JP2000199723A - Apparatus and method for measurement of load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a load measuring apparatus, whose basic constitution is simple, which can be miniaturized and which is easily made low-cost, and to obtain a load measuring method. SOLUTION: A sensor S1 detects a load amount as a capacitance value. A Wien bridge circuit is formed by containing the sensor S1. Thereby, a load detector 1 is constituted. The load detector 1 and an oacillation circuit 2 constitute a Wien-bridge oscillation circuit. An oscillation frequency is changed according to the change in a load amount. The change numerical value of the oscillation frequency is counted. The magnitude of a load is measured by a measuring circuit 4. With this constitution, a drive power supply which is supplied to the load detector, an amplifier which amplifies a detection signal, an A/D converter which converts an analog signal into a digital signal and the like are not required in order to measure the load. Thereby, the constitution of this load measuring apparatus is simplified, the apparatus can be miniaturized, and the apparatus can be made low-cost. Especially, the load measuring apparatus whose high accuracy is not required can be miniaturized easily, and the apparatus can easily be made low-cost, and high mass-production effect of the apparatus can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load measuring device and a load measuring method, and more particularly to a load measuring device and a load measuring method which can simplify a circuit configuration and can be easily reduced in size and mass during mass production.

[0002]

2. Description of the Related Art Conventionally, a load measuring device and a load measuring method generally comprise a load detector and a load measuring device. These load detectors receive a load to be measured, and detect and output an electric signal corresponding to the received load amount. The load measuring device receives an electric signal output from the load detector and performs processing such as signal amplification, A / D conversion, and load display.

FIG. 3 shows an example of a block configuration of a conventional load measuring device. In FIG. 3, the load detector 11 of the conventional load measuring device is constituted by a Wheatstone bridge. This Wheatstone bridge has two sensors S11 and S12 and two dummy D11 and D12.
And form a bridge circuit.

The load measuring device includes a driving power supply 12 for driving the load detector, an amplifier (AMP) 13 for amplifying an output signal output from the load detector 11, and a digital signal for converting the analog signal amplified by the amplifier 13 into a digital signal. A / D to convert to
It comprises a converter 14, a display 15 for displaying a detected load value, and a control unit 16 for controlling various operations of the system.

[0005] In the components of the load measuring device constructed as described above, the sensors S11 and S12 are, for example, strain gauges whose resistance value changes due to expansion or contraction, or capacitor type sensors whose capacitance value changes due to a change in the distance between the two poles. A sensor or the like is used. As the drive power supply 12 of the load measuring device 11, a DC or AC type constant voltage power supply is generally used.

[0006] The load measuring device having the above configuration can obtain high accuracy such as an error rate of 0.1% FS (full scale) or less. In order to obtain such a high-precision measurement accuracy, processing such as using a drive power supply having an accuracy equal to or higher than a desired error rate or correcting a measured value according to a change in the output voltage of the drive power supply is performed.

As described above, since a highly accurate load measuring device can be easily obtained, the above-described conventional measuring system measures static load, dynamic load, pressure, impact force, etc., and is particularly used as an industrial load measuring device. Widely used.

[0008]

However, the above-mentioned conventional load measuring device can form a high-precision measuring system as described above, but has a load detector driving power supply, an amplifier (AMP), and an A / A. A D converter and the like are required, and the basic configuration of the device is complicated. In other words, in the conventional load measuring device, a driving power supply for driving the load detector, an amplifier (AMP) for amplifying a weak analog measurement signal measured by the load detector, and an amplifier for configuring a complete measuring system are provided. A that converts the analog measurement signal into a digital measurement signal
A / D converter and the like are indispensable.

In this basic configuration, in particular, an analog circuit and a digital circuit, a power supply for driving a load detector that requires higher precision, and a power supply for driving the analog circuit and the digital circuit are required. IC circuitization,
It is a configuration that makes it difficult to integrate it into a single chip and integrate circuits. Although it is not so difficult to reduce the power consumption of the control circuit, there is a restriction that the power supply capacity of the power supply for driving the load detector must satisfy the required capacity of the load detector.

