How to select a suitable linear scale?
1. The linear scale in precision index choice
One of the important indices for evaluation of nc machine tool is the accuracy of machine tools. High precision machine tool selection of high precision grating ruler is inevitable. The accuracy of the grating ruler and the resolution of the grating scale are the two concepts. Accuracy refers to the grating ruler grating stripe location accuracy. To achieve high accuracy, not only requires each lithography stripe location accurate, and it requires each grating stripe uniform, clear edges. High accuracy grating on the manufacturing production environment and equipment requirements are very high. Such as Germany HEIDENHAIN company at 15 m underground established a dust-free, constant temperature (temperature control in 0.01 C) grating etching workshop, to ensure the accuracy and precision of the grating stripes. Resolution is another indicator of evaluation of grating. We know that the relative movement and each tape grating scanning grating a lattice spacing, then produce a set of alternating sine signal. This signal is output raster ruler of the original signal. So, tape cycle is the basis of the resolution raster stripe. Request high resolution, first choose a grating ruler of small signal cycle. In this way, can improve the dynamic characteristic of the system, make the system's speed, acceleration and frequency response speed (cut-off frequency) to reach a higher level. The resolution of the grating ruler and accuracy is different, but it is complementary to each other. The high accuracy grating ruler of the original signal cycle is lesser also.
Signal after segmentation, there will be a segmentation error, segmentation error is mechanical feet of the error of the original signal cycle, and it is also a cyclical error signal. The error will cause the oscillation of the servo system, affect the stability of servo system data. If the grating stripe uneven, moment magnitude edge is not clear, relative segmentation error will be larger.
2. To efficiency index selection linear scale
The linear scale is incremental. More incremental linear scale has a reference mark signal. Using incremental grating ruler, in machine tools power to boot or restarts, usually will slowly move to the reference marks the location of linear scale. Finding reference marks and memorize the numerical control system. The past grating ruler usually have a fixed reference point mark. If the journey is long, machine tool to find reference points will occupy a lot of time. In order to reduce the numerical control machine tool, the processing time, the best machine tools in the boot when they perceive the position of the reference point or known machine tool coordinate axis position. To this, the HEIDENHAIN company made many improvements on the reference mark. And realized the purpose of quick take return reference point.Absolute type linear scale boot can be set for the position of the reference point. Absolute type grating ruler is made up of multiple sets of different period of the grating groove lines, arranged according to certain rules of cell receives the light through the raster scanning and tape grating light intensity signal, and will be converted into a binary signal. The numerical control system with raster ruler has a certain communication protocols between interface, will be converted to binary code machine tool coordinate axis location information. HEIDENHAI on 3 m long absolute type grating ruler is the development direction in the future.
3. Select linear scale in electrical interface form
Select linear scale as suitable as data system should be paid attention to. Different nc systems require different electrical interface.
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