JPH05172661A - Trouble shooter and self return apparatus for force or load detection sensor - Google Patents

Abstract

PURPOSE:To prevent erroneous measurement and obtain a normal measured value even when aging occurs by judging whether the aging occurs in a force or load detection sensor or not. CONSTITUTION:A full bridge circuit 50 for detecting force or a load is made separable with half bridge circuits 50a and 50c, changeover switches 70 and 74 and dummy resistors 64 and 66. An allowable value which is determined based on zero-point outputs of the half bridges 50a and 50c when the full bridge circuit 50 operates normally is stored into a memory means 78b. Comparison is performed by a comparison means 78b to determine that any of outputs of the half bridge circuits 50a and 50c at zero points exceeds corresponding allowable values or not. When the allowable value is exceeded, an alarm means 78c is actuated to notify that any of the half bridge circuits operates abnormally. The output of the normal half bridge circuit is converted to the output of the full bridge circuit 50 by a conversion means 78d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnostic device for diagnosing whether a force or load detection sensor using a strain gauge such as an electric resistance wire type strain gauge or a semiconductor strain gauge has a fault, and a fault. And a device for self-recovering when diagnosed.

[0002]

2. Description of the Related Art A sensor using a strain gauge as described above is widely used in industrial measurement fields such as load and pressure, and has a high accuracy and a relatively low failure rate, so that it is highly reliable. It is used as a sensor. 5A and 5B show a sensor using such a strain gauge. FIG. 5A shows a sensor used for a compression type load cell, and FIG. 5B shows a sensor used for a dual beam type load cell. ..

In the compression type load cell, a strain-flexing portion 12 is provided on the support portion 10, and a force receiving portion 14 is provided on the strain-generating portion 12, and the strain-generating portion 12 receives the force receiving portion. When 14 receives a force it is compressed. Strain gauges 16 and 18 are attached to the strain-flexing portion 12 in parallel with the axial direction of the strain-flexing portion 12 to detect a compression force, and the strain gauge 2
0 and 22 are attached at right angles to the axial direction of the strain-flexing part 12 to detect the pulling force. Further, in the double beam type load cell, the strain generating section 28 is formed so as to form the two beams (beams) 24 and 26, and the load is applied to the strain generating section 28 by, for example, the strain generating section 28. This is done by placing an article on the platform 37 connected to the. When a load is applied on the mounting table 37, the strain gauges 32 and 34 receive bending stress in the direction in which the gauge bonding surface extends, and the strain gauges 30 and 36 receive bending stress in the direction in which the gauge bonding surface contracts.

These strain gauges 16, 18, 2
0, 22, 30, 32, 34 and 36 are connected to each other to form a bridge circuit 38 as shown in FIG. However, the strain gauges forming the opposite sides of the bridge circuit 38 are connected so as to receive the same type of force, such as the tensile force if the tensile force is the tensile force and the compressive force is the compressive force. A DC voltage for excitation is applied to two opposing connection points 40, 40 of this bridge circuit, and a connection point 4 located at a right angle to these connection points 40, 40.
The detected voltage of the force or load is taken out from Nos. 2 and 42, and this is converted into a digital signal by the A / D converter 44 and supplied to the measurement data output unit 46, where it is processed and the measured value Display and printing are performed.

[0005]

However, the sensor using such a strain gauge is a highly reliable sensor as described above, but the failure is not zero, and a shock load exceeding the rating or , Performance may deteriorate or malfunction due to adverse environment (temperature, humidity, gas, static electricity, etc.). If it becomes completely unusable due to damage or disconnection, it will be impossible to measure because of failure.
There is no erroneous measurement. However, if the performance is gradually deteriorating but no noticeable failure has occurred yet, it may be difficult to notice that the error is included even though the measurement value has an error. In particular, in the field of industrial measurement and control, there is a big problem that raw materials are directly connected to human life accidents such as inferior products due to measurement error or explosion due to defective mixing in raw material mixing equipment. In addition, if the sensor used for the scale used for commerce has the above-mentioned failure, the error will increase without noticing and fair trade will not be possible,
Losing credibility socially and becoming a big problem.

