Machine tool error correction method, machine tool error correction system, and machine tool

Abstract

A machine tool (1) comprises a table (12) on which a workpiece is placed, a main shaft (16) on which a tool (17) is mounted, a movement mechanism (18) which moves the table (12) and the tool (17) relative to one another, and a control device (20) which controls the movement mechanism (18), said machine tool (1) including: a reference instrument (31) installed in a first portion (table (12)) of the machine tool (1), said reference instrument (31) having an optical scale disposed unidirectionally; an imaging detector (32) installed in a second portion (main shaft head (15)) which moves relative to the first portion due to the movement mechanism (18), said imaging detector (32) performing detection on an image of the reference instrument (31); and an error correction device (33) which reads the optical scale from the detection image from the imaging detector (32), measures a positional error between the first portion and the second portion, and corrects the operation of the movement mechanism (18) on the basis of the measured positional error.

Description

Machine tool error correction method, machine tool error correction system, and machine tool

[0001] The present invention relates to a method for correcting an error in a machine tool, a system for correcting an error in a machine tool, and a machine tool.

[0002] In machine tools, machining is performed by moving the table on which the workpiece is placed and the spindle on which the tool is attached relative to each other using a moving mechanism. During machining, a control device such as a CNC (Computer Numerical Control) executes a machining program to control the movement of the moving mechanism and the rotation of the spindle. In machine tools, the mechanical accuracy of the structure, including the support structure for the table and spindle, affects machining accuracy. Thermal deformation of the structure due to temperature changes is a cause of deterioration in the mechanical accuracy of the structure. In particular, with large machine tools, there are limitations to maintaining a uniform room temperature within a large factory space due to factors such as heat conduction from the foundation (ground). In response to this, machine tools avoid deterioration in the mechanical accuracy of the structure by performing periodic calibration operations.

[0003] Calibration operations involve measuring and correcting the positional accuracy of each of the X, Y, and Z axes of the moving mechanism. Furthermore, because the displacement of large machine tools is complex, spatial correction is also performed by dividing the entire moving space into a grid and providing correction values ​​to each point. In Patent Document 1, a tracking laser interferometer is installed on the machine, constantly monitoring its position and sending the difference to the machine for correction. In Patent Document 2, a reference gauge with multiple spheres arranged on a long arm is installed on the machine tool, and a touch probe attached to the machine tool measures the center positions of the spheres to determine the position error. The correction value is then registered in the control device to improve machining accuracy.

[0004] JP 2016-206065 A Japanese Patent No. 6960893 A

[0005] The correction method of Patent Document 1 requires expensive equipment costing tens of millions of yen, making it unsuitable for general machine tools. Furthermore, accuracy is easily affected by the temperature and airflow in the space through which the laser passes, making it difficult to implement. The correction method of Patent Document 2 requires highly accurate measurement of the position of the sphere of the reference gauge in advance, which can be achieved using, for example, a three-dimensional coordinate measuring machine. However, when the reference gauge is long, a large, expensive three-dimensional coordinate measuring machine is required. Furthermore, if an arm is used that is sufficiently rigid to ensure accuracy as a reference gauge, an increase in weight is unavoidable, and this tendency increases with increasing length, making it difficult to handle. Furthermore, touch probe measurement using a machine tool is time-consuming and difficult to implement.

[0006] An object of the present invention is to provide an error compensation method for a machine tool, an error compensation system for a machine tool, and a machine tool that are easy to operate, can reduce equipment costs, and can achieve high accuracy.

[0007] The machine tool of the present invention is an error correction method for a machine tool having a table on which a workpiece is placed, a spindle to which a tool is attached, a movement mechanism that moves the table and the spindle relatively, and a control device that controls the movement mechanism, which includes a standard device installed in a first part of the machine tool and having optical scales arranged in one direction, and an image detector installed in a second part that moves relatively to the first part by the movement mechanism and detects an image of the standard device, and the optical scale is read from the image detected by the image detector to measure the position error between the first part and the second part, and the operation of the movement mechanism is corrected based on the measured position error.

[0008] In the present invention, the first and second parts can be two parts of a machine tool that move relative to each other and affect machining accuracy. For example, the table can be the first part and the spindle head can be the second part. By structurally separating the first and second parts, position errors in the machine tool can be measured and corrected overall. Alternatively, the column supporting the spindle head can be the second part, and the table that moves relative to the column can be the first part. By structurally separating the first and second parts, local position errors in the machine tool can be measured and corrected. In the present invention, the reference device can be an existing general-purpose product, such as a ruler with a high-precision optical scale engraved on the surface of a long substrate or a position detection scale for industrial machinery. Furthermore, the image detector can be a general-purpose product consisting of a high-magnification microscope head with a solid-state image sensor camera attached.

[0009] In this invention, by issuing a predetermined movement command to the machine tool, the first member and the second member are moved relative to each other by the moving mechanism. The relative movement by the moving mechanism is position-controlled by referring to a scale and a sensor provided on the moving mechanism. At this time, an image detector installed in the second section can magnify and read the optical scale of the reference device installed in the first section. Then, by comparing the control position for the moving mechanism with the position indicated by the optical scale, or by measuring the change between the position indicated by the optical scale before movement and the position indicated by the optical scale after movement, the position error caused by the moving mechanism can be measured, and the operation of the moving mechanism can be corrected based on the obtained position error. Therefore, according to this invention, by adding a reference device and an image detector to the machine tool, it is possible to measure or correct overall or local position errors of the moving mechanism. In this case, the reference device and the image detector can be easily installed at low cost using general-purpose components. Furthermore, error measurement or operation correction can be easily configured by adding software to the machine tool control device. As a result, a machine tool error correction method can be provided that is easy to operate, reduces equipment costs, and achieves high accuracy.

