Improvement in Arteral Oxygen Control Using Multiple-Model Adaptive Control Procedures

A computer-based proportional-integral (PI) controller has been developed to control arterial oxygen levels in mechanically ventilated animals. Arterial oxygen saturation is monitored using a noninvasive oximeter and control is effected by adjusting the inspired oxygen fraction. The performance of the feedback system is sensitive to the open-loop gain so that the desired transient specifications can be achieved only by empirical adjustments of the PI controller. Because the open-loop gain includes the animal's response, it may vary with time and with the administration of positive end-expiratory pressure. Multiple-model adaptive control procedures were therefore used to desensitize the system to these variable gains. Computer simulations demonstrated the effectiveness of the algorithm over a wide variation of plant parameters. A comparison to a fixed, well-tuned proportional-integral controller showed an improvement in the regulatory response to a step disturbance. Animal experiments confirmed the feasibility of using multiple-model adaptive control to regulate arterial oxygen saturation.     

Task-based methods for evaluating electrically stimulatedantagonist muscle controllers

Single-joint motor neural prosthesis control algorithms were tested in a novel animal model. The model consisted of a human subject who provided joystick inputs to a controller. The controller output determined the stimulus activation levels of two antagonist muscles which manipulated the ankle joint of an intact, anesthetized cat. Using visual feedback, the subject manipulated the system to perform positioning tasks which simulated normal activity of an intact limb. Three controllers were evaluated, open-loop reciprocal control, P-D closed-loop reciprocal control, and open-loop cocontraction control. The results demonstrated that in the presence of visual feedback, open-loop cocontraction control compared favorably in performance to a P-D closed loop controller. This has a practical value for the implementation of clinical neural prostheses since it suggests that in some cases, feedback transducers may not be required for fine control.     

Robust output regulation of a class of smart actuators described by a minimum phase LPV dynamics

This paper presents a new control strategy for a class of minimum phase linear parameter-varying (LPV) systems representative of smart material actuators. In position control applications of such devices, one is typically interested in achieving output regulation with an arbitrary exponential decay rate. In principle, this problem can be tackled by assigning an exponential decay rate to the full system state, by means of well-established linear matrix inequalities (LMI) methods. For the class of systems under investigation, however, this approach leads to excessively large controller gains in case the desired decay rate is faster than the open-loop zero dynamics. In addition, the existence of unmeasurable state variables related to the material microstructure makes it not possible to directly implement full state feedback laws which are commonly adopted in LPV theory. To overcome these issues, a new design strategy is proposed. The key idea relies on arbitrarily shaping the output exponential decay rate without requiring fast convergence of the full state vector. This goal is achieved by means of a partial state feedback control law which solely depends on the measurable system states. A LMI algorithm is also developed to systematically address the design of the partial state feedback controller. The method is validated by means of simulations on generic examples, as well as via experiments on a mechatronic positioning system based on a dielectric elastomer membrane. In case the desired output convergence speed is faster than the open-loop zero dynamics, it is shown that the new approach leads to better transient behaviors and significantly smaller controller gains than standard LPV design techniques.     

Application of combined optimum control and estimation theory to direct digital control

This paper demonstrates methods for applying combined optimum control and estimation theory to serial systems with time delay. The case of serial linear systems with time delay is considered in detail; a result analogous to the separation theorem of linear systems is presented. Illustrative examples of serial chemical reactors, rolling mills, and second-order plus dead-time approximations of higher order systems are discussed. Numerical results for a second-order plus dead-time system are presented: these results are compared with a suboptimal feedback controller (modified Smith predictor) and the open-loop response. It is shown that, in this case, the optimum estimation and control gains may be approximated by constants which further simplify the DDC algorithm. In the second-order plus dead-time approximation to higher order overdamped systems, the optimum algorithm can be reduced to recursive estimation with constant gain and linear state variable feed forward control. This algorithm may be used as a direct replacement for digital controllers used in the process industries.     