[0006]

A fault diagnosis apparatus according to the present invention which solves the above-mentioned problems has a pair of force or load detection sensors which can be separated into two sets of force or load detection means. Separation into two sets of detection means is performed by the separation means. In addition to this, a storage unit is provided, which stores an allowable value determined based on the outputs of the two sets of detection units in a specific state during normal operation of the detection sensor. This allowable value is compared with the outputs of the two sets of detecting means when the detection sensor is separated into the two sets of detecting means by the separating means, and the comparing means. Further, in the failure diagnosis device according to the present invention, the comparison means is
It is also possible to have an alarm means which is activated when it is determined that one of the outputs of the two sets of detection means exceeds the corresponding allowable value corresponding to each of them. The specific state may be a state in which no force or load is applied, for example. Further, instead of comparing the output in a specific state with the allowable value therefor, the relational expression of the output with respect to the force or load of the two sets of detecting means is obtained and compared with the allowable value of the relational expression. Good.

In the self-recovery device according to the present invention, when one of the two detecting means determines that the corresponding allowable value exceeds the allowable value, the failure diagnosing device outputs the output of the other detecting means. A conversion means for converting the output of the load sensor is provided.

[0008]

In the fault diagnosis apparatus according to the present invention, the detection sensor is divided into two sets of detection means, and the outputs of the two sets of detection means at that time are respectively output in a specific state, for example, in the state where no force or load is applied. The corresponding allowable value is compared with the comparison means. If any of the outputs of the detecting means exceeds the allowable value, it can be determined that the deterioration has progressed. Therefore, for example, an alarm device is activated to notify that deterioration is progressing.

In the self-recovery device according to the present invention, when it is determined that any one of the detecting means is deteriorated as described above, the output of the remaining detecting means is converted into the output obtained by the detecting sensor by the converting means. Convert to the equivalent.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION This embodiment has a bridge circuit 50 as shown in FIG. The bridge circuit 50 has strain gauges 52 of an electric resistance wire type on each side,
54, 56, 58, and these strain gauges 52
Nos. 58 to 58 are attached to the strain-flexing portion so as to receive a compressive force or a tensile force, similarly to the strain gauge shown in FIG. 5A or 5B. This bridge circuit 5
Connection point 60 of strain gauges 52 and 58 at 0
And a connection point 61 of the strain gauges 54 and 56, a DC voltage for excitation is applied by a DC power supply 62.

Dummy resistors 64 and 66 connected in series are connected to the connection points 60 and 61, and a connection point 68 of the strain gauges 52 and 54 is connected to a changeover switch 70.
Of the contacts 70a, 70b. The other contact 70c of the changeover switch 70 is connected to the dummy resistor 6
It is connected to the connection points 72 of 4, 66. This connection point 7
2 is also connected to the contact 74a of the changeover switch 74, and the other contacts 74b and 74c are connected to the strain gauges 56 and 58.
Is connected to the connection point 76.

The changeover switches 70 and 74 respectively have interlocking contacts 70d and 74d.
When d and 74d are in contact with the contacts 70a and 74a, the strain gauges 52 and 54 and the dummy resistor 6 are provided between the contacts 70d and 74d as shown in FIG.
The output of a bridge (hereinafter referred to as a half-bridge circuit) circuit 50a formed by 4 and 66 is supplied.

The contacts 70d and 74d are connected to the contact 70.
b, 74b, contacts 70d, 74d
In between, as shown in Fig. 1 (a), the strain gauge 5
An output of a bridge circuit (hereinafter, referred to as a full bridge circuit) 50 constituted by 2, 54, 56 and 58 is supplied.

Further, the contacts 70d and 74d are connected to the contact 7
0c and 74c are in contact with the contacts 70d and 74
Between d, as shown in FIG. 1C, a bridge circuit composed of strain gauges 56 and 58 and dummy resistors 64 and 66 (hereinafter referred to as a half bridge circuit).
The output of 50c is supplied.

That is, the full bridge circuit 50 is separated by the separating means composed of the dummy resistors 64 and 66 and the changeover switches 70 and 74, respectively, as shown in FIG.
Half bridge circuits 50a and 50c as shown in (c)
Can be separated into The changeover switches 70, 7
The switching control of the four contactors 70d and 74d will be described later.

