Lead measuring machine

Abstract

To accurately measure the lead of a screw shaft without stressing the measuring instrument or the screw shaft. [Solution] The lead measuring machine 100 includes a non-contact profile sensor 1 that irradiates a laser onto the screw groove and measures the cross-sectional shape of the screw groove as profile data, and a measurement processing unit 7 that measures the lead of the screw shaft 200 based on the measurement results of the non-contact profile sensor. The measurement processing unit 7 determines an approximate circle C1 based on the profile data of the reference screw groove cross section 21, determines an approximate circle C2 based on the profile data of the target screw groove cross section 22 located away from the reference screw groove cross section 21 in the axial direction of the screw shaft, and measures the lead of the screw shaft between the reference screw groove cross section 21 and the target screw groove cross section 22 based on the axial center position of the approximate circle C1 in the reference screw groove cross section 21 and the axial center position of the approximate circle C2 in the target screw groove cross section 22.

Description

Technical Field

[0001] The present invention relates to a lead measuring machine that measures the lead of a screw shaft by a non-contact method.

Background Art

[0002] As a measuring machine for measuring the groove shape of a screw shaft constituting a ball screw, for example, a measuring machine disclosed in Patent Document 1 is known. In this device, the screw shaft is rotated around its central axis with the touch probe in contact with the screw groove. The touch probe moves along the screw groove while in contact with it, and measures irregularities on the inner surface of the groove.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the measuring machine of Patent Document 1, since the touch probe moves while being dragged while in contact with the screw groove, non-uniform stress is likely to be applied to the touch probe during measurement. When non-uniform stress is applied to the touch probe, the touch probe is likely to deform and wear. Similarly, in this measuring machine, since the load due to contact with the touch probe is also applied to the screw groove during measurement, the screw groove may be damaged depending on the magnitude of the load.

[0005] Further, assume that the lead of a screw shaft is measured using a touch probe as disclosed in Patent Document 1. That is, assume that the screw shaft is rotated by the amount of lead while the touch probe is in contact with the screw groove. In this case, although the ball probe of the touch probe is pressed against the feed side surface of the screw groove, it is not pressed against the opposite side surface. Therefore, in such a measurement method, a difference in measurement accuracy is likely to occur between the feed side surface and the opposite side surface of the screw groove.

[0006] The present invention aims to accurately measure the lead of a screw shaft without stressing the measuring instrument or the screw shaft. [Means for solving the problem]

[0007] The lead measuring machine of the present invention uses a non-contact profile sensor to measure the shape of a reference thread groove cross-section, which is one of the cross-sections in a thread groove, and the shape of a target thread groove cross-section, which is a cross-section located in the axial direction of the thread axis from the reference thread groove cross-section. The lead measuring machine determines an approximate circle that follows the cross-sectional shape of each measured thread groove cross-section. The lead measuring machine measures the lead between each thread groove cross-section by calculating the distance between the centers of the approximate circles of each thread groove cross-section. [Effects of the Invention]

[0008] The lead measuring machine of the present invention measures the cross-sectional shape of the screw groove using a non-contact profile sensor and measures the lead from the measurement result. In other words, the lead measuring machine measures the lead without contacting the screw shaft. Therefore, no stress is applied to the measuring machine or the screw shaft. Furthermore, because the cross-sectional shape of the screw groove is measured using a non-contact profile sensor, there is no difference in measurement accuracy between one side of the screw groove (the first groove surface in this application) and the other side (the second groove surface in this application), as is the case when using a touch probe. In addition, the lead measuring machine obtains an approximate circle from the cross-sectional shape of the screw groove measured as data. This approximate circle is a circle that is approximately tangent to the first groove surface and the second groove surface in the screw groove cross-section. In other words, this approximate circle simulates the ball of the ball nut that is fitted into the screw groove. By obtaining such an approximate circle in both the reference screw groove cross-section and the screw groove cross-section to be measured, the lead between the reference screw groove cross-section and the screw groove cross-section to be measured can be measured with high accuracy. Therefore, the lead measuring device of the present invention can accurately measure the lead of a screw shaft without putting stress on the measuring device or the screw shaft. [Brief explanation of the drawing]

[0009] [Figure 1] This is a front view of the lead measuring machine. [Figure 2] This is a side view of the lead measuring machine. [Figure 3] This is a top view of the lead measuring machine. [Figure 4] This is a cross-sectional view obtained by cutting the screw shaft through a plane that includes its central axis and the Z-direction. [Figure 5] This is a schematic top view showing a screw shaft and a non-contact profile sensor. [Figure 6] This diagram schematically shows the profile data of the screw thread cross-section. [Figure 7] This is a side view showing the configuration near the linear scale in a lead measuring machine. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings.

[0011] Figure 1 is a front view of the lead measuring machine. The lead measuring machine 100 measures the lead and lead accuracy of the screw shaft 200. The lead is the actual axial movement when the screw shaft 200 rotates for any number of rotations. The screw shaft 200, together with a ball nut (not shown), constitutes a ball screw. The screw shaft 200 has a cylindrical shape and a helical screw groove on its surface. The lead measuring machine 100 moves the non-contact profile sensor 1 in the axial direction of the screw shaft 200 and sequentially measures the shape of the screw groove cross-sections aligned in the axial direction. Based on the measured shape of the screw groove cross-section, the lead measuring machine 100 determines an approximate circle that simulates the ball of the ball nut fitted into the screw groove cross-section. The lead measuring machine 100 determines the distance between at least two of the determined approximate circles and measures the lead and lead accuracy. In this specification, the axial direction of the screw shaft 200 is defined as the X direction, the vertical direction as the Z direction, and the direction perpendicular to the X and Z directions as the Y direction. The following describes each configuration in detail.