[0010] In the error correction method for a machine tool of the present invention, the operation correction of the movement mechanism can be a method of registering accuracy information including the measured position error in the control device, and the control device performing correction so as to reduce the error when the movement mechanism operates, or a method of registering the accuracy information including the measured position error in the control device, and rewriting the movement command values ​​of the machining program input to the control device so as to reduce the error. In this way, the present invention can appropriately perform high-precision operation correction of the machine tool based on the measured position error.

[0011] In the error correction method for a machine tool of the present invention, it is preferable that the reference device and the image detector are installed for each moving axis of the movement mechanism. In this invention, by installing a set of reference device and image detector for each moving axis of the movement mechanism, for example, for the table and column relatively moved by the X-axis movement mechanism, the crossbar and spindle head saddle relatively moved by the Y-axis movement mechanism, and the saddle and spindle head or ram relatively moved by the Z-axis movement mechanism, the position error of each axis movement mechanism can be detected individually. Then, the positioning accuracy of each axis can be obtained from the position error of each axis, and the squareness and parallelism between multiple axes can also be measured.

[0012] In the method for correcting errors in a machine tool of the present invention, it is preferable that the reference devices are arranged at a plurality of positions and directions within the movement space of the machine tool, the positions of the plurality of reference devices are detected by the image detector, and at least one of the individual positioning accuracy of each movement axis of the machine tool, the perpendicularity between the plurality of axes, and the parallelism between the plurality of axes is measured and corrected. In this way, the individual positioning accuracy of each movement axis of the machine tool, the perpendicularity between the plurality of axes, and the parallelism between the plurality of axes can be measured or corrected from position errors at a plurality of positions and directions within the movement space, making it possible to perform high-precision operation correction with easy operation and reduced equipment costs.

[0013] In the method for correcting errors in a machine tool according to the present invention, it is preferable that the motion correction of the moving mechanism is performed for each lattice point obtained by dividing the movement space of the machine tool into a lattice. In this way, spatial correction for the entire movement space makes it possible to obtain high accuracy even in a large machine tool.

[0014] In the error correction method for a machine tool of the present invention, it is preferable that a plurality of auxiliary standards, each having a marker indicating a single point formed on its surface, are installed on the machine tool, the positions of the plurality of auxiliary standards are detected and recorded by an auxiliary image detector, and the position error between the first portion and the second portion measured using the standards is recorded, the markers of the plurality of auxiliary standards are detected by the auxiliary image detector, the displacement of the auxiliary standards is detected by referring to the recorded positions of the auxiliary standards, and the position error between the first portion and the second portion measured using the recorded standards is used to calculate the position error between the first portion and the second portion without using the standards. In the present invention, the auxiliary standards can be, for example, a plate or block having a marker such as a "+" mark formed on its surface indicating a single point. The auxiliary image detector can be the same device as the image detector described above, or the image detector described above may also serve as the auxiliary image detector. In this invention, the position error between the first part and the second part can be corrected by referring to the positions of multiple auxiliary standards using an auxiliary standard that is simple in configuration and handling, and the position error between the first part and the second part can be measured without using a long standard, improving workability. Note that the marker indicating a point on the auxiliary standard is used to detect the directional displacement of the standard to be corrected and perform a correction calculation for the position error between the first part and the second part measured by this standard. The same auxiliary standard may be used to correct multiple standard devices, or a separate auxiliary standard may be installed for each standard device to be corrected. The marker on the auxiliary standard indicates a point on the auxiliary standard and does not itself indicate a point on a plane or in space.

[0015] In the error correction method for a machine tool according to the present invention, it is preferable that, when measuring the position error, the moving mechanism is controlled with reference to the detected image detected by the image detector, and the focus of the image detector is adjusted to the optical scale of the reference device. In the present invention, an existing automatic focus adjustment function (such as an autofocus mechanism) can be used to control the moving mechanism. For example, the moving mechanism can acquire detected images while changing the distance between the reference device and the image detector, and the focus can be determined from the contrast of the images. In this invention, the optical scale of the reference device can be clearly read at all times using the image detector. In particular, by using the moving mechanism to move the image detector and the reference device relative to each other during focus adjustment, it is not necessary to add a separate mechanical focus adjustment mechanism to the image detector. Furthermore, the position in the optical axis direction can be detected during the automatic focus adjustment operation using the moving mechanism. Furthermore, using a general-purpose component such as the aforementioned existing autofocus mechanism allows for easy and low-cost installation. Furthermore, the optical scale of the reference device only needs to have unidirectional length accuracy, and the requirement for high accuracy for other elements related to straightness and rigidity can be relaxed, thereby reducing the strictness of installation accuracy.

[0016] The error compensation system for a machine tool of the present invention is an error compensation system for a machine tool having a table on which a workpiece is placed, a spindle on which a tool is attached, a movement mechanism for moving the table and the spindle relatively to each other, and a control device for controlling the movement mechanism, further comprising: a standard mounted on a first part of the machine tool and having optical scales arranged in one direction, an image detector mounted on a second part moved relatively to the first part by the movement mechanism and for detecting an image of the standard, and an error compensation device that reads the optical scale from the image detected by the image detector to measure a position error between the first part and the second part, and corrects the operation of the movement mechanism on the basis of the measured position error. Such an error compensation system of the present invention can achieve the effects described for the error compensation method for a machine tool of the present invention described above.

[0017] The machine tool of the present invention is a machine tool having a table on which a workpiece is placed, a spindle on which a tool is attached, a movement mechanism for moving the table and the spindle relatively to each other, and a control device for controlling the movement mechanism, and also having a standard mounted on a first section of the machine tool and having optical scales arranged in one direction, an image detector mounted on a second section moved relatively to the first section by the movement mechanism and for detecting an image of the standard, and an error correction device that reads the optical scale from the image detected by the image detector to measure a position error between the first section and the second section, and corrects the operation of the movement mechanism on the basis of the measured position error. With such a machine tool of the present invention, it is possible to obtain the effects described above for the error correction method for a machine tool of the present invention.

