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Study on the Friction Coefficient in Grinding

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厦门大学学报（自然科学版） 2002年第S1期41卷 119-120页

作者： CAI Guang-qi 1, FENG Bao-fu 1, JIN Tan 2, GONG Ya-dong 1 (1. School of Mechanical Engineering & Automation, Northeastern Unive rsity, Shenyang 110004, China 2. School of Industrial & Manufacturing Science, Cranfield University, Cranfield, Bedfordshire, UK)

The friction between the abrasive grains and workpi ec e is a crutial factor determining the main grinding output. Few studies have bee n carried out investigating the values of the friction coefficient in grinding, due to the difficulty of direct measurement. In this paper, a mathematical model of the friction coefficient in grinding has been established with the aid of a new grinding parameter C ge, which has close relations to wheel wear rate Z s, metal removal rate Z w, specific energy u and grinding force ratio λ(λ=F n/F t). By monitoring the process forces, C ge can be obtained and used easily for different grinding methods. Heavy grinding with different wheels and also single-grit grinding tests have been conducted for various work materials. The friction coefficients under different grinding conditions have been obtaine d using the model and the experimental results. For most materials tested in pap er, the friction coefficients decrease with the grinding speed. The friction coe fficients in single-grit grinding are 0.61～0.84 at the speed of 0.028 m/s, and 0.09～0.34 at the speed of 67～120 m/s. In single-grit grinding for 45 # a nd 20Cr steels, the friction coefficients decrease with the increase of the grindi ng speed while below a critical speed, and increase slightly with the increase o f grinding speed while above the critical grinding speed. Owing probably to the high surface temperature caused by high power consumption and dry condition, the friction coefficients in heavy grinding are 0.09～0.19, distinctly lower than t h ose of single-grit grinding, and also lower than those of ordinary grinding. Du e to the softening of the metals, the friction coefficients in heavy grinding un der dry condition are lower than that in wet condition. Owing probably to the di fference of hardness and roughness, while using different types of wheel and abr asive, the friction coefficients for the same work material changes even at same grinding speed. The work materials a

关键词： grinding friction coefficient model

Hierarchical Architecture for Enterprise Information System under Dynamic Environment

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厦门大学学报（自然科学版） 2002年第S1期41卷 224-225页

作者： TIAN Chun-hua, CHAI Yue-ting, LIU Yi (Department of Automation, Tsinghua University, Beijing 100084, China)

In a dynamic environment, it is vital for enterpris e to have flexible information system architecture to integrate ERP, Supply Chain Management (SCM) and E-Commerce (EC). The traditional systems are established o n the ERP-centered flat architecture. This architecture has some disadvantages in supporting the dynamics of enterprises. Firstly, ERP is already a very expens ive and complex system; the extension based on it can only increase the complexi ty and make the implementation more expensive and risky. Secondly, under the arc hitecture, the flexibility is reduced sharply although the execution efficiency is maintained. In a rapid changing environment, flexibility is also an equally i mportant factor besides execution efficiency. Thirdly, it cannot support the dyn amic collaboration efficiently. The prevailing of the flat architecture is not d ue to its advantage but to the big software providers. From the system viewpoint , a hierarchical architecture is proposed. Difference from the current architect ure, in the hierarchical paradigm, ERP is put in the bottom level rather centere d. SCM is the center system, which adopts a multi-agent structure. EC is regard ed as its foreground interface, while ERP and other information system of the pa rtner or internal units are the background executors. EC is the extension of mar ket agent and purchase agent. It fulfills the function of trade on Internet by s ending orders to be executed to SCM and receiving the progress information of th e orders from SCM. After receiving orders from EC, the agent in charge of schedu le in SCM makes preliminary plan in form of instructions (which may be infeasibl e) based on the information of source. Trough the coordination of multi agent, the plan is adjusted to be feasible. Compared with current ERP-centered flat ar chitecture, the hierarchical structure pays more attention to dynamic collaborat ion rather the optimization within the enterprise. At last, two engineering case s, Beijing

关键词： ERP Supply Chain Management E-Commerce Multi -Agent system information system architecture

Study on the Vibrational Power Flow Transmission Characteristics of Gearb ox

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厦门大学学报(自然科学版) 2002年第S1期 84-85页

