JP4641555B2 - Screw hole shape measurement method - Google Patents

Description

The present invention relates to a screw hole shape measuring method, in particular by using a general three-dimensional measuring machine, relates to a screw hole shape measuring method capable of measuring a characteristic value of the screw hole shape.

Conventionally, a three-dimensional measuring machine is often used for measuring the shape of the surface of an article or the like.
In the three-dimensional measuring machine, an article or the like (work) whose shape is to be measured is placed on a table, and a stylus at the tip of a probe that moves relative to the table in three dimensions is brought into contact with the work surface. Then, the three-dimensional shape of the workpiece surface can be accurately captured by sequentially repeating the reading of the three-dimensional coordinate position of the contact point.

In such a three-dimensional measuring machine, conventionally, in addition to the general shape measurement of the workpiece surface, the measurement of the inner diameter and the central axis position of the hole formed in the workpiece surface has been performed.
Further, with respect to screw holes formed on the workpiece surface, the measurement of the respective central axis positions or the measurement of the interaxial distances of a plurality of screw holes is also performed (for example, see Patent Document 1).

Regarding the screw shape (screw hole = female screw, screw shaft = male screw), there are various parameters (characteristic values) that define the screw shape characteristics in addition to the central axis position. For example, thread pitch, effective thread diameter, thread angle, threading length, and the like.
Conventionally, various measuring methods are known as techniques for measuring the characteristic values of these screw shapes.

  For example, by measuring the thread pitch, thread height, thread diameter, thread taper, etc. by moving an optical displacement sensor in the axial direction with respect to the thread shape and measuring the thread contour in a non-contact manner. (See, for example, Patent Documents 2 and 3). In addition, a technique is also known in which a screw-shaped axial contour is measured by contact measurement instead of non-contact, and then a screw-shaped precision measurement is performed by measuring the shape along the screw groove (see, for example, Patent Document 4).

  As a technique for measuring the effective diameter of the screw shaft, a three-needle measurement method has been conventionally known. This is based on the known needle diameter, with two needles on one side of the screw shaft and one needle on the opposite side, each placed in a screw groove, sandwiched by a micrometer spindle to hold the needle on each side. Thus, the effective screw diameter is calculated from a predetermined arithmetic expression. For this purpose, dedicated three-needle gauges, three-needle adapters, and three-needle measurement bases have been developed. These three-needle type measurements are stipulated in JIS B 0271.

JP-A-6-341826 JP-A-62-27607 JP-A-9-264719 JP-A-55-113907

As described above, although there are various measurement techniques for the characteristic value of the screw shape, the measurement of the screw shape as part of the shape measurement using a general three-dimensional measuring machine has not been performed.
This is because existing probe and stylus hardware is not suitable for performing various screw shape measurements using a coordinate measuring machine, and for measuring various screw shapes in operation programs. This is because no command or measurement algorithm was prepared.
However, since the introduction of a three-dimensional measuring machine has been advanced for in-line measurement in the product manufacturing process, there has been a demand for automatic measurement of various screw shapes by the three-dimensional measuring machine.

An object of the present invention is to provide a screw hole shape measuring method capable of measuring various characteristic values of the screw hole shape using a three-dimensional measuring machine.

(Basic configuration)
The present invention relates to a screw hole shape measuring method for measuring the threaded hole shape using a coordinate measuring machine, a coordinate measuring machine which works with a screw hole shape to be measured is mounted, the three-dimensional An axis that aligns the scanning measurement axis of the scanning probe with the central axis of the screw hole shape using a scanning probe mounted on the measuring machine and a stylus that is mounted on the scanning probe and has a contact portion that contacts the workpiece. the combined process and the profiling measurement step of moving the stylus along said threaded hole shape the said scanning probe while in contact with the scanning measurement axis, various characteristics of the screw hole shape from the measurement data obtained by the scanning measurement A step of calculating a value using a branching stylus having a contact portion branched laterally in the scanning measurement step, wherein the calculation step includes the branching contact portion. The measurement contour shape of the screw part is taken out from the measurement data obtained by the touched measurement, and the approximate contour shape is taken out by approximating the screw slope portion with a straight line in this measurement contour shape. An effective diameter calculation process is included, in which a virtual circle that is an alternative to the above is brought into contact, and an effective diameter of the screw hole shape is calculated by a conventional three-needle method.

(Elements of basic configuration)
The threaded hole shape of the measurement object, a threaded hole (female thread). Further, in addition to normal screw holes, partial screw holes for a half circumference may be targeted.
For the center axis of the screw hole shape in the axis alignment step, workpiece design data may be referred to, or provisional measurement may be performed by other measurement operations.
When calculating each characteristic value, the calculation process may be performed in parallel with the scanning measurement process, or after performing the scanning measurement process for a certain characteristic value, the calculation process for the characteristic value is performed, and then another characteristic value is calculated. After performing the scanning measurement process for the value, the characteristic value calculation process may be performed.

As the scanning probe, if an existing scanning measurement probe used to perform so-called scanning measurement, which measures the contour shape of the surface by sliding the attached stylus while making contact with the surface to be measured, is used. Good.
As the stylus, an existing one having a spherical contact portion at the tip may be used. At this time, not only one having a single contact portion, but also one having a plurality of contact portions with its tip branched in a branch shape, such as a cross-shaped stylus, may be used.

