Wide-range absolute linear displacement sensor based on photoelectric linear coding and measurement method

Abstract

The invention discloses a wide-range absolute type linear displacement sensor based on photoelectric linear coding and a measuring method. The upper surface of a sizing base body is provided with a row of excitation electrodes and covered with a light absorption insulating layer covering all the excitation electrodes, and the light absorption insulating layer is provided with two columns of reflective patterns; and the two columns of reflective patterns are different and coprime in quantity. The area corresponding to the unit length of each reflective pattern changes in a function relation mode in the length direction. The lower surface of the movable ruler base body is provided with an induction electrode, a light-emitting module and two rows of photoelectric sensors, the two rows of photoelectric sensors directly face the two rows of reflective patterns, and the number of each row of photoelectric sensors is two. The light emitting module sends light beams to the two columns of reflective patterns, and the photoelectric sensor collects light intensity reflected by the reflective patterns and outputs obtained photoelectric signals to the signal processing circuit. The photoelectric sensing principle is adopted for rough measurement, the transverse size of the sensor can be greatly reduced, fine measurement and rough measurement do not interfere with each other, the measurement precision is high, and implementation is easy.

Description

Technical Field

[0001] This invention relates to precision displacement measurement, specifically to a large-range absolute linear displacement sensor and measurement method based on photoelectric linear encoding. This sensor obtains absolute position using different methods for fine and coarse measurements, and belongs to the field of precision measurement and sensing technology. Background Technology

[0002] High-precision and large-range linear displacement sensors are widely used in precision equipment, such as precision machine tools, military weapons, automobiles, medical devices, and high-precision worktables, serving as key functional units in these devices. Absolute sensors enable absolute displacement measurement, effectively solving the problem of data loss during power outages. They also allow for fully closed-loop control and feedback, reducing interference from external factors such as temperature, and improving sensor measurement accuracy, thus broadening their application range.

[0003] Currently, absolute measurement of grating displacement sensors is mainly achieved by using differential pole or coprime methods. Although absolute measurement is achieved, there are also drawbacks.

[0004] 1. When using differential or coprime positioning to achieve absolute positioning, two rows of sensors need to be set up. For example, two rows of excitation electrodes and two rows of sensing electrodes need to be set up on the fixed scale base and the moving scale base respectively, which increases the size of the sensor, especially the lateral width of the sensor, which is not conducive to compactness and miniaturization.

[0005] 2. When using a differential pole structure, the difficulty of achieving absolute positioning over a large range increases significantly, mainly due to positioning errors. Where L is the length of the sensor, and N and N-1 are the number of cycles of the two rows of sensors, respectively. As the range increases, the number of cycles required increases, the requirements for positioning error become higher, and the more difficult it is to achieve.

[0006] 3. When using differential or coprime sensors to achieve absolute positioning, there is mutual interference between the two rows of sensors, which will affect the measurement accuracy and is not conducive to high-precision, large-range measurement. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a large-range absolute linear displacement sensor and measurement method based on photoelectric linear encoding. The present invention can significantly reduce the lateral size of the sensor, and the fine and coarse measurements do not interfere with each other. It has high measurement accuracy, simple structure, and is easy to implement.

[0008] The technical solution of this invention is implemented as follows:

[0009] A large-range absolute linear displacement sensor based on photoelectric linear encoding includes a movable scale base and a fixed scale base arranged in parallel with a gap. A row of excitation electrodes is uniformly arranged along the length direction on the surface of the fixed scale base facing the movable scale base. A sensing electrode is provided on the surface of the movable scale base facing the fixed scale base, with the sensing electrode on the movable scale base directly opposite the excitation electrode on the fixed scale base. A light-absorbing insulating layer covering all excitation electrodes is placed on the surface of the fixed scale base facing the movable scale base. Two rows of reflective patterns extending along the length direction are arranged on the surface of the light-absorbing insulating layer. Each row of reflective patterns consists of several complete... The system consists of identical, end-to-end reflective patterns. The two columns of reflective patterns are different and their quantities are coprime. The total length of the two columns of reflective patterns is the same and equal to the length of the fixed-length base. The area per unit length of each reflective pattern varies along the length direction as a function. A light-emitting module and two columns of photoelectric sensors are provided on the surface of the moving-scale base facing the fixed-scale base. The two columns of photoelectric sensors are respectively opposite to the two columns of reflective patterns, and there are two photoelectric sensors in each column. The light-emitting module is used to send a light beam to the two columns of reflective patterns, and the photoelectric sensors are used to collect the light intensity reflected by the reflective patterns and output the obtained photoelectric signal to the signal processing circuit.

