WO2023155657A1 - Codeur à réseau absolu à six degrés de liberté - Google Patents

Codeur à réseau absolu à six degrés de liberté Download PDF

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Publication number
WO2023155657A1
WO2023155657A1 PCT/CN2023/073097 CN2023073097W WO2023155657A1 WO 2023155657 A1 WO2023155657 A1 WO 2023155657A1 CN 2023073097 W CN2023073097 W CN 2023073097W WO 2023155657 A1 WO2023155657 A1 WO 2023155657A1
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Prior art keywords
absolute
freedom
degree
grating
measurement module
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PCT/CN2023/073097
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English (en)
Chinese (zh)
Inventor
李星辉
汪盛通
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清华大学深圳国际研究生院
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Publication of WO2023155657A1 publication Critical patent/WO2023155657A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/36—Forming the light into pulses
    • G01D5/38—Forming the light into pulses by diffraction gratings

Definitions

  • the invention relates to the technical field of pose measurement, in particular to an absolute six-degree-of-freedom grating encoder.
  • the electromagnetic measurement method there are electromagnetic displacement measurement and optical displacement measurement, among which the electromagnetic measurement method Among them, the accuracy of the capacitive sensor can reach the nanometer level, and it is a multi-degree-of-freedom measurement system composed of multiple capacitive sensors. At present, it has been used for real-time detection of the sub-mirror pose of the Keck and Canary large telescopes, which has high accuracy and stability, but the measurement system composed of capacitive sensors is not only complicated, but also sensitive to temperature and humidity. There is a problem of large errors in accumulation.
  • the invention provides an absolute six-degree-of-freedom grating encoder, which includes a light source module, an absolute four-degree-of-freedom measurement module, and an absolute two-degree-of-freedom measurement module; the collimated light beam generated by the light source module passes through a polarization beam splitter Generate the first collimated beam L1 and the second collimated beam L2, the second collimated beam L2 is first divided into the beam L2-1, the beam L2-2 and the beam L2-3 through the composite grating beam splitting module, the beam L2-1 utilizes The two-dimensional grating area of the composite grating generates diffracted light, and the diffracted light is measured by the absolute four-degree-of-freedom measurement module to measure the absolute pose of the composite grating in the ⁇ x , ⁇ y , ⁇ z and z directions, the beam L2-2 and the beam L2- 3 Enter the X reference code channel through the X-direction mask, and enter the Y reference code channel through the Y-dire
  • the X-direction mask and the X reference code have the same code
  • the reference code track has the same code
  • a negative pulse is generated to mark the zero position
  • the beam L2-1 passes through the compound grating
  • the light beam produced by the diffraction of the grating area, and the beam produced by the first collimated light beam L1 in the two-dimensional reference grating produce interference phenomenon, and is received by the absolute two-degree-of-freedom measurement module, and the phase change in the x and y directions is analyzed to obtain the displacement Incremental information and the pulse signal generated at the same time can be zero-calibrated for incremental displacement to obtain its absolute displacement.
  • the absolute four-degree-of-freedom measurement module includes three four-quadrant photodetectors.
  • the diffracted light includes ⁇ 1st-order diffracted light and zero-order light in the x direction, the positions of the three beam spots on the four-quadrant photodetector change, and the ⁇ x , ⁇ y , ⁇ z and z directions are calculated absolute pose.
  • the absolute two-degree-of-freedom measurement module includes a two-degree-of-freedom incremental signal measurement module and a two-degree-of-freedom zero pulse signal measurement module.
  • the DC removing module includes a depolarizing beam splitter, a first polarizing plate, a third quarter glass plate, a second polarizing plate and a photodetector.
  • the two-degree-of-freedom zero pulse signal measurement module includes a composite grating spectroscopic module and a photodetector.
  • the two-degree-of-freedom zero-position pulse signal measurement module enters the two beams of light L2-2 and L2-3 into the X reference code track through the X-direction mask plate, and enters the Y reference code track through the Y-direction mask plate .
  • the two-degree-of-freedom incremental signal measurement module generates x s+1 , x s-1 , y s+1 and y s-1 beams through the two-dimensional grating area of the composite grating, and generates the two-dimensional reference grating
  • the x r+1 , x r-1 , y r+1 and y r-1 light beams produce interference phenomenon, and are received by the photodetector, and the phase changes in the x and y directions are respectively analyzed to obtain the displacement incremental information, and at the same time
  • the generated pulse signal can be used for zero calibration of the incremental displacement to obtain its absolute displacement.
  • the light source module includes a collimating lens and a diaphragm.
