Displacement measurement system design method based on imaging scanning

Abstract

The invention discloses a displacement measurement system design method based on imaging scanning. The displacement measuring system is characterized in that the displacement measuring system is composed of a light source, a collimating lens, a scale grating, a linear array CCD and a signal processing circuit, the scale grating is composed of an absolute code and an increment code, the absolute code is coded through a natural binary system and used for obtaining absolute position information, and the increment code is a periodic grating scribed line and achieves high subdivision of signals. Compared with a traditional method, the system has the advantages that only one scale grating is used for imaging scanning, the light path structure is simplified, and the measurement system is more compact; the scale grating absolute code has a positioning effect, so that the influence of accumulative errors on a measurement result is reduced, and micron-level measurement precision is achieved through high-power subdivision of the increment code; the absolute code and the incremental code of the scale grating are arranged in the same code channel, the problem of multi-code-channel coding of traditional absolute coding is solved, signal receiving of multiple sets of photoelectric detectors is avoided, the system structure is further simplified, and the system stability is improved. The micrometer displacement sensor can be used for micrometer displacement measurement and can be widely applied to digital display, numerical control machine tools and measuring instruments.

Description

(I) Technical field

[0001] The invention belongs to the field of photoelectric detection technology, and specifically relates to a displacement measurement system design method based on imaging scanning, which can be used for micron-level displacement measurement of digital display, CNC machine tools and measuring instruments. (II) Background technology

[0002] As a high-precision displacement measurement tool, the working principle of the grating ruler is mainly to convert the physical displacement into electrical signal output through grating and photoelectric conversion technology.

[0003] Due to the high measurement accuracy and simple operation of grating rulers, they are widely used in mechanical processing, control and other fields.

[0004] According to the different scanning principles of photoelectric signals, grating rulers can be divided into imaging scanning grating rulers and interference scanning principle grating rulers. Imaging scanning grating rulers use geometric optical shading to produce shadows, and fit the grating surface of the scale grating and the indicator grating to form shading. When the scale grating and the indicator grating move relative to each other, the photoelectric sensor can receive the light intensity change information with the scale grating pitch as the period. The interference scanning principle grating ruler diffracts the incident light by irradiating the fine transmission scale grating. The light is diffracted by the reflected scale grating and then passes through the transmission indicator grating. Finally, it passes through the lens to form interference fringes, which are received by the photoelectric sensor and converted into periodic light intensity change information.

[0005] However, the existing grating ruler system is relatively complex. For example, Wang Han et al. disclosed "A single-track absolute grating ruler system" (Chinese patent: 201810844200.3) in 2018. By setting an absolute code channel with long grating stripes and short grating stripes of equal width and spacing on the grating ruler, the long grating stripes and short stripes are distributed according to the binary pseudo-random sequence code, so that the image collected by the image collector has a complete set of pseudo-random code stripes. The controller decodes the pseudo-random code stripes to obtain the absolute position value of the grating ruler corresponding to the pseudo-random code; Deng Shijie et al. 202 In 2014, a "high-speed grating ruler system based on CMOS imaging" (Chinese patent: 202410719703.3) was disclosed. The proposed measurement system forms an absolute position image through the absolute code channel in the scale grating, which is detected by the CMOS imaging device in the dedicated image sensor and the photodiode on its right. At the same time, parallel light passes through the incremental code channel and the indicator grating to form moiré fringes, which are detected by the photodiode array in the dedicated image sensor. For each code generated by the photodiode, the corresponding incremental code channel moiré fringes increase by one cycle, thereby obtaining the absolute position in operation.

[0006] These grating scales usually need to form moiré fringes through scale gratings and indicator gratings, and absolute grating scales generally require multi-channel encoding. Even if single-channel encoding is used, the incremental channel and the absolute channel must be separated, and different photoelectric sensors are used to receive incremental and absolute code signals respectively. The system is complex and costly, and the system stability is easily affected by its optical path and circuit.