Therefore, there is a limit in simplifying the circuit configuration and circuit scale of the device, and it is difficult to simply configure the device. In particular, there is a problem that a limit is imposed on a simple load measuring device, for example, a load meter and a weight scale used for cooking in a general household, a reduction in size of a load meter that requires carrying, and the like. In addition, a detection device such as a bench balance using an industrial load converter is heavy equipment, and the emergence of a light equipment detection device is desired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a load measuring device and a load measuring method which have a simple basic structure and are easy to reduce in size and cost.

[0012]

In order to achieve the above object, a load measuring device according to the first aspect of the present invention includes a load detector that changes a predetermined value according to the magnitude of a load, and a load detector. An oscillation circuit that is connected to the oscillator and changes the oscillation frequency in accordance with a change in a predetermined value; and a measurement circuit that counts the change value of the oscillation frequency and measures the magnitude of the load. Features.

The above-mentioned predetermined value is a value including at least one of a resistance value, an inductance value and a capacitance value, and this value becomes an oscillation element of the oscillator. Alternatively, it is an LR oscillator, and the oscillation circuit has a differential amplifier, and the differential amplifier and the load detector may be configured as a Wien bridge oscillator.

Further, the load detector is a capacitance type detector, and the detectors are laminated at least in two layers in the direction of applying a load, and the capacitances of the laminated layers are parallel. And connected to the oscillation circuit.

According to a sixth aspect of the present invention, there is provided a load measuring method comprising: a load detecting step of changing a predetermined value according to a magnitude of a load; and an oscillating step of changing an oscillation frequency according to a change of the predetermined value. And a measuring step of counting the change value of the oscillation frequency to measure the magnitude of the applied load.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a load measuring apparatus and a load measuring method according to the present invention. Referring to FIG. 1, FIG. 2 and FIGS. 4 to 6, there is shown an embodiment for explaining the configuration of a load measuring device and a load measuring method of the present invention.

FIG. 1 shows an example of a block configuration of the load measuring device according to the present embodiment. 1, the load measuring device of the present embodiment includes a load detector 1, an oscillation circuit 2, a display 3, and a measurement circuit 4.

The load detector 1 is configured as a bridge circuit with one sensor S1 and three dummys D1, D2 and D3. This bridge circuit is more specifically configured, for example, as a Wien bridge circuit. Also, the sensor S1
A capacitor type that detects a load as a change in capacitance, a resistance gauge type that detects a change in resistance value, or the like is used. When the load detector 1 and the oscillation circuit 2 are configured as a Wien bridge oscillator, the oscillation circuit 2
The oscillation frequency f of the output signal output from is as follows.

F∝1 / (S 1 · D 1 · D 2 · D 3) ^1/2 (1)

In the above equation, the impedance of the sensor S1 is made variable according to the load W received by the sensor S1, and the impedance of the dummy D1, D2, D3 is made constant regardless of the load W received by the sensor S1.

From the oscillation circuit 2 having the above structure, based on the equation (1), an output signal whose oscillation frequency f changes in accordance with the load received by the load detector 1, more precisely, the load W received by the sensor S1. Can be obtained. Therefore, the fluctuation value Δf of the oscillation frequency f from the predetermined value f1 to the predetermined value f2 can be converted into the load amount W based on a predetermined procedure exemplified below.

The above-described procedure includes, for example, at least three types of load amounts W1, W2, and W3 applied to the sensor S1.
And the frequencies f1, f2, and f3 obtained as a result of the load application, or may be configured as a conversion table format of the load amount W versus the transmission frequency f. In the case of the latter conversion table format, the adjacent load interval ΔW forming the table is determined according to the magnitude of the non-linearity of the oscillation frequency f. It is also possible to use a proportional calculation.

In FIG. 2, a sensor S1 constituting the load detector 1 is a specific example of a structure in which the distance d between two flat plate electrodes 5a and 5b varies.
The sensor is of the capacitance change type. 2 poles 5 of this sensor S1
a and 5b are mutually flat plates having an area A,
A spring material 6 is sandwiched between the two poles 5a and 5b, and the distance between the two poles 5a and 5b is changed according to the load W applied to the surface of the plate constituting the two poles 5a and 5b. The structure is such that d changes.

As the material of the spring material 6, a material which is deformed by the load W, changes the distance d, and has high repeatability and restorability is required. Further, a material that is electrically non-conductive is preferable. For example, rubber, resin, reinforced glass fiber processed into a spring shape, or the like. When copper, iron, or the like is used, it is necessary to insulate between the two electrodes.

