Adaptive Feedforward Cancellation Research Articles

Adaptive feedforward control of sinusoidal disturbances with applications to electric propulsion systems

Generalized adaptive feedforward cancellation with a reference sensor is considered to specifically suppress second harmonic torque oscillations with an ac fed propulsion system for an electric train. A single complex-valued design parameter is tracked through gradient-type adaptation. Both Cartesian and polar parameter representations are considered, resulting in quite varying convergence properties. Three different adaptation algorithms are proposed and evaluated using power lab experiments. At fixed operating conditions, a Cartesian form parameter adaptation is shown to be more robust to the choice of initial conditions, whereas a polar form representation shows better performance when covering a wide range of operating points.

Adaptive Feedforward Cancellation for Precise Repetitive Motion in Coarse-Fine Control System

Adaptive Feedforward Cancellation for Precise Repetitive Motion in Coarse-Fine Control System

Control Scheme of RRO Compensation for Track Mis-registration in HDDs

Hard disk drives (HDDs) which can store of large amount of digital data are supporting information society. To read/write the digital data on the disk, the magnetic head must be controlled precisely. The data is recorded as concentric orbits called as tracks on the disk. In the controller design, servo engineer must evaluate track mis-registration (TMR) for the reliability. The TMR is one of criteria of relative positioning accuracy for the tracks for risk assessment of data incorrectly writing. The risk means that the magnetic heads write on the different track from the target track. The relative positioning accuracy in the tracks should be improved to decrease the risk. In this paper, we have proposed a control scheme to compensate of repeatable runout (RRO) for the TMR. In the proposed control system, we distinguished the RRO by “synchronous RRO” and “asynchronous RRO”. Two types of RROs are compensated by using an adaptive feedforward cancellation (AFC). The AFC is designed to generate the suitable compensation signal for each type of RRO, and the proposed control system improves the relative positioning accuracy. The effectiveness of the proposed scheme has been verified by using a HDD benchmark model developed by IEEJ Industry Applications Society.

High-Precision Trajectory Tracking Control of a Multifrequency Whirling Orbit Using Adaptive Feedforward Cancellation for the Efficient Experimental Estimation of Fluid Force

Abstract In recent years, there has been a demand for turbomachinery with increasing speed, pressure, and compactness owing to the increasing demand for high output and efficiency. Consequently, various shaft vibration problems have become apparent. The rotor dynamic (RD) forces are one of the causes of these axial vibrations, which can lead to instability of the rotor system. To ensure the reliability of turbomachinery, the effect of RD fluid force should be analyzed at the design stage. In this study, high-precision tracking control of a complex orbit was analyzed using an experimental approach, and a highly efficient and low-dispersion estimation of the RD fluid force was achieved. The target was a parallel annular seal, and an experimental system was developed to control the rotor position using a piezo-electric actuator. Using the adaptive feedforward cancellation (AFC), we suppressed the periodic disturbance caused by rotation, whirling, and disturbances, such as noise that existed uniformly at all frequencies. Thus, a high-precision tracking control with an orbit tracking error of approximately 1 μm was achieved. The RD fluid force was estimated from the output signal of the AFC during high-precision tracking control, and the RD coefficient was calculated using spectral analysis. Consequently, a highly accurate RD fluid force estimation with reduced dispersion was achieved. In addition, a multifrequency orbit control and RD fluid force estimation method were developed to improve the efficiency of the RD force estimation, which agreed well with the results of a single-frequency orbit.

Robust indirect adaptive control of electromechanical servo systems with uncertain time-varying parameters

This paper focuses on high-accuracy motion control for electromechanical servo systems with time-varying parameter estimation. A robust indirect adaptive controller based on a nonlinear X-swapping technique is proposed to achieve the online estimation of the time-varying parameters. The time-varying parametric uncertainties can be well compensated via the adaptive feedforward cancellation technique, and the residual model uncertainties are suppressed by a nonlinear robust control law. The Lyapunov-based stability analysis illustrates that the proposed method obtains a prescribed estimating result and an excellent asymptotic tracking performance. Extensive experimental results are acquired to affirm the applicability of the proposed control strategy.

