Closed-loop Bandwidth Research Articles

光雷一体化测量系统的谐振特性及组合补偿

To overcome the adverse effect of complicated resonant vibration resulting from the OE-radar integrative measuring system on a servo unit, a hybrid compensating method combined an adaptive notch filter and the feedback of observer filtering was proposed to restrain the resonant vibration. Firstly, the resonant characteristics of the system were analyzed according to the mechanical structure and tested frequency properties. It indicates that there are three kinds of primary resonant modes in the system, which is the radar antenna resonance, radar cabin resonance and the antenna high-order and bearing coupling resonance. The rule of resonant characteristics varying with an elevation angle was also obtained. Then, a compensating method to the complicated resonant vibration was discussed. The adaptive notch filter in series was applied to compensation of the radar antenna resonance and the radar cabin resonance, and the feedback of the Kalman observer filtering was used to restrain the antenna high-order and bearing coupling resonance. Experimental results indicate that all kinds of resonances are restrained effectively by the hybrid compensating method, the velocity close-loop bandwidth of servo unit is up to 115 rad/s, and the transient time of step response is 0.35 s. The method proposed can satisfy the system requirements for high bandwidth and stabilization.

Proportional electro-hydraulic valves: from analogue to digital control

Proportional electro-hydraulic valves are ubiquitous as flow actuators in hydraulic systems. Flow regulation is the result of the accurate positioning of a spool driven by a solenoid and a position sensor. The overall control consists of two hierarchical loops: the inner loop is the solenoid current regulator with a closed-loop bandwidth close to 1 kHz. A model-based digital regulator of this kind has been presented elsewhere. The outer loop is a position tracking control, in charge of an accurate positioning of the spool with respect to the valve openings. The paper addresses the outer loop and concentrates on the conversion of an existing industrial analogue controller into a digital one. The analogue controller is a non-linear proportional, integrative and derivative controller including a second-order derivative, and is capable of recovering a dead-band hysteresis. The digital conversion provides the necessary position derivatives through a state predictor, in order to withstand the 5-kHz Nyquist limi...

Tape drive track following using cascade control

Ultra-precise positioning of the recording head over the data tracks is required to achieve the aggressive track density scaling envisioned for future tape storage systems. The track-follow control system is responsible for reducing the misalignment between the tape and the head created primarily by lateral motion of the flexible medium. The challenge of improving the track-following accuracy becomes even more difficult in the presence of external vibration disturbances. Typically, position error signal (PES) information is measured at the tape head using pre-formatted servo information and is used in a feedback controller during track-following to maintain the position of the read/write elements at the desired position during tape transport. In this paper, a track-follow scheme is introduced in which a high-bandwidth low-noise position sensor is used in conjunction with the position information read back by the head from preformatted servo patterns on the tape. A cascade control configuration is proposed, in which first an inner loop is designed based on the actuator position information provided by the sensor. The high-bandwidth and low-noise characteristics of the sensor enable a high closed-loop bandwidth of the inner system that effectively compensates for external vibration disturbances. Subsequently, using a cascade structure, a PES-based controller is designed that compensates for the lateral tape motion disturbances. Simulation and experimental results are presented that illustrate the performance of the proposed scheme compared to a conventional PES-based track-follow control system.

Performance Limitations Arising in Closed Loop Control of Blood Glucose in Type 1 Diabetes

This paper presents a preliminary study of performance limitations that arise in the closed-loop control of blood glucose, using an autonomous artificial pancreas. It is shown that a major source of limitations is due to model uncertainty, specifically due to the combined effect of the insulin infusion system (IIS), the continuous glucose monitor (CGM) and the human glucose regulatory system. It is argued that the uncertainty associated with each of these elements compromises the achievable closed-loop bandwidth, and, in the presence of disturbances, e.g. meal intake and exercise, the closed-loop response will necessarily be poor. A proposition to overcome this problem is given based on feedforward action.

