Ball screw effective diameter measurement system and processing device including said system

Abstract

To precisely measure an effective diameter of a ball screw without receiving an effect or else due to flexure and swing-prevention of the ball screw even when measuring an effective diameter of a relatively long-size ball screw and to correct and machine the ball screw into desirable dimensions.SOLUTION: An effective diameter measuring system of a ball screw which measures an effective diameter of a screw groove machined onto a ball screw shaft as a machining object includes a first process of measuring and evaluating an outer diameter of the ball screw shaft, and a second process of measuring and evaluating a groove bottom of the screw groove. Therein, a difference between evaluations equivalent to the outer diameter and the groove bottom concerning position corresponding in a longitudinal direction of the ball screw is calculated by dividing the difference into the first process and the second process, thereby, the system of evaluating the effective diameter of the ball screw is provided. Correction machining is practiced by using evaluation of the system, and signs and sizes of correction are automatically adjusted by using changes before and after the correction machining.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a system for measuring the effective diameter of a screw shaft that constitutes a ball screw and a processing device including said system, and in particular to a system that automatically measures and evaluates the longitudinal distribution of the effective diameter of a ball screw shaft during processing at a site where ball screw shafts are produced using a screw grinding machine or the like, and performs correction processing. [Background technology]

[0002] A ball screw is a machine element used in industrial machines, robots, etc., and includes a screw shaft having a screw groove on its outer circumferential surface, a nut having a screw groove on its inner circumferential surface, and a number of balls (usually steel balls) accommodated in a rolling path consisting of the screw groove of the screw shaft and the screw groove of the nut, and converts rotational motion into linear motion (or converts linear motion into rotational motion) with high power transmission efficiency and positional accuracy. That is, a ball screw is composed of a screw shaft having a helical ball rolling groove formed with a predetermined lead on its outer circumferential surface, and a nut member having a helical ball rolling groove facing the ball rolling groove on the screw shaft side on its inner circumferential surface, which is screwed onto the screw shaft via balls, and is configured so that the nut member moves in the axial direction of the screw shaft according to the rotation of the screw shaft. Such a ball screw is used, for example, to move the feed table of a machine tool in sub-micrometer units, but in order to ensure the feed accuracy, it is necessary to measure the effective diameter of the ball screw shaft, and as a measurement method for this purpose, a method of measuring the effective diameter by contacting a touch probe with the ball screw groove has been conventionally known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 2-135804 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, various systems have been proposed as ball screw effective diameter measurement systems, typically evaluating the change in the ball screw effective diameter in the longitudinal direction of the workpiece. This method takes the form of a radius method in the classification of diameter measurement methods. This method is effective for short measurement objects, but when measuring long objects, especially on a processing machine, it is difficult to evaluate them on the order of micrometers. In other words, there is a problem that the bending of the object cannot be ignored, and depending on the configuration direction of the device, deformation due to gravity cannot be ignored. In addition, when the measurement system is integrated with the processing machine, the workpiece is held down by something called a vibration rest to suppress the vibration of the workpiece to be measured. This suppresses the vibration at the holding position when the workpiece is rotated, but there is a drawback in that it increases the bending. FIG. 1 is a diagram for explaining the problems of the conventional measurement method (radius method) for the effective diameter of a ball screw. (A) shows the case where a slightly thick part of a workpiece 10 is measured with a stylus 12, and (B) shows the case where the workpiece 10 is supported by a steady rest 14 at a certain point in the longitudinal direction and the forward movement of the workpiece 10 due to the steady rest 14 is measured with the stylus 12. For example, when trying to evaluate the diameter in the longitudinal direction, as shown in FIG. 1, it is impossible to resolve whether the diameter has increased locally or whether the sensor sensed an increase in diameter even though the diameter has not increased due to bending (it is assumed in FIG. 1 that the steady rest 14 pushed). On the other hand, there are machining systems that can produce cylindricity on the order of several micrometers on a cylindrical grinding machine for the outer diameter of a cylindrical workpiece, and there are also systems that evaluate the outer diameter on that order, so it is easier to obtain a device to manage the cylindricity of the outer diameter.