[0010] Furthermore, the reflective pattern is a sine wave or a triangle, with the base of the triangle perpendicular to the length direction of the fixed-length base.

[0011] Furthermore, the excitation electrode is composed of 4k rectangular excitation electrodes of the same size with an electrode spacing of W1. Every four adjacent excitation electrodes form a group, and the 4k excitation electrodes form k groups. In each group, the excitation electrodes in the first position are connected together to form excitation phase A, the excitation electrodes in the second position are connected together to form excitation phase B, the excitation electrodes in the third position are connected together to form excitation phase C, and the excitation electrodes in the fourth position are connected together to form excitation phase D. There are four sensing electrodes, which correspond to excitation phases A, B, C and D respectively.

[0012] Furthermore, the center distance between the two photoelectric sensors in each column is ww o Where w is the period width of the light field, w o This refers to the width of the photoelectric sensor.

[0013] The measurement method for the large-range absolute linear displacement sensor based on photoelectric linear encoding described above includes the following steps:

[0014] 1) An excitation signal is applied to the excitation electrode. Under the action of the excitation electrode, the induction electrode outputs a corresponding traveling wave signal. The signal processing circuit processes the induction traveling wave signal and the reference signal of the same frequency accordingly to obtain a square wave signal. Then, relevant calculations are performed to obtain the displacement value x. i And used as a precise measurement value;

[0015] 2) The control light-emitting module emits a beam of light and illuminates two columns of reflective patterns. The two columns of photoelectric sensors collect the corresponding reflected light and output photoelectric signals to the signal processing circuit. After processing by the signal processing circuit, the displacement values ​​measured by the two columns of photoelectric sensors are obtained respectively. Let the number of periods of the two columns of reflective patterns be m and n, m and n be coprime and n > m, and the total length of the sensor be L. The displacement value x1 measured by the photoelectric sensor with period number m changes periodically within [0-L / m], and the displacement value x2 collected by the photoelectric sensor with period number n changes periodically within [0-L / n]. Let δ represent the displacement difference between the two columns of photoelectric sensors, δ = x1-x2. By determining the number of periods N1 of the reflective pattern where the photoelectric sensor with period number n is located, the rough absolute displacement value x = (N1-1)L / n + x2.

[0016] 3) Divide the coarse absolute displacement value x by the fine measurement period width W and round it to obtain the fine measurement period N of the moving ruler base; NW is the coarse measurement value;

[0017] 4) Combine the precise measurement value xi obtained in step 1) and the coarse measurement value NW obtained in step 3) to obtain the final absolute displacement value xa = NW + xi.

[0018] This invention generates four excitation signals with equal amplitude and 90° phase difference through an excitation module, which serve as inputs to an electric field-type grating displacement sensor. The output signals of the electric field-type grating displacement sensor and the photoelectric sensor are connected to a signal processing circuit. This circuit processes the traveling wave signal and reference signal generated by the grating displacement sensor, and enhances the analog voltage signal converted from the amplitude sampling of the photoelectric sensor to improve the signal-to-noise ratio and ensure a clear signal. Finally, the processed signal is input to an FPGA module. The FPGA module receives the input signal from the processing circuit, demodulates the analog voltage signal processed by the photoelectric sensor to obtain coarse periodic data, and performs phase measurement on the signal generated by the grating displacement sensor to obtain fine measurement data. Combining fine and coarse measurements enables absolute displacement measurement.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The coarse measurement signal of this invention is based on the amplitude sampling of the light field intensity by the photocell in the photoelectric sensor. The light field intensity collected by the photocell is proportional to the area of ​​the reflected pattern facing the photoelectric sensor. The output displacement signal is proportional to the area integral of the reflected pattern. The encoded pattern is simple, the output displacement is linear, and the absolute position can be obtained through simple calculation. The encoding and decoding are simple.

