Full-automatic grating type length measuring instrument for detecting inner diameter and outer diameter of high-precision thin-walled part and measuring method of full-automatic grating type length measuring instrument

Abstract

The invention discloses a full-automatic grating type length measuring instrument for detecting the inner diameter and the outer diameter of a high-precision thin-wall part and a measuring method thereof, and belongs to the technical field of precision measuring instruments. The full-automatic grating type length measuring instrument comprises a measuring head and a measuring arm, and the output end of the measuring arm is connected with the measuring head through a rotating disc; the output end of the measuring arm is also provided with a driving mechanism for driving the measuring head to rotate; one end of a short arm side is connected with the internal measuring body, and one end of a long arm side is connected with the external measuring body; the long arm side middle of the main body is connected with a measuring arm; and the internal measuring body extends into the workpiece to be measured. The internal measuring unit is matched with the external measuring body to measure the inner diameter and the wall thickness of the measured workpiece, so that the inner diameter and the outer diameter of the measured workpiece are obtained; the device can be applied to detection and calibration of inner and outer diameters of high gauge blocks, gauges, ultrahigh-precision workpieces and high-precision thin-wall parts, perfects tool clamps corresponding to detected measuring tools and gauges, and has the advantages of being accurate in measured data, high in automation degree and wide in application range.

Description

Technical Field

[0001] This invention belongs to the field of precision measuring instrument technology, and more specifically relates to a fully automatic grating-type length measuring instrument and its measuring method for detecting the inner and outer diameters of high-precision thin-walled parts. Background Technology

[0002] For high-precision thin-walled mechanical parts, their dimensions and geometry are the main factors affecting accuracy, and measurement is an essential means of evaluating dimensions and geometry. When measuring thin-walled workpieces with traditional measuring tools, comparative measurement is required. This involves first zeroing the dial indicator, then measuring the part with the measuring tool and observing the change in the dial indicator's value. Due to manufacturing errors in the dial indicator, workers need to convert the measured value to the actual value during inspection, which can easily lead to calculation errors. Furthermore, transmission-based measuring tools have large system errors, are bulky and heavy, and have low measurement accuracy.

[0003] Therefore, how to provide a fully automatic grating-type length measuring instrument and its measurement method for high-precision detection of the inner and outer diameters of thin-walled parts is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a fully automatic grating-type length measuring instrument and its measurement method for high-precision detection of the inner and outer diameters of thin-walled parts, which has the advantages of accurate measurement data, high degree of automation and wide applicability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A fully automatic grating-type length measuring instrument for high-precision detection of the inner and outer diameters of thin-walled parts includes a measuring head and a measuring arm. The output end of the measuring arm is connected to the measuring head via a rotating disk. The output end of the measuring arm is also provided with a drive mechanism for driving the measuring head to rotate. The measuring head includes a main body, an internal measuring body, and an external measuring body. The main body is configured as an inverted J-shape, with one end of the short arm connected to the internal measuring body and one end of the long arm connected to the external measuring body. The measuring arm is connected to the middle of the long arm side of the main body. The internal measuring body extends into the workpiece being measured.

[0006] Furthermore, the internal measuring body includes a first internal measuring arm, a second internal measuring arm, two sets of internal measuring probes, and an internal measuring unit; the upper ends of the first and second internal measuring arms are rotatably connected to one end of the main short arm, and the lower ends are respectively connected to a set of internal measuring probes; the two sets of internal measuring probes are arranged back to back, and their outer ends abut against the inner wall of the workpiece being measured; the internal measuring unit is connected between the first and second internal measuring arms.

[0007] Furthermore, both the first and second internal measuring arms are rotatably provided with connecting grooves at their bottom ends, and the two sets of connecting grooves are open at one end and arranged opposite each other; an internal measuring probe is provided at the end of the connecting groove away from the opening; a guide rod is provided through the two sets of connecting grooves, and a guide slider is fixedly provided at each end of the guide rod, and the two sets of guide sliders are slidably arranged in the two sets of connecting grooves respectively.

