Device and method for improving the forming accuracy of powder-laying workpiece based on full-closed-loop real-time control of grating ruler

Abstract

The present invention relates to the field of additive manufacturing technology, and in particular to a device and method for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler, comprising a forming cylinder, a motor, a grating ruler displacement sensor, a driver, and a controller, wherein the motor, the grating ruler displacement sensor, the driver, and the controller form a closed-loop feedback system, the controller can interact with data information collected by the grating ruler displacement sensor, and utilize the characteristics of the grating ruler displacement sensor with high detection accuracy and fast response speed to accurately measure the moving position of a substrate, and feed back the position data to the controller in real time, the programmable controller transmits the real-time data of the moving position of the substrate as a reference to a servo system, so that when the substrate is lifted or lowered to a specified position, the position information is the actual measurement value of the grating ruler displacement sensor, and real-time full-closed-loop position control of the thickness of the powder-laying layer is realized, the height of each descent is controlled to be consistent, the thickness of each layer of powder-laying is kept consistent, and the accuracy of laser sintering powder is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a device and method for improving the forming accuracy of a powder-spreading workpiece based on full-closed-loop real-time control of a grating ruler. Background Art

[0002] Powder-spreading metal 3D printing is an important branch of metal additive manufacturing technology. This technology uses metal powder pre-placed on a powder platform as raw material, based on the three-dimensional digital model of the part, and uses high-energy beams such as lasers or electron beams to melt the powder layer by layer on a series of two-dimensional planes discrete from the three-dimensional model, and finally manufacture three-dimensional metal parts. Currently, the most widely used is powder-spreading metal 3D printing that uses laser as an energy source, also known as Selective Laser Melting (SLM).

[0003] Before printing begins, the powder is stored in the powder preparation cylinder, and the printing substrate is placed in the powder forming cylinder. After printing begins, the powder preparation cylinder moves upward to deliver a certain amount of powder. The powder spreading scraper scrapes the powder toward the powder forming cylinder and spreads it on the printing platform to form a powder layer with uniform thickness. The laser light source emits laser light, which is focused by the focusing light path and controlled by the XY scanning galvanometer. According to the scanning path in the STL file, the powder layer on the printing substrate is scanned. The powder on the scanning path is melted by the laser energy and forms a metallurgical bond with the substrate (or the previously formed layer). After the laser scanning and melting of a layer of powder is completed, the printing platform drops one layer of powder height and repeats the laser scanning until all two-dimensional planes of the digital model are scanned, and the printing of the entire three-dimensional product is completed.

[0004] In 3D powder printing additive manufacturing, the precision control of the descent of the printing substrate in the forming cylinder plays a vital role in the forming of the workpiece size. The thickness of the powder layer in powder printing affects the forming of the workpiece size. The uneven thickness of the powder layer directly affects the quality of the process. If the powder is too thick, the laser sintering will be insufficient, which will cause the current layer to be disconnected from the previous layer and lead to the failure of the workpiece printing. If the powder is too thin, it will cause damage to the inside of the workpiece due to excessive sintering, resulting in the failure of the workpiece printing.

[0005] At present, there are two main ways to control the descent of the substrate in the forming cylinder:

[0006] 1) Use a servo motor with an encoder. The encoder can identify the deflection angle of the motor. However, due to the physical gap between the mechanically mounted motor and the lead screw, this is a semi-closed loop control. The actual position of the substrate cannot be represented based on the encoder feedback position.

[0007] 2) Use an external grating ruler and a difference compensation algorithm: print one layer, calculate the difference between the encoder position value and the grating ruler position value of the current layer, and compensate the difference to the next layer. Although this control method is a full closed-loop control and the accuracy will be improved, there is a slight difference between each layer and the expected position value, and it is impossible to achieve real-time and accurate control of the powder layer thickness. Summary of the invention

[0008] The present invention proposes a technical solution, a device for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler, comprising:

[0009] A forming cylinder, wherein a base plate capable of moving up and down and used to carry powder is provided inside, and a bottom plate parallel to the base plate is fixedly connected to the base plate through a guide rod;

[0010] A motor is configured to drive the substrate to move up and down through a screw transmission mechanism;

