Hybrid charge control for stick-slip piezoelectric actuators

The article describes an analog electronic circuit for driving stick-slip piezoelectric linear actuators. The task for the amplifier is to provide a high-voltage asymmetric sawtooth-like signal and feed it into a capacitive load. Generation of excessive heat must be avoided while maximizing the slew rate. In order to guarantee a steady translation, the hysteretic behaviour of the piezoelectric material must be compensated. Combination of a charge control scheme with switching is proposed as an efficient solution. Laboratory experiments confirm the superiority of this tailored solution over other existing techniques based on versatile linear voltage amplifiers.     

Tracking position control of piezoelectric actuators for periodic reference inputs

The hysteresis characteristic is one of the major setbacks in precise tracking position control of piezoelectric actuators. In this paper, a position control method for a piezoelectric actuator is presented. The controller is based on PID control method augmented with feedback linearization loop. The feedback linearization loop uses a plant model drawn from the Maxwell slip model. The control strategy is then further extended to include a repetitive control algorithm for tracking periodic inputs. Experiments were performed on a 2-axis linear positioner driven by piezoelectric actuators. The experimental results show that the tracking performance is noticeably improved by augmenting a PID controller with both feedback linearization loop and a repetitive controller.     

Passivity-based fractional-order integral sliding-mode control design for uncertain fractional-order nonlinear systems

This paper concerns with the problem of designing a passivity-based fractional-order (FO) integral sliding mode controller for uncertain FO nonlinear systems. Utilizing the FO calculus, it is showed that the state trajectories of the closed-loop system reach the FO switching manifold in finite time. The control law ensures the asymptotical stability on the sliding surface. A parameter adjustment scheme for FO integral sliding surface is proposed by using the linear matrix inequality (LMI) approach. The proposed controller can be applied to different systems such as chaotic systems. Finally, simulation results are provided to show the effectiveness of the proposed method controlling chaos in FO Chua circuit and FO Van-der-Pol oscillator.     

Vibration reduction of resonant structures using charge controlled piezoelectric actuators

A new charge controller design for piezoelectric transducers attached to highly resonant flexible beams is presented that significantly dampens the structure and naturally reduces the negative effects of hysteresis. Experimental results demonstrating the effectiveness of this technique are included.     

Optimal integral force feedback and structured PI tracking control: Application for objective lens positioner

This paper describes a new vibration damping technique based on Integral Force Feedback (IFF). Classical IFF utilizes a force sensor and integral controller to damp the resonance modes of a mechanical system. However, the maximum modal damping depends on the frequency difference between the system’s poles and zeros. If the frequency difference is small, the achievable modal damping may be severely limited. The proposed technique allows an arbitrary damping ratio to be achieved by introducing an additional feed-through term to the control system. This results in an extra degree of freedom that allows the position of the zeros to be modified and the maximum modal damping to be increased. The second contribution of this paper is a structured PI tracking controller that is parameterized to cancel the additional pole introduced by integral force feedback. The parameterized controller has only one tuning parameter and does not suffer from reduced phase margin. The proposed techniques are demonstrated on a piezoelectric objective lens positioner. The results show exceptional tracking and damping performance while maintaining insensitivity to changes in resonance frequency. The maximum bandwidth achievable with a commercial PID controller is 26.1 Hz. In contrast, with the proposed damping and tracking controller, the bandwidth is increased to 255 Hz.     

Design and performance test of a two-axis fast steering mirror driven by piezoelectric actuators

A novel design of a two-axis fast steering mirror (FSM) with piezoelectric actuators is proposed for incoherent laser beam combination. The mechanical performance of the FSM is tested. The results show that the tilting range of the mirror is about 4 mrad, and the 1st-order resonance frequency is about 250 Hz. A self-designed grating encoder is taken as the sensor, which ensures the optimal precision of 10 μrad. The novel mechanical design can meet the requirement of engineering in incoherent laser beam combination.     

Resonance frequency tracking control for piezoelectric transformerDC-DC converter

A control strategy for piezoelectric transformer DC-DC converters based on a phase and frequency detector circuit is presented. The control always tracks transformer resonance frequency, independently of differences between devices of the same type and temperature variation. Voltage regulation is achieved by adopting the pulse width modulation technique. A prototype confirmed the expected results     

UPS inverter design using discrete-time sliding-mode control scheme

This paper presents a novel discrete-time sliding-mode control algorithm for an uninterruptible power supply (UPS) inverter design. The approach offers a dual-loop design, in which a current predictor utilizes the tracking error of output voltage to estimate the desired inductor current, while a current controller is adopted to regulate the inductor current and, thus, produces a control command to the pulsewidth modulation inverter. An explicit condition for stable controller design is derived. The efficacy of this scheme is validated via a successful implementation on a digital-signal-processor-based UPS inverter. The proposed scheme has shown its robustness on low output voltage distortion, excellent voltage regulation, and it is insensitive to load variation, even under nonlinear loads. Experimental studies were performed to further validate the effectiveness of this scheme     

