JP4208357B2 - Thread shape measurement method - Google Patents

Description

【００７１】
従って、ねじ穴WHの有効径SDは次式の通りとなる。
【００７２】
【数２】

【００７３】
次に、ねじ穴WHの内周のねじ長SLを測定するために、ねじ形状WSの倣い動作を行う（処理ST8）。この倣い動作の詳細は前述の図５の手順である。
そして、ここで得られた倣い測定データに基づいて、ねじ形状WSの不完全ねじ部S2と完全ねじ部s1との境界位置を割出し、これにより完全ねじ部S1の長さとしてねじ長SLを演算する（処理ST9）。
【００７４】
具体的には次のような演算手順を採用する。
図１２において、ねじ形状WSは完全ねじ部S1の下方には不完全ねじ部S2があり、更に下方にはドリル下穴S3が続いている。倣い測定軌跡WS1は、先の倣い動作の際の接触部136の中心位置を順次記録したものである。
【００７５】
倣い測定軌跡WS1を直線近似することで、各ねじ山の斜面に沿った直線的な近似軌跡WS2を計算する。この近似軌跡WS2の山側の交点および谷側の交点は、加工誤差や丸み変形等を含まないため実際のねじ山先端およびねじ谷先端よりも高精度に位置を確定できる。そして、各交点のうち谷側の交点の中心軸線S4からの距離（＝半径Ri）を順次計算する。
【００７６】
ここで、公称のねじ外径R0に対し、その90％以上あれば完全ねじ部F1、以下であれば不完全ねじ部F2と規定する。つまり、真境界半径RS'=R0×0.9とする。そして、対応するねじ谷に対する接触部136（半径r）の中心位置の中心軸線S4からの距離を仮境界半径RS=RS'-rとする。
【００７７】
このような仮境界半径RSに基づいて、先に計算した各谷の交点の半径Riを評価すると、例えば半径Rn+1以上は仮境界半径RSより大きく、Rn以下が仮境界半径RSより小さければ、この２つの谷の間に実際の境界が存在することになる。
【００７８】
この実際の境界のZ軸位置は次のように確定することができる。
図１３に示すように、完全ねじ部S1に属する半径Rn+1の谷と不完全ねじ部S2に属する半径Rnの谷とは１ピッチP分だけZ軸位置がずれている。そして、図から明らかなように(RS-Rn)/ΔZ=(Rn+1-Rn)/Pの関係があり、これからΔZ=P(Rn+1-Rn)/(RS-Rn)となる。従って、半径Rnとなった谷のZ軸位置からΔZを差引けば、実際の境界の位置が求まる。そして、この値から更にねじ穴WHの開口SOのZ軸位置を差引けば、完全ねじ部S1のねじ長SLが算出できる。
【００７９】
なお、図１３では谷部深さが直線的に変化する場合を示したが、この変化は他の関数、例えば指数関数的に変化するものであってもよい。
更に、これらの関係はテーブルに予め格納しておき、適宜参照できるようにしてもよい。
以上により、ねじ形状WSのドリル下穴の深さSM、完全ねじ部S1のねじ長SL、完全ねじ部S1のねじ有効径SD、ねじ形状WSの中心軸線S4の位置SPが全て測定できたことになる。
【００８０】
このような本実施形態によれば次に示すような効果がある。
すなわち、三次元測定機10により通常のワークＷ表面の形状測定を行うことができる。つまり、プローブ13、スタイラス134,135に至るプローブ群は既存の構成であり、通常のワークＷ表面の形状測定動作を妨げるものではない。
【００８１】
一方、ワークＷに形成されたねじ形状WSについても、同じ装置のままねじ形状の各種特性値の測定を行うことができる。
すなわち、軸合わせ工程により、倣いプローブがワークＷ表面のねじ形状WSに対して、その軸線方向に倣い方向が合わせられた所定の姿勢でセットされる。そして、倣い測定工程により、ねじ形状WSが倣い測定される。さらに、演算工程により、倣い測定によるデータから、ねじ形状WSの各特性値を演算することができる。
【００８２】
従って、三次元測定機10を用いて、通常のワークＷ表面の形状測定から、従来は別途作業が必要だったねじ形状WSの測定までをシームレスに実行することができ、製造ライン等でのインライン測定を行うことも可能となる。
【００８３】
なお、本発明は前記実施形態に限定されるものではなく、以下に示す変形等も本発明に含まれるものである。
すなわち、前記実施形態では、測定するねじ形状WSの特性値として、ドリル下穴の深さSM、完全ねじ部S1のねじ長SL、完全ねじ部S1のねじ有効径SD、ねじ形状WSの中心軸線S4の位置SPの４つを設定したが、他の特性値を選択してもよい。
【００８４】
すなわち、前記実施形態では専らワークの設計データから得たピッチPを用いていたが、倣い測定軌跡WS1の直線近似で得られた近似軌跡WS2（図１２参照）におけるねじ山側の交点あるいは谷側の交点の位置から正確なピッチP'を求めてもよい。
また、同じく近似軌跡WS2において、ねじ山側の交点あるいは谷側の交点の交叉角度からねじ山角度を求めても良い。
【００８５】
前記実施形態においては、座標系の設定（処理ST1）の後、既存方法による中心座標の仮測定（処理ST2）を行ったが、これは適宜省略してもよい。省略した場合、ワークＷの設計データを代用する等ができる。
【００８６】
また、前記実施形態では、4回のポイント測定の前に倣い動作１（処理ST5）を行い、その後にねじ長測定のための倣い動作２（処理8）を行ったが、これは兼用してもよい。例えば、先にねじ長測定を行い、後でポイント測定を行ってもよい。あるいは、ポイント測定の前の倣い動作１を省略してもよい。この場合、ワークＷの設計データを参照する等によりねじ谷を探る等すればよい。
【００８７】
更に、前記実施形態では各測定動作の都度、各特性値を演算するようにしたが、全ての測定動作を行った後に一括して演算工程を実施してもよい。
