Wide Control Bandwidth Research Articles

A Study on the FPGA Implementation of the Bilateral Control Algorithm Towards Haptic Teleoperation

This paper presents the FPGA implementation of the sliding mode control algorithm for bilateral teleoperation, such that, the problem of haptic teleoperation is addressed. The presented study improves haptic fidelity by the widening the control bandwidth. For wide control bandwidth, short control periods as well as short sampling periods are required that can be achieved by FPGA. The presented FPGA design methodology applies basic optimization methods in order to meet the requirements in terms of the control period and the hardware resource consumption. The circuit specification was performed by the high-level programing language LabVIEW and using the fixed-point data type. Furthermore, the design methodology allows achieving short design times for producing the FPGA logic circuit. The proposed FPGA-based bilateral teleoperation was validated by 2-DoF master-slave experimental device.

State-space Modelling and Digital Controller Design for DC-DC Converter

The recent development in digital technology offers better platform for easy implementation of advance control algorithm in power converter design making digital control a viable alternative to analogue counterpart. Controller design for power converters has been very challenging due to non-linear characteristics of power switches, the supply voltage variability, load current changes and circuit element variation. This paper presents dynamic averaged state-space modelling of non-ideal dc-dc boost converter with parasitic and digital controller design for boost converter using digital redesign and direct digital design methods. The system was simulated in Matlab/Simulink to investigate the dynamic performance of the two controllers’ transient response, control bandwidth and response to variable supply voltage. The results demonstrated fast transient and wide control bandwidth for tight voltage regulation of variable input voltage.

Use of Boundary Control With Second-Order Switching Surface to Reduce the System Order for Deadbeat Controller in Grid-Connected Inverter

Deadbeat control is commonly used in grid-connected inverter with L filter, but it faces the challenge of having filter resonance in inverter with LCL filter. Although many active damping techniques have been proposed to tackle such phenomenon, their digital implementation would introduce nonminimum phase characteristics. Furthermore, the plant viewed by the deadbeat controller is of high order, making the system performance be susceptible to the drift of the filter parameters. This paper introduces a new perspective of using boundary control with second-order switching surface to reduce the order of the plant viewed by the deadbeat controller. The structure hybridizes the merits of the deadbeat control in its simplicity and the boundary control in achieving wide control bandwidth. Small-signal dynamic modeling of the boundary control is formulated. The performance sensitivities of the overall system to filter parameters and grid inductance variations are studied with the derived models. An online grid inductance estimation algorithm is proposed to assure sufficient phase margin under an extremely weak-grid condition. A 2-kW, 220-V, 50-Hz prototype with the switching frequency of 8 kHz has been built and evaluated. Its steady-state and transient behavior, and harmonic rejection capability under stiff- and weak-grid conditions are discussed.

High speed laser scanning microscopy by iterative learning control of a galvanometer scanner

Iterative learning control (ILC) for a galvanometer scanner is proposed to achieve high speed, linear, and accurate bidirectional scanning for scanning laser microscopy. A galvanometer scanner, as a low stiffness actuator, is first stabilized with a feedback control compensating for disturbances and nonlinearities at low frequencies, and ILC is applied for the control of the fast scanning motion. For stable inversion of the non-minimum phase zeros, a time delay approximation and a zero phase approximation are used for design of ILC, and their attainable bandwidths are analyzed. Experimental results verify the benefits of ILC of its wide control bandwidth, enabling a faster, more linear, and more accurate scanning without a phase lag and a gain mismatch. At the scan rate of 4112 lines per second, the root mean square (RMS) error of the ILC can be reduced by a factor of 73 in comparison with the feedback controlled galvanometer scanner of the commercial system.

