A MEMS accelerometer nonlinearity batch testing device and method

Abstract

The application discloses a kind of MEMS accelerometer nonlinearity batch testing device and method, including test tooling, the test tooling is fixed on centrifuge, and install multiple MEMS accelerometers on test tooling, each MEMS accelerometer is connected to the input end of multichannel analog-digital converter respectively, is converted into digital signal, and the digital signal output by analog-digital converter sequentially passes through microcontroller, serial port level conversion chip and is converted into serial port data.The application installs test tooling on test station, increases the number of testing devices, converts device output signal and the mode of automatic data processing improves test efficiency, reduces test cost, realizes single multiple devices synchronous testing, positive and negative synchronous testing batch testing mode.The application is divided into two kinds based on MEMS accelerometer sensitive axis, designs two different test toolings, to adapt to different MEMS acceleration test.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of MEMS accelerometer testing, in particular to a MEMS accelerometer nonlinearity batch testing device and method. BACKGROUND

[0002] MEMS accelerometer products have various packaging forms, such as LCC20, LCC28 and LCC32, etc., and the output signals are led out through a clamp and a test board during testing. The nonlinearity of a MEMS accelerometer is one of the important indicators for engineering application, and is an important indicator affecting the accuracy of a MEMS accelerometer. The nonlinearity of the full range needs to be tested during production, and there are various existing MEMS accelerometer nonlinearity testing methods, such as using a gravity field to test the nonlinearity of a MEMS accelerometer, which can only test the nonlinearity within ±1g range, and the testing error is large; using an electric excitation method to test the nonlinearity of a MEMS accelerometer full range, the electric excitation and the external acceleration input have a deviation, which affects the testing accuracy; using a precision centrifuge to test the nonlinearity of a MEMS accelerometer full range, the existing testing method only tests a single product per station at a time, which has the disadvantages of high cost and being uneconomical.

[0003] In the design and processing of a precision centrifuge, in order to ensure the testing accuracy of the nonlinearity of a MEMS accelerometer and reduce the production cost, the centrifuge manufacturers usually optimize the way of separately processing the test station on the centrifuge table. Therefore, the existing testing method of a MEMS accelerometer tests a single product per station and a single direction at a time, and after testing a positive direction, the clamp and the test board need to be rotated by 180° and fixed again for negative direction testing. Although this testing method is comprehensive and has high accuracy, it has the disadvantages of high cost and being uneconomical. SUMMARY

[0004] The purpose of the present application is to provide a MEMS accelerometer nonlinearity batch testing device and method, which increases the number of testing devices on the test station, converts the output signals of the devices, and automatically processes the data to improve the testing efficiency and reduce the testing cost, and realizes the batch testing mode of single-time multi-device synchronous testing and positive-negative direction synchronous testing.

[0005] The technical solution of the present application is:

[0006] A MEMS accelerometer nonlinearity batch testing device, comprising a test tool, the test tool is fixed on a centrifuge, and a plurality of MEMS accelerometers are installed on the test tool, each MEMS accelerometer is connected to the input end of a multi-channel analog-to-digital converter, and is converted into a digital signal, and the digital signal output by the analog-to-digital converter is converted into serial port data through a microcontroller and a serial port level conversion chip in sequence.

[0007] Preferably, the power management module is further provided for the MEMS accelerometer, the analog-digital converter, the microcontroller and the serial port level conversion chip.

[0008] Preferably, the MEMS accelerometer output signal is converted into SPI or I2C bus signal by the analog-digital converter, and the serial port data converted by the serial port level conversion chip is RS422, RS232 or RS485 bus signal.

[0009] Preferably, the sensitive axis of the MEMS accelerometer is divided into two types, one of which is parallel to the surface of the MEMS accelerometer, and the other of which is perpendicular to the surface of the MEMS accelerometer.

[0010] Preferably, the test tool with the sensitive axis perpendicular to the surface of the MEMS accelerometer comprises a bottom surface and a vertical surface, the bottom surface is used for fixing the test tool to the centrifuge, and the vertical surface is provided with the MEMS accelerometers on both sides, the sensitive axes of the MEMS accelerometers are parallel to the radius direction from the center of the centrifuge to the center of the bottom surface of the test tool, and the sensitive axes of the MEMS accelerometers on both sides of the vertical surface are opposite after installation, the MEMS accelerometers on each side of the vertical surface are installed on the same plane, and the equivalent radii are the same.