[0008] Furthermore, the internal measuring unit includes a connecting arm, a slider, a slide rail, a lead screw, and a first drive motor; the first drive motor is fixedly mounted on the second internal measuring arm, and its output end is fixedly connected to one end of the lead screw; the lead screw is rotatably disposed inside the second internal measuring arm; one end of the connecting arm is rotatably connected to the first internal measuring arm, and the other end is rotatably connected to the slider; the slider is threaded onto the lead screw; the slide rail is fixed to the inner wall of the second internal measuring arm, and one side of the slider is slidably connected to the slide rail.

[0009] Furthermore, a groove matching the shape of the slide rail is provided on one side of the slider, and a first grating ruler is embedded in the center of the slide rail facing the slider; a first reading head is embedded in the inner wall of the groove, corresponding to the first grating ruler and at a certain distance.

[0010] Furthermore, the external measuring body includes an external measuring probe, a gear, a rack, a second reading head, a second grating ruler, and a second drive motor; the external measuring probe is slidably mounted on one end of the long arm of the main body, with the measuring end facing the workpiece being measured; the rack is fixedly mounted on the external measuring probe, and the gear is rotatably mounted inside the main body; the rack meshes with the gear for transmission; the output end of the second drive motor is connected to the gear through a bevel gear set; the second grating ruler is mounted on one side of the rack, and the second reading head is mounted above the second grating ruler and fixedly mounted inside the main body.

[0011] Furthermore, the internal measuring probe has the same structure as the external measuring probe, both being hollow inside, with a sliding cavity and an adjustment cavity inside, the sliding cavity and the adjustment cavity being connected, a movable column for abutting the workpiece being measured being slidably disposed in the sliding cavity, and an adjustment unit for adjusting the measuring force being disposed in the adjustment cavity, the movable column being connected to the adjustment unit.

[0012] Furthermore, the movable column is provided with a ball head that rolls against the top of the workpiece being tested.

[0013] Furthermore, the adjustment unit includes a moving block, a first electromagnet, and a second electromagnet; one end of the moving block is connected to the movable column, and the other end is disposed in the adjustment cavity; the first electromagnet is disposed on one side wall of the adjustment cavity located on one side of the moving block, and the second electromagnet is disposed on the other side wall of the adjustment cavity located on the other side of the moving block, and the first electromagnet and the second electromagnet are arranged opposite to each other in the moving direction of the moving block.

[0014] A measurement method for a fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts includes the following steps: In the initial state of the measuring instrument, the external measuring probe abuts against the internal measuring probe on the second internal measuring arm; the internal measuring probe on the second internal measuring arm abuts against the back of the internal measuring probe on the first internal measuring arm; the measuring arm control body moves and rotates to extend the internal measuring body into the workpiece being measured. First, the internal measuring probe of the second internal measuring arm is placed against the inner wall of the workpiece to be measured. While the main body is being straightened, the outer measuring probe is driven to move the second grating ruler so that the internal measuring probe and the outer measuring probe are on the same horizontal line, and the wall thickness of the measured point of the workpiece is obtained. Then, the internal measuring unit drives the first and second internal measuring arms to open, so that the two sets of internal measuring probes abut against the inner wall of the workpiece to measure the inner diameter of the workpiece, and the outer diameter of the workpiece is obtained by measuring the wall thickness of the workpiece by the outer measuring probe.

[0015] The beneficial effects of this invention are as follows: This invention provides a fully automatic grating-type length measuring instrument for detecting the inner and outer diameters of high-precision thin-walled parts. It utilizes an internal measuring unit in conjunction with an external measuring body to measure the inner diameter and wall thickness of the workpiece, thereby obtaining the inner and outer diameters of the workpiece. It can be applied to the detection and calibration of the inner and outer diameters of high-precision gauge blocks, gauges, ultra-high precision workpieces, and high-precision thin-walled parts, and to improve the tooling fixtures corresponding to the gauges and measuring tools being inspected.

[0016] This invention incorporates adjustment units within both the internal and external measuring probes. These units regulate the measuring force exerted by the movable column against the workpiece. In ultra-high precision measurements at the 1-100nm level, variations in measuring force significantly impact the measurement results. Finite element analysis and experiments show that every 0.1N of measuring force affects the accuracy of the high-rigidity measuring hook by approximately 0.05μm. This invention can provide more accurate measurement data.

