Calibration method and calibration system for machine tools

Abstract

The present invention discloses a correction method and correction system for a machine tool, wherein the correction method for the machine tool includes: providing a workpiece to the machine tool; rotating the workpiece with a first rotation axis of the machine tool parallel to its main axis and processing the workpiece in a first processing mode; measuring a first dimensional error of the workpiece along a first linear axis and a second linear axis of the machine tool perpendicular to the first rotation axis; calculating a position error of the first rotation axis based on the first dimensional error to correct the rotation center of the machine tool; rotating the workpiece with a second rotation axis of the machine tool perpendicular to its main axis and processing the workpiece in a second processing mode different from the first processing mode; measuring a second dimensional error of the workpiece along a third linear axis of the machine tool perpendicular to the second rotation axis; calculating a position error of the second rotation axis based on the second dimensional error to correct the rotation center of the machine tool.

Description

Technical Field

[0001] The invention relates to a calibration method and a calibration system for a machine tool. Background Art

[0002] In recent years, an increasing number of machine tools have evolved into multi-dimensional processing machines, enabling them to produce more complex products. Multi-axis machine tools, in addition to the traditional three linear axes, also include several rotary axes, which increases the potential for machining errors. Machine tool precision errors can be categorized as static and dynamic. Static errors can be easily measured with simple measuring tools, such as straightedges and dial indicators, while dynamic errors often require expensive measuring instruments to measure and calibrate, which is undoubtedly a significant cost burden.

[0003] However, dynamic error is often a factor that directly affects processing yield. Therefore, how to achieve dynamic error measurement while overcoming cost issues has become a goal that practitioners in this field strive to achieve. Summary of the Invention

[0004] In view of the problems in the existing technology, the present invention proposes a compensation and correction technology for the rotation center of a machine tool. The technology mainly processes the workpiece by cooperating the rotary axis with the linear axis. The rotation center offset error can be determined by measuring the workpiece, and the error is then compensated in reverse to correct the rotation center of the machine tool without the need for expensive measuring instruments.

[0005] According to one aspect of the present invention, a calibration method for a machine tool is provided, comprising the following steps. A workpiece is provided to the machine tool. The workpiece is rotated about a first rotational axis of the machine tool and machined in a first machining mode, wherein the first rotational axis is parallel to the main axis of the machine tool. A first dimensional error of the workpiece is measured along a first linear axis and a second linear axis of the machine tool, wherein the first linear axis and the second linear axis are perpendicular to the first rotational axis. Based on the first dimensional error of the workpiece, a position error of the first rotational axis is calculated to correct the rotation center of the machine tool. The workpiece is rotated about a second rotational axis of the machine tool and machined in a second machining mode different from the first machining mode, wherein the second rotational axis is perpendicular to the main axis of the machine tool. A second dimensional error of the workpiece is measured along a third linear axis of the machine tool, wherein the third linear axis is perpendicular to the second rotational axis. Based on the second dimensional error of the workpiece, a position error of the second rotational axis is calculated to correct the rotation center of the machine tool.

[0006] According to another aspect of the present invention, a calibration system for calibrating a machine tool is provided. The calibration system includes a workpiece, a measuring unit, and a processing control unit. The workpiece is provided to the machine tool. After the workpiece rotates about a first rotational axis of the machine tool and is processed in a first processing mode, the measuring unit is configured to measure a first dimensional error of the workpiece along a first linear axis and a second linear axis of the machine tool, wherein the first rotational axis is parallel to the main axis of the machine tool and the first and second linear axes are perpendicular to the first rotational axis. Furthermore, after the workpiece rotates about a second rotational axis of the machine tool and is processed in a second processing mode different from the first processing mode, the measuring unit is configured to measure a second dimensional error of the workpiece along a third linear axis of the machine tool, wherein the second rotational axis is perpendicular to the main axis of the machine tool and the third linear axis is perpendicular to the second rotational axis. The processing control unit is configured to calculate a position error of the first rotational axis based on the first dimensional error of the workpiece to calculate and calibrate the rotation center of the machine tool, and to calculate a position error of the second rotational axis based on the second dimensional error of the workpiece to calibrate the rotation center of the machine tool.

[0007] In order to better understand the above and other aspects of the present invention, the following embodiments are given and described in detail with reference to the accompanying drawings: BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a flow chart of a calibration method for a machine tool according to an embodiment of the present invention;

[0009] Figure 2 is a schematic diagram of an example machine tool to which the calibration method according to an embodiment of the present invention may be applied;

[0010] Figure 3 is a schematic diagram of a first processing mode in a calibration method according to an embodiment of the present invention;

[0011] Figure 4 Schematic diagram of measuring a first external dimension error of a workpiece along a first linear axis and a second linear axis in a correction method according to an embodiment of the present invention;

[0012] Figure 5 is a schematic diagram of a second processing mode in the calibration method according to an embodiment of the present invention; and

[0013] Figures 6A to 6C This is a schematic diagram of measuring a second external dimension error of a workpiece along a third linear axis in a correction method according to an embodiment of the present invention.