As the three-dimensional measuring machine, an existing one in which the table on which the workpiece is placed and the probe mounting portion are relatively moved in three dimensions can be used.
In order to make the coordinate measuring machine execute each process, it is used as a control means between the host computer used for controlling the operation of the coordinate measuring machine and data processing, and between the host computer and the coordinate measuring machine. An existing device used for controlling the coordinate measuring machine, such as a controller for operating the coordinate measuring machine based on an operation command from the host computer, may be used.
The operation program for executing each process may be created externally and loaded into the control means by an existing information recording medium such as a magnetic tape or disk, or by online communication.

(Effects of basic configuration)
In the present invention as described above, the shape of the normal workpiece surface can be measured by a three-dimensional measuring machine or stylus. That is, the probe group leading to the scanning probe and the stylus has an existing configuration and does not hinder a normal workpiece surface shape measurement operation. On the other hand, various characteristic values of the screw hole shape can be measured for the screw hole shape formed in the workpiece with the same apparatus.

That is, the scanning probe is set in a predetermined posture in which the scanning direction is aligned with the axial direction of the screw hole shape on the workpiece surface by the axis alignment process. Then, the shape of the screw hole is copied and measured by the scanning measurement process. Furthermore, characteristics such as screw pitch, screw thread angle, thread cutting depth, and the like of the screw hole shape can be calculated from the data obtained by scanning measurement through the calculation process.

Therefore, using a three-dimensional measuring machine, it is possible to seamlessly execute from the normal shape measurement of the workpiece surface to the measurement of the screw hole shape, which conventionally required separate work, and in-line measurement on the production line etc. It is also possible to do this.

(Regarding the alignment process)
In the present invention, before the axis alignment step, each of a machine coordinate system set for the coordinate measuring machine, a workpiece coordinate system set for the workpiece, and a probe coordinate system set for the scanning probe and the stylus It is desirable to perform a coordinate alignment process for adjusting the relative relationship between the two.

  The machine coordinate system is a coordinate system set on a table or the like of a coordinate measuring machine, and the coordinate measuring machine operates based on this coordinate system. In order to calibrate a coordinate system such as a probe to be exchanged as appropriate to this machine coordinate system, for example, a spherical calibration point is set on the table. The coordinate system can be calibrated by contacting such a calibration point from a plurality of directions.

  The work coordinate system is a coordinate system set for a work, and the design data generally takes a coordinate system unique to the work. When a workpiece is placed on a table of a coordinate measuring machine and measurement is performed, the position of each part of the workpiece needs to be expressed in a machine coordinate system. Here, if each axis of the workpiece XYZ coincides with each axis direction of the machine coordinate system of the coordinate measuring machine, the machine coordinate value of the workpiece coordinate origin may be added or subtracted as a simple offset. On the other hand, if each of the XYZ axes of the workpiece is inclined with respect to the direction of the machine coordinate system, conversion including a rotation component is necessary, but in any case, integration can be performed by existing arithmetic processing.

  The probe coordinate system represents the position of the contact portion that is specified relative to the reference position of the probe mounting portion of the coordinate measuring machine, and the origin position of the current probe coordinate system in the machine coordinate system and the probe coordinate system. From the contact part coordinate value, the coordinate value of the contact part in the machine coordinate system is obtained. As in the case of the workpiece coordinate system, simple addition and subtraction are sufficient when the directions of the axes are the same, but if the axis is tilted or rotating around the axis, calculations including angles are required. Become.

Furthermore, the following can be said about the alignment process.
First, the scanning measurement axis of the scanning probe is a scanning movement direction when the scanning probe performs scanning measurement. The scanning measurement axis can be specified based on the rotation angle and tilt angle of the rotary probe head and the moving position of the coordinate measuring machine. That is, if the initial state of the probe coordinate system is confirmed with respect to the machine coordinate system of the coordinate measuring machine, the position and orientation of the stylus thereafter can be uniquely determined.

On the other hand, the central axis of the screw hole shape can be specified from the workpiece coordinate system corresponding to the workpiece design data and the machine coordinate system of the coordinate measuring machine. That is, the fixed state of the workpiece in the machine coordinate system of the coordinate measuring machine the workpiece coordinate system and the machine coordinate system offset (displacement and inclination of the three axes) is determined, the screw holes on the design data of the offset and the workpiece By combining the central axis (position and direction) of the shape, the central axis of the screw hole shape in the machine coordinate system can be calculated.
Thus, if each axis is converted into a machine coordinate system, the operation for matching each axis can be appropriately performed by existing techniques.

Note that a screw hole- shaped reference surface can be assumed at a position where the depth of the center axis of the screw hole shape is zero. At this time, the center axis of the screw hole shape as a reference plane normal to the threaded hole shape.
Usually, since the screw hole shape is carved perpendicularly to the surface of the workpiece, the reference surface of the screw hole shape is parallel to the surface of the workpiece, and the opening surface where the depth of the screw hole shape is 0, that is, the workpiece surface becomes the reference surface. . Therefore, it is common to normal perpendicular direction to the surface of the threaded hole shape forming portion of the work is in the axis of the threaded hole shape, also determine an axial threaded hole shape from the shape of the workpiece surface it can. However, for the screw hole shape inclined from the workpiece surface, it is desirable that the reference plane does not coincide with the workpiece surface, and the axial direction is determined from design data or the like.

