Three-dimensional linear quantity simultaneous measurement and compensation system and method based on single detector

Abstract

The invention provides a three-dimensional linear quantity simultaneous measurement and compensation system based on a single detector, and belongs to the technical field of optical precision measurement instruments. The system structure is simplified, synchronous measurement of three-dimensional linear quantity (X-axis length and Y / Z-axis straightness) and light two-dimensional drift angle (pitch / deflection angle drift) is realized by using a single four-quadrant detector, a compensation model is established based on angle drift, interference to straightness error is reduced, measurement precision, stability and integration are improved, and the system is suitable for large-scale popularization and application. And finally, the problems of complexity and coupling in multi-dimensional geometric error measurement are solved, and simultaneous high-precision measurement of multi-degree-of-freedom errors is realized. The optical path design is simplified, and the measurement stability is improved.

Description

Technical Field

[0001] This invention relates to the field of optical precision measuring instrument technology, specifically to a system and method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector. Background Technology

[0002] In high-end equipment fields such as precision manufacturing, micro-nano fabrication, and aerospace assembly, the demand for high-precision measurement of three-dimensional linear quantities of moving parts (including X-axis length error and Y / Z-axis straightness error) and two-dimensional light drift angles (pitch and yaw drift) is constantly increasing. However, these parameters are often coupled with each other, especially in long-distance optical path propagation. Affected by environmental disturbances such as temperature gradients, airflow, and mechanical vibration, angle drift and straightness error are superimposed, significantly reducing measurement accuracy. Existing laser interferometers are mostly limited to single-degree-of-freedom measurement, making it difficult to achieve simultaneous acquisition of multi-dimensional errors; while existing multi-degree-of-freedom measurement systems generally rely on multiple detectors and complex optical paths, which are not only bulky and difficult to adjust, but also lack effective compensation for errors caused by angle drift in straightness measurement. The proposed six-degree-of-freedom error measurement methods, including linear and rotational axes, also suffer from the problem of system complexity due to multiple detectors and multiple optical paths.

[0003] Existing measurement systems neglect the additional impact of angle drift on beam offset in straightness error assessment, failing to compensate for it in real time and resulting in reduced measurement accuracy. An integrated method is needed to simultaneously measure three-dimensional linear quantities and two-dimensional drift angles using a single four-quadrant detector, and to establish a compensation model to eliminate the interference of angle drift on straightness error, thereby improving system stability and reliability. Therefore, the objective of this invention is to propose a compact integrated system based on a single detector, enabling simultaneous measurement of three-dimensional linear quantities (X-direction length, Y / Z straightness) and two-dimensional beam drift angles (pitch / yaw), and effectively correcting straightness error through an angle compensation model to improve overall measurement accuracy and system stability.

[0004] With the rapid development of precision machinery, aerospace, ultra-precision motion platforms, and high-end equipment manufacturing technologies, higher requirements are being placed on the measurement of geometric errors of objects in three-dimensional space. In CNC machine tools, coordinate measuring machines, and optical assembly platforms, geometric errors directly affect machining and assembly accuracy. These errors include linear displacement (length and straightness). Especially in long-distance optical paths, the light beam is easily affected by environmental factors such as air disturbances, thermal gradients, and vibrations, leading to wavefront tilt and phase changes, which affect the accuracy of linear displacement measurement. Traditional optical measurement techniques, such as laser interferometers, have been widely used in length measurement, but they are difficult to process multi-dimensional parameters simultaneously and lack error compensation mechanisms.

[0005] Traditional laser interferometers (such as the Michelson interferometer) are mainly used for length measurement in a single direction, utilizing optical path difference to generate interference fringes for demodulation displacement. In recent years, multi-channel interferometric systems have attempted to achieve three-dimensional measurement, for example, systems using multiple detectors combined with beam splitters to separate the measurement light and reference light, thereby achieving X-axis length and Y / Z-axis straightness measurement. However, these schemes require multiple independent detectors (such as PSDs, CCDs, or QPDs).

[0006] Chinese invention patent application No. 2021113387116 discloses a method and system for simultaneously measuring multi-degree-of-freedom geometric errors using lasers. When measuring three-degree-of-freedom linear errors, it employs multiple detectors and interferometric length measurement modules (such as a first analyzer, an unpolarized beam splitter, and a phase retarder). This results in a complex system structure, cumbersome optical adjustments, high costs, and a large measurement system size, hindering integrated applications. Furthermore, in this method and system for simultaneously measuring multi-degree-of-freedom geometric errors, angular drift during straightness measurement interferes with the results. Without a real-time compensation model, the accuracy of straightness measurement is easily affected by environmental disturbances. Summary of the Invention

[0007] The purpose of this invention is to provide a system and method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector, so as to solve at least one of the technical problems existing in the background art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a three-dimensional linear quantity simultaneous measurement and compensation system based on a single detector, comprising a measurement unit and a target mirror unit. The measurement unit includes a laser emission module, a half-wave plate, a polarizing beam splitter, a fixed reflector, a right-angle reflector, an analyzer, and a four-quadrant photodetector. The target mirror unit includes a movable reflector.

[0010] The laser emission module is used to generate emitted light;

[0011] The half-wave plate is used to adjust the polarization direction of the outgoing polarized light. When the optical axis of the outgoing light is aligned with the polarizing beam splitter, the half-wave plate can be removed.