[0014] Explanation of symbols

[0015] 11: Workpiece

[0016] 12: Measurement unit

[0017] F,G,H,I: Processing position

[0018] F1, G1, H1: Depth

[0019] D M1 :The first largest step difference

[0020] D M2 : The second largest step difference

[0021] E1, E2: Processing surface

[0022] K: Knife

[0023] M1, M2: milling depth

[0024] O:Offset

[0025] P:Platform

[0026] S1, S2, S2', S3, S3', S4: surface

[0027] S110~S170: Steps

[0028] V: Virtual rotation center

[0029] W: True rotation center DETAILED DESCRIPTION

[0030] Please refer to Figures 1 and 2 , Figure 1 A flow chart of a calibration method for a machine tool according to an embodiment of the present invention is shown. Figure 2 A schematic diagram illustrating an example machine tool to which the calibration method according to an embodiment of the present invention can be applied is shown. Figure 3 FIG. 4 is a schematic diagram illustrating a first processing mode in a calibration method according to an embodiment of the present invention.

[0031] The calibration method of the present invention can be implemented by a calibration system comprising a workpiece 11, a measuring unit 12, and a processing control unit (not shown in the figure, such as a programmable controller). The calibration method of the embodiment of the present invention can be applied to machine tools such as multi-axis machining centers commonly found in the mechanical field, such as Figure 2 The five-axis machine tool shown has at least three linear axes (such as the X-axis, Y-axis, and Z-axis commonly known in the mechanical field) and two rotational axes (such as any two of the A-axis, B-axis, and C-axis commonly known in the mechanical field), where the A-axis, B-axis, and C-axis correspond to the rotation axes rotating along the X-axis, Y-axis, and Z-axis, respectively.

[0032] In step S110 , a workpiece 11 is placed on a machine tool, for example, by being secured to a platform P. First, a measurement is performed on a rotational axis parallel to the machine tool's spindle (the C-axis in this example). The spindle of the machine tool is the axis that mounts and drives the tool.

[0033] In step S120, the workpiece 11 is rotated about the first rotation axis (C axis) of the machine tool and the workpiece 11 is machined in the first machining mode, wherein the first rotation axis (C axis) is parallel to the main axis of the machine tool. Figure 3 As shown, Figure 3 The upper left half of the middle portion is a front view schematic diagram of the relative positions of the workpiece 11 and the machining tool K, that is, the viewing angle along the Y direction; Figure 3 The lower left half of the middle portion is a side view schematically showing the relative positions of the workpiece 11 and the machining tool K, that is, the viewing angle along the X direction. Figure 3 The middle right half is a top view schematic diagram of the rotation stage P, that is, the viewing angle along the Z direction.

[0034] Specifically, workpiece 11 is initially cut at processing position F to form a groove of depth F1. Next, the machine tool's platform P rotates, for example, 90 degrees (counterclockwise), driving workpiece 11 from processing position F to processing position G. Simultaneously, the machine tool's tool K is raised horizontally. Tool K also follows the workpiece 11 to processing position G using a five-axis simultaneous motion path, where it performs cutting at this elevated position. If the center of rotation of the machine tool's first rotational axis (C-axis) has an offset error, tool K will cut a platform structure of depth G1 (corresponding to the dotted circle at processing position G) into the workpiece 11.

[0035] In the same operating mode, the machine tool's stage P rotates 90 degrees (counterclockwise), rotating the workpiece 11 from processing position G to processing position H. Simultaneously, the machine tool's tool K is raised horizontally. Tool K also follows the workpiece 11 to processing position H using a five-axis simultaneous motion path, where it performs cutting at this elevated position. If the center of rotation of the machine tool's first rotational axis (C-axis) has an offset error, tool K will cut a structure on the workpiece 11 to a depth of H1 (corresponding to the dotted circle at processing position H).

[0036] In the same operating mode, the machine tool's platform P rotates 90 degrees (counterclockwise), driving the workpiece 11 from processing position H to processing position I. Simultaneously, the horizontal position of the machine tool's tool K is raised, and tool K also follows the workpiece 11 to processing position I using a five-axis synchronous motion path, performing cutting at this raised horizontal position. If the center of rotation of the machine tool's first rotation axis (C-axis) has an offset error, but the offset is not greater than the offsets of the previous processing positions G and H, then after the first processing mode is applied, no deep platform structure will be visible on the workpiece 11 at processing position I (although the actual position corresponds to the dotted circle at processing position I). In short, the dotted circle represents the dynamic offset error, which results in step / dimensional errors after actual cutting. If there is no dynamic deviation, the four cut holes will be located at the same processing position F, and there will be no step / dimensional errors in the finished product.