(Regarding the scanning measurement process)
In the present invention, it is desirable that the scanning measurement step performs a scanning operation along an axis at each of a plurality of circumferential positions of the screw hole shape.
The following forms can be selected as the copying operation.

When targeting screw holes, a method of proceeding from the opening side to the back and a method of proceeding to the tip (bottom) first and returning to the opening can be employed.
Specifically, as the former, first, the stylus is brought into contact with the periphery of the screw hole opening of the work, and in this state, the stylus is moved to the inside of the screw hole to enter the screw hole. Then, following the screw shape of the inner peripheral surface, the copy is moved to the tip of the screw hole. As the latter, first, a stylus is inserted along the central axis into the tip (bottom surface) of the screw hole of the workpiece, and the outer side is brought into contact with the screw shape of the inner peripheral surface. Then, it is moved along the central axis to the opening.

The plurality of positions to mimic have work, 3-4 sites can be said to be appropriate, for example, 90 degrees apart. If the number is less than three, the calculation is difficult, and if the number is more than four, the man-hours increase.

When the copying operation is performed toward the bottom surface of the screw hole, it is desirable that the copying operation is finished at a position where the screw hole- shaped incomplete screw portion starts.
At this time, it is preferable that the end of the complete threaded portion is determined to be ended when the change in the contour data of the screw hole shape detected during the copying operation becomes equal to or less than a certain width.

If so this avoids disorders such as collision of the stylus with respect to the screw hole bottom and the workpiece surface in advance.

The following can be said about the above-described calculation process.
It is preferable that the calculation step includes an incomplete screw portion determination process for determining an incomplete screw portion from a change in thread depth of a screw portion or a change in screw pitch of measurement data obtained by the scanning measurement.

In general, the screw hole shape can be divided and full thread portion continued from the base portion (opening near beside the threaded holes), in the incomplete thread portion present near the distal end. Since the characteristic value of the screw hole shape measured in the present invention is an original screw hole shape, it is desirable that the complete screw portion is a measurement target and information on the incomplete screw portion is not included. Further, since the screw length is the length of the complete thread portion, in order to take this value, it is essential to determine the incomplete thread portion.

The incomplete thread portion determination processing is performed by approximating the incomplete thread based on a function or a numerical table obtained in advance from a change in thread valley depth or a change in screw pitch in the screw hole shape axial direction. It is desirable to determine the start point of the part.
In this way, the boundary of the complete thread portion can be defined by proportional calculation etc. even for continuous screw hole shapes, and the effective screw length can be measured by determining the section of the complete thread portion. it can.

The calculation step takes out the measurement contour shape of the screw portion from the measurement data by the scanning measurement, takes out the approximate contour shape by approximating the screw slope portion with a straight line in the measurement contour shape, and calculates the screw pitch from the approximate contour shape, It is desirable to include approximate contour shape processing for determining the thread angle and threading depth.
In this way, it is possible to easily measure various characteristic values of the screw shape such as the screw pitch, the screw thread angle, and the thread cutting depth.

In the calculation step, the measurement contour shape of the screw portion is extracted from the measurement data obtained by the scanning measurement, and the approximate contour shape is extracted by approximating the screw slope portion with a straight line in the measurement contour shape. It is desirable to include an effective diameter calculation process in which a virtual circle as an alternative to the method needle is brought into contact and an effective diameter of the screw hole shape is calculated by the conventional three-needle method.
If it does in this way, the measurement of the effective diameter of a screw hole shape can be performed easily.

(Regarding the probe)
In the present invention, the scanning probe is preferably attached to the coordinate measuring machine via a rotating probe head, and the rotating probe head is tilted so that the axis of the stylus is aligned with the scanning axis in the axis alignment step.

  As a rotating probe head, the base can be mounted on the probe mounting portion of the coordinate measuring machine, other probes can be mounted on the tip, and the tip can be rotated or rotated in any direction with respect to the base. What is necessary is just to use the existing thing which became. Usually, a probe having two degrees of freedom that can be rotated around the mounting axis of the probe mounting portion and can be tilted from 0 to 90 degrees with respect to this axis.

In the present invention, it is desirable to use a branched stylus having a contact portion branched to the side in the scanning measurement step.
As the branch stylus, for example, a cross contact having a contact portion at each tip branched into a cross shape can be used.

In this way, for example, when measuring a plurality of locations on the inside of the screw shape, an auxiliary operation such as rotating the stylus according to the measurement location by using the closest contact portion at each measurement location. Can be omitted.
In addition, a standard stylus having only one spherical contact portion at the tip of a normal linear shaft portion can be used on the outer periphery of the screw shaft, and a stylus with a tip bent into an L-shape is used. Measurement in screw holes is possible.

In the present invention, prior to performing the scanning measurement step using the branching stylus, the direction in which the contact portion of the branching stylus protrudes coincides with the direction of contour variation detected by the scanning measurement. It is desirable to adjust.
Such an operation can be easily executed by using the rotary probe head described above. Alternatively, it can be realized by re-gripping from the tool stocker without a rotating probe head.
In this way, it is possible to execute a measurement operation with an optimum posture for the scanning measurement.