[0012] <Structure of a lead measuring machine> The lead measuring machine 100 comprises a stand 11 and a surface plate 12 mounted on the stand 11. The surface plate 12 is generally rectangular in shape. The surface plate 12 has its longitudinal direction in the X direction. The surface plate 12 is, for example, a granite surface plate. The stand 11 is, for example, a passive stand and supports the surface plate 12. A screw shaft 200 is placed on the surface plate 12. The surface plate 12 has a longitudinal length that is longer than the axial length of the screw shaft 200. Area curtain sensors 13 for detecting human approach may be provided at each end of the surface plate 12 in the X direction. The screw shaft 200 is placed on the surface plate 12 via at least one support member 14. The support member 14 is, for example, a V-block. One end of the screw shaft 200 may be in contact with a regulating member 15. The regulating member 15 is, for example, a stopper block. The restricting member 15 restricts the movement of the screw shaft 200 in the X direction (left direction in the figure).

[0013] The lead measuring machine 100 is equipped with a non-contact profile sensor 1 that measures the cross-sectional shape of a screw groove without contacting the screw shaft 200. The non-contact profile sensor 1 is a light section profile sensor that utilizes the light section method. In the light section method, a strip-shaped laser is irradiated onto the target. In the light section method, the entire shape of one screw groove cross-section can be measured at once. The non-contact profile sensor 1 is installed above the screw shaft 200. The non-contact profile sensor 1 includes a housing and a laser oscillating element, various lenses, an image sensor, etc., housed in the housing. The non-contact profile sensor 1 is configured to irradiate a strip-shaped laser toward the screw groove. The non-contact profile sensor 1 is configured to receive reflected light reflected from the screw groove.

[0014] The lead measuring machine 100 includes a measurement processing unit 7 that measures the lead of the screw shaft 200 based on the measurement results of a non-contact profile sensor 1. The measurement processing unit 7 is composed of a computer including a processor. The measurement processing unit 7 performs various processes by executing a computer program stored on a recording medium. The measurement processing unit 7 is connected to the non-contact profile sensor 1 by wire or wireless. The measurement processing unit 7 may be provided integrally with the lead measuring machine 100 or separately from the lead measuring machine 100.

[0015] Figure 2 is a side view of the lead measuring machine. The lead measuring machine 100 includes a rotating stage 2 that supports a non-contact profile sensor 1. The rotating stage 2 is located above the non-contact profile sensor 1. The rotating stage 2 is connected to the non-contact profile sensor 1 via a cylindrical support rod 16. The support rod 16 extends in the Z direction. The rotating stage 2 is capable of rotating the support rod 16 around its central axis (i.e., around an axis parallel to the Z direction). This allows the rotating stage 2 to rotate the non-contact profile sensor 1 around an axis parallel to the Z direction. The rotating stage 2 is capable of rotating the non-contact profile sensor 1 by any angle and then stopping it at that angle of rotation. The rotating stage 2 is not particularly limited, but it is preferable that it has a small control resolution for the rotation angle. The rotating stage 2 is attached to an arm 3.

[0016] Arm 3 extends in the Y direction. The front end of arm 3 is attached to the rotary stage 2. The rear end of arm 3 is attached to the Z-axis stage 4.

[0017] The Z-axis stage 4 is provided below the arm 3. The Z-axis stage 4 can move the arm 3 in the Z direction. That is, the Z-axis stage 4 can move the non-contact profile sensor 1 in the Z direction. The Z-axis stage 4 moves the non-contact profile sensor 1 in the Z direction according to the size of the screw shaft 200. The Z-axis stage 4 moves the non-contact profile sensor 1 to a predetermined position above the screw shaft 200. The predetermined position is appropriately set according to the size of the screw shaft 200. The Z-axis stage 4 is not particularly limited, but for example, it is a wedge type. The Z-axis stage 4 preferably has a small control resolution of the moving amount. The Z-axis stage 4 is attached to the moving mechanism 5.

[0018] The moving mechanism 5 is provided below the Z-axis stage 4. The moving mechanism 5 supports the Z-axis stage 4. The moving mechanism 5 is placed on the surface plate 12. The moving mechanism 5 can move the Z-axis stage 4 in the X direction. That is, the moving mechanism 5 can move the non-contact profile sensor 1 in the X direction. In this embodiment, the moving mechanism 5 is a linear motor. However, the moving mechanism 5 is not limited to this. The moving mechanism 5 may be a ball screw device or the like.

[0019] The moving mechanism 5 includes a table 51, a driving magnet plate 52, and two guide rails 53. The table 51 is attached to the Z-axis stage. The driving magnet plate 52 is provided below the table 51. The driving magnet plate 52 extends in the X direction. In the Y direction, guide rails 53 are provided on both sides of the driving magnet plate 52 respectively. Each guide rail 53 extends in the X direction. The guide rails 53 guide the table 51 to move in the X direction. The table 51 moves in the X direction by the magnetic action with the driving magnet plate 52 and the guide rails 53. A linear scale 6 is provided in front of the moving mechanism 5 (in the right direction in the figure).