[0037] Finally, the machine tool carrier P rotates 90 degrees (counterclockwise), driving the workpiece 11 to rotate from the processing position I back to the initial processing position F, thus completing the first processing mode. In short, the first processing mode is: the machine tool tool K cuts the workpiece 11. Every time the machine tool carrier P rotates (counterclockwise) the workpiece 11 by an angle (90 degrees), the horizontal position of the tool K is raised and the tool K follows the workpiece 11 in a five-axis synchronous path and cuts at the raised horizontal position. It should be noted that Figure 3 The X'-Y', X'-Z', and Y'-Z' coordinates are the workpiece coordinates of the workpiece 11. The X'-Y' workpiece coordinates rotate in response to the rotation of the workpiece so as to correspond to the mechanical coordinates of the platform P of the machine tool after completing the first processing mode, thereby facilitating subsequent linear axial measurement and calculation.

[0038] Next, in step S130, the first dimension error of the workpiece 11 is measured along the first linear axis (X axis) and the second linear axis (Y axis) of the machine tool. The first dimension error includes a first step difference D M1 and the second segment difference D M2 The first linear axis (X axis) and the second linear axis (Y axis) of the machine tool are perpendicular to the first rotary axis (C axis) of the machine tool. Figure 4 , Figure 4 FIG. 1 is a schematic diagram illustrating the measurement unit 12 measuring a first dimensional error of the workpiece 11 along the first linear axis (X axis) and the second linear axis (Y axis).

[0039] The measuring unit 12 can be fixed to the spindle end of the machine tool. The measuring unit 12 is, for example, a dial indicator or a micrometer. Figure 4 As shown (upper half of the figure), the measuring unit 12 contacts the workpiece 11 processed in the first processing mode along the direction of the first linear axis (X axis), wherein the workpiece 11 forms a step structure between the surface S1 (the side wall cut by the processing position F) and the surface S2 (the side wall cut by the processing position H) after processing. The measuring unit 12 measures the first step difference D between the surface S1 and the surface S2, which are the farthest apart in this step structure, along the direction of the first linear axis (X axis). M1 Since the measurement unit 12 moves from the surface S1 to the surface S2 for measurement in the positive X direction, the first step difference D M1 Take it as a positive value. Figure 4In the figure, since the surface S1' formed on the workpiece 11 after processing and opposite to the surface S1 is a flat sidewall, there is no step structure on the side of the surface S1'. However, if the surface S1' is not a flat sidewall but has a step structure, the step difference between the surface S1' and the surface farthest from the surface S1' needs to be measured by the measuring unit 12 along the direction of the first linear axis (X axis). In this case, the measuring unit 12 will measure from the surface S1' toward the negative X direction, so the measured step difference needs to be taken as a negative value. In other words, the first step difference D M1 It is the step difference between the original processing position F and the processing positions G, H, and I in the direction of the first linear axis (X axis). The actual means is to measure the maximum offset of a single side wall in the X axis direction.

[0040] Measure the first step difference D along the direction of the first linear axis (X axis) M1 After that, the measuring unit 12 is used to contact the workpiece 11 processed by the first processing mode along the direction of the second linear axis (Y axis). Figure 4 As shown in the lower half of the figure, after machining, the workpiece 11 forms a step structure between surface S3 (the side wall cut at machining position F) and surface S4 (the side wall cut at machining position H). The second step difference D between surface S3 and surface S4, which are the farthest apart in this step structure, is measured by the measuring unit 12 along the second linear axis (Y axis). M2 Since the measurement unit 12 moves from the surface S3 to the surface S4 for measurement in the negative Y direction, the second step difference D M2 Takes a negative value. Figure 4 In the figure, since the surface S3' formed on the workpiece 11 after processing and opposite to the surface S3 is a flat sidewall, no step structure is formed on the side of the surface S3'. However, if the surface S3' is not a flat sidewall but has a step structure, the step difference between the surface S3' and the surface farthest from the surface S3' needs to be measured by the measuring unit 12 along the second linear axis (Y axis). In this case, the measuring unit 12 will measure from the surface S3' toward the positive Y direction, so the measured step difference needs to be taken as a positive value. Therefore, at least the first step difference D can be obtained. M1 and the second segment difference D M2 In other words, the second step difference D M2 It is the step difference between the original processing position F and the processing positions G, H, and I in the direction of the second linear axis (Y axis). The actual means is to measure the maximum offset of a single side wall in the Y axis direction.

