JP3832582B2

JP3832582B2 - Screw hole position measurement method

Info

Publication number: JP3832582B2
Application number: JP2002366718A
Authority: JP
Inventors: 哲也松川; 哲司川上
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2002-12-18
Filing date: 2002-12-18
Publication date: 2006-10-11
Anticipated expiration: 2022-12-18
Also published as: JP2004198238A

Description

【０００１】
【産業上の利用分野】
本発明は、３次元測定機を用いてネジ穴の中心位置の座標を正確に測定するためのネジ穴位置度測定方法に関するものである。
【０００２】
【従来の技術】
一般的に、エンジンのシリンダブロック、シリンダヘッド等の機械加工製品の寸法精度を測定するために、３次元測定機が用いられている。ところで、ネジ穴等の内面に細かい凹凸を有する穴の寸法を正確に測定することは困難であり、従来から、このような穴の寸法を測定するための装置が種々提案されている（例えば特許文献１および２参照）。このような事情から、機械加工製品のネジ穴の中心位置を測定する場合には、専用のゲージを用いて測定される場合が多い。
【０００３】
【特許文献１】
特開平７−１２８００５号公報
【特許文献２】
特開平１１−２５０３号公報
【０００４】
しかしながら、専用のゲージは、測定すべき機械加工製品毎に準備する必要があり、コストがかかるため、汎用の３次元測定機を用いてネジ穴の中心位置の座標を正確に求めることが要求されている。そこで、従来、３次元測定機を用いてネジ穴の中心位置の座標を求めるために、例えば次のような測定方法がとられている。
【０００５】
３次元測定機を用いた従来のネジ穴位置度測定方法について、図７を参照して説明する。図７に示されるように、直径がネジピッチＰの１．２５倍程度(約３mm）の球状の先端部形状を有する３次元測定機の測定子２を製品図面上の寸法に基づいて、ネジ穴１の中心に所定の深さで挿入する。測定子２をネジ穴１の軸に直交する方向に移動させて、測定子２がネジ穴１の内周部(ネジ部)に当接する点Ａの座標を求める。次に、測定子２をネジ穴の中心に沿って１／４ピッチ(Ｐ／４)移動させ、点Ａから９０°異なる位置でネジ穴１のネジ部に当接する点Ｂの座標を求める。同様に測定子２を１／４ピッチおよび９０°ずつ移動させて、順次ネジ穴１のネジ部に当接する点Ｃおよび点Ｄの座標を求める。
【０００６】
このようにして、測定子２をネジ穴１の軸に沿って１／４ピッチおよび９０°ずつ異なる位置でネジ穴１のネジ部に当接させることにより、測定子２は、ネジ部のネジ山−ネジ溝間の同様の位置に当接することになるので、４つの点Ａ、Ｂ、ＣおよびＤは、ネジ穴１と同心で同じ直径を有する円周上に位置することになる。したがって、これらの４つの点Ａ、Ｂ、ＣおよびＤの位置に基づいて、ネジ穴１の中心位置の座標を求めることができる。
【０００７】
【発明が解決しようとする課題】
しかしながら、上記従来のネジ穴位置度測定方法では、次のような問題がある。図８に示されるように、測定子２は、先端部の直径がネジピッチＰよりも大きいため、ネジ部のネジ山３に当接することになるが、ネジ部を機械加工する際、ネジ山３の頂部に高さ０．１５mm程度のバリ４が生じることがあり、測定子２の当接位置がバリ４によって変動してしまう。このため、ネジ穴１の中心位置の座標を正確に求めることができない。
【０００８】
なお、測定子２の先端部の直径をネジピッチＰより小さくして、測定子２をネジ部のネジ溝５に当接させることにより、バリ４の影響を解消することができるが、測定子２は、必ずしもネジ溝５に当接するわけではなく、ネジ山３に当接する可能性があるため、依然として問題の解決にはならない。