[0018] According to the present invention, it is possible to provide an error correction method for a machine tool, an error correction system for a machine tool, and a machine tool that are easy to operate, can reduce equipment costs, and can achieve high accuracy.

[0019] 1 is a perspective view showing a machine tool according to an embodiment of the present invention; a plan view showing a reference device according to the embodiment; a schematic view showing image detection of the reference device by the image detector according to the embodiment; a schematic view showing pitching and yawing of the reference device according to the embodiment; a schematic view showing curvature of the reference device and the influence of errors according to the embodiment; a schematic view showing automatic focus adjustment of the image detector according to the embodiment; a schematic view showing error correction according to the embodiment; a flowchart showing processing according to the embodiment; a schematic view showing spatial correction according to the embodiment; a perspective view showing an example arrangement of the reference device according to the embodiment; an exploded perspective view showing a stand that supports the reference device according to the embodiment; a perspective view showing an example use of the stand according to the embodiment; a perspective view showing an example use of the stand according to the embodiment; a perspective view showing an example use of the stand according to the embodiment; a perspective view showing an example arrangement of the reference device during machining according to the embodiment; a schematic view showing correction of squareness error according to the embodiment; a schematic view showing correction of squareness error according to the embodiment; Schematic diagrams showing correction of squareness error in the embodiment. Schematic diagrams showing torsion error in the embodiment. Schematic diagrams showing correction of torsion error in the embodiment. Schematic diagrams showing torsion error in the embodiment. Schematic diagrams showing torsion error in the embodiment. Schematic diagrams showing correction of torsion error in the embodiment. Schematic diagrams showing correction of torsion error in the Y-axis direction in the embodiment. Schematic diagrams showing correction of torsion error in the Y-axis direction in the embodiment. Schematic diagrams showing correction of torsion error in the Z-axis direction in the embodiment. Schematic diagrams showing correction of torsion error in the Z-axis direction in the embodiment. A perspective view showing tool position detection in the embodiment. A perspective view showing an auxiliary standard in the embodiment.

[0020] 1 shows a machine tool 1 according to the present invention. The machine tool 1 includes a machine tool main body 10 and a control device 20, and the machine tool main body 10 and the control device 20 are provided with an error correction system 30 according to the present invention.

[0021] The machine tool main body 10 has a bed 11 fixed to a foundation. A table 12 is installed on the upper surface of the bed 11. The table 12 is movable in the X-axis direction relative to the bed 11 by an X-axis movement mechanism 121 installed inside the bed 11. When the machine tool 1 is performing machining, a workpiece (not shown) is placed on the upper surface of the table 12. Figure 1 shows the state before machining, and a reference device 31 of an error correction system 30 is placed on the upper surface of the table 12 (details will be described later).

[0022] A gate-shaped frame 13 is installed across the bed 11. The frame 13 has a pair of columns 131, with a crossbar 14 spanning between them. The crossbar 14 is movable in the Z-axis direction relative to the bed 11 by Z-axis movement mechanisms 141 installed inside each column 131. A spindle head 15 is supported on the crossbar 14. The spindle head 15 is movable in the Y-axis direction relative to the bed 11 by a Y-axis movement mechanism 151 installed inside the crossbar 14. The X-axis movement mechanism 121, Z-axis movement mechanism 141, and Y-axis movement mechanism 151 described above constitute a movement mechanism 18 of the machine tool 1.

[0023] A spindle 16 is supported on the spindle head 15, and the spindle 16 is rotatable by being driven by a main motor (not shown) installed inside the spindle head 15. A cutting tool 17 is attached to the tip of the spindle 16. An image detector 32 of an error correction system 30 is attached to the side of the spindle head 15 near the tool 17 (details will be described later).

[0024] The control device 20 is a general-purpose CNC device (computer numerical control device) that is often used for machine control, and by executing a machining program 22 in the operation control unit 21, the operation control unit 21 controls the movement mechanism 18 to move the tool 17, thereby enabling the desired machining of the workpiece on the table 12. An error correction unit 33 of the error correction system 30 is configured in the control device 20 by adding software. The error correction unit 33 has the function of reading the optical scale of the reference device 31 from the image detected by the image detector 32, measuring the position error between the table 12 (first part) and the spindle head 15 (second part), and correcting the operation of the movement mechanism 18 by the operation control unit 21 based on the measured position error (details will be described later).

[0025] FIG. 2 shows a reference device 31 placed on the table 12. The reference device 31 is a ruler or a position detection scale for industrial machinery, with a highly accurate optical scale 311 and markings 312 indicating the approximate position engraved on the surface of a long substrate 310, and is an existing general-purpose product. The optical scale 311 is formed by a large number of markings or prints linearly arranged along the substrate 310. The optical scale 311 is optically machine-readable and has a resolution of microns (μm), which is necessary for error correction of the machine tool 1. The markings 312 indicating the approximate position are formed by numbers or barcodes and indicate the approximate position of the continuously arranged optical scale 311. In the reference device 31, by setting one or more detection points 313 on the continuously arranged optical scale 311, an image of the detection point 313 is detected by the image detector 32, and the positions of the detection points 313 (e.g., Ps1, Ps2) on the optical scale 311 can be detected with high accuracy by image processing.

