Grating ruler speed measuring device

Abstract

The invention discloses a grating ruler speed measuring device which is a Mach-Zehnder interferometer composed of a collimation coherent light source, a first light beam, a first beam splitter, a second light beam, a third light beam, a first grating, a second grating, a first interface, a second interface, a third interface and an interference point. Wherein the collimated coherent light source, the first light beam, the first beam splitter, the second light beam, the third light beam and the interference point are always relatively fixed to form a stator of the device, the first grating and the second grating are always relatively fixed to form a rotor of the device, and the phase shift between the second light beam and the third light beam can be adjusted through the relative displacement between the rotor and the stator. The Doppler effect of the moving grating and the double-grating interference phase cancellation principle are utilized, an interference signal which is in direct proportion to the relative speed between the rotor and the stator and is irrelevant to the relative displacement between the rotor and the stator can be generated, and direct measurement of the speed is achieved.

Description

Technical Field

[0001] The present invention relates to a grating ruler speed measuring device capable of generating an interference signal related only to the relative speed between a follower (313) and a stator (312), thereby realizing direct speed measurement, and belongs to the field of photoelectric detection technology. Background Art

[0002] Grating scales are high-precision position / displacement measurement devices based on the grating fringe period (pitch). Compared with equally high-precision laser interferometers, grating scales have more stable pitches and are less affected by the external environment. The accuracy of grating scales based on moiré fringe is related to the grating pitch. As the grating pitch decreases to the wavelength of the incident light, new problems will arise: the distance between different gratings in the grating scale is usually a 2 The magnitude of the grating pitch is on the order of / λ, where a is the grating pitch and λ is the wavelength of the incident light in a vacuum. As the grating pitch decreases, the distance between gratings decreases dramatically, making the installation tolerance of the scale even tighter. The diffraction effect of light becomes non-negligible, and higher-order diffracted beams gradually separate from the main beam, reducing the contrast of the moiré fringes and limiting further accuracy improvements. Interferometric scales based on diffracted beams offer another solution for high-precision position / displacement measurement.

[0003] like Figure 1 The single grating diffraction process shown is based on the grating equation: a(n2 sinθ2-n1 sinθ1)=m1λ, (1) Where n1 and n2 are the refractive indices of the first interface (308) and the second interface (309), respectively; θ1 and θ2 are the incident angle and the exit angle of the 02nd light beam (100) at the first grating (306), respectively; m1 is the diffraction order of the 02nd light beam (100) at the first grating (306), and m1 is an integer. When m1=0, for a transmission grating, θ1 and θ2 have the same sign, and n1 and n2 may have different values; for a reflection grating, θ1 and θ2 have opposite signs, and n1 and n2 have the same value. According to the relationship between the wavelength λ of light in a vacuum and the frequency ν of light, λν=c, where c is the speed of light in a vacuum, i.e., 299792458 m / s, when the first grating (306) has a certain speed v relative to the zero-second light beam (100), the frequencies of the zero-second light beam (100) incident thereon and the zero-second light beam (100) emitted therefrom should remain consistent when observed from the perspective of the first grating (306), and this frequency is recorded as ν. 12 , according to the Doppler effect: Where ν1 and ν2 are the frequencies of the 02nd light beam (100) incident on the first grating (306) and the 02nd light beam (100) emitted by the first grating (306) under a static viewing angle, respectively. Formulas (1)–(3) can be further calculated to obtain: For the first grating (306) moving at a low speed, formula (4) can be approximated as: That is, the low-speed movement of the first grating (306) causes the frequency shift of the zero-second light beam (100).

[0004] like Figure 2 In the double grating diffraction process shown, the first grating (306) and the second grating (307) are always placed relatively parallel and relatively fixed, forming a mover (313); the first grating (306) and the second grating (307) have the same grating pitch. The transmission time t2 of the zero-third light beam (200) in the second interface (309) satisfies: Where n2 is the refractive index of the second interface (309), d is the thickness of the second interface (309), or the distance between the first grating (306) and the second grating (307), then the optical path difference D can be expressed as D=n2d, θ2 is the exit angle of the first grating (306), or the incident angle of the second grating (307). From formulas (5) and (6), it can be further calculated that the phase shift φ and frequency shift ν3-ν1 between the zero-third light beam (200) incident on the first grating (306) and the zero-third light beam (200) emitted by the second grating (307) respectively satisfy: Wherein m1 and m2 are the diffraction orders of the zeroth third light beam (200) at the first grating (306) and the second grating (307), respectively.

