JPH112643A - Equipment for inspecting frequency characteristic of acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten an inspecting time required on the occasion of inspecting the frequency characteristic of an acceleration sensor. SOLUTION: This equipment for inspecting the frequency characteristic of an acceleration sensor has a white noise generator 11 which generates white noise containing a frequency component in an inspecting frequency band, and an acceleration sensor 15 to be inspected and a reference acceleration sensor 16 are vibrated together therein. The equipment is constituted by having a shaker 10 which receives the white noise from the white noise generator 11 and gives white noise acceleration to the acceleration sensor 15 to be inspected and the reference acceleration sensor 16 and by having an FFT analyzer 8 which applies fast Fourier transformation to a ratio between acceleration detection outputs of the acceleration sensor 15 to be inspected and the reference acceleration sensor 16 and thereby outputs the characteristic wherein a frequency and the detection output ratio are made to correspond to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor frequency characteristic inspection apparatus suitable for inspecting the frequency characteristic of an acceleration sensor, for example, in a semiconductor acceleration sensor production line.

[0002]

2. Description of the Related Art When inspecting the frequency characteristics of an acceleration sensor, the acceleration sensor to be inspected is mounted on a stage of a vibrator, and acceleration is applied to the acceleration sensor by the vibrator, and the frequency of the applied acceleration is changed. ing. And when such acceleration is applied,
By judging whether or not the change characteristic of the detection output outputted from the inspection target acceleration sensor, that is, the frequency characteristic is within a predetermined normal specification, the quality of the inspection target acceleration sensor is determined. ing.

[0003]

In the above conventional configuration, the inspection frequency band is, for example, between 10 Hz and 2 kHz, and the frequency of the acceleration applied to the acceleration sensor is 10
Hz to 2 kHz (so-called sweep). In this case, as shown in FIG. 8, the frequency is changed at intervals of about several Hz at first, and then gradually increased, and then changed at intervals of several hundred Hz at the end. With this, from the above 10 Hz to 2k
In the range up to Hz, several tens of acceleration detection points are set, and acceleration is detected by an acceleration sensor at each of these acceleration detection points.

However, this configuration has a disadvantage that it takes a considerably long time, for example, about 3 minutes, to change the acceleration frequency stepwise from the above 10 Hz to 2 kHz. In particular, there is a problem that the inspection time becomes longer as the number of steps for changing the frequency is increased by increasing the number of acceleration detection points in order to increase the inspection accuracy.

An object of the present invention is to provide an apparatus for inspecting the frequency characteristics of an acceleration sensor, which can shorten the inspection time.

[0006]

According to the first aspect of the present invention, a white noise acceleration including a frequency component in a test frequency band is added to an acceleration sensor to be inspected and a reference acceleration sensor. By subjecting the ratio of the acceleration detection output output from the reference acceleration sensor to fast Fourier transform, a characteristic in which the frequency and the detection output ratio correspond to each other, that is, a frequency characteristic is output. According to this configuration, the quality of the acceleration sensor can be determined by determining whether the output frequency characteristic belongs to a normal standard.

In the above configuration, the minimum time required to apply white noise acceleration to the two acceleration sensors is one of the lowest frequency components in the test frequency band.
This is the time for the cycle. For example, if the lowest frequency component is 1
If it is 0 Hz, it will be 0.1 second. Also, the time required for fast Fourier transform of the ratio of the acceleration detection outputs output from the two acceleration sensors depends on the data processing capacity of the fast Fourier transform means, but usually a few seconds are sufficient. Therefore, the inspection time is about several seconds as a whole, so that the inspection time can be significantly reduced as compared with the conventional configuration.