また、前記実施形態ではねじ穴の内側のねじ形状の測定を行ったが、ねじ軸の外側のねじ形状の測定を行ってもよい。
【００８８】
また、前記実施形態ではスタイラスを穴の奥から開口側へ戻る形で倣い動作を行ったが、開口側から奥側へ向けて倣い動作を行うようにしてもよい。
図１４ないし図１６には本発明の他の実施形態が示されている。
図１６に示すように、本実施形態では前記実施形態と同じ装置構成を用いるが、スタイラス135はねじ穴WHの開口SO側から内部へと向う倣い動作を3回繰返してねじ形状WSの測定を行うようになっている。
【００８９】
図１４において、座標系の設定（処理ST31）、スタイラス軸線の設定（処理ST32）は前記実施形態と同様である。続く倣い測定開始位置への移動（処理33）は、ねじ穴WHの開口SOのやや上方にスタイラス135を配置する。この開始位置から、続く3回の倣い測定（処理ST34〜ST36）を行う。
【００９０】
図１５において、各倣い測定においては、先ずスタイラス135をねじ穴WHの開口SOのやや上方に配置する（処理ST41）。次に、スタイラス135をワークＷに近接させ（処理ST42）、ねじ穴WHの周辺のワークＷの表面W1に倣い測定する接触部136を当接させる（処理ST43）。そして、当接状態のままスタイラス135をねじ穴WHの中心向きに移動させ（処理ST44）、接触部136がねじ穴WHの開口SOに達するまで続ける（処理ST45）。
【００９１】
続いて、接触部136をねじ穴WHのねじ形状WSに当接させたまま、スタイラス135をねじ穴WHの中心軸線S4（図３参照）に沿って下降させ、ねじ形状WSの輪郭を倣い測定する（処理ST46）。この倣い測定は、不完全ねじ部F2（図３参照）が検出されるまで続ける。
【００９２】
ここで、不完全ねじ部F2の検出は、倣い測定における輪郭データの径方向の値の変動が一定以下になった時（ねじ山ねじ谷の高さが小さくなった時）に検出と判定する（処理ST47）。不完全ねじ部が検出されたら、スタイラス135をねじ穴WHの中心に寄せ、外へ引出す（処理ST48）。
【００９３】
これら3回の倣い測定の後、ねじ形状の各特性値を演算する（処理ST37）。ここでは、倣い測定によりねじ形状WSのねじ長SL、ねじピッチP'の他、周方向に3点の位置を測定することで中心軸線S4の位置や傾き等も検出可能できる。
【００９４】
【発明の効果】
以上に述べたように、本発明によれば、一般的な三次元測定機を利用してねじ形状の各種特性値の測定を行うことができる。
【図面の簡単な説明】
【図１】本発明の一実施形態の装置構成を示す斜視図。
【図２】前記実施形態のプローブを示す分解斜視図。
【図３】前記実施形態のねじ穴を示す模式断面図。
【図４】前記実施形態の基本工程を示すフローチャート。
【図５】前記実施形態の倣い動作を示すフローチャート。
【図６】前記実施形態のポイント測定を示すフローチャート。
【図７】前記実施形態のドリル下穴深さ測定を示す模式断面図。
【図８】前記実施形態の倣い動作を示す模式断面図。
【図９】前記実施形態のポイント測定を示す模式断面図。
【図１０】前記実施形態のポイント測定を示す模式平面図。
【図１１】前記実施形態の有効径の演算を示す模式断面図。
【図１２】前記実施形態の完全ねじ部境界の演算を示す模式平面図。
【図１３】前記実施形態の完全ねじ部境界の演算を示すグラフ。
【図１４】本発明の他の実施形態の基本工程を示すフローチャート。
【図１５】前記他の実施形態の倣い動作を示すフローチャート。
【図１６】前記他の実施形態の倣い動作を示す模式斜視図。
【符号の説明】
10 三次元測定機
11 三次元測定機本体
12 ホストコンピュータ
13 プローブ
131 回転プローブヘッド
134 標準スタイラス
135 十字スタイラス
136 接触部
Ｗ ワーク
WH ねじ穴
WS ねじ形状
W1 ワーク表面
SO 開口
S1 完全ねじ部
S2 不完全ねじ部
S3 ドリル下穴
S4 中心軸線
SP 中心軸線の位置
SM ドリル下穴深さ
SL ねじ長
SD 有効径[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screw shape measuring method, and more particularly, to a screw shape measuring method that enables a characteristic value of a screw shape to be measured using a general three-dimensional measuring machine.
[0002]
[Background]
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.
[0003]
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 the screw holes formed on the workpiece surface, the measurement of the position of each central axis or the measurement of the distance between the axes of a plurality of screw holes is also performed (Japanese Patent Laid-Open No. 6-341826, etc.)
[0004]
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.
[0005]