【０００９】
本発明は、上記の点に鑑みてなされたものであり、３次元測定機を用いてネジ穴の中心位置の座標を正確に測定することができるネジ穴位置度測定方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
上記の課題を解決するために、請求項１の発明に係るネジ穴位置度測定方法は、測定子をネジ穴内に挿入し、前記測定子を前記ネジ穴の軸に直交する等間隔の３方向に移動させて、前記測定子が前記ネジ穴のネジ部に当接する３点を表す第１位置を測定し、その後、前記測定子を前記ネジ穴の軸に沿って前記ネジ部の１／２ピッチに相当する分だけ異なる位置に移動させ、前記測定子を前記３方向に沿って移動させて、前記測定子が前記ネジ部に当接する３点を表す第２位置を測定し、前記第１位置および前記第２位置が表す６点の中から、前記測定子が前記ネジ部のネジ溝に当接する３点を抽出し、この３点の位置に基づいて、前記ネジ穴の中心位置を求めることを特徴とする。
このように構成したことにより、第１位置の３点のうち、少なくとも１点は、ネジ溝に位置する点となり、第２位置の３点のうち、第１位置のネジ溝に位置する点に対応する点は、ネジ山の点となり、また、第１位置のネジ山の点に対応する点は、ネジ溝に位置する点となるので、第１位置および第２位置の６点の中からネジ溝に位置する３点を抽出し、そのネジ溝に位置する３点の位置に基づいて、ネジ穴の中心位置の座標を決定することができる。
請求項２の発明に係るネジ穴位置度測定方法は、上記請求項１の構成において、前記測定子は、主軸に直交する等間隔の３方向に突出する接触子を有していることを特徴とする。
このように構成したことにより、測定子の接触子がネジ部に当接する。
請求項３の発明に係るネジ穴位置度測定方法は、上記請求項１又は２の構成において、前記第１位置および前記第２位置が表す６点の中から２点を選ぶ全ての組合わせについて、その２点間の距離を計算し、その距離が大きい方から３つの組合わせを抽出し、その３つの組合わせに含まれる３点の位置に基づいて、前記ネジ穴の中心位置を求めることを特徴とする。
このように構成したことにより、簡単なアルゴリズムによってネジ溝に位置する３点を抽出することができる。
また、請求項４の発明に係るネジ穴位置度測定方法は、上記請求項１又は２の構成において、前記第１位置および前記第２位置が表す６点について、前記ネジ穴の所定の仮想中心からの距離を計算し、その距離が大きい方から順に３点を抽出し、該抽出された３点の位置に基づいて、前記ネジ穴の中心位置を求めることを特徴とする。
このように構成したことにより、簡単なアルゴリズムによってネジ溝に位置する３点を抽出することができる。
【００１１】
【発明の実施の形態】
以下、本発明の一実施形態を図面に基づいて詳細に説明する。なお、上記従来例と同様の部分については同一の符号を付して説明する。
本実施形態に係る３次元測定機の測定子について、図２および図３を参照して説明する。図２及び図３に示されるように、測定子６は、主軸７の先端部側面に、主軸７と直交する３つの接触子８Ａ、８Ｂ及び８Ｃが等間隔すなわち１２０°間隔で突出されている。これらの接触子８Ａ、８Ｂ及び８Ｃは、長さが等しく、先端部９Ａ、９Ｂ及び９Ｃが球状に形成されている。先端部９Ａ、９Ｂ及び９Ｃの直径は、測定すべきネジ穴１のネジピッチＰよりも充分小さく、好ましくは１mm程度(後述)とされる。また、主軸７の直径および接触子８Ａ、８Ｂ及び８Ｃの長さは、測定子６がネジ穴１に挿入できるように、３つの接触子８Ａ、８Ｂ及び８Ｃの先端を通る円の直径がネジ穴１の直径よりも充分小さくなるようにしてある。
【００１２】