Robust closed-loop control of isometric muscle force usingpulsewidth modulation

The design of feedback controllers to accurately and robustly regulate the properties of electrically stimulated muscle is considered. Reliable, precise control is necessary for the development of neuroprosthetic devices to improve gradation and repeatability of force. A digital closed-loop controller has been developed which regulates muscle force by modulating the pulsewidth of a constant-amplitude electrical simulation pulse train. This controller has been evaluated in slow- and fast-twitch muscles (cat soleus and plantaris) in acute experiments. In isometric tests, it was found to regulate muscle force with low sensitivity to modeling errors and disturbances while satisfying stability, repeatability, linearity, and step/ramp response criteria over a wide range of commands     

Sliding mode closed-loop control of FES: controlling the shank movement

Functional electrical stimulation (FES) enables restoration of movement in individuals with spinal cord injury. FES-based devices use electric current pulses to stimulate and excite the intact peripheral nerves. They produce muscle contractions, generate joint torques, and thus, joint movements. Since the underlying neuromuscular-skeletal system is highly nonlinear and time-varying, feedback control is necessary for accurate control of the generated movement. However, classical feedback/closed-loop control algorithms have so far failed to provide satisfactory performance and were not able to guarantee stability of the closed-loop system. Because of this, only open-loop controlled FES devices are in clinical use in spite of their limitations. The purpose of the reported research was to design a novel closed-loop FES controller that achieves good tracking performance and guarantees closed-loop stability. Such a controller was designed based on a mathematical neuromuscular-skeletal model and is founded on a sliding mode control theory. The controller was used to control shank movement and was tested in computer simulations as well as in actual experiments on healthy and spinal cord injured subjects. It demonstrated good robustness, stability, and tracking performance properties.     

Locally optimal-digital redesign of continuous-time systems

The authors present a novel optimal digital redesign technique for finding a dynamic digital control law from the given continuous-time counterpart by minimizing a local quadratic performance index. The quadratic performance index is chosen as the integral of the weighted squared difference between the states of the original closed-loop system and those of the digitally controlled open-loop system at any instant between each sampling period. The developed optimal digital redesign control law enables the states of the digitally controlled open-loop system to match closely those of the original closed-loop system at any instant between each sampling period, and it can easily be implemented using microcomputers with a relatively large sampling period. An illustrative example is presented to demonstrated the effectiveness of the proposed method     

Control of ionic polymer metal composites

Robotic devices are traditionally actuated by hydraulic systems or electric motors. However, with the desire to make robotic systems more compact and versatile, new actuator technologies are required. In this paper, the control of ionic polymer metal composite actuators is investigated from a practical perspective. The actuator characteristics are examined through the unblocked maximum displacement and blocked force output. An open-loop position control and closed-loop position proportional-integral-derivative (PID) control are then applied to a strip of actuators. Finally, the performance of the polymer is investigated when implementing an impedance controller (force/position control).     

Design, fabrication, and real-time neural network control of athree-degrees-of-freedom nanopositioner

A nanometric precision three-degrees-of-freedom positioner is designed and fabricated. Actuation is based on piezoelectric stacks. Capacitive gap sensors with less than 1.0-nm resolution are used for position feedback. In order to design a proper closed-loop controller, the open-loop characteristics of the nanopositioner (static stiffness, hysteresis, drift, frequency response, and the coupling effects) are experimentally investigated. A cerebellar model articulation controller neural network control algorithm was applied in order to provide real-time learning and better tracking capability compared to a standard proportional-integral-derivative control algorithm     