[0012] The polarizing beam splitter is used to split polarized light into measurement light and reference light;

[0013] The measurement light, carrying error information, is reflected by the moving reflector and returns to the measurement unit. After being combined with the reference light, it is interfered with the four-quadrant detector by the right-angle mirror and the analyzer, thus realizing the spatial superposition and interference of the beams.

[0014] As a further limitation of the first aspect of the present invention, the laser emission module is a dual-frequency laser; the fixed reflector and the moving reflector are both corner cube prisms.

[0015] As a further definition of the first aspect of the invention, the analyzer is a 45° analyzer.

[0016] Secondly, the present invention provides a method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector, applied to the system described in the first aspect, to realize the measurement of straightness error along the Y-axis and Z-axis based on the laser collimation principle, including:

[0017] The output light of the dual-frequency laser is adjusted to align its polarization direction with the optical axis by passing through a half-wave plate, forming linearly polarized light. When the linearly polarized light is incident on a polarizing beam splitter, it is split into a measurement light and a reference light. The measurement light is transmitted through the polarizing beam splitter, and the reference light is reflected by the polarizing beam splitter. Both the measurement light and the reference light are linearly polarized, and their polarization directions are perpendicular to each other.

[0018] After the measurement light is emitted from the measurement unit, it is incident on the target mirror unit. After being reflected back by the corner prism of the target mirror unit, the spatial position of the measurement light changes with the straightness error of the target mirror unit along the Y-axis and Z-axis. The measurement light carries this two-dimensional straightness error information back to the measurement unit, so that the measurement light passes through the polarization beam splitter again.

[0019] After the reference light is reflected back by the fixed-angle cone prism, it passes through the polarizing beam splitter again and is combined with the measuring light that has passed through the polarizing beam splitter again. Then, after the beam propagation direction is changed by the right-angle mirror, it passes through the analyzer set at 45°, and the polarization direction is unified, causing interference and incident on the four-quadrant detector. The overlapping part of the combined beam spot formed by the two beams interferes to generate an AC signal, while the non-overlapping part is a DC component.

[0020] The four-quadrant detector receives the combined beam spot, and its DC component reflects the center position of the combined beam spot. The initial position of the combined beam spot is recorded, with the optimal overlap between the two beam spots being the initial position, located at the center of the four-quadrant photodetector. The current position of the combined beam spot is recorded and compared with the initial position to obtain the change in the position of the combined beam spot. Since the change in the position of the combined beam spot is caused by the change in the position of the measurement light, which leads to changes in the overlap between the two beam spots and their positions on the detector, the straightness error of the target mirror unit along the Y-axis and Z-axis is calculated based on the DC change generated in the change in the position of the combined beam spot.

[0021] As a further limitation of the second aspect of the present invention, the realization of X-direction length error measurement based on laser heterodyne interferometry includes:

[0022] The output light of the dual-frequency laser is orthogonally polarized light with a fixed frequency difference. After the polarization direction is adjusted to be aligned with the optical axis by a half-wave plate, the output light is then incident on a polarizing beam splitter.

[0023] A polarizing beam splitter splits the outgoing light into a reference beam and a measurement beam based on the polarization state of the outgoing light. The reference beam propagates inside the measurement unit and is reflected back by the fixed-angle prism of the measured unit. The polarization direction, frequency, and phase are theoretically unchanged, thus constituting the reference beam for interferometric measurement.

[0024] The measuring light is transmitted through a polarizing beam splitter and directed toward a target mirror unit. It is then reflected back to the polarizing beam splitter by the target mirror mounted on the object under test. The displacement of the target mirror under test in the X-axis direction causes a change in the round-trip optical path of the measuring light, which in turn causes a change in its phase. This axial displacement information is then returned to the measuring unit.

[0025] The reference light and the measurement light are spatially superimposed at the polarization beam splitter to obtain a combined beam. The combined beam is reflected by the right-angle mirror and then passes through the analyzer 6 set at 45°, so that the two beams of light that were originally orthogonally polarized are converted to the same polarization state in the polarization direction and interfere. The interference fringes illuminate the surface of the four-quadrant detector.

[0026] Since the reference light and the measurement light propagate parallel to each other in space, the interference wavefront is approximately flat relative to the surface of the four-quadrant detector. Therefore, the phase changes of the interference fringes received by the four quadrant detectors are approximately the same. By demodulating the interference intensity signals output from the four quadrants, the total displacement can be approximated as the average value of the phase changes in all quadrants. ;

[0027] The average phase change represents the phase difference between the measurement light and the reference light caused by the X-axis displacement. This average phase signal, together with the reference beat frequency signal provided by the dual-frequency laser itself, is input to the phase calculation module, and the displacement change in the X-axis direction is extracted by heterodyne demodulation.

[0028] As a further limitation of the second aspect of the present invention, the displacement change in the X-axis direction is extracted by heterodyne demodulation, and is proportional to the average value of its phase change, i.e. If the output wavelength of the dual-frequency laser is λ, then the displacement Δx of the target mirror unit in the X-axis direction is N( )·λ / 2, where N is the stripe count.

