Silk screen printing method for special-shaped workpieces

Abstract

The present invention provides a method for screen printing a special-shaped workpiece, belonging to the field of curved surface screen printing processing, comprising step S1, drawing a contour curve of the screen printing surface of the special-shaped workpiece, discretizing the contour curve, and converting each discrete point to a coordinate value in the machine tool coordinate system XOY; step S2, synchronously moving the screen printing head and the transfer belt to print the screen pattern on the transfer belt; step S3, using the length of the contact portion between the transfer belt and the rotating wheel and the tangency of the transfer belt and the printing trajectory of the special-shaped workpiece as constraints, and minimizing the transfer belt movement value, the special-shaped workpiece movement value, and the special-shaped workpiece rotation angle as optimization goals, to calculate the optimal screen printing posture of each discrete point; step S4, controlling the movement of the transfer belt, the movement of the special-shaped workpiece, and the rotation of the special-shaped workpiece according to the optimal screen printing posture to transfer the screen pattern on the transfer belt to the screen printing surface of the special-shaped workpiece. The present invention replaces manual printing and effectively improves printing efficiency and printing quality.

Description

Technical Field

[0001] The invention belongs to the field of curved surface silk screen processing, and in particular relates to a silk screen printing method for special-shaped workpieces. Background Art

[0002] A screen printer, or silk screen printer, is a machine tool that uses a silk screen to print on a workpiece surface. It is widely used in applications such as automotive glass printing. Because the screen is typically fixed in a horizontal position, existing technology can only print on convex surfaces. Printing on concave surfaces can only be achieved through manual printing, which is not only inefficient but also heavily dependent on the quality of the work. Summary of the Invention

[0003] The purpose of the present invention is to provide a screen printing method for special-shaped workpieces, which can replace manual printing and effectively improve printing efficiency and printing quality.

[0004] The present invention is achieved through the following technical solutions:

[0005] A screen printing method for a special-shaped workpiece comprises the following steps:

[0006] Step S1: Draw the contour curve of the screen printing surface of the special-shaped workpiece, discretize the contour curve, and convert each discrete point to the coordinate value under the machine tool coordinate system XOY to obtain the printing trajectory, wherein the screen printing surface is a concave surface, and the base coordinate system of the contour curve is X L O L Y L , the rotation center of the special-shaped workpiece coincides with the origin of the machine tool coordinate system XOY;

[0007] Step S2: setting a transfer belt that is tightly sleeved on the main rotating wheel and the slave rotating wheel so that the transfer belt at the end of the main rotating wheel maintains pure rolling contact with the screen, and synchronously moving the screen printing head and the transfer belt to print the screen pattern on the transfer belt;

[0008] Step S3, using the length of the contact portion between the transfer belt and the rotating wheel, and the tangency between the transfer belt and the printing trajectory of the special-shaped workpiece as constraints, and minimizing the transfer belt movement value, the special-shaped workpiece movement value, and the special-shaped workpiece rotation angle as optimization goals, to calculate the optimal screen printing posture for each discrete point of the contour curve;

[0009] Step S4: Control the movement of the transfer belt, the movement of the special-shaped workpiece, and the rotation of the special-shaped workpiece according to the optimal silk-screen posture, so as to transfer the silk-screen pattern on the transfer belt to the silk-screen surface of the special-shaped workpiece.

[0010] Furthermore, in step S1, discretizing the contour curve includes:

[0011] If the contour curve is an arc primitive, each arc primitive is discretized from the starting angle at a set angle, and the discrete points P of the arc primitive are i Expressed as Among them, (x c ,y c ) is the coordinate of the center of the arc primitive, r is the arc radius, α is the starting point phase angle, β is the center angle, n is the number of discrete points of the contour curve, i = 1, 2, ..., n;

[0012] If the contour curve is an elliptical arc primitive, each elliptical arc primitive is discretized from the starting angle at a set angle, and the discrete points P of the elliptical arc primitive are i Expressed as Among them, (x c ,y c ) are the coordinates of the ellipse center, a is the major axis, b is the minor axis, α is the starting point phase angle, β is the central angle, n is the number of discrete points of the contour curve, i = 1, 2, ..., n;

[0013] If the contour curve is a cubic spline curve primitive, each cubic spline curve primitive is discretized at a set distance in the horizontal axis direction, and the discrete points P of the cubic spline curve primitive are i Indicated as S Li (x) = a Li +b Li (xx Li )+c Li (xx Li ) 2 +d Li (xx Li ) 3 , where S Li (x) is the coordinate equation corresponding to the i-th segment of the cubic spline curve, a Li , b Li , c Li , d Li are the 4n unknowns of the cubic spline curve.