  • the present invention can more stably and accurately measure the absolute pose of the sub-mirror in six degrees of freedom, and has the advantage of being able to measure the absolute pose compared with the known solutions, with simple structure, more stability and stronger robustness. Because the measurement accuracy of the grating encoder mainly depends on the pitch of the grating, the physical structure is not easy to change, so it is more robust. And compared with the capacitive displacement sensor currently used, it has better robustness, is hardly affected by large changes in ambient temperature, humidity, etc., and has better integration, which can realize the measurement of absolute pose.
  • FIG. 1 is a schematic plan view of an absolute six-degree-of-freedom grating encoder provided by an embodiment of the present invention
  • Fig. 2 is a three-dimensional structural schematic diagram of an absolute six-degree-of-freedom grating encoder provided by an embodiment of the present invention
  • Fig. 3 is the main diagram of the composite grating provided by the embodiment of the present invention.
  • FIG. 4 is a schematic diagram of an X-direction mask plate provided by an embodiment of the present invention.
  • FIG. 5 is a schematic diagram of a Y-direction mask plate provided by an embodiment of the present invention.
  • FIG. 6 is a schematic structural diagram of a composite grating light splitting module provided by an embodiment of the present invention.
  • FIG. 7 is a schematic diagram of assembly site measurement points provided by an embodiment of the present invention.
  • Fig. 8 is a schematic diagram of spot measurement points for pose adjustment provided by an embodiment of the present invention.
  • Fig. 9 is a schematic diagram of the change rule of the spot position with the displacement provided by the embodiment of the present invention.
  • Fig. 10 is a schematic diagram of a DC optical path module
  • Fig. 11 is a schematic diagram of the generation principle of the pulse signal
  • Fig. 12 is a schematic diagram of the generation form of the pulse signal
  • Figure 13 is a schematic diagram of the detection of the absolute position
  • Fig. 14 is a schematic diagram of the zero point marked by the zero position signal on the incremental signal
  • Fig. 16 is a schematic diagram of the relationship between the phase and the displacement of the reading head within the incremental signal period
  • Fig. 18 is a schematic diagram of single-point measurement composite integrated grating
  • the second beam splitting prism BS2 splits x s+1 , x s-1 and zero-order light, and the generated beam is set to x ⁇ s+1 , x ⁇ s-1 and zero Level light enters the absolute four-degree-of-freedom measurement module, and the absolute pose in the ⁇ x , ⁇ y , ⁇ z and z directions can be obtained by decoupling the position changes of the three light spots on the four-quadrant photodetector.
  • the absolute two-degree-of-freedom measurement module 30 includes a two-degree-of-freedom zero pulse signal measurement module and a two-degree-of-freedom incremental signal measurement module.
  • the two-degree-of-freedom zero pulse signal measurement module includes a polarization beamsplitter prism PBS, a second quarter-wave plate QWP2, a second beam-splitting prism BS2, a first prism collimation unit 1, a first quarter-wave plate QWP1, and a first quarter-wave plate QWP1.
  • the actual use is the splicing of multiple sub-mirrors.
  • All the sub-mirrors are spliced into a complete telescope main mirror at the assembly site, and the wavefront sensor is used to adjust the pose of each sub-mirror until the wavefront sensor obtains a complete interference image without distortion.
  • the relative pose of the two sub-mirrors can be guaranteed to return to the pose state of the assembly stage, and then the installation of the rest of the sub-mirrors can be completed.
  • the posture is monitored during use for the actuator to adjust the posture.
  • the absolute six-degree-of-freedom readhead can obtain the pose data of the sub-mirror in real time, and the active controller can adjust the sub-mirror according to the feedback information.
  • Mirror pose to restore to the pose state of each sub-mirror of the telescope in the assembly stage. In this way, a closed-loop control system is formed, which can adjust the position and orientation of the sub-mirror in real time when the telescope is working.
  • the specific positions x A , y A , x B , y B , x C , y C of the light spot are calculated according to the back-end photocurrent information I, and the specific calculation formula can be expressed as:
  • the coordinates of the spot position are transformed into the coordinates of the origin, that is, when it is not measured, its coordinate system is artificially defined, so that all diffracted light can be located at the origin of the coordinates.
  • Figure 9 shows the position change of the light spot when the specified displacement of the measurement grating occurs.
  • the position of the spot on the four-quadrant photodetector QPDA and the four-quadrant photodetector QPDC will also change under the influence of the attitude changes of ⁇ x and ⁇ y , which can be calculated by the asymmetric influence factor and the influence can be excluded.
  • the ⁇ z attitude change only changes the y-direction spot position of QPDA and QPDB
  • the z-direction attitude change only changes the x-direction spot position of QPDA and QPDB
  • the z direction at this time is measured by the incremental displacement module, and the data value is the incremental displacement.
