Closed transmission grating self-imaging wide-range displacement sensor

Abstract

The invention belongs to the technical field of displacement measurement, and particularly relates to a closed transmission grating self-imaging wide-range displacement sensor which comprises a ruler shell and a reading head, the ruler shell is connected with the reading head, the reading head comprises a transmission mechanism and a measuring mechanism, the transmission mechanism is connected with the measuring mechanism, and the measuring mechanism is connected with the ruler shell. The ruler shell comprises a grating sensor outer shell and a metering grating clamping device, the transmission mechanism and the measuring mechanism are both arranged in the grating sensor outer shell, the metering grating clamping device is arranged in the grating sensor outer shell, and a metering grating is arranged in a groove of the metering grating clamping device. The bilinear guide rail has the advantages of being compact in structure, stable in movement, small in generated vibration, small in point-surface contact, small in friction resistance and capable of conducting fine movement, and high-precision positioning of a control device and the like is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of displacement measurement, and in particular relates to a closed transmission grating self-imaging large-range displacement sensor. Background Art

[0002] The closed large-range grating displacement sensor plays an important role in the displacement monitoring and position feedback of precision motion platforms. In industrial manufacturing, it is often used in instruments and equipment such as lithography machines, CNC manufacturing equipment, and three-coordinate machines. The typical measurement range of the closed large-range grating displacement sensor is ≥50mm. Its structure mainly consists of two parts: the scale housing and the reading head, in which the reading head is divided into two parts: the measuring mechanism and the transmission mechanism. At present, the scale housing of the grating displacement sensor is often extruded by aluminum alloy. Through this process, a special inner cavity is extruded to prevent foreign matter from infecting the internal optical sensitive components and provide grating position positioning. The reading head measurement mechanism often consists of a laser source, a double-layer grating, a photoelectric conversion module and a signal processing circuit. The transmission mechanism often uses a five-point trolley positioning structure, that is, five small bearings are close to the upper and lower grating line surfaces and the left and right side tables. This structure is used for linear transmission, which can provide guarantee for displacement measurement. However, the above method has the following problems: 1. The aluminum alloy extrusion molding process is prone to generate internal stress during the production process, resulting in deformation of the profile. As the extrusion length increases, the deformation also increases, which has a great impact on the installation straightness and parallelism of the metrological grating. 2. The transmission rolling bearing in the five-point trolley positioning structure is difficult to accurately install and cannot be disassembled. The cylindrical tolerance of the rolling bearing will also introduce certain errors as the displacement measurement continues. The above problems lead to the degradation of the accuracy and straightness of large-scale displacement detection. Summary of the invention

[0003] In view of the technical problems in the above-mentioned prior art that lead to the degradation of the accuracy and straightness of large-range displacement detection, the present invention provides a closed transmission grating self-imaging large-range displacement sensor.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A closed transmission grating self-imaging large-range displacement sensor comprises a ruler housing and a reading head, wherein the ruler housing is connected to the reading head, the reading head comprises a transmission mechanism and a measuring mechanism, the transmission mechanism is connected to the measuring mechanism, the ruler housing comprises a grating sensor outer housing and a metrological grating clamping device, the transmission mechanism and the measuring mechanism are both arranged in the grating sensor outer housing, the metrological grating clamping device is arranged in the grating sensor outer housing, and a metrological grating is arranged in the groove of the metrological grating clamping device.

[0006] The measuring mechanism includes a laser, a collimating beam expander, a metering grating, an indicating grating, and a photodetector. The collimating beam expander is arranged in the optical path direction of the laser, the metering grating is arranged in the optical path direction of the collimating beam expander, the indicating grating is arranged in the optical path direction of the metering grating, and the photodetector is arranged in the optical path direction of the indicating grating.

[0007] The outer shell of the grating sensor includes a top end cover, a bottom end cover, and a side end cover. Two side end covers are provided, and the bottom end cover is connected to the top end cover through the two side end covers.

[0008] The transmission mechanism includes a slide body, a sealing strip, a linear guide rail, a six-dimensional adjustment frame, a U-shaped groove, a cylindrical clamp, and a reading head slider. A sealing strip installation groove is provided in the middle of the top end cover, and a sealing strip is provided in the sealing strip installation groove. A linear guide rail is provided on the bottom end cover, and a reading head slider is fixed to the bottom of the U-shaped groove. The reading head slider is slidably connected to the linear guide rail. The six-dimensional adjustment frame is arranged in the U-shaped groove, and the six-dimensional adjustment frame is connected to the indicating grating. The U-shaped groove is connected to the slide body through a cylindrical clamp, and the slide body is arranged on the sealing strip.

