Friction Compensation Algorithm Research Articles

Friction modeling and compensation for haptic master manipulator based on deep Gaussian process

This paper investigates friction modeling and compensation for haptic master manipulator used in robot-assisted minimally invasive surgical system. Friction modeling and compensation is based on deep Gaussian process (DGP) and it does not require the utilization of explicit friction models. Therefore, the proposed friction modeling and compensation algorithm can circumvent the drawbacks associated with model-based methods. Through the adoption of implicit posterior variational inference, the proposed algorithm can accurately predict and compensate friction even when there exists parametric uncertainty in the dynamics of the haptic master manipulator. The effectiveness and feasibility of the proposed approach is validated experimentally through the robot-assisted minimally invasive surgical system. Experimental results demonstrate that the proposed method outperforms several existing alternatives in representing and compensating friction effects.

Torque Control of a Series Elastic Tendon-Sheath Actuation Mechanism

Tendon-sheath actuation mechanisms can provide compact and lightweight tendon routing. However, torque control of a tendon-sheath actuation system is challenging because of variable friction with respect to the sheath configuration. Model-based feedforward friction compensation algorithms have been developed to accurately deliver desired torque, but it is difficult to apply such algorithms to multi-degrees of freedom (DOFs) systems because of changes in sheath configurations that in turn alter the base tension and friction parameters. In this article, we develop a series elastic tendon-sheath actuation mechanism that allows feedforward torque control in multi-DOFs systems. The mechanism features series elastic elements on the motor side to reduce base tension changes and enable accurate input torque control. Friction is compensated by a feedforward controller with a modeled friction parameter to transmit desired torque to the distal joint under varying sheath configurations. The performance of the proposed series elastic tendon-sheath actuation mechanism is demonstrated in experiments using a control interface for a tele-operation system.

Planar motion controller design for a modular mechatronic device with heading compensation

MechaCells are designed as closed, scalable and modular semi-autonomous devices that can be used alone or part of a pack. In this paper, we discuss a locomotion system that uses the reaction force produced by a rotating unbalance that moves in a spherical domain with a steering mechanism. In order to produce the precise motion capability, a multi-loop controller is developed. This controller uses a friction compensation algorithm based on the mathematical model of the locomotion system. To improve the accuracy of tracking, conventional LuGre friction estimation model is extended for rapid directional changes of the MechaCell during planar motion. The linear and rotational acceleration of the device is also included in controller calculations since it affects the locomotion force generated by the unbalanced mass. The resulting control system is validated both with simulations and experiments and the effectiveness of the extended model and the controller is verified. Our results show significant improvement when a detailed friction compensation observer is used in the controller that includes the effect of sudden steering changes for precise path following.

Embedded Sliding Mode Controller Applied to Control Valves with High Friction

Friction is one of the most frequent causes of oscillations in process control loops. Normally, the first step in resolving this problem should be to stop the process and to perform valve maintenance. However, it is not always possible to do it, because it can lead to a loss of production and some processes are not simple to halt, e.g. a nuclear power plant or an oil refinery. Therefore, it is important to find other ways to solve this problem. Lately, many academic works have proposed the use of the integrative sliding mode controller to reduce the friction effect in control loops. This paper proposes to discretize this controller and to implement it in a microcontroller, acting as a control valve positioner. The experiments were conducted in a hardware-in-the-loop simulation environment running in real time. Tests are performed under various conditions, and the results are compared to a widely used friction compensation algorithm and a control disable technique. The results show that the implementation of the sliding mode controller in digital positioners is an interesting alternative for friction compensation in control valves in the industry.

Control of a Master–Slave Pneumatic System for Teleoperated Needle Insertion in MRI

This paper presents the control of a pneumatically actuated master–slave system intended for teleoperated needle insertion in the liver under magnetic resonance imaging (MRI) guidance. It addresses the challenge of achieving accurate needle positioning and force feedback to the operator in the case of pneumatic actuation with significant friction. Using time-delay position control as the basis, we investigate force feedback via impedance control and admittance control. For impedance control, we propose a new adaptive friction compensation algorithm that only requires a single tuning parameter. Experiments on a 1-degree of freedom prototype system using silicone rubber phantoms with distinct densities highlight the differences between impedance control and admittance control, and demonstrate superior performance compared with a traditional impedance control scheme.

Motorized vehicle active suspension damper control with dynamic friction and actuator delay compensation for a better ride quality

This paper describes motorized active suspension damper control with dynamic friction and actuator delay compensation for an enhanced ride quality. The control algorithm consists of a supervisory controller, an upper-level controller and a lower-level controller. The supervisory controller determines the control modes, such as the passive control modes and the active control mode. The upper-level controller, which incorporates the existing actuator delay, computes the damping force using linear quadratic control theory. The actuator input is determined by the lower-level controller by compensating the dynamic friction torque. To estimate the sprung-mass displacement, the sprung-mass velocity, the unsprung-mass displacement and the unsprung-mass velocity, two state estimators are proposed. An adaptive observer is developed for the non-linear dry friction to estimate the ball-screw dynamic friction caused by the axial movement of the actuator and the viscosity. The performance of the proposed control algorithm was evaluated from simulations. It was shown from simulations that the proposed motorized active suspension damper control with a friction and delay compensation algorithm can improve the ride quality.