[0021] 2. The present invention uses optical field amplitude sampling to achieve absolute displacement period positioning for coarse measurement. Coarse period positioning only requires locating the period value of the incremental linear displacement sensor, and period positioning can be achieved without fine pattern printing. The positioning method is simple, and reflective pattern printing is simple and easy to implement.

[0022] 3. This invention achieves absolute positioning without employing a dual-row structure, fully utilizing the sensor's thickness space. The coarse-measurement reflective pattern and the fine-measurement excitation electrode are arranged in a two-layer structure, with the reflective pattern thickness only on the micrometer scale (20µm in the example), thus its impact on the sensor thickness is negligible. Compared to existing two-row structures in the width direction, this invention effectively reduces the sensor's volume, facilitating compact and miniaturized design.

[0023] 4. The present invention employs two different positioning and signal transmission methods for coarse and fine measurement. Since coarse measurement only needs to determine the period in which fine measurement is performed, the allowable absolute positioning error is large, enabling large-range measurement. At the same time, there is no signal interference between the two methods, ensuring high measurement accuracy while achieving large-range absolute positioning. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the sensor's length-fixing section in this invention.

[0025] Figure 2 This is a schematic diagram of the moving scale part of the sensor in this invention.

[0026] Figure 3 This is a schematic diagram of the layered structure of the sensor of the present invention.

[0027] Figure 4 This is a schematic diagram of the sensor installation according to the present invention.

[0028] Figure 5 This is a schematic diagram of the fixed-length substrate and the excitation electrode arrangement on it (without light-absorbing insulating layer).

[0029] Figure 6 This is a schematic diagram of the arrangement of two rows of reflective patterns on the light-absorbing insulating layer of the present invention.

[0030] Figure 7 This is a schematic diagram of the photoelectric periodic signal conversion process of the present invention.

[0031] Figure 8 This is a schematic diagram of the absolute positioning of photoelectric amplitude sampling according to the present invention.

[0032] Figure 9 This is a flowchart of the signal generation and data processing of the present invention. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0034] See Figures 1-6 This invention discloses a large-range absolute linear displacement sensor based on photoelectric linear encoding, comprising a movable scale base 2 and a fixed scale base 1 arranged vertically and horizontally with a gap (d) between them. A row of excitation electrodes 1-1 is uniformly arranged along the length direction on the upper surface of the fixed scale base 1. A sensing electrode 2-1 is provided on the lower surface of the movable scale base 2, with the sensing electrode on the movable scale base facing the excitation electrode on the fixed scale base. A light-absorbing insulating layer 1-2, covering all excitation electrodes, is placed on the upper surface of the fixed scale base 1. Two rows of reflective patterns 1-3 extending along the length direction are arranged on the upper surface of the light-absorbing insulating layer 1-2. Each row of reflective patterns 1-3 consists of several identical reflective patterns connected end-to-end. The two rows of reflective patterns have different shapes and are coprime in number. The total length of the two rows of reflective patterns is the same and equal to the length of the fixed scale base. The area per unit length of each reflective pattern varies functionally along the length direction. A light-emitting module and two rows of photoelectric sensors 2-2 are provided on the lower surface of the movable ruler base 2. The two rows of photoelectric sensors 2-2 are respectively directly opposite the two rows of reflective patterns 1-3, with two photoelectric sensors in each row. The light-emitting module is used to send a light beam (which can be invisible or visible light) to the two rows of reflective patterns, and the photoelectric sensors are used to collect the light intensity reflected by the reflective patterns and output the obtained photoelectric signal to the signal processing circuit. Since the area per unit length of each reflective pattern changes functionally along the length direction, correspondingly, as the movable ruler base moves along the fixed ruler base, the area (overlapping area) of the photoelectric sensor and the reflective pattern changing functionally with the displacement.

