3D printing system and coordinate system calibration conversion method and device thereof

Abstract

The invention provides a 3D printing system and a coordinate system calibration conversion method and device thereof. The method comprises the steps that the positions, with Z equal to a specified value, in a pixel coordinate system and an XYZ coordinate system are calibrated; calibrating a first conversion coefficient in a first coordinate axis direction and a second conversion coefficient in a second coordinate axis direction in the pixel coordinate system; wherein the conversion coefficient is used for representing the number of pixels corresponding to the unit distance or the distance corresponding to a single pixel; calibrating a first offset of a pixel reference point in the pixel coordinate system and a nozzle of the printing head assembly in the Y-axis direction, and a second offset of the pixel reference point and the nozzle of the printing head assembly in the X-axis direction; and determining the conversion relation between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z is equal to the specified value, the first conversion coefficient, the second conversion coefficient, the first offset and the second offset. And conversion of the two coordinate systems is realized through coordinate system calibration, so that accurate measurement of absolute coordinates under a pixel coordinate system is realized.

Description

Technical Field

[0001] This application relates to the field of 3D printing technology, and in particular to a 3D printing system and its coordinate system calibration and transformation method and apparatus. Background Technology

[0002] With the development and advancement of various technologies in the additive manufacturing industry, the speed of additive printing is getting faster and the printing size is getting larger and larger. At the same time, the requirements for system control are getting higher and higher.

[0003] In additive manufacturing 3D printing systems, two coordinate systems are involved: one is the XYZ coordinate system, formed by the coordinated movement of the print head assembly and the printing platform in the XYZ directions, also known as the absolute coordinate system; the other is the pixel coordinate system, which corresponds to the horizontal and vertical axes, resulting from images of the model captured by a camera on the printing platform. In existing technologies, when a laser camera is mounted in an additive printing system, only relative coordinate measurements can be performed. That is, the relative position can only be determined by the positional changes in the images captured by the laser camera under different XYZ coordinate systems; it is impossible to determine the absolute coordinates corresponding to the XYZ coordinate system within the pixel coordinate system. Summary of the Invention

[0004] The purpose of this application is to provide a 3D printing system and its coordinate system calibration and transformation method and apparatus, which can determine the transformation relationship between the pixel coordinate system and the XYZ coordinate system through the coordinate system calibration process, thereby achieving accurate measurement and transformation of the absolute coordinates corresponding to the XYZ coordinate system in the pixel coordinate system.

[0005] In a first aspect, this application provides a coordinate system calibration and transformation method for a 3D printing system. The method is applied to the 3D printing system, which includes: a print head assembly equipped with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is configured with an XYZ coordinate system; the laser is used to emit laser light onto the printing platform; the camera is used to acquire images of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to either the Y-axis or the X-axis in the XYZ coordinate system; the method includes: calibrating the pixel coordinate system and the Z-axis in the XYZ coordinate system. The system is configured to: determine the position where Z equals a specified value; calibrate the first transformation coefficient in the first coordinate axis direction and the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system; wherein the transformation coefficient is used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel; calibrate the first offset of the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction and the second offset of the pixel reference point and the nozzle of the printhead assembly in the X-axis direction; and determine the transformation relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals a specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset.

[0006] Furthermore, the above-mentioned step of calibrating the position where Z equals the specified value in the pixel coordinate system and the XYZ coordinate system includes: controlling the printing platform to move upward along the Z axis in the XYZ coordinate system, or controlling the print head assembly to move downward along the Z axis, until the printing platform is detected to be in contact with the nozzle of the print head assembly, and recording the current coordinate value on the Z axis in the XYZ coordinate system as the specified value; controlling the printing platform / print head assembly to continue moving downward / upward along the Z axis in the XYZ coordinate system by a scanning height Hc, and determining the coordinate position of the laser on the first coordinate axis in the pixel coordinate system in the image currently acquired by the camera, corresponding to the position in the XYZ coordinate system where Z equals the specified value + scanning height Hc.

[0007] Furthermore, the step of calibrating the first transformation coefficient in the first coordinate axis direction of the pixel coordinate system includes: increasing the distance between the printing platform and the print head assembly by one unit distance, acquiring a first image captured by the camera before the distance increase and a second image captured by the camera after the distance increase; detecting the pixel change value corresponding to the laser's position on the first coordinate axis in the first image and the second image; and determining the pixel change value as the first transformation coefficient in the first coordinate axis direction of the pixel coordinate system.

[0008] Furthermore, the step of calibrating the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system includes: acquiring an image of a specified model on a printing platform using a camera; the specified model includes at least two points in the second coordinate axis direction; identifying the captured image to determine the pixel value corresponding to the center of the two points; and applying the pixel value divided by the distance between the centers of the two points to obtain the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system.

[0009] Furthermore, the step of calibrating the first offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the Y-axis direction includes: printing a first regular model on the printing platform through the nozzle of the printhead assembly; adjusting the Y-coordinate of the nozzle center so that the Y-coordinate of the nozzle center corresponds to the center position of the first regular model, and obtaining the first Y-coordinate corresponding to the nozzle center; adjusting the X-coordinate of the nozzle center so that the X-coordinate of the laser position in the image captured by the camera is aligned with the lateral center point of the first regular model, and recording the second Y-coordinate corresponding to the laser center; calculating the difference between the first Y-coordinate and the second Y-coordinate to obtain the first offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the Y-axis direction.

[0010] Further, the step of calibrating the second offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the X-axis direction includes: printing a second regular model on the printing platform using the printhead assembly; adjusting the Y-axis coordinate of the printhead assembly to offset the current Y-axis by a first offset; adjusting the X-axis coordinate of the printhead assembly according to a preset distance, and acquiring images of the laser scanning second regular model after each adjustment using a camera; finding a target image from multiple images showing the laser passing through the center point of the second regular model; determining the first X-axis coordinate corresponding to the laser and the second X-axis coordinate corresponding to the nozzle center from the target image; and calculating the difference between the first X-axis coordinate and the second X-axis coordinate to obtain the second offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the X-axis direction.

[0011] Furthermore, the step of determining the transformation relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals a specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset includes: determining the transformation relationship between the nozzle XY coordinates and the pixel reference point XY coordinates based on the first offset and the second offset; determining the transformation relationship between the YZ / XZ coordinates of any laser point in the camera image and the YZ / XZ coordinates of the pixel reference point based on the calibration position where Z equals a specified value, the first transformation coefficient, and the second transformation coefficient; and determining the transformation relationship between the XYZ coordinate system and the pixel coordinate system based on the transformation relationship between the nozzle XY coordinates and the pixel reference point XY coordinates, and the transformation relationship between the YZ / XZ coordinates of any laser point in the camera image and the YZ / XZ coordinates of the pixel reference point.

[0012] Secondly, this application also provides a coordinate system calibration and transformation device for a 3D printing system. The device is applied to the 3D printing system. The 3D printing system includes: a print head assembly equipped with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is equipped with an XYZ coordinate system; the laser is used to emit laser light to the printing platform; the camera is used to acquire images of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to the Y-axis or X-axis in the XYZ coordinate system; the device includes: a calibration module for calibrating the pixel coordinate system and the XYZ coordinate system. The system is configured to: a position where Z equals a specified value; calibrate a first transformation coefficient along the first coordinate axis and a second transformation coefficient along the second coordinate axis in the pixel coordinate system; wherein the transformation coefficient is used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel; calibrate a first offset of the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction and a second offset of the pixel reference point and the nozzle of the printhead assembly in the X-axis direction; and a conversion module is used to determine the conversion relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals a specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset.