[0011] Preferably, the test tool with the sensitive axis parallel to the surface of the MEMS accelerometer comprises a bottom surface, the bottom surface is used for fixing the test tool to the centrifuge and for installing the MEMS accelerometers, the sensitive axes of the MEMS accelerometers are parallel to the radius direction from the center of the centrifuge to the center of the bottom surface of the test tool, and the sensitive axes of the MEMS accelerometers on both sides of the bottom surface are opposite after installation, the MEMS accelerometers on each side of the bottom surface are installed on the same plane, and the equivalent radii are the same.

[0012] A batch test method for the nonlinearity of a MEMS accelerometer, which adopts the test device, and comprises the following steps:

[0013] S1, installing the test tool on the table surface of the centrifuge so that the sensitive axes of the MEMS accelerometers are parallel to the radius direction from the center of the centrifuge to the center of the bottom surface of the test tool, and placing the MEMS accelerometers in the clamps of the test tool;

[0014] S2, connecting the corresponding cables and supplying power to the MEMS accelerometers through the power supply to test the output of the MEMS accelerometers to ensure the correct connection;

[0015] S3, powering on and enabling the centrifuge, controlling the centrifuge to rotate to positions 0°, 90°, 180° and 270° in position mode, respectively, recording and calculating the average values of the four position outputs of all the MEMS accelerometers, which are V ip0, V ip90 , V ip18 0 and V ip270 , i represents the MEMS accelerometer serial number;

[0016] S4, control the centrifuge to rotate in the centrifugal force mode 1g, record and calculate the output mean value V of all MEMS accelerometers at 1g under the default radius 400mm i1g ;

[0017] S5, calculate the radius of the MEMS accelerometer by public 1:

[0018]

[0019] In the formula:

[0020] R i is the radius of the i-th accelerometer, unit: millimeter mm;

[0021] SF i is the scale factor of the i-th accelerometer, unit: digital quantity per gravitational acceleration LSB / g.

[0022] S6, calculate the angular velocity array of the input g value array according to the radius of the MEMS accelerometer according to formula 2, and round up the angular velocity, because the radii of the accelerometers installed in the positive direction are approximately the same, and the radii of the accelerometers installed in the negative direction are approximately the same, take the angular velocity array of the positive direction and the negative direction;

[0023]

[0024] In the formula:

[0025] g i is the i-th g value of the g value array, unit: gravitational acceleration g;

[0026] ω i is the angular velocity corresponding to the i-th g value of the g value array, unit: degrees per second ° / s.

[0027] S7, rotate according to the positive and negative angular velocity arrays calculated, record and calculate the output mean value of the MEMS accelerometer at each rotation speed, and take the corresponding MEMS accelerometer output according to the positive and negative angular velocities;

[0028] S8, calculate the corresponding centrifugal acceleration input array according to the radius of the MEMS accelerometer and the positive and negative angular velocity arrays, as shown in formula 3:

[0029]

[0030] In the formula:

[0031] g aiω i Corresponding acceleration, unit: gravity acceleration g;

[0032] ω i g is the angular velocity corresponding to the i-th g value of the g value array, unit: degrees per second ° / s.

[0033] R i R is the radius of the i-th accelerometer, unit: millimeter mm;

[0034] S9, the positive or negative nonlinearity is calculated by least square method according to the output mean value array of MEMS accelerometer and the corresponding centrifugal acceleration input array, as shown in formula 4;

[0035]

[0036] In the formula:

[0037] V ai V is the fitting value of the accelerometer corresponding to the i-th rotation speed point, unit: digital quantity LSB;

[0038] V is the average value output by the accelerometer at the i-th rotation speed point, unit: digital quantity LSB;

[0039] K a1 K is the slope of the fitting straight line, that is, the fitting scale factor of the accelerometer, unit: digital quantity per gravity acceleration (LSB / g);

[0040] X FS X is the absolute value of the upper limit value or the lower limit value of the acceleration, unit: gravity acceleration g.

[0041] S10, after rotating the test tool 180° and fixing it, repeating steps S2 to S9 to calculate the positive or negative nonlinearity of the MEMS accelerometer, and taking the larger value of the positive and negative nonlinearity of the single MEMS accelerometer as the nonlinearity of the MEMS accelerometer.

[0042] The advantages of the present application are:

[0043] 1. The present application increases the number of test devices on the test site, converts the device output signal, and improves the test efficiency and reduces the test cost in the way of automatic data processing, realizes single multiple device synchronous test, positive and negative synchronous test batch test mode.

