Proposed Friction Compensation Research Articles

Tracking Control of Robot Manipulator with Friction Compensation Using Time-Delay Control and an Adaptive Fuzzy Logic System

This paper aims to highlight the critical role of robot manipulators in industrial applications and elucidate the challenges associated with achieving high-precision control. In particular, the detrimental effects of nonlinear friction on manipulators are discussed. To overcome this challenge, a novel friction compensation controller (FCC) that combines time-delay estimation (TDE) and an adaptive fuzzy logic system (AFLS) is proposed in this paper. The friction compensation controller is designed to take advantage of the time-delay estimation algorithm’s strengths in eliminating and estimating unknown dynamic functions of the system using information from the previous sampling period. Simultaneously, the adaptive fuzzy logic system compensates for the hard nonlinearities in the system and suppresses the errors generated by time-delay estimation, thus improving the accuracy of the robotic arm’s tracking. The numerical experimental results demonstrate that the proposed friction compensation controller can significantly enhance the tracking accuracy of the robotic arm, with the addition of the adaptive fuzzy logic system improving time delay estimation’s performance by an average of 90.59%. Moreover, the proposed controller is more straightforward to implement than existing methods and performs exceptionally well in practical applications.

하모닉 감속기가 장착된 모터 구동식 회전 관절의 마찰 보상

This paper describes a method for compensating friction caused by the harmonic gear in revolute joint. A torque sensor is attached to the output member of the harmonic gear to measure the friction torque during back driving, and, contrary to conventional methods, torque data according to both the angular velocity and angular acceleration was measured to consider hysteresis. After dividing the measured data into four sections, a friction model was modeled in a quintic polynomial through the curve fitting method in each section. We experimented to estimate the reduction in resistive friction torque during back driving using a 1-DOF test platform with the proposed friction compensation. Moreover, we experimentally compared the position tracking performance with and without friction compensation using the cycling motion of a 2-DOF test platform. Finally, the performance of the friction model proposed in this paper was successfully verified.

Adaptive Friction Compensation: Modular Design with Passive Identifier

AbstractFor a second‐order mechanical system incorporating Coulomb frictional effect, a nonlinear adaptive control that achieves a controller‐identifier separation is designed. This modularity is made possible by the strong input‐to‐state stability (ISS) property of the ISS controller with respect to the parameter estimation error as input. This input is independently guaranteed to be bounded by the passive identifier. We use two types of passive identifiers: z‐scheme passive identifier and x‐scheme passive identifier. These designs are more flexible than the Lyapunov‐based design and lead to lower control effort. In addition, the advantages and disadvantages of z‐scheme and x‐scheme are presented. Transient performance of the system is enhanced with a trajectory initialization technique. The validity and effectiveness of the proposed friction compensator is verified by simulation for position tracking control under the influence of Coulomb friction.

모터 제어 정밀도 향상을 위한 정지 마찰력 보상

DC motor is a representative electric motor commonly utilized in various motion control fields. However, DC motor-based motion control systems suffer from degradation of position precision due to nonlinear static friction. In order to enhance control precision, friction model-based compensators have been introduced in previous researches, where friction models are identified and counter inputs are added to control inputs for cancelling out the identified friction forces. In this paper, a static friction compensator is proposed without use of a friction model. The proposed compensation algorithm utilizes internal state manipulation to generate compensation pulses, and related parameters are easily tuned experimentally. The proposed friction compensator is applied to a DC motor-based motion control system, and results are presented in comparison with those without a friction compensator.

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%.

Control system design of a linear motor feed drive system using virtual friction

Abstract This paper proposes a friction compensator and a design method for control systems to improve the response characteristics of linear motor feed drive systems. The proposed friction compensator cancels the real nonlinear friction of feed drive systems by using the nonlinear friction model proposed in this study and introduces virtual linear friction to facilitate the control system design. The proposed design method enables the determination of servo gains and friction compensator parameters that lead to desirable tracking performance and disturbance rejection without many trial-and-error tuning processes. In addition, the proposed method facilitates the design of the velocity feedforward compensator by using the inverse transfer function of the velocity control loop to correct the position tracking errors for various position commands. The effectiveness of the proposed method with the friction compensator and the velocity feedforward compensator was verified in simulations and experiments using a one-axis feed drive system consisting of a rod-type linear motor and linear roller guides. The results confirmed that the proposed method enables desirable overshoot-free responses and corrects motion trajectory errors due to nonlinear friction characteristics, and the proposed velocity feedforward compensator can correct tracking errors in both constant velocity motion and circular motion.