[0013] Thirdly, this application also provides a 3D printing system, comprising: a print head assembly equipped with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is configured with an XYZ coordinate system; the laser is used to emit laser light to the printing platform; the camera is used to acquire images of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to the Y-axis or X-axis in the XYZ coordinate system; the system is used to perform the coordinate system calibration and transformation method of the 3D printing system as described in the first aspect.

[0014] Fourthly, this application also provides a computer-readable storage medium storing computer-executable instructions. When the computer-executable instructions are called and executed by a processor, the computer-executable instructions cause the processor to implement the coordinate system calibration and transformation method of the 3D printing system described in the first aspect.

[0015] The 3D printing system and its coordinate system calibration and transformation method and apparatus provided in this application are applied to a 3D printing system. The 3D printing system includes: a print head assembly equipped with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is equipped with an XYZ coordinate system; the print head assembly and the printing platform work together to complete printing in the XYZ directions; the laser is used to emit laser light to the printing platform; the camera is used to acquire images of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to the Y-axis or X-axis in the XYZ coordinate system; the method includes: calibration. The process involves: determining the position where Z equals a specified value in both the pixel coordinate system and the XYZ coordinate system; calibrating a first transformation coefficient along the first coordinate axis and a second transformation coefficient along the second coordinate axis in the pixel coordinate system; wherein the transformation coefficient represents the number of pixels per unit distance or the distance corresponding to a single pixel; calibrating a first offset between the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction and a second offset between the pixel reference point and the nozzle of the printhead assembly in the X-axis direction; and determining the transformation relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals the specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset. This application can determine the transformation relationship between the pixel coordinate system and the XYZ coordinate system through a coordinate system calibration process, thereby achieving accurate measurement and conversion of the absolute coordinates in the pixel coordinate system to obtain the corresponding absolute coordinates in the XYZ coordinate system. The absolute coordinates can then be used to perform high-precision absolute coordinate detection of the printing platform and objects on the printing platform. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a 3D printing system provided in an embodiment of this application;

[0017] Figure 2 A flowchart illustrating a coordinate system calibration and transformation method for a 3D printing system provided in this application embodiment;

[0018] Figure 3 This application provides a schematic diagram of laser position in a pixel coordinate system.

[0019] Figure 4 This application provides a schematic diagram of laser position comparison in a pixel coordinate system.

[0020] Figure 5 A schematic diagram of a sticker model provided in an embodiment of this application;

[0021] Figure 6 This application provides a schematic diagram of the offset between the nozzle and the pixel coordinate center in an embodiment of the present application.

[0022] Figure 7A schematic diagram of a nozzle-pixel coordinate center offset detection and a first rule model provided in an embodiment of this application;

[0023] Figure 8 This is a schematic diagram illustrating another nozzle-pixel coordinate center offset provided in an embodiment of this application;

[0024] Figure 9 A schematic diagram of a nozzle-pixel coordinate center offset detection and a second rule model provided in an embodiment of this application;

[0025] Figure 10 A full-scale diagram of a pixel coordinate system provided in an embodiment of this application;

[0026] Figure 11 This application provides a schematic diagram of the pixel center in a pixel coordinate system.

[0027] Figure 12 A schematic diagram of a calibration model and a model topology provided for embodiments of this application;

[0028] Figure 13 A schematic diagram of a scanned image and a binary image provided in an embodiment of this application;

[0029] Figure 14 A schematic diagram of camera printhead offset calculation provided in this application embodiment;

[0030] Figure 15 This is a structural block diagram of a coordinate system calibration and transformation device for a 3D printing system provided in an embodiment of this application. Detailed Implementation

[0031] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] To address the problem in existing technologies that cannot determine the absolute coordinates corresponding to the XYZ coordinate system in the pixel coordinate system, this application provides a 3D printing system and its coordinate system calibration and transformation method and apparatus. It can determine the transformation relationship between the pixel coordinate system and the XYZ coordinate system through the coordinate system calibration process, thereby achieving accurate measurement and transformation of the absolute coordinates corresponding to the XYZ coordinate system in the pixel coordinate system. The absolute coordinates can be used to perform high-precision absolute coordinate detection on the printing platform and the objects on the printing platform.

[0033] To facilitate understanding of this embodiment, a coordinate system calibration and transformation method for a 3D printing system disclosed in this application embodiment will be described in detail first.

[0034] This application provides a coordinate system calibration and transformation method for a 3D printing system, which is applied to a 3D printing system; see also Figure 1 As shown, the 3D printing system includes: a print head assembly 13 with a laser 11 and a camera 12 fixedly configured, and a printing platform 14 disposed below the print head assembly 13; the 3D printing system is configured with an XYZ coordinate system; the print head assembly and the printing platform work together to complete printing in the three XYZ directions; there are various implementation methods, such as the print head assembly moving on one of the X, Y, and Z coordinate axes, and the printing platform moving on the other two coordinate axes, or the print head assembly moving on two coordinate axes, and the platform moving on another coordinate axis, or both the print head assembly and the printing platform can move on all three coordinate axes, or the print head assembly covering the X or Y axis so that the axis does not move, and the print head assembly and the printing platform moving on the other two coordinate axes, etc.

[0035] The printhead assembly 13 includes a printing material 131 composed of filaments or powder / granules, an extruder 132, a nozzle 133, and an XY-axis assembly (not shown in the figure) for controlling the movement of the printhead assembly. A sensor 15 (such as a strain gauge) is also provided on the printing platform 14. A laser 11 and a camera 12 are fixedly connected to the printhead assembly 13. As the nozzle 133 of the printhead assembly 13 moves, the laser 11 and camera 12 also move accordingly. In this embodiment, the printhead assembly 13 can reciprocate along the XY-axis of the system; the printing platform 14 can reciprocate along the Z-axis of the system. Therefore, the free movement along the XYZ axes constitutes the XYZ coordinate system of the system. In fact, the XY coordinate values ​​of the system refer to the XY coordinate values ​​of the nozzle 133 on the printhead assembly 13.

[0036] The aforementioned laser 11, camera 12, or additional lighting, constitute a laser measurement system. Laser 11 emits a laser beam onto the printing platform 14; camera 12 captures an image of the printing platform 14 under laser illumination, thereby determining the position of the laser line in the image; during camera 12 calibration, if the lighting is insufficient, supplementary lighting can be provided using an additional lighting lamp. The image captured by camera 12 is composed of a matrix of pixel coordinates, corresponding to a pixel coordinate system; the first coordinate axis of the pixel coordinate system corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to either the Y-axis or X-axis in the XYZ coordinate system; the first and second coordinate axes can be the horizontal and vertical axes of the pixel coordinate system, or they can be the vertical and horizontal axes, respectively.

[0037] Laser 11 must be installed parallel to the X-axis or Y-axis. Figure 1 The image shows the case where laser 11 is parallel to the Y-axis, and the camera 12 is mounted at a different angle. Figure 1 When the laser position remains unchanged after a 90° rotation, the horizontal and vertical axes of the pixel coordinate system are interchanged. At this point, the horizontal axis corresponds to the Z-axis of the XYZ coordinate system, and the vertical axis corresponds to the Y-axis. When laser 11 is compared to... Figure 1 When the installation position is rotated 90° while the camera position remains unchanged, the laser line is parallel to the X-axis, the horizontal axis still corresponds to the Z-axis of the XYZ coordinate system, and the vertical axis corresponds to the X-axis of the XYZ coordinate system. Combined with... Figure 1 The dark gray vertical bars represent the effective travel of the printing platform in the Z direction of the XYZ coordinate system. The light gray vertical bars represent the effective range of the laser measurement system in the XYZ coordinate system. The system can calibrate the camera's pixel coordinate system with the Y-axis (or X-axis) and Z-axis of the XYZ coordinate system and establish a transformation relationship between the two coordinate systems. The specific process is as follows.