According to the second aspect of the present invention, as the reference acceleration sensor, an acceleration sensor having the same structure as that of the acceleration sensor to be inspected, the frequency characteristic of which is known in advance and which is within the normal specification is used. did. In the case of this configuration, when determining whether the wind wave number characteristic output from the fast Fourier transform means belongs to the normal standard, the upper limit value of the normal standard and the lower limit of the normal standard are determined for the entire inspection frequency band. Each value becomes a constant value, and it is sufficient to prepare these two numerical values. Thereby, the configuration for the above determination can be simplified.

According to the third aspect of the present invention, a characteristic in which the frequency output from the fast Fourier transform means is made to correspond to the detected output ratio is input, and it is automatically determined whether or not this characteristic belongs to the normal specification. A configuration is provided that includes a determination unit that determines the quality of the inspection target acceleration sensor based on the determination. Accordingly, the quality of the acceleration sensor to be inspected is automatically determined, so that the inspection operation is further simplified.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the present invention is applied to a frequency characteristic inspection apparatus for a semiconductor acceleration sensor will be described below with reference to FIGS. First, FIG.
FIG. 1 is a view schematically showing an example of a semiconductor acceleration sensor 1. In FIG. 2, a semiconductor type acceleration sensor 1 includes a base 2, a frame 3 mounted on the base 2,
A weight portion 5 supported by four beams 4 is provided inside the frame 3. A piezo element (not shown) is formed on the four beams 4.

When acceleration is applied to the acceleration sensor 1 having such a configuration, the weight portion 5 moves according to the magnitude of the acceleration, and the beam 4 is deformed accordingly, and the resistance of the piezo element changes. Here, by applying a voltage to the piezo element, an electric signal corresponding to a resistance change of the piezo element (that is, an applied acceleration) can be extracted as an acceleration detection signal.

In the manufacturing line for manufacturing the acceleration sensor 1 having the above-described structure, a step of inspecting the frequency characteristics of the manufactured acceleration sensor 1 is performed in the final step. In this inspection process, a frequency characteristic inspection device 6 as shown in FIG. 1 is used. FIG. 1 is a diagram showing an electrical configuration of the frequency characteristic inspection device 6 by combining functional blocks. As shown in FIG. 1, the frequency characteristic inspection device 6 includes a personal computer 7, an FFT analyzer 8, a voltage generator 9, a vibrator 10, and a white noise generator 11 connected to the personal computer 7. I have.

The personal computer 7 includes a frequency characteristic inspection device 6
Has a function of controlling the overall operation of the system, and stores a control program therefor. This personal computer 7 constitutes the judgment means. The personal computer 7 is configured to be able to drive and control the FFT analyzer 8, the voltage generator 9, the vibrator 10, and the white noise generator 11, respectively.

Here, the exciter 7 is, as shown in FIG.
It comprises a base 12 and a vibration mechanism 13 supported by the base 12. Stage 1 of the vibration mechanism 13
On the top 4, an inspection acceleration sensor 15 and a reference acceleration sensor 16 are fixedly mounted. As a result, the vibration exciter 7 is connected to the inspected acceleration sensor 15 and the reference acceleration sensor 1.
6 can be excited together (at the same time), that is, acceleration can be applied. In addition, the manufactured acceleration sensor 1 to be inspected is attached as the acceleration sensor 15 to be inspected. The reference acceleration sensor 16 is an acceleration sensor having the same structure as the above-mentioned inspection target acceleration sensor 15, that is, an already manufactured acceleration sensor 1 whose frequency characteristic is inspected and known in advance. The acceleration sensor 1 whose frequency characteristic is within the normal specification is used. In particular, in the case of the present embodiment, the acceleration sensor 1 whose frequency characteristic substantially coincides with the design center is used as the reference acceleration sensor 16.

The white noise generator 11 has a function of generating white noise including frequency components in the inspection frequency bands f1 to f2 (for example, f1 is 10 Hz and f2 is 2 kHz). I have. In this case, the white noise generator 11 constitutes a white noise generator. The white noise signal generated from the white noise generator 11 is provided to the vibrator 10. Then, the vibration exciter 10 is configured to receive the white noise and apply a white noise acceleration to the acceleration sensor under test 15 and the reference acceleration sensor 16.