[0041] In step S140, the position error of the first rotation axis (C axis) is calculated based on the first external dimension error of the workpiece 11 to calibrate the rotation center of the machine tool. M1 and the second segment difference D M2, calculate the position error of the first rotation axis (C axis). Specifically, the first step difference D M1 and the second segment difference D M2 Substitute the following algebraic expressions to obtain the position error XOC and position error YOC of the first rotation axis (C axis), such as: XOC = -(dx max +dx min ) / 2; YOC=-(dy max +dy min ) / 2, the algebraic expression means taking the step difference caused by the offset of the two side walls of the workpiece in a single axis direction (X-axis or Y-axis) as the average, and then multiplying it by a negative sign (because the position error XOC and the position error YOC are in the opposite direction of the measurement). The step difference caused by the offset of the two side walls of the workpiece in the X-axis direction includes at least the first step difference D M1 The step difference caused by the offset of the other two side walls of the workpiece formed by machining in the Y-axis direction includes at least the second step difference D M2 Among them, dx max Substitute the first positive value of the maximum X-axis difference D M1 , dx min Since the surface S1' is flat and has no step structure, it is zero; max Since the surface S3' is flat and has no step structure, it is zero. min Substitute the second segment difference D with the minimum segment difference in the Y direction and a negative value M2 The resulting position errors XOC and YOC represent the linear offsets in the X and Y directions between the actual installation center of the machine tool's C-axis and its ideal position. The processing control unit then inversely compensates for these offsets. For example, by adding or subtracting the origin of the first rotational axis (C-axis) from the position errors XOC and YOC, the rotational center of the machine tool's first rotational axis (C-axis) is corrected to its ideal position. This can then be followed by calibration of the machine tool's second, different rotational axis (A-axis).

[0042] Next, the second rotation axis (A axis in this example) perpendicular to the main axis direction of the machine tool is measured. In step S150, the workpiece 11 is rotated about the second rotation axis (A axis) of the machine tool and the workpiece 11 is processed in a second processing mode, wherein the second processing mode is obviously different from the processing method of the first processing mode, as described below. Figure 5 , Figure 5 A schematic diagram of the so-called second processing mode is shown, wherein Figure 5 The left half shows a front view of the workpiece 11 after the second processing mode, that is, a viewing angle along the Y direction; Figure 5 The right half shows a side view of the workpiece 11 in the second processing mode, that is, a viewing angle along the X direction.

[0043] like Figure 5 As shown, the coordinates of the machine tool tool K are first fixed. The workpiece 11 is then rotated about its second rotational axis (A-axis). The machine tool tool K, while stationary, mills the workpiece 11 to form a first machined curved surface E1. Specifically, the machine tool's platform P rotates about its second rotational axis (A-axis), causing the workpiece 11 to swing in a cradle-like motion relative to the fixed tool K, thereby milling the recessed first machined curved surface E1 into the workpiece 11.

[0044] After milling a concave first machined surface E1 on a workpiece 11, a displacement O is generated between the machine tool tool K and the workpiece 11 along the second rotational axis (A-axis). The machine tool tool K then mills the surface of the workpiece 11 in a circular motion. The milling depth M2 during circular milling is set to be greater than the milling depth M1 during stationary milling. Thus, by dynamically rotating the machine tool tool K about its virtual rotational center V, a concave second machined surface E2 is milled on the stationary workpiece 11. The second machined surface E2 is misaligned with the first machined surface E1 due to the displacement O. If the center of rotation of the machine tool tool K's second rotational axis (A-axis) has an offset error, the virtual rotational center V and the actual rotational center W will not be concentric, and the second machined surface E2 will not be parallel to the second machined surface E1. Therefore, the offset of the center of rotation of the second rotational axis (A-axis) must be measured for correction. In short, the second processing mode is: rotating the workpiece 11 along the second rotation axis (A-axis), and making the tool K of the machine tool mill the workpiece 11 in a fixed state to form a first processing surface E1; and after generating a displacement O between the tool K and the workpiece 11 along the direction of the second rotation axis (A-axis), making the tool K mill the workpiece 11 in a circular manner to form a second processing surface E2, wherein the milling depth M2 when the tool K mills in a circular manner is set to be greater than the milling depth M1 when the tool K mills in a fixed state. Figure 5 It is a side view of the projected and superimposed first machined curved surface E1 and the second machined curved surface E2 for the convenience of explanation.