[0005] The second light beam (304) and the third light beam (305) are respectively incident (θ1=0) on the first grating (306), and double grating interference occurs. The initial phase shifts of the second light beam (304) and the third light beam (305) are φ 12 、φ 13 The second light beam (304) undergoes -m-order diffraction at the first grating (306) and +m-order diffraction at the second grating (307); the third light beam (305) undergoes +m-order diffraction at the first grating (306) and -m-order diffraction at the second grating (307); where m is a positive integer. According to formula (1), the exit angles θ of the second light beam (304) and the third light beam (305) on the first grating (306) are22 ,θ 32 Satisfy respectively: Combined with formula (7), after passing through the first grating (306) and the second grating (307) in sequence, the phase shifts Φ2 and Φ3 of the second light beam (304) and the third light beam (305) satisfy: The phase shift difference (phase difference) Φ3-Φ2 satisfies: The phase difference is linearly related to the speed v of the mover (313) formed by the first grating (306) and the second grating (307) relative to the second light beam (304) and the third light beam (305). The sum of the diffraction orders of the second light beam (304) and the third light beam (305) at the first grating (306) and the second grating (307) is m1+m2=0. According to formula (8), the corresponding frequency shift ν3-ν1=0, and the frequency shift is independent of the position of the first grating (306) and the second grating (307). In summary, the phase difference between the second light beam (304) and the third light beam (305) is linearly related to the speed of the mover (313) relative to the second light beam (304) and the third light beam (305), and is independent of the displacement of the mover (313) relative to the second light beam (304) and the third light beam (305). Summary of the Invention

[0006] Using the above principle, the present invention discloses a grating ruler speed measurement device that can achieve direct speed measurement. The purpose of the present invention is achieved as follows: The block diagram of the grating ruler speed measurement device is as follows Figure 3As shown, the grating ruler speed measuring device is composed of a collimated coherent light source (301), a first light beam (302), a first beam splitter (303), a second light beam (304), a third light beam (305), a first grating (306), a second grating (307), a first interface (308), a second interface (309), a third interface (310), and an interference point (311); wherein the first beam splitter (303) is used to separate the first light beam (302) emitted by the collimated coherent light source (301) into the second light beam (304) and the third light beam (305); wherein the second light beam (304) passes through the first grating (306), the second grating (307), the first interface (308), the second interface (309), the third interface (310), and the interference point (311); The first interface (308), the first grating (306), the second interface (309), the second grating (307), and the third interface (310) are diffracted at the first grating (306) and the second grating (307); the third light beam (305) passes through the first interface (308), the first grating (306), the second interface (309), the second grating (307), and the third interface (310) in sequence, and is diffracted at the first grating (306) and the second grating (307); the interference point (311) is used to cause the second light beam (304) and the third light beam (305) to interfere with each other, thereby generating a light beam having the same wavelength as the second light beam. The invention relates to an interference signal related to the phase shift and frequency shift between the first beam (304) and the third beam (305); wherein the collimated coherent light source (301), the first beam (302), the first beam splitting device (303), the second beam (304), the third beam (305), and the interference point (311) are always relatively fixed, constituting a stator (312) in the grating ruler speed measurement device; wherein the first grating (306) and the second grating (307) are always relatively fixed, constituting a mover (313) in the grating ruler speed measurement device; a one-dimensional relative displacement can occur between the mover (313) and the stator (312); wherein The first interface (308) can be fixed relative to the stator (312) or the mover (313); the second interface (309) can be fixed relative to the stator (312) or the mover (313); the third interface (310) can be fixed relative to the stator (312) or the mover (313); the interference signal at the interference point (311) can change with the relative speed between the mover (313) and the stator (312); the interference signal at the interference point (311) is independent of the relative displacement between the mover (313) and the stator (312).

[0007] The collimated coherent light source (301) in the grating ruler speed measuring device is a light source system formed by collimating and expanding a laser, and is capable of outputting a first light beam (302). The collimated coherent light source (301) is characterized in that the first light beam (302) emitted by the collimated coherent light source (301) has a relatively small beam divergence angle, and the full width at half maximum of the beam divergence angle is less than 10 mrad; the first light beam (302) emitted by the collimated coherent light source (301) has a relatively narrow spectral width, and the full width at half maximum of the spectrum is less than 10 nm.

[0008] The first beam splitter (303) in the grating ruler speed measurement device can be any one of a non-polarizing beam splitter, a polarizing beam splitter, a blazed grating, and a birefringent crystal, and can separate the first light beam (302) into a second light beam (304) and a third light beam (305). The first beam splitter (303) is characterized in that: the first beam splitter (303) comprises at least two input ports and at least two output ports, the first light beam (302) is incident through one of the input ports, and the second light beam (304) and the third light beam (305) are emitted through two of the output ports respectively; the second light beam (304) and the third light beam (305) emitted by the first beam splitter (303) have the same frequency, which is the same as the frequency of the light beam incident thereon. The frequency of the first light beam (302) emitted by the first beam splitter (303) is consistent, which is recorded as ν; correspondingly, the second light beam (304) and the third light beam (305) emitted by the first beam splitter (303) have the same wavelength in vacuum, which is consistent with the wavelength of the first light beam (302) incident thereon in vacuum, which is recorded as λ; the intensity of the first light beam (302) incident on the first beam splitter (303) is U1; the intensities of the second light beam (304) and the third light beam (305) emitted by the first beam splitter (303) are U2 and U3 respectively; the phase shifts of the second light beam (304) and the third light beam (305) emitted by the first beam splitter (303) relative to the first light beam (302) incident thereon are φ respectively. 12 、φ 13 ; The parameters of the first beam splitter (303) are U2 / U1, U3 / U1, φ 12 、φ 13 Should Figure 4 The corresponding parameters in the second beam splitter (403) used in the Mach-Zehnder interferometer shown are consistent.