2ステージアクチュエータを用いた広帯域バイラテラル制御

This paper proposes a two-stage actuator system that consists of a coarse actuator driven by a ball screw with an AC motor (the first stage) and a fine actuator driven by a voice coil motor (the second stage). The proposed two-stage actuator system is applied to make a wide-bandwidth bilateral control system without needing expensive high-performance actuators. In the proposed system, the first stage has a wide moving range with a narrow control bandwidth, and the second stage has a narrow moving range with a wide control bandwidth. By consolidating these two inexpensive actuators with different control bandwidths in a complementary manner, a wide bandwidth bilateral control system can be constructed based on a mechanical impedance control. To show the validity of the proposed method, a prototype of the two-stage actuator system has been developed and basic performance was evaluated by experiment. The experimental results showed that a light mechanical impedance with a mass of 10 g and a damping coefficient of 2.5 N/(m/s) that is an important factor to establish good transparency in bilateral control has been successfully achieved and also showed that a better force and position responses between a master and slave is achieved by using the proposed two-stage actuator system compared with a narrow bandwidth case using a single ball screw system.

High-precision optical phase-locking based on wideband acousto-optical frequency shifting

We present a high-precision optical phase-locking based on wideband acousto-optical frequency shifting. Increasing the modulating bandwidth stabilizes the loop at a high loop gain, thus improving phase correction capability. An optical phase-locked loop with a wide control bandwidth is constructed. The closed-loop residual phase error is only 0.26o or smaller than \lambda/1000. The loop exhibits excellent correction capability for high-frequency noises. The correctable frequency range reaches 35 kHz when the noise amplitude is +(-)\lambda/2, and becomes even wider for smaller noise amplitudes.

외부짐발 선구동에 의한 EOTS의 기동성 개선

An EOTS (Electro-Optical Tracking System) provides stabilized images while tracking a moving target. This paper presents a novel concept of driving the outer gimbal first for improving the maneuverability of an EOTS, contrary to the conventional inner gimbal mode. It has the advantages of faster positioning performance and stable operation in Nadir-point. Analysis of frequency responses reveal that the present scheme results in a wider control bandwidth and larger gain margin, compared to those of the previous one. The actual experimental results confirm that the maneuvering is stable although the input command has a large angular acceleration.

Analysis and Design of Average Current Mode Control Using a Describing-Function-Based Equivalent Circuit Model

This paper proposes a small-signal model for average current mode control based on an equivalent circuit. The model uses a three-terminal equivalent circuit model based on a linearized describing function method to include the feedback effect of the sideband frequency components of the inductor current. The model extends the results obtained in peak current mode control to average current mode control. The proposed small-signal model is accurate up to half switching frequency, predicting the subharmonic instability. The proposed model is verified using SIMPLIS simulation and hardware experiments, which show good agreement with the measurement results. Based on the proposed model, new feedback design guidelines are presented. The proposed design guidelines are compared with several conventional, widely used design criteria. By designing the external ramp following the proposed design guidelines, the quality factor of the double poles at half of the switching frequency in the control-to-output transfer function can be precisely controlled. This helps the feedback loop design to achieve wide control bandwidth and proper damping.

A Study on the FPGA Implementation of the Bilateral Control Algorithm Towards Haptic Teleoperation

This paper presents the FPGA implementation of sliding mode control algorithm for bilateral teleoperation, such that, the problem of haptic teleoperation is addressed. The presented study improves haptic fidelity by widening the control bandwidth. For wide control bandwidth, short control periods as well as short sampling periods are required that was achieved by the FPGA. The presented FPGA design methodology applies basic optimization methods in order to meet the required control period as well as the required hardware resource consumption. The circuit specification was performed by the high-level programing language LabVIEW using the fixed-point data type. Hence, short design times for producing the FPGA logic circuit can be achieved. The proposed FPGA-based bilateral teleoperation was validated by master-slave experimental device.