[0045] In step S160, a second dimension error of the workpiece 11 is measured along the third linear axis (Z axis) of the machine tool, wherein the third linear axis (Z axis) is perpendicular to the second rotation axis (A axis). The second dimension error includes the first depth difference, the second depth difference, and the third depth difference. Figures 6A to 6C , Figures 6A to 6C FIG. 1 is a schematic diagram showing the measurement unit 12 measuring the second dimension error of the workpiece 11 along the direction of the third linear axis (Z axis), wherein Figure 6A FIG. 1 is a schematic diagram showing that the measuring unit 12 measures the first machined curved surface E1 and the first machined curved surface E2 of the workpiece 11 at the first rotation angle θ1 along the direction of the third linear axis (Z axis). Figure 6B Schematic diagram showing the measurement unit 12 measuring the first machined curved surface E1 and the second machined curved surface E2 of the workpiece 11 at the second rotation angle θ2 along the direction of the third linear axis (Z axis). Figure 6C Schematic diagram showing that the measuring unit 12 measures the first machined curved surface E1 and the first machined curved surface E2 of the workpiece 11 at the third rotation angle θ3 along the direction of the third linear axis (Z axis).

[0046] Specifically, the measuring unit 12 can be fixed to the spindle end of the machine tool. Figure 6A As shown, the workpiece is rotated by the second rotation axis (A axis) by the first rotation angle θ1, wherein the so-called rotation angle is the angle of the carrier P rotated along the second rotation axis (A axis) relative to the horizontal line L. Figure 6A For example, the first rotation angle θ1 is, but not limited to, 0 degrees. Figure 6A As shown in the upper half, the measuring unit 12 contacts the workpiece 11 at the first rotation angle θ1 along the direction of the third linear axis (Z axis) and measures the depth reading of the first machined curved surface E1, and then Figure 6A As shown in the lower half, the measuring unit 12 contacts the workpiece 11 at the first rotation angle θ1 along the direction of the third linear axis (Z axis) and measures the depth reading of the second machined curved surface E2. Figure 6B As shown, the workpiece is rotated by the second rotation axis (A axis) by a second rotation angle θ2. In this example, the second rotation angle θ2 is an acute angle relative to the horizontal line L when the carrier P rotates counterclockwise along the second rotation axis (A axis). Figure 6B As shown in the upper half, the measuring unit 12 contacts the workpiece 11 at the second rotation angle θ2 along the direction of the third linear axis (Z axis) and measures the depth reading of the first machined curved surface E1, and then Figure 6B As shown in the lower half, the measuring unit 12 contacts the workpiece 11 at the second rotation angle θ2 along the direction of the third linear axis (Z axis) and measures the depth reading of the second machined curved surface E2. Figure 6C As shown, the workpiece is rotated by the second rotation axis (A axis) by a third rotation angle θ3. In this example, the third rotation angle θ3 is an acute angle relative to the horizontal line L when the carrier P rotates clockwise along the second rotation axis (A axis). Figure 6C As shown in the upper half, the measuring unit 12 contacts the workpiece 11 at the third rotation angle θ3 along the direction of the third linear axis (Z axis) and measures the depth reading of the first machined curved surface E1, and then Figure 6C As shown in the lower half, the measuring unit 12 contacts the workpiece 11 at the second rotation angle θ2 along the direction of the third linear axis (Z axis) and measures the depth reading of the second machined curved surface E2.

[0047] Thus, recording these readings can be used to calculate the difference in depth readings between the two curved surfaces (i.e., the first machined curved surface E1 and the second machined curved surface E2) formed after milling the workpiece 11 at the same rotation angle. Specifically, the processing control unit can calculate a first depth difference between the depths of the first machined curved surface E1 and the second machined curved surface E2 at a first rotation angle θ1; a second depth difference between the depths of the first machined curved surface E1 and the second machined curved surface E2 at a second rotation angle θ2; and a third depth difference between the depths of the first machined curved surface E1 and the second machined curved surface E2 at a third rotation angle θ3. Thus, a second external dimension error can be obtained, comprising at least the first depth difference, the second depth difference, and the third depth difference.

