Integrated Linear Motion Measurement System and Method for Discontinuous Reference Grating Guide

Abstract

This invention discloses an integrated linear motion measurement system and method for discontinuous reference grating guide rails, comprising a grating guide rail with through holes, a reading body, a data processing module, and a host computer. Several grating segments are etched on the grating guide rail, and the reading body is mounted on a slider. The reading body includes 2 to 4 reading heads, which are rigidly connected. The data processing module uses an FPGA chip as the main controller to decode and process the encoded data output by the reading body, sending real-time continuous feedback signals to the CNC system and simultaneously sending position information to the host computer via a serial port. The host computer displays the data and sends commands to the data processing module via the serial port. This invention's measurement system directly etches the grating onto the guide rail, solving the technical problem of Abbe error generated when the grating ruler is installed on a machine tool. The direct integration of the reading body with the slider results in high compactness and achieves continuous signal output from the motion-measurement common base plane and the discontinuous grating.

Description

Technical Field

[0001] This invention belongs to the field of guide rail devices and grating applications, specifically relating to an integrated linear motion measurement system for discontinuous reference grating guide rails, and also to a method for integrated linear motion measurement of discontinuous reference grating guide rails. Background Technology

[0002] Manufacturing errors of the grating ruler, Abbe errors during application, and measurement errors are key factors affecting measurement accuracy. Conventional linear motion systems using guide rails require external measuring systems, such as grating rulers, to measure the linear motion of a slider or a fixed object on the slider. However, the external grating ruler causes a misalignment between the guide rail's motion axis / plane and the measurement reference axis / plane of the measuring system. Under the unavoidable influence of angular errors, Abbe errors arise.

[0003] Existing linear encoder measurement systems typically mount the linear encoder to a guide rail mechanically. This approach not only considers factors such as encoder selection, design, and installation location, but also suffers from problems like short measuring range and large size. During installation, a base of equal length to the encoder's body is required to ensure its parallelism is within a certain range. A limiting device must also be installed on the machine tool guide rail to prevent the reading head from colliding with the ends of the main scale during product movement, thus preventing damage. Therefore, the quality of the linear encoder's installation determines its final accuracy. Improper installation not only introduces Abbe error but also increases the system's size. In large-range, high-precision displacement measurements or machining, a single linear encoder often cannot achieve the measurement of discontinuous gratings. Furthermore, in machine tool applications, the linear encoder is easily contaminated by environmental factors, leading to measurement errors. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated linear motion measurement system for discontinuous reference grating guideways, which solves the problem of low measurement accuracy of discontinuous reference gratings applied to machine tools under low Abbe error conditions.

[0005] The first technical solution adopted in this invention is: a discontinuous reference grating guide rail integrated linear motion measurement system, including a grating guide rail with through holes, a reading body, a data processing module, and a host computer; the grating guide rail is engraved with several grating segments, and the reading body is mounted on a slider; the reading body includes 2 to 4 reading heads, which are rigidly connected to each other; the data processing module uses an FPGA chip as the main controller to decode and process the encoded data output by the reading body, sends the real-time continuous feedback signal to the CNC system, and simultaneously sends the position information to the host computer through a serial port. The host computer displays the data and sends commands to the data processing module through the serial port.

[0006] Gratings are etched onto the grating guide surface using photolithography, imprinting, or transfer printing techniques.

[0007] The reading element is mounted on the slider, and the slider moves linearly along the grating guide rail to achieve a common base plane for measurement and motion.

[0008] The reading body includes two reference reading heads and 0-2 auxiliary reading heads. The auxiliary reading heads are evenly installed between the two reference reading heads to average out errors and further improve accuracy.

[0009] The distance between the two reference reading heads is greater than the distance between adjacent gratings; the reference reading heads are installed at the front and rear ends of the slider, respectively.

[0010] The grating includes at least one absolute code and at least one incremental code, with the grating pitch range of the incremental code track being [20um, 120um]. The absolute position information comes from a series of gratings composed of absolute codes, and the incremental position information is composed of periodic gratings. The reading head includes an absolute reading unit and an incremental reading unit.

[0011] The data processing module includes a subdivision subsystem, an FPGA processing subsystem, and an ARM processing subsystem. The subdivision subsystem is used to subdivide the sinusoidal incremental signal. The incremental reading unit signal acquired by the reading head enters the subdivision subsystem, which outputs a continuous incremental feedback signal conforming to the RS485 / RS232 / TTL standard. The FPGA processing subsystem is used to condition the absolute reading unit signal of the reading head and output a continuous absolute feedback signal conforming to the EnDat 2.2 interface standard, as well as to complete the acquisition of the incremental feedback signal. The ARM processing subsystem is used to realize real-time signal judgment and send commands to the FPGA processing subsystem.

