CN108413855B - Calibration and evaluation method of electronic caliper - Google Patents
Calibration and evaluation method of electronic caliper Download PDFInfo
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- CN108413855B CN108413855B CN201810156287.5A CN201810156287A CN108413855B CN 108413855 B CN108413855 B CN 108413855B CN 201810156287 A CN201810156287 A CN 201810156287A CN 108413855 B CN108413855 B CN 108413855B
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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Abstract
A calibration and evaluation method of an electronic card gauge aims at the electronic card gauge commonly used in the production process of the equipment manufacturing industry at present, and provides a standard detection control method for ensuring that various electronic card gauges can meet the detection technical requirements and the use requirements, namely, the calibration and evaluation method of the indication value error of the electronic card, which meets the product precision and the use requirements and is feasible, is carried out by utilizing a special standard component. The quality control method of the electronic caliper gauge commonly used on the standard production line determines the technical state of the electronic caliper gauge by calibrating the core metering characteristic-indicating value error of various electronic calipers, thereby meeting the technical measurement and use requirements; and (3) evaluating the compliance of the electronic card gauge according to the specified error allowable value requirement so as to realize accurate and consistent measurement results and meet the national uniform quantity value traceability requirement, thereby ensuring the improvement of the product detection quality.
Description
Technical Field
The invention belongs to the technical field of detection of precision measuring instruments in machine manufacturing, and relates to a method for calibrating and evaluating an electronic caliper.
background
today, the electronic card gauge is widely applied to the manufacture of mechanical products, especially to a mass machining production line (such as an automobile part production line) in the rapid development of equipment manufacturing industry in China. With the continuous improvement of product quality, the detection requirement of the electronic caliper gauge on the product is higher and higher. Whether the size and the precision of a plurality of general mechanical products can meet the technical requirements or not needs to be directly measured, checked and evaluated by adopting an electronic caliper. The electronic caliper gauge is a special measuring tool for rapidly measuring the size and error of a part by using a comparison method, and is used for measuring the thickness, the diameter, the distance between surfaces and the like, wherein the electronic caliper gauge for a shaft (hereinafter referred to as an electronic caliper gauge or caliper gauge) is the most common.
The common electronic card gauges can be divided into an adjustable type and a non-adjustable type, the non-adjustable type caliper only aims at the measurement of one size, and the adjustable type caliper can measure various sizes through adjustment; the sensor configured by the electronic caliper gauge has an inductive type and a capacitive grating type, the measurement accuracy is 2 micrometers and 6 micrometers respectively, the measurement range of the electronic caliper gauge digital display device is the tolerance of theoretical size required by drawing design, and the main structural appearance of the electronic caliper gauge is shown in figure 1. The electronic caliper gauge is required to be a theoretical size L in a free state, and when the electronic caliper gauge is used for measurement, the electronic caliper gauge generates elastic deformation along with the overall size of a measured part, triggers the built-in sensor, and reads out the measured size through the connected digital display device. The same electronic caliper can be used for measuring two parts with the same shaft diameter size and different tolerance requirements.
At present, various electronic calipers manufactured at home and abroad are used in a large amount in the production process, and because the country does not stipulate a calibration method of the electronic calipers and does not have a uniform detection result evaluation standard, the accuracy of the electronic cards in use is difficult to guarantee, the measurement accuracy of some electronic calipers used for a long time is gradually reduced, the result of detecting mechanical parts of the electronic calipers is misjudged, and the quality improvement of mechanical products is directly influenced. In order to ensure that various electronic calipers can meet the detection technical requirements and the use requirements, the core metering characteristics of the electronic calipers (mainly indicating value errors and proofreading parts) need to be calibrated, and the electronic calipers can effectively trace the source according to the national quantity system requirements, so that the electronic calipers calibration and evaluation method with unified specifications is necessary.
Disclosure of Invention
The invention aims to provide a standard product detection control method aiming at an electronic caliper commonly used in the production process of equipment manufacturing industry, namely a method for calibrating and evaluating the electronic caliper, which meets the product precision and the use requirement and is feasible by utilizing a standard component for calibration (hereinafter referred to as the standard component).