Contact 7 of these changeover switches 70 and 74
The output of the full bridge circuit 50 or the half bridge circuits 50a and 50c supplied between 0d and 74d is A /
The signal is converted into a digital signal by the D converter 76 and is supplied to the failure diagnosis alarm and self-recovery circuit 78. This circuit 78 is composed of, for example, a microcomputer together with a measurement data output circuit 80, which will be described later, and includes a storage means 78a, a comparison means 78b, an alarm means 78c, and a conversion means 78d.

The storage means 78a stores the allowable values of the half bridge circuits 50a and 50c. These allowable values are determined as follows, for example.

As shown by the straight line B in FIG. 2, the full bridge circuit 50 can measure from 0 Kg to 3 Kg, and in a normal state, a voltage of 0 mV at 3 Kg is applied at 0 Kg.
At a voltage of 10 mV, the output voltage Y for a force or load X between 0 Kg and 3 Kg becomes (10
/ 3) Assume that there is a linear relationship of X.

In such a case, for example, the changeover switch 7
The contacts 70d and 74d of 0 and 74 are connected to the contacts 70a and 74a.
When the half bridge circuit 50a as shown in FIG. 1 (b) is configured by switching to, the output is 3 mV at 0 Kg and 7.8 mV at 3 Kg, as shown by a straight line A in FIG.
Then, it is assumed that the output voltage Y1 has a linear relationship of 3 + [(7.8-3) / 3] X with respect to the force or load X between 0 kg and 3 kg.

Similarly, when the contacts 70d and 74d of the changeover switches 70 and 74 are switched to the contacts 70c and 74c to form a half bridge circuit 50c as shown in FIG. 1C, a straight line C in FIG. As shown, the output shows -3 mV at 0 Kg, 2.2 mV at 3 Kg, and 0 Kg to 3 K
Output voltage Y2 for force or load X up to g
, But there is a linear relationship of −3 + [(2.2 + 3) / 3] X.

The half bridge circuit 50a or 5
When configured as 0c, 3 mV or -3 at 0 Kg
The output of mV is generated by strain gauges 52, 54 and 64, 66 or 56, 5 which form a half bridge.
It is based on the non-uniformity of the resistance values of 8 and 64 and 66,
It is not based on force or load. And output Y
An output Y is obtained by adding 1 and Y2.

By the way, such a strain gauge 5
In Nos. 2, 54, 56 and 58, the deterioration occurs as described above, but the deterioration does not occur evenly so as not to affect the output of the full bridge circuit 50. As the deterioration mechanism, first, the strain gauges 52, 5
When the resistance value of any one of 4, 56, and 58 changes, the balance is greatly disturbed, the zero point (output in the state where a force or load of 0 Kg is applied) changes, and if deterioration further progresses, the span (Fig. Change of the straight line A of 2).

FIG. 3 shows, for example, strain gauges 56, 5
Full bridge circuit 5 when deterioration occurs in any of 8
0, the output of the half bridge circuits 50a and 50c. The output Y11 of the half bridge circuit 50a as shown in FIG. 1B is the output Y shown by the straight line A in FIG.
It is the same as 1 and there is no change at all. However, the output Y21 of the half-bridge circuit 50c shown in FIG. 1C has a zero point of 2 m in the positive direction, as is clear from a comparison with Y2 shown by the dotted line.
When V is moved and a force or load of 3 Kg is applied, the output changes to 3.5 mV. Therefore, output sensitivity (straight line C
Slope of) was (2.2 + 3) / 3,
It has fallen to (3.5 + 1) / 3. As a result, the output sensitivity of the full-bridge circuit 50, which was 10/3, is reduced to 9.3 mV / 3.

As described above, since the deterioration causes the movement of the zero point and the deterioration of the sensitivity, it is possible to detect the deterioration by checking any one of them. However, the simplest method for detecting this deterioration is to detect the movement of the zero point. Generally, the zero point of the sensor does not change so much. For example, if 10% of the full scale (10 mV in the above example) changes after adjustment in a normal state, it can be determined that there is an abnormality somewhere. Therefore, in this embodiment, in the normal state, the straight line A in FIG.
As the characteristics shown in B and C by the full bridge circuit 50 and the half bridge circuits 5a and 50b, respectively, the allowable value of the half bridge circuit 50a is 3 mV ±
1 mV as the allowable value of the half bridge circuit 50c-
The storage means 78a stores 3 mV ± 1 mV.