[0017] This invention utilizes a connecting measuring arm to drive the measuring head to move and rotate, which can increase the degree of automation in the measurement process, improve detection efficiency while ensuring measurement accuracy, and reduce labor intensity. Furthermore, the semi-U-shaped design of the measuring head can accommodate a wider range of thin-walled workpieces of different sizes and shapes. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the measuring head of the present invention.

[0020] Figure 2 This is a schematic diagram of the internal structure of the internal measuring body and the external measuring body of the present invention.

[0021] Figure 3 for Figure 2 Sectional view of AA.

[0022] Figure 4 This is a schematic diagram of the internal or external measuring probe of the present invention.

[0023] In the figure: 1-Measuring head; 2-Measuring arm; 3-Rotating disk; 4-Main body; 5-Internal measuring body; 6-External measuring body; 7-First internal measuring arm; 8-Second internal measuring arm; 9-Internal measuring probe; 10-Internal measuring unit; 11-Connecting arm; 12-Slider; 13-First reading head; 14-First grating ruler; 15-Slide rail; 16-Lead screw; 17-First drive motor; 18-External measuring probe; 19-Gear; 20-Rack; 21-Second reading head; 22-Second drive motor; 23-Moving column; 24-Moving block; 25-First electromagnet; 26-Second electromagnet; 27-Connecting slide; 28-Guide rod. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see the appendix Figure 1-4The present invention provides a fully automatic grating-type length measuring instrument for detecting the inner and outer diameters of high-precision thin-walled parts, including a measuring head 1 and a measuring arm 2. The measuring head 1 is installed at the output end of the measuring arm 2, and the measuring arm 2 is set as an automatic robotic arm, which can control the multi-degree-of-freedom movement of the measuring head 1 and cooperate with the turntable to complete the close-range inner and outer diameter measurement of high-precision thin-walled parts.

[0026] The output end of the measuring arm 2 is connected to the measuring head 1 via a rotary disk 3; the output end of the measuring arm 2 is also provided with a drive mechanism for driving the measuring head 1 to rotate, so that the measuring trajectory of the measuring head 1 conforms to the workpiece being measured. The drive mechanism uses existing technology and will not be described in detail here.

[0027] The measuring head 1 includes a main body 4, an internal measuring body 5, and an external measuring body 6. The main body 4 is configured in a semi-U-shape, with one end of the short arm connected to the internal measuring body 5 and one end of the long arm connected to the external measuring body 6. The measuring arm 2 is connected to the middle of the long arm of the main body 4. The short arm of the main body 4 drives the internal measuring body 5 to extend into the workpiece being measured, for measuring the inner diameter of the workpiece. The long arm of the main body 4 drives the external measuring body 6 to be positioned outside the workpiece being measured, for cooperating with the internal measuring body 5 to measure the sidewall thickness of the workpiece, thereby obtaining the outer diameter of the workpiece.

[0028] The internal measuring body 5 includes a first internal measuring arm 7, a second internal measuring arm 8, two sets of internal measuring probes 9, and an internal measuring unit 10. The upper ends of the first internal measuring arm 7 and the second internal measuring arm 8 are rotatably connected to one end of the short arm of the main body 4, and the lower ends are respectively connected to a set of internal measuring probes 9. The two sets of internal measuring probes 9 are arranged back to back, and their outer ends abut against the inner wall of the workpiece being measured. The internal measuring unit 10 is connected between the first internal measuring arm 7 and the second internal measuring arm 8 and is used to measure the opening distance of the first internal measuring arm 7 and the second internal measuring arm 8, thereby obtaining the inner diameter of the workpiece being measured.

