Reflective displacement measuring device

Abstract

The present invention provides a reflective displacement measuring device, comprising: a projection system, an indicator grating, a reflective scale grating and a receiving system, wherein parallel light emitted by the projection system is incident on the indicator grating, and is incident on the surface of the reflective scale grating through the indicator grating, and then reflected back to the indicator grating to generate moiré fringes, which are projected to the receiving system and converted into electrical signals; the indicator grating comprises a glass substrate, a light-absorbing film is plated on the glass substrate, and a complex amplitude grating composed of an amplitude grating and a phase grating having only ±1-order diffraction fringes is etched on the light-absorbing film. The reflective displacement measuring device provided by the present invention can obtain an ideal light intensity distribution under the conditions of improving energy utilization and reducing the difficulty of manufacturing the grating.

Description

Technical Field

[0001] The invention relates to the technical field of encoders, and in particular to a reflective displacement measuring device. Background Art

[0002] As a precision sensor for position detection, displacement sensors have different technical specifications according to different usage scenarios and technical requirements. Among them, split reflective displacement sensors are widely used in high-precision and high-resolution usage scenarios. Displacement sensor systems used to read grating position information are currently available in two forms on the market: image and projection. Among them, the projection type is mainly represented by two categories of products, Renishaw and Heidenhain. The projection and receiving methods used in Renishaw's products are relatively easy to implement, but the problem is that the light energy utilization rate per unit area is very low, requiring stronger light intensity and greater electronic gain, which makes the system generate a lot of heat and is not suitable for highly integrated structures with high heat dissipation requirements; Heidenhain uses a dual-phase grating projection structure, which can achieve ideal light intensity distribution, but the grating is very difficult to manufacture.

[0003] In summary, there is an urgent need for a high-precision displacement sensor system with high light energy utilization and low grating manufacturing difficulty. Summary of the invention

[0004] In view of the above problems, an object of the present invention is to provide a reflective displacement measuring device to reduce the difficulty of grating manufacturing and improve the utilization rate of light energy.

[0005] To achieve the above object, the present invention adopts the following specific technical solutions:

[0006] The present invention provides a reflection type displacement measuring device, comprising: a projection system, an indicator grating, a reflection scale grating and a receiving system, wherein parallel light emitted by the projection system is incident on the indicator grating, and is incident on the surface of the reflection scale grating through the indicator grating, and then is reflected back to the indicator grating to generate moiré fringes, which are projected to the receiving system and converted into electrical signals; the indicator grating comprises a glass substrate, a light absorbing film is plated on the glass substrate, and a complex amplitude grating composed of an amplitude grating and a phase grating and has only ±1-order diffraction fringes is etched on the light absorbing film.

[0007] Preferably, first grooves penetrating the thickness of the light-absorbing film and arranged at equal intervals are etched on the light-absorbing film to form an amplitude grating, and second grooves are etched into the glass substrate within the spaced first grooves to form a phase grating; the width of the second groove is twice the length of the light-absorbing film on both sides of the first groove.

[0008] Preferably, the number of the complex amplitude gratings is at least two, and two adjacent complex amplitude gratings are arranged in a staggered manner.

[0009] Preferably, the reflective scale grating comprises a substrate, and the substrate is divided into an incremental area and a zero position encoding area according to regions.

[0010] Preferably, the receiving system includes a zero-position signal photoelectric receiver array and a displacement signal photoelectric receiver array; wherein the zero-position signal photoelectric receiver array includes alternately arranged zero-position signal receivers, which respectively generate Z+ signals and Z- signals; the displacement signal photoelectric receiver array is at least one group and is arranged in a row, each group includes four displacement signal photoelectric receivers, and the four displacement signal receivers in each group respectively generate A+ signals, B+ signals, A- signals and B- signals.

[0011] Preferably, the displacement signal photoelectric receiver arrays are arranged in two rows and are relatively staggered.

[0012] Preferably, the period of the complex amplitude grating is Tz, the period of the reflection scale grating is Tb, and the period of the displacement signal photoelectric receiver array is Tg, and the three satisfy the following relationship:

[0013] (m±n)×Tz=m×Tb=Tg, m and n are positive integers, and m>n.

[0014] Preferably, a first light-transmitting window for transmitting the moiré fringes is etched on the light-absorbing film, and the depth of the first light-transmitting window is equal to the thickness of the light-absorbing film.

