Method for measuring correction values ​​for position measurement sensors of machine tools and system for measuring correction values ​​for position measurement sensors

Abstract

The objective is to provide a method for measuring the correction value of a machine tool's position measurement sensor, and a system for measuring the correction value of a position measurement sensor, which can minimize errors in the longitudinal correction value of the position measurement sensor even when the ambient temperature changes, and which can also provide a wider table area for placing the workpiece. [Solution] The numerically controlled machine tool M comprises a table 3 that can move with one or more degrees of freedom and can hold a workpiece, a spindle 2 that can rotate with a tool attached and has two or more translational axes and can move relative to the table 3 with two or more translational degrees of freedom, and a laser sensor 40 that can measure the position of a tool attached to the spindle 2, and the position of a workpiece held on the table 3 can be measured by a touch probe 30 that can be attached to the spindle 2, and the laser sensor 40 comprises a laser 43 that detects the object to be detected and a reference part 45 that is arranged near the laser 43 and integrated with the laser sensor 40 and serves as a position reference for the laser sensor 40.

Description

Technical Field

[0001] The present disclosure relates to a method for measuring a correction value of a position measurement sensor and a position measurement sensor correction value measurement system for a machine tool that measures the position of a workpiece in a machine tool in which a table holding a workpiece and a spindle holding a tool move relative to each other along a translation axis.

Background Art

[0002] In a numerically controlled machine tool M having three translation axes as shown in FIG. 1, when machining a workpiece placed on a table 3 with a tool mounted on a spindle 2, it is necessary to record in a control device the position that serves as a reference for machining the workpiece. The position serving as a reference for machining is obtained, for example, by measuring the position of the workpiece.

[0003] As a method for measuring the position of a workpiece, a method using a touch probe which is a position measurement sensor mounted on a spindle is known. When a stylus attached to the touch probe contacts the workpiece, a signal is transmitted at that moment. The NC control device provided in the machine tool receives the signal with a connected receiver. When the NC control device receives the signal, it calculates the position of the workpiece taking into account the correction value in the length direction of the touch probe at the positions of each axis at that time. However, the touch probe undergoes changes over time such as thermal deformation due to the influence of room temperature changes, for example. Therefore, in order to accurately measure the position of the workpiece, it is necessary to appropriately obtain the correction value in the length direction of the touch probe again.

[0004] As a method for measuring the longitudinal correction value of a touch probe, the applicant has disclosed a method as described in Patent Document 1. The method described in Patent Document 1 uses a tool sensor such as a laser sensor or a touch sensor, a reference block placed on the base of the tool sensor, and a reference tool of known length. The detection position of the tool sensor, the relative position of the reference block with respect to the detection position, and the longitudinal correction value of the touch probe are obtained in advance. Then, by measuring the detection position of the reference tool with the tool sensor and measuring the position of the reference block with the touch probe, the longitudinal correction value of the touch probe can be calculated. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 7266511 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, if the relative position of the reference block with respect to the detection position of the tool sensor, which has been acquired in advance, changes, errors may occur in the correction value in the longitudinal direction of the touch probe. For this reason, Patent Document 1 reduces the change in relative position by installing the reference block on the same base as the tool sensor. However, for example, if the coefficient of linear expansion of the tool sensor and the reference block are different, even if the tool sensor and the reference block are installed on the same base, the relative position will change in response to changes in ambient temperature. As a result, the problem of errors occurring in the correction value in the longitudinal direction of the touch probe remained. Furthermore, in many cases, as shown in Patent Document 1, the tool sensor and the reference block are separate components, and each is installed at an arbitrary position on the table. Therefore, there has been a need to solve the problem of the table area for placing the workpiece being narrowed.