A dynamic feedback control strategy for control loops with time-varying delay

Dynamic systems of nth order with time-varying delay in the control loop are examined in this paper. The infinite-dimensional pure delay problem is approximated using a jth-order Padé approximation. Although the approximation provides a well-matched finite-dimensional configuration, it poses a new challenge in terms of unstable internal dynamics for the resulted non-minimum phase system. Such a non-minimum phase characteristic limits the closed-loop system bandwidth and leads to an imperfect tracking performance. To circumvent this problem, the unstable internal dynamics of the system is captured and a new dynamic compensator is proposed to stabilise it in a systematic framework. A dynamic controller is developed, which provides the overall system stability against unmatched perturbation and meets the desired tracking error dynamics. The proposed approach is then applied to fuelling control in gasoline engines addressing the varying transport delay of the oxygen-sensor measurement in the exhaust. The developed methodology is finally validated on a Ford F-150 SI lean-burn engine model with large time-varying delay in the control loop.

Large Aperture, Tip Tilt Mirror for Beam Jitter correction in High Power Lasers

This paper describes a large aperture tip-tilt mirror (TTM) assembly for correction of beam jitter in high power lasers. The design intricacies and trade-offs among various parameters of TTM to meet the desired goals are discussed. The TTM assembly uses a 180 mm diameter and 5 mm thick silicon mirror glued onto the movable ring of a solid flexure. Four stacked piezo-ceramic based actuators have been used to incorporate angular tilts of the mirror along two orthogonal directions. Simulation studies have been carried out to study the dynamics of the TTM. The performance of the TTM assembly in both static and dynamic condition is provided. An experimental set-up is described to test the TTM performance in closed loop conditions. A tilt correction of ±200 micro-radians along two orthogonal directions with a closed loop bandwidth of 20 Hz has been achieved.Defence Science Journal, 2013, 63(6), pp.606-610, DOI:http://dx.doi.org/10.14429/dsj.63.5760

Spectral Analysis of Vibratory Gyro Noise

This paper presents analysis of the noise spectra of closed-loop mode-matched vibratory gyros. Closed-form expressions for the noise-equivalent angular rate spectrum as well as the integrated angular rate (angle) variance are derived to explore the effects of modal frequency mismatch, closed-loop bandwidth, and the spectra of noise sources appearing at the sensor's input and output. It is shown that noise sources located at the output of the sensor's electromechanical transfer function create angle white noise in the closed-loop sensor. The angle white noise dominates the integrated rate behavior until it crosses the angle random walk asymptote at integration times exceeding the sensor's open-loop time constant. Even though the closed-loop sensor asymptotically recovers the angle random walk figure associated with the mode-matched open-loop sensor, the results can be used to quantify the larger integrated rate variance that is produced as a consequence of extending the sensor's bandwidth through feedback. A parameter, called the effective bandwidth, is introduced to capture the relative importance of the input noise versus output noise in determining the noise-equivalent rate spectrum. It is shown that the rate noise spectrum is robust to frequency mismatch as long as it does not exceed the effective bandwidth parameter. Empirical data obtained with a high performance MEMS vibratory gyro shows excellent agreement with the model predictions for a variety of sensor configurations including frequency-matched, frequency-mismatched, modified bandwidth, and manipulated input noise intensity cases.

Switching Gain-Scheduled Control Design for Flexible Ball-Screw Drives

This paper proposes an application of the switching gain-scheduled control technique to the flexible ball-screw drive servo system with a wide range of operating conditions. The wide operating range is caused by the change of the table position and the workpiece mass during the machining operation, and leads to plant dynamics variations. To achieve high tracking performance of the table position against the dynamics variations and the cutting force disturbance, a set of gain-scheduled controllers is designed so that each controller damps out the resonance of the ball-screw system and increases the closed-loop bandwidth for a local operating range, and tracking performance is guaranteed under the switching between these controllers. Experimental results with a laboratory-scale ball-screw drive setup demonstrate that the switching gain-scheduled controller outperforms the nonswitching one by up to 52% in tracking accuracy.