  At this time, it is desirable that the stylus in the tool stocker is always held so that the axial direction of each stylus is in a predetermined posture corresponding to the axial direction of the CMM when mounted on the CMM. .

In this way, when using a branching stylus having a contact portion branched in a specific direction, the protruding side of the contact portion can be reliably identified from the coordinate system of the coordinate measuring machine, and the specific side of the screw shape can be identified. A reliable response can be taken in the copying measurement.
However, even in this case, it is desirable that the direction check with the calibration point and the like and the direction adjustment with the rotary probe head or the like be surely performed after mounting.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a three-dimensional measuring machine 10 capable of measuring a screw shape according to the present invention.
The coordinate measuring machine 10 includes a coordinate measuring machine main body 11 and a host system 12 for fetching necessary measurement values from the coordinate measuring machine main body 11 and processing them.

The three-dimensional measuring machine body 11 is configured as follows.
That is, a surface plate 112 (table) is placed on the vibration isolation table 111 so as to coincide with a horizontal surface with the upper surface as a base surface, and arm supports 113 and 114 erected from both side ends of the surface plate 112. An X-axis guide 115 is supported on the upper end of the X-axis.

  The arm support 113 is arranged such that its lower end is movable in the Y-axis direction along the Y-axis guide 116, and the arm support 114 is moved in the Y-axis direction on the surface plate 112 by the air bearing. Supported as possible.

  The X-axis guide 115 guides a Z-axis guide 117 extending in the vertical direction in the X-axis direction. A Z-axis arm 118 is provided on the Z-axis guide 117 so as to move along the Z-axis guide 117, and a contact type probe 13 is attached to the lower end of the Z-axis arm 118.

  The probe 13 continuously contours by using an existing touch trigger probe that outputs a contact detection signal to the host system 12 when it contacts the workpiece W placed on the surface plate 112 or by following the contact state. A scanning probe or the like to output, and X, Y, Z axis coordinate values at the time of contact or continuous scanning measurement data is sent to the host system 12 for definition calculation processing.

  As will be described later, the probe 13 is connected to the Z-axis arm 118 via a rotating probe head, and the tip stylus can be appropriately replaced. At this time, in order to suppress a variation error for each replaced stylus, the coordinate measuring machine 10 performs a calibration operation each time the stylus is replaced. For this purpose, calibration points 119 are installed at the corners of the surface plate 112.

The calibration point 119 has a spherical tip, and its center position and radius have been accurately measured. Accordingly, when the stylus is exchanged, the error of each stylus can be calculated by the measurement of the calibration point 119 and the correction can be made accordingly.
Thereby, the coordinate alignment between the machine coordinate system defined in the coordinate measuring machine 10 and the probe coordinate system set in the probe 13 or the stylus is performed.

The host system 12 is configured as follows.
That is, the host system 12 includes a host computer 121, a monitor 122, a printer 123, and a keyboard 124.
The host computer 121 includes an existing software program that calculates the shape data of the workpiece W from the signal from the probe 13, and can execute these appropriately to perform predetermined calculation processing.

Specifically, when the probe 13 is a touch trigger probe, the current position coordinate value of the coordinate measuring machine main body 11 is read based on the contact signal, and the coordinate position of the contact portion at the tip of the probe 13 is determined. This value is the position of the surface of the workpiece W with which the probe 13 is in contact.
When the probe 13 is a scanning probe, the coordinate measuring machine main body 11 is caused to execute a predetermined scanning operation, and measurement data from the probe 13 is continuously monitored and recorded as a contour shape. Thereby, the outline shape of the specific part of the workpiece | work W can be measured.

FIG. 2 shows the probe 13.
As described above, the probe 13 of this embodiment is attached to the Z-axis arm 118 via the rotating probe head 131. As described above, as the probe 13, a touch trigger probe or a scanning probe is appropriately selected.

The rotary probe head 131 is rotatable so that the probe 13 is inclined from 0 degrees to 90 degrees around the rotation axis 132 (A direction in the figure). Further, the main body portion is rotatable 360 degrees with respect to the connecting shaft 133 with respect to the Z-axis arm 118 (direction B in the figure).
As the stylus mounted on the probe 13, a linear standard stylus 134 or a cross stylus 135 having branches in four directions is appropriately selected. Each stylus includes a spherical contact portion 136 at the tip.

  The above-described probe 13 and stylus 134 and 135 are appropriately replaced based on an operation command from the host computer 121. Further, the probe 13 and the stylus 134 and 135 that are selectively used can be automatically replaced by preparing them in a tool stocker arranged within the moving range of the coordinate measuring machine main body 11 (not shown in FIG. 1). ).

Next, the measurement of the screw shape performed using the coordinate measuring machine 10 will be described.
FIG. 3 shows the characteristic values of the screw shape measured in this embodiment.
In FIG. 3, a screw hole WH is formed on the surface W1 of the workpiece W, and a screw shape WS is formed on the inner periphery thereof. The thread shape WS has a complete thread S1, an incomplete thread S2, and a drill pilot hole S3 from the opening SO to the back. Here, the depth SM of the drill pilot hole, the thread length SL of the complete thread portion S1, the effective thread diameter SD of the complete thread portion S1, and the position SP of the center axis S4 of the thread shape WS are characteristic values to be measured. .