作者： ZHANG Bing, SONG Kong-jie, SUN Ling-ling, QI Wen-guo (School of Mechanical Engineering, Shandong University, Jinan 250061, China)

Gearbox as an important source of noise and vibration, its structure-borne nois e has drawn more and more attentions and has become an important investigation t opic. The gearbox is extremely complicated mechanical equipment. In general, the profiles of gear teeth are not perfect. Together with the time-varying stiffne ss during tooth mesh, an in-plane force will be induced at the rim of a rotatin g gearwheel, which creates the vibration. These vibrations are transmitted throu gh the shafts, the bearings, and finally to the gearbox. At the same time, they will produce air-borne noise during tooth mesh, which radiate directly to the g earbox and through the gearbox radiate to the neighboring environment. In this paper, the overall dynamics of a gear system that includes a spur gear p air, shafts, bearings and a flexible gearbox is investigated. At first, the gear ed rotor system comprising gears, shafts, bearings and gearbox is set up and sim plified into a Source-Path-Receiver (SPR) model. Here, the rotating system inc luding the gears, shafts, primer mover and load is considered as the Source whil e the gearbox is regarded as the receiver and the bearings are treated as the Pa th. The dynamics of the SPR model is analyzed and the power flow transmitted fro m the source to the receiver is derived. Then the geared motor system is studied by finite element method (FEM), and corresponding mobility matrices are built b y choosing proper FEM model. Based on these data and the bearing’s mobility mat rix, the overall model of gearbox is developed using the component mobility meth od. At last the power flow transmission properties between substructures or subs ystem of gearbox are studied from the viewpoint of energy. The result will provi de the reliable computational foundation for improving the gearbox’s dynamical performance.

关键词： vibration isolation vibration measurement pow er flow

Cutting Temperature and Tool Wear of Hard Turning Hardened Bearing Steel

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厦门大学学报（自然科学版） 2002年第S1期41卷 128-129页

作者： LIU Xian-li 1, WEN Dong-hui 2, LI Zhen-jia 1, XIAO Lu 1, YAN Fu-gang 1 (1. Dept of Mechanical Engineering, Harbin University of Science and Technology, Harbin 150080, China 2. Dept of Precision Instrunmetns & Mechanol ogy, Tsinghua University, Beijing 100084, China)

A study was undertaken to investigate the performan ce of PCBN tool in the finish turning GCr15 bearing steel with different hardness between 30～64 HRC. The natural thermocouple was used to measure the cutting tem p erature, tool life and cutting temperature were investigated and compared. The m aterial can be heated by this instrument which using low voltage and high elec trical current, while PCBN can’t be heated by electrifying directly, so the ke ntanium layer coating over the PCBN is heated, so the PCBN is heated and its th ermoelectric property is got by this method. [TPP129,+60mm88mm,Y,PZ#] Fig.1 Effect of cutting depth and workpiec hardness on. the cutting temperatureThe objective was to determine the influence of the workpiece hardness on change s in cutting temperature and tool wear characterize. It can be found from Fig.1 that the cutting temperature show an increasing tendency with the improvement of workpiece hardness within the cutting speed scope when the workpiece hardness i s under HRC50. And on the other hand, it is found that the cutting temperature s how the downtrend with the improvement of workpiece hardness when the workpiece hardness is over HRC50. According to experimental results, the critical hard ness when turning hardened GCr15 bearing steel with PCBN tool is about HRC50. Th e wear causes of PCBN tool have been found out through taking photos on the micr o-shape of PCBN poly-laminate initial surface as well as face and flank of wea r tool and analysis on chemical elements. It is discovered that the PCBN tools a re not suitable for cutting the workpiece at nearly critical hardness, because n ear the critical hardness, PCBN wear at the highest speed. For researching the w ear rule of PCBN tool, the tool wear experiments have been carried on by using b earing steel GCr15 at hardness HRC40 and HRC60 with changing cutting speed. The indexes of tool life equations is gained under two kinds of conditions w hich are bigger than 0.6, so the effec

关键词： cutting temperature tool wear hard turning pol ycrystalline cubic boron nitride (PCBN) hardened bearing steel

Development of a Wire Driven Robot for Grinding with Stiffness Adapted

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厦门大学学报（自然科学版） 2002年第S1期41卷 81-82页

作者： ZHANG Bo 1,2, ZHAO Ming-yang 2 (1. Graduate School of the Chinese Academy of Sciences, Beijing 100039 , China 2. Robotics Laboratory, Shenyang Institute of Automation, Chinese Academy of S ciences, Shenyang 110016, China)

Along with development of new design and machining me thod production with more complex surface can be manufactured. Researching on th e new equipment used for surface disposal has become the important matter. Grind ing and polishing are a common surface processing method. A new type wire driven parallel robot used for grinding processing is proposed in this paper. Wire driven parallel robot is developed from parallel robot and serial wire driven r obot. Steel wire is used to replace the leg of parallel robot. Compared with par allel robot, this kind of robot has lager workspace, lower weight, higher rigidi ty and higher load/deadweight ratio. And the stiffness of robot is controlled by changing the tension of wire. The robot proposed in this paper has three DOF. T he moving part is driven by four wires, three of them are used to drive and the rest to keep them tension, with a restraining machine. The position sensors are installed in restraining machine. The position of terminating of end-effecter c an be ascertained in the space. The tension sensors are installed in each wire t o form force feedback system. By changing the tension the force on the workpiece can be controlled. Also the stiffness of robot can be adjusted.

关键词： wire driven parallel robot stiffness control

Modelling and Identification of a Digital Feed Drive

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厦门大学学报（自然科学版） 2002年第S1期41卷 21-22页

作者： LI Sheng, RUAN Jian, YUAN Ju-long, ZHANG Li-bin, JI Shi-ming (College of Mechanical & Electrical Engineering, Zhejinag University of Technology, Hangzhou 310014, China)

In many cases, the cutting method is usually adopted for the efficient machining of non-circular body of revolution and a feed drive is needed to actuate the cutting tool to and fro according to input signal wave. The feed drive for the purpose is required of fast response and accurate positioning. Both of these are highly dependent upon the actuating elements. Several schemes of actuation are specially interested. One is the introduction of piezoelectric actuation. However, the tiny working stroke of the piezoelectric material limits its application to a narrow range. Another is the application of electro-magnetic actuator. An innovative feed drive actuated by the stepper motor is introduced for the purpose. For a conventional step operating mode, a stepper motor can only be controlled to position at finite discrete points. Thus, when it is applied as an actuator of the feed drive, it is very difficult to maintain high accuracy and fast response. To eliminate quantitative error, the stepper motor is controlled under the continual mode. It is achieved with a micro-controller system and a built-in control algorithm program, called "tracking algorithm". Within each sampling cycle, the micro-controller will sample the input signal and the time interval will be divided into two parts according to the relative position between two adjacent stepping points. The phase coils correspondent to the two adjacent stepping points are energized respectively with calculated time duration. In the way, the motion of the tool frame smoothly tracks the input signal. This paper presents modeling and identification of frequency response of the proposed drive. The dynamic response of the feed drive is manly decided by the natural frequency of the stepper motor. For the conventional small-size stepper motors, the natural frequency is within the range 200～400 Hz. Experimental results show that the stepper motor actuated tool frame can smoothly keep in track of the input signal wave under "t

关键词： feed drive digital control frequency response identification

Analysis of Accuracy of a High-speed Mobile Platform Control System

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厦门大学学报（自然科学版） 2002年第S1期41卷 38-39页

作者： RUAN Jian, YUAN Ju-long, ZHANG Li-bin, JI Shi-ming, LI Sheng (College of Mechanical & Electrical Engineering, Zhejinag University of Technology, Hangzhou 310014, China)

The efficient manufacture technique involves a high-speed control of platform mobile system. A linear acutor is presented in this paper. The linear acutor is constructed as a linear stepper motor. However, to sustain both high accuracy and high speed for the position and speed control, A single-stack computer system is constructed and a special control algorithm is prescribed to controled the linear actuator continuously. In this paper, the nonlinear errors resulted from the magnetic saturation and the hysteresis is anaysis and discussed. In the view of electromagnetic propotional control, the actuator is a stage proportional magnet, because the driving current to the linear acuator changes for a number of cycles and a series of reset points will occur as the current undergoes cyclic changes. At each reset point the original starting characteristics of the system are re-established. A large number of reset points across the full stroke of the platform results in a significant reduction in the nonlinear behavior. The stage control is first discussed. Experiments carried out to obtain the characteristics of the mobile platform control system. It is demonstrated that with the introduction of stage control, nonlinearities, such as saturation and hysteresis, are greatly reduced, system stiffness is increased, and the positioning accuracy and resolution are improved. The effect of dither due to a "digital fragment" signal is also examined and found to be crucial in reducing the hysteresis and in improving the resolution accuracy.

关键词： high-speed control mobile platform nonlinearities

Active Vibration Isolation of Micro-Manufacturing Platform Based on Neural Network

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厦门大学学报（自然科学版） 2002年第S1期41卷 67-68页

作者： ZHANG Chun-liang, MEI De-qing, CHEN Zi-chen (Institute of Production Engineering, Zhejiang University, Hangzhou 310027, China)

The micromation and precision of the Micro-Electromechanical System demand that its manufacturing, measuring and assembling must work in a micro-manufacturing platform with good ability to isolate vibrations. This paper develops a vibration isolation system of micro-manufacturing platform. The brains of many kinds of birds can isolate vibrations well, such as woodpecker’s brain. When a woodpecker pecks the wood at the speed as 1.6 times as the velocity of sound, its brain will tolerate the wallop 1 500 times of the weight of itself without any damage. The isolation mechanics and organic texture of woodpecker’s brain that has good isolation characteristics were studied. A structure model of vibration isolation system for the micro-manufacturing platform is established based on the bionics of the bird’s brain vibration isolation mechanism. In order to isolate effectively the high frequency vibrations from the ground, a rubber layer is used to isolate vibrations passively between the micro-manufacturing platform’s pedestal and the ground. This layer corresponds to the cartilage and muscles in the outer meninges of the bird’s brain. The active vibration isolation technique is adopted to isolate vibrations between the micro-manufacturing platform and the pedestal. Air springs are used as elastic components, which correspond to the interspaces between the outer meninges and the encephala of the bird’s brain. Actuators are made of giant magnetostrictive material, and it corresponds to the nerves and neural muscles linking the meninges and the encephala. The actuators and air springs are arranged vertically in parallel to make use of the giant magnetostrictive actuators effectively. The air springs support almost all weight of the micro-manufacturing platform and the giant magnetostrictive actuators support almost no weight. In order to realize high performance to isolate complex micro-vibration, the control method using a three-layer neural network is presented. This vibra

关键词： micro-manufacturing platform active vibration isolation bionic mechanics neural network

Robust Iterative Learning Controller for the Non-zero Initial Error Problem on Robot Manipulator

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厦门大学学报（自然科学版） 2002年第S1期41卷 -页

作者： TAO Li-li 1,YANG Fu-wen 2 (1. Department of Automation, University of Xiamen, Xiamen 361005, Chi na 2. Department of Electrical Engineering, University of Fuzhou, Fuzhou 350002, C hina)

Industrial robot system is a kind of dynamic system w ith strong nonlinear coupling and high position precision. A lot of control ways , such as nonlinear feedbackdecomposition motion and adaptive control and so o n, have been used to control this kind of system, but there are some deficiencie s in those methods: some need accurate and some need complicated operation and e tc. In recent years, in need of controlling the industrial robots, aiming at com pletely tracking the ideal input for the controlled subject with repetitive character, a new research area, ILC (iterative learning control), has been devel oped in the control technology and theory. The iterative learning control method can make the controlled subject operate as desired in a definite time span, merely making use of the prior control experie nce of the system and searching for the desired control signal according to the practical and desired output signal. The process of searching is equal to that o f learning, during which we only need to measure the output signal to amend the control signal, not like the adaptive control strategy, which on line assesses t he complex parameters of the system. Besides, since the iterative learning contr ol relies little on the prior message of the subject, it has been well used in a lot of areas, especially the dynamic systems with strong non-linear coupling a nd high repetitive position precision and the control system with batch producti on. Since robot manipulator has the above-mentioned character, ILC can be very well used in robot manipulator. In the ILC, since the operation always begins with a certain initial state, init ial condition has been required in almost all convergence verification. Therefor e, in designing the controller, the initial state has to be restricted with some condition to guarantee the convergence of the algorithm. The settle of initial condition problem has long been pursued in the ILC. There are commonly two kinds of initial condition pro

关键词： robust control iterative learning control non- zero initial error robot manipulator