[0035] In this invention, the positional relationship between the movable scale base 2 and the fixed scale base 1 is relative. Alternatively, the movable scale base 2 can be below and the fixed scale base 1 can be above, which is equivalent to flipping the entire sensor by 180° without changing its structure.

[0036] The inventive concept of this invention lies in using displacement data generated by an incremental linear displacement sensor for fine measurement and optical amplitude decoding values ​​generated by an absolute photoelectric sensor for coarse measurement. The combination of these two methods achieves absolute measurement using the linear displacement sensor. The moving scale base, the fixed scale base, and their excitation and sensing electrodes constitute the main body of the incremental linear displacement sensor, while the reflective pattern, the light-emitting module, and the photoelectric sensor constitute the main body of the absolute photoelectric sensor. The measurements of these two parts are independent of each other; they are only combined in the algorithm, whereby the coarse measurement result is used to determine the fine measurement period, and thus the fine absolute displacement value.

[0037] The excitation electrodes consist of 4k rectangular excitation electrodes of the same size with a spacing of W1. Starting from the first excitation electrode at the end, every four adjacent excitation electrodes form a group, with 4k excitation electrodes forming k groups. Each group constitutes one excitation cycle, and the number of excitation cycles for the fixed length is k. The excitation electrodes in the first position of each group are connected together to form excitation phase A, the excitation electrodes in the second position of each group are connected together to form excitation phase B, the excitation electrodes in the third position of each group are connected together to form excitation phase C, and the excitation electrodes in the fourth position of each group are connected together to form excitation phase D. There are four sensing electrodes, corresponding to excitation phases A, B, C, and D respectively. The excitation module inputs four excitation signals to the four excitation phases of the fixed length. The four excitation signals are represented as follows: , , , The moving scale and the fixed scale move against each other, generating an induced traveling wave signal on the sensing electrode of the moving scale. The signal processing circuit amplifies and filters the induced traveling wave signal and the reference signal of the same frequency. After the traveling wave signal and the reference signal are shaped into a square wave by the zero-crossing comparator, the data is output to the FPGA module for high-frequency clock interpolation calculation to obtain the precise measurement value.

[0038] like Figure 2 As shown, the sensing electrode 2-1 consists of a row of sensing electrodes of identical size and shape with a spacing of 2W1, with two sensing electrodes forming one cycle. In this embodiment, the outer contour of the sensing electrodes is composed of a symmetrical double sine pattern.

