Positioning device, thread measuring machine and method

Abstract

The invention discloses a positioning device, a thread measuring machine and a method, solves the problem that the position of a measured piece cannot be accurately positioned in the prior art, and has the beneficial effect of ensuring the accuracy and precision of a measurement result, and the specific scheme is as follows: the positioning device comprises a measurement reference piece, the measuring reference part is connected with the thread measuring machine to provide a measuring reference surface, the measuring reference part is provided with an opening, the measuring reference surface of the measuring reference part is provided with a supporting part, the supporting part forms a supporting groove to support one side of the measured part, one end of the connecting part is fixed, the connecting part is movably connected with the pressing part, and one end of the measured part abuts against the measuring reference surface. One section of the measured piece is in contact with the supporting part, the other end of the measured piece is provided with a pressing force towards the direction of the thread measuring machine by the pressing part, and a probe of the thread measuring machine passes through the open hole and then arrives at a to-be-measured external thread structure of the measured piece.

Description

Technical Field

[0001] The present invention relates to the technical field of external thread detection, and in particular to a positioning device, a thread measuring machine and a method. Background Art

[0002] The statements in this section merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Components with external thread structures usually have simple structures. If a fixed thread detection machine is used for detection, it is necessary to uniformly measure at a fixed place and then transport it to a designated location after the detection. However, during the transportation process, the external thread structure is also easily damaged, and on-site measurement is required again. If re-measurement is carried out, it is obviously inappropriate to carry the fixed thread detection machine.

[0004] For this reason, portable thread machines have been developed in the prior art. Portable thread machines are movable and can be carried to wherever they are needed, which is very convenient. However, in the detection of external thread structures, the portable thread machine is only placed at a set position, and the component is only held by hand or supported by other structural members, so the initial position of the component is not accurately determined, thus easily affecting the measurement accuracy.

[0005] In addition, to achieve accurate measurement, in addition to positioning, the component also needs to be accurately fixed. In the prior art, the component is mostly pressed manually, and obviously the accuracy and precision of the measurement results are affected.

[0006] Generally, the probe of the thread machine needs to be above or below the maximum longitudinal section of the component to ensure the accuracy of the measurement results. It is difficult to determine this in the prior art and multiple measurements are required.

[0007] In addition, because there are many components with external thread structures to be detected on-site, for components of different sizes, the position of the component needs to be adjusted each time, and the position of the component is not easily determined accurately, resulting in low detection efficiency. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the first object of the present invention is to provide a positioning device capable of realizing the detection and calibration of an external thread machine.

[0009] To achieve the above object, the present invention is realized by the following technical solutions:

[0010] A positioning device includes a measurement reference part, which is connected to a thread measuring machine to provide a measurement reference surface. The measurement reference part is provided with an opening. A support part is arranged at the measurement reference surface of the measurement reference part. One end of the connecting part is fixed, and the connecting part is movably connected to the pressing part. One end of the measured part abuts against the measurement reference surface, a section of the measured part contacts the support part, and the other end of the measured part is provided with a pressing force towards the thread measuring machine by the pressing part. After the probe of the thread measuring machine passes through the opening, it reaches the outer thread structure to be measured of the measured part.

[0011] For the positioning device as described above, the measurement reference part is fixed to the thread measuring machine. The measurement reference part is provided with a support part, and the support part forms a support groove that allows the outer thread structure to be measured of the measured part to be supported through the support groove. The position of the support groove is determined, and naturally the position of the measured part is determined, achieving accurate positioning of the measured part. In this way, by determining the depth of the probe extending out of the opening, the X-direction position of the probe can be determined. After the position of the measured part is limited, the Y-direction position when the probe contacts the measured part can be determined accordingly. In this way, the initial position of ensuring the probe to contact the outer thread structure to be measured is realized, so as to improve the accuracy of the measurement result.

[0012] For a positioning device as described above, the center line in the width direction of the opening and the center line of the initial position of the probe are in the same plane, and the center position of the support groove and the center line in the width direction of the opening are arranged on the same straight line to ensure that the Y-direction position at the initial position of the probe is arranged along the central axis of the measured part, and correspondingly ensure that the central axis of the probe is located above the central axis of the outer thread structure to be measured.