次に、測定子６を用いてネジ穴１の中心位置の座標を測定するためのネジ穴位置度測定方法について主に図１を参照して説明する。図１に示されるように、測定すべき製品の図面上の寸法に基づいて、測定子６をネジ穴１の(仮想)中心に所定の深さで挿入する。このときの３つの接触子８Ａ、８Ｂ及び８Ｃの先端部９Ａ、９Ｂ及び９Ｃの中心を通る平面を第１断面とする。そして、測定子６を第１断面上において、ネジ穴１の中心から順次３つの接触子８Ａ、８Ｂ及び８Ｃに沿って(すなわち、ネジ穴１の軸に直交する等間隔の３方向に）移動させて、各接触子の先端部９Ａ、９Ｂ及び９Ｃをネジ部に順次当接させ、各接触子の先端部９Ａ、９Ｂ及び９Ｃがそれぞれネジ部に当接する３点Ａ１、Ｂ１及びＣ１(第１位置)の座標を求める。
【００１３】
このとき、３つの接触子８Ａ、８Ｂ及び８Ｃは、１２０°間隔で配置されているので、３つの接触子の先端部９Ａ、９Ｂ及び９Ｃのうち、少なくとも１つは、ネジ溝５に当接することになる(図示の例では、接触子８Ａの先端部９Ａが点Ａ１においてネジ溝５に当接し、接触子８Ｂ及び８Ｃの先端部９Ｂ及び９Ｃが点Ｂ１及びＣ１においてネジ山３に当接している）。
【００１４】
次いで、測定子６をネジ穴１の軸に沿って１／２ピッチだけ移動させる。このとき、３つの接触子８Ａ、８Ｂ及び８Ｃの先端部９Ａ、９Ｂ及び９Ｃの中心を通る平面を第２断面とする。そして、測定子６を第２断面上において、ネジ穴１の中心から順次３つの接触子８Ａ、８Ｂ及び８Ｃに沿って(すなわち、ネジ穴１の軸に直交する等間隔の３方向に）移動させて、各接触子の先端部９Ａ、９Ｂ及び９Ｃをネジ部に順次当接させ、各接触子の先端部９Ａ、９Ｂ及び９Ｃがそれぞれネジ部に当接する３点Ａ２、Ｂ２及びＣ２(第２位置)の座標を求める。
【００１５】
このとき、第１断面と第２断面とは、１／２ピッチだけ離れており、ネジ山３及びネジ溝５の位相が１８０°異なるので、第１断面においてネジ溝５に当接した接触子８Ａ、８Ｂ又は８Ｃは、第２断面においてネジ山３に当接し、第１断面においてネジ溝５に当接した接触子８Ａ、８Ｂ又は８Ｃは、第２断面においてネジ山３に当接することになる(図示の例では、接触子８Ａの先端部９Ａが点Ａ２においてネジ山３に当接し、接触子８Ｂ及び８Ｃの先端部９Ｂ及び９Ｃが点Ｂ２及びＣ２においてネジ溝５に当接している）。したがって、第１断面上の３点Ａ１、Ｂ１、Ｃ１及び第２断面上の３点Ａ２、Ｂ２、Ｃ２の合計６点のうち３点は、必ずネジ溝５に位置する点である。
【００１６】
なお、第１断面と第２断面とでネジ部の位相が１８０°異なれば、上記と同じ結果が得られるので、測定子６の移動量は、ネジ部の１／２ピッチに限らず、３／２ピッチ、５／２ピッチ等、１／２ピッチに相当するネジ部の位相変化が得られる移動量とすることができる。
【００１７】
次に、第１断面上の３点Ａ１、Ｂ１、Ｃ１及び第２断面上の３点Ａ２、Ｂ２、Ｃ２の合計６点のうちからネジ溝５に位置する３点を抽出する方法について説明する。
上記６点Ａ１、Ｂ１、Ｃ１、Ａ２、Ｂ２及びＣ２のうちから２点を選んだ１５通りの全ての組合わせについて、その２点間の距離を計算する。このうち、２点間の距離が大きい方から３つの組合わせを抽出する(図１の例では、Ａ１Ｂ２、Ａ１Ｃ２及びＢ２Ｃ２）。これらの３つの組合わせに含まれる３点(図１の例では、Ａ１、Ｂ２及びＣ２)がネジ溝５に位置する点となる。このようにして、簡単なアルゴリズムによってネジ溝５に位置する３点を抽出することができる。
【００１８】
このようにして抽出したネジ溝５に位置する３点の座標に基づいて、ネジ穴１の中心位置の座標を計算することにより、ネジ溝５に位置する点データのみに基づいてネジ穴１の中心位置の座標を求めることができるので、ネジ山３に生じたバリ４(図４参照)の影響を受けることなく、正確な座標を求めることができる。
【００１９】
このほか、第１断面上において、製品図面上の寸法に基づくネジ穴１の(仮想)中心から３点Ａ１、Ｂ１およびＣ１までの距離をそれぞれ計算し、また、第２断面上において、ネジ穴１の(仮想)中心から３点Ａ２、Ｂ２およびＣ２までの距離をそれぞれ計算し、ネジ穴１の(仮想)中心からの距離が大きい方から３点を抽出することにより、ネジ溝５に位置する３点を決定することができる。このようにして、簡単なアルゴリズムによってネジ溝５に位置する３点を抽出することができる。