Application of Controller with Complex Zeros in the Photoelectric Tracking System

In the photoelectric imaging tracking system with the low frame-frequency CCD, low sampling frequency and delay in the system restrain the closed-loop bandwidth and the tracking precision of the system. In general, the zeros-poles cancellation method is employed in this system to cure for resonance and broaden the bandwidth of the system, but the method depends on the precise mathematical model and relatively higher sampling frequencies. In this paper, a PID controller with complex zeros is proposed and analyzed, which is applied to the FSM system based on the low frame-frequency CCD; next, good closed-loop performance obtained through the controller is presented. It is found from many experiments that zeros-poles cancellation cannot be applied to the tracking system with low sampling frequency without other assistant methods, which may not be required in the new method. Finally, the CCD with a frequency of 200Hz is used in the FSM tracking experiment to verify the method, and the experiment result shows that the performance of the system achieved by means of the novel controller can meet the design requirements.

Large dynamic range nanopositioning using iterative learning control

Abstract This paper presents the control system design and tracking performance for a large range single-axis nanopositioning system that is based on a moving magnet actuator and a flexure bearing. While the physical system is designed to be free of friction and backlash, the nonlinearities in the electromagnetic actuator as well as the harmonic distortion in the drive amplifier degrade the tracking performance for dynamic commands. It is shown that linear feedback and feedforward proves to be inadequate to overcome these nonlinearities. This is due to the low open-loop bandwidth of the physical system, which limits the achievable closed-loop bandwidth given actuator saturation concerns. For periodic commands, like those used in scanning applications, the component of the tracking error due to the system nonlinearities exhibits a deterministic pattern and repeats every period. Therefore, a phase lead type iterative learning controller (ILC) is designed and implemented in conjunction with linear feedback and feedforward to reduce this periodic tracking error by more than two orders of magnitude. Experimental results demonstrate the effectiveness of ILC in achieving 10 nm RMS tracking error over 8 mm motion range in response to a 2 Hz band-limited triangular command. This corresponds to a dynamic range of more than 10 5 for speeds up to 32 mm/s, one of the highest reported in the literature so far, for a cost-effective desktop-sized single-axis motion system.

Integral resonant damping for high-bandwidth control of piezoceramic stack actuators with asymmetric hysteresis nonlinearity

This paper presents a novel control scheme for high-bandwidth control of piezoceramic stack actuators (PSAs). For this purpose, we first characterize and compensate for the asymmetric hysteresis nonlinearity of the PSA. A linear integral resonant controller is then designed as a means for damping the resonant modes of the dynamic system with the hysteresis compensation. Finally, a tracking controller and feedforward input are developed to minimize the tracking errors and improve the closed-loop tracking bandwidth. To verify the effectiveness and efficiency of the proposed control scheme, a PSA-actuated positioning platform is built and comparative experiments are conducted. Experimental results demonstrate that the proposed controller achieves robust broadband nanopositioning of the PSA by improving the tracking bandwidth from 22Hz (with an integral controller) to 657Hz.

Reducing rotor speed variations of floating wind turbines by compensation of non‐minimum phase zeros

Applying a land-based designed pitch controller on a floating wind turbine may cause severe instability. A common strategy to overcome this problem is to reduce the closed-loop bandwidth of the pitch control system. In doing so, the generator speed variation increases possibly leading to shutdowns because of overspeed. This study uses a parallel path modification to avoid instability without increasing the generator speed variation. The results of comprehensive simulations and load calculations carried out on a benchmark wind turbine are presented. These demonstrate that by using the proposed method it is possible to apply the land-based designed pitch controller on its floater-based equivalent.