[0048] In step S170, the position error of the second rotation axis (A axis) is calculated based on the second dimensional error to correct the rotation center of the machine tool. Specifically, the coordinates of the first contact point, the second contact point and the third contact point between the measuring unit 12 and the first machining surface E1 of the workpiece 11 at the first rotation angle θ1, the second rotation angle θ2 and the third rotation angle θ3 are first obtained. The coordinates of the first, second and third contact points of the first machining surface E1 and the measuring unit 12 at the three rotation angles obtained by the first milling can be directly known by the processing control unit of the machine tool. Then, the processing control unit calculates the coordinates of the center of the circle corresponding to the first machining surface E1 based on the coordinates of the first contact point, the second contact point and the third contact point. This can be achieved by substituting the coordinates of the three first, second and third contact points into the general formula of the circle: y 2 +z 2 +a1y+b1z+c1=0 Solve and we can get the constants a1, b1, c1, which gives us the general formula for a circle, and then convert it to (y-d1). 2 +(z-e1) 2 =r1 2 Obtain the ZY coordinates (d1, e1) of the center of the circle corresponding to the first processed surface E1. Next, based on the coordinates of the first contact point and the first depth difference, calculate the coordinates of the fourth contact point between the measuring unit 12 and the second processed surface E2 of the workpiece at the first rotation angle θ1; based on the coordinates of the second contact point and the second depth difference, calculate the coordinates of the fifth contact point between the measuring unit 12 and the second processed surface E2 of the workpiece 11 at the second rotation angle θ2; and based on the coordinates of the third contact point and the third depth difference, calculate the coordinates of the sixth contact point between the measuring unit 12 and the second processed surface E2 of the workpiece 11 at the third rotation angle θ3. The coordinates of the fourth, fifth, and sixth contact points can be obtained based on the first, second, and third contact points plus the first, second, and third depth differences with the trigonometric functions (sine, cosine, cosine) of the first rotation angle θ1, the second rotation angle θ2, and the third rotation angle θ3, respectively. Figures 6A to 6C The Z'-Y' coordinate system shown is converted to Figures 6A to 6C Then, the coordinates of the third, fifth, and sixth contact points can be substituted into the circle general formula: 2 +z 2 +a2y+b2z+c2=0 Solve and we can get the constants a2, b2, c2, which gives us the general formula for a circle, and then convert it to (y-d2) 2 +(z-e2) 2 =r2 2 The ZY coordinates (d2, e2) of the center of the circle corresponding to the second machined surface E2 are obtained. Then, by comparing the ZY coordinates of the center of the circle corresponding to the first machined surface E1 (e.g., (d1, e1)) with the ZY coordinates of the center of the circle corresponding to the second machined surface E2 (e.g., (d2, e2)), the Z-axis difference d2-d1 and the Y-axis difference e2-e1 are calculated. These Z-axis difference and Y-axis difference correspond to the position error YOA and position error ZOA of the second rotational axis (A-axis). The resulting position error YOA and position error ZOA represent the linear offsets in the Y and Z directions between the actual installation center of the machine tool's A-axis and its ideal position. The processing control unit then reversely compensates for these offsets in position error YOA and position error ZOA, for example by adding / subtracting the origin of the second rotational axis (A-axis), such as the virtual rotation center V or the actual rotation center W, from the position error YOA and position error ZOA. This calibrates the rotation center of the machine tool's second rotational axis (A-axis) to its ideal position.

[0049] As described above, the present invention provides a calibration method and system for a machine tool. In the process of measuring the rotation center error, there is no need to use expensive instruments or special fixtures. Only the simplest dial indicator or micrometer is used to measure the workpiece. Then, the rotation center error can be obtained through simple mathematical calculations by a processing control unit, thereby performing correction.

[0050] In summary, while the present invention has been disclosed in conjunction with the above embodiments, they are not intended to limit the present invention. Persons skilled in the art may make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A calibration method for a machine tool, comprising: Provide workpieces to machine tools; Rotating the workpiece about a first rotation axis of the machine tool and machining the workpiece in a first machining mode, wherein the first rotation axis is parallel to a main axis of the machine tool; measuring a first dimensional error of the workpiece along a first linear axis and a second linear axis of the machine tool, wherein the first linear axis and the second linear axis are perpendicular to the first rotation axis; Calculating a position error of the first rotation axis according to a first dimensional error of the workpiece to correct a rotation center of the machine tool; Rotating the workpiece about a second rotation axis of the machine tool and machining the workpiece in a second machining mode different from the first machining mode, wherein the second rotation axis is perpendicular to a main axis of the machine tool; measuring a second dimensional error of the workpiece along a third linear axis of the machine tool, wherein the third linear axis is perpendicular to the second rotation axis; as well as The position error of the second rotation axis is calculated according to the second external dimension error of the workpiece to correct the rotation center of the machine tool.

2. The calibration method for a machine tool according to claim 1, wherein the first machining mode is: The workpiece is cut with the tool of the machine tool. Whenever the platform of the machine tool rotates the workpiece angle, the horizontal position of the tool is increased and the tool is made to follow the workpiece in a five-axis synchronous path and cut at the increased horizontal position. 3 . The machine tool calibration method according to claim 2 , wherein the angle is approximately 90 degrees.

4. The machine tool calibration method according to claim 2, further comprising: contacting the workpiece processed by the first processing mode with a measuring unit along the direction of the first linear axis; Measuring a first step difference between two surfaces of the workpiece that are farthest apart after being processed along the direction of the first linear axis; contacting the workpiece processed by the first processing mode with the measuring unit along the direction of the second linear axis; as well as A second step difference between two other surfaces of the workpiece that are formed after processing and are farthest apart from each other is measured along the direction of the second linear axis.

