JP2021060673A - Adjustment method allowing for improved accuracy of machine tool - Google Patents

Abstract

To provide an adjustment method which allows for improved accuracy of a machine tool.SOLUTION: A machine tool has three axes X, Y and Z and has linear axes which are parallel with them respectively or each of which can be made parallel with one of them by a rotation axis, and relations between set positions (inputs) and displacements (outputs) of these linear axes are calibrated by a separate calibration device to improve feed pitch accuracy of the machine tool by software. Measurement for calibration of the pitch accuracy is performed twice, and a position of an axis being parallel or made parallel with an evaluation object in the second measurement is slightly changed from that in the first measurement to calibrate even non-linearity of the calibration device, and with respect to a long-cycle component, overall evaluation is used if the overall evaluation is performed in only one of two evaluations, and with respect to a short-cycle component, a correction value allowing for the non-linearity of a calibrator estimated from two evaluations is generated.SELECTED DRAWING: Figure 5

Description

The present invention relates to an adjustment method capable of increasing the accuracy of a machine tool.

Conventionally, a machine tool (grinding machine) as shown in FIG. 1 described later has been put into practical use. That is, it has a linear X-axis, a Y-axis, and a Z-axis, and has a redundant W-axis parallel to the Z-axis. The distance of the straight U-axis to the XY plane can be adjusted by the straight Z axis, and the direction maintained parallel to the XY plane and perpendicular to the Z axis can be set by the swivel C axis.
Although not shown for any of the X, Y, Z, W, C, and U axes, it has a position detection mechanism such as a pulse coder with a built-in motor or a separate linear scale or rotary encoder, or a pulse motor. It has a position control mechanism, and the position of the grindstone as a tool can be changed according to the command of the controller.
In this type of machine tool, a probing device is connected to the controller (see, for example, Patent Document 1). The moment the probing device detects a contact, a signal is sent to the controller, and the controller that receives the signal has a function of immediately stopping the feed (hereinafter, such a function is referred to as a skip function). When stopped by this skip function, the stop position can be acquired, and the shape can be evaluated from this stop position. Measurements are made at a plurality of points and the dimensions are evaluated from the differences (see, for example, Patent Document 2).
On the other hand, there are many types of position detection mechanisms such as linear scales and rotary encoders mentioned above, but the position control mechanism is open-loop, which uses only the rotation angle of the lead screw (lead screw) for detection and control. There are loop and semi-closed loop control and full closed loop control that detects and controls the position.

Japanese Unexamined Patent Publication No. 2007-007822 Japanese Unexamined Patent Publication No. 2003-31153

Research on in-situ autonomous calibration method for geometric quantity sensors (Kiyono et al., Journal of Precision Engineering, Vol. 63, No. 10, 1997, pp. 1417-21)

Depending on the quality of the lead screw and linear scale and the condition of assembly, the relationship between the input position command and the output displacement is often non-linear. Especially for lead screws, periodic deviations tend to remain. Also, if you look closely at the linear scale, there are many cases where slits, engraved lines, etc. are combined to generate a periodic signal level change according to the displacement, and interpolation is performed to ensure resolution, and the periodic deviation is perfect. It cannot be avoided.
These non-linearities are often calibrated using a calibrator that utilizes light interference or a reference scale, but it should be noted that the calibration criteria themselves also have periodic non-linear components. ..

An object of the present invention is to provide an adjustment method capable of improving the accuracy of a machine tool.

As a result of diligent research on a manufacturing method or an adjustment method capable of improving the precision of a machine tool, the present inventor has three axes of XYZ as the method, and a linear axis or a linear axis parallel to each of them. It has a linear axis that can be parallel to any one axis by the rotation axis, and the relationship between the set position (input) and displacement (output) of these linear axes is calibrated by another calibration device, and the feed pitch accuracy is improved by software. The machine tool is being operated, and the measurement for calibrating this pitch accuracy is performed twice, and the position of the axis parallel to or parallel to the evaluation target is slightly changed in the first and second times on the side of the calibrator. If the non-linearity is calibrated and only one of the two evaluations is performed for the long-period component, the side that has been evaluated for the entire period is used, and the short-period component is used. For the components, it was found that a correction value was created in consideration of the non-linearity of the calibrator estimated from the two evaluations.

