Design of a Variable Constraint Hip Mechanism for a Hybrid Neuroprosthesis to Restore Gait After Spinal Cord Injury

A variable constraint hip mechanism (VCHM) has been developed for a hybrid neuroprosthesis system (HNP) to provide postural stability and uninhibited sagittal hip rotation throughout the gait of individuals with paraplegia. This paper describes the design concepts used in the development of the VCHM. The VCHM utilizes a hydraulic system to reciprocally couple the hips or individually lock and/or free a hip to rotate in one or both sagittal directions. Bench testing results show the feasibility of utilizing a portable hydraulic system in controlling hip joint kinematics. The passive resistive torques of the VCHM against user hip rotation at hip angular velocities typical of gait does not exceed 10% of the achievable hip torque generated by functional neuromuscular stimulation of paralyzed muscle. With the state of the VCHM configured to reciprocally couple the hips, the normalized mechanical efficiency of the VCHM was determined to be 0.7. Since each hip will be independently driven by the FNS of muscle, high torque transfer efficiency between the hips is not essential for successful operation of the VCHM. Future work will focus on the development of a sensor-based feedback controller to modulate the hip constraints of the VCHM and validation of the VCHM as part of a HNP for paraplegic individuals implanted with FNS systems.     

Lower extremity angle measurement with accelerometers-error andsensitivity analysis

Closed-loop control techniques for the restoration of locomotion of paraplegic subjects are expected to improve the quality of functional neuromuscular stimulation (FNS). We investigated the use of accelerometers for the assessment of feedback parameters. Previously, the possibility of angle assessment of the lower extremities using accelerometers, but without integration, was demonstrated. The current paper evaluates and assesses this method by an error and sensitivity analysis using healthy subject data. Of three potential error sources, the reference system, the accelerometers, and the model assumptions, the last was found to be the most important. Model calculations based on data obtained by the Elite video motion analysis system showed the rigid-body assumption error to be dominant for high frequencies (greater than 10 Hz), with vibrations in the order of 1 mm resulting in errors of one radial or more. For low frequencies (less than 5 Hz), the imperfect fixation of the accelerometers combined with a nonhinge type knee joint gave an error contribution of +/- 0.03 rad. The walking pattern was assumed to be two-dimensional which was shown to result in an error of +/- 0.04 rad. Accelerations due to rotations of the segments could be neglected. The total error computed for low frequencies (+/- 0.07 rad) was comparable to the experimental difference between the current and the reference system.     

Control of end-point forces of a multijoint limb by functionalneuromuscular stimulation

A multivariable feedback controller was designed and tested for regulating the magnitude and orientation of the force vector at the end point of a multijoint limb in contact with an isometric load. The force vector was produced by electrical stimulation of muscles. To achieve arbitrary control of end-point force magnitude and orientation, two coupling issues must be dealt with by the control system. First, there is a geometric coupling between the end-point force vector and joint torques. The amplitude and orientation of the force vector depend on the limb geometry. Second, torques at two joints may be coupled due to activation of muscles that cross them (biarticular coupling). To eliminate the geometric coupling, a transformation of controller error from the Cartesian space to the joint space was employed. A multivariable proportional-plus-integral (PI) control law was used to calculate muscle activation based on the transformed controller error. Centralized and decentralized controls were investigated for decoupling the effects of biarticular muscles. The results obtained from cat experiments showed that the magnitude and orientation of the end-point forces of the cat hindlimb could be regulated by this controller. In the presence of strong biarticular coupling, centralized control yielded better performance than decentralized control during transient responses. Both control strategies could decouple the biarticular muscle at steady state. When no biarticular coupling was present, centralized control sometimes performed worse than decentralized control. This is the first step in the simultaneous control of multiple joints by functional neuromuscular stimulation (FNS). The controller has broad potential applications in FNS neural prostheses.     