[0039] The photoelectric sensing part of this invention is further described below, and can also be found in [reference 1]. Figure 6 The light-absorbing insulating layer covering the excitation stage of the fixed-length substrate is a black cover film, and the reflective pattern is white. The area of ​​the reflective pattern has a certain functional relationship with the displacement, and its shape can be sinusoidal or triangular. The base of the triangle must be perpendicular to the length direction of the fixed-length substrate. Taking the triangular signal as an example, the FPGA module controls the light-emitting module to emit invisible light with constant intensity. After being reflected by the fixed-length reflective pattern, the invisible light returns to the photoelectric sensor. The intensity of the light received by the photoelectric sensor is linearly related to the area between the photoelectric sensor and the reflective pattern. By area integration, it can be seen that the magnitude of the light signal collected by the photoelectric sensor is linearly related to the displacement. In this invention, each column of photoelectric sensors consists of two sensors, and their arrangement requirements are as follows: the first photoelectric sensor is spatially lagging behind the second photoelectric sensor by ww. o Another photoelectric sensor is placed at the position (w is the period width of the light field, i.e., the period width of one cycle of the reflected pattern). Figure 6 In the diagram, w1 represents the period width of the first column of graphics, and w2 represents the period width of the second column of graphics; o(which is the width of the photoelectric sensor). Through area integration, it is also obtained that the optical signal collected by the second photoelectric sensor has a linear relationship with displacement. The photoelectric sensor converts the collected light intensity signal into a current signal through circuit processing. The current signal is converted from current to voltage, amplified, filtered, and after ADC amplitude sampling, the collected voltage signal is sent to the FPGA for demodulation processing. Since the collected voltage signal is a triangular wave with a rising section and a falling section, there is a problem that the same voltage signal value cannot be confirmed whether it is in the rising section or the falling section. For this reason, the FPGA of this invention reverses the triangular waveform output by one of the photoelectric sensors and makes a periodic judgment with the corresponding triangular waveform of the other photoelectric sensor, so as to convert the trigonometric function into a linearly varying displacement signal with periodic changes. This is also the reason for setting two photoelectric sensors in each column. The specific principle can be seen in Figure 7 , taking one of the two columns of photoelectric sensors as an example, the voltage converted by the first photoelectric sensor in this column is U(x), as shown in Figure 7 the red line in the first group of lines from top to bottom, and the reference voltage Vref is the middle level, and the voltage converted by the second photoelectric sensor in this column is , as shown in Figure 7 the blue line in the first group of lines from top to bottom. The voltage value of the second photoelectric sensor is voltage-reversed to , as shown in Figure 7 the second group of lines. Comparing the first group of lines and the second group of lines, it can be seen that the blue in the second group of lines is flipped up and down. When U(x) < , = , when < U(x), = , are the voltage values output under different conditions; see Figure 7 the third group of lines; when U(x) > [[ID=​​​​​​​​​​​​​​Let the period numbers of the two reflective patterns be m and n, respectively, where m and n are coprime and n > m. The total length of the sensor is L. The displacement value x1 measured by the sensor corresponding to the reflective pattern with period number m varies periodically within [0-L / m], and the displacement value x2 collected by the sensor corresponding to the reflective pattern with period number n varies periodically within [0-L / n]. Let δ represent the displacement difference between the two sensor columns, δ = x1 - x2. Figure 8 It can be seen that no repeated δ values ​​appear within the entire travel range L, meaning that each displacement difference δ uniquely corresponds to a cycle number. Therefore, this unique δ value can be used as the absolute positioning sequence value to determine the sensor's cycle number N1 by looking up a table. The coarse absolute displacement value x = (N1-1)L / n + x2. Here, the absolute displacement value x is the coarse absolute displacement value. Although its accuracy is relatively poor, it can be used to locate the moving scale in the fine measurement cycle, thereby obtaining a high-precision displacement xa.

[0042] The displacement value measured by two coprime photoelectric sensors is a linear displacement value with a relatively large error. The linear displacement value measured by the photoelectric sensors can uniquely determine the period value N of the incremental linear displacement sensor. The displacement value measured by the incremental sensor is a linearly periodically changing displacement value with high accuracy. The combination of the two sensors can measure an absolute displacement value with high accuracy and a large range.