[0014] Furthermore, in step S1, each discrete point is converted to a coordinate value in the machine tool coordinate system XOY to obtain a printing trajectory, specifically:

[0015] Let discrete point P i The coordinates are [x Li ,y Li ], its coordinate value converted to the machine tool coordinate system XOY is [x i ,y i ],but Where M represents the deviation between the origin of the base coordinate system of the contour curve and the rotation center of the special-shaped workpiece in the X direction, and N represents the deviation between the origin of the base coordinate system of the contour curve and the rotation center of the special-shaped workpiece in the Y direction.

[0016] Furthermore, in step S2, the transfer belt and the screen printing head are simultaneously moved to the starting position of the screen pattern and move at the same speed.

[0017] Furthermore, the step S3 is specifically as follows:

[0018] Let discrete point P i In the optimal screen printing posture, the horizontal movement value of the transfer belt is x bi , the vertical movement value of the transfer belt is y bi , the horizontal movement value of the special-shaped workpiece is x pi , the rotation angle of the special-shaped workpiece is θ;

[0019] Two adjacent discrete points P i 、P i+1 Initially, the coordinates in the machine tool coordinate system XOY are [x i ,y i ]、[x i+1 ,y i+1 ], after the workpiece rotates θ, the coordinates of these two discrete points become [x′ i ,y′ i ]、[x′ i+1 ,y′ i+1 ],in,

[0020] The two discrete points P i 、P i+1 The point at the optimal screen printing posture is P″ i , P″ i+1 , whose coordinates are [x″ i ,y″ i ]、[x″ i+1 ,y″ i+1 ],in,

[0021] Point P″ i and point P″ i+1 The slope of the connecting line is

[0022] In the optimal screen printing posture, the coordinates of the center of the rotating wheel are [Lb+x pi ,Hb-Hr+y bi ], the rotating wheel and the special-shaped workpiece are P i The equation of the tangent line with ″ as the tangent point is The slope of the tangent line is Where Lb is the horizontal distance between the transfer belt origin and the origin of the machine coordinate system, Hb is the vertical distance between the transfer belt origin and the origin of the machine coordinate system, and Hr is the distance from the center of the rotating wheel to the transfer belt origin;

[0023] The transfer function can only be achieved from the contact part between the rotating wheel and the transfer belt. Combined with the optimization objectives of the horizontal movement value of the transfer belt, the vertical movement value of the transfer belt, the movement value of the special-shaped workpiece and the minimum rotation angle of the special-shaped workpiece, the optimal posture of each discrete point can be calculated.

[0024] Furthermore, in step S3, when the screen printing reaches the discrete point P i When the discrete point P i The length from the starting point of silk screen printing to the special-shaped workpiece is According to the length S i Calculate the angular displacement of the main rotating wheel, where j = 1, 2, ..., i.

[0025] Furthermore, in step S2, the diameter of the main rotating wheel is larger than that of the slave rotating wheel.

[0026] The present invention has the following beneficial effects:

[0027] The present invention first discretizes the contour curve of the silk-screened surface of the special-shaped workpiece and converts it into the machine tool coordinate system to obtain a printing trajectory, and then prints the silk-screen pattern onto a transfer belt. Secondly, the length of the contact portion between the transfer belt and the rotating wheel, and the tangency of the transfer belt and the printing trajectory of the special-shaped workpiece are used as constraints, and the minimization of the transfer belt movement value, the special-shaped workpiece movement value and the special-shaped workpiece rotation angle are used as optimization goals. The optimal silk-screen posture of each discrete point of the contour curve is calculated. Finally, according to the optimal silk-screen posture, the movement of the transfer belt, the movement of the special-shaped workpiece and the rotation of the special-shaped workpiece are controlled to transfer the silk-screen pattern on the transfer belt to the silk-screened surface of the special-shaped workpiece. The printing of the concave surface of the special-shaped workpiece is achieved through a CNC machine tool throughout the process, without the need for human intervention, completely replacing manual printing, and effectively improving efficiency and printing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described in detail below with reference to the accompanying drawings.

[0029] Figure 1 Flowchart of the present invention.

[0030] Figure 2 Schematic diagram of the special-shaped workpiece and the transfer belt (the special-shaped workpiece is in a rotating state).