  • the absolute four-degree-of-freedom measurement module it can be converted into absolute position coordinates.
  • the two-dimensional reference grating and the incremental grating have the same grating period, so when the reading head moves along the X direction, the photodetector PD3 and photodetector PD4 convert the interference signal into an electrical signal at the coincident beam for processing and calculation to obtain the incremental displacement information.
  • the second collimated light beam L2 emitted by the second beam-splitting prism BS2 passes through the composite grating beam-splitting module 4, and then splits into beams L2-1, L2-2, and L2-3, respectively irradiating the two-dimensional grating areas 5-1, X-direction reference code track 5-2 and Y-direction reference code track 5-3, light beam L2-2 and L2-3 respectively pass through the X-direction mask and the Y-direction mask and reflect to the photodetector PD1 and photodetector PD2.
  • the X-direction mask, the Y-direction mask and the corresponding reference code track are equipped with zero marks of the same code.
  • the photodetector can detect a corresponding negative pulse zero position signal, and the generation principle and form of the pulse signal are shown in Fig. 11 and Fig. 12 .
  • the light beams L2-2 and L2-3 can pass through the X-direction mask and the Y-direction mask respectively to the X reference code track and the Y reference code track, and finally Received by photodetectors PD1 and PD2 respectively. Therefore, when the X-direction mask and the Y-direction mask are displaced relative to the composite grating, the reflected light signals received at PD1 and PD2 are a negative pulse signal.
  • the absolute position of the current reading head can be obtained according to the incremental signal and the zero position signal.
  • a negative pulse signal is formed after the first zero mark, and the reference point R1 is determined by the pulse signal.
  • the zero negative pulse signal can determine the reference point Point R2, and finally the reading head continues to move to A and stops.
  • the distance between the reference points R1 and R2 is D1
  • the distance between the reference point R2 and the reference point R3 is D2
  • so on are respectively D3, D4, D5, . . . .
  • D1, D2, D3, etc. are set as distance codes.
  • the incremental signal can calculate the incremental displacement between any adjacent zero reference points.
  • the zero signal and the reference signal are sampled at the same time. According to the reference points R1 and R2 determined by the zero signal, the corresponding incremental signal from R1 to R2 can be calculated. Displacement, by which the absolute position is determined against the coded distance.
  • the absolute positions of R1 and R2 are determined, the current position PA of the reading head can be calculated according to the geometric position relationship, as shown in Figure 13.
  • phase cooperation for positioning within the range of zero pulse positioning accuracy, which is a combination of coarse and fine positioning, as shown in Figure 14 and Figure 15. That is, within the pulse positioning range, only the pulse peak can be fitted, so the position of the pulse tip point changes with the degree of fitting within this range, and the accuracy cannot be guaranteed. Therefore, with the help of the phase assistance of the incremental signal, within each different pulse positioning accuracy range, it corresponds to a certain phase in a 0.5 ⁇ m phase in the incremental signal, that is, the zero true value point. Finally, there is no need for fitting to find the pulse tip point, and the absolute positioning analysis is performed on this true value point, which avoids errors caused by noise and data fluctuations, and its positioning accuracy is directly related to the subdivision accuracy of the incremental signal of the grating ruler.
  • ⁇ X is the phase of the incremental signal
  • ⁇ X0 is the initial phase of the incremental signal
  • ⁇ X is the incremental displacement in the X direction
  • g is the grating pitch of the measuring grating.
  • phase displacement of the incremental signal is shown in Figure 16.
  • This position (phase) in the incremental signal period can be marked as the position of the zero pulse.
  • the three-dimensional structural diagram of the single-point measurement absolute six-degree-of-freedom grating encoder is shown in Figure 17, the single-point measurement composite integrated grating 6 is shown in Figure 18, and the single-point measurement composite integrated mask 7 is shown in Figure 19.
  • the X- and Y-direction reference code tracks of the composite grating are integrated with the two-dimensional grating area.
  • the advantage is that a single measuring point can generate the required five beams of diffracted light, avoiding the Abbe error. While ensuring the interference effect of the grating diffracted light, the reference code in the grating area can be used for absolute positioning, forming an absolute six-degree-of-freedom grating encoder with a single measuring point.
  • an image analysis method can be used to analyze the position of the measuring grating relative to the mask.
  • the judgment process is to extract the image codes of the mask plate and the measurement grating respectively, and perform real-time position comparison.
  • the degree of overlap and direction between the two changes with the position, so as to obtain the absolute coordinates in the x and y directions.