[0012] The resolution range of the sub-subsystem is [0.0002um, 1.2um].

[0013] The second technical solution adopted in this invention is an integrated linear motion measurement method for discontinuous reference grating guide rails, the specific operation steps of which are as follows:

[0014] After the system is powered on, the absolute reading unit in the reading cell acquires the absolute code to obtain the absolute reading unit signal. The absolute reading unit signal is sent to the FPGA processing subsystem for signal conditioning and then outputs an absolute feedback signal. At the same time, the current system absolute position information is recorded. The incremental reading unit acquires the incremental code and sends it to the subdivision subsystem. The incremental feedback signal output by the subdivision subsystem is used to update the system position in real time. The data processing module can simultaneously output the system absolute position after processing the absolute reading unit signal and the system absolute position after algorithm processing. The real-time continuous feedback signal is sent to the CNC system, and the output position information is output to the host computer through the serial port.

[0015] The invention is further characterized in that,

[0016] When the reference reading head 1 is in the grid line area, the photoelectric sensor inside its incremental reading unit will transmit four incremental signals. Ideally, the incremental signals are expressed as follows:

[0017] Among them, A C θ is the DC component of the electrical signal output by the reference reading head 1 (V), and θ is the phase angle of the electrical signal corresponding to the relative displacement between the grating and the reference reading head 1 (rad).

[0018] The data processing module performs pairwise subtraction on the four signals to obtain two signals with a 90° phase difference: C = C1 - C2 = 2Asinθ and D = D1 - D2 = 2Acosθ, satisfying:

[0019] C 2 +D 2 =4A 2 (1)

[0020] Where: A is the amplitude (V) of the electrical signal output by reference reading head 1. When When the reading head signal is abnormal, it indicates that the reading head has entered the non-grid area, and ξ is the set allowable error. When the signal output by the reference reading head 1 satisfies formula (1), the signal output by the ARM processing subsystem is 1; when the signal output by the reference reading head 1 does not satisfy formula (1), the signal output by the ARM processing subsystem is 0.

[0021] Define x and y as the start and end positions of a grating segment, and m and n as the start and end positions of the adjacent gratings; the two reference reading heads are reference reading head 1 and reference reading head 2, respectively; a is the position of reference reading head 1, and b is the position of reference reading head 2.

[0022] When the measuring system moves in the forward direction,

[0023] ① When x≤a≤y, and the reference reading head 1 is at point x, the signal output by the ARM processing subsystem changes from 0 to 1. After clearing the subdivision pulse count of the reference reading head 1 to zero, counting begins. The absolute position P of the reference reading head 1 at that point is stored in a variable. At this time, the current absolute position of the system is:

[0024] P = P A x +T A λ(2)

[0025] Where P is the current absolute position of the system, P A x T represents the absolute position of reference reading head 1 at point x. A Let λ be the number of subdivided pulses during the time interval from point x to the position of reference reading head 1, where λ is the resolution; simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 1. A ;

[0026] ②When y < a < m, and the reference reading head 1 is at point y, the signal output by the ARM processing subsystem changes from 1 to 0. After clearing the subdivision pulse count of the reference reading head 2, it starts counting and stores the absolute position P of the reference reading head 1 at that point into a variable. At this time, the current absolute position of the system is:

[0027] P = P A y +T B λ(3)

[0028] Among them, P A y T represents the absolute position of reference reading head 1 at point y. B Let λ be the number of subdivided pulses experienced by reference reading head 2 during the time period from when reference reading head 1 reaches point y to when it ends at this position, where λ is the resolution; simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 2. B ;

[0029] When the measurement system moves in the opposite direction,

[0030] ① When m≤a≤n, and the reference reading head 1 is at point n, the signal output by the ARM processing subsystem changes from 0 to 1. After clearing the subdivision pulse count of the reference reading head 1 to zero, counting begins. The absolute position P of the reference reading head 1 at that point is stored in a variable. At this time, the current absolute position of the system is:

[0031] P = P A n -T A λ(4)

[0032] Among them, PA n T represents the absolute position of reference reading head 1 at point n. A Let λ be the number of subdivided pulses during the time interval from point n to the current position of the reference reading head 1; λ is the resolution. Simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of the reference reading head 1. A ;