[0013] For a positioning device as described above, the support part is multiple rollers. The rollers are rotatable relative to the reference measurement part. The space between two adjacent rollers forms the support groove. The rollers are arranged on the side of the opening, and the probe can extend from the upper side or the lower side of the measured part to realize the separate contact measurement of the upper side and the lower side of the outer thread structure to be measured.

[0014] For a positioning device as described above, there are two pressing parts. One ends of the two pressing parts are respectively fixed at the corresponding connecting parts, and the two connecting parts are respectively arranged on both sides of the measurement reference part. By arranging the two pressing parts, the stable pressing of the measured part is ensured, avoiding skew and ensuring the accuracy of the measurement result.

[0015] For a positioning device as described above, one end of the pressing part is fixed to a collar. The collar is sleeved on the circumferential direction of the connecting part. The collar is movable relative to the connecting part, and a bushing is arranged between the collar and the connecting part, and there is friction between the bushing and the connecting part.

[0016] A positioning device as described above, wherein one end of the pressing member is fixed to the collar and is inclined relative to the connecting member, such that the other end of the pressing member is inclined towards the direction of the roller. One end of the pressing member for pressing the measured part is bent, and the pressing member inclined relative to the connecting member enables a frictional force to be generated between the collar and the connecting member, ensuring the position of the pressing member.

[0017] A positioning device as described above, wherein the pressing member is an elastic steel sheet which is deformable. When one end of the elastic member contacts one end of the measured part and the collar is pushed along the connecting member, the position of the elastic steel sheet can be locked, thereby ensuring the stable pressing of the pressing member on the elastic member.

[0018] A positioning device as described above, wherein the connecting member is detachably connected to the measurement reference member or the thread measuring machine, so that the connecting member can be installed according to requirements, and an appropriate number of connecting members can be installed according to requirements.

[0019] A positioning device as described above, wherein the roller is a conical roller for mating with the structure of external conical threads.

[0020] A positioning device as described above, wherein the openings of the measurement reference member include a first opening and a second opening. The first opening and the second opening are arranged at an interval distance, and the center lines in the width direction of the first opening and the second opening are located in the same plane. The roller is arranged between the first opening and the second opening, and the first opening and the second opening are communicated. In this way, after the probe is retracted, it can come to the lower part of the external thread structure to be measured through the communication part of the first opening and the second opening for relevant detection work.

[0021] A positioning device as described above, wherein a convex part is provided on one side of the measurement reference member away from the support part. The convex part is hollow for the probe to pass through, and the convex part is engaged with the groove of the thread measuring machine. The measurement reference member is provided with a through hole for connecting the measurement reference member and the thread measuring machine with a fastener, so as to ensure the stable connection between the measurement reference member and the thread measuring machine.

[0022] In a second aspect, the present invention further provides a portable thread measuring machine adopting the described positioning device.

[0023] In a third aspect, the present invention further provides an external thread measurement method adopting the described positioning device, including the following steps:

[0024] Connect the measurement reference member to the thread measuring machine;

[0025] Install the pressing member at the connecting member;

[0026] Place the workpiece to be measured at the support part. One end of the workpiece to be measured abuts against the measurement reference surface, and the external thread structure to be measured of the workpiece to be measured contacts the support part;

[0027] Move the pressing component along the connecting piece, and press the workpiece to be measured through the pressing component;

[0028] After the probe of the thread measuring machine passes through the opening, it comes to the external thread structure to be measured of the workpiece to be measured, and starts to measure the external thread structure to be measured.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1) The positioning device provided by the present invention has a reasonable structure. The measurement reference part is provided with a support part, and the support part forms a support groove, which enables the external thread structure to be measured of the workpiece to be measured to be supported through the support groove. The position of the support groove is determined, and naturally the position of the workpiece to be measured is determined, realizing the accurate positioning of the workpiece to be measured. In this way, by determining the depth of the probe extending out of the opening, the X-direction position of the probe can be determined. After the position of the workpiece to be measured is limited, the Y-direction position when the probe contacts the workpiece to be measured can be determined accordingly. In this way, the initial position of the probe contacting the external thread structure to be measured is ensured, and the workpiece to be measured is pressed through the pressing component without manual pressing. Each component cooperates with each other to ensure the accuracy and precision of the measurement result.