Generation Mechanism of Quadrant Glitches and Compensation for it in Feed Drive Systems of NC Machine Tools

Circular motion tests are commonly used to evaluate the accuracy of the motion of feed drive systems. However, large quadrant glitches are often observed in circular trajectories as the motion changes across thexandyquadrants. It is well known that this phenomenon is caused by friction forces acting on the feed drive mechanism. This paper investigates the generation process of quadrant glitches and proposes a quadrant glitch compensator based on the investigation. As a result of the experiments and simulations, it is clarified that the axis velocity does not stay at zero during direction changes and that the proposed generation mechanism model for quadrant glitches accurately describes actual behavior. It is also confirmed that the proposed friction compensator can eliminate quadrant glitches effectively even if the radius and feed rate change.

Design Method for High-gain Control of Linear Motor Feed Drive Systems Using Virtual Linear Friction

This paper describes a method for stabilizing feed drive systems by introducing virtual friction characteristics having higher vibration damping with a friction compensator. The validity of the proposed friction compensator is verified by experiments using a one-axis feed drive system consisting of a rod type linear motor and linear roller guides. In addition, this paper proposes a control design method to determine the servo gains and the virtual friction parameters that lead to overshoot-free responses. It is confirmed that the step response curves under the servo gains and the virtual friction parameters determined by the proposed method have no overshoots and amplitude dependence due to the nonlinear friction characteristics.

Sliding Observer for Friction Compensation in a Linear-Motor-Driven Motion System

In this work, a sliding-mode observer is developed for estimating unavoidable frictions and undesired disturbance in motion systems. The estimated parameters are then feedback for compensation to achieve precise control. With proper observability analysis performed by using Lie derivative method, the design of observer is based on the underlying nonlinear system with LuGre friction Model. While maintaining the stability of the observer, we choose the observer gains to make the system a dissipative one. As a conclusion in the last section, the proposed method is applied to a linear-motordriven motion system. The experimental results show that the tracking and positioning performance with the proposed friction compensation method are smaller than those of the disturbance observer (DOB) compensation or without friction compensation.

Robust Tracking Controller Design With Uncertain Friction Compensation Based on a Local Modeling Approach

This paper presents a new methodology for the design of a robust controller to compensate for friction-induced dynamical characteristics inherently present in servodrives systems. A friction model is developed using a local modeling approach of the physical properties of friction along the operating range of the underlying system. Generally, developing a faithful model for physical nonlinearities is still a challenging task that is strongly related to the identification effort required by the structure of the model and the complexity of the control algorithm. The proposed model has the advantage of being simple and able to describe friction locally. The accuracy of the estimator based on the model structure can be improved by a gain-scheduled input signal obtained for different velocities and used as a precompensator of nonlinear friction. This leads to an effective linearzing strategy of the controlled system that subsequently simplifies the controller implementation stage. A stabilizing-state feedback controller is designed, assuming an inexact compensation of friction, which guarantees robustness against uncertainties arising from modeling errors and achieves high tracking performance of the overall controlled system. Experimental tests performed on a robot joint laboratory prototype demonstrate the effectiveness of the proposed friction compensation scheme to improve the performance of the overall system.

Adaptive Trajectory Control and Dynamic Friction Compensation for a Flexible-Link Robot

AbstractFriction compensation techniques are studied for control of a flexible-link robot based on the LuGre friction model. To overcome the problem of uncertain parameters in the friction model, adaptive control schemes are used for two different types of parametric uncertainties. A novel dual-observer technique is proposed to estimate the internal state inside the friction model. A distributed-parameter dynamic model is used for the flexible arm to design the controllers. The Lyapunov stability theorem is used to guarantee the global asymptotic stability of the controllers. The performance of position tracking and link vibration attenuation is verified through experimental results. The results also confirm the effectiveness of the proposed friction compensation schemes.

Sliding mode-based friction control with adaptive dual friction observer and intelligent uncertainty compensator

A robust friction compensation scheme is studied using a dual-friction-parameter observer and a recurrent neural network combined with sliding mode control. To handle non-linear friction parameters, a dual-friction-model-based observer is used to estimate the friction parameter of the LuGre friction model. In addition, an approximating method for the system uncertainty is developed using a recurrent neural network approach to improve the precision positioning degree. Simulated and experimental results are presented that validate the performance of the proposed friction compensation scheme.