[0033] ②When y < a < m, and the reference reading head 1 is at point m, the signal output by the ARM processing subsystem changes from 1 to 0. After clearing the subdivision pulse count of the reference reading head 2, it starts counting and stores the absolute position P of the reference reading head 1 at that point into a variable. At this time, the current absolute position of the system is:

[0034] P = P A m -T B λ(5)

[0035] Among them, P A m T represents the absolute position of reference reading head 1 at point m. B This refers to the number of subdivided pulses experienced by reference reading head 2 during the time period from when reference reading head 1 reaches point m to when it ends at that position; simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 2. B ;

[0036] When the signal output by the reference reading head 1 satisfies formula (1), the ARM processing subsystem outputs 1, selects the incremental reading unit signal of the reference reading head 1 to enter the subdivision subsystem, selects the absolute reading unit signal of the reference reading head 1 to enter the FPGA processing subsystem for signal conditioning; the absolute position of the system is: the absolute position output by the absolute reading unit signal of the reference reading head 1 after processing;

[0037] When the signal output by reference reading head 1 does not satisfy formula (1), the ARM processing subsystem outputs 0, selects reference reading head 2 to enter the subdivision subsystem, and selects the absolute reading unit signal of reference reading head 2 to enter the FPGA processing subsystem for signal conditioning; the absolute position of the system is: the absolute position output by the absolute reading unit signal of reference reading head 2 after processing minus Ld, where Ld is the lateral distance set by reference reading head 1 and reference reading head 2 during manufacturing. The above realizes the generation of continuous incremental signals and continuous absolute feedback signals by discontinuous gate lines.

[0038] When the signal output by the ARM processing subsystem changes, the FPGA processing subsystem receives the absolute position signal from reference reading head 1 and stores it in a variable, which is the absolute position. When the signal output by the ARM processing subsystem is a rising edge, the subdivision pulse count of reference reading head 1 is cleared to zero and counting begins. When the signal output by the ARM processing subsystem is a falling edge, the subdivision pulse count of reference reading head 2 is cleared to zero and counting begins. The subdivision pulse count multiplied by the system resolution is the relative displacement. When the system moves forward, the absolute position of the system is: absolute position + relative position. When the system moves backward, the absolute position of the system is: absolute position - relative position.

[0039] The beneficial effects of this invention are as follows: The integrated linear motion measurement system of the discontinuous reference grating guide rail of this invention etches the grating onto the guide rail using photolithography, imprinting, or transfer printing techniques, minimizing Abbe error while also reducing the system's size; the reading body is directly combined with the slider, resulting in high compactness; and continuous signal output from the common datum plane of motion measurement and the discontinuous grating is achieved. The measurement method of this invention can determine whether each reading head is in the grating line area, enabling continuous signal output from the discontinuous grating, solving the problem of difficulty in measurement when the grating is directly etched onto the guide rail, and also solving the error problem caused by grating line loss due to contamination of the grating ruler, thus improving its resistance to contamination. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of the integrated linear motion measurement system of the discontinuous reference grating guide rail of the present invention;

[0041] Figure 2 This is a system block diagram of the present invention;

[0042] Figure 3 This is a schematic diagram of the grating encoding of the present invention;

[0043] Figure 4 This is a schematic diagram of the reading body and slider position structure of the present invention;

[0044] Figure 5 This is a schematic diagram of the working state of the reading element of the present invention;

[0045] Figure 6 This is a schematic diagram of the overall system algorithm flow of the present invention;

[0046] Figure 7 This is a schematic diagram of the algorithm flow of the FPGA processing subsystem in this invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0048] like Figure 1-2 As shown, the discontinuous reference grating guide rail integrated linear motion measurement system of the present invention mainly includes a grating guide rail, a reading body, a data processing module, and a host computer. The grating guide rail is constructed by photolithography, imprinting, or transfer printing techniques to etch gratings onto the rail. The reading body consists of 2 to 4 reading heads. The spacing between adjacent gratings etched on the guide rail does not need to be consistent; the spacing between reference reading heads 1 and 2 only needs to be greater than the spacing between adjacent gratings. The data processing module includes a subdivision subsystem, an FPGA processing subsystem, and an ARM processing subsystem. The subdivision subsystem can be constructed from conventional electrical components or can employ a dedicated subdivision chip. The subdivision subsystem is used to subdivide the sinusoidal incremental signal. The incremental reading unit signal from the reading head enters the subdivision subsystem, which outputs a continuous incremental feedback signal conforming to RS485 / RS232 / TTL standards. The FPGA processing subsystem is used to condition the absolute reading unit signal from the reading head and output a continuous absolute feedback signal conforming to the EnDat 2.2 interface standard, as well as to acquire the incremental feedback signal. The ARM processing subsystem is used to realize real-time signal judgment and send commands to the FPGA processing subsystem. The data processing module uses an FPGA chip as the main controller to decode and process the encoded data output by the reading head. It can send the data to the host computer via serial port or output corresponding signals according to the requirements of the CNC system. The host computer displays the data and sends commands to the data processing module via serial port.