[0031] 2) In the present invention, the center position of the support groove and the center line in the width direction of the opening are arranged on the same straight line, ensuring that the Y-direction position at the initial position of the probe is arranged along the central axis of the workpiece to be measured, and correspondingly ensuring that the central axis of the probe is located above the central axis of the external thread structure to be measured. Thus, the probe is placed above or below the maximum longitudinal section of the workpiece to be measured, realizing precise positioning.

[0032] 3) In the present invention, the support part is a roller, and the distance between the rollers is set. The support groove is formed by the rollers, meeting the detection of external thread structures to be measured with different sizes. The rollers can rotate to facilitate the placement of the workpiece to be measured.

[0033] 4) In the present invention, the structure of the pressing component is reasonable. The pressing component is sleeved on the connecting piece through a collar and can move relative to the connecting piece. The pressing component is fixed at one end of the collar and is inclined relative to the connecting piece. Under the action of an external force, the collar moves relative to the connecting piece, and the pressing component gradually moves through the connecting piece. The position of the pressing component is maintained by the friction between the bushing and the connecting piece. In this way, after the precise positioning of the workpiece to be measured, the workpiece to be measured is pressed through the pressing component to ensure the stable setting of the workpiece to be measured, thereby realizing precise measurement.

[0034] 5) In the present invention, there are two pressing components, which can ensure the symmetry and uniformity of the pressing force on the workpiece to be measured, and are beneficial to ensuring the accuracy of the measurement result.

[0035] 6) In the present invention, the structure of the measurement reference part is reasonably arranged. The measurement reference part is engaged with the groove of the thread measuring machine through the convex part to preliminarily position the position of the measurement reference part, and then the connection between the measurement reference part and the thread measuring machine is realized through the fastener, ensuring the stable connection between the measurement reference part and the thread measuring machine, and correspondingly ensuring the accuracy of the position of the measurement reference part.

[0036] 7) The present invention provides an external thread measurement method. By arranging a support part on the measurement reference part, accurate positioning of the position of the measured part can be achieved. After the position of the measured part is determined, the position of the probe relative to the measurement reference part is fixed, and then the initial position where the probe contacts the external thread structure to be measured can be determined, thereby realizing the accurate measurement of the external thread structure to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The attached drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0038] Figure 1 is an enlarged schematic view of the cooperation between a positioning device and a thread measuring machine according to one or more embodiments of the present invention.

[0039] In the figure: The distances or sizes between each part are exaggerated for showing the positions of each part, and the schematic view is only for illustration.

[0040] Among them: 1. Thread measuring machine, 2. Measurement reference part, 3. Probe, 4. First opening, 5. Roller, 6. Second opening, 7. Compression component, 8. Measured part, 9. Collar, 10. Wedge sleeve, 11. Bushing, 12. Connecting piece. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] It should be noted that the following detailed description is illustrative and is intended to provide further description of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments of the present invention. As used herein, unless the present invention clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof;

[0043] As introduced in the background art, in the prior art, the position of the workpiece to be measured cannot be accurately positioned, and manual pressing is required, resulting in limited accuracy and precision of the measurement results. To solve the above technical problems, the present invention proposes a positioning device.

[0044] Embodiment 1

[0045] In a typical embodiment of the present invention, with reference to Figure 1 As shown, a positioning device includes a measurement reference member 2. The measurement reference member 2 is connected to a thread measuring machine 1 to provide a measurement reference surface. The measurement reference member 2 is provided with an opening. A support portion is provided at the measurement reference surface of the measurement reference member 2. One end of a connecting member 12 is fixed, and the connecting member 12 is movably connected to a pressing member 7. One end of the workpiece to be measured 8 abuts against the measurement reference surface, and a section of the workpiece to be measured 8 contacts the support portion. Thus, the position of the workpiece to be measured can be accurately positioned. By determining the depth of the probe 3 extending out of the opening, the X-direction position of the probe can be determined. After the position of the workpiece to be measured 8 is defined, the Y-direction position when the probe 3 contacts the workpiece to be measured 8 can be correspondingly determined. In this way, the initial position of the probe 3 contacting the external thread structure to be measured is ensured, so as to improve the accuracy of the measurement result. The other end of the workpiece to be measured 8 is provided with a pressing force towards the thread measuring machine direction by the pressing member 7. After the probe of the thread measuring machine 1 passes through the opening and reaches the external thread structure to be measured of the workpiece to be measured 8, the pressing of the workpiece to be measured is realized through the pressing member 7, without manual pressing. The cooperation of each component ensures the accuracy and precision of the measurement result.