Development and experimental evaluation of multi-fingered robot hand with adaptive impedance control for unknown environment grasping

SUMMARYThis paper presents adaptive impedance controllers with adaptive sliding mode friction compensation for anthropomorphic artificial hand. A five-fingered anthropomorphic artificial hand with multi-sensory and Field-Programmable Gate Arra (FPGA)-based control hardware and software architecture is designed to fulfill the requirements of the grasping force controller. In order to improve the force-tracking precision, the indirect adaptive algorithm was applied to estimate the parameters of the environment. The generalized momentum-based disturbance observer was applied to estimate the contact force from the torque sensor. Based on the sensors of the finger, an adaptive sliding mode friction compensation algorithm was utilized to improve the accuracy of the position control. The performances of the force-tracking impedance controller and position-based joint impedance control for the five-fingered anthropomorphic artificial hand are analyzed and compared in this paper. Furthermore, the performances of the force-tracking impedance controller with environmental parameters adaptive estimation and without environmental parameters estimation are analyzed and compared. Experimental results prove that accurate force-tracking and stable torque/force response under uncertain environments of unknown stiffness and position can be achieved with the proposed adaptive force-tracking impedance controller with friction compensation on five-finger artificial hand.

FRICTION MODELLING AND ROBUST ADAPTIVE COMPENSATION

In this paper, a friction model is proposed which can easily be introduced in adaptive control algorithms. Based on the model, a robust adaptive friction compensation algorithm is developed for high precision positioning systems. It is shown that the proposed compensation scheme guarantees a prescribed accuracy for trajectory tracking. The paper also presents experimental results to demonstrate the applicability of the proposed control algorithm.

Servo Pneumatic Position Control Using Fuzzy PID Gain Scheduling

In this paper, a design procedure and experimental implementation of a PID controller is presented. The PID controller is tuned according to damping optimum in order to achieve precise position control of a pneumatic servo drive. It is extended by a friction compensation and stabilization algorithm in order to deal with friction effects. In a case of supply pressure variations, more robust control system is needed. It is implemented by extending the proposed PID controller with friction compensator with the gain scheduling algorithm, which is provided by means of fuzzy logic. The effectiveness of proposed control algorithms is experimentally verified on an industrial cylindrical rodless actuator controlled by a proportional valve.

Performance robustness and stiffness analysis on a machine tool servo design

The machine tool servo design is very different from the traditional high performance servo systems. Traditional servo design depends heavily on a precise system model so that frequency domain or time domain compensation techniques can be applied, and many synthesis tools such as LQG, H ∞, or LMI, … are available based on this concept. While these synthesis tools are becoming very useful in many situations, they are not used in the machine tool servo design. Most high performance machine tool systems still rely on the more primitive PID or PDF controllers in conjunction with complicated friction and temperature compensation algorithms. This paper investigates the different approaches based on a house-designed servo control board. With the ability to change the servo control algorithms on a test machine tool, the performance robustness and servo stiffness were tested both numerically and experimentally. The numerical tests conducted with PID, PDF, and LQG controllers showed that the PID controller is the easiest to achieve good performance, but the PDF controller contains the best performance robust margin. Experimental results also indicated that the PDF controller exhibits far superior robustness properties over the other two controllers.

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.

Performance Robustness and Stiffness Analysis on a Machine Tool Servo

The machine tool servo design is very different from the traditional high performance servo systems. The machine tool servo systems seldom use the common control synthesis process. Instead, most high performance machine tool systems still use the classic PID or PDF controllers in conjunction with complicate friction and temperature compensation algorithms. This paper would like to explore the reason, and have studied the different designs based on a house designed servo control board. The performance robustness was tested both numerically and experimentally. The numerical tests conducted with PID, PDF, and LQG controllers showed that the PID controller is the easiest to achieve good performance, but the PDF controller contains the best performance robust margin. Experimental results also indicated that the PDF controller provides the most robust stiffness margin.

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.

H ∞ -Based Robust Torque Control of Harmonic Drive Systems

In this paper, the torque control of a harmonic drive system for constrained-motion and free-motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using this information in an H∞-framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well. To further improve the performance of the system for free-motion case, a feedforward friction-compensation algorithm is implemented in addition to the robust torque control. It is shown that friction-compensation will shrink the model uncertainty at low frequencies and hence, the performance of the closed-loop system will be improved at those frequencies.