[0009] Figure 4The principle of the Mach-Zehnder interferometer is schematically shown. The Mach-Zehnder interferometer consists of a first light beam (302), a first beam splitter (303), a second light beam (304), a third light beam (305), a phase plate (402), a second beam splitter (403), a fourth light beam (404), and a fifth light beam (405); the first beam splitter (303) has two input ports, which are respectively recorded as the first port and the second port; the first beam splitter (303) has two output ports, which are respectively recorded as the third port and the fourth port; the third port of the first beam splitter (303) is a reflection port of the first port and a transmission port of the second port; the fourth port of the first beam splitter (303) is a transmission port of the first port and a reflection port of the second port; the efficiency of the reflection port of the first beam splitter (303) is R, which satisfies R=U2 / U1, and the phase shift of the emitted light beam relative to the light beam incident thereon is φ 12 The efficiency of the transmission port of the first beam splitter (303) is T, which satisfies T=U3 / U1, and the phase shift of the emitted light beam relative to the light beam incident thereon is φ 13 ; Under ideal conditions, the efficiency R of the reflection port and the efficiency T of the transmission port on the first beam splitter (303) satisfy R+T=1; the characteristics of the first port, second port, third port, fourth port, reflection port, and transmission port of the second beam splitter (403) are consistent with the corresponding characteristics of the first beam splitter (303); the first light beam (302) is incident through the first port of the first beam splitter (303); the second light beam (304) is emitted through the third port of the first beam splitter (303) and then is incident through the first port of the second beam splitter (403); the third light beam (305) is emitted through the fourth port of the first beam splitter (303), passes through the phase plate (402), and then is incident through the second port of the second beam splitter (403); the fourth light beam (404) and the fifth light beam (405) are emitted through the third port and the fourth port of the second beam splitter (403), respectively.

[0010] Figure 4 In the Mach-Zehnder interferometer shown, the intensity U1 and the complex amplitude u1 of the first light beam (302) satisfy: U1=|u1| 2 , (14) The complex amplitudes u2 and u3 of the second light beam (304) and the third light beam (305) passing through the first beam splitter (303) respectively satisfy: The third light beam (305) will introduce a phase shift φ after passing through the phase plate (402), and the corresponding complex amplitude u3' satisfies: The second light beam (304) and the third light beam (305) are incident on the second beam splitting device (403) to interfere, and the complex amplitudes u4 and u5 of the output fourth light beam (404) and fifth light beam (405) satisfy: The corresponding light intensities U4 and U5 of the fourth light beam (404) and the fifth light beam (405) satisfy: U4=|u4| 2 =(R 2 +T 2 )U1+2RTU1 cos[2(φ 13 -φ 12 )+φ], (20) U5=|u5| 2 =2RTU1+2RTU1 cosφ. (21) For an ideal Mach-Zehnder interferometer, R+T=1, U4+U5=U1 should be satisfied, corresponding to φ 12 、φ 13 Should meet the following requirements: cos[2(φ 13 -φ 12 )+φ]+cosφ=0, |φ 13 -φ 12 |=π / 2. (22) Correspondingly, Figure 3 The phase shift φ of the second light beam (304) and the third light beam (305) emitted by the first beam splitter (303) relative to the first light beam (302) incident thereon is 12 、φ 13 Can be the same or different; preferably, |φ 13 -φ 12 |=π / 2; preferably, φ 12 =-π / 4, φ 13 =+π / 4. According to formula (22), formula (20) can be simplified to: U4=(R 2 +T 2 )U1-2RTU1 cosφ. (23) Figure 4 The relationship between the interference contrast V of the Mach-Zehnder interferometer shown as R and T satisfies: In order to make the contrast of the Mach-Zehnder interferometer satisfy V>1 / 2, according to the relationship R+T=1, it can be deduced that: Correspondingly, by Figure 3The intensity ratio U2:U3=R:T of the second light beam (304) and the third light beam (305) emitted by the first beam splitter (303) shown, or incident on the interference point (311), is between 15:85 and 85:15; preferably, between 35:65 and 65:35; preferably, between 45:55 and 55:45.

[0011] The first grating (306) in the grating ruler speed measurement device is a transmission or reflection grating, which can cause the second light beam (304) and the third light beam (305) to diffract, and is characterized in that: the first grating (306) is based on a glass material or a metal material, and is plated with periodic absorption or reflection stripes; the grating pitch of the first grating (306) is between 0.5μm and 20μm; the stripe width of the first grating (306) is 1 / 2 of the grating pitch, which is between 0.25μm and 10μm; the stripe direction of the first grating (306) is consistent with the direction of the relative displacement between the mover (313) and the stator (312).

[0012] The second grating (307) in the grating ruler speed measurement device is a transmission or reflection grating, which can cause the second light beam (304) and the third light beam (305) to diffract, and is characterized in that: the second grating (307) is based on a glass material or a metal material, and is coated with periodic absorption or reflection stripes; the grating pitch of the second grating (307) is between 0.5μm and 20μm; the stripe width of the second grating (307) is 1 / 2 of the grating pitch, which is between 0.25μm and 10μm; the stripe direction of the second grating (307) is consistent with the direction of the relative displacement between the mover (313) and the stator (312).

