Method and system for processing workpiece

Abstract

A method for machining a workpiece (5) that is carried out by a machining system (1) has: a first step for finding a first error, which is a contour error of a tool found from an outer shape of a tool (3) as measured by a tool-shaped measurement device (31); a second step for finding a second error, where a machining error found from the shape of a machining surface of the workpiece (5) as measured by three-dimensional workpiece measurement devices (32, 51) has been converted into the contour error of the tool; and a third step where a movement means moves the tool (3) with the respect to the workpiece on the basis of a prescribed NC program. In the third step, the NC program corrects the position of the tool (3) on the basis of a combined error in which the second error has been added to the first error.

Description

[Technical field]

[0001] The present invention relates to a method and system for machining a workpiece, and more particularly to a method and system for machining a workpiece by correcting the contour of a tool. [Background technology]

[0002] Conventionally, there has been known a workpiece machining system (NC machining system) having a machining machine (NC machine tool) that processes a workpiece by moving a tool relative to the workpiece according to an NC program.

[0003] In a conventional NC machining system, for example, a tool such as an end mill is rotated while the tool is relatively moved according to specific numbers (numeric values ​​such as decimals) included in an NC program to machine a workpiece. Here, Patent Document 1 is cited as a document showing the conventional technology.

[0004] The applicant has also proposed a technique for correcting the position of a held tool by incorporating an arithmetic expression for calculating the position of the held tool into an NC program (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 63-233403 [Patent Document 2] Patent No. 6574915 Summary of the Invention [Problem to be solved by the invention]

[0006] Meanwhile, tools have contour errors (differences between the ideal contour shape of a tool and the actual contour shape of the tool). In machine tools that perform ultra-precision machining, contour errors of tools such as end mills account for a large proportion of the causes of shape errors in workpieces.

[0007] According to a technique proposed by the present applicant for correcting the position of a held tool by incorporating an arithmetic expression for calculating the position of the held tool into an NC program (Patent Document 2), errors caused by the tool can be completely eliminated.

[0008] However, it is not possible to correct machining errors caused by factors other than the tool.

[0009] Normally, when correcting machining errors caused by factors other than tools, the only way to make corrections was to measure the machining shape of the machined workpiece on or off the NC machine tool, modify the 3D model in CAD based on the measurement results, and then modify the NC program in CAM based on the modified 3D model.

[0010] However, modifying the 3D model requires a lot of work and time.

[0011] The present invention has been made in consideration of the above problems, and has an object to provide a method and system for machining a workpiece that can correct machining errors without recreating an NC program and accurately machine the workpiece. [Means for solving the problem]

[0012] One aspect of the present invention is a method for machining a workpiece, performed by a machining system having workpiece holding means for holding a workpiece, tool holding means for holding a tool for machining the workpiece held by the workpiece holding means, and moving means for moving the tool relative to the workpiece in order to machine the workpiece with the tool held by the tool holding means, the method comprising: a first step of determining a first error, which is a contour error of the tool, from an outer shape of the tool measured by a first measuring device; a second step of determining a second error by converting a machining error, which is determined from a shape of the machining surface of the workpiece measured by a second measuring device, into a contour error of the tool; and a third step of the moving means moving the tool relative to the workpiece based on a predetermined NC program, wherein in the third step, the NC program corrects the position of the tool based on a composite error obtained by adding the second error to the first error.

[0013] Another aspect of the present invention is a workpiece processing system for carrying out the above-mentioned workpiece processing method. Effect of the Invention

[0014] According to the present invention, it is possible to correct machining errors without recreating an NC program, and it is possible to machine a workpiece with high precision. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic configuration diagram of a processing system that performs a method for processing a workpiece according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing a workpiece and a tool in a machine for processing a workpiece according to an embodiment of the present invention; [Diagram 3] 3 is a diagram for explaining a contour error (first error) of a tool in a machine tool for processing a workpiece according to an embodiment of the present invention. FIG. [Figure 4] 3 is a diagram for explaining a contour error (first error) of a tool in a machine tool for processing a workpiece according to an embodiment of the present invention. FIG. [Diagram 5]FIG. 1 is a schematic diagram of a workpiece 3D measuring device configured with a touch sensor mounted on an NC machine tool. [Figure 6] 1 is a schematic diagram of a workpiece three-dimensional measuring device that measures the machined shape of a workpiece 5 outside an NC machine tool. [Figure 7] 2 is a flowchart showing a processing procedure of a processing machine for a workpiece in the processing system shown in FIG. 1. [Figure 8] FIG. 4 is an explanatory diagram showing a first tool error shape due to a contour error of a tool. [Figure 9] 1 is an explanatory diagram showing a machining range of a workpiece that changes depending on the arc radius of a tool and the arc radius of a machined surface of the workpiece; FIG. [Figure 10] 6 is a schematic diagram showing how the shape of the machined surface of a workpiece is measured by a workpiece three-dimensional measuring device configured with the touch sensor shown in FIG. 5. [Figure 11] FIG. 11 is an explanatory diagram showing a second tool error shape as a tool contour shape including a compensation value of the tool 3 when there is a 2 μm uncut portion on a 45° surface of the machined surface of the workpiece as the machining error exemplified in FIG. 10 . [Figure 12] FIG. 4 is an explanatory diagram showing a composite tool shape obtained by superimposing a first tool error shape and a second tool error shape. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A processing system 1 for performing a method for processing a workpiece according to an embodiment of the present invention will be described.