That is, according to the aspect of the present invention, it has three XYZ axes, and each has a linear axis parallel to the axis or a linear axis that can be made parallel to any one axis by a rotation axis, and the setting of these linear axes. It is a machine tool that calibrates the relationship between position (input) and displacement (output) with another calibrator and improves the feed pitch accuracy with software, and performs measurements for calibrating this pitch accuracy twice. In the 1st and 2nd times, the position of the axis parallel to or parallel to the evaluation target is slightly changed to calibrate to the non-linearity on the side of the calibrator, and for the long-period component, either evaluation is performed twice. If only one of them is evaluated over the whole, the side evaluated over the whole is used, and for the short-period component, the correction value considering the non-linearity of the calibrator estimated from the two evaluations is used. A method of adjusting a machine tool, which is characterized by making it, is obtained.

According to the present invention, it is possible to provide a method for adjusting a machine tool capable of increasing accuracy.

It is a figure which shows the basic structure of the machine tool (grinding machine) to which this invention is applied. It is an enlarged view around the U-axis feed device and the grindstone shaft in the machine tool (grinding machine) shown in FIG. It is a block diagram which shows the outline of the control system of the machine tool (grinding machine) shown in FIG. It is a figure which shows the basic structure of the machine tool (grinding machine) to which the adjustment method of this invention is applied. It is a flowchart which shows the process of the adjustment method which can improve the precision of the machine tool which concerns on embodiment of this invention. It is a figure which shows the example of the appearance of the long-period component and the example of the appearance of the short-period component together with the graph showing the change of the output with respect to the input in the adjustment method of the machine tool according to the embodiment of the present invention. (a) is a graph showing an example of how long-period components are output by changing the output (displacement display) with respect to input (displacement), and (b) is an example of how short-period components are output (displacement). It is a graph represented by the change of the output (non-linearity) with respect to). It is a figure for demonstrating the adjustment method of the machine tool which concerns on the modification of embodiment of this invention, (a) is the figure which shows the example which the evaluation part is provided at several places in the longitudinal direction of a scale, (b). ) Is an example showing how the phase offset λ (x) appears.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of a grinding machine to which the present invention is applied, and FIG. 2 is an enlarged view of the U-axis feed device and the periphery of the grindstone shaft. In the grinding machine 10 to which the present invention is applied, as shown in FIG. 1, a table feeding device 36 and a table 30 are supported on a bed 12 so as to be movable in the Y-axis direction (front-rear direction) via a rail 16. .. Although the column 14 is fixed to the bed 12, as described above, a relative motion can be applied to and from the feeding device 36 in the direction along the rail 16. A motor for moving the feed device 36 (not shown) is arranged at the rear of the bed 12, and the table feed device 36 is moved back and forth along the rail 16 via a ball screw (not shown) or the like. A head 18 is supported on the column 14 so as to be movable (elevable) in the W-axis direction, a grindstone shaft 20 is provided at the tip of the head 18, and a grindstone 100 (FIG. 2) is provided at the tip of the grindstone shaft 20. See) is installed. A head elevating motor (not shown) is arranged on the upper part of the column 14, and the head 18 is elevated by this motor via a ball screw (not shown) or the like. A grindstone shaft (for rotation) motor 24 (see FIG. 2) is arranged at the rear portion of the head 18, and the grindstone shaft 20 is rotated by this motor. The head elevating motor is provided with an encoder that constitutes a measuring means (not shown). The linear shaft and the rotating shaft other than the grindstone shaft are equipped with an encoder and a motor so that the feed amount or the rotation amount can be calculated and controlled even if they are not shown. From the data output from this encoder, the amount of lifting and lowering of the head 18 and the amount of cut into a workpiece (not shown) are calculated. The Z-axis is provided parallel to the W-axis direction, and the Z-axis motion can be given without hindering the movement of the head of the W-axis, the rotation of the C-axis, and the linear motion of the U-axis.