[0005] The present invention has been made in view of the above circumstances, and its object is to provide a technique for solving the problems associated with the radius method, for accurately measuring the effective diameter of a comparatively long ball screw without being affected by bending of the ball screw or by a vibration prevention device, and for correcting the measurement to the desired dimension, even when the effective diameter of the ball screw is being measured. [Means for solving the problem]

[0006] In order to achieve the above object of measuring the effective diameter of a ball screw, the present inventors have conducted extensive research and have found that: The method is divided into a first step of measuring the outer periphery of a portion of the long ball screw shaft that does not have a groove along the longitudinal direction and calculating the distribution of diameter variation along the longitudinal direction at the measured outer periphery, and a second step of measuring the diameter of the groove bottom of the screw groove along the longitudinal direction and calculating the distribution of diameter variation along the longitudinal direction at the measured groove bottom, and by calculating the difference between the distribution of diameter variation between the outer periphery and the groove bottom at corresponding positions along the longitudinal direction of the ball screw shaft, the longitudinal distribution of the effective diameter of the ball screw is accurately calculated. It was found that it is possible. Furthermore, by using the calculation results of the longitudinal distribution of the effective diameter of the ball screw as described above, it is possible to perform correction processing and machine a ball screw with a desired effective diameter distribution on the order of several micrometers. When performing correction processing, if the magnitude and sign of the correction coefficient are incorrect, the desired value will not be converged even if the correction processing is repeated. Therefore, a mechanism that detects convergence and divergence and automatically adjusts the correction coefficient is added to ensure stable convergence of the correction processing. This coefficient error is typically caused by the direction in which the correction is applied, confusion between values ​​treated as diameters and values ​​treated as radiuses, and a mistake in the number of digits.

[0007] That is, the correction processing system for the longitudinal distribution of the effective diameter of a ball screw according to the first aspect of the present invention is a ball screw shaft that is a long ball screw shaft and can be processed so that the effective diameter varies in the longitudinal direction of the ball screw shaft due to the influence of bending and vibration prevention, and is a ball screw shaft that is processed so that the effective diameter varies in the longitudinal direction of the ball screw shaft. Calculate a first step of measuring an outer periphery of a portion of the long ball screw shaft that does not have a groove along the longitudinal direction and calculating a distribution of diameter variation at the measured outer periphery along the longitudinal direction, and a second step of measuring a diameter at a groove bottom of the thread groove along the longitudinal direction and calculating a distribution of diameter variation at the measured groove bottom along the longitudinal direction, the first step and the second step being separated to calculate a difference in distribution of diameter variation between the outer periphery and the groove bottom at corresponding positions in the longitudinal direction of the ball screw shaft, thereby calculating a longitudinal distribution of the effective diameter of the ball screw; M Using the calculated difference in distribution of diameter fluctuations between the outer periphery and the groove bottom, the difference in distribution of diameter fluctuations between the outer periphery and the groove bottom in the longitudinal direction is eliminated. The amount of cutting into the ball screw shaft is adjusted according to the position in the longitudinal direction of the ball screw shaft. Execute compensation processing Suruko It is characterized by:

[0008] Also, In the correction processing system, the magnitude of the increase / decrease in the amount of cutting is expressed as a coefficient, and the direction of the increase / decrease in the amount of cutting is expressed as a sign, so that the sign and magnitude of the increase / decrease in the correction processing can be automatically adjusted, or the operator can be prompted to make the adjustment, using the change in the difference in distribution of diameter fluctuations of the outer periphery and the groove bottom before and after the correction processing. Effect of the Invention

[0010] According to the present invention, even when measuring the effective diameter of a relatively long ball screw, it is possible to accurately measure the effective diameter of the ball screw without being affected by bending or anti-vibration, and further, a technology can be provided that allows the correction processing to converge stably without making mistakes in the magnitude and sign of the correction coefficient. [Brief description of the drawings]