The comparing means 78b compares these allowable values with A /
Half bridge circuit 50 supplied from the D converter 76
Compare the corresponding digital signal at the output of a, 50c. That is, the contact 70 of the changeover switches 70 and 74
The digital signal from the A / D converter 76 in the state where d and 74d are switched to the contacts 70a and 74a is set to 3
Compared with the allowable value of mV ± 1 mV, changeover switches 70, 7
The digital signal from the A / D converter 76 in the state where the four contactors 70d and 74d are switched to the contacts 70c and 74c is compared with -3 mV ± 1 mV.

This comparison is performed when the zero point measuring means 82 indicates that it is the zero point. As the zero-point measuring means 82, for example, it is possible to visually confirm whether or not an article is present on the impact receiving portion 14 shown in FIG. 5A or the mounting table 37 shown in FIG. The zero-point adjusting device may be manually operated, or a photoelectric detector that detects the presence / absence of an article on the platform 37 can be used as an automatic method. Further, the changeover switches 70 and 74 are also switched by the failure diagnosis alarm and self-recovery circuit 78 based on the zero point instruction from the zero point measuring means 82.

When the output of the half bridge circuit 50a or 50c shown in FIG. 1 (b) or (c) exceeds an allowable value as a result of the comparison by the comparing means 78a, the alarm means 78c gives a notification to that effect. It is for.

The converting means 78d, when the result of the comparison by the comparing means 78a indicates that one of the half bridge circuits 50a and 50c shown in FIG. 1B or 1C is abnormal, the changeover switch 70d. , 74 is switched, and the output from the normal half bridge circuit is always the A / D converter 7.
When the force or load is applied, the output of the normal half bridge circuit is to be converted into the applied force or load.

For example, as shown by the straight line B in FIG. 2, the output Y in the normal state of the full bridge circuit 50 is (1
0/3) X has a linear relationship, and the output Y1 in the normal state of the half bridge circuit 50a of FIG. 1B is 3 + [(7.8− 3) / 3]
There is a linear relationship of X, and as shown by the straight line C in FIG.
The output Y2 in the normal state of the half bridge circuit 50c in (c) has a linear relationship of -3 + [(2.2 + 3) / 3] X with X.

Therefore, for example, when there is an abnormality in the half bridge circuit 50c of FIG. 1C, when the output Y1 of the half bridge circuit 50a of FIG. 1B is to be obtained, the zero point of Y1 and Y is obtained. The output difference 3 in 3 is subtracted from Y1 at that time, and the subtracted value is multiplied by the ratio of the inclination of the straight line A to the inclination of the straight line A. Similarly, FIG.
If there is an abnormality in the half bridge circuit 50a of (b),
When Y is to be obtained from the output Y2 of the half bridge circuit 50c of FIG. 1C, the output difference -3 at the zero point between Y2 and Y is subtracted from the output of Y2 at that time, and this subtraction value is obtained. , The ratio of the slope of the straight line B to the slope of the straight line C may be multiplied.

Therefore, the conversion means 78d has the output difference at the zero point between Y1 and Y, the output difference at the zero point between Y2 and Y, the ratio of the slope of the straight line B to the slope of the straight line A, and the slope of the straight line C. Remember the ratio of the slope of line B,
The half bridge circuit that is not judged to be abnormal,
For example, in the half bridge circuit 50a of FIG. 1B, the changeover switches 70 and 74 are changed over to output the output Y
Y1 is converted into the output of the full-bridge circuit 50 using the difference between the output of 1 and the output of Y1 and Y at the zero point and the ratio of the inclination of the straight line A to the inclination of the straight line A. Similarly, if the half-bridge circuit that is not determined to be abnormal is the half-bridge circuit 50c of FIG. 1C, its outputs Y2 and Y2 are output.
Using the difference in output at the zero point between Y and Y and the ratio of the slope of the straight line B to the slope of the straight line C, Y2 is set to the full bridge circuit
Convert to 0 output.