[0009] The collimating beam expander is arranged in a cylindrical fixture, the metering grating clamping device is fixed on the lower surface of the upper end surface of the U-shaped groove, and the indicating grating and the photoelectric detector are arranged in the U-shaped groove.

[0010] The sealing strip is an arc-shaped structure and is made of rubber material; the linear guide rail adopts a side-by-side double linear guide rail, the bottom end cover is provided with a scale boss as a positioning surface, and the side-by-side double linear guide rail is installed on both sides of the scale boss as the positioning surface by screws.

[0011] The indicating grating is arranged in the self-imaging area of ​​the metering grating, and the metering grating is perpendicular to the grating line direction of the indicating grating.

[0012] The photoelectric detector and the indicating grating are both designed as a multi-quadrant structure, and the quadrant area and number of the photoelectric detector match the quadrant setting of the indicating grating.

[0013] The top layer end cover, the bottom layer end cover and the side end cover are assembled in a splicing manner.

[0014] A method for measuring a closed transmission grating self-imaging large-range displacement sensor comprises the following steps:

[0015] S1. The indicator grating is placed in the self-imaging area of ​​the metering grating. The metering grating is perpendicular to the grating lines of the indicator grating. During the displacement measurement, the slider of the reading head makes a one-dimensional linear displacement relative to the metering grating in the direction perpendicular to the grating lines of the indicator grating. The self-imaging area calculation formula is:

[0016]

[0017] Where B is the height of the Talbot region, N is the number of grating periods, and Z m is the length of a single Talbot period; the length of a single Talbot period Z m It is expressed as:

[0018]

[0019] Where T is the grating period; λ is the wavelength of incident light, and P is the diffraction order;

[0020] S2. The range of displacement measurement is determined by the difference between the effective scale area lengths of the measuring grating and the indicating grating. The formula is:

[0021] L c =L b ―L c

[0022] Among them, L c is the measuring range, L b is the effective line length of the major axis of the measuring grating, L a It indicates the effective line length of the grating major axis;

[0023] S3. The resolution of displacement detection is:

[0024]

[0025] Where N is the resolution of displacement detection, T is the grating period, and E is the subdivision multiple;

[0026] S4. Both the photoelectric detector and the indicator grating are designed as a multi-quadrant structure, and the quadrant area and number of the photoelectric detector match the quadrant setting of the indicator grating;

[0027] S5, the photoelectric detector outputs multiple analog signals, which are input into the subdivision box for analog-to-digital conversion and electrical subdivision, and the subdivided digital signals are counted by the host computer software. The final displacement value D is calculated as follows:

[0028]

[0029] Where D is the displacement value, F is the square wave number, T is the grating period, and E is the subdivision multiple.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention solves the problem of unstable movement and local point jump error caused by the non-roundness of the bearing when the traditional five-point trolley structure of the grating displacement sensor is used for displacement transmission by utilizing the characteristics of the double linear guide rail with compact structure, stable movement, small vibration, point-to-surface contact, small friction resistance, and fine movement. In addition, the present invention solves the problem of easy deformation of profiles and complex process in the aluminum alloy extrusion molding process by utilizing the characteristics of simple structure of the spliced ​​ruler shell, easy disassembly and maintenance, high processing accuracy, and small deformation in the process, thereby improving the indicators such as straightness and accuracy in the process of large-scale displacement detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0033] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0034] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0035] Figure 2 It is a structural schematic diagram of the measuring mechanism of the present invention;

[0036] Figure 3 It is a structural schematic diagram of the transmission mechanism of the present invention;

[0037] Figure 4 This is a structural diagram of the installation of the reading head of the present invention;

[0038] Figure 5 This is an assembly and disassembly diagram of the metering grating of the present invention;

[0039] Figure 6 This is a schematic block diagram of the connection of the displacement detection device of the present invention;

[0040] Figure 7 It is a schematic diagram of the structure of the metering grating and the indicating grating of the present invention;

[0041] Figure 8 It is a schematic diagram of the structure of the photoelectric detector of the present invention;

[0042] Fig. 9 This is a schematic diagram of the output signal of the photoelectric detector of the present invention;

[0043] Fig.10 This is a schematic diagram of the digital signal output by the segmentation box of the present invention.

