CN100480636C - Digital capacitance corner sensor calibrating system and calibrating method - Google Patents
Digital capacitance corner sensor calibrating system and calibrating method Download PDFInfo
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Abstract
This invention disclosed a calibration system and method for corner sensor which consists of a machine case, an engine, a grating corner sensor with high precision. The sensor was fixed on the transmission shaft; the shaft can be extended to the outer side of the case so that the sensor can be fixed on it; the upper machine can output control signals to control the engine; the upper machine connects with the sensors via the communication port, sample the angle signal and analyze the data; the formula can be downloaded so that automatic calibration was realized. The efficiency was highly improved by this invention.
Description
Technical Field
The invention belongs to the technical field of corner sensors, and particularly relates to a calibration system and a calibration method of a digital capacitive corner sensor.
Background
The capacitive corner sensor has the characteristics of simple structure, high measurement precision, sensitivity, suitability for dynamic measurement and the like, and is widely applied to instruments and meters of angle monitoring automobile, aerospace and military equipment. In recent decades, a great deal of research has been carried out by many researchers at home and abroad, and a remarkable result is that in 1996 Brasseur et al, a capacitive rotation angle Sensor based on a new measurement principle, which is called a proportional measurement principle (see g. Brasseur, a Robust capacitive Position Sensor, in IEEE Conference on Instrumentation and measurement technology (IMTC/96), Brussels, Belgium, June 4-61996, pp.1081-1086), has both proportional and differential characteristics, can counteract a considerable degree of amplifier gain error and system error, and can eliminate mechanical installation error within a certain range, and theoretically overcome a certain degree of adverse effects of ambient temperature, humidity, dust, and dew on the Sensor. On the basis of the above, Tianjin university develops a digital capacitive rotation angle sensor (see patent application of Xuying et al: CN200510013574 and CN200510013575) with a measurement range of 180 degrees, wherein the rotating polar plate is made of metal and is designed to be electrically suspended. The metal rotating pole plate has the advantages that the metal rotating pole plate in the suspension design can enable the sensitive elements with the same size and structure to effectively measure the capacitance and improve the sensitivity, and meanwhile, the other direct effect of the suspension design is to replace an electric brush design, eliminate mechanical wear, improve the reliability and prolong the service life of the sensor.
However, due to the limitations of the current processing technology level and material characteristics, the quality indexes of the proportional capacitive rotation angle sensor with the suspended rotating plate design, such as basic error, linearity and standard uncertainty, are still to be improved, and therefore, a full-automatic precise angle calibration system suitable for calibrating the proportional digital capacitive rotation angle sensor needs to be researched.
Disclosure of Invention
The invention aims to provide a full-automatic precise angle calibration system for a digital capacitance corner sensor, in particular to a proportional digital capacitance corner sensor, and provides a calibration method adopted by the system so as to improve the basic error, linearity and standard uncertainty of the digital capacitance corner sensor.
The technical scheme of the full-automatic precise angle calibration system is as follows:
a calibration system of a proportional digital capacitive angle sensor is used for calibrating the proportional digital capacitive angle sensor and comprises a case, a stepping motor and a transmission shaft thereof, and a high-precision grating angle sensor, wherein the grating angle sensor is arranged on the transmission shaft and synchronously rotates with the stepping motor; the transmission shaft extends to the outside of the case, and a positioning mechanism is arranged on the transmission shaft outside the case and used for mounting a proportional digital capacitance corner sensor to be calibrated; the upper computer outputs control signals through an interface component connected with the stepping motor to control the starting, stopping and rotating directions and the stepping angle of the stepping motor; the upper computer is further connected with the proportional type digital capacitance corner sensor to be calibrated and the grating corner sensor respectively through the communication interface, the angle signal values of the two sensors are sampled, the output angle of the grating corner sensor is used as a standard, data fitting is carried out, a fitting formula is obtained and stored, then the fitting formula is downloaded to the digital capacitance corner sensor, and automatic calibration of the proportional type digital capacitance corner sensor is achieved.
The invention also provides a calibration method adopted by the calibration system, which comprises the following steps:
(1) installing a digital capacitance corner sensor to be calibrated on a transmission shaft of a calibration system by using a positioning mechanism;
(2) the upper computer controls the start-stop, the rotation direction and the stepping angle of the motor;
(3) the grating corner sensor transmits the measured rotation angle value of the transmission shaft to an upper computer;
(4) the capacitance corner sensor transmits the measured rotation angle value of the transmission shaft to an upper computer;
(5) the upper computer takes the output angle of the grating corner sensor as a standard and performs data fitting to obtain a fitting formula and store the fitting formula;
(6) and the upper computer downloads the fitting formula to the digital capacitance corner sensor to realize the automatic calibration of the proportional digital capacitance corner sensor.