[0017] FIG. 1 is a schematic configuration diagram of a processing system 1 that performs a method for processing a workpiece according to an embodiment of the present invention.

[0018] As shown in FIG. 1, the processing system 1 has an NC machine tool 2 such as a machining center as a processing machine, and this NC machine tool 2 uses a tool 3 (machining tool: for example, a ball end mill) to machine a workpiece (work) 5.

[0019] This NC machine tool 2 includes a workpiece holding section 7 and a tool holding section 9, and the tool holding section 9 is adapted to be moved in a predetermined direction by a moving section (moving means) 11.

[0020] A control unit 13 (control device) is connected to the NC machine tool 2, and the control unit 13 is equipped with a PC 33a or PC 33 and a CAM 39 which create the NC programs used by the control unit 13, and the operation of the NC machine tool 2 is controlled by the control unit 13 based on the NC programs created by the PC 33a or PC 33 and CAM 39.

[0021] The NC machine tool 2 further includes a tool shape measuring device 31 and a workpiece three-dimensional measuring device 32. The tool shape measuring device 31 and the workpiece three-dimensional measuring device 32 will be described in detail later.

[0022] Further, the workpiece three-dimensional measuring device 32 will be described in an embodiment in which measurements are performed on the NC machine tool 2, but it may also be configured to perform measurements outside the NC machine tool 2 as described later.

[0023] The gist of the present invention is to machine a workpiece by correcting errors caused by the tool (contour error of the tool itself) and errors caused by factors other than the tool through a technology that incorporates an equation for calculating the position of the tool (held tool) into an NC program and corrects the position of the tool.

[0024] Examples of errors caused by factors other than the tool include errors caused by the shape of the workpiece and errors caused by individual differences in processing machines.

[0025] Errors caused by the shape of the workpiece refer to errors that occur when the cutting resistance changes depending on the shape of the workpiece and the machining allowance of the tool differs. For example, when machining a square pocket, the cutting resistance is small on straight sections because the tool contacts at one point. On the other hand, the cutting resistance increases at corner sections because the number of contact points of the tool increases. In this case, the cutting resistance changes between straight sections and corner sections, and the amount of tool clearance changes at corner sections, resulting in uncut portions.

[0026] Errors caused by individual differences in processing machines refer to errors that occur when the tool movement trajectory differs due to the unique characteristics of the processing machine. Differences in processing machine movement appear due to parameters such as servo motor gain. In particular, processing machines may correct the tool movement trajectory so that it moves smoothly, rather than moving precisely along the specified points in the code specified in the NC program. In this case, differences in the processing machine movement cause differences in the tool movement trajectory. In addition, the tool position may be offset from its original position due to mechanical bending caused by the surrounding environment (such as a high-temperature environment) or the effects of the processing machine itself (such as heat generation). In such cases, differences in the tool movement trajectory also occur.

[0027] Errors caused by factors other than the tool include errors that occur accidentally, such as due to disturbances, but in this specification, we consider reproducible errors, such as machining errors caused by the shape of the workpiece and machining errors caused by individual differences in the machining machine.

[0028] That is, in the NC machine tool 2 of the embodiment, a first tool error shape including errors caused by the tool 3 measured by the tool shape measuring device 31 is obtained, a second tool error shape measured by the workpiece 3D measuring device 32 is obtained so as to cancel out errors caused by elements other than the tool 3, the first tool error shape and the second tool error shape are synthesized, and based on the synthesized tool error shape, the shape of the tool 3 is corrected so as to remove the errors caused by the tool 3 and the errors caused by elements other than the tool 3, and the workpiece is machined.

[0029] The shape correction of the tool 3 is performed by a technique for correcting the position of the tool 3 by incorporating an arithmetic expression for calculating the position of the tool 3 into an NC program.

[0030] In Fig. 1, the workpiece holder 7 is configured to hold a workpiece 5. The tool holder 9 is configured to hold a tool 3. The workpiece 5 held by the workpiece holder 7 is machined by the tool 3 held by the tool holder 9. One example of the machining is cutting.

[0031] 2 is a diagram showing a workpiece 5 and a tool 3 in an NC machine tool 2 according to an embodiment of the present invention. In the following description, a ball end mill is exemplified as the tool 3. A cutting edge is provided on the outer periphery of the tool 3.

[0032] Here, one specific direction in space is defined as the X direction (X-axis direction; horizontal direction), and another specific direction in space that is perpendicular to the X direction is defined as the Y direction (Y-axis direction; front-back direction). The direction perpendicular to the X and Y directions is defined as the Z direction (Z-axis direction; up-down direction). In this definition, the X and Y directions are horizontal directions and the Z direction is the up-down direction, but this is not limited to this. The X or Y direction may be the up-down direction, or the X, Y, and Z directions may be oblique to the horizontal or up-down direction.

[0033] 2, the tool 3 is configured to include a cylindrical base end 15 and a hemispherical tip end 17. The outer diameter of the base end 15 and the diameter of the tip end 17 are the same, and the tip end 17 is attached to one end of the base end 15 in the extension direction of the central axis C1. The central axis of the tip end 17 and the central axis C1 of the base end 15 are the same.

[0034] In this embodiment, a ball end mill is described as the tool 3, but this is not limited to this, and other tools such as a radius end mill (an end mill with a flat bottom and rounded corners) may also be used.

