An analysis of stick-slip motion

A theory for stick-slip motion for the case of constant static and constant dynamic coefficients of friction has been derived. The theory was checked using a specimen of rubber and the experimentally observed results were in very good agreement with the results predicted by the theory.     

Computer simulation of stick-slip motion in machine tool slideways

Especially in CNC (Computer Numerical Control) machine tools, stick-slip motion should be eliminated even at very low sliding speeds. Otherwise, the table begins oscillating around the desired position and exact positioning can never be achieved. In this study, stick-slip motion of plain machine tool slideways is simulated using a two-degree of freedom mathematical model. The governing equations are solved with the help of a mathematical package, MathCad 6.0. The results are compared with experimental ones and a good agreement is observed.     

Hybrid fuzzy sliding mode for stick-slip suppression in drill string systems

Journal of Mechanical Science and Technology - Stick-slip vibration is one of the main factors that contribute greatly to reducing the service life of drill string equipment and decreasing the...     

黏滑驱动式小型精密运动平台

为满足微纳操作系统对精密驱动技术的需求,本文提出了一种基于黏滑原理的小型精密运动平台。该平台将柔性铰链、惯性质量块以及弹性元件结合为独立的定子基座,并与压电叠堆、陶瓷球固连为定子,安装在平台基座底部,通过螺钉调节弹性元件端部垂直方向的位置,就可以改变定子与移动台间的预压力,进而获得最佳的驱动力。为研究黏滑驱动的运动机理,分析各参数对平台运动的影响,进行了力学建模;而摩擦力作为黏滑驱动的关键因素,为了能准确地表达黏滑驱动的摩擦机理,在力学建模中引入了LuGre摩擦模型,并利用Matlab/Simulink软件进行了仿真分析。设计加工的黏滑驱动平台的整体尺寸为40mm×40mm×18mm,质量为32g。试验表明:该平台最小可实现10nm的运动步长,速度最高可达2.5mm/s,行程为22mm。     

A new theory of hysteretic sliding friction

This paper supports the concept that the damping properties of rubber contribute the greater proportion of frictional resistance when rubber slides on an irregular lubricated surface. The author presents and largely validates his rigorous mathematical mechano-lattice analogy analysis for calculating the hysteretic sliding friction of, and stresses in rubber sliding on, variously shaped asperities. The analysis allows large deformations and any Poisson's ratio, rigidity or damping factor of the rubber. A method of applying the results of this analysis to the problem of predicting the coefficient of lubricated friction of rubber sliding on roadstones is shown to be reasonably accurate.     

液压伺服系统低速爬行的最优控制

针对一类液压伺服系统的低速爬行问题,提出了一种基于神经网络反馈线性化的控制方法,对线性化后的系统设计了最优控制律。仿真实验表明,该方法能有效提高系统的低速动态品质,并使系统具有鲁棒性,而且有很强的实用性,便于工程实现和应用。     

Dynamic behaviour of geared systems with backlash due to stick-slip vibratory motion

Stick-slip phenomena occur with low speed rotors in fluid bearings. A typical case is the turning gear mechanism of large turbomachinery which becomes vulnerable to damage. In other cases such as rolling mills or textile machinery the stick-slip phenomenon influences product quality.An analytical investigation of a linear rotor with a complex turning gear system of many degrees of freedom is presented. Gearing backlash was included in the model. The mechanism of backlash was found to be of considerable importance for the appearance of instability. Velocity and damping were the most influential factors on the amplitude of stick-slip motion and instability.In highly unstable areas of system operation, stick-slip is not present owing to the violent nature of the unstable motion. At the onset of instability and during the transients of stable systems, stick-slip is present. Fatigue damage may result from gear backlash, even in stable systems.     

Stability criterion for stick-slip motion using a discontinuous dynamic friction model

An analysis of stick-slip stability is presented using a discontinuous friction model which consists of a negative damping action for the slip acceleration phase and a constant frictional resistance for the slip deceleration phase. Limiting conditions for stability due to a positive viscous damping action are defined, where transition from self-generated vibrations to smooth sliding occurs. The implications of the theory are discussed for the design and analysis of equipment subject to such vibrations.     

Two dimensionless parameters controlling the occurrence of stick-slip motion in a 1-DOF system with Coulomb friction

The condition for the occurrence of stick-slip motion is examined analytically based on a 1-DOF system with Coulomb friction which includes seven independent parameters. There exist two dimensionless parameters which control the occurrence of stick-slip motion, one denotes the easiness for the occurrence of stick-slip motion and the other is the damping ratio acting to suppress the motion. A simple non-occurrence inequality of stick-slip motion is derived with the two dimensionless parameters through dimensionless analysis and numerical simulation, which has both high accuracy and high usability. Its validity is confirmed by the comparison with the experimental results reported by Singh.     

A new technique for the investigation of stick-slip

The stick-slip phenomenon has been investigated using an existing high frequency friction machine at very low speed. Static friction was found to vary with frequency and to approach a maximum as the length of time during which the contacting surfaces were at rest increased. This was thought to be due to a squeeze film effect leading to increasing asperity contact.     

Elastohydrodynamic problem for journal sliding bearing under reciprocating motion

A plane elastohydrodynamic problem for a radial sliding bearing with a thin liner under reciprocating motion under a constant load is considered. It has been shown that at the moment of time when the velocity becomes equal to zero the thickness of the lubricating film exceeds zero and that it continues to decrease during a period of time after changing the direction of rotation of the shaft. Film thickness and pressure distributions at various moments in time, as well as time dependences of the eccentricity and the minimum film thickness along the spatial coordinate, are presented for various values of the dimensionless parameter, which depends on the period of reciprocating motion. It has been shown that the smallest value of film thickness over the entire period of reciprocating motion increases with shortening period of reciprocating motion.     

