therapeutic efficacy of the adaptive-impedance-control-based AAN gait training strategy.

An iterative fuzzy controller for pneumatic muscle driven rehabilitation robot

Pneumatic muscle actuators (PMA) show great potential in wearable and compliant rehabilitation devices as they are flexible and lightweight. However, the varying and non-linear behavior of the actuators imposes modeling and control challenges, which are difficult to comprehend. This research proposes a new wearable ankle rehabilitation robot, first of its kind in the world driven by PMAs in a parallel form. The focus of this presented work is to develop an iterative controller to overcome the challenges for PMA driven devices. A fuzzy feedforward controller is proposed to accurately predict the behavior of PMA. A modified Genetic Algorithm (GA) is developed to identify the optimal set of parameters for the fuzzy controller. The iterative controller has been tested on the proposed PMA driven ankle rehabilitation robot, and is found capable of mapping the complex relationship in length, force and pressure of the PMA with high accuracy. Experimental results show excellent trajectory tracking performance of the controller when given various desired trajectories.

Kinematic design optimization of a parallel ankle rehabilitation robot using modified genetic algorithm

Rehabilitation robotics is an evolving area of active research and recently novel mechanisms have been proposed to reinstate complex human movements. Parallel robots are of particular interest to researchers since they are rigid and can provide enough load capacity for human joint movements. This paper proposes a soft parallel robot (SPR) for ankle joint rehabilitation. Kinematic workspace analysis is carried out and the singularity criterion of the SPRs Jacobian matrix is used to define the feasible workspace. A global conditioning number (GCN) is defined using the Jacobian matrix as a performance index for the evaluation of the robot design. An optimization problem is formulated to minimize the GCN using modified genetic algorithm (GA). Results from simple GA and modified GA are compared and discussed. As a result of the optimization, an optimal robot design is obtained which has a near unity GCN with almost uniform distribution in the entire feasible workspace of the robot.

Robust Nonlinear Control of an Intrinsically Compliant Robotic Gait Training Orthosis

Robot-assisted gait therapy is an emerging rehabilitation practice. This paper presents new experimental results with an intrinsically compliant robotic gait training orthosis and a trajectory tracking controller. The intrinsically compliant robotic orthosis has six degrees of freedom. Sagittal plane hip and knee joints were powered by the actuation of pneumatic muscle actuators in opposing pair configuration. The orthosis has passive hip abduction/adduction joint and passive mechanisms to allow vertical and lateral translations of the trunk. A passive foot lifter having a spring mechanism was used to ensure sufficient dorsiflexion during swing phase. A trajectory tracking controller based on a chattering-free robust variable structure control law was implemented in joint space to guide the subjects limbs on physiological gait trajectories. The performance of the robotic orthosis was evaluated during two gait training modes, namely, “trajectory tracking mode with maximum compliance” and “trajectory tracking mode with minimum compliance.” The experimental evaluations were carried out with ten neurologically intact subjects. The results show that the robotic orthosis is able to perform the gait training task during the two gait training modes. All the subjects tend to deviate from the reference joint angle trajectories with an increase in robotic compliance as the subjects have more freedom to voluntarily drive the robotic orthosis.

An intrinsically compliant robotic orthosis for treadmill training

A new intrinsically compliant robotic orthosis powered by pneumatic muscle actuators (PMA) was developed for treadmill training of neurologically impaired subjects. The robotic orthosis has hip and knee sagittal plane rotations actuated by antagonistic configuration of PMA. The orthosis has passive mechanisms to allow vertical and lateral translations of the trunk and a passive hip abduction/adduction joint. A foot lifter having a passive spring mechanism was used to ensure sufficient foot clearance during swing phase. A trajectory tracking controller was implemented to evaluate the performance of the robotic orthosis on a healthy subject. The results show that the robotic orthosis is able to perform the treadmill training task by providing sufficient torques to achieve physiological gait patterns and a realistic stepping experience. The orthosis is a new addition to the rapidly advancing field of robotic orthoses for treadmill training.

