Novel frictional algorithm implementing angular increment for two-dimensional frictional systems

This study proposes a new frictional algorithm that implements angular increment. The proposed algorithm is used to solve the numerical solutions of dynamic problems in two-dimensional frictional systems. It can accurately obtain the motion responses of a lumped mass under time-varying external forces, and it can compensate for the shortcomings of the numerical frictional algorithm that implements a time step. Specifically, the proposed algorithm 1) overcomes the difficulties encountered when the angles between resultant tangential forces and slip motion are infinitely close, 2) provides accurate solutions for two-dimensional systems under fierce planar motions, and 3) calculates the responses of the mass within a reasonable period. We compare the computation accuracy, efficiency, and robustness of the proposed frictional algorithm and the previous frictional algorithm [1] through several representative scenarios. We reveal that the proposed algorithm has superior computation accuracy, efficiency, and robustness for two-dimensional frictional problems involving slip/stick transitions and sharp bending.

     

Response of frictional receding contact problems to cyclic loading

Dundurs [Properties of elastic bodies in contact. In: de Pater AD, Kalker JJ, editors. The mechanics of the contact between deformable bodies. Delft: Delft University Press; 1975. p. 54–66] has shown that if the contact area in a frictionless elastic system under load is equal to or smaller than that before loading (i.e. the contact is receding), the extent of the contact area is load-independent and the stress field varies linearly with load. Similar results apply to problems with Coulomb friction as long as the loading is monotonic, but otherwise non-linearities and variation in the contact area occur. In this paper, we examine this effect for the simple case of an elastic block pressed against a frictional rigid plane. During unloading there is continuous variation of both contact and slip/stick boundaries. For the important case where the loading contains a mean and a periodic component, the system approaches a steady periodic state relatively slowly and in this final state there is continuous variation of the contact area, with the minimum (i.e. the maximum amount of separation) occurring at the minimum applied load.     

Active damping of frictional self-vibrations in systems with a cubic characteristic of the frictional force

Analytical solutions are obtained for the laws of damping of self-vibrations that ensure the stability and uniqueness of self-vibration regimes with minimal intensity.     

Analysis of frictional energy dissipation on an annular surface with harmonic loading

Metallic mating surfaces in structural joints offer a good source of frictional energy dissipation resulting in a damped dynamic structural response. This paper reports the results of experiments where the energy dissipation per cycle occurring at a preloaded flat metallic annular interface subjected to cyclic tangential forces is measured. The effects of certain pertinent joint variables on this frictional energy dissipation are investigated by the application of Response Surface Methodology. A central composite rotatable design was utilized for developing empirical expressions for energy loss. The methodology presented suggests a useful technique for tribological research.     

Machine loading in flexible manufacturing systems considering routeing flexibility

The key competitive strength of a manufacturing system lies in its flexibility, which represents the ability to respond effectively to changing circumstances. Flexible manufacturing systems (FMSs) react appropriately to change. The relevance of a particular type of flexibility depends upon the system and problem being considered. In this paper, the machine loading problem in a flexible manufacturing system is addressed. The loading problem is concerned with the allocation of part operations and required tools to the machines, so as to optimise some objective(s) subject to some technological constraints. Several objectives have been considered in the past such as maximisation of the utilisation of resources, minimisation of processing and tooling costs and maximisation of throughput rates. In such procedures, it is quite probable that a rigid loading schedule is obtained and in cases of machine breakdowns and tool failures alternate routeings are often not available. Therefore, in this paper, we develop a mathematical model which considers maximisation of the production routeings available for the parts and hence increases the routeing flexibility. The model is illustrated by examples.     

Analysis of internal loading at multiple robotic systems

When multiple robotics systems with several sub-chains grasp a common object, the inherent force redundancy provides a chance of utilizing internal loading. Analysis of grasping space based internal loading is proposed in this work since this method facilitates understanding the physical meaning of internal loadings in some applications, as compared to usual operational space based approach. Investigation of the internal loading for a triple manipulator has been few as compared to a dual manipulator. In this paper, types of the internal loading for dual and triple manipulator systems are investigated by using the reduced row echelon method to analyze the null space of those systems. No internal loading condition is derived and several load distribution schemes are compared through simulation. Furthermore, it is shown that the proposed scheme based on grasping space is applicable to analysis of special cases such as three-fingered and three-legged robots having a point contact with the grasped object or ground.     