As described above, the X-axis feed device 36 is mounted on the bed 12 via the rail 16. The X-axis feed device 36 is configured to be able to linearly move back and forth in the Y direction along the direction of the rail 16. A table 30 is further supported on the X-axis feed device 36 via a rail (not shown). The table 30 is configured to be able to linearly move in the left-right direction with respect to the X-axis feed device 36. A work (not shown) is detachably installed and fixed on the upper surface. As a matter of course, a motor for moving the X-axis feed device 36 is provided on the bed 12, and the X-axis feed device 36 is moved along the rail 16 via a ball screw or the like (not shown) by this motor. There is. Similarly, the table 30 moves on the X-axis feed device 36 via a motor, a ball screw, or the like (not shown). Then, in a state where the grindstone shaft 20 is rotated by the grindstone shaft rotation motor 24, the head 18 (grindstone shaft 20) is lowered by the head elevating motor, and the grindstone 100 attached to the tip of the grindstone shaft 20 is moved. It is brought into contact with the surface of the work on the table 30. The table 30 can be freely moved in the XY directions by the above-mentioned two motors. As a result, the surface of the work is ground by the grindstone 100.

As described above, the machine tool (grinding machine) 10 shown in FIG. 1 is a CNC-controlled machine tool (grinding machine) capable of simultaneously controlling at least three axes of XYZ, and further, a grindstone shaft. It has a drive shaft (rotary shaft or linear drive shaft) whose axial direction is parallel to the rotation shaft of 20. That is, the machine tool (grinding machine) 10 has a U-axis feed device 40 at the lower part of the head 18, and the U-axis feed device 40 includes a grindstone shaft 20 and a disk body 27 above the grindstone shaft 20. It is a mechanism, and is a device that linearly moves the grindstone shaft 20 and the disk body 27 above the grindstone shaft 20 within a predetermined stroke range according to the angular position of the C axis at that time, and the linear movement direction is the U axis (direction). Is defined as. That is, in the machine tool (grinding machine) 10 shown in FIG. 1, the head 18 can be linearly moved (moved up and down) in the Z-axis direction. To distinguish it from the Z-axis, it is called a W-axis feed device. Further, the U-axis feed device 40 can be swiveled with respect to the head 18 in a Z-axis linear movement and a Z-axis rotation (referred to as a C-axis). The U-axis feed device 40 can linearly move the grindstone shaft 20 in the U-axis direction. More specifically, the drive axis control of the machine tool (grinding machine) 10 will be described more specifically with reference to FIGS. 2 and 3. In the machine tool (grinding machine) 10, the U-axis linear feed mechanism is on the rotation side of the C-axis. It is listed in. The U-axis feed device 40 can be linearly moved along the direction of the U-axis by the feed command of the grindstone shaft (U-axis). The center of the grindstone shaft is rotated by the rotation command of the C shaft. Further, this C-axis device can be linearly moved in the vertical direction by the Z-axis device.

FIG. 3 is a block diagram showing an outline of the control system of the jig grinding machine shown in FIG. The jig grinding machine according to the present invention has a control device 300, an input / output device 310, each axis motor 320, each motor driver 330, a grindstone rotation motor 102A, and a grindstone motor inverter 102inv as control systems. The control device 300 includes a computer numerical control unit (CNC) 302, a programmable controller 304, and an I / O (input / output) module 306. The control system of the jig grinding machine according to the present invention also includes a keyboard, various switches, a temperature sensor and the like, a tools setter related to a skip signal, an AE sensor and the like as an input / output device 310.

As described above, as a result of diligent research on a method for manufacturing or adjusting a machine tool capable of increasing accuracy, the present inventor has XYZ3 axes as the method, and straight lines parallel to each of them. It has a linear axis that can be parallel to any one axis depending on the axis or the rotating axis, and the relationship between the set position (input) and displacement (output) of these linear axes is calibrated by another calibration device, and the feed pitch accuracy is adjusted by software. It is a machine tool characterized by being improved by the above, and the measurement for calibration of this pitch accuracy is performed twice, and the position of the axis parallel to or parallel to the evaluation target is slightly changed in the first and second times. The non-linearity on the side of the calibrator is calibrated, and one of the evaluations is used for the long-period component, and the non-linearity of the calibrator estimated from the two evaluations is taken into consideration for the short-period component. Found to create a correction.

