Search

Dynamic mechanical tracking errors occur in ball screw drives typically due to inertial, frictional and external forces. This results in axial elongation and compression of key components of the drive that deteriorate the dynamic tracking accuracy. In order to improve tracking accuracy, this paper presents a feedforward compensation method of dynamic mechanical tracking errors. A dynamic model is proposed to offset the position commands that are fed to the servo controller. The accuracy of the model can be improved by considering the torque transmission between the nut and the ball screw, which is not considered in existing models. To obtain the stiffness and friction parameters in the model, a new method of parameter identification is proposed. The method can simultaneously identify friction in key components leading to greatly improved efficiency and accuracy. The dynamic model and parameter identification method are validated by comparing simulation and experimental results for trapezoidal and sinusoidal trajectories. To validate the simulation results, the sinusoidal trajectories are used to compensate the tracking errors of the ball screw. The results confirm that most of the dynamic mechanical tracking errors are eliminated after compensation. Therefore, the compensation method based on the proposed dynamic model and parameter identification method is effective in improving the tracking accuracy of ball screw drives.

In order to meet the rigorous requirement for transient and static performance of automobile electronic throttle control systems, an adaptive finite time servo control (AFTSC) strategy is investigated by integrating adaptive backstepping recursive technique into the framework of finite-time stability theory. The required transient performance of the throttle opening trajectory tracking is guaranteed theoretically by the finite convergence time and the convergence rate related to the adjustable control parameters. The static performance is enhanced by introducing the tracking error integral into the system state variables. The robustness of the satisfactory transient and static performance is improved by the adaptive update law in the light of system parameter uncertainties due to production deviations, different working conditions and aging. Meanwhile, the advantage of the proposed AFTSC strategy is validated by demonstrating the comparison results with the existing strategies both in the critical operating cases under Matlab/Simulink simulation environment and in the actual operating cases on the dSPACE rapid-control-prototype (RCP) test platform for a real electronic throttle system.

This paper proposes a new algorithm for estimating the resonant frequency of adaptive notch filters used in servo systems. Notch filters and adaptive notch filters are widely used in commercial servo systems for suppressing a resonance which is a major obstacle in improving their performance. However, the conventional frequency estimation algorithm gives a dynamic behavior that is proportional to the difference between the square of the estimated frequency and the square of the actual frequency. This can cause the estimation dynamics to be too slow for low-frequency resonances, if both low- and high-frequency resonances are present and if the estimator gain is designed for a high frequency. This paper develops a new algorithm to give a dynamic behavior that is proportional to the difference in the estimated frequency and actual frequency. This allows selecting the estimation parameters independent from the value of resonant frequencies. The developed algorithm is implemented to a production servo controller and applied to a production printed-circuit-board inspection system. The experimental results show that the developed algorithm is much more effective in suppressing the resonances of both low- and high-frequencies, compared to the pervious algorithm. Furthermore, the ability to suppress vibration allows increasing the feedback gain, which in turn allows improving the tack time performance from 190 ms to 100 ms. All experiments reported in this paper were performed in an actual industrial environment using a production system, and the developed algorithms are applied to the production system.

As the core of Industry 4.0, the intelligent manufacturing technology requires robotic arms to be networked, customized and flexible. Traditional industrial robots have a large number of electrical cables. The end effectors cannot be easily replaced. In this paper, a reconfigurable modular arm with quick replacement of tools and its neural adaptive control system are developed. It consists of an anthropomorphic 7 degree-of-freedom (DOF) manipulator, a reconfigurable connection mechanism (RCM) and a wireless controller. Based on the modular design ideas, each joint is integrated with a motor, a harmonic reducer, two encoders and a servo controller to achieve high torque capacity but keep light weight. Shape Memory Alloy (SMA) wires and steel spheres are used in the RCM to provide mechanical and electrical connections between the arm and the end effector for rapid replacement. The central controller communicates with each servo controller through wireless communication links. Furthermore, the neural adaptive control method compensating position and force tracking errors caused by the model uncertainty and time delay is addressed. Finally, the prototype is fabricated and experiments are carried out. The developed arm has high position accuracy, force control accuracy, and reliable reconfigurable capability.