[0020] The linear scale 6 is provided between the moving mechanism 5 and the non-contact profile sensor 1 in the Y direction. The linear scale 6 is attached to the table 51 via brackets. The linear scale 6 measures the position of the moving mechanism 5 in the X direction (axial direction of the screw shaft 200).

[0021] Thus, by means of the Z-axis stage 4 and the moving mechanism 5, the non-contact profile sensor 1 can be moved in the Z and X directions. Also, by means of the rotary stage 2, the non-contact profile sensor 1 can be rotated about an axis parallel to the Z direction. The Z-axis stage 4, the moving mechanism 5, and the rotary stage 2 are controlled by the operation control unit 17. The operation control unit 17 is composed of a computer including a processor. The operation control unit 17 executes various processes by executing a computer program stored in a recording medium. The operation control unit 17 is connected to the Z-axis stage 4, the moving mechanism 5, and the rotary stage 2 respectively by wireless or wired means. The operation control unit 17 may be provided integrally with the lead measuring machine 100, or may be provided separately from the lead measuring machine 100. The operation control unit 17 may be implemented on the same computer as the measurement processing unit 7, or may be implemented on a different computer. For reference, a top view of the lead measuring machine 100 is shown as FIG. 3.

[0022] Subsequently, the lead measurement and lead accuracy measurement (measurement of representative movement error and variation) of the screw shaft 200 by the lead measuring machine 100 having the above-described configuration will be described.

[0023] <Lead Measurement> Figure 4 is a cross-sectional view of a screw groove. The screw groove cross-section 21 in the figure is a plane that includes the central axis and Z direction of the screw shaft 200, inclined by a lead angle along the width direction of the screw groove, and shows the cross-sectional shape of the screw groove when the screw shaft 200 is cut. In this specification, the term "screw groove" refers to the screw groove within the effective length range of the screw groove. Within the effective length range, the cross-sectional shape of the screw groove is assumed to be substantially uniform. Hereinafter, the screw groove cross-section 21 will be referred to as the reference screw groove cross-section 21. The reference screw groove cross-section 21 is the screw groove cross-section located at one end within the effective length range of the screw groove. The reference screw groove cross-section 21 includes a first groove surface 211 and a second groove surface 212 provided on both sides of the groove bottom 213. The first groove surface 211 and the second groove surface 212 are each configured to be arc-shaped in a portion from the groove bottom 213 to the groove edges 214, 215. However, the arc center in the first groove surface 211 is different from the arc center in the second groove surface 212. That is, the shape of the reference screw groove cross-section 21 is a Gothic arc shape.

[0024] Figure 5 is a schematic top view showing the screw shaft and the non-contact profile sensor. First, the lead measuring machine 100 operates the moving mechanism 5 and the Z-axis stage 4 to move the non-contact profile sensor 1 above the position where the reference screw groove cross-section 21 is to be measured. Next, the lead measuring machine 100 operates the rotating stage 2 to rotate the non-contact profile sensor 1 so that the width direction of the strip-shaped laser LA irradiated by the non-contact profile sensor 1 is perpendicular to the extension direction (helical direction) of the screw groove when viewed from above. The lead measuring machine 100 rotates the non-contact profile sensor 1 so that, when viewed from above, the width direction of the strip-shaped laser LA is inclined by a lead angle D with respect to the axial direction of the screw shaft 200 (dotted line in the figure). More specifically, the position of the non-contact profile sensor 1 positioned so that the width direction of the strip-shaped laser LA is parallel to the axial direction of the screw shaft 200 is taken as the reference position. From this reference position, the rotation stage 2 rotates the non-contact profile sensor 1 by a lead angle D around an axis parallel to the Z direction (around the optical axis of the laser LA). As a result, in the view from the direction of laser irradiation (view from the optical axis direction), the width direction of the strip-shaped laser LA is tilted with respect to the axial direction of the screw shaft 200. Alternatively, the non-contact profile sensor 1 may be moved above the position for measuring the reference screw groove cross-section 21 while the width direction of the strip-shaped laser LA is tilted with respect to the axial direction of the screw shaft 200.

[0025] The non-contact profile sensor 1 irradiates a strip-shaped laser LA whose width direction is parallel to the width W direction of the reference screw groove cross-section 21. The non-contact profile sensor 1 irradiates the reference screw groove cross-section 21 with a laser having a width wider than the width W of the reference screw groove cross-section 21. The non-contact profile sensor 1 irradiates the laser with at least the entire width of the reference screw groove cross-section 21. The non-contact profile sensor 1 irradiates the laser with at least the entire width direction of the first groove surface 211 and the second groove surface 212 of the reference screw groove cross-section 21.