[0011] A grating ruler displacement sensor, comprising a grating ruler arranged parallel to the moving direction of the substrate and a grating ruler reader movably mounted on the grating ruler, wherein the grating ruler reader is fixedly mounted on the bottom plate so that the grating ruler reader and the substrate synchronously generate the same displacement, so that the grating ruler displacement sensor can obtain the value of the moving distance of the substrate;

[0012] A driver configured to drive the motor;

[0013] A controller is configured to be electrically connected to the grating ruler displacement sensor and the driver;

[0014] Among them, the motor, grating scale displacement sensor, driver and controller form a closed-loop feedback system. The controller can interact with the data information collected by the grating scale displacement sensor to obtain the position information of the grating scale reader on the grating scale in real time, and use the acquired real-time position information as closed-loop feedback information. The driver controls the motor to drive the grating scale reader to move to the set position based on the real-time position information and stop rotating.

[0015] As an optional implementation, the height of the substrate in one movement cycle is defined as H, and the initial position of the substrate is defined as H. 始 , the end point is H 终 , the height of the substrate during movement is H 1 , where H 始 ≤H i ≤H 终 ;

[0016] In one movement cycle, the substrate is composed of H 始 Move to H 终The grating ruler reader is used to obtain H in real time i The position information of the grating ruler displacement sensor is H i The position information is transmitted to the controller in real time, and the controller is configured to:

[0017] When H 始 <H i <H 终 When the controller sends a driving signal to the driver, the driver controls the motor to rotate;

[0018] When H i =H 终 When the controller sends a stop signal to the driver, the driver controls the motor to stop. At this time, the grating ruler reading head stops at H 终 Location.

[0019] As an optional implementation, an encoder is further included. The encoder is electrically connected to the motor and the controller and is used to obtain the output shaft rotation speed of the motor and transmit the obtained rotation speed information to the controller.

[0020] As an optional implementation, the controller includes a programmable controller, and the controller is configured to determine the moving speed of the substrate according to the rotation speed of the motor fed back by the encoder.

[0021] As an optional implementation, the motor includes a servo motor, the grating scale displacement sensor includes a differential pulse grating scale, and the acquisition frequency range is 0 to 50 KHz.

[0022] As an optional embodiment, the screw transmission mechanism includes a screw vertically fixed between the base plate and the bottom plate and a sleeve sleeved on the outside of the screw. The sleeve is rotatably installed on the mounting platform. The output end of the motor drives the sleeve to rotate through a transmission belt, so that the sleeve and the screw transmit information to each other, driving the base plate to move up and down.

[0023] As an optional implementation, the forming cylinder and the motor are both fixedly mounted on the mounting platform, and the guide rod passes through the mounting platform, so that the base plate, the guide rod and the bottom plate can move up and down relative to the mounting platform.

[0024] As an optional implementation, the substrate, guide rods, bottom plate and grating scale reading head are rigidly connected.

[0025] The second aspect of the present invention provides a technical solution, a control method for improving the forming accuracy of a powder-spreading workpiece based on a grating ruler full closed-loop real-time control, using the above-mentioned device for improving the forming accuracy of a powder-spreading workpiece based on a grating ruler full closed-loop real-time control, comprising the following steps:

[0026] Step 1: Get the single moving distance and number of moves in the current printing workpiece, define the single moving distance as H, and the number of moves required to complete printing as M;

[0027] Step 2: define the height of the substrate in one movement cycle as H, and the initial position of the substrate as H 始 , the end point is H 终 , the height of the substrate during movement is H i , where H 始 ≤H i ≤H 终 ;

[0028] In a motion cycle, when the motor drives the substrate to move, the grating ruler reader is used to obtain H in real time. i The position information of the grating ruler displacement sensor is H i The position information is transmitted to the controller in real time, and the controller is configured to:

[0029] When H 始 <H i <H 终 When the controller sends a driving signal to the driver, the driver controls the motor to rotate;

[0030] When H i =H 终 When the controller sends a stop signal to the driver, the driver controls the motor to stop. At this time, the grating ruler reading head stops at H 终 Location;

[0031] Step 3, after the substrate has descended for one cycle, it stops, and a powder spreading mechanism spreads powder to the uppermost layer of the substrate, and the powder spreading height is equal to the descending height H of the substrate;

[0032] Step 4: The laser printing head prints and sinter the top layer of powder;

[0033] Step 5, repeating steps 2 to 4, after the substrate is lowered M times, the printing of the entire workpiece is completed.

