A control method for resuming printing after power failure of a 3D printer

Abstract

The present invention discloses a control method for resume printing after power failure of a 3D printer, which is based on a 3D printer with a collision sensor on the print head. The lifting movement axis of the printing platform of the 3D printer is the Z-axis, and the horizontal movement axes of the print head are the X-axis and the Y-axis. The control method for resume printing after power failure of the present invention adopts a way of the printing platform stepping up combined with path scanning of the print head, which can effectively avoid problems such as failure or error in storing coordinates before power failure, resulting in the print head hitting the model during the movement of the print head, causing the motor to be blocked and burned out, and the distortion of the print head and the X-axis and / or Y-axis, and avoiding great losses to the hardware and accuracy of the 3D printer.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing, and specifically to a control method for power-off continuation printing of a 3D printer. Background Art

[0002] Fused Deposition Modelling (FDM) is a technology invented by Scott Crump of Stratasys in the United States in the late 1980s. It is another widely used 3D printing technology after Stereolithography (SLA) and Laminated Object Manufacturing (LOM). In 1992, Stratasys launched the world's first 3D printer based on FDM technology - 3D Modeler, marking the commercialization of FDM technology.

[0003] The working principle of FDM is to heat and melt a filamentous thermoplastic material through a nozzle. The bottom of the nozzle is equipped with a micro-nozzle, and the diameter of the nozzle hole is generally 0.2 - 0.6 mm. Under computer control, the nozzle moves to the specified position according to the data of the 3D model, and extrudes and finally solidifies the molten liquid material. After the material is extruded, it is deposited on the previously cured material of the previous layer, and the final product is formed by layer-by-layer stacking of the material.

[0004] Before a 3D printer works, data information such as the layer spacing and path width of the three-dimensional model needs to be set first, and then the slicing engine slices the three-dimensional model and generates a printing movement path. Under computer control, the printing nozzle makes planar movements along the X-axis and Y-axis according to the horizontal layer data, and the vertical movement in the Z-axis direction is completed by the lifting of the printing platform. At the same time, the filament consumable is sent to the hot melt cavity by the extruder, heated, melted, and then extruded from the nozzle and bonded to the workbench surface, and quickly cooled and solidified. In this way, the printed material quickly fuses with the previous layer. When each layer is completed, the workbench descends by the height of one layer, and the printer continues to print the next layer, repeating such steps until the printing of the entire object is completed.

[0005] Currently, 3D printers based on FDM technology generally have the function of power-off continuation printing. It records the nozzle coordinates before power-off through a program. After power-on, the 3D printer automatically moves the nozzle to the coordinates before power-off and then continues to print. However, if the coordinate storage before power-off fails or is incorrect, it will cause the printing nozzle to hit the model during the movement, which is very likely to cause problems such as the X-axis or Y-axis motor being blocked and burned out, and the distortion and deformation of the print head and the X and / or Y axes, resulting in greater losses to the hardware and accuracy of the 3D printer. Summary of the Invention

[0006] The present invention aims to solve at least one of the above technical problems to some extent: to provide a control method for power-off resume printing of a 3D printer.

[0007] The technical solution of the present invention is as follows: A control method for power-off resume printing of a 3D printer, based on a 3D printer with a collision sensor on the print head, the lifting movement axis of the printing platform of the 3D printer is the Z-axis, and the horizontal movement axes of the print head are the X-axis and the Y-axis; the specific control method includes the following steps: During the printing process of the 3D printer, the position coordinate information of the current print head and the printing platform is stored in real time. After the power is automatically started, the print head break point coordinate value [X 断点 , Y 断点 and the printing platform break point coordinate value Z 断点 stored last before the power-off of the 3D printer are read. First, the printing platform is lowered along the Z-axis to the lowest Z-axis zero position coordinate Z 0 , and then the print head is moved along the X-axis and the Y-axis to the zero position coordinate [X 0 , Y 0 . When the print head is at the zero position coordinate [X 0 , Y 0 , the projection of the print head on the printing platform is located at its edge. The center coordinate when the projection of the print head on the printing platform is located at its center is recorded as [X 中 , Y 中 . The following steps are executed in a loop:

[0008] a) Control the printing platform to rise along the Z-axis by a step value H, where H < |Z 断点 - Z 0 |;

[0009] b) Control the print head to perform an empty scan along the path from the zero position coordinate to the center coordinate to the break point coordinate and then back to the zero position coordinate.

