Flight printing position compensation method

Abstract

The invention belongs to the field of additive manufacturing, and relates to a flight printing position compensation method which comprises the following steps: 1) judging whether a to-be-processed point has position offset during flight printing or not, and if so, performing a step 2); if not, exiting; and 2) performing position offset compensation on the galvanometer according to the movement speed of the moving device. The invention provides the flight printing position compensation method capable of effectively avoiding position deviation of the processing point and improving the printing precision at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of additive manufacturing and relates to a position compensation method, in particular to a flying printing position compensation method. Background Art

[0002] During the actual laser emitting process of the forming equipment used in the selective laser melting process based on the flying printing method, the laser emitting position, reflection angle and the position of the corresponding processing point on the forming substrate may change due to the movement of the moving device such as the gantry equipped with the galvanometer, thereby causing the position of the processing point to shift. For example, see Figure 1 , is a comparison of the galvanometer offset at different gantry positions. When the galvanometer prints position x1 at positions A and B, the galvanometer offset (the galvanometer deflection angle of the X and Y axes) is different. In other words, the movement of the galvanometer will cause the position of the printing point to shift, thereby affecting the printing accuracy. Summary of the Invention

[0003] In order to solve the above technical problems existing in the background technology, the present invention provides a flying printing position compensation method that can effectively avoid position deviation of processing points and improve printing accuracy.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for compensating a printing position on the fly, characterized in that the method comprises the following steps:

[0006] 1) Determine whether the position of the processing point is offset during flight printing. If so, proceed to step 2); if not, exit;

[0007] 2) Compensate for the position offset of the galvanometer according to the movement speed of the mobile device.

[0008] The above step 2) is specifically:

[0009] 2.1) Obtaining the running speed of the mobile device;

[0010] 2.2) Compensating for the steady-state position offset of the galvanometer based on the velocity reference value;

[0011] 2.3) Based on the steady-state position offset compensation, transient compensation is performed on the position offset of the galvanometer according to the predicted motion state of the mobile device.

[0012] The above step 2.2) is to plan the motion path of the mobile device in advance, subtract the motion displacement of the mobile device from the motion path of the mobile device to obtain the path responsible for the galvanometer, and realize steady-state position offset compensation for the galvanometer.

[0013] The above step 2.2) is specifically:

[0014] 2.2.1) Obtaining the coordinates of a theoretical galvanometer printing path, wherein the coordinates of the theoretical galvanometer printing path include the location of the theoretical galvanometer scanning starting point and the location of the theoretical galvanometer scanning end point; the theoretical galvanometer printing path is a trajectory running from the theoretical galvanometer scanning starting point to the theoretical galvanometer scanning end point along a direction parallel to the X-axis or along a direction parallel to the Y-axis;

[0015] 2.2.2) Calculating the displacement S of the mobile device during uniform motion based on the mobile device's operating speed V; S = ΔtV; Δt is the time it takes the galvanometer to travel from the start point to the end point of the scan;

[0016] 2.2.3) Obtaining the coordinates of the actual printing path of the galvanometer based on the coordinates of the theoretical printing path of the galvanometer obtained in step 2.2.1) and the motion displacement of the moving device obtained in step 2.2.2); the actual printing path coordinates of the galvanometer include the actual scanning starting point and the actual scanning end point of the galvanometer;

[0017] 2.2.4) The actual printing path coordinates of the galvanometer are used as the galvanometer working path to complete the steady-state position offset compensation of the galvanometer.

[0018] The above step 2.2.3) is specifically: subtract the motion displacement of the moving device obtained in step 2.2.2) from the position of the galvanometer mirror's theoretical scanning starting point and the position of the galvanometer mirror's theoretical scanning end point of the coordinates of the galvanometer mirror's theoretical printing path obtained in step 2.2.1) to obtain the position of the galvanometer mirror's actual scanning starting point and the position of the galvanometer mirror's actual scanning end point. The position of the galvanometer mirror's actual scanning starting point and the position of the galvanometer mirror's actual scanning end point constitute the coordinates of the galvanometer mirror's actual printing path.

