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Heavy-duty vertical lathes, horizontal extended lathes, etc., followed by a number of machine tools in the former Soviet Union, Germany, the United Kingdom, Italy and the United States, from the time sequence of these machine tools, we can clearly see the development of the gear device technology process. The toothed device consists of the following components: the displacement moving part (machine tool itself).
"Displacement measuring element (precision rack and pinion), photoelectric sensor.
The pointer type instrument is composed of digital display instruments in the later stage.
China imported Skoda new machine tools from the beginning of the "century" era. The toothed device of this machine tool is made up of gears (double gears with elastic joints to eliminate side gaps), racks, multiplication mechanism (mechanical frequency multiplication or mechanical subdivision, The composition of the DC directional indicator scale meter (scale subdivision, grid) is estimated below, the coordinate positioning accuracy is increased every time (note that it can be positive or negative), and the cumulative error is related to the geometric accuracy of the guide rail. It is related to rack manufacturing, installation and commissioning, and is related to temperature changes. The toothed device plays a heavier role. At that time, industrialized countries used toothed devices as the best choice for large displacement measurements. Due to the technical development of the time, there are some unsatisfactory places for the toothed device: the gear type multiplying mechanism has a large transmission ratio (equivalent to a laborious lever), and when the double gear that meshes with the rack drives the multiplying mechanism to start and stop, it generates a large The moment of inertia and impact, which requires the torsion spring of the double-gear elastic joint to have sufficient elastic torque to withstand the moment of inertia impact. The above reasons make the gear wear faster, the gear indexing circle expands long, the modulus, the number of teeth, and the pressure angle.
The rack is manufactured as a milling tooth. The tooth shape and pressure angle are not ideal, and the system accuracy is stable for about a year.
The first improvement, the structure and manufacturing process of the rack, the line meshing of the straight teeth is changed to the point meshing of the (toothed) curved teeth, and the milling teeth are changed to grinding teeth, which are adopted by all countries for the characteristics of the rack processing. Two-dimensional space grinding method in one-dimensional space, but the parameters of companies in different countries are inconsistent (British and American adopt inch standard, other countries adopt non-standard metric or non-standard modular), this processing method is traditional to rack The manufacturing process has produced a major breakthrough, which greatly improves the accuracy of the rack and ensures the stability of the coordinate accuracy.
The second improvement is also the one with the biggest change, the gear rack modulus is reduced, the gear torque is reduced, and the indexing circle is extended (reducing the three-tooth error interference). The reason for the gear change is to eliminate the multiplier mechanism and the resolver, and replace it with a photoelectric pulse encoder (the optical subdivision amount reaches the initial stage of the photoelectric integrated large displacement measurement digital display device.
There is no reduction in the accuracy of the gears and racks, and the conclusion is that they can be used as permanent displacement detection components. Photoelectric pulse encoders (thermal light sources) and grating digital display meters (separating components) have also lagged behind China. By replacing the encoder and digital display and adjusting the mounting accuracy of the rack, the system is stable and effective after the modification, and the gear devices of various countries can be divided into two types according to the structure. The first type of double gear structure is produced in the Czech Republic. Germany (we only see the two). The advantage of the double-tooth structure is that the meshing force is extremely small. If the gear rack is properly installed, the rack and pinion (limited to the age of use) can not see any decrease in accuracy. It can be regarded as a permanent or lifetime displacement detecting component. Unsatisfactory is the error. There are many factors and complicated installations. The installers must have a wide range of knowledge and experience, and must have strong hands-on ability. The second type of single gear structure (without gap engagement is done by elastic bracket), the single-tooth structure is produced in the United States (manufactured by many companies), the United Kingdom, Italy, the former Soviet Union, etc. This structure can ensure the coordinate precision as long as the elastic bracket design is reasonable. Long-term stability, simple installation, equivalent to absolute friction rolling grating.
Since the opening of the market in China, people in the industry have been paying attention to the development of Japan. The economical line scale and optical reading microscope (geometric optical displacement measuring device) of Japanese machine tool configuration are the industrial revolution of machining and measurement, but it is geared with Europe and America. The device is slightly worse than the level, the former is the static measurement of geometric optics, the latter is the dynamic side of the machine photoelectric integration. China has a history of the former (precision coordinate trampoline optical positioning system), but there is no history of the latter (about a year or so).
At present, there are several types of products (large displacement measuring components) in the Chinese market: inductive synchronizers, gratings (glass gratings, ribbon gratings) and ball grids. The price of strip gratings and ribbon magnetic grids is lower, but it is elastic under tension. The deflection caused by the modulus and the horizontal installation affects the temperature difference and the deformation is large. The common disadvantage of the above products is that as long as the scratches and bumps are completely scrapped, and the toothed device only replaces the faulty rack, there is no effect on the overall coordinate accuracy. Gears and racks benefit from a lifetime investment, and the life of encoders and digital meters is more than one year. The displacement detecting components described above are designed according to the measurement method of the measuring instrument. They can only be parallel to the machine guide rail in violation of the Abbe principle, that is, the measuring line (displacement detecting component) is parallel to the measured line (tool cutting point or surface), and the guide rail is straight. Degree and clearance directly affect the coordinate precision. The error they generate is called Abbe error. The parallel distance is proportional to the Abbe error. The straightness error and clearance of the guide are proportional to the Abbe error. Therefore, the guide rail is repaired when the machine is modified. The repair of the guiding surface can achieve the desired effect of the straightness of the guide rail and the matching clearance, and the Abbe error can be controlled to a very small state. Otherwise, the accuracy of the displacement detecting component is high and the coordinate precision is not ideal. Known as the golden saddle with the bad horse.
In recent years, we have seen that the precision rack and pinion mechanism is not only used for displacement measurement and displacement signal feedback, but it has been widely used as a transmission mechanism (kinetic component) of a major CNC machine tool without gap drive (rigid anti-backlash gear set). , Switzerland large flat panel plotter, French CNC vertical car, Japan Toshiba large floor CNC boring and milling machine. The transmission mechanism of the Toshiba CNC boring and milling machine is adopted.
We are very optimistic about the development and future of the precision gear set (rigid anti-backlash) rack structure, especially in the major machine tool manufacturing industry. Compared with the ball screw, the ball screw can not meet the requirements of large displacement transmission (the manufacturing length is limited) In particular, the deflection caused by gravity during horizontal transmission makes the lower half of the rolling nut raceway more stressed, and the lubrication is not good, the dust and the ball cause sharp wear of the ball screw and the nut, and the screw Partial damage can only be scrapped as a whole. Limited by the ball screw structure, the axial positioning end of the lead screw will never coincide with the machining origin, resulting in linear temperature drift, which is proportional to the relationship between the two points.
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