[0011] [Figure 1] This figure explains the problems with the conventional measurement method (radius method) for the effective diameter of a ball screw. (A) shows the case where a slightly thicker part of the workpiece is measured with a stylus, and (B) shows the case where the workpiece is supported by a steady rest at a certain point in the longitudinal direction, and the forward movement of the steady rest is measured with the stylus. [Diagram 2] Fig. 1 is a first diagram for explaining a method for measuring the effective diameter of a ball screw according to a first embodiment of the present invention, in which (A) shows the diameter variation at the groove bottom, i.e., the variation in the measured value when the groove bottom of the ball screw is measured, (B) shows the diameter variation at the outer periphery, i.e., the variation in the measured value when the outer periphery of the ball screw is measured, and (C) is a diagram for explaining the coordinate system in this application including this diagram. [Diagram 3] 1 shows an example of evaluation in the method for measuring the effective diameter of a ball screw according to the first embodiment of the present invention, where (A) shows the case where diameter variation is evaluated only by measurement at the groove bottom, (B) shows the case where diameter variation is evaluated only by measurement at the outer periphery, and (C) shows the difference between the variation evaluation at the groove bottom and the variation evaluation at the outer periphery. Note that the average values ​​of (A) and (B) are adjusted to be 0. [Figure 4] FIG. 2 is a second diagram for explaining the method for measuring the effective diameter of a ball screw according to the first embodiment of the present invention (in the case of spiral measurement), where (A) shows the state in which the groove bottom is being measured (spiral), and (B) shows the state in which the outer periphery is being measured (spiral). [Diagram 5] 11A and 11B are diagrams for explaining a method for measuring the effective diameter of a ball screw according to a second embodiment of the present invention (when evaluating intermittently in the longitudinal direction), in which (A) shows a case in which Z scanning is performed while controlling the probe output to be constant, (B) shows a case in which the distance to the groove bottom is evaluated based on the periphery of the groove, and (C) shows a case in which the distance to a point at a certain constant slope inclination angle is evaluated based on the periphery of the groove. [Figure 6] FIG. 11 is a diagram showing an example of evaluation in a method for measuring the effective diameter of a ball screw according to a second embodiment of the present invention, and is a graph showing deviation of the effective diameter from a target. [Figure 7]FIG. 13 is a diagram for explaining a method for measuring the effective diameter of a ball screw according to a modified example of the second embodiment of the present invention, showing a case in which a laser (non-contact) displacement meter is used. [Figure 8] 10A and 10B are diagrams for explaining an example in which correction does not converge when correction processing is performed using the method for measuring the effective diameter of a ball screw according to the modified example of the first embodiment of the present invention. [Figure 9] 10A to 10C are diagrams for explaining conditions under which correction converges when correction processing is performed using the method for measuring the effective diameter of a ball screw according to a modified example of the first embodiment of the present invention. [Figure 10] FIG. 11 is a diagram for explaining an example in which the correction converges when correction processing is performed using the method for measuring the effective diameter of a ball screw according to a modified example of the first embodiment of the present invention, but a large number of repetitions are required. [Figure 11] FIG. 11 is a flow diagram of a system for performing correction machining by utilizing a method for measuring an effective diameter of a ball screw according to a modified example of the first embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First, in order to facilitate understanding of the present invention, the problems of the conventional measurement method for measuring the effective diameter of a ball screw will be explained. FIG. 1 is a diagram for explaining the problems, and shows an example of a conventional method for measuring the effective diameter using the radius method as described above. In FIG. 1, (A) shows a case where a slightly thick part of a workpiece 10 is measured with a stylus 12, and (B) shows a case where the workpiece 10 is supported by a steady rest 14 at a certain point in the longitudinal direction, and the forward movement of the workpiece 10 due to the steady rest 14 is measured by the stylus 12. As shown in FIG. 1(A), it is possible to measure a slightly thick part of the workpiece 10 with the stylus 12. However, as shown in FIG. 1(B), when a long ball screw (which can be evaluated as a long elastic cylinder) is supported in various places by the steady rest 14, the part that is held down by the steady rest 14 and moves forward in the direction of the stylus 12 is mixed into the measured value, so there is a difficulty in that even if the diameter of a long elastic cylinder held down by the steady rest 14 is measured by the radius method, it is not possible to evaluate the diameter on the order of micrometers.