[0035] Here, the center of the circular end face of the tip portion 17 (the end face attached to the circular end face of the base end portion 15) is defined as the center C2 of the tip portion 17. This center C2 exists on the central axis C1 of the tool 3.

[0036] The cutting edge of the tool 3 is formed on the outer periphery of the tip portion 17 and on an end portion (the end portion on the tip portion 17 side) of the base portion 15. The other end portion of the base portion 15 of the tool 3 engages with the tool holder 9 and is held by the tool holder.

[0037] The tool 3 held by the tool holder 9 is rotated (rotates about its axis C1) to cut the workpiece 5 with its cutting edge.

[0038] The moving unit 11 is configured to move the tool 3 relatively to the workpiece 5 in order to machine the workpiece 5 with the tool 3. In other words, the moving unit 11 may be configured so that the tool 3 moves with respect to the workpiece 5, or the workpiece 5 moves with respect to the tool 3.

[0039] The control unit 13 is configured to control the moving unit 11 based on an NC program and move the tool 3 relative to the workpiece 5.

[0040] More specifically, as shown in FIG. 1, the NC machine tool 2 for the workpiece 5 is configured to include a bed 19, a table 21, a column 23, a spindle support 25, a spindle housing 27, and a spindle 29.

[0041] The table 21 is supported by the bed 19 via a linear guide bearing (not shown), and is adapted to move (be moved and positioned) relative to the bed 19 in the X direction by an actuator such as a linear motor (not shown).

[0042] The column 23 is provided integrally with the bed 19. The spindle support 25 is supported by the column 23 via a linear guide bearing (not shown), and is adapted to be moved relative to the column 23 in the Y direction by an actuator such as a linear motor (not shown).

[0043] The spindle housing 27 is supported by the spindle support 25 via a linear guide bearing (not shown), and is adapted to move relative to the spindle support 25 in the Z direction by an actuator such as a linear motor (not shown).

[0044] The spindle 29 is supported on the spindle housing 27 via bearings, and is freely rotatable relative to the spindle housing 27 around a central axis C1 (a central axis shared with the tool 3 extending in the Z direction) by an actuator such as a motor (not shown).

[0045] A tool holder 9 is provided on the spindle 29, and a workpiece holder 7 is provided on the upper surface of the table 21. This allows the tool 3 to move relatively to the workpiece 5 in the X, Y, and Z directions.

[0046] Next, a first tool error shape for removing the contour error (first error) of the tool 3 measured by the tool shape measuring device 31 will be described.

[0047] As will be described later, the NC program also incorporates an arithmetic expression (for example, a mathematical expression using arithmetic operations) for calculating the position of the tool 3 (coordinates relative to the workpiece 5).

[0048] That is, the present invention is configured to synthesize a first tool error shape described below and a second tool error shape described later, and determine the compensation position coordinates when the tool 3 moves based on the synthesized tool error shape by solving the above equation.

[0049] The position of the tool 3 is corrected using a normal vector V1 with respect to the machining surface at a machining point T1 (details will be described later) of the tool 3 and a contour error with the tool 3. This allows the three-dimensional position of the tool 3 to be corrected in at least one of the X, Y, and Z directions (determined by the form of the normal vector V1).

[0050] More specifically, the contour error of the tool 3 is obtained in advance by a tool shape measuring device 31 shown in FIG.

[0051] The tool shape measuring device 31 is installed at a predetermined position on the NC machine tool 2. The tool 3 is positioned at a position where the shape of the tool 3 can be measured by the tool shape measuring device 31 (laser, camera, etc.) and rotated (around the central axis C1), so that the outer shape of the tool 3 is measured on the machine (on the NC machine tool 2).

[0052] The difference (difference between each part of the tool 3) between this measured outer shape of the tool 3 and the ideal outer shape of the tool 3 (the outer shape of the tool 3 without any shape error) is defined as the contour error (first error) of the tool 3 itself.

[0053] FIG. 3 is a diagram for explaining a contour error (first error) of a tool in a machine tool for processing a workpiece according to an embodiment of the present invention.

[0054] The dashed line in Fig. 3(a) shows the ideal outer shape of the tool 3, and the solid line in Fig. 3(a) shows the actual outer shape of the tool 3 with a shape error. In Fig. 3(a), the tool is not rotated around the central axis C1. Also, the tool 3 shown by the solid line in Fig. 3(a) is positioned slightly offset to the right with respect to the central axis C1.

[0055] The dashed line in Figure 3(b) shows the outer shape of an ideal tool 3, and the solid line in Figure 3(b) shows the outer shape of an actual tool 3 with shape error (tool 3 shown by the solid line in Figure 3(a)) when it is rotated around the central axis C1.

[0056] The outer shape of the tool 3 shown by the solid line in Fig. 3(b) is naturally symmetrical with respect to the central axis C1. If the workpiece 5 is machined by the tip 17 of the tool 3, the contour error of the tool 3 should be found in a 1 / 4 arc of the tip 17 (i.e., a range of an angle of 90°) as shown in Fig. 4.

[0057] FIG. 4 is a diagram for explaining a contour error (first error) of a tool in a machine tool for processing a workpiece according to an embodiment of the present invention.

[0058] As the tool shape measuring device 31, for example, the one disclosed in Japanese Patent Application Laid-Open No. 63-233403 can be mentioned.