[0038] See Figure 2 The flowchart shown illustrates the coordinate system calibration and transformation method for the 3D printing system. This method specifically includes the following steps:

[0039] Step S202: Calibrate the positions in the pixel coordinate system and the XYZ coordinate system where Z equals the specified value;

[0040] Step S204: calibrate the first transformation coefficient in the first coordinate axis direction and the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system; wherein, the transformation coefficient is used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel; for example, the transformation coefficient is the number of pixels per millimeter or the number of millimeters per pixel.

[0041] Step S206: calibrate the first offset of the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction, and the second offset of the pixel reference point and the nozzle of the printhead assembly in the X-axis direction.

[0042] The aforementioned pixel reference point can be a pixel in the image captured by the camera. In a preferred embodiment, it can be the center point of the pixel coordinates corresponding to the laser line.

[0043] It should be noted that the execution order of steps S204 and S206 can be changed without affecting the overall calibration process.

[0044] Step S208: Based on the calibration position where Z equals the specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset, determine the transformation relationship between the XYZ coordinate system and the pixel coordinate system.

[0045] The following section will explain the above calibration steps in detail with the laser mounted parallel to the Y-axis:

[0046] Step S202: Calibrate the positions in the pixel coordinate system and the XYZ coordinate system where Z equals the specified value:

[0047] Specifically, taking a specified value of 0 as an example, the printing platform is controlled to move upward along the Z-axis in the XYZ coordinate system, or the printhead assembly is controlled to move downward along the Z-axis, until the printing platform and the nozzle of the printhead assembly are detected to be in contact, and the current coordinate value on the Z-axis in the XYZ coordinate system is recorded as 0. The printing platform / printhead assembly is then controlled to continue moving downward / upward along the Z-axis in the XYZ coordinate system by a scan height Hc, determining the coordinate position of the laser on the first coordinate axis (i.e., the Z-axis) in the pixel coordinate system of the image currently captured by the camera, corresponding to the position in the XYZ coordinate system where Z equals 0 + Hc. The specified value can also be any position such as ±1, ±2, etc.

[0048] For specific implementation, please refer to Figure 3 As shown, the system selects a point at any location on the printing platform and controls the printhead assembly to move to that point via the XY axis assembly. The mechanical XY coordinates of this point are determined. Then, the printing platform is moved until the Z-coordinate of the XYZ coordinate system reaches a position where Z equals 0. During this movement, when the nozzle surface impacts the printing platform surface, the two surfaces make physical contact. At this point, a sensor fixed to the printing platform can detect this "impact" trigger signal. Upon detecting this "impact" trigger signal, the system immediately stops the Z-axis movement and records the current Z-axis coordinate value. The system considers this value to be the coordinate value where Z equals 0 (in fact, the system redefines the position where Z equals 0; that is, the position where the nozzle surface and the printing platform surface make physical contact is the position where Z equals 0). Based on the current position where Z equals 0, upward movement of the printing platform's Z-coordinate is considered a negative value in the Z-coordinate system, and downward movement is considered a positive value.

[0049] In practical applications, the Z-coordinate of the printing platform needs to be adjusted downwards again to the specific scanning height Hc for laser camera scanning (to avoid interference between the nozzle surface and the platform surface when the nozzle moves in the XY direction, the nozzle surface needs to be a certain distance Hc higher than the printing platform surface when the laser camera scans). After this adjustment, the laser will appear at the center of the pixel coordinates. At this point, it is necessary to read and record the position of the laser line in the pixel coordinate system as it illuminates the printing platform (e.g., ...). Figure 3 The gray "laser" indicates the location. At this point, each pixel containing the laser line represents the XYZ coordinate system Z = 0 + Hc. This completes the location calibration process.

[0050] The first sub-step in step S204: calibrate the first transformation coefficient in the first coordinate axis direction of the pixel coordinate system.

[0051] Increase the distance between the printing platform and the printhead assembly by one unit (e.g., 1 mm), and acquire a first image captured by the camera before the distance increase and a second image captured by the camera after the distance increase; detect the pixel change value corresponding to the position of the laser line on the first coordinate axis in the first and second images; determine the pixel change value as the first transformation coefficient in the direction of the first coordinate axis in the pixel coordinate system.

[0052] In practice, if the printing platform is positioned in the XYZ coordinate system where Z equals the specified value plus the scan height, and the pixel coordinate system has already been calibrated to the position where Z equals the specified value plus the scan height, then adjusting the printing platform to increase or decrease the Z coordinate value will cause the laser's position in the pixel coordinate system to move up or down. This upward or downward movement is the deviation from the calibrated position where "Z equals the specified value plus the scan height". By adding this deviation value to the specified Z value in the XYZ coordinate system, the absolute coordinate value of each pixel corresponding to the laser in the XYZ coordinate system can be obtained.

[0053] Taking the first conversion factor as an example with the number of pixels per millimeter, the specific calibration process is as follows:

[0054] See Figure 4 As shown, keeping the printing platform in the XYZ coordinate system Z = 0 + Hc at the laser camera scanning height, for example, adjust the printing platform downwards by 1 mm and record the pixel difference before and after the movement, i.e., the number of pixels; when the printing platform moves downwards by 1 mm, the pixel difference of the laser image before and after the two operations is 6 pixels. Given that the movement distance is 1 mm, find the number of pixels K per millimeter in the Z-axis direction. Z =6÷1=6; K Z This means that if the pixel difference between the ordinate position relative to the specified Z value and the current depth position is 6 pixels, then this movement results in a 1mm downward position in the XYZ coordinate system. At this time, the position of the XYZ coordinate system output by the laser measurement system is Z = (0 + Hc) + 1 - Hc = 1. In other words, a deviation of 6 pixels in each column of the ordinate represents a downward movement of 1mm by the printing platform, resulting in the output mechanical coordinate Z = (0 + Hc) + 1 - Hc = 1. Because scanning is prone to interference with the model, it is necessary to offset the scanning height. The actual output coordinates are obtained by subtracting the scanning height.

[0055] The laser measurement system uses the mechanical coordinate system with Z equal to a specified value plus the scanning height as a reference to detect height in the Z direction. The system outputs the Z-direction coordinates in the XYZ coordinate system. Within the effective measurement range (M... LDepth measurement is performed within the specified area and superimposed on the XYZ coordinate system. The formula for outputting the measurement range of the Z-axis of the XYZ coordinate system is: Z = 0 + Hc ± 0.5 * M L .

[0056] It should be noted that the calibration process described above, besides moving the printing platform to induce one or more displacements, can also be achieved by illuminating a contour block with a laser or by taking a picture of the calibration label. When the printing platform moves to a certain height along the Z-axis, the laser measurement system can maintain the same height for imaging, or it can lower the printing platform to take a picture. This section mainly explains the method of taking pictures at the same height. In practical applications, it is necessary to lower the printing platform to take pictures. That is to say, the Z-axis height for laser imaging must be higher than the surface of the printing platform. The purpose of this is to prevent the nozzle from interfering with the measured object on the surface of the printing platform during laser camera positioning. Therefore, the nozzle surface must be higher than the surface of the measured object during imaging.

[0057] The second sub-step in step S204: calibrate the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system.

[0058] The camera captures images of a specified model on the printing platform; the specified model includes at least two points along the second coordinate axis; the captured images are identified to determine the pixel values ​​between the centers of the two points; the pixel values ​​are divided by the distance between the centers of the two points to obtain the second transformation coefficient along the second coordinate axis in the pixel coordinate system.