[0049] like Figure 1 As shown, the guide rail does not require pre-drilled threaded holes, only through holes, resulting in more reasonable stress distribution and reducing the likelihood of irregular deformation. The grating pattern is engraved onto the upper surface of the guide rail using photolithography, embossing, or transfer techniques, aligning with the guide rail's installation direction (screw insertion direction). Figure 4 As shown, the reading head can be installed either inside the slider or outside the slider using a fixture; the installation position does not affect the slider's structure. The distance between the two reading heads is greater than the distance between adjacent grating rulers.

[0050] The reading unit consists of 2 to 4 reading heads, including 2 reference reading heads and 0-2 auxiliary reading heads. The reading heads are rigidly connected, with reference reading heads 1 and 2 used for reading and output, and auxiliary reading heads used to average errors and further improve accuracy. Each reading head contains at least one incremental reading unit and one absolute reading unit.

[0051] Since incremental and absolute code channels coexist, one type of signal or both types of signals can be output as required.

[0052] like Figure 3As shown, the etched grating includes at least one absolute code and at least one incremental code. Absolute position information comes from a series of gratings composed of absolute codes, while incremental position information consists of periodic gratings. The grating pitch range of the incremental code track is [20µm, 120µm]. The minimum subdivision factor used by the subdivision subsystem is 100x, and the maximum is 10000x, i.e., the resolution range is [0.0002µm, 1.2µm]. After the encoder is powered on, the position value is immediately obtained using the absolute code and can be read by subsequent signal processing circuitry at any time. The sinusoidal incremental signal is subdivided to generate position values, and its position information is obtained by calculating the number of increments starting from a point.

[0053] After the system powers on, it acquires absolute position information, updates the position using incremental encoding, and simultaneously collects absolute encoding data. The position data obtained using absolute feedback signals can be used for verification. The data processing module sends real-time continuous feedback signals to the CNC system and outputs the position information directly to the host computer via serial port. This counting method significantly improves the real-time performance of position information acquisition. The absolute reading unit signal enters the FPGA processing subsystem for signal conditioning, while the incremental reading unit signal is directly transmitted to the subdivision subsystem. The data processing module processes the absolute and incremental reading unit signals to obtain the position information. The serial communication protocol can be the manufacturer-specified protocol or an open serial communication protocol such as Biss or SSI.

[0054] When the reference reading head 1 is in the grid line area, the photoelectric sensor inside its incremental reading unit will transmit four incremental signals. Ideally, the incremental signals are expressed as follows:

[0055] Among them, A C θ is the DC component of the output electrical signal of the reading head (V), and θ is the phase angle of the electrical signal corresponding to the relative displacement of the scale grating and the reading head (rad).

[0056] The data processing module performs pairwise subtraction on the four signals to obtain two signals with a 90° phase difference: C = C1 - C2 = 2Asinθ and D = D1 - D2 = 2Acosθ, satisfying C 2 +D 2 =4A 2 (Formula 1), where A is the amplitude of the electrical signal output by the reading head in V.

[0057] when When the reading head signal is abnormal, it indicates that the reading head has entered the non-grating line area, where ξ is the set allowable error. The generation of continuous subdivision signals depends on the extraction of valid grating increment signals. That is, in a multi-reading head configuration, if valid grating increment signals can be continuously extracted, then regardless of whether the grating lines are continuous, standard subdivision signals such as RS232 / RS485 / TTL, which are accepted by common digital displays and CNC systems, can be continuously output for system feedback.

[0058] The following is based on Figure 5 Taking the first to fourth motion states as examples, and combining the integrated linear motion measurement method of discontinuous reference grating guide rail, the method for generating continuous feedback signals of the present invention is explained.

[0059] like Figure 6 As shown, we first initialize by setting A, ξ, and the subdivision number.