[0007] Therefore, the present disclosure aims to provide a method for measuring the correction value of a position measuring sensor for a machine tool, and a system for measuring the correction value of a position measuring sensor, which can minimize errors in the longitudinal correction value of the position measuring sensor even when the ambient temperature changes, and which can provide a wider table area for placing the workpiece. [Means for solving the problem]

[0008] To solve the above problems, a first aspect of the present disclosure is a machine tool comprising a table capable of holding a workpiece, a spindle capable of rotating with a tool attached, a translation axis capable of relative motion of the spindle and the table with two or more translational degrees of freedom, and a tool sensor capable of measuring the position of a tool attached to the spindle, wherein the position of a workpiece held on the table can be measured by a position measuring sensor that can be attached to the spindle, and a method for measuring a correction value of the position measuring sensor in the longitudinal direction of the position measuring sensor of a machine tool, wherein the tool sensor comprises a detection unit that detects an object to be detected, and a reference unit that is provided integrated with the tool sensor near the detection unit and serves as a position reference for the tool sensor, a tool sensor detection position measurement step of attaching a reference tool of known length to the spindle, causing the detection unit of the tool sensor to detect the tip of the reference tool to obtain the tip position of the reference tool, and calculating the position of the detection unit of the tool sensor from the obtained tip position of the reference tool and the length of the reference tool, and after obtaining the reference position using the reference tool attached to the spindle, attaching the position measuring sensor to the spindle, measuring the reference position using the position measuring sensor to obtain the position measuring sensor reference position, and The method is characterized by performing the following steps: a position measurement sensor length measurement step which calculates the length of the position measurement sensor from the reference position of the position measurement sensor and the length of the reference tool; a relative position measurement step which involves mounting the position measurement sensor on the main shaft, measuring the position of the reference part, and calculating the relative position of the reference part to the position of the detection part from the measured position of the reference part, the position of the detection part calculated in the tool sensor detection position measurement step, and the length of the position measurement sensor calculated in the position measurement sensor length measurement step; a reference tool tip position measurement step which involves mounting the reference tool on the main shaft, bringing the tip of the reference tool into contact with the detection part, and measuring the position of the tip of the reference tool; a tool sensor position measurement step which involves mounting the position measurement sensor on the main shaft, measuring the position of the reference part, and obtaining the position of the tool sensor; and a position measurement sensor length direction correction value calculation step which calculates a correction value in the length direction of the position measurement sensor from the length of the reference tool, the relative position calculated in the relative position measurement step, the position of the tip of the reference tool measured in the reference tool tip position measurement step, and the position of the tool sensor obtained in the tool sensor position measurement step. Another aspect of the first configuration of this disclosure is characterized in that, in the above configuration, the steps from the tool sensor detection position measurement step to the relative position measurement step are performed once, and the steps from the reference tool tip position measurement step to the position measurement sensor length direction correction value calculation step are performed multiple times. Another aspect of the first configuration of this disclosure is characterized in that, in the above configuration, the detection unit and the reference unit are made of a material that does not change in the relative position between the detection unit and the reference unit in the ambient temperature range observed during machining by a machine tool. To solve the above problems, a second aspect of the present disclosure is a machine tool comprising a table capable of holding a workpiece, a spindle capable of rotating with a tool attached, a translation axis capable of relative motion of the spindle and the table with two or more translational degrees of freedom, a control device for controlling the table, the translation axis and the spindle, and a tool sensor capable of measuring the position of a tool attached to the spindle, wherein the position of a workpiece held on the table can be measured by the position measuring sensor that can be attached to the spindle, and the machine tool is a correction value measurement system for a position measuring sensor of a machine tool that calculates a correction value in the longitudinal direction of the position measuring sensor, wherein the tool sensor detects an object to be detected. The tool sensor detection position measurement unit comprises a detection unit and a reference unit provided near the detection unit and integrated with the tool sensor, which serves as the position reference for the tool sensor, a reference tool of known length, a tool sensor detection position measurement unit that mounts the reference tool on the spindle, operates the translation axis to detect the tip of the reference tool on the detection unit of the tool sensor to obtain the tip position of the reference tool, and calculates the position of the detection unit of the tool sensor from the obtained tip position of the reference tool and the length of the reference tool, and after mounting the reference tool on the spindle and operating the translation axis to obtain the reference position, a position measurement sensor is mounted on the spindle and the translation axis is operated to use the position measurement sensor to obtain the reference position A position measurement sensor length measuring unit measures the position to obtain the reference position of the position measurement sensor, and calculates the length of the position measurement sensor from the length of the reference tool, the reference position, and the reference position of the position measurement sensor. A relative position measuring unit mounts the position measurement sensor on the main spindle, operates the translation axis to measure the position of the reference part, and calculates the relative position of the reference part to the position of the detection part from the measured position of the reference part, the position of the detection part calculated by the tool sensor detection position measuring unit, and the length of the position measurement sensor calculated by the position measurement sensor length measuring unit. A reference tool is mounted on the main spindle, and the translation axis is operated to detect The device is characterized by comprising: a reference tool tip position measuring unit that measures the position of the tip of a reference tool by bringing the tip of the reference tool into contact with a part; a tool sensor position measuring unit that attaches a position measuring sensor to the main spindle, operates the translation axis to measure the position of the reference part, and obtains the position of the tool sensor; and a position measuring sensor length direction correction value calculation unit that calculates a correction value in the length direction of the position measuring sensor from the length of the reference tool, the relative position calculated by the relative position measuring unit, the position of the tip of the reference tool measured by the reference tool tip position measuring unit, and the position of the tool sensor obtained by the tool sensor position measuring unit. Another aspect of the second configuration of this disclosure is characterized in that, in the above configuration, the detection unit and the reference unit are made of a material that does not change in the relative position between the detection unit and the reference unit in the ambient temperature range observed during machining by a machine tool. [Effects of the Invention]