  In order to measure these characteristic values, a series of processes shown in FIGS. 4, 5, and 6 are executed in this embodiment. These processes are executed by the coordinate measuring machine main body 11 operating according to an operation command based on a program executed by the host computer 121.

First, the coordinate system is set (processing ST1).
In this process, with the touch trigger probe that is normally used and the standard stylus 134 mounted, the machine coordinate system and the probe coordinate system are aligned by the calibration point 119 described above, and then a predetermined surface portion of the workpiece W is obtained. Measure several points. That is, the surface portion of the workpiece W is known in advance based on the design data, but the measured value of each point changes according to the mounting state of the workpiece W on the surface plate 112. Therefore, the calibration value is calculated from the measurement values at a plurality of points here, and the measurement values of each part of the workpiece W thereafter are corrected.

Next, provisional measurement of the center coordinate SP ′ of the thread shape WS of the workpiece W is performed (processing ST2).
In this process, an existing thread measurement macro command or the like is used. Specifically, the conventional screw shaft position measuring method described above is used. By this processing, the position SP ′ of the central axis S4 of the thread shape WS is provisionally measured.

When the provisional position SP ′ of the central axis S4 is obtained, the drill pilot hole depth SM, which is one of the characteristic values to be measured, is measured (processing ST3).
In this process, the probe 13 is first exchanged from a touch trigger probe to a scanning probe. The stylus is a standard stylus 134. After replacement, calibrate at calibration point 119.

In this state, the probe 13 is moved, the stylus 134 is introduced into the screw hole WH, and lowered along the central axis S4, so that the contact portion 136 at the tip is brought into contact with the bottom center S5 as shown in FIG. The moving distance to the contact may be roughly determined with reference to the design data of the workpiece W.
In the state where the contact portion 136 of the stylus 134 is in contact with the bottom center S5, X = (d / 2) tanθ-r / cosθ is the drill pilot hole portion as the radius r of the contact portion 136 and the inner diameter d of the drill pilot hole portion S3. The distance from the lower end of S3 to the center of the contact portion 136. Therefore, the depth SM of the drill pilot hole is obtained by subtracting X from the coordinate position in the direction of the central axis S4.

Next, the process moves to the main measurement of the center coordinate SP of the thread shape WS, which is the characteristic value of the measurement target, and the measurement of the effective diameter SD.
First, the standard stylus 134 is removed from the probe 13 serving as a scanning probe, and the cross stylus 135 is attached. Once installed, calibrate at calibration point 119. At the same time, the posture of the stylus 135 is adjusted. Specifically, the orientation of the stylus 135 is adjusted so that the contact portions 136 on the + Y axis side, the −Y axis side, the + X axis side, and the −X axis side of the stylus 135 correctly face each axial direction of the machine coordinate system.
In this state, the rotary probe head 131 is operated to align the scanning axis of the probe 13 with the central axis S4 of the screw hole WH. For the central axis S4, the design data value of the workpiece W is referred to (process ST4).

In this state, the copying operation of the thread shape WS on the inner periphery of the screw hole WH is performed (processing ST5). Details of the copying operation are shown in FIG.
That is, the stylus 135 is arranged at the opening center position of the screw hole WH (process ST11), introduced into the screw hole WH, and then lowered (moved to the back side) along the central axis S4 (process ST12). Based on the design data of the workpiece W or the previously measured drill pilot hole depth SM, the contact portion 136 is decelerated when it reaches the vicinity of the bottom of the screw hole, and when it reaches the bottom surface, the movement is stopped (processing ST13).

  Subsequently, it is moved in the radial direction in the direction of any one of the contact parts 136 (for example, + Y direction) (process ST14), and stopped when the contact part 136 contacts the screw shape WS (process ST15). In this state, the stylus 135 is raised (moved toward the opening side) along the central axis S4 (processing ST16), and when the screw hole opening SO is reached (processing ST17), the stylus 135 is taken out of the screw hole WH (processing). ST18). Among these, the contour data of the thread shape WS is measured during the process ST16.

A series of these operations is as shown in FIG. In FIG. 8, each arrow indicates the locus of the contact portion 136.
As a result, the contour in one direction (+ Y direction) of the screw shape SW is temporarily measured, and a mountain valley from the screw hole opening SO in this direction is grasped.

  Returning to FIG. 4, in order to measure the effective diameter SD and the center position SP of the screw hole WH, the point measurement is repeated four times at intervals of 90 degrees in each of the + Y, -Y, + X, and -X directions (processing ST6). ). Details of this point measurement are shown in FIG.

  In other words, the stylus 135 is placed at the center of the opening of the screw hole WH (process ST21), introduced into the screw hole WH, lowered (moved to the back side) along the center axis S4, and first selected in process ST14. The same contact portion 136 (here, the + Y direction) as that moved moves from the screw hole opening SO to the Z-axis position that is the fourth valley (processing ST22).