[0060] When reference reading head 1 and reference reading head 2 are in their initial positions between x and y ( Figure 5 (As shown in the first state position), monitor the four sinusoidal signals C1, C2, D1, D2 of the incremental reading unit of the reference reading head 1 with a 90° phase difference, and calculate C = 2Asinθ, D = 2Acosθ; determine if the calculation result satisfies Formula 1, and the ARM processing subsystem gives a judgment value of 1; therefore, select the incremental reading unit signal of the reference reading head 1 to enter the subdivision subsystem, and select the absolute reading unit signal of the reference reading head 1 to enter the FPGA processing subsystem for signal conditioning; after processing, the subdivision subsystem outputs an incremental feedback signal conforming to the RS485 / RS232 / TTL standard, and the FPGA processing subsystem outputs a continuous absolute feedback signal conforming to the EnDat2.2 interface standard.

[0061] When reference reading head 1 is positioned between x and y, and reference reading head 2 is positioned between y and m ( Figure 5 (As shown in the second state), monitor the four sinusoidal signals C1, C2, D1, and D2 of the incremental reading unit of the reference reading head 1 with a 90° phase difference, and calculate C = 2Asinθ and D = 2Acosθ; determine if the calculation results satisfy Formula 1, and the ARM processing subsystem gives a judgment value of 1; therefore, select the incremental reading unit signal of the reference reading head 1 to enter the subdivision subsystem, and select the absolute reading unit signal of the reference reading head 1 to enter the FPGA processing subsystem for signal conditioning; after processing, the subdivision subsystem outputs an incremental feedback signal conforming to the RS485 / RS232 / TTL standard, and the FPGA processing subsystem outputs a continuous absolute feedback signal conforming to the EnDat2.2 interface standard.

[0062] When reference reading head 1 is between y and m, and reference reading head 2 is between m and n ( Figure 5(As shown in the third state position), monitor the four sinusoidal signals C1, C2, D1, D2 of the incremental reading unit of the reference reading head 1 with a 90° phase difference, and calculate C=0, D=0; if the calculation result does not satisfy Formula 1, the ARM processing subsystem gives a judgment value of 0; the reference reading head 1 must have passed the gate edge y, and the moment of passing the edge y is the jump moment when the judgment value given by the ARM processing subsystem changes from 1 to 0. From the moment of passing the gate edge y, the incremental reading unit signal of the reference reading head 2 is selected to enter the subdivision subsystem and the absolute reading unit signal of the reference reading head 2 is selected to enter the FPGA processing subsystem for signal conditioning. The absolute position signal of the reference reading head 2 is at this time different from the system's real absolute position signal by a distance Ld, which is the lateral distance set by the reference reading head 1 and the reference reading head 2 during manufacturing; after processing, the subdivision subsystem outputs an incremental feedback signal conforming to the RS485 / RS232 / TTL standard, and the FPGA processing subsystem outputs a continuous absolute feedback signal conforming to the EnDat2.2 interface standard.

[0063] When both reference reading head 1 and reference reading head 2 are in positions between m and n ( Figure 5 (As shown in the fourth state position), monitor the sinusoidal signals C1, C2, D1, D2 of the incremental reading unit of the reference reading head 1 with a phase difference of 90°, and calculate C = 2Asinθ, D = 2Acosθ; determine if the calculation result satisfies Formula 1, and the ARM processing subsystem gives a judgment value of 1; the reference reading head 1 must have passed the gate edge m, and the moment of passing the edge m is the jump moment when the judgment value given by the ARM processing subsystem changes from 0 to 1. Starting from the moment of passing the gate edge m, the incremental reading unit signal of the reference reading head 1 is reselected to enter the subdivision subsystem, and the absolute reading unit signal of the reference reading head 1 is selected to enter the FPGA processing subsystem for signal conditioning; after processing, the subdivision subsystem outputs an incremental feedback signal conforming to the RS485 / RS232 / TTL standard, and the FPGA processing subsystem outputs a continuous absolute feedback signal conforming to the EnDat2.2 interface standard.

[0064] Thus, a complete process of generating a continuous subdivision signal across discontinuous gate lines is completed. Inevitably, the judgment and switching of reference reading head 1 and 2 signals will occur during the above process. This process can be completed within 100ns using conventional electrical chips such as FPGA / DSP / ARM. Furthermore, the time consumed by the judgment and switching procedure is on the same order of magnitude as the time consumed by the sinusoidal signal subdivision. Therefore, it is assumed that the generation of the subdivision signal and the absolute position signal is continuous, thus proving that this system can provide continuous displacement feedback functionality.

[0065] When the solution of the present invention is adopted, it is possible to measure both the "absolute position" using absolute code tracks and the "relative displacement" using incremental code tracks.