[0026] 3 shows the image detector 32 attached to the spindle head 15. The image detector 32 is a high-magnification microscope head with a solid-state image sensor camera attached, and is capable of detecting images of detection points 313 on the optical scale 311 that is arranged facing the reference 31 and continuously arranged. General-purpose microscope heads and cameras can be used for the image detector 32. The image detector 32 needs to be able to clearly identify the optical scale 311 in the detected image of the reference 31 output from the camera. For this reason, the microscope head is set to a magnification that allows for the acquisition of a detected image in which the optical scale 311 can be identified, even if there is a distance between the reference 31 on the table 12 and the image detector 32 attached to the spindle head 15.

[0027] As shown in Figure 4, the reference device 31 placed on the table 12 may pitch (see Figures 4A to 4C) or yawing (see Figures 4D to 4F) depending on the straightness of the table 12 of the machine tool 1 when it moves. As shown in Figure 5, the reference device 31 may be curved depending on the flatness of the surface of the table 12 that supports the reference device 31 (see Figure 5A). If the reference device 31 pitches, yawing, or curves in this way, the optical scale 311 formed on the surface of the reference device 31 will be tilted with respect to the X-axis, causing an error in reading the optical scale 311 by the image detector 32. For example, if the reference device 31 is installed over a length of 1000 mm in the X-axis direction and the image detector 32 is displaced 1 mm in the direction of the reading optical axis (Z-axis), the tilt angle θ = tan －１ If the standard 31 is uniformly tilted, the effect on the absolute length accuracy in the X-axis direction will be dX = 1000 × (1 - cos (0.0573°)) = 0.0005 mm. In this embodiment, this value is sufficiently small relative to the accuracy required of the machine tool 1. On the other hand, a tilt of 0.0573° is extremely large in terms of the motion accuracy of the machine tool 1 and the machining accuracy of the structure, and with today's technology, it is easy to produce values ​​that are one order of magnitude smaller than this under normal circumstances. Therefore, the effect on the reading error of the optical scale 311 due to the straightness or curvature of the standard 31 shown in Figure 4 or Figure 5 can be ignored.

[0028] In FIG. 6 , the focus of the image detector 32 is adjusted by an automatic focus adjustment function incorporated in the error correction unit 33. The error correction unit 33 moves the spindle head 15 to position the image detector 32 facing the reference 31 and align the optical axis with the detection point 313 of the detection target. Then, the image detector 32 is gradually brought closer to the reference 31 while repeatedly capturing images. As a result, the image detector 32 sequentially outputs multiple detection images 321 at different distances to the detection point 313. The error correction unit 33 sequentially performs image processing on the multiple detection images 321 obtained, calculates an evaluation value using contrast, and determines that a detection image 321 with sufficiently high contrast is in focus. This focus determination can utilize existing autofocus camera technology. This automatic focus adjustment of the image detector 32 makes the optical scale 311 clearly identifiable in the detection image output from the image detector 32, and the position of the detection point 313 can be detected with high accuracy through image processing.

[0029] The error correction unit 33 performs the automatic focus adjustment of the image detector 32 described above, detects the position of the detection point 313 from the detected image of the image detector 32, measures the position error at the obtained detection point 313, and corrects the operation of the moving mechanism 18 based on the measured position error. For example, the error correction unit 33 can measure the position error at the detection point 313 by obtaining the current control position of the detection point 313 from the operation control unit 21 and comparing it with the detected position of the detection point 313. In FIG. 7 , if the current detection point 313, which is arranged opposite the image detector 32, is at the control position Pm1 of the operation control unit 21 and at the detected position Ps1 detected from the detected image of the image detector 32, the error correction unit 33 measures a position error D1 of the current detection point 313: Ps1 - Pm1. When the image detector 32 moves to the next detection point 313, if the control position of the operation control unit 21 is Pm2 and the detection position detected from the detection image of the image detector 32 is Ps2, the error correction unit 33 measures the position error D2 = Ps2 - Pm2 of the current detection point 313.

[0030] The error correction unit 33 measures the position error at each of the multiple detection points 313 on the optical scale 311 of the reference device 31, and sends the obtained position error information to the operation control unit 21. The operation control unit 21 stores the position error for each control position corresponding to the multiple detection points 313 sent, and uses it to correct the operation of the moving mechanism 18. When correcting the operation of the moving mechanism 18, a method can be used in which accuracy information including the position error measured by the error correction unit 33 is registered in the operation control unit 21, and the operation control unit 21 corrects the operation of the moving mechanism 18 so as to reduce the position error. Alternatively, a method can be used in which the operation control unit 21 rewrites the movement command values ​​of the machining program 22 that it refers to during machining operation using the accuracy information including the position error measured by the error correction unit 33 so as to reduce the position error.

[0031] Figure 8 shows the error correction procedure in the machine tool 1 of this embodiment. First, the reference device 31 and the image detector 32 are installed on the machine tool 1 (step S1 in Figure 8). For example, when correcting a position error in the X-axis direction of the machine tool 1, the reference device 31 is installed on the table 12, and the image detector 32 is installed on the spindle head 15, as shown in Figure 1. The reference device 31 is positioned so that the optical scale 311 is aligned with the X-axis direction. The spindle head 15 is moved to face the reference device 31, and the image detector 32 is positioned so that it can photograph the optical scale 311. A plurality of detection points 313 on the optical scale 311 of the reference device 31, which are to be used for position error detection, are specified in the error correction unit 33.