[0044] Among them: a is the ruler shell, b is the reading head, 1 is the measuring grating, 2 is the measuring grating clamping device, 3 is the slide body, 4 is the sealing strip, 5-1 is the top end cover, 5-2 is the bottom end cover, 6 is the side end cover, 7 is the linear guide rail, 8 is the six-dimensional adjustment frame, 9 is the U-shaped groove, 10 is the cylindrical clamp, 11 is the laser, 12 is the collimating beam expander, 13 is the indicating grating, 14 is the photoelectric detector, and 15 is the reading head slider. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. These descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0046] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0047] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0048] A closed transmission grating self-imaging large-range displacement sensor, such as Figure 1 As shown, it includes a ruler housing a and a reading head b, the ruler housing a is connected to the reading head b, the reading head b includes a transmission mechanism and a measuring mechanism, the transmission mechanism is connected to the measuring mechanism, the ruler housing a includes a grating sensor outer housing and a metering grating clamping device 2, the transmission mechanism and the measuring mechanism are both arranged in the grating sensor outer housing, and the metering grating clamping device 2 is arranged in the grating sensor outer housing, as shown in FIG. Figure 5As shown, a metering grating 1 is provided in the groove of the metering grating clamping device 2.

[0049] Further, if Figure 2 As shown, the measuring mechanism includes a laser 11, a collimating beam expander 12, a metering grating 1, an indicating grating 13, and a photodetector 14. The collimating beam expander 12 is arranged in the optical path direction of the laser 11, the metering grating 1 is arranged in the optical path direction of the collimating beam expander 12, the indicating grating 13 is arranged in the optical path direction of the metering grating 1, and the photodetector 14 is arranged in the optical path direction of the indicating grating 13.

[0050] Further, if Figure 3 As shown, the outer shell of the grating sensor includes a top end cover 5 - 1 , a bottom end cover 5 - 2 , and a side end cover 6 . Two side end covers 6 are provided, and the bottom end cover 5 - 2 is connected to the top end cover 5 - 1 through the two side end covers 6 .

[0051] Further, if Figure 3 , Figure 4 As shown, the transmission mechanism includes a slide body 3, a sealing strip 4, a linear guide rail 7, a six-dimensional adjustment frame 8, a U-shaped groove 9, a cylindrical clamp 10, and a reading head slider 15. A sealing strip installation groove is provided in the middle of the top end cover 5-1, and a sealing strip 4 is provided in the sealing strip installation groove. A linear guide rail 7 is provided on the bottom end cover 5-2. A reading head slider 15 is fixed to the bottom of the U-shaped groove 9. The reading head slider 15 is slidably connected to the linear guide rail 7. The six-dimensional adjustment frame 8 is arranged in the U-shaped groove 9. The six-dimensional adjustment frame 8 is connected to the indicating grating 13. The U-shaped groove 9 is connected to the slide body 3 through the cylindrical clamp 10, and the slide body 3 is arranged on the sealing strip 4.

[0052] Furthermore, the collimating beam expander 12 is arranged in the cylindrical fixture 10 , the metrological grating clamping device 2 is fixed on the lower surface of the upper end surface of the U-shaped groove 9 , and the indicating grating 13 and the photodetector 14 are arranged in the U-shaped groove 9 .

[0053] Further, preferably, the sealing strip 4 is an arc-shaped structure, and the sealing strip 4 is made of rubber material; the linear guide rail 7 adopts a side-by-side dual linear guide rail, and the bottom end cover 5-2 is provided with a scale boss as a positioning surface, and the side-by-side dual linear guide rails are installed on both sides of the scale boss as the positioning surface by screws.

[0054] Further, preferably, Figure 7 As shown, the indicating grating 13 is arranged in the self-imaging area of ​​the metering grating 1 , and the grating lines of the metering grating 1 and the indicating grating 13 are perpendicular.

[0055] Further, if Figure 8 As shown, the photoelectric detector 14 and the indicating grating 13 are both designed as a multi-quadrant structure, and the quadrant area and number of the photoelectric detector 14 match the quadrant setting of the indicating grating 13.

[0056] Further, preferably, the top end cover 5 - 1 , the bottom end cover 5 - 2 and the side end cover 6 are assembled in a splicing manner.

