CN103234456A - Ultrahigh resolution linear encoder - Google Patents

Abstract

An ultrahigh resolution linear encoder comprises a plane light source, a fixed grating, a moving grating and a linear array CCD (charge coupled device) sensor, wherein the fixed grating, the moving grating and the linear array CCD sensor are mutually parallel, sequentially arranged in an irradiation direction of the plane light source and perpendicular to the irradiation direction of the plane light source. The linear array CCD sensor is fixed to the moving grating side by side. Photosensitive units of the linear array CCD sensor are as long as the moving grating. Grids of the N-1 length part of the fixed grating are as exactly N grids of the moving grating, namely grating spacing of the moving grating is equal to the number of ((n-1)/n) multiplied by grating spacing of the fixed grating, wherein the letter n refers to the number of gratings that can be described within the length of the moving grating. Displacement is measured for both the fixed grating and the moving grating according to the measurement principle of vernier caliper, measurement signals are acquired through the linear array CCD sensor, and accordingly resolution of the ultrahigh resolution linear encoder is increased. The ultrahigh resolution linear encoder is especially applicable to places having high requirement on measurement precision.

Description

Ultra High Resolution Grating Scale

technical field

The invention relates to a grating ruler with sub-nanometer resolution, which belongs to the technical field of measurement.

Background technique

Grating ruler (that is, grating ruler displacement sensor) is a measurement feedback device that uses the optical principle of grating. It has the characteristics of large detection range, high detection accuracy and fast response speed. It is often used in the closed-loop servo system of CNC machine tools. The core components of the grating ruler are the fixed grating and the moving grating. In the existing grating ruler, the gratings of the fixed grating and the moving grating are equidistant, and there is a small angle between them. The resolution of this kind of grating ruler can reach several nanometers, but with the continuous development of the manufacturing industry, the requirements for measurement accuracy are getting higher and higher, so it is necessary to design a grating ruler with higher resolution.

Contents of the invention

The purpose of the present invention is to provide an ultra-high-resolution grating scale to meet the precision requirements of the manufacturing industry, aiming at the drawbacks of the prior art.

Problem described in the present invention is realized with following technical scheme:

An ultra-high-resolution grating ruler, which includes a plane light source and a fixed grating, a moving grating and a linear array CCD sensor that are perpendicular to the irradiation direction of the plane light source and arranged in sequence along the irradiation direction of the plane light source and are parallel to each other. The sensor and the moving grating are fixed side by side, and the length of the photosensitive unit of the linear array CCD sensor corresponds to the length of the moving grating; the number of grids of the moving grating is exactly N-1 on the length of the fixed grating. N grids, that is, the pitch of the moving grating is equal to the pitch of the fixed grating*[(n-1)/n], where n is the number of gratings that can be drawn within the length of the moving grating.

In the above ultra-high resolution grating scale, the length of the photosensitive area of the linear CCD sensor is greater than or equal to the length of the moving grating.

In the above ultra-high resolution grating scale, the distance between the photosensitive units of the linear CCD sensor is equal to the grating pitch of the moving grating.

The fixed grating and the moving grating of the present invention use the measuring principle of the vernier caliper to measure the displacement, and at the same time use the linear array CCD sensor to collect the measurement signal, which greatly improves the resolution of the grating, and is especially suitable for occasions requiring high measurement resolution.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is a structural representation of the present invention;

Figure 2 is the readout potential corresponding to each pixel point when the moving grating is aligned with the first grid at the left end of the fixed grating;

Figure 3 is the read potential corresponding to each pixel point when the moving grating moves to the right by 1/4 pitch;

Figure 4 is the readout potential corresponding to each pixel point when the moving grating moves to the right by 1/2 pitch;

Figure 5 is the read potential corresponding to each pixel point when the moving grating moves to the right for 3/4 pitch;

Fig. 6 is a structural representation of the present invention;

Fig. 7 is an electrical schematic diagram of the control circuit.

、光敏电阻，BJ、比较器。 The list of labels in the figure is: 1. Fixed grating, 2. Moving grating, 3. Linear array CCD sensor, 4. Planar light source, VR, potentiometer, R1, first resistor, R2, second resistor,

, Photoresistor, BJ, comparator.