The calibration method adopted by the technical scheme further comprises the following steps: and (4) respectively acquiring the rotation angle measurement values of the proportional digital capacitance rotation angle sensor before and after the steps (1) to (6) by the upper computer, comparing the rotation angle measurement values with the rotation angle measurement values of the grating rotation angle sensor, and calculating the basic error, the linearity and the corrected standard uncertainty.
According to the comparison of the basic error and the linearity of the capacitance rotation angle sensor before and after the prototype calibration and the standard uncertainty analysis of the calibrated capacitance rotation angle sensor, the quality index of the measured object can be effectively improved by adopting the calibration system and the calibration method. The work efficiency is satisfactory because the calibration process is fully automated. In addition, the system can be used as a calibration tool of a digital capacitance corner sensor based on a proportional type, and meanwhile, the calibration device of an angle sensor with electric signal output and other measurement principles can be used as the calibration device of the angle sensor based on other measurement principles only by slightly modifying an external positioning assembly mechanism, so that the calibration device has better universality.
Drawings
FIG. 1 is a block diagram of a calibration system according to the present invention;
FIG. 2 is a schematic diagram of a grating rotation angle sensor; the labels in the figure are: 1, a transmission shaft; 2, an optical code disc; 3, a slit; 4 lenses; 5 a light emitting element;
FIG. 3 grating angular sensor pulse output;
FIG. 4 shows a rule for determining facies;
FIG. 5 comparison of basic errors of capacitive corner sensors before and after calibration;
FIG. 6 is a comparison of the linearity of capacitive corner sensors before and after calibration;
FIG. 7 is a calibrated capacitive rotation angle sensor standard uncertainty.
Detailed Description
The invention is described in further detail below with reference to the figures and examples.
The overall design block diagram of the system is shown in figure 1, and a calibrated sensor, namely a proportional capacitance corner sensor, a standard sensor, namely a high-precision grating corner sensor, and a power driving unit, namely a stepping motor, of the system are strictly coaxially arranged by 1 and synchronously rotate; the capacitance corner sensor and the grating corner sensor exchange data with an upper computer through RS232 communication interfaces; the starting, stopping and positive and negative rotation of the stepping motor are realized by the software of an upper computer through controlling a PCI bus interface card serving as an interface component and outputting switching values, and the upper computer simultaneously completes the functions of data acquisition, data processing, database management, report output and the like. In structural layout, the stepping motor and the grating angle sensor are both packaged in a stainless steel case to shield electromagnetic interference, and a base is arranged below the stepping motor and the grating angle sensor to eliminate the influence of environmental vibration interference on measurement precision. The proportional capacitive corner sensor is a calibration object and is assembled outside the case by a positioning mechanism, so that the proportional capacitive corner sensor is convenient to disassemble.
The contents of the structure and the angle calculation method of the proportional capacitive rotation angle sensor can be found in the patent application of Xuying et al: CN200510013574 and CN 200510013575.
The grating angle sensor is used as a standard sensor because of the clear technical index advantage with high precision. The system adopts a Japanese original LFA small-sized high-precision grating angle sensor as a standard, 25000 pulses can be output every revolution, and the resolution reaches 0.014 degrees. The principle is shown in fig. 2. The light source is focused by the convex lens 4 and enters the circular optical code disc 2, and then is filtered out by the slit 3 to the receiving element, the rotation angle of the rotating shaft is converted into two paths of electric pulse signals (A, B) with the phase difference of 90 degrees by photoelectric conversion and output, and the two paths of electric pulse signals are sent to the intelligent processing unit, and the judgment of the reversing and the calculation of the angle are realized by software programming. The decision of commutation is determined by the phase sequence and level of A and B, and the calculation of the angle is realized by accumulating the number of falling edges of A or B. And the upper computer acquires the angle value of the grating angle sensor through RS232 serial port communication.
The output waveforms of the grating angle sensor are shown in fig. 3, wherein A, B have a phase difference of 90 degrees and the output pulse numbers are the same.