[0009] According to this disclosure, by integrating the reference unit with the tool sensor near the detection unit, changes in relative position can be minimized even when the ambient temperature changes. Therefore, when measuring the longitudinal correction value of a position measurement sensor using the relative position with the position of the reference unit on the tool sensor, errors in the longitudinal correction value of the position measurement sensor can be minimized. In addition, since a separate reference block from the tool sensor is not required, the table area for placing the workpiece can be made larger. Furthermore, by forming the detection unit and the reference unit from materials that do not change their relative position within the ambient temperature range observed during machining by machine tools, the relative position change due to temperature changes can be further reduced. [Brief explanation of the drawing]

[0010] [Figure 1] This is an explanatory diagram showing the correction value measurement system for the position measurement sensor disclosed herein. [Figure 2] NC control system configuration block. [Figure 3] This is an explanatory diagram showing the laser sensor of this disclosure. [Figure 4] This is an explanatory diagram showing the touch sensor of the present disclosure. [Figure 5] This is an explanatory diagram for measuring the reference position on the table surface using a touch probe. [Figure 6] This is a flowchart relating to the pre-setting of the longitudinal correction value of the touch probe of this disclosure. [Figure 7] This is an explanatory diagram regarding the acquisition of a reference position on the table surface using a reference tool. [Figure 8] This is an explanatory diagram relating to the position measurement of the reference part of a laser sensor. [Figure 9]This is an explanatory diagram relating to the position measurement of the reference part of a touch sensor. [Figure 10] This is a flowchart relating to the measurement method for the longitudinal correction value of the touch probe of this disclosure. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described below with reference to the drawings. In this embodiment, as an example of a machine tool, Figure 1 shows a machining center-based numerically controlled machine tool M having three translational axes: the X-axis, Y-axis, and Z-axis. However, other machine tools such as multi-axis controlled machine tools having rotary axes in addition to translational axes, or lathe-based numerically controlled machine tools may also be used.

[0012] The numerically controlled machine tool M in this disclosure is a machining center-based machine tool having three translational axes consisting of the X-axis, Y-axis, and Z-axis, as shown in Figures 1 and 2. The numerically controlled machine tool M comprises a bed 1, a spindle 2 on which a tool (not shown) can be mounted, a table 3 on which a workpiece (not shown) can be held, and an NC control device 21. Furthermore, the numerically controlled machine tool M comprises a tool sensor and a position measurement sensor. It is desirable that the numerically controlled machine tool M is equipped with a magazine for storing multiple tools and a tool changer that can automatically exchange the tools stored in the magazine with the tools mounted on the spindle 2. By storing the reference tool 10 and position measurement sensor, which will be described later, in the magazine, they can be automatically attached to and detached from the spindle 2, thereby improving work efficiency. However, the attachment and detachment of tools to and from the spindle 2 may be performed manually by the operator.

[0013] The numerically controlled machine tool M is a so-called gantry-type machine tool. Therefore, a saddle 6 is movably provided on a rail 5 formed in a column 4 and extending in the X-axis direction. Further, a spindle ram 7 is movably provided on the saddle 6 in the Z-axis direction. And a spindle 2 is provided at the lower end of the spindle ram 7. Therefore, the spindle 2 can move along the Z-axis and the X-axis, which are two translational axes orthogonal to each other. That is, the spindle 2 can perform a translational movement with two degrees of freedom with respect to the bed 1. The movement of the spindle 2 in the X-axis direction is executed by driving a feed shaft by an X-axis translation servo motor 11a to move the saddle 6. The movement of the spindle 2 in the Z-axis direction is executed by driving a feed shaft by a Z-axis translation servo motor 11c to move the spindle ram 7. Further, an X-axis position detector 8a is provided on the surface of the saddle 6 on the column 4 side. A Z-axis position detector 8c is provided on the surface of the spindle ram 7 on the saddle 6 side.