A clustering-based color model and integral images for fast object tracking

The paper presents a clustering-based color model and develops a fast algorithm for object tracking. The color model is built upon K-means clustering, by which the color space of the object can be partitioned adaptively and the histogram bins can be determined accordingly. In addition, in each bin the multi-channel gray level is modelled as Gaussian distribution. Defined in this way the color model can describe accurately the color distribution with very little bins. To evaluate similarity between the reference model and the candidate model, a similarity measure based on Bhattacharrya distance is introduced and its simplified form is derived under assumption that in each bin distribution of gray level in different channel is independent of each other. Motivated by the paper of Viola and Jones, the Integral Images for computation of histogram, mean and variance are proposed, with which the similarity measure can be evaluated at negligible computational cost. Thus, exhaustive search is made efficiently for object localization which guarantees the global maximum be achieved. Comparisons with the well-known mean shift algorithm demonstrate that the proposed algorithm has better performance while having the same (or less) computational cost.     

Improving the linearity of piezoelectric ceramic actuators

It is shown that the linearity of a piezoelectric ceramic actuator may be greatly improved if the applied electric charge, rather than the applied voltage, is varied to control the extension. Hysteresis is virtually eliminated.     

Micropositioning device using impact force of piezoelectric flying wires

In this paper, a micropositioning device for precision positioning of miniaturized parts is proposed. This device uses piezoelectric flying wires to generate impact forces for actuating a target object to be positioned. The proposed device features two main characteristics: the impact force can actuate a half-tightened object with a high degree of precision, and the thin flying wire is suitable for the actuation of miniaturized object. Fundamental properties of the proposed device were examined experimentally and theoretically based on a basic positioning unit. Furthermore, for the practical application in assembly works, the control system for a three degrees-of-freedom micropositioning device with positioning range of (/spl plusmn/250 /spl mu/m, /spl plusmn/250 /spl mu/m, /spl plusmn/30 mrad) along the X-, Y-, and /spl Theta//sub z/-axes was implemented. The target object (16/spl times/24/spl times/6 mm) was successfully positioned with positioning accuracies of (/spl plusmn/1 /spl mu/m, /spl plusmn/1 /spl mu/m, /spl plusmn/0.2 mrad), based on a derived heuristic control model.     

基于扩展滑膜控制器的PMSM无速度传感器研究

本文设计了一种基于永磁同步电机（PMSM）直接转矩控制（DTC）的扩展滑膜观测器,通过测量定子电压与电流,获得电机的转速和转子位置。MATLAB仿真结果表明,扩展的滑膜观测器在空间矢量电压直接转矩控制（SVPWM-DTC）中,所得转速更接近实际转速。     

Adaptive integral robust control of hydraulic systems with asymptotic tracking

In this paper, an adaptive integral robust controller is developed for high accuracy motion tracking control of a double-rod hydraulic actuator. We take unknown constant parameters including the load and hydraulic parameters, and lumped unmodeled disturbances in inertia load dynamics and pressure dynamics into consideration. A discontinuous projection-based adaptive control law is constructed to handle parametric uncertainties, and an integral of the sign of the extended error based robust feedback term to attenuate unmodeled disturbances. Moreover, the present controller does not require a priori knowledge on the bounds of the lumped disturbances and the gain of the designed robust control law can be tuned itself. The major feature of the proposed full state controller is that it can theoretically guarantee global asymptotic tracking performance with a continuous control input, in the presence of various parametric uncertainties and unmodeled disturbances such as unmodeled dynamics as well as external disturbances via Lyapunov analysis. Comparative experimental results are obtained for motion control of a double-rod hydraulic actuator and verify the high-performance nature of the proposed control strategy.     

Novel models for one-sided hysteresis of piezoelectric actuators

The hysteretic behavior of a plant with a non-negative input, referred to as one-sided hysteresis, is characterized by an initial ascending curve and hysteresis loops. It is observed that the widely-used classical Preisach hysteresis model and its modifications cannot represent such one-sided hysteresis due to the limitation of the Preisach hysteresis operator. To address this issue, a novel hysteresis operator modified from the Preisach hysteresis operator is proposed in this study and on this basis, a rate-independent hysteresis model and a rate-dependent hysteresis model are developed with methods to estimate their parameters. An algorithm to invert the rate-independent hysteresis model and its application to tracking control are also presented. The models and control schemes developed were verified experimentally on a commercially-available piezoelectric actuator. The results obtained show that the models developed are promising to represent the one-sided hysteresis of the piezoelectric actuator and that the inverting algorithm of the rate-independent hysteresis model is effective as applied to the tracking control of piezoelectric actuators.     