[0013] It is worth noting that the base material of the first grating (306) and the second grating (307) are consistent; the stripe material of the first grating (306) and the second grating (307) are consistent; the grating pitch of the first grating (306) and the second grating (307) are the same, and the grating pitch is recorded as a.

[0014] The first interface (308) in the grating scale speed measuring device can be any one of vacuum, air, water, and glass, and is a transparent medium capable of transmitting the second light beam (304) and the third light beam (305). The device is characterized in that: the first interface (308) has a high transmittance, which is greater than 90%; the first interface (308) has a certain refractive index, preferably, its refractive index is equal to 1; the first interface (308) can be fixed relative to the stator (312) or to the mover (313); and the refractive index of the first interface (308) remains consistent throughout the entire range of relative displacement between the mover (313) and the stator (312).

[0015] The second interface (309) in the grating ruler speed measuring device can be any one of vacuum, air, water, and glass, and is a transparent medium capable of transmitting the second light beam (304) and the third light beam (305), and is characterized in that: the second interface (309) has a high transmittance, and its transmittance is greater than 90%; the second interface (309) has a certain refractive index, which is recorded as n; preferably, n is between 1 and 1.5; the second interface (309) can be relatively fixed with the stator (312) or with the mover (313). It is worth noting that n remains consistent throughout the entire range of relative displacement between the mover (313) and the stator (312); the second interface (309) has a large optical path difference, and its optical path difference is greater than 16 times the Talbot distance, where the Talbot distance z T Satisfy z T =2na 2 / λ.

[0016] The third interface (310) in the grating scale speed measuring device can be any one of vacuum, air, water, and glass, and is a transparent medium capable of transmitting the second light beam (304) and the third light beam (305). The characteristics are: the third interface (310) has a high transmittance, and its transmittance is greater than 90%; the third interface (310) has a certain refractive index, preferably, its refractive index is equal to 1; the third interface (310) can be relatively fixed with the stator (312) or relatively fixed with the mover (313); the third interface (310) remains consistent throughout the entire range of relative displacement between the mover (313) and the stator (312).

[0017] It is worth noting that the first interface (308) and the third interface (310) have the same refractive index, which is denoted as n0; wherein n0 may be the same as the refractive index n of the second interface (309) or different from n.

[0018] In a specific implementation, the first grating (306), the second grating (307), and the second interface (309) may be formed by coating the same periodic stripes on both sides of a glass substrate. In this case, n0 may be different from n, the first interface (308) and the third interface (310) are fixed relative to the stator (312), and the second interface (309) is fixed relative to the mover (313). The first grating (306), the second grating (307), and the second interface (309) may also be a combination system of a reflective grating and a reflector, which can allow the second light beam (304) and the third light beam (305) emitted by the reflective grating to be incident on the reflective grating again through the reflector. In this case, n0 is the same as n, and the first interface (308), the second interface (309), and the third interface (310) are fixed relative to the stator (312).

[0019] The interference point (311) in the grating ruler speed measurement device is a measurement system composed of a beam splitter and at least three photoelectric detection devices, characterized in that: the beam splitter in the interference point (311) includes at least two input ports and at least three output ports, and the number of the output ports is consistent with the number of the photoelectric detection devices, which is recorded as N; the photoelectric detection devices in the interference point (311) correspond to the numbers of the output ports in the beam splitter, and are used to measure the light intensity of the light beam emitted by the corresponding output port of the beam splitter; the second light beam (304) and the third light beam (305) are incident through two of the input ports of the beam splitter; the phase shift of the light beam emitted by the beam splitter relative to the second light beam (304) and the third light beam (305) incident thereon is φ respectively. 2o 、φ 3o , where o is a non-negative integer, representing the light beam emitted from the corresponding output port on the beam splitter, satisfying o <N。