【００２０】
上記のほか、他の公知の数学的手法によって、上記６つの点Ａ１、Ｂ１、Ｃ１、Ａ２、Ｂ２及びＣ２から、ネジ溝５に位置する３点を抽出することもできる。
【００２１】
次に、図５を参照して上述のネジ穴位置度測定方法のフローについて説明する。図５を参照して、ステップＳ１では、３次元測定機の測定子６を製品図面上の寸法に基づいて、ネジ穴１の中心に所定の深さで挿入して、接触子８Ａ、８Ｂ及び８Ｃを第１断面上に配置する。ステップＳ２では、第１断面上において、測定子６を１２０°間隔の３方向に移動させて、接触子の先端部９Ａ、９Ｂ及び９Ｃがそれぞれネジ部(ネジ山３又はネジ溝５)に当接する３点Ａ１、Ｂ１及びＣ１の座標を測定する。
【００２２】
ステップＳ３では、測定子６をネジ穴１の軸に沿って１／２ピッチ移動させて、接触子８Ａ、８Ｂ及び８Ｃを第２断面上に移動させる。ステップＳ４では、第２断面上において、測定子６を１２０°間隔の３方向に移動させて、接触子の先端部９Ａ、９Ｂ及び９Ｃがそれぞれネジ部(ネジ山３又はネジ溝５)に当接する３点Ａ２、Ｂ２及びＣ２の座標を測定する。
【００２３】
ステップＳ５では、第１および第２断面上の点Ａ１、Ｂ１、Ｃ１、Ａ２、Ｂ２及びＣ２から、上述の数学的手法によって、ネジ溝５に位置する３点を決定する。ステップＳ６では、ネジ溝５に位置する３点に基づいて、公知の数学的手法によって、ネジ穴１の中心の座標を計算する。
【００２４】
このようにして、ネジ溝５に位置する３点の座標に基づいて、ネジ穴１の中心位置の座標を求めることにより、ネジ山３に生じたバリ４の影響を受けることなく、正確な座標を求めることができる。
【００２５】
次に、本発明のネジ穴位置度測定方法による測定精度と接触子の先端部９Ａ、９Ｂ及び９Ｃの直径との関係について、図６を参照して説明する。図６は、接触子先端部９Ａ、９Ｂ及び９Ｃの直径を５mm、３mm及び１mmとした場合におけるネジ穴１の中心位置のズレ量についての測定値と真値との関係を示している。図６から分かるように、直径５mm又は３mmとした場合、測定値と真値との間に一定の割合でズレが生じるのに対して、直径１mmとした場合には、測定値と真値とが一致している。このことから、接触子先端部９Ａ、９Ｂ及び９Ｃの直径は１mm程度とすることが望ましい。
【００２６】
【発明の効果】
以上詳述したように、本発明に係るネジ穴位置度測定法法によれば、３次元測定機を用いて、ネジ穴の中心位置の座標を正確に測定することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係るネジ穴位置度測定方法を示す説明図である。
【図２】本発明の一実施形態に係るネジ穴位置度測定方法に使用する測定子を示す側面図である。
【図３】図２に示す測定子の正面図である。
【図４】図２に示す測定子がネジ溝に当接した状態を示す図である。
【図５】本発明の一実施形態に係るネジ穴位置度測定方法を示すフローチャートである。
【図６】本発明の一実施形態に係るネジ穴位置度測定方法による測定精度と接触子の先端部の直径との関係を示す図である。
【図７】３次元測定機による従来のネジ穴位置度測定方法を示す説明図である。
【図８】従来のネジ穴位置度測定方法に用いる測定子がネジ山に当接した状態を示す図である。
【符号の説明】
１ネジ穴
３ネジ山
５ネジ溝
６接触子
Ａ１、Ｂ１、Ｃ１点(第１位置)
Ａ２、Ｂ２、Ｃ２点(第２位置)[0001]
[Industrial application fields]
The present invention relates to a screw hole position degree measuring method for accurately measuring the coordinates of the center position of a screw hole using a three-dimensional measuring machine.