When the comparison means 78a determines that there is no failure, the output of the full bridge circuit 50 is also set to A /
The digital data converted by the D converter 76 is supplied to the measurement data output circuit 80, and when it is determined that there is a failure, the output of the conversion means 78d is supplied to the measurement data output circuit 80 thereafter. In the measurement data processing circuit 80, the signal from the A / D converter 76 or the conversion means 78
The signal from d is displayed on a display device or printed by a printer.

FIG. 4 shows a fault diagnosis alarm and self-recovery circuit 7.
8. The operation of the measurement data output circuit 80 is shown in a flowchart. First, a normal measurement operation is performed (step S
10). That is, the detected voltage from the full-bridge circuit 50 is converted into a digital signal by the A / D converter 76 and displayed on a display device or printed by a printer. Following this, it is judged whether or not a signal indicating the zero point is supplied from the zero point measuring means 82 (step S12). If it is not the zero point, the process returns to step S10 and the normal measurement operation is performed.

If it is zero (YES in step S12), the changeover switches 70 and 74 are changed over so that the detection output from the half bridge circuit 50a of FIG. 1B is supplied to the A / D converter 76. The digital signal of the A / D converter 76 is read, and the changeover switches 70 and 74 are switched so that the detection output from the half bridge circuit 50c of FIG. 1C is supplied to the A / D converter 76. The digital signal of the / D converter 76 is read (step S14).

Then, it is judged whether or not the signal indicating the zero point is still supplied from the zero point measuring means 82 (step S16). If there is no signal indicating the zero point (No in step S16), step S1
Force or load is applied during execution of step 4, step S14
Since it is uncertain whether the value read in step 1 is truly reading the output at the zero point, the process returns to step S10 and the normal measurement operation is performed.

When the output at the true zero point is read (Yes in step S16), the digital signal output from the half bridge circuit 50a in FIG. 1 (b) is within the corresponding allowable range of 3 ± 1 mV. And the digital signal at the output of the half bridge circuit 50c of FIG.
It is determined whether or not it is within the range of the allowable value −3 ± 1 mV corresponding to this (step S18). If all the outputs are within the permissible values (No in step S18), since no deterioration has occurred, the process returns to step S10 and the normal measurement operation is performed.

When any of the outputs deviates from the corresponding allowable value (Yes in step S18), a sensor error alarm is output, and thereafter, the normal half bridge circuit detection output is the A / D converter 76. The changeover switches 70 and 74 are switched so as to be supplied to (step S2
0).

When a force or a load is applied, the digital value of the normal detection output of the half bridge circuit at that time is converted into the output of the full bridge circuit 50 by the conversion operation as described above (step S22). ). Therefore, until the sensor is replaced, the force or load is detected in step S22.

In the above embodiment, the full bridge circuit 5
0, the outputs of the half-bridge circuits 50a and 50c are linearly related to the force or the load, but they are not necessarily linearly related. For example, when the output to the force or the load is represented by a quadratic equation. There is also. In such a case, it is necessary to change the conversion formula used in the conversion means 78d.

In the above embodiment, the output of each half bridge circuit 50a, 50c at the zero point is compared with the allowable value. However, the half bridge circuit in the state where a certain force or load is applied in addition to the zero point. The allowable values of the outputs of 50a and 50c are stored in the storage unit 78a, and the half bridge circuit 50 in a state where a specific force or load is applied.
The outputs of a and 50c may be compared with the allowable value.

In the above embodiment, it is assumed that the zero point can always be detected. However, when it is used as a load sensor in a device such as a hopper scale in which articles to be weighed are always housed. , It is impossible to detect the zero point. In such a case, the procedure is as follows.

That is, the storage means 74 stores the allowable values such as the constants and gradient coefficients of the relational expressions for the output force or load of the full bridge circuit 50 and the half bridge circuits 50a and 50c.
When the load of the hopper scale is not changed, it is detected and the outputs of the full bridge circuit 50 and the half bridge circuits 50a and 50b at that time are read.

This operation is repeated several times, and when the load is small, the load is medium, and the output when it is large is read a plurality of times, the average output when the load is small, the average output when the load is intermediate, and the average output when the load is small. Obtain the average output when it is large, and based on these average outputs, the full bridge circuit 5
0, the relational expression with respect to the output force or load of the half bridge circuits 50a and 50c is obtained, and the constants and coefficients of this relational expression are calculated.

