A method for measuring the surface profile of a weakly stiff freeform resin lens

Abstract

This invention belongs to the field of optical measurement technology, specifically relating to a method for measuring the surface shape of a weakly stiff freeform resin lens. Compared with existing contact measurement technology, this invention uses a white light sensor to obtain the surface height information of the freeform resin lens, avoiding the deviation caused by contact measurement and the scratches caused to the resin lens surface. Through program-controlled automated measurement, batch inspection of freeform resin lenses is achieved, shortening the measurement cycle and overcoming the problems of easy deformation and low measurement accuracy of traditional measurement methods.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, specifically relating to a method for measuring the surface shape of a weakly stiff freeform resin lens. Background Technology

[0002] Helmet-mounted displays (HUDs) are information display terminals in modern military aircraft. Pilots rely on this interface to obtain flight information and battlefield situational awareness throughout combat and flight operations. The display visor, as a crucial component of the helmet-mounted aiming and display system, directly affects the imaging accuracy of the product, and consequently, the pilot's aiming accuracy.

[0003] The display goggles are made of polycarbonate (PC), which is manufactured through a single injection molding process. Injection-molded parts have low rigidity and poor surface profile, which can scratch the parts during contact measurement, and contact deformation can introduce measurement errors. Fixed-chord length goggles interfere with sphere diameter meters, making it impossible to measure the sphere diameter. Furthermore, the poor surface profile of the goggles prevents measurement with laser interferometers. Currently, it is difficult to perform high-precision surface profile measurement on display goggles, thus severely restricting the high-precision manufacturing of display goggles.

[0004] In conclusion, the study of measuring the surface profile of weakly stiff freeform resin lenses is of great significance. Summary of the Invention

[0005] In view of this, the present invention provides a method for measuring the surface shape of a weak stiffness freeform resin lens. Relying on a coordinate measuring machine and using a non-contact probe, the method achieves automated and high-precision measurement of the surface shape of a weak stiffness freeform resin lens by programming and planning the measurement path.

[0006] The technical solution of this invention:

[0007] A method for measuring the surface profile of a weakly stiff freeform resin lens includes the following steps:

[0008] Step 1: Calibrate the probe: Calibrate the main probe, and based on the positioning standard ball of the main probe, obtain the diameter and position of the main probe; calibrate the working probe, obtain the diameter of the working probe tip, perform radius compensation on the probe, and obtain the positional relationship between the working probe and the main probe, as well as the probe length relationship;

[0009] Step 2: Define the storage rack and set up automatic probe replacement;

[0010] Step 3: Establish the detection coordinate system and create a safety plane: Based on the working probe, make contact-type markings on the surface of the fixture on which the lens is clamped to establish a point, line, and surface relationship on the outer surface of the fixture to determine the detection coordinate system; create a safety plane to protect the probe from collisions.

[0011] Step 4: Compile the measurement process: Plan the measurement path, determine the location and number of nominal points to be measured on the part surface, consider the measurement edge effect, and set the distance between the nominal points and the edge of the part;

[0012] Step 5: Calibrate the probe: Based on the DotScan probe, set the working angle and measure the surface of the part in different areas. The DotScan probe is calibrated for each increase in angle. If the working angle of the DotScan probe increases or if there are point errors that cannot be measured during non-contact measurement of the part surface, the DotScan probe is recalibrated at the working angle using a matte sphere.

[0013] Step 6: Measurement: The surface profile of the weak stiffness freeform resin lens is measured based on the defined measurement procedure.

[0014] Furthermore, before performing step 5, the following steps are also included: performing dark balance on the DotScan probe; between step 4 and step 5, the following steps are also included: calibrating the DotScan probe based on a matte sphere.

[0015] Furthermore, in step 4, the method for defining the nominal point is as follows:

[0016] The number of nominal points in the opposite region is defined according to the two directions U and V, and all nominal points in the surface region are generated.

[0017] or,

[0018] Import the lens theoretical model, cross-section the surface of the lens theoretical model according to the preset spacing and form multiple intersection lines, define multiple sampling points on the intersection lines, and use each sampling point as a nominal point.

[0019] Furthermore, the method for measuring the surface profile of weakly stiff freeform resin lenses also includes step 7: Surface profile evaluation.

[0020] Step 6 uses the detection coordinate system obtained in step 3 to obtain the first surface error result, and step 6 does not use the detection coordinate system obtained in step 3 to obtain the second surface error result.

