JPS6133364B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a method for measuring straightness.

Accurately measure the straightness of guide surfaces, slides, and straightness of tool rests in machine tools, etc., where improved accuracy is desperately desired as industrial products become more sophisticated and machine tools and precision machines become numerically controlled. Accurately measuring the straightness of a workpiece is a prerequisite for increasing the drive accuracy of slides and tool stands, which have a large effect on machining accuracy. In particular, it is important to know the relationship between the movement of the machine tool slide and tool rest and the shape of the workpiece. Traditionally, straightness has been measured using methods such as directly measuring the straightness of the bed guide surface using a spirit level, using a steel wire, or using an autocollimator. Measuring the straightness of a machine's guide surface is also inefficient because it is measured by moving a spirit level and reading it or using a microscope to measure the difference in image position.
Furthermore, it is not appropriate to know the linearity, that is, the dynamic accuracy, of the slide of a machine tool at its actual moving speed.
Recently, a method of measuring straightness using a laser interferometer has been attempted to provide an answer to the above problems. However, when using this method, the linearity of the slide and tool stand is statically
Although it can be grasped dynamically, it is not possible to measure the straightness of the workpiece at the same time.

The above concerns the straightness of the guide surface itself, but for workpieces machined by a tool on a slide guided by the guide surface, conventionally, for example, the straightness of the workpiece, such as a cylinder machined by a turning machine, is To measure the workpiece, a linear guide parallel to the workpiece is provided as a measuring device, a displacement meter is attached to a slide that slides on the linear guide, and the slide is sent and the displacement meter is read and calculated. The straightness is being measured. One such measuring method involves placing, for example, a dial gauge on a slide and running the stylus of the dial gauge over the generatrix of the workpiece to determine the straightness. In the case of using this one displacement meter, the straightness of the slide is affected by the straightness of the linear guide, so the linear guide must be extremely accurate. Furthermore, if the degree of straightness of the linear guide and the degree of straightness of the workpiece are close to each other, there is a problem that the straightness of the workpiece cannot be obtained.

As a method for measuring the straightness of a workpiece without the above-mentioned drawbacks, there is an invention disclosed in Japanese Patent Application Laid-open No. 109660/1983. The invention provides three displacement meters on the same plane.
A slide equipped with detectors arranged at equal intervals and each detecting displacement independently is sent in the same direction over the surface to be measured by linear guide at each displacement meter interval, and the slide is placed at each measurement point. Determine the deviation between the surface to be measured and the center of the displacement meter from the displacement amount of the three displacement meters, and then determine the deviation between each adjacent measurement point. A three-point straightener characterized by calculating the deviation, correcting the measurement error due to the tilt of the slide, and finding the true deviation between adjacent measurement points to detect the straightness error of the surface to be measured. The gist of this paper is the method of measuring temperature.

However, the invention of this prior application requires (1) three displacement meters. (2) Only the object to be measured can be measured. (3) It is difficult to arrange the displacement meters at equal intervals and on the same plane, and any deviation in these will cause errors. (4) Calibration of displacement meter error is difficult. (5) Correction is made for the tilt of the displacement meter, but this value is negligible as long as normal linear guidance is used.
Furthermore, since the resolution limit of the displacement meter is exceeded, there is a problem that such correction is wasteful.

This invention relates to the linear movement of slides such as saddles, tables, tool stands, etc. that engage with bed guide surfaces or guide bars of machine tools, precision instruments, etc. It is an object of the present invention to provide a straightness measuring method that can measure the straightness of a workpiece, etc., and also determine the straightness of an object to be measured, that is, a workpiece.

In this invention, two displacement meters are arranged in parallel at short pitches on a slide engaged with a linear guide, and arranged in a direction perpendicular to the axial direction of an object to be measured, such as a workpiece, supported parallel to the linear guide. At a fixed position of the object to be measured, calculate the distance between each of the two displacement meters and the object to be measured, then feed the slide by one pitch, obtain the measured values from the two displacement meters again, and repeat the data sequentially. This method calculates the straightness of a linear guide and the straightness of an object to be measured through arithmetic processing. Know the distance to and measure static accuracy. Furthermore, the dynamic accuracy can be determined by providing a recording device or a data processing circuit for measuring the slide movement speed in an actual machine.

