Friction Compensation Scheme Research Articles

Friction model identification and compensation strategy for photoelectric tracking system

Friction model identification and compensation strategy for photoelectric tracking system

Medical Grabbing Servo System with Friction Compensation Based on the Differential Evolution Algorithm

This paper introduces a pneumatic finger cylinder servo control system for medical grabbing. First, according to the physical structure of the proportional directional valve and the pneumatic cylinder, the state equation of the gas in the servo system was obtained. The Stribeck friction compensation model of a pneumatic finger cylinder controlled by a proportional valve was established and the experimental platform built. To allow the system output to better track the change in the input signal, the flow-gain compensation method was adopted. On this basis, a friction compensation control strategy based on a differential evolution algorithm was proposed and applied to the position control system of a pneumatic finger cylinder. Finally, the strategy was compared with the traditional proportional derivative (PD) strategy and that with friction compensation. The experimental results showed that the position accuracy of the finger cylinder position control system can be improved by using the friction compensation strategy based on the differential evolution algorithm to optimize the PD parameters.

Synchronization Control With Adaptive Friction Compensation of Treadmill-Based Testing Apparatus for Wheeled Planetary Rover

This article studies synchronization control of a novel devised treadmill-based testing apparatus for wheeled planetary rover roaming at low speed. To offer satisfactory tracking performance and to ameliorate internal conflicts amongst individual treadmills during rover-treadmill interaction, a decentralized synchronization control strategy integrating an adaptive friction compensation scheme is proposed. To overcome the nonlinear friction effect at low-velocity scenarios, the LuGre model based friction compensation scheme is constructed with a dual-observer structure that can handle parametric uncertainties without recourse to the high-resolution encoder-required parameter identification. With the proposed control design, asymptotic stability of the closed-loop system is guaranteed with the tracking error and synchronization error converging to zero in presence of parametric uncertainties. Experimental results demonstrate the effectiveness of the proposed control strategy, which significantly improves the tracking performance in comparison with the existing proportional differential (PD)-type controller and synchronization controller without friction compensation.

A New Uniformly Ultimate Boundedness Criterion for Temperature Dependent Average Bristle Deflections

Temperature variation intensively affects parameters of the friction force, particularly the average bristle deflections. In our earlier research work, a temperature dependent friction compensation scheme was developed for serial rigid robot manipulators which was comprised of a temperature dependent viscous friction compensation scheme and a temperature dependent disturbance rejection scheme. In this paper, a new criterion for the uniformly ultimate boundedness of the temperature dependent average bristle deflections is proposed in such a way that the temperature dependent average bristle deflections preserve the property of uniformly ultimately boundedness in a larger region. This is an improvement to our earlier research work. As the result of this improvement, it is shown that the proposed method in our earlier work, is applicable to larger temperature dependent disturbance terms. These two improvements are the main contributions of this paper that augment our earlier research work. The idea is supported by a new theorem.

High precision position control of electro-hydrostatic actuators in the presence of parametric uncertainties and uncertain nonlinearities

Characterized by high power-to-weight ratio, modularity and energy efficiency, electro-hydrostatic actuators (EHAs) have been successfully applied to aircrafts and submarines, where high precision and repeatability are in high demand. The position tracking performance, however, can be inevitably affected by parametric uncertainties and uncertain nonlinearities. Model inaccuracy or system variations normally require a large loop gain to achieve robust performance, which leads to over-design. Leakage in the fluid power system decreases steady-state accuracy, and friction in the actuator degrades the transient performance or even causes stick-slip motion at low speeds. Furthermore, the system may exhibit limit cycle (or hunting) due to Stribeck friction and integral action. This paper proposes a robust high precision position control strategy incorporating leakage and friction compensation for EHAs. Quantitative feedback theory (QFT) is applied to design a robust controller that satisfies the prescribed performance specifications without over-design, considering model inaccuracy and system variations. The internal leakage is subsequently compensated based on experimental data instead of incorporating an integrator in the controller; hence, limit cycle is avoided, and response speed is improved. Friction in the actuator is identified based on the LuGre friction model and compensated through an observer in the loop. Friction variation and load fluctuation are considered to be output disturbances to be suppressed by the QFT controller. The QFT controller with leakage and friction compensation scheme is verified through experiments on a typical EHA. Both the steady-state and transient position tracking performances are greatly improved.

Adaptive Controller Based on Spatial Disturbance Observer in a Microgravity Environment.