Track-Following Controller Design Using an Active Magnetic Bearing for Measurement of the Rotor Dynamics Coefficient of the Annular Seal

Abstract This study introduces a track-following controller design to measure the rotor dynamics (RD) coefficient of the annular seal using active magnetic bearings. The annular seal is implemented contiguously to prevent leakage of fluid between the rotating shaft and stationary area of a rotating machine. The force caused by the seal at the contact point can cause vibrations, which should be identified for designing rotating machinery. The RD force is coupled with mechanical and fluid dynamics. Moreover, the dynamics depend on the operating conditions of the rotating machine, namely, the rotating speed and orbit of the rotating shaft. This study proposes a control system for the active magnetic bearing to measure the RD force directly at the arbitrary operating condition. The main controller is designed to satisfy a criterion of the frequency characteristics of the rotating system. In addition, the control system employs adaptive feed-forward cancellation (AFC). This can estimate and compensate for the RD force in the control system simultaneously. The experimental results indicate that the control system can achieve an arbitrary operating condition and measure the RD coefficient of the annular seal in real-time. As a result, the RD coefficient is identified based on the equation of motion.

Suppression of harmonic positioning errors in ball-screw drives using Adaptive Feedforward Cancellation

Harmonic positioning errors can negatively affect the positioning accuracy of the ball screw drive system. This paper addresses the problem of harmonic positioning error suppression in ball-screw drives using Adaptive Feedforward Cancellation (AFC). AFC method is integrated with the dual (i.e., rotational and translational) feedback structure used in ball-screw drives. The ability of AFC to quench harmonic positioning errors originating from multiple input sources is analyzed, considering the effects of the commanded trajectory, motor torque ripples, rotary encoder measurement errors, and lead errors coming from the ball-screw mechanism. A new approach for parameter tuning of the AFC resonators is proposed which considers both the performance deterioration issue at frequencies outside the target harmonics, and also the robust stability requirement in the sense of limiting the peak loop sensitivity value. Effectiveness of the proposed AFC scheme for ball-screw drives is validated in experiments, demonstrating successful rejection of time-periodic machining force disturbances, as well as mitigation of displacement-periodic lead error and misalignment type errors. In the case of machining force rejection, 50–78% improvement is achieved in the standard deviation of the translational positioning error. In the case of position dependent disturbances, the improvement is typically in the 10–20% range and is most effective during constant velocity motion.

Control scheme of adaptive feedforward cancellation considering of Bode’s integral theorem for synchronous vibration suppression in rotating machineries

Synchronous vibration is a major obstacle to the stable operation of rotating machineries. In previous studies, active control methods were developed to compensate for synchronous vibration using actuators, such as an active magnetic bearing or a piezo actuator. Adaptive feedforward cancellation is another well-known control method and is used to compensate for the synchronous vibration in the actual system. The control methods can compensate for the synchronous vibration; however, the amplitude of the vibration in other frequency ranges can be increased by the waterbed effect due to Bode’s integral theorem. Therefore, there is a trade-off between the compensation of the synchronous vibration and the negative impact of other vibration. In this article, a novel control scheme for the adaptive feedforward cancellation is proposed to eliminate the negative impact due to the waterbed effect. The proposed method controlled the input signal of the adaptive algorithm in the adaptive feedforward cancellation and realized an ideal feedforward controller worked independently from the feedback loop. The effectiveness of this method was verified experimentally using a test rig.

Development of Adaptive Feed-Forward Cancellation With Frequency Estimation Algorithm for Compensation of Periodic Disturbance at Arbitrary Frequency

Abstract In this study, an adaptive feed-forward cancellation (AFC) with frequency estimation algorithm has been developed to compensate for periodic disturbance at an arbitrary frequency. Conventional AFC was developed to compensate for periodic disturbance at a fixed frequency and cannot compensate for the disturbance in which the frequency varies in real-time. The proposed method can estimate the frequency of the disturbance in real-time by using the input and output signals of the AFC. It can compensate for the periodic disturbance at an arbitrary frequency. In addition, the stability of the feedback control system with the proposed AFC can be optimized at any frequency based on the vector locus of the open-loop characteristic on the Nyquist diagram. The effectiveness of the proposed AFC was confirmed in experiments compensating for whirling vibration, whose frequency varies in real-time in rotating machinery. The proposed AFC can estimate the frequency of the disturbance automatically and compensate for this adequately.