Counting rules: positive rotation is carried out, and the count value is increased progressively; reversing, and decrementing the count value; after the rotation is stopped, the counter value indicates the amount of angular displacement for forward or reverse rotation. The output pulse of the grating rotating shaft is 25000 after one rotation, and if the counter value is n, the rotating angle is 360 x (n/25000) which is 0.0144 x n.
Direction judgment rules are as follows: as shown in fig. 4, if the direction of rotation is constant, the A, B phase relationship remains 90 °, and when commutation occurs, the phase relationship changes accordingly, with a 0 ° or 180 ° difference. Because the starting potential amplitude of A, B is different (00, 01, 10, 11) when the counting is started, 4 reversing points appear when the forward rotation is reversed to the reverse rotation; conversely, switching from reverse to forward would also occur at 4 commutation points. In the design, software is used for analyzing the phase, so that the hardware overhead is saved, namely when B is a falling edge, the state of A indicates the rotation direction, and when A is 0, the rotation is positive; when a is 1, the inversion is performed.
In order to carry out precise corner control, a stepping motor of Beijing motor factory is selected as an execution element and a driving source in the system, the minimum stepping angle is 0.05 degrees, a constant-current chopping pulse width voltage regulation driving mode is adopted, the dynamic performance is good, phase sequence signals are subjected to multi-stage processing, the anti-interference capability of a driving power supply is enhanced, the operation is stable, the noise is low, the short-circuit protection is fast, overvoltage and overheating protection measures are provided, and the reliability, the servo performance and the controllability are high. In addition, the driver has small volume and light weight, and is suitable for the requirement of the system.
The upper computer is a PC and realizes functions by using C language programming.
The calibration of the proportional digital capacitance corner sensor adopts the following calibration steps:
(1) the upper computer controls the rotation direction, speed and angle of the stepping motor through the switching value PCI card and controls serial port communication with the capacitor and the grating corner sensor to obtain an angle detection value. The number of experiments is 1 (positive and negative 2 strokes), and a sampling point is arranged at intervals of 10 degrees, and the range is as follows: 0-170 degrees, and 36 sampling points are counted in positive and negative strokes;
(2) the upper computer draws a curve according to the sampling data;
(3) fitting the sampled data curve by using a least square method (3-order or 5-order fitting);
(4) calculating the accuracy of the fitting curve, and storing the mathematical model of the fitting formula into a database when the maximum error is less than 0.5%; meanwhile, the digital capacitance corner sensor is downloaded to the digital capacitance corner sensor, so that the automatic calibration of the sensor is realized;
(5) in order to further verify whether the precision of the capacitive rotation angle sensor with the correction calculation model is effectively improved, the capacitive rotation angle sensor needs to be verified. The process experiment is performed with one sampling point every 10 degrees, and the range is as follows: 5-175 degrees, and 18 sampling points in a single stroke. The number of assays was increased to 3 (6 passes forward and reverse).
(6) And the upper computer collects the rotation angle measurement values of the proportional digital capacitance rotation angle sensor before and after calibration respectively, compares the rotation angle measurement values with the rotation angle measurement values of the grating rotation angle sensor respectively, and calculates the basic error, the linearity and the standard uncertainty after correction before and after calibration.
The evaluation indexes mainly comprise basic errors, linearity and standard uncertainty, and the formula is as follows:
● basic error
Wherein, thetac-begin、θg-begin-capacitance and grating corner sensor starting angle; thetaci、θgi-both currently detect the angle; 180-the range of measurement of the capacitive rotation angle sensor.
● degree of linearity
ζ1＝[(θgi-θgi-1)-(θci-θci-1)]/180 (2)
Wherein subscripts i and i-1 represent the current and last measurements, respectively;
● standard uncertainty
Wherein,
relative standard uncertainty for the jth angle measurement; thetajkA sample value of kth time which is a jth angle measurement value; thetajIs the average of the jth angle measurement; n is the total number of samples of the jth angle measurement, 10 in the experiment.
The calibration experiment is respectively carried out on a plurality of capacitance corner sensors. A prototype was selected for analysis, and the basic errors and linearity before and after calibration, i.e. calibration and verification experiments, are shown in fig. 5 and 6, respectively. The standard uncertainty of the calibrated capacitive rotation angle sensor is shown in fig. 7. The analysis was as follows:
● FIG. 5: from the distribution, the basic error after calibration is obviously better than that before calibration, the average value is reduced from 2% to about 0.2%, and is almost improved by one order of magnitude; the maximum value is reduced from 4.4% to 0.7%;
● FIG. 6: the linearity index is also improved, the average value is reduced from 0.58% before calibration to 0.22% after calibration, and the maximum value is also reduced by 1%;
FIG. 7: the standard uncertainty of the calibrated capacitance rotation angle sensor fluctuates between 0.16% and 0.25%, and the average value is 0.2%.