[0019] The above step 2.3) is to predict the motion state at the next moment based on the historical motion state of the mobile device on the basis of steady-state position offset compensation, obtain a prediction result, and compensate for the position offset of the galvanometer according to the prediction result.

[0020] The compensation for the position offset of the galvanometer based on the predicted motion state of the mobile device is specifically as follows:

[0021] 2.3.1) Use Kalman filtering to model the motion position of the mobile device;

[0022] 2.3.2) Convert the model constructed in step 2.3.1) into an observation equation;

[0023] 2.3.3) According to the observation equation obtained in step 2.3.2), the parameters are adjusted and the position information sent by the sensor is obtained at t n-1The optimal estimate of the galvanometer position at the moment

[0024] 2.3.4) According to step 2.3.3) obtained t n-1 The optimal estimate of the galvanometer position at the moment And the position information z(t n-1 +ΔT), and obtain the transient error of the moving device Determine the transient error. When the transient error is greater than the threshold, use z(t n-1 +ΔT) instead As the input value of the next observation equation; when the transient error is less than the threshold, it is still used As the input value of the next observation equation; t is calculated according to the observation equation n The optimal estimate of the galvanometer position at the moment

[0025] 2.3.5) According to step 2.3.4) n The optimal estimate of the galvanometer position at the moment Correct the coordinates of the working path of the galvanometer to compensate for the position offset of the galvanometer.

[0026] The expression of the model constructed in step 2.3.1) above is:

[0027]

[0028] in:

[0029] θ(t) is the target position;

[0030] w(t) is the angular velocity

[0031] The control input is the torque τ(t);

[0032] J is the moment of inertia;

[0033] B is the damping coefficient.

[0034] The expression of the observation equation in step 2.3.2) above is:

[0035] x(t+1)=A1x(t)+A2u(t)+f1(t)

[0036] in:

[0037]

[0038] T is the sampling time;

[0039]

[0040] u(t) = τ(t);

[0041] f1(t) is the process noise;

[0042] The position information z(t n-1 +ΔT) is obtained based on the measurement model, and the expression of the measurement model is:

[0043] z(t)=Hx(t)+f2(t), H=[1 0]

[0044] f2(t) is the measurement noise.

[0045] The above step 2.3.5) is specifically as follows: based on the steady-state position offset compensation, the value of the X direction of the galvanometer working path coordinate is subtracted from the t obtained in step 2.3.4) n The optimal estimate of the galvanometer position at the moment Complete the position offset compensation of the galvanometer in the X direction.

[0046] The advantages of the present invention are:

[0047] The present invention provides a flying printing position compensation method, which aims to solve the problem that the laser light emitting position, reflection angle and the position of the corresponding point to be processed on the forming substrate change due to the movement of the mobile device in the flying printing mode, thereby causing the position offset of the processing point. It further provides two different methods that can be selectively used according to the state of the galvanometer to compensate for the position offset of the galvanometer. That is, in the galvanometer flying printing mode, the steady-state offset error is compensated to the galvanometer by making use of the advance planning of the position of the moving platform of the mobile device. At the same time, in order to realize a closed-loop control system and solve the real-time problem, the Kalman filter method is used to predict the model of the moving platform of the mobile device, and the predicted transient position offset is compensated to the galvanometer, so that the precise printing of the processing point can be achieved. The flying printing position compensation method provided by the present invention can effectively avoid the position offset of the processing point while improving the printing accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram comparing the galvanometer offset at different positions of the mobile device;

[0049] Figure 2 It is a schematic diagram of steady-state position offset compensation when the printing trajectory is parallel to the x-axis;

[0050] Figure 3 It is a schematic diagram of steady-state position offset compensation when the printing trajectory is parallel to the y-axis. DETAILED DESCRIPTION

[0051] The present invention provides a method for compensating a flying printing position, comprising the following steps:

[0052] 1) Determine whether the position of the processing point is offset during flight printing. If so, proceed to step 2); if not, exit;