[0015] Preferably, a zero-position grating for generating zero-position signal projection fringes is also etched on the light-absorbing film.

[0016] Preferably, a second light-transmitting window for transmitting the zero-position signal projection fringes is etched on the light-absorbing film.

[0017] The present invention can achieve the following technical effects:

[0018] 1. The complex amplitude grating can obtain the desired light intensity distribution, which is conducive to the encoding of light modulation, and the complex amplitude grating does not need to undergo S i The O2 coating process can reduce the difficulty of production.

[0019] 2. By staggering the complex amplitude grating, the harmonics caused by processing errors can be eliminated, the tolerance in the processing process can be enlarged, the system's requirements for devices can be further reduced, and the qualified rate of finished products can be improved.

[0020] 3. The staggered arrangement of the displacement signal photoelectric receiver array can eliminate harmonics.

[0021] 4. The periodic relationship between the complex amplitude grating, the reflection scale grating and the displacement signal photoelectric receiver array can obtain sine and cosine electrical signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a reflection type displacement measuring device according to an embodiment of the present invention;

[0023] Figure 2 is a schematic structural diagram of an indicator grating according to an embodiment of the present invention;

[0024] Figure 3 It is a schematic diagram of the structure of a traditional phase grating;

[0025] Figure 4 It is the light intensity distribution diagram of the traditional phase grating;

[0026] Figure 5 It is a schematic diagram of the structure of a traditional amplitude grating;

[0027] Figure 6 It is the light intensity distribution diagram of the traditional amplitude grating;

[0028] Figure 7 is a front view of a complex amplitude grating according to an embodiment of the present invention;

[0029] Figure 8 is a top view of a complex amplitude grating according to an embodiment of the present invention;

[0030] Fig. 9 is a light intensity distribution diagram of a complex amplitude grating according to an embodiment of the present invention;

[0031] Fig.10 is a diagram of a staggered arrangement of three complex amplitude gratings according to an embodiment of the present invention;

[0032] Fig.11 is a schematic structural diagram of a reflective scale grating according to an embodiment of the present invention;

[0033] Fig.12 is a schematic structural diagram of a receiving system according to an embodiment of the present invention;

[0034] Fig.13 Schematic diagram of the structure of another displacement signal photoelectric receiver array according to an embodiment of the present invention.

[0035] The figure marks include: projection system 1, light source 11, collimating mirror 12, indicator grating 2, glass substrate 21, light absorbing film 22, complex amplitude grating 23, first groove 231, second hook groove 232, first light-transmitting window 24, zero position grating 25, second light-transmitting window 26, reflection scale grating 3, substrate 31, incremental area 32, zero position encoding area 33, receiving system 4, zero position signal photoelectric receiver array 41, first zero position signal receiver 411, second zero position signal receiver 412, displacement signal photoelectric receiver array 42, first displacement signal receiver 421, second displacement signal receiver 422, third displacement signal receiver 423, fourth displacement signal receiver 424. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0037] The reflective displacement measuring device provided by the embodiment of the present invention will be described in detail below.

[0038] Figure 1 The structure of a reflection type displacement measuring device according to an embodiment of the present invention is shown.

[0039] like Figure 1 As shown, the reflective displacement measuring device provided by the embodiment of the present invention includes: a projection system 1, an indicator grating 2, a reflective scale grating 3 and a receiving system 4, the projection system 1 includes a light source 11 and a collimator 12, the light source 11 is preferably an LED light source for emitting light; the collimator 12 is used to convert the light emitted by the light source 11 into parallel light, the parallel light is incident on the indicator grating 2, and is incident on the surface of the reflective scale grating 3 through the indicator grating 2, and then reflected back to the indicator grating 2 to generate moiré fringes projected to the receiving system 4, which are converted into electrical signals for output by the receiving system 4.

[0040] The present invention generates moiré fringes by the cooperation of the indicator grating 2 and the reflective scale grating 3. The indicator grating 2 is the key design of the reflective displacement measuring device, and the structure of the indicator grating 2 is described in detail below.

[0041] Figure 2 The structure of the indicator grating according to one embodiment of the present invention is shown.