A heuristic algorithm for the loading problem in flexible manufacturing systems

The paper considers the loading problem in flexible manufacturing systems (FMSs). This problem involves the assignment to the machine tools of all operations and associated cutting tools required for part types that have been selected to be produced simultaneously. The loading problem is first formulated as a linear mixed 0–1 program with the objective to minimize the greatest workload assigned to each machine. A heuristic procedure is presented in which an assignment of operations to machine tools is obtained by solving a parameterized generalized assignment problem with an objective function that approximates the use of tool slots required by the operations assigned to the machines. The algorithm is coded in FORTRAN and tested on an IBM-compatible personal computer. Computational results are presented for different test problems to demonstrate the efficiency and effectiveness of the suggested procedure.     

矿井提升钢丝绳断绳分析与预防措施

分析了造成提升钢丝绳断丝的原因,提出了相应的预防措施.通过采取正确、有效的防护措施,延长了设备的使用寿命,保证了安全生产     

无极绳绞车压绳装置的改进分析

针对无极绳绞车在使用过程压绳装置存在容易跳绳、设备容易松动的问题,通过对压绳装置受力、改进技术原理进行分析,提出对压绳装置进行改进的措施.提出的压绳装置改进措施简单、实用性强,在井下即可完成改进操作.改进完成并现场应用后发现,压绳装置故障发生率显著降低,为无极绳绞车高效运行提供了可靠保障.     

多绳缠绕式超深矿井提升机主动调绳装置性能研究

针对多绳缠绕式超深矿井提升机主动调绳装置,探究多绳缠绕式超深矿井提升机浮动天轮主动调绳能力。采用电液伺服系统实现浮动天轮的主动调绳,调整钢丝绳张力差。通过建立提升系统的数学模型,创建MATLAB/simulink模型,对系统进行仿真,分别用不同的正弦扰动频率模拟钢丝绳振动,用阶跃扰动模拟钢丝绳在卷筒上层与层过渡的工况,分析在提升机运行过程中实时调绳的能力,获得调节钢丝绳张力的规律,对多绳缠绕式超深矿井提升机主动调绳装置设计有一定的指导意义。     

Life of magnetic-fluid frictional components in gas

Formulas are derived for the life of magnetic-fluid frictional components as a function of the limiting solid-phase concentration.     

The frictional behaviour of materials

A review of friction is made and a general equation of friction, based on dimensional analysis, is presented. The equation takes into account the environment, material properties, surface roughness, the area of real contact, rubbing velocity, deformation and surface energy, and suggests friction to be system dependent. By imposing certain conditions, it was shown that the equation satisfies equations based on the adhesion and agrees with deformation and surface energy theories. A model of friction is presented which suggests that the friction force results from adhesion, plowing and interlocking of asperities, the magnitude of which is governed by surface energy and the nature and magnitude of surface deformation.The experimental results presented suggest the dependence of friction on load and velocity to be heavily influenced by the oxidation characteristics of the materials in rubbing contact.     

A new branch and bound algorithm for loading problems in flexible manufacturing systems

Loading problems in flexible manufacturing systems involve assigning operations for selected part types and their associated tools to machines or machine groups. One of the objectives might be to maximize the expected production rate (throughput) of the system. Because of the difficulty in dealing with this objective directly, a commonly used surrogate objective is the closeness of the actual workload allocation to the continuous workload allocation that maximizes throughput. We test several measures of closeness and discuss correlations between these measures and throughput. Using the best measure, we show how to modify an existing branch and bound algorithm which was developed for the case of equal target workloads for all machine groups to accommodate unequal target workloads. We also develop a new branch and bound algorithm which can be used for both types of problems. The efficiency of the algorithm in finding optimal solutions is achieved through the application of better branching rules and improved dominance results. Computational results on randomly generated test problems indicate that the new algorithm performs well.     

Multicriterion analysis of the loading problem in flexible manufacturing systems using Min-Max approach

The loading problem in flexible manufacturing systems warrants the consideration of multiple objectives for effective use of its capabilities. The problem is formulated as a multicriterion programming model. The min-max approach is used to find the solution. The results of a particular example are presented to illustrate the application of the model.     

Modeling of thermoelastic frictional contact

A model of thermoelastic frictional interaction based on nonideal thermal contact under friction of a corrugated elastic solid on an absolutely flat rigid solid is developed. The proposed model may be used for the estimation of the capability and durability of tribological conjunctions of the type frictional polymer material-metal.     

Laser modification of frictional surfaces

Improvement in the physicomechanical properties and frictional characteristics of cylinder and piston surfaces in airplane internal-combustion engines is considered. A method of developing recommendations regarding the optimization of laser treatment is proposed on the basis of experiments and a model of surface wear.     

Adjustment of frictional safety clutches

The relation between the working-load field of a machine and the triggering fields of the frictional safety clutch is considered, with different clutch adjustment. Clutch adjustment with minimal frictional coefficient ensures the greatest operational reliability.