In this paper, a new controller for an operating manipulator work in the space microgravity environment is proposed. First, on the basis of the load variation caused by microgravity, a sliding mode control method is used to model the gravity term, and the logistic function is introduced as the approaching function. An improved sliding mode reaching law is proposed to control the manipulator effectively, and Lyapunov theory is used to deduce its closed-loop stability. A friction compensation scheme, which regards friction as disturbance, is introduced to the microgravity environment, and a space disturbance observer (SDO) is designed from the viewpoint of disturbance suppression to identify the friction characteristics of the control system accurately. To model the lagging friction phenomenon caused by velocity inversion during operation tasks, an adaptive compensation scheme based on the LuGre model is proposed. Finally, the design of a manipulator system, which consists of a robot arm, dexterous hand, teleoperation system, central controller, and visual system, is presented. On-orbit maintenance and capture experiments are carried out successively. The effectiveness and reliability of the controller are verified, and the on-orbit operation tasks are completed successfully.

Intelligent Friction Compensation: A Review

High-precision motion control is highly desirable in process and industrial automation, including the domains of machine tools, ultra-precision spindles, micro-manufacturing, biotechnology, disk drive read/write mechanisms, air-bearing positioning stages, etc. However, their performances are limited by various nonlinear factors in the actuators behind the applications, such as friction, creep, force ripples, and hysteresis. In this paper, we focus on the friction compensation schemes, reviewing literature focusing on the intelligent designs of friction compensation in motion control systems. Different types of friction models, from simple to complex structures, are reviewed, followed by detailed discussions on the friction compensation schemes. Finally, we highlight the advantages and disadvantages of the methods in these two categories, and offer recommendations for possible research directions.

Implementation of KPIs for Analyzing Control Loop Performance by using PI System of the OSIsoft Enterprise

In this paper, Key Performance Indicators - KPIs are developed as a cheap alternative to systems that are specifically designed to perform a continuous monitoring of the process variables. In this work, the KPIs are implemented in a high performance data-historian (OSIsoft Enterprise PI Server), as well as a methodology for analyzing and monitoring of control loops that allow quantifying the divergences between the set point and process variables and analyze possible problems in the measuring and actuating instruments. This methodology is applied to a pH Neutralization Pilot Plant. In order to reduce the variability of the control loops generated by control valves with excessive friction, a friction compensation strategy is developed and implemented.

Sensorless model-based object-detection applied on an underactuated adaptive hand enabling an impedance behavior

This paper introduces a sensorless object-detection control strategy designed for an underactuated three fingers hand. The proposed algorithm achieves a very accurate object-detection, through a simple joint impedance control scheme combined with a state-observer. The joint impedance control adapts the position set-point of each finger according to the estimated kinematics state computed from the kinematics model of the finger. The additional control loop is applied as external controller w.r.t. the standard one. The object-detection is obtained without any external sensors using only the measures of position and current provided by the fingers actuators. A friction compensation strategy based on a probabilistic approach has been implemented. An impedance control algorithm avoids the tuning of grasping parameters (i.e. grasping velocity and holding force). In this way developed controller provides adaptive behavior enabling the manipulation of objects made by unknown materials, without producing damages on their surfaces. This approach represents a step ahead to the flexibility of the grasping devices, in particular in manufacturing production, where the variability of manipulated pieces, in terms of shape and materials can be very high. An experimental campaign demonstrates the feasibility of the proposed method.

A continuous version of the LuGre friction model applied to the adaptive control of a pneumatic servo system

This work presents the application of a friction compensation scheme to the trajectory-tracking control of a pneumatic servo actuator. Such scheme is based on a continuous approximation of the LuGre friction model, developed so as to allow complete Lyapunov stability analyses without resorting to assumptions that are difficult to satisfy in practice due to their physical meaning. By using adaptive estimation, extensive identification procedures are also avoided for determining friction parameters. Experimental results illustrate the most significant advantages and potential limitations of the proposed scheme in real applications.

High precision tracking control of a servo gantry with dynamic friction compensation

This paper is concerned with the tracking control problem of a voice coil motor (VCM) actuated servo gantry system. By utilizing an adaptive control technique combined with a sliding mode approach, an adaptive sliding mode control (ASMC) law with friction compensation scheme is proposed in presence of both frictions and external disturbances. Based on the LuGre dynamic friction model, a dual-observer structure is used to estimate the unmeasurable friction state, and an adaptive control law is synthesized to effectively handle the unknown friction model parameters as well as the bound of the disturbances. Moreover, the proposed control law is also implemented on a VCM servo gantry system for motion tracking. Simulations and experimental results demonstrate good tracking performance, which outperform traditional control approaches.

