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This paper presents an enhanced adaptive robust disturbance observer-based motion tracking control methodology. This control approach is established and investigated for a semi-automated hand-held ear surgical device for the treatment of Otitis Media with Effusion. The proposed control methodology is utilised for tracking a desired motion trajectory in the presence of unknown or uncertain system parameters, nonlinearities including hysteresis, and disturbances in the motion system. The stability of the control approach is analysed. The convergence of position and velocity tracking errors is proven theoretically. A precise tracking performance following desired motion trajectory is demonstrated in the experimental study., (Copyright © 2019 ISA. Published by Elsevier Ltd. All rights reserved.)

This work presents a new method of sensitivity shaping for motion control systems with disturbance observer (DOB). Although the traditional DOB design has been proved to be an effective means of rejecting disturbances in many applications, shaping of the closed-loop sensitivity is constrained since the Q-filter in DOB is usually restricted to a standard Butterworth or binomial form, where the cutoff frequency is the only tunable parameter. To overcome this limitation and achieve better performance for more demanding motion systems, a general form of the Q-filter is employed in this work. An data-based iteratively tuning procedure is subsequently developed according to a pre-defined cost function, so that the disturbance rejection in the low-frequency band is improved while the high-frequency noise attenuation and robust stability are not compromised. This method is data-based in the sense that the sensitivity shaping process is conducted based on the input-output data collected from the operating motion system, instead of relying on the identified system model. Simulation and experimental results are presented to show the advantage of this data-based sensitivity shaping approach., (Copyright © 2018 ISA. Published by Elsevier Ltd. All rights reserved.)

The biaxial gantry is widely used in many industrial processes that require high precision Cartesian motion. The conventional rigid-link version suffers from breaking down of joints if any de-synchronization between the two carriages occurs. To prevent above potential risk, a flexure-linked biaxial gantry is designed to allow a small rotation angle of the cross-arm. Nevertheless, the chattering of control signals and inappropriate design of the flexure joint will possibly induce resonant modes of the end-effector. Thus, in this work, the design requirements in terms of tracking accuracy, biaxial synchronization, and resonant mode suppression are achieved by integrated optimization of the stiffness of flexures and PID controller parameters for a class of point-to-point reference trajectories with same dynamics but different steps. From here, an H 2 optimization problem with defined constraints is formulated, and an efficient iterative solver is proposed by hybridizing direct computation of constrained projection gradient and line search of optimal step. Comparative experimental results obtained on the testbed are presented to verify the effectiveness of the proposed method., (Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.)

The majority of current industrial process control systems are based on PID control. However, in many of these systems, once the initial setup has been carried out, it is difficult to implement subsequent continuous improvements on the control performance without shutting down the production and disarming the overall system to retrofit alternative controllers. These measures to integrate additional instruments for allowing such flexibility incur heavy costs in terms of time and resources. In this paper, we propose an approach towards achieving the control adaptations which cannot be achieved easily with an existing closed-architectural system. The approach leverages on a set-point manipulation mechanism which allows a virtual modification of the closed-architectural system. In this way, process performance of existing plants can be continuously improved without the need to continuously alter the existing closed loop system. The implementation of the proposed configuration is illustrated with respect to a PID controller although the framework proposed is amenable to higher order controller as well. Simulation examples and experimental results are furnished to show the motivation for such an approach and the improved performance achievable with the proposed approach., (Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.)

The disturbance observer is one of the useful tools for estimating the contact force between the subject body and the environment in robotic and mechatronic systems. This paper introduced a novel automatic office-based ear surgical device for the treatment of Otitis Media with Effusion (OME) under the guidance of force sensing information. Since the force sensing information must be reliable so as to ensure the safety of the device, a contact force estimation method based on the disturbance observer is proposed. The system model is built and a control strategy is proposed and developed. In the control strategy, a composite motion controller for an ultrasonic motor (USM) stage is presented, and then the design and the stability analysis of an advanced disturbance observer is given. Furthermore, a contact estimator and a failure detector, aiming to enhance the safety and reliability enhancement, are designed. Finally, the proposed control strategy is studied with both simulation and experiment. The experimental results show that the advanced disturbance observer can estimate the actual contact force correctly and precisely, and the disturbance observer based force estimation and failure detection method is feasible which can be used in force sensing, contact detection and fault diagnosis., (Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.)

To treat a worldwide common ear disease (OME), a device allowing fast grommet tube insertion has been designed in our earlier works (Gao et al., 2015 [1] and Liang et al., 2013 [2]). However, the instrument has to be manually placed as close as to the Tympanic Membrane before the insertion procedures. To realize a fully automated surgical process, the instrument shall be automatically manipulated to align to the axial direction of ear canal and proceed to complete the surgery. A vision-based servomechanism is proposed to solve the path planning problem. A fuzzy-gain-scheduled controller is proposed to minimize the projection error based on the image detection and the proximity measurement. The proposed controller is proven to outperform the traditional PI controller in pre-clinical trials., (Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.)