In this paper, we propose a new control scheme that provides position and velocity profile tracking control for next-generation servo track writing (STW). Whereas conventional servo track writers require controllers that perform fast positioning control with fast track seeking and regulation, spiral servo track writers require accurate position and velocity profile tracking control to achieve high quality servo patterns on the media disk. Because STW timing eventually renders geometrically accurate servo patterns, both position and velocity error signals should be regulated within small bounds in a constant velocity region. Regulation via an integral sliding mode controller (SMC) is known to provide good tracking performance; however, use of a high switching gain is inappropriate for an actuator with resonance modes. In this paper, we therefore apply integral sliding mode control with a disturbance observer to STW. The relationship between eigenvalues and control gains is mathematically analyzed to improve dynamic tracking response. To verify the utility of the proposed position and velocity profile tracking control, we perform a comparative study between the proposed and conventional control methods and experimentally validate the performance of the proposed method.

Servos (as commonly used in radio controlled vehicles and small scale robotics) are DC actuators which use a potentiometer to provide built-in feedback to localise an actuator arm. To minimise jerky control movements, many servo controllers include velocity and acceleration control which operate using a defined velocity profile resulting in the Pulse Width Modulation (PWM) control value being changed over time. On power-up the initial position of the servo arm is unknown to external controller—resulting in the arm moving to the starting value at maximum speed (which may be mechanically hazardous). In this paper two different techniques for performing a soft-start for servos are described and evaluated, namely: voltage profiling and intermittent drive. The different techniques are implemented and evaluated using four different servos based on measured velocity profiles, current consumption, and peak torque.

This paper presents a mode switching control (MSC) scheme in discrete-time domain for fast and precise set-point tracking in servo systems subject to control saturation and unknown disturbance. The basic idea is to combine the proximate time-optimal servomechanism (PTOS) and the composite nonlinear feedback (CNF) control, using the output position as the only measurable information for feedback. The PTOS is responsible for fast targeting in servo systems when the tracking error is large, and once the system trajectory enters into some specified region, the CNF will take over the control to ensure a smooth settling without compromising the fast transient performance. A reduced-order extended state observer is adopted to estimate the speed signal for feedback and the disturbance for compensation. The asymptotical stability of the proposed MSC scheme is analyzed and the switching conditions are provided. Simulation and experimental results on a permanent magnet synchronous motor (PMSM) servo system verify that the proposed control scheme is effective in improving the tracking performance for a wide range of target set-points.

In this paper, a modified force decoupling method for improved servo control of a magnetically suspended double-layer single-sided linear induction motor (LIM) is presented. In this study, the primary is magnetically suspended under and moved along the double-layer secondary which consists of an aluminum plate with a back-iron. In order to decoupled the normal and thrust force, analytical expressions for the forces as function of the slip frequency and the primary current are obtained by curve fitting on steady-state FEM results. From these steady-state force models, the required current amplitude and slip frequency are solved for given force setpoints. The setpoints are generated by a position controller which is designed based on a dynamical model of the LIM. The dynamical model is estimated by injecting noise into a transient FE-model and measurements. Transient FEM simulations and measurements show the effectiveness of the proposed controller and decoupling method when they are used to magnetically suspend and position the LIM.

This paper deals with position control of a single degree of freedom (sdof) manipulator actuated by Pneumatic Artificial Muscle (PAM) actuator. Though the compliance characteristics of these actuators are desirable, their inherent non-linearities due to compressibility of air and non-linear load–contraction characteristics make them difficult to model and design of controller becomes very complex. To overcome this, a novel method is hereby proposed to establish an accurate empirical model for the system. The quasi-static characteristics of the PAM are first modelled followed by the dynamic characteristics through spectral analysis. For cost competitiveness, the present work incorporates inexpensive on–off switching valves operated using a novel model based proportional pressure regulator developed using a modified PWM algorithm. Finally, a conventional PID position controller is extended using the empirical PAM model and an inner pressure regulation loop to achieve trajectory tracking of a sdof manipulator. Results for pressure regulation and position control confirm the effectiveness of the adopted approach in achieving performance comparable to the state-of-the-art results at a reduced control complexity and total set-up cost.