Neural network control of functional neuromuscular stimulationsystems: computer simulation studies

A neural network control system has been designed for the control of cyclic movements in functional neuromuscular stimulation (FNS) systems. The design directly addresses three major problems in FNS control systems: customization of control system parameters for a particular individual, adaptation during operation to account for changes in the musculoskeletal system, and attaining resistance to mechanical disturbances. The control system was implemented by a two-stage neural network that utilizes a combination of adaptive feedforward and feedback control techniques. A new learning algorithm was developed to provide rapid customization and adaptation. The control system was evaluated in a series of studies on a computer simulated musculoskeletal model. The model of electrically stimulated muscle used in the study included nonlinear recruitment, linear dynamics, and multiplicative nonlinear torque-angle and torque-velocity scaling factors. The skeletal model consisted of a one-segment planar system with passive constraints on joint movement. Results of the evaluation have demonstrated that the control system can provide automated customization of the feedforward controller parameters for a given musculoskeletal system. It can account for changes in the musculoskeletal system by adapting the feedforward controller parameters on-line and it can resist the effects of mechanical disturbances. These results suggest that this design may be suitable for the control of FNS systems and other dynamic systems     

Precise Tip Positioning of a Flexible Manipulator Using Resonant Control

A single-link flexible manipulator is fabricated to represent a typical flexible robotic arm. This flexible manipulator is modeled as an SIMO system with the motor torque as the input and the hub angle and the tip position as the outputs. The two transfer functions are identified using a frequency-domain system identification method, and the resonant modes are determined. A feedback loop around the hub angle response with a resonant controller is designed to damp the resonant modes. A high-gain integral controller is also implemented to achieve zero steady-state error in the tip position response. Experiments are performed to demonstrate the effectiveness of the proposed control scheme.     

Open-loop control of the freely-swinging paralyzed leg

An experimental model has been used to study issues that are relevant to the use of electrical stimulation to help paralyzed individuals walk. Modulated stimulation sequences for the quadriceps muscles were manually selected using an iterative trial-and-error procedure to cause the knee angle to follow a specific movement pattern (desired trajectory). Four paraplegic subjects were tested before and after an eight-week program in which the quadriceps were exercised daily with electrical stimulation. It was found that 12.6 +/- 2.9 iterations were required to approximate the desired trajectory. The average error of the final match between the actual and desired trajectories was 2.1 degrees +/- 0.7. Repeated responses were extremely consistent; the average difference between successive trials was less than 1 degree in 81 percent of the trials. When the stimulation sequence was repeated every 3 s for 50 cycles, however, there was a progressive degradation in the response, even in exercised legs, that demonstrated the limitations of open-loop control. Stimulus modulation envelopes for all four subjects were similar in shape (although varied in amplitude) indicating that the iterative process can be shortened by starting with an "average" modulation envelope. Stimulation sequences achieved accurate matches of the desired trajectory on subsequent days when adjusted by a simple gain factor. The relevance of these results to multichannel control of walking is discussed.     

Robust tracking servo system considering force disturbance for the optical disk recording system

This paper proposes a new robust tracking servo system for the optical disk recording system with feedforward controller based on the prediction of the tracking error. In optical recording systems, the feedback servo system must suppress the influence of force disturbance and parameter variation. To overcome this problem, this paper designs the robust feedback control system by using coprime factorization and disturbance observer. The detecting signal of the optical disk recording system is only a tracking error. Hence, the feedforward controller of the proposed tracking control system is constructed based on both the "zero-phase-error tracking" control theory and the prediction of the tracking error. The experimental results point out that the proposed tracking servo system has a quick and precise tracking response and keeps the residual tracking error below its tolerance.     