[0059] Further, details of the process for removing the contour error of the tool 3 measured by the tool shape measuring device 31 are described in Japanese Patent No. 6,574,915 by the present applicant.

[0060] Next, a second tool error shape based on machining errors such as uncut portions of the workpiece 5 measured by the workpiece three-dimensional measuring device 32 in order to remove errors (machining errors) caused by factors other than the tool 3 will be described.

[0061] First, there will be described a workpiece three-dimensional measuring device 32 that measures the machined shape of a workpiece 5 on an NC machine tool 2. Fig. 5 is a schematic diagram of a workpiece three-dimensional measuring device that is configured with a touch sensor on an NC machine tool.

[0062] As shown in the schematic configuration of FIG. 1 and FIG. 5, the workpiece three-dimensional measuring device 32 is composed of a touch sensor generally called a touch probe.

[0063] This touch sensor 32 is provided on the spindle housing 27 of the spindle support 25 of the NC machine tool 2 separately from the tool 3, and can be replaced with the tool 3. The touch sensor 32 is configured to measure the dimensions of the machined surface of the workpiece 5 machined by the NC machine tool 2.

[0064] Then, data on the shape of the machined surface of the workpiece 5 measured by the touch sensor 32 is sent to the PC 33a and stored therein.

[0065] This workpiece 5 is the same (sample) as the workpiece 5 that will be machined by the main machining. Therefore, the machined surface of the workpiece 5 will be the same as the machined surface that will be machined by the main machining.

[0066] As described below, PC 33a uses specified software based on the dimensional data of the measured machined surface of workpiece 5 to obtain measurement points (design values), shape errors, normal vectors of the measurement points, etc. of the measured machined surface of workpiece 5.

[0067] In the case of a workpiece three-dimensional measuring device 32 configured with an on-machine touch sensor as shown in Figure 5, the machined surface of the workpiece 5 can be measured without moving the machined workpiece 5 from on the NC machine tool 2.

[0068] In this case, however, a mechanism for providing a touch sensor 32 in addition to the tool 3 on the spindle housing 27 of the spindle support 25 of the NC machine tool 2 is required.

[0069] In the above embodiment, a touch sensor that measures the machined shape of the workpiece 5 on the NC machine tool 2 is used as the workpiece 3D measuring device 32. However, in another embodiment, a workpiece 3D measuring device 51 that measures the machined shape of the workpiece 5 outside the NC machine tool 2 can also be used.

[0070] FIG. 6 is a schematic diagram of a workpiece three-dimensional measuring device 51 that measures the machined shape of the workpiece 5 outside the NC machine tool 2.

[0071] As shown in Figure 6, this workpiece 3D measuring device 51 has a table 53 for placing the workpiece 5 machined by the NC machine tool 2 at a predetermined position, and a shape sensor 55 above the workpiece 5 placed on the table 53 for measuring the machined surface of the machined workpiece 5. The shape sensor 55 moves up, down, left and right relative to the fixedly installed workpiece 5 to measure the machined surface of the workpiece 5.

[0072] Here, the workpiece 3D measuring device 51 outside the NC machine tool 2 obtains the measurement points (design values), shape errors, normal vectors of the measurement points, etc. based on the data of the dimensions of the machined surface of the measured workpiece 5, and sends them to the PC 33a.

[0073] In this embodiment, it goes without saying that a workpiece 3D measuring device 51 is required outside the NC machine tool 2 to measure the machined shape of the workpiece 5 and obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc.

[0074] Next, a processing procedure for a workpiece (workpiece) by a processing machine according to the embodiment of the present invention will be described with reference to FIG.

[0075] FIG. 7 is a flowchart of a processing procedure for a workpiece by a processing machine according to an embodiment of the present invention.

[0076] 7, an NC program for machining the workpiece 5, i.e., three-dimensional coordinates of the machining path by the tool 3, is generated based on a commercially available CAM. In this example, a ball end mill is used as the tool 3.

[0077] Next, in step S12, a correction vector (normal vector) is added to the NC program, and in step S13, the control unit 13 of the NC machine tool 2 reads the NC program.

[0078] The processing in steps S11 to S13 is performed by the PC 33a or the PC 33 and the CAM 39 which create the NC program.

[0079] Here, the position of the tool 3 is corrected using a normal vector to the machining surface at the machining point of the tool 3 and a contour error with the tool 3. This allows the three-dimensional position of the tool 3 to be corrected in at least one of the X, Y, and Z directions (determined by the form of the normal vector).

[0080] Next, a process for removing errors caused by the tool 3 and errors caused by factors other than the tool in steps S14 to S16 will be described.

[0081] First, in step S14, the shape of the tool 3 for machining the workpiece 5 is measured by a tool shape measuring device 31 using a laser or the like, a first error which is a contour error of the tool 3 is obtained from the shape of the tool 3, and a first tool error shape is obtained from the first error (first step). The first tool error shape means the contour shape of the tool 3 including the first error.

[0082] That is, as shown in FIG. 1, the tool shape measuring device 31 is installed at a predetermined position on the NC machine tool 2, and the tool 3 is positioned at a position where it can be measured by the tool shape measuring device 31 (laser, camera, etc.), and the tool 3 is rotated (rotated around the central axis C1) to measure the outer shape of the tool 3 on the machine (on the NC machine tool 2).