[0059] The following explanation uses the calibration of the number of pixels per millimeter along the Y-axis in the pixel coordinate system as an example: In practice, the horizontal coordinate of the laser measurement system's pixel coordinate system is calibrated, that is, the correspondence between the length of the laser's horizontal coordinate in the pixel coordinate system and its actual length in the Y-direction of the XYZ coordinate system is determined. Based on this correspondence, the pixel reference point position, and the offset on the horizontal coordinate in the pixel coordinate system, the pixel coordinate system can be converted into the XYZ coordinate system, thereby enabling the system to output absolute coordinates.

[0060] The specific calibration process is as follows:

[0061] The system uses a camera to capture images, either photographing or scanning the outer contour of a target at a known fixed distance at a scanning height. Figure 5The sticker shown is affixed to a printing platform. For example, the horizontal or vertical center-to-center distance between any two dots in the image is 5mm. A camera is used to photograph the sticker, obtaining an image. By identifying the dots in the image, the pixel difference between the centers of any two horizontally aligned dots is calculated. For example, if the calculated pixel difference is 30, and the distance between the horizontally aligned center and the actual center is 5mm, then the number of pixels per millimeter in the Y-axis direction is K. Y =30÷5=6; K Y This means that if the measured object has a pixel difference of 6 pixels in the x-axis direction of the pixel coordinate system, then the measured object has a length of 1mm in the y-direction of the XYZ coordinate system. This achieves the function of converting pixel difference into actual length.

[0062] The first sub-step in step S206: calibrating the first offset of the pixel reference point in the pixel coordinate system from the nozzle of the printhead assembly in the Y-axis direction:

[0063] A first regular model is printed on the printing platform through the nozzle of the printhead assembly. The first regular model can be a model of various shapes such as rectangle, trapezoid, and rhombus. The Y coordinate of the nozzle center is adjusted so that the Y coordinate of the nozzle center corresponds to the center position of the first regular model, and the first Y coordinate corresponding to the nozzle center is obtained. The X coordinate of the nozzle center is adjusted so that the X coordinate of the laser line position in the image captured by the camera is aligned with the horizontal center point of the first regular model, and the second Y coordinate corresponding to the laser center is recorded. The difference between the first Y coordinate and the second Y coordinate is calculated to obtain the first offset of the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the Y-axis direction.

[0064] In practice, since the laser measurement system is mounted and fixed on the printhead assembly, it is inevitable that the nozzle and pixel coordinate center positions on the printhead assembly will deviate in the Y direction. This deviation is called manufacturing deviation. Figure 6 As shown, the gray line on the left of the image represents the laser line, and the black dot at the center of the line corresponds to the black dot on the right, representing the pixel center position. The left side of the image shows the offset ΔY of the nozzle center and the pixel coordinate center in the Y direction of the XYZ coordinate system.

[0065] In this embodiment, the pixel coordinate center is used as the pixel reference point. Taking a rectangular model as an example, the specific calibration process is as follows:

[0066] ① The system prints a rectangular model of a specified height using a nozzle;

[0067] ②Then adjust the mechanical coordinate value of the nozzle center in the Y direction so that the Y coordinate of the nozzle is exactly at the position of half the length L of the rectangular model.

[0068] ③ Then adjust the X-axis coordinate so that the X-coordinate of the laser line position in the image captured by the camera is aligned with the horizontal center point of the rectangular model, such as... Figure 7 As shown, the laser line divides the model into two symmetrical halves. The image on the right shows the effect of the laser illuminating the rectangular model.

[0069] ④ Calculate half the distance L between the laser beams illuminating the centers of the two contours of the model, and subtract half the total laser length L1. Subtracting these two values ​​gives the offset ΔY between the nozzle center and the pixel coordinate center.

[0070] By calculating ΔY using calibration methods, the nozzle center in the XYZ coordinate system can be aligned with the pixel coordinate center. This allows for direct coordinate system transformation. If the nozzle center is slightly above the pixel coordinate center in the horizontal direction, it indicates a positive offset in the Y direction (ΔY). Conversely, it indicates a negative offset in the Y direction (ΔY).

[0071] The second sub-step in step S206: calibrating the second offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the X-axis direction:

[0072] A second regular model is printed on a printing platform using a printhead assembly. This second regular model can be a centrally symmetrical pattern with its maximum diameter at its center point along the scanning direction, such as a rhombus, ellipse, or circle. The Y-axis coordinate of the printhead assembly is adjusted to offset the current Y-coordinate by a first offset amount. The X-coordinate of the printhead assembly is adjusted according to a preset distance, and an image of the laser scanning second regular model is captured by a camera after each adjustment. The target image from multiple images is searched for where the laser line passes through the center point of the second regular model. The first X-coordinate corresponding to the laser line and the second X-coordinate corresponding to the nozzle center are determined from the target image. The difference between the first X-coordinate and the second X-coordinate is calculated to obtain the second offset amount in the X-axis direction between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly.

[0073] The following explanation uses a circular model with a known diameter as an example, with the pixel coordinate center as the pixel reference point:

[0074] In practice, since the laser measurement system is mounted and fixed on the printhead assembly, it is inevitable that the nozzle and pixel coordinate center positions on the printhead assembly will deviate in the X direction. This deviation is called manufacturing deviation. Figure 8 As shown in the figure, the distance indicated by the double arrows is the offset ΔX between the nozzle and the center position of the pixel coordinates; for example, in engineering, this deviation will produce a deviation of 10mm±2mm under assembly deviation, and fluctuate within this range.

[0075] like Figure 9 As shown, the calibration process is as follows:

[0076] ① The system prints a circular model of known diameter and height using a nozzle, for example, a diameter of 15mm;

[0077] ② Adjust the XY coordinate values ​​of the print head and offset the Y coordinate by a calibration value of ΔY (as in step (4) above, so that the horizontal coordinate of the camera pixel coincides with the center of the circle), so that the nozzle moves to the center coordinate of the model and records the current coordinate;

[0078] ③ Then, activate the camera and laser, and move the printhead assembly in the X direction by a fixed distance D. Combined with the aforementioned fluctuation of ΔX within a range of 10mm ± 2mm, for example, each movement of D = 0.1mm, a total of 10 / 0.1 = 100 movements are required. This allows the laser and camera to scan the printed circular mold. A laser image is taken after each movement, for a total of 100 images, which are then numbered.

[0079] ④ Calculate the diameter of the model illuminated by the laser in each image. When the detected model diameter is between 15mm and 14.6mm, the system considers the coordinates corresponding to the current image number to coincide with the pixel coordinate center. The offset ΔX between the pixel coordinate center and the nozzle center is equal to the current image number * 0.1mm.

[0080] It should be noted that the pixel coordinate center mentioned above is the same as the pixel center point corresponding to the laser line in the image.

[0081] Figure 9 In the diagram, black circles represent the printed circular model, dashed circles represent the trajectory of the nozzle moving to the left at a certain distance, such as 0.1mm, and vertical lines represent the trajectory of the laser line. The trajectories are numbered from right to left in ascending order. Due to space limitations, not all trajectories can be drawn; they are only used here to more clearly illustrate the specific movement process.

[0082] After completing the calibration of the position where Z equals the specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset, step S208 can be further executed: based on the calibration position where Z equals the specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset, determine the transformation relationship between the XYZ coordinate system and the pixel coordinate system.