Control of a robotic orthosis for gait rehabilitation

Robot assisted gait training may help in producing rapid improvements in functional gait parameters. This paper presents new experimental results with an intrinsically compliant robotic gait training orthosis. The newly developed robotic orthosis has 6 degrees of freedom (DOFs). A trajectory tracking controller based on the boundary layer augmented sliding control (BASMC) law was implemented to guide the subjects limbs on physiological gait trajectories. The compliance of the robotic orthosis sagittal plane hip and knee joints was also controlled, independently of the trajectory tracking control. The robotic orthosis and the control scheme were evaluated on three neurologically intact subjects walking on a treadmill. A maximum trajectory tracking error of 10^o was recorded at the hip and knee sagittal plane joints. The results showed that subjects can walk in the robotic orthosis with comfort and the BASMC law was able to guide the subjects limbs on reference physiological trajectories.

Effect of Cadence Regulation on Muscle Activation Patterns During Robot-Assisted Gait: A Dynamic Simulation Study

Cadence or stride frequency is an important parameter being controlled in gait training of neurologically impaired subjects. The aim of this study was to examine the effects of cadence variation on muscle activation patterns during robot-assisted unimpaired gait using dynamic simulations. A 2-D musculoskeletal model of human gait was developed considering eight major muscle groups along with an existing ground contact force model. A 2-D model of a robotic orthosis was also developed that provides actuation to the hip, knee, and ankle joints in the sagittal plane to guide subjects limbs on reference trajectories. A custom inverse dynamics algorithm was used along with a quadratic minimization algorithm to obtain a feasible set of muscle activation patterns. Predicted patterns of muscle activations during slow, natural, and fast cadence were compared and the mean muscle activations were found to be increasing with an increase in cadence. The proposed dynamic simulation provides important insight into the muscle activation variations with change in cadence during robot-assisted gait and provides the basis for investigating the influence of cadence regulation on neuromuscular parameters of interest during robot-assisted gait.

Three-Stage Design Analysis and Multicriteria Optimization of a Parallel Ankle Rehabilitation Robot Using Genetic Algorithm

This paper describes the design analysis and optimization of a novel 3-degrees of freedom (DOF) wearable parallel robot developed for ankle rehabilitation treatments. To address the challenges arising from the use of a parallel mechanism, flexible actuators, and the constraints imposed by the ankle rehabilitation treatment, a complete robot design analysis is performed. Three design stages of the robot, namely, kinematic design, actuation design, and structural design are identified and investigated, and, in the process, six important performance objectives are identified which are vital to achieve design goals. Initially, the optimization is performed by considering only a single objective. Further analysis revealed that some of these objectives are conflicting, and hence these are required to be simultaneously optimized. To investigate a further improvement in the optimal values of design objectives, a preference-based approach and evolutionary-algorithm-based nondominated sorting algorithm (NSGA II) are adapted to the present design optimization problem. Results from NSGA II are compared with the results obtained from the single objective optimization and preference-based optimization approaches. It is found that NSGA II is able to provide better design solutions and is adequate to optimize all of the objective functions concurrently. Finally, a fuzzy-based ranking method has been devised and implemented in order to select the final design solution from the set of nondominated solutions obtained through NSGA II. The proposed design analysis of parallel robots together with the multiobjective optimization and subsequent fuzzy-based ranking can be generalized with modest efforts for the development of all of the classes of parallel robots.

Impedance Control of an Intrinsically Compliant Parallel Ankle Rehabilitation Robot

Robot-aided physical therapy should encourage subjects voluntary participation to achieve rapid motor function recovery. In order to enhance subjects cooperation during training sessions, the robot should allow deviation in the prescribed path depending on the subjects modified limb motions subsequent to the disability. In the present work, an interactive training paradigm based on the impedance control was developed for a lightweight intrinsically compliant parallel ankle rehabilitation robot. The parallel ankle robot is powered by pneumatic muscle actuators (PMAs). The proposed training paradigm allows the patients to modify the robot imposed motions according to their own level of disability. The parallel robot was operated in four training modes namely position control, zero-impedance control, nonzero-impedance control with high compliance, and nonzero-impedance control with low compliance to evaluate the performance of proposed control scheme. The impedance control scheme was evaluated on 10 neurologically intact subjects. The experimental results show that an increase in robotic compliance encouraged subjects to participate more actively in the training process. This work advances the current state of the art in the compliant actuation of parallel ankle rehabilitation robots in the context of interactive training.