[0044] 2. The device output signal conversion part of the test device of the present application is divided into analog signal conversion and digital signal conversion two parts, the analog signal is converted into digital signal through multi-channel analog to digital converter, the digital signal is converted into serial port data with long transmission distance and strong anti-interference ability through microcontroller and serial port level conversion chip.

[0045] 3. The application is based on the sensitive axis of MEMS accelerometer, which is divided into two types, and two different test fixtures are designed to adapt to different MEMS acceleration tests. BRIEF DESCRIPTION OF DRAWINGS

[0046] The application will be further described below in combination with the drawings and examples:

[0047] Figure 1 The device output signal conversion schematic of the test device of the application;

[0048] Figure 2 The structural schematic of the first test fixture of the application;

[0049] Figure 3 The structural schematic of the second test fixture of the application. DETAILED DESCRIPTION

[0050] The application adopts the test device to install the test fixture on the test station to increase the number of test devices, convert the device output signal, and automatically process the data, so as to improve the test efficiency and reduce the test cost, realize the batch test mode of single-time multi-device synchronous test and positive-negative synchronous test.

[0051] The MEMS accelerometer non-linearity batch test device of the application comprises a test fixture, the test fixture is fixed on a centrifuge, and a plurality of MEMS accelerometers are installed on the test fixture, each MEMS accelerometer is connected to the input end of a multi-channel analog-to-digital converter, converted into a digital signal, and the digital signal output by the analog-to-digital converter is converted into serial port data through a microcontroller and a serial port level conversion chip in sequence. The device output signal conversion principle is shown in Figure 1 .

[0052] The power management module provides stable and small ripple power for the device output signal conversion of the test device. If the MEMS accelerometer output signal is an analog signal, the MEMS accelerometer output signal needs to be converted into SPI (Serial Peripheral Interface, digital serial peripheral interface) or I2C (Inter-Integrated Circuit, internal integrated circuit bus) through the analog-to-digital converter in the dashed box. The SPI or I2C data is converted into a serial communication interface RS422 (RS232 or RS485) with long transmission distance and strong anti-interference ability through the microcontroller and the serial port level conversion chip.

[0053] MEMS accelerometers have two sensing axes: one with the sensing axis parallel to the MEMS accelerometer surface, and the other with the sensing axis perpendicular to the MEMS accelerometer surface. A test fixture with the sensing axis perpendicular to the MEMS accelerometer surface is shown below. Figure 2 As shown, the bottom surface of the test fixture is used to fix the test fixture to the precision centrifuge, and the upper surface is used to install the MEMS accelerometers, fixtures, and test plates. The sensitive axis of the MEMS accelerometers is parallel to the radial direction from the center of the precision centrifuge to the center of the bottom surface of the test fixture. MEMS accelerometers can be installed on both sides of the upper surface. Depending on the size of the upper surface and the size of the MEMS accelerometer test plate, multiple MEMS accelerometers can be placed. After installation, the sensitive axes of the MEMS accelerometers on both sides of the upper surface are opposite, and the MEMS accelerometers on each side of the upper surface are installed on the same plane with the same equivalent radius.

[0054] Test fixtures with the sensitive axis parallel to the surface of the MEMS accelerometer, such as Figure 3 As shown. The bottom surface of the test fixture is used to fix the test fixture to the precision centrifuge and to mount the MEMS accelerometers. The sensitive axis of the MEMS accelerometer is parallel to the radial direction from the center of the precision centrifuge to the center of the bottom surface of the test fixture. MEMS accelerometers are mounted on both sides of the bottom surface. Depending on the size of the bottom surface and the size of the MEMS accelerometer test plate, multiple MEMS accelerometers can be placed. After installation, the sensitive axes of the MEMS accelerometers on both sides of the bottom surface are opposite, and the MEMS accelerometers on each side of the bottom surface are mounted on the same plane with the same equivalent radius.

[0055] The specific testing steps of this invention are as follows:

[0056] S1. Mount the test fixture onto the precision centrifuge table, ensuring that the sensitive axis of the MEMS accelerometer is parallel to the radial direction from the center of the precision centrifuge to the center of the bottom surface of the test fixture. Place the MEMS accelerometer in the fixture;

[0057] S2. Connect the corresponding cables and power the MEMS accelerometer with a power supply. Test the MEMS accelerometer output to ensure that the connection is correct.