Model Predictive Control of Si1−xGex Thin Film Chemical–Vapor Deposition

This paper integrates in situ robust and efficient fundamental models and noninvasive optical sensors with state-of-the-art estimation and model predictive control techniques in order to grow unusual and aggressive Si_1-xGe_x alloy films. A model predictive controller is presented that utilizes a dynamic process model and feedback from a spectral ellipsometer to reconstruct the current state of a Si_1-xGe_x growing film in real time. Si _1-xGe_x films grown utilizing feedback from a spectral ellipsometer are compared to films grown using open-loop recipes, which is the current industrial practice. These films are compared quantitatively utilizing the offline characterization techniques, auger spectrometry, and secondary-ion-mass-spectrometry analysis. The model predictive controller presented in this paper detects and rejects unmeasured disturbances allowing for precise control over film qualities. In this paper, films grown utilizing feedback from an optical sensor are shown to be up to 51% truer to desired profiles, when compared with similar films grown using open-loop recipes. The experimental results presented in this paper provide the first demonstration of feedback control using online optical film measurements to grow aggressive alloy composition profiles in which flow rates of several component gases and reactor temperatures must be varied simultaneously in order to achieve the profile of interest     

Feedback control of coronal plane hip angle in paraplegic subjectsusing functional neuromuscular stimulation

This paper reports on an investigation of feedback control of coronal plane posture in paraplegic subjects who stand using functional neuromuscular stimulation (FNS). A feedback control system directed at regulating coronal plane hip angle in neutral position was designed, implemented, and evaluated in two paraplegic subjects. The control system included sensor mounting and signal processing techniques, a two-stage feedback controller, stimulation hardware, and a set of percutaneous intramuscular electrodes. The feedback controller consisted of two-stages in cascade: a modified discrete-time proportional-integral-derivative (PID) stage and a nonlinear single-input, multiple-output stage to determine the stimulation to be sent to several muscles. The focus of this work was on evaluating the performance of the feedback controller by comparing the response of the feedback-controlled system to that of an open-loop stimulation system. In an evaluation based on temporal response characteristics the controlled system exhibited a 41% reduction in root-mean-squared (rms) error (where error is defined as the deviation from the desired angle), a 52% reduction in steady-state error, and a 22% reduction in hip compliance. In addition, the feedback-controlled system exhibited significant reductions in variability of these measures on several days. These results demonstrate the ability of the feedback controller to improve the temporal response characteristics of the FNS control system.     

Sensitivity reduction in feedback eigenvalue controller design

The problem of reducing sensitivity to variations of the open-loop system parameters is considered for the case where the objective is to design a feedback controller which drives the open-loop eigenvalues to desired positions. The results are based on the assumption that the open-loop multivariable system is transformed to a phase-variable canonical form prior to the application of the control design procedure.     

Digital control of three-phase PWM inverter with LC filter

A digital control algorithm for the three-phase sinusoidal voltage inverter with an output LC filter has been developed. To take the transient of the LC filter during the discretization time into consideration, a fourth-order matrix state equation of the current and the voltage on the d-q frame is discretized. Precise discrete equations for the inverter are introduced. Using these equations, a deadbeat controller consisting of a d-g current minor loop and a d-q voltage major loop, with precise decoupling of the d-q components, was developed. The voltage major loop controller assures the sinusoidal output voltage and stabilizes the system. A deadbeat controller is used because both the current minor loop and the voltage major loop can used one sampling response. The validity of these techniques is confirmed by simulation studies. This method is expected to be useful for direct digital control of large-capacity sinusoidal voltage inverters using low-switching-frequency devices     

Stepper motors: application and selection

A common denominator of most sophisticated manufacturing equipment is a positioning system. A part or workpiece must be brought into a predefined location envelope so that operations may be performed upon it. Since much of this type of manufacturing equipment is computer-controlled, flexible positioning systems are necessary to derive all of the advantages that the computer can provide. Flexibility can be achieved via closed-or open-loop motor-driven systems?each offering distinct advantages. But whereas stepper motors are optional in the former instance, for an open-loop system, a digital driving device such as a stepper motor must be used to maintain control.     

