Automatic leveling method for large-caliber planar optical element
Technical Field
The invention belongs to the technical field of optics, and particularly relates to an automatic leveling method for a large-caliber planar optical element.
Background
Under the background of the demand for large optical devices such as space telescopes and laser drivers, the processing of optical elements is also developing towards large aperture and high precision. Planar optical elements, such as mirrors and optical windows, play an irreplaceable important role as one of the most commonly used optical elements in optical devices. The caliber of the plane optical element is larger and larger, the requirement on surface precision is higher and higher, and more severe examination is provided for the detection technology of the large-caliber plane optical element. At present, a microscopic imaging system is mainly adopted to scan and image the surface of a detected sample, so that the appearance and distribution of surface defects are obtained. Because the focal plane of the microscopic imaging system is usually a plane with a fixed position, when a sample is placed, if the surface of the sample and the focal plane are inclined, the surface of the sample is gradually far away from the focal plane in the scanning process, and the defocusing condition occurs, so that the final imaging quality and the detection precision are affected. Today's large aperture optical elements have evolved to hundreds to thousands of millimeters, and when inspecting such large aperture samples, even if the sample is placed with a slight tilt, significant defocus results. Therefore, there is a need for an apparatus and method for automatically leveling large-aperture planar optical elements.
A conventional leveling device for a planar optical element, such as chinese patent document No. CN204700607U, discloses a portable leveling device for a planar optical element, which uses four adjusting nuts to achieve adjustment of workpiece clamping, but does not provide an automatic leveling method for an optical element.
Chinese patent publication No. CN102680477A discloses a method and an apparatus for high-precision leveling of large-size optical elements, which uses a high power microscope to collect images of characteristic points on a sample surface, and obtains the defocus amount of the characteristic points, thereby calculating the plane tilt and converting the tilt into the adjustment amount required for pitching and yawing. The method needs to use a microscope to sample three characteristic points on the surface, and when the processing quality of the detected optical element is good, the distribution of the characteristic points is less, and proper characteristic points are often difficult to find; in addition, the microscope needs to be moved to three feature points respectively, and the time required for leveling is increased.
Therefore, there is a need to provide a simple and efficient apparatus and method for achieving automatic leveling of a large-aperture planar optical device.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an automatic leveling method for a large-caliber planar optical element, which can realize non-contact, quick and automatic leveling of the large-caliber planar optical element.
The technical scheme of the invention is as follows:
an automatic leveling method for a large-caliber plane optical element adopts an automatic leveling device, wherein the automatic leveling device comprises a sample adjusting platform, a three-dimensional displacement table, three laser displacement sensors arranged on the three-dimensional displacement table, a data acquisition unit electrically connected with the laser displacement sensors, a data analysis processing unit electrically connected with the data acquisition unit, and a control unit for receiving feedback of the data analysis processing unit and adjusting the pitching and rotating angle of the sample adjusting platform;
the method specifically comprises the following steps:
(1) calibrating the initial relative distances of the three laser displacement sensors, and determining a distance difference value delta dy measured by the first laser displacement sensor and the second laser displacement sensor and a distance difference value delta dx measured by the second laser displacement sensor and the third laser displacement sensor in a leveling state;
(2) fixing a large-caliber planar optical element to be leveled on a sample adjusting platform in a vertical placing posture;
(3) moving X, Y two shafts of the three-dimensional displacement platform to enable three sampling points of the three laser displacement sensors to be all positioned on the surface of the large-caliber planar optical element; wherein the X, Y axis of the three-dimensional displacement table is parallel to the surface of the planar optical element in the leveling state;
(4) moving the Z axis of the three-dimensional displacement table to enable all three laser displacement sensors to be located within the working distance, and obtaining the relative distance d between the three sampling points on the large-caliber plane optical element and the three corresponding laser displacement sensors through the data acquisition unit1、d2、d3;
(4) The control unit controls the sample adjusting platform to move along the pitching axis until | d is satisfied1-d2|<Δdy;
(5) The control unit controls the sample adjusting platform to move the rotating shaft until | d is satisfied2-d3|<Δdx;
(6) If at this time | d1-d2If | is more than delta dy, repeating the steps (4) to (6), feeding back the relative distance of the three sampling point distances corresponding to each laser displacement sensor in real time by the data analysis processing unit, and correcting the movement amount of the sample adjusting platform until | d is satisfied simultaneously1-d2|<Δdy、|d2-d3< Δ dx, finishThe large-caliber plane optical element is automatically leveled.
