Automatic focusing system and method for 3D printing equipment and 3D printing equipment

Abstract

The invention relates to an automatic focusing system of 3D printing equipment and a printing method thereof, the system comprises a laser, a collimator, a beam splitter, a galvanometer system, a first focusing module, a second focusing module, a photoelectric detector and a control system, laser emitted by the laser sequentially enters the collimator and the beam splitter, and enters the galvanometer system and the second focusing module after being transmitted by the beam splitter; after the laser is deflected by the galvanometer system and focused by the second focusing module, the laser enters a working plane with a reflecting function, so that at least reflected light reflected by the working plane returns to the beam splitter after being deflected by the galvanometer system and focused by the second focusing module; and the laser is reflected by the beam splitter to enter the first focusing module for condensation, and the laser output by the first focusing module is collected by the photoelectric detector and converted into an electric signal. According to the method, the light spot condition of a real working surface can be detected more accurately, namely, the method has the advantages of high precision, online performance and real-time performance when the light spot focusing position is determined.

Description

Technical Field

[0001] The present application relates to the field of additive manufacturing technology, and in particular to a 3D printing device autofocus system, method and 3D printing device. Background Art

[0002] Additive manufacturing technology is a rapid manufacturing technology that forms three-dimensional objects by controlling the laser to scan layer by layer and stacking layer by layer. The process flow is as follows: first, the three-dimensional model of the workpiece is sliced ​​to obtain the cross-sectional information of each layer of the workpiece; the powdered material is evenly spread on the surface of the work platform, and the laser selectively melts the powder according to the system instructions; after a section is completed, a new layer of material is spread, and the scanning continues to be selective according to the cross-sectional information corresponding to the three-dimensional object; according to this method, the next section is scanned for powder spreading, and finally a three-dimensional object is obtained.

[0003] Among the above technologies, the focal plane calibration of the laser beam is a basic step in the application process in the field of industrial additive manufacturing. Making the working plane of the laser consistent with the set printing plane, or adjusting the working plane of the laser to a predetermined position, is the basis for ensuring the printing quality. The current focal plane adjustment scheme is to adjust the substrate to the target working height, and place a beam measuring device with a reflector on the substrate to turn the laser to the beam measuring instrument to measure the spot state (including spot size and spot shape). The principle of the beam measuring instrument is to use slit scanning to filter the spot and then use a photoelectric detector of the corresponding wavelength for photoelectric conversion to obtain the spot data. This method can only use the substrate as a reference during use. The placement of the beam measuring device is prone to height errors, and the focused plane cannot be guaranteed to coincide with the actual working plane. In addition, the beam measuring instrument is expensive and has high after-sales costs. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a 3D printing device automatic focusing system, method and 3D printing device, wherein the photoelectric detector used for detection in the 3D printing device automatic focusing system, method and 3D printing device does not need to be placed on the working plane, and the position placement is flexible, thereby avoiding excessive manual operations on the working plane, and facilitating laser focus adjustment. In addition, since the adjustment position of the present invention is not limited by the working cavity space, it is easy to realize the focus detection at any position of the full-width surface, and reduces the error caused by the placement of the detection equipment, and can more accurately detect the light spot of the real working surface, that is, it has the advantages of high precision, online and real-time when determining the light spot focus position.

[0005] In order to achieve the above-mentioned purpose, the present invention provides an automatic focusing system for 3D printing equipment, comprising a laser, a collimator, a beam splitter, a galvanometer system, a first focusing module, a second focusing module, a photoelectric detector and a control system, wherein the laser emitted by the laser is incident on the collimator and the beam splitter in sequence, and is incident on the galvanometer system and the second focusing module after being transmitted by the beam splitter, and is incident on a working plane having a reflection function for the laser after being deflected by the galvanometer system and focused by the second focusing module, so that at least the reflected light reflected by the working plane returns to the beam splitter after being deflected by the galvanometer system and focused by the second focusing module, and is incident on the first focusing module under the reflection of the beam splitter for focusing, and the photoelectric detector collects the laser output by the first focusing module and converts it into an electrical signal, wherein,

[0006] The control system is used to receive the electrical signal data of the photodetector in real time, and automatically adjust the position of the collimator and / or the height of the working plane to make the received electrical signal data change in strength, until the electrical signal received by the control system is the strongest, the position of the collimator and / or the height of the working plane is stopped, and automatic focusing is completed. The first focusing module of the present application should have the function of focusing or imaging, so that the working surface and the receiving surface of the photodetector are mutually imaged, for example, it can be a separate focusing mirror or a lens group.