[0014] The table 3 is formed on the bed 1 and is movably provided on a rail 9 extending along the Y-axis, which is a translational axis orthogonal to the Z-axis and the X-axis. That is, the table 3 can perform a translational movement with one degree of freedom with respect to the bed 1. Further, the movement of the table 3 in the Y-axis direction is executed by driving a feed shaft by a Y-axis translation servo motor 11b. Furthermore, a Y-axis position detector 8b is provided on the surface of the table 3 on the bed 1 side.

[0015] As shown in FIG. 2, the NC control device 21 has functions as a recording unit 22, a display unit 23, and a servo command value generation unit 24. The NC control device 21 includes a CPU and a memory connected to the CPU, and realizes various processes by using them.

[0016] The recording unit 22 can record information such as a machining program input by an input unit 26 described later, the length of the reference tool 10, the detection position of the tool sensor, the relative position of the reference portion with respect to the detection position, and the correction value in the length direction of the position measurement sensor. Furthermore, the recording unit 22 stores a program for the NC control device 21 to function as a tool sensor detection position measurement unit, a position measurement sensor length measurement unit, a relative position measurement unit, a reference tool tip position measurement unit, a tool sensor position measurement unit, and a position measurement sensor length direction correction value calculation unit, as described in this disclosure. The display unit 23 is, for example, a monitor, which displays information such as the machining program and the position of each translation axis.

[0017] Furthermore, the NC control device 21 is connected to the X-axis position detector 8a, the Y-axis position detector 8b, and the Z-axis position detector 8c, as well as the X-axis translation servo amplifier 12a, the Y-axis translation servo amplifier 12b, and the Z-axis translation servo amplifier 12c. The servo amplifiers 12a to 12c are each further connected to the X-axis translation servo motor 11a, the Y-axis translation servo motor 11b, and the Z-axis translation servo motor 11c. Therefore, the NC control device 21 drives the servo motors 11a to 11c appropriately based on the position information of each axis acquired from the position detectors 8a to 8c, thereby performing machining on the workpiece held in the table 3 using a tool held in the spindle 2.

[0018] Here, we will explain a method for generating servo command values ​​for the translation axis, which is performed by the servo command value generation unit 24, and an example of relative position control between the table 3 and the main shaft 2 based on the servo command values. When a machining program is input to the NC control device 21, the servo command value generation unit 24 generates command values ​​for each translation axis based on position information from the position detectors 8a to 8c of each axis and the previously acquired position information of the workpiece. The generated command values ​​for each translation axis are sent to the servo command value conversion unit 25 and converted into servo command values. Subsequently, the respective servo command values ​​for the X, Y, and Z axes are sent to the servo amplifiers 12a to 12c. The servo amplifiers 12a to 12c drive the servo motors 11a to 11c based on the acquired servo command values ​​for the X, Y, and Z axes, respectively. Therefore, the relative position of the spindle 2 with respect to the table 3 is controlled by the driving of the servo motors 11a to 11c.

[0019] The NC control device 21 is further connected to a tool sensor and a position measurement sensor. The connection to the tool sensor and position measurement sensor may be wireless, with a receiver connected to the NC control device 21 to obtain information from the sensors, or it may be wired. In this embodiment, it is assumed that the NC control device 21 and the tool sensor are wired together. On the other hand, it is assumed that the NC control device 21 and the position measurement sensor are wirelessly connected. Therefore, a receiver 33 for receiving signals from the position measurement sensor is connected to the NC control device 21. Furthermore, the NC control device 21 is connected to an input unit 26, such as a keyboard and touch panel, for the operator to execute various inputs, including machining programs.