[0007] The displacement measurement system design method based on imaging scanning provided by the present invention only uses a scale grating for imaging scanning. Compared with the traditional method that requires a scale grating and an indicator grating to generate fringe signals, the present method simplifies the optical path structure and makes the measurement system more compact. Due to the positioning function of the absolute code of the scale grating, the influence of the cumulative error on the measurement result is reduced, and the micron-level measurement accuracy is achieved through the high-multiple subdivision of the incremental code. The absolute code and incremental code of the scale grating are arranged in the same code channel, which overcomes the multi-code channel encoding problem of traditional absolute encoding, avoids multiple groups of photoelectric detectors for signal reception, further simplifies the system structure, and improves the stability of the system. (III) Summary of the invention

[0008] The object of the present invention is to provide a displacement measurement system design method based on imaging scanning, which can be used for micron-level displacement measurement of digital displays, CNC machine tools and measuring instruments.

[0009] The object of the present invention is achieved in the following way: a light source (1) generates a divergent light beam, a collimating lens (2) collimates the divergent light beam into a parallel light beam, when a displacement measurement system is started, the parallel light beam passes through an absolute code (31) in a scale grating (3) to form an image, the image is detected by a linear array CCD (4) and decoded into reference position information through a signal processing circuit (5), the parallel light beam passes through an incremental code (32) in the scale grating (3) to form grating stripes, the grating stripes are detected by the linear array CCD (4) and form a sinusoidal signal through a signal processing circuit (5), and the absolute position at this time can be further determined by calculating the number of incremental codes (32).

[0010] In the system, the absolute code (31) in the scale grating (3) adopts four-bit natural binary coding for obtaining reference position information; there are a plurality of incremental codes (32) between two groups of absolute codes (31) for realizing high subdivision of the signal and improving the resolution of the system.

[0011] In the system, the width of the absolute code (31) in the scale grating (3) is twice the width of the incremental code (32), so that the linear array CCD (4) can identify the absolute code (31) and the incremental code (32).

[0012] In the system, after the light intensity data detected by the linear array CCD (4) is processed by a subsequent signal processing circuit (5), a waveform width exceeding a threshold is identified as an absolute code (31), and a waveform width below the threshold is identified as an incremental code (32). Among the identified absolute codes (31), a waveform exceeding the amplitude threshold is coded as 1, and a waveform below the threshold is coded as 0.

[0013] The system obtains the light intensity data of 600 pixel points detected by the linear array CCD (4), selects the 100th, 200th, 300th, 400th and 500th points as reference points, and divides the data into 10 groups. It is determined whether the data group contains a complete absolute code (31). If it contains a complete absolute code (31), the data group is stored, otherwise the data group is discarded. The absolute code (31) in the data group is decoded and the number of incremental codes (32) is calculated. The position calculation results are averaged to obtain the current absolute position.

[0014] In order to further illustrate the displacement measurement system design method based on imaging scanning provided by the present invention, a more detailed description is given below in conjunction with the accompanying drawings. (IV) Description of the drawings

[0015] Figure 1 The present invention is a structural diagram of a displacement measurement system based on imaging scanning. The displacement measurement system is composed of a light source (1), a collimating lens (2), a scale grating (3), a linear array CCD (4), and a signal processing circuit (5), wherein the scale grating (3) is composed of an absolute code (31) and an incremental code (32). The light source (1) generates a divergent light beam, and the collimating lens (2) collimates the divergent light beam into a parallel light beam. The parallel light beam forms an image through the absolute code (31) in the scale grating (3), and the image is detected by the linear array CCD (4) and decoded into reference position information through the signal processing circuit (5). The parallel light beam forms grating stripes through the incremental code (32) in the scale grating (3), and the grating stripes are detected by the linear array CCD (4) and form a sinusoidal signal through the signal processing circuit (5) for signal segmentation.