[0066] The following is combined Figure 5 , Figure 6 and Figure 7 The algorithm describes the continuous position measurement method of this invention:

[0067] During the movement of the reading body, both reference reading head 1 and reference reading head 2 are in counting mode. Here, 'a' represents the position of reference reading head 1, and 'b' represents the position of reference reading head 2. 'x' to 'y' represents the k-th grid line region, 'y' to 'm' represents the k-th non-grid line region, and 'm' to 'n' represents the (k+1)-th grid line region.

[0068] Assume the system starts moving in the forward direction.

[0069] 1. When the measuring system is moving in the forward direction,

[0070] ① When x ≤ a ≤ y, and the reference reading head 1 is at point x, the signal output by the ARM processing subsystem changes from 0 to 1, clears the subdivision pulse count of the reference reading head 1 to zero, and starts counting, storing the absolute position of the reference reading head 1 at that point into a variable. At this time, the current absolute position of the system is P = P A x +T A λ, P is the current absolute position of the system, P A x T represents the absolute position of reference reading head 1 at point x (read from the absolute reading unit of reference reading head 1). A λ represents the number of subdivision pulses during the time interval from point x to the current position of the reference reading head 1 (read by the incremental reading unit of the reference reading head 1), where λ is the resolution (determined by the grid pitch and subdivision number, resolution = grid pitch / subdivision number); simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of the reference reading head 1. A It can be used to verify the absolute position of the system output by the algorithm, P = P A .

[0071] ②When y < a < m, and the reference reading head 1 is at point y, the signal output by the ARM processing subsystem changes from 1 to 0. After clearing the subdivision pulse count of the reference reading head 2, it begins counting and stores the absolute position of the reference reading head 1 at that point into a variable. At this time, the system's current absolute position is P = P. A y +T B λ, P is the current absolute position of the system, P A y T represents the absolute position of reference reading head 1 at point y (read from the absolute reading unit of reference reading head 1). Bλ represents the number of subdivision pulses experienced by reference reading head 2 during the time period from when reference reading head 1 reaches point y to when it ends at that position (read by the incremental reading unit of reference reading head 2), where λ is the resolution (determined by the grid pitch and subdivision number, resolution = grid pitch / subdivision number); simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 2. B It can be used to verify the absolute position of the system output by the algorithm, P = P B -Ld.

[0072] 2. When the measuring system moves in the opposite direction,

[0073] ① When m≤a≤n, and the reference reading head 1 is at point n, the signal output by the ARM processing subsystem changes from 0 to 1, clears the subdivision pulse count of the reference reading head 1 to zero, and starts counting. The absolute position of the reference reading head 1 at that point is stored in a variable. At this time, the current absolute position of the system is P=P A n -T A λ, P is the current absolute position of the system, P A n T represents the absolute position of reference reading head 1 at point n (read from the absolute reading unit of reference reading head 1). A λ represents the number of subdivision pulses during the time interval from point n to the current position of the reference reading head 1 (read by the incremental reading unit of the reference reading head 1), and λ is the resolution (determined by the grid pitch and the number of subdivisions, resolution = grid pitch / number of subdivisions); simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of the reference reading head 1. A It can be used to verify the absolute position of the system output by the algorithm, P = P A .

[0074] ②When y < a < m, and the reference reading head 1 is at point m, the signal output by the ARM processing subsystem changes from 1 to 0. After clearing the subdivision pulse count of the reference reading head 2, it starts counting and stores the absolute position of the receiving reference reading head 1 at that point into a variable. At this time, the system's current absolute position is P = P A m -T B λ, P is the current absolute position of the system, P A m T represents the absolute position of reference reading head 1 at point m (read from the absolute reading unit of reference reading head 1). Bλ represents the number of subdivision pulses experienced by reference reading head 2 during the time period from when reference reading head 1 reaches point m to when it ends at that position (read by the incremental reading unit of reference reading head 2), where λ is the resolution (determined by the grid pitch and the number of subdivisions, resolution = grid pitch / number of subdivisions). Simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 2. B It can be used to verify the absolute position of the system output by the algorithm, P = P B -Ld.

[0075] The key innovation of this invention lies in:

[0076] 1. The measurement system of this invention directly engraves the grating onto the guide rail, solving the technical problem of Abbe error generated when the grating ruler is installed on the machine tool; it directly combines the reading body with the slider, solving the technical problem of large system size and high compactness; and it realizes the common base plane for motion measurement.

[0077] 2. The measurement method of the present invention uses only the reference reading head 1 for reading output, and the reference reading head 2 for displacement compensation.

[0078] 3. The technical solution of the present invention includes using signal processing to determine in real time whether the reading head is abnormal, which solves the technical problem that multiple calibrations are required when the grating ruler is contaminated or other abnormal, which is cumbersome and inefficient. This results in the technical effect of real-time detection and processing of abnormalities by the reading head.