[0083] In practice, the transformation relationship between the nozzle's XY coordinates and the pixel reference point's XY coordinates can be determined based on the first offset and the second offset. For example, in the XYZ coordinate system, the coordinates corresponding to the nozzle are X1 and Y1, and the coordinates corresponding to the printing platform are Z1. Based on the first offset ΔY1 between the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction, and the second offset ΔX1 between the pixel reference point and the nozzle of the printhead assembly in the X-axis direction, the X and Y coordinates of the pixel reference point (X2, Y2, Z2) can be determined as: X2 = X1 + ΔX1; Y2 = Y1 + ΔY1.

[0084] Furthermore, based on the calibration position where Z equals a specified value, the first conversion coefficient, and the second conversion coefficient, the conversion relationship between the YZ / XZ coordinates of any laser point in the camera image and the YZ / XZ coordinates of the pixel reference point can be determined.

[0085] After pre-calibrating the position where Z equals a specified value, the Z coordinate corresponding to the pixel reference point is the Z coordinate corresponding to the printing platform, i.e., Z2 = Z1. In other words, the mechanical coordinates corresponding to the pixel reference point are: X2, Y2, Z2. Based on this, and according to the first and second conversion coefficients, the conversion relationship between the YZ coordinates of any laser point in the camera image and the YZ coordinates of the pixel reference point can be determined. Taking the ZY coordinates corresponding to the pixel coordinate system as an example, if the distance between the target laser point and the pixel reference point is 12 pixels in the Y direction and 12 pixels in the Z direction, the first unit millimeter in the Z-axis direction has 4 pixels, and the second unit millimeter in the Y-axis direction has 6 pixels; this is equivalent to the target laser point being offset by 12 / 6 = 2 millimeters in the Y direction and 12 / 4 = 3 millimeters in the Z direction from the pixel reference point. Since the X coordinate is consistent with the pixel reference point coordinate, the coordinates corresponding to the target laser point are: X3 = X2; Y3 = Y2 + 2; Z3 = Z3 + 3.

[0086] Therefore, based on the transformation relationship between the nozzle XY coordinates and the pixel reference point XY coordinates, and the transformation relationship between the YZ / XZ coordinates of any laser point and the pixel reference point YZ / XZ coordinates in the camera image, the transformation relationship between the XYZ coordinate system and the pixel coordinate system can be determined.

[0087] In this embodiment, the "calibration position where Z equals a specified value" of the two coordinate systems primarily serves to establish a connection between them, specifically between the XYZ coordinate system and the pixel coordinate system. The specified Z value serves as an alignment reference between the pixel coordinate system and the XYZ coordinate system. During detection, when the laser illuminates the printing platform and forms an image in the camera, the system calculates the laser's position in the pixel coordinate system. Then, based on the aforementioned calibration values—such as the first transformation coefficient in the Z-axis direction, the second transformation coefficient in the Y-axis direction, the first offset of the pixel reference point in the pixel coordinate system from the nozzle of the printhead assembly in the Y-axis direction, and the second offset of the pixel reference point in the pixel coordinate system from the nozzle of the printhead assembly in the X-axis direction—the system obtains the absolute coordinate values ​​of the XYZ coordinate system.

[0088] When performing detection in the Z-axis direction, the laser measurement system uses the mechanical coordinate Z equal to a specified value as a reference, within the effective measurement range (M). L Depth measurement is performed within the specified area and superimposed on the XYZ coordinate system. The measurement range of the Z-axis of the XYZ coordinate system is calculated using the formula: Z = specified value + Hc ± 0.5 * M. L ,like Figure 10 As shown. It should be noted that the position where Z equals the specified value + Hc in the XYZ coordinate system is not necessarily half of the effective range; for ease of explanation, this situation is described here.

[0089] Since the laser camera measurement component is mounted and fixed on the print head assembly, the center position of the vertical and horizontal pixels in the camera pixel coordinate system (e.g., Figure 11 The black pixels in the image are offset from the nozzle position. When performing XYZ coordinate system Y-axis detection, it is necessary to calibrate the offset ΔY in the Y-axis between the printhead XYZ coordinate system and the pixel coordinate system at the center of the horizontal and vertical pixels (or the four corners of the pixel matrix or other positions). The formula for calculating the XYZ coordinate system Y-axis position of the center of the horizontal and vertical pixels is Y = Y + ΔY; the formula for calculating the mechanical coordinate position of other pixels is: Y = Y + ΔY + (±P*K);

[0090] In the formula, P is the distance of the current pixel from the center of the pixel (e.g., ...). Figure 11 The positive and negative pixel increment values ​​of the black pixels in the graph, where K is the aforementioned second conversion coefficient, such as the number of pixels per millimeter (obtained through calibration).

[0091] The system, through a series of calibrations, enables the laser to be transformed from the pixel coordinate system to the XYZ coordinate system. That is, after the pixel coordinate system is transformed, it can directly output the coordinate values ​​in the XYZ coordinate system. Therefore, each pixel on the ordinate of the camera's pixel coordinate system represents the height value of the printing platform surface on the Z-axis in the XYZ coordinate system. Thus, the detection performed using the pixel coordinate system is actually based on the detection of absolute coordinate values ​​in the XYZ coordinate system, not relative coordinate values. Therefore, by using laser scanning, not only can the absolute Y (or X) and Z coordinates of any position on the printing platform surface be measured, but the height of any object on the printing platform surface can also be detected, yielding absolute coordinate values ​​in the XYZ coordinate system.

[0092] In another implementation, the steps of calibrating the first offset of the pixel reference point in the pixel coordinate system from the nozzle of the printhead assembly in the Y-axis direction, and the second offset of the pixel reference point from the nozzle of the printhead assembly in the X-axis direction, can also be achieved in the following way:

[0093] It should be noted that in this embodiment, the mechanical coordinates of the printhead are consistent with the mechanical coordinates of the nozzle in the aforementioned printhead assembly. The final calibration value actually includes the first offset ΔY in the Y-axis direction and the second offset ΔX in the X-axis direction.

[0094] (1) Print the calibration model on the printing platform through the print head; the calibration model includes: a rectangular border line and a line connecting a preset point on one border line to two vertices of the opposite border line;

[0095] A schematic diagram of the above calibration model is shown below. Figure 12 As shown in the left figure, the model consists of rectangle FCDE, line segments IC and ID. Point I is a point on the border line FE. In this model, the mechanical coordinates (gcode coordinates) of the five points FCDEI are all available, i.e., known. For ease of calculation, point I can be set as the midpoint of the FE border line.

[0096] (2) The line laser emitted by the laser is used to scan the calibration model in the direction from the edge line to the opposite edge line, and multiple scan images are captured by the camera during the scanning process; the topological diagram of the relationship between the model and the laser line is formed by the intersection of the laser line and the calibration model.

[0097] In practice, a line laser scans from the FE border line to the CD border line, or from the CD border line to the FE border line. During the scan, the model topology formed by the intersection of the laser line and the model is as follows: Figure 12As shown in the right figure, HG represents the state of the laser line illuminating the model; the four intersection points of the laser line HG and the model are A, B, J, and K, respectively. The actual image of the laser illuminating the calibration model, that is, the scanned image captured by the camera, is shown below. Figure 13 As shown in the left figure, points K, J, B, and A are respectively... Figure 12 The points with the same number in the middle correspond one-to-one.

[0098] (3) For each scanned image, determine the pixel coordinates of multiple intersection points between the laser line and the calibration model based on the scanned image; perform calculations based on the pixel coordinates of multiple intersection points and the mechanical coordinates of the model points in the topology diagram to obtain the mechanical coordinates of the specified intersection point; calculate the camera printhead offset distance based on the specified intersection point, the mechanical coordinates of the printhead, and the pixel coordinates of the camera center based on the mechanical coordinates of the specified intersection point.