[0029] As a further limitation of the second aspect of the present invention, the measurement of pitch and yaw angle drift based on differential wavefront measurement includes: in the X-direction length error measurement based on laser heterodyne interferometry, the reference light propagates within the measurement unit, has a short path, and is generally in a closed environment of the mechanical housing, making it stable and reliable with virtually no directional change; while the measurement light needs to travel back and forth between the measurement unit and the target mirror unit, and its propagation direction drifts in space, manifested as the light direction deviating from the original propagation axis, i.e., producing an angular drift in the propagation direction; when the measurement light is disturbed and deviates from the optical axis during its round-trip propagation, forming a propagation direction offset Δθ, the beam direction of its return path will no longer completely coincide with the reference light; due to The measurement light is deflected, creating a small angle between the P-beam and S-beam in the combined beam. This causes the interference wavefront to no longer be an ideal plane, but rather exhibit a certain tilt or curvature. After being reflected by a right-angle mirror, the combined beam passes through a 45° analyzer, converting the originally orthogonally polarized P-beam and S-beam into the same polarization state, resulting in interference on the surface of the four-quadrant detector. Due to the angular drift of the measurement light, the interference wavefront changes accordingly, no longer parallel to the surface of the four-quadrant detector, but rather a tilted wavefront with a certain slope. This leads to phase differences in the interference fringes received in each quadrant of the four-quadrant detector. The system performs heterodyne demodulation on the interference signals acquired in the four quadrants of the four-quadrant detector to obtain the phase changes in each quadrant. , , , If the phases of the upper and lower quadrants of the four quadrants of the four quadrant detector are different, it indicates that the measurement light has undergone a change in pitch angle around the Y-axis; if the phases of the left and right quadrants of the four quadrant detector are different, it indicates that the measurement light has undergone a change in yaw angle around the Z-axis. Based on the differential wavefront measurement principle, the angle drift is calculated using the phase distribution characteristics between the quadrants of the four quadrant detector. The pitch and yaw angle drifts caused by factors such as airflow disturbances can be calculated by using the phase weighted average of adjacent quadrants.

[0030] As a further limitation of the second aspect of the invention, the drift due to the ray sway angle and the pitch angle can be calculated respectively by using the phase-weighted average of adjacent quadrants:

[0031] ;

[0032] .

[0033] As a further limitation of the second aspect of the present invention, the measurement of straightness error in the Y / Z direction based on the measured angle error compensation includes:

[0034] In the measurement of straightness error along the Y-axis and Z-axis based on the laser collimation principle, the straightness errors Δy and Δz of the target mirror unit II along the Y-axis and Z-axis directions are measured by the laser collimation principle. These errors include the actual position error and the additional offset caused by beam deflection.

[0035] In realizing the X-direction length error measurement based on laser heterodyne interferometry, the system, based on the differential wavefront measurement principle, has extracted the pitch angle drift θ of the measurement light around the Y-axis during propagation. Y With the yaw angle drift θ around the Z-axis Z This angle information can accurately reflect the amount of drift in the direction of light propagation.

[0036] As a further limitation of the second aspect of the present invention, an error compensation model is established based on the angle drift θ. Y θ Z The geometric relationship between the measured light propagation distance D and the calculated additional spot offset caused by angular drift is used to calculate the additional spot offset caused by angular drift.

[0037] The spot position offset value measured by the original four-quadrant detector in the straightness error measurement along the Y-axis and Z-axis based on the laser collimation principle is corrected to remove the additional offset caused by angle drift in order to obtain the true straightness error.

[0038] Terminology Explanation:

[0039] Six-degree-of-freedom geometric errors: In the XYZ three-dimensional coordinate system, the geometric errors generated when an object moves include linear errors (position / straightness) along the X, Y, and Z directions, as well as angular errors (roll, pitch, and yaw) around the X, Y, and Z axes.

[0040] Three-dimensional linear quantities: In the XYZ three-dimensional coordinate system, these include length errors along the X-axis and straightness errors along the Y and Z axes.

[0041] Two-dimensional light drift angle: The tiny angular deviation of a laser beam around the Y and Z axes caused by environmental disturbances and other factors during its propagation along the X-axis, i.e., the pitch angle drift error and the yaw angle drift error.

[0042] Quadrant Photodetector (QPD): A type of photodetector, it consists of four photodiodes with identical performance arranged in a rectangular coordinate system. It can simultaneously detect changes in the position of the light spot on the detection surface, the phase difference of the interference fringes, and the intensity distribution. It is the core detection element of this invention.

[0043] Cornerstone prism / hollow cornerstone prism: It has back reflection characteristics and can strictly reflect the incident light back to the incident direction. It is widely used in high-precision interferometry.

[0044] Spot position change method: By analyzing the position change of the returned spot on the four-quadrant detector, the corresponding straightness error in the X and Y directions is calculated.

[0045] Heterodyne interferometry: an interferometric measurement method based on a dual-frequency laser. The dual-frequency laser outputs two orthogonally polarized beams with a fixed frequency difference, which form a beat frequency signal through interference, enabling high-precision length measurement.

[0046] Differential wavefront principle: Based on the phase difference of interference fringes received in adjacent quadrants, the tilt of the wavefront is reflected, and then the angular drift of the light is measured.

[0047] Target mirror unit: A reflective component mounted on the object under test, used to reflect the measurement beam back and carry the geometric error information of the object under test.

[0048] Measurement unit: An assembly containing a laser source, optical beam splitters and combiners, and detectors, used to emit laser light, process the returned beam, and extract error signals.

[0049] Light ray naming rules: It always starts with L, and after each optical element it passes through, a number is added (such as L1, L2, L21, L22). The number 1 usually indicates the transmission path, and the number 2 indicates the reflection path.