[0020] As shown in Figure 3, the laser sensor 40, which serves as a tool sensor, comprises a laser light-emitting unit 41 that emits a laser 43 which is a detection unit, a laser light-receiving unit 42 that receives the laser 43, and a base unit 44. Furthermore, the laser sensor 40 has a reference unit 45 integrated into the upper surface of the laser light-emitting unit 41. The reference unit 45 is made of the same material as the laser light-emitting unit 41 and the laser light-receiving unit 42, or a material having a similar coefficient of thermal expansion. The laser sensor 40 can be mounted at any position on the table 3.

[0021] Furthermore, the touch sensor 50, which serves as a tool sensor, consists of a touch sensor body 51, a detection unit 52 for detecting the position of the tool tip, and a base unit 53, as shown in Figure 4. In addition, the touch sensor 50 has a reference unit 54 integrated into the upper surface of the touch sensor body 51. The reference unit 54 is made of the same material as the detection unit 52 and the touch sensor body 51, or a material having a similar coefficient of thermal expansion. The touch sensor 50 can be attached to any position on the table 3.

[0022] Herein, in this disclosure, a similar coefficient of linear expansion refers to a coefficient of linear expansion that, in the ambient temperature range observed during the machining of a workpiece by a numerically controlled machine tool M, does not cause a change in the relative position between the detection unit and the reference unit, or, even if a change in the relative position occurs, exhibits a similarity such that the machined product falls within an acceptable quality range. The laser sensor 40 and the touch sensor 50 will be selected based on various factors such as the structure and installation environment of the numerically controlled machine tool M, and will be mounted on the numerically controlled machine tool M.

[0023] Thus, in the correction value measurement system for position measurement sensors of this disclosure, the laser sensor 40 includes a reference section 45 on the laser light-emitting section 41, formed of the same material as the laser light-emitting section 41 and the laser light-receiving section 42, or a material having a similar coefficient of linear expansion. Therefore, even if the temperature around the laser sensor 40 changes and the laser light-emitting section 41 undergoes thermal deformation, the relative position between the laser 43 and the reference section 45 is unlikely to change. Similarly, the touch sensor 50 includes a reference section 54 on the touch sensor body 51, formed of the same material as the detection section 52 and the touch sensor body 51, or a material having a similar coefficient of linear expansion. Therefore, even if the temperature around the touch sensor 50 changes and the touch sensor body 51 undergoes thermal deformation, the relative position between the detection section 52 and the reference section 54 is unlikely to change. Consequently, errors occurring in the calculation of the correction value in the longitudinal direction of the position measurement sensor can be minimized.

[0024] Furthermore, the reference unit 45 is provided integrally with the laser sensor 40. Similarly, the reference unit 54 is provided integrally with the touch sensor 50. Therefore, the table area for placing the workpiece can be made wider.

[0025] As shown in Figure 5, the touch probe 30, used as a position measurement sensor, consists of a touch probe body 31, a stylus 32 attached to its tip, and a receiver 33 connected to the NC control device 21. As described above, in order to measure the position of a workpiece or other object using the touch probe 30, it is necessary to obtain a longitudinal correction value for the touch probe 30 in advance and record it in the recording unit 22 of the NC control device 21.

[0026] The following describes the method for measuring the longitudinal correction value of the touch probe 30 in this disclosure. First, the calculation of the relative position between the detection unit and the reference unit in the tool sensor, which is a pre-setting for measuring the longitudinal correction value of the touch probe 30 of this disclosure, will be explained based on the flowchart in Figure 6.

[0027] In order to perform tool measurement using a tool sensor, it is necessary to acquire the detection position of the tool sensor in advance and record it in the recording unit 22 of the NC control device 21. Therefore, as S1, the detection position, which is the position for detecting the position of the tool tip of the laser sensor 40 or touch sensor 50 used as a tool sensor, is acquired. S1 is the tool sensor detection position measurement step in this disclosure. Here, we will explain using the acquisition of the detection position in the Z-axis direction of the tool tip as an example.

[0028] First, a reference tool 10 of known length is mounted on the spindle 2. Then, the tip of the reference tool 10 is positioned directly above the laser 43. Subsequently, as shown in Figure 3, the Z-axis is moved in the negative direction, and when the laser 43 is blocked by the tip of the reference tool 10, it is determined that detection has occurred, and a signal is transmitted from the laser receiver 42 to the NC control device 21. When the NC control device 21 receives the signal from the laser sensor 40, it stops the Z-axis translation servo motor 11c. In addition, the NC control device 21 calculates a detection position Zrt' by adding the length Lr of the reference tool 10 to the Z-axis position Zrt at the time of signal reception, using equation (1). The detection position Zrt' thus calculated is the detection position in the Z-axis direction for detecting the position of the tool tip that should be acquired in advance. The detection position Zrt' is recorded in the recording unit 22.