[0034] As an optional implementation, in one cycle in step 2, the moving speed of the substrate is preset to be V, the acceleration is preset to be A, and the deceleration position in the preset cycle is preset to be HH according to the acceleration A and the speed V. i ;

[0035] After the encoder obtains the speed information of the motor, it transmits the speed information to the controller. The controller drives the motor to accelerate at an acceleration of A through the driver. The substrate moves at a constant speed after accelerating to a set speed V, and moves when the grating ruler reader reaches HH iThe motor decelerates when the motor reaches the position H, and stops at the position H within the cycle, wherein the range of H is 0.04 mm to 0.06 mm, the range of V is 0.02 mm / s to 0.1 mm / s, and the range of A is 0.5 m / s 2 ~1.0m / s 2 .

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] The present invention proposes a device and method for controlling substrate movement in real time in a full closed loop based on a grating ruler. The grating ruler has the characteristics of high detection accuracy and fast response speed to accurately measure the moving position of the substrate, and feed back the position data to the controller in real time. The programmable controller transmits the real-time data of the moving position of the substrate as a reference to the servo system, so that when the substrate is lifted to a specified position, the position information is the actual measurement value of the grating ruler, thereby realizing real-time full closed loop position control of the powder layer thickness, controlling the height of each descent to remain consistent, making the thickness of each layer of powder consistent, and improving the accuracy of laser sintering powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For clarity, not every component is labeled in every figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0039] Figure 1 It is a schematic diagram of the three-dimensional structure of a device for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler as shown in an embodiment of the present invention;

[0040] Figure 2 It is a schematic diagram of a control system of a device for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler as shown in an embodiment of the present invention;

[0041] Figure 3 It is a bidirectional linear error curve diagram of a substrate under the control of an external grating ruler combined with a difference compensation algorithm in the prior art;

[0042] Figure 4 It is a bidirectional linear error curve diagram of a substrate under a control method for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler as shown in an embodiment of the present invention.

[0043] Figure 5 yes Figure 3 and Figure 4 Comparison chart of test results under substrate control mode;

[0044] Figure 6It is a speed and displacement relationship diagram of a control method for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler in an embodiment of the present invention, in which a grating ruler adjusts the lower substrate in real time to move 20.00 mm at a speed of 5.00 mm / s;

[0045] Figure 7 This is a speed and displacement relationship diagram of a control method for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler shown in an embodiment of the present invention, in which the grating ruler real-time adjusts the lower substrate to move 20.00 mm at a speed of 13.00 mm / s. DETAILED DESCRIPTION

[0046] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0047] At present, the displacement control of the substrate in the forming cylinder is not precise enough, especially the single descent distance of the substrate cannot be accurately controlled. The inaccurate descent will lead to uneven powder thickness of each subsequent layer. The uneven powder layer thickness directly affects the quality of the process. If the powder is too thick, the laser sintering will be insufficient, which will cause the current layer to be disconnected from the previous layer, resulting in workpiece printing failure. If the powder is too thin, excessive sintering will cause damage to the inside of the workpiece, resulting in workpiece printing failure.

[0048] [Device based on grating ruler full closed loop real-time control to improve the forming accuracy of powder-laying workpiece]

[0049] The first aspect of the present invention proposes a technical solution, a device based on a grating scale full closed-loop real-time control to improve the forming accuracy of the powder-spreading workpiece, which aims to improve the height of each descent in the forming cylinder during the descent of the substrate, keep the thickness of each layer of powder consistent, and improve the accuracy of laser sintering powder.

[0050] like Figure 1 and Figure 2 As shown, the device mainly includes a forming cylinder 1, a motor 2, a grating ruler displacement sensor 3, an encoder 4, a driver 5 and a controller 6.

[0051] A base plate 11 which can move up and down and is used to carry powder is provided inside the forming cylinder 1 , and a bottom plate 14 which is parallel to the base plate 11 is fixedly connected to the bottom of the base plate 11 through a guide rod 13 .

[0052] In a specific embodiment, the forming cylinder 1 is constructed as a rectangular box with an open upper end, and its cross-sectional dimensions are generally set between 280mm×280mm-650mm×650mm. The four sides of the substrate 11 fit and slide with the inner wall of the forming cylinder 1 and can ensure sealing. During the descent process, the powder is always above the substrate 11, supporting the powder. As the substrate 11 descends layer by layer, the laser print head prints the top layer of powder layer by layer.