[0002]
[Prior art]
Generally, a three-dimensional measuring machine is used to measure the dimensional accuracy of machined products such as engine cylinder blocks and cylinder heads. By the way, it is difficult to accurately measure the size of a hole having fine irregularities on the inner surface thereof such as a screw hole, and various devices for measuring the size of such a hole have been conventionally proposed (for example, patents). Reference 1 and 2). For these reasons, when measuring the center position of a threaded hole of a machined product, the measurement is often performed using a dedicated gauge.
[0003]
[Patent Document 1]
JP-A-7-128005 [Patent Document 2]
Japanese Patent Application Laid-Open No. 11-2503
However, it is necessary to prepare a dedicated gauge for each machined product to be measured, which is costly. Therefore, it is required to accurately obtain the coordinates of the center position of the screw hole using a general-purpose three-dimensional measuring machine. ing. Therefore, conventionally, in order to obtain the coordinates of the center position of the screw hole using a three-dimensional measuring machine, for example, the following measuring method is taken.
[0005]
A conventional screw hole position measuring method using a three-dimensional measuring machine will be described with reference to FIG. As shown in FIG. 7, the measuring element 2 of the three-dimensional measuring machine having a spherical tip shape whose diameter is about 1.25 times the screw pitch P (about 3 mm) is formed on the screw hole based on the dimensions on the product drawing. Inserted into the center of 1 at a predetermined depth. The probe 2 is moved in a direction perpendicular to the axis of the screw hole 1 to obtain the coordinates of the point A where the probe 2 contacts the inner peripheral portion (screw portion) of the screw hole 1. Next, the measuring element 2 is moved by ¼ pitch (P / 4) along the center of the screw hole, and the coordinates of the point B contacting the screw part of the screw hole 1 at a position different from the point A by 90 ° are obtained. Similarly, the measuring element 2 is moved by 1/4 pitch and 90 °, and the coordinates of the points C and D that are in contact with the threaded portions of the screw holes 1 are obtained.
[0006]
In this way, the probe 2 is brought into contact with the screw portion of the screw hole 1 at a position that is different from each other by ¼ pitch and 90 ° along the axis of the screw hole 1. The four points A, B, C, and D are located on a circumference that is concentric with the screw hole 1 and has the same diameter. Therefore, the coordinates of the center position of the screw hole 1 can be obtained based on the positions of these four points A, B, C, and D.
[0007]
[Problems to be solved by the invention]
However, the above-described conventional screw hole position measuring method has the following problems. As shown in FIG. 8, the diameter of the tip of the measuring element 2 is larger than the screw pitch P, so that it contacts the screw thread 3 of the screw part. However, when machining the screw part, the screw thread 3 The burrs 4 having a height of about 0.15 mm may be generated at the top of the rim, and the contact position of the probe 2 varies depending on the burrs 4. For this reason, the coordinates of the center position of the screw hole 1 cannot be obtained accurately.
[0008]
The influence of the burr 4 can be eliminated by making the diameter of the tip of the probe 2 smaller than the screw pitch P and bringing the probe 2 into contact with the screw groove 5 of the screw part. Is not necessarily in contact with the screw groove 5, but may still be in contact with the screw thread 3, and thus still does not solve the problem.
[0009]
The present invention has been made in view of the above points, and an object thereof is to provide a screw hole position degree measuring method capable of accurately measuring the coordinates of the center position of a screw hole using a three-dimensional measuring machine. And
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the screw hole position degree measuring method according to the invention of claim 1 is characterized in that the measuring element is inserted into the screw hole, and the measuring element is arranged in three directions at equal intervals perpendicular to the axis of the screw hole. To measure the first position representing the three points where the probe contacts the screw portion of the screw hole, and then the probe is halved along the axis of the screw hole. Move to different positions corresponding to the pitch, move the probe along the three directions, measure a second position representing the three points where the probe contacts the screw portion, and From the six points represented by the position and the second position, three points where the probe contacts the screw groove of the screw portion are extracted, and the center position of the screw hole is obtained based on the positions of the three points. It is characterized by that.