[0053] 2) Compensate the position offset of the galvanometer according to the movement speed of the mobile device (for example, in order to explain the technical solution adopted by the present invention in detail and to facilitate understanding, the mobile device will be replaced by the gantry in the following text). Specifically, step 2) includes the following methods: obtain the gantry running speed, and when the gantry is in uniform motion, compensate the steady-state position offset of the galvanometer based on the speed reference value; however, during the movement of the moving platform, since the gantry cannot completely maintain a uniform speed, it is necessary to achieve high-precision trajectory printing by feedback of the motor speed. However, there is a certain time difference between the encoder, the decoder, and the position compensation of the galvanometer, and real-time compensation cannot be achieved. If more accurate compensation is to be performed, the lag problem of this process must be solved. Considering the overall quality of the gantry motion platform and the galvanometer, its motion state is not prone to sudden changes under uniform motion. Therefore, the next moment can be predicted based on the historical motion state of the gantry motion platform, and the position offset of the current galvanometer is compensated with the predicted value, that is, the position offset of the galvanometer is compensated based on the predicted motion state of the gantry.

[0054] Among them, when the gantry is moving at a constant speed, the steady-state position offset compensation of the galvanometer is performed based on the speed reference value. The gantry motion path is planned in advance, and the gantry motion displacement is subtracted from the gantry motion path to obtain the path responsible for the galvanometer, thereby realizing steady-state position offset compensation of the galvanometer.

[0055] Specifically, the method of compensating the steady-state position offset of the galvanometer based on the speed reference value adopted by the present invention is:

[0056] a.1) Obtaining the coordinates of the galvanometer's theoretical printing path, which includes the theoretical scanning starting point and the theoretical scanning end point of the galvanometer. The galvanometer's theoretical printing path is the trajectory from the theoretical scanning starting point to the theoretical scanning end point of the galvanometer along a direction parallel to the X-axis or along a direction parallel to the Y-axis.

[0057] a.2) Calculate the gantry's displacement S during uniform motion based on the gantry's operating speed V; S = ΔtV, where Δt is the time it takes the galvanometer to travel from the start point to the end point of the scan.

[0058] a.3) Based on the coordinates of the galvanometer theoretical printing path obtained in step a.1) and the motion displacement of the gantry obtained in step a.2), the coordinates of the actual printing path of the galvanometer are obtained; the coordinates of the actual printing path of the galvanometer include the position of the actual scanning starting point of the galvanometer and the position of the actual scanning end point of the galvanometer; specifically: the position of the theoretical scanning starting point of the galvanometer and the position of the theoretical scanning end point of the coordinates of the galvanometer theoretical printing path obtained in step a.1) are respectively subtracted from the motion displacement of the gantry obtained in step a.2) to obtain the position of the actual scanning starting point of the galvanometer and the position of the actual scanning end point of the galvanometer, and the position of the actual scanning starting point of the galvanometer and the position of the actual scanning end point of the galvanometer constitute the coordinates of the actual printing path of the galvanometer.

[0059] For example, see Figure 2 as well as Figure 3 , in the case of uniform motion, for the steady-state position offset, the present invention adopts a method of planning the gantry motion platform speed in advance. This method plans the gantry motion platform path in advance, subtracts the gantry motion from the overall motion to obtain the path responsible for the galvanometer, thereby achieving steady-state position offset compensation for the galvanometer. Specifically: See Figure 2 , when the gantry motor speed is planned in advance to be V, in order to achieve a printing trajectory parallel to the x-axis (x0, y0) -> (x1, y0), the steady-state position offset compensation of the galvanometer's command path is issued, and the command path is issued as (x0-vt1, y0) -> (x1-vt2, y0). See Figure 3 , when the gantry motor speed is planned in advance to be V, in order to achieve a printing trajectory parallel to the y-axis (x0, y0) -> (x0, y1), the steady-state position offset compensation of the galvanometer's command path is issued, and the command path is issued to (x0-vt1, y0) -> (x0-vt2, y1).

[0060] a.4) The actual printing path coordinates of the galvanometer are used as the galvanometer working path to complete the steady-state position offset compensation of the galvanometer.