Multivariable friction compensation control for a variable stiffness actuator

A novel decentralised friction compensation control approach for a specific electro-pneumatic adjustable impedance actuator (EPAIA) is presented in this paper. EPAIA employs a rotary pneumatic actuator to provide an adjustable compliant element in series to the gear train. The compliant element is thereby inserted between a brushless direct current motor, a gear reduction and the load. The decentralised control system consists of two control-loops and a decoupler. In a first control-loop, the interaction torque between actuator and load is controlled with a cascaded/post-compensator architecture involving a norm-optimal strictly positive-real H2-controller to minimise the actuator output impedance. In a second control-loop, a stiffness controller continuously adjusts the pressure of the pneumatic chambers to realise a certain interaction stiffness. Since first hardware validation tests identified the occurrence of nonlinear friction effects that worsened the control performance, the control strategy has been extended with a new adaptive friction compensation scheme. This approach is based on the two-state dynamic friction model with elasto-plasticity (2SEP) for which an Extended Kalman Filter (EKF) friction observer has been developed and incorporated to the decentralised control strategy. The resulting overall controller has been validated in nonlinear simulations and in a test bench under variable load conditions.

Adaptive Friction Compensation: A Globally Stable Approach

In this paper, an adaptive friction compensation scheme is proposed. The friction force is computed as a time-varying friction coefficient multiplied by the sign of the velocity and an online update law is designed to estimate this coefficient based on the actual position and velocity errors. Furthermore, a modified signum function definition is proposed to better capture the behavior of friction over varying velocity profiles than the signum function commonly used in friction models. The properties of the closed-loop behavior of the proposed scheme are analyzed and stability of the closed-loop system is proven. Simulations and real-world experimental results are provided to confirm the theoretical findings: the compensator is able to eliminate steady-state errors, significantly decrease the stick-slip effect and compensate even rapidly varying friction forces.

Adaptive robust motion trajectory tracking control of pneumatic cylinders with LuGre model-based friction compensation

Friction compensation is particularly important for motion trajectory tracking control of pneumatic cylinders at low speed movement. However, most of the existing model-based friction compensation schemes use simple classical models, which are not enough to address applications with high-accuracy position requirements. Furthermore, the friction force in the cylinder is time-varying, and there exist rather severe unmodelled dynamics and unknown disturbances in the pneumatic system. To deal with these problems effectively, an adaptive robust controller with LuGre model-based dynamic friction compensation is constructed. The proposed controller employs on-line recursive least squares estimation (RLSE) to reduce the extent of parametric uncertainties, and utilizes the sliding mode control method to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbances. In addition, in order to realize LuGre model-based friction compensation, the modified dual-observer structure for estimating immeasurable friction internal state is developed. Therefore, a prescribed motion tracking transient performance and final tracking accuracy can be guaranteed. Since the system model uncertainties are unmatched, the recursive backstepping design technology is applied. In order to solve the conflicts between the sliding mode control design and the adaptive control design, the projection mapping is used to condition the RLSE algorithm so that the parameter estimates are kept within a known bounded convex set. Finally, the proposed controller is tested for tracking sinusoidal trajectories and smooth square trajectory under different loads and sudden disturbance. The testing results demonstrate that the achievable performance of the proposed controller is excellent and is much better than most other studies in literature. Especially when a 0.5 Hz sinusoidal trajectory is tracked, the maximum tracking error is 0.96 mm and the average tracking error is 0.45 mm. This paper constructs an adaptive robust controller which can compensate the friction force in the cylinder.

Mode Switching Feedback Compensation Considering Rolling Friction Characteristics for Fast and Precise Positioning

This paper presents a mode switching feedback (FB) compensation methodology based on rolling friction models for the fast and precise positioning of table drive systems. Rolling friction in the table drive mechanisms behaves as a nonlinear elastic component in the micro displacement region and deteriorates the position settling performance with slow responses. Effects of the rolling friction on the positioning, therefore, should be compensated to provide the desired control performance. The authors have already proposed a rolling friction model-based friction compensation scheme to improve the slow settling responses. The conventional approach, however, could not suppress vibratory settling responses due to unknown model errors and/or plant perturbations, and there still remains the performance deterioration in the positioning accuracy to be solved. In this research, therefore, a novel mode switching FB compensation considering the rolling friction properties is applied to provide the desired settling performance with well-suppression of both vibratory response and slow response. The feature of the proposed approach is that the vibratory and slow responses at the settling are handled as an initial value response of the FB control system in the micro displacement region and can be suppressed in a mode switching control manner on the basis of initial value compensation frameworks utilizing the elastic characteristic of the rolling friction. The proposed approach has been verified by numerical simulations and experiments using a prototype of industrial table positioning devices.