Compensating for some errors related to time delay in a charge-coupled-device-based fast steering mirror control system using a feedforward loop

In many control systems, the most effective method to improve the performance of the closed-loop system is by enhancing the gain of the control system, which results in a wide control bandwidth. However, in the control system of a charge-coupled-device-based tracking loop for a fast steering mirror, the bandwidth of the closed loop is greatly limited by the large time delay of the TV tracker. Additionally, the time delay leads to instability of the system when the closed-loop system has high gain. We propose a new feedforward control to compensate some errors related to the time delay of the tracker, meanwhile improving the performance of the closed-loop fast steering mirror system. The control structure we propose includes two closed loops; a tracking loop and a fast position loop. The fast position loop is produced using an eddy current sensor, and the tracking loop is the outer loop, enveloping the fast position loop. The feedforward signal is estimated from the signal of the eddy current sensor and the TV tracker, which is added to the input of the fast position loop. Experimental results show that our proposed feedforward system can effectively enhance trajectory tracking and pointing performance.

The Robust Control of Magnetic Suspension with Rapidly Changing of Rotor Speed

An optimal robust vibration control of a rotor supported magnetically over a wide angular speed range is presented in the paper. The laboratory stand with the high speed rotor (max. 24000 rpm) was designed. The wide bandwidth controller with required gain, which is necessary to stabilize the structurally unstable and active magnetic bearing system was computed. For controller design, the weighting functions putted on the input and output signals were chosen. For control design, the dynamics of the rotor and uncertain parameters were considered. The optimized control system by minimization of the H norm putted on transient process of the system was presented. The robust controller was designed with considered asymmetrically magnetic bearings, signal limits and power amplifiers dynamic. The success of the robust control is demonstrated through computer simulations and experimental results. Matlab-Simulink was used for the numerical simulation. The experimental results show the effectiveness of the control system as good vibrations reducing and robustness of the designed controller in all dynamic states.

Sensor Fusion for Improved Control of Piezoelectric Tube Scanners

In nanopositioning applications, capacitive or inductive sensors are used to measure displacement and provide feedback to eliminate actuator nonlinearity, dynamics, cross-coupling between axes, and thermal drift. Due to their noise density, typically 20 pm/radicHz for 100-mum range transducers, feedback loops are restricted to a few tens of Hertz if nanometer precision is required. In this study, a capacitive displacement sensor is used with a piezoelectric strain voltage measurement to reduce sensor noise at frequencies above 1 Hz. The piezoelectric strain voltage is derived from an open-circuit electrode on a four-quadrant piezoelectric tube actuator and requires no additional hardware. The noise density of the piezoelectric strain voltage is measured to be three orders of magnitude lower than the capacitive sensor. This allows a large increase in closed-loop bandwidth with no penalty on sensor-induced noise. The advantageous properties of the capacitive sensor and piezoelectric strain voltage are discussed and utilized to design a Kalman filter that combines the two signals in a statistically optimal way. A receding horizon control strategy is then introduced as a technique for controlling the tube scanner. A wide-bandwidth controller is implemented that provides reference tracking and damping of the actuator resonance, with root-mean-square displacement noise below 0.4 nm.

Design of swing arm type actuators considering thermal and dynamic characteristics

The present state of the design of swing arm actuators for optical disc drives is to obtain the highly efficient dynamic characteristics within a very compact volume. As a necessary consequence, the need of the small form factor (SFF) storage device has arisen as a major interest in the information storage technology. Due to the size constraint, the thermal stability of the optical pick-up head is important: therefore, the actuator is designed to emit the heat, which is generated by the optical pick-up, along the structural body easily. In this paper, we suggest the miniaturized swing arm type actuator that has effective heat emission quality as well as satisfies the dynamic requirements for the SFF optical disk drive (ODD). The actuator is targeted to be installed in CF-II card size drive to be competitive with flash memory or mini hard disk drive used in mobile electric devices; therefore the dimension of the actuator is required as 11.0 mm × 2.5 mm × 25.0 mm (width × height × length). Because of its small size, the dynamic requirements are severe to ensure the enough gain-margin for the system control together with satisfying the DC/AC sensitivity conditions. Moreover, due to the small size, the maximum pick-up temperature is critical in design because the system has high possibility to reach the shut-down temperature. For the operating mechanism, it uses a tracking electromagnetic (EM) circuit for the focusing motion together and the initial model is designed and promoted by the design of experiments (DOE) only considering the dynamic characteristics. New concept design is suggested based on the topology optimization method considering the thermal conductivity. Furthermore, the new design is modified by DOE to maintain the high sensitivity and to have wide control bandwidth and decreasing mass and inertia. The final design of a swing arm type actuator for SFF ODD is suggested and its dynamic characteristics are verified.