[0020] It is worth noting that after passing through the first interface (308), the first grating (306), the second interface (309), the second grating (307), and the third interface (310), the second light beam (304) and the third light beam (305) have phase shifts Φ2 and Φ3 relative to the first light beam (302), wherein Φ2 and Φ3 satisfy formulas (11) and (12), respectively. The corresponding complex amplitudes u2" and u3" of the second light beam (304) and the third light beam (305) respectively satisfy: Wherein K2 and K3 are proportional to the light intensity of the second light beam (304) and the third light beam (305) incident on the beam splitter at the interference point (311). Under ideal conditions, K2=K3=K, the second light beam (304) and the third light beam (305) are incident on the beam splitter at the interference point (311) and interfere with each other, and the complex amplitude w of the light beam emitted from the output port numbered o on the beam splitter is o satisfy: Where K2' and K3' are the efficiencies of the beam splitter at the interference point (311) for the second light beam (304) and the third light beam (305). Under ideal conditions, K2' = K3' = K' is also satisfied, so formula (29) can be rewritten as: Correspondingly, the intensity W of the light beam emitted from the output port numbered o on the beam splitter is o satisfy: Furthermore, the following operation is performed on formula (31): When |φ is satisfied 3o -φ 2o When |=2πo / N, the summation terms in the square brackets in formula (32) are all 0, and formula (32) can be rewritten as: According to the complex number calculated in formula (33), the phase difference shown in formula (13) can be obtained by solving its argument. Correspondingly, the light beam emitted from the corresponding numbered output port on the beam splitter at the interference point (311) is phase shifted by φ relative to the second light beam (304) and the third light beam (305). 2o 、φ 3o Satisfy |φ 3o -φ 2o |=2πo / N;Preferably, φ 2o =-πo / N, φ 3o =+πo / N. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The single grating diffraction process is shown, wherein the zero-second light beam (100) passes through the first interface (308), the first grating (306), and the second interface (309) in sequence; wherein the refractive indices of the first interface (308) and the second interface (309) are n1 and n2 respectively; the zero-second light beam (100) is incident on the first grating (306) at an angle θ1, undergoes m1-order diffraction at the first grating (306), and is emitted at an angle θ2; when the speed of the first grating (306) relative to the zero-second light beam (100) is v, the frequencies of the zero-second light beam (100) at the first interface (308) and the second interface (309) are ν1 and ν2 respectively.

[0022] Figure 2The double grating diffraction process is shown. The zero-third light beam (200) passes through the first interface (308), the first grating (306), the second interface (309), the second grating (307), and the third interface (310) in sequence. The first grating (306) and the second grating (307) are always relatively fixed, forming a mover (313). The refractive indices of the first interface (308), the second interface (309), and the third interface (310) are n1, n2, and n3 respectively. The zero-third light beam (200) is incident on the first grating (306) at an angle θ1, and m1-order diffraction occurs at the first grating (306). The invention discloses a method for providing a light beam of the invention for the invention. The light beam of the invention is incident on the second grating (307) at an angle of θ2, undergoes m2-order diffraction at the second grating (307), and is emitted at an angle of θ3. The light beam of the invention is incident on the second grating (307) at an angle of θ2, undergoes m2-order diffraction at the second grating (307), and is emitted at an angle of θ3. The second interface (309), or the optical path difference between the first grating (306) and the second grating (307) is d. When the speed of the mover (313) formed by the first grating (306) and the second grating (307) relative to the light beam of the invention is v, the frequencies of the light beam of the invention (200) at the first interface (308), the second interface (309), and the third interface (310) are ν1, ν2, and ν3, respectively.

[0023] Figure 3 The invention provides a block diagram of a grating ruler speed measuring device, which comprises a collimated coherent light source (301), a first light beam (302), a first beam splitting device (303), a second light beam (304), a third light beam (305), a first grating (306), a second grating (307), a first interface (308), a second interface (309), a third interface (310), and an interference point (311); the second light beam (304) and the third light beam (305) sequentially pass through the first interface (308), the first light beam (309), the third light beam (310), and the interference point (311); The invention relates to a grating (306), a second interface (309), a second grating (307), and a third interface (310); wherein the collimated coherent light source (301), the first light beam (302), the first beam splitting device (303), the second light beam (304), the third light beam (305), and the interference point (311) are always relatively fixed, constituting a stator (312) of a grating ruler speed measuring device; wherein the first grating (306) and the second grating (307) are always relatively fixed, constituting a mover (313) of the grating ruler speed measuring device.

[0024] Figure 4The invention shows the principle of Mach-Zehnder interference, wherein a first light beam (302) is incident on a first beam splitting device (303), a second light beam (304) and a third light beam (305) are emitted from the first beam splitting device (303) and are incident on a second beam splitting device (403) to interfere, and a fourth light beam (404) and a fifth light beam (405) are emitted from the second beam splitting device (403); wherein the third light beam (305) is emitted from the first beam splitting device (303), passes through a phase plate (402), introduces a phase shift φ, and is then incident on the second beam splitting device (403).

[0025] Figure 5 The invention shows a block diagram of an interference point (311) in a grating ruler speed measurement device when N=3. The interference point (311) is a measurement system composed of a third beam splitter (503) and three photoelectric detection devices, namely a third zero detector (520), a third first detector (521), and a third second detector (522). The second light beam (304) and the third light beam (305) are incident on the third beam splitter (503) to interfere. The third zero light beam (510), the third first light beam (511), and the third second light beam (512) are emitted from the third beam splitter (503) and are respectively incident on the third zero detector (520), the third first detector (521), and the third second detector (522) to detect light intensity. The light intensities detected by the third zero detector (520), the third first detector (521), and the third second detector (522) are W0, W1, and W2, respectively.