[0013] Therefore, the present inventor discovered that, as described below in detail, when measuring the effective diameter, the process is divided into a first step of measuring and evaluating the outer periphery of the ball screw (shaft) and a second step of measuring and evaluating the groove bottom of the screw groove, and the effective diameter of the ball screw is evaluated by calculating the difference between the evaluation of the outer diameter and the diameter of the part corresponding to the groove bottom at the same position in the longitudinal direction of the ball screw. FIG. 2 is a diagram for explaining a method for measuring the effective diameter of a ball screw according to a first embodiment of the present invention, in which (A) shows the diameter fluctuation of the groove bottom, i.e., the fluctuation of the measured value when the groove bottom of the ball screw is measured, and (B) shows the diameter fluctuation of the outer periphery, i.e., the fluctuation of the measured value when the outer diameter of the ball screw is measured. That is, in this embodiment, in the evaluation system for the effective diameter of a ball screw, when the fluctuation of the effective diameter in the longitudinal direction is evaluated as shown in FIG. 2(A) and (B), the evaluation of the lower part (B) is corrected (subtracted) from the evaluation of the upper part (A) to obtain the longitudinal fluctuation evaluation of the effective diameter. Here, Z is written in Fig. 2(A) and (B), but the coordinate system is defined as shown in (C). That is, the Z axis is taken in the longitudinal direction of the workpiece 10, and the X axis is taken perpendicular to that. The C axis is rotated around the Z axis. The outer periphery is the part of the workpiece 10 where there are no grooves, and the diameter evaluated at the outer periphery is called the outer diameter. This definition of coordinates will be used hereafter. Fig. 3 shows an example of the variation evaluation, where (A) shows the diameter variation at the groove bottom, (B) shows the diameter variation at the outer periphery, and (C) shows the difference in distribution between the diameter variation at the groove bottom and the diameter variation at the outer periphery. In this way, the evaluation of the diameter variation at the outer periphery (B) is corrected (subtracted) from the diameter variation at the groove bottom (A) to obtain (C), and this is used as the longitudinal variation evaluation of the effective diameter, which solves the problems with the radius method and allows for a relatively long Even when measuring the effective diameter of a 100mm ball screw, it is possible to measure accurately without being affected by bending of the ball screw or by anti-vibration. Note that the longitudinal distribution evaluation of the outer diameter of the ball screw (evaluation of the cylindricity of the outer periphery) may be performed by a separate system. Also, in the case of a nut instead of a ball screw, it goes without saying that the outer diameter is replaced with the inner diameter.

[0014] FIG. 4 is the second diagram for explaining the measurement method of the effective diameter of the ball screw (in the case of helical measurement) according to the first embodiment of the present invention, in which (A) shows a state in which the groove bottom of the workpiece 10 is (helically) measured with the stylus 12, and (B) shows a state in which the outer circumference of the workpiece 10 is (helically) measured with the stylus 12. That is, as a specific example of a method for performing the measurement of the first embodiment described above, as shown in FIG. 4(A), the tip of the probe of the stylus 12 is placed on the bottom of the groove of the workpiece 10 and helically scanned to check the fluctuation of the reading in the longitudinal direction. Next, as shown in FIG. 4(B), the tip of the probe of the stylus 12 is placed on the outer diameter part of the workpiece 10 without a groove and helically scanned to check the fluctuation of the reading in the longitudinal direction. At this time, the probe of the stylus 12 picks up a component corresponding to the runout of the workpiece 10, but it is possible to remove it by filtering with a low-pass filter or to eliminate it by aligning the phase of the data. However, since the workpiece usually has scratches and dirt attached locally, it is optimal to filter it with a low-pass filter. In this case, if the purpose of filtering is achieved, a general low-pass filter will do, or a smoothing spline, polynomial approximation, weighted polynomial approximation, etc., which are so-called smoothing, will do. It goes without saying that extrapolation, interpolation, interpolation, thinning, etc. can be used to calculate the difference between the evaluation sequences in the workpiece's longitudinal direction so that the deviation in the longitudinal direction does not become a problem.