Furthermore, by attaching the rotary encoder to the machine tool main shaft and capturing the generated pulses every rotation, the straightness of one generatrix of the workpiece can be measured while the workpiece is rotating in conjunction with the displacement meter. , the center method is carried out by measuring the straightness on the generating line at separate positions on the circumference of the workpiece while the workpiece is rotating in conjunction with the displacement meter at each divided position of the circumference of the workpiece. It is possible to know the roundness, cylindricity, and shape accuracy at the same time. This can be automatically measured by providing a data processing circuit.

Examples of the present invention will be described below. 1st
The figure shows a method for measuring straightness according to the present invention. 1
is a headstock of a machine tool, for example, a lathe headstock; 2 is a tailstock; one end of the workpiece 3 is attached to the spindle end of the headstock 1 via a fixture grasped by a chuck; The sleeve of the tailstock 2 is extended away from the headstock 1 by being locked by a fixture fixed to the tailstock 2. The object to be measured 3 in Fig. 1 is a long piece of aluminum whose plate surface is perpendicular to the plane of the drawing in Fig. 1, and has no relation to its straightness with the bed guide surface 5 for purposes of experiment and explanation. . In a workpiece such as a lathe, there is a correlation between the bed guide surface 5 and the straightness of the workpiece. A saddle 4 is engaged on the guide surface 5 of the bed and is movable parallel to the center line of the main shaft. That is, a movable slide is engaged with the linear guide.

Displacement meters 6 and 7 are attached to the saddle 4 at regular intervals in a direction perpendicular to the spindle centerline.

In Fig. 1, the shapes of the object to be measured 3 and the bed guide surface 5 are shown to be larger in the vertical direction and smaller in the horizontal direction for the sake of explanation, but as will be explained later, these shapes are shown in the vertical direction. It is extremely small and sufficiently large in the horizontal direction.

Now, with the saddle 4 at the position shown by the solid line in Figure 1, find the reading of the distance between the displacement gauges 6, 7 and the object to be measured 3, and then move the saddle 4 to the left in Figure 1 to the distance between the displacement gauges 6, 7. Send only one pitch. The position of the saddle also changes in the vertical direction, as shown by the two-dot chain line. Obtain the readings of displacement meters 6 and 7 at this position. Next, the saddle 4 is moved one pitch in the same direction by the distance between the displacement gauges 6 and 7, and the readings of the displacement gauges 6 and 7 are obtained at the position shown by the dotted line in FIG. Thereafter, the entire length of the object to be measured 3 is measured by sending one pitch in the same manner.

From the difference in the above readings, the straightness of the object to be measured 3 and the straightness of the head guide surface 5 are determined as shown below.

Now assume that displacement meters 6 and 7 are eddy current type displacement meters. Bring the displacement gauges 6, 7 close to the object to be measured 3, move them in the cutting direction, read the output of the displacement gauges 6, 7 at that time, and calculate the distance-voltage curve 8 (Figure 2) of each displacement gauge 6, 7. create. In FIG. 2, the horizontal axis shows the voltage V of the displacement meter 6 or 7, and the vertical axis shows the distance F·V between the object to be measured 3 and the displacement meter. Therefore, as shown in the figure, if the distance F·V of the positions 9 and 10 obtained by moving the displacement meter 6 or 7 in the vertical direction is expressed as F·V ₂ and F·V ₁ , then the displacement meter 6 or 7 is The voltages are shown as V ₁ and V ₂ , and the distance traveled by displacement meter 6 or 7 is F・V ₂ −F・V ₁ ∽V ₂ −V ₁
becomes.