Detailed ways

和定光栅的第

个栅格

恰好对齐，每当动光栅向右移动个栅距时，所对齐的栅格号也向右移动一位，当动光栅向右移动1个栅距（

）时，动光栅的n号栅格和定光栅的n号栅格对齐。光源通过动光栅与定光栅的栅格照射在线阵CCD传感器上，栅格对齐时光照最强，对应的感光单元产生的电荷就多，读出来的该点电位就低。动光栅不同位置栅格对齐时对应各像素点读出电位如图2～图5所示，其中图2是左端对齐的情况，图3～图5分别是动光栅向右移动1/4、1/2,和3/4栅距时各点电位图。每当动光栅向右移动1个栅距，各点电位自左向右交替变化一个周期，哪个位置对齐了，线阵CCD对应点的电位就最低，把线阵CCD输出的信号与一个固定电位相比较，并把比较结果送到单片机的输入端，单片机就可以通过计算比较结果的上升沿和下降沿，得到所对齐光栅的序号，通过记录电平变化周期个数，得到动光栅向右移动的光栅格数，从而计算出动光栅向右移动的准确位移。 Referring to Fig. 1, the present invention is made of light source 4, fixed grating 1, moving grating 2 and linear array CCD sensor 3, and it is similar to existing grating ruler structure, and appearance is identical, and difference is that the moving grating outside of this grating ruler has a line Array CCD sensor, the length of the photosensitive unit of the linear array CCD sensor is the same as the length of the grid of the moving grating (of course, the length of the linear array CCD sensor 3 may not be equal to the length of the moving grating 2; the distance of the photosensitive unit can be equal to the grating of the moving grating pitch, or not equal to the grating pitch of the moving grating). The moving grating pitch of the present invention is smaller than the fixed grating pitch grid pitch, when the first grid at the left end of the moving grating and the first grid at the left end of the fixed grating When aligning, move the nth grid from the left of the raster

and the fixed grating's

raster

Exactly aligned, whenever the moving raster moves to the right When the grating distance is 1, the aligned grid number also moves one bit to the right, and when the moving grating moves to the right by 1 pitch (

), the nth grid of the moving grating is aligned with the nth grid of the fixed grating. The light source shines on the linear CCD sensor through the grid of the moving grating and the fixed grating. When the grid is aligned, the light is the strongest, and the corresponding photosensitive unit will generate more charges, and the potential of the point read out will be low. The readout potentials of each pixel point corresponding to the grid alignment at different positions of the moving grating are shown in Figures 2 to 5, where Figure 2 shows the left end alignment, and Figures 3 to 5 show that the moving grating moves 1/4 and 1 to the right, respectively. /2, and 3/4 grid pitch potential diagram of each point. Whenever the moving grating moves to the right by 1 grating pitch, the potential of each point changes alternately from left to right for a period. Whichever position is aligned, the potential of the corresponding point of the linear array CCD will be the lowest. The signal output by the linear array CCD is compared with a fixed potential Compare and send the comparison result to the input terminal of the single-chip microcomputer. The single-chip microcomputer can obtain the serial number of the aligned grating by calculating the rising edge and falling edge of the comparison result, and obtain the rightward movement of the moving grating by recording the number of level change cycles. The number of gratings, so as to calculate the exact displacement of the moving grating to the right.

Fig. 6 is the waveform of the readout signal, the comparison voltage and the output signal of the comparator when the No. X grid of the moving grating is assumed to be aligned. Comparing Vs with VREF, the comparator circuit is shown in Figure 7. The output of the comparator will rise to a high level at point D and fall to a low level at point E. Input this signal into the microcontroller to calculate , taking an integer X point is the grid serial number of the moving grating alignment.

个栅距。可见基于线阵CCD的超高分辨率光栅尺的分辨率是

栅距。 For example: the number of level change periods is M, and the serial number of the currently aligned grating is x, then the current moving distance is:

grid pitch. It can be seen that the resolution of the ultra-high resolution grating ruler based on the linear array CCD is

grating pitch.

，在2.5μm栅距的情况下实现了次纳米级的分辨率。通过改进算法，把

中的X取到0.5可以把分辨率提高到

。 When the grating pitch is equal to 2.5μm and the number of moving gratings is 10000, the resolution is μm, ie

, a sub-nanometer resolution is achieved with a 2.5 μm pitch. By improving the algorithm, the

Taking X in 0.5 can increase the resolution to

.

In the above cases, the effective length of the moving grating and the effective length of the linear CCD sensor should be 2.5 X10000μm=25mm, which is almost equivalent to the size of the existing grating ruler.

找到感光度最大的像素单元，计算出对应的删格位置。实现

栅距的分辨率。 When the resolution of the linear array CCD sensor is less than 2.5μm, the microcontroller can also

Find the pixel unit with the highest sensitivity, and calculate the corresponding grid position. accomplish

The resolution of the pitch.

Claims (3)

1. ultrahigh resolution grating chi, it is characterized in that, it comprises planar light source (4) and is arranged in order and parallel to each other decides grating (1), moving grating (2) and line array CCD sensor (3) perpendicular to the direction of illumination of planar light source (4) and along the direction of illumination of planar light source (4), described line array CCD sensor (3) is fixed together side by side with moving grating (2), and the length of the photosensitive unit of described line array CCD sensor is corresponding with the length of moving grating (2); Be that the grid number of the moving grating of length of N-1 is N grid just at the grid number of deciding grating, namely the pitch of moving grating equals to decide the pitch * [(n-1)/n] of grating, and wherein n is the raster count that can depict in moving grating length.

2. ultrahigh resolution grating chi according to claim 1 is characterized in that, the photosensitive region length of described line array CCD sensor (3) is more than or equal to (2) length of moving grating.

3. ultrahigh resolution grating chi according to claim 1 and 2 is characterized in that, the photosensitive unit distance of described line array CCD sensor (3) equals the pitch of moving grating (2).

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