[0083] The difference (difference for each part of the tool 3) between this measured outer shape of the tool 3 and the ideal outer shape of the tool 3 (the outer shape of the tool 3 without any shape error) is calculated and is regarded as the contour error (first error) of the tool 3. The ideal outer shape of the tool 3 is stored in the control unit 13 as outer shape data and is defined from the shape and dimensions of the tool 3.

[0084] Fig. 8 is an explanatory diagram showing a first tool error shape due to a contour error of the tool. As described above, when the contour error of the tool 3 is measured at intervals of, for example, 0.1° which is a fine angle, a finely wavy contour error CV1 as shown by the curve in Fig. 8(a) is obtained.

[0085] When filtering is performed to remove high frequency components from the curve (contour error CV1) shown in Fig. 8(a), a contour error CV2 with a certain degree of wavy shape is obtained as shown by the curve in Fig. 8(b). As described below, the contour shape of the tool 3 including the contour error CV2 shown by the curve in Fig. 8(b) is used as a first tool error shape for correction (hereinafter referred to as the "first tool error shape CV2").

[0086] 9 is a diagram showing the machining range of a workpiece, which changes depending on the radius of the arc of the tool 3 and the radius of the arc of the machined surface of the workpiece. When the difference between the radius of the arc of the tool 3 and the radius of the machined surface of the workpiece 5 is small, the value of the contact length (contact area) CT3 between the workpiece 5 and the tool 3 becomes large.

[0087] In this way, even if the shape of the tool 3 for machining the workpiece 5 is measured by a tool shape measuring device 31 using a laser or the like, the first error is calculated from the shape of the tool 3, and the first tool error shape is obtained from the first error, tool correction based on this first tool error shape alone may result in errors (machining errors) caused by factors other than the tool 3.

[0088] In order to deal with such processing errors, the present invention performs the processes from step S15 onwards, which will be described below.

[0089] 7, in order to remove machining errors caused by factors other than the tool 3, a second error is obtained by converting the machining error determined from the shape of the machined surface of the machined workpiece 5 measured by the workpiece three-dimensional measuring device 32 into a contour error of the tool 3, and a second tool error shape is obtained from the second error (second step). The second tool error shape means the contour shape of the tool 3 including the second error.

[0090] Below, a detailed description will be given of how to determine the contour error of the tool 3 from the shape of the machined surface of the workpiece 5 measured by the workpiece three-dimensional measuring device 32, and how to determine the second tool error shape including the second error, which is the contour error of the tool 3.

[0091] First, test machining is performed on a test workpiece 5. During the test machining, the moving unit 11 moves the tool 3 to the test workpiece 5 based on the NC program. At this time, the NC program corrects the position of the tool 3 based on the correction amount of the NC program as described later. That is, the NC program corrects the position of the tool 3 based on the first tool error shape CV2 including the first error. As a result, the machining error of the workpiece 5 due to the contour error of the tool 3 is corrected, and the tool 3 is operated to machine the test workpiece 5.

[0092] As shown in FIG. 5, the shape of the machined surface of a test workpiece 5 is measured by a workpiece three-dimensional measuring device 32 configured with a touch sensor mounted on an NC machine tool 2.

[0093] That is, before the actual machining, the tip of the touch sensor 32 is brought into contact with the machined surface of the test workpiece 5 machined by the NC machine tool 2, and the shape of the machined surface of the test workpiece 5 is measured.

[0094] Here, the test workpiece 5 is the same as the workpiece 5 for actual machining (test piece) that will be subjected to the actual machining. Therefore, the machined surface of the test workpiece 5 will be the same as the machined surface of the workpiece 5 for actual machining that will be subjected to the actual machining.

[0095] By bringing the tip of the touch sensor 32 into contact with the machined surface of the test workpiece 5, the touch sensor 32 measures the shape of the machined surface of the test workpiece 5. The measurement data is sent to and stored in the PC 33a which creates the NC program used in the control unit 13.

[0096] In the PC 33a, based on the measured dimensional data of the machined surface of the test workpiece 5, the measurement points (design values), shape errors, normal vectors of the measurement points, etc. are obtained using predetermined software.

[0097] In other words, the PC33a uses measurement software for machine tools developed by, for example, a 3D measuring machine manufacturer such as Hexagon to approach and measure from the CAD along a vector perpendicular to the surface of the measurement point, thereby achieving advanced on-machine measurement and obtaining the measurement point (design value), shape error, normal vector of the measurement point, etc.

[0098] Then, the PC 33a calculates and determines the amount of machining error in which part of the machining surface 5a of the test workpiece 5 is located by comparing the measurement points (design values), shape errors, and normal vectors of the measurement points of the test workpiece 5 obtained using the above-mentioned machine tool measurement software with a CAD model that shows the ideal workpiece shape after machining.

[0099] FIG. 10 is a schematic diagram showing how the shape of the machined surface 5a of the workpiece 5 is measured by the workpiece three-dimensional measuring device 32 configured with the touch sensor shown in FIG.

[0100] FIG. 10 illustrates an example of a machining error in which there is a 2 μm uncut portion on the 45° surface of the machined surface 5 a of the test workpiece 5 .

[0101] In this embodiment, the machining surface 5a of the test workpiece 5 is measured using a workpiece 3D measuring device 32 consisting of a touch sensor on the NC machine tool 2, and based on the dimensional data of the measured machining surface of the test workpiece 5, the PC 33a obtains the measurement points (design values), shape errors, normal vectors of the measurement points, etc. using specified software on the PC 33a.