[0029] The bottom ends of the first internal measuring arm 7 and the second internal measuring arm 8 are both rotatably provided with connecting grooves 27. The two sets of connecting grooves 27 are open at one end and are arranged opposite each other. An internal measuring probe 9 is provided at the end of the connecting groove 27 away from the opening. A guide rod 28 is provided through the two sets of connecting grooves 27. A guide slider is fixedly provided at both ends of the guide rod (28). While the first internal measuring arm 7 and the second internal measuring arm 8 drive the internal measuring probe 9 to move, the two sets of guide sliders slide in the two sets of connecting grooves 27 respectively, so that the two sets of internal measuring probes 9 are always on the same horizontal line.

[0030] The internal measuring unit 10 includes a connecting arm 11, a slider 12, a first reading head 13, a first grating ruler 14, a slide rail 15, a lead screw 16, and a first drive motor 17. The first drive motor 17 is fixedly mounted on the second internal measuring arm 8, and its output end is fixedly connected to one end of the lead screw 16. The lead screw 16 is rotatably disposed inside the second internal measuring arm 8. One end of the connecting arm 11 is rotatably connected to the first internal measuring arm 7, and the other end is rotatably connected to the slider 12. The slider 12 is sleeved on the lead screw 16 and threadedly connected to the lead screw 16. The slide rail 15 is fixedly disposed on the inner wall of the second internal measuring arm 8. A groove matching the shape of the slide rail 15 is provided on one side of the slider 12, so that the slider 12 and the slide rail 15 are slidably connected. A groove is provided at the center position of the slide rail 15 facing the slider 12, and the first grating ruler 14 is embedded in the groove. The first reading head 13 is embedded in the inner wall of the groove, corresponding to the first grating ruler 14, and at a certain distance.

[0031] The straightness and rigidity of the guide rail 15 affect the deflection, tilt, and distance of the grating, thus affecting the grating signal. Therefore, the guide rail 15 is made of a special high-rigidity, gapless, and low-resistance material to ensure straightness and thus ensure the stability of the grating signal.

[0032] The first drive motor 17 drives the lead screw 16 to rotate, which in turn drives the slider 12 to move along the slide rail 15, thereby driving the first reading head 13 to move relative to the first grating ruler 14. The opening distance of the first internal measuring arm 7 and the second internal measuring arm 8 can be calculated by the moving distance of the first reading head 13 relative to the first grating ruler 14.

[0033] The external measuring body 6 includes an external measuring probe 18, a gear 19, a rack 20, a second reading head 21, a second grating ruler, and a second drive motor 22. The external measuring probe 18 is slidably mounted on one end of the long arm of the main body 4, with the measuring end facing the workpiece being measured. The rack 20 is fixedly mounted on the external measuring probe 18, and the gear 19 is rotatably mounted inside the main body 4. The rack 20 and the gear 19 mesh and drive each other. The output end of the second drive motor 22 is connected to the gear 19 through a bevel gear set, driving the gear 19 to rotate. The second grating ruler is located on one side of the rack 20, and the second reading head 21 is located above the second grating ruler and is fixedly mounted inside the main body 4.

[0034] The second drive motor 22 drives the gear 19 to rotate, which in turn drives the rack 20 to move, thereby driving the external measuring probe 18 to move. At the same time, it drives the second grating ruler to move relative to the second reading head 21. The moving distance of the external measuring probe 18 is calculated by the moving distance of the second grating ruler.

[0035] The internal measuring probe 9 has the same structure as the external measuring probe 18, both being hollow internally. Each probe contains a sliding cavity and an adjusting cavity, which are connected. A movable column 23, for contacting the workpiece being measured, is slidably disposed within the sliding cavity. An adjusting unit, for adjusting the measuring force, is disposed within the adjusting cavity. The movable column 23 is connected to the adjusting unit, which adjusts the magnitude of the measuring force exerted by the movable column 23 against the workpiece. A ball head is rolled at the top of the movable column 23 where it contacts the workpiece.