[0053] Furthermore, four guide rods 13 are arranged in parallel at the four corners of the substrate 11, and the bottom plate 14 is constructed as a rectangular thin plate, which is distributed parallel to the substrate 11, and the substrate 11, the guide rods 13, and the bottom plate 14 are rigidly connected without any movable margin, so that the substrate 11, the guide rods 13, and the bottom plate 14 can be guaranteed to move synchronously.

[0054] Specifically, the motor 2 is configured to drive the substrate 11 to move up and down through a screw transmission mechanism, wherein the motor 2 adopts a servo motor, the rotor speed of the servo motor is controlled by an input signal, and can respond quickly. In the automatic control system, it is used as an actuator and has the characteristics of high control accuracy and good low-speed operation stability.

[0055] Furthermore, the forming cylinder 1 and the motor 2 are both fixedly mounted on the mounting platform 12, and the guide rod 13 passes through the mounting platform 12, so that the substrate 11, the guide rod 13 and the bottom plate 14 can move up and down relative to the mounting platform 12, and the screw transmission mechanism includes a screw 23 vertically fixed between the substrate 11 and the bottom plate 14 and a sleeve 22 sleeved on the outside of the screw 23, and the sleeve 22 is rotatably mounted on the mounting platform 12, and the output end of the motor 2 drives the sleeve 22 to rotate through the transmission belt 21, so that the sleeve 22 and the screw 23 transmit information to each other, thereby driving the substrate 11 to move up and down.

[0056] During operation, the motor 2 drives the sleeve 22 to rotate through the gear transmission belt 21 (using a synchronous belt) of the output shaft. The sleeve 22 is rotatably installed on the mounting platform 12 through a bearing. While the transmission belt 21 drives the rotation, it can be connected to the screw rod 23 to drive the screw rod 23 to move upward or downward, so that the base plate 11, guide rod 13, and bottom plate 14 fixed with the screw rod 23 move synchronously.

[0057] Combination Figure 1 As shown, the grating scale displacement sensor 3 includes a grating scale 31 arranged parallel to the moving direction of the substrate 11 and a grating scale reader 32 movably installed on the grating scale 31. The grating scale reader 32 is fixedly installed on the base plate 14, so that the grating scale reader 32 and the substrate 11 produce the same displacement synchronously, so that the grating scale displacement sensor 30 can obtain the numerical value of the moving distance of the substrate 11. Among them, the grating scale displacement sensor 3 adopts a differential pulse grating scale, and the acquisition frequency range is 0-50KHz. The measurement output signal is a digital pulse, which has the characteristics of a large detection range, high detection accuracy, and fast response speed, and the measurement is more accurate. At the same time, the grating scale reader 32 is rigidly connected to the base plate 14, and can produce the same displacement synchronously with the substrate 11, representing the movement trajectory of the substrate 11, and avoiding errors in the connection between the substrate 11 and the grating scale reader 32.

[0058] Further, such as Figure 2As shown, the encoder 4 is configured to be electrically connected to the motor 2 and the controller 6, and is used to obtain the output shaft rotation speed of the motor 2 and transmit the obtained rotation speed information to the controller 6. The controller 6 is configured to be able to judge the moving speed of the substrate 11 according to the rotation speed of the motor 2 fed back by the encoder 4. The driver 5 is configured to drive the motor 2, and the controller 6 is configured to be electrically connected to the grating scale displacement sensor 3 and the driver 5.

[0059] Among them, the motor 2, the grating scale displacement sensor 3, the driver 5 and the controller 6 form a closed-loop feedback system. The controller 6 adopts a programmable controller, such as a PLC or an embedded single-chip microcomputer. The controller 6 can interact with the data information collected by the grating scale displacement sensor 3, and send a request for position data feedback to the grating scale displacement sensor 3 in real time, so as to obtain the position information of the grating scale reader 32 on the grating scale 31 in real time, and use the obtained real-time position information as closed-loop feedback information. By controlling the driving state of the driver 5, the motor 2 is controlled to drive the substrate 11 to move to the set position based on the real-time position information, and the motor 2 stops rotating when the substrate 11 moves to the set position.