Design and implementation of servo controller for a hydraulic servo system with a load of large inertia, low stiffness and multi-stage resonance is considered. To achieve a set of desired requirements, this paper is divided into three parts of work. First, notch filters and peak filters extracted from the general phase stabilized controller are applied in order to restrain the resonance peak of the load. Second, a disturbance observer in the feedback path is used for rejecting low-frequency disturbance and high-frequency noises. Third, as the complete inversion of the closed-loop dynamics at the whole frequency band does not necessarily give the best performance, low-pass filter, proportional derivative (PD) compensation, and lead correction are adopted in the feedforward path. The work proposed here overcomes the challenge of improving amplitude margin and phase margin while eliminating resonance simultaneously. The effectiveness of the combined control is investigated through simulation and experiment results, which show that the control strategies raised here successfully complete resonance rejection and also give ideal performances that meet the indices.

Traditionally, a visual servo control problem is formulated in the teach by showing framework with an objective to regulate a camera based on a reference (or desired) image obtained by a priori positioning the same camera at the desired task-space location. A new strategy is essential for a variety of applications where it may not be possible to position the camera a priori at the desired position/orientation. In this paper, a visual servo control approach, called ‘‘teach by zooming’’, is formulated where the objective is to position/orient a camera based on a reference image obtained by another camera. For example, a fixed camera providing a wide area view of the scene can zoom in on an object and record a desired image for another camera. A non-linear Lyapunov-based controller is designed to regulate the image features acquired by an on-board camera to the corresponding image feature coordinates in the desired image acquired by the fixed camera in the presence of uncertain camera calibration parameters. The proposed control formulation becomes identical to the well-known teach by showing controller when the camerain-hand can be located a priori to the desired position/orientation; thus enabling control in a wide range of applications. Experimental results for regulation control of a 7 degrees-of-freedom robotic manipulator are provided to demonstrate the performance of the proposed visual servo controller.

In a tape drive, the head assembly hosting servo readers and data writers/readers must initially be moved to a target position, so that information can be written to or read from the desired tracks. In tape systems with flangeless rollers, as recently introduced in IBM’s tape drives for improved performance and extended drive and tape lifetime, the initial positioning of the servo readers over the servo bands, from which the position-error signal for steady-state track-following operation is obtained, has to be fast. This requirement is dictated by the nonnegligible lateral tape motion experienced in tape paths with flangeless rollers. In this paper, a method is proposed to utilize both the servo readers and the data readers in a drive to detect the presence of a valid servo signal. If the servo readers are not positioned over a servo band, the distance between servo readers and servo band can thereby be continuously estimated by identifying the data reader detecting the presence of a servo signal. This information is then provided to a control element that controls the joint operation of a coarse stepper motor and a voice-coil motor based fine actuator with large stroke in a feedback or feed-forward configuration to achieve fast servo reader positioning. In the feedback-based approach, all data channels are continuously monitored to detect the presence of a valid servo signal and a pseudo position-error signal is generated and fed back to the control unit to drive the actuator towards the target position. In the feed-forward approach, a trajectory for the actuator is determined as soon as the servo band is in the capture range of the fine actuator and a control signal is generated so that the servo reader rapidly lands over the servo band with optimum control effort.