In this paper, the singular value decomposition (SVD) based identification and compensation of the hysteretic phenomenon in piezo actuators are addressed using a Preisach model. First, this paper presents an SVD-based least squares algorithm and a revision approach of the identification through updating the SVD. With the identified parameters and a log of the memory curve, a Preisach-based inversion compensator is constructed which is complemented with a feedback controller to address the inevitable and residual modeling errors. Experimental results are furnished for both the identification and compensation approaches. The Preisach-based feedforward controller significantly improves the tracking performance and reduces the root-mean-square (RMS) tracking error of a PID controller by 76.7% and 89% at 1 Hz and 25 Hz, respectively. With the proposed composite controller, the percent-RMS errors at 1 Hz and 25 Hz are reduced to 0.035% and 0.31%, respectively., (Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.)

In this paper, the development of an automated umbilical cord blood (UCB) collection instrument, comprising of mechanical, electronics and control components, is provided in detail. UCB from the placenta provides a rich source of highly proliferative cells for many clinical uses as it contains rich Hematopoietic Stem Cells (HSCs) which yield many benefits over traditional sources such as the bone marrow and periphery blood. Current collection of UCB uses a syringe to extract blood from placenta, which is highly limited in volume and cell numbers. This paper will present the development of an automated UCB collection instrument to yield improved performance which comprised four subsystems. First, a placenta handling system is designed to produce air pressure which can realize the emulation of the uterus compression on the placenta. Second, an auto-medium injector system is presented to enable perfusion automatically. Third, a time window widening system is developed which generates vibrations during the perfusion phase and helps the exposed end of the cord cool down to a low temperature. Finally, a control platform is used to integrate all systems working together, hosting the control algorithms which operate the instrument automatically., (Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.)

This paper presents the development of a microdispensing system based on a contacting method, with an aim to lowering production and maintenance cost. The liquid, to be dispensed, is brought into contact with the work piece, thus dispensing a droplet by making use of the adhesion force between the liquid and the work piece. A piezoelectric actuator is employed as the drive for the system to achieve high precision. The control of the system is accomplished with a PID controller; controlling the dispensing process and trajectory tracking., (Copyright © 2010 ISA. Published by Elsevier Ltd. All rights reserved.)

Fault diagnosis and predictive maintenance address pertinent economic issues relating to production systems as an efficient technique can continuously monitor key health parameters and trigger alerts when critical changes in these variables are detected, before they lead to system failures and production shutdowns. In this paper, we present a decoupled tracking and thermal monitoring system which can be used on non-stationary targets of closed systems such as machine tools. There are three main contributions from the paper. First, a vision component is developed to track moving targets under a monitor. Image processing techniques are used to resolve the target location to be tracked. Thus, the system is decoupled and applicable to closed systems without the need for a physical integration. Second, an infrared temperature sensor with a built-in laser for locating the measurement spot is deployed for non-contact temperature measurement of the moving target. Third, a predictive motion control system holds the thermal sensor and follows the moving target efficiently to enable continuous temperature measurement and monitoring.

This paper proposes a new method for automatic tuning of the Smith predictor controller based on a Repetitive Control (RC) approach. The method requires the input of a periodic reference signal which can be derived from a relay feedback experiment. A modified repetitive control scheme repetitively changes the control signal to achieve tracking error convergence. Once a satisfactory performance is achieved through the learning control, the parameters of the Smith predictor controller can be computed from the signals using a nonlinear least squares algorithm. The same relay feedback experiment can provide an initial parameter vector for an efficient implementation of the parameter estimation. Simulations and experimental results will be furnished to illustrate the effectiveness of the proposed tuning method.

High precision motion control of gantry stages has found numerous applications in the manufacturing industries where precise positioning is crucial. This paper presents a survey of existing control schemes as well as the development of enhanced schemes for the coordinated motion control of moving gantry stages. In particular, a robust control scheme is proposed which uses a feedback controller with a sliding mode to correct for the tracking error and to coordinate multiple axis to move in tandem. Simulation and experimental results will illustrate and compare the performance of the control schemes presented in the paper.

In this paper, a hybrid control scheme utilizing a PID feedback control with an additional regulated chatter signal is developed to compensate motion impeding influences such as the effects due to friction, force ripples, and hysteresis in linear piezoelectric motor. The regulated chatter signal is a pulse sequence superimposed on the PID control signal. It has a fixed amplitude, and a pulse width regulated via iterative learning control. As such, the scheme is expected to be useful for applications involving iterative motion sequences. An analysis of the closed-loop performance is presented in the paper. Simulation and experimental results are also furnished to demonstrate that the proposed control scheme can reduce tracking errors significantly.