[0010] The main controller continuously judges the distance between Z 断点 and the current coordinate value Z 当前 of the printing platform. When |Z 断点 - Z 当前 | < H, the loop of step a) and step b) is ended, and the print head is moved to the break point coordinate value [X 断点 , Y 断点 , and the printing platform is moved to the break point coordinate value Z 断点 to continue printing the unfinished part before the power-off; during the execution of the loop of step a) and step b), if the main controller receives a collision feedback from the print head collision sensor, the printing is stopped and an error is reported.

[0011] The print head of the 3D printer includes an extruder, a throat tube, and a heating body; a hot melt cavity is provided inside the heating body, one end of the throat tube is communicated with the output end of the extruder, and the other end is communicated with the hot melt cavity of the heating body; a nozzle communicated with the hot melt cavity is provided on the heating body, and the print head further includes a heat dissipation body and a heat insulation sleeve; the heat dissipation body cooperates with the throat tube to dissipate heat from the throat tube; the heat insulation sleeve cooperates with the heating body to keep the heating body warm and insulated; the print head further includes at least one stress sensor.

[0012] As an optimization, the stress sensor includes a substrate and a strain gauge; the strain gauge is pasted on the surface of the substrate.

[0013] Mounting pieces are provided on the upper and lower sides of the substrate; the substrate and the mounting pieces are connected by at least one spring piece.

[0014] The front surface of the substrate is a plane, and the back surface is a concave surface; the strain gauge is pasted on the front surface of the substrate, and the sensitive grid of the strain gauge is sensitive to the stress change caused by the expansion and contraction of the substrate in the up and down directions.

[0015] The spring piece is in an "S" shape, the front and back surfaces of the spring piece are both planes parallel to the front surface of the substrate, and the distance between the front and back surfaces of the spring piece is equal to the maximum distance between the front and back surfaces of the substrate; the left and right surfaces of the spring piece are both curved surfaces, and the distance between the left and right surfaces of the spring piece is less than the distance between the front and back surfaces of the spring piece.

[0016] As an optimization, the thickness of the upper and lower ends of the substrate is greater than the thickness in the middle.

[0017] As an optimization, the mounting pieces at both ends of the stress sensor are respectively fixed on the heat dissipation body and the heat insulation sleeve.

[0018] The print head includes 2 stress sensors, and the front surfaces of the substrates of the 2 stress sensors are respectively arranged parallel to the front surface and the side surface of the heat insulation sleeve; when the print head is installed on the 3D printer, the front surface of the substrate of one stress sensor faces the positive direction of the Y axis, and is used to detect the stress generated on the substrate of the stress sensor when a force in the Y-axis direction is applied to the nozzle; the front surface of the substrate of the other stress sensor faces the positive direction of the X axis, and is used to detect the stress generated on the substrate of the stress sensor when a force in the X-axis direction is applied to the nozzle.

[0019] As an optimization, a motor for driving the extrusion of consumables is provided on the extruder; a sheet metal frame is provided on the motor; a model cooling fan is provided on the sheet metal frame; a wind guide nozzle is provided on the model cooling fan; the outlet of the wind guide nozzle faces the nozzle and the printing platform.

[0020] The heat insulation sleeve is made of heat-insulating materials, such as porous ceramics, mica, fiberglass, etc.

[0021] As an optimization, the side wall of the heat insulation sleeve is connected to the air guide nozzle through a fixing piece.

[0022] The extruder is a double-gear extruder.