FIG. 3 is an enlarged view of a part of FIG. 1. As shown by the appended symbols from the right to the left in the figure, the distance is set to the pitch of the displacement meters 6 and 7, and the spindle center line is set as an ideal straight line in the direction of movement of the object to be measured 3, with the vicinity of its right end as a reference. The distance to the object to be measured 3 at those positions, that is, the straightness, is y ₁ , y ₂ , y ₃ , etc.
...y _o The distance from the reference position that bisects the distance between the displacement gauges 6 and 7 at the right end position to the ideal straight line of the bed guide surface 5 is x ₀ , x ₁ , x ₂ ... x _o The position of the subscript 0,
The distances between the displacement gauges 6, 7 and the object to be measured 3 at points 1, 2, 3...n are respectively F _A (V _0A ), F _A (V _1A ), F
_A (V _2A ), F _A (V _3A )...F _A (V _oA ), F _B (V
_0B ), F _B (V _1B ), F _B (V _2B ), F _B (V _3B )...
If F _B (V _oB ), F _A (V _1A ) - F _A (V _0A ) = y ₁ - x ₁ (1) F _B (V _1B ) - F _B (V _0B ) = (y ₂ - _{y 1} )−x ₁ (2) F _A (V _2A )−F _A (V _0A )=y ₂ −x ₂ (3) F _B (V _2B )−F _B (V _0B )=(y ₃ −y ₁ ) -x ₂ (4) F _A (V _3A ) - F _A (V _0A ) = y ₃ - x ₃ (5) F _B (V _3B ) - F _B (V _0B ) = (y ₄ - _{y 1} ) - x ₃ (6) (2)−(3)+(1) x ₂ =F _A (V _1A )−F _A (V _2A )+F _B (V _1B ) −F _B (V _0B )+x ₁ +x ₁ From (4)-(5)+(1), x ₃ = F _A (V _1A ) - F _A (V _3A ) + F _B (V _2B - F _B (V _0B ) + x ₂ + x ₁ ∴x _o = F _A (V _1A ) - F _A (V _oA ) + F _B (V _(o-1)B ) - F _B (V _0B ) + x _o-1 + x ₁ Therefore, the unknown x ₁ becomes the DC component, so x If ₁ = 0, all straightness x _o can be found by a simple mathematical formula. In addition, the straightness of the object to be measured 3 can also be found as y _o = x _o + F _A (V _oA ) - F _A (V _0A ).

The k-th displacement is determined by measurement or setting errors such as the distance between the displacement gauges 6 and 7, the difference in height of their tips, parallelism, and the inclination in a plane perpendicular to the center line of the principal axes of the object to be measured 3 and the displacement gauges 6 and 7. Total 6 and (k-1)
It is possible that the position or direction of the second displacement meter 7 is different. For example, if the error in distance measurement between both displacement meters 6 and 7 is 0.2 mm, the straightness of the surface of the measured object 3 is at most 100 mm and 50 μ or less. Therefore, the displacement measurement error of the displacement meters 6 and 7 is 0.1μ or less.
Therefore, the setting error between the displacement meters 6 and 7 can be ignored.

When the object 3 to be measured is obtained by turning, grinding, or processing, the straightness of one generatrix is measured. It will be clear from the above description that the straightness of a workpiece to be measured can be measured while it is attached to a machine that performs turning work.

FIG. 4 shows an embodiment of the invention and is a block diagram when data processing is performed automatically. The object to be measured 3 shown in Fig. 1 is a workpiece 3' in this figure.
It is becoming. The workpiece 3' is gripped by the chuck and supported by a center mounted on the tailstock 2. The saddle 4 is a drive device 1 such as a pulse motor.
5, it is adapted to be fed via a feed screw. A rotary encoder 11 is coupled to a main shaft mounted on a headstock 1.

12 is a counting circuit, 13 is an AD converter for the output voltage of the displacement meters 6 and 7, and 14 is a microcomputer, ie, an arithmetic control device such as a microcomputer.

Now, when the main shaft is driven to rotate the work 3' and send the saddle 4, the pulses generated by the rotary encoder 11 are counted by the counting circuit 12 and sent to the microcomputer 14. Every time the pitch between the displacement gauges 6 and 7 and the saddle 4 are sent, a measurement command is issued from the microcomputer 14 at one generatrix position on the workpiece 3' by the rotary encoder 11, and the output of the displacement gauges 6 and 7 at that position is The data is AD converted by the AD converter 13, counted, and output through arithmetic processing by the microcomputer 14. Work 3'
By measuring with the displacement meters 6 and 7 at positions divided into the circumference, the roundness and cylindricity can be determined simultaneously by the center method.