In this state, the previous contact portion 136 in the + Y direction is moved in the corresponding + Y direction, and is brought into contact with the opposing valley of the thread shape WS, and the position thereof is measured (processing 23).
Next, the stylus 135 is returned to the center, and the Z-axis position is lowered by a quarter pitch (processing ST24). The thread pitch P at this time uses the design data of the workpiece W.
In this state, the adjacent + X direction contact part 136 is moved in the corresponding + X direction, and is brought into contact with the opposing valley of the thread shape WS, and the position thereof is measured (processing 25).

At this time, the Z-axis position is shifted by P / 4. Therefore, the contact portion 136 in the + X direction enters a screw valley that is continuous with the screw valley in which the contact portion 136 in the + Y direction is first inserted.
By repeating these radial movements and Z-axis P / 4 movements at the center, point measurement in the -Y direction and -X direction is also sequentially performed (processing ST26 to ST29). When the point measurement in the + X direction is completed, the stylus 135 is taken out of the screw hole WH (processing ST30).

A series of these operations is as shown in FIGS. In each figure, each circle indicates the position of each process of the contact portion 136, and each arrow indicates the locus of the contact portion 136.
As a result, the four directions of + Y, -Y, + X, and -X, that is, the points for one round every 90 degrees, are measured with respect to the series of thread valleys of the thread shape SW.

  Returning to FIG. 4, the host computer 121 calculates the point data in the four directions + Y, -Y, + X, and -X related to the series of thread valleys of the thread shape SW measured as described above, so that the screw holes WH are processed. The effective diameter SD and the center position SP are grasped (process ST7).

The calculation of the effective diameter SD of the screw hole WH is performed as follows by applying a known three-needle calculation method used for the screw shaft to the screw hole.
First, since the center coordinates of the contact portion 136 in the four contact states are obtained from the four points measured point data, the diameter SD1 of one circle passing through the center coordinates is obtained. Here, when the radius r of the contact portion 136, the nominal pitch P of the screw, the thread angle α, and the thread height h0, the relationship shown in FIG. 11 is established.
That is, the distances h1, h3, and h in the figure are as follows.

(Equation 1)
h1 = h2 cosec (α / 2) = r cosec (α / 2)
h3 = h0 / 2 = (P / 4) cot (α / 2)
h = h1-h3 = {r cosec (α / 2)} − {(P / 4) cot (α / 2)}

  Therefore, the effective diameter SD of the screw hole WH is as follows.

(Equation 2)
SD = SD1 + 2h
= SD1 + 2 [{r cosec (α / 2)} − {(P / 4) cot (α / 2)}]
= SD1 + 2r cosec (α / 2) − (P / 2) cot (α / 2)

Next, in order to measure the screw length SL of the inner periphery of the screw hole WH, the copying operation of the screw shape WS is performed (processing ST8). The details of the copying operation are the procedure shown in FIG.
Then, based on the scanning measurement data obtained here, the boundary position between the incomplete screw portion S2 and the complete screw portion S1 of the screw shape WS is determined, and thereby the screw length SL is set as the length of the complete screw portion S1. Calculate (process ST9).

Specifically, the following calculation procedure is adopted.
In FIG. 12, the thread shape WS has an incomplete screw portion S2 below the complete screw portion S1, and a drill pilot hole portion S3 further below. The scanning measurement trajectory WS1 is obtained by sequentially recording the center position of the contact portion 136 in the previous scanning operation.

  By linearly approximating the scanning measurement trajectory WS1, a linear approximate trajectory WS2 along the slope of each thread is calculated. The intersections on the crest and trough sides of the approximate locus WS2 do not include machining errors, roundness deformation, and the like, so that the positions can be determined with higher accuracy than the actual thread crest and thread trough tips. Then, the distance (= radius Ri) from the central axis S4 of the intersection on the valley side among the intersections is sequentially calculated.

  Here, if it is 90% or more of the nominal thread outer diameter R0, it is defined as a complete thread part F1, and if it is less than that, it is defined as an incomplete thread part F2. That is, the true boundary radius RS ′ = R0 × 0.9. The distance from the central axis S4 of the center position of the contact portion 136 (radius r) with respect to the corresponding thread valley is assumed to be a temporary boundary radius RS = RS′−r.

  Based on such a temporary boundary radius RS, if the radius Ri of the intersection of the valleys calculated earlier is evaluated, for example, if the radius Rn + 1 or larger is larger than the temporary boundary radius RS, and if Rn or smaller is smaller than the temporary boundary radius RS, , There will be an actual boundary between the two valleys.

The actual Z-axis position of the boundary can be determined as follows.
As shown in FIG. 13, the Z-axis position is shifted by one pitch P between the valley of radius Rn + 1 belonging to the complete screw portion S1 and the valley of radius Rn belonging to the incomplete screw portion S2. As is apparent from the figure, there is a relationship of (RS−Rn) / ΔZ = (Rn + 1−Rn) / P, and from this, ΔZ = P (Rn + 1−Rn) / (RS−Rn). Therefore, if ΔZ is subtracted from the Z-axis position of the valley having the radius Rn, the actual boundary position can be obtained. Then, by subtracting the Z-axis position of the opening SO of the screw hole WH from this value, the screw length SL of the complete screw portion S1 can be calculated.