[0060] In an optional implementation example, the height of the substrate 11 in one movement cycle is defined as H, and the initial position of the substrate 11 is defined as H. 始 , the end point is H 终 , the height of the substrate 11 during the movement is H i , where H 始 ≤H i ≤H 终 ;

[0061] In one movement cycle, the substrate 11 is 始 Move to H 终 , the grating ruler reading head 32 is used to obtain H in real time i The position information of the grating ruler displacement sensor 3 is H i The position information is transmitted to the controller 6 in real time, and the controller 6 is configured as follows:

[0062] When H 始 <H i <H 终 When , the controller 6 sends a driving signal to the driver 5, and the driver 5 controls the motor 2 to rotate;

[0063] When H i =H 终 When the controller 6 sends a stop signal to the driver 5, the driver 5 controls the motor 2 to stop. At this time, the grating ruler reading head 32 stops at H 终 Location.

[0064] In this way, the characteristics of high detection accuracy and fast response speed of the grating scale displacement sensor 3 are utilized to accurately measure the moving position of the substrate 11, and the position data is fed back to the controller 6 in real time. The programmable controller 6 passes the real-time data of the moving position of the substrate 11 as a reference to the servo system, replacing the position measurement function of the original servo encoder 4, so that when the substrate 11 is raised or lowered to the specified position, the position information is the actual measurement value of the grating scale displacement sensor 3, realizing real-time full closed-loop position control of the powder layer thickness, so the accuracy of each powder layer thickness can be guaranteed.

[0065] [Control method for improving the forming accuracy of powder-laying workpiece based on full closed-loop real-time control of grating ruler]

[0066] The second aspect of the present invention proposes a technical solution, a control method for improving the forming accuracy of a powder-spreading workpiece based on a grating ruler full closed-loop real-time control, using the above-mentioned device for improving the forming accuracy of a powder-spreading workpiece based on a grating ruler full closed-loop real-time control, comprising the following steps:

[0067] Step 1. Get the single moving distance and number of moves in the current printing workpiece. Define the single moving distance as H, that is, the layer height of each powder laying, and the number of moves as M, that is, the number of layers required to complete the workpiece printing, which is set according to the height of the printed workpiece.

[0068] Step 2: Define the height of the substrate 11 in one movement cycle as H, and the initial position of the substrate 11 as H 始 , the end point is H 终 , the height of the substrate 11 during the movement is H i , where H 始 ≤H i ≤H 终 ;

[0069] In a motion cycle, when the motor 2 drives the substrate 11 to move, the grating ruler reader 32 is used to obtain H in real time. i The position information of the grating ruler 3 is H i The position information is transmitted to the controller 6 in real time, and the controller 6 is configured as follows:

[0070] When H 始 <H i <H 终 When , the controller 6 sends a driving signal to the driver 5, and the driver 5 controls the motor 2 to rotate;

[0071] When H i =H 终 When the controller 6 sends a stop signal to the driver 5, the driver 5 controls the motor 2 to stop. At this time, the grating ruler reading head 32 stops at H 终 Location.

[0072] Combination Figure 3-Figure 5 , Figure 3 This is the bidirectional linear error curve of the substrate under the control of the existing grating scale compensation algorithm. Figure 4 It is a bidirectional linear error curve diagram of the substrate under the control method for improving the forming accuracy of the powder-laying workpiece based on the grating ruler full closed-loop real-time control shown in the embodiment of the present invention, Figure 5 yes Figure 3 and Figure 4 From the comparison chart of the results, it can be seen that the error of the motion state of the substrate under the control of the current grating scale difference compensation algorithm is in a divergent mode and the accuracy cannot be guaranteed. However, the error of the motion state of the substrate under the full-closed-loop real-time control method based on the grating scale of the present application is in a convergent mode and the accuracy is controllable. Combined with the comparison results, it can be seen that the accuracy and repeatability are at a high level, and the descent height of the substrate 11 can be accurately controlled, so that the accuracy of the thickness of each powder layer can be guaranteed.