The invention adopts the following technical scheme to achieve the aim:
1. designing a standard part: in the domestic and foreign electronic caliper gauge products used in production, a special proofreading piece is mostly arranged, and the special proofreading piece is mainly used for proofreading before being matched with a single electronic caliper gauge and checking in use; the technical requirements of the proofreading pieces are not uniform and standard, and the proofreading pieces can only be used for corresponding single electronic calipers and cannot be used as standard pieces for calibrating the electronic calipers generally; for an electronic caliper lacking a special calibration piece, a unified standard piece needs to be designed to calibrate the caliper regularly; an electronic caliper for measuring parts of the same shaft diameter but with different tolerance requirements should design a set of more than two calibration components (or assemblies) to meet the requirements of use and calibration. The standard component is usually a high-precision cylinder, and its design is determined according to the nominal size and precision of the electronic card gauge to be calibrated, for example, the standard component with size Φ D is only used for calibrating the electronic card gauge with the same specification (as in fig. 1), the design outer diameter (size diameter) of the standard component is respectively consistent with the upper limit size and the lower limit size of the calibrated card gauge, i.e. respectively designed as Φ D and Φ D-T (as in fig. 2, T is the difference between the upper limit size and the lower limit size of the electronic card gauge), and its size precision is usually designed according to about 1/4 which is less than or equal to the resolution of the electronic card gauge, i.e. meeting the calibration requirement of the calibrated electronic card gauge: for example, according to the precision of the capacitive-gate caliper gauge, the tolerance of the outer diameter of the standard part is designed to be 1.5 mu m, while the tolerance of the outer diameter of the standard part of the inductive caliper gauge can be designed to be about 0.5 mu m, and the technical requirements can be properly relaxed for the electronic caliper gauge with the measuring range of more than 100 mm; other design parameters of the standard component also comprise roundness, cylindricity, coaxiality, end surface planeness or axis verticality, surface roughness and the like, and the other design parameters are matched with the size precision of the standard component; the accuracy limit of the standard part is given in table 1, and should meet the technical requirements for calibrating the electronic caliper.
Design requirements of standard parts for calibrating electronic card gauge of meter 1
the design types of the standard parts can be divided into two types: a single standard (see fig. 2) and a modular standard (see fig. 3), which mainly takes into account two reasons: the electronic card gauge is suitable for two types of adjustable and non-adjustable electronic card gauges on one hand and is convenient for practical application on the other hand. It is recommended here that: for an electronic caliper with the nominal size of more than or equal to 100mm, a standard part is designed independently, namely one standard part is only used for calibrating one electronic caliper, the upper limit size and the lower limit size of the standard part are designed, meanwhile, the end face size L is designed to be the same as the nominal size of the electronic caliper, the standard part is used as auxiliary calibration, the L can be used as a standard value to calibrate the electronic caliper, and the upper limit size, the lower limit size and the end face size of the designed standard part all meet the technical requirements of calibrating the corresponding electronic caliper; for calipers with nominal size less than 100mm, the standard parts can be designed in groups, namely, two groups of standard cylinders with different nominal sizes are combined into one standard part (as shown in figure 3), and the calibration of the calipers corresponds to the calibration of two different electronic calipers; in special cases, e.g. for sizes smaller than 50mm
The adjustable electronic caliper gauge can also be designed into a combined standard component with three different sizes, which corresponds to the adjustable electronic caliper gauge
And (4) calibrating the upper limit value and the lower limit value of the calipers with three different sizes.
The manufactured standard part is calibrated before use to determine the upper limit size and the lower limit size of the diameter of the standard part, and the specific calibration method can adopt four equal measuring blocks on a length measuring machine to carry out measurement and determination by a comparison method (the calibration of a calibration piece can be referred to a caliper); other technical parameters of the standard part can be measured and controlled by a corresponding instrument so as to ensure that the standard part meets the technical requirements.
Calibrating an electronic caliper: the electronic caliper calibration is to calibrate the indication error of the electronic caliper, and generally, the calibration is carried out on the indication error of the electronic caliper by using a designed standard component and adopting two methods of comparative measurement: one is to clamp the electronic caliper gauge in the lower limit size of the standard part to zero the digital display meter, then clamp the caliper gauge in the upper limit size of the standard part, read the digital display meter, and subtract the upper limit size of the standard part from the read value to obtain the single measurement indicating value error of the caliper gauge, wherein the calculation formula is as follows:
ei = li-l 【1】
E i -upper limit size indication error measurement ith single indication error;
l i -indication of the upper limit size record of the ith measurement caliper;
l — upper calibration piece limit actual size (usually nominal);
The other method is that the electronic caliper gauge is clamped on the nominal size L of the standard part to zero, then the caliper gauge is clamped on the upper limit size and the lower limit size of the standard part respectively, the reading is read from the digital display device respectively, the actual values of the upper limit size and the lower limit size of the standard part are subtracted from the reading values respectively, the error e i of the single measurement indicating value of the upper size and the lower size of the caliper gauge is obtained, e i can be calculated according to the formula (1), only when the error of the lower limit indicating value is calibrated, L i in the formula is the indicating value recorded by the lower limit size of the caliper gauge measured at the ith time, and L is the actual size of the lower limit of the calibration part.