[0016] Figure 2 The present invention is a structural diagram of a scale grating used in a displacement measurement system based on imaging scanning. The absolute code (31) in the scale grating (3) adopts a four-bit natural binary code for obtaining reference position information; there are a plurality of incremental codes (32) between two groups of absolute codes (31) for realizing high subdivision of the signal and improving the resolution of the system. The line width of the absolute code (31) in the scale grating (3) is twice the line width of the incremental code (32), and is used for the linear array CCD (4) to identify the absolute code (31) and the incremental code (32).

[0017] Figure 3This is a flow chart of the algorithm of the displacement measurement system based on imaging scanning. The light intensity data of 600 pixels detected by the linear array CCD (4) are obtained, and the 100th, 200th, 300th, 400th, and 500th points are selected as reference points to divide the data into 10 groups. It is determined whether the data group contains a complete absolute code (31). If it contains a complete absolute code (31), this group of data is stored, otherwise this group of data is discarded. The absolute code (31) in the data group is decoded and the number of incremental codes (32) is calculated. The position calculation results are averaged to obtain the current absolute position. (V) Specific implementation methods

[0018] according to Figure 1 From the structure diagram of the displacement measurement system based on imaging scanning, it can be seen that the displacement measurement system consists of a light source (1), a collimating lens (2), a scale grating (3), a linear array CCD (4), and a signal processing circuit (5). Figure 2 From the scale grating structure diagram of the displacement measurement system based on imaging scanning, it can be seen that the scale grating (3) is composed of an absolute code (31) and an incremental code (32). The absolute code (31) uses natural binary encoding to obtain absolute position information, and the incremental code (32) is a periodic grating line, which is used to achieve high subdivision of the signal and improve the resolution of the system. When the displacement measurement system is started, the light source (1) generates a divergent light beam, and the collimating lens (2) collimates the divergent light beam into a parallel light beam. The parallel light beam passes through the absolute code (31) in the scale grating (3) to form an image. According to Figure 3 As can be seen from the algorithm flow chart of the displacement measurement system based on imaging scanning, the image is detected by the linear array CCD (4) and decoded into reference position information through the signal processing circuit (5), the parallel light beam passes through the incremental code (32) in the scale grating (3) to form grating stripes, the grating stripes are detected by the linear array CCD (4) and form sinusoidal signals through the signal processing circuit (5), and the signal can be subdivided by recognizing the incremental code (32), thereby obtaining the absolute position of the displacement measurement system during operation.

Claims

1. A method for designing a displacement measurement system based on imaging scanning, characterized in that: The displacement measurement system is composed of a light source (1), a collimating lens (2), a scale grating (3), a linear array CCD (4), and a signal processing circuit (5), wherein the scale grating (3) is composed of an absolute code (31) and an incremental code (32), the absolute code (31) adopts natural binary coding and is used to obtain absolute position information and reduce the cumulative error of the measurement system, and the incremental code (32) is a periodic grating line, which is used to achieve high subdivision of the signal and improve the resolution of the system; in the system, the scale grating (3) is fixed on a displacement platform, and the light source (1) generates a divergent The collimating lens (2) collimates the divergent light beam into a parallel light beam. When the displacement measurement system is started, the parallel light beam passes through the absolute code (31) in the scale grating (3) to form an image. The image is detected by the linear array CCD (4) and decoded into reference position information through the signal processing circuit (5). The parallel light beam passes through the incremental code (32) in the scale grating (3) to form grating stripes. The grating stripes are detected by the linear array CCD (4) and form a sinusoidal signal through the signal processing circuit (5). The absolute position at this time can be determined by calculating the number of incremental codes (32).

2. The method for designing a displacement measurement system based on imaging scanning according to claim 1, characterized in that: The light intensity data of 600 pixel points detected by the linear CCD (4) are obtained, and the 100th, 200th, 300th, 400th, and 500th points are selected as reference points to divide the data into 10 groups; it is determined whether the data group contains a complete absolute code (31). If it contains a complete absolute code (31), the data group is stored, otherwise the data group is discarded. The absolute code (31) in the data group is decoded and the number of incremental codes (32) is calculated, and the position calculation results are averaged to obtain the current absolute position.

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