Track-Following Control of Four-Bar Structured HDD via Parameter-Dependent Low-Frequency Precompensation

This paper considers track-following control of four-bar structured hard disk drive (HDD) systems. Compared with the traditional single-arm HDD, the four-bar structure potentially leads to higher achievable closed-loop bandwidth, but also brings challenges in control design due to nonlinearity. In track-following control design, exact linearization is impossible in practice due to mechanic resonances and measurement constraints. In this paper, instead of exact linearization, we propose a kind of prefilter to compensate for the low-frequency nonlinearities so that the compensated system has the same linear approximation at different track positions subjected to different high-frequency resonances. With this prefilter, many existing track-following control methods can be applied to the compensated plant. In this paper, $H_{\infty}$ loop shaping is used and simulation results show that the resulting controller preserves similar track-following performance at different track positions.

A Novel Piezoelectric Strain Sensor for Simultaneous Damping and Tracking Control of a High-Speed Nanopositioner

This paper presents a novel piezoelectric strain sensor for damping and accurate tracking control of a high-speed nanopositioning stage. Piezoelectric sensors have the benefit of simple interface circuitry, low cost, high sensitivity, and high bandwidth. Although piezoelectric sensors have been successfully used as vibration sensors in smart structures, complications arise when they are used in a feedback loop for tracking. As piezoelectric strain sensors exhibit a capacitive source impedance, a high-pass filter is created, typically with a cut-off frequency of 1 to 10 Hz. This filter can cause significant errors and destabilize a tracking control system. Here, we overcome this problem by using a low-frequency bypass technique to replace the low-frequency component of the strain measurement with an estimate based on the open-loop system. Once the low-frequency filter is accounted for, any standard control system can be applied. In this paper, an analog integral resonant controller together with an integral tracking controller are implemented on a flexure-guided nanopositioner. The resulting closed-loop bandwidth is experimentally demonstrated to be 1.86 kHz. The nanopositioner is installed in an Atomic Force Microscope to obtain open- and closed-loop images at line rates of 40 and 78 Hz. Images recorded in closed loop show a significant improvement due to the elimination of nonlinearity.

PID Tuning for Optimal Closed-Loop Performance With Specified Gain and Phase Margins

A new robust proportional-integrative-derivative (PID) tuning method based on nonlinear optimization is developed. The closed-loop bandwidth is maximized for specified gain and phase margins (GPM) with constraint on overshoot ratio, so that criteria of closed-loop performance and robustness are both satisfied. The equations of open-loop amplitude ratio and phase change are derived based on frequency analysis for the first-order plus time delay system with a PID controller in parallel form. The equation of closed-loop amplitude ratio is also explicitly given. The formulated optimization problem from the tuning method based on GPM with constraint on closed-loop amplitude ratio is further given. The method is demonstrated in simulation examples and compared with previous work on this topic.

Critical review of the circuit architecture of CFOA

This study investigates the closed-loop performance of the basic current feedback operational amplifier (CFOA), with particular emphasis on its dynamic response. It also focuses on the design, performance and advantages of the CFOA in its ability to provide a substantially constant closed-loop bandwidth for closed-loop voltage gain. Furthermore, an improved CFOA with wide bandwidth and common-mode-rejection ratio (CMRR) performance is also presented. The design presented in this article uses a bootstrapping technique with Quasi-Darlington in the input stage to reduce the influence of the Early effect which results in improved performance. Another advantage of this design is that the inverting input impedance is reduced significantly, which leads to further improvement in bandwidth and CMRR.