[0043] The complete signal generation and processing flow of this invention is as follows: Figure 9 As shown, the excitation control module in the FPGA generates four excitation voltage signals U with a 90° phase difference. S+ U C+ U S- U C- (corresponding to the aforementioned U) a U b U c U dThe excitation electrode on the fixed-scale substrate of the incremental linear displacement sensor is activated. Under the action of the excitation electrode, the induction electrode on the moving scale substrate senses and outputs a corresponding traveling wave signal. The signal processing circuit processes the sensed traveling wave signal and the reference signal of the same frequency accordingly, such as amplification, filtering, differential processing, and shaping, to obtain a square wave signal. The square wave signal is then input into the FPGA module for calculation, which yields the displacement value xi, used as the fine measurement value. Simultaneously, the light emission control module in the FPGA module controls the light emission module in the signal processing circuit to emit invisible light, which illuminates two columns of reflective patterns on the fixed-scale substrate. The corresponding reflected light is collected by two rows of photoelectric sensors on the moving scale substrate, and photoelectric signals are output to the signal processing circuit. The signal processing circuit processes the light accordingly, such as amplification, filtering, and analog-to-digital conversion, to obtain the amplitude displacement signal. The two sets of amplitude displacement signals are then input into the FPGA module. After demodulation of the two sets of amplitude displacement values, the displacement value NW is obtained and used as the coarse measurement value. N represents the current fine measurement cycle number of the moving scale substrate, and W is the width of the fine measurement cycle, which is 4W1 here. The period N is obtained by dividing the coarse absolute displacement value x by the fine period width W and rounding it down. Finally, the fine and coarse values ​​are combined to achieve the absolute linear displacement measurement, i.e., the final absolute displacement value xa = NW + xi.

[0044] This invention's sensor comprises two parts: an incremental linear displacement sensor and an absolute photoelectric sensor. The incremental linear displacement sensor, serving as the precision measurement component, generates four excitation signals with equal amplitude and orthogonal phase through an excitation module, which are applied to the excitation electrodes on the fixed-scale substrate. The sensing electrodes on the moving-scale substrate generate two differential traveling wave signals. These signals are amplified, filtered, and differentially processed by a signal processing circuit. Finally, the incremental precision displacement value is obtained using high-frequency pulse interpolation technology in the FPGA module. The absolute photoelectric sensor performs absolute position periodic measurement, serving as the coarse measurement component. Two columns of reflective patterns with mutually prime period numbers are covered on the fixed-scale substrate; the area of ​​the reflective patterns is a function of the displacement. A light-emitting module located on the moving scale substrate emits invisible light towards the fixed scale substrate. The reflective pattern covering the fixed scale substrate converts the area of ​​the pattern into light intensity, which is then reflected onto the photoelectric sensor. The photoelectric sensor converts the acquired optical-electrical signal into an analog signal. A signal processing circuit processes this analog signal, and the amplitude of the processed analog signal changes with the displacement. Finally, in the FPGA module, the absolute displacement cycle number is obtained by calculating the amplitude of the two analog signals that change with displacement. The incremental precise displacement value obtained from the incremental linear displacement sensor and the absolute displacement cycle number obtained from the absolute photoelectric sensor are combined to obtain the absolute displacement value, thus realizing absolute measurement by the linear displacement sensor.

[0045] Compared with existing technologies, this invention employs a two-layer design structure to achieve precise measurement and absolute positioning, resulting in a more compact design and easier miniaturization. The upper layer uses two rows of photoelectric sensors and a reflective pattern to obtain the absolute position cycle count for coarse measurement. The printing of the reflective pattern does not require high precision to achieve absolute cycle measurement. Displacement calculation is performed by using the facing area of ​​the reflective pattern and photoelectric sensors, linearizing the pattern encoding and simplifying encoding and decoding. The lower layer uses an incremental grating displacement sensor to measure the precise displacement value within a cycle for fine measurement, ensuring high accuracy while miniaturizing the device. The combination of fine and coarse measurement achieves absolute measurement without mutual interference, ensuring that obtaining the absolute position cycle count does not affect the precision measurement signal.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the applicant has described the present invention in detail with reference to preferred embodiments, those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A large range absolute linear displacement sensor based on photoelectric linear encoding, comprising a moving scale base and a fixed scale base arranged in parallel with a gap left between them, the surface of the fixed scale base facing the moving scale base is uniformly provided with a row of excitation electrodes along the length direction, and the surface of the moving scale base facing the fixed scale base is provided with a sensing electrode, the sensing electrode on the moving scale base is opposite to the excitation electrode on the fixed scale base; characterized in that: The surface of the fixed scale base facing the movable scale base is covered with a light-absorbing insulating layer covering all the excitation electrodes, and two rows of light-reflecting patterns extending in the length direction are arranged on the surface of the light-absorbing insulating layer; each row of light-reflecting patterns is composed of a plurality of light-reflecting patterns that are identical and connected end to end, and the two rows of light-reflecting patterns are different and the number of each row is prime to each other; the total length of the two rows of light-reflecting patterns is the same and equal to the length of the fixed scale base; the area corresponding to the unit length of each light-reflecting pattern changes in a functional relationship along the length direction; a light-emitting module and two rows of photoelectric sensors are arranged on the surface of the movable scale base facing the fixed scale base, the two rows of photoelectric sensors are respectively opposite to the two rows of light-reflecting patterns, and each row of photoelectric sensors has two photoelectric sensors; the light-emitting module is used to send light beams to the two rows of light-reflecting patterns, and the photoelectric sensors are used to collect the light intensity reflected by the light-reflecting patterns and output the obtained photoelectric signals to a signal processing circuit. ​ 2. A large range absolute linear displacement sensor based on photoelectric linear encoding according to claim 1, characterized in that: The light-reflecting pattern is a sinusoidal pattern or a triangle, and the base of the triangle is perpendicular to the length direction of the fixed scale base.