[0102] However, it is also possible to measure the shape of the machined surface of the test workpiece 5 using the aforementioned workpiece 3D measuring device 51 outside the NC machine tool 2, and obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc. from the measurement data.

[0103] Next, the PC 33a calculates how much machining error exists in which part of the machining surface 5a of the test workpiece 5. The PC 33a extracts, from the calculation data, a tool contour shape including a contour error of the tool 3 obtained so as to cancel out the machining error of the machining surface 5a of the workpiece 5, as a second tool error shape 3a1.

[0104] Fig. 11 is a schematic diagram showing a second tool error shape as a tool contour shape including a compensation value of the tool 3 in the case where there is a 2 μm uncut portion on the surface near 45° of the machining surface 5a of the workpiece 5 as the machining error exemplified in Fig. 10. In Fig. 11, the solid line indicates the tool contour shape, and the dotted line indicates the tool contour shape including the compensation value.

[0105] As shown by the dotted line in Figure 11, the tool contour shape including the dotted correction value results in a second tool error shape 3a1 that cancels out the 2 μm of unmachined material on the surface near 45° of the machining surface 5a of the test workpiece 5, which is the machining error exemplified in Figure 10.

[0106] Here, the second tool error shape 3a1 is a concave shape on the surface near 45° of the machined surface 5a of the test workpiece 5 so as to cancel out the 2 μm of unmachined portion.

[0107] In other words, if there is a remaining part in the test workpiece 5, it can be regarded as the same as if there is a concave part in the tool shape. Therefore, by adding a concave part to the correction value of the tool shape, the correction works as if there is a concave part in the tool, and the remaining part in the workpiece 5 is eliminated.

[0108] When there is overcutting on the machined surface 5a of the test workpiece 5, the second tool error shape becomes a convex shape that cancels out the overcutting.

[0109] Next, in step S16, the control unit 13 creates a composite tool error shape (CV2+3a1) by combining the first tool error shape CV2 and the second tool error shape 3a1 (fourth step).

[0110] That is, a first tool error shape CV2 including a contour error (first error) of the tool shown in Fig. 8 and a second tool error shape 3a1 including a contour error (second error) of the tool 3 shown in Fig. 11 are superimposed and synthesized to obtain a synthesized tool error shape (CV2+3a1) as shown in Fig. 12. That is, the synthesized tool error shape (CV2+3a1) is a tool error shape including a synthesized error obtained by adding the second error to the first error.

[0111] Specifically, the contour of the tool 3 from the first transition point X1 to the second transition point X2 of the second tool error shape 3a1 shown in FIG. 11 is replaced with a wavy contour shown by the curve CV2 in FIG. 8(b) to obtain a composite tool error shape (CV2+3a1) as shown in FIG. 12.

[0112] That is, transition points X1 and X2 at which the second tool error shape 3a1 transitions to a concave shape that cancels out the remaining cutting portions are obtained, and the contour between the transition points X1 and X2 in the first tool error shape CV2 is replaced with the concave shape of the second tool error shape 3a1 to obtain a composite tool shape.

[0113] FIG. 12 is an explanatory diagram showing a composite tool error shape (CV2+3a1) obtained by superimposing and combining the first tool error shape CV2 and the second tool error shape 3a1.

[0114] In reality, the shape of the tool 3 shown by the solid line in FIG. 3(b) is, of course, symmetrical with respect to the central axis C1.

[0115] That is, since the tip 17 of the tool 3 is line-symmetrical with respect to the central axis C1, the contour error of the tool 3 is the same on the left and right within a 1 / 4 arc (that is, within a range of an angle of 90°) as shown in FIG.

[0116] Therefore, if the workpiece 5 is machined by the tip 17 of the tool 3, the contour error of the tool 3 can be found over a 1 / 4 arc of the tip 17 on either side (i.e., an angle range of 90°).

[0117] Next, in step S16, a correction amount for the NC program is calculated based on a composite tool shape (CV2+3a1) obtained by superimposing the first tool error shape CV2 and the second tool error shape 3a1 as shown in FIG. 12, and the correction amount is set in the memory of the control unit 13, etc.

[0118] Here, the NC program incorporates an arithmetic expression (for example, a mathematical expression using arithmetic operations) for calculating the position (coordinates relative to the workpiece 5) of the tool 3. In other words, the position coordinates when the tool 3 moves are determined by the solution of the arithmetic expression.

[0119] In other words, the NC program is configured to correct the position of the tool 3 according to the correction amount using an arithmetic formula in order to remove machining errors of the workpiece 5 caused by contour errors of the tool 3, as well as to remove machining errors caused by factors other than the tool.

[0120] In other words, if specific numbers were used, the NC program would have to be remade each time the processing machine was changed, the tool was replaced, or the tool wore out, but by making it into a calculation formula, it is possible to deal with tool contour errors that change from time to time as needed.

[0121] In addition, by using an arithmetic expression, the measured tool contour values ​​are stored in variables and calculations (operations) are performed during machining, so once an NC program is created, it can be used continuously. In addition, since the calculations of the arithmetic expressions of the NC program are performed by the control unit 13, a dedicated device is not required.

[0122] The correction of the tool position using the above-mentioned calculation formula is described in detail in Japanese Patent No. 6574915, a previous application filed by the present applicant.

[0123] In this embodiment, the process for obtaining the composite tool shape (CV2+3a1) is executed in the PC 33a. However, the composite process may be executed in the PC 33 and the CAM 39 other than the PC 33a.