[0007] As a further preferred embodiment of the present invention, the automatic focusing system of the 3D printing device also includes a driving system for adjusting the position of the collimator and the height of the working plane.

[0008] As a further preferred embodiment of the present invention, the 3D printing device autofocus system also includes a quarter wave plate, which is arranged between the beam splitter and the galvanometer system, or between the beam splitter and the second focusing module, for changing the polarization state of the reflected light.

[0009] As a further preferred embodiment of the present invention, the laser emitting power is 1-30W.

[0010] As a further preferred embodiment of the present invention, the second focusing module is a field lens or a focusing lens. When the second focusing module is a focusing lens, the second focusing module is arranged between the beam splitter and the galvanometer system; when the second focusing module is a field lens, the second focusing module is arranged in the optical path between the galvanometer system and the working plane.

[0011] As a further preferred embodiment of the present invention, the automatic focusing system of the 3D printing device also includes an attenuation mirror and a filter, which are sequentially arranged between the first focusing module and the beam splitter, so that the laser emitted through the beam splitter is sequentially attenuated and filtered so that the optical intensity is adjusted to the detection range of the optical detector, and after being converged by the first focusing module, it is collected by the photoelectric detector.

[0012] As a further preferred embodiment of the present invention, the photodetector is a photodiode, a photomultiplier tube, a CCD or a CMOS, an avalanche photodiode, or a single photon detector.

[0013] The present invention also provides a 3D printing device, comprising any one of the above-mentioned 3D printing device automatic focusing systems.

[0014] The present invention also provides an auto-focusing method for the auto-focusing system of a 3D printing device as described in any one of the above, comprising the following steps:

[0015] The laser is adjusted to emit light at a preset power, and the photoelectric detector at least collects the laser reflected by the working plane;

[0016] The control system receives the reflected light collected by the photodetector in real time and converts it into electrical signal data, and changes the strength of the received electrical signal data by adjusting the position of the collimator and / or the height of the working plane. When the electrical signal received by the control system is the strongest, the control system stops adjusting the position of the collimator and / or the height of the working plane, and automatic focusing is completed.

[0017] As a further preferred embodiment of the present invention, adjusting the position of the collimator and / or the height of the working plane so that the received electrical signal data changes in strength specifically includes:

[0018] The collimator position is fixed, and the working plane is adjusted up and down by the driving system; or the height position of the working plane is fixed, and the position of the collimator is adjusted by the driving system to make the received electrical signal data change in strength.

[0019] The 3D printing device automatic focusing system, method and 3D printing device of the present invention, by adopting the above technical solution, have the following beneficial technical effects:

[0020] 1. The photoelectric detector used for detection in the automatic focusing system of the 3D printing device of the present invention does not need to be placed on the working plane, and the position is flexible, thereby avoiding excessive manual operations on the working plane, and the laser focus adjustment is convenient;

[0021] 2. Compared with the prior art, the present invention is not limited by the placement position because the detection equipment does not need to be placed on the working plane, and can thus realize focus detection at any position of the full-width area; and compared with the detection equipment in the prior art that may cause errors due to the position deviation of the working plane, the present invention can more accurately detect the light spot situation of the actual working surface, that is, it has the advantages of high precision, online, and real-time when determining the light spot focus position;

[0022] 3. The present invention uses a sensitive photoelectric detection method to obtain high-precision real-time detection data. With the automatic control of collimator position adjustment and / or working plane height adjustment, the laser working plane can be automatically focused, thereby improving the debugging efficiency and automation level of the 3D printing equipment;

[0023] 4. The present invention directly adjusts the working plane (i.e., the actual printing plane) of the 3D printing device or directly performs focus adjustment on the position of the collimator of the optical path system in the 3D printing device. If the focus is successful, the 3D printing work can be directly performed, thereby better ensuring the adjustment accuracy of the 3D printing device.