[0032] Next, the spindle head 15 is moved under the control of the error correction unit 33, and the image detector 32 is moved to a position facing the first detection point 313 on the optical scale 311 (step S2 in FIG. 8 ), and an image of the detection point 313 is detected (step S3). The error correction unit 33 processes the detected image of the detection point 313 to calculate an evaluation value of the focus state (step S4) and determines whether the evaluation value is equal to or less than a threshold (step S5). The evaluation value of the focus state is, for example, a contrast evaluation value, and is a value that changes depending on the focus state, as in the detected image 321 in FIG. 6 described above. A value indicating a focus state sufficient for detecting the position of the detection point 313 is registered in advance in the error correction unit 33 as a threshold. If the evaluation value is equal to or less than the threshold, the error correction unit 33 controls to move the spindle head 15 and the image detector 32 in the Z-axis direction, which is the optical axis direction of the image detector 32. This executes the autofocus operation (step S6) described above in FIG. 6 , so that a detection image in a sufficient focus state can be obtained from the image detector 32. If the evaluation value is higher than the threshold value, the detected image currently obtained from the image detector 32 is in a sufficiently focused state, so the autofocus operation (step S6) is omitted and the process proceeds to the next step.

[0033] Next, error correction unit 33 performs image processing on the detected image from image detector 32 to detect the position of detection point 313 (e.g., detection position Ps1 in FIG. 7 ), and also acquires the control position on the machine tool 1 side (e.g., control position Pm1 in FIG. 7 ) from operation control unit 21 to calculate the position error at the current detection point 313 (e.g., position error D1 in FIG. 7 ) (step S7). Error correction unit 33 stores the obtained position error together with the control position of detection point 313 as accuracy information at detection point 313.

[0034] When steps S2 to S7 are completed for the first detection point 313, the error correction unit 33 determines whether or not accuracy information has been measured for all detection points 313 (step S8 in FIG. 8). If there are any unmeasured detection points 313, the error correction unit 33 returns to the above-mentioned step S2, moves the image detector 32 to the next detection point 313, and repeats the above-mentioned steps S3 to S8 to store the accuracy information for each detection point 313.

[0035] Once all detection points 313 have been measured, error correction unit 33 corrects the operation of machine tool 1 by referring to the stored accuracy information of each detection point 313 (step S9). To correct the operation of machine tool 1, a method can be used in which the accuracy information of each detection point 313 is registered in control device 20, and correction is performed so that errors are reduced when operation control unit 21 controls the operation of movement mechanism 18. Alternatively, a method can be used in which the accuracy information of each detection point 313 is registered in control device 20, and the movement command values ​​of machining program 22 input to operation control unit 21 are rewritten so that errors are reduced.

[0036] The above explanation has been about correcting a position error along one axis, the X-axis direction, of machine tool 1, but it is also possible to arrange reference unit 31 in multiple positions and directions within the movement space of machine tool 1, detect the positions of multiple reference units 31 with image detector 32, and measure and correct the individual positioning accuracy of each movement axis of machine tool 1, the perpendicularity between multiple axes, and the parallelism between multiple axes. Furthermore, actual operation correction of machine tool 1 requires spatial correction for the three axes X, Y, and Z throughout the movement space of machine tool 1.

[0037] 9, spatial correction of the machine tool 1 is performed by dividing the movement space of the machine tool 1 into a grid and measuring the three-dimensional position error D for each grid point Pm. To measure the XYZ three-dimensional position error D at each grid point Pm, a reference device 31 is installed in the XYZ axis directions on the machine tool 1, and the position or error of detection point 313 corresponding to grid point Pm is detected. Furthermore, in order to measure the distortion of each grid, it is preferable to also measure the position error between grid points Pm located at diagonal positions on the grid.

[0038] 10, in order to measure the above-mentioned XYZ three-dimensional position error D, for example, the reference unit 31 can be installed on the table 12 horizontally along the X-axis and Y-axis directions or vertically along the Z-axis direction, and the reference unit 31 can be installed at an angle to measure the distance between lattice points at diagonal positions. To efficiently install the reference unit 31 in various ways along each axis, for example, a stand 40 as shown in FIG. 11 can be used.

[0039] In FIG. 11 , the stand 40 is composed of a main body 41, an intermediate member 42, and a support member 43. The main body 41 has a triangular top plate 411 connected to its base with a triangular bottom plate 412, which is supported vertically by support rods 413. The top plate 411 has mounting holes 414 formed at multiple different heights. The intermediate member 42 has mounting pins on its back surface, which can be fitted into the mounting holes 414 to mount the main body 41 at different heights. The support member 43 can be mounted at any rotation angle relative to the intermediate member 42 by fitting the mounting pin at one end into the mounting hole in the intermediate member 42. As shown in FIGS. 12A , 12B , and 12C , the stand 40 can support the datum 31 at a desired inclination by connecting the support member 43 via the intermediate member 42 to the main body 41 at a desired height. For example, as shown in FIG. 12A , two stands 40 can be placed side by side to support a single datum 31 horizontally. 12B, by changing the height of the support members 43 of the two stands 40, one reference device 31 can be supported in an inclined state. Furthermore, as shown in FIG. 12C, the reference device 31 can be supported vertically along the front plate 411 of the stand 40.

[0040] When the machine tool 1 is not in a machining state, the reference device 31 can be positioned relatively freely on the table 12. However, when the machine tool 1 is in a machining state, a workpiece is placed on the table 12, and there are restrictions on where the reference device 31 can be positioned on the table 12. However, by placing the reference device 31, for example, near the periphery of the table 12 where it does not interfere with the machining of the workpiece, limited error correction is possible. In FIGS. 13 and 14 , when machining a workpiece 2 with the machine tool 1, the workpiece 2 is placed on the table 12, and the spindle head 15 and tool 17 are moved toward and away from the workpiece 2 by the movement mechanism 18. Therefore, the reference device 31 can be placed on the edge of the table 12, leaving a space around the workpiece 2 that does not interfere with the tool 17, spindle head 15, and image detector 32. In FIG. 13 , the reference devices 31 are positioned along both side edges of the table 12. In FIG. 14 , a pair of reference devices 31 are positioned on both sides of one edge of the table 12. Such error correction during machining does not allow spatial correction over the entire machine tool 1. However, if spatial correction is performed over the entire machine tool 1 before machining, even if the error correction during machining is limited, it is possible to perform operational correction equivalent to spatial correction over the entire machine tool 1 during machining by correcting the accuracy information of the original spatial correction with reference to the accuracy information during machining.