Design and test of a novel closed-loop system that exploits the nociceptive withdrawal reflex for swing-phase support of the hemiparetic gait

A novel closed-loop system for improving gait in hemiparetic patients by supporting the production of the swing phase using electrical stimulations evoking the nociceptive withdrawal reflex was designed. The system exploits the modular organization of the nociceptive withdrawal reflex and its stimulation site- and gait-phase modulation in order to evoke movements of the hip, knee, and ankle joints during the swing phase. A modified model-reference adaptive controller (MRAC) was designed to select the best stimulation parameters from a set of 12 combinations of four electrode locations on the sole of the foot and three different stimulation onset times between heel-off and toe-off. It was hypothesized that the MRAC system would result in a better walking pattern compared with an open-loop preprogrammed fixed pattern of stimulation (FPS) controller. Thirteen chronic or subacute hemiparetic subjects participated in a study to compare the performance of the two control schemes. Both control schemes resulted in a more functional gait compared to no stimulation (P < 0.05) with a weighted joint angle peak change of 4.0 ± 1.6 (mean ± Standard deviation) degrees and 3.1 ± 1.4 degrees for the MRAC and FPS schemes, respectively. This indicates that the MRAC scheme performed better than the FPS scheme (P < 0.001) in terms of reaching the control target.     

A Computer-Controlled Multichannel Stimulation System for Laboratory Use in Functional Neuromuscular Stimulation

Laboratory instrumentation systems for developing functional neuromuscular stimulation (FNS) orthoses must be flexible in command processing and in multichannel stimulus control and coordination. For research and development of new FNS systems to control the musculoskeletal function of disabled individuals, we have developed a computer-controlled multichannel stimulation system. This system both processes patient generated input commands delivered from a variety of sources, and coordinates the multichannel stimulation to achieve the desired movement. The flexibility provided by this system has proven to be of great value in both upper and lower extremity FNS.     

压电微动平台的极点配置PID控制

为提高压电微动平台的位移输出精度,设计极点配置比例、积分、微分(PID)控制器对其进行控制。首先,在对压电执行器进行电学特性、机电特性分析的基础上,建立了压电执行器的数学模型;其次,在对平台进行受力分析、运动分析的基础上,建立了平台的动力学模型;然后,在保持平台极点虚部不变,且将系统闭环阻尼比取为1的情况下,将平台极点沿着平行于实轴的方向平移,设计出平台的PID反馈控制器;最后,实验验证了所设计控制器的有效性。实验结果表明,所设计的控制器可使平台具有较快的响应,在不考虑传感器噪声水平的情况下,平台在控制系统作用下的定位误差基本为0。     

Elbow extension in the C5 quadriplegic using functionalneuromuscular stimulation

A system has been designed to provide overhead reach in C5/6 quadriplegic subjects using functional neuromuscular stimulation (FNS) for control of the triceps muscle. The system uses the position of the arm in space as the input command, relieving the user from having to supply a conscious command signal. By measuring the position of the arm, the magnitude of the gravitational and passive torques opposing elbow extension can be calculated. This torque is counteracted by electrical activation of the triceps muscle, with the appropriate stimulus parameters determined from the recruitment characteristics of each electrode. Sufficient stimulus is applied to produce full elbow extension. Intermediate elbow angles are achieved using voluntary elbow flexor torque to counteract the effects of the stimulation. System performance was tested in two subjects. Subjects were asked to reach targets with and without stimulation, with loads up to 500 g in the hand. Using the FNS system, subjects were able to successfully reach the target positions above the horizontal that were inaccessible without stimulation.     

Stimulation Pattern-Free Control of FES Cycling: Simulation Study

The aim of this paper is to investigate control strategies for functional electrical simulation (FES) cycling, with particular focus on the generation of stimulation intensities for multiple muscles, without any predetermined stimulation pattern. The control system is developed by imitating the biological neuronal control system. Specifically, the control signal on the level of joint torque (quasi-joint torque) is generated from the feedback information of lower extremities. The quasi-joint torque is then distributed to each muscle and the muscle delay is compensated, and finally, the stimulation intensity is determined. Parameters of the control system are optimized by the genetic algorithm with cost function of energy consumption and cadence error. The proposed control system is evaluated by computer simulation. The controller generates efficient stimulation even during the muscle fatigue process and successfully continues cycling without any predetermined stimulation pattern. Moreover, the controller is robust to the parameter error in the muscle delay compensator and also to the disturbances. It is expected that the proposed method would improve the FES cycling performance and relieve patients by eliminating the experimental determination of the stimulation patterns.     