Here, the white noise acceleration is an acceleration having an acceleration component in the inspection frequency band f1 to f2. This white noise acceleration is used as the acceleration sensor 1 to be inspected.
The addition to the acceleration sensor 5 and the reference acceleration sensor 16 means that the acceleration components in the inspection frequency bands f1 to f2 are simultaneously applied to the acceleration sensor under test 15 and the reference acceleration sensor 16. Therefore, adding the white noise acceleration to the acceleration sensors 15 and 16 involves changing the frequency of the acceleration applied to the acceleration sensor stepwise in the inspection frequency bands f1 to f2 (sweep) as in the conventional configuration (see FIG. 8).
It is practically the same as just doing it, except for the time difference.

The voltage generator 9 is a power supply circuit for applying a voltage for detecting operation to the acceleration sensor 15 to be inspected and the reference acceleration sensor 16. When the white noise acceleration is applied by the vibrator 10 in a state where the voltage is applied, the acceleration sensor 15 to be inspected and the reference acceleration sensor 16 detect the white noise acceleration and output the acceleration as an acceleration detection output. It outputs detection signals S1 and S2. These acceleration detection signals S1 and S2 are shown in (a) and (b) of FIG.

Subsequently, the acceleration detection signals S1 and S2 output from the test acceleration sensor 15 and the reference acceleration sensor 16 are provided to the FFT analyzer 8. The FFT analyzer 8 performs a fast Fourier transform on a ratio S1 / S2 of the two acceleration detection signals S1 and S2, thereby obtaining a characteristic in which a frequency is associated with a detection output ratio (detection signal ratio), that is, a frequency characteristic. It is configured to output. Specifically, the FFT analyzer 8 is configured to output a characteristic diagram (graph) as shown in FIG. The horizontal axis in FIG. 5 indicates the frequency, and the vertical axis indicates the gain (dB) of the detection output ratio S1 / S2. In this case, the FFT analyzer 8 constitutes a fast Fourier transform unit.

The FFT analyzer 8 has a function of, for example, printing and outputting the graph of the frequency characteristic, converting the graph of the frequency characteristic into digital data, and outputting the frequency characteristic data to the personal computer 7. doing. Then, the personal computer 7 receives the frequency characteristic data from the FFT analyzer 8 and automatically determines whether or not the characteristic belongs to the normal specification, and determines whether the acceleration sensor 15 to be inspected is good or not. Is configured. In this case, the personal computer 7 constitutes the determination means. The specific contents of the determination operation of the personal computer 7 will be described later.

Here, how to read the frequency characteristic graph (FIG. 5) output from the FFT analyzer 8 will be described. First, at one frequency in the test frequency band, if the acceleration detection signal S1 output from the test acceleration sensor 15 and the acceleration detection signal S2 output from the reference acceleration sensor 16 are equal, the ratio S1 / S2 is determined. At this time, the gain becomes 0 dB. If the acceleration detection signal S1 becomes smaller than the acceleration detection signal S2,
The ratio S1 / S2 becomes smaller than 1, and the gain (dB) becomes a negative value. Conversely, if the acceleration detection signal S1 becomes larger than the acceleration detection signal S2, the ratio S1 / S2 becomes larger than 1, and the gain (dB) becomes a positive value. Here, it is known that the reference acceleration sensor 16 outputs the value of the design center within the normal specification as the acceleration detection signal S2 in the entire inspection frequency band (f1 to f2).

Therefore, if the acceleration sensor under test 15 outputs an acceleration detection output S1 having the same value as the acceleration detection output S2 of the reference acceleration sensor 16 in the entire inspection frequency band (f1 to f2), Band (f1-f
The gain is 0 dB in the entire region of 2). On the other hand, at a certain frequency in the inspection frequency band (f1 to f2), the acceleration sensor 15 to be inspected has an acceleration detection output S larger than the acceleration detection output S2 of the reference acceleration sensor 16.
1, the gain becomes a positive value. If the acceleration sensor under test 15 outputs an acceleration detection output S1 having a value smaller than the acceleration detection output S2 of the reference acceleration sensor 16, the gain becomes negative. Value.