[0029] Zrt' = Zrt - Lr (1)

[0030] The method of measuring a tool using the touch sensor 50 is essentially the same as the method of measuring a tool using the laser sensor 40 described above, except for the detection method. With the touch sensor 50, as shown in Figure 4, when the tip of the tool comes into contact with the detection unit 52 of the touch sensor 50, it is determined that detection has occurred, and a signal is transmitted from the touch sensor body 51 to the NC control device 21.

[0031] After obtaining the detection position Zrt' of the tool sensor, the length of the touch probe 30 is measured as S2. S2 is the position measurement sensor length measurement step in this disclosure. Similar to S1, the reference tool 10 is mounted on the spindle 2 and positioned so that its tip is located near the top surface of the table 3. Then, as shown in Figure 7, the tip of the reference tool 10 is brought into contact with a reference block 13 of known thickness placed on the table 3. The contact position between the reference tool 10 and the reference block 13 is acquired by the Z-axis position detector 8c as the position Z1 on the top surface of the table via the known thickness t of the reference block 13. The reference position Z1' is then calculated from the acquired position Z1, the thickness t of the reference block 13, and the length Lr of the reference tool 10 using equation (2).

[0032] Z1' = Z1 - Lr - t (2)

[0033] Subsequently, the touch probe 30 is attached to the main spindle 2, and the tip of the stylus 32 is positioned near the position where the reference position Z1' is acquired. Then, as shown in Figure 5, when the Z-axis is moved in the negative direction and the stylus 32 makes contact with the reference position Z1', a signal is transmitted from the touch probe body 31 to the receiver 33 connected to the NC control device 21. The contact position Z2 at this time is the reference position of the position measurement sensor in this disclosure. The length Lp of the touch probe is calculated from the contact position Z2, which is the reference position of the position measurement sensor, and the reference position Z1', using equation (3), and is recorded in the recording unit 22. Lp = Z2 - Z1' (3)

[0034] After acquiring the length Lp of the touch probe 30, in step S3, the relative position of the reference unit 45 with respect to the laser 43, which is the detection unit of the laser sensor 40, or the relative position of the reference unit 54 with respect to the detection unit 52 of the touch sensor 50 is measured. Step S3 is the relative position measurement step in this disclosure. As shown in Figures 8 and 9, the tip of the stylus 32 of the touch probe 30 mounted on the main spindle 2 is positioned near the reference part 45 of the laser sensor 40 or the reference part 54 of the touch sensor 50. When the Z-axis is moved in the negative direction and the stylus 32 makes contact with the reference part 45 of the laser sensor 40 or the reference part 54 of the touch sensor 50, a signal is transmitted from the touch probe body 31 to the receiver 33 connected to the NC control device 21. At this time, the contact position Z3, the detection position Zrt', and the length Lp of the touch probe 30 are used to calculate the relative position dZ3, which is calculated by number (4) and recorded in the recording unit 22.

[0035] dZ3 = Z3 - Lp - Zrt' (4)

[0036] As described above, by executing S1 to S3 and storing the relative positions dZ3 of the reference units 45 and 54 with respect to the detection units 43 and 52 of the laser sensor 40 or touch sensor 50, the pre-setting for measuring the longitudinal correction value of the touch probe 30 is completed. Next, the method for measuring the longitudinal correction value of the touch probe 30, which is performed after the pre-configuration is complete, will be explained based on the flowchart in Figure 10.

[0037] In step S11, the detection position of the tool sensor is remeasured. Following the same procedure as in S1 described above, the detection position Zrt'' is calculated as shown in Figures 3 and 4. S11 is the reference tool tip position measurement step in this disclosure. In step S12, the touch probe 30 is attached to the spindle 2 and positioned so that the tip of the stylus 32 is near the reference portion 45 of the laser sensor 40 or the reference portion 54 of the touch sensor 50, which was measured in step S3. Then, as shown in Figures 8 and 9, the Z-axis is moved in the negative direction to bring the stylus 32 into contact with the reference portion 45 of the laser sensor 40 or the reference portion 54 of the touch sensor 50, and the contact position Z3' is acquired. The contact position Z3' is the sensor position in this disclosure, and S12 is the tool sensor position measurement step.