[0042] like Figure 2 As shown, the indicator grating 2 includes a glass substrate 21, on which a light absorbing film 22 is plated, and on the light absorbing film 22, a complex amplitude grating 23, a first light-transmitting window 24, a zero position grating 25 and a second light-transmitting window 26 are etched toward the glass substrate 21. The complex amplitude grating 23 is used to generate incremental signal projection fringes, which are incident on the reflection scale grating 3 to form moiré fringes, and the moiré fringes are ±1-order diffraction fringes, which are emitted from the first light-transmitting window 24 after being reflected by the reflection scale grating 3 and received by the receiving system 4; the zero position grating 24 is used to generate zero position signal projection fringes, and its specific structure is the prior art and will not be repeated here. The zero position signal projection fringes are emitted from the second light-transmitting window 26 after being reflected by the reflection scale grating 3 and received by the receiving system 4.

[0043] The light absorbing film 22 is made of chromium or chromium and chromium oxide and other materials, and is used to block and absorb light.

[0044] Since there is a diffraction effect when light passes through a slit, when the gap between the complex amplitude grating 23 and the reflection scale grating 3 is far, the energy distribution cannot be completely calculated according to the divergence angle of the collimated light source in applied optics to calculate the projected energy distribution. It is necessary to use scalar theory to calculate the energy distribution of the projected light field. In order to suppress the diffraction fringes of other orders except the first-order diffraction fringes, it is necessary to use a phase grating and an amplitude grating to modulate the parallel light in a composite form to obtain the light energy distribution required by the present invention.

[0045] Figure 3 Figure 2 shows the structure of a conventional phase grating. Figure 3 As shown in the figure, a phase grating is made by etching grooves on a glass substrate. The light energy modulation is achieved through the optical path difference at the grooves. The light intensity distribution is shown in Figure 4 The light intensity distribution is shown, but not intended to be obtained by the present invention.

[0046] Figure 5 Figure 2 shows the structure of a conventional amplitude grating. Figure 5 As shown in the figure, a light-shielding film is plated on a glass substrate to form an amplitude grating. According to the direction of the incident light, the traditional amplitude grating is divided into two types: transmission type and reflection type. The light intensity distribution is shown in Figure 6 As shown, it is not the intention of the present invention to obtain light intensity distribution.

[0047] The light intensity distribution desired by the present invention is as follows Fig. 9 In order to obtain Fig. 9 The light intensity distribution shown is a complex amplitude grating 23 formed by combining the amplitude grating with the traditional phase grating.

[0048] Figure 7 and Figure 8 The main view structure and the top view structure of the complex amplitude grating according to an embodiment of the present invention are respectively shown.

[0049] like Figure 2 , Figure 7 and Figure 8 As shown, first grooves 231 penetrating the thickness of the light absorbing film 22 and distributed at equal intervals are etched on the light absorbing film 22 to form an amplitude grating. The first grooves 231 divide the width of the light absorbing film 22 into two equal parts. Corresponding to the spaced first grooves 231, second grooves 232 are etched on the glass substrate 21 to form a phase grating. That is, after the amplitude grating is formed, the phase grating is etched on the glass substrate 21 to form the phase grating. The complex amplitude grating 23 is composed of the phase grating and the amplitude grating.

[0050] The light absorbing film 22 can modulate the position of the phase grating to obtain a light intensity distribution as shown in FIG9 , which is beneficial to realize the encoding of light modulation.

[0051] Since the second grooves 232 are arranged at equal intervals on the glass substrate 21 , a complex amplitude grating 23 with a continuous periodic structure is formed, and its period is Tz.

[0052] In order to suppress diffraction fringes of other energy levels except the first-order diffraction fringes, the width A2 of the second groove 232 is twice the width A1 of the light-absorbing film 22 on both sides of the second groove 232, A1+A2=Tz, that is, the phase difference between the light phase here and the adjacent light-transmitting window is half a period.

[0053] When preparing the complex amplitude grating 23 designed in the present invention, a second groove 232 with a depth of π is etched on the glass substrate 21. i The O2 coating process can reduce the difficulty of production.