Quadrant Glitch Compensator Based on Friction Characteristics in Microscopic Region

This paper proposes a friction compensator based on the friction characteristics in the microscopic displacement region. In order to evaluate the motion accuracy of feed drive systems for the NC machine tools, circular tests are generally applied. It is known that the large quadrant glitches are often observed on the circular trajectories, and it is caused by the friction forces of the mechanism. In this paper, the relationship between table displacement and total friction torque around the motor axis is modeled by a simple friction model which can accurately estimate the behavior of the friction torque. The proposed friction model is a function of the table displacement, not a function of velocity. Based on the friction model, a friction compensator is invented. The proposed friction compensator consists of a table position estimator, an inverse transfer function of the servo motor, and the friction model. From the experimental and simulation results, it is clarified that the quadrant glitches can be effectively eliminated by the proposed friction compensator, even if the radius and feed rate of circular motion change.

Adaptive friction compensation for precision machine tool drive

In this paper, two robust adaptive control algorithms are proposed for friction compensation in high performance machine tools. The first controller utilizes an adaptive friction compensation scheme based on a postulated linear-in-the-parameters friction model. The proposed friction compensation algorithm explicitly accounts for time varying normal forces as well as dependence of the friction coefficient on velocity. The Stribeck friction characteristic and variations in static friction are treated as bounded disturbances, and compensated for by adaptive bounding functions. In the second controller, a special form of the Takagi–Sugeno fuzzy system is utilized to adaptively learn unknown friction behavior and compensate for it. This approach assumes that no a priori knowledge about frictional effects in the strut joints is available. The proposed controllers are compared based on simulation and experimental results of tracking performance at low speeds, since frictional effects dominate strut dynamics at low speeds. The results indicate that the large tracking errors caused by friction at the velocity reversals when conventional control algorithms are used, are reduced greatly by the adaptive controllers. Instability of the gradient-type adaptive algorithms is observed when the adaptation rate is high. Inclusion of a dead-zone modification of the adaptive laws eliminates the instability.

Position control of X-Y table at velocity reversal using presliding friction characteristics

This paper aims at precision position control of the X-Y table of a computerized numeric control (CNC) machining center at velocity reversal. The characteristics of presliding friction are analyzed, and a simple and effective method is proposed to compensate the friction on the basis of these characteristics. A large position tracking error occurs at velocity reversal due to the sudden transition of friction between presliding regime and sliding regime. This paper investigates the transition time to reduce the tracking error, and derives a relationship between the transition time and the acceleration at zero velocity. This paper also proposes a method of estimating the transition time using this relationship, without having to measure velocity. Experimental observations confirm this correlation holds over a large dynamic range. In addition to friction, there is a large change in a torsional displacement at velocity reversal in a two-inertia system with finite stiffness like an X-Y table linked to a motor through a ballscrew. The proposed friction compensation scheme can be easily incorporated with the compensation method for torsional displacement to achieve good tracking performance. The experimental results are described to show the effectiveness of the proposed method.

Adaptive Friction Compensation for Stewart Platform Machine Tool Structures

In this paper, two robust adaptive control algorithms are proposed for friction compensation in high performance machine tools. The first controller utilizes an adaptive friction compensation scheme based on a postulated linear-in-the-parameters friction model. The proposed friction compensation algorithm explicitly accounts for time varying normal forces as well as dependence of the friction coefficient on velocity. The Stribeck friction characteristic and variations in static friction are treated as bounded disturbances, and compensated for by adaptive bounding functions. In the second controller, a special form of the Takagi-Sugeno fuzzy system is utilized to adaptively learn unknown friction behavior and compensate for it. This approach assumes that no a priori knowledge about frictional effects in the strut joints is available. The proposed controllers are compared based on simulation and experimental results of tracking performance at low speeds, since frictional effects dominate strut dynamics at low speeds. The results indicate that the large tracking errors caused by friction at the velocity reversals when conventional control algorithms are used, are reduced greatly by the adaptive controllers. Instability of the gradient type adaptive algorithms is observed when the adaptation rate is high. Inclusion of a dead-zone modification of the adaptive laws eliminates the instability.

Decomposition-based friction compensation of mechanical systems

In this paper, a linear parametric friction model is formulated by linearizing a nonlinear empirical friction model in parameters. A proposed decomposition-based control design framework is applied to synthesize the friction compensation scheme. A separate compensator is designed for each type of friction utilizing the most suitable control technique. The nominal friction is compensated by feed forward. An adaptive compensator is derived to compensate for parametric unmodeled friction with unknown but constant parameters, and a robust compensator is used to deal with friction model parameter variations, as well as non-parametric unmodeled friction. The combination of the compensators yields the overall compensation scheme. Adaptive and robust compensators complement each other in compensating the effects of model uncertainties. The analytical and simulation studies have confirmed the efficiency of the proposed friction compensation method.