Adaptive feedforward cancellation with gain and damping control system considering helium leakage in HDDs

This study developed an adaptive feedforward cancellation system with gain and damping control for hard disk drives (HDDs). The system was developed to compensate for fluid-induced vibration due to helium leakage. Helium-filled HDDs are used in data servers around the world to support the information society. One of the concerns in helium-filled HDDs is the deterioration of positioning accuracy of the control system due to helium leakage. The proposed head positioning control system can compensate for the fluid-induced vibration by updating the characteristics of the control system in real-time. Real-time simulations based on MATLAB/Simulink were performed to demonstrate that fluid-induced vibrations due by helium leakage in the head positioning control system of HDDs can be compensated. The results indicated that the characteristics of the control system were updated in real-time to compensate for fluid-induced vibrations in conformity with the variation in characteristics due to helium leakage and that the fluid-induced vibrations can be adequately compensated.

Development of a Measurement System for Analyzing Periodic External Forces Acting on Rotating Machineries

In this study, a measurement system is developed to analyze periodic external forces acting on a rotating machinery. The dynamics of a rotating machineries are influenced by various periodic external forces such as unbalanced forces, oil film forces at a journal bearing, and seal contact forces. The characteristics of periodic external forces are dependent on the rotating conditions, rotational speed, and rotating orbit of the rotating shaft. The proposed system employs an active magnetic bearing (AMB), which is implemented using an adaptive feed-forward cancellation (AFC). The use of AFC ensures that the proposed system can realize the desired harmonic orbit assuming actual operations under the periodic external forces. Moreover, AFC can measure the periodic external forces in real-time using an adaptive algorithm. The effectiveness of the proposed system is verified experimentally. Experimental results show that the control system can control the rotating shaft to an accuracy of micrometer order using the implemented AFC. The measurement error of the periodic external forces acting on the rotating system is less than 2%.

Adaptive feedforward cancellation with damping control system in head positioning systems of HDDs

Adaptive feedforward cancellation (AFC) with a damping control system has been developed to improve the head-positioning accuracy in hard disk drives (HDDs). There are various disturbances that reduce the head-positioning accuracy in a head-positioning system. The control system must compensate for these disturbances to improve the head-positioning accuracy. In addition, the robustness of the control system should be considered to realize stable operation for a mass-produced product such as HDDs. The proposed AFC updates a forgetting factor that corresponds to a damping factor in the adaptive algorithm to minimize the position error signal in real-time, and it can optimize the characteristics of the control system according to individual variations. We verified effectiveness of the proposed AFC in the HDD benchmark model. It was confirmed that the proposed AFC can adequately compensate for the vibration caused by flow-induced vibration defined in the benchmark model.

Compensation of mechanical resonances by adaptive feed-forward cancellation for head positioning control system in hard disk drives

Compensation of mechanical resonances by adaptive feed-forward cancellation for head positioning control system in hard disk drives

Development of Active Magnetic Bearing Device using Adaptive Feedforward Cancellation for Analysis of External Forces in Precision Rotating Machinery

Development of Active Magnetic Bearing Device using Adaptive Feedforward Cancellation for Analysis of External Forces in Precision Rotating Machinery

Design and Control of a Novel Fast Tool Servo Used in Diamond Turning of Freeform Optics

Optical free-form surfaces are becoming more and more popular in the industry application, which can be fabricated by diamond turning based on fast tool servo (FTS). It is an efficient, precise and low-cost processing method. In order to use diamond turning to fabricate the freeform optics, this paper develops a novel long range fast tool servo which is actuated by voice coil motor. The total range can reach up to 30 mm. The important parts of the FTS have been simulated and analyzed. The transfer function model identification of the FTS has been accomplished. Since the desired tool trajectories are approximately periodic signals in freeform surfaces turning, and the adaptive feedforward cancellation (AFC) control can achieve perfect tracking and disturbance rejection of periodic signals, the AFC control is designed to be added on the IMC-PID controller.

Micro-patterning technique using a rotating cutting tool controlled by an electromagnetic actuator

This work describes a micro-patterning or surface texturing technique on the fixed work surface using a proposed new spindle system with a rotating cutting tool controlled in real time. The proposed spindle system creates micro-sized patterns using rotating tools such as a micro-milling tool and a micro-grinding wheel. The shaft of the spindle is suspended by air bearings, and an electromagnetic actuator controls the radial motion of the spindle housing instead of the shaft. This generates a micro-pattern array on the electro-less Ni-coated workpiece in the micro-milling process. A PID controller is adopted to make the system stable, and adaptive feedforward cancellation is used to effectively compensate for the run-out of the spindle system during machining. The machining results show that this compensation improves the pattern accuracy. It is expected that micro-patterning using the proposed spindle system can be applied over a large surface area.