The above method is repeated 5 times for a single measurement, and a calibration result e of taking the largest absolute value in e i as the corresponding size index error of e i (i.e. e 1, e 2, e 3, e 4, e 5) is obtained, namely:
e = Max｛ei｝= Max｛e1、e2、e3、e4、e5｝ 【2】
the following table 2 shows the indication error limit value requirement according to the precision and the use requirement of various electronic calipers, namely when the tolerance T of a measured piece is less than or equal to 10 mu m, the allowable value of the card indication error is 1 mu m; when the tolerance T of the measured piece is more than 10 μm and less than or equal to 30 μm, the allowable value of the card gauge value error is 2 μm; when the tolerance T of the measured piece is more than 30 μm, the allowable value of the error of the card gauge value is T/10 μm; the accuracy of the detection data of the card gauge can be ensured only if the specified technical requirements of the table are met, namely the calibration result e of the electronic card gauge does not exceed the specified indication error allowable value requirement.
TABLE 2 tolerance error allowance value of electronic card
note: t in the table is the tolerance requirement of the measured workpiece dimension, and can be the difference between the upper limit dimension and the lower limit dimension of the electronic caliper gauge in general.
The calibration of the proofreading piece of the caliper is to calibrate not only the electronic caliper but also the accompanying proofreading piece to meet the actual working requirement, so as to calibrate the electronic caliper used on site at any time and ensure the electronic caliper to be in an accurate and stable technical state, generally, for the calibration of the proofreading piece, four equal blocks are adopted on a length measuring instrument or a length measuring machine to carry out measurement and calibration by a comparison method, the nominal upper limit size of the proofreading piece is firstly synthesized by using a block group during calibration, the block group size data l b is read on the length measuring instrument, then the block is taken down to place the upper limit size of the proofreading piece on the length measuring instrument to read the upper limit size reading l 1, the difference between two readings is the indication value error e 2 measured once of the upper limit size of the proofreading piece, at least three times of equal precision repeated measurement are carried out according to the same procedure, three values l i (i 1,2 and 3) are respectively subtracted by l b, the indication value error 1, e 5 e obtained by three times, the measurement result is taken as the average value 67 3, and is taken as the measurement result, namely the three times of the measurement error 678678:
ep =Σei/3 =Σ（li- lb）/3 【3】
in the formula, l b is the combined size of the gauge blocks, and the values of i are 1,2 and 3 respectively;
the lower limit size of the proofreading piece is calibrated by the same method, and the average value of repeated measurement of the proofreading piece is taken as the error calibration result of the indication value of the lower limit size; re-assigning values to the calibrated proofreading piece according to application requirements, namely replacing the upper limit size nominal value and the lower limit size nominal value on the original proofreading piece with a calibration result (actual value) so as to ensure the accuracy of using the calibration result to proofread and check the electronic caliper in use; the calibrated calibration piece can also be used for calibrating the error of the indication value of the matched card when the relevant condition is met.