[0058] S3. Power on and enable the precision centrifuge. Control the centrifuge to rotate to positions 0°, 90°, 180°, and 270° in position mode. Record and calculate the average output values ​​of all MEMS accelerometers at the four positions, which are V... ip0 V ip90 V ip180 and V ip270 (i represents the MEMS accelerometer serial number);

[0059] S4. Control the precision centrifuge to rotate at 1g in the centrifugal force mode (default radius 400mm), record and calculate the average output of all MEMS accelerometers at 1g under the default radius V i1g (i represents the serial number of the MEMS accelerometer);

[0060] S5. Calculate the radius of the MEMS accelerometer by public 1:

[0061]

[0062] In the formula:

[0063] R i --The radius of the i-th accelerometer, unit: millimeter (mm);

[0064] SF i --The scale factor of the i-th accelerometer, unit: digital quantity per gravitational acceleration (LSB / g).

[0065] S6. Calculate the angular velocity array of the input g value array according to the radius of the MEMS accelerometer according to formula 2, and round up the angular velocity, because the radii of the accelerometers installed in the positive direction are approximately the same, and the radii of the accelerometers installed in the negative direction are approximately the same, take the angular velocity arrays of the positive and negative directions;

[0066]

[0067] In the formula:

[0068] g i --The i-th g value of the g value array, unit: gravitational acceleration (g);

[0069] ω i --The angular velocity corresponding to the i-th g value of the g value array, unit: degrees per second (° / s).

[0070] S7. Rotate according to the positive and negative angular velocity arrays calculated, record and calculate the average output of the MEMS accelerometer at each rotation speed, and take the corresponding MEMS accelerometer output according to the positive and negative angular velocities;

[0071] S8. Calculate the corresponding centrifugal acceleration input array according to the radius of the MEMS accelerometer and the positive and negative angular velocity arrays, as shown in formula 3:

[0072]

[0073] In the formula:

[0074] g ai --ω i Corresponding acceleration, unit: gravitational acceleration (g);

[0075] ω i --the angular velocity corresponding to the i-th g value of the g value array, unit: degree per second (° / s).

[0076] R i --the radius of the i-th accelerometer, unit: millimeter (mm);

[0077] S9. The positive or negative nonlinearity is calculated by the least square method according to the output mean value array of the MEMS accelerometer and the corresponding centrifugal acceleration input array, as shown in formula 4.

[0078]

[0079] In the formula:

[0080] V ai --the fitting value of the accelerometer at the i-th rotational speed point, unit: digital quantity (LSB);

[0081] --the average value output by the accelerometer at the i-th rotational speed point, unit: digital quantity (LSB);

[0082] K a1 --the slope of the fitting straight line, that is, the fitting scale factor of the accelerometer, unit: digital quantity per gravitational acceleration (LSB / g);

[0083] X FS --the absolute value of the upper limit value or the lower limit value of the acceleration, unit: gravitational acceleration (g).

[0084] S10. After rotating the test tool 180° and fixing it, steps 2 to 9 are repeated to calculate the positive or negative nonlinearity of the MEMS accelerometer, and the greater value of the positive and negative nonlinearity of a single MEMS accelerometer is taken as the nonlinearity of the MEMS accelerometer.

[0085] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any modification made according to the spirit and essence of the main technical solution of the present application should be covered within the protection scope of the present application.