The capacitance value C [F] of the load detector having the above configuration.
Is obtained by the following equation (2). In the following formula, the symbol A is the surface area [m2] of the plates constituting the two poles 5a and 5b, and d is the distance [m] between the plates of the two poles 5a and 5b.

C∝A / d (2)

The above relationship will be examined more specifically. The sensor S1 is a 10 cm square plate and the distance between the two poles is 10
mm and configured as an air condenser. The capacitance of the sensor S1 is approximately 10 [pF].

When a Wien bridge oscillator is formed by using two 10 pF capacitors and two 10 K ohm resistors, a high-frequency signal having an oscillation frequency of about 1.6 [MHz] can be obtained. This Wien bridge oscillator is configured to include, for example, a differential amplifier. In this configuration,
It is assumed that the load converter 1 of 10 pF fluctuates to 20 pF at the time of rated load when there is no load. The fluctuation of the oscillation frequency value under this condition changes from 1.6 MHz under no load heavy to 2.4 MHz or 3.2 MHz under rated load. In this case, 2.4 MHz is a case where the capacitance C of one side of the bridge is changed, and 3.2 MHz is a case where the capacitance C of two sides of the bridge is changed.
Is changed.

This relationship is based on the above equations (1) and (2). The relationship between the values of these signs in the sensor S1 and the dummy D1 to D3 is as follows: S1 = D1
(Or S2) = 10 pF, D2 = D3 = 10K ohm. It should be noted that the above can be detected in the same manner as above when the resistance is changed according to the load amount and the dummy is configured as a fixed capacitance.

In the load measuring device configured as described above,
The load W applied to the sensor S1 is converted into an oscillation signal of a predetermined frequency f by the oscillation circuit 2.

The measuring circuit 4 receives the oscillation signal, converts the signal into a pulse signal using a limiter, a comparator, and the like, and counts the frequency f of the oscillation signal. By measuring the frequency Δf of the difference between the frequency f0 when no load is applied to the sensor S1 and the frequency f1 at the time when the load W is applied, and converting the measured difference frequency Δf into a value corresponding to the load amount, Load amount W
Can be obtained.

The display 3 is a digital display such as an LCD, and displays a measured value from the measuring circuit 4. A signal at the time of no load is input by an operation switch (not shown) to perform zero point correction and display “0”, and a load measurement value “W” at the time of applying a load to the sensor S1 can be read. However, the switch for zero point correction is an automatic correction by tracking, and may be unnecessary or supplementary.

According to the above embodiment, a dedicated power supply for driving the load detector or the load sensor is not required. Further, since the load detection signal is a transmission signal, an A / D converter is not required for digital signal conversion. Further, the entire power supply for load detection, measurement, and control can be configured by one power supply. The load measurement system of the present embodiment based on the above requirements has a simple system configuration.
For this reason, it is easy to integrate the circuits, and higher cost reduction can be expected as a mass production effect. Specific examples will be described in detail below.

(Embodiment 1) FIG. 4 is a block diagram showing an example of the system configuration of Embodiment 1 of the load measuring device. In FIG. 4, the load measuring device according to the first embodiment includes a capacitance type load detector 10, an oscillation circuit 20 including a capacitor capacitance amplification circuit 21 and an astable vibrator 22, a display 30, and a measurement circuit 40. You. In this configuration,
The capacitor capacitance amplification circuit 21 of the oscillation circuit 20 is provided to obtain a more stable oscillation output from the astable vibrator 22.
Is used when the capacitance value is small. Therefore, it is unnecessary when the capacitance value of the capacitive load detector 10 is large and the oscillation signal is stable with respect to the required accuracy.

FIG. 5 is a side sectional view showing a configuration example of the capacitive load detector 10. As shown in FIG. In FIG. 5, a capacitive load detector 10 applied to the first embodiment includes a loading plate 101, a base plate (minus plate) 102, an insulating plate 103, a plus plate 104, and a spring 105. Is done.

The base plate (minus electrode plate) 102 receives the load to be measured, constitutes the mechanical bottom surface of the capacitive load detector 10, and forms a capacitance measuring unit serving as a load measuring element. Construct an electrode plate.

The insulating plate 103 is an insulating plate for ensuring electrical insulation between the base plate (negative electrode plate) 102 and the positive electrode plate 104.