4. The influence of the measurement uncertainty is mainly derived from the following aspects that a. influence u (l i) is introduced by a repeatability S (l i) for calibrating the upper limit size of an electronic caliper, b. influence u (δ α i) is introduced by a difference of linear expansion coefficients δ α i, of the electronic caliper and the upper limit size standard, c. influence u (δ ti) is introduced by an average temperature difference δ t i of the electronic caliper and the upper limit size standard, d. influence u (δ ti) is introduced by an uncertainty component u (l 2) for calibrating the repeatability introduction of the lower limit size of the electronic caliper, e. influence u (δ α 82923) is introduced by a difference of linear expansion coefficients δ α b of the electronic caliper and the upper limit size standard, f b f, influence of the uncertainty component u (δ α) is introduced by an average temperature difference δ t 5 of the electronic caliper and the lower limit size standard, and the uncertainty component u (δ α 493) is introduced by a reference to a difference of the line expansion coefficients δ α t b of the electronic caliper and the lower limit size standard, and the influence u (δ c) is calculated by a correlation coefficient of each of the respective uncertainty component introduced into a correlation formula 387 5, and the respective uncertainty component introduced into each other formula 387, thus the respective sensitivity component is calculated as follows:
uc=[c1.u2（li）+c2.u2（δαi）+c3.u2（δti）+c4.u2（lb）+c5.u2（δαb）+c6.u2（δtb）]½ 【4】
expanding the calculation formula of the measurement uncertainty U, wherein U = k.u c [ 5 ]
5. And (3) judging the compliance of the electronic caliper: typically, the calibrated electronic caliper, whose indication error calibration result expression, should contain the measured value e of the indication error and its corresponding measurement uncertainty U. The indication error conformity of the electronic card gauge is evaluated according to use requirements, generally when the ratio of the measurement uncertainty to the maximum allowable error is small, U can be ignored, namely when U/M is less than or equal to 1/4, the electronic card gauge can be considered to be qualified when the indication error is less than the maximum allowable error value; otherwise, accurate judgment needs to be carried out after the measurement uncertainty of the indicating value error is considered: when the absolute value E of the indication error E of the electronic card gauge is less than or equal to the difference between the maximum allowable error absolute value M and the expansion uncertainty U of the indication error, namely E is less than or equal to M-U, the electronic card gauge can be judged to be qualified; when the absolute value E of the indication value error of the electronic card is larger than the sum of the maximum allowable error absolute value mu m and the expansion uncertainty U of the indication value error, namely E is larger than mu m + U, the card can be judged to be unqualified; in a special case, when the indication error of the electronic card gauge is neither qualified nor unqualified, i.e., E is between (m-U) to (m + U), a calibration standard with higher precision is selected and used, and the conformity determination can be made after further calibration. As for the adjustable electronic caliper, due to the calibration of multiple size points, the evaluation conclusion of single value of each corresponding point can be given in the analysis and evaluation, and the evaluation conclusion of the electronic caliper can also be given, and the conclusion that the whole electronic caliper meets the requirement can be obtained only if the indication errors of the size points of the electronic caliper meet the requirement.
By adopting the technical scheme, the invention can achieve the following positive effects: the quality control method of the electronic caliper gauge commonly used on the standard production line determines the technical state of the electronic caliper gauge by calibrating the core metering characteristic-indicating value error of various electronic calipers, thereby meeting the technical measurement and use requirements; and (3) evaluating the compliance of the electronic card gauge according to the specified error allowable value requirement so as to realize accurate and consistent measurement results and meet the national uniform quantity value traceability requirement, thereby ensuring the improvement of the product detection quality. The invention has been tried out in the enterprise and has obtained better application effect.
Drawings
FIG. 1 is a schematic diagram of a conventional electronic caliper calibration;
FIG. 2 is a schematic view of a calibration standard designed according to the present invention;
FIG. 3 is a schematic view of a modular component of the present invention;
FIG. 4 is a diagram illustrating the error compliance determination according to the present invention.
Detailed Description
the invention is further described below with reference to the accompanying drawings. As shown in fig. 1 to 4, a method for calibrating and evaluating an error of a specification value of an electronic card comprises the following steps:
1. adjusting an electronic caliper: the electronic caliper (as in fig. 1) comprises: the digital display device comprises a fixed jaw 1, a digital display device 2, a caliper gauge handle 3, a sensor 4, a caliper gauge elastic element 5 and a micro-motion jaw 6; when calibration is carried out, the fixed jaw 1, the digital display device 2, the caliper handle 3, the sensor 4, the elastic element 5 and the micro jaw 6 of the caliper gauge are normally connected through fastening screws, the functions of all buttons are kept stable, digital display is clear, work is reliable, the indoor working temperature is controlled to be 20 +/-2 ℃, the time of indoor balance temperature of the calibrated electronic caliper gauge is not less than 2 hours, the deformation of the caliper gauge elastic element 5 and the jaw 6 is stable, and the calibrated electronic caliper gauge is matched with a standard part 7 matched with the design in a free state; the electronic caliper is calibrated to the standard (see fig. 2 and 3) designed, and after the completion of the machining, the calibration is performed to determine the magnitude of the standard.