[0050] The beneficial effects of this invention are: it simplifies the system structure, utilizes a single four-quadrant detector to achieve simultaneous measurement of three-dimensional linear quantities (X-axis length, Y / Z-axis straightness) and two-dimensional light drift angles (pitch / yaw angle), and establishes a compensation model based on angle drift to reduce the interference of air drift on straightness error, thereby improving measurement accuracy, stability and integration. Ultimately, it solves the complexity and coupling problems in multi-dimensional geometric error measurement, and achieves high-precision measurement of multi-degree-of-freedom errors simultaneously; it also simplifies the optical path design and improves measurement stability.

[0051] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a structural diagram of the transmission-type three-dimensional linear quantity simultaneous measurement and compensation system based on a single detector, as described in an embodiment of the present invention.

[0054] Figure 2 This is a flowchart of the method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector, as described in an embodiment of the present invention.

[0055] Figure 3 This is a structural diagram of the reflective three-dimensional linear quantity simultaneous measurement and compensation system based on a single detector, as described in an embodiment of the present invention.

[0056] Figure 4 This is a structural diagram of the simultaneous measurement and compensation system for three-dimensional linear quantities based on a single detector with added waveplates, as described in an embodiment of the present invention. Detailed Implementation

[0057] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0058] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as here.

[0060] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.

[0061] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0062] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0063] In the description of this specification, the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this technology and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this technology.

[0064] Unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of these terms in this art according to the specific circumstances.

[0065] To facilitate understanding of the present invention, the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments, and the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0066] Those skilled in the art should understand that the accompanying drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily essential for implementing the present invention.

[0067] like Figures 1 to 2 As shown, in this embodiment, a three-dimensional linear quantity simultaneous measurement and compensation system based on a single detector is first provided, including a measurement unit and a target mirror unit. The measurement unit includes a laser emission module, a half-wave plate, a polarizing beam splitter, a fixed reflector, a right-angle reflector, an analyzer, and a four-quadrant detector; the target mirror unit includes a movable reflector.

[0068] The laser emission module is used to generate emitted light;

[0069] The half-wave plate is used to adjust the polarization direction of the outgoing light. When the optical axis of the outgoing light is aligned with the polarizing beam splitter, the half-wave plate can be removed.

[0070] The polarizing beam splitter is used to split polarized light into measurement light and reference light;

[0071] The measurement light, carrying error information, is reflected by the moving reflector and returns to the measurement unit. After being combined with the reference light, it is interfered with the four-quadrant detector by the right-angle mirror and the analyzer, thus realizing the spatial superposition and interference of the beams.

[0072] In one specific embodiment, the laser emission module is a dual-frequency laser; both the fixed reflector and the movable reflector are corner cube prisms. The analyzer is a 45° analyzer.

[0073] like Figure 2 As shown, in this embodiment, a method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector is implemented using the aforementioned system. Combined with... Figure 1 In this embodiment, the measurement unit I emits a dual-frequency laser L1, which is polarized to L2 by a half-wave plate 2. The polarization beam splitter 3 splits the beam into a measurement beam L21 (transmitted to the target mirror unit II) and a reference beam L22 (reflected to the fixed-angle cone prism 4). The measurement beam L21 is reflected back by the target mirror, carrying error information, and is combined with the reference beam L22 to form L3. This L3 then interferes with the four-quadrant detector via a right-angle mirror 5 and a 45° analyzer 6. This structure achieves spatial superposition and interference of the beams. The entire measurement process is performed synchronously, including measuring straightness by changing the spot position, measuring length by averaging the phase values, measuring angle by quadrant phase difference, and compensating for straightness based on an angle model.

[0074] Step 1: Measure the straightness error along the Y-axis and Z-axis based on the laser collimation principle.

[0075] Step 1.1: The output light L1 of the dual-frequency laser 1 is adjusted by the half-wave plate 2 to align its polarization direction with the optical axis, forming linearly polarized light L2. When L2 is incident on the polarizing beam splitter 3, it is split into measurement light L21 and reference light L22. The measurement light L21 is transmitted through the polarizing beam splitter 3, and the reference light L22 is reflected by the polarizing beam splitter 3. Both the measurement light L21 and the reference light L22 are linearly polarized, and their polarization directions are perpendicular to each other.

[0076] Step 1.2: After the measurement light L21 is emitted from the measurement unit I and incident on the target mirror unit II, it is reflected back by the corner prism 7 of the target mirror unit II. The spatial position of L21 changes with the straightness error of the target mirror unit II along the Y-axis and Z-axis. L21 carries the two-dimensional straightness error information back to the measurement unit I, so that L21 passes through the polarization beam splitter 3 again.

[0077] Step 1.3: After the reference light L22 is back-reflected by the fixed corner bevel prism 4, it passes through the polarizing beam splitter 3 again and is combined with L21, which passed through the polarizing beam splitter again in step 1.2. This combined beam is denoted as L3. Then, after the beam propagation direction is changed by the right-angle mirror 5, it passes through the analyzer 6 set at 45°. The polarization direction is unified, interference occurs, and the beam is incident on the four-quadrant detector. The overlapping part of the combined beam spot formed by the two beams interferes to generate an AC signal, while the non-overlapping part is a DC component.

