A calibration method for thread scanning measuring instrument

Abstract

The present invention discloses a calibration method for a thread scanning measuring instrument, comprising: connecting multiple angle gauge blocks and multiple length gauge blocks to simulate thread tooth surfaces through a connecting tool, fixing the two ends with two end caps to form a combined thread standard, wherein the angle gauge blocks have two symmetrical, stable and accurate working angles and one stable and accurate working length; installing the combined thread standard on the thread scanning measuring instrument, scanning the simulated thread tooth surfaces of the combined thread standard using the measurement of the thread scanning measuring instrument, then fitting the curve of the tooth surface, calculating the corresponding measured values ​​of the thread pitch diameter, tooth flank angle and pitch parameters, subtracting the measured values ​​from the standard values, and obtaining the indication errors of the corresponding parameters as the calibration results of the thread scanning measuring instrument. The present invention can improve the accuracy of the thread scanner standard by replacing the standard thread gauge with a combined thread standard that is easy to trace, thereby meeting the calibration requirements of the thread scanning measuring instrument.

Description

Technical Field

[0001] The invention belongs to the field of metrology and calibration, and relates to a calibration method for a thread scanning measuring instrument. Background Art

[0002] Threads are a common connection method used in mechanical transmission. Threads are continuous, helical projections with a specific cross-section, created on the surface of a cylindrical or conical matrix. Threads are classified by the shape of the matrix into cylindrical and conical threads; by their position within the matrix into external and internal threads; and by their cross-sectional shape (tooth profile), into triangular, rectangular, trapezoidal, and sawtooth threads. Triangular threads are primarily used for connection, while rectangular, trapezoidal, and sawtooth threads are primarily used for transmission. Depending on their application and function, threads can be categorized as fastening threads, pipe threads, transmission threads, and special-purpose threads.

[0003] Thread measurement can be performed using two methods: single-item measurement and comprehensive measurement. Single-item measurement measures only parameters such as pitch diameter, pitch, and thread half-angle separately. While accurate, this method is inefficient. Comprehensive measurement can often determine the overall thread parameters, but generally cannot provide accurate data for each parameter. Thread scanning measuring instruments, on the other hand, are capable of measuring individual thread parameters simultaneously, and as such, have become increasingly popular in recent years.

[0004] The thread scanning measuring instrument uses a metrological grating ruler as a length standard and is controlled by an industrial computer. After the user clicks "Start Calibration," the computer sends corresponding control instructions to the microprocessor in the control box based on the user's selected thread standard and input of thread parameter values, measurement range, and other information. Upon receiving the instructions, the measurement and control box automatically controls a micro-DC motor to precisely drive the measuring needle to contact and scan the measured thread. The grating measurement system records the horizontal and vertical coordinate changes during the contact scanning process, forming a calibration record and conclusion.

[0005] National regulations require the use of standard thread gauges to calibrate thread scanning measuring instruments. However, due to the limitations of thread grinding machines, the machining error is typically within 5 microns. High-precision thread grinders from abroad can achieve machining errors within 2 microns. Furthermore, traceability of standard thread gauges is inherently problematic, and thread scanning measuring instruments also have a maximum allowable error of 2 microns. Therefore, standard thread gauges cannot meet the measurement and transmission requirements of thread scanning measuring instruments. Summary of the Invention

[0006] The purpose of the present invention is to provide a calibration method for a thread scanning measuring instrument. By using a combined thread standard instead of a standard thread gauge, the accuracy of the standard can be improved to meet the calibration requirements of the thread scanning measuring instrument.

[0007] In order to achieve the above object, one aspect of the present invention provides a calibration method for a thread scanning measuring instrument, comprising:

[0008] A plurality of angle gauge blocks and a plurality of length gauge blocks are connected by a connecting tool to simulate the thread tooth surface, and the two ends are fixed by two end caps to form a combined thread standard. The angle gauge block has six working surfaces, which are ground and parallel to each other to form two symmetrical, stable and accurate working angles and one stable and accurate working length.