5. The machine tool calibration method according to claim 4, further comprising: Calculating a position error of the first rotation axis according to the first step difference and the second step difference includes: taking the step difference caused by the deviation of two side walls formed after the workpiece is processed in the direction of the first linear axis as an average value, wherein the step difference caused by the deviation of the two side walls formed after the workpiece is processed includes at least the first step difference; taking the step differences caused by the offset of the other two side walls formed after the workpiece is processed in the direction of the second linear axis as an average value, wherein the step differences caused by the offset of the other two side walls formed after the workpiece is processed at least include the second step difference; as well as The position error of the first rotation axis is obtained by multiplying the average value obtained in the direction of the first linear axis by a negative sign and the average value obtained in the direction of the second linear axis by a negative sign.

6. The calibration method for a machine tool as claimed in claim 1, wherein the second machining mode is: Rotating the workpiece about the second rotation axis and causing the tool of the machine tool to mill the workpiece in a fixed state to form a first machined curved surface; and After causing displacement between the tool and the workpiece along the direction of the second rotation axis, the tool is caused to mill the workpiece in a circular manner to form a second machined surface, wherein the milling depth of the tool when milling in a circular manner is set to be greater than the milling depth of the tool when milling in a fixed state.

7. The machine tool calibration method according to claim 6, further comprising: Rotate the workpiece by a first rotation angle along the second rotation axis; contacting the workpiece at the first rotation angle with a measuring unit along the direction of the third linear axis and measuring the depth of the first machined curved surface and the depth of the second machined curved surface; Calculating a first depth difference between a depth of the first processed curved surface and a depth of the second processed curved surface at the first rotation angle; Rotating the workpiece about the second rotation axis by a second rotation angle; contacting the workpiece at the second rotation angle with the measuring unit along the direction of the third linear axis and measuring the depth of the first machined curved surface and the depth of the second machined curved surface; Calculating a second depth difference between the depth of the first machined curved surface and the depth of the second machined curved surface at the second rotation angle; Rotating the workpiece about the second rotation axis by a third rotation angle; contacting the workpiece at the third rotation angle with the measuring unit along the direction of the third linear axis and measuring the depth of the first machined curved surface and the depth of the second machined curved surface; and A third depth difference between the depth of the first machined curved surface and the depth of the second machined curved surface at the third rotation angle is calculated.

8. The machine tool calibration method according to claim 7, further comprising: Obtaining coordinates of a first contact point, a second contact point, and a third contact point between the measuring unit and the first machined curved surface of the workpiece at the first rotation angle, the second rotation angle, and the third rotation angle; Calculating the coordinates of the center of the circle corresponding to the first machined curved surface according to the coordinates of the first contact point, the second contact point, and the third contact point; Calculating the coordinates of a fourth contact point between the measuring unit and the second machined curved surface of the workpiece at the first rotation angle according to the coordinates of the first contact point and the first depth difference; Calculating the coordinates of a fifth contact point between the measuring unit and the second machined curved surface of the workpiece at the second rotation angle according to the coordinates of the second contact point and the second depth difference; Calculating the coordinates of a sixth contact point between the measuring unit and the second machined curved surface of the workpiece at the third rotation angle according to the coordinates of the third contact point and the third depth difference; Calculating the coordinates of the center of the circle corresponding to the second machined curved surface according to the coordinates of the fourth contact point, the fifth contact point, and the sixth contact point; and Calculating the position error of the second rotation axis according to the center coordinates corresponding to the first processed curved surface and the center coordinates corresponding to the second processed curved surface includes: The center coordinates corresponding to the first processed surface and the center coordinates corresponding to the second processed surface are compared to calculate the difference along the third linear axis and the difference along the second linear axis. The difference along the third linear axis and the difference along the second linear axis correspond to the position error of the second rotation axis.

9. A calibration system for calibrating a machine tool, comprising: A workpiece is provided to the machine tool; a measuring unit configured to measure a first dimensional error of the workpiece along a first linear axis and a second linear axis of the machine tool when the workpiece is rotated about a first rotational axis of the machine tool and machined in a first machining mode, wherein the first rotational axis is parallel to a main axis of the machine tool and the first and second linear axes are perpendicular to the first rotational axis; and to measure a second dimensional error of the workpiece along a second linear axis and a third linear axis of the machine tool when the workpiece is rotated about a second rotational axis of the machine tool and machined in a second machining mode different from the first machining mode, wherein the second rotational axis is perpendicular to the main axis of the machine tool and the second and third linear axes are perpendicular to the second rotational axis; as well as A processing control unit is used to calculate the position error of the first rotation axis based on the first external dimension error of the workpiece to correct the rotation center of the machine tool, and to calculate the position error of the second rotation axis based on the second external dimension error of the workpiece to correct the rotation center of the machine tool.