[0078] Step 1.4: The four-quadrant detector receives the combined beam spot, and its DC component reflects the position of the combined beam center; record the initial position (y0, z0) of the combined beam spot. The initial position is the state where the two beam spots have a better degree of overlap, which is located at the center of the four-quadrant detector; record the current position (y0, z0) of the combined beam spot. t , z t The position change of the L3 spot is obtained by comparing it with the initial position (y0, z0). Since the position change of the L3 spot is caused by the change in the position of the measuring light L21, which leads to changes in the degree of overlap between the two spots and their positions on the detector, the straightness error Δy of the target mirror unit along the Y-axis and Z-axis is calculated based on the DC change generated in the position change of the L3 spot. t - y0), Δz=1 / 2×(z t - z0).

[0079] Step 2: Measure the length error in the X direction based on laser heterodyne interferometry.

[0080] Step 2.1: The output light L1 of the dual-frequency laser 1 is orthogonally polarized light with a fixed frequency difference. After the polarization direction is adjusted to be aligned with the optical axis by the half-wave plate 2, it is output as beam L2. L2 is incident on the polarization beam splitter 3.

[0081] Step 2.2: The polarizing beam splitter 3 splits L2 into a reference beam L22 and a measurement beam L21 according to its polarization state. The reference beam L22 propagates inside the measurement unit and is reflected back by the fixed-angle cone prism 4 of the measured unit I. The polarization direction, frequency, and phase are theoretically unchanged, thus constituting the reference beam for interferometric measurement.

[0082] Step 2.3: The measuring light L21 is transmitted through the polarizing beam splitter 3 and directed towards the target mirror unit II. It is then reflected back to the polarizing beam splitter 3 by the target mirror mounted on the object under test. Due to the displacement of the target mirror under test in the X-axis direction, the round-trip optical path of the measuring light L21 changes, which in turn causes a change in its phase. This axial displacement information is then carried back to the measurement unit I.

[0083] Step 2.4: After the reference light L22 and the measurement light L21 are spatially superimposed at the polarization beam splitter 3, they are combined into L3. After being reflected by the right-angle mirror 5, L3 passes through the analyzer 6 set at 45°, so that the two beams of light that were originally orthogonally polarized are converted to the same polarization state in the polarization direction and interfere. The interference fringes illuminate the surface of the four-quadrant detector.

[0084] Step 2.5: Since the reference light and the measurement light propagate parallel to each other in space, the interference wavefront is approximately flat relative to the surface of the four-quadrant detector. Therefore, the phase changes of the interference fringes received in the four quadrants of the detector are approximately consistent. The system demodulates the interference intensity signals output from the four quadrants, and the total displacement can be approximated as the average value of the phase changes in all quadrants. ;

[0085] Step 2.6, Average Phase Change This represents the phase difference change between the measurement light and the reference light caused by the X-axis displacement. This average phase signal, along with the reference beat frequency signal provided by laser 1, is input to the phase calculation module. The displacement change in the X-axis direction is extracted using heterodyne demodulation, and is proportional to its average phase change. If the output laser wavelength of dual-frequency laser 1 is λ, then the displacement Δx of target mirror unit II in the X-axis direction is N( )·λ / 2, where N is the stripe count.

[0086] Step 3: Measure the pitch and yaw angle drift of the light beam based on the differential wavefront.

[0087] Step 3.1: In the measurement in step 2, the reference light L22 propagates within the measurement unit I. The path is short and it is generally in a closed environment with a mechanical casing, making it stable and reliable with virtually no change in direction. However, the measurement light L21 needs to travel back and forth between the measurement unit I and the target mirror unit II. The farther the measurement distance, the longer the propagation path, making it susceptible to the influence of factors such as ambient temperature gradients, airflow disturbances, and mechanical vibrations. This causes a slight drift in its propagation direction in space, which manifests as the light direction deviating from the original propagation axis, i.e., an angular drift in the propagation direction.

[0088] Step 3.2: When the measuring light L21 is disturbed and deviates from the optical axis during its round-trip propagation, resulting in a propagation direction offset θ, the direction of the beam on its return path will no longer completely coincide with that of the reference light L22. Although the two beams still combine to form L3 at the polarizing beam splitter 3, due to the deflection of the measuring light direction, a small angle is formed between the P-beam and the S-beam in the combined beam of L3, causing the interference wavefront to no longer be an ideal plane, but exhibiting a certain tilt or curvature.

[0089] Step 3.3: After being reflected by the right-angle mirror 5, L3 passes through the 45° analyzer 6, causing the originally orthogonally polarized P-beam and S-beam to be converted to the same polarization state, resulting in interference on the surface of the four-quadrant detector. Due to the angular drift of the measurement light, the interference wavefront changes accordingly, no longer parallel to the surface of the four-quadrant detector, but rather as a tilted wavefront with a certain slope, leading to phase differences in the interference fringes received in each quadrant of the four-quadrant detector.

[0090] Step 3.4: The system performs heterodyne demodulation on the interference signals acquired by the four quadrant detectors to obtain the phase change in each of the four quadrants. , , , If the phases of the upper and lower quadrants of the four quadrants of the four quadrant detector are different, it indicates that the measurement light has undergone a change in pitch angle around the Y-axis; if the phases of the left and right quadrants of the four quadrant detector are different, it indicates that the measurement light has undergone a change in yaw angle around the Z-axis.

[0091] Step 3.5: Based on the differential wavefront measurement principle, the system calculates the angular drift using the phase distribution characteristics between quadrants of a four-quadrant detector. Using the phase-weighted average of adjacent quadrants, the yaw and pitch drift caused by the light rays can be calculated separately as follows:

[0092] ;

[0093] .