[0026] A laser irradiated onto the screw groove at the measurement position of the reference screw groove cross-section 21 is diffusely reflected from the surface of the reference screw groove cross-section 21 (first groove surface 211 and second groove surface 212, etc.). The non-contact profile sensor 1 receives the reflected light from the reference screw groove cross-section 21. The non-contact profile sensor 1 includes an image sensor that converts the received reflected light into an electrical signal. The non-contact profile sensor 1 measures the shape of the reference screw groove cross-section 21 as profile data using the image sensor. Profile data is data discretized from the cross-sectional shape of the screw groove. More specifically, the profile data is composed of a screw groove cross-section obtained by cutting the screw groove with a plane including the X and Z directions, and dividing it into multiple meshes. Preferably, each of the multiple meshes has the same shape and size. Preferably, each of the multiple meshes is a rectangular grid or an orthogonal grid. Some or all of the multiple meshes contain information on the physical quantity (e.g., brightness) of the laser reflected from the screw groove. This physical quantity of the laser indicates the position of the screw groove cross-section in that mesh. The non-contact profile sensor 1 acquires multiple mesh data (multiple point data, each indicating the position of the screw groove cross-section) discretized from the reflected light of the irradiated laser. The non-contact profile sensor 1 measures the shape of the screw groove cross-section at once with a single laser irradiation. The non-contact profile sensor 1 measures the shape of one screw groove cross-section at the same position. The non-contact profile sensor 1 transmits the profile data of the measured reference screw groove cross-section 21 to the measurement processing unit 7.

[0027] Figure 6 is a schematic diagram showing the profile data of the screw groove. The measurement processing unit 7 sets the first measurement area A1 and the second measurement area A2 based on the design value of the screw shaft 200. In this embodiment, the first measurement area A1 and the second measurement area A2 are set in advance. However, the first measurement area A1 and the second measurement area A2 do not have to be set in advance and may be set at an appropriate timing. The first measurement area A1 is set within a predetermined range of the first groove surface 211. The first measurement area A1 is set in at least a part of the first groove surface 211. The first measurement area A1 is set in at least a part between the groove bottom 213 and the groove edge 214. The first measurement area A1 is set in at least a part of the part of the first groove surface 211 that has an arc shape. The first measurement area A1 is set to include a plurality of point data which are profile data. The second measurement area A2 is set in the same way as the first measurement area A1. However, the second measurement area A2 is set on the second groove surface 212. The second measurement area A2 may be provided symmetrically with respect to the first measurement area A1, with a line parallel to the Z-axis passing through the groove bottom 213 in between.

[0028] The measurement processing unit 7 determines the approximate circle C1 based on the profile data included in the first measurement area A1 and the profile data included in the second measurement area A2. The measurement processing unit 7 determines the approximate circle C1 based on the position information of each of the multiple point data that constitute the profile data. The position information is information regarding the position in the X direction and the Z direction of the multiple point data. The measurement processing unit 7 determines the approximate circle C1 using the least squares method. That is, the measurement processing unit 7 determines the approximate circle C1 in such a way that the error with each of the multiple point data included in the first measurement area A1 and the second measurement area A2 is minimized. However, the calculation method for determining the approximate circle C1 is not particularly limited. For example, the measurement processing unit 7 may select any multiple point data from the multiple point data included in the first measurement area A1 and the second measurement area A2, and use the circumcircle or incircle of the selected point data as the approximate circle. In addition, the measurement processing unit 7 may determine the approximate circle using any known calculation method.

[0029] The measurement processing unit 7 determines the center position of the obtained approximate circle C1. That is, the measurement processing unit 7 determines the position information in the X direction (the axial direction of the screw axis 200) for the center position. The measurement processing unit 7 may also determine the position information in the Z direction for the center position.

[0030] In this embodiment, the non-contact profile sensor 1 measures the shape of the reference screw groove cross-section 21 with the width direction of the strip-shaped laser LA tilted with respect to the axial direction of the screw shaft 200. In this case, the X-direction position information of the center of the approximate circle C1 obtained from the profile data is a value in coordinates tilted with respect to the axial direction of the screw shaft 200. That is, the X-direction position information of the center of the obtained approximate circle is strictly different from the value in coordinates along the axial direction of the screw shaft 200.

[0031] Therefore, the measurement processing unit 7 corrects the position information of the center of the approximate circle in the X direction. The measurement processing unit 7 uses the cos component of the obtained position information of the center of the approximate circle in the X direction as the position information of the center of the approximate circle in the X direction. As will be described later, the measurement processing unit 7 uses this corrected position information in the X direction to measure the lead between the reference screw groove cross section 21 and the screw groove cross section 22 to be measured. With this configuration, even if a non-contact profile sensor 1 using the light section method is used, the lead of the screw shaft 200 can be measured with high accuracy. However, the measurement processing unit 7 does not need to perform the above correction process when the lead angle is small or when high measurement accuracy is not required.

[0032] After measuring the shape of the reference screw groove cross-section 21, the motion control unit 17 activates the moving mechanism 5 to move the non-contact profile sensor 1 in the X direction. At this time, the motion control unit 17 moves the non-contact profile sensor 1 in the X direction by one lead, which is the design value of the screw shaft 200. One lead, as the design value, corresponds to the design value (reference movement amount) of the axial movement when the screw shaft rotates once. As a result, the non-contact profile sensor 1 is positioned above the screw groove cross-section adjacent to the reference screw groove cross-section 21 when viewed from above. At this position, the non-contact profile sensor 1 measures the shape of the screw groove cross-section (hereinafter referred to as the screw groove cross-section to be measured 22) in the same way as the reference screw groove cross-section 21. The screw groove cross-section to be measured 22 is located at a position away from the reference screw groove cross-section 21 along the X direction.