Feedback regulation of hand grasp opening and contact force duringstimulation of paralyzed muscle

A fixed-parameter, discrete-time, first-order, feedback control system is described for regulating grasp during electrical stimulation of paralyzed muscles of the hand. The stiffness of the grasp (relationship between grasp force and grasp opening) is kept constant by linearly combining force and position feedback signals. Thus, a single continuous command signal can control the size of the grasp opening prior to object acquisition and both grasp force and opening after contact. The controller achieves this change in controlled variables by scaling and summing the force and position feedback signals, rather than by a discrete switch in control strategy. Experimental tests of the control system in quadriplegic subjects show that control can be obtained over conditions ranging from unloaded position regulation to isometric force regulation, as well as in the transition between these conditions. The robustness of the control system was evaluated during force regulation with isometric loads. Step response rise time and overshoot were much more dependent on system gain than on the location of the controller zero. Responses with rise time less than two seconds and overshoot less than 30% were obtained over a gain range up to ten, indicating good robustness to muscle gain reductions such as might be caused by fatigue.     

Evaluation of shoulder movement as a command control source

The purpose of this study was to evaluate the use of scapular shoulder movement as a command control source. The focus of this study was on the evaluation of movement signals from quadriplegic subjects as well as on the processing of these signals for use as command inputs to a functional neuromuscular stimulation (FNS) hand-grasp system. The shoulder movement of three C5-level quadriplegic and nine normal subjects was studied using externally mounted two-degree-of-freedom transducers overlying the sternum and clavicles. The C5-level quadriplegic subjects tested had a considerably poorer range of motion than the normal subjects. The range of motion was greatest in elevation but was coupled with a significant component of retraction. The vertical command resolution of the quadriplegic subjects ranged from eight to 13 command levels, whereas the horizontal range contained four or fewer command levels. Normal subjects were able to produce 26 to 79 command levels along the vertical axis and 18 to 85 along the horizontal axis. Subjects were able to maintain a static command level to within several percent of their range in trials lasting from 10 to 30 s. The quadriplegic subjects performed poorly in tasks where they were required to move to a point along the horizontal or vertical central axis and then along the opposite axis. The normal subjects were readily able to perform these tasks. The interference with the command signal due to movement of the opposite extremity was significant, with a maximum error ranging between 25 and 86% along the vertical axis and between 38 and 105% along the horizontal axis. Rise time and normalized velocity (velocity divided by the size of the movement) were found to be suitable for distinguishing different types of shoulder movements independent of the size of the movement. Shoulder movement in quadriplegics is suitable as a command control source for a FNS hand-grasp system requiring one proportional command signal and at least one logical command signal with appropriate processing of the signals. The available transducers are cosmetically acceptable and are easy to don and doff. Use of shoulder movement as a command control source does not interfere with other activities of the user such as eating or talking. Shoulder movement also provides a command control source that is easy for the user to learn and provides some feedback to the user through shoulder proprioception.     

位置和艏向角约束的非对角欠驱动USV轨迹跟踪

仅配备有纵向推进力和转船力矩装置的无人水面艇是典型的欠驱动系统,不能通过定常光滑反馈控制律镇定到平衡状态。本文针对一类惯性矩阵和阻尼矩阵非对角的欠驱动无人水面艇,设计了基于附加控制器和反步法的光滑时变跟踪控制律,在保证跟踪误差暂态性能的前提下,实现了曲线和直线情形下的轨迹跟踪。首先,通过状态变换将非对角模型转化为对角形式,并运用反馈线性化理论简化控制输入。其次,通过设计虚拟控制函数来镇定误差运动学方程,并通过引入障碍Lyapunov函数(BLF)来保证跟踪误差满足规定的性能。然后,通过在误差镇定函数中引入虚拟控制量解决了系统的欠驱动问题,稳定性分析表明本文控制策略能够保证闭环系统中的所有状态是一致最终有界的。最后,Matlab/Simulink仿真结果表明了该控制器的有效性。     