[0038] Then, in S13, the correction value Lp' in the length direction of the touch probe 30 is calculated using equation (5) from the detection position Zrt'' calculated in S11, the contact position Z3' acquired in S12, and the relative position dZ3 acquired in S3 and recorded in the recording unit 22, and recorded in the recording unit 22. S13 is the position measurement sensor length direction correction value calculation step in this disclosure. In the correction value measurement method for the position measurement sensor disclosed herein, steps S11 to S13 may be executed multiple times, provided that steps S1 to S3, which are pre-settings for measuring the longitudinal correction value of the touch probe 30, are executed once.

[0039] Lp' = Z3' - Zrt'' - dZ3 (5)

[0040] The correction value Lp' in the longitudinal direction of the touch probe 30, calculated as described above, is used to correct the measurement position when measuring the position of a workpiece. In the correction value measurement method for a position measurement sensor disclosed herein, a laser sensor 40 is used as the tool sensor, which includes a reference section 45 formed on the laser light-emitting section 41 and the laser light-receiving section 42 from the same material or a material having a similar coefficient of thermal expansion. Therefore, even if the temperature around the laser sensor 40 changes and the laser light-emitting section 41 undergoes thermal deformation, the relative position between the laser 43 and the reference section 45 is unlikely to change. Similarly, when a touch sensor 50 is used as the tool sensor, the touch sensor 50 includes a detection section 52 and a reference section 54 formed on the touch sensor body 51 from the same material or a material having a similar coefficient of thermal expansion. Therefore, even if the temperature around the touch sensor 50 changes and the touch sensor body 51 undergoes thermal deformation, the relative position between the detection section 52 and the reference section 54 is unlikely to change. Consequently, errors occurring in the calculation of the correction value in the longitudinal direction of the position measurement sensor can be minimized.

[0041] The configuration of the correction value measurement method and system for the position measurement sensor of a machine tool in this disclosure is not limited in any way to the embodiments described above, and can be modified as necessary without departing from the spirit of the invention. For example, the reference part does not need to be located on the upper surface of the tool sensor, as long as it is provided near the detection part and integrated with the tool sensor. Also, although the above embodiment and drawings emphasize the reference part, any predetermined part of the tool sensor excluding the detection part may be treated as the reference part. While the tool sensor and position measurement sensor were described using laser sensors, touch sensors, and touch probes as examples, other sensors may also be used. [Explanation of Symbols]

[0042] 2...Spindle, 3...Table, 8c...Z-axis position detector (translational axis position detector), 10...Reference tool, 21...NC control device (control device), 30...Touch probe (position measurement sensor), 40...Laser sensor (tool sensor), 43...Laser (detection unit), 45...Reference unit, 50...Touch sensor (tool sensor), 52...Detection unit, 54...Reference unit, M...Numerically controlled machine tool (machine tool).

Claims

1. A machine tool comprising a table capable of holding a workpiece, a spindle capable of rotating with a tool attached, a translation axis capable of relative motion of the spindle and the table with two or more translational degrees of freedom, and a tool sensor capable of measuring the position of the tool attached to the spindle, wherein the position of a workpiece held on the table can be measured by the position measuring sensor attached to the spindle, a method for measuring a correction value for the position measuring sensor of a machine tool, wherein the correction value for the longitudinal direction of the position measuring sensor is calculated, The tool sensor comprises a detection unit for detecting an object to be detected, and a reference unit which is provided near the detection unit and integrated with the tool sensor, and which serves as a position reference for the tool sensor. A tool sensor detection position measurement step involves mounting a reference tool of known length on the spindle, having the detection unit of the tool sensor detect the tip of the reference tool to obtain the tip position of the reference tool, and calculating the position of the detection unit of the tool sensor from the obtained tip position of the reference tool and the length of the reference tool. A position measurement sensor length measurement step involves obtaining a reference position using the reference tool mounted on the main spindle, then mounting the position measurement sensor on the main spindle, measuring the reference position using the position measurement sensor to obtain the position measurement sensor reference position, and calculating the length of the position measurement sensor from the obtained position measurement sensor reference position, the length of the reference tool, and the reference position. A relative position measurement step involves mounting the position measuring sensor on the main shaft, measuring the position of the reference part, and calculating the relative position of the reference part with respect to the position of the detection part from the measured position of the reference part, the position of the detection part calculated in the tool sensor detection position measurement step, and the length of the position measuring sensor calculated in the position measuring sensor length measurement step. A reference tool tip position measurement step involves mounting the reference tool onto the main spindle, bringing the tip of the reference tool into contact with the detection unit, and measuring the position of the tip of the reference tool. A tool sensor position measurement step involves mounting the position measurement sensor on the main spindle, measuring the position of the reference part, and obtaining the position of the tool sensor. A position measurement sensor length direction correction value calculation step calculates a correction value in the length direction of the position measurement sensor from the length of the reference tool, the relative position calculated in the relative position measurement step, the position of the tip of the reference tool measured in the reference tool tip position measurement step, and the position of the tool sensor acquired in the tool sensor position measurement step. A method for measuring the correction value of a position measurement sensor for a machine tool, characterized by performing the following:

2. The steps from the tool sensor detection position measurement step to the relative position measurement step are performed once. The method for measuring a correction value for a position measuring sensor of a machine tool according to claim 1, characterized in that the steps from the reference tool tip position measurement step to the position measuring sensor length direction correction value calculation step are performed multiple times.

3. The method for measuring a correction value for a position measuring sensor of a machine tool according to claim 1 or 2, characterized in that the detection unit and the reference unit are made of a material that does not cause any change in the relative position between the detection unit and the reference unit in the ambient temperature range observed during the machining by the machine tool.

4. A machine tool comprising a table capable of holding a workpiece, a spindle capable of rotating with a tool attached, a translation axis capable of relative motion of the spindle and the table with two or more translational degrees of freedom, a control device for controlling the table, the translation axis and the spindle, and a tool sensor capable of measuring the position of the tool attached to the spindle, wherein the position of a workpiece held on the table can be measured by the position measuring sensor attached to the spindle, wherein a correction value measurement system for the position measuring sensor of the machine tool calculates a correction value in the longitudinal direction of the position measuring sensor, The tool sensor comprises a detection unit for detecting an object to be detected, and a reference unit which is provided near the detection unit and integrated with the tool sensor, and which serves as a position reference for the tool sensor. A reference tool of known length, A tool sensor detection position measurement unit mounts the reference tool on the main spindle, operates the translation axis to detect the tip of the reference tool at the detection unit of the tool sensor to obtain the tip position of the reference tool, and calculates the position of the detection unit of the tool sensor from the obtained tip position of the reference tool and the length of the reference tool. A position measurement sensor length measuring unit mounts the reference tool on the main spindle, operates the translation axis to obtain a reference position, then mounts the position measuring sensor on the main spindle, operates the translation axis to measure the reference position using the position measuring sensor to obtain a position measuring sensor reference position, and calculates the length of the position measuring sensor from the length of the reference tool, the reference position, and the position measuring sensor reference position. A relative position measuring unit is provided that mounts the position measuring sensor on the main shaft, operates the translation shaft to measure the position of the reference part, and calculates the relative position of the reference part to the position of the detection part from the measured position of the reference part, the position of the detection part calculated by the tool sensor detection position measuring unit, and the length of the position measuring sensor calculated by the position measuring sensor length measuring unit. A reference tool tip position measuring unit is provided, which mounts the reference tool on the main spindle, operates the translation axis to bring the tip of the reference tool into contact with the detection unit, and measures the position of the tip of the reference tool. A tool sensor position measurement unit is provided, which mounts the position measurement sensor on the main spindle, operates the translation axis to measure the position of the reference part, and obtains the position of the tool sensor. A position measurement sensor length direction correction value calculation unit calculates a correction value in the length direction of the position measurement sensor from the length of the reference tool, the relative position calculated by the relative position measurement unit, the position of the tip of the reference tool measured by the reference tool tip position measurement unit, and the position of the tool sensor acquired by the tool sensor position measurement unit. A correction value measurement system for a machine tool's position measurement sensor, characterized by having the following features.

5. The correction value measurement system for a machine tool position measurement sensor according to claim 4, characterized in that the detection unit and the reference unit are made of a material that does not cause any change in the relative position between the detection unit and the reference unit in the ambient temperature range observed during the machining by the machine tool.

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