[0057] A method for measuring a closed transmission grating self-imaging large-range displacement sensor comprises the following steps:

[0058] S1. The indicator grating 13 is placed in the self-imaging area of ​​the metering grating 1. The metering grating 1 is perpendicular to the grating lines of the indicator grating 13. During the displacement measurement, the slider 15 of the reading head makes a one-dimensional linear displacement relative to the metering grating 1 in the direction perpendicular to the grating lines of the indicator grating 13. The self-imaging area calculation formula is:

[0059]

[0060] Where B is the height of the Talbot region, N is the number of grating periods, and Z m is the length of a single Talbot period; the length of a single Talbot period Z m It is expressed as:

[0061]

[0062] Where T is the grating period; λ is the wavelength of incident light, and P is the diffraction order;

[0063] S2. The range of displacement measurement is determined by the difference in length between the effective grating area of ​​the measuring grating 1 and the indicating grating 13. The formula is:

[0064] L c =L b ―L c (3)

[0065] Among them, L c is the measuring range, L b is the effective length of the major axis of the measuring grating 1, L a It indicates the effective length of the major axis of the grating 13;

[0066] S3. The resolution of displacement detection is:

[0067]

[0068] Where N is the resolution of displacement detection, T is the grating period, and E is the subdivision multiple;

[0069] S4, the photoelectric detector 14 and the indicator grating 13 are designed as a multi-quadrant structure, and the quadrant area and number of the photoelectric detector 14 match the quadrant setting of the indicator grating 13;

[0070] S5, such as Figure 6 , Fig. 9 , Fig.10As shown, the photoelectric detector 14 outputs multiple analog signals, which are input into the subdivision box for analog-to-digital conversion and electrical subdivision, and the subdivided digital signals are counted by the host computer software. The final displacement value D is calculated as follows:

[0071]

[0072] Where D is the displacement value, F is the square wave number, T is the grating period, and E is the subdivision multiple.

[0073] The specific implementation parameters are as follows:

[0074] Measuring grating period: 20μm

[0075] Effective line length of the major axis of the measuring grating: 110mm

[0076] Indicator grating period: 20μm

[0077] Indicator grating long axis effective line length: 10mm

[0078] Subdivision box subdivision multiple: 1000

[0079] First, assemble the various parts of the sensor according to the spatial position relationship of the sensor parts mentioned above, turn on the laser and photodetector, use the six-dimensional adjustment frame to adjust the spatial dimension distribution of the indicator grating, place it in the self-imaging area of ​​the metering grating, connect the rear end of the photodetector to the oscilloscope, give the sensor a small displacement, and adjust the position of the indicator grating through the six-dimensional adjustment frame so that the oscilloscope interface displays two sine and cosine signal outputs with a phase difference of 90° and an amplitude that meets the subdivision conditions. Then, connect the subdivision box, turn on the subdivision box and set the subdivision multiple of the subdivision box to 1000. Connect the rear end of the subdivision box to the oscilloscope and the host computer, and display the output square wave signal on the oscilloscope. Finally, open the host computer software to count the square wave signal and calculate the displacement value.

[0080] Under the above conditions, it can be calculated from formula (3) that the range of the closed transmission grating self-imaging large-range displacement sensor is 100mm. When the subdivision multiple of the subdivision box is set to 1000 times, the resolution of the displacement sensor can be calculated to be 20nm from formula (4). Assuming that the number of square waves counted by the host computer is 4999957, it can be calculated from formula (5) that the measurement value of the closed transmission grating self-imaging large-range displacement sensor is 99.99914mm, and the measurement error is 100.0000mm-99.99914mm=0.00086mm.

[0081] Only the preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention, and various changes should be included in the protection scope of the present invention.

Claims

1. A closed transmission grating self-imaging large-range displacement sensor, characterized in that: The invention comprises a ruler housing (a) and a reading head (b), wherein the ruler housing (a) is connected to the reading head (b), the reading head (b) comprises a transmission mechanism and a measuring mechanism, the transmission mechanism is connected to the measuring mechanism, the ruler housing (a) comprises an outer housing of a grating sensor and a metrological grating clamping device (2), the transmission mechanism and the measuring mechanism are both arranged in the outer housing of the grating sensor, the metrological grating clamping device (2) is arranged in the outer housing of the grating sensor, and a metrological grating (1) is arranged in a groove of the metrological grating clamping device (2).

2. The closed transmission grating self-imaging large-range displacement sensor according to claim 1, characterized in that: The measuring mechanism comprises a laser (11), a collimating beam expander (12), a metering grating (1), an indicating grating (13), and a photodetector (14); the collimating beam expander (12) is arranged in the optical path direction of the laser (11); the metering grating (1) is arranged in the optical path direction of the collimating beam expander (12); the indicating grating (13) is arranged in the optical path direction of the metering grating (1); and the photodetector (14) is arranged in the optical path direction of the indicating grating (13).