Therefore, as shown in FIG. 5, the upper limit value of the normal specification is set to X dB, and the lower limit value is set to -X dB, and the detection output ratio S1 / S2 is set over the entire inspection frequency band (f1 to f2). Is the upper limit value XdB and the lower limit value −Xd
If it can be confirmed that it belongs to the area B, the frequency characteristic output from the FFT analyzer 8, that is, the frequency characteristic of the acceleration sensor under test 15 can be confirmed to be within the normal specification. Then, when this check is performed, the inspection target acceleration sensor 15 can be determined to be non-defective.

On the other hand, the test frequency bands (f1 to f
If it can be confirmed that the gain of the detection output ratio S1 / S2 exceeds the upper limit value XdB or becomes smaller than the lower limit value −XdB at a certain frequency in the entire range of 2), the acceleration sensor 15 to be inspected is checked. It can be confirmed that the frequency characteristics do not belong to the normal standard.
In this case, the acceleration sensor under test 15 can be determined to be defective.

Next, the inspection operation of the frequency characteristic inspection apparatus 6 having the above configuration will be described with reference to FIG. FIG.
5 is a flowchart schematically showing control contents of a control program of a personal computer 7 of the frequency characteristic inspection device 6. First,
As shown in FIG. 3, the acceleration sensor 15 to be inspected is to be inspected.
And the reference acceleration sensor 16 to the stage 1 of the vibration mechanism unit 13.
4 Subsequently, the inspection operation is started by operating the keyboard of the personal computer 7 (step S in FIG. 6).
1).

Then, the personal computer 7 drives the voltage generator 9 to drive the acceleration sensor under test 15 and the reference acceleration sensor 16.
Is applied with a voltage for an inspection operation (step S2). Then, the personal computer 7 drives the white noise generator 11 and the vibration exciter 10 to apply the white noise acceleration to the acceleration sensor 15 to be inspected and the reference acceleration sensor 16, and vibrates both the acceleration sensors 15, 16 with white noise. (Step S3). Here, the time during which the white noise acceleration is applied is 1 second, which is, for example, 10 cycles of the lowest frequency component (10 Hz in this case) in the inspection frequency band. The time during which the white noise acceleration is applied may be 0.1 seconds or more, which is the time of one cycle of the lowest frequency component, and a specific time value may be set as appropriate.

At the same time, the personal computer 7 operates the FFT analyzer 8 to output two acceleration detection outputs S output from the acceleration sensor 15 to be inspected and the reference acceleration sensor 16.
1. A fast Fourier transform process (FFT analysis) for fast Fourier transform of the ratio S1 / S2 of S2 is started (step S4). As a result, the FFT analyzer 8 calculates and outputs the frequency characteristic of the gain of the acceleration detection output ratio S1 / S2 in the entire inspection frequency band (f1 to f2). In this case, the FFT analyzer 8 sets the acceleration detection output ratio S1 / over the entire inspection frequency band (f1 to f2).
It is preferable that the maximum value and the minimum value are obtained and output from the frequency characteristics of the gain of S2.
Then, the frequency characteristics of the acceleration detection output ratio S1 / S2 (and the maximum and minimum values thereof) output from the FFT analyzer 8 are transmitted to the personal computer 7 (step S5).

Subsequently, the personal computer 7 determines whether or not the frequency characteristic of the acceleration detection output ratio S1 / S2 output from the FFT analyzer 8 falls between the upper limit value XdB and the lower limit value -XdB of the normal specification. (Step S6). In this case, the personal computer 7 obtains the maximum value and the minimum value from the transmitted frequency characteristics, and obtains the maximum value and the minimum value (or the maximum value and the minimum value of the transmitted frequency characteristics).
Is between the upper limit value XdB and the lower limit value -XdB of the normal specification.