[0021] The surface shape of the lens is evaluated jointly based on the first surface shape error result and the second surface shape error result.

[0022] Furthermore, in step 6, the switching between contact and non-contact probes is controlled by a program to achieve automated measurement of the lens according to a preset measurement trajectory.

[0023] Furthermore, in step 6, the DotScan probe scanning measurement rate is greater than 800 points / second; the DotScan probe resolution is better than 50nm.

[0024] The DotScan probe has a unidirectional length measurement error better than 2.0+L / 350μm, where L is the longest dimension of the part.

[0025] The beneficial effects of this invention are:

[0026] This invention utilizes a white light ranging sensor to acquire surface elevation information of freeform resin lenses, avoiding deviations caused by contact measurements and scratches on the resin lens surface. Through program-controlled automated measurement, batch inspection of freeform resin lenses is achieved, shortening the measurement cycle and overcoming the problems of easy deformation and low measurement accuracy of traditional measurement methods. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the measurement process of the present invention;

[0029] Figure 2 This is a schematic diagram of the measurement of the freeform resin lens of the goggles according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the surface shape result of an embodiment of the present invention. Detailed Implementation

[0031] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0032] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0033] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0034] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this disclosure. The illustrations only show the components related to this disclosure and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0035] Additionally, in the following description, specific details are provided to provide a thorough understanding of the examples. However, one skilled in the art will appreciate that the aspects described may be practiced without these specific details.

[0036] In one embodiment of the present invention, a method for measuring the surface profile of a weakly stiff freeform resin lens is proposed, such as... Figure 1 As shown, it includes the following steps:

[0037] Step 1: Calibrate the probe: Calibrate the main probe, and based on the positioning standard ball of the main probe, obtain the diameter and position of the main probe; calibrate the working probe, obtain the diameter of the working probe tip, perform radius compensation on the probe, and obtain the positional relationship between the working probe and the main probe, as well as the probe length relationship;

[0038] Step 2: Define the storage rack and set up automatic probe replacement;

[0039] Step 3: Establish the detection coordinate system and create a safety plane: Based on the working probe, make contact-type markings on the surface of the fixture on which the lens is clamped to establish a point, line, and surface relationship on the outer surface of the fixture to determine the detection coordinate system; create a safety plane to protect the probe from collisions.

[0040] Step 4: Compile the measurement process: Plan the measurement path, determine the location and number of nominal points to be measured on the part surface, consider the measurement edge effect, and set the distance between the nominal points and the edge of the part;

[0041] Step 5: Calibrate the probe: Based on the DotScan probe, set the working angle and measure the surface of the part in different areas. The DotScan probe is calibrated for each increase in angle. If the working angle of the DotScan probe increases or if there are point errors that cannot be measured during non-contact measurement of the part surface, the DotScan probe is recalibrated at the working angle using a matte sphere.

[0042] Step 6: Measurement: The surface profile of the weak stiffness freeform resin lens is measured based on the defined measurement procedure.

[0043] In this embodiment, before performing step 5, the following steps are also included: performing dark balance on the DotScan probe; between step 4 and step 5, the following steps are also included: calibrating the DotScan probe based on a matte sphere.

[0044] In this embodiment, the method for defining the nominal point in step 4 is as follows:

[0045] The number of nominal points in the opposite region is defined according to the two directions U and V, and all nominal points in the surface region are generated.

[0046] or,

[0047] Import the lens theoretical model, cross-section the surface of the lens theoretical model according to the preset spacing and form multiple intersection lines, define multiple sampling points on the intersection lines, and use each sampling point as a nominal point.

[0048] In this embodiment, the method for measuring the surface profile of a weakly stiff freeform resin lens further includes step 7: surface profile evaluation.

[0049] Step 6 uses the detection coordinate system obtained in step 3 to obtain the first surface error result, and step 6 does not use the detection coordinate system obtained in step 3 to obtain the second surface error result.

[0050] The surface shape of the lens is evaluated jointly based on the first surface shape error result and the second surface shape error result.

[0051] In this embodiment, step 6 involves switching between contact and non-contact probes via program control, and achieving automated measurement of the lens according to a preset measurement trajectory.

[0052] In this embodiment, in step 6, the DotScan probe scanning measurement rate is greater than 800 points / second; the DotScan probe resolution is better than 50nm.

[0053] The DotScan probe has a unidirectional length measurement error better than 2.0+L / 350μm, where L is the longest dimension of the part.