Design and analysis of an optimal controller for parallel multi-inverter systems

Optimal control methodology is applied to the design of the feedback loops of a multi-inverter uninterruptible power supplies system. The control signals thus obtained will minimize a performance index, which is a function of the output voltage error, the inductor currents of all inverters and the reference signals. This enables the controller to achieve the desired objectives like minimization of the circulating current and reduction of error of the output voltage. The robustness of the controller has also been investigated. Through frequency-domain analysis, it is shown that variations in the number of paralleled inverters in the system have only small influence on the performance of the system. Therefore, the optimal controller designed for a fixed number of inverters can also work well in systems with variable number of paralleled inverters. Three experimental 110 Vac/1.1 KVA inverters are built and paralleled to verify the analysis and theoretical predictions.     

A flexible, portable system for neuromuscular stimulation in the paralyzed upper extremity

A portable functional neuromuscular stimulation (FNS) system for control of the muscles of the paralyzed upper extremity has been developed and evaluated for outpatient use. The system, which has been tested over a five-year period, incorporates an 8-bit CMOS microprocessor which can be programmed to accept and process a variety of user-generated commands and to output complex stimulus patterns. Eight channels of analog input can be used to control four channels of constant-current-compensation monophasic stimulus output. The portable FNS system is programmed using a multichannel laboratory stimulation system.<>     

A voltage control strategy for current-regulated PWM inverters

Alternative voltage control strategies for current-regulated PWM inverters are analyzed, including previously established feedforward and feedforward/feedback controllers and a newly proposed decoupling feedback control strategy. The steady-state and dynamic characteristics of each of these control methods are illustrated and compared for a selected inverter design. It is shown that the feedforward controller exhibits steady-state error and an undesirable overshoot of the output voltages during startup. The addition of a feedback loop eliminates the steady-state error and reduces the overshoot; however, the natural response is underdamped regardless of the choice of feedback gains. A decoupling feedback control strategy that eliminates the disadvantages of the feedforward and feedforward/feedback controllers is described. Using the decoupling feedback controller, it is possible to eliminate the steady-state error and place the closed-loop poles wherever desired. Moreover, if the closed-loop poles are selected appropriately, it is possible to eliminate the overshoot of the output voltages during startup transients     

基于线性状态反馈方法的Nadolschi混沌系统同步

研究了一类新型混沌系统——Nadolschi系统的同步控制问题。首先为响应系统设计一个多变量线性状态反馈控制器,进而将Nadolschi系统的同步控制问题转化为误差系统零平衡点的镇定问题。然后,根据Lyapunov稳定性理论,得出使Nadolschi混沌系统达到渐近同步的充分条件。仿真结果验证了所提方法的有效性,所设计的控制器具用结构简单,易于实现等优点。     

Neural-network-based adaptive control for induction servomotordrive system

A neural-network-based adaptive control (NNAC) design method is proposed to control an induction servomotor. In this NNAC design, a neural network (NN) controller is investigated to mimic a feedback linearization control law; and a compensation controller is designed to compensate for the approximation error between the feedback linearization control law and the NN controller. The interconnection weights of the NN can be online tuned in the sense of the Lyapunov stability theorem; thus, the stability of the control system can be guaranteed. Additionally, in this NNAC system design, an error estimation mechanism is investigated to estimate the bound of approximation error so that the chattering phenomenon of the control effort can be reduced. Simulation and experimental results show that the proposed NNAC servomotor control systems can achieve favorable tracking and robust performance with regard to parameter variations and external load disturbances