[0033] After the non-contact profile sensor 1 moves to the position to measure the target screw groove cross-section 22, the lead measuring machine 100 determines an approximate circle C2 for the target screw groove cross-section 22, similar to the reference screw groove cross-section 21. That is, the non-contact profile sensor 1 irradiates the screw groove with a laser at the position where the target screw groove cross-section 22 is to be measured. The non-contact profile sensor 1 receives the reflected light and measures the cross-sectional shape of the screw groove (shape of the target screw groove cross-section 22) as profile data. The target screw groove cross-section 22 has substantially the same cross-sectional shape as the reference screw groove cross-section 21. The measurement processing unit 7 determines an approximate circle C2 based on the profile data of the target screw groove cross-section 22. At this time, it is desirable that the measurement areas A1 and A2 in the target screw groove cross-section 22 be set to the same positions as the measurement areas set for the reference screw groove cross-section 21.

[0034] The measurement processing unit 7 determines the center position of the obtained approximate circle C2. That is, the measurement processing unit 7 obtains position information in the X direction (axis direction of the screw shaft 200) for the center position. Also, the measurement processing unit 7 corrects the obtained position information in the X direction as described above. The measurement processing unit 7 calculates the difference between the position information in the X direction of the center of the corrected approximate circle C2 and the position information in the X direction of the center of the corrected approximate circle C1. As a result, the measurement processing unit 7 measures the lead L1 of the screw shaft 200 between the reference screw groove cross section 21 and the screw groove cross section 22 to be measured.

[0035] Subsequently, the lead measuring machine 100 moves the non-contact profile sensor 1 in the X direction by one lead, which is the design value of the screw shaft 200. That is, in a top view, the lead measuring machine 100 moves the non-contact profile sensor 1 above the screw groove section adjacent to the screw groove section 22 to be measured (the second screw groove section 23 to be measured). The lead measuring machine 100 performs the same measurement on the second screw groove section 23 to be measured as on the screw groove sections 21 and 22 described above, and measures the lead between the reference screw groove section 21 and the second screw groove section 23 to be measured. The lead measuring machine 100 performs such measurements sequentially for each screw groove section while moving in the X direction. The lead measuring machine 100 ends the lead measurement when it measures the lead between the last screw groove section to be measured, i.e., the screw groove section located at the end opposite to the reference screw groove section 21 in the effective length range of the screw groove, and the reference screw groove section 21. In this way, the lead between each of the multiple screw groove sections to be measured and the reference screw groove section 21 is measured.

[0036] <Lead accuracy measurement> It is assumed that the actual lead L1 between the measured screw groove cross-section 22 and the reference screw groove cross-section 21 perfectly matches the design value. In this case, the position of the non-contact profile sensor 1 in the X direction relative to the measured screw groove cross-section 22 is substantially the same as the position of the non-contact profile sensor 1 in the X direction relative to the reference screw groove cross-section 21 when the profile data was measured. However, the actual lead L1 does not often perfectly match the design value. Therefore, the measurement processing unit 7 uses the measured lead to determine the lead accuracy of the screw shaft 200.

[0037] Specifically, lead accuracy measurement conforms to JIS B 1192 or ISO 3408. The measurement processing unit 7 determines the representative displacement error between the reference screw groove cross-section 21 and the screw groove cross-section to be measured, based on the measured lead of the screw groove and the reference displacement of the screw shaft 200. In this embodiment, the lead was measured for all of the multiple screw groove cross-sections to be measured. Therefore, the measurement processing unit determines the representative displacement from the measured lead for each screw groove cross-section to be measured, and determines the representative displacement error between the reference screw groove cross-section 21 and the last screw groove cross-section to be measured (the screw groove cross-section located at the end opposite to the reference screw groove cross-section within the effective length range of the screw groove) based on the determined representative displacement and the reference displacement.

[0038] Furthermore, the measurement processing unit 7 determines the variation between the reference screw groove cross-section 21 and the screw groove cross-section 22 to be measured, based on the measured lead of the screw shaft 200. The measurement processing unit determines the variation in the range from the reference screw groove cross-section 21 to the last screw groove cross-section to be measured, from the lead measured for each screw groove cross-section to be measured, i.e., the actual amount of movement.

[0039] As explained above, the lead measuring machine 100 measures the lead without contacting the screw shaft 200 using a non-contact profile sensor 1. Therefore, no stress is applied to the measuring machine or the screw shaft 200. Furthermore, since the cross-sectional shape of the screw groove is measured using the non-contact profile sensor 1, there is no difference in measurement accuracy between one side of the screw groove (the first groove surface 211 in this application) and the other side (the second groove surface 212 in this application), as is the case when using a touch probe. In addition, the non-contact profile sensor 1 measures the cross-sectional shape of the screw groove using the light section method. Therefore, even though it is a non-contact method, it can measure more efficiently compared to measuring the cross-sectional shape of the screw groove point by point.

[0040] Furthermore, the lead measuring machine 100 determines approximate circles C1 and C2 from the cross-sectional shapes of the reference screw groove cross-section 21 and the screw groove cross-section 22 to be measured, respectively, which are measured as data. These approximate circles C1 and C2 are circles that approximately tangent to the first groove surface and the second groove surface of the reference screw groove cross-section 21 and the screw groove cross-section 22 to be measured, respectively. In other words, these approximate circles C1 and C2 mimic the balls of the ball nuts that are fitted into the reference screw groove cross-section 21 and the screw groove cross-section 22 to be measured, respectively. By performing lead measurement using these approximate circles C1 and C2, the lead between the reference screw groove cross-section 21 and the screw groove cross-section 22 to be measured can be measured with high accuracy. Therefore, with the lead measuring machine 100, the lead of the screw shaft 200 can be measured with high accuracy without putting stress on the measuring machine or the screw shaft 200.