2. The calibration of the electronic caliper is to use a standard part meeting requirements to carry out calibration on the error of the indication value of the electronic caliper by adopting two comparison measurement methods, namely, the electronic caliper is placed at the lower limit size of the standard part, the digital display device 2 is adjusted to enable the reading to be zero, then the micro-motion clamping jaws 6 and the fixed clamping jaws 1 are clamped at the upper limit size of the standard part 7, the reading is carried out from the digital display device 2, the actual value of the upper limit size of the standard part 7 is subtracted from the reading value, namely, the error e i of the single measurement of the caliper is obtained, the calculation is carried out according to a formula [ 1 ], the other method is that the fixed clamping jaws 1 and the micro-motion clamping jaws 6 of the electronic caliper are clamped at the upper limit size and the lower limit size of the standard part, the reading is carried out from the digital display device 2, the actual values of the upper limit size and the lower limit size of the standard part are subtracted from the reading value, namely, the single measurement error of the upper limit and the lower limit of the measurement of the standard part is obtained by taking the absolute value as the absolute value of the absolute measurement of the absolute displacement indicator 2, wherein the absolute displacement of the absolute displacement indicator, the absolute displacement of the absolute displacement indicator, the absolute displacement of the absolute displacement indicator, the absolute displacement of the.
In the field experiment, two electronic calipers (1 #, 2 #) are selected, the upper limit sizes of the two electronic calipers respectively correspond to ø 125.988 and ø 45.017 standard parts, when the electronic calipers are calibrated, the lower limit sizes ø 125.948 and ø 45.001 of the standard parts are respectively used as reference centering, the reading of the digital display device of the calipers are consistent with the lower limit size of the standard parts, then the reading of the upper limit sizes of the two electronic calipers is calibrated, the actual value of the upper limit size of the corresponding standard part is subtracted from the calibrated value, and the error is the indication value of the upper limit size of the calipers, the upper limit sizes of the two electronic calipers are respectively calibrated, each size value is respectively measured for 5 times with equal precision to obtain 5 indication error calibration values, the difference between the calibration value and the actual value of the upper limit size of the corresponding standard part is respectively calculated according to formulas (1) and (2), and the maximum difference is taken as the final calibration result of the indication value error of the electronic calipers (as table 3).
Table 3 summary unit of electronic caliper calibration data: mm is
for example, the indication errors of two sizes of adjustable electronic card gauges L A and L B can be calibrated, two single standard members (such as shown in figure 2) with corresponding sizes can be selected, a combined standard member (such as shown in figure 3) with two corresponding sizes can be selected, the indication errors e Ai, e Bi of the two sizes are calibrated respectively, 5 times of repeated measurement is carried out to obtain the maximum value of the indication errors as the measured value e A, e B of the corresponding sizes, the value of the indication errors does not exceed the maximum allowable error specified in the table 2, the subsequent conformity judgment work can be directly carried out on the unadjustable electronic card gauge for single size measurement after the indication error measurement result e is carried out, and the corresponding size points of the adjustable electronic card gauges for multi-size measurement can be calibrated according to the requirements of the indication errors of the points only if the indication errors of the points obtained by the method meet the qualification judgment requirements of the electronic card gauges.
3. The calibration of the caliper gauge calibration piece is that for the calibration piece attached to the electronic caliper gauge, four equal blocks can be adopted on a length measuring instrument for measurement and calibration by a comparison method, the specific calibration technical requirement is shown in table 4, a length measuring instrument with the specification of 0-100mm, the division value of 1 mu m and the uncertainty of 0.3 mu m is adopted during calibration, meanwhile, four equal blocks with the specification of 0.5-100mm and the uncertainty of 0.20 mu m + 2 multiplied by 10 -6 L are selected and carried out in a room with the temperature of 20 +/-2) DEG C and the relative humidity of 45% -75%, and the calibration piece with the size of more than 100mm is calibrated by using a length measuring machine addition block.
TABLE 4 technical requirements for calibrating the calibrating parts of the electronic calipers
When a calibration piece is calibrated, four standard measuring blocks are combined into the nominal upper limit size of the calibration piece, the calibration piece is placed between two measuring heads on a length measuring instrument which meets the requirement to read measuring block combined size data d b, then the measuring block is taken down to place the upper limit size of the calibration piece between the two measuring heads of the length measuring instrument, the upper limit size reading d 1 is read, the difference of the two readings is the indication error e 1 of single measurement of the upper limit size of the calibration piece, repeated measurement is carried out for at least three times according to the same procedure, d b is subtracted from the obtained d i (i values 1,2 and 3) to obtain the indication error e 1, e 2, e 3 of the three times of measurement, the average value e p of the three times of measurement results is taken as the calibration result of the upper limit size indication error of the calibration piece according to the formula [ 8653 ], the average value e 2 of the lower limit size of the calibration piece is calibrated by the same method, the average value of the repeated measurement results of the lower limit size of the calibration piece is taken as the lower limit size indication error of the calibration piece, the calibration result of the field calibration piece used in the experiment, the calibration result of the field calibration piece is taken as the calibration result of the calibration of the lower limit size of the calibration piece, the calibration piece calibration method, the calibration method is taken as the calibration error of the.