When the device disclosed by the invention is used for automatic leveling, the data acquisition unit is connected with the three laser displacement sensors, receives the relative distances of the three sampling points in real time, transmits the relative distances to the data analysis processing unit, and feeds the relative distances back to the control unit after analysis processing, so as to perform pitching and rotation angle leveling. And in the leveling process, the relative distance of the three sampling points is fed back in real time, the movement amount of the sample adjusting platform is corrected, and closed-loop control is realized.
The laser displacement sensor is a non-contact measuring sensor, and the linear distance between an object to be measured and the sensor is obtained by applying the laser triangular reflection principle; the measuring direction of the laser displacement sensor is the emergent laser direction of the laser displacement sensor.
In the automatic leveling device, three laser displacement sensors are installed on a three-dimensional displacement table in a triangular shape, and the measuring directions of the three laser displacement sensors are parallel to the Z axis.
The X, Y axis direction of the three-dimensional displacement platform can bear the laser displacement sensor to perform two-dimensional translation; the Z axis is perpendicular to the surface of the plane optical element and can bear the axial translation of the laser displacement sensor.
Preferably, the three laser displacement sensors are arranged on the three-dimensional displacement table in a right triangle shape, and the connecting line of the mounting positions of the first laser displacement sensor and the second laser displacement sensor is parallel to the Y axis; and the connecting line of the mounting positions of the second laser displacement sensor and the third laser displacement sensor is parallel to the X axis.
The large-caliber plane optical element is fixed on the sample adjusting platform through the clamping mechanism.
The specific steps of the step (1) are as follows:
(1-1) fixing a large-caliber planar optical element for calibration on a sample adjusting platform through a clamping mechanism by adopting a vertical placing posture;
(1-2) moving X, Y two shafts of the three-dimensional displacement platform to enable three sampling points of the three laser displacement sensors to be located on the surface of the planar optical element;
(1-3) moving the Z axis of the three-dimensional displacement table to enable all three laser displacement sensors to be located within the working distance of the three laser displacement sensors, and obtaining the relative distance between three sampling points on the large-caliber planar optical element and the laser displacement sensors;
(1-4) moving the three-dimensional displacement table to enable any laser displacement sensor to scan a section line of the large-caliber planar optical element along the X direction, and recording the relative distance d acquired by the first laser displacement sensor1During the scanning process d1Is recorded as Δ d1;
(1-5) rotating the rotating shaft of the sample adjusting platform, and repeating the steps (1-4) until the maximum variation delta d1When the value is smaller than the set threshold value, the leveling calibration of the sample leveling platform in the rotating shaft direction is completed;
(1-6) moving the three-dimensional displacement table in the Y direction to enable any laser displacement sensor to scan a section line of the large-caliber planar optical element in the Y direction according to the methods of the steps (1-4) to (1-5) until d is in the scanning process1Maximum amount of change Δ d of1When the value is smaller than the set threshold value, the leveling calibration of the sample leveling platform in the pitch axis direction is completed;
(1-7) recording the relative distance | d acquired by the three laser displacement sensors at the moment1-d2|=Δdy、|d2-d3And finishing the initial relative distance calibration of the three laser displacement sensors.
The purpose of calibrating the initial relative distances of the three laser displacement sensors is as follows: when the system is installed, three laser displacement sensors cannot be strictly ensured to be positioned in the same plane; therefore, before automatic leveling, the initial relative distances of the three laser displacement sensors need to be calibrated to obtain the relative position information of the three laser displacement sensors. If the relative positions of the three laser displacement sensors are not changed, calibration work is only needed to be carried out when the system is used for the first time.
Preferably, in steps (1-5) and (1-6), the set threshold value can be determined according to the measurement accuracy of the laser displacement sensor, and generally the set threshold value should be greater than the measurement accuracy of the laser displacement sensor.
In the step (2), the vertical placement posture means that the surface of the planar optical element is placed perpendicular to the horizontal plane.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts three laser displacement sensors to perform real-time closed-loop adjustment, and does not need to scan a sample during leveling, thereby greatly improving the leveling speed and precision. The leveling method is simple and high in efficiency, does not need complex data processing operation, and can effectively solve the defocusing problem during the microscopic imaging of the large-caliber planar optical element.