[0041] <Variation> As described above, in the lead measuring machine 100, the non-contact profile sensor 1 moves from the reference screw groove cross section 21 to the screw groove cross section 22 to be measured, by the design value of the lead in that distance. Then, the accuracy of the lead is measured by comparing this design value with the measured lead. In lead accuracy measurement, the accuracy of the non-contact profile sensor 1 moving by the design value of the lead is important. Therefore, in order to improve the accuracy of lead accuracy measurement, the lead measuring machine 100 may have the following configuration.

[0042] Figure 7 is a side view showing the configuration near the linear scale in a lead measuring machine. The lead measuring machine 100 includes a linear scale 6 and a scale holder 8. The linear scale 6 is not particularly limited. The linear scale 6 may be, for example, an optical scale, a magnetic scale, etc. The linear scale 6 may utilize, for example, polarization or light interference. The linear scale 6 includes a scale 61 and a detection head 62.

[0043] The scale 61 is roughly plate-shaped. The scale 61 extends in the X direction. The X direction is the longitudinal direction of the scale 61. The scale 61 is provided between the non-contact profile sensor 1 and the moving mechanism 5 in the Y direction. The scale 61 is made of a different material than the screw shaft 200. The scale 61 has a different coefficient of thermal expansion than the screw shaft 200. For example, the scale 61 has a smaller coefficient of thermal expansion than the screw shaft 200.

[0044] The detection head 62 is slidably mounted on the scale 61. The detection head 62 is also mounted on the table 51 of the moving mechanism 5 via a bracket 63. The detection head 62 moves together with the table 51. The detection head 62 detects the position of the table 51 in the X direction. That is, the detection head 62 detects the position of the non-contact profile sensor 1 in the X direction.

[0045] The scale holder 8 supports the scale 61. The scale holder 8 is located below the scale 61. The scale holder 8 has a roughly rectangular parallelepiped shape. The scale holder 8 extends in the X direction. The X direction is the longitudinal direction of the scale holder 8. The scale holder 8 is located between the non-contact profile sensor 1 and the moving mechanism 5 in the Y direction.

[0046] The scale holder 8 is made of the same material as the screw shaft 200. The scale holder 8 has the same coefficient of thermal expansion as the screw shaft 200. The scale holder 8 is made of a different material than the scale 61. The scale holder 8 has a different coefficient of thermal expansion than the scale 61. The scale holder 8 has a larger coefficient of thermal expansion than the scale 61.

[0047] The scale holder 8 includes a recess 81 provided at its upper end. The recess 81 is located on the upper surface of the scale holder 8. The recess 81 is located in the center of the scale holder 8 in the Y direction. The recess 81 extends in the X direction. The lower end of the scale 61 is inserted into the recess 81. The recess 81 is longer than the scale 61 in the X direction. That is, the lower end of the scale 61 is inserted into the recess 81 over its entire length.

[0048] The scale holder 8 and the scale 61 are fixed together by fixing members 9. Although one fixing member 9 is shown in the figure, multiple fixing members 9 are provided. Multiple fixing members 9 are arranged in a line in the X direction. Multiple fixing members 9 are, for example, bolts. Multiple fixing members 9 are inserted from the front or rear of the scale holder 8. The tips of the multiple fixing members 9 contact the scale 61. Multiple fixing members 9 apply force to the scale 61 in the Y direction. Multiple fixing members 9 press the scale 61 against the scale holder 8 (recess 81). Multiple fixing members 9 fix the scale 61 and the scale holder 8 so that the scale 61 follows the thermal expansion of the scale holder 8 (i.e., the thermal expansion of the screw shaft 200). Multiple fixing members 9 fix the scale 61 so that it is forced to conform to the thermal expansion of the scale holder 8.

[0049] The lower end of the scale holder 8 rests on the base plate 12. The scale holder 8 is fixed to the base plate 12. One end of the scale holder 8 in the X direction is fixed to the base plate 12. The other end of the scale holder 8 is a free end. The other end of the scale holder 8 is not fixed to the base plate 12. The other end of the scale holder 8 is made thermally expandable in the X direction. That is, the scale holder 8 is fixed to the base plate 12 so as to be thermally expandable in accordance with the thermal expansion of the screw shaft 200. The method of fixing the scale holder 8 to the base plate 12 is not particularly limited. The scale holder 8 and the base plate 12 are fixed together, for example, with bolts.

[0050] With this configuration, even if the screw shaft 200 expands axially (in the X direction), the scale holder 8, which has the same coefficient of thermal expansion as the screw shaft 200, will expand in the X direction in the same way as the screw shaft 200. Generally, the scale 61 has a different coefficient of thermal expansion than the screw shaft 200. However, in the lead measuring machine 100, the scale 61 is fixed so that it can expand thermally in accordance with the scale holder 8. The scale 61 is configured to forcibly follow the thermal expansion of the scale holder 8 and the screw shaft 200. Even if the screw shaft 200 expands thermally, the scale 61 will also expand thermally in the same way as the screw shaft 200. Therefore, the measurement error of the lead due to the difference in the coefficients of thermal expansion between the screw shaft 200 and the scale 61 is reduced. This configuration is particularly effective when the screw shaft 200 is long, i.e., for lead measuring machines with a long lead in the X direction.