Virtual device network (VDN) is an intelligent integrated form of a device (control) network and IP network. If a fieldbus based distributed control system (DCS) is implemented on a global VDN, efficiency and flexibility can be significantly improved. In this study DCS implemented on the LonWorks/IP VDN is investigated with an example of model reference adaptive control (MRAC) of a geared DC motor. In order to compensate for the network induced uncertain time delay inherently present on VDN, the modified Smith predictor based internal model controller was integrated to MRAC (MRAC–IMC). The effectiveness of the proposed control scheme was tested through experiment. The proposed control scheme exhibited the robustness to noise and external disturbances and the good tracking performance around zero velocity point occurring due to overshoot and stick friction. Result of this study suggests that sophisticated servo control of dynamic systems is possible from a remote client PC on VDN by properly compensating the network delay.

Digital servo control was introduced in mass production hard disk drives (HDD) in 1986. Since then various kinds of digital control technologies have been applied to HDD servo systems, and the performance has been improved dramatically. A 3.5-in. HDD capacity, which was 251 MB in 1988, is 2000,000 MB (2.0 TB) in 2009. Faster access (high quality motion control), more precise positioning (nanometer scale control), and more robustness against disturbances and plant fluctuations are required to meet the increasing demand for larger capacity and higher performance HDDs. The field of HDD servo technology provides an example of techniques for micro or nanometer accuracy. Although the application aspects may be different in other fields requiring high positioning accuracy, the methods used in HDDs are general enough that they can be transferred. This paper is not intended to act as a review paper, but presents several fundamental ideas of precision positioning servo control, especially ones derived from the history of HDD servo control.

Due to the renowned superparamagnetic effect encountered in conventional magnetic data storage, many alternative futuristic data storage platforms have been proposed, e.g. Probe-Based Storage Systems (PBSS) successfully demonstrated in the ‘‘Millipede” project [Eletheriou E, Antonakopoulos T, Binning GK, Cherubini G, Despont M, Dholakia A, et al. Millipede—a MEMS-based scanning-probe data-storage system. IEEE Trans Magn 2003;39(2):938–45]. In this paper, a micro X–Y stage with 6 mm � 6 mm recording media platform actuated by capacitive comb drives is designed and fabricated in a so-called ‘‘Nanodrive” PBSS. The developed prototype is fabricated by micromachining techniques with the integration of a 40 nm thick PolyMethyl-MethAcrylate (PMMA) recording media. Using Finite Element Analysis (FEA) on the developed platform, the first two dominant in-plane resonant modes of the micro X–Y stage at 440 Hz are captured. A displacement range of up to 20lm can be achieved at an input driving voltage of 55 V. A Capacitive Self-Sensing Actuation (CSSA) circuit and robust decoupling control scheme are also designed for the micro X–Y stage for improved servo control. 2009 Published by Elsevier Ltd.

In this paper, a new desktop NC machine tool with the ability of compliance control is presented for finishing of metallic molds with small curved surface. The NC machine tool consists of a three-axis robot whose single one has a high position accuracy of 1 μm, which means that it can perform higher resolutions of position and force, compared to general industrial robots. A ball-end abrasive tool is attached to the tip of z-axis through a force sensor. In order to first confirm the application limit of an industrial robot to a finishing task, we evaluate the backlash that causes inaccuracy in position at the tip of the abrasive tool, by simply measuring the position and force. The basic resolution of the proposed NC machine tool is shown through the similar position and force measurement to one used in the conventional robot. Next, a CAD/CAM-based position/force control method with a fine-velocity pulse converter is proposed for a pulse-based servo controller that actuates the single-axis of the robot. We further introduce a systematic method for tuning a desired damping, which is coming from the critically damped condition used in a static force control system. The desired damping is the most important factor when an impedance model following force control is applied. Finally, to evaluate the characteristics of the NC machine tool, a profiling control experiment is conducted along a spiral path for a plastic lens mold with axis-symmetric concave areas. Consequently, it is confirmed that the proposed NC machine tool has a good performance, which can be applied to the finishing process of plastic lens molds.