As is clear from the above description, the apparatus for carrying out the method of the present invention includes a slide that engages with a linear guide, a support device for the object to be measured 3 parallel to the linear guide, a slide feeding device, and a slide. It consists of displacement gauges 6 and 7 arranged in parallel at right angles to the linear guide above, and the feeding device has a function that allows it to stop every pitch between the displacement gauges 6 and 7 in the case of manual measurement. is necessary. Therefore, in ordinary lathes and the like, it can be determined that the displacement gauges 6 and 7 have been fed one pitch by reading the scale on the longitudinal feed handle provided on the apron and the scale fixed in the longitudinal direction on the lathe bed. The straightness measuring method shown in FIG. 4 as an embodiment is carried out using a numerically controlled lathe with saddle
is sent by a pulse motor as the driving device 15, but it is not necessary to stop every pitch of the displacement gauges 6 and 7, and a feeding device that continuously sends it digitally may be used. In other words, the slide feeding device only needs to measure the distance between the displacement gauges 6 and 7 and the object 3 at one pitch between the displacement gauges 6 and 7, so whether or not to send the slide intermittently depends on the control method. do.

As described above, according to the straightness measuring method of the present invention, it is possible to measure with a high signal-to-noise ratio using a simple device, and both the straightness of the linear guide and the straightness of the object to be measured can be determined. Measurement is completed with just one movement. Since only two displacement meters are placed in parallel, the influence of setting errors on measured values is small. Using an eddy current type displacement meter, the output data can be instantaneously processed by a microcomputer or minicomputer, etc. If connected to a numerical control device, it can be measured in real time and precision machining can be performed to control straightness to zero. It can be made possible.

[Brief explanation of the drawing]

Fig. 1 is a drawing showing the method of this invention, Fig. 2 is a drawing showing the characteristics of a displacement meter, Fig. 3 is a partially enlarged drawing of Fig. 1, and Fig. 4 is a block diagram showing an embodiment of this invention. Drawing shown in. 3...Object to be measured, 3'...Work, 4...Saddle, 5...Bed guide surface, 6, 7...Displacement meter.

Claims (1)

[Claims] 1. Two displacement gauges are placed in parallel with a short pitch on a slide movably engaged with a linear guide parallel to the object to be measured on a straight line, and the slide is moved toward the object to be measured. The distance between two displacement meters and the object to be measured is measured by the displacement meters at each position by sending the data once in one direction over the entire length of one pitch, and by processing the data, the distance between the two displacement meters and the object to be measured is processed. Straightness measurement method to determine the straightness of. 2. A linear guide, a slide movably engaged with the linear guide, a support device that supports the object to be measured parallel to the linear guide, and a slide supported by the support device at a short pitch perpendicular to the linear guide. Displacement meters arranged on a slide in parallel facing the object to be measured, a sending device capable of sending the parallel displacement meters to the pitch and detecting their positions, and calculating the signals obtained from the sending device and the displacement meter. Straightness measuring device consisting of a processing device. 3. A linear guide, a slide movably engaged with the linear guide, a headstock and a tailstock that rotatably support the object to be measured in parallel with the linear guide, and a spindle provided on the headstock that controls the rotation of the spindle. A spindle rotational position detection device that generates a signal at a circumferentially divided and indexed position, a counter that is engaged with the spindle rotational position detection device and counts the signal generated by the spindle rotational position detection device, and a linear A displacement meter is placed on the slide in parallel at a short pitch facing the object to be measured, which is perpendicular to the guide and supported by the headstock and tailstock, and a feed screw and digital sensor that engage with a nut fixed to the slide. A feeding device connected to a feedable prime mover and the displacement meter.
A straightness measuring device capable of measuring the shape of a rotating cylindrical object to be measured, which includes input via an AD converter and a counter, and an arithmetic control device coupled to the feeding device.