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. (Japanese Patent Laid-Open No. 62-27607, Japanese Patent Laid-Open No. 9-264719, etc.). In addition, a technique is also known in which a screw shape is accurately measured by contact measurement of an axial contour of a screw shape instead of non-contact, and further by measuring a shape along a screw groove (Japanese Patent Laid-Open No. 55-113907). Such).
[0006]
As a technique for measuring the effective diameter of the screw shaft, a three-needle measurement method has been conventionally known. This is done by placing two needles on one side of the screw shaft and one needle on the opposite side so that each needle fits in the screw groove, and holding the needle on each side with a micrometer spindle to obtain a known needle diameter. Based on this, a screw effective 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.
[0007]
[Problems to be solved by the invention]
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.
[0008]
An object of the present invention is to provide a screw shape measuring method capable of measuring various characteristic values of a screw shape using a three-dimensional measuring machine.
[0009]
[Means for Solving the Problems]
(Basic configuration) The present invention is a screw shape measuring method for measuring a screw shape using a three-dimensional measuring machine, and a three-dimensional measuring machine to which a workpiece having a screw shape to be measured is attached, and this tertiary Using a scanning probe mounted on the former measuring machine and a stylus having a contact portion mounted on the scanning probe and in contact with the workpiece, the surface of the workpiece at a position where the central axis depth of the screw shape is zero is determined. assuming as a reference plane of the thread profile, alignment of the normal of the assumed reference surface determined as the center axis of the thread profile, combining the scanning measurement axis of the scanning probe above the central axis of the determined thread form A scanning measurement step of moving the scanning probe along the scanning measurement axis while bringing the stylus into contact with the screw shape, and measurement data obtained by the scanning measurement. Anda calculation step of calculating the various characteristic values of the thread profile, the scanning measurement step, you and performs the copying operation in each along the axis for a plurality of locations in the circumferential direction of the thread form.