Table 5 summary units of calibration experimental data for calibration pieces: mm is
4. calibration method uncertainty evaluation, according to the previous analysis, the influence of measurement uncertainty introduced in the calibration process of an electronic caliper is mainly derived from six aspects, wherein the influence comprises U (l i), U (delta alpha i), U (delta ti), U (l b), U (delta alpha b) and U (delta tb), so that the synthetic standard uncertainty U c is obtained according to a formula [ 4 ], the expanded measurement uncertainty U is obtained according to a formula [ 5 ], generally, an influence coefficient k =2 is taken, an error value of a gauge value of the electronic caliper is obtained according to a formula U = k.u c, and various uncertainty components are obtained through the calibration experiment analysis of the No. 1 electronic caliper in the table 3, and U c =1.3 μm is calculated, so that U =2.6 μm.
5. And (3) judging the compliance of the electronic caliper: the conformity of the electronic card gauge is judged according to actual use requirements, and the following table 6 is a judgment basis of the indicating value error calibration result in two different ranges according to the accuracy and indicating value error evaluation requirements of various electronic card gauges in use, and is used as a reference for judging whether the electronic card gauge can be used continuously, so that the conclusion whether the electronic card gauge is qualified or not can be obtained only if corresponding technical requirements are met.
TABLE 6 electronic card indication error conformity judgment table
Generally, when the ratio of the uncertainty of the measurement to the maximum allowable error is small, i.e. when U/M is less than or equal to 1/4, U is negligible, and the electronic card is qualified when the error of the indicated value is less than the maximum allowable error value. From the above example analysis, the nominal upper and lower limit sizes of the electronic caliper gauge # 1 are 125.988mm and 125.948mm, respectively, the difference between the nominal upper and lower limit sizes is T =0.04mm, the maximum allowable value of the indicating error is set to T/10, i.e., M =4 μ M, and U =2.6 μ M, so that the requirement of U/M ≦ 1/4 cannot be met, and therefore, the influence of the measurement uncertainty must be considered when the compliance of the electronic caliper gauge is determined; in practical work, the measurement uncertainty of the indicating value error is further considered to be accurately judged, and when the absolute value E of the indicating value error E of the electronic caliper is smaller than or equal to the difference between the maximum allowable error absolute value M and the expansion uncertainty U of the indicating value error, namely the absolute value E is expressed as E ≦ M-U, the caliper can be judged to be qualified (such as the lower half area of FIG. 4); from the analysis and calculation in table 3, it can be known that the error E =1.0 μm in the calibrated electronic card specification, i.e. E ≦ 4-2.6=1.4 μm, and the electronic card specification is determined to be qualified; similarly, when the absolute value E of the indicating value error of the electronic card gauge is larger than the sum of the maximum allowable error absolute value M and the expansion uncertainty U of the indicating value error, the formula can be used for: e > M + U, the card can be judged to be unqualified (such as the upper half area of the figure 4); from the example analysis and calculation of the uncertainty of the measurement, if the indication error E of the calibrated electronic card gauge is more than 6.6 μm, the electronic card gauge can be judged to be unqualified; in special cases, when the indication error of the electronic card gauge can not be judged to be qualified according to E ≦ M-U or can not be judged to be unqualified according to E > M + U, the judgment of qualification or not can not be made (such as the middle area of FIG. 4), and a standard part with higher precision is selected for further calibration; from the above example analysis, it can be known that if the error E of the calibrated electronic card is between 1.4 μm and 6.6 μm, i.e. 1.4 μm < E < 6.6 μm, the electronic card will be qualified after a higher level calibration.