If the verification result shows that the quality index of the calibrated capacitive angle sensor is still poor, generally caused by mechanical faults, whether the assembly problem exists in the capacitive angle sensor needs to be rechecked, and after the capacitive angle sensor is remounted, calibration and verification are carried out again.
Claims (2)
1. A calibration system of a proportional digital capacitive angle sensor is used for calibrating the proportional digital capacitive angle sensor and comprises an upper computer, a case, a stepping motor and a transmission shaft thereof, and a high-precision grating angle sensor, wherein the grating angle sensor is arranged on the transmission shaft and synchronously rotates with the stepping motor; the transmission shaft extends to the outside of the case, and a positioning mechanism is arranged on the transmission shaft outside the case and used for mounting a proportional digital capacitance corner sensor to be calibrated; the upper computer outputs control signals through an interface component connected with the stepping motor to control the starting, stopping and rotating directions and the stepping angle of the stepping motor; the upper computer is further connected with the proportional type digital capacitance corner sensor to be calibrated and the grating corner sensor respectively through the communication interface, the angle signal values of the two sensors are sampled, the output angle of the grating corner sensor is used as a standard, data fitting is carried out, a fitting formula is obtained and stored, then the fitting formula is downloaded to the digital capacitance corner sensor, and automatic calibration of the proportional type digital capacitance corner sensor is achieved.
2. A method for calibrating a proportional digital capacitive rotation angle sensor used in the calibration system of claim 1, comprising the steps of:
(1) installing a digital capacitance corner sensor to be calibrated on a transmission shaft of a stepping motor by using a positioning mechanism;
(2) the upper computer controls the starting, stopping, rotating directions and stepping angles of the stepping motor;
(3) the grating corner sensor transmits the measured rotation angle value of the transmission shaft to an upper computer;
(4) the digital capacitance corner sensor transmits the measured rotation angle value of the transmission shaft to an upper computer;
(5) the upper computer takes the output angle of the grating corner sensor as a standard and performs data fitting to obtain a fitting formula and store the fitting formula;
(6) and the upper computer downloads the fitting formula to the digital capacitance corner sensor to realize the automatic calibration of the proportional digital capacitance corner sensor.
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| US7761251B2 (en) * | 2007-06-15 | 2010-07-20 | Gm Global Technology Operations, Inc. | Systems and method for improving accuracy of sensor signals received via SENT protocol |
| CN101739019B (en) * | 2008-11-23 | 2011-10-12 | 三科电器有限公司 | Method and equipment to debug the system controlled volume by the host computer |
| CN102064762A (en) * | 2010-11-22 | 2011-05-18 | 柳州五菱汽车有限责任公司 | System and method for generating extrinsic parameter value of separately excited machine controller |
| CN102253243B (en) * | 2011-06-08 | 2014-02-26 | 中北大学 | Phase difference calibrating system for rotating shaft |
| CN102506695B (en) * | 2011-10-09 | 2014-08-27 | 联合汽车电子有限公司 | Precision detection system for rotary transformer |
| CN103557830B (en) * | 2013-10-30 | 2017-02-08 | 北京理工大学 | Angle measuring plate card compatible with various sensors |
| CN103983294A (en) * | 2014-05-28 | 2014-08-13 | 天津瑞能电气有限公司 | Electronic and electrical appliance part linearity and non-linearity detection method |
| WO2017041294A1 (en) | 2015-09-11 | 2017-03-16 | Wuhan Tailimeixin Healthcare Technologies Co., Ltd | Integrated measuring system and method |
| CN105180995B (en) * | 2015-09-11 | 2019-02-19 | 武汉泰利美信医疗科技有限公司 | A kind of measurement calibration system and method |
| CN106546163A (en) * | 2015-09-23 | 2017-03-29 | 上海世德子汽车零部件有限公司 | The detection correction system of magneto resistive angular sensor |
| CN107702913A (en) * | 2017-11-10 | 2018-02-16 | 苏州新里程电控系统有限公司 | A kind of new leveling switch detection means |
| CN108132452B (en) * | 2018-02-06 | 2024-10-01 | 苏州硬木智能科技有限公司 | Test calibration board for signal acquisition board and calibration and test method thereof |
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