A novel disturbance-observer based friction compensation scheme for ball and plate system

Friction is often ignored when designing a controller for the ball and plate system, which can lead to steady-error and stick-slip phenomena, especially for the small amplitude command. It is difficult to achieve high-precision control performance for the ball and plate system because of its friction. A novel reference compensation strategy is presented to attenuate the aftereffects caused by the friction. To realize this strategy, a linear control law is proposed based on a reduced-order observer. Neither the accurate friction model nor the estimation of specific characteristic parameters is needed in this design. Moreover, the describing function method illustrates that the limit cycle can be avoided. Finally, the comparative mathematical simulations and the practical experiments are used to validate the effectiveness of the proposed method.

Prestiction friction compensation in direct-drive mechatronics systems

LuGre model has been widely used in friction modeling and compensation. However, the new friction regime, named prestiction regime, cannot be accurately characterized by LuGre model in the latest research. With the extensive experimental observations of friction behaviors in the prestiction, some variables were abstracted to depict the rules in the prestiction regime. Based upon the knowledge of friction modeling, a novel friction model including the presliding regime, the gross sliding regime and the prestiction regime was then presented to overcome the shortcomings of the LuGre model. The reason that LuGre model cannot estimate the prestiction friction was analyzed in theory. Feasibility analysis of the proposed model in modeling the prestiction friction was also addressed. A parameter identification method for the proposed model based on multilevel coordinate search algorithm was presented. The proposed friction compensation strategy was composed of a nonlinear friction observer and a feedforward mechanism. The friction observer was designed to estimate the friction force in the presliding and the gross sliding regimes. And the friction force was estimated based on the model in the prestiction regime. The comparative trajectory tracking experiments were conducted on a simulator of inertially stabilization platforms among three control schemes: the single proportional-derivative (PD) control, the PD with LuGre model-based compensation and the PD with compensator based on the presented model. The experimental results reveal that the control scheme based on the proposed model has the best tracking performance. It reduces the peak-to-peak value (PPV) of tracking error to 0.2 mrad, which is improved almost 50% compared with the PD with LuGre model-based compensation. Compared to the single PD control, it reduces the PPV of error by 66.7%.

마찰 보상과 지도 정합에 의한 미끄럼 조향 이동로봇의 실내 주행

This paper deals with the indoor localization problem for a SSMR (Skid Steering Mobile Robot) subjected to wheel-ground friction and with one LRF (Laser Range Finder). In order to compensate for some friction effect, a friction related coefficient is estimated by the recursive least square algorithm and appended to the maneuvering command. Also to reduce odometric information based localization errors, the lines are extracted with scan points of LRF and matched with the ones of the corresponding map built in advance. The present friction compensation and scan map matching schemes have been applied to a laboratory SSMR, and experimental results are given to validate the localization performance along an indoor corridor.

Backstepping Control of Electrical Load Simulator with Adaptive Tracking Performance Controller

Electrical Load simulator (ELS) is an important aerodynamics forces/torque loading device which is used for qualification of flight actuation system in ground based experiments. This paper focuses on Backstepping control design with fuzzy logic compensator for extra torque disturbance. To reduce number of fuzzy rules and processing time LuGre model based friction compensation scheme is proposed. Practically fuzzy logic compensation may induce approximation error. A novel PI type tracking performance controller is proposed to compensate tracking error due to parametric uncertainty in the ELS system and LuGre friction model. The tracking performance controller is tuned online based on saturation function based adaptive law derived from the error dynamics between state predictor and actual plant to eliminate chattering from control signal. The validity of control scheme is verified using numerical simulations for desired tracking performance.

Recursive model free controller: Application to friction compensation and trajectory tracking

In this paper friction compensation and trajectory tracking scheme is proposed for an X-Y robot using a Recursive Model Free Controller (RMFC). This controller is based on the theory of piecewise continuous systems which are a particular class of hybrid systems with autonomous switchings and controlled impulses. RMFC uses only the robot position measurements and does not require knowledge of electromechanical system parameters. The proposed control scheme is validated on a real time X-Y robot system.