Here, if the maximum value and the minimum value of the frequency characteristic fall between the upper limit value XdB and the lower limit value -XdB of the normal specification, the acceleration sensor 15 to be inspected is determined to be non-defective, and the above-mentioned step S6 is performed. Then, the process proceeds to “YES”, and the display of the personal computer 7 displays that the inspection target acceleration sensor 15 is non-defective (step S).
7).

On the other hand, if the maximum value and the minimum value of the frequency characteristic do not belong to the range between the upper limit XdB and the lower limit -XdB of the normal specification, it is determined that the acceleration sensor 15 to be inspected is defective, and the above-mentioned step S6 is performed. Then, the process proceeds to "NO", and the display of the personal computer 7 is configured to display that the acceleration sensor under test 15 is defective (step S8). Thus, the operator can visually check the display of the personal computer 7 to obtain the acceleration sensor 15 to be inspected.
You can see if it is good or bad.

According to the present embodiment having such a configuration, the minimum time required to apply the white noise acceleration to the two acceleration sensors 15 and 16 is the inspection frequency band (f1 to f).
In 2), the time corresponding to one cycle of the lowest frequency component, for example, if the lowest frequency component is 10 Hz, the time is 0.1 second. In this embodiment, the time is one second, which is the time corresponding to 10 cycles. The ratio S1 / S2 of the acceleration detection outputs S1 and S2 output from the two acceleration sensors 15 and 16
The time required to perform the fast Fourier transform on the FFT depends on the data processing capability of the FFT analyzer 8, but is usually on the order of several seconds. Therefore, the inspection time required for inspecting the acceleration sensor 15 to be inspected is about several seconds as a whole, so that the inspection time can be greatly reduced as compared with the conventional configuration.

In the above embodiment, the reference acceleration sensor 16 is an acceleration sensor having the same structure as that of the acceleration sensor 15 to be inspected, the frequency characteristic of which is known in advance and exists within normal specifications. Specifically, an acceleration sensor whose frequency characteristic is the design center of the normal standard was used. For this reason, in determining whether the wind wave number characteristic output from the FFT analyzer 8 belongs to the normal standard, the upper limit value X of the normal standard and the lower limit value of the normal standard − X takes a constant value. The personal computer 7 prepares these two numerical values A and B, and determines whether to compare the maximum value and the minimum value of the frequency characteristic output from the FFT analyzer 8 with the two numerical values X and -X. Just do it.
Thereby, the configuration for the above determination can be simplified.

It is not an essential condition that the frequency characteristics of the reference acceleration sensor 16 be the design center of the normal standard, but it is sufficient if the frequency characteristics are within the normal standard. In this case, the upper limit value X and the lower limit value −X may be changed so as to correspond to the deviation from the design center of the normal standard.

Further, in the above embodiment, the frequency characteristic output from the FFT analyzer 8 is input to the personal computer 7, and the personal computer 7 automatically determines whether or not the frequency characteristic belongs to the normal specification. In this case, the quality of the inspected acceleration sensor 15 is determined. As a result, the quality of the inspected acceleration sensor 15 is automatically determined, and the inspection work is further simplified.

On the other hand, a commercially available capacitive acceleration sensor may be used as the reference acceleration sensor instead of the reference acceleration sensor 16. This configuration will be described as a second embodiment with reference to FIG. In the case of the second embodiment, the frequency characteristic of the ratio S1 / S2 of the acceleration detection signals S1 and S2 output from the FFT analyzer 8 is as shown in FIG.
, A graph shown by a solid line P is obtained. The reason why the frequency characteristic P as shown in FIG.
This is because a characteristic is required in which the acceleration detection output decreases as the frequency decreases. Such characteristics are necessary for confirming that the structure for preventing resonance in the acceleration sensor 1 is functioning normally.