Claims

1. A method for batch testing nonlinearity of a MEMS accelerometer, the method comprising: The application relates to a batch testing device for the nonlinearity of MEMS accelerometers, which comprises a testing tool fixed on a centrifuge and a plurality of MEMS accelerometers installed on the testing tool, wherein each MEMS accelerometer is connected to the input end of a multichannel analog-digital converter, converted into a digital signal, and the digital signal output by the analog-digital converter is converted into serial port data through a microcontroller and a serial port level conversion chip. The testing method comprises the following steps: S1, installing the testing tool on the centrifuge table surface so that the sensitive axis of the MEMS accelerometer is parallel to the radius direction from the centrifuge center to the center of the testing tool bottom surface, and placing the MEMS accelerometer in the testing tool clamp; S2, connecting the corresponding cable and supplying power to the MEMS accelerometer through a power supply to test the MEMS accelerometer output and ensure correct connection; S3, centrifuge on, enable, control the centrifuge to rotate to positions 0°, 90°, 180° and 270° in position mode respectively, record and calculate the average of the four position outputs of all MEMS accelerometers, V ip0 , V ip90 , V ip18 0 and V ip270 , i represents the serial number of the MEMS accelerometer; S4, control centrifuge to run in centrifugal force mode at 1g, record and calculate the mean of all MEMS accelerometer outputs at 1g at default radius of 400mm V i1g ; S5, calculating the radius of the MEMS accelerometer through formula 1: （1） In the formula, Ri is the radius of the i-th accelerometer in mm; Scale factor for the i-th accelerometer, units: digital counts per gravitational acceleration LSB / g; S6, calculating the angular velocity array of the input g value array according to the radius of the MEMS accelerometer through formula 2, and rounding up the angular velocity, because the radii of the accelerometers installed in the positive direction are approximately the same and the radii of the accelerometers installed in the negative direction are approximately the same, the angular velocity arrays in the positive direction and the negative direction are taken; （2） In the formula, gi is the i-th g value of the array of g values in units of gravitational acceleration g; ωi is the angular velocity corresponding to the i-th g value of the g value array, in degrees per second ° / s; S7, rotating according to the calculated angular velocity arrays in the positive direction and the negative direction, recording and calculating the average output of the MEMS accelerometer under each rotating speed, and taking the corresponding MEMS accelerometer output according to the angular velocity in the positive direction and the angular velocity in the negative direction; S8, calculating the corresponding centrifugal acceleration input array according to the radius of the MEMS accelerometer and the angular velocity arrays in the positive direction and the negative direction, as shown in formula 3: （3） In the formula, For Corresponding acceleration, in units of g, the gravitational acceleration. ωi is the angular velocity corresponding to the i-th g value of the g value array, in degrees per second ° / s; Ri is the radius of the i-th accelerometer in mm; S9, calculating the nonlinearity in the positive direction or the negative direction according to the average output array of the MEMS accelerometer and the corresponding centrifugal acceleration input array through the least square method, as shown in formula 4; （4） In the formula, is the fitting value of the accelerometer at the i-th rotational speed point, unit: digital quantity LSB; is the average value of the output of the accelerometer at the i-th rotational speed point, unit: digital quantity LSB; To fit the slope of the straight line, i.e. the accelerometer fit scale factor, unit: digital counts per gravitational acceleration (LSB / g); absolute value of the upper or lower limit value of the acceleration amount, unit: gravitational acceleration g; S10, fixing the testing tool after rotating by 180 degrees, repeating steps S2 to S9 to calculate the nonlinearity of the MEMS accelerometer in the negative direction or the positive direction, and taking the greater value of the nonlinearity of the MEMS accelerometer in the positive direction and the nonlinearity of the MEMS accelerometer in the negative direction as the nonlinearity of the MEMS accelerometer.

2. The MEMS accelerometer non-linearity batch test method of claim 1, wherein, The testing device further comprises a power management module which provides working power for the MEMS accelerometer, the analog-digital converter, the microcontroller and the serial port level conversion chip.

3. The MEMS accelerometer non-linearity batch test method of claim 2, wherein, The MEMS accelerometer output signal is converted into an SPI or I2C bus signal through the analog-digital converter; The serial port data converted by the serial port level conversion chip is an RS422, RS232 or RS485 bus signal.

4. The MEMS accelerometer non-linearity batch test method of claim 2, wherein, The sensitive axis of the MEMS accelerometer is divided into two types, one of which is parallel to the surface of the MEMS accelerometer, and the other of which is perpendicular to the surface of the MEMS accelerometer.

5. The MEMS accelerometer non-linearity batch test method of claim 4, wherein, The testing tool with the sensitive axis perpendicular to the surface of the MEMS accelerometer comprises a bottom surface and a vertical surface, the bottom surface is used for fixing the testing tool on the centrifuge, and the MEMS accelerometers are installed on the two sides of the vertical surface, and the sensitive axis of the MEMS accelerometer is parallel to the radius direction from the centrifuge center to the center of the testing tool bottom surface. The sensitive axes of the MEMS accelerometers installed on the two sides of the facade are opposite to each other, and the MEMS accelerometers on each side of the facade are installed on the same plane and have the same equivalent radius.

6. The MEMS accelerometer non-linearity batch test method of claim 4, wherein, The test tool with the sensitive axis parallel to the surface of the MEMS accelerometer comprises a bottom surface, the bottom surface is used for fixing the test tool to a centrifuge and for installing the MEMS accelerometer, the sensitive axis of the MEMS accelerometer is parallel to the radius direction from the center of the centrifuge to the center of the bottom surface of the test tool; the MEMS accelerometers are installed on the two sides of the bottom surface, the sensitive axes of the MEMS accelerometers installed on the two sides of the bottom surface are opposite to each other, and the MEMS accelerometers on each side of the bottom surface are installed on the same plane and have the same equivalent radius.

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