10. The calibration system as claimed in claim 9, wherein the first processing mode is: The workpiece is cut by a tool of the machine tool, and the horizontal position of the tool is raised every time the platform of the machine tool rotates the workpiece by an angle. The calibration system of claim 10 , wherein the angle is approximately 90 degrees.

12. The calibration system of claim 10, wherein the measuring unit is further configured to: contacting the workpiece processed by the first processing mode along the direction of the first linear axis; Measuring a first step difference between two surfaces of the workpiece formed after machining that are the farthest apart along the direction of the first linear axis; contacting the workpiece processed by the first processing mode along the direction of the second linear axis; as well as A second step difference between two other surfaces that are farthest apart from each other and formed after the workpiece is cut is measured along the direction of the second linear axis.

13. The calibration system of claim 12, wherein the processing control unit is further configured to: Calculating a position error of the first rotation axis according to the first step difference and the second step difference includes: taking the step difference caused by the deviation of two side walls formed after the workpiece is processed in the direction of the first linear axis as an average value, wherein the step difference caused by the deviation of the two side walls formed after the workpiece is processed includes at least the first step difference; taking the step differences caused by the offset of the other two side walls formed after the workpiece is processed in the direction of the second linear axis as an average value, wherein the step differences caused by the offset of the other two side walls formed after the workpiece is processed include at least the second step difference; and The position error of the first rotation axis is obtained by multiplying the average value obtained in the direction of the first linear axis by a negative sign and the average value obtained in the direction of the second linear axis by a negative sign.

14. The calibration system as claimed in claim 9, wherein the second processing mode is: The workpiece is rotated about the second rotation axis, and the tool of the machine tool mills the workpiece in a fixed state to form a first machined curved surface; and After causing displacement between the tool and the workpiece along the direction of the second rotation axis, the tool is caused to mill the workpiece in a circular manner to form a second machined surface, wherein the milling depth of the tool when milling in a circular manner is set to be greater than the milling depth of the tool when milling in a fixed state.

15. The calibration system of claim 14, wherein the measuring unit is further configured to: Rotate the workpiece by a first rotation angle along the second rotation axis; contacting the workpiece at the first rotation angle along the direction of the third linear axis and measuring the depth of the first machined curved surface and the depth of the second machined curved surface; Rotating the workpiece about the second rotation axis by a second rotation angle; contacting the workpiece at the second rotation angle along the direction of the third linear axis and measuring the depth of the first machined curved surface and the depth of the second machined curved surface; Rotating the workpiece about the second rotation axis by a third rotation angle; as well as The workpiece at the third rotation angle is contacted along the direction of the third linear axis and the depth of the first machined curved surface and the depth of the second machined curved surface are measured.

16. The calibration system of claim 15, wherein the processing control unit is further configured to: Calculating a first depth difference between a depth of the first processed curved surface and a depth of the second processed curved surface at the first rotation angle; calculating a second depth difference between the depth of the first machined curved surface and the depth of the second machined curved surface at the second rotation angle; and A third depth difference between the depth of the first machined curved surface and the depth of the second machined curved surface at the third rotation angle is calculated.

17. The calibration system of claim 16, wherein the processing control unit is further configured to: Obtaining coordinates of a first contact point, a second contact point, and a third contact point between the measuring unit and the first machined curved surface of the workpiece at the first rotation angle, the second rotation angle, and the third rotation angle; Calculating the coordinates of the center of the circle corresponding to the first machined curved surface according to the coordinates of the first contact point, the second contact point, and the third contact point; Calculating the coordinates of a fourth contact point between the measuring unit and the second machined curved surface of the workpiece at the first rotation angle according to the coordinates of the first contact point and the first depth difference; Calculating the coordinates of a fifth contact point between the measuring unit and the second machined curved surface of the workpiece at the second rotation angle according to the coordinates of the second contact point and the second depth difference; Calculating the coordinates of a sixth contact point between the measuring unit and the second machined curved surface of the workpiece at the third rotation angle according to the coordinates of the third contact point and the third depth difference; Calculating the coordinates of the center of the circle corresponding to the second machined curved surface according to the coordinates of the fourth contact point, the fifth contact point, and the sixth contact point; and Calculating the position error of the second rotation axis according to the center coordinates corresponding to the first processed curved surface and the center coordinates corresponding to the second processed curved surface includes: The center coordinates corresponding to the first processed surface and the center coordinates corresponding to the second processed surface are compared to calculate the difference along the third linear axis and the difference along the second linear axis. The difference along the third linear axis and the difference along the second linear axis correspond to the position error of the second rotation axis.

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