[0031] Among them, 1. special-shaped workpiece; 11. screen printing surface; 2. transfer belt; 3. rotating wheel. DETAILED DESCRIPTION

[0032] like Figure 1 As shown, the screen printing method for special-shaped workpieces includes the following steps:

[0033] Step S1, drawing a contour curve of the screen printing surface 11 of the special-shaped workpiece 1, discretizing the contour curve, and converting each discrete point into a coordinate value under the machine tool coordinate system XOY to obtain a printing trajectory, wherein the rotation center of the special-shaped workpiece 1 coincides with the origin of the machine tool coordinate system XOY;

[0034] like Figure 2 As shown, the upper surface of the special-shaped workpiece 1 is a screen printing surface 11, which is a concave surface. The lower end of the special-shaped workpiece 1 can be rotatably set on a CNC machine tool. The base coordinate system of the contour curve of the screen printing surface 11 is X L O L Y L The process of drawing the contour curve of the screen printing surface 11 of the special-shaped workpiece 1 is the existing technology. The contour curve is a two-dimensional curve on the XY plane. The process of discretizing the contour curve is processed differently according to the different types of contour curves, specifically:

[0035] If the contour curve is an arc primitive, each arc primitive is discretized from the starting angle at a set angle, and the discrete points P of the arc primitive are i Expressed as Among them, (x c ,y c ) is the coordinate of the center of the arc primitive, r is the arc radius of the arc primitive, α is the starting point phase angle, β is the center angle, n is the number of discrete points of the contour curve, i = 1, 2, ..., n;

[0036] If the contour curve is an elliptical arc primitive, each elliptical arc primitive is discretized from the starting angle at a set angle, and the discrete points P of the elliptical arc primitive are i Expressed as Among them, (x c ,y c ) are the coordinates of the ellipse center, a is the major axis, b is the minor axis, α is the starting point phase angle, β is the central angle, n is the number of discrete points of the contour curve, i = 1, 2, ..., n;

[0037] If the contour curve is a cubic spline curve primitive, each cubic spline curve primitive is discretized at a set distance in the horizontal axis direction, and the discrete points P of the cubic spline curve primitive are i Indicated as S Li (x) = a Li +b Li (xx Li )+c Li (xx Li ) 2 +d Li (xxLi ) 3 , where S Li (x) is the coordinate equation corresponding to the i-th segment of the cubic spline curve, a Li , b Li , c Li , d Li are the 4n unknowns of the cubic spline curve.

[0038] Convert each discrete point to the coordinate value of the machine tool coordinate system XOY to obtain the printing trajectory, specifically:

[0039] Let discrete point P i The coordinates are [x Li ,y Li ], and its coordinate value after conversion to the machine tool coordinate system XOY is [x i ,y i ],but Where M represents the base coordinate system X of the contour curve L O L Y L The deviation value between the origin and the rotation center of the special-shaped workpiece 1 in the X direction, N represents the base coordinate system X of the contour curve L O L Y L Deviation between the origin and the rotation center of the special-shaped workpiece 1 in the Y direction.

[0040] Step S2: setting a transfer belt 2 which is tightly sleeved on the main rotating wheel and the slave rotating wheel 3 so that the belt at the end of the main rotating wheel maintains pure rolling contact with the screen, and synchronously moving the screen printing head and the transfer belt 2 to print the screen pattern onto the transfer belt 2;

[0041] Specifically, if Figure 2 As shown, the main rotating wheel and the slave rotating wheel 3 are both rotatably set on the CNC machine tool. The diameter of the main rotating wheel is larger than that of the slave rotating wheel 3. At the beginning, the transfer belt 2 and the screen printing head are moved to the starting position of the screen pattern at the same time, and the belt at the upper end of the main rotating wheel is kept in contact with the screen printing head. Then, the screen printing head and the transfer belt 2 are moved uniformly at the same speed on the screen, and the main rotating wheel and the second pulley are rotated to ensure pure rolling contact between the belt and the screen until the screen pattern is completely screen-printed on the transfer belt 2.