[0009] The combined thread standard is installed on the thread scanning measuring instrument, and the simulated thread tooth surface of the combined thread standard is scanned using the measurement of the thread scanning measuring instrument. The curve of the tooth surface is then fitted, and the corresponding thread diameter, tooth side angle and pitch parameters are calculated to obtain the standard value. The indicated value of the thread scanning measuring instrument is subtracted from the calculated standard value to obtain the indicated error of the corresponding parameter as the calibration result of the thread scanning measuring instrument.

[0010] Preferably, the pitch is calculated as follows:

[0011] P=L+H

[0012] Among them, P-the pitch of the simulated thread;

[0013] L-working length of the angle gauge block;

[0014] H-length: the working length of the gauge block.

[0015] Preferably, the thread pitch diameter is calculated as follows:

[0016]

[0017] Where, d2-the median diameter of the simulated thread;

[0018] M-M value when measuring the median diameter using the three-needle method;

[0019] L-working length of the angle gauge block;

[0020] H- working length of the length gauge block;

[0021] d 针 - measuring needle diameter;

[0022] α-The working angle of the angle gauge block.

[0023] Preferably, the flank angle is calculated as follows:

[0024] β=α / 2

[0025] Among them, β-the flank angle of the simulated thread;

[0026] α-The working angle of the angle gauge block.

[0027] According to the calibration method of the thread scanning measuring instrument of the above aspect of the present invention, by using the combined thread standard to replace the standard thread gauge, the accuracy of the standard can be improved to meet the calibration requirements of the thread scanning measuring instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0029] Figure 1 This is a schematic diagram of the various parts of a combined thread standard according to an embodiment of the present invention before assembly;

[0030] Figure 2 This is a schematic diagram of a combined thread standard according to an embodiment of the present invention;

[0031] Figure 3 It is a principle diagram of a calibration method for a thread scanning measuring instrument according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0033] One embodiment of the present invention provides a method for calibrating a thread scanning measuring instrument, using a combined thread standard to replace the existing standard thread gauge as a calibration standard for calibrating the thread scanning measuring instrument. Figure 1 and Figure 2 As shown, the combined thread standard of an embodiment of the present invention includes a connecting tool 1, multiple angle gauge blocks 2, multiple length gauge blocks 3, and two end caps 4. The connecting tool 1 and the two end caps 4 constitute a combined thread standard fixture, used to stably connect multiple angle gauge blocks 2 and length gauge blocks 3 to simulate thread flanks. By connecting and securing different angle gauge blocks 2 and corresponding length gauge blocks 3, ensuring overall stability and accuracy, a combined thread standard is formed.

[0034] Angle Block 2 and Length Block 3 are available in different sizes to accommodate different thread pitches. Angle Block 2 shares the same thread profile as the thread flanks, with the same order of magnitude for flatness and parallelism errors as standard blocks, and the same angular and flatness errors as standard angle blocks. By utilizing the proven machining processes of standard and angle blocks, pitch and flank angle errors can be minimized, minimizing the impact of working surface shape errors on measurement results.

[0035] Angle gauge block 2 has 6 working surfaces. These 6 working surfaces are processed by high-precision grinding so that the flatness and roughness of each surface meet the technical requirements of standard gauge blocks and angle blocks. The 6 surfaces are parallel to each other, forming two symmetrical, stable and accurate angles and a stable and accurate length. The 6 surfaces are perpendicular to the end faces, further reducing the angle and length errors, and can be ground well together with the length gauge block 3.

[0036] Angle gauge block 2 has both the standard length size of the gauge block and the standard angle size of the angle block. As an angle and length standard, it constitutes the main body of the standard and provides two key dimensions: working length L and working angle α. Together with the working length H of length gauge block 3 and the M value of the three-needle method to measure the pitch diameter (the maximum distance between the outer contours of the measuring needle when measuring the pitch diameter of the thread using the three-needle method), these four key dimensions together constitute all the elements of the simulated thread, such as Figure 3 As shown, parameters such as the pitch diameter d2, pitch P, and tooth side angle β can be constructed.

[0037] The calibration method of the thread scanning measuring instrument according to the embodiment of the present invention uses the above-mentioned combined thread standard to calibrate the thread scanning measuring instrument, and the specific process is as follows.