[0041] The following method can be used to measure and correct the squareness and parallelism between multiple axes of machine tool 1. As shown in Figures 15A, 15B, and 15C, for the squareness of two axes that intersect at lattice point Pm, a high-precision reference gauge 39 can be placed diagonally between two points on the coordinate system on either side of lattice point Pm, and the error can be found using Pythagoras' theorem. Note that the high-precision reference gauge 39 described in Japanese Patent No. 6960893 (Patent Document 2) can be used.

[0042] In Figure 15A, if the perpendicularity of the X-axis and Y-axis intersecting at lattice point Pm is ideal, and if the length of reference gauge 39 is 500 mm, the distance in the X-axis direction between reference point 391 and reference point 392 on reference gauge 39 and the distance in the X-axis direction between reference point 392 on reference gauge 39 are 353.553 mm = (500^2 - 353.553^2)^0.5. In Figure 15B, assume that there is an error in the perpendicularity of the X-axis and Y-axis intersecting at lattice point Pm, and the distance in the X-axis direction is 360 mm. In Figure 15C, if the distance in the X-axis direction, which should ideally be 353.553 mm, is actually 360 mm, then 360 - 353.553 = 6.447 mm, so the squareness error of the X-axis and Y-axis intersecting at lattice point Pm is 6.447 mm relative to 353.553 mm. In the above-described error measurement, the reference gauge 39 does not need to be positioned exactly at 45°; even if it is positioned appropriately, squareness errors will appear in the measured values.

[0043] 16, in a coordinate system in which the Y axis has a squareness error with respect to the X axis, when diagonal length measurement is performed, it is known that the error angle θe ≈ (Li2 + Li1) (Li2 - Li1) / (4LxLy), and this can also be utilized. Furthermore, diagonal measurement requires only absolute length accuracy, so the standard device 31 based on the present invention can be used in place of existing high-accuracy length standard gauges.

[0044] In FIG. 17 , a coordinate system "Xm1-Zm1" corrected by obtaining the squareness of the X and Z axes at a certain Y position (Py1) relative to the ideal XYZ coordinate system, and a coordinate system "Xm2-Zm2" at a distant Y position (Py2) may have a torsion TW (axis parallelism error) around the Y axis. This torsion TW cannot be eliminated simply by correcting the squareness of each coordinate system. As shown in FIG. 18 , for example, by imagining a cube CB in which the coordinate axes of each coordinate system have two faces facing each other in the Y axis direction, and measuring the distance LD at the diagonal positions, a difference from the true value appears, which can be used to determine and correct the torsion. Even in such corrections, the standard 31 based on the present invention can be used to replace existing high-precision length standard gauges.

[0045] In Figure 19, there are two orthogonal coordinate systems (for example, the aforementioned coordinate system "Xm1-Zm1" and coordinate system "Xm2-Zm2"), and if one of these coordinate systems (including side SZ1) is true (aligned with the ideal coordinate system), and the other coordinate system (including side SZ2) is generated using sides SY2 and SZ2 as the reference for perpendicularity, the surface formed by sides SY2 and SZ2 will extend in a direction that deviates from the true value, causing a twist in space. Figures 20(A) to (C) and Figure 21 respectively show the twist in space that occurs in the two coordinate systems of Figure 19.

[0046] For such spatial distortion, measuring the positions of two diagonal vertices of two coordinate systems and calculating the lengths (coordinate differences) in each direction allows the error causing the distortion to be determined. In FIG. 22, point P11 on the XZ plane and point P12 on the Y axis are used as the two diagonal vertices of the two coordinate systems. By measuring the distance between these two points, the error in the Y axis direction can be detected. In FIG. 23, when using an existing reference gauge, the distance between points P11 and P12 is expressed as follows: Lg = {Lx^2 + (Ly - Ey)^2 + Lz^2}^0.5. Here, Lg: reference gauge length (true value), Lx: measured X-direction coordinate difference, Ly: measured Y-direction coordinate difference, Lz: measured Z-direction coordinate difference, and Ey: Y-direction error. In such measurements, the reference gauge 31 based on the present invention can be used in place of an existing reference gauge.

[0047] In Figure 24, point P21 on the XY plane and point P22 on the Z axis are used as the two diagonal vertices of the two coordinate systems, and the error in the Z axis direction can be detected by measuring the distance between these two points. In Figure 25, when an existing reference gauge is used, the distance between points P21 and P22 is Lg = {Lx^2 + Ly^2 + (Lz - Ez)^2}^0.5, where Lg: reference gauge length (true value), Lx: measured X-direction coordinate difference, Ly: measured Y-direction coordinate difference, Lz: measured Z-direction coordinate difference, and Ez: Z-direction error. In such measurements, the existing reference gauge can be replaced with the reference device 31 based on the present invention.

[0048] As a method for correcting and utilizing the spatial correction performed for the entire machine tool 1 before machining, an existing origin resetting method can be used. In FIG. 26 , a tip position detector 3 for the tool 17 is installed on the table 12 of the machine tool 1, and spatial correction is performed for the entire machine tool 1 before machining, while measuring the origin position of the tool 17 using the tip position detector 3. Then, while machining the workpiece 2 with the machine tool 1, the tip position detector 3 measures the origin position of the tool 17 at any point during machining, and determines the difference from the origin position before machining. By correcting the accuracy information of the spatial correction using this difference, spatial correction can be performed according to the machine tool 1 during machining. Note that, as the tip position detector 3, for example, a detection unit such as that disclosed in the method for measuring the center position of the rotation axis of a machine tool in Japanese Patent Application Laid-Open No. 2022-008099 can be used.