[0036] The adjustment unit includes a moving block 24, a first electromagnet 25, and a second electromagnet 26. One end of the moving block 24 is connected to the movable column 23, and the other end is disposed within the adjustment cavity. The first electromagnet 25 is disposed on one side wall of the adjustment cavity, located on one side of the moving block 24, and the second electromagnet 26 is disposed on the other side wall of the adjustment cavity, located on the other side of the moving block 24. The first electromagnet 25 and the second electromagnet 26 are arranged opposite to each other in the moving direction of the moving block 24. This arrangement controls the moving block 24 to approach the first electromagnet 25 or the second electromagnet 26, thereby controlling the movable column 23 to abut against the measuring force of the workpiece being measured. Furthermore, the magnitude of the measuring force can be recorded through the current fluctuations transmitted back by the first electromagnet 25 and the second electromagnet 26. The arrangement of the first electromagnet 25 and the second electromagnet 26 ensures the stability, constancy, and continuous adjustability of the measuring force.

[0037] The present invention also provides a measurement method using the above-mentioned fully automatic grating-type length measuring instrument for high-precision detection of the inner and outer diameters of thin-walled parts, comprising the following steps: When the external measuring probe 18 is in the initial state of the measuring instrument, it abuts against the internal measuring probe 9 on the second internal measuring arm 8; the internal measuring probe 9 on the second internal measuring arm 8 abuts against the back of the internal measuring probe 9 on the first internal measuring arm 7; the measuring arm 2 controls the main body 4 to move and rotate, so that the internal measuring body 5 is inserted into the workpiece being measured.

[0038] First, the internal measuring probe 9 of the second internal measuring arm 8 is placed against the inner wall of the workpiece to be measured. The current fluctuation transmitted back by the first electromagnet 25 is used to monitor whether the internal measuring probe 9 of the second internal measuring arm 8 is against the inner wall of the workpiece to be measured. At the same time as the main body 4 is aligning, the outer measuring probe 18 is driven to move the second grating ruler so that the internal measuring probe 9 and the outer measuring probe 18 are on the same horizontal line, and the wall thickness of the measured point of the workpiece is obtained. Then, the internal measuring unit 10 drives the first internal measuring arm 7 and the second internal measuring arm 8 to open, so that the two sets of internal measuring probes 9 abut against the inner wall of the workpiece to measure the inner diameter of the workpiece, and the outer diameter of the workpiece is obtained by measuring the wall thickness of the workpiece by the outer measuring probe 18.

[0039] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0040] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fully automatic grating-type length measuring instrument for high-precision detection of the inner and outer diameters of thin-walled parts, characterized in that, It includes a measuring head (1) and a measuring arm (2), the output end of which is connected to the measuring head (1) via a rotating disk (3); the output end of the measuring arm (2) is also provided with a driving mechanism for driving the measuring head (1) to rotate; The measuring head (1) includes a main body (4), an internal measuring body (5) and an external measuring body (6); the main body (4) is configured as an inverted J-shape, with one end of the short arm connected to the internal measuring body (5) and one end of the long arm connected to the external measuring body (6); the measuring arm (2) is connected to the middle of the long arm side of the main body (4); the internal measuring body (5) extends into the workpiece being measured.

2. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 1, characterized in that, The internal measuring body (5) includes a first internal measuring arm (7), a second internal measuring arm (8), two sets of internal measuring probes (9), and an internal measuring unit (10); the upper ends of the first internal measuring arm (7) and the second internal measuring arm (8) are rotatably connected to one end of the short arm of the main body (4), and the lower ends are respectively connected to a set of internal measuring probes (9); the two sets of internal measuring probes (9) are arranged back to back, and the outer ends abut against the inner wall of the workpiece being measured; the internal measuring unit (10) is connected between the first internal measuring arm (7) and the second internal measuring arm (8).

3. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 2, characterized in that, The bottom ends of the first internal measuring arm (7) and the second internal measuring arm (8) are rotatably provided with connecting grooves (27). The two sets of connecting grooves (27) are open at one end and are arranged opposite to each other. An internal measuring probe (9) is provided at the end of the connecting groove (27) away from the opening. A guide rod (28) is provided through the two sets of connecting grooves (27). A guide slider is fixed at both ends of the guide rod (28). The two sets of guide sliders are slidably arranged in the two sets of connecting grooves (27).

4. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 2, characterized in that, The internal measuring unit (10) includes a connecting arm (11), a slider (12), a slide rail (15), a lead screw (16), and a first drive motor (17); the first drive motor (17) is fixedly installed on the second internal measuring arm (8), and its output end is fixedly connected to one end of the lead screw (16); the lead screw (16) is rotatably disposed inside the second internal measuring arm (8); one end of the connecting arm (11) is rotatably connected to the first internal measuring arm (7), and the other end is rotatably connected to the slider (12); the slider (12) is threaded onto the lead screw (16); the slide rail (15) is fixedly disposed on the inner wall of the second internal measuring arm (8), and one side of the slider (12) is slidably connected to the slide rail (15).

5. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 4, characterized in that, The slider (12) has a groove on one side that matches the shape of the slide rail (15). The slide rail (15) is fitted with a first grating ruler (14) at the center of the side facing the slider (12). A first reading head (13) is fitted on the inner wall of the groove, corresponding to the first grating ruler (14) and at a certain distance.

6. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 2, characterized in that, The external measuring body (6) includes an external measuring probe (18), a gear (19), a rack (20), a second reading head (21), a second grating ruler, and a second drive motor (22); the external measuring probe (18) is slidably mounted on one end of the long arm of the main body (4), with the measuring end facing the workpiece being measured; the rack (20) is fixedly mounted on the external measuring probe (18), and the gear (19) is rotatably mounted inside the main body (4); the rack (20) meshes with the gear (19) for transmission; the output end of the second drive motor (22) is connected to the gear (19) through a bevel gear set; the second grating ruler is mounted on one side of the rack (20), and the second reading head (21) is mounted above the second grating ruler and fixedly mounted inside the main body (4).

7. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 6, characterized in that, The internal measuring probe (9) has the same structure as the external measuring probe (18), both being hollow inside. The internal measuring probe has a sliding cavity and an adjustment cavity, which are connected. The sliding cavity has a movable column (23) for abutting the workpiece being measured, which is slidably arranged inside the sliding cavity. The adjustment cavity has an adjustment unit for adjusting the measuring force, and the movable column (23) is connected to the adjustment unit.

8. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 7, characterized in that, The movable column (23) is provided with a ball head that rolls against the top of the workpiece being tested.

9. The fully automatic grating-type length measuring instrument for high-precision inner and outer diameter detection of thin-walled parts according to claim 7, characterized in that, The adjustment unit includes a moving block (24), a first electromagnet (25), and a second electromagnet (26); one end of the moving block (24) is connected to the movable column (23), and the other end is disposed in the adjustment cavity; the first electromagnet (25) is disposed on one side wall of the adjustment cavity, located on one side of the moving block (24), and the second electromagnet (26) is disposed on the other side wall of the adjustment cavity, located on the other side of the moving block (24). The first electromagnet (25) and the second electromagnet (26) are disposed opposite to each other in the moving direction of the moving block (24).

10. A measurement method for a fully automatic grating-type length measuring instrument for high-precision detection of the inner and outer diameters of thin-walled parts, characterized in that, Includes the following steps: When the measuring instrument is in its initial state, the external measuring probe (18) abuts against the internal measuring probe (9) on the second internal measuring arm (8); the internal measuring probe (9) on the second internal measuring arm (8) abuts against the back of the internal measuring probe (9) on the first internal measuring arm (7); the measuring arm (2) controls the main body (4) to move and rotate, and inserts the internal measuring body (5) into the workpiece being measured; First, the internal measuring probe (9) of the second internal measuring arm (8) is placed against the inner wall of the workpiece to be measured. While the main body (4) is being straightened, the outer measuring probe (18) is driven to move the second grating ruler so that the internal measuring probe (9) and the outer measuring probe (18) are on the same horizontal line, and the wall thickness of the measured point of the workpiece is obtained. Then, the internal measuring unit (10) drives the first internal measuring arm (7) and the second internal measuring arm (8) to open, so that the two sets of internal measuring probes (9) abut against the inner wall of the workpiece to be measured, measure the inner diameter of the workpiece, and obtain the outer diameter of the workpiece by measuring the wall thickness of the workpiece by the outer measuring probe (18).

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