In this paper, we present a new statistical approach towards soft geometrical error compensation of machines with significant errors. The approach, based on an analysis of the probability of the random error recurring, can reduce the adverse influence of random errors on the compensation of systematic errors. The proposed methodology is made up of three steps. First, error classes are defined from the error bands obtained from calibration. Second, the probability of the magnitude of random error belonging to each of these classes is computed based on the density of the data set within the class. Based on these probabilities, the most probable systematic part of the error measurement can be statistically deduced. Finally, the geometrical error compensation is carried out based on this value. Experimental results are provided for the linear error compensation of a single-axis piezo-ceramic motion system.

In this paper, we address the problem relating to the precision control of permanent magnet linear motors to track repeated motion trajectories. A high gain disturbance compensator is developed to improve the control performance degraded due to the presence of significant disturbances. An inverse gain of the overall system model is used to set up a disturbance observer. The observed disturbance is then used to generate a "knocker" signal, to be augmented to the control signal, which can provide the additional energy necessary to overcome the effects of the disturbances. A learning scheme is used to adjust the knocker signal iteratively over the repeated cycles. Simulation and experimental results are furnished to demonstrate the effectiveness of the proposed control scheme.

In this paper, the development of relay-enhanced multi-loop PI controllers is described for multivariable processes. The control system employs a relay in series with the controller. The relay can ensure a satisfactory level of closed-loop performance and it also yields oscillations for tuning of the PI controller based on an equivalent process model for each loop. A simulation example [on a two-inputs-two-outputs (TITO) process] is provided to illustrate the effectiveness of the proposed method and to compare its performance to an existing method.

This paper presents the design and realization of a feedforward dither signal to reduce the force ripple in an iron-core permanent magnet linear motor (PMLM). A composite control structure is used, consisting of three components: a simple feedforward component, a PID feedback component, and a ripple compensator (RC). The first two components are designed based on a dominant linear model of the motor. The dither signal is generated based on a signal model which is identified using a multidimensional simplex downhill method. In this way, a simple approach is available to eliminate or suppress the inherent force ripple, thus facilitating smooth precise motion while uncompromising on the maximum force achievable. Real-time experimental results verify the effectiveness of the proposed scheme for high precision motion trajectory tracking.

In this paper, we propose a composite control scheme for a gyro mirror line-of-sight stabilization system. It comprises of an adaptive controller augmented with a variable structure (VS) to remain efficient in the face of modeling errors and extraneous disturbances. Under an adequate selection of control parameters, the control scheme guarantees an asymptotically stable closed-loop response. An automatic tuning method is developed for the proposed control scheme which explicitly uses inherent properties of the control structure for tuning purposes. Simulation and experimental results are provided to illustrate the operational principles of the proposed scheme and to demonstrate its viability in real practical applications.

In this paper, we present a new simultaneous online automatic tuning method for cascade control using a relay feedback approach. Departing from the traditional approach towards tuning of cascade control systems where the secondary and primary loops are tuned in strict sequence, the proposed approach is to carry out the entire tuning process in one experiment. For ease of practical applications, the entire procedure of controller design may be automated and carried out online. A direct controller tuning approach to tune the controllers is proposed here. Robustness analysis of the new cascade control design is further carried out in the paper by drawing on existing results for SISO feedback systems. Simulations are provided to illustrate the applicability and effectiveness of both the online autotuning approach and the new cascade control design.

Till now, traditional low-order control schemes have never been applicable to unstable systems with deadtime. In this paper, we present the first application of a PID controller with time-scheduled gains to unstable systems with deadtime, consisting of a single unstable pole. The control gains are designed based on a generalised predictive control (GPC) approach. The only user specifications required are simple and classical desired properties as in the natural frequency and the damping ratio of the closed-loop system. An approach is further developed to subsequent on-line self-tuning of control weights so that the overall control system remains applicable and effective in the face of disturbances and slowly varying dynamics. A detailed analysis of the closed-loop stability of the thus designed control system is further provided in the paper. Based on stability conditions developed, the prediction horizon for the GPC-based controller may be effectively computed. Finally, simulation examples illustrate the performance of the control system.

In this paper, a robust on-line relay automatic tuning method for PID control systems is developed which expand on the application domain of Astrom's renowned relay autotuning method. In the proposed configuration, a relay is applied to an inner loop of a controller-stabilised process in the usual manner. Using the induced limit cycle oscillations from the closed-loop system, the controller settings may be re-tuned non-iteratively to achieve enhanced performance without disrupting closed-loop control. Two control tuning methodologies are developed -- a direct and an indirect method based on an explicit process model. Simulation examples and a real-time experiment are provided to illustrate the practical appeal and potential advantages of the proposed method over the basic one.