Drawings
FIG. 1 is a schematic structural view of an automatic leveling device according to the present invention;
FIG. 2 is a schematic diagram of the calibration of the initial relative distance (rotation direction) of the laser displacement sensor according to the present invention;
FIG. 3 is a schematic diagram of the calibration of the initial relative distance (pitch direction) of the laser displacement sensor according to the present invention;
FIG. 4 is a flow chart of the automatic leveling method of the large-aperture planar optical element according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings, in which the following embodiments are provided to facilitate understanding of the present invention and are not intended to limit the present invention in any way.
The automatic leveling device is shown in fig. 1. A large-caliber planar optical element 8 to be leveled is fixed on a sample platform adjusting platform 7 in a vertical placing posture, and the surface of the element is vertical to the horizontal plane. The sample adjusting platform 7 can carry a sample to adjust two angles of pitch theta x and rotation theta y. The three laser displacement sensors are respectively as follows: the displacement sensor comprises a first laser displacement sensor 1, a second laser displacement sensor 2 and a third laser displacement sensor 3. Three laser displacement sensors are fixed on a three-dimensional displacement table, and an X, Y axis of the three-dimensional displacement table is parallel to the surface of the planar optical element 8 and can bear the laser displacement sensors to perform two-dimensional translation; the Z axis is perpendicular to the surface of the planar optical element 8 and can carry the laser displacement sensor to axially translate. The three laser displacement sensors are arranged in a plane parallel to the surface 8 of the planar optical element, and the connecting lines of the arrangement positions form a right triangle. The connecting line of the positions where the first laser displacement sensor 1 and the second laser displacement sensor 2 are placed is parallel to the Y axis; the connecting line of the positions where the second laser displacement sensor 2 and the third laser displacement sensor 3 are placed is parallel to the X axis.
The measuring directions of the three laser displacement sensors are parallel to the Z axis and serve as three sampling points, and the relative distances from the three sampling points on the planar optical element 8 to the laser displacement sensors are provided. Wherein, the sampling point 4 corresponds to the first laser displacement sensor 1, the sampling point 5 corresponds to the second laser displacement sensor 2, and the sampling point 6 corresponds to the third laser displacement sensor 3.
Before leveling, the initial relative distances of the three laser displacement sensors are calibrated. And during leveling, the data acquisition unit is connected with the three laser displacement sensors, receives the relative distances of the three sampling points in real time, transmits the relative distances to the data analysis processing unit, and feeds the relative distances back to the control unit after analysis processing to perform pitching and rotation angle leveling. In the leveling process, the relative distance of the three sampling points is fed back in real time, the movement amount of the sample adjusting platform 7 is corrected, and closed-loop control is realized.
As shown in fig. 2 and 3, the method for calibrating the initial relative distance of the three laser displacement sensors is as follows:
step 1, as shown in fig. 2 (a), a large-caliber planar optical element 9 for calibration is fixed on a sample adjusting platform 7 through a clamping mechanism by adopting a vertical placing posture;
step 2, moving X, Y two shafts of the three-dimensional displacement table to enable three sampling points of the three laser displacement sensors to be located on the surface of the planar optical element 9;
step 3, moving the Z axis of the three-dimensional displacement table to enable all three laser displacement sensors to be located within the working distance, and obtaining the relative distance between three sampling points on the large-caliber planar optical element 9 and the laser displacement sensors;
step 4, moving the three-dimensional displacement table to enable the first laser displacement sensor 1 to scan a section line of the large-caliber planar optical element 9 along the X direction, and recording the relative distance d acquired by the laser displacement sensor1During the scanning process d1Maximum change ofThe quantity is recorded as Δ d1;
Step 5, as shown in fig. 2 (b), rotating the rotating shaft of the sample adjustment platform 7, and repeating step 4 until the maximum variation Δ d1When the value is smaller than the set threshold value, the leveling calibration of the sample leveling platform 7 in the rotating shaft direction is completed;
step 6, as shown in (a) and (b) of FIG. 3, repeating steps 4-5 in the Y direction until d is in the scanning process1Maximum amount of change Δ d of1When the value is smaller than the set threshold value, the leveling calibration of the sample leveling platform 7 in the pitch axis direction is completed;
step 7, recording the relative distance | d acquired by the three laser displacement sensors at the moment1-d2|=Δdy、|d2-d3And finishing the initial relative distance calibration of the three laser displacement sensors.