[0099] First, based on the binary image of the scanned image, the pixel coordinates of multiple intersection points A, B, J, and K between the laser line and the calibration model are calculated. Then, combined with the mechanical coordinates of model points in the model topology diagram, such as the mechanical coordinates of the four vertices F, C, D, E and the midpoint I, the mechanical coordinates of the specified intersection points (such as points A and / or K) are calculated. Further, based on the mechanical coordinates of the specified intersection points (such as points A and / or K), the known mechanical coordinates of the printhead, and the known pixel coordinates of the camera center, the camera printhead offset distance is calculated with the specified intersection points (such as points A and / or K) as the reference. The specific calculation process is as follows:

[0100] The implementation process of the sub-step "determining the pixel coordinates of multiple intersection points between the laser line and the calibration model based on the scanned image" is as follows:

[0101] The intersection of the laser line and the calibration model appears as a notch in the scanned image, with one intersection corresponding to one notch;

[0102] (1) Convert the scanned image into a binary image;

[0103] (2) Determine the centerline coordinates of the laser line in the binary image;

[0104] (3) Using the centerline coordinates as the starting point for retrieval, perform a row-by-row traversal retrieval of the binary image to determine the pixel coordinates corresponding to the multiple gap edge points;

[0105] In one implementation, the binary image is traversed row by row to detect pixels, starting from the center line coordinates. If no target laser pixel is detected in the right neighboring region of the current pixel, the pixel coordinates of the current pixel are determined as the pixel coordinates of the left edge of the notch. The target laser pixel is a laser pixel with a pixel value of 255. If no target laser pixel is detected in the left neighboring region of the current pixel, but there is a target laser pixel in the right neighboring region, the pixel coordinates of the current pixel are determined as the pixel coordinates of the right edge of the notch.

[0106] (4) Identify multiple pairs of edge points from multiple gap edge points; a pair of edge points includes the adjacent left edge point and right edge point of the gap;

[0107] (5) For each pair of edge points, calculate the coordinates of the midpoint of the gap based on the pixel coordinates of the left edge point and the right edge point of the gap, respectively, and use them as the pixel coordinates of the intersection point of the pair of edge points.

[0108] In practice, the first step is to input a binary image, such as... Figure 13 As shown in the right figure, the laser line appears as a white stripe. The coordinates m of the laser line's center line need to be calculated, as indicated by the lines formed by the small black dots in the right figure. In other words, m represents the median Y-coordinate of the entire laser line's center line. Starting from (0, m), pixel points are searched row by row from left to right. By searching the neighborhood of each pixel, the edge of the laser line gap is determined. If there is no pixel with a value of 255 in the right neighborhood, the current pixel coordinates (A1, L1) of the laser pixel are recorded as the left edge of the gap. If there is no laser pixel in the left neighborhood but there is in the right neighborhood, the current pixel coordinates (A2, L2) are recorded as the right edge of the gap. The final intersection point coordinates are the midpoints of the two gap edges: gapACents = [(A1+A2) / 2, (L1+L2) / 2)].

[0109] The implementation process of the sub-step "calculating based on the pixel coordinates of multiple intersection points and the mechanical coordinates of model points in the topology map to obtain the mechanical coordinates of a specified intersection point" is as follows:

[0110] (1) Determine the first triangle △FIC and the second triangle △ABC in the calibration model; the three sides of the first triangle △FIC include: the first target border line FC through which the laser line passes through the calibration model, and the line segments IC and IF between the preset point and the two vertices of the target border line respectively; the three vertices of the second triangle △ABC include: the first intersection point A between the laser line HG and the target border line FC, the second intersection point B between the laser line HG and the line IC connecting the preset point I to the target border line FC, and the third intersection point C between the target border line FC and the connecting line IC;

[0111] (2) Calculate the first distance c between the two intersection points based on the pixel coordinates corresponding to the first intersection point A and the second intersection point B (which have been calculated previously);

[0112] (3) Based on the mechanical coordinates of the three vertices (F, I, C) of the first triangle △FIC, calculate the first angle value ∠ACB corresponding to the third intersection point C in the second triangle △ABC;

[0113] (4) Based on the pixel coordinates corresponding to the first intersection point A and the second intersection point B, and the pixel coordinates of the first intersection point A in each binary image, determine the second angle value ∠ABC corresponding to the second intersection point B in the second triangle △ABC; specifically, this is achieved through the following process: (4.1) Based on the pixel coordinates corresponding to the first intersection point A and the second intersection point B, perform least squares fitting to obtain the first straight line, i.e., the line where AB is located; (4.2) Fit the pixel coordinates of the first intersection point A in each binary image to obtain the second straight line, i.e., the line where FC is located; (4.3) Calculate the third angle value ∠CAB corresponding to the first intersection point A in the second triangle △ABC based on the first straight line and the second straight line; (4.4) Determine the second angle value ∠ABC corresponding to the second intersection point B in the second triangle △ABC based on the third angle value ∠CAB and the first angle value ∠ACB.

[0114] (5) Based on the first distance c, the first angle value ∠ACB, and the second angle value ∠ABC, calculate the second distance b between the first intersection point A and the third intersection point C; b can be calculated using the triangle area formula.

[0115] (6) Based on the mechanical coordinates of the third intersection point C and the second distance b, the mechanical coordinates corresponding to the first intersection point A are calculated.

[0116] For example, the coordinates of point C obtained in the gcode file are (ptC.x, ptC.y), and the coordinates of the intersection point A in the XYZ coordinate system are: ptOfGcode = (ptC.xb, ptC.y).

[0117] Furthermore, the above method also includes: flipping the topology map where the laser line intersects the model vertically, and calculating the mechanical coordinates corresponding to the fourth intersection point according to the above process. The fourth intersection point is the intersection point K of the laser line HG and the second target border line ED of the model before the topology map is flipped. That is, for each scanned image, two specified intersection points A and K can be calculated by combining the topology map, and then the camera printhead offset distance can be calculated based on the mechanical coordinates corresponding to A and K respectively.

[0118] The following example, using intersection point A, illustrates the process of calculating the camera printhead offset distance:

[0119] The implementation process of the sub-step "calculating the camera-printhead offset distance based on the specified intersection point, the machine coordinates of the printhead, and the pixel coordinates of the camera center" is as follows:

[0120] Using the Y and X directions in the machine coordinate system as the current directions, perform the following steps:

[0121] (1) Calculate the first offset distance of the specified intersection point relative to the print head in the current direction based on the mechanical coordinates of the specified intersection point in the current direction and the mechanical coordinates of the print head in the current direction;

[0122] (2) Calculate the second offset distance of the specified intersection point relative to the camera in the current direction based on the pixel coordinates of the specified intersection point in the current direction and the pixel coordinates of the camera center in the current direction;

[0123] Specifically, the pixel difference between the pixel coordinates of the specified intersection point in the current direction and the pixel coordinates of the camera center in the current direction is calculated; based on the pixel difference and the pre-calibrated conversion coefficients of the current direction, the second offset distance of the specified intersection point relative to the camera in the current direction is determined; wherein, the conversion coefficients are used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel.

[0124] (3) Calculate the difference between the first offset distance and the second offset distance to obtain the camera printhead offset distance in the current direction with the specified intersection point as the reference.

[0125] Finally, we can obtain the first camera printhead offset distance ΔY in the Y direction based on the specified intersection point, which is the first offset ΔY between the laser pixel center and the nozzle of the printhead assembly in the Y-axis direction, and the second camera printhead offset distance ΔX in the X direction based on the specified intersection point, which is the second offset ΔX between the laser pixel center and the nozzle of the printhead assembly in the X-axis direction.