The interaction between structural components flexibility and closed-loop servo system determines primarily the performance of all electro-mechanical systems. Taking hard disk drives as a typical example of high-precision servo systems, this paper focuses on servo system modeling and reduction through quantitative analysis using finite element method. A finite element model of a full head actuator is established. Detailed dynamic characteristics of the head actuator assembly have been investigated. Combined with analytical results, a full model for the servo control of the assembly has been established. The model can be reduced by modifying the full modal matrix, selecting modes based on dc gain and peak gain under constrained operating conditions. Only the most important modes were kept for servo system modeling. This results in a general procedure to analyze the characteristics of servo system that can be adequately modeled by finite element method for servo control design and simulation. Frequency response functions between the VCM input current and velocity response of the slider were measured using LDV to validate the model for further analysis. Both simulation and experiments for servo controller design and evaluation have been conducted in this paper. The results show that the modeling method can be used for the simulation of finial servo control design to achieve effective and integrated system design for mechatronic systems.

This paper takes into consideration the rejection of narrow-band disturbances at two frequencies higher than servo bandwidth in order to obtain good positioning accuracy for a micro-actuator. A phase stabilized feedback controller combined with a disturbance observer structure is applied to achieve the rejection of the two disturbances. A high frequency bandpass filter is adopted in the disturbance observer in order to reject the high frequency disturbance, and simultaneously the stability of the feedback control loop is remained when the disturbance observer is added on to the external stabilized controller. The effectiveness of the combined control is investigated through simulation and experiment results, which show that this control scheme can reduce position error significantly and is better than using phase stabilized feedback control only or proportional-integral-derivative (PID) controller with notch filters.

A discrete-time hierarchical sliding-mode control scheme for a dual-stage tracking control system with bounded parameter variation and external disturbance is proposed in this study. This scheme is capable of performing a positioning servo control task that requires driving both coarse tracking and fine tracking stages simultaneously. The desired tracking performances, both the coarse tracking and fine tracking, are ensured. The settling time of the controlled system could be pre-specified by selecting a sliding hyperplane. Furthermore, explicit conditions, involving inequality constraints on the controller parameters, to ensure a one-sided behavior, quasi-sliding mode and chattering-alleviated performance with uncertainty and/or external perturbation of known bounds of the plant are derived. Experimental studies on the design of a track-seeking controller for an optical pick-up head is conducted to further illustrate its feasibility and effectiveness. The experimental results also demonstrate that the proposed scheme provides better performance than a discrete-time sliding mode control method with controller switching method.

The paper proposes a fine seek servo controller for the digital versatile disk (DVD). The proposed control is an integration of a hybrid track position detector, a position accumulator, a position profile generator, a control finite state machine, an estimator, a defect detector, an RFRP signal compensator, a tracking servo equalizer (for both track-following and fine-seek) and a sled servo equalizer. The integration of these blocks enables a wider range of pull-in area for the servo to switch from track seeking to track following. The implementation results show that the proposed control achieves better performance over the conventional velocity control approach. The experimental results also demonstrated the ability of the control to effectively deal with disks with defects or fingerprints.

In this paper, the control plant is a ball screw actuated milling machine table which has been retrofit with DC servo motor control. The retrofit milling machine has nonlinear time-varying behaviors because of the effect of irregular Coulomb friction of the sliding surface and obvious backlash. Thus, it is difficult for a conventional digital controller to provide a high contouring accuracy as well as adequate disturbance rejection and parameter variation robustness. To improve contouring performance of the retrofitted milling machine, a self-tuning adaptive control strategy, combined with cross-coupled control of axial motion is proposed. The proposed control scheme has been verified as being internally stable. Experimental results show that this control method achieves satisfactory contouring accuracy, transient response, tracking and robustness under the influence of backlash on each axis and irregular Coulomb friction. This performance verifies the applicability of this economic approach to automation of traditional milling machines.