[0023] A heating wire and a thermocouple temperature sensor are arranged in the heating body. The heating wire and the thermocouple temperature sensor are signal-connected to the main controller through a driving circuit.

[0024] The electrodes of the strain gauge are electrically connected to the main controller of the 3D printer through a Wheatstone bridge.

[0025] The print head further includes a cooling fan for accelerating the heat dissipation of the heat dissipation body;

[0026] Heat dissipation fins are arranged on the heat dissipation body. The cooling fan is arranged on the side of the extruder, and the air outlet of the cooling fan faces the gap between the heat dissipation fins.

[0027] The present invention has the following beneficial effects: The control method for resume printing after power failure of the present invention can effectively avoid problems such as the failure or error of coordinate storage before power failure, resulting in the motor being blocked and burned when the print head moves and touches the model, and the distortion of the print head and the X and / or Y axes, and avoid causing great losses to the hardware and accuracy of the 3D printer. Description of the Drawings

[0028] Figure 1 It is a three-dimensional structural schematic diagram of the print head in the embodiment.

[0029] Figure 2 It is a three-dimensional structural schematic diagram of the print head in the embodiment.

[0030] Figure 3 It is a three-dimensional structural schematic diagram of the print head in the embodiment.

[0031] Figure 4 It is a front view structural schematic diagram of the print head in the embodiment.

[0032] Figure 5 It is a side view structural schematic diagram of the print head in the embodiment.

[0033] Figure 6 It is an exploded structural schematic diagram of the print head in the embodiment.

[0034] Figure 7 It is an exploded structural schematic diagram of the print head in the embodiment.

[0035] Figure 8 It is a structural schematic diagram of the stress sensor of the print head in the embodiment.

[0036] Figure 9 Schematic diagram of the deformation state of the stress sensor of the print head in the embodiment.

[0037] Figure 10 Schematic diagram of the explosion structure of the heating element and the heat insulation sleeve of the print head in the embodiment.

[0038] Figure 11 Schematic cross-sectional structure diagram of the heating element and the heat insulation sleeve of the print head in the embodiment.

[0039] Figure 12 Schematic diagram of the relative coordinates of the nozzle and the printing platform of the print head in the embodiment.

[0040] Wherein, 1, extruder; 2, throat tube; 3, heating element; 4, nozzle; 5, heat sink; 6, heat insulation sleeve; 7, stress sensor; 71, substrate; 72, strain gauge; 73, mounting piece; 74, spring piece; 8, motor; 9, sheet metal frame; 10, model cooling fan; 101, air guide nozzle; 11, heat dissipation fan. Specific embodiments

[0041] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation of the present invention.

[0042] Embodiment

[0043] Figure 1-11 A print head of a 3D printer provided in this embodiment includes an extruder 1, a throat tube 2 and a heating element 3; a hot melt cavity is provided in the heating element 3, one end of the throat tube 2 is communicated with the output end of the extruder 1, and the other end is communicated with the hot melt cavity of the heating element 3; a nozzle 4 communicated with the hot melt cavity is provided on the heating element 3, and the print head further includes a heat sink 5 and a heat insulation sleeve 6; the heat sink 5 cooperates with the throat tube 2 to dissipate heat from the throat tube 2, specifically, the throat tube 2 penetrates through the heat sink 5 and is in close contact and cooperation with it; the heat insulation sleeve 6 cooperates with the side wall of the heating element 3 to insulate and heat the heating element 3; the print head further includes 2 stress sensors 7.

[0044] As Figure 8 shown, the stress sensor 7 includes a substrate 71 and a strain gauge 72; the strain gauge 72 is pasted on the surface of the substrate 71. Preferably, the strain gauge 72 is completely covered and sealed with silicone rubber.

[0045] Mounting pieces 73 are provided on the upper and lower sides of the substrate 71; the substrate 71 and the mounting pieces 73 are connected by three spring pieces 74. The substrate 71, the mounting pieces 73 and the spring pieces 74 are integrally cut from a metal sheet.