[0046] In this embodiment, the support portion is multiple rollers 5. Specifically, two rollers 5 are provided. The center line between the rollers 5 and the center line in the width direction of the opening are arranged in the same plane. Thus, it can be determined that the central axis of the workpiece to be measured 8 coincides with the center line in the width direction of the opening. The plane where the central axis of the workpiece to be measured 8 and the center line in the width direction of the opening are located is perpendicular to the plane where the central axes of the two rollers 5 are located. The rollers 5 are rotatable relative to the reference measurement member 2. The space between two adjacent rollers 5 forms a support groove. The rollers 5 are arranged at the side of the opening. The probe can extend from the upper side or the lower side of the workpiece to be measured, realizing the separate contact measurement of the upper side and the lower side of the external thread structure to be measured.

[0047] The positioning device provided in this embodiment can realize the detection of the tapered external thread structure. For effective cooperation with the external thread structure to be measured, the rollers 5 are tapered rollers to cooperate with the tapered external thread structure. Considering that the outer diameter of one end of the tapered external thread structure facing the measurement reference surface is small, the outer diameter of the natural tapered roller 5 gradually increases from one end far from the measurement reference surface to the other end.

[0048] It should be noted that, to further ensure the measurement accuracy, the center line in the opening width direction and the center line of the initial position of the probe are in the same plane, and the center position of the support groove and the center line in the opening width direction are set on the same straight line, so as to ensure that the Y-direction position at the initial position of the probe 3 is set along the central axis of the measured part, and correspondingly ensure that the central axis of the probe 3 is located above the central axis of the external thread structure to be measured, making the starting position of the probe more accurate.

[0049] Moreover, the measurement reference part 2 is a measurement reference plate, and the measurement reference part has a set thickness.

[0050] In this embodiment, the openings of the measurement reference part 2 include a first opening 4 and a second opening 6. The first opening 4 and the second opening 6 are arranged at an interval. The first opening is on the upper side of the second opening. The length of the first opening is greater than the length of the second opening. Both the first opening 4 and the second opening 6 are long holes. The widths of the first opening 4 and the second opening 6 are the same. The center lines in the width direction of the first opening 4 and the second opening 6 are in the same plane. The first opening 4 and the second opening 6 are connected through a communication groove. The rollers are arranged on both sides of the communication groove between the first opening and the second opening. The width of the communication groove is smaller than the diameter of the measured part. The first opening 4 and the second opening 6 are connected. In this way, after the probe is retracted, it can come to the lower part of the external thread structure to be measured through the connection part of the first opening and the second opening for relevant detection work.

[0051] In addition, it is easy to understand that a convex part is arranged on the side of the measurement reference part 2 away from the support part. The convex part is hollow for the probe to pass through. The convex part is engaged with the groove of the thread measuring machine. The convex part can be two slideways. Through the two slideways, the convex part can be snapped into the groove of the thread measuring machine 1. The measurement reference part is provided with through holes. The through holes are located on both sides of the first opening 4 and in the middle section of the measurement reference part. Fasteners such as bolts or screws are connected to the thread measuring machine through the through holes, realizing the connection between the measurement reference part 2 and the thread measuring machine 1, so as to ensure the stable connection between the measurement reference part and the thread measuring machine.

[0052] It should be noted that the connecting part 12 is detachably connected to the measurement reference part 2 or the thread measuring machine 1. In this way, the connecting part 12 can be installed according to requirements, and the appropriate number of connecting parts can be installed according to requirements. Specifically, there are two threaded holes on the upper side of the end of the thread measuring machine 1 that is matched with the measurement reference part. The threaded holes are located on both sides of the measurement reference part. The connecting part 12 is a connecting rod. One end of the connecting rod is connected to the threaded hole through a threaded structure.

[0053] It is easily understandable that there are two pressing components 7. One end of each of the two pressing components 7 is respectively fixed at the corresponding connecting member 12. The two connecting members 12 are respectively arranged on both sides of the measurement reference member. Through the arrangement of the two pressing components, the stable pressing of the measured part 8 is ensured (at this time, the two pressing components form a V shape to ensure the pressing force), avoiding skew and ensuring the accuracy of the measurement result.