The positive electrode plate 104 is mechanically attached to the loading plate 101 via the insulating plate 103. The positive electrode plate 104 and the base plate (minus electrode plate) 102 form a capacitor of a capacitance measuring unit which becomes a load measuring element.

The spring 105 is provided between the loading plate 101 and the base plate (minus pole plate) 102, and
1 is compressed in accordance with the magnitude of the load applied to 1. Due to this compression / extension, the capacitance value serving as a load measuring element changes between large and small.

In the capacitive load detector 10 configured as described above, the loading plate 101 is a plate that receives a load to be measured.
For example, an object to be measured is loaded. The spring 105 is compressed according to the magnitude of the loaded load, and the capacitance value serving as a load measuring element changes.

FIG. 6 is a circuit diagram showing a detailed oscillation circuit 20, showing an example of the configuration of the capacitor capacitance amplifier circuit 21 and the astable vibrator 22. In the oscillation circuit of FIG. 6, the base plate (minus plate) 102 and the plus plate 104 of the capacitive load detector 10 are connected to the input terminal SENS IN, and the output terminal PULS OUT
Is connected to the measurement circuit 40. Base plate (minus plate) 102 and positive plate 10 of capacitive load detector 10
The frequency of the oscillation signal output from the astable vibrator 22 fluctuates in accordance with the magnitude of the capacitance value of the capacitance measurement unit formed by the step 4 and the capacitance measurement unit.

The measuring circuit 40 includes, for example, a central processing circuit (CPU) (not shown). The central processing circuit (CPU) counts the frequency of the oscillation signal output from the oscillation circuit 20, and converts the count number counted by the counter function unit into a load value in a predetermined procedure. An arithmetic function unit and an output unit that outputs the load value calculated by the arithmetic function unit are provided. The display unit 3 based on a signal output from the central processing circuit (CPU)
0 indicates the measured load value.

In the above load measurement, in order to obtain higher measurement accuracy, it is necessary to ensure a more stable oscillation operation at a higher oscillation frequency in the oscillation circuit 20. To stabilize the oscillation, it is one measure to increase the capacitance signal of the capacitive load detector 10 by the capacitor capacitance amplifier circuit 21, but this is a secondary stabilization measure. The direct and temporary stabilization measures further increase the output signal of the capacitive load detector 10 with respect to the load,
The purpose is to increase the output sensitivity of the capacitive load detector 10.

In order to increase the sensitivity of the capacitive load detector 10, the amount of change of the output signal with respect to the applied load is increased, that is, the dynamic range is expanded, and the output value is increased, that is, the output signal is increased. There is. First, the structural requirements for improving the sensitivity of the capacitive load detector 10 are to increase the capacitance value, that is, to increase the area of the electrode plates, and to reduce the distance d between the plus / minus electrode plates. That is. Second, the amount of change in the distance d between the electrode plates with respect to the applied load is increased.

The first requirement and the second requirement are mutually opposed, and cannot simply satisfy each of them. In addition, enlargement of the area of the electrode plate is achieved by the capacitive load detector 1.
With a mechanical increase of zero. Further, the increase in the amount of change in the distance d between the electrode plates is to reduce the rigidity of the spring 105, and this reduction in rigidity is accompanied by instability of the zero point and slow response. Confirmed by load test.

(Embodiment 2) FIG. 7 shows an embodiment in which the capacitive load detectors are configured as capacitive load detectors 10a and 10b having a two-layer structure. The capacitive load detectors 10a and 10b according to the second embodiment are intended to improve the mutually contradictory first and second requirements.

The two-layer capacitive load detector 10 according to the second embodiment.
In a and 10b, three pole plates are used in the load direction, and two capacitors “C” are configured as “C1 + C2”. By connecting these two capacitors “C1 + C2” in parallel, the load W is applied to each of the capacitors “C1 + C2”. The output of the capacitors C connected in parallel is the sum of the output signals of the respective capacitors “C1 + C2” corresponding to the load W, and is increased.

According to the above configuration, the capacitive load detector 1
A larger output signal can be obtained from 0a and 10b, a stable signal of a higher frequency is output from the oscillation circuit 20, and a high-precision measurement result is obtained by the measurement circuit 40. Although the second embodiment has a two-layer structure, it has been confirmed that a signal having a higher and stabilized frequency can be obtained from the oscillation circuit 20 if the number of layers is further increased. Reference data associated with these experiments are listed below.