[0046] The front surface of the substrate 71 is flat, and the back surface is concave; the strain gauge 72 is pasted on the front surface of the substrate 71, and the sensitive grid of the strain gauge 72 is sensitive to the stress change caused by the expansion and contraction of the substrate 71 in the up and down directions. That is, as Figure 9 shown in the direction of deformation is the sensitive direction of the sensitive grid of the strain gauge 72.

[0047] The spring piece 74 is in an "S" shape. The front and back surfaces of the spring piece 74 are both planes parallel to the front surface of the substrate 71, and the distance between the front and back surfaces of the spring piece 74 is equal to the maximum distance between the front and back surfaces of the substrate 71; the left and right surfaces of the spring piece 74 are both curved surfaces, and the distance between the left and right surfaces of the spring piece 74 is less than the distance between the front and back surfaces of the spring piece 74. The thickness of the upper and lower ends of the substrate 71 is greater than the middle thickness. The mounting pieces 73 at both ends of the stress sensor 7 are respectively fixed on the heat sink 5 and the heat insulation sleeve 6; the distance between the heat sink 5 and the heat insulation sleeve 6 is greater than the distance between the upper and lower end faces of the substrate 71. As Figure 8-9 shown, the structure of the above stress sensor 7 can make the substrate 71 generate the maximum expansion and contraction amount for the bending deformation in the length direction as Figure 9 shown. Due to the structural characteristics of the spring piece 74, the misalignment deformation of the upper and lower mounting pieces 73 of the stress sensor 7 in the width direction has a small influence on the deformation of the substrate 71. Coupled with the fact that the sensitive grid of the strain gauge 72 is sensitive to the stress change caused by the expansion and contraction of the substrate 71 in the up and down directions. The stress sensor 7 has a stronger sensitive directivity for the deformation direction.

[0048] The front sides of the substrates 71 of the two stress sensors 7 are respectively arranged parallel to the front side and the side of the heat insulation sleeve 6; when the print head is installed on the 3D printer, the front side of the substrate 71 of one stress sensor 7 faces the positive Y-axis direction, and is used to detect the stress generated on the substrate 71 of the stress sensor 7 when a force in the Y-axis direction is applied to the nozzle 4; the front side of the substrate 71 of the other stress sensor 7 faces the positive X-axis direction, and is used to detect the stress generated on the substrate 71 of the stress sensor 7 when a force in the X-axis direction is applied to the nozzle 4. When the nozzle 4 collides with the model during the operation in the XY-axis plane, the heating body 3 drives the heat insulation sleeve 6 to be displaced relative to the heat dissipation body 5, and then stress is generated on the substrate 71 of the stress sensor 7. By solving the magnitude of the change vector of the stress data of the two sensors in the XY-axis plane, the force vector received by the nozzle 4 in the XY-axis plane can be reflected. By comparing with the magnitude of the force vector received by the nozzle 4 during normal operation, it can be determined whether the nozzle 4 collides with an obstacle such as a model.

[0049] A motor 8 for driving the extrusion of consumables is provided on the extruder 1; a sheet metal frame 9 is provided on the motor 8; a model cooling fan 10 is provided on the sheet metal frame 9; a wind guiding nozzle 101 is provided on the model cooling fan 10; the outlet of the wind guiding nozzle 101 faces the nozzle 4 and the printing platform.

[0050] The heat insulation sleeve 6 is made of porous ceramic heat insulation material. The side wall of the heat insulation sleeve 6 is connected to the wind guiding nozzle 101 through a fixing piece. The inner wall of the heat insulation sleeve 6 is matched with the heating body 3 through flanges at the upper and lower ends, and there is an annular hollow area between the inner wall of the heat insulation sleeve 6 and the outer wall of the heating body 3, making the heat insulation effect better.

[0051] The extruder 1 includes a filament material input port and an extrusion port. The extruder 1 is an extruder for an FDM 3D printer, such as a double gear extruder, which can be commercially available and belongs to the prior art, so it will not be elaborated here.