Robust gap-control is applied to compensate for electrode wear in an electric discharge scanning (ED-Scanning) process. This control compensates for the wear without reference to the wear ratio of the electrodes. An auxiliary gap-control loop in the vertical direction can compensate for the wear of the electrode, according to the discharge voltage when the electrode is driven along the two horizontal axes. A proportional controller for a gap-control system with maximal robustness is designed and robustly analyzed to override the non-linear and time-varying feedback. The simulated and practical responses of such a robust gap-control system yield favorable performances. The controller can maintain the location of the discharge on the vertical axis and fix the depth of the removal to that of a particular layer. The practical scanning process reveals that the dimension of a hole can be guaranteed only if the data concerning the depth of removal under specific discharge conditions and electrode diameters are applied.

We consider in this paper the design and implementation of a dual-stage actuated hard disk drive (HDD) servo system, in which an additional piezoelectric actuator is mounted on top of the conventional voice-coil-motor (VCM) actuator to provide a faster and finer response. More specifically, the dual-stage actuated HDD servo system consists of a primary VCM actuator and a secondary suspension piezoelectric microactuator. The VCM actuator is used to quickly move the read/write (R/W) head of the HDD servo system to a target track, whereas the microactuator is used to fine-tune the R/W head position when it is getting closer to the target. In our design, the primary actuator is controlled by a newly developed composite nonlinear feedback (CNF) control law, which has fast rise time and small overshoot, and the microactuator is controlled through a simple static gain together with a low-pass filter and a notch filter. Simulation and implementation results show that in track following, the dual-stage actuated HDD servo system has outperformed the single-stage actuated counterpart by more than 47% in settling time and by 39% in position error signal (PES) tests.

Most servomechanisms use encoders whose output signals are 90° phase-shifted sinusoidal waves for detecting angular position. These two-phase signals are not true sinusoidal waves and their distortion makes the positioning accuracy worsen. In this paper, the authors propose non-sinusoidal two-phase type PLL (Phase-Locked Loop) to increase positioning accuracy of servomechanisms. To obtain high-precision detection of angular position, an iterative learning method to compensate the wave distortion was tried, and a high-resolution and high-precision positioning controller that can use low-resolution encoders was obtained. This paper discusses the proposed method and gives experimental results.

>The earth moving equipment industry is quickly gearing up to achieve great gains in efficiency, performance, safety, and operator comfort by the rapid deployment of recent digital control technology in its products. There are two major types of earth moving equipment operating in large numbers: excavators and wheel type loaders. Excavators have received much attention by the industry recently. The wheel type loader product studied in this paper is another example of a high volume versatile machine at the opposite end of the configuration spectrum. A state of the art electro-hydraulic open centered non-pressure compensated valve control system is studied to evaluate the potential gains by implementing digital velocity servo control. The control objectives are to (1) meet operator perceived response requirements, (2) meet operator perceived smoothness requirements, (3) create a sub-system that could accept commands from an autonomous high level planning controller. Closed loop digital velocity control is successfully implemented in the racking motion of a wheel loader using a standard proportional-integral (PI) and a dynamic valve transform algorithm. The dynamic valve transform is a function of hydraulic flow rate which is a function of engine speed and rod end cylinder pressure. Robustness of performance was verified through extensive system modeling, validation, and hardware tests on a large Caterpillar wheel loader model 990. © 1998 Published by Elsevier Science Ltd. All rights reserved.

Diamond turning of brittle materials such as glass, ceramic, germanium and zinc sulfide has been of considerable research interest in recent years due to applications in optics and precision engineering systems. When diamond turning brittle materials, material removal should be kept within the ductile regime to avoid subsurface damage [1, 2]. It is generally accepted that ductile regime machining of brittle materials can be accomplished using extremely low depth of cut and feed rates. Nanometric level positioning accuracy of the machine tool axes is difficult particularly at low feed rates due to friction and backlash. Friction at extremely low feed rates is highly nonlinear due to the transition from stiction to coulomb friction, and as such is very difficult to model. In order to compensate the effect of friction and backlash of a machine tool stage, a nano-metric precision three degrees of freedom (DOF) positioner is designed and fabricated as a fast tool servo. The fast tool servo, which is an independently operated positioning device, would have a small range but high bandwidth and accuracy compared to the conventional lead-screw mechanism. The nano positioner as a fast tool servo and motor-driven feedback controller were combined in order to obtain large motion with high positioning accuracy. A CMAC neural network control algorithm was applied in order to provide on-line learning and better tracking capability compared to standard PID control algorithm. The learning controller was implemented using “C” language on DSP based PC-bus board to control both diamond turning machine and nano positioner.

