Calibration method of thread scanning measuring instrument

Abstract

The invention discloses a calibration method of a thread scanning measuring instrument, which comprises the following steps of: connecting a plurality of angle gauge blocks and a plurality of length gauge blocks through a connecting tool to simulate a thread tooth surface, and fixing two ends through two end covers to form a combined thread etalon, the angle gauge block has two symmetrical, stable and accurate working angles and a stable and accurate working length; the combined thread etalon is installed on a thread scanning measuring instrument, a measuring needle of the thread scanning measuring instrument is used for scanning a simulated thread tooth surface of the combined thread etalon, then a curve of the tooth surface is fitted, measured values of corresponding pitch diameter, flank angle and pitch parameters of a thread are calculated, and the measured values are subtracted from standard values to obtain the pitch diameter, flank angle and pitch parameter of the thread. And the indication error of the corresponding parameter is used as the calibration result of the thread scanning measuring instrument. According to the invention, the combined thread standard device which is convenient to trace is used for replacing a standard thread gauge, so that the accuracy of the thread scanner standard device can be improved, and the calibration requirement of a thread scanning measuring instrument is met.

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] Thread is a common connection form in mechanical transmission. Thread refers to a continuous raised part with a specific cross section and a spiral shape made on the surface of a cylindrical or conical matrix. Threads are divided into cylindrical threads and conical threads according to the shape of their matrix; they are divided into external threads and internal threads according to their position on the matrix; threads are divided into triangular threads, rectangular threads, trapezoidal threads and sawtooth threads according to their cross-sectional shape (tooth profile). Triangular threads are mainly used for connection, and rectangular, trapezoidal and sawtooth threads are mainly used for transmission; according to different occasions and functions, they can be divided into fastening threads, pipe threads, transmission threads, special threads, etc.

[0003] There are two methods for thread measurement: single measurement and comprehensive measurement. Single measurement can only measure the thread's mid-diameter, pitch, and thread profile half-angle parameters separately. Although accurate, it is inefficient. Comprehensive measurement can usually determine whether the overall parameters of the thread are qualified, but generally cannot provide accurate data for each parameter. The thread scanning measuring instrument is a measuring device that can obtain single thread parameters at the same time, so it has been increasingly used in recent years.

[0004] The thread scanning measuring instrument uses a measuring grating ruler as the length standard and is controlled by an industrial computer. After the user clicks "Start Calibration", the computer will send corresponding control instructions to the microprocessor of the control box according to the standard of the measured thread selected by the user and the parameter value, detection range and other information of the measured thread input; after receiving the instruction, the measurement and control box automatically controls the micro DC motor to accurately drive the measuring needle to contact and scan the measured thread, and the grating measurement system records the coordinate changes in the horizontal and vertical directions during the contact scanning process to form a calibration record and conclusion.

[0005] National standards require the use of standard thread gauges to calibrate thread scanning measuring instruments. However, due to the limitations of thread processing grinders, the processing error is usually within 5 microns, and the processing error of foreign high-precision thread grinders is within 2 microns. The traceability of standard thread gauges also has problems. The maximum allowable error of thread scanning measuring instruments is also 2 microns. Therefore, standard thread gauges cannot meet the measurement and transmission requirements of thread scanning measuring instruments. Summary of the invention

[0006] The object of the present invention is to provide a calibration method for a thread scanning measuring instrument, which can improve the accuracy of the standard instrument and meet the calibration requirements of the thread scanning measuring instrument by using a combined thread standard instrument to replace the standard thread gauge.

[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 covers to form a combined thread standard. The angle gauge block has 6 working surfaces, and the 6 working surfaces are ground and processed, and the 6 working surfaces are parallel to each other to form two symmetrical, stable and accurate working angles and a 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 center diameter, tooth side angle and pitch parameters are calculated to obtain the standard value. The indication of the thread scanning measuring instrument is subtracted from the calculated standard value to obtain the indication 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-pitch of simulated thread;

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

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

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

[0016]

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

[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 a 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 solution 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. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

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

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

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

[0032] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are 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 the embodiment of the present invention includes a connecting tool 1, a plurality of angle gauge blocks 2, a plurality of 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, which is used to stably connect a plurality of angle gauge blocks 2 and length gauge blocks 3 to simulate the thread tooth surface. The combined thread standard is formed by connecting and fixing different angle gauge blocks 2 and corresponding length gauge blocks 3 and ensuring the overall stability and accuracy.

[0034] Angle block 2 and length block 3 provide different sizes to achieve different pitches. Angle block 2 has the same tooth profile as the thread tooth side, the same order of magnitude of flatness error and parallelism error as the standard block, and the same angle error and flatness error as the standard angle block. By using the mature processing technology of the standard block and angle block, the pitch and tooth side angle errors can be processed to the minimum, thereby minimizing the influence of the working surface shape error on the measurement result.

[0035] The angle gauge block 2 has 6 working surfaces. These 6 working surfaces are processed through 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, respectively, which further reduces the angle and length errors, and can be well ground together with the length gauge block 3.

[0036] Angle gauge block 2 has both the standard length dimension of the gauge block and the standard angle dimension of the angle block. As the main body of the angle and length standard, it 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 median diameter measured by the three-needle method (the maximum distance of the outer contour of the measuring needle when the three-needle method measures the median diameter of the thread), these four key dimensions together constitute all the elements of the simulated thread, such as Figure 3 As shown, parameters such as the mean diameter d2, pitch P, and tooth side angle β can be constructed.

[0037] The calibration method of the thread scanning measuring instrument in 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, the connection tool 1, multiple angle gauge blocks 2, multiple length gauge blocks 3 and two end caps 4 are combined as described above to form a combined thread standard. Secondly, the combined thread standard is installed on the thread scanning measuring instrument. After adjusting the direction, the thread scanning measuring instrument is used to scan the simulated thread tooth surface of the combined thread standard, and then the corresponding software function is used to fit the curve of the tooth surface to calculate the corresponding parameters such as the middle diameter, tooth side angle, and pitch. The measurement result is subtracted from the calculated standard value to obtain the indication error of the corresponding parameter 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 length gauge block.

[0046] Thread 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 and other instruments used in three-needle method measurement);

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

[0051] H——working length of length gauge block;

[0052] d 针 —— measuring needle diameter;

[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 measurement of the center diameter and pitch, greatly reducing the influence of the tooth side angle and pitch error on the measurement of the center diameter and pitch, 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, which greatly improves the accuracy of the standard and improves the overall measurement accuracy, and is very suitable for the calibration of thread measuring equipment.

[0060] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

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 covers to form a combined thread standard. The angle gauge block has 6 working surfaces, and the 6 working surfaces are ground and processed, and the 6 working surfaces are parallel to each other, forming two symmetrical, stable and accurate working angles and a 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 center diameter, tooth side angle and pitch parameters are calculated to obtain the standard value. The indication of the thread scanning measuring instrument is subtracted from the calculated standard value to obtain the indication error of the corresponding parameter as the calibration result of the thread scanning measuring instrument.

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

3. The method according to claim 1 or 2, characterized in that The pitch diameter of the thread is calculated as follows: Where, d2-median diameter of 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, characterized in that: The flank angle is calculated as follows: β＝α / 2 Among them, β-simulated thread flank angle; α-The working angle of the angle gauge block.

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