[0124] After that, in step S17, the actual machining is started by the tool 3 in the NC machine tool 2. The movement unit 11 moves the tool 3 relative to the workpiece 5 for the actual machining based on the NC program (third step).

[0125] At this time, the NC program corrects the position of the tool 3 based on the correction amount of the NC program. That is, the NC program corrects the position of the tool 3 based on the tool error shape including the combined error obtained by adding the second error to the first error. In this way, the machining error of the workpiece 5 caused by the contour error of the tool 3 and the machining error of the workpiece 5 caused by factors other than the tool 3 are corrected, and the tool 3 is operated to machine the workpiece 5.

[0126] According to the NC machine tool 2 of this embodiment, the contour error of the tool 3 is removed, and furthermore, machining errors caused by factors other than the tool 3 are removed, so that very accurate machining can be achieved.

[0127] Furthermore, according to the NC machine tool 2 in this embodiment, an arithmetic formula for calculating the position (coordinate value) of the tool 3 is incorporated into the NC program, which eliminates the need to recreate the NC program each time a tool is replaced or worn out.

[0128] The present invention is not limited to the above-described embodiment of the invention, and can be embodied in other forms by making appropriate modifications.

[0129] For example, in addition to correcting the errors caused by the tool 3 and the errors caused by factors other than the tool 3 described above, the amount of wear on the tool 3 from the start to the end of machining of the workpiece 5 with the tool 3 can be measured, and the NC program can be corrected taking into account the shape of the tool 3 that changes due to this amount of wear, in addition to the machining errors caused by factors other than the tool 3 described above, thereby machining the workpiece 5 with higher precision.

[0130] The correction of the NC program taking into consideration the shape of the tool 3 that changes due to the amount of wear is described in detail in Japanese Patent No. 6574915, a previous application filed by the applicant.

[0131] In addition, in the above-described embodiment, when the first tool error shape CV2 including the contour error of the tool shown in FIG. 8 and the second tool error shape 3a1 including the contour error of the tool 3 shown in FIG. 11 are superimposed and synthesized to obtain a synthesized tool error shape (CV2+3a1) as shown in FIG. 12, the contour of the tool 3 from the first transition point X1 to the second transition point X2 of the second tool error shape 3a1 shown in FIG. 11 is replaced with the wavy contour error CV2 shown by a curve in FIG. 8(b) to obtain a synthesized tool error shape (CV2+3a1) as shown in FIG. 12, but this is not limited to the above and the synthesis may be performed as follows.

[0132] That is, a second tool error shape 3a1 including the contour error of the tool 3 shown in FIG. 11 may be added to the portion of the wavy contour error CV2 shown by a curve in FIG. 8(b) that corresponds to the surface near 45° of the machining surface 5a of the workpiece 5 to obtain a composite tool error shape (CV2+3a1).

[0133] In addition, as a means for measuring the shape of the machined surface of the workpiece 5 and obtaining the measurement points (design values), shape errors, normal vectors of the measurement points, etc. from the measurement data, a workpiece 3D measuring device 32 consisting of a touch sensor is used on the NC machine tool 2, and in the PC 33a, based on the measured dimensional data of the machined surface of the machined workpiece 5, a predetermined software is used on the PC 33a to obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc., and outside the NC machine tool 2, a workpiece 3D measuring device 51 is used to obtain the measurement points (design values), shape errors, normal vectors of the measurement points, etc., but this is not limited to this and any form may be used as long as the shape of the machined surface of the workpiece 5 can be measured and the measurement points (design values), shape errors, normal vectors of the measurement points, etc. can be obtained from the measurement data.

[0134] In the above-described embodiment, prior to the actual machining, a test workpiece 5 is machined to correct the machining error of the workpiece 5 due to the contour error of the tool 3 and the machining error of the workpiece 5 due to factors other than the tool 3. That is, the outline of the machining method according to this embodiment is as follows.

[0135] (1) Before test machining, the shape of the tool 3 is measured to obtain a first tool error shape (step S14 in FIG. 7). (2) Test processing is performed on test workpiece 5. (3) The machined surface of the test workpiece 5 is measured to obtain a second tool error shape (step S15 in FIG. 7). (4) The first tool error shape and the second tool error shape are synthesized to obtain a synthetic tool error shape, and a compensation amount is calculated from this synthetic tool error shape and set in the control unit 13 (step S16 in FIG. 7). (5) Using the calculated correction amount, machining is performed on the workpiece 5 for main machining (step S17 in FIG. 7).

[0136] However, the machining method according to the present embodiment may be carried out during the actual machining without carrying out the test machining. For example, the machining method according to the present embodiment is carried out during the initial machining of the workpiece 5 for the actual machining. The outline of the machining method in this case is as follows.

[0137] (1) Before the actual machining, the shape of the tool 3 is measured to obtain a first tool error shape (corresponding to step S14 in FIG. 7). (2) Processing is performed on the workpiece 5 for main processing. (3) The machining surface of the workpiece 5 for main machining is measured to obtain a second tool error shape (corresponding to step S15 in FIG. 7). (4) The first tool error shape and the second tool error shape are synthesized to obtain a synthetic tool error shape, and a compensation amount is calculated from this synthetic tool error shape and set in the control unit 13 (corresponding to step S16 in FIG. 7). (5) In the second and subsequent machining operations, the calculated correction amount is used to perform the main machining on the workpiece 5 for main machining (corresponding to step S17 in FIG. 7).