[0049] An auxiliary standard 34 shown in Figure 27 can be used as a method for correcting and utilizing the spatial correction performed over the entire machine tool 1 before machining. In Figure 27, a workpiece 2 is placed on the table 12 of the machine tool 1, and an auxiliary standard 34 is installed in a corner of the table 12 away from the workpiece 2. The auxiliary standard 34 is formed of a plate or block with a "+" shaped marker indicating a point formed on its surface. The error correction unit 33 detects an image of the surface of the auxiliary standard 34 with the image detector 32 (which also serves as the auxiliary image detector), thereby detecting the planar position of the auxiliary standard 34 along the surface of the table 12 and recording the detected position in the error correction unit 33.

[0050] Here, the machine tool 1 shown in FIG. 27 is spatially corrected using a reference 31 and an image detector 32 before machining. Therefore, the spatial correction performed before machining is applied to the control device 20's control of the movement of the moving mechanism 18 and the tip position of the tool 17. However, as machining is repeated, errors in each part of the machine tool 1 change. In particular, compared to the table 12 supported by the bed 11, the gate-shaped frame 13 that stands across the bed 11 and the crossbar 14 and spindle head 15 supported thereon are more susceptible to errors due to thermal deformation caused by changes in room temperature. Errors in the frame 13, crossbar 14, and spindle head 15 manifest as deformation in the Z-axis direction intersecting the surface of the table 12, tilt deformation relative to the Z-axis, and torsional deformation around the Z-axis, but are less likely to manifest as deformation in the X-axis and Y-axis directions along the surface of the table 12. Therefore, by detecting the position of an auxiliary reference 34 attached to the table 12 during machining and detecting errors in the X-axis and Y-axis directions of the spindle head 15 relative to the table 12, the accuracy information of the spatial correction performed before machining can be corrected. By modifying the spatial correction in this manner, errors of the spindle head 15, which are mainly deformation in the Z-axis direction intersecting the surface of the table 12, tilt deformation relative to the Z-axis, and torsional deformation around the Z-axis, can be corrected.

[0051] In other words, before the machine tool 1 is subjected to processing, a plurality of auxiliary standards 34, each having a marker indicating a single point formed on its surface, are placed on the table 12 of the machine tool 1, the positions of the plurality of auxiliary standards 34 are detected by the image detector 32, and each position is recorded as accuracy information for spatial correction. The position error between the table 12 and the spindle head 15 measured using the standard 31 is also recorded. During processing, the markers on the plurality of auxiliary standards 34 are detected by the image detector 32, and the displacement of the auxiliary standard 34 is detected by referring to the recorded positions of the auxiliary standard 34. From the displacement of the auxiliary standard 34 and the accuracy information for spatial correction measured using the standard 31, the position error between the table 12 and the spindle head 15 can be calculated without using the standard 31, thereby replacing the current spatial correction.

[0052] According to the present embodiment described above, the following advantages can be obtained. In this embodiment, the optical scale 311 of the reference unit 31 is magnified and read by the image detector 32, and the position error of the moving mechanism 18 can be measured from the control position for the moving mechanism 18 and the position indicated by the optical scale 311. The operation of the moving mechanism 18 can be corrected based on the obtained position error. In this embodiment, by adding the reference unit 31 and the image detector 32 to the machine tool 1, it is possible to measure or correct overall or local position errors of the moving mechanism 18. In this case, the reference unit 31 and the image detector 32 can be easily installed at low cost using general-purpose components. Furthermore, the error correction unit 33 that performs error measurement or operation correction can be easily configured by adding software to the control device 20 of the machine tool 1. As a result, error correction of the machine tool 1 is easy to operate, reduces equipment costs, and achieves high accuracy.

[0053] In this embodiment, when measuring the position error, the moving mechanism 18 is controlled with reference to the detected image detected by the image detector 32, and the focus of the image detector 32 is adjusted to the optical scale 311 of the reference device 31. This allows the image detector 32 to always clearly read the optical scale 311 of the reference device 31. In particular, by using the moving mechanism 18 to move the image detector 32 and the reference device 31 relative to each other during focus adjustment, there is no need to add a separate mechanical focus adjustment mechanism to the image detector 32. Furthermore, position detection in the optical axis direction can also be performed during the automatic focus adjustment operation by the moving mechanism 18.

[0054] In this embodiment, auxiliary reference devices 34 that are simple in configuration and handling can be used to refer to the positions of multiple auxiliary reference devices 34 to correct spatial correction based on the position error between the table 12 and the spindle head 15, and accuracy information on the current spatial correction can be obtained without using a long reference device 31, improving workability.

[0055] The present invention is not limited to the above-described embodiment, and modifications within the scope of achieving the object of the present invention are encompassed within the scope of the present invention. In the above embodiment, error correction was performed in the relative movement between the table 12 and the spindle head 15. However, error correction may also be performed for each individual axis movement mechanism. For example, a set of reference device 31 and image detector 32 may be installed for each movement axis of the movement mechanism 18, for example, for the table 12 and the column 131 of the frame 13, which are relatively moved by the X-axis movement mechanism 121; for the column 131 and the crossbar 14, which are relatively moved by the Z-axis movement mechanism 141; and for the crossbar 14 and the spindle head 15, which are relatively moved by the Y-axis movement mechanism 151. This allows the position error of each axis movement mechanism to be detected individually. The positioning accuracy of each axis can then be obtained from the position error of each axis, and the squareness and parallelism between multiple axes may also be measured.