FIG. 4 is a diagram showing a basic configuration of a machine tool (grinding machine) to which the adjustment method of the present invention is applied. That is, first, the machine tool (grinding machine) to which the adjustment method of the present invention is applied has substantially the same basic configuration as the machine tool (grinding machine) shown in FIG. 1 (see FIG. 1 for the basic configuration). That is, as shown in FIG. 4, it has three axes XYZ, and each has a linear axis parallel to this or a linear axis that can be made parallel to any one axis by a rotation axis, and these linear axes. This is a machine tool in which the relationship between the set position (input) and the displacement (output) of is calibrated by another calibration device (system) 92, and the feed pitch accuracy is improved by software. Note that FIG. 4 shows an example of calibrating the X-axis with the linear scale 94, which includes the linear scale detection head 96, but the periodicity appears even when the laser interference system is used. Then, in the manufacturing method or adjustment method of the present invention, in the machine tool (grinding machine) as described above, the measurement for calibrating the pitch accuracy is performed twice, and the first and second measurements are parallel or parallel to the evaluation target. The position of the set axis is slightly changed to calibrate to the non-linearity on the side of the calibration device, and one of the evaluations is used for the long-period component, and the short-period component is estimated from two evaluations. Create a correction that takes into account the non-linearity of the calibrator.

Hereinafter, the main part of the adjustment method of the present invention will be described with reference to FIGS. 5 to 7. FIG. 5 is a flowchart showing a process of an adjustment method capable of improving the accuracy of the machine tool according to the embodiment of the present invention. First, the positioning deviation is evaluated using the reference scale as a calibration reference (first time) (step S101). Subsequently, the calibration scale is offset by δ (step S102). When evaluating the X-axis, the direction of the U-axis should be parallel to the X-axis. When evaluating the Y-axis, the direction of the U-axis should be parallel to the Y-axis. When evaluating the U-axis, keep the X-axis parallel. The Z-axis and the W-axis are originally parallel. The offset is performed on the side of the parallel axes that is not evaluated. Further, this time, the deviation of positioning is evaluated with reference to the calibration scale (second time) (step S103). Within the range of repeatability, the first and second movements should be the same. However, because the offset is given, the range that appears as the output is different. If the linearity on the reference scale side is high, the output will only be offset, but there will be a difference other than the offset in the output due to the non-linearity. Non-Patent Document 1 described above shows that calibration can be performed by giving the same input offset in this way as an input of a certain length measuring instrument and comparing the outputs. However, since it takes time to evaluate twice with a fine pitch, the evaluation should be limited to a short range. Then, for the long period, pitch correction is performed using the evaluation of the entire length, whichever is the first time or the second time, (step S104A). On the other hand, for the short period, the non-linearity is evaluated in the first and second times, approximated as a periodic function, and the pitch correction is superimposed over the entire area (step S104B). Here, the boundary between the short period and the long period is generally shorter than the period when using a system in which the basic period is likely to appear, such as an optical scale, a laser interference type length measuring system, and a lead screw of a calibrator. A period is defined, and a period larger than that period is defined as a long period. Assuming that the first measurement is performed over the entire length, in this measurement, the measurement pitch is taken longer and the range to be evaluated in the second measurement is finely measured at a short pitch. For example, when evaluating a scale with an issue cycle of 8 micrometers before internal insertion and a total length of 1 meter with a reference scale with a signal cycle of 2 micrometers, the signal cycle before internal insertion is on the order of micrometers, so 16 micrometers or Local short pitch measurement and evaluation are performed at a pitch of 1 micrometer or 0.5 micrometer within a range of 24 micrometers, etc., and evaluation is performed at large intervals such as 5 mm or 10 mm pitch over the entire length. Depending on the order of correction to be obtained, a pitch of 50 mm or the like may be used. In the first evaluation, both the evaluation over the entire length performed at a large pitch and the local evaluation in the local evaluation range in the second evaluation are performed, and in the second evaluation, only the local evaluation is required.