[0026] Figure 6 The invention shows a block diagram of an interference point (311) in a grating ruler speed measurement device when N=4. The interference point (311) is a measurement system composed of a fourth beam splitter (604) and four photoelectric detection devices, namely a fourth zero detector (620), a fourth first detector (621), a fourth second detector (622), and a fourth third detector (623); the second light beam (304) and the third light beam (305) are incident on the fourth beam splitter (604) to interfere with each other, and the fourth zero light beam (610), the fourth first detector (621), the fourth second detector (622), and the fourth third detector (623) are incident on the fourth beam splitter (604) to interfere with each other. The light beam (611), the forty-second light beam (612), and the forty-third light beam (613) are emitted from the fourth beam splitter (604) and are incident on the fourth zero detector (620), the fourth first detector (621), the fourth second detector (622), and the fourth third detector (623) respectively for light intensity detection. The light intensities detected by the fourth zero detector (620), the fourth first detector (621), the fourth second detector (622), and the fourth third detector (623) are W0, W1, W2, and W3 respectively. DETAILED DESCRIPTION

[0027] exist Figure 5In one embodiment shown, the interference point (311) in the grating ruler speed measurement device is a measurement system composed of a third beam splitter (503) and three photoelectric detection devices. The third beam splitter (503) in the interference point (311) includes two input ports and three output ports. The second light beam (304) and the third light beam (305) are incident from two of the input ports, interfere with the third beam splitter (503), and then emit a third zero light beam (510), a third first light beam (511), and a third second light beam (512) from the three output ports. The phase shift φ of the third zero light beam (510) relative to the second light beam (304) is 20 =0; wherein the phase shift φ of the third zero beam (510) relative to the third beam (305) 30 = 0; wherein the phase shift φ of the third light beam (511) relative to the second light beam (304) 21 =-π / 3; wherein the phase shift φ of the third light beam (511) relative to the third light beam (305) 31 =+π / 3; wherein the phase shift φ of the third light beam (512) relative to the second light beam (304) 22 =-2π / 3; wherein the phase shift φ of the third light beam (512) relative to the third light beam (305) 32 =+2π / 3. The third zero light beam (510), the third first light beam (511), and the third second light beam (512) emitted by the third beam splitter (503) in the interference point (311) are incident on three photoelectric detection devices, namely the third zero detector (520), the third first detector (521), and the third second detector (522). The light intensity of the third zero light beam (510) detected by the third zero detector (520) is W0; the light intensity of the third first light beam (511) detected by the third first detector (521) is W1; and the light intensity of the third second light beam (512) detected by the third second detector (522) is W2.

[0028] According to formula (33), the phase shift difference Φ3-Φ2 of the second light beam (304) and the third light beam (305) relative to the first light beam (302) is calculated as follows: When the mover (313) and the stator (312) in the grating scale speed measuring device are relatively stationary, Φ3-Φ2 calculated using formula (34) is recorded as Φ0; when the relative speed between the mover (313) and the stator (312) is v, Φ3-Φ2 calculated using formula (34) is recorded as Φ1. The relative speed v between the mover (313) and the stator (312) is calculated as follows: Where c and π are constants, and a, n, m, λ, and d are known quantities.

[0029] exist Figure 6 In the preferred embodiment shown, the interference point (311) in the grating ruler speed measurement device is a measurement system composed of a fourth beam splitter (604) and four photoelectric detection devices. The fourth beam splitter (604) in the interference point (311) includes two input ports and four output ports. The second light beam (304) and the third light beam (305) are incident from two of the input ports, interfere with the fourth beam splitter (604), and then emit a fourth zero light beam (610), a fourth first light beam (611), a fourth second light beam (612), and a fourth third light beam (613) from the four output ports. The phase shift φ of the fourth zero light beam (610) relative to the second light beam (304) is 20 =0; wherein the phase shift φ of the fourth zero light beam (610) relative to the third light beam (305) 30 =0; wherein the phase shift φ of the fourth light beam (611) relative to the second light beam (304) 21 =-π / 4; wherein the phase shift φ of the fourth light beam (611) relative to the third light beam (305) 31 =+π / 4; wherein the phase shift φ of the fourth second light beam (612) relative to the second light beam (304) 22 =-π / 2; wherein the phase shift φ of the fourth second light beam (612) relative to the third light beam (305) 32 =+π / 2; wherein the phase shift φ of the fourth third light beam (613) relative to the second light beam (304) 23 =-3π / 4; wherein the phase shift φ of the fourth third light beam (613) relative to the third light beam (305) 33 =+3π / 4. The fourth zero light beam (610), the fourth first light beam (611), the fourth second light beam (612), and the fourth third light beam (613) emitted by the fourth beam splitter (604) in the interference point (311) are incident on the four photoelectric detection devices, namely the fourth zero detector (620), the fourth first detector (621), the fourth second detector (622), and the fourth third detector (623). The light intensity of the fourth zero light beam (610) detected by the fourth zero detector (620) is W0; the light intensity of the fourth first light beam (611) detected by the fourth first detector (621) is W1; the light intensity of the fourth second light beam (612) detected by the fourth second detector (622) is W2; and the light intensity of the fourth third light beam (613) detected by the fourth third detector (623) is W3.

[0030] According to formula (33), the phase shift difference Φ3-Φ2 of the second light beam (304) and the third light beam (305) relative to the first light beam (302) is calculated as follows: Φ3-Φ2=arg(W0+jW1-W2-jW3). (36) When the mover (313) and the stator (312) in the grating scale speed measuring device are relatively stationary, Φ3-Φ2 calculated using formula (36) is recorded as Φ0; when the relative speed between the mover (313) and the stator (312) is v, Φ3-Φ2 calculated using formula (36) is recorded as Φ1. The relative speed v between the mover (313) and the stator (312) can be calculated using formula (35).

