• Title/Summary/Keyword: Coulomb friction

### A Dry Friction Model to Realize Stick for Simulation of the System with Friction and Accuracy Verification of the Friction Model (마찰력이 작용하는 동적 시스템의 점착 구현을 위한 마찰모델 제안 및 정확성 검증)

• Choi, Chan-Kyu;Yoo, Hong-Hee
• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.748-755
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• 2012
• Friction causes self-excited vibration, stick-slip vibration and any other friction-induced phenomena. That kinds of vibrations cause chatter and squeal. In order to predict such vibrations accurately, employing an accurate friction model is very important because a dynamic behavior of a system with friction is dominantly governed by a friction model. A Coulomb friction model is the most widely known model. Coulomb friction model is useful model to obtain analytical solutions of the system with friction and the model gives relatively good simulation result. However, defining a friction force at a stick state in simulation is hard because of the characteristic itself and a Coulomb friction model is discontinuous function between a static and a dynamic friction coefficient. Therefore, applying the Coulomb friction model to a simulation is not appropriate. In order to resolve these problems, an approximated Coulomb friction model was developed using simple and continuous function. However, an approximated Coulomb friction model cannot realize stick. Therefore, an approximated Coulomb friction model cannot describe friction phenomena accurately. In order to analyze a friction phenomenon accurately, a friction model for a simulation was proposed in this paper. A proposed friction model realizes stick and gives reasonably good results compared to results obtained by the simulation employing an approximated Coulomb friction model. Accuracy of a proposed friction model was verified by comparing experimental results.

### Control System Design for a UAV-Mounted Camera Gimbal Subject to Coulomb Friction (쿨롱마찰을 고려한 무인항공기용 영상 김발의 제어시스템 설계)

• Hwang, Sung-Pil;Park, Jea-Ho;Hong, Sung-Kyung
• Journal of Institute of Control, Robotics and Systems
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• v.18 no.7
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• pp.680-687
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• 2012
• One of the frequent problems in the stabilized gimbal system is the rejection of disturbances associated with moving components. Very often such disturbances have non-linear characteristics. In a typical gimbal system, each gimbal and platform are connected by a mutual bearing which induces inevitable friction. Particularly, the non-linear Coulomb friction causes position errors as well as slow responses that lead to unfavorable performance. In this paper, a modified PID controller that is augmented by Coulomb friction estimator is presented. Through constantly estimating the Coulomb friction torque, it is applied to the output of the existing PID controller. The effectiveness of the proposed controller is evaluated through a series of experiments.

### Estimation and Compensation of the Coulomb Friction in an Inverted Pendulum (쿨롱 마찰력 추정과 보상을 통한 역진자 시스템의 제어 성능 개선)

• Park, Duck-Gee;Chwa, Dong-Kyoung;Hong, Suk-Kyo
• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.11
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• pp.483-490
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• 2006
• When the nonlinearities, such as friction and backlash, are not considered in the controller design, undesirable oscillations can occur in the steady-state response of a control system. This paper deals with a method to reduce oscillations that often appear in the steady-state response of a pendulum system, which is controlled by a state feedback controller based on the linearized system model. With an assumption that the oscillations shown in the steady-state are caused by the Coulomb friction, we improve the performance of stabilization and tracking by estimating and compensating for the Coulomb friction in the pendulum system. Experimental results show that the control performance can be improved sufficiently by the proposed method, when it is applied to an inverted cart pendulum which is a multi-variable unstable system. Furthermore, we could see that the Coulomb friction model used in the estimation of the friction is valid in applying the suggested method.

### Position Control of Ball-Screw Systems with Compensation of Estimated Coulomb Friction (추정된 쿨롱 마찰을 보상한 볼-스크류 시스템의 위치제어)

• Kim, Han-Me;Choi, Jeong-Ju;Lee, Young-Jin;Kim, Jong-Shik
• Proceedings of the KSME Conference
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• pp.893-898
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• 2003
• Coulomb friction is an important factor for precise position tracking control systems. The control systems with friction causes the steady state error because of being sensitive to the change of system condition and highly nonlinear characteristics. To overcome these problems, we use an estimation scheme of Coulomb friction to experiment for it's compensating. The estimated factor for Coulomb friction is used as a feed-forward compensator to improve the tracking performance of ball-screw systems. The tracking performance was improved by compensating the estimated friction torque in the feed-forward term. And, the sliding mode control which is derived from the Lyapunov stability theorem is applied for robust stability and reducing chattering. The experimental results show that the sliding mode controller with adaptive friction compensator has a good tracking performance compared with the friction uncompensated controller.