[0052] A heating wire and a thermocouple temperature sensor are provided in the heating body 3. The heating wire and the thermocouple temperature sensor are signal-connected to the main controller through a driving circuit.

[0053] The electrodes of the strain gauge 72 are electrically connected to the main controller of the 3D printer through a Wheatstone bridge.

[0054] The print head further includes a cooling fan 11 for accelerating the heat dissipation of the heat dissipation body 5; heat dissipation fins are provided on the heat dissipation body 5, the cooling fan 11 is arranged on the side of the extruder 1, and the air outlet of the cooling fan 11 faces the gap between the heat dissipation fins, which is beneficial to enhancing the heat dissipation effect.

[0055] Based on a 3D printer with the print head structure of this embodiment, this embodiment provides a control method for power-off resume printing of a 3D printer. The lifting motion axis of the printing platform of the 3D printer is the Z-axis, and the horizontal motion axes of the print head are the X-axis and the Y-axis. The specific control method includes the following steps:

[0056] After the 3D printer is just started, first lower the printing platform to the lowest zero position, and then the main controller reads the initial values of the stress sensors 7 in the X-axis direction and the stress sensors 7 in the Y-axis direction and stores the initial values, which are respectively denoted as; during the working process of the 3D printer, the main controller periodically reads the current values of the stress sensors 7 in the X-axis direction and the stress sensors 7 in the Y-axis direction, which are respectively denoted as, and substitutes them into the following formula for calculation,

[0057] ; during the printing process of the 3D printer, the position coordinate information of the current print head and the printing platform is stored in real time. After the power is automatically started, the print head break point coordinate value [X 断点 , Y 断点 and the printing platform break point coordinate value Z 断点 stored before the power-off of the 3D printer are read. As Figure 12 shown, first lower the printing platform along the Z-axis to the lowest Z-axis zero position coordinate Z 0 , that is, at this time the vertical distance between the print head and the printing platform is the farthest. Then move the print head along the X-axis and the Y-axis to the zero position coordinate [X 0 , Y 0 . When the print head is at the zero position coordinate [X 0 , Y 0 , the projection of the print head on the printing platform is located at its edge, that is, the print head leaves the printing area at this time. Denote the center coordinate when the projection of the print head on the printing platform is located at its center as [X 中 , Y 中 . Loop to execute the following steps:

[0058] a) Control the printing platform to rise by a step value H along the Z-axis, where H < |Z 断点 - Z 0 | and H < (the vertical distance between the bottom surface of the air guiding nozzle 101 and the tip of the nozzle 4);

[0059] b) Control the print head to perform an empty scan along the path from the zero position coordinate to the center coordinate to the break point coordinate to the zero position coordinate. Among them, the paths between the zero position coordinate and the center coordinate, between the center coordinate and the break point coordinate, and between the break point coordinate and the zero position coordinate are all straight paths. The meaning of the empty scan is just to run without extruding materials for printing.

[0060] The current coordinate value of the printing platform is denoted as Z 当前 , and the main controller judges Z 断点 and Z 当前The distance between, when |Z 断点 -Z 当前 | < H, then end the loop of step a) and step b), move the print head to the breakpoint coordinate value [X 断点 , Y 断点 , and move the print platform to the breakpoint coordinate value Z 断点 to continue printing the unfinished part before power-off; when calculating during the loop of step a) and step b), stop the printing of the 3D printer and give a power-off resume printing error warning; H is set according to the maximum value during the normal printing of the 3D printer model, > the maximum value during the normal printing of the 3D printer model.

[0061] In specific use, it is determined by the user according to the maximum value collected during the normal printing of the 3D printer model. If it is denoted as specifically adjusted according to the required collision sensitivity.

[0062] In this embodiment, the setting that H is less than the vertical distance between the bottom surface of the air guide nozzle 101 and the tip of the nozzle 4 can effectively prevent the printed model from hitting other parts on the upper part of the print head that cannot be sensed by other strain gauges 72 during the loop of step a) and step b), resulting in the failure of collision detection.