[0024] 5. The automatic focusing system of the 3D printing device of the present invention adds a beam splitter and a photodetector to the existing optical path system on the 3D printing device, and can separate the coaxial reflected laser wavelength from the main optical path based on the coaxial optical system to achieve independent detection of the target laser signal, and determine the focusing working position by searching the detection signal intensity during the movement of the optical path, thereby achieving the focusing function, that is, the overall system cost is low, the modification is small, and the space occupied in the equipment cavity is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A structural block diagram of the first embodiment of the automatic focusing system for a 3D printing device of the present invention;

[0026] Figure 2 A structural block diagram of the second embodiment of the automatic focusing system for a 3D printing device of the present invention;

[0027] Figure 3 A structural block diagram of the third embodiment of the automatic focusing system for a 3D printing device of the present invention;

[0028] Figure 4 An optical principle diagram of the third embodiment of the automatic focusing system for a 3D printing device of the present invention;

[0029] Figure 5 A structural block diagram of a fourth embodiment of the automatic focusing system for a 3D printing device of the present invention;

[0030] Figure 6 A structural block diagram of a fifth embodiment of the automatic focusing system for a 3D printing device of the present invention;

[0031] Markings in the figure:

[0032] 1. Laser; 2. Collimator; 3. Beam splitter; 4. First reflector; 5. Second reflector; 6. Field mirror; 7. Working plane; 8. Attenuation filter lens group; 9. First focusing module; 10. Photodetector; 11. Control system; 12. Quarter wave plate. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0034] Embodiment 1

[0035] like Figure 1 As shown, the automatic focusing system of the 3D printing device of this embodiment includes a laser 1, a collimator 2, a beam splitter 3, a galvanometer system (also referred to as a galvanometer), a second focusing module, a first focusing module 9, a photodetector 10 and a control system 11. The laser emitted by the laser 1 is incident on the collimator 2 and the beam splitter 3 in sequence, and is incident on the galvanometer system and the second focusing module after being transmitted by the beam splitter 3, and is incident on the working plane 7 having a reflection function for the laser after being deflected by the galvanometer system and focused by the second focusing module, so that at least the reflected light reflected by the working plane 7 returns to the beam splitter 3 after the deflection of the galvanometer system and the focusing of the second focusing module, and is incident on the first focusing module 9 under the reflection of the beam splitter 3 for focusing, and the focused laser is collected by the photodetector 10 and converted into an electrical signal, wherein,

[0036] The control system 11 is used to receive the electrical signal data of the photodetector 10 in real time, and adjust the position of the collimator 2 and / or the height of the working plane 7 to make the received electrical signal data change in strength, until the electrical signal received by the control system 11 is the strongest, then stop adjusting the position of the collimator 2 and / or the height of the working plane 7, and the automatic focusing is completed. At this time, the position of the collimator 2 and the height of the working plane 7 are the optimal positions, and 3D printing can be performed according to the position of the collimator 2 and the height of the working plane 7. The working plane 7 of the present application is an actual 3D printing working surface, so that the light spot condition of the real printing surface can be detected more accurately, and it has the advantages of high precision, online, and real-time when determining the light spot focusing position.

[0037] It should be noted that the photoelectric detector 10 mainly uses the reflected signal of the working plane 7 for detection, and the detection target is consistent with the actual working area of ​​the laser. In fact, the detection signal is mainly the laser signal reflected by the working plane 7, and of course it can also include the optical radiation signal converted after the laser acts on the working surface. The working plane 7 of this application needs to have a reflection function for the laser emitted by the above-mentioned laser 1. In a specific implementation, the paved powder material or the substrate or bottom plate without powder generally has a reflection function. Preferably, the working plane 7 is a metal substrate or powder material, which has a better reflection effect.

[0038] In a specific implementation, the automatic focusing system of the 3D printing device also includes a driving system for adjusting the position of the collimator 2 and the height of the working plane 7. For example, the position of the focused light spot on the detection plane can be obtained by searching for the position with the strongest light intensity detected on the working plane 7.

[0039] Specifically, the laser 1 emits a low-power laser, and preferably, the power of the laser 1 is 1-30W. The control system 11 can be a host computer, or a device with processing and control functions, which is not limited here. The main function of the above-mentioned beam splitter 3 is to separate the laser emitted by the laser 1 and the laser reflected by the working plane 7. For example, when the laser is transmitted from the laser 1 to the working plane 7, that is, in the forward direction, about 50% of the light intensity can be transmitted, and when the laser is transmitted from the working plane 7 to the beam splitter 3, that is, in the reverse direction, the reflected light can reflect more than 99% of the light.