[0061] When the movement speed of the gantry is non-uniform, then on the basis of the aforementioned steady-state position offset compensation, the position offset of the galvanometer is compensated based on the predicted movement state of the gantry. The movement state at the next moment is predicted based on the historical movement state of the gantry to obtain the prediction result, and the position offset of the galvanometer is transiently compensated according to the prediction result.

[0062] The following is an example of compensation for the working path coordinate X of the galvanometer to explain in detail the compensation for the position offset of the galvanometer based on the predicted motion state of the gantry. The compensation for the position offset of the galvanometer based on the predicted motion state of the gantry is as follows:

[0063] b.1) The Kalman filter method is used to model the gantry motion position. The model expression is:

[0064]

[0065] in:

[0066] θ(t) is the target position;

[0067] w(t) is the angular velocity

[0068] The control input is the torque τ(t);

[0069] J is the moment of inertia;

[0070] B is the damping coefficient.

[0071] b.2) Convert the model constructed in step b.1) into an observation equation, where the expression of the observation equation is:

[0072] x(t+1)=A1x(t)+A2u(t)+w(t)

[0073] in:

[0074]

[0075] u(t) = τ(t);

[0076] w(t) is the process noise (uncertainty of the prediction model).

[0077] b.3) According to the observation equation obtained in step b.2), the parameters are adjusted and the position information sent by the sensor is obtained at t n-1 The optimal estimate of the galvanometer position at the moment

[0078] b.4) t obtained according to step b.3) n-1 The optimal estimate of the galvanometer position at the moment And the position information z(t n-1 +ΔT), and obtain the transient error of the moving device Determine the transient error. When the transient error is greater than the threshold, use z(t n-1 +ΔT) instead As the input value of the next observation equation; when the transient error is less than the threshold, it is still used As the input value of the next observation equation; t is calculated according to the observation equation n The optimal estimate of the galvanometer position at the moment Among them, the position information z(t n-1+ΔT) is obtained based on the measurement model, and the expression of the measurement model is:

[0079] z(t)=Hx(t)+v(t), H=[1 0]

[0080] v(t) is the measurement noise.

[0081] b.5) ​​t obtained according to step b.4) n The optimal estimate of the galvanometer position at the moment Correct the coordinates of the working path of the galvanometer to complete the compensation of the position offset of the galvanometer. Based on the steady-state position offset compensation, subtract the value of the X direction of the coordinate of the working path of the galvanometer from the t obtained in step b.4) n The optimal estimate of the galvanometer position at the moment The position offset compensation of the galvanometer in the X direction is completed. For example, the coordinates of the galvanometer working path after the original steady-state compensation (such as the steady-state position offset compensation shown in steps a.1) to a.4) described above) can be corrected to Where v(t) is the set speed of the flight axis.

[0082] Of course, if the Y direction of the galvanometer working path coordinate also needs to be compensated, it is performed according to the above method, which will not be repeated here.

Claims

1. A method for compensating a printing position on the fly, characterized by: The flying printing position compensation method comprises the following steps: 1) Determine whether the position of the processing point is offset during flight printing. If so, proceed to step 2); if not, exit; 2) Compensate for the position offset of the galvanometer according to the movement speed of the mobile device.

2. The flying printing position compensation method according to claim 1, characterized in that: The step 2) is specifically: 2.1) Obtaining the running speed of the mobile device; 2.2) Compensating for the steady-state position offset of the galvanometer based on the velocity reference value; 2.3) Based on the steady-state position offset compensation, transient compensation is performed on the position offset of the galvanometer according to the predicted motion state of the mobile device.

3. The flying printing position compensation method according to claim 2, characterized in that: The step 2.2) is to plan the motion path of the mobile device in advance, subtract the motion displacement of the mobile device from the motion path of the mobile device to obtain the path responsible for the galvanometer, and realize steady-state position offset compensation for the galvanometer.