[0138] In addition, in the second and subsequent machining operations, the above steps (2) to (5) may be performed for each machining operation, or the above steps (2) to (5) may be performed periodically when the number of machining operations reaches a certain number. In addition, when the main machining includes multiple processes such as rough machining, medium machining, and finish machining, it is preferable to measure the machined surface of the workpiece 5 for main machining after the final finish process. In addition, when the machined surface of the workpiece 5 for main machining is measured, if there is no machining error or the machining error is smaller than the reference value for judging whether the machining is good or bad, the steps (4) to (5) may be skipped.

[0139] In the former method of performing compensation using test machining, the compensation of machining errors is reflected when performing actual machining. The actual machining in (5) in the former method is performed on a workpiece 5 for actual machining that is different from the test workpiece 5 for which the machining surface was measured in (3) to obtain the second tool error shape. On the other hand, in the latter method of performing compensation during actual machining, the compensation of machining errors may be reflected during actual machining of the next workpiece 5 for actual machining, or may be reflected during correction machining of the same workpiece 5 for actual machining. That is, the actual machining in (5) in the latter method may be performed on a new workpiece 5 for actual machining that is different from the workpiece 5 for actual machining for which the machining surface was measured in (3) to obtain the second tool error shape, or may be performed on the workpiece 5 for actual machining for which the machining surface was measured in (3) to obtain the second tool error shape. [Explanation of symbols]

[0140] 1 Processing system 2 NC machine tools 3 Tools (ball end mill) 3a1 Second tool error shape 5 Workpiece 5a Machining surface 7 Workpiece holding part 9 Tool holding part 11 Mobile section 13 Control section 31 Tool shape measuring device 32, 51 Work 3D measuring device 33 PC 39 CAM 41, 43 Machining path C1 center axis C2 center CV1, CV2 contour error CV2 1st tool error shape 3a1 Second tool error shape T1 processing point X1 First Transition Point X2 The second transition point

Claims

1. A workpiece holding means for holding a workpiece; a tool holding means for holding a tool for processing the workpiece held by the workpiece holding means; a moving means for moving the tool held by the tool holding means relative to the workpiece in order to process the workpiece with the tool, a first step of determining a first error, which is a contour error of the tool determined from an outer shape of the tool measured by a first measuring device; a second step of calculating a second error by converting a machining error calculated from a shape of a machined surface of the workpiece measured by a second measuring device into a contour error of a tool; and a third step of the moving means moving the tool relative to the workpiece based on a predetermined NC program, In the third step, the NC program corrects the position of the tool based on a combined error obtained by adding the second error to the first error, the first step includes a process of measuring a shape of the tool by the first measuring device and determining a contour error between the measured outer shape of the tool and an ideal outer shape of the tool as the first error; the second step includes a process of measuring a shape of the machined surface of the workpiece by the second measuring device, and determining, as the second error, a contour error of a tool that cancels out a machining error that is a difference between the measured shape of the machined surface of the workpiece and an ideal shape of the machined surface of the workpiece; a measurement point, a shape error, and a normal vector of the measurement point of the measured machining surface of the workpiece are obtained from the shape of the machining surface of the workpiece measured by the second measuring device, and the second error is calculated from the measurement point, the shape error, and the normal vector of the measurement point of the machining surface of the workpiece.

2. A workpiece holding means for holding a workpiece; a tool holding means for holding a tool for processing the workpiece held by the workpiece holding means; a moving means for moving the tool held by the tool holding means relative to the workpiece in order to process the workpiece with the tool, a first step of determining a first error, which is a contour error of the tool determined from an outer shape of the tool measured by a first measuring device; a second step of calculating a second error by converting a machining error calculated from a shape of a machined surface of the workpiece measured by a second measuring device into a contour error of a tool; and a third step of the moving means moving the tool relative to the workpiece based on a predetermined NC program, In the third step, the NC program corrects the position of the tool based on a combined error obtained by adding the second error to the first error, the first step includes a process of measuring a shape of the tool by the first measuring device and determining a contour error between the measured outer shape of the tool and an ideal outer shape of the tool as the first error; the second step includes a process of measuring a shape of the machined surface of the workpiece by the second measuring device, and determining, as the second error, a contour error of a tool that cancels out a machining error that is a difference between the measured shape of the machined surface of the workpiece and an ideal shape of the machined surface of the workpiece; The first step further includes a process of extracting a contour shape of a tool including the first error as a first tool error shape, The second step further includes a process of extracting a contour shape of a tool including the second error as a second tool error shape, The method for processing the workpiece comprises the steps of: a fourth step of calculating a correction amount of the NC program based on a composite tool error shape obtained by combining the first tool error shape and the second tool error shape, A method for machining a workpiece, characterized in that in the third step, the NC program corrects the position of the tool based on the correction amount.

3. The method for processing a workpiece according to claim 1 or 2, A method for machining a workpiece, characterized in that the NC program incorporates an arithmetic formula for calculating the position of the tool, and the NC program corrects the position of the tool using the arithmetic formula.

4. The method for processing a workpiece according to claim 1 or 2, 2. A method for machining a workpiece, wherein the tool is a ball end mill or a radius end mill for machining the workpiece.

5. A workpiece processing system for carrying out the workpiece processing method according to claim 1 or 2.

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