[0040] In a specific implementation, the photodetector 10 is a photodiode, a photomultiplier tube, CCD or CMOS, an avalanche photodiode, a single photon detector or other photoelectric detection components, which collects and analyzes the electrical signal after photoelectric conversion to determine whether the laser is focused at the current working position. The specific judgment method is to search for the position where the strongest reflected light signal is detected by adjusting the light beam, and this position is the focus position of the laser in the current state.

[0041] Specifically, the second focusing module is a field lens 6 or a focusing lens. When the second focusing module is a focusing lens, the focusing lens is arranged between the beam splitter 3 and the galvanometer system; when the second focusing module is a field lens 6, the field lens 6 is arranged in the optical path between the galvanometer system and the working plane 7. Figure 1 shown.

[0042] Embodiment 2

[0043] This embodiment is a preferred solution of the present application. Compared with the first embodiment, an attenuation mirror and a filter are added, and the second focusing module is a focusing mirror. The attenuation mirror and the filter are installed before the photodetector, which can filter out the stray light outside the laser band and adjust the laser power to a suitable size, so that the automatic focusing of the present application is more accurate.

[0044] like Figure 2 As shown, the automatic focusing system of the 3D printing device of this embodiment includes a laser 1, a collimator 2, a beam splitter 3, a galvanometer system, a first focusing module 9, a focusing mirror, a photodetector 10, an attenuation mirror, an optical filter and a control system 11. The laser emitted by the laser 1 is incident on the collimator 2 and the beam splitter 3 in sequence, and is incident on the focusing mirror and the galvanometer system after being transmitted by the beam splitter 3, and is incident on the working plane 7 having a reflection function for the laser after the focusing action of the focusing mirror and the deflection action of the galvanometer system, so that at least the reflected light reflected by the working plane 7 returns to the beam splitter 3 after the focusing action of the focusing mirror and the deflection action of the galvanometer system, and is incident on the attenuation mirror, the optical filter and the first focusing module 9 in sequence under the reflection of the beam splitter 3, and the laser output by the first focusing module 9 is collected by the photodetector 10 and converted into an electrical signal, wherein,

[0045] The control system 11 is used to receive the electrical signal data of the photodetector 10 in real time, and adjust the position of the collimator 2 and / or the height of the working plane 7 to make the received electrical signal data change in strength until the electrical signal received by the control system 11 is the strongest, then stop adjusting the position of the collimator 2 and / or the height of the working plane 7, and autofocus is completed.

[0046] Embodiment 3

[0047] This embodiment is another preferred solution of the present application. Compared with the second embodiment, a quarter wave plate 12 is added, and the second focusing module is a field lens 6. The quarter wave plate 12 is arranged between the beam splitter 3 and the galvanometer system, or between the beam splitter 3 and the second focusing module, and is used to change the polarization state of the reflected light, so that the beam splitter 3 can reflect more laser to the attenuation mirror.

[0048] like Figure 3 and Figure 4 As shown, the 3D printing device autofocus system of this embodiment includes a laser 1, a collimator 2, a beam splitter 3, a galvanometer system, a first focusing module 9, a field lens 6, a photodetector 10, an attenuation lens, a filter ( Figure 4The attenuation mirror and the filter are collectively referred to as the attenuation filter lens group 8) and the control system 11, the laser emitted by the laser 1 is incident on the collimator 2 and the beam splitter 3 in sequence, and is incident on the galvanometer system and the field lens 6 after being transmitted by the beam splitter 3, and is incident on the working plane 7 having a reflection function for the laser after being deflected by the galvanometer system and focused by the field lens 6, so that at least the reflected light reflected by the working plane 7 returns to the beam splitter 3 after being deflected by the galvanometer system and focused by the field lens 6, and is incident on the attenuation mirror, the filter, and the first focusing module 9 in sequence under the reflection of the beam splitter 3, and the laser output by the first focusing module 9 is collected by the photoelectric detector 10 and converted into an electrical signal, wherein,

[0049] The control system 11 is used to receive the electrical signal data of the photodetector 10 in real time, and adjust the position of the collimator 2 and / or the height of the working plane 7 to make the received electrical signal data change in strength until the electrical signal received by the control system 11 is the strongest, then stop adjusting the position of the collimator 2 and / or the height of the working plane 7, and autofocus is completed.