[0094] Step 4: Compensate for straightness error in the Y / Z directions based on the measured angle error.

[0095] Step 4.1: In step 1, the straightness errors Δy and Δz of the target mirror unit II along the Y-axis and Z-axis directions are measured by the laser collimation principle. These errors include the actual position error and the additional offset caused by beam deflection.

[0096] Step 4.2: In step 3, based on the differential wavefront measurement principle, the system has extracted the pitch angle error θ of the measurement light L21 around the Y-axis during propagation. Y The yaw angle error θ around the Z-axis Z This angle information can accurately reflect the amount of drift in the direction of light propagation.

[0097] Step 4.4: The system establishes an error compensation model based on the angle drift θ. Y θ Z The geometric relationship between the measured light propagation distance D and the additional spot offset caused by angular drift is calculated as follows:

[0098] δy=D×tan(θ Z )≈D•θ Z ;

[0099] δz=D×tan(θ Y )≈D•θ Y ;

[0100] Step 4.4: The system corrects the spot position offset value measured by the original four-quadrant detector in Step 1, removing the additional offset caused by angle drift, to obtain the true straightness error as follows:

[0101] Δy true =Δy-1 / 2×δy=1 / 2×(y t - y0 - D•θ Z );

[0102] Δz true =Δz - 1 / 2 × δz = 1 / 2 × (z t - z0 - D•θ Y ).

[0103] In this embodiment, a single four-quadrant detector is used to process all error signals, avoiding crosstalk from multiple detectors and complex adjustments, thus improving integration. The optical path is compact and easy to adjust. Angles are extracted directly from quadrant phase differences using a differential wavefront, and a compensation model is established to reduce the coupling interference of angles on straightness, thereby improving measurement accuracy. Furthermore, compared to existing common multi-degree-of-freedom measurement methods, this embodiment has the advantages of "simplified optical path, reduced components, lower cost and size, and ease of practical application," making it suitable for precision machining, assembly, and motion platform inspection.

[0104] In other specific embodiments, the reflector can be replaced with a corner cube prism, a corner cubic back reflector, a right-angle prism, or a hollow corner cube prism. The four-quadrant detector can be replaced with any one of a PSD, CCD, or CMOS image sensor. The analyzer is set at 45°, but can be adjusted to optimize interference. The right-angle mirror can be replaced with a plane mirror, or omitted altogether. The polarizing beam splitter can be replaced with a polarizing flat beam splitter or a cubic beam splitter, any one of a Wollaston prism, a Lochte polarizer, a Glan polarizing prism, a cubic polarizing beam splitter, or a Sava polarizing beam splitter. However, the placement of the two intensity detectors will differ for different polarizing beam splitters.

[0105] In terms of the optical path, the polarizable beam splitter 3 has a transmission and reflection structure. Figure 1 For a transmission-type measurement system, the polarizing beam splitter 3 measures multiple degrees of freedom errors via transmitted light L21 and reflected light L22. Alternatively, the directions of the target mirror and the fixed reflector can be interchanged to achieve reflection-type measurements, such as... Figure 3 As shown.

[0106] like Figure 4As shown, a λ / 4 waveplate can be added to rotate the polarization of the returning light by 90°, changing the outgoing direction. The function of the λ / 4 waveplate is that light originally reflected by the polarizing beam splitter 3 will be transmitted after passing through two λ / 4 waveplates and returning to the polarizing beam splitter 3; light originally transmitted by the polarizing beam splitter 3 will be reflected after passing through two λ / 4 waveplates and returning to the polarizing beam splitter 3. Therefore, when the first λ / 4 waveplate 9 and the second λ / 4 waveplate 10 are added, and the right-angle reflecting mirror 5 is removed, the optical path will change, but the principle of all measurements remains the same.

[0107] The system employs a dual-channel design, incorporating both transmission and reflection paths. One path serves as the transmission measurement channel, while the other acts as the reflection compensation channel. Combining a cornerstone prism with a plane mirror, the dual-path collaboration achieves decoupling and enhanced compensation for multidimensional measurements. Embedded real-time calculation integrates FPGA / DSP signal processing, enabling real-time closed-loop calculation across the entire process, from signal acquisition and interferometric phase demodulation to angle drift measurement and compensation modeling. Adaptable to extreme environments, the system utilizes vacuum-compatible components and features environmentally resistant packaging and signal redundancy design for extreme conditions such as high temperature, vacuum, and microgravity. All optical components are mounted within an integrated vacuum cavity via a heat-free optical path support. Data acquisition and signal transmission utilize remote fiber optic links. The system integrates an anti-disturbance algorithm to filter out random micro-interferences caused by the absence of gravity. A composite target mirror structure, combining a cornerstone prism and a plane mirror, enhances decoupling. A hybrid catadioptric and reflective target mirror configuration is used, with a dual-channel reflection loop introduced into the measurement path to improve the decoupling capability for angle and position drift. Furthermore, replacing the right-angle mirror with the plane mirror, the polarizing beam splitter with the flat beam splitter, the corner cube prism with the hollow corner cube prism, and the four-quadrant detector with the PSD / CCD can also achieve the invention's purpose, and these variations keep the core principle unchanged.

[0108] The principle of a four-quadrant detector: A four-quadrant detector (QPD) is a position-sensitive device that accurately calculates the offset of the laser spot center position by comparing the signal differences in the four quadrants, used for Y / Z axis straightness measurement; simultaneously, it utilizes the phase difference between quadrants to achieve differential wavefront angle measurement. This device is widely used in laser interferometry systems, capable of processing multidimensional signals without additional separation circuitry, thus improving system response speed. Furthermore, the detection signal of the four-quadrant detector can be filtered to separate its DC and AC signals, better decoupling and measuring error signals.

[0109] The compensation model approximates: tan(Δθ) ≈ Δθ (small angle), where D is the effective propagation distance, which can be calibrated. The mathematical derivation of the compensation model is based on geometric optics: when the measuring light experiences an angular drift Δθ, the resulting additional spot offset δ at the propagation distance D ≈ D·Δθ (small angle approximation, in radians). In practice, this model can be experimentally calibrated to fit different optical path lengths and environmental conditions, specifying D and the scaling factor μ.

[0110] Different types of polarizing beam splitters can be selected: Lochtein polarizers (split angle 0.5°-4°, suitable for applications requiring rotational polarization), Glan polarizing prisms (for high-energy lasers, side-window emission and reflection), and Wollaston prisms (split angle 1°-20°, high extinction ratio >10000:1, used for polarization analysis). Different types affect the beam split angle and damage threshold; laser power and wavelength range must be considered when selecting one.

[0111] Application areas: Suitable for geometric error compensation of precision manufacturing equipment (ultra-precision machine tools, semiconductor exposure machines), coordinate measuring machines, aerospace structure assembly and on-orbit inspection, and optical system assembly and stability monitoring.

[0112] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solutions disclosed in the present invention, various modifications or variations that can be made by those skilled in the art without creative effort should be included within the scope of protection of the present invention.

Claims

1. A simultaneous measurement and compensation system for three-dimensional linear quantities based on a single detector, comprising a measurement unit and a target mirror unit, characterized in that: The measurement unit includes a laser emission module, a half-wave plate, a polarizing beam splitter, a fixed reflector, a right-angle reflector, a polarizer, and a four-quadrant detector; the target mirror unit includes a movable reflector. The laser emission module is used to generate emitted light; The half-wave plate is used to adjust the polarization direction of the outgoing light; The polarizing beam splitter is used to split polarized light into measurement light and reference light; The measurement light, carrying error information, is reflected by the moving reflector and returns to the measurement unit. After being combined with the reference light, it is interfered with the four-quadrant detector by the right-angle mirror and the analyzer, thus realizing the spatial superposition and interference of the beams.

2. The simultaneous measurement and compensation system for three-dimensional linear quantities based on a single detector according to claim 1, characterized in that: The laser emission module is a dual-frequency laser; both the fixed reflector and the moving reflector are corner cube prisms.

3. The simultaneous measurement and compensation system for three-dimensional linear quantities based on a single detector according to claim 1, characterized in that: The analyzer is a 45° analyzer.

4. A method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector, applied to the system as described in any one of claims 1-3, characterized in that: To achieve the measurement of straightness error along the Y-axis and Z-axis based on the laser collimation principle, including: The orthogonally linearly polarized light emitted from the dual-frequency laser is adjusted by a half-wave plate, aligning its polarization direction with the optical axis of the polarizing beam splitter. If the emitted laser light is dual-frequency circularly polarized, the half-wave plate should be a quarter-wave plate. When the linearly polarized light is incident on the polarizing beam splitter, it is split into a measurement beam and a reference beam. The measurement beam is transmitted through the polarizing beam splitter, while the reference beam is reflected. Both the measurement beam and the reference beam are linearly polarized, and their polarization directions are perpendicular to each other. After the measurement light is emitted from the measurement unit, it is incident on the target mirror unit. After being reflected back by the corner prism of the target mirror unit, the spatial position of the measurement light changes with the straightness error of the target mirror unit along the Y-axis and Z-axis. The measurement light carries this two-dimensional straightness error information back to the measurement unit, so that the measurement light passes through the polarization beam splitter again. After the reference light is reflected back by the fixed-angle cone prism, it passes through the polarizing beam splitter again and is combined with the measuring light that has passed through the polarizing beam splitter again. Then, after the beam propagation direction is changed by the right-angle mirror, it passes through the analyzer set at 45°, and the polarization direction is unified, causing interference and incident on the four-quadrant detector. The overlapping part of the combined beam spot formed by the two beams interferes to generate an AC signal, while the non-overlapping part is a DC component. The four-quadrant detector receives the combined beam spot, and its DC component reflects the position of the combined beam center. The initial position of the combined beam spot is recorded, with the optimal overlap between the two beam spots being the initial position, located at the center of the four-quadrant detector. The current position of the combined beam spot is recorded and compared with the initial position to obtain the change in the position of the combined beam spot. Since the change in the position of the combined beam spot is due to the change in the position of the measurement light within it, which causes a change in the overlap between the two beam spots, the straightness error of the target mirror unit along the Y-axis and Z-axis is calculated based on the DC change generated in the change in the position of the combined beam spot.