3. The closed transmission grating self-imaging large-range displacement sensor according to claim 1, characterized in that: The outer shell of the grating sensor comprises a top end cover (5-1), a bottom end cover (5-2), and a side end cover (6), two side end covers (6) are provided, and the bottom end cover (5-2) is connected to the top end cover (5-1) via the two side end covers (6).

4. The closed transmission grating self-imaging large-range displacement sensor according to claim 3, characterized in that: The transmission mechanism comprises a slide body (3), a sealing strip (4), a linear guide rail (7), a six-dimensional adjustment frame (8), a U-shaped groove (9), a columnar clamp (10), and a reading head slider (15). A sealing strip installation groove is provided in the middle of the top end cover (5-1), a sealing strip (4) is provided in the sealing strip installation groove, a linear guide rail (7) is provided on the bottom end cover (5-2), a reading head slider (15) is fixed at the bottom of the U-shaped groove (9), the reading head slider (15) is slidably connected to the linear guide rail (7), the six-dimensional adjustment frame (8) is arranged in the U-shaped groove (9), the six-dimensional adjustment frame (8) is connected to the indicating grating (13), the U-shaped groove (9) is connected to the slide body (3) through the columnar clamp (10), and the slide body (3) is arranged on the sealing strip (4).

5. The closed transmission grating self-imaging large-range displacement sensor according to claim 2, characterized in that: The collimating beam expander (12) is arranged in a cylindrical fixture (10), the metering grating clamping device (2) is fixed on the lower surface of the upper end surface of the U-shaped groove (9), and the indicating grating (13) and the photoelectric detector (14) are arranged in the U-shaped groove (9).

6. The closed transmission grating self-imaging large-range displacement sensor according to claim 4, characterized in that: The sealing strip (4) is an arc-shaped structure, and the sealing strip (4) is made of rubber material; the linear guide rail (7) is a side-by-side double linear guide rail, the bottom end cover (5-2) is provided with a scale boss as a positioning surface, and the side-by-side double linear guide rail is installed on both sides of the scale boss as the positioning surface by screws.

7. The closed transmission grating self-imaging large-range displacement sensor according to claim 2, characterized in that: The indicating grating (13) is arranged in the self-imaging area of ​​the measuring grating (1), and the grating lines of the measuring grating (1) and the indicating grating (13) are perpendicular.

8. The closed transmission grating self-imaging large-range displacement sensor according to claim 2, characterized in that: The photoelectric detector (14) and the indicating grating (13) are both designed as a multi-quadrant structure, and the quadrant area and number of the photoelectric detector (14) match the quadrant setting of the indicating grating (13).

9. The closed transmission grating self-imaging large-range displacement sensor according to claim 3, characterized in that: The top layer end cover (5-1), the bottom layer end cover (5-2) and the side end cover (6) are assembled in a splicing manner.

10. A method for measuring a closed transmission grating self-imaging large-range displacement sensor according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. The indicating grating (13) is placed in the self-imaging area of ​​the measuring grating (1). The grating lines of the measuring grating (1) and the indicating grating (13) are perpendicular to each other. During the displacement measurement process, the reading head slider (15) performs a one-dimensional linear displacement relative to the measuring grating (1) in a direction perpendicular to the grating lines of the indicating grating (13). The self-imaging area is calculated by the formula: Where B is the height of the Talbot region, N is the number of grating periods, and Z m is the length of a single Talbot period; the length of a single Talbot period Z m It is expressed as: Where T is the grating period; λ is the wavelength of incident light, and P is the diffraction order; S2. The range of displacement measurement is determined by the difference between the effective grating area lengths of the measuring grating (1) and the indicating grating (13), and the formula is: L c =L b -L c Among them, L c is the measuring range, L b is the effective length of the major axis of the measuring grating (1), L a is the effective length of the major axis of the indicator grating (13); S3. The resolution of displacement detection is: Where N is the resolution of displacement detection, T is the grating period, and E is the subdivision multiple; S4, the photoelectric detector (14) and the indicating grating (13) are all designed as a multi-quadrant structure, and the quadrant area and number of the photoelectric detector (14) match the quadrant setting of the indicating grating (13); S5, the photoelectric detector (14) outputs multiple analog signals, which are input into the subdivision box for analog-to-digital conversion and electrical subdivision, and the subdivided digital signals are counted by the host computer software. The final displacement value D is calculated as follows: Where D is the displacement value, F is the square wave number, T is the grating period, and E is the subdivision multiple.

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