[0042] Step S3, using the length of the contact portion between the transfer belt 2 and the rotating wheel 3 and the tangency of the printing trajectory of the transfer belt 2 and the special-shaped workpiece 1 as constraints, and minimizing the movement value of the transfer belt 2, the movement value of the special-shaped workpiece 1, and the rotation angle of the special-shaped workpiece 1 as optimization goals, calculating the optimal screen printing posture of each discrete point of the contour curve;

[0043] Specifically:

[0044] Since each discrete point has multiple postures during the screen printing process, it is necessary to calculate the optimal screen printing posture for each discrete point. i In the optimal screen printing posture, the horizontal movement value of the transfer belt 2 is x bi , the vertical movement value of transfer belt 2 is y bi , the horizontal movement value of the special-shaped workpiece 1 is x pi , the rotation angle of the special-shaped workpiece 1 is θ;

[0045] Two adjacent discrete points P i 、P i+1 Initially, the coordinates in the machine tool coordinate system XOY are [x i ,y i ]、[x i+1 ,y i+1 ], after the workpiece 1 rotates counterclockwise by θ, the coordinates of these two discrete points become [x′ i ,y′ i ]、[x′ i+1 ,y′ i+1 ],in,

[0046] The two discrete points P i 、P i+1 The point at the optimal screen printing posture is P″ i , P″ i+1 , whose coordinates are [x″ i ,y″ i ]、[x″ i+1 ,y″ i+1 ],in,

[0047] Point P″ i and point P″ i+1 The slope of the connecting line is

[0048] In the optimal screen printing posture, the coordinates of the center of the rotating wheel 3 are [Lb+x pi ,Hb-Hr+y bi ], the slave rotating wheel 3 and the special-shaped workpiece 1 are P i The equation of the tangent line with ″ as the tangent point is The slope of the tangent line is Wherein, Lb is the horizontal distance between the origin of the transfer belt 2 and the origin of the machine coordinate system, Hb is the vertical distance between the origin of the transfer belt 2 and the origin of the machine coordinate system, Hr is the distance from the center of the rotating wheel 3 to the origin of the transfer belt 2, and the origin of the transfer belt 2 is the set value;

[0049] Because the transfer function can be realized from the contact part between the rotating wheel 3 and the transfer belt 2, the By combining the optimization objectives of the horizontal movement value of the transfer belt 2, the vertical movement value of the transfer belt 2, the movement value of the special-shaped workpiece 1 and the minimum rotation angle of the special-shaped workpiece 1, the optimal posture of each discrete point can be calculated;

[0050] In addition, the optimal posture also includes the angular displacement of the main rotating wheel. i When the discrete point is , the length between the discrete point and the starting point of the screen printing of the special-shaped workpiece 1 is According to the length S i The angular displacement of the main rotating wheel can be calculated, where j = 1, 2, ..., i.

[0051] Step S4: The CNC machine tool controls the movement of the transfer belt 2, the movement of the special-shaped workpiece 1, the rotation of the special-shaped workpiece 1 and the rotation of the main rotating wheel according to the optimal silk screen posture, so as to transfer the silk screen pattern on the transfer belt 2 to the silk screen surface 11 of the special-shaped workpiece 1.

[0052] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made according to the scope of the patent application and the contents of the specification should still fall within the scope of the patent of the present invention.

Claims

1. A screen printing method for special-shaped workpieces, characterized by: The steps include: Step S1: Draw the contour curve of the screen printing surface of the special-shaped workpiece, discretize the contour curve, and convert each discrete point to the coordinate value under the machine tool coordinate system XOY to obtain the printing trajectory, wherein the screen printing surface is a concave surface, and the base coordinate system of the contour curve is X L O L Y L , the rotation center of the special-shaped workpiece coincides with the origin of the machine tool coordinate system XOY; Step S2: setting a transfer belt that is tightly sleeved on the main rotating wheel and the slave rotating wheel so that the transfer belt at the end of the main rotating wheel maintains pure rolling contact with the screen, and synchronously moving the screen printing head and the transfer belt to print the screen pattern on the transfer belt; Step S3, using the length of the contact portion between the transfer belt and the rotating wheel, and the tangency between the transfer belt and the printing trajectory of the special-shaped workpiece as constraints, and minimizing the transfer belt movement value, the special-shaped workpiece movement value, and the special-shaped workpiece rotation angle as optimization goals, to calculate the optimal screen printing posture for each discrete point of the contour curve; Step S4: Control the movement of the transfer belt, the movement of the special-shaped workpiece, and the rotation of the special-shaped workpiece according to the optimal silk-screen posture, so as to transfer the silk-screen pattern on the transfer belt to the silk-screen surface of the special-shaped workpiece.