With this configuration, at least one of the three points at the first position is a point located in the screw groove, and of the three points at the second position, the point is located in the screw groove at the first position. The corresponding point is a thread point, and the point corresponding to the thread point in the first position is a point located in the screw groove, so the point is selected from among the six points in the first position and the second position. Three points located in the screw groove are extracted, and the coordinates of the center position of the screw hole can be determined based on the positions of the three points located in the screw groove.
A screw hole position degree measuring method according to a second aspect of the invention is characterized in that, in the configuration of the first aspect, the measuring element has contacts protruding in three directions at equal intervals orthogonal to the main axis. And
With this configuration, the contact of the measuring element comes into contact with the screw portion.
The screw hole position degree measuring method according to the invention of claim 3 is the configuration of claim 1 or 2 for all combinations in which two points are selected from the six points represented by the first position and the second position. , Calculating the distance between the two points, extracting three combinations from the larger distance, and determining the center position of the screw hole based on the positions of the three points included in the three combinations It is characterized by.
With this configuration, three points located in the thread groove can be extracted by a simple algorithm.
According to a fourth aspect of the present invention, there is provided a screw hole position degree measuring method according to the first or second aspect, wherein a predetermined virtual center of the screw hole is defined for the six points represented by the first position and the second position. Is calculated, the three points are extracted in order from the largest one, and the center position of the screw hole is obtained based on the positions of the extracted three points.
With this configuration, three points located in the thread groove can be extracted by a simple algorithm.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the part similar to the said prior art example.
A probe of the coordinate measuring machine according to the present embodiment will be described with reference to FIGS. 2 and 3. As shown in FIG. 2 and FIG. 3, the measuring element 6 has three contacts 8 A, 8 B, and 8 C perpendicular to the main shaft 7 projecting at equal intervals, that is, 120 ° intervals, on the side surface of the main shaft 7. . These contacts 8A, 8B, and 8C are equal in length, and the tip portions 9A, 9B, and 9C are formed in a spherical shape. The diameters of the tip portions 9A, 9B and 9C are sufficiently smaller than the screw pitch P of the screw hole 1 to be measured, preferably about 1 mm (described later). Further, the diameter of the main shaft 7 and the length of the contacts 8A, 8B and 8C are such that the diameter of a circle passing through the tips of the three contacts 8A, 8B and 8C is a screw so that the measuring element 6 can be inserted into the screw hole 1. It is made to be sufficiently smaller than the diameter of the hole 1.
[0012]
Next, a screw hole position degree measuring method for measuring the coordinates of the center position of the screw hole 1 using the probe 6 will be described mainly with reference to FIG. As shown in FIG. 1, the measuring element 6 is inserted into the (virtual) center of the screw hole 1 at a predetermined depth based on the dimensions of the product to be measured on the drawing. A plane passing through the centers of the tip portions 9A, 9B and 9C of the three contacts 8A, 8B and 8C at this time is defined as a first cross section. Then, the measuring element 6 is moved along the three contacts 8A, 8B and 8C sequentially from the center of the screw hole 1 on the first cross section (that is, in three directions at equal intervals orthogonal to the axis of the screw hole 1). Thus, the tip portions 9A, 9B and 9C of the respective contacts are sequentially brought into contact with the screw portions, and the three points A1, B1 and C1 (the first points where the tip portions 9A, 9B and 9C of the respective contacts are brought into contact with the screw portions, respectively. Find the coordinates of 1 position.
[0013]
At this time, since the three contacts 8A, 8B and 8C are arranged at intervals of 120 °, at least one of the tip portions 9A, 9B and 9C of the three contacts contacts the screw groove 5. (In the example shown in the figure, the tip 9A of the contact 8A contacts the screw groove 5 at the point A1, and the tips 9B and 9C of the contacts 8B and 8C contact the thread 3 at the points B1 and C1. ing).