[0050] The galvanometer system includes a first reflecting mirror 4 and a second reflecting mirror 5 .

[0051] Embodiment 4

[0052] This embodiment is another preferred solution of the present application. Compared with the third embodiment, the only difference is that the second focusing module is a focusing lens.

[0053] like Figure 5 As shown, the automatic focusing system of the 3D printing device of this embodiment includes a laser 1, a collimator 2, a beam splitter 3, a galvanometer system, a first focusing module 9, a focusing mirror, a photodetector 10, an attenuation mirror, an optical filter and a control system 11. The laser emitted by the laser 1 is incident on the collimator 2 and the beam splitter 3 in sequence, and is incident on the focusing mirror and the galvanometer system after being transmitted by the beam splitter 3, and is incident on the working plane 7 having a reflection function for the laser after the focusing action of the focusing mirror and the deflection action of the galvanometer system, so that at least the reflected light reflected by the working plane 7 returns to the beam splitter 3 after the focusing action of the focusing mirror and the deflection action of the galvanometer system, and is incident on the attenuation mirror, the optical filter and the first focusing module 9 in sequence under the reflection of the beam splitter 3, and the laser output by the first focusing module 9 is collected by the photodetector 10 and converted into an electrical signal, wherein,

[0054] The control system 11 is used to receive the electrical signal data of the photodetector 10 in real time, and adjust the position of the collimator 2 and / or the height of the working plane 7 to make the received electrical signal data change in strength until the electrical signal received by the control system 11 is the strongest, then stop adjusting the position of the collimator 2 and / or the height of the working plane 7, and autofocus is completed.

[0055] Embodiment 5

[0056] This embodiment is another preferred solution of the present application. Compared with the fourth embodiment, the only difference is that a laser absorption pool is added. Since 50% of the light intensity is transmitted in the forward direction, the other light may be reflected. This embodiment can absorb the reflected light by adding a laser absorption pool, thereby preventing laser leakage, and making the automatic focusing system of the 3D printing device of the present invention safer.

[0057] like Figure 6 As shown, the automatic focusing system of the 3D printing device of this embodiment includes a laser 1, a collimator 2, a beam splitter 3, a galvanometer system, a first focusing module 9, a focusing mirror, a photodetector 10, an attenuation mirror, a filter, a laser absorption pool and a control system 11. The laser emitted by the laser 1 is incident on the collimator 2 and the beam splitter 3 in sequence, and is incident on the focusing mirror and the galvanometer system after being transmitted by the beam splitter 3, and is incident on the working plane 7 having a reflection function for the laser after the focusing action of the focusing mirror and the deflection action of the galvanometer system, so that at least the reflected light reflected by the working plane 7 returns to the beam splitter 3 after the focusing action of the focusing mirror and the deflection action of the galvanometer system, and is incident on the attenuation mirror, the filter and the first focusing module 9 in sequence under the reflection of the beam splitter 3, and the laser output by the first focusing module 9 is collected by the photodetector 10 and converted into an electrical signal, and the beam splitter 3 is also connected to a laser absorption pool for absorbing the reflected laser; wherein,

[0058] The control system 11 is used to receive the electrical signal data of the photodetector 10 in real time, and adjust the position of the collimator 2 and / or the height of the working plane 7 to make the received electrical signal data change in strength until the electrical signal received by the control system 11 is the strongest, then stop adjusting the position of the collimator 2 and / or the height of the working plane 7, and autofocus is completed.

[0059] Embodiment 6

[0060] This embodiment provides a 3D printing device, which includes the 3D printing device automatic focusing system described in any of the above embodiments.

[0061] Embodiment 7

[0062] The automatic focusing method of the automatic focusing system of the 3D printing device of this embodiment comprises the following steps:

[0063] The laser 1 is adjusted to emit light at a preset power, and the photodetector 10 at least collects the laser reflected by the working plane 7;

[0064] The control system 11 receives the reflected light collected by the photodetector 10 in real time and converts it into electrical signal data, and changes the strength of the received electrical signal data by adjusting the position of the collimator 2 and / or the height of the working plane 7. When the electrical signal received by the control system 11 is the strongest, the position of the collimator 2 and / or the height of the working plane 7 is stopped, and automatic focusing is completed.