[0054] In order to eliminate the kth harmonic caused by the processing error, enlarge the tolerance in the processing process, further reduce the system's requirements on the device, and improve the qualified rate of finished products, the number of complex amplitude gratings 23 is at least two. Fig.10 Three complex amplitude gratings are shown, and two adjacent complex amplitude gratings are spliced ​​together with a preset distance x, thereby eliminating the kth harmonic, reducing the process difficulty of the grating, and avoiding the situation where the light intensity distribution is not ideal during the production process. For example: two adjacent complex amplitude gratings are staggered by Tz / 2 to eliminate the 2nd harmonic, and for another example: two adjacent complex amplitude gratings are staggered by Tz / 3 to eliminate the 3rd harmonic.

[0055] Of course, a plurality of dislocated complex amplitude gratings 23 can be made into an integrated structure, and dislocated grooves can be etched on the same glass substrate to achieve the purpose of eliminating harmonics.

[0056] The first light-transmitting window 24 is located at one side of the complex amplitude grating 23 . The depth of the first light-transmitting window 24 is equal to the thickness of the light-absorbing film 22 . That is, the first light-transmitting window 24 is not etched to the glass substrate 21 .

[0057] The second light-transmitting window 26 is located at one side of the null grating 25 , and the depth of the second light-transmitting window 26 is also equal to the thickness of the light-absorbing film 22 .

[0058] Fig.11 The structure of a reflective scale grating according to an embodiment of the present invention is shown.

[0059] like Fig.11As shown, the reflective scale grating is both a scale grating and a reflective grating, which specifically includes a substrate 31. The substrate 31 is a high-polished surface for enhancing corrosion resistance. The corrosion resistance can also be enhanced by plating a metal film. The substrate 31 is divided into an incremental area 32 and a zero-position coding area 33 according to the region. The incremental area 32 uses a periodic structure formed by alternating high-polished areas and black areas on the surface of the substrate 31, and its period is Tb. The zero-position coding area 33 also uses a structure for zero-position coding formed by alternating high-polished areas and black areas on the surface of the substrate 31.

[0060] Fig.12 The structure of a receiving system according to an embodiment of the present invention is shown.

[0061] like Fig.12 As shown, the receiving system includes a zero-position signal photoelectric receiver array 41 for receiving zero-position signal projection fringes and a displacement signal photoelectric receiver array 42 for receiving incremental signal projection fringes; wherein, the zero-position signal photoelectric receiver array 41 includes a first zero-position signal receiver 411 and a second zero-position signal receiver 412 arranged alternately, the first zero-position signal receiver 411 is used to generate a Z+ signal, and the second zero-position signal receiver 412 is used to generate a Z- signal, and after the Z+ signal and the Z- signal enter the comparator to compare the levels, a zero-position pulse is output.

[0062] The displacement signal photoelectric receiver array 42 is composed of a first displacement signal receiver 421, a second displacement signal receiver 422, a third displacement signal receiver 423 and a fourth displacement signal receiver 424. Four displacement signal receivers form a periodic structure, and the width of a single period is Tg. The displacement signal photoelectric receiver array 42 includes at least one group of periodic structures, and multiple groups of periodic structures are arranged in a row. The first displacement signal receiver 421 is used to generate an A+ signal, the second displacement signal receiver 422 is used to generate a B+ signal, the third displacement signal receiver 423 is used to generate an A- signal, and the fourth displacement signal receiver 424 is used to generate a B- signal.

[0063] In a specific embodiment of the present invention, the first displacement signal receiver 421 , the second displacement signal receiver 422 , the third displacement signal receiver 423 and the fourth displacement signal receiver 424 increase their light receiving areas as much as possible to improve the light energy utilization rate per unit area.

[0064] Fig.13 The structure of another displacement signal photoelectric receiver array according to an embodiment of the present invention is shown.

[0065] like Fig.13As shown, in order to eliminate the hth harmonic, the displacement signal photoelectric receiver array 42 is arranged in two rows, and the periodic structures of the upper and lower rows are arranged at a staggered preset distance y. For example, the periodic structures of the upper and lower rows are staggered by Tg / 2 to eliminate the 2nd harmonic, and for example, two adjacent complex amplitude gratings are staggered by Tg / 3 to eliminate the 3rd harmonic.

[0066] In order to obtain sine and cosine signals, the periods of the complex amplitude grating 23, the reflection scale grating 3 and the displacement signal photoelectric receiver array 42 need to satisfy the following relationship:

[0067] (m±n)×Tz=m×Tb=Tg, wherein m and n are positive integers, and m>n.