Whether these are within the permissible values of the corresponding constants and coefficients stored in the storage means 78a is compared with the comparison means 78b.
In this case, since the zero point is not known, only the change in the proportional constant of the equation will be seen. Therefore, even if the abnormality is known, it is not possible to determine which half bridge is abnormal, but it is possible to issue an alarm indicating that it is abnormal.

Further, in the above embodiment, the full bridge circuit 50 has one strain gauge on one side, but a full bridge circuit using a plurality of strain gauges on one side can be used. .. Further, in the above-mentioned embodiment, the strain gauge of the electric resistance wire type is used, but the strain gauge of the semiconductor strain gauge type can also be used.

[0046]

As described above, according to the present invention, when the force or load detecting sensor is divided into two sets of detecting means, it is almost the case that the two sets of detecting means are deteriorated equally at the same time. By utilizing the fact that there is no gradual deterioration, if any of the detection means is deteriorated, the user is informed that a failure is occurring. By replacing the, it is possible to prevent erroneous measurement from being performed for a long time. Further, according to the present invention, when it is determined that one of the detection means is abnormal, the output of another normal detection means can be converted into the original output of the force or load detection sensor by the conversion means. Therefore, it is possible to prevent the transaction or the production line from being stopped until the user replaces the force or load detection sensor.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a failure diagnosis device and a self-recovery device for a force or load detection sensor according to the present invention.

FIG. 2 is a diagram showing a change state of output with respect to an applied force or a load in a normal state of a full bridge circuit 50 and half bridge circuits 50a and 50c in the embodiment.

FIG. 3 is a half bridge circuit 50a according to the embodiment.
It is a figure which shows the change state of the output with respect to the applied force or load of the full bridge circuit 50 and the half bridge circuits 50a and 50c, when abnormality generate | occur | produces in either of 50c.

FIG. 4 is a flowchart of the same embodiment.

FIG. 5 is a diagram showing a usage state of a conventional force or load detection sensor.

FIG. 6 is a block diagram of a conventional force or load detection sensor.

[Explanation of symbols]

 50 Full Bridge Circuit 50a 50c Half Bridge Circuit 64 66 Dummy Resistor 70 74 Changeover Switch 78a Storage Means 78b Comparison Means 78c Warning Means 78d Conversion Means

Claims (5)

[Claims] 1. A force or load detection sensor configured to be separable into two sets of force or load detection means, and a separation means for separating the load detection sensor into the two sets of detection means.
Storage means for storing an allowable value determined based on outputs of the two sets of detection means in a specific state during normal operation of the detection sensor; and the detection sensor by the separation means in the two sets of detection means. Either of the outputs of the two sets of detection means when separated and brought into the specific state is
A failure diagnosing device for a force or load detection sensor, comprising: comparing means for comparing whether or not the allowable values respectively corresponding to these are exceeded. 2. The force or load detection sensor failure diagnosing device according to claim 1, wherein the comparing means causes one of the outputs of the two sets of detecting means to exceed the permissible value corresponding thereto. A failure diagnosing device for a force or load detection sensor, which is provided with an alarming device which is activated when it is determined that the force or load is detected. 3. The failure diagnosis device for a force or load detection sensor according to claim 1, wherein the specific state is a state in which no force or load is applied. .. 4. The force or load detection sensor failure diagnosis device according to claim 1, 2 or 3, wherein one of the two sets of detection means determines that the corresponding allowable value is exceeded. A failure self-recovery device for a load detection sensor, comprising conversion means for converting an output from the other of the two sets of detection means into an output of the load sensor. 5. A force or load detection sensor configured to be separable into two sets of force or load detection means, and a separation means for separating the load detection sensor into the two sets of detection means.
The permissible value of the relational expression with respect to the force or load of the output of each of the detection means, which is determined based on the output of each of the two sets of detection means at the time of normal operation of the detection sensor when different forces or loads are applied, is stored. The storage means and the detection sensor are separated into the two sets of detection means by the separation means, and a relational expression with respect to the force or load of the output of the two sets of detection means is obtained. A failure diagnosing device for a force or load detecting sensor, comprising: comparing means for comparing whether or not the corresponding allowable values are exceeded.