[0015] The result of subtracting the "evaluation of the outer periphery" from the "evaluation of the groove bottom" represents the depth of the groove based on the outer periphery, which is a more accurate "evaluation of the change in the effective diameter of the ball screw in the workpiece longitudinal direction" than the conventional measurement method. In other words, by making a local evaluation of the outer diameter measurement of the periphery and the groove bottom measurement, it is possible to greatly reduce the impact of long-period bending in the workpiece longitudinal direction on the evaluation of the variation in the effective diameter.

[0016] Furthermore, if the longitudinal variation of the outer diameter of the workpiece without grooves can be evaluated by, for example, clamping the workpiece locally with a micrometer as a separate measurement, or if there is a tendency for a certain taper component to remain as a result of the equipment used to finish the outer diameter before groove machining, further corrections can be made. If the "evaluation of the outer circumference" mentioned above is called "on-site longitudinal distribution evaluation of the outer diameter" and the "evaluation of the outer diameter" mentioned here is called "pre-evaluation longitudinal distribution evaluation of the outer diameter", then a more accurate "evaluation of the change in the effective diameter of the ball screw in the workpiece longitudinal direction" can be obtained by using "evaluation of the groove bottom" - "on-site longitudinal distribution evaluation of the outer diameter" - "pre-evaluation longitudinal distribution evaluation of the outer diameter". It goes without saying that the coefficients should be adjusted appropriately even if a measuring instrument that evaluates by diameter, a measuring instrument that evaluates by radius, or a measuring instrument that evaluates with the sign reversed is used in combination.

[0017] Furthermore, when using a feed axis calibrated in the direction of probe insertion, in order to avoid problems with the linearity of the probe, it is a good idea to adjust the calibrated feed axis so that the probe output is roughly the same when measuring the groove bottom and when measuring the outer diameter. Furthermore, if possible, it is even better to use the calibrated feed axis to slightly insert the probe and recalibrate the relationship between the probe's input and output on the spot. Of course, this is not essential if the probe also has a calibrated relationship between the insertion amount and output and is sufficiently linear. Conversely, if the feed axis is not calibrated but the probe is calibrated, it is a good idea to adjust so that the difference in the insertion amount of the feed axis is small within the measurement range of the probe.