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  • General Physics & Mathematics (AREA)
  • Optical Transform (AREA)

Abstract

Codeur à réseau absolu à six degrés de liberté. Un faisceau collimaté qui est généré par un module de source de lumière (10) traverse un PBS pour générer un faisceau L1 et un faisceau L2. Le faisceau L2 est d'abord divisé en un faisceau L2-1, un faisceau L2-2 et un faisceau L2-3 au moyen d'un module de division de lumière à réseau composite (4). Le faisceau L2-1 génère une lumière diffractée à l'aide d'une région de réseau bidimensionnel (5-1) d'un réseau composite (5), et la lumière diffractée traverse un module de mesure absolue à quatre degrés de liberté (20) pour mesurer une pose absolue du réseau composite (5) dans des directions θx, θy, θz et z. Le faisceau L2-2 et le faisceau L2-3 entrent respectivement dans des canaux de code de référence par le biais d'un masque de direction X et d'un masque de direction Y. Les masques présentent le même code que les canaux de code de référence et, lorsqu'ils sont alignés avec les canaux de code, les masques génèrent une impulsion négative, de façon à marquer une position zéro. Des faisceaux qui sont générés par la diffraction du faisceau L2-1 et des faisceaux qui sont générés par le faisceau L1 au niveau d'un réseau de référence bidimensionnel (3) génèrent un phénomène d'interférence, et sont reçus par un module de mesure absolue à deux degrés de liberté (30), des changements de phase dans une direction x et une direction y sont analysés pour obtenir des informations d'incrément de déplacement, et une pose absolue correspondante est obtenue au moyen du couplage d'une marque de l'impulsion négative.
PCT/CN2023/073097 2022-02-21 2023-01-19 Codeur à réseau absolu à six degrés de liberté WO2023155657A1 (fr)

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CN114459516B (zh) * 2022-02-21 2023-07-28 清华大学深圳国际研究生院 一种绝对式六自由度光栅编码器
CN114877809B (zh) * 2022-05-27 2023-10-20 中北大学 一种基于二维复合平面大量程光栅结构的位移测量系统

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