As shown in fig. 4, the automatic leveling method of the large-caliber planar optical element is as follows:
s01, fixing the large-caliber planar optical element 8 to be leveled on the sample leveling platform 7 through a clamping mechanism by adopting a vertical placing posture;
s02, moving two shafts X, Y of the three-dimensional displacement table to enable three sampling points of the three laser displacement sensors to be located on the surface of the planar optical element 8;
s03, moving the Z axis of the three-dimensional displacement table to enable all three laser displacement sensors to be located within the working distance, and obtaining the relative distance d between three sampling points on the large-caliber planar optical element 8 and the laser displacement sensors1、d2、d3;
S04, the sample adjusting platform 7 moves along the pitch axis theta x until | d is satisfied1-d2|<Δdy;
S05, the sample adjusting platform 7 moves the rotation axis theta y until | d is satisfied2-d3|<Δdx;
S06, if so, | d1-d2If the | is more than the Δ dy, repeating the steps S04-S05, feeding back the relative distances of the three sampling points in real time, and correcting the movement amount of the sample adjusting platform 7 until | d is satisfied simultaneously1-d2|<Δdy、|d2-d3< delta dx to finish the large mouthThe radial plane optical element is automatically leveled.
To verify the effect of the present invention, an example of the present invention applied to the automatic leveling of a large-caliber planar optical element is described below.
The large-caliber planar optical element 8 to be leveled is a planar optical element with the length of 800mm, the width of 600mm and the thickness of 20 mm; the used laser displacement sensors are three laser displacement sensors with the same model, the working distance is 90 +/-20 mm, and the linear precision is +/-12 mu m; the three-dimensional displacement table is a large-stroke high-precision three-dimensional displacement table, and the positioning precision of the three-dimensional displacement table is +/-10 mu m. Three laser displacement sensors were placed on a three-dimensional displacement table at a distance of about 90mm from the planar optical element 8. The connecting line of the positions where the first laser displacement sensor 1 and the second laser displacement sensor 2 are placed is parallel to the Y axis; the connecting line of the placing positions of the second laser displacement sensor 2 and the third laser displacement sensor 3 is parallel to the X axis; the connecting line of the placing positions of the two right-angle connecting rods form a regular triangle, and the side lengths of the two right-angle connecting rods are 300 mm.
Firstly, the initial relative distance calibration method of the laser displacement sensor is used for calibrating the initial relative distance of three laser displacement sensors, and the result is shown in the table 1:
TABLE 1
Obtaining Δ dx ═ d1-d2|=0.015mm;Δdy=|d1-d3|=0.020mm。
The automatic leveling method of the large-caliber planar optical element is used for leveling. According to S01-S03, the relative distances from the laser displacement sensor to three sampling points on the large-caliber planar optical element 8 are obtained as shown in Table 2:
TABLE 2
According to S04-S05, the pitching axis theta x and the rotating axis theta y of the adjusting platform 7 are sequentially moved, the relative distances of three sampling points are fed back in real time, and if the relative distances do not meet the requirement of | d1-d2|<Δdy、|d2-d3If | < Δ dx, repeat S04-S05, with the results shown in Table 3:
TABLE 3
After four iterations, | d is satisfied simultaneously1-d2|=0.007<Δdy,|d2-d3And (4) finishing the leveling if the |, 0.017 < delta dx.
In this embodiment, the automatic leveling device and method for the large-aperture planar optical element of the present invention completes leveling through four iterations. The laser displacement sensor can feed back the relative position in real time to realize closed-loop control, so that the iteration speed is high. The leveling error mainly comes from the displacement error of the sample leveling platform and the measurement error of the laser displacement sensor, and the leveling precision can be greatly improved by selecting the sample leveling platform and the laser displacement sensor with higher precision. Therefore, the device and the method can realize non-contact, quick and high-precision automatic leveling of the large-caliber planar optical element.
The above description is only exemplary of the preferred embodiments of the present invention, and is not intended to limit the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.