[0054] In this embodiment, one end of the pressing component 7 is fixed at the collar 9. The collar 9 is sleeved on the circumferential direction of the connecting member 12. The collar 9 is movable relative to the connecting member 12. A bushing 11 is arranged between the collar 9 and the connecting member 12. There is friction between the bushing 11 and the connecting member 12. The bushing 11 can be a rubber bushing. The connecting member is a smooth rod. The collar can be pushed relative to the connecting member 12, thereby driving the pressing component to move.

[0055] Furthermore, the section of the pressing component 7 fixed to the collar 9 is inclined relative to the connecting member 12, so that the pressing component is inclined towards the direction of the roller 5. One end of the pressing component 7 for pressing the measured part 8 is bent. That is, one end of the pressing component 7 for pressing the measured part is bent into a V shape. For the pressing component 7 inclined relative to the connecting member, because the pressing component 7 is inclined, after the collar 9 is pushed relative to the connecting member to the set position, the pressing component 7 is gradually straightened, and under the action of the bushing, the collar 9 can generate friction with the connecting member, ensuring the position of the pressing component.

[0056] In this embodiment, the collar 9 includes a fixed sleeve. One side of the fixed sleeve is fixed with a first wedge-shaped sleeve. The first wedge-shaped sleeve and the second wedge-shaped sleeve clamp one side of the pressing component 7. The first wedge-shaped sleeve and the second wedge-shaped sleeve are fixedly connected to ensure the initial state of the pressing component 7. The bushing 11 is located inside the fixed sleeve, the first wedge-shaped sleeve and the second wedge-shaped sleeve.

[0057] Specifically, the pressing component 7 is an elastic steel sheet, which can be deformed. From the end of the pressing component 7 connected to the connecting member 12 to the other end of the pressing component, the width of the pressing component 7 gradually decreases. When one end of the elastic member contacts one end of the measured part, pushing the collar 9 along the connecting member 12 can ensure that the position of the elastic steel sheet is locked, thereby ensuring the stable pressing of the pressing component on the elastic member.

[0058] The positioning device provided in this embodiment has the measuring reference member 2 fixed to the thread measuring machine 1. The measuring reference member is provided with a supporting portion, and the supporting portion forms a supporting groove through which the to-be-measured external thread structure of the to-be-measured part can be supported. The position of the supporting groove is determined, and naturally the position of the to-be-measured part is determined. After the position of the to-be-measured part is determined, the position of the probe 3 relative to the measuring reference member 2 is fixed. Furthermore, the initial position where the probe contacts the to-be-measured external thread structure can be determined, and the probe 3 can be placed above or below the maximum longitudinal section of the to-be-measured part to achieve precise positioning. And the to-be-measured part is stably pressed by the pressing member 7 without manual pressing, realizing accurate measurement of the to-be-measured external thread structure and ensuring the accuracy and precision of the measurement result.

[0059] Embodiment Two

[0060] The difference between this embodiment and Embodiment One lies in:

[0061] The collar is a nut structure, and the connecting rod is a screw rod. The collar is fitted with the connecting rod through a threaded structure. One end of the pressing member is fixed at the collar. With the assistance of a person's hand for the to-be-measured part, the collar is rotated relative to the screw rod so that one end of the pressing member contacts one end of the to-be-measured part to realize pressing of the to-be-measured part. Of course, the collar and the connecting rod with the threaded structure fit are not as convenient to operate as the solution in Embodiment One and need to be rotated.

[0062] Embodiment Three

[0063] This embodiment provides a portable thread measuring machine, which adopts a positioning device described in Embodiment One or Embodiment Two. The portable thread measuring machine is a prior art. The portable thread measuring machine is provided with a probe, and the probe is a double-headed probe. The portable thread measuring machine can drive the probe to move and make the probe extend beyond the measuring reference member.