[0014]
Next, the probe 6 is moved along the axis of the screw hole 1 by ½ pitch. At this time, a plane passing through the centers of the tip portions 9A, 9B, and 9C of the three contacts 8A, 8B, and 8C is defined as a second cross section. Then, the probe 6 is sequentially moved along the three contacts 8A, 8B and 8C from the center of the screw hole 1 on the second cross section (that is, in three directions at equal intervals orthogonal to the axis of the screw hole 1). Thus, the tip portions 9A, 9B and 9C of each contact are sequentially brought into contact with the screw portions, and the three points A2, B2 and C2 (the first points where the tip portions 9A, 9B and 9C of the respective contacts come into contact with the screw portions, respectively. 2) coordinates are obtained.
[0015]
At this time, the first cross section and the second cross section are separated from each other by ½ pitch, and the phase of the screw thread 3 and the screw groove 5 are 180 ° different from each other. Therefore, the contact that contacts the screw groove 5 in the first cross section. 8A, 8B or 8C is in contact with the screw thread 3 in the second cross section, and the contact 8A, 8B or 8C in contact with the screw groove 5 in the first cross section is in contact with the screw thread 3 in the second cross section. (In the illustrated example, the tip 9A of the contact 8A is in contact with the screw thread 3 at a point A2, and the tips 9B and 9C of the contacts 8B and 8C are in contact with the screw groove 5 at points B2 and C2. ). Therefore, three points out of a total of six points including the three points A1, B1, and C1 on the first cross section and the three points A2, B2, and C2 on the second cross section are points that are always located in the screw groove 5.
[0016]
In addition, if the phase of the screw portion is different by 180 ° between the first cross section and the second cross section, the same result as described above can be obtained. Therefore, the moving amount of the probe 6 is not limited to the 1/2 pitch of the screw portion. The amount of movement can be obtained such that the phase change of the screw portion corresponding to ½ pitch, such as / 2 pitch, 5/2 pitch, and the like.
[0017]
Next, a method of extracting three points located in the screw groove 5 out of a total of six points of the three points A1, B1, C1 on the first cross section and the three points A2, B2, C2 on the second cross section will be described. .
The distance between the two points is calculated for all 15 combinations in which two points are selected from the six points A1, B1, C1, A2, B2, and C2. Among these, three combinations are extracted from the one having the larger distance between the two points (A1B2, A1C2, and B2C2 in the example of FIG. 1). Three points (A1, B2, and C2 in the example of FIG. 1) included in these three combinations are points located in the screw groove 5. In this way, three points located in the screw groove 5 can be extracted by a simple algorithm.
[0018]
By calculating the coordinates of the center position of the screw hole 1 based on the coordinates of the three points located in the screw groove 5 extracted in this way, the screw hole 1 is determined based only on the point data located in the screw groove 5. Since the coordinates of the center position can be obtained, accurate coordinates can be obtained without being affected by the burr 4 (see FIG. 4) generated in the thread 3.
[0019]
In addition, on the first cross section, the distances from the (virtual) center of the screw hole 1 to the three points A1, B1 and C1 based on the dimensions on the product drawing are calculated, respectively. By calculating the distances from the (virtual) center of 1 to the three points A2, B2 and C2, respectively, and extracting the three points from the larger distance from the (virtual) center of the screw hole 1, the position in the screw groove 5 Three points can be determined. In this way, three points located in the screw groove 5 can be extracted by a simple algorithm.
[0020]
In addition to the above, three points located in the thread groove 5 can be extracted from the six points A1, B1, C1, A2, B2, and C2 by other known mathematical methods.
[0021]
Next, the flow of the above-described screw hole position degree measuring method will be described with reference to FIG. Referring to FIG. 5, in step S 1, the probe 6 of the three-dimensional measuring machine is inserted into the center of the screw hole 1 at a predetermined depth based on the dimensions on the product drawing, and the contacts 8 A, 8 B and 8C is arranged on the first cross section. In step S2, on the first cross section, the probe 6 is moved in three directions at intervals of 120 °, and the tip portions 9A, 9B, and 9C of the contacts contact the screw portions (thread 3 or screw groove 5), respectively. The coordinates of the three points A1, B1 and C1 in contact are measured.