[0126] The following explanation uses the X direction as an example. Figure 14 As shown, first calculate the first offset distance nozzleOffset of point A in the X direction relative to the print head. X nozzleOffset X =ptOfGcode X -nozzlePos X Among them, ptOfGcode X This represents the mechanical coordinate in the X direction corresponding to intersection point A, nozzlePos X This represents the mechanical coordinates of the print head in the X direction.

[0127] Then, based on the pixel coordinates in the X direction of the specified intersection point and the pixel coordinates in the X direction of the camera center, calculate the second offset distance lightCentOffset of the specified intersection point relative to the camera in the X direction. X ;

[0128] Specifically, the pixel difference between the pixel coordinates in the X direction of the specified intersection point and the pixel coordinates in the X direction of the camera center is calculated; based on the pixel difference and the pre-calibrated transformation coefficients in the X direction, the second offset distance of the specified intersection point relative to the camera in the X direction is determined, as shown in the following formula:

[0129] lightCentOffset X =(gapACents X -lightCent X )*pixSize X ;

[0130] Among them, gapACents X The pixel coordinates in the X direction of intersection point A are represented; lightCentX represents the pixel coordinates in the X direction of the camera center; pixelSizeX represents the pre-calibrated number of pixels per millimeter in the X direction, or the reciprocal of the number of pixels per millimeter.

[0131] Finally, calculate the first offset distance nozzleOffset. X The second offset distance is lightCentOffset X The difference is used to obtain the camera printhead offset distance ΔX in the X direction with the specified intersection point as the reference (as shown in camOffset in the figure). X ):

[0132] For example: ΔX = nozzleOffset X -lightCentOffset X .

[0133] The calculation method for the first offset ΔY is the same as above, except that the corresponding mechanical coordinates in the Y direction, pixel coordinates in the Y direction, and conversion coefficients in the Y direction are replaced, which will not be repeated here.

[0134] In this embodiment, the mechanical coordinates of intersection point A are used as intermediate variables to solve for the offset of the camera printhead. By solving for the positional relationship between point A and the printhead and the camera, the positional relationship between the camera and the printhead can be solved.

[0135] The method provided here for calibrating the positional relationship between the laser camera and the 3D printer head uses a specially designed calibration model to acquire scanned images. Based on the scanned images and the model's topology, the positional relationship between the camera and the print head is calibrated. This method eliminates the need for additional supplementary lighting components or additional visual labels, resulting in low calibration costs and high efficiency.

[0136] Based on the above method embodiments, this application also provides a coordinate system calibration and transformation device for a 3D printing system. The device is applied to the 3D printing system. The 3D printing system includes: a print head assembly with a laser and a camera fixedly configured, and a printing platform disposed below the print head assembly. The 3D printing system is configured with an XYZ coordinate system. The print head assembly and the printing platform cooperate to complete printing in the XYZ directions. The laser is used to emit laser light to the printing platform. The camera is used to acquire images of the printing platform under laser illumination. The first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to either the Y-axis or the Z-axis in the XYZ coordinate system. See also... Figure 15 As shown, the device includes: a calibration module 152, used to calibrate the position where Z equals a specified value in the pixel coordinate system and the XYZ coordinate system; calibrate a first transformation coefficient in the direction of the first coordinate axis and a second transformation coefficient in the direction of the second coordinate axis in the pixel coordinate system; wherein, the transformation coefficient is used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel; calibrate a first offset of the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction and a second offset of the pixel reference point and the nozzle of the printhead assembly in the X-axis direction in the pixel coordinate system; and a conversion module 154, used to determine the conversion relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals the specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset.

[0137] Furthermore, the aforementioned calibration module 152 is used to control the printing platform to move upward along the Z-axis in the XYZ coordinate system, or to control the printhead assembly to move downward along the Z-axis, until the printing platform is detected to be in contact with the nozzle of the printhead assembly, and to record the current coordinate value on the Z-axis in the XYZ coordinate system as a specified value; to control the printing platform / printhead assembly to continue moving downward / upward along the Z-axis in the XYZ coordinate system by a scanning height Hc, and to determine the coordinate position of the laser on the first coordinate axis in the pixel coordinate system in the image currently acquired by the camera, corresponding to the position in the XYZ coordinate system where Z equals the specified value + scanning height Hc.

[0138] Furthermore, the aforementioned calibration module 152 is used to increase the distance between the printing platform and the printhead assembly by one unit distance, acquire a first image captured by the camera before the distance is increased and a second image captured by the camera after the distance is increased; detect the pixel change value corresponding to the position of the laser on the first coordinate axis in the first image and the second image; and determine the pixel change value as a first transformation coefficient in the direction of the first coordinate axis in the pixel coordinate system.

[0139] Furthermore, the aforementioned calibration module 152 is used to acquire images of a specified model on a printing platform via a camera; the specified model includes at least two points along the second coordinate axis; the captured image is identified to determine the pixel value between the centers of the two points; the pixel value is divided by the distance between the centers of the two points to obtain a second transformation coefficient along the second coordinate axis in the pixel coordinate system.

[0140] Furthermore, the aforementioned calibration module 152 is used to: print a first regular model on the printing platform through the nozzle of the printhead assembly; adjust the Y coordinate of the nozzle center so that the Y coordinate of the nozzle center corresponds to the center position of the first regular model, and obtain the first Y coordinate corresponding to the nozzle center; adjust the X coordinate of the nozzle center so that the X coordinate of the laser position in the image captured by the camera is aligned with the horizontal center point of the first regular model, and record the second Y coordinate corresponding to the laser center; calculate the difference between the first Y coordinate and the second Y coordinate to obtain the first offset of the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the Y-axis direction.

[0141] Further, the calibration module 152 described above is used to: print a second regular model on a printing platform using a printhead assembly; adjust the Y-axis coordinate of the printhead assembly to offset the current Y-axis by a first offset; adjust the X-axis coordinate of the printhead assembly according to a preset distance, and acquire images of the laser scanning second regular model after each adjustment using a camera; find the target image from multiple images where the laser passes through the center point of the second regular model; determine the first X-axis coordinate corresponding to the laser and the second X-axis coordinate corresponding to the nozzle center from the target image; calculate the difference between the first X-axis coordinate and the second X-axis coordinate to obtain the second offset of the pixel reference point in the pixel coordinate system from the nozzle of the printhead assembly in the X-axis direction.

[0142] Furthermore, the aforementioned conversion module 154 is used to determine the conversion relationship between the nozzle XY coordinates and the pixel reference point XY coordinates based on the first offset and the second offset; to determine the conversion relationship between the YZ / XZ coordinates of any laser point in the camera image and the YZ / XZ coordinates of the pixel reference point based on the calibration position where Z equals a specified value, the first conversion coefficient, and the second conversion coefficient; and to determine the conversion relationship between the XYZ coordinate system and the pixel coordinate system based on the conversion relationship between the nozzle XY coordinates and the pixel reference point XY coordinates, and the conversion relationship between the YZ / XZ coordinates of any laser point in the camera image and the YZ / XZ coordinates of the pixel reference point.

[0143] The device provided in this application embodiment has the same implementation principle and technical effect as the aforementioned method embodiment. For the sake of brevity, any parts of the device embodiment not mentioned can be referred to the corresponding content in the aforementioned method embodiment.

[0144] Thirdly, embodiments of this application also provide a 3D printing system, see [link to relevant documentation]. Figure 1 As shown, the 3D printing system includes: a print head assembly with a laser and a camera fixedly configured, and a printing platform disposed below the print head assembly; the 3D printing system is configured with an XYZ coordinate system; the print head assembly and the printing platform work together to complete printing in the XYZ directions; the laser is used to emit laser light to the printing platform; the camera is used to acquire images of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to the Y-axis or X-axis in the XYZ coordinate system; the system is used to perform the coordinate system calibration and transformation method of the 3D printing system as described above.