[0051] In addition, the lead measuring machine 100 may also include a temperature adjustment member 10 for adjusting the temperature of the scale holder 8. The temperature adjustment member 10 includes a flow path 101 for circulating a temperature adjustment liquid and a circulation pump (not shown) connected to the flow path. The flow path 101 is composed of, for example, a pipe. The flow path 101 is provided so as to sandwich the scale holder 8. The flow path 101 is provided over almost the entire area of ​​the scale holder 8 in the X direction. The flow path 101 is provided at least in the portion of the scale holder 8 where the scale 61 extends in the X direction. The flow path 101 is provided so as to be in contact with the scale holder 8. The flow path 101 is provided so as to be able to exchange heat between the scale holder 8 and the temperature adjustment liquid. With this configuration, the temperature distribution of the scale 61 in the X direction becomes uniform. However, in the lead measuring machine 100, an error may occur between the position of the non-contact profile sensor 1 and the position of the linear scale 6 in the X direction due to the influence of changes in the posture of the arm 3, etc. Therefore, the lead measuring machine 100 may perform error correction processing before lead measurement (for example, when the lead measuring machine 100 is started up). In such cases, it is desirable that the temperature distribution of the scale 61 in the X direction be uniform. Accordingly, the lead measuring machine 100 equipped with the temperature adjustment member 10 can suppress the influence of errors between the position of the non-contact profile sensor 1 and the position of the linear scale 6. As a result, highly accurate lead measurement becomes possible over the entire longitudinal direction of the screw shaft 200. In addition, the lead measuring machine 100 may have the following configurations.

[0052] The lead measuring machine 100 of this embodiment has been described above. The embodiment described above is merely an example. The present invention is not to be interpreted in any way as being limited by the embodiment described above.

[0053] For example, the above description described a case in which the cross-sectional shape of a screw groove is measured by a non-contact profile sensor 1 in a position where the width direction of the strip-shaped laser is tilted by a lead angle from the axial direction of the screw shaft 200. However, the position in which the non-contact profile sensor 1 measures the cross-sectional shape of the screw groove is not limited to this. The non-contact profile sensor 1 may also measure the cross-sectional shape of the screw groove in a position in which the width direction of the strip-shaped laser is parallel to the axial direction of the screw shaft 200.

[0054] For example, the above description described a case where the non-contact profile sensor 1 is a sensor that utilizes the light section method. However, the non-contact profile sensor 1 may be a sensor that does not utilize the light section method. The non-contact profile sensor 1 may be a sensor that emits a laser beam. The non-contact profile sensor 1 may be a sensor that utilizes ultrasound, electromagnetic waves, etc. In short, the non-contact profile sensor 1 only needs to be able to measure the shape of an object without contact.

[0055] For example, the above explanation described a case where the measurement processing unit 7 measures not only the lead but also the accuracy of the lead. However, the measurement processing unit 7 does not necessarily have to measure the accuracy of the lead.

[0056] For example, the above description described a case where the screw groove cross-section located at one end of the effective length range of the screw groove is designated as the reference screw groove cross-section 21. However, the reference screw groove cross-section 21 is not limited to this. The reference screw groove cross-section 21 may be a screw groove cross-section at any position within the effective length range of the screw groove. Also, the above description described a case where the screw groove adjacent to the reference screw groove cross-section 21 is designated as the screw groove cross-section to be measured 22. However, the screw groove cross-section to be measured 22 does not have to be located adjacent to the reference screw groove cross-section 21. The screw groove cross-section to be measured 22 may be a screw groove cross-section located in the X direction away from the reference screw groove cross-section 21, and may be a screw groove cross-section at any position within the effective length range of the screw groove. Furthermore, the above description described a case where the non-contact profile sensor measures the shape of all of multiple screw groove cross-sections. However, the non-contact profile sensor 1 does not have to measure the shape of all screw groove cross-sections. The non-contact profile sensor 1 may measure the shape of at least two or more of the multiple screw groove cross-sections.

[0057] The above explanation described the case where the cross-sectional shape of the screw groove is a Gothic arc shape. However, the cross-sectional shape of the screw groove does not have to be a Gothic arc shape. The cross-sectional shape of the screw groove may also be a circular arc shape. In short, the cross-sectional shape of the screw groove only needs to have a circular arc shape in at least part of it.

[0058] The above description described the case where the measurement processing unit 7 sets two measurement ranges, a first measurement range A1 and a second measurement range A2. However, the measurement processing unit 7 may set three or more measurement ranges. The measurement processing unit 7 may also set only one measurement range.

[0059] The above explanation described the case where the thermal expansion coefficient of the scale holder 8 is greater than that of the scale. However, the thermal expansion coefficient of the scale holder 8 may be less than or equal to that of the scale.