そして、スケールの内挿前の信号周期の整数倍だけの１回目、２回目の評価を上記非特許文献１の方法で処理し、内挿の偏差を推定する。この周期的な偏差の傾向が全長に亘って分布していると考え、周期的なピッチ補正を行うようにする（長周期のピッチ補正に重畳する）。 FIG. 6 shows an example of how long-period components are output and an example of how short-period components are output in the machine tool adjustment method according to the embodiment of the present invention, together with graphs showing changes in output with respect to input. FIG. 6A is a graph showing an example of how long-period components are output by changing the output (displacement display) with respect to input (displacement), and FIG. 6B is an example of how short-period components are output. Is a graph represented by a change in output (non-linearity) with respect to input (displacement). In FIG. 6B, the interval l on the horizontal axis is the signal period (or lead of the lead screw) before the scale is inserted. As shown in FIGS. 6A and 6B, the appearance of the short-period component is non-linear as compared with the appearance of the long-period component, but the appearance of the substantially periodic component is the main component. Therefore, it is confirmed that the component is substantially periodic in this way, and it is assumed that this continues over the entire length, and the mathematical formula (1) of periodic function approximation is used.

Then, the first and second evaluations of only an integral multiple of the signal period before interpolation of the scale are processed by the method of Non-Patent Document 1 to estimate the deviation of interpolation. Considering that the tendency of this periodic deviation is distributed over the entire length, the periodic pitch correction is performed (superimposed on the long-period pitch correction).

以上のように、本発明の実施形態又はその変形例によれば、工作機械の高精度化が可能な調整方法を得ることができる。 By the way, if it is considered that the tendency of the periodic deviation of only an integral multiple of the signal period before the interpolation of the scale is distributed over the entire length and only the periodic pitch correction is performed, the resolution is particularly high as an evaluation standard. When scaled, the phase may shift at the edge. FIG. 7 is a diagram for explaining a method of adjusting a machine tool according to a modified example of the embodiment of the present invention, and FIG. 7A is a diagram showing an example in which evaluation points are provided at several points in the longitudinal direction of the scale. Yes, (b) is an example showing how the phase offset λ (x) appears. As shown in FIGS. 7A and 7B, as a modification of this embodiment, for example, phase offsets λ (x) are set at several points such as A, B, C, D, E, and F in the longitudinal direction of the scale. , Λ is evaluated based on how many non-linearities are minimized, and λ (x) is determined. Based on this, the phase of the correction may be adjusted. In order to adjust the phase of this correction, the following formula (2) may be used as the correction correction formula, and this may be superimposed on the long-period pitch correction.

As described above, according to the embodiment of the present invention or a modification thereof, it is possible to obtain an adjustment method capable of improving the accuracy of the machine tool.

10 Grinding machine, 12 beds, 14 columns, 16 rails, 18 heads, 20 grindstone shafts, 24 grindstone shafts (for rotation) motors, 30 tables, 36 table feed devices, 40 U-axis feed devices 92 calibrators (systems), 94 Linear scale, 96 linear scale detection head, 100 grindstone,

Claims (1)

It has three XYZ axes, and each has a linear axis parallel to it or a linear axis that can be parallel to any one axis by a rotation axis, and the set position (input) and displacement (output) of these linear axes. It is a machine tool that calibrates the relationship with another calibrator and improves the feed pitch accuracy by software. The measurement for calibrating this pitch accuracy is performed twice, and the evaluation target is the first and second times. The position of the parallel or parallel axes is slightly changed to calibrate to the non-linearity on the side of the calibrator, and for the long-period component, only one of the two evaluations is evaluated over the whole. In the case of a machine tool, the side evaluated over the whole is used, and for short-period components, a correction value considering the non-linearity of the calibrator estimated from two evaluations is created. Adjustment method.

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