Claims (1)
1. a calibration and evaluation method of an electronic caliper is characterized in that:
1) Calibration standard design: the standard part for calibrating the electronic caliper is a high-precision cylinder, the design parameters of the standard part are determined according to the size and precision of the calibrated electronic caliper, the large diameter and the small diameter of the standard part are consistent with the upper limit size and the lower limit size of the calibrated caliper, namely the standard part is respectively designed to be phi D and phi D-T, T is the difference between the upper limit size and the lower limit size of the electronic caliper, the size precision of the standard part is designed according to 1/4 which is less than or equal to the resolution of the electronic caliper, the form and position errors and the surface quality of the standard part are matched with the size precision, and the precision limit value and the related technical requirements of the standard part are given in table 1:
TABLE 1 design requirements for standard parts of electronic calipers
The design types of the standard parts can be divided into two types: the standard part is designed into a single standard part for an electronic caliper with the nominal size of more than or equal to 100mm, namely, one standard part only aims at the calibration of one electronic caliper, the end face size L is designed to be the same as the nominal size of the electronic caliper except the upper limit size phi D and the lower limit size phi D-T of the standard part and is used as an auxiliary calibration, the standard part precision is respectively 0.5-0.7 mu m and 1.5-2.0 mu m for the inductive caliper and the capacitive caliper, and the designed standard part can meet the technical requirement of calibrating the corresponding electronic caliper; for calipers with the nominal size smaller than 100mm, the standard parts can be designed in groups, namely, the standard parts are designed to be combined into a combined standard part by combining two groups of standard cylinders with different nominal sizes, and the calibration is carried out corresponding to two different electronic calipers or one adjustable electronic caliper; aiming at the inductive or capacitive electronic caliper, the precision of the combined standard part is 0.5 μm and 1.5 μm respectively, the size of a single standard part is phi D, phi D-T or phi D, phi D-T respectively, and the size corresponds to the upper limit size and the lower limit size of each standard part; under special conditions, for example, for an adjustable electronic caliper with the size less than 50mm, a combined standard part with more than two different size combinations can be designed, and the calibration of the upper limit value and the lower limit value of the caliper with different sizes is corresponded; the manufactured standard part is calibrated before use according to the indicating value errors of the sizes of all sections of the standard part so as to determine the upper limit size, the lower limit size and the end face size of the diameter of the standard part, and the specific calibration method can be used for measuring and determining the standard part on a length measuring machine by adopting four equal measuring blocks in a comparison method so as to ensure that the precision of the standard part meets the technical requirement;
2) Calibration of the electronic caliper: the standard component meeting the requirements is utilized, and the method of comparative measurement is adopted to calibrate the error of the indication value of the electronic card; before calibration, the time of the calibrated electronic caliper gauge at indoor equilibrium temperature is not less than 2 hours, the indoor working temperature is controlled to be 20 +/-2 ℃ and the relative humidity is controlled to be 45% -75%, the deformation of the elastic element and the jaw of the caliper gauge is stable, and after the standard part designed by the caliper gauge calibration is processed, calibration is carried out to determine the magnitude of the standard part; two methods of comparing errors in the measured calibration card's gauge are as follows: the method comprises the following steps of firstly clamping an electronic caliper in the lower limit size of a standard part to enable a digital display meter to be zero, then clamping the caliper in the upper limit size of the standard part, reading from the digital display meter, subtracting the actual value of the upper limit size of the standard part from the read value to obtain the single measurement indicating value error of the caliper, and expressing the error by a formula as follows:
ei = li-l 【1】
e i -upper limit size indication error measurement ith single indication error;
l i -indication of the upper limit size record of the ith measurement caliper;
l-Upper calibration Limit actual size, usually nominal;
the other method is that the electronic caliper gauge is firstly clamped on the nominal size L of the standard part to zero, then the caliper gauge is respectively clamped on the upper limit size and the lower limit size of the standard part, the reading is respectively carried out on a digital display device, the actual values of the upper limit size and the lower limit size of the standard part are respectively subtracted from the reading values, and the result is the single measurement indicating value error e i of the upper limit size and the lower limit size of the caliper gauge, e i can still be calculated according to the formula (1), only when the lower limit value error is calibrated, L i in the formula is the indicating value recorded by the lower limit size of the caliper gauge measured at the ith time, and L is the actual lower limit size of the calibration part;
The above calibration method is repeated 5 times for a single measurement, and e i,, namely the calibration result e of the corresponding dimension indicating error is obtained by taking the maximum absolute value in e i as the value of e in e 1, e 2, e 3, e 4 and e 5, and the expression is as follows:
e = Max｛ei｝= Max｛e1，e2，e3，e4，e5｝ 【2】
The following table 2 shows the indication error limit value requirement according to the precision and the use requirement of various electronic calipers, wherein T is the tolerance requirement of the dimension of the workpiece to be measured, and can be the difference between the upper limit dimension and the lower limit dimension of the selected electronic calipers generally; generally, the accuracy of the detected data of the electronic card gauge can be ensured only when the electronic card gauge meets the technical requirement, so that the error calibration result e of the indicated value of the card cannot exceed the allowed value of the indicated value error;
TABLE 2 tolerance error allowance value of electronic card
3) the calibration of the electronic caliper calibration piece comprises the steps of calibrating an attached calibration piece after an electronic caliper is calibrated to meet the requirement of site calibration and verification of the caliper to ensure that the electronic caliper is in an accurate and stable technical state, calibrating the calibration piece for the electronic caliper calibration piece by using a length measuring instrument with the specification of 0-100mm, the division value of 1 mu m and the uncertainty of 0.3 mu m, simultaneously selecting four equal blocks with the specification of 0.5-100mm and the uncertainty of 0.20 mu m + 2 multiplied by 10 -6 L, performing calibration in a room with the temperature of 20 +/-2℃ and the relative humidity of 45% -75%, calibrating the calibration piece with a length measuring machine addition block with the size of more than 100mm, combining the four equal blocks into a nominal value with the upper limit size of the calibration piece when the calibration piece is calibrated, reading a combined block standard value b on the length measuring instrument with the requirement, taking the lower block, placing the upper limit size of the calibration piece on the length measuring instrument, namely reading a 581L upper limit size measuring error value which is used as a single measurement result of a once repeated calibration error measurement by using a three-time measurement error measurement program which is represented by subtracting a three times by a measurement error value of a numeral 4623, namely a numeral 19, and a measurement error which is obtained by subtracting a measurement error of a numeral 1L equivalent by using a measurement program which is represented by a numeral 1 equivalent by a numeral 1L, wherein:
ep =Σei/3 =Σ（li- lb）/3 【3】
In the formula, l b is the combined size of the gauge blocks, and the values of i are 1,2 and 3 respectively;
Calibrating the lower limit size of the calibration piece by the same method, taking the average value of at least three repeated measurements as the lower limit size indication error calibration result, wherein the method is also suitable for calibrating the standard piece; re-assigning values to the calibrated proofreading piece, namely replacing the upper and lower limit nominal values of the original proofreading piece with the actual value of the calibration result so as to ensure the accuracy of the proofreading and checking of the electronic caliper in use by the actual value of the calibration result; the calibrated calibration piece can also be used for calibrating the error of the indication value of the matched card when the relevant conditions are met;
4) electronic caliper compliance determination: the electronic card, usually calibrated, provides a measured value e indicating the value error and its corresponding measurement uncertainty U; analyzing a main source of influence of the measurement uncertainty in the calibration process of the electronic caliper, and synthesizing and calculating the extended uncertainty U according to each numerical formula; the indication error conformity of the electronic card gauge is evaluated according to use requirements, when the ratio U/M of the measurement uncertainty U and the maximum allowable error M is less than or equal to 1/4, U can be ignored, and the electronic card gauge can be judged to be qualified when the indication error is less than the maximum allowable error value; when the U/M is larger than 1/4, the measurement uncertainty of the indicating value error needs to be considered in the conformity judgment of the electronic caliper for accurate judgment; the following table 3 provides a method for judging the calibration result of the indicating value error in two different ranges according to the evaluation requirements of the accuracy and the indicating value error of various electronic calipers in use, and the conclusion whether the electronic calipers are qualified or not can be obtained only by meeting the technical requirements, so that the method is used as a reference for evaluating whether the electronic calipers can be used continuously or not; when the absolute value E of the indication error calibration result E is less than or equal to mu-U, the electronic caliper is qualified, and when E is more than mu + U, the caliper is unqualified; when E is in an undetermined area between (mu-U) to (mu + U), a standard component with a higher level is adopted for calibration and then further judgment; for the adjustable electronic caliper, due to the calibration of multiple size points, the evaluation conclusion of single values of corresponding size points can be given in the analysis and evaluation, and the evaluation conclusion of the electronic caliper can also be given, and only if the indication errors of the size points of the electronic caliper meet the requirements, the conclusion that the whole electronic caliper is qualified can be obtained;
TABLE 3 electronic card indicating value error conformity judging table
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