Mechatronic design and injection speed control of an ultra high-speed plastic injection molding machine

This paper presents pragmatic techniques for mechatronic design and injection speed control of an ultra high-speed plastic injection molding machine. Practical rules are proposed to select specifications of key mechatronic components in the hydraulic servo system, in order to efficiently construct an industry-level machine. With reasonable assumptions, a mathematical model of the injection speed control system is established and open-loop experimental data are then employed to validate the system model. By the model, a gain-scheduling PI controller and a fuzzy PI controller are presented, compared and then implemented into a digital signal processor (DSP) using standard C programming techniques. Experimental results are conducted to show that the two proposed controllers are capable of achieving satisfactory speed tracking performance. These developed techniques may provide useful references for engineers and practitioners attempting to design pragmatic, low-cost but high-performance ultra high-injection speed controllers.     

基于IMAC的高精度扫描架控制器设计

扫描架是天线测试系统的重要组成设备,扫描架控制器是其控制中枢。论述了硬件组成及伺服控制原理,采用高性能的IMAC(Integrated Multi-Axis Controller)运动控制器作为核心控制单元,可兼容多种伺服驱动器,通过触摸屏实时显示各轴参数并可手动控制。设计了PLC程序、界面程序、软件接口,分别实现了数字量开关的响应、触摸屏控制和远程控制。描述了到位脉冲、位置掉电保存等主要功能,为证明该控制器的控制精度,将其用于某天线测试系统,实测发现定位精度小于0.05mm,实现了扫描架的高精度控制。     

D类音频功率放大器的研究与实现

介绍了采用D类放大器来完成音频信号变换与放大的电路设计。D类放大器采用了改进的方案,即用FPGA作为逻辑控制器实现对PWM H全桥功率放大电路的控制。设计的D类放大器可对数字音源输出的音频信号进行直接放大,为数字音源和功率放大的整合提供了完整的解决方案。他具有比其他类型放大器更高的效率和更低的转换失真,正越来越多地应用在便携式器件中,因此设计课题具有很好的现实意义。     

An Optimal Control Method for Buck ConvertersUsing a Practical Capacitor ChargeBalance Technique

A novel control method is presented in this paper which utilizes the concept of capacitor charge balance to achieve optimal dynamic response for Buck converters undergoing a rapid load change. The proposed charge balance method is implemented with analog components and is cheaper and more effective than its digital counterparts since complex arithmetic and sampling delay is eliminated. The proposed controller will consistently cause the Buck converter to recover from an arbitrary load transient with the smallest possible voltage deviation in the shortest possible settling time. Since the controller is nonlinear during transient conditions, it is not limited by bandwidth/switching frequency. Unlike conventional linear controllers, the dynamic response (voltage deviation, settling time) of the proposed controller can be estimated using a set of equations. This greatly simplifies the design process of the output filter. Simulation and experimental results show the functionality of the controller and demonstrate the superior dynamic response over that of a conventional linear controller.      

Digital system for 1/f fluctuation-speed control of asmall-fan motor

To produce a comfortable breeze similar to a natural one, a digital open-loop control system was utilized to control the speed of a small fan motor with 1/f fluctuation. The system was modeled as a first-order lag element with a time constant of 1.1 s. The output was controlled by commands and produced 1/f fluctuations, even though it was an open-loop system when the holding time of the data for 1/f fluctuation was set at more than 2 s     

Sampled-data modeling and digital control of resonant converters

A sampled-data model to describe the dynamics of large signals and of small perturbations away from a cyclic steady state is developed. Associated transfer functions are obtained. The application of the model is illustrated by correlating the analysis with simulation results obtained for a series resonant DC/DC power converter. A discrete-time microprocessor-based controller, designed using the aforementioned dynamic model, has been built and tested using a simulation for a series-resonant DC/DC converter set up on the Massachusetts Institute of Technology Parity Simulator. The control methods implemented are state feedback and periodic output feedback, each designed to achieve a specified set of closed-loop poles. The controller has been implemented using the Parity Simulator generalized controller. Results of the closed-loop response showed an improvement over the open-loop response. In addition, the effect of the microprocessor computation delay on the closed-loop dynamics of the converter is investigated