Claims

1. A grating ruler speed measurement device, characterized by: The grating ruler speed measurement device is composed of a collimated coherent light source, a first light beam, a first beam splitter, a second light beam, a third light beam, a first grating, a second grating, a first interface, a second interface, a third interface, and an interference point; wherein the first beam splitter is used to separate the first light beam emitted by the collimated coherent light source into a second light beam and a third light beam; wherein the second light beam passes through the first interface, the first grating, the second interface, the second grating, and the third interface in sequence, and is diffracted at the first grating and the second grating; wherein the third light beam passes through the first interface, the first grating, the second interface, the second grating, and the third interface in sequence, and is diffracted at the first grating and the second grating; wherein the interference point is used to allow the second light beam and the third light beam to interfere with each other, generating a phase shift between the second light beam and the third light beam. Related interference signals; the collimated coherent light source, the first light beam, the first beam splitting device, the second light beam, the third light beam, and the interference point are always relatively fixed, constituting the stator in the grating scale speed measuring device; the first grating and the second grating are always relatively fixed, constituting the mover in the grating scale speed measuring device; one-dimensional relative displacement can occur between the mover and the stator; the first interface can be fixed relative to the stator or the mover; the second interface can be fixed relative to the stator or the mover; the third interface can be fixed relative to the stator or the mover; the interference signal at the interference point can change with the relative speed between the mover and the stator, and has nothing to do with the relative displacement between the stator and the mover.

2. The grating ruler speed measurement device according to claim 1, characterized in that: The collimated coherent light source is a light source system formed by collimating and expanding a laser, and is capable of outputting a first light beam. The first light beam outputted by the collimated coherent light source has a relatively small beam divergence angle, and the full width at half maximum of the beam divergence angle is less than 10 mrad. The first light beam outputted by the collimated coherent light source has a relatively narrow spectral width, and the full width at half maximum of the spectrum is less than 10 nm.

3. The grating ruler speed measurement device according to claim 1, characterized in that: The first beam splitter can be any one of a non-polarizing beam splitter, a polarizing beam splitter, a blazed grating, and a birefringent crystal, and can separate the first light beam into a second light beam and a third light beam; the first beam splitter comprises at least two input ports and at least two output ports, the first light beam is incident through one of the input ports, and the second light beam and the third light beam are emitted through two of the output ports respectively; the second light beam and the third light beam emitted by the first beam splitter have the same frequency, which is consistent with the frequency of the first light beam incident thereon; correspondingly, the second light beam and the third light beam emitted by the first beam splitter have the same wavelength in vacuum, which wavelength The wavelength of the second light beam and the third light beam emitted by the first beam splitter is consistent with that of the first light beam incident thereon in a vacuum; the second light beam and the third light beam emitted by the first beam splitter have similar intensities, the intensity ratio of the second light beam and the third light beam is between 15:85 and 85:15, preferably between 35:65 and 65:35, and optimally between 45:55 and 55:45; the second light beam and the third light beam emitted by the first beam splitter have a certain phase shift relative to the first light beam incident thereon, the phase shifts of the second light beam and the third light beam relative to the incident light beam can be the same or different, it is better when the absolute value of the difference between the phase shifts is equal to π / 2, and it is optimal when the phase shifts are equal to -π / 4 and +π / 4 respectively.

4. The grating ruler speed measurement device according to claim 1, characterized in that: The first grating is a transmissive or reflective grating that can diffract the second and third light beams. The first grating is based on a glass or metal material and is coated with periodic absorption or reflection stripes. The stripe period of the first grating is between 0.5 μm and 20 μm. The stripe width of the first grating is 1 / 2 of the stripe period and is between 0.25 μm and 10 μm. The stripe direction of the first grating is consistent with the direction of relative displacement between the mover and the stator.

5. The grating ruler speed measurement device according to claim 1, characterized in that: The second grating is a transmissive or reflective grating that can diffract the second and third light beams. The substrate material and stripe material of the second grating are consistent with those of the first grating, and are also based on glass or metal, with periodic absorption or reflection stripes coated on them. The stripe period of the second grating is consistent with that of the first grating, ranging from 0.5 μm to 20 μm. The stripe width of the second grating is 1 / 2 of the stripe period, ranging from 0.25 μm to 10 μm. The stripe direction of the second grating is consistent with the direction of relative displacement between the mover and the stator.

6. The grating ruler speed measuring device according to claim 1, wherein: The first interface can be any one of vacuum, air, water, and glass, and is a transparent medium capable of transmitting the second light beam and the third light beam; the first interface has a high transmittance, and its transmittance is greater than 90%; the first interface has a certain refractive index, and its optimal refractive index is equal to 1; the first interface can be fixed relative to the stator or relative to the mover; the refractive index of the first interface remains consistent throughout the entire range of relative displacement between the mover and the stator.

