JPS6341005B2 - - Google Patents

Description

Detailed Description of the Invention (1) Technical Field of the Invention The present invention relates to a load cell scale using a plurality of load cells.

(2) Conventional technology and its problems Conventionally, this type of load cell type scales connected the output terminals of multiple load cells in parallel to take out the load cell output. There was a problem that each load cell could not be used efficiently because the number of load cells was reduced to approximately one-fold of the number of load cells.

Therefore, the inventors have found that by taking out each load cell output through a buffer amplifier and then adding them together in an adder, it is possible to take out each load cell output without decreasing it and to utilize each load cell efficiently. It was clarified.

However, in this case, there is a problem that the influence of the offset voltage of the buffer amplifier and the adder on the measured value cannot be ignored.

(3) Purpose of the Invention This invention enables the output of multiple load cells to be taken out without reduction, allowing each load cell to be used efficiently, and moreover, preventing the effects of offset voltages of amplifiers and adders, thereby enabling accurate measurement. The purpose is to provide a load cell type scale.

(4) Structure of the Invention The present invention connects a plurality of load cells to a DC power supply via a switch element, and amplifies the output of each load cell with a plurality of buffer amplifiers and adds them together with an adder. Connect an analog switch via a capacitor between the output terminals of
The above switch element and analog switch are controlled ON and OFF alternately for a certain period of time by the switch control circuit, and when the analog switch is OFF, the adder output is input to the A/D converter via the capacitor and counted by the A/D converter. This is converted into data, and then converted into data in weight units using an arithmetic circuit.

(5) Embodiments of the invention In Fig. 1, 1, 2, 3, and 4 are load cells each having a Roberval mechanism, and each load cell 1, 2, 3, and 4 has a strain gauge attached to each side at four locations. It constitutes a four-sided resistance bridge. Each of the load cells 1, 2, 3, and 4 is attached to, for example, the four corners of the base of the device body, and a tray is placed on top of the load cells. Each of the load cells 1, 2, 3, and 4 has one opposing contact in the bridge connected to the positive terminal of a battery 5 as a DC power source, and the other connected to the battery via a phototransistor 6Tr of a photocoupler 6 as a switch element. It is connected to the negative terminal of No.5. The load cells 1, 2, 3, and 4 have one of the other opposing contacts in the bridge connected to the input terminals of the buffer amplifiers 7, 8, 9, and 10, respectively, and the other is grounded. each of the slow amplifiers 7;
8, 9, and 10 have their output terminals connected to each input terminal of the adder 11, respectively. The adder 11
is four variable resistors 12, 13, 14, 15 and 1
operational amplifiers 16 are provided, and each of the variable resistors 1
One ends of the buffer amplifiers 2, 13, 14, and 15 are connected as input terminals to the output terminals of the buffer amplifiers 7, 8, 9, and 10, respectively, and the other ends are connected to the inverting input terminal of the operational amplifier 16. The operational amplifier 16 has its non-inverting input terminal (+) grounded and its output terminal connected via a resistor 17 to its own inverting input terminal (-). The adder 11 uses the output terminal of the operational amplifier 16 as an output terminal, and a resistor 18 and a capacitor 19 are connected between the output terminal and the ground.
The analog switch 20 is connected in series with the analog switch 20. The capacitor 19 and analog switch 2
0 is connected to the non-inverting input terminal (+) of the operational amplifier 21.

Further, a reference voltage generator 22 is connected to the battery 5. The reference voltage generator 22 consists of two buffer amplifiers 23 and 24, one differential amplifier 25, and a series circuit of a resistor 26, a potentiometer 27, and a resistor 28, and the non-inverting input terminal ( +) is connected to the positive terminal of the battery 5, and the non-inverting input terminal (+) of the buffer amplifier 24 is connected to the negative terminal of the battery 5. The output terminal of the buffer amplifier 23 is connected to the non-inverting input terminal (+) of the differential amplifier 25 via a resistor 29, and further connected to a resistor 30.
It is grounded through. The output terminal of the buffer amplifier 24 is connected to the inverting input terminal (-) of the differential amplifier 25 via a resistor 31. The output terminal of the differential amplifier 25 is connected to its own inverting input terminal (-) via a resistor 32, and the resistor 2
6. Grounded via a series circuit of a potentiometer 27 and a resistor 28. