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GEAR AND SHAFT INTRODUCTION
Abstract: The important position of the wheel gear and shaft can't falter in traditional machine and modern machines.The wheel gear and shafts mainly install the direction that delivers the dint at the principal axis box.The passing to process to make them can is divided into many model numbers, useding for many situations respectively.So we must be the multilayers to the understanding of the wheel gear and shaft in many ways .
Key words: Wheel gear;Shaft
In the force analysis of spur gears, the forces are assumed to act in a single plane. We shall study gears in which the forces have three dimensions. The reason for this, in the case of helical gears, is that the teeth are not parallel to the axis of rotation. And in the case of bevel gears, the rotational axes are not parallel to each other. There are also other reasons, as we shall learn.
Helical gears are used to transmit motion between parallel shafts. The helix angle is the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix. The shape of the tooth is an involute helicoid. If a piece of paper cut in the shape of a parallelogram is wrapped around a cylinder, the angular edge of the paper becomes a helix. If we unwind this paper, each point on the angular edge generates an involute curve. The surface obtained when every point on the edge generates an involute is called an involute helicoid.
The initial contact of spur-gear teeth is a line extending all the way across the face of the tooth. The initial contact of helical gear teeth is a point, which changes into a line as the teeth come into more engagement. In spur gears the line of contact is parallel to the axis of the rotation; in helical gears, the line is diagonal across the face of the tooth. It is this gradual of the teeth and the smooth transfer of load from one tooth to another, which give helical gears the ability to transmit heavy loads at high speeds. Helical gears subject the shaft bearings to both radial and thrust loads. When the thrust loads become high or are objectionable for other reasons, it may be desirable to use double helical gears. A double helical gear (herringbone) is equivalent to two helical gears of opposite hand, mounted side by side on the same shaft. They develop opposite thrust reactions and thus cancel out the thrust load. When two or more single helical gears are mounted on the same shaft, the hand of the gears should be selected so as to produce the minimum thrust load.
Crossed-helical, or spiral, gears are those in which the shaft centerlines are neither parallel nor intersecting. The teeth of crossed-helical fears have point contact with each other, which changes to line contact as the gears wear in. For this reason they will carry out very small loads and are mainly for instrumental applications, and are definitely not recommended for use in the transmission of power. There is on difference between a crossed helical gear and a helical gear until they are mounted in mesh with each other. They are manufactured in the same way. A pair of meshed crossed helical gears usually have the same hand; that is ,a right-hand driver goes with a right-hand driven. In the design of crossed-helical gears, the minimum sliding velocity is obtained when the helix angle are equal. However, when the helix angle are not equal, the gear with the larger helix angle should be used as the driver if both gears have the same hand.
Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch cylinder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angular-velocity reduction between nonintersecting shafts which are usually at right angle. The worm gear is not a helical gear because its face is made concave to fit the curvature of the worm in order to provide line contact instead of point contact. However, a disadvantage of worm gearing is the high sliding velocities across the teeth, the same as with crossed helical gears.
Worm gearing are either single or double enveloping. A single-enveloping gearing is one in which the gear wraps around or partially encloses the worm.. A gearing in which each element partially encloses the other is, of course, a double-enveloping worm gearing. The important difference between the two is that area contact exists between the teeth of double-enveloping gears while only line contact between those of single-enveloping gears. The worm and worm gear of a set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm is generally quite large, and that on the gear very small. Because of this, it is usual to specify the lead angle on the worm, which is the complement of the worm helix angle, and the helix angle on the gear; the two angles are equal for a 90-deg. Shaft angle.
When gears are to be used to transmit motion between intersecting shaft, some of bevel gear is required. Although bevel gear are usually made for a shaft angle of 90 deg. They may be produced for almost any shaft angle. The teeth may be cast, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gear is often mounted outboard of the bearing. This means that shaft deflection can be more pronounced and have a greater effect on the contact of teeth. Another difficulty, which occurs in predicting the stress in bevel-gear teeth, is the fact the teeth are tapered.
Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and positively. As in the case of squr gears, however, they become noisy at higher values of the pitch-line velocity. In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel counterpart of the helical gear. As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered.
It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to bevel gears but with the shaft offset. Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution. The tooth action between such gears is a combination of rolling and sliding along a straight line and has much in common with that of worm gears.
A shaft is a rotating or stationary member, usually of circular cross section, having mounted upon it such elementsas gears, pulleys, flywheels, cranks, sprockets, and other power-transmission elements. Shaft may be subjected to bending, tension, compression, or torsional loads, acting singly or in combination with one another. When they are combined, one may expect to find both static and fatigue strength to be important design considerations, since a single shaft may be subjected to static stresses, completely reversed, and repeated stresses, all acting at the same time.
The word “shaft” covers numerous variations, such as axles and spindles. Anaxle is a shaft, wither stationary or rotating, nor subjected to torsion load. A shirt rotating shaft is often called a spindle.
When either the lateral or the torsional deflection of a shaft must be held to close limits, the shaft must be sized on the basis of deflection before analyzing the stresses. The reason for this is that, if the shaft is made stiff enough so that the deflection is not too large, it is probable that the resulting stresses will be safe. But by no means should the designer assume that they are safe; it is almost always necessary to calculate them so that he knows they are within acceptable limits. Whenever possible, the power-transmission elements, such as gears or pullets, should be located close to the supporting bearings, This reduces the bending moment, and hence the deflection and bending stress.
Although the von Mises-Hencky-Goodman method is difficult to use in design of shaft, it probably comes closest to predicting actual failure. Thus it is a good way of checking a shaft that has already been designed or of discovering why a particular shaft has failed in service. Furthermore, there are a considerable number of shaft-design problems in which the dimension are pretty well limited by other considerations, such as rigidity, and it is only necessary for the designer to discover something about the fillet sizes, heat-treatment, and surface finish and whether or not shot peening is necessary in order to achieve the required life and reliability.
Because of the similarity of their functions, clutches and brakes are treated together. In a simplified dynamic representation of a friction clutch, or brake, two inertias I1 and I2 traveling at the respective angular velocities W1 and W2, one of which may be zero in the case of brake, are to be brought to the same speed by engaging the clutch or brake. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in a temperature rise. In analyzing the performance of these devices we shall be interested in the actuating force, the torque transmitted, the energy loss and the temperature rise. The torque transmitted is related to the actuating force, the coefficient of friction, and the geometry of the clutch or brake. This is problem in static, which will have to be studied separately for eath geometric configuration. However, temperature rise is related to energy loss and can be studied without regard to the type of brake or clutch because the geometry of interest is the heat-dissipating surfaces. The various types of clutches and brakes may be classified as fllows:
1. Rim type with internally expanding shoes
2. Rim type with externally contracting shoes
3. Band type
4. Disk or axial type
5. Cone type
6. Miscellaneous type
The analysis of all type of friction clutches and brakes use the same general procedure. The following step are necessary:
1. Assume or determine the distribution of pressure on the frictional surfaces.
2. Find a relation between the maximum pressure and the pressure at any point
3. Apply the condition of statical equilibrium to find (a) the actuating force, (b) the torque, and (c) the support reactions.
Miscellaneous clutches include several types, such as the positive-contact clutches, overload-release clutches, overrunning clutches, magnetic fluid clutches, and others.
A positive-contact clutch consists of a shift lever and two jaws. The greatest differences between the various types of positive clutches are concerned with the design of the jaws. To provide a longer period of time for shift action during engagement, the jaws may be ratchet-shaped, or gear-tooth-shaped. Sometimes a great many teeth or jaws are used, and they may be cut either circumferentially, so that they engage by cylindrical mating, or on the faces of the mating elements.
Although positive clutches are not used to the extent of the frictional-contact type, they do have important applications where synchronous operation is required.
Devices such as linear drives or motor-operated screw drivers must run to definite limit and then come to a stop. An overload-release type of clutch is required for these applications. These clutches are usually spring-loaded so as to release at a predetermined toque. The clicking sound which is heard when the overload point is reached is considered to be a desirable signal.
An overrunning clutch or coupling permits the driven member of a machine to “freewheel” or “overrun” because the driver is stopped or because another source of power increase the speed of the driven. This type of clutch usually uses rollers or balls mounted between an outer sleeve and an inner member having flats machined around the periphery. Driving action is obtained by wedging the rollers between the sleeve and the flats. The clutch is therefore equivalent to a pawl and ratchet with an infinite number of teeth.
Magnetic fluid clutch or brake is a relatively new development which has two parallel magnetic plates. Between these plates is a lubricated magnetic powder mixture. An electromagnetic coil is inserted somewhere in the magnetic circuit. By varying the excitation to this coil, the shearing strength of the magnetic fluid mixture may be accurately controlled. Thus any condition from a full slip to a frozen lockup may be obtained.
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NC technology development trends
1 NC system developments at home and abroad
With the rapid development of computer technology, the traditional beginning of a fundamental change manufacturing, the industrial developed countries spent huge sums of money on the modern manufacturing technology research and development, to create a new model. In modern manufacturing systems, CNC technology is the key to technology, which combines microelectronics, computers, information processing, automatic detection, automatic control, such as the integration of advanced, a high-precision, high-efficiency, flexible automation, and other characteristics, the manufacturing industry Flexible automation, integrated, intelligent play the pivotal role. At present, NC technology is undergoing a fundamental change, from a special closed-loop control mode to general-purpose real-time dynamic open all closed-loop control mode. In the integrated on the basis of the CNC systems ultra-thin, ultra-light; on the basis of the intelligent, integrated computers, multimedia, fuzzy control, neural network and other technical disciplines, NC system to achieve high-speed, high-precision, Efficient control, automatic processing can be amended to regulate compensation and the parameters for an online intelligent fault diagnosis and treatment of the network based on the CAD / CAM and CNC systems integration as one machine network, makes the central government centralized control of the group control processing.
For a long time, China''s CNC system for traditional closed architecture, but only as a non-intelligent CNC machine controller. Process variables based on experience in the form of pre-fixed parameters, processing procedures before the actual processing by hand or through CAD / CAM and automatic programming system prepared. CAD / CAM and CNC have no feedback control link, the entire manufacturing process CNC is a closed ring-opening implementing agencies. In a complex and changing environment under the conditions of processing tool in the process of composition, workpiece material, spindle speed, feed rate, tool path, cutting depth, step, allowance and other processing parameters, not at the scene circumstances under external interference and real-time dynamic random factors, not by random amendment feedback control link CAD / CAM settings volume, in turn, affect the work of CNC machining efficiency and product quality. Clearly, the traditional fixed CNC system that controlled mode and closed architecture, limiting the CNC to the development of more intelligent control variables, can no longer meet the increasingly complex manufacturing process, therefore, the CNC technology in the potential for change inevitable.
2 NC technology development trends
2.1 Performance development direction
(1) high-speed high-precision efficient speed, accuracy and efficiency of machinery manufacturing technology is the key performance indicators. As a result of the high-speedCPU chips, RISC chip, as well as multi-CPU control system with high-resolution detector of the absolute exchange digital servo system, taken at the same time improve the machine dynamic and static characteristics of effective measures, the high-speed high-precision machine has been efficient greatly enhanced.
(2) Flexible includes two aspects: CNC system itself flexibility, NC system is modular in design, functional coverage, can be cut and strong, and easy to meet the needs of different users; group control system flexibility, with a control system pursuant to the requirements of different production processes, materials flow and information flow automatically dynamically adjusted to maximize their group control system performance.
(3) Process of composite and multi-axis to reduce the process time for the main purpose of supporting the composite processing, and are moving towards multi-axis, multi-function control of the direction of series development. NC Machine Tool Technology composite refers to the workpiece in a single machine on a fixture, through an automatic tool change, rotating spindle head or turntable, and other measures to accomplish multiple processes, multi-surface machining compound. Axis CNC technology, Siemens 880-axis control system for up to 24 axes.
(4) Real-time Intelligent early for the real-time system is usually relatively simple ideal environment, and its role is to scheduling tasks, to ensure that the task be completed within a specified time limit. And artificial intelligence is used to model the realization of mankind''s various intelligent behaviors. To the development of science and technology today, real-time systems and artificial intelligence combined with each other towards artificial intelligence is a real-time response, a more realistic field of development, and also in the real-time system with intelligent behavior, the more complex application development, resulting in the Intelligent real-time control of this new area. NC technology in the field, real-time intelligent control of the research and application of development along several main branches: adaptive control, fuzzy control, neural network control, experts control, learning control, feed-forward control. For example, in CNC programming system with expert systems, fault diagnosis expert system parameters automatically set and tool management and automatic compensation, such as adaptive conditioning systems, in high-speed processing of the integrated motion control ahead of the introduction of budget projections and functional, dynamic Feedforward functions in pressure, temperature, position, velocity, control, fuzzy control, the control of the NC system performance greatly improved, so as to achieve optimal control purposes.
2.2 functional development direction
(1) The user interface is graphical user interface with the CNC system of dialogue between the user interface. Since different users interface requirements are different, thus the development of the workload of great user interface, user interface software developed into the most difficult part of. At present INTERNET, virtual reality, visualization in scientific computing and multimedia technologies, such as the user interface has put a higher demand. Graphical user interface greatly facilitates the use of non-professional users, it can be carried out through the window and menu operation, ease of programming and blueprint for rapid programming, three-dimensional dynamic three-dimensional color graphics, graphics, simulation, graphics, dynamic tracking and simulation, and the different directions view and partial display ratio scaling function can be achieved.
(2) visualization in scientific computing visualization in scientific computing can be used for efficient data processing and interpretation of data, so that the exchange of information is no longer limited to using the written word and language, and can direct the use of graphics, image, animation, video and other information. Visualization technology and virtual environment technology, to further broaden the application areas, such as a drawing design, virtual prototyping technology, which shorten product design cycles, improving product quality, reduce production cost is of great significance. NC technology in the areas of visualization technology can be used for CAD / CAM, such as automatic programming design parameters automatically set, tool compensation and tool management of dynamic data processing and display, as well as the processing of visual simulation, and other presentations.
(3) interpolation, and a variety of methods of compensation interpolation methods such as multiple linear interpolation, circular interpolation, cylindrical interpolation, space elliptical surface interpolation, thread interpolation, polar coordinates interpolation, 2 D +2 helical interpolation , NANO interpolation, interpolation NURBS (non-uniform rational B-spline interpolation), spline interpolation (A, B, C kind), such as polynomial interpolation. A variety of functions such as compensation gap compensation vertical compensation quadrant error compensation, and measurement systems pitch error compensation, and speed-related feedforward compensation and temperature compensation, with nearly smooth and exit, as well as the opposite point of the cutter radius compensation.
(4) high-performance PLC contents contents performance CNC system PLC control module can be directly used ladder diagram or high-level language programming, with intuitive online debugging and online help function. Programming tools include the standard used lathe and milling machine PLC user program an example, users may PLC user program standards on the basis of editorial changes, thus easily build their own applications.
(5) application of multimedia technology of multimedia technology-computers, audio-visual and communication technology, and it has the computer integrated voice, text, images and video information. In NC technology, multimedia technology can be applied to information processing integrated, intelligent, real-time monitoring system in the field and production equipment fault diagnosis, monitoring of process parameters such as production has a significant value.
2.3 Development of the Architecture
(1) integration of a highly integrated CPU, programmable RISC chips and large-scale integrated circuits FPGA, EPLD, CPLD and ASIC ASIC chips that can improve the CNC system integration and hardware and software operating speed. Application FPD flat panel display technology can improve display performance. Flat-panel displays with high science and technology content, light weight, small size, low power consumption and portability advantages can be realized Supersized, a counterweight to the emerging and CRT display technology, display technology in the 21st century the mainstream. Application of advanced packaging and interconnect technologies, semiconductors and surface mount technology integration. By increasing the density of integrated circuits, reducing the length and number of interconnection products to reduce prices, improve performance, reduce component size, improve the reliability of the system.
(2) easy to implement modular hardware modular NC systems integration and standardization. According to various functional requirements, the basic modules, such as CPU, memory, position servo, PLC, the input and output interfaces, and communications modules, making the standard Series products, through functional building-block approach to cutting the number of steps and modules, a NC system at different grades.
(3) machine interconnection network for remote control of unmanned operation. Machine through networking, can be in any one machine on the other machine programming, configuration, operation, operating, different machine can be displayed on the screen each machine on the screen.
(4) general-open the closed-loop control mode to adopt a common computer component Bus, modular, open, embedded architecture, ease of cutting, expansion and upgrading, can be composed of different grades, different types, different degree of integration CNC system. Closed-loop control mode is the traditional CNC system only for single closed-open-loop control mode proposed. The manufacturing process is a multi-variable control and the role of integrated processing complex process, including processing, such as size, shape, vibration, noise, temperature and thermal deformation, and other factors, therefore, to achieve the process of multi-objective optimization, Multivariable must adopt the closed-loop control, real-time processing in the dynamic adjustment process variables. Processing the adoption of open universal real-time closed-loop control mode the whole dynamic, easy real-time intelligent computer technology, network technology, multimedia technology, CAD / CAM, servo control, adaptive control, dynamic data management and dynamic tool compensation, dynamic simulation and other high technology into one, a tight closed-loop manufacturing process control system to achieve integrated, intelligent, network-based.
3 PCNC new generation of intelligent CNC system
Research and Development adapted to the current complexity of the manufacturing process, with the structure of the closed-loop control system, a new generation of intelligent PCNC CNC system has become possible. PCNC NC intelligent system will be a new generation of intelligent computer technology, network technology, CAD / CAM, servo control, adaptive control, dynamic data management and dynamic tool compensation, dynamic simulation and other high technology into one, a tight closure of the manufacturing process Central control system.
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