Data-driven control design for neuroprotheses: a virtual reference feedback tuning (VRFT) approach

This paper deals with design of feedback controllers for knee joint movement of paraplegics using functional electrical stimulation (FES) of the paralyzed quadriceps muscle group. The controller design approach, virtual reference feedback tuning (VRFT), is directly based on open loop measured data and fits the controller in such a way that the closed-loop meets a model reference objective. The use of this strategy, avoiding the modeling step, significantly reduces the time required for controller design and considerably simplifies the rehabilitation protocols. Linear and nonlinear controllers have been designed and experimentally tested, preliminarily on a healthy subject and finally on a paraplegic patient. Linear controller is effective when applied on small range of knee joint angle. The design of a nonlinear controller allows better performances. It is also shown that the control design is effective in tracking assigned knee angle trajectories and rejecting disturbances

Preparation of NiO catalyst on FeCrAI substrate using various techniques at higher oxidation process

The cheap nickel oxide (NiO) is a potential catalyst candidate to replace the expensive available platinum group metals (PGM). However, the current methods to adhere the NiO powder on the metallic substrates are complicated. Therefore, this work explored the development of nickel oxide using nickel (Ni) on FeCrAl substrate through the combination of nickel electroplating and oxidation process for catalytic converter application. The approach was started with assessment of various nickel electroplating process based on the weight gain during oxidation. Then, the next experiment used the best process in which the pre-treatment using the solution of SiC and/or Al2O3 in methanol. The specimens then were carried out to short term oxidation process using thermo gravimetric analysis (TGA) at 1000 o C. Meanwhile, the long term oxidation process was conducted using an automatic furnace at 900, 1000 and 1100 o C. The atomic force microscopy (AFM) was used for surface analysis in nanometer range scale. Meanwhile, roughness test was used for roughness measurement analysis in micrometer range scale. The scanning electron microscope (SEM) attached with energy dispersive X-ray (EDX) were used for surface and cross section morphology analysis. The specimen of FeCrAl treated using ultrasonic prior to nickel electroplating showed the lowest weight gain during oxidation. The surface area of specimens increased after ultrasonic treatment. The electroplating process improved the high temperature oxidation resistance. In short term oxidation process indicated that the ultrasonic with SiC provided the lower parabolic rate constant (kp) and the Al2O3 and NiO layers were also occurred. The Ni layer was totally disappeared and converted to NiO layer on FeCrAl surface after long term oxidation process. From this work, the ultrasonic treatment prior to nickel electroplating was the best method to adhere NiO on FeCrAl substrate

Online identification and nonlinear control of the electrically stimulated quadriceps muscle

A new approach for estimating nonlinear models of the electrically stimulated quadriceps muscle group under nonisometric conditions is investigated. The model can be used for designing controlled neuro-prostheses. In order to identify the muscle dynamics (stimulation pulsewidth-active knee moment relation) from discrete-time angle measurements only, a hybrid model structure is postulated for the shank-quadriceps dynamics. The model consists of a relatively well known time-invariant passive component and an uncertain time-variant active component. Rigid body dynamics, described by the Equation of Motion (EoM), and passive joint properties form the time-invariant part. The actuator, i.e. the electrically stimulated muscle group, represents the uncertain time-varying section. A recursive algorithm is outlined for identifying online the stimulated quadriceps muscle group. The algorithm requires EoM and passive joint characteristics to be known a priori. The muscle dynamics represent the product of a continuous-time nonlinear activation dynamics and a nonlinear static contraction function described by a Normalised Radial Basis Function (NRBF) network which has knee-joint angle and angular velocity as input arguments. An Extended Kalman Filter (EKF) approach is chosen to estimate muscle dynamics parameters and to obtain full state estimates of the shank-quadriceps dynamics simultaneously. The latter is important for implementing state feedback controllers. A nonlinear state feedback controller using the backstepping method is explicitly designed whereas the model was identified a priori using the developed identification procedure

Genetic Algorithms Based Approach for Designing Spring Brake Orthosis – Part Ii: Control of FES Induced Movement