[0018] FIG. 5 is a diagram for explaining a method for measuring the effective diameter of a ball screw according to a second embodiment of the present invention (when evaluating intermittently in the longitudinal direction). (A) shows a case where the workpiece 10 is Z-scanned while controlling the axis (X-axis) that feeds the probe in the pushing direction so as to keep the output of the probe of the stylus 12 constant because the measurement range of the probe in the X-direction is narrow. (B) shows a case where the distance to the bottom of the groove is evaluated based on the groove periphery of the workpiece 10 [see FIG. 5(A)]. (C) shows a case where the distance to a point with a certain slope inclination angle is evaluated based on the groove periphery of the workpiece 10 [see FIG. 5(A)]. That is, in this embodiment, as shown in FIG. 5(A), it is also possible to apply control so that the output of the probe of the stylus 12 is constant. Instead of the output of the probe of the stylus 12, the position coordinate of the feed device in the X-direction of the probe is used. In this case, the stylus 12 is moved linearly in the longitudinal direction instead of measuring in a spiral. However, the evaluation of the diameter of the workpiece 10 [see FIG. 5(A)] is discontinuous in the longitudinal direction. At this time, local scratches and dirt adhesion are considered, so it is optimal to perform smoothing at the evaluation points in the vicinity in the longitudinal direction. In addition, considering the influence of vibration that is likely to occur when the anti-vibration (not shown in FIG. 5) is not pressed sufficiently, it is better to rotate the workpiece 10 [see FIG. 5(A)] by half a revolution or the like and perform Z scanning several times to smooth or average. Here, even if the distance to a point with a constant inclination angle is evaluated, if the design shape is applied, the diameter equivalent to the groove bottom of the workpiece 10 [see FIG. 5(A)] can be estimated, and the effective diameter when the workpiece 10 [see FIG. 5(A)] is used as a ball screw can also be estimated, and it is possible to align the evaluation items with other items. In this application, it is possible to use it directly without converting it to the groove bottom diameter, or to estimate the groove bottom diameter and use it, or to convert it to the effective diameter and then use it, so this is defined as the equivalent groove bottom diameter.

[0019] Fig. 6 is a diagram showing an example of evaluation in the method for measuring the effective diameter of a ball screw according to the second embodiment of the present invention, and is a graph showing the deviation of the effective diameter from a target. That is, Fig. 6 shows data equivalent to Fig. 3(C) in the first embodiment as an evaluation example obtained in the second embodiment. As shown in Fig. 6, in the illustrated example evaluated by the measurement method of the second embodiment described above, diameter data is obtained at intervals in the longitudinal direction, and each shows the deviation from the target effective diameter as shown.

[0020] FIG. 7 is a diagram for explaining a method for measuring the effective diameter of a ball screw according to a modified example of the second embodiment of the present invention, and shows a case where Z scanning of the workpiece 10 of the second embodiment is performed using a laser (non-contact) displacement meter 17. That is, as shown in FIG. 7, a non-contact measuring device that can ensure linearity over a long range [in this example, a laser (non-contact) displacement meter 17] may be used. This makes it possible to omit adding control so that the output of the probe of the stylus 12 [see FIG. 5(A)] is constant. Therefore, high-speed measurement is possible with simpler control.

[0021] If the longitudinal distribution of the effective diameter of the ball screw can be evaluated, it can be used in the correction process to correct it to an arbitrary distribution. However, if the coefficient used for the correction is too large, the distribution may not converge to a certain distribution even if the correction process is repeated. Figure 8 is a diagram for explaining the case where the correction does not converge even if the correction process is repeated, where (a) shows the case where the correction (coefficient) is too large, and (b) shows the case where the sign of the correction is incorrect. That is, in the correction process, the amount of cut is increased or decreased in the longitudinal direction of the ball screw, and the magnitude of the increase or decrease is expressed as the coefficient, and the direction of the increase or decrease is expressed as the sign. First, as shown in Figure 8(b), if the sign of the correction is incorrect, the longitudinal distribution of the effective diameter deviates significantly from the desired distribution each time the correction evaluation is repeated from the first evaluation, the second evaluation, and the third evaluation. Next, as shown in Figure 8(a), if the correction (coefficient) is too large, the distribution in the first evaluation is closer to the + side as the length increases (the graph shows an evaluation curve that rises to the right). On the other hand, in the second evaluation, the longer the length, the more the distribution is on the negative side (the graph has a downward sloping evaluation curve). Furthermore, in the third evaluation, the longer the length, the more the distribution is on the positive side (the graph has an upward sloping evaluation curve). In this way, if the sign is incorrect, the distribution of the effective diameter in the longitudinal direction will deviate significantly from the desired distribution each time the correction is repeated. Even if the sign can be avoided, if the magnitude of the coefficient is significantly incorrect, oscillation will occur at an amplitude near the target. Therefore, as shown in FIG. 9, a correction coefficient in an appropriate range is obtained. FIG. 9 is a diagram for explaining the conditions for performing correction processing and for the correction to converge. As shown in FIG. 9, if the correction coefficient is within an appropriate range and the correction sign is not incorrect, the distribution of the effective diameter in the longitudinal direction will converge to the desired distribution each time the correction evaluation is repeated from the first evaluation to the third evaluation. On the other hand, as shown in FIG. 10, even if the absolute value of the correction coefficient is too small, the correction processing will need to be repeated many times. FIG. 10 shows an example in which the correction converges but many iterations are required. Because the absolute value of the correction coefficient is too small, the correction has not yet converged even after the third evaluation, and many more iterations of the correction process are required.