[0056] In the above embodiment, as explained in FIG. 7 etc., the position errors D1, D2 of the detection point 313 are detected by comparing the control positions Pm1, Pm2 of the operation control unit 21 for the moving mechanism 18 with the detection positions Ps1, Ps2 of the detection point 313 on the optical scale 311. However, the detected position indicated by the optical scale 311 before the movement of the moving mechanism 18 is recorded, and the error may be detected by measuring the change from the position indicated by the optical scale 311 after the movement.

[0057] In the above embodiment, an example of application of the present invention to a machine tool 1 having a gate-shaped frame 13 has been described, but the present invention can also be applied to vertical or horizontal machine tools. The reference device of the present invention is not limited to a ruler having a high-precision optical scale 311 engraved on the surface of a long base material such as the reference device 31 in the above embodiment, but a position detection scale for industrial machinery having an optically readable scale may also be used. The image detector of the present invention may be a general-purpose product having a solid-state image sensor camera attached to a high-magnification microscope head, or may be an optical device for other purposes such as a high-magnification telescope.

[0058] The present invention relates to a method for correcting an error in a machine tool, a system for correcting an error in a machine tool, and a machine tool.

[0059] 1...machine tool, 10...machine tool body, 11...bed, 12...table, 121...X-axis movement mechanism, 13...frame, 131...column, 14...crossbar, 141...Z-axis movement mechanism, 15...spindle head, 151...Y-axis movement mechanism, 16...spindle, 17...tool, 18...movement mechanism, 2...workpiece, 20...control device, 21...motion control unit, 22...machining program, 3...tip position detector, 30...error correction system, 31...reference device, 310...substrate, 311...optical scale, 312...display, 313...detection point, 3 2...image detector, 321...detected image, 33...error correction unit, 34...auxiliary standard, 39...reference gauge, 391, 392...reference point, 40...stand, 41...main body, 411...top plate, 412...bottom plate, 413...support rod, 414...mounting hole, 42...intermediate member, 43...support member, CB...cube, D, D1, D2...position error, LD...distance, P11, P12, P21, P22...point, Pm...lattice point, Pm1, Pm2...control position, Ps1, Ps2...detection position, S1 to S9...procedure, SY2, SZ1, SZ2...side.

Claims

1. A method for correcting errors in a machine tool having a table on which a workpiece is placed, a spindle on which a tool is attached, a movement mechanism that moves the table and the spindle relatively, and a control device that controls the movement mechanism, comprising: a standard device that is installed in a first part of the machine tool and has optical scales arranged in one direction; and an image detector that is installed in a second part that moves relatively to the first part by the movement mechanism and detects an image of the standard device; the optical scale is read from the image detected by the image detector to measure the position error between the first part and the second part, and the operation of the movement mechanism is corrected based on the measured position error.

2. A method for correcting errors in a machine tool as described in claim 1, wherein the operation correction of the moving mechanism is performed by registering accuracy information including the measured position error in the control device, and the control device corrects the error so as to reduce it when the moving mechanism operates, or by registering accuracy information including the measured position error in the control device, and rewriting the movement command values ​​of the machining program input to the control device so as to reduce the error.

3. The method for correcting errors in a machine tool according to claim 1, wherein the reference device and the image detector are installed for each of the movement axes of the movement mechanism.

4. A method for correcting errors in a machine tool as set forth in claim 1, wherein the reference devices are arranged at a plurality of positions and directions within the movement space of the machine tool, the positions of the plurality of reference devices are detected by the image detector, and at least one of the individual positioning accuracy of each movement axis of the machine tool, the perpendicularity between the plurality of axes, and the parallelism between the plurality of axes is measured and corrected.

5. A method for correcting errors in a machine tool according to claim 4, wherein the motion correction of the moving mechanism is performed for each lattice point obtained by dividing the moving space of the machine tool into a lattice.

6. A method for correcting errors in a machine tool as described in claim 5, which comprises installing a plurality of auxiliary standards on the machine tool, each having a marker indicating a single point formed on its surface, detecting the positions of the plurality of auxiliary standards with an auxiliary image detector and recording each position, and recording the position error between the first part and the second part measured using the standard, detecting the markers of the plurality of auxiliary standards with the auxiliary image detector, detecting the displacement of the auxiliary standards by referring to the recorded positions of the auxiliary standards, and calculating the position error between the first part and the second part without using the standard from the displacement of the auxiliary standard and the position error between the first part and the second part measured using the recorded standard.

7. An error correction method for a machine tool as described in any one of claims 1 to 6, wherein, when measuring the position error, the moving mechanism is controlled by referring to the detected image detected by the image detector, and the focus of the image detector is brought into focus on the optical scale of the reference device.

8. An error correction system for a machine tool having a table on which a workpiece is placed, a spindle to which a tool is attached, a movement mechanism for moving the table and the spindle relatively, and a control device for controlling the movement mechanism, comprising: a standard installed in a first part of the machine tool and having optical scales arranged in one direction; an image detector installed in a second part that moves relatively to the first part by the movement mechanism and detects an image of the standard; and an error correction device that reads the optical scale from the image detected by the image detector, measures a position error between the first part and the second part, and corrects the operation of the movement mechanism based on the measured position error.

9. A machine tool having a table on which a workpiece is placed, a spindle to which a tool is attached, a movement mechanism for moving the table and the spindle relative to one another, and a control device for controlling the movement mechanism, the machine tool also having: a standard installed in a first part of the machine tool and having optical scales arranged in one direction; an image detector installed in a second part that moves relatively to the first part by the movement mechanism and detects an image of the standard; and an error correction device that reads the optical scale from the image detected by the image detector, measures the position error between the first part and the second part, and corrects the operation of the movement mechanism based on the measured position error.

Images