Spring brake orthotic swing phase for paraplegic gait is initiated through releasing the brake on the knee mounted with a torsion spring. The stored potential energy in the spring, gained from the previous swing phase, is solely responsible for swing phase knee flexion. Hence the later part of the SBO operation, functional electrical stimulation (FES) assisted extension movement of the knee has to serve an additional purpose of restoring the spring potential energy on the fly. While control of FES induced movement as such is often a challenging task, a torsion spring, being antagonistically paired up with the muscle actuator, as in spring brake orthosis (SBO), only adds to the challenge. Two new schemes are proposed for the control of FES induced knee extension movement in SBO assisted swing phase. Even though the control schemes are closed-loop in nature, special attention is paid to accommodate the natural dynamics of the mechanical combination being controlled (the leg segment) as a major role playing feature. The schemes are thus found to be immune from some drawbacks associated with both closed-loop tracking as well as open-loop control of FES induced movement. A leg model including the FES knee joint model of the knee extensor muscle vasti along with the passive properties is used in the simulation. The optimized parameters for the SBO spring are obtained from the earlier part of this work. Genetic algorithm (GA) and multi-objective GA (MOGA) are used to optimize the parameters associated with the control schemes with minimum fatigue as one of the control objectives. The control schemes are evaluated in terms of three criteria based on their ability to cope with muscle fatigue

Nonlinear robust control of functional electrical stimulation system for paraplegia

The study was directed towards enhancing Functional Electrical Stimulation (FES) for sit-to-stand movement restoration in paraplegia subjects. The scarcity of FES assistive devices was due to the inability of the developed equipment to attain clinical acceptance. Applications of control systems have shown fruitful results. And based on the literature, further improvements in model, trajectory and control systems are needed. Model with a higher level of accuracy and continuous as well as bump-free trajectories are essential ingredients for better control systems. The control systems can be enhanced by giving considering to changes in mass of the subject, disturbance rejection and stability. Hence, the comprehensive control scheme is necessary for this application as well as a better model and trajectory. In modelling an additional joint has been considered to improve the accuracy. In trajectory planning, the six-order polynomial has been used to refine the desired trajectory. The comprehensive control systems have been designed with consideration of robustness, disturbance rejection, and stability. Three nonlinear control approaches have been investigated; the Sliding Mode Control (SMC), Feedback Linearisation Control (FLC), and Back-Stepping Control (BSC). Results reveal improvements in the accuracy of the kinematic model by 24%, and the dynamic model by 47%. The trajectory planning parameters are continuous, and not susceptible to jerks or spikes. Execution time enhanced by 11%, the upper and lower terminal velocities improved by 16.9% and 20.9% respectively. The system response without disturbance shows good results with the SMC, FLC, and BSC. Revelations by robustness examination also maintain remarkable enhancements in the parameters with both 53% and 126% mass. The results for disturbance rejection examinations with fatigue, spasm, tremor, and combined disturbance effects showed sustenance of refinement in the response parameters. Therefore, indicating improvements despite the changes to the system. The BSC showed the best performance, followed by the FLC, and the SMC. Hence, the BSC is recommended for such systems

Design of a gain scheduling controller for knee-joint angle control by using functional electrical stimulation

A gain scheduling approach to the feedback control of the knee-joint movement in paraplegic patients, who have recovered partial functionality of muscles through functional electrical stimulation (FES), is studied. Since it was not possible to perform stimulation sessions on the patient during the work development, collected experimental data have been used to tune a known physiological model of the musculo-skeletal system involved FES, which is here adopted as a "virtual patient," i.e., as the system to control. So, a nonlinear black box model is developed, by using I/O data set obtained from the physiological model simulator. With reference to such a black box model a nonlinear gain scheduling controller is designed, by using the knee-joint position as a scheduling variable and by properly interpolating different linear quadratic regulators. It is proven that the linearization property holds for the proposed controller. Furthermore, the performance of such a controller are analyzed through closed-loop simulations, where the physiological model simulator is used to represent the knee-joint dynamics. The proposed controller shows good tracking and robustness properties on the full range of extension of the knee joint angle and simulation show that the presented strategy could perform better than any proposed linear approach to this problem