3. A large range absolute linear displacement sensor based on photoelectric linear encoding according to claim 1, characterized in that: The excitation electrodes are arranged by 4k rectangular excitation electrode pieces with the same size and a pole distance W1; every four adjacent excitation electrode pieces form a group, and the 4k excitation electrode pieces form k groups; the excitation electrode piece in the first sequence position of each group is connected together to form an excitation phase A, the excitation electrode piece in the second sequence position of each group is connected together to form an excitation phase B, the excitation electrode piece in the third sequence position of each group is connected together to form an excitation phase C, and the excitation electrode piece in the fourth sequence position of each group is connected together to form an excitation phase D; the sensing electrodes are four, corresponding to the excitation phase A, the excitation phase B, the excitation phase C and the excitation phase D respectively.

4. The large range absolute linear displacement sensor based on photoelectric linear encoding of claim 1, wherein: The centers of the two photosensors in each column are separated by w-w o where w is the period width of the light field, w o is the photosensor width.

5. The measuring method of the absolute linear displacement sensor with a large measuring range based on the optoelectronic linear encoding according to claim 1, characterized in that: The steps are as follows, 1) applying an excitation signal to the excitation electrode, under the action of the excitation electrode, the inductive electrode inductively outputs a corresponding traveling wave signal, the signal processing circuit processes the inductive traveling wave signal and the same frequency reference signal, obtains a square wave signal, and then calculates the displacement value x i and as a fine measurement value; 2) control the light-emitting module to emit light beams and irradiate on the two rows of light-reflecting patterns, the two rows of photoelectric sensors collect the corresponding reflected light and output photoelectric signals to the signal processing circuit, and the displacement values measured by the two rows of photoelectric sensors are obtained respectively after corresponding processing by the signal processing circuit; the period numbers of the two rows of light-reflecting patterns are respectively m and n, m and n are prime to each other and n > m, the total length of the sensors is L, the displacement value x1 measured by the photoelectric sensor corresponding to the period number m changes periodically in [0-L / m], the displacement value x2 collected by the photoelectric sensor corresponding to the period number n changes periodically in [0-L / n], and δ represents the displacement difference between the two rows of photoelectric sensors, δ = x1- x2; the period number N1 of the light-reflecting pattern corresponding to the photoelectric sensor of the period number n is determined by the value of δ, and then the absolute displacement value x = (N1-1) L / n + x2 is obtained; 3) divide the absolute displacement value x by the fine measurement period width W and take the integer part to obtain the fine measurement period N of the movable scale base; NW is the coarse measurement value; 4) combine the fine measurement value xi obtained in step 1) and the coarse measurement value NW obtained in step 3) to obtain the final absolute displacement value xa = NW + xi.

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