4. The flying printing position compensation method according to claim 3, characterized in that: The step 2.2) is specifically: 2.2.1) Obtaining the coordinates of a theoretical galvanometer printing path, wherein the coordinates of the theoretical galvanometer printing path include the location of the theoretical galvanometer scanning starting point and the location of the theoretical galvanometer scanning end point; the theoretical galvanometer printing path is a trajectory running from the theoretical galvanometer scanning starting point to the theoretical galvanometer scanning end point along a direction parallel to the X-axis or along a direction parallel to the Y-axis; 2.2.2) Calculating the displacement S of the mobile device during uniform motion based on the mobile device's operating speed V; S = ΔtV; Δt is the time it takes the galvanometer to travel from the start point to the end point of the scan; 2.2.3) Obtaining the coordinates of the actual printing path of the galvanometer based on the coordinates of the theoretical printing path of the galvanometer obtained in step 2.2.1) and the motion displacement of the moving device obtained in step 2.2.2); the actual printing path coordinates of the galvanometer include the actual scanning starting point and the actual scanning end point of the galvanometer; 2.2.4) The actual printing path coordinates of the galvanometer are used as the galvanometer working path to complete the steady-state position offset compensation of the galvanometer.

5. The flying printing position compensation method according to claim 4, characterized in that: The specific step 2.2.3) is: subtract the motion displacement of the moving device obtained in step 2.2.2) from the position of the galvanometer mirror's actual scanning starting point and the position of the galvanometer mirror's actual scanning end point of the coordinates of the galvanometer mirror's theoretical printing path obtained in step 2.2.1) to obtain the position of the galvanometer mirror's actual scanning starting point and the position of the galvanometer mirror's actual scanning end point. The position of the galvanometer mirror's actual scanning starting point and the position of the galvanometer mirror's actual scanning end point constitute the coordinates of the galvanometer mirror's actual printing path.

6. The flying printing position compensation method according to any one of claims 1 to 5, characterized in that: The step 2.3) is to predict the motion state at the next moment based on the historical motion state of the mobile device on the basis of steady-state position offset compensation, obtain a prediction result, and perform transient compensation on the position offset of the galvanometer according to the prediction result.

7. The flying printing position compensation method according to claim 6, characterized in that: The step 2.3) is specifically: 2.3.1) Use Kalman filtering to model the motion position of the mobile device; 2.3.2) Convert the model constructed in step 2.3.1) into an observation equation; 2.3.3) According to the observation equation obtained in step 2.3.2), and based on the position information sent by the sensor, obtain the n-1 The optimal estimate of the galvanometer position at the moment 2.3.4) According to step 2.3.3) obtained t n-1 The optimal estimate of the galvanometer position at the moment And the position information z(t n-1 +ΔT), and obtain the transient error of the moving device Determine the transient error. When the transient error is greater than the threshold, use z(t n-1 +ΔT) instead As the input value of the next observation equation; When the transient error is less than the threshold, the As the input value of the next observation equation; According to the observation equation, t n The optimal estimate of the galvanometer position at the moment 2.3.5) According to step 2.3.4) n The optimal estimate of the galvanometer position at the moment Correct the coordinates of the working path of the galvanometer to compensate for the position offset of the galvanometer.

8. The flying printing position compensation method according to claim 7, characterized in that: The expression of the model constructed in step 2.3.1) is: in: θ(t) is the target position; w(t) is the angular velocity The control input is the torque τ(t); J is the moment of inertia; B is the damping coefficient.

9. The flying printing position compensation method according to claim 8, characterized in that: The expression of the observation equation in step 2.3.2) is: x(t+1)=A1x(t)+A2u(t)+f1(t) in: T is the sampling time; u(t) = τ(t); f1(t) is the process noise; The position information z(t n-1 +ΔT) is obtained based on the measurement model, and the expression of the measurement model is: z(t)=Hx(t)+f2(t), H=[1 0] f2(t) is the measurement noise.

10. The flying printing position compensation method according to claim 9, characterized in that: The step 2.3.5) is specifically: On the basis of steady-state position offset compensation, the X-direction coordinate value of the galvanometer working path is subtracted from the t obtained in step 2.3.4) n The optimal estimate of the galvanometer position at the moment Complete the position offset compensation of the galvanometer in the X direction.

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