滑片压缩机滑片倾角对滑片运动的影响分析

滑片压缩机特别适用于单级压缩以及其它类似的中、低压力场合，滑片压缩机的滑片倾角影响到滑片的运动情况，从而对滑片与气缸及转子之间的摩擦、磨损产生影响。本文对滑片压缩机的几何结构，运动情况进行了分析研究，讨论了滑片倾角对滑片运动速度、加速度的影响，研究表明，滑片沿滑片槽的相对运动速度和加速度随倾角的增大而增大，且加速度的变化率增大而不均匀；倾角为0时，滑片沿滑片槽的相对运动速度和加速度最小，且加速度的变化率最小而均匀。     

Comparison of two stick-slip testers and recommendations for repeatable and significant stick-slip testing

Because of the interaction of the large number of parameters influencing stick-slip, it is very difficult to perform repeatable and reproducible tests that define the anti-stick-slip properties of lubricants. In order better to understand the difficulties encountered in stick-slip testing, an overview of the influencing parameters, with a discussion of each parameter, is given in this paper. Some modifications of the reciprocating stick-slip tester that was used in the ASTM test procedure before the latter was withdrawn, in order to improve the repeatability of its test results, are discussed. The significance of the results is checked by comparison with a rotary stick-slip tester. Finally, recommendations for correct stick-slip testing and interpretation of stick-slip results are presented.     

基于位移累加原理的SMA直线电机

针对航空航天等领域(如变后掠翼无人机)需要大推力、长行程、高功重比的驱动器,提出一种用形状记忆合金片(SMA)驱动的直线电机,利用位移累加的原理,能够获得较大推力,并具有较长的行程。与同样功率的传统驱动器相比,形状记忆合金智能驱动器有着推重比高,传动系统易于操作,结构简单,重量低等优势。     

Ultra‐high frequency tribometer for reciprocating sliding motion

A novel tribometer has been designed using commercially available components for sliding motion at 40kHz with amplitude between 2.5 and 5µm. The tribometer is equipped with means to measure amplitude, frequency, power required to keep the sample in motion and load applied. The effective motion between the two contacting bodies is monitored. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set‐up was tested using novel, non‐commercial substrates such as AlFeCrTi‐alloys and tungsten carbide‐based coatings as well as Magnéli‐type coatings (Ti_n−2Cr₂O_2n−1 and Ti_nO_2n−1). This paper presents the principle of the ultra‐high frequency tribometer and first tribological quantities of materials and coatings tested. Copyright © 2007 John Wiley & Sons, Ltd.     

Triboactive materials for dry reciprocating sliding motion at ultra-high frequency

High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 μm and 5 μm. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set-ups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Ti_n?2Cr₂O_2n?1 and Ti_nO_2n?1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 10¹¹ cycles. Very low wear rates in the range 10^?8 mm³/Nm down to 10^?10 mm³/Nm were determined under dry oscillation in air.     

Feedback attitude sliding mode regulation control of spacecraft using arm motion

The problem of spacecraft attitude regulation based on the reaction of arm motion has attracted extensive attentions from both engineering and academic fields.Most of the solutions of the manipulator’s motion tracking problem just achieve asymptotical stabilization performance,so that these controllers cannot realize precise attitude regulation because of the existence of non-holonomic constraints.Thus,sliding mode control algorithms are adopted to stabilize the tracking error with zero transient process.Due to the switching effects of the variable structure controller,once the tracking error reaches the designed hyper-plane,it will be restricted to this plane permanently even with the existence of external disturbances.Thus,precise attitude regulation can be achieved.Furthermore,taking the non-zero initial tracking errors and chattering phenomenon into consideration,saturation functions are used to replace sign functions to smooth the control torques.The relations between the upper bounds of tracking errors and the controller parameters are derived to reveal physical characteristic of the controller.Mathematical models of free-floating space manipulator are established and simulations are conducted in the end.The results show that the spacecraft’s attitude can be regulated to the position as desired by using the proposed algorithm,the steady state error is 0.000 2 rad.In addition,the joint tracking trajectory is smooth,the joint tracking errors converges to zero quickly with a satisfactory continuous joint control input.The proposed research provides a feasible solution for spacecraft attitude regulation by using arm motion,and improves the precision of the spacecraft attitude regulation.     

多轴亚微米级平面定位台的滑模观测器无传感控制

针对Sawyer电机驱动的平面定位台的多轴精密定位问题(X、Y和θz轴),提出了一种新的部分无传感控制方法。用激光干涉仪检测定位台一个方向上的平移运动和摆动,并构建相应的闭环控制;同时,应用滑模观测器估计另一个方向上的平移运动并构建对应轴的闭环控制。在此基础上,通过实验从开环控制、多轴全闭环控制及部分无传感控制三方面对比了定位性能。实验结果表明:采用部分无传感控制,多轴平面定位台的重复定位精度达到亚微米(0.25μm)级;部分无传感控制下的动子行程与开环控制相同(X轴300mm、Y轴300mm),远大于基于多轴位置传感的全闭环控制下的动子行程(X轴100mm、Y轴100mm);获得的结果可满足应用设计要求。