[0063] Since it is difficult for the print head to detect collisions when the printed model hits any position, in step b) of this embodiment, the path from the zero coordinate to the center coordinate to the breakpoint coordinate to the zero coordinate is specifically from [X 0 , Y 0 along the vector [X 中 -X 0 , Y 中 -Y 0 to [X 中 , Y 中 , then from [X 中 , Y 中 along the vector [X 断点 -X 中 , Y 断点 -Y 中 to [X 断点 , Y 断点 , and finally from [X 断点 , Y 断点 along the vector [X 0 -X 断点 , Y 0 -Y 断点 to [X 0 , Y 0, in this way, the path scans through the center of the printing platform and the breakpoint area before power-off, effectively scanning through the center of the printed model and above the breakpoint, so as to avoid missing the model area and causing the printed model to touch the upper part of the print head where other strain gauges 72 cannot sense. Even if the stored coordinates are incorrect and the coordinates of the breakpoint are no longer accurate, since the scanning path passes through the center of the printing area of the printing platform, the occurrence of missed scanning is effectively reduced.

[0064] The control method for resume printing after power-off of the present invention can effectively avoid the problems that the print head touches the model during the movement of the print head due to the failure or error of coordinate storage before power-off, resulting in the motor being blocked and burned out, and the distortion of the print head and the X and / or Y axes.

[0065] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0066] For those skilled in the art, various changes and modifications will undoubtedly be obvious after reading the above description. Therefore, the appended claims should be regarded as covering all changes and modifications that embrace the true spirit and scope of the present invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to still fall within the spirit and scope of the present invention.

Claims

1. A control method for resuming printing after power failure of a 3D printer, based on a 3D printer with a collision sensor on the print head. The lifting movement axis of the printing platform of the 3D printer is the Z-axis, and the horizontal movement axes of the print head are the X-axis and the Y-axis; It is characterized in that, The specific control method includes the following steps: During the printing process, the 3D printer stores the position coordinate information of the current print head and the printing platform in real time. After automatically starting up when power is restored, it reads the print head breakpoint coordinate value [X 断点 , Y 断点 and the printing platform breakpoint coordinate value Z 断点 stored last before the 3D printer lost power. First, lower the printing platform along the Z-axis to the lowest Z-axis zero position coordinate Z 0 . Then, move the print head along the X-axis and Y-axis to the zero position coordinate [X 0 , Y 0 . When the print head is at the zero position coordinate [X 0 , Y 0 , the projection of the print head on the printing platform is located at its edge. Denote the center coordinate when the projection of the print head on the printing platform is at its center as [X 中 , Y 中 . Loop and execute the following steps: a) Control the step value H for the printing platform to rise along the Z-axis, where H < |Z 断点 - Z 0 |; b) Control the print head to perform an empty scan along the path from the zero position coordinate to the center coordinate to the break point coordinate to the zero position coordinate. Among them, the paths between the zero position coordinate and the center coordinate, between the center coordinate and the break point coordinate, and between the break point coordinate and the zero position coordinate are all straight-line paths. The meaning of the empty scan is just to run without extruding materials for printing; The current coordinate value of the printing platform is denoted as Z 当前 , and the main controller continuously judges Z 断点 and Z 当前 The distance between them. When |Z 断点 -Z 当前 | < H, the loops of step a) and step b) are terminated, and the print head is moved to the breakpoint coordinate value [X 断点 , Y 断点 , and the printing platform is moved to the breakpoint coordinate value Z 断点 to continue printing the unfinished part before power-off. During the execution of the loops of step a) and step b), if the main controller receives a collision feedback from the print head collision sensor, the printing is stopped and an error is reported.