7. The grating ruler speed measurement device according to claim 1, characterized in that: The second interface can be any one of vacuum, air, water, and glass, and is a transparent medium capable of transmitting the second and third light beams; the second interface has a high transmittance, which is greater than 90%; the second interface has a certain refractive index, which can be the same as or different from the refractive index of the first interface, and is optimally between 1 and 1.5; the second interface can be fixed relative to the stator or the mover; the refractive index of the second interface remains consistent throughout the entire range of relative displacement between the mover and the stator; the second interface has a large optical path difference, and its optical path difference D is greater than 16 times the Talbot distance, that is, D>16z T , where the Talbot distance z T Satisfy z T =2a 2 / λ, where n is the refractive index of the second interface, a is the fringe period of the first grating and the second grating, and λ is the wavelength of the first light beam, the second light beam, and the third light beam in vacuum.

8. The grating ruler speed measuring device according to claim 1, wherein: The third interface described above can be any one of vacuum, air, water, and glass, and is a transparent medium capable of transmitting the second light beam and the third light beam; the third interface has a high transmittance, and its transmittance is greater than 90%; the refractive index of the third interface is the same as that of the first interface, and it is optimal when its refractive index is equal to 1; the third interface can be relatively fixed to the stator or relatively fixed to the rotor; within the entire range of relative displacement between the rotor and the stator, the refractive index of the third interface remains consistent.

9. The first grating, the second grating, the first interface, the second interface, and the third interface according to claims 4-8, characterized in that: The first grating and the second grating are always relatively fixed and constitute the rotor of the grating scale velocity measuring device; in a specific implementation, the first grating, the second grating, and the second interface can be that the two sides of a glass substrate are coated with the same periodic stripes. In this case, the refractive index of the second interface is different from that of the first interface and the third interface, and the first interface and the third interface are relatively fixed to the stator, and the second interface is relatively fixed to the rotor; the first grating, the second grating, and the second interface can also be a combined system of a reflective grating and a reflector, which can make the second light beam and the third light beam emitted by the reflective grating be incident on the reflective grating again through the reflector. In this case, the refractive index of the second interface is the same as that of the first interface and the third interface, and the first interface, the second interface, and the third interface are relatively fixed to the stator; the second light beam and the third light beam sequentially pass through the first interface, the first grating, the second interface, the second grating, and the third interface; the first light beam undergoes -m-order diffraction at the first grating and +m-order diffraction at the second grating; The second light beam undergoes +m-order diffraction at the first grating and -m-order diffraction at the second grating; the diffraction order m is a positive integer and satisfies mλ < na, and it is optimal to take m = 1; the second light beam and the third light beam that have sequentially passed through the first interface, the first grating, the second interface, the second grating, and the third interface have similar intensities, and the intensity ratio of the second light beam and the third light beam is between 15:85 and 85:15, more preferably between 35:65 and 65:35, and most preferably between 45:55 and 55:

45.

10. The grating ruler speed measurement device according to claim 1, characterized in that: The interference point is a measurement system composed of a beam splitting device and at least 3 photodetectors; the beam splitting device in the interference point includes at least 2 input ports and at least 3 output ports, and the number of output ports is the same as the number of photodetectors; the photodetectors in the interference point correspond one-to-one with the output ports on the beam splitting device and are used to measure the light intensity of the light beam emitted from the corresponding output port on the beam splitting device. The second beam and the third beam are incident through two input ports on the beam splitting device; the phase shifts of the beams emitted by the beam splitting device in the interference point relative to the second beam and the third beam incident on it are φ 2o and φ 3o , where o is a non - negative integer, representing the beam emitted from the output port with the corresponding number in the beam splitting device, satisfying o < N, where N is the number of output ports on the beam splitting device and the number of photodetectors; the phase shifts of the beams emitted from the output ports with the corresponding numbers on the beam splitting device in the interference point relative to the second beam and the third beam satisfy |φ 3o - φ 2o | = 2πo / N, and the condition φ 2o = -πo / N, φ 3o = +πo / N is optimal.

11. The grating ruler speed measurement device according to claim 1, characterized in that: The interference point can detect the light intensity emitted from the N output ports of the beam splitter through the N photoelectric detection devices, calculate the phase shift difference between the second light beam and the third light beam relative to the first light beam, and estimate the relative speed between the mover and the stator; in a specific implementation, the light intensity of the light beam emitted from the output port numbered o in the beam splitter obtained by the photoelectric detection device is W o According to the formula The phase shift difference Φ3 - Φ2 between the second light beam and the third light beam relative to the first light beam can be calculated; according to the formula The relative velocity v between the rotor and the stator can be calculated, where Φ0 is the Φ3 - Φ2 measured when the rotor and the stator are relatively stationary, and Φ1 is the Φ3 - Φ2 measured when the relative velocity between the rotor and the stator is v.

12. The grating ruler speed measurement device according to claim 1, characterized in that: The phase shift difference between the second and third light beams relative to the first light beam measured at the interference point can change with the relative speed between the mover and the stator, and is independent of the relative displacement between the stator and the mover. By calculating the phase shift difference between the second and third light beams relative to the first light beam, direct measurement of the relative speed between the mover and the stator can be achieved.

Images