A study of equivalence between adaptive learning and loop shaping methods for disturbance compensation

AbstractThis paper introduces a theoretical analysis of the disturbance compensation methods in positioning systems. Thereare two major methods used to compensate for disturbances. The first one is based on a loop shaping method andthe second one is based on an adaptive learning method. We make a comparison between a resonant filter used asthe loop shaping method and an enhanced adaptive feed-forward cancellation (AFC) method used as the adaptivelearning method. To compensate disturbances, the resonant filter decreases the gain of the sensitivity function atthe disturbance frequency by using the vector locus. The adaptive learning method adjusts the coefficients of theenhanced AFC to compensate for a disturbance. We found that the LTI model of an enhanced AFC is the sameas that for a resonant filter when we compared their characteristics. A simulation of the disturbance compensationin a hard disk drive showed that these time responses and frequency responses coincided. Moreover, the resultsshowed advantages of each of the control methods with the exception of the performance. A resonant filter realizeslow cost implementation with compare to an enhanced AFC. That is, a resonant filter easier to implement than anenhanced AFC. An enhanced AFC has the utility to realize a high quality function control system simultaneouslyable to compensate and estimate for disturbances. The results of the evaluation in this study will provide designengineers with guidelines for selecting an optimum control strategy in actual applications.Key words : Disturbance compensation, Periodic disturbance, Non-periodic disturbance, Adaptive feed-forward

Robustness analysis of enhanced adaptive feed-forward cancellation

This paper presents a robustness analysis of an enhanced adaptive feed-forward cancellation (AFC) function for a control system. The AFC is known as an adaptive control method, and the adaptive algorithm can estimate a periodic disturbance. In a previous study, an enhanced AFC was developed to compensate for non-periodic disturbances. The effectiveness of the enhanced AFC there was shown with only simulation results. In this study, the stable robustness of the enhanced AFC is analyzed for a one degree of freedom system. When the enhanced AFC is implemented to around a resonant frequency, the variations in the mechanical characteristics may cause instabilities in the control system, because the performance of the enhanced AFC depends on the phase condition of the mechanical characteristics. The experimental results show that variations in the resonant frequency may cause oscillation when the enhanced AFC design does not consider this kind of variation. The study confirms that the enhanced AFC must be designed considering variations in the resonant frequency.

Rolling bearing-suspended spindle run-out control using repetitive control and adaptive feedforward cancellation

The wettability, friction, adhesion, and optical characteristics of a surface are affected by its micro-topography. In turn, the characteristics of a surface micro-topography can be determined by controlling the trajectory of a cutting tool mounted on a spindle. However, this method is constrained by the tool’s cutting accuracy, which is limited by the run-out error and thermal behavior of the spindle. In this work, an electromagnetic actuator (EMA) is installed at the end of the spindle to compensate for the spindle run-out error and the thermal displacement in real time. The spindle system model includes a cross-coupled stiffness and damping term for the ball bearings. Repetitive controller (RC) reduces the repeatable run-out (RRO) while adaptive feedforward cancellation (AFC) reduces the non-repeatable run-out (NRRO). The control system uses a zero phase error tracking controller (ZPETC) to compensate for its total phase delay. Experimental results show a 70% reduction in run-out error at rotation speeds of 6,000 rpm and 12,000 rpm. The thermal displacement in the radial direction is regulated within a range of 1 µm for more than 3 hours.

Hybrid adaptive feedforward cancellation against time‐varying discrete systems with non‐stationary random periodic disturbance

This study presents a novel hybrid adaptive feedforward cancellation (AFC) methodology in particular for time-varying discrete systems with stochastic periodic disturbance. The proposed hybrid AFC framework is composed of conventional AFC modules and auxiliary PID control variables. The former is traditionally constructed with sinusoidal functions and parameters of the AFC system, and the latter is added for compensating perturbation because of non-stationary random disturbance in practice. The authors derive an estimation algorithm of parameters in the hybrid AFC system by using a gradient descent based optimisation method. In addition, a theoretical investigation is conducted for verifying convergence property of the parameter estimation by means of a well-known Lyapunov stability theory. Lastly, the authors achieve numerical simulation to prove reliability and superiority of the proposed AFC algorithm by comparing to a conventional AFC approach.