[0064] Embodiment Four

[0065] This embodiment provides an external thread measurement method, which adopts a positioning device described in Embodiment One, including the following steps:

[0066] Connect the measuring reference member 2 to the thread measuring machine 1;

[0067] Set a connecting member 12 at the thread measuring machine 1, and the connecting member 12 is connected to the pressing member 7;

[0068] Set the to-be-measured part 8 at the two rollers 5. One end of the to-be-measured part abuts against the measuring reference surface, and the to-be-measured external thread structure of the to-be-measured part contacts the rollers. An operating personnel provides a pressing force to the to-be-measured part;

[0069] Move the pressing member along the connecting member 12, and one end of the pressing member 7 abuts against the end of the to-be-measured part away from the measuring reference member 2 to press the to-be-measured part through the pressing member;

[0070] After the probe 3 of the thread measuring machine 1 passes through the first opening, it comes to the outer thread structure to be measured above the workpiece to be measured and starts to measure the outer thread structure to be measured;

[0071] The probe retracts, extends from the second opening, comes to the outer thread structure to be measured below the workpiece to be measured, and starts to measure the outer thread structure to be measured.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A positioning device, characterized in that, It includes a measurement reference piece which is connected to a thread measuring machine to provide a measurement reference surface. The measurement reference piece is provided with an opening. A support part is arranged at the measurement reference surface of the measurement reference piece. The support part forms a support groove to support one side of the measured part. One end of the connecting piece is fixed, and the connecting piece is movably connected to the pressing part. One end of the measured part abuts against the measurement reference surface. One section of the measured part contacts the support part. The other end of the measured part is provided with a pressing force towards the thread measuring machine by the pressing part. After the probe of the thread measuring machine passes through the opening, it reaches the to-be-measured external thread structure of the measured part.

2. The positioning device according to claim 1, characterized in that, The center line in the width direction of the opening and the center line of the initial position of the probe are in the same plane. The central position of the support groove and the center line in the width direction of the opening are arranged on the same straight line to ensure that the Y-direction position at the initial position of the probe is arranged along the central axis of the measured part.

3. The positioning device according to claim 1, characterized in that, The support part is multiple rollers. The space between two adjacent rollers forms the support groove. The rollers are rotatable relative to the reference measuring piece. The rollers are arranged at the side of the opening. The probe can extend from the upper side or the lower side of the measured part.

4. A positioning device according to claim 1, characterized in that, There are two pressing parts. One ends of the two pressing parts are respectively fixed at the corresponding connecting pieces. The two connecting pieces are respectively arranged on both sides of the measurement reference piece.

5. The positioning device according to claim 1, characterized in that, One end of the pressing part is fixed at a collar. The collar is sleeved on the circumferential direction of the connecting piece. The collar is movable relative to the connecting piece.

6. The positioning device according to claim 5, characterized in that, The section of the pressing part fixed at the collar is inclined relative to the connecting piece, so that the other end of the pressing part is inclined towards the direction of the roller. The pressing part is used for pressing one end of the measured part which is bent.

7. The positioning device according to claim 1, characterized in that The pressing part is an elastic steel sheet.

8. A positioning device according to claim 1, wherein, The connecting piece is detachably connected to the measurement reference piece or the thread measuring machine.

9. The positioning device according to claim 3, characterized in that, The roller is a conical roller.

10. A positioning device according to claim 3, characterized in that, The opening of the measurement reference piece includes a first opening and a second opening. The first opening and the second opening are arranged at an interval distance. The center lines in the width direction of the first opening and the second opening are in the same plane. The rollers are arranged between the first opening and the second opening. The first opening and the second opening are communicated.

11. A positioning device according to claim 1, characterized in that, A convex part is arranged on the side of the measurement reference piece far from the support part. The convex part is hollow for the probe to pass through. The convex part is engaged with the groove of the thread measuring machine. The measurement reference piece is provided with a through hole for a fastener to connect the measurement reference piece and the thread measuring machine.

12. A portable thread measuring machine, characterized in that, Use a positioning device according to any one of claims 1-11.

13. A method for measuring external threads, characterized in that, Use a positioning device according to any one of claims 1-11, including the following: Connect the measurement reference piece to the thread measuring machine; Install the pressing part at the connecting piece; Set the measured part at the support part. One end of the measured part abuts against the measurement reference surface. The to-be-measured external thread structure of the measured part contacts the support part; Move the pressing part along the connecting piece and press the measured part through the pressing part; After the probe of the thread measuring machine passes through the opening, it reaches the to-be-measured external thread structure of the measured part, and starts to measure the to-be-measured external thread structure.

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