[0054] This embodiment can be described in its entirety as follows:

[0055] Step 1: Calibrate the main probe and the working stylus. Position the main probe using a standard sphere to obtain its diameter and position (set the zero point to provide a reference for the working stylus), i.e., (X:0, Y:0, Z:0). The main probe is not used for measurement, only for calibration. Reference sphere 1 (matte sphere) is used to calibrate the Dotscan probe, and reference sphere 2 is used to calibrate the working stylus. Create the working stylus, calibrate the working probe using the standard sphere to obtain its diameter, and perform radius compensation on the stylus; obtain the relationship between the stylus and the main probe (including position, probe length, etc.).

[0056] Step 2: Define storage racks: Define storage racks for automatic switching between probes;

[0057] Step 3: Establish the inspection coordinate system and safety plane. The coordinate system should conform to the right-hand rule. The simplest method is to determine the coordinate system using surfaces, points, and lines. Surface one has four points to define the surface, surface two has two points to define the line, and surface three has a single point to define the point, thus establishing the coordinate system. When establishing the coordinate system, try to ensure that the coordinate system you establish is consistent with the machine coordinate system in direction. The purpose of establishing the safety plane is to allow the measuring machine to move the probe around the workpiece in CNC mode without collision, protecting the probe from impact.

[0058] Step 4: Develop the measurement program: Plan the measurement path, and determine the location and number of nominal points to be measured on the part surface using either surface-generated points or cross-sectional line-defined points methods. Consider the measurement edge effect and set the distance between the nominal points and the part edge. Surface-generated points method: Click on the model surface to be measured, select the number of rows and columns to generate nominal points, define the distance between the nominal edge points and the part edge, and create the points. The number and order of points can be manually modified later to determine the nominal points. Cross-sectional method: Select a plane in a certain direction to cut off the surface of the part to be measured, generate a cross-section, define the number of cross-section points and the distance between the edge points and the part edge, and create the points. Repeat this method to create multiple cross-sections to determine nominal points. The cross-sectional data can be retrieved through the surface to evaluate the surface profile data of the part.

[0059] Step 5: Calibrate the probe: 1) Perform dark balance on the probe in an environment without a physical object to filter out errors caused by reflected light in the environment during the measurement of the actual part;

[0060] 2) A matte sphere is used, where the light emitted by the probe undergoes diffuse reflection on its surface. The DotScan probe is calibrated by receiving this reflected light. Simultaneously, for different part shapes, it is ensured that the probe can receive the reflected light from the part's surface.

[0061] 3) The DotScan probe is set to measure the part surface in sections by working angle. Each time the angle is increased, the DotScan probe must be calibrated at each angle to ensure measurement accuracy at each angle. If the working angle increases or some points fail to measure during non-contact measurement of the part surface, the DotScan probe needs to be recalibrated at the working angle using a matte sphere.

[0062] Step 6: Measurement: The surface shape of the weak stiffness freeform resin lens is automatically measured through program control.

[0063] The following measurement experiment was conducted using a 236*125*215mm low-stiffness freeform resin lens. The low-stiffness freeform resin lens described in this embodiment has the following shape... Figure 2 As shown, the surface accuracy requirement is PV≤80μm.

[0064] The following is in accordance with Figure 1 The following steps were taken to measure the embodiment:

[0065] Step 1: Calibrate the probe:

[0066] 1) Position the main probe using a standard sphere to obtain the diameter and position of the main probe (set the zero point to provide a reference for the working probe), i.e., (X:0, Y:0, Z:0). The main probe is not used for measurement, only for calibration;

[0067] 2) Reference sphere 1, also known as the matte sphere, is used to calibrate the Dotscan probe, and reference sphere 2 is used to calibrate the working probe. The working probe is calibrated using the standard spheres to obtain the probe diameter and perform radius compensation; the relationship between the probe and the main probe (including position, probe length, etc.) is also determined.

[0068] Step 2: Define the storage rack:

[0069] Define storage racks and set up storage locations for contact probes and non-contact DotScan probes;

[0070] Step 3: Establish the detection coordinate system and create a safety plane:

[0071] 1) The coordinate system should conform to the right-hand rule. The simplest method is to determine the coordinate system using surfaces, points, and lines. For working contact probes, make contact points on the working surface. Surface 1 makes four points to define the surface, surface 2 makes two points to define the line, and surface 3 makes one point to define the point. The detection coordinate system is then determined using points, lines, and surfaces. Try to ensure that the coordinate system you establish is consistent with the machine coordinate system in terms of direction.