[0022]
In step S3, the measuring element 6 is moved by 1/2 pitch along the axis of the screw hole 1 to move the contacts 8A, 8B, and 8C on the second cross section. In step S4, on the second cross section, the probe 6 is moved in three directions at intervals of 120 °, and the tip portions 9A, 9B, and 9C of the contacts contact the screw portions (thread 3 or screw groove 5), respectively. The coordinates of the three points A2, B2, and C2 that are in contact are measured.
[0023]
In step S5, three points located in the screw groove 5 are determined from the points A1, B1, C1, A2, B2, and C2 on the first and second cross sections by the mathematical method described above. In step S6, the coordinates of the center of the screw hole 1 are calculated based on the three points located in the screw groove 5 by a known mathematical method.
[0024]
In this way, by obtaining the coordinates of the center position of the screw hole 1 based on the coordinates of the three points positioned in the screw groove 5, accurate coordinates can be obtained without being affected by the burr 4 generated in the screw thread 3. Can be requested.
[0025]
Next, the relationship between the measurement accuracy by the screw hole position degree measuring method of the present invention and the diameters of the tip portions 9A, 9B and 9C of the contact will be described with reference to FIG. FIG. 6 shows the relationship between the measured value and the true value of the shift amount of the center position of the screw hole 1 when the diameters of the contact tip portions 9A, 9B and 9C are 5 mm, 3 mm and 1 mm. As can be seen from FIG. 6, when the diameter is 5 mm or 3 mm, there is a deviation between the measured value and the true value at a constant rate, whereas when the diameter is 1 mm, the measured value and the true value are Match. For this reason, it is desirable that the diameters of the contact tip portions 9A, 9B and 9C be about 1 mm.
[0026]
【The invention's effect】
As described above in detail, according to the screw hole position degree measuring method according to the present invention, the coordinates of the center position of the screw hole can be accurately measured using a three-dimensional measuring machine.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a screw hole position degree measuring method according to an embodiment of the present invention.
FIG. 2 is a side view showing a probe used for a screw hole position degree measuring method according to an embodiment of the present invention.
3 is a front view of the measuring element shown in FIG. 2. FIG.
4 is a view showing a state where the measuring element shown in FIG. 2 is in contact with a screw groove. FIG.
FIG. 5 is a flowchart illustrating a screw hole position degree measuring method according to an embodiment of the present invention.
FIG. 6 is a diagram showing the relationship between the measurement accuracy by the screw hole position degree measuring method according to one embodiment of the present invention and the diameter of the tip of the contact.
FIG. 7 is an explanatory diagram showing a conventional method for measuring screw hole position using a three-dimensional measuring machine.
FIG. 8 is a diagram showing a state in which a probe used in a conventional method for measuring the position of a screw hole is in contact with a screw thread.
[Explanation of symbols]
1 Screw hole 3 Screw thread 5 Screw groove 6 Contact A1, B1, C1 point (first position)
A2, B2, C2 points (second position)

Claims

A measuring element is inserted into the screw hole, and the measuring element is moved in three directions at equal intervals perpendicular to the axis of the screw hole, so that the measuring element comes into contact with the screw portion of the screw hole. The position is measured, and then the measuring element is moved along the axis of the screw hole to a different position by an amount corresponding to 1/2 pitch of the screw portion, and the measuring element is moved along the three directions. And measuring the second position representing the three points where the probe contacts the screw part, and the measuring element is a screw groove of the screw part among the six points represented by the first position and the second position. A method for measuring the degree of screw hole position, wherein three points in contact with the screw hole are extracted and a center position of the screw hole is obtained based on the positions of the three points.

The screw hole position measuring method according to claim 1, wherein the measuring element has contacts protruding in three directions at equal intervals orthogonal to the main axis.

For all combinations in which two points are selected from the six points represented by the first position and the second position, the distance between the two points is calculated, and the three combinations are extracted from the larger distance, The screw hole position degree measuring method according to claim 1 or 2, wherein a center position of the screw hole is obtained based on positions of three points included in the three combinations.

For the six points represented by the first position and the second position, the distance from the predetermined virtual center of the screw hole is calculated, three points are extracted in order from the largest, and the extracted three points The screw hole position degree measuring method according to claim 1 or 2, wherein a center position of the screw hole is obtained based on the position.