[0010]
(Elements of basic configuration)
The screw shape to be measured may be any of a screw hole (female screw) and a screw shaft (male screw). Further, in addition to normal screw holes and screw shafts, a partial screw for a half circumference may be used.
For the central axis of the screw 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.
[0011]
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.
[0012]
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.
[0013]
(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, with respect to the screw shape formed on the workpiece, various characteristic values of the screw shape can be measured with the same apparatus.
[0014]
That is, in the axis alignment step, the scanning probe is set in a predetermined posture in which the scanning direction is aligned with the axial direction of the thread shape on the workpiece surface. Then, the thread shape is measured by the scanning measurement process. Furthermore, characteristics such as screw pitch, thread angle, thread cutting depth, and the like can be calculated from the data obtained by scanning measurement through the calculation process.
[0015]
Therefore, using a three-dimensional measuring machine, it is possible to seamlessly carry out everything from normal workpiece surface shape measurement to screw shape measurement, which previously required separate work, and in-line measurement on a production line, etc. It is also possible.
[0016]
(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.
[0017]
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.
[0018]
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.
[0019]
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.
[0020]
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.
[0021]
On the other hand, the central axis of the screw 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 offset (three-axis displacement and inclination) between the workpiece coordinate system and the machine coordinate system is determined by the fixed state of the workpiece in the machine coordinate system of the coordinate measuring machine. The center axis of the screw shape in the machine coordinate system can be calculated by combining the center axis (position and direction).
Thus, if each axis is converted into a machine coordinate system, the operation for matching each axis can be appropriately performed by existing techniques.
[0022]
It should be noted that a screw-shaped reference surface can be assumed at a position of depth 0 of the screw-shaped central axis. At this time, the screw-shaped central axis is the screw-shaped reference surface normal.
Usually, since the screw shape is carved perpendicularly to the surface of the workpiece, the screw-shaped reference surface is parallel to the surface of the workpiece, and the opening surface where the screw shape has a depth of 0, that is, the workpiece surface becomes the reference surface. Therefore, the normal direction perpendicular to the surface of the thread shape forming part of the workpiece is generally a screw-shaped axis, and the screw-shaped axis direction can be determined from the shape of the workpiece surface. However, for a screw shape inclined from the workpiece surface, the reference plane does not coincide with the workpiece surface, and it is desirable to determine the axial direction from design data or the like.
[0023]
(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 locations of the screw shape.
The following forms can be selected as the copying operation.
[0024]
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.
[0025]
When targeting the screw shaft, a method of proceeding from the root side toward the tip and a method of proceeding to the tip first and returning to the root can be employed.
Specifically, as the former, first, the stylus is brought into contact with the work surface around the root of the screw shaft, and is brought into contact with the screw shape toward the inside. Then, it is moved along the screw shaft to the tip.
[0026]
On the other hand, as the latter, first, a stylus is arranged in the vicinity of the outer periphery of the tip of the screw shaft and brought into contact with the outer peripheral surface. Then, it is moved along the screw shaft to the root.
As a plurality of places where the copying operation is performed, for example, 3 to 4 places at an interval of 90 degrees are appropriate. If the number is less than three, the calculation is difficult, and if the number is more than four, the man-hours increase.
[0027]
When the copying operation is performed toward the bottom surface of the screw hole, it is preferable that the copying operation is finished at a position where a screw-shaped incomplete screw portion starts.
At this time, it is preferable that the end of the complete thread portion is determined to be ended when the change in the thread-shaped contour data detected during the copying operation becomes a certain width or less.
[0028]
When copying along the root of the screw shaft, the length of the screw-shaped complete screw part should be stored in advance by referring to the design data of the workpiece, and when it has moved by this length, it should be decelerated, etc. Is desirable.
In this way, obstacles such as collision of the stylus against the bottom surface of the screw hole and the workpiece surface can be avoided in advance.
[0029]
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.