Therefore, as shown in FIG. 7, the upper limit of the normal specification of the frequency characteristic of the ratio S1 / S2 of the acceleration detection outputs S1 and S2 is a solid line P1, and the lower limit is a solid line P2. Therefore, in the second embodiment, the personal computer 7
The upper limit value data corresponding to the solid line P1 of the upper limit value and the lower limit data corresponding to the solid line P2 of the lower limit value are previously stored in advance, and the frequency output from the FFT analyzer 8 for the entire test frequency band is stored. It is configured to determine whether the characteristic belongs between the upper limit value data and the lower limit value data. If the frequency characteristic from the FFT analyzer 8 falls between the upper limit value data and the lower limit value data, the personal computer 7 determines that the inspected acceleration sensor 15 is a non-defective product. The acceleration sensor 15 is configured to determine that the product is defective.

The configuration of the second embodiment other than that described above is the same as that of the first embodiment. Therefore, in the second embodiment, substantially the same operation and effect as in the first embodiment can be obtained.

In each of the above embodiments, the fast Fourier transform means is constituted by the FFT analyzer 8. However, the present invention is not limited to this. The personal computer may be provided with a fast Fourier transform function. With this configuration, the configuration of the frequency inspection device is further simplified. Furthermore, in each of the above embodiments, the present invention is applied to the case where the frequency characteristic of the semiconductor type acceleration sensor 1 is inspected. However, the frequency characteristic of another acceleration sensor (for example, a capacitive type acceleration sensor, a piezoelectric type acceleration sensor, a servo type acceleration sensor, etc.) May be applied to the case of inspecting.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a perspective view of an acceleration sensor.

FIG. 3 is a side view of a shaker.

4A is a time chart illustrating an acceleration detection signal output from an acceleration sensor to be inspected, and FIG. 4B is a time chart illustrating an acceleration detection signal output from a reference acceleration sensor.

FIG. 5 is a characteristic diagram showing frequency characteristics output from an FFT analyzer.

FIG. 6 is a flowchart.

FIG. 7 is a view corresponding to FIG. 5, showing a second embodiment of the present invention.

FIG. 8 shows a conventional configuration, and is a time chart showing a state when an acceleration frequency is swept.

[Explanation of symbols]

1 is a semiconductor type acceleration sensor, 6 is a frequency characteristic inspection device,
7 is a personal computer (determination means), 8 is an FFT analyzer (fast Fourier transform means), 10 is a vibrator, 11 is a white noise generator (white noise generation means), 15 is an acceleration sensor to be inspected, and 16 is a reference acceleration sensor. Is shown.

Claims (3)

[Claims] 1. A white noise generating means for generating white noise including a frequency component of an inspection frequency band, and an excitation sensor to be inspected and a reference acceleration sensor are vibrated together. A vibrator that receives white noise and applies white noise acceleration to the acceleration sensor under test and the reference acceleration sensor; and a fast Fourier transform of a ratio of acceleration detection outputs output from the acceleration sensor under test and the reference acceleration sensor. A frequency characteristic inspection device for an acceleration sensor, comprising: a fast Fourier transform unit that outputs a characteristic in which a frequency and a detection output ratio correspond to each other. 2. An acceleration sensor having the same structure as that of the acceleration sensor to be inspected, the frequency characteristic of which is known in advance and which is within a normal standard is used as the reference acceleration sensor. The frequency characteristic inspection device for an acceleration sensor according to claim 1. 3. A method in which a characteristic corresponding to a frequency output from the fast Fourier transform means and a detected output ratio is input, and it is automatically determined whether or not the characteristic belongs to a normal specification. 3. The frequency characteristic inspection apparatus for an acceleration sensor according to claim 1, further comprising a determination unit configured to determine whether the inspection target acceleration sensor is good or not.