[0073] Furthermore, in one cycle in step 2, the moving speed of the substrate 11 is preset to be V, the acceleration is A, and the deceleration position in the preset cycle is HH according to the acceleration A and the speed V. 1 ;

[0074] After the encoder 4 obtains the speed information of the motor 2, it transmits the speed information to the controller 6. The controller 6 drives the motor 2 to accelerate at an acceleration A through the driver 5. After the substrate 11 accelerates to the set speed V, it moves at a constant speed and reaches HH when the grating ruler reader 32 reaches HH. 1 When the motor 2 reaches the position, it decelerates and stops at the H position within the cycle, where the range of H is 0.04mm~0.06mm, the range of V is 0.02mm / s~0.1mm / s, and the range of A is 0.5m / s 2 ~1.0m / s 2 , the magnitude of acceleration can be preset according to the moving speed of the substrate 11, and the deceleration position of the substrate 11 can be preset. When the substrate 11 moves to this position, the motor 2 controls the substrate 11 to decelerate, and the substrate 11 can be accurately controlled to reach the preset end position, thereby achieving high-precision layer height control.

[0075] like Figure 6 and Figure 7 As shown, in the control method for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of grating scale shown in an embodiment of the present invention, the speed and displacement relationship diagram of the substrate moving 20.00 mm at speeds of 5.00 mm / s and 13.00 mm / s is adjusted in real time by the grating scale. It can be seen that the accuracy of the movement control of the substrate 11 based on the full-closed-loop real-time control method of the grating scale of the present invention is great.

[0076] Step 3: After the substrate 11 descends for a cycle, it stops and the powder spreading mechanism spreads powder to the uppermost layer of the substrate 11 , and the powder spreading height is equal to the descending height H of the substrate 11 .

[0077] Step 4: The laser printing head prints and sinter the top layer of powder.

[0078] Step 5: Repeat steps 2 to 4. After the substrate 11 descends M times, the printing of the entire workpiece is completed.

[0079] In combination with the above embodiments, the device and method based on full-closed-loop real-time control of the grating scale proposed in the present invention utilize the characteristics of high detection accuracy and fast response speed of the grating scale displacement sensor 3 to accurately measure the moving position of the substrate 11, and feed back the position data to the controller 6 in real time. The programmable controller 6 passes the real-time data of the moving position of the substrate 11 as a reference to the servo system, so that when the substrate 11 is raised or lowered to the specified position, the position information is the actual measurement value of the grating scale displacement sensor 3, realizing real-time full-closed-loop position control of the powder layer thickness, controlling the height of each descent to remain consistent, making the thickness of each layer of powder consistent, and improving the accuracy of laser sintering powder.

[0080] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A device for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of a grating ruler, characterized in that: include: A forming cylinder (1) is provided with a base plate (11) which can move up and down and is used to carry powder, and a bottom plate (14) which is arranged parallel to the base plate (11) is fixedly connected to the bottom of the base plate (11) via a guide rod (13); A motor (2) is configured to drive the substrate (11) to move up and down through a screw transmission mechanism; A grating ruler displacement sensor (30), comprising a grating ruler (31) arranged parallel to the moving direction of the substrate (11) and a grating ruler reader (32) movably mounted on the grating ruler (31), wherein the grating ruler reader (32) is fixedly mounted on the base plate (14), and the base plate (11), the guide rod (13), and the base plate (14) are rigidly connected without any movable margin, and the grating ruler reader (32) is rigidly connected to the base plate (14), so that the grating ruler reader (32) and the substrate (11) synchronously generate the same displacement, representing the movement trajectory of the substrate (11), so that the grating ruler displacement sensor (30) can obtain the movement distance of the substrate (11); A driver (5) configured to drive the motor (2); A controller (6) is configured to be electrically connected to the grating scale displacement sensor (30) and the driver (5); The motor (2), the grating scale displacement sensor (30), the driver (5) and the controller (6) form a closed-loop feedback system, and the controller (6) is configured to obtain the position information of the grating scale reader (32) on the grating scale (31) in real time, and control the driving state of the driver (5) so that the motor (2) stops rotating when the grating scale reader (32) moves to a set position.

2. The device for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of grating ruler according to claim 1 is characterized in that: The height of the substrate (11) in one movement cycle is defined as H, and the initial position of the substrate (11) is defined as H. 始 , the end point is H 终 , the height of the position of the substrate (11) during the movement is H i , where H 始 ≤H i ≤H 终 ; In one movement cycle, the substrate (11) is composed of H 始 Move to H 终 The grating ruler reader (32) is used to obtain H in real time. i The grating ruler displacement sensor (30) will H i The position information is transmitted to the controller (6) in real time, and the controller (6) is configured to: When H 始 <H i <H 终 When the controller (6) sends a driving signal to the driver (5), the driver (5) controls the motor (2) to rotate; When H i =H 终 When the controller (6) sends a stop signal to the driver (5), the driver (5) controls the motor (2) to stop. At this time, the grating ruler reading head (32) stops at H 终 Location.