[0038] First, combine the connection tool 1, multiple angle gauge blocks 2, multiple length gauge blocks 3, and two end caps 4 as described above to form a combined thread standard. Next, install the combined thread standard on a thread scanning measuring instrument. After adjusting the orientation, use the thread scanning measuring instrument to scan the simulated thread tooth surface of the combined thread standard. Then, use the corresponding software function to fit the curve of the tooth surface to calculate the corresponding parameters such as the pitch diameter, tooth flank angle, and pitch. Subtract the measured result from the calculated standard value to obtain the indication error of the corresponding parameter, which serves as the calibration result of the thread scanning measuring instrument.

[0039] In the calculation of parameters, the value reproduced by the combined thread standard can be expressed by the following formula:

[0040] Pitch P:

[0041] P=L+H (1)

[0042] Where:

[0043] P——Simulated pitch ( Figure 3 P1, P2, and P3 are the pitches at three different positions);

[0044] L - working length of angle gauge block;

[0045] H - working length of the length gauge block.

[0046] Thread pitch diameter d2:

[0047]

[0048] d2——simulated median diameter;

[0049] M-M value measured by other length measuring equipment (length measuring machine, length measuring instrument, lever micrometer, micrometer, etc. used in three-needle method measurement);

[0050] L - working length of angle gauge block;

[0051] H - working length of the length gauge block;

[0052] d 针 ——diameter of measuring needle;

[0053] α——working angle of angle gauge block.

[0054] Flank angle β:

[0055] β=α / 2 (3)

[0056] Where:

[0057] β--simulated tooth flank angle;

[0058] α--working angle of angle gauge block.

[0059] In summary, according to the calibration method of the thread scanning measuring instrument in the embodiment of the present invention, a combined thread standard is used to replace the existing standard thread gauge as the calibration standard for calibrating the thread scanning measuring instrument, and a grinding surface is used to replace the spiral processing surface of the standard thread gauge, thereby avoiding the influence of the thread helix angle on the mean diameter and pitch measurement, greatly reducing the influence of the tooth side angle and pitch error on the mean diameter and pitch measurement, eliminating the influence of the thread processing straightness being restricted by the processing machine tool, reducing the influence of shape error on measurement, and using high-precision ground angle blocks and length blocks to simulate the thread tooth surface, thereby greatly improving the accuracy of the standard and improving the overall measurement accuracy, and is very suitable for the calibration of thread measuring equipment.

[0060] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A method for calibrating a thread scanning measuring instrument, characterized in that: include: A plurality of angle gauge blocks and a plurality of length gauge blocks are connected by a connecting tool to simulate the thread tooth surface, and the two ends are fixed by two end caps to form a combined thread standard. The angle gauge block has six working surfaces, which are ground and parallel to each other to form two symmetrical, stable and accurate working angles and one stable and accurate working length. The combined thread standard is installed on the thread scanning measuring instrument, and the simulated thread tooth surface of the combined thread standard is scanned using the measurement of the thread scanning measuring instrument. The curve of the tooth surface is then fitted, and the corresponding thread diameter, tooth side angle and pitch parameters are calculated to obtain the standard value. The indicated value of the thread scanning measuring instrument is subtracted from the calculated standard value to obtain the indicated error of the corresponding parameter as the calibration result of the thread scanning measuring instrument.

2. The method according to claim 1, wherein The thread pitch is calculated as follows: P=L+H Among them, P-the pitch of the simulated thread; L-working length of the angle gauge block; H-length: the working length of the gauge block.

3. The method according to claim 1 or 2, wherein: The thread pitch diameter is calculated as follows: Where, d2-the median diameter of the simulated thread; M-M value when measuring the median diameter using the three-needle method; L-working length of the angle gauge block; H- working length of the length gauge block; d 针 - measuring needle diameter; α-The working angle of the angle gauge block.

4. The method according to claim 1 or 2, wherein: The flank angle is calculated as follows: β＝α / 2 Among them, β-the flank angle of the simulated thread; α-The working angle of the angle gauge block.

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