The capacitance type load detectors 10a and 10b were set to the size of the effective electrode plate; approximately 100 × 150 mm, the thickness of the insulating plate;
3mm, electrode plate thickness; 0.5mm, free height of spring; 7m
m, the maximum gap displacement amount: about 2 mm, the number of layers: two poles, and a resolution of approximately 1/2000 was obtained. However, the circuit configuration is based on the value obtained by counting the output signal of the oscillation circuit 20 at a sampling interval of one second based on FIG.

According to the first and second embodiments, the load detector does not need to use a sensor component such as a strain gauge, a load cell (load converter), and the like. Further, the measurement circuit does not require a drive power supply for the load detector, an A / D converter for converting an analog signal into a digital signal, and the like. With a simpler configuration with these requirements, a highly accurate load measuring device can be obtained.

The number of stacked capacitive load detectors 10 is not limited to two. By increasing the number of poles, the obtained measurement accuracy is further improved for the reasons described above.

The above embodiment is an example of a preferred embodiment of the present invention. However, it is not limited to this.
Various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the sensor of the load detector is changed in capacitance value. However, in addition to the resistance value, the load value can be detected as a change in frequency, such as a change in the reactance (L) of the coil. Any may be used.

[0053]

As is clear from the above description, the load measuring device and the load measuring method of the present invention change a predetermined value in accordance with the magnitude of a load and oscillate in response to a change in the predetermined value. The frequency is changed, and the change value of the oscillation frequency is counted to measure the magnitude of the applied load. Since the load is measured by this configuration, a drive power supply for detecting the load, an amplifier for amplifying the detection signal, an A / D converter for converting an analog signal to a digital signal, and the like are not required. Therefore, the configuration is simplified, and the size and cost of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit configuration block diagram showing an embodiment of a load measuring device of the present invention.

FIG. 2 is a conceptual vertical sectional view showing a configuration example of a load detector.

FIG. 3 is a block diagram showing a circuit configuration example of a conventional load measuring device.

FIG. 4 is a circuit block diagram showing a first embodiment of the load measuring device.

FIG. 5 is a longitudinal sectional view illustrating a configuration example of a capacitive load detector according to the first embodiment.

FIG. 6 is a circuit diagram illustrating a configuration example of an oscillation circuit.

FIG. 7 is a diagram illustrating a configuration example of a two-layer capacitive load detector according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Load detector 2 Oscillation circuit 3 Display 4 Measurement circuit 5 Electrode 6 Spring material S1 Sensor D1, D2, D3 Dummy d Distance between two poles 10 Capacitive load detector 20 Oscillation circuit 21 Capacitor capacity amplification circuit 22 Unstable Vibrator 30 Indicator 40 Measurement circuit 101 Loading plate 102 Base plate (minus plate) 103 Insulating plate 104 Plus plate 105 Spring

Claims (6)

[Claims] A load detector configured to change a predetermined value according to a magnitude of a load; an oscillation circuit connected to the load detector and configured to change an oscillation frequency according to the change in the predetermined value; And a measuring circuit for counting a change value of the oscillation frequency to measure the magnitude of the applied load. 2. The apparatus according to claim 1, wherein the predetermined value is a value including at least one of a resistance value, an inductance value, and a capacitance value, and this value is an oscillation element of the oscillator. The load measuring device as described. 3. The load detector and the oscillating circuit include a CR.
The load measuring device according to claim 1, wherein the load measuring device is an oscillator or an LR oscillator. 4. The oscillation circuit according to claim 1, wherein the oscillation circuit has a differential amplifier, and is configured as a Wien bridge oscillator by the differential amplifier and the load detector. Load measuring device. 5. The load detector is a capacitance type detector, and the detectors are stacked in at least two layers in a direction in which the load is applied, and the capacitances of the stacked layers are parallel. 5. The load measuring device according to claim 1, wherein the load measuring device is connected to the oscillation circuit. 6. A load detecting step of changing a predetermined value according to a magnitude of a load, an oscillation step of changing an oscillation frequency according to the change of the predetermined value, and counting a change value of the oscillation frequency. And a measuring step of measuring the magnitude of the applied load.