5. The method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector according to claim 4, characterized in that, To achieve X-direction length error measurement based on laser heterodyne interferometry, including: The output light of the dual-frequency laser is orthogonally polarized light with a fixed frequency difference. After the polarization direction is adjusted to be aligned with the optical axis by a half-wave plate, the output light is then incident on a polarizing beam splitter. The polarization beam splitter splits the outgoing light into a reference beam and a measurement beam according to the polarization state of the outgoing light. The reference beam propagates inside the measurement unit and is reflected back by the fixed-angle prism of the measured unit. Its polarization direction, frequency, and phase remain unchanged, thus forming the reference beam for interferometric measurement. The measuring light is transmitted through a polarizing beam splitter and directed toward a target mirror unit. It is then reflected back to the polarizing beam splitter by the target mirror mounted on the object under test. The displacement of the target mirror under test in the X-axis direction causes a change in the round-trip optical path of the measuring light, which in turn causes a change in its phase. This axial displacement information is then returned to the measuring unit. The reference light and the measurement light are spatially superimposed at the polarization beam splitter to obtain a combined beam. The combined beam is reflected by the right-angle mirror and then passes through the analyzer 6 set at 45°, so that the two beams of light that were originally orthogonally polarized are converted to the same polarization state in the polarization direction and interfere. The interference fringes illuminate the surface of the four-quadrant detector. Since the reference light and the measurement light propagate parallel to each other in space, the interference wavefront is approximately flat relative to the surface of the four-quadrant detector. Therefore, the phase changes of the interference fringes received by the four quadrant detectors are approximately the same. By demodulating the interference intensity signals output from the four quadrants, the total displacement can be approximated as the average value of the phase changes in all quadrants. ; The average phase change represents the phase difference between the measurement light and the reference light caused by the X-axis displacement. This average phase signal, together with the reference beat frequency signal provided by the dual-frequency laser itself, is input to the phase calculation module, and the displacement change in the X-axis direction is extracted by heterodyne demodulation.

6. The method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector according to claim 5, characterized in that, The displacement change along the X-axis is extracted using heterodyne demodulation, and is proportional to the average phase change. If the output wavelength of the dual-frequency laser is λ, then the displacement Δx of the target mirror unit in the X-axis direction is N( )·λ / 2, where N is the stripe count.

7. The method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector according to claim 5, characterized in that, The implementation of pitch and yaw angle measurement based on differential wavefront measurement includes: In X-direction length error measurement based on laser heterodyne interferometry, the reference light propagates within the measurement unit, with a short path and generally within a closed mechanical enclosure, ensuring stability and reliability with minimal directional change; however, the measurement light must travel back and forth between the measurement unit and the target mirror unit, causing its propagation direction to drift in space, manifested as a deviation from the original propagation axis, i.e., an angular drift in the propagation direction; when the measurement light is disturbed and deviates from the optical axis during its round-trip propagation, a propagation direction offset Δθ occurs. After this offset, the beam direction on its return path will no longer perfectly coincide with the reference light; due to the measurement light's... When the beam is deflected, a small angle is formed between the P-beam and the S-beam in the combined beam, causing the interference wavefront to no longer be an ideal plane, but exhibiting a certain tilt or curvature. After being reflected by a right-angle mirror, the combined beam passes through a 45° analyzer, converting the originally orthogonally polarized P-beam and S-beam into the same polarization state, causing interference on the surface of the four-quadrant detector. Due to the angular drift of the measurement light, the interference wavefront changes accordingly, no longer parallel to the surface of the four-quadrant detector, but a tilted wavefront with a certain slope, resulting in a systematic difference in the phase of the interference fringes received in each quadrant of the four-quadrant detector. The system performs heterodyne demodulation on the interference signals acquired in the four quadrants of the four-quadrant detector to obtain the phase change in each quadrant. , , , If the phases of the upper and lower quadrants of the four quadrants of the four quadrant detector are different, it indicates that the measurement light has undergone a change in pitch angle around the Y-axis; if the phases of the left and right quadrants of the four quadrant detector are different, it indicates that the measurement light has undergone a change in yaw angle around the Z-axis. Based on the differential wavefront measurement principle, the angle drift is calculated using the phase distribution characteristics between the quadrants of the four quadrant detector. The pitch and yaw angle drifts caused by the light drift can be calculated separately by using the phase weighted average of adjacent quadrants.

8. The method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector according to claim 7, characterized in that, The yaw and pitch drift caused by ray drift can be calculated separately using the phase-weighted average of adjacent quadrants: ； 。 9. The method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector according to claim 8, characterized in that, To achieve Y / Z direction straightness error measurement based on the measured angle error compensation, including: In the measurement of straightness error along the Y-axis and Z-axis based on the laser collimation principle, the straightness errors Δy and Δz of the target mirror unit II along the Y-axis and Z-axis directions are measured by the laser collimation principle. These errors include the actual position error and the additional offset caused by beam deflection. In realizing the X-direction length error measurement based on laser heterodyne interferometry, the system, based on the differential wavefront measurement principle, has extracted the pitch angle error θ of the measurement light around the Y-axis during propagation. y The yaw angle error θ around the Z-axis z This angle information can accurately reflect the amount of drift in the direction of light propagation.

10. The method for simultaneous measurement and compensation of three-dimensional linear quantities based on a single detector according to claim 9, characterized in that, Establish an error compensation model based on the angle drift θ y θ z The geometric relationship between the measured light propagation distance D and the calculated additional spot offset caused by angular drift is used to calculate the additional spot offset caused by angular drift. The spot position offset value measured by the original four-quadrant detector in the straightness error measurement along the Y-axis and Z-axis based on the laser collimation principle is corrected to remove the additional offset caused by angle drift in order to obtain the true straightness error.

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