[0030]
In general, the screw shape can be classified into a complete screw portion continuing from the base (near the opening of the screw hole, the root of the screw shaft) and an incomplete screw portion existing near the tip. Since the characteristic value of the screw shape measured in the present invention is an original screw 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.
[0031]
The incomplete thread portion determination processing is performed by approximating the incomplete thread portion based on a function or a numerical table obtained in advance from a change in the thread root depth or a change in the screw pitch in the screw shape axial direction. It is desirable to determine the starting point.
In this way, the boundary of the complete thread portion can be defined by proportional calculation or the like for a continuous thread shape, and the effective screw length can be measured by determining the section of the complete thread portion. .
[0032]
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.
[0033]
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 the effective diameter of the screw shape is calculated by the conventional three-needle method.
In this way, the effective diameter of the screw shape can be easily measured.
[0034]
(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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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.
[0039]
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. .
[0040]
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.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
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.
[0042]
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.
[0043]
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.
[0044]
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.
[0045]
The probe 13 continuously contours by following 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 in a contact state. A scanning probe or the like that is output in this manner, 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.
[0046]
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 11 performs a calibration operation every time the stylus is replaced. For this purpose, calibration points 119 are installed at the corners of the surface plate 112.
[0047]
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.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
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.
[0052]
The probe 13 and the stylus 134 and 135 described above are appropriately replaced based on an operation command from the host computer 12. 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). ).
[0053]
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. .
[0054]
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 12.
[0055]
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.
[0056]
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.
[0058]
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.
When 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.
[0059]
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).
[0060]
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).
[0061]
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.
[0062]
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 thread shape SW is temporarily measured, and the peaks and valleys from the opening SO in this direction are grasped.
[0063]
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.
[0064]
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).
[0065]
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).
[0066]
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).
[0067]
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.
[0068]
Returning to FIG. 4, the host computer 12 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. The effective diameter SD and the center position SP are grasped (process ST7).
[0069]
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, assuming that the radius r of the contact portion 136, the nominal pitch P of the screw, the angle α of the thread, and the height h0 of the thread are as shown in FIG.
That is, the distances h1, h3, and h in the figure are as follows.
[0070]
[Expression 1]

[0071]
Therefore, the effective diameter SD of the screw hole WH is as follows.
[0072]
[Expression 2]

[0073]
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).
[0074]
Specifically, the following calculation procedure is adopted.
In FIG. 12, the thread shape WS has an incomplete thread portion S2 below the complete thread portion S1, and a drill pilot hole S3 continues 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.
[0075]
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.
[0076]
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.
[0077]
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.
[0078]
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 clear 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.
[0079]
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.
[0080]
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.
[0081]
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.
[0082]
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.
[0083]
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.
[0084]
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 screw 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.
[0085]
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.
[0086]
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.
[0087]
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.
[0088]
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 thread shape WS. To do.
[0089]
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.
[0090]
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 that follows 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 while maintaining the contact state (process ST44), and is continued until the contact portion 136 reaches the opening SO of the screw hole WH (process ST45).
[0091]
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.
[0092]
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).
[0093]
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.
[0094]
【The invention's effect】
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.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an apparatus configuration according to an embodiment of the present invention.
FIG. 2 is an exploded perspective view showing the probe of the embodiment.
FIG. 3 is a schematic cross-sectional view showing a screw hole of the embodiment.
FIG. 4 is a flowchart showing basic steps of the embodiment.
FIG. 5 is a flowchart showing the copying operation of the embodiment.
FIG. 6 is a flowchart showing point measurement of the embodiment.
FIG. 7 is a schematic cross-sectional view showing drill pilot hole depth measurement of the embodiment.
FIG. 8 is a schematic cross-sectional view showing the copying operation of the embodiment.
FIG. 9 is a schematic cross-sectional view showing point measurement of the embodiment.
FIG. 10 is a schematic plan view showing point measurement of the embodiment.
FIG. 11 is a schematic cross-sectional view showing calculation of an effective diameter of the embodiment.
FIG. 12 is a schematic plan view showing calculation of a complete thread boundary in the embodiment.
FIG. 13 is a graph showing calculation of a complete thread boundary in the embodiment.