[0060] The above description described the case where the motion control unit 17 controls all of the Z-axis stage 4, the moving mechanism 5, and the rotating stage 2. However, the motion control unit 17 may control at least one of the Z-axis stage 4, the moving mechanism 5, and the rotating stage 2. Also, if the non-contact profile sensor 1 is not moved automatically, the lead measuring machine 100 does not need to have a motion control unit 17. [Explanation of Symbols]

[0061] 100: Lead measuring machine 1: Non-contact profile sensor 2: Rotating Stage 3: Arm 4: Z-axis stage 5: Movement mechanism 51: Table 52: Drive magnet plate 53: Guide rail 6: Linear Scale 61: Scale 62: Detection head 63: Bracket 7: Measurement Processing Unit 8: Scale holder 81: Recess 9: Fixing member 10: Temperature control component 11: Stand 12: Surface plate 13: Area Curtain Sensor 14: Support member 15: Regulating member 16: Support rod 17: Operation Control Unit 21: Reference thread groove cross-section 22: Cross-section of the screw groove to be measured 23: Second measurement target: cross-section of the screw groove 101: Flow channel 200: Screw shaft 211: First groove surface 212: Second groove surface 213: Groove bottom 214,215: Groove edge A1: First measurement area A2: 2nd measurement area C1: Approximate circle C2: Approximate circle D: Lead angle L1: Lead LA: Laser

Claims

1. A lead measuring machine that measures the lead in a screw shaft having a helical screw groove, which constitutes a ball screw, A non-contact profile sensor that irradiates the screw groove with a laser and measures the cross-sectional shape of the screw groove as profile data, The system includes a measurement processing unit that measures the lead of the screw shaft based on the measurement results of the non-contact profile sensor, The cross-section of the screw groove includes a first groove surface and a second groove surface provided on both sides of the groove bottom, The measurement processing unit is An approximate circle is determined based on the profile data in a first measurement area including at least a portion of the first groove surface and a second measurement area including at least a portion of the second groove surface of a reference screw groove cross-section, which is one of the cross-sections of the screw groove measured by the non-contact profile sensor. An approximate circle is determined based on the profile data in a first measurement area that includes at least a portion of the first groove surface and a second measurement area that includes at least a portion of the second groove surface in the measurement target screw groove cross-section located in the axial direction of the screw shaft from the reference screw groove cross-section. A lead measuring machine that measures the lead of the screw shaft between the reference screw groove cross-section and the screw groove cross-section to be measured, based on the axial center position of the approximate circle in the reference screw groove cross-section and the axial center position of the approximate circle in the screw groove cross-section to be measured.

2. A lead measuring machine according to claim 1, The screw groove cross-section to be measured is located adjacent to the reference screw groove cross-section in the axial direction, The measurement processing unit is a lead measuring machine that measures the lead of the screw shaft between the reference screw groove cross section and the screw groove cross section to be measured.

3. A lead measuring machine according to claim 1, The measurement processing unit is Based on the measured lead of the screw groove and the reference displacement of the screw shaft, the representative displacement error between the reference screw groove cross-section and the measured screw groove cross-section, and / or A lead measuring machine that determines the variation between the reference screw groove cross-section and the screw groove cross-section to be measured, based on the measured lead of the screw shaft.

4. A lead measuring machine according to claim 1, The non-contact profile sensor is a light-section type profile sensor that irradiates a strip-shaped laser onto the screw groove, The aforementioned lead measuring device further, A lead measuring machine comprising a rotating stage that supports the non-contact profile sensor and rotates around the optical axis of the laser.

5. A lead measuring machine according to claim 4, The rotating stage rotates the non-contact profile sensor from a reference position where the width direction of the laser is parallel to the axial direction of the screw shaft, such that, in view of the optical axis direction of the laser, the width direction of the strip-shaped laser intersects with the axial direction of the screw shaft. The measurement processing unit is a lead measuring machine that measures the lead of the screw shaft between the reference screw groove cross section, which has been corrected based on the rotation angle from the reference position, and the screw groove cross section to be measured.

6. A lead measuring machine according to claim 1, The aforementioned lead measuring device further, A moving mechanism for moving the non-contact profile sensor in the axial direction, The system comprises a motion control unit that controls the moving mechanism and the non-contact profile sensor, The aforementioned operation control unit, The movement mechanism is controlled to move the non-contact profile sensor from the position where the cross-sectional shape of the reference screw groove cross-section is measured by a design value of the lead between the reference screw groove cross-section and the screw groove cross-section to be measured. A lead measuring machine that controls the non-contact profile sensor to measure the cross-sectional shape of the screw groove cross-section to be measured after the non-contact profile sensor has moved by the design value.

7. A lead measuring machine according to claim 1, The aforementioned lead measuring device further, A moving mechanism for moving the non-contact profile sensor in the axial direction, A linear scale that extends in the axial direction and measures the axial position of the moving mechanism, and has a different coefficient of thermal expansion than the screw shaft, A scale holder that extends in the axial direction and supports the linear scale, and has the same coefficient of thermal expansion as the screw shaft, The scale holder is supported by a surface plate, The scale holder is fixed to the surface plate so as to be able to expand in the axial direction in accordance with the thermal expansion of the screw shaft. A lead measuring machine wherein the linear scale is fixed to the scale holder so as to expand in accordance with the thermal expansion of the screw shaft, together with the scale holder.

8. A lead measuring machine according to claim 7, The aforementioned lead measuring device further, A lead measuring machine comprising a temperature adjustment member that extends in the axial direction, contacts the scale holder, and circulates a temperature adjustment liquid inside to adjust the temperature of the scale holder.

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