A traditional manually operated milling machine with a lead screw transmission system is retrofitted to an A.C. servo motor control. This obsolescent milling machine has nonlinear time-varying behavior due to obvious backlash and irregular coulomb friction of the sliding surfaces. If a traditional digital controller is employed, its gain values have to be adjusted corresponding to the system parameters' change by trial and error. In addition, this approach cannot assure the required stability and accuracy of a closed loop system under the environmental variation of machining operations. Hence, a self-tuning control strategy is proposed for this nonlinear system by introducing an on-line estimator of system parameters to adjust the feedback gains for the desired dynamic characteristics. The concept of feed-forward control is employed to improve the accuracy of the trajectory tracking control. The experimental results show that this control method achieves satisfactory performance of stability transient response, tracking and robustness under the influence of about 0.4 mm backlash on each axis and large stick friction.

Coordinate measuring machines (CMM) are widely used in manufacturing processes for accurate and rapid inspection of machine products. Accuracy and speed are two conflicting design requirements of the CMM control system which are dictated by the servo control loops and dynamics of the arms. The CMM considered here consists of three independent servo controlled orthogonal arms, a two degrees-of-freedom (DOF) probe, a granite table and a computer for the man-machine interface. The objective of this paper is to develop a computer-based design framework to optimize the CMM performance so that an optimal control solution to the probe positioning problem may be found. The control and optimization framework consist of the nonlinear mathematical model of the CMM implemented on the Boeing simulation package EASY5×, a test rig constructed to test and evaluate the controllers and a set of control and optimization algorithms developed specifically for the CMM application. The velocity loop is optimized for maximum bandwidth using the Sequential Quadratic Programing technique. A H ∞ - based PI position controller is then developed to meet the control design performance requirements. The control tuning is made automatic by developing an autotuner which identifies the system dynamics and calculates a set of controller parameters for the optimal performance. Adaptive features are then introduced to compensate the effect of load and CMM design variations. Finally, simulation and experimental results are presented to evaluate the proposed integrated system and control design procedure.

In this paper, a hybrid actuation method for robotic manipulators is proposed. The actuator employs a hybrid combination of D.C. servo motors and more recently developed muscle-like bladder actuators. One D.C. motor-muscle actuator pair is arranged co-antagonistically with an identical D.C. motor-muscle actuator pair to drive a manipulator joint. Through a suitable control applied to the hybrid actuator, independent control of joint torsional stiffness and joint position is made possible. When air pressure is varied in the muscle actuators, the muscle actuator stiffness and length change. In order to only affect the hybrid actuator stiffness with this pressure change, D.C. servo motors are used to compensate for muscle actuator length changes, hence joint position is unaffected. High grain servo motor control ensures a response to disturbances due almost solely to the muscle actuator stiffness characteristics. Dynamic equations of motion are developed for a two joint manipulator with a hybrid actuator to drive the final link. A control is formulated for this system to achieve, in addition to independent joint torsional stiffness the joint position control, approximately decoupled and linearized dynamics. A numerical simulation of these two degrees of freedom is presented to verify the performance of the closed-loop system.

Servo control systems are used in many industries involving motion control. Many new industries are beginning to apply servo systems that traditionally did not use servos. Machine tools, assembly machines, material handling, web processing, paper, printing, packaging and test equipment industries are some examples of applications where servo control systems are widely used. As servo systems find more and more applications, the analysis, design, and sizing of appropriate servo system for a particular application become more and more important. Computer aided design and analysis tools are needed to address all of these applications to optimize performance and cost. This paper presents a computer aided design (CAD) tool for servo system analysis, design, and sizing for various applications.