Although FIG. 13 shows the case where the valley depth changes linearly, this change may change in another function, for example, an exponential function.
Further, these relationships may be stored in advance in a table so that they can be referred to as appropriate.
As a result, the drilling hole depth SM of the thread shape WS, the thread length SL of the complete thread portion S1, the effective thread diameter SD of the complete thread portion S1, and the position SP of the central axis S4 of the thread shape WS were all measured. become.

According to this embodiment, there are the following effects.
That is, the surface shape of the normal workpiece W can be measured by the coordinate measuring machine 10. That is, the probe group extending from the probe 13 to the stylus 134, 135 has an existing configuration, and does not hinder a normal shape measuring operation on the surface of the workpiece W.

On the other hand, with respect to the thread shape WS formed on the workpiece W, various characteristic values of the thread shape can be measured with the same apparatus.
That is, the scanning probe is set in a predetermined posture in which the scanning direction is aligned with the axial direction of the thread shape WS on the surface of the workpiece W by the axis alignment process. Then, the thread shape WS is copied and measured by the scanning measurement process. Furthermore, each characteristic value of the screw shape WS can be calculated from the data obtained by scanning measurement by the calculation process.

  Therefore, it is possible to seamlessly execute from the shape measurement of the normal workpiece W surface to the measurement of the screw shape WS, which conventionally required separate work, using the CMM 10, and inline on the production line etc. Measurement can also be performed.

In addition, this invention is not limited to the said embodiment, The deformation | transformation etc. which are shown below are also included in this invention.
That is, in the embodiment, as the characteristic value of the thread shape WS to be measured, the drill pilot hole depth SM, the thread length SL of the complete thread portion S1, the effective thread diameter SD of the complete thread portion S1, the central axis of the thread shape WS Although the four positions SP of S4 are set, other characteristic values may be selected.

That is, in the above-described embodiment, the pitch P obtained exclusively from the workpiece design data is used. However, in the approximate trajectory WS2 (see FIG. 12) obtained by linear approximation of the scanning measurement trajectory WS1, the intersection on the thread side or the trough side. You may obtain | require exact pitch P 'from the position of an intersection.
Similarly, in the approximate locus WS2, the thread angle may be obtained from the crossing angle of the thread side intersection or the valley side intersection.

  In the embodiment, after the coordinate system is set (processing ST1), the center coordinates are temporarily measured by the existing method (processing ST2). However, this may be omitted as appropriate. If omitted, the design data of the workpiece W can be substituted.

  In the above-described embodiment, the copying operation 1 (processing ST5) is performed before the four point measurements, and then the copying operation 2 (processing 8) for measuring the screw length is performed. Also good. For example, the screw length measurement may be performed first and the point measurement may be performed later. Alternatively, the copying operation 1 before the point measurement may be omitted. In this case, the thread valley may be searched by referring to the design data of the workpiece W.

Furthermore, in the above-described embodiment, each characteristic value is calculated for each measurement operation. However, the calculation process may be performed collectively after all measurement operations are performed.
In the above embodiment, the measurement of the screw shape inside the screw hole is performed, but the measurement of the screw shape outside the screw shaft may be performed.

In the above-described embodiment, the copying operation is performed with the stylus returning from the back of the hole to the opening side. However, the copying operation may be performed from the opening side to the back side.
14 to 16 show another embodiment of the present invention.
As shown in FIG. 16, in this embodiment, the same apparatus configuration as that of the previous embodiment is used, but the stylus 135 repeats the copying operation from the opening SO side of the screw hole WH to the inside three times to measure the screw shape WS. To do.

  In FIG. 14, the setting of the coordinate system (processing ST31) and the setting of the stylus axis (processing ST32) are the same as in the above embodiment. In the subsequent movement to the scanning measurement start position (process 33), the stylus 135 is disposed slightly above the opening SO of the screw hole WH. From this starting position, the following three scanning measurements (processes ST34 to ST36) are performed.

  In FIG. 15, in each scanning measurement, first, the stylus 135 is disposed slightly above the opening SO of the screw hole WH (processing ST41). Next, the stylus 135 is brought close to the workpiece W (processing ST42), and the contact portion 136 to be measured following the surface W1 of the workpiece W around the screw hole WH is brought into contact (processing ST43). Then, the stylus 135 is moved toward the center of the screw hole WH in the contact state (process ST44), and is continued until the contact portion 136 reaches the opening SO of the screw hole WH (process ST45).

  Subsequently, with the contact portion 136 in contact with the screw shape WS of the screw hole WH, the stylus 135 is lowered along the central axis S4 (see FIG. 3) of the screw hole WH, and the contour of the screw shape WS is measured. (Processing ST46). This scanning measurement is continued until the incomplete thread portion F2 (see FIG. 3) is detected.

  Here, the detection of the incomplete thread portion F2 is determined to be detected when the variation in the radial value of the contour data in the scanning measurement becomes below a certain value (when the height of the thread thread valley becomes small). (Processing ST47). When the incomplete screw portion is detected, the stylus 135 is moved to the center of the screw hole WH and pulled out (processing ST48).

  After these three scanning measurements, each characteristic value of the screw shape is calculated (processing ST37). Here, in addition to the thread length SL and thread pitch P ′ of the thread shape WS by scanning measurement, the position and inclination of the central axis S4 can be detected by measuring the positions of three points in the circumferential direction.