### Quasi-LQG/$H_{infty}$/LTR Control for a Nonlinear Servo System with Coulomb Friction and Dead-zone

• Han, Seong-Ik
• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.24-34
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• 2000
• In this paper we propose a controller design method, called Quasi-LQG/$H_{\infty}$/LTR for nonlinear servo systems with hard nonlinearities such as Coulomb friction, dead-zone. Introducing the RIDF method to model Coulomb friction and dead-zone, the statistically linearized system is built. Then, we consider $H_{\infty}$ performance constraint for the optimization of statistically linearized systems, by replacing a covariance Lyapunov equation into a modified Riccati equation of which solution leads to an upper bound of the LQG performance. As a result, the nonlinear correction term is included in coupled Riccati equation, which is generally very difficult to thave a numerical solution. To solve this problem, we use the modified loop shaping technique and show some analytic proofs on LTR condition. Finally, the Quasi-LQG/$H_{\infty}$/LTR controller for a nonlinear system is synthesized by inverse random input describing function techniques (ITIDF). It is shown that the proposed design method has a better performance robustness to the hard nonlinearity than LQG/$H_{\infty}$/LTR method via simulations and experiments for the timing-belt driving servo system that contains the Coulomb friction and dead-zone.

### A Design of NAC(Natural Admittance Controller) for Coulomb Friction Compensation

• Sungmin Jang;Kim, Seungwoo
• Proceedings of the IEEK Conference
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• pp.596-599
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• 2000
• A natural admittance control system design is presented for a particular type of interaction controller that achieve high-performance and guarantees stability. The admittance control Significantly improves performance when Coulomb friction is present in the one link robot system. The technique requires a careful choice of the target impedance. Experimental performance results are presented for a two-mass system with internal Coulomb friction. Results demonstrate that the admittance control law is successful in rejecting internal Coulomb friction force disturbances. The controller was designed and implemented on our system that we set up one link robot system and hardware configuration system, and performance results are presented.

### Position Control of Sliding Mode Control Systems with Compensation of Estimated Coulomb friction (추정된 쿨롱 마찰을 보상한 슬라이딩 모드 제어 시스템의 위치제어)

• 김한메;최정주;이영진;김종식
• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.35-42
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• 2004
• The control systems with friction cause the steady state error and slow response, because friction is a sensitive to the change of system condition and has highly nonlinear characteristics. To overcome these problems and do precise position control for a ball-screw system, we use Coulomb friction estimator and the sliding mode control(SMC) to compensate its negative effect. The applied SMC for tracking position has a characteristics of robust stability and reducing chattering, and is derived from the Lyapunov stability theorem and reaching condition. Compensating the estimated friction torque to the bounded disturbance term of the SMC's equivalent control input, it has a tracking performance better than the PID from the experimental results.

### Adaptive Control of a Single Rod Hydraulic Cylinder - Load System under Unknown Nonlinear Friction

• Lee Myeong-Ho;Park Hyung-Bae
• Journal of Advanced Marine Engineering and Technology
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• v.29 no.3
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• pp.251-259
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• 2005
• A discrete time model reference adaptive control has been applied in order to compensate the nonlinear friction characteristics in a hydraulic proportional position control system. As nonlinear friction, static and coulomb friction forces are considered and modeled as dead zone and external disturbance respectively. The model reference adaptive control system consists of a cascade combination of the dead zone. external disturbance and linear dynamic block. For adaptive control experiment. the DSP(Digital Signal Processor) board has been interfaced the hydraulic proportional position control system. The experimental results show that the MRAC(Model Reference Adaptive Control) for compensation of static and coulomb friction are very effective.

### QLQG/LTR Control of the Nonlinear Timing-Belt Driving Systme Using DSP (DSP를 이용한 비선형 타이밍 벨트 구동시스템의 QLQG/LTR 제어)

• 한성익;방두열
• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.4
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• pp.40-47
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• 2001
• In this pater, the QLQG/LTR control method is applied for the position control of the nonlinear timing belt driving sys-tem. Parameters fo the plant are identified by genetic algorithm and nonlinear elements, such as Coulomb friction and dead-zone, and quasi-linearized by RIDE method. Comparing with the LQG/LTR contro. the QLQG/LTR has similar structures of the LQG/LTR, but this method can consider nonlinear effects in designing the controller. Thus, the QLQG/LTR control system is robust to hard nonlinearities such as Coulomb friction, dead-zone, etc. Forma given hard non-linear system through experiments, it is shown that the tracking performance of the QLQG/LTR control system can be very improved that the LQF/LTR control system.

### Contact Modeling between the Ground and the Galloping Quadruped Robot Considering Statistical Characteristics of Coulomb Friction Coefficients (쿨롱 마찰계수들의 통계적 특성을 고려한 지면과 갤러핑을 하는 4 족 로봇간 접촉 모델링)

• Kwon, Sung-Hun;Park, Jong-Hyeon;Yoo, Hong-Hee
• Proceedings of the KSME Conference
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• pp.826-830
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• 2007
• The effects of the statistical properties of the Coulomb friction coefficients on the dynamic responses of a galloping quadruped robot are investigated in this paper. In general, the Coulomb friction coefficients are assumed to be deterministic for a controller design to achieve required motion characteristics. However, the friction coefficients between the ground and the robot legs are not constant in reality. Therefore, statistical characteristics of the friction coefficients need to be considered for a multi-body modeling of the robot galloping on the ground. The effects of the statistical properties on the dynamic responses of the quadruped robots are investigated.