[0145] The system provided in this application embodiment has the same implementation principle and technical effects as the aforementioned method embodiment. For the sake of brevity, any parts not mentioned in the system embodiment can be referred to the corresponding content in the aforementioned method embodiment.

[0146] This application also provides a computer-readable storage medium storing computer-executable instructions. When the computer-executable instructions are called and executed by a processor, the computer-executable instructions cause the processor to implement the above-described method. For specific implementation details, please refer to the foregoing method embodiments, which will not be repeated here.

Claims

1. A coordinate system calibration and transformation method for a 3D printing system, characterized in that, The method is applied to a 3D printing system; the 3D printing system includes: a print head assembly configured with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is configured with an XYZ coordinate system; the laser is used to emit laser light onto the printing platform; the camera is used to acquire an image of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to either the Y-axis or the X-axis in the XYZ coordinate system; the method includes: Calibrate the position in the pixel coordinate system and the XYZ coordinate system where Z equals a specified value; The first transformation coefficient in the first coordinate axis direction and the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system are calibrated; wherein the transformation coefficient is used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel; The pixel reference point in the pixel coordinate system is calibrated by a first offset in the Y-axis direction from the nozzle of the printhead assembly, and a second offset in the X-axis direction from the pixel reference point to the nozzle of the printhead assembly. Based on the calibration position where Z equals a specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset, the transformation relationship between the XYZ coordinate system and the pixel coordinate system is determined.

2. The method according to claim 1, characterized in that, The step of calibrating the pixel coordinate system and the position in the XYZ coordinate system where Z equals a specified value includes: Control the printing platform to move upward along the Z-axis in the XYZ coordinate system, or control the print head assembly to move downward along the Z-axis, until the printing platform is detected to be in contact with the nozzle of the print head assembly, and record the current coordinate value on the Z-axis in the XYZ coordinate system as a specified value; Control the printing platform / printhead assembly to continue moving down / up along the Z-axis in the XYZ coordinate system by a scanning height Hc, and determine the coordinate position of the laser on the first coordinate axis in the pixel coordinate system in the image currently acquired by the camera, which corresponds to the position in the XYZ coordinate system where Z equals a specified value + scanning height Hc.

3. The method according to claim 1, characterized in that, The step of calibrating the first transformation coefficient in the first coordinate axis direction of the pixel coordinate system includes: Increase the distance between the printing platform and the printhead assembly by one unit, and obtain a first image captured by the camera before the distance is increased and a second image captured by the camera after the distance is increased; detect the pixel change value corresponding to the position of the laser on the first coordinate axis in the first image and the second image. The pixel change value is determined as the first transformation coefficient in the direction of the first coordinate axis in the pixel coordinate system.

4. The method according to claim 1, characterized in that, The step of calibrating the second transformation coefficient in the second coordinate axis direction of the pixel coordinate system includes: The camera captures images of a specified model on the printing platform; the specified model includes at least two points along the second coordinate axis. The captured image is identified to determine the pixel values ​​corresponding to the centers of two circles; By dividing the pixel value by the distance between the centers of the two points, a second transformation coefficient is obtained in the direction of the second coordinate axis in the pixel coordinate system.

5. The method according to claim 1, characterized in that, The step of calibrating the first offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the Y-axis direction includes: The first regular model is printed on the printing platform through the nozzles of the printhead assembly; Adjust the Y-coordinate of the nozzle center so that the Y-coordinate of the nozzle center corresponds to the center position of the first rule model, and obtain the first Y-coordinate corresponding to the nozzle center; Adjust the X coordinate of the nozzle center so that the X coordinate of the laser position in the image captured by the camera is aligned with the horizontal center point of the first regular model, and record the second Y coordinate corresponding to the laser center; The difference between the first Y coordinate and the second Y coordinate is calculated to obtain the first offset of the pixel reference point in the pixel coordinate system from the nozzle of the printhead assembly in the Y-axis direction.

6. The method according to claim 1 or 5, characterized in that, The step of calibrating the second offset between the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the X-axis direction includes: A second rule model is printed on the printing platform via the printhead assembly; Adjust the Y-axis coordinate of the printhead assembly so that the current Y-axis is offset by the first offset amount; The X coordinate of the printhead assembly is adjusted according to a preset distance, and the camera captures an image of the second rule model after each adjustment using laser scanning. Find the target image from multiple images where the laser passes through the center point of the second rule model; The first X coordinate corresponding to the laser and the second X coordinate corresponding to the nozzle center are determined from the target image; The difference between the first X coordinate and the second X coordinate is calculated to obtain the second offset of the pixel reference point in the pixel coordinate system and the nozzle of the printhead assembly in the X-axis direction.

7. The method according to claim 1, characterized in that, The step of determining the transformation relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals a specified value, the first transformation coefficient, the second transformation coefficient, the first offset, and the second offset includes: Based on the first offset and the second offset, determine the transformation relationship between the nozzle XY coordinates and the pixel reference point XY coordinates; Based on the calibration position where Z equals the specified value, the first conversion coefficient, and the second conversion coefficient, determine the conversion relationship between the YZ / XZ coordinates of any laser point in the camera image and the YZ / XZ coordinates of the pixel reference point; Based on the transformation relationship between the nozzle XY coordinates and the pixel reference point XY coordinates, and the transformation relationship between the YZ / XZ coordinates of any laser point and the pixel reference point in the camera image, the transformation relationship between the XYZ coordinate system and the pixel coordinate system is determined.

8. A coordinate system calibration and transformation device for a 3D printing system, characterized in that, The device is applied to a 3D printing system; the 3D printing system includes: a print head assembly configured with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is configured with an XYZ coordinate system; the laser is used to emit laser light onto the printing platform; the camera is used to acquire images of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to either the Y-axis or the X-axis in the XYZ coordinate system; the device includes: The calibration module is used to calibrate the pixel coordinate system and the position where Z equals a specified value in the XYZ coordinate system; calibrate a first transformation coefficient in the first coordinate axis direction and a second transformation coefficient in the second coordinate axis direction in the pixel coordinate system; wherein, the transformation coefficient is used to characterize the number of pixels corresponding to a unit distance or the distance corresponding to a single pixel; and calibrate a first offset between the pixel reference point and the nozzle of the printhead assembly in the Y-axis direction and a second offset between the pixel reference point and the nozzle of the printhead assembly in the X-axis direction in the pixel coordinate system. The conversion module is used to determine the conversion relationship between the XYZ coordinate system and the pixel coordinate system based on the calibration position where Z equals a specified value, the first conversion coefficient, the second conversion coefficient, the first offset, and the second offset.

9. A 3D printing system, characterized in that, The 3D printing system includes: a print head assembly equipped with a laser and a camera, and a printing platform disposed below the print head assembly; the 3D printing system is configured with an XYZ coordinate system; the laser is used to emit laser light onto the printing platform; the camera is used to acquire an image of the printing platform under laser illumination; the first coordinate axis of the pixel coordinate system corresponding to the image corresponds to the Z-axis in the XYZ coordinate system, and the second coordinate axis corresponds to the Y-axis or X-axis in the XYZ coordinate system; the system is used to perform the coordinate system calibration and transformation method of the 3D printing system as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when invoked and executed by a processor, cause the processor to implement the coordinate system calibration and transformation method of the 3D printing system according to any one of claims 1 to 7.

Images