[0068] In a specific example of the present invention, the period of the reflection scale grating 3 is Tb=20μm, m=40, then Tg=800μm; at this time, n=1, m±n is mn, then Tz=20.5128μm, at this time, the complex amplitude grating 23 and the displacement signal photoelectric receiver array 42 can respectively use the staggered arrangement of harmonic elimination schemes, or the complex amplitude grating 23 chooses the harmonic elimination scheme, and the displacement signal photoelectric receiver array 42 does not choose the harmonic elimination scheme, or the complex amplitude grating 23 does not choose the harmonic elimination scheme, and the displacement signal photoelectric receiver array 42 chooses the harmonic elimination scheme.

[0069] The present invention can choose to eliminate harmonics once or in batches. When eliminating harmonics once, all harmonics can be eliminated once through the complex amplitude grating 23 or the displacement signal photoelectric receiver array 42. When eliminating harmonics in batches, part of the harmonics can be eliminated through the complex amplitude grating 23 and the other part of the harmonics can be eliminated through the displacement signal photoelectric receiver array 42. Make the most suitable choice according to the actual situation.

[0070] In the description of this specification, the description with reference to the terms "one embodiment", "another embodiment", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0071] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

[0072] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A reflective displacement measuring device, characterized in that: include: A projection system, an indicator grating, a reflective scale grating and a receiving system, wherein the projection system comprises a light source and a collimator, wherein the light source is used to emit light, and the collimator is used to convert the light emitted by the light source into parallel light, and the parallel light emitted by the projection system is incident on the indicator grating, passes through the indicator grating, is incident on the surface of the reflective scale grating, and then is reflected back to the indicator grating to generate moiré fringes, which are projected to the receiving system and converted into electrical signals; The indicator grating includes a glass substrate, a light-absorbing film is coated on the glass substrate, and a complex amplitude grating composed of an amplitude grating and a phase grating and having only ±1-order diffraction stripes is etched on the light-absorbing film; first grooves that penetrate the thickness of the light-absorbing film and are arranged at equal intervals are etched on the light-absorbing film to form the amplitude grating, and second grooves are etched toward the glass substrate in the spaced-apart first grooves to form the phase grating; the width of the second groove is twice the length of the light-absorbing film on both sides of the first groove.

2. The reflective displacement measuring device according to claim 1, characterized in that: The number of the complex amplitude gratings is at least two, and two adjacent complex amplitude gratings are arranged in a staggered manner.

3. The reflective displacement measuring device according to claim 1, characterized in that: The reflective scale grating includes a substrate, and the substrate is divided into an incremental area and a zero position encoding area according to regions.

4. The reflective displacement measuring device according to any one of claims 1 to 3, characterized in that: The receiving system includes a zero-position signal photoelectric receiver array and a displacement signal photoelectric receiver array; wherein, The zero-position signal photoelectric receiver array includes alternately arranged zero-position signal receivers, which respectively generate a Z+ signal and a Z- signal; The displacement signal photoelectric receiver array is at least one group and is arranged in a row, each group includes four displacement signal photoelectric receivers, and the four displacement signal receivers in each group generate A+ signal, B+ signal, A- signal and B- signal respectively.

5. The reflective displacement measuring device according to claim 4, characterized in that: The displacement signal photoelectric receiver arrays are arranged in two rows and are relatively staggered.

6. The reflective displacement measuring device according to claim 4 or 5, characterized in that: The period of the complex amplitude grating is Tz, the period of the reflection scale grating is Tb, and the period of the displacement signal photoelectric receiver array is Tg, and the three satisfy the following relationship: (m±n)×Tz=m×Tb=Tg, m and n are positive integers, and m>n.

7. The reflective displacement measuring device according to claim 1, characterized in that: A first light-transmitting window for transmitting moiré fringes is etched on the light-absorbing film, and the depth of the first light-transmitting window is equal to the thickness of the light-absorbing film.

8. The reflective displacement measuring device according to claim 7, characterized in that: A zero-position grating for generating zero-position signal projection fringes is also etched on the light-absorbing film.

9. The reflective displacement measuring device according to claim 8, characterized in that: A second light-transmitting window for transmitting the zero-position signal projection stripe is etched on the light-absorbing film.

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