[0072] 2) A safety plane is established by adding a certain distance outward from the part and the inspection fixture as a whole, so that the measuring machine can move the probe around the workpiece in CNC mode without collision, thus protecting the probe from collision;

[0073] Step 4: Establish the detection coordinate system:

[0074] Step 4: Compile the measurement process:

[0075] Six working angles are set for the area to be measured. The positions and number of nominal points to be measured on the surface of the part are determined by the method of generating points from the surface or defining points by forming lines from the cross section. In this example, a total of 50 lines are set with a line spacing of 5 mm, and a total of 1068 nominal points are set with a point spacing of 2 mm. Considering the measurement edge effect, the distance between the nominal point and the edge of the part is set to 4 mm.

[0076] Step 5: Calibrate the probe:

[0077] 1) The probe is dark-balanced in an environment without a physical object to be measured;

[0078] 2) A matte sphere is used, and the light emitted by the probe is diffusely reflected on the surface of the matte sphere. The DotScan probe is calibrated by receiving the reflected light.

[0079] 3) The DotScan probe is calibrated at 6 angles to ensure measurement accuracy at each angle. If the working angle increases or certain points fail to be measured during non-contact measurement of the part surface, the DotScan probe needs to be recalibrated at the working angle using a matte sphere.

[0080] Step 6: Measurement: The surface shape of the weak stiffness freeform resin lens is automatically measured through program control.

[0081] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for measuring the surface profile of a weakly stiff freeform resin lens, characterized in that, Includes the following steps: Step 1: Calibrate the probe: Calibrate the main probe, and based on the positioning standard ball of the main probe, obtain the diameter and position of the main probe; calibrate the working probe, obtain the diameter of the working probe tip, perform radius compensation on the probe, and obtain the positional relationship between the working probe and the main probe, as well as the probe length relationship; Step 2: Define the storage rack and set up automatic probe replacement; Step 3: Establish the detection coordinate system and create a safety plane: Based on the working measurement, make contact-type markings on the surface of the fixture on which the lens is clamped, and establish a point, line and surface relationship on the outer surface of the fixture to determine the detection coordinate system; Establish a safety plane to protect the probe from collisions; Step 4: Compile the measurement process: Plan the measurement path, determine the location and number of nominal points to be measured on the part surface, consider the measurement edge effect, and set the distance between the nominal points and the edge of the part; Step 5: Calibrate the probe: Based on the DotScan probe, set the working angle and measure the surface of the part in different areas. The DotScan probe is calibrated for each increase in angle. If the working angle of the DotScan probe increases or if there are point errors that cannot be measured during non-contact measurement of the part surface, the DotScan probe is recalibrated at the working angle using a matte sphere. Step 6: Measurement: Measure the surface profile of the weak stiffness freeform resin lens based on the defined measurement procedure; In step 4, the method for defining the nominal point is as follows: The number of nominal points in the opposite region is defined according to the two directions U and V, and all nominal points in the surface region are generated. or, Importing the theoretical model of the lens, the surface of the theoretical model is cross-sectioned at preset intervals to form multiple weakly stiff freeform surfaces. The resin lens surface shape measurement method also includes step 7: Surface shape evaluation. Step 6 uses the detection coordinate system obtained in step 3 to obtain the first surface error result, and step 6 does not use the detection coordinate system obtained in step 3 to obtain the second surface error result. The surface intersection line of the lens is jointly evaluated based on the first surface error result and the second surface error result. Multiple sampling points are defined on the intersection line, and each sampling point is used as a nominal point.

2. The method for measuring the surface shape of a weakly stiff freeform resin lens according to claim 1, characterized in that, Before performing step 5, the following steps are also included: performing dark balance on the DotScan probe; between step 4 and step 5, the following steps are also included: calibrating the DotScan probe based on a matte sphere.

3. The method for measuring the surface shape of a weakly stiff freeform resin lens according to claim 1, characterized in that, In step 6, the switching between contact and non-contact probes is controlled by a program, and the lens is automatically measured according to a preset measurement trajectory.

4. The method for measuring the surface shape of a weakly stiff freeform resin lens according to claim 3, characterized in that, In step 6, the DotScan probe scanning measurement rate is greater than 800 points / second; the DotScan probe resolution is better than 50 nm. The DotScan probe has a unidirectional length measurement error better than 2.0+L / 350μm, where L is the longest dimension of the part.

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