2. The screen printing method for special-shaped workpieces according to claim 1, characterized in that: In the step S1, discretizing the contour curve includes: If the contour curve is an arc primitive, each arc primitive is discretized from the starting angle at a set angle, and the discrete points P of the arc primitive are i Expressed as Among them, (x c ,y c ) is the coordinate of the center of the arc primitive, r is the arc radius, α is the starting point phase angle, β is the center angle, n is the number of discrete points of the contour curve, i = 1, 2, ..., n; If the contour curve is an elliptical arc primitive, each elliptical arc primitive is discretized from the starting angle at a set angle, and the discrete points P of the elliptical arc primitive are i Expressed as Among them, (x c ,y c ) are the coordinates of the ellipse center, a is the major axis, b is the minor axis, α is the starting point phase angle, β is the central angle, n is the number of discrete points of the contour curve, i = 1, 2, ..., n; If the contour curve is a cubic spline curve primitive, each cubic spline curve primitive is discretized at a set distance in the horizontal axis direction, and the discrete points P of the cubic spline curve primitive are i Indicated as S Li (x) = a Li +b Li (xx Li )+c Li (xx Li ) 2 +d Li (xx Li ) 3 , where S Li (x) is the coordinate equation corresponding to the i-th segment of the cubic spline curve, a Li , b Li , c Li , d Li are the 4n unknowns of the cubic spline curve.

3. The screen printing method for special-shaped workpieces according to claim 2, characterized in that: In step S1, the coordinate values ​​of each discrete point are converted to the coordinate value of the machine tool coordinate system XOY to obtain the printing trajectory, specifically: Let discrete point P i The coordinates are [x Li ,y Li ], its coordinate value converted to the machine tool coordinate system XOY is [x i ,y i ],but Where M represents the deviation between the origin of the base coordinate system of the contour curve and the rotation center of the special-shaped workpiece in the X direction, and N represents the deviation between the origin of the base coordinate system of the contour curve and the rotation center of the special-shaped workpiece in the Y direction.

4. A screen printing method for special-shaped workpieces according to claim 1, 2 or 3, characterized in that: In step S2, the transfer belt and the screen printing head are simultaneously moved to the starting position of the screen pattern and move at the same speed.

5. A screen printing method for special-shaped workpieces according to claim 1, 2 or 3, characterized in that: The step S3 is specifically as follows: Let discrete point P i In the optimal screen printing posture, the horizontal movement value of the transfer belt is x bi , the vertical movement value of the transfer belt is y bi , the horizontal movement value of the special-shaped workpiece is x pi , the rotation angle of the special-shaped workpiece is θ; Two adjacent discrete points P i 、P i+1 Initially, the coordinates in the machine tool coordinate system XOY are [x i ,y i ]、[x i+1 ,y i+1 ], after the workpiece rotates θ, the coordinates of these two discrete points become [x i ′,y i ′]、[x′ i+1 ,y′ i+1 ],in, The two discrete points P i 、P i+1 The point at the optimal screen printing posture is P″ i , P″ i+1 , whose coordinates are [x″ i ,y″ i ]、[x″ i+1 ,y″ i+1 ],in, Point P″ i and point P″ i+1 The slope of the connecting line is In the optimal screen printing posture, the coordinates of the center of the rotating wheel are [Lb+x pi ,Hb-Hr+y bi ], the rotating wheel and the special-shaped workpiece are P i The equation of the tangent line with ″ as the tangent point is The slope of the tangent line is Where Lb is the horizontal distance between the transfer belt origin and the origin of the machine coordinate system, Hb is the vertical distance between the transfer belt origin and the origin of the machine coordinate system, and Hr is the distance from the center of the rotating wheel to the transfer belt origin; The transfer function can only be achieved from the contact part between the rotating wheel and the transfer belt. Combined with the optimization objectives of the horizontal movement value of the transfer belt, the vertical movement value of the transfer belt, the movement value of the special-shaped workpiece and the minimum rotation angle of the special-shaped workpiece, the optimal posture of each discrete point can be calculated.

6. A screen printing method for special-shaped workpieces according to claim 1, 2 or 3, characterized in that: In step S3, when the screen print reaches the discrete point P i When the discrete point P i The length from the starting point of silk screen printing to the special-shaped workpiece is According to the length S i Calculate the angular displacement of the main rotating wheel, where j = 1, 2, ..., i.

7. A screen printing method for special-shaped workpieces according to claim 1, 2 or 3, characterized in that: In step S2, the diameter of the main rotating wheel is larger than that of the slave rotating wheel.

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