FIG. 14 is a flowchart showing basic steps of another embodiment of the present invention.
FIG. 15 is a flowchart showing a copying operation according to another embodiment.
FIG. 16 is a schematic perspective view showing the copying operation of the other embodiment.
[Explanation of symbols]
10 CMM
11 CMM body
12 Host computer
13 Probe
131 Rotating probe head
134 Standard stylus
135 Cross Stylus
136 Contact W Work
WH screw hole
WS thread shape
W1 Work surface
SO opening
S1 Full thread
S2 Incomplete thread
S3 Drill hole
S4 center axis
SP center axis position
SM Drill pilot hole depth
SL thread length
SD effective diameter

Claims (9)

A screw shape measuring method for measuring a screw shape using a three-dimensional measuring machine,
A coordinate measuring machine on which a workpiece having a screw shape to be measured is mounted, a scanning probe mounted on the coordinate measuring machine, and a stylus having a contact portion mounted on the scanning probe and in contact with the workpiece. Use
Assuming a central axis depth the surface of the workpiece is the position of the zero of the thread profile as the reference plane of the thread profile, to determine the normal of the assumed reference plane as the central axis of the thread profile, and this decision An axis alignment step for aligning the central axis of the screw shape with the scanning measurement axis of the scanning probe;
A scanning measurement step of moving the scanning probe along the scanning measurement axis while bringing the stylus into contact with the screw shape;
A calculation step of calculating various characteristic values of the screw shape from the measurement data obtained by the scanning measurement,
In the scanning measurement step, a scanning operation is performed along each axis at a plurality of circumferential positions of the screw shape.   2. The thread shape measuring method according to claim 1, wherein in the calculation step, an approximate contour is obtained by taking a measurement contour shape of a screw portion from measurement data obtained by the scanning measurement and approximating a screw slope portion with a straight line in the measurement contour shape. It includes an effective diameter calculation process for taking out the shape, bringing a virtual circle that replaces the conventional three-needle method needle into contact with this contour shape, and calculating the effective diameter of the screw shape by the conventional three-needle method. Screw shape measurement method.   3. The screw shape measuring method according to claim 1, wherein a branching stylus having a contact portion branched laterally is used in the scanning measurement step. 4. The thread shape measurement method according to claim 3 , wherein a contour projecting direction in which a contact portion of the branched stylus protrudes is detected by the scanning measurement prior to performing the scanning measurement step using the branched stylus. A screw shape measuring method, wherein the posture is adjusted so as to match the direction of the screw. In the thread profile measurement method according to any one of claims 1 to 4, wherein prior to the alignment process, the workpiece coordinate system set in the machine coordinate system set in the three-dimensional measuring machine work And a probe alignment system for adjusting the relative relationship between the scanning probe and the probe coordinate system set on the stylus. The thread shape measuring method according to any one of claims 1 to 5 , wherein the calculation step includes an incomplete screw from a change in a thread valley depth or a change in a thread pitch of a thread portion of measurement data by the scanning measurement. A screw shape measuring method comprising: an incomplete thread portion determination process for determining a portion. 7. The thread shape measuring method according to claim 6 , wherein the incomplete thread portion determination processing is performed by using a function or a numerical value table obtained in advance from a change in thread depth of a thread portion or a change in screw pitch with respect to the screw shape axis direction. A screw shape measuring method characterized by determining a starting point of the incomplete screw portion by performing approximation based on this. The screw shape measuring method according to any one of claims 1 to 7 , wherein the calculation step takes out a measurement contour shape of a screw portion from measurement data obtained by the scanning measurement, and defines a screw slope portion in the measurement contour shape. A thread shape measuring method comprising: an approximate contour shape processing which takes out an approximate contour shape by approximating with a straight line and determines a screw pitch, a thread angle, and a thread cutting depth from the approximate contour shape. The screw shape measuring method according to any one of claims 1 to 8 , wherein the scanning probe is attached to the coordinate measuring machine via a rotating probe head, and the axis of the stylus is attached to the coordinate measuring step. A method of measuring a screw shape, wherein the rotary probe head is tilted so as to match a scanning axis.

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