Robust adaptive sliding-mode control using fuzzy modeling for aninverted-pendulum system

In this paper, a new robust adaptive control architecture is proposed for operation of an inverted-pendulum mechanical system. The architecture employs a fuzzy system to adaptively compensate for the plant nonlinearities and forces the inverted pendulum to track a prescribed reference model. When matching with the model occurs, the pendulum will be stabilized at an upright position and the cart should return to its zero position. The control scheme has a sliding control input to compensate for the modeling errors of the fuzzy system. The gain of the sliding input is automatically adjusted to a necessary level to ensure the stability of the overall system. Global asymptotic stability of the algorithm is established via Lyapunov's stability theorem. Experiments on an inverted-pendulum system are given to show the effectiveness of the proposed control structure     

Current distribution control design for paralleled DC/DC converters using sliding-mode control

This paper shows the analysis and design of a parallel-connected converter system using sliding mode control techniques. The design is particularised for a system that consists of N boost converters and a current feedback loop based on a proportional-integral compensator of the output voltage error. The paper emphasises the advantages of the sliding-mode control over the classic design method based on small-signal models, thus providing an effective and robust means of controlling nonlinear multi-input converters. The design is based on the Utkin conditions, which permit us to know the regions under which a sliding mode exists. This fact allows us to design the compensator and to introduce some modifications in the control loop that avoids input-current overshoots during the system startup. Simple design expressions are obtained and verified with simulation and experimental results, thus showing the improvements achieved with the proposed modifications.     

Position control of hybrid pneumatic–electric actuators using discrete-valued model-predictive control

The design, modeling and position control of a novel hybrid pneumatic–electric actuator for applications in robotics and automation is presented. The design incorporates a pneumatic cylinder and DC motor connected in parallel. By avoiding the need for a high ratio transmission, the design greatly reduces the mechanical impedance that can make collisions with conventionally actuated robot arms dangerous. A novel discrete-valued model-predictive control (DVMPC) algorithm is proposed for controlling the position of the pneumatic cylinder with inexpensive on/off solenoid valves. A variant of inverse dynamics control is proposed for the DC motor. A prototype was built for validating the actuator design and control algorithms. It is used to rotate a single-link robot arm. The actuator inertia and static friction torque values for the prototype were only 0.6% and 4%, respectively, of the values found for a comparable actuator from an industrial robot. Simulation results for position control of pneumatic actuators with different valve speeds and friction coefficients show that the DVMPC algorithm outperforms a sliding mode control algorithm in terms of position error and expected valve life. Experimental results are presented for vertical rotary cycloidal trajectories. Even with the poor quantization caused by the on/off valves, the pneumatic cylinder controlled by the proposed DVMPC algorithm achieved a 0.7% root mean square error (RMSE) and a 0.25% steady-state error (SSE). With the addition of the DC motor to form the hybrid actuator, the RMSE and SSE were reduced to 0.12% and 0.04%, respectively. By incorporating a novel estimation algorithm, the system was made robust to an unknown payload.     

Flexure control using piezostack actuators: design and implementation

In this paper, the application of high control authority piezostack actuators (PSAs) for active vibration control of large-scale flexible structures is studied. The idea is to add PSAs at appropriate locations of a flexible structure in order to strengthen its stiffness characteristics. In this regard, a flexible link of a macro-micro manipulator system actuated with PSAs is considered. The design of a mechanism for converting the force produced by a PSA to a bending moment is presented and a model for a system consisting of a flexible beam and a PSA is obtained. To this end, the solution of the governing partial differential equation with nonhomogeneous boundary conditions is obtained. Using singular value decomposition of the controllability Grammian of the system, optimum values for actuator parameters are obtained. The experimental results confirm that the suggested method can open up new possibilities in active vibration control of large-scale structures that require a large amount of control authority.     

A new algorithm for discrete-time sliding-mode control using fastoutput sampling feedback

This paper presents a new approach for sliding-mode control (SMC) of discrete-time systems using the reaching law approach together with the fast output sampling (FOS) feedback technique. This method does not need the system states for feedback as it makes use of only the output samples for designing the controller. Thus, this methodology is more practical and easy to implement. A numerical example demonstrates the design technique. Simulation results show that the proposed FOS SMC technique produces the same results as obtained by state feedback SMC technique