Design of a repetitive controller: an application to the track-following servo system of optical disk drives

In an optical disk drive servo system, disturbances with significant periodic components cause tracking errors of a periodic nature. As an effective control scheme for improving periodic disturbance attenuation performance, repetitive control has been applied successfully to the track-following servo system of optical disk drives. The increase in disk rotational speed to achieve a better data throughput leads to the increase in the frequency of periodic disturbance, which needs a high loop gain in a wider control bandwidth. However, this requirement is not easily accomplished because plant uncertainty hinders selecting the bandwidth of a filter in the repetitive controller. The problem of add-on type repetitive controller design for a track-following servo with norm-bounded uncertainties in optical disk drives with high rotational speed is examined. Using the Lyapunov functional for time-delay systems, a sufficient condition for robust stability of the repetitive control system is derived in terms of an algebraic Ricatti inequality or a linear matrix inequality (LMI). On the basis of the derived condition, it is shown that the repetitive controller design problem can be reformulated as an optimisation problem with an LMI constraint on the free parameter. The validity of the proposed method is verified through experiments using a DVD-ROM drive.

Evaluation of Dynamic Parameters for Underdamped Grinding Machines

Evaluation of the dynamic parameters of a modulator based grinding machine system, which is underdamped, is presented. The modulator is one of a displacement-frequency type for dynamic manipulation of the stepping motor of a tool feed system which is part of a composite grinding system for a wide bandwidth control involving both low and high frequency signals. To obtain the parameters of the underdamped system, a method of multiple uses of the transient displacement responses to step commands is proposed to reduce assessment errors. The parameters to be obtained include damping ratio, undamped natural frequency, time constant, and settling time. The evaluation results were obtained based on the minimum of a composite error index using a second order dynamic system model for reference. The parameters will be useful for further development of the composite control for the precision machining process.

A 100 kW high-performance PWM rectifier with a ZCT soft-switching technique

This paper presents a 100 kW three-phase pulse-width modulated (PWM) boost rectifier that serves as the front-end power source for a DC distributed power system. A zero current transition (ZCT) soft-switching technique is applied to achieve greater performance in this high-power converter. This ZCT soft-switching technique assists the turn-on as well as the turn-off of the main and auxiliary insulated gate bipolar transistor (IGBT) switches. An issue about the implementation of the ZCT soft-switching technique in three-phase applications is discussed. A space vector modulation (SVM) scheme suitable for high power applications with high performance is identified. Experimental results demonstrate that high performance is achieved, in terms of wide control bandwidth, low total harmonic distortion (THD), unity power factor and high efficiency.

Design and Positioning Control of Microhead Actuator for Optical Disk Storage System (Design Guidelines for a Collocation-Type Actuator)

This paper describes the mechanical design of a microhead actuator for disk storage systems and its positioning control method. A new concept called ""quasi collocation"" is introduced to discuss the stability of positioning control systems for the structure. A simple actuator model is fabricated, and its dynamic characteristics are numerically and experimentally examined. On the basis of these results, a sensor and driving coils are positioned appropriately to achieve the quasi collocation. A trial servo system for this actuator experimentally confirms a wide control bandwidth beyond the mechanical resonance frequency.

Design and Positioning Control of Microhead Actuator for Optical Disk Storage System. Design Guidelines for a Collocation-Type Actuator.

This paper describes the mechanical design of a microhead actuator for disk storage systems and its positioning control method. A new concept called collocation is introduced to discuss the stability of positioning control systems for the structure. A simple actuator model is fabricated, and its dynamic characteristics are numerically and experimentally examined. On the basis of these results, a sensor and driving coils are positioned appropriately to achieve the quasi collocation. A trial servo system for this actuator experimentally confirms a wide control bandwidth beyond the mechanical resonance frequency.