[0022] FIG. 11 is a diagram for explaining the addition of a flow for correcting these defects. That is, as shown in FIG. 11, when the correction process starts (S101), a first evaluation is performed before the correction (S102). Next, the correction process is performed (S103), and an evaluation after the correction is performed (S104). Next, the evaluations before and after the correction are compared to determine whether or not they are within an allowable deviation. That is, it is monitored whether the correction process is excessive or insufficient, and whether or not there is an error in the sign (S105), and if it is within an allowable deviation (YES in S105), the correction process is terminated (S106). On the other hand, if it is not within an allowable deviation (NO in S105), the progress of the evaluation is confirmed, and the coefficient is adjusted (S107). In addition, if an error is detected, the coefficient may be changed to make it easier to converge, by presenting the operator with a change in the coefficient. Alternatively, the coefficient may be changed automatically, without the operator.

[0023] According to the present invention, even when measuring the effective diameter of a relatively long ball screw, the process can be divided into a first step of measuring and evaluating the outer circumference of the ball screw shaft and a second step of measuring and evaluating the groove bottom of the screw groove without being affected by bending or anti-vibration, and the difference between the outer diameter and the evaluation equivalent to the groove bottom at the same position in the longitudinal direction of the ball screw can be calculated, and an apparatus can be constructed that performs stable correction processing using the calculation results. [Explanation of symbols]

[0024] 10 workpiece, 12 stylus, 14 vibration rest, 17 laser (non-contact) displacement meter

Claims

1. A ball screw effective diameter distribution calculation system for calculating a distribution of effective diameters of thread grooves machined on a long ball screw shaft that can be machined so that the effective diameter varies in the longitudinal direction of the ball screw shaft due to the influence of bending or vibration prevention, a first step of measuring an outer periphery of a groove-free portion of the long ball screw shaft along a longitudinal direction and calculating a distribution of diameter variation along the longitudinal direction at the measured outer periphery; and a second step of measuring a diameter of the groove bottom of the thread groove along a longitudinal direction and calculating a distribution of diameter variation at the measured groove bottom along the longitudinal direction, a ball screw effective diameter distribution calculation system for calculating a difference in distribution of diameter fluctuations between an outer periphery and a groove bottom at corresponding positions in a longitudinal direction of the ball screw shaft by dividing the process into the first process and the second process, and calculating a longitudinal distribution of an effective diameter of the ball screw, a correction processing system for a longitudinal distribution of an effective diameter of a ball screw, characterized in that a correction processing is performed in which an amount of cutting into the ball screw shaft is increased or decreased depending on a longitudinal position of the ball screw shaft so as to eliminate the difference in distribution of diameter variation between the outer periphery and the groove bottom in the longitudinal direction, using the difference in distribution of diameter variation between the outer periphery and the groove bottom calculated by the effective diameter distribution calculation system.

2. A correction processing system for the longitudinal distribution of the effective diameter of a ball screw as described in claim 1, characterized in that the magnitude of the increase / decrease in the amount of cut is expressed as a coefficient and the direction of the increase / decrease in the amount of cut is expressed as a sign, and the sign and magnitude of the increase / decrease in the correction processing is automatically adjusted or the operator is prompted to make the adjustment using the change in the difference in distribution of diameter fluctuations of the outer periphery and the groove bottom before and after the correction processing.

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