[0079] 4. This invention achieves continuous incremental signal output of discontinuous grating lines, continuous absolute signal output of discontinuous grating lines, avoids Abbe error generated during grating ruler installation, achieves large-range high-precision measurement of discontinuous grating lines, and can reduce system size.

Claims

1. A linear motion measurement system integrating a discontinuous reference grating guide rail, characterized in that, The system includes a grating guide rail with through holes, a reading body, a data processing module, and a host computer. The grating guide rail is engraved with several grating segments. The reading body is mounted on a slider, which moves linearly along the grating guide rail to achieve a common measurement-motion plane. The reading body includes 2 to 4 reading heads, which are rigidly connected. The reading body includes 2 reference reading heads and 0-2 auxiliary reading heads. The auxiliary reading heads are evenly installed between the two reference reading heads. The distance between the two reference reading heads is greater than the distance between adjacent gratings. The reference reading heads are respectively installed at the front and rear ends of the slider; the data processing module uses an FPGA chip as the main controller to decode and process the encoded data output by the reading head, send the real-time continuous feedback signal to the CNC system, and send the position information to the host computer through the serial port. The host computer displays the data and sends commands to the data processing module through the serial port. The grating includes at least one absolute code and at least one incremental code, with the grating pitch range of the incremental code track being [20um, 120um]. The absolute position information comes from a series of gratings composed of absolute codes, and the incremental position information is composed of periodic gratings. The reading head includes an absolute reading unit and an incremental reading unit.

2. The integrated linear motion measurement system for discontinuous reference grating guide rails according to claim 1, characterized in that, The grating is etched onto the grating guide surface using photolithography, imprinting, or transfer printing techniques.

3. The integrated linear motion measurement system for discontinuous reference grating guides according to claim 1, characterized in that, The data processing module includes a subdivision subsystem, an FPGA processing subsystem, and an ARM processing subsystem. The subdivision subsystem is used to subdivide the sinusoidal incremental signal. The incremental reading unit signal acquired by the reading head enters the subdivision subsystem, which outputs a continuous incremental feedback signal conforming to RS485 / RS232 / TTL standards. The FPGA processing subsystem is used to condition the absolute reading unit signal of the reading head and output a continuous absolute feedback signal conforming to the EnDat 2.2 interface standard, as well as to complete the acquisition of the incremental feedback signal. The ARM processing subsystem is used to realize real-time signal judgment and send commands to the FPGA processing subsystem. The resolution range of the subdivision subsystem is [0.0002um, 1.2um].

4. A linear motion measurement method integrating discontinuous reference grating guide rails, characterized in that, The specific operation steps of the integrated linear motion measurement system for discontinuous reference grating guide rails as described in any one of claims 1-3 are as follows: After the system is powered on, the absolute reading unit in the reading cell acquires the absolute code to obtain the absolute reading unit signal. The absolute reading unit signal is sent to the FPGA processing subsystem for signal conditioning and then outputs an absolute feedback signal. At the same time, the current absolute position information of the system is recorded. The incremental reading unit acquires the incremental code and sends it to the subdivision subsystem. The incremental feedback signal output by the subdivision subsystem is used to update the position of the system in real time. The data processing module can simultaneously output the absolute position of the system after processing the absolute reading unit signal of the reading cell and the absolute position of the system after algorithm processing. The real-time continuous feedback signal is sent to the CNC system, and the output position information is output to the host computer via serial port.