  As described above, according to the present invention, various characteristic values of the screw shape can be measured using a general three-dimensional measuring machine.

The present invention relates to a screw hole shape measuring method, in particular using a general three-dimensional measuring machine is suitable threaded hole shape measuring method capable of measuring a characteristic value of the screw hole shape.

The perspective view which shows the apparatus structure of one Embodiment of this invention. The disassembled perspective view which shows the probe of the said embodiment. The schematic cross section which shows the screw hole of the said embodiment. The flowchart which shows the basic process of the said embodiment. The flowchart which shows the copying operation | movement of the said embodiment. The flowchart which shows the point measurement of the said embodiment. The schematic cross section which shows the drill pilot hole depth measurement of the said embodiment. FIG. 6 is a schematic cross-sectional view showing the copying operation of the embodiment. The schematic cross section which shows the point measurement of the embodiment. The schematic plan view which shows the point measurement of the said embodiment. The schematic cross section which shows the calculation of the effective diameter of the said embodiment. The schematic plan view which shows the calculation of the complete thread part boundary of the said embodiment. The graph which shows the calculation of the complete thread part boundary of the said embodiment. The flowchart which shows the basic process of other embodiment of this invention. The flowchart which shows the copying operation | movement of the said other embodiment. The schematic perspective view which shows the copying operation | movement of the said other embodiment.

Explanation of symbols

10 CMM
11 CMM body
13 Probe
121 Host computer
131 Rotating probe head
134 Standard stylus
135 Cross Stylus
136 Contact part W Workpiece
WH screw hole
WS thread shape
W1 Work surface
SO Screw hole opening
S1 Full thread
S2 Incomplete thread
S3 Drill pilot hole
S4 center axis
SP center axis position
SM Drill pilot hole depth
SL thread length
SD effective diameter

Claims (8)

A screw hole shape measuring method for measuring a screw hole shape using a three-dimensional measuring machine,
A three-dimensional measuring machine on which a workpiece having a screw hole shape to be measured is mounted, a scanning probe mounted on the three-dimensional measuring machine, and a stylus having a contact portion mounted on the scanning probe and in contact with the workpiece Use
An alignment step of aligning the scanning measurement axis of the scanning probe with the central axis of the screw hole shape;
A scanning measurement step of moving the scanning probe along the scanning measurement axis while bringing the stylus into contact with the screw hole shape;
A calculation step of calculating various characteristic values of the screw hole shape from the measurement data obtained by the scanning measurement,
In the scanning measurement step, using a branched stylus having a contact portion branched to the side,
The calculation step takes out a measurement contour shape of a screw portion from measurement data obtained by scanning measurement in which the branched contact portion is brought into contact, and takes out an approximate contour shape by approximating a screw slope portion with a straight line in this measurement contour shape, A screw hole shape characterized by including an effective diameter calculation process in which a virtual circle that is an alternative to the needle of the conventional three-needle method is brought into contact with this contour shape, and the effective diameter of the screw hole shape is calculated by the conventional three-needle method Measuring method. In the screw hole shape measuring method according to claim 1, wherein the scanning-measurement process, the screw hole shape measuring method and performing the copying operation, respectively along the axis for a plurality of locations in the circumferential direction of the threaded hole shape. 3. The screw hole shape measuring method according to claim 1, wherein, prior to performing the scanning measurement step using the branched stylus, a direction in which a contact portion of the branched stylus protrudes is the scanning measurement. A screw hole shape measuring method, wherein the posture is adjusted so as to coincide with the direction of the contour variation detected in step (1). 4. The screw hole shape measuring method according to claim 1, wherein a mechanical coordinate system set in the coordinate measuring machine and a workpiece coordinate set in the workpiece are set before the axis alignment step. 5. A screw hole shape measuring method, comprising: performing a coordinate alignment step of adjusting a relative relationship between a system and a probe coordinate system set on the scanning probe and the stylus. 5. The screw hole shape measuring method according to claim 1, wherein the calculation step is incomplete from a change in a thread valley depth or a change in a screw pitch of a thread portion of measurement data by the scanning measurement. A screw hole shape measuring method comprising: an incomplete screw portion determination process for determining a screw portion. 6. The screw hole shape measuring method according to claim 5, wherein the incomplete thread portion determination process is a function or a numerical value obtained in advance from a change in a thread valley depth or a screw pitch in the screw portion with respect to the screw hole shape axial direction. A screw hole shape measuring method, wherein the starting point of the incomplete thread portion is determined by approximation based on a table. The screw hole shape measuring method according to any one of claims 1 to 6, wherein the calculation step extracts a measurement contour shape of a screw portion from measurement data obtained by the scanning measurement, and a screw slope portion in the measurement contour shape. A screw hole shape measuring method comprising: an approximate contour shape processing for extracting an approximate contour shape by approximating a straight line and determining a screw pitch, a thread angle, and a thread cutting depth from the approximate contour shape. The screw hole shape measuring method according to any one of claims 1 to 7, wherein the scanning probe is attached to the coordinate measuring machine via a rotating probe head, and the axis of the stylus is adjusted in the axis alignment step. A screw hole shape measuring method, wherein the rotary probe head is tilted so as to be aligned with the scanning axis.

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