Receptacle normal position control for automated aerial refueling

Novel flight control laws are presented for the receiver aircraft during aerial refueling. The case of a large transport aircraft refueling a similarly sized aircraft is investigated. The controller focuses on the normal position of the receiver aircraftʼs refueling receptacle during automated aerial refueling. Specifically the effect of the relatively long distance between the receiver aircraftʼs center of gravity and the refueling receptacle is analyzed. An existing linear aircraft model is adapted to describe the dynamics from the perspective of the refueling receptacle on the receiver aircraft. It is found that the receptacle dynamics contain a complex pair of zeroes in the left half of the S-plane. Three possible control architectures are considered. The analysis indicates that, when controlling a large receiver, the inclusion of the receptacle dynamics is essential for adequate low frequency disturbance rejection. It is found that the presence of the zeros degrade the systemʼs response when the closed loop bandwidth nears the zerosʼ frequency; effectively limiting the attainable bandwidth. A method is presented to compensate for the presence of the zeros and improve the receptacleʼs response. Suitable pole locations are chosen for all required flight points. The effect of tanker downwash uncertainties on the closed loop system is investigated. High fidelity nonlinear simulation results show that the control laws can successfully regulate the receptacle at the required points while subjected to light turbulence and expected tanker downwash.

Fundamental Limits in Combine Harvester Header Height Control

This paper investigates fundamental performance limitations in the control of a combine harvester's header height control system. There are two primary subsystem characteristics that influence the achievable bandwidth by affecting the open loop transfer function. The first subsystem is the mechanical configuration of the combine and header while the second subsystem is the electrohydraulic actuation for the header. The mechanical combine + header subsystem results in an input-output representation that is underactuated and has a noncollocated sensor/actuator pair. The electrohydraulic subsystem introduces a significant time delay. In combination, they each reinforce the effect of the other thereby exacerbating the overall system limitation of the closed loop bandwidth. Experimental results are provided to validate the model and existence of the closed loop bandwidth limitations that stem from specific system design configurations.

Design of an Inertially Counterbalanced $Z$ -Nanopositioner for High-Speed Atomic Force Microscopy

In many conventional atomic force microscopes (AFMs), one of the key hurdles to high-speed scanning in constant-force contact mode is the low-feedback control bandwidth of the -axis loop. This paper presents the design of a fast -nanoposi-tioner to overcome this limitation. The -nanopositioner has its first resonant mode at 60 kHz and a travel range of 5 m. It consists of a piezoelectric stack actuator and a diaphragm flexure. The flexure serves as a linear spring to preload the actuator and to prevent it from getting damaged during high-speed operations. The -nanopositioner is mounted to an XY-nanopositioner. To avoid exciting the resonance of the XY -nanopositioner, an inertial counterbalance configuration was incorporated in the design of the -nanopositioner. With this configuration, the resonances of the XY-nanopositioner were not triggered. A closed-loop vertical control bandwidth of 6.5 kHz is achieved. High-speed constant-force contact-mode images were recorded at a resolution of 200 200 pixels at 10, 100, and 200 Hz line rates without noticeable image artifacts due to insufficient control bandwidth and vibrations. Images were also recorded at 312- and 400-Hz line rates. These images do not show significant artifacts. These line rates are much higher than the closed-loop bandwidth of a conventional AFM in which this nanopositioner was tested.

A Micro Dynamically Tuned Gyroscope with Adjustable Static Capacitance

This paper presents a novel micro dynamically tuned gyroscope (MDTG) with adjustable static capacitance. First, the principle of MDTG is theoretically analyzed. Next, some simulations under the optimized structure parameters are given as a reference for the mask design of the rotor wafer and electrode plates. As two key components, the process flows of the rotor wafer and electrode plates are described in detail. All the scanning electron microscopy (SEM) photos show that the fabrication process is effective and optimized. Then, an assembly model is designed for the static capacitance adjustable MDTG, whose static capacitance can be changed by rotating the lower electrode plate support and substituting gasket rings of different thicknesses. Thus, the scale factor is easily changeable. Afterwards, the digitalized closed-loop measurement circuit is simulated. The discrete correction and decoupling modules are designed to make the closed-loop stable and cross-coupling effect small. The dual axis closed-loop system bandwidths can reach more than 60 Hz and the dual axis scale factors are completely symmetrical. All the simulation results demonstrate the proposed fabrication of the MDTG can meet the application requirements. Finally, the paper presents the test results of static and dynamic capacitance values which are consistent with the simulation values.