5. The method for measuring linear motion of a discontinuous reference grating guide rail as described in claim 4, characterized in that, When the reference reading head 1 is in the grid line area, the photoelectric sensor inside its incremental reading unit will transmit four incremental signals. Ideally, the incremental signals are expressed as follows: , , , , Among them, A C θ is the DC component of the electrical signal output by the reference reading head 1 (V), and θ is the phase angle of the electrical signal corresponding to the relative displacement between the grating and the reference reading head 1 (rad). The data processing module performs pairwise subtraction on the four signals to obtain two signals with a 90° phase difference. and ,satisfy: C 2 +D 2 =4A 2 (1) Where: A is the amplitude / V of the electrical signal output by the reference reading head 1, when C 2 +D 2 [4A 2 -ξ,4A 2 When +ξ], it means that the reading head signal is abnormal, indicating that the reading head has entered the non-grid area, and ξ is the set allowable error; when the signal output by the reference reading head 1 satisfies the formula (1), the signal output by the ARM processing subsystem is 1; when the signal output by the reference reading head 1 does not satisfy the formula (1), the signal output by the ARM processing subsystem is 0. Define x and y as the start and end positions of a grating segment, and m and n as the start and end positions of the adjacent gratings; the two reference reading heads are reference reading head 1 and reference reading head 2, respectively; a is the position of reference reading head 1, and b is the position of reference reading head 2; When the measuring system moves in the forward direction, ① When x≤a≤y, and the reference reading head 1 is at point x, the signal output by the ARM processing subsystem changes from 0 to 1. After clearing the subdivision pulse count of the reference reading head 1 to zero, counting begins. The absolute position P of the reference reading head 1 at that point is stored in a variable. At this time, the current absolute position of the system is: P=P A x +T A λ(2) Where P is the current absolute position of the system, P A x T represents the absolute position of reference reading head 1 at point x. A Let λ be the number of subdivided pulses during the time interval from point x to the position cutoff point for reference reading head 1, where λ is the resolution. Simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal from reference reading head 1. A ; ②When y < a < m, and the reference reading head 1 is at point y, the signal output by the ARM processing subsystem changes from 1 to 0. After clearing the subdivision pulse count of the reference reading head 2, it starts counting and stores the absolute position P of the reference reading head 1 at that point into a variable. At this time, the current absolute position of the system is: P=P A y +T B λ(3) Among them, P A y T represents the absolute position of reference reading head 1 at point y. B Let λ be the number of subdivided pulses experienced by reference reading head 2 during the time period from when reference reading head 1 reaches point y to when the position ends, and let λ be the resolution. Simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 2. B ; When the measuring system moves in the opposite direction, ① When m≤a≤n, and the reference reading head 1 is at point n, the signal output by the ARM processing subsystem changes from 0 to 1. After clearing the subdivision pulse count of the reference reading head 1 to zero, counting begins. The absolute position P of the reference reading head 1 at that point is stored in a variable. At this time, the current absolute position of the system is: P=P A n -T A λ(4) Among them, P A n T represents the absolute position of reference reading head 1 at point n. A Let λ be the number of subdivided pulses during the time interval from point n to the position cutoff point of reference reading head 1, where λ is the resolution; simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 1. A ; ②When y < a < m, and the reference reading head 1 is at point m, the signal output by the ARM processing subsystem changes from 1 to 0. After clearing the subdivision pulse count of the reference reading head 2, it starts counting and stores the absolute position P of the reference reading head 1 at that point into a variable. At this time, the current absolute position of the system is: P=P A m -T B λ(5) Among them, P A m T represents the absolute position of reference reading head 1 at point m. B This refers to the number of subdivided pulses experienced by reference reading head 2 during the time period from when reference reading head 1 reaches point m to when the position ends; simultaneously, the data processing module outputs the real-time position P after processing the absolute reading unit signal of reference reading head 2. B ; When the signal output by the reference reading head 1 satisfies formula (1), the ARM processing subsystem outputs 1, selects the incremental reading unit signal of the reference reading head 1 to enter the subdivision subsystem, selects the absolute reading unit signal of the reference reading head 1 to enter the FPGA processing subsystem for signal conditioning; the absolute position of the system is: the absolute position output by the absolute reading unit signal of the reference reading head 1 after processing; When the signal output by reference reading head 1 does not satisfy formula (1), the ARM processing subsystem outputs 0, selects reference reading head 2 to enter the subdivision subsystem, selects the absolute reading unit signal of reference reading head 2 to enter the FPGA processing subsystem for signal conditioning; the absolute position of the system is: the absolute position output by the absolute reading unit signal of reference reading head 2 after processing minus Ld, where Ld is the lateral distance set by reference reading head 1 and reference reading head 2 during manufacturing; the above realizes the generation of continuous incremental signal and continuous absolute feedback signal by discontinuous gate lines.

6. The method for measuring linear motion of a discontinuous reference grating guide rail as described in claim 5, characterized in that, When the signal output by the ARM processing subsystem changes, the FPGA processing subsystem receives the absolute position signal from reference reading head 1 and stores it in a variable, which is the absolute position. When the signal output by the ARM processing subsystem is a rising edge, the subdivision pulse count of reference reading head 1 is cleared to zero and counting begins. When the signal output by the ARM processing subsystem is a falling edge, the subdivision pulse count of reference reading head 2 is cleared to zero and counting begins. The subdivision pulse count multiplied by the system resolution is the relative displacement. When the system moves forward, the absolute position of the system is: absolute position + relative position. When the system moves backward, the absolute position of the system is: absolute position - relative position.

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