2. The control method for resuming printing after power failure of a 3D printer according to claim 1, It is characterized in that, The print head of the 3D printer includes an extruder (1), a throat tube (2) and a heating body (3); a hot melt cavity is provided in the heating body (3). One end of the throat tube (2) is communicated with the output end of the extruder (1), and the other end is communicated with the hot melt cavity of the heating body (3); a nozzle (4) communicated with the hot melt cavity is provided on the heating body (3). It is characterized in that: the print head further includes a heat dissipation body (5) and a heat insulation sleeve (6); the heat dissipation body (5) cooperates with the throat tube (2) to dissipate heat from the throat tube (2); the heat insulation sleeve (6) cooperates with the heating body (3) to keep the heating body (3) warm and insulated; the print head further includes at least one stress sensor (7).

3. The control method for resuming printing after power failure of a 3D printer according to claim 2, It is characterized in that, The stress sensor (7) includes a substrate (71) and a strain gauge (72); the strain gauge (72) is pasted on the surface of the substrate (71); mounting pieces (73) are provided on the upper and lower sides of the substrate (71); the substrate (71) and the mounting pieces (73) are connected by at least one spring piece (74).

4. The control method for resuming printing after power failure of a 3D printer according to claim 3, It is characterized in that, The front surface of the substrate (71) is a plane, and the back surface is a concave surface; the strain gauge (72) is pasted on the front surface of the substrate (71), and the sensitive grid of the strain gauge (72) is sensitive to the stress change caused by the expansion and contraction of the substrate (71) in the up and down directions; the spring piece (74) is in an "S" shape, and the front and back surfaces of the spring piece (74) are both planes parallel to the front surface of the substrate (71), and the distance between the front and back surfaces of the spring piece (74) is equal to the maximum distance between the front and back surfaces of the substrate (71); the left and right surfaces of the spring piece (74) are both curved surfaces, and the distance between the left and right surfaces of the spring piece (74) is less than the distance between the front and back surfaces of the spring piece (74); the thickness of the upper and lower ends of the substrate (71) is greater than the thickness of the middle part.

5. The control method for resuming printing after power failure of a 3D printer according to claim 4, It is characterized in that, The mounting pieces (73) at both ends of the stress sensor (7) are respectively fixed on the heat sink (5) and the heat insulation sleeve (6); the print head includes two stress sensors (7), and the fronts of the substrates (71) of the two stress sensors (7) are respectively arranged parallel to the front and side surfaces of the heat insulation sleeve (6); when the print head is installed on the 3D printer, the front of the substrate (71) of one stress sensor (7) faces the positive direction of the Y axis, and is used to detect the stress generated on the substrate (71) of this stress sensor (7) when a force in the Y-axis direction is applied to the nozzle (4); the front of the substrate (71) of the other stress sensor (7) faces the positive direction of the X axis, and is used to detect the stress generated on the substrate (71) of this stress sensor (7) when a force in the X-axis direction is applied to the nozzle (4).

6. The control method for power-off resume printing of the 3D printer according to claim 5, characterized in that, a motor (8) for driving the extrusion of consumables is provided on the extruder (1); a sheet metal frame (9) is provided on the motor (8); a model cooling fan (10) is provided on the sheet metal frame (9); a wind guiding nozzle (101) is provided on the model cooling fan (10); the outlet of the wind guiding nozzle (101) faces the nozzle (4) and the printing platform.

7. The control method for power-off resume printing of the 3D printer according to claim 6, characterized in that, the heat insulation sleeve (6) is made of a heat-insulating material, and the side wall of the heat insulation sleeve (6) is connected to the wind guiding nozzle (101) through a fixing piece; a heating wire and a thermocouple temperature sensor are provided in the heating body (3); the heating wire and the thermocouple temperature sensor are signal-connected to the main controller through a driving circuit; the electrodes of the strain gauge (72) are electrically connected to the main controller of the 3D printer through a Wheatstone bridge.

8. The control method for power-off resume printing of the 3D printer according to claim 7, characterized in that, the print head further includes a cooling fan (11) for accelerating the heat dissipation of the heat sink (5); heat dissipation fins are provided on the heat sink (5), the cooling fan (11) is arranged on the side of the extruder (1), and the air outlet of the cooling fan (11) is directly opposite to the gap between the heat dissipation fins.

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