3. The device for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of grating ruler according to claim 1 is characterized in that: It also includes an encoder (4), which is electrically connected to the motor (2) and the controller (6) and transmits the acquired rotation speed information of the motor (2) to the controller (6).

4. The device for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of grating ruler according to claim 3 is characterized in that: The controller (6) comprises a programmable controller, and the controller (6) is configured to determine the moving speed of the substrate (11) according to the rotation speed of the motor (2) fed back by the encoder (4).

5. The device for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of grating ruler according to claim 1 is characterized in that: The motor (2) comprises a servo motor, and the grating ruler displacement sensor (30) comprises a differential pulse grating ruler, and the acquisition frequency range is 0-50 kHz.

6. The device for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler according to any one of claims 1 to 5, characterized in that: The screw drive mechanism comprises a screw (23) vertically fixedly arranged between the base plate (11) and the bottom plate (14), and a sliding sleeve (22) sleeved on the outside of the screw (23); the sliding sleeve (22) is rotatably mounted on the mounting platform (12); the output end of the motor (2) drives the sliding sleeve (22) to rotate via a transmission belt (21), so that the sliding sleeve (22) and the screw (23) transmit power to each other, thereby driving the base plate (11) to move up and down.

7. The device for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of grating ruler according to claim 6 is characterized in that: The forming cylinder (1) and the motor (2) are both fixedly mounted on the mounting platform (12), and the guide rod (13) passes through the mounting platform (12), so that the base plate (11), the guide rod (13) and the bottom plate (14) can move up and down relative to the mounting platform (12).

8. A control method for improving the forming accuracy of powder-laying workpieces based on full-closed-loop real-time control of a grating ruler, characterized in that: The device for improving the forming accuracy of a powder-laying workpiece based on full-closed-loop real-time control of a grating ruler as described in claim 1 comprises the following steps: Step 1: Get the single moving distance and number of moves in the current printing workpiece, define the single moving distance as H, and the number of moves required to complete printing as M; Step 2: define the height of the substrate (11) in one movement cycle as H, and the initial position of the substrate (11) as H. 始 , the end point is H 终 , the height of the position of the substrate (11) during the movement is H i , where H 始 ≤H i ≤H 终 ; In a movement cycle, when the motor (2) drives the substrate (11) to move, the grating ruler reader (32) is used to obtain H in real time. i The grating ruler displacement sensor (30) will H i The position information is transmitted to the controller (6) in real time, and the controller (6) is configured to: When H 始 <H i <H 终 When the controller (6) sends a driving signal to the driver (5), the driver (5) controls the motor (2) to rotate; When H i =H 终 When the controller (6) sends a stop signal to the driver (5), the driver (5) controls the motor (2) to stop. At this time, the grating ruler reading head (32) stops at H 终 Location; Step 3, after the substrate (11) has descended for a cycle and then stopped, a powder spreading mechanism spreads powder on the uppermost layer of the substrate (11), and the powder spreading height is equal to the descending height H of the substrate (11); Step 4: The laser printing head prints and sinter the top layer of powder; Step 5, repeating steps 2 to 4, after the substrate (11) descends M times, the printing of the entire workpiece is completed.

9. The control method for improving the forming accuracy of powder-laying workpieces based on grating ruler full-closed-loop real-time control according to claim 8 is characterized in that: In one cycle in step 2, the moving speed of the substrate (11) is preset to be V, the acceleration is preset to be A, and the deceleration position in the cycle is preset to be HH according to the acceleration A and the speed V. i ; The encoder (4) obtains the speed information of the motor (2) and transmits the speed information to the controller (6). The controller (6) drives the motor (2) to accelerate at an acceleration A through the driver (5). The substrate (11) moves at a constant speed after accelerating to a set speed V and moves when the grating ruler reader (32) reaches HH. i The motor (2) decelerates when the motor reaches the position H, and stops at the position H within the cycle, wherein the range of H is 0.04 mm to 0.06 mm, the range of V is 0.02 mm / s to 0.1 mm / s, and the range of A is 0.5 m / s 2 ~1.0m / s 2 .

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