[0065] Specifically, adjusting the position of the collimator 2 and / or the height of the working plane 7 so that the received electrical signal data changes in strength specifically includes:

[0066] The position of the collimator 2 is fixed, and the working plane 7 is adjusted up and down by the driving system; or the height position of the working plane 7 is fixed, and the position of the collimator 2 is adjusted by the driving system, so that the received electrical signal data changes in strength. For example, when the height of the working plane is continuously adjusted upward and the electrical signal becomes weak, the height of the working plane is adjusted downward, and the electrical signal may become stronger, until the electrical signal strength is the highest, and then the adjustment is stopped.

[0067] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A 3D printing device autofocus system, characterized in that: The invention comprises a laser, a collimator, a beam splitter, a galvanometer system, a first focusing module, a second focusing module, a photoelectric detector and a control system. The laser emitted by the laser is incident on the collimator and the beam splitter in sequence, and is incident on the galvanometer system and the second focusing module after being transmitted by the beam splitter, and is incident on a working plane having a reflection function for the laser after being deflected by the galvanometer system and focused by the second focusing module, so that at least the reflected light reflected by the working plane returns to the beam splitter after being deflected by the galvanometer system and focused by the second focusing module, and is incident on the first focusing module under the reflection of the beam splitter for focusing, and the photoelectric detector collects the laser output by the first focusing module and converts it into an electrical signal, wherein: The control system is used to receive the electrical signal data of the photodetector in real time, and adjust the position of the collimator and / or the height of the working plane to make the received electrical signal data change in strength until the control system stops adjusting the position of the collimator and / or the height of the working plane when the electrical signal received is the strongest, and automatic focusing is completed.

2. The 3D printing device autofocus system according to claim 1, characterized in that: The 3D printing device automatic focusing system also includes a driving system for automatically adjusting the position of the collimator and the height of the working plane.

3. The 3D printing device autofocus system according to claim 1, characterized in that: The 3D printing device autofocus system also includes a quarter wave plate, which is arranged between the beam splitter and the galvanometer system, or between the beam splitter and the second focusing module, and is used to change the polarization state of the reflected light.

4. The 3D printing device autofocus system according to claim 1, characterized in that: The laser emits a laser with a power of 1-30W.

5. The 3D printing device autofocus system according to claim 1, characterized in that: The second focusing module is a field lens or a focusing lens. When the second focusing module is a focusing lens, the second focusing module is arranged between the beam splitter and the galvanometer system; when the second focusing module is a field lens, the second focusing module is arranged in the optical path between the galvanometer system and the working plane.

6. The 3D printing device autofocus system according to claim 1, characterized in that: The 3D printing device autofocus system also includes an attenuation mirror and a filter, which are sequentially arranged between the first focusing module and the beam splitter, so that the laser emitted by the beam splitter is sequentially attenuated and filtered so that the optical intensity is adjusted to the detection range of the optical detector, and after being converged by the first focusing module, it is collected by the photoelectric detector.

7. The 3D printing device autofocus system according to any one of claims 1 to 6, characterized in that: The photodetector is a photodiode, a photomultiplier tube, a CCD or a CMOS, an avalanche photodiode, or a single photon detector.

8. A 3D printing device, characterized in that: An automatic focusing system for a 3D printing device comprising any one of claims 1 to 7.

9. An auto-focusing method using the auto-focusing system of a 3D printing device according to any one of claims 1 to 7, characterized in that: The following steps are involved: The laser is adjusted to emit light at a preset power, and the photoelectric detector at least collects the laser reflected by the working plane; The control system receives the reflected light collected by the photodetector in real time and converts it into electrical signal data, and changes the strength of the received electrical signal data by adjusting the position of the collimator and / or the height of the working plane. When the electrical signal received by the control system is the strongest, the control system stops adjusting the position of the collimator and / or the height of the working plane, and automatic focusing is completed.

10. The automatic focusing method according to claim 9, characterized in that: By adjusting the position of the collimator and / or the height of the working plane, the received electrical signal data may have a change in strength, specifically including: The collimator position is fixed, and the working plane is adjusted up and down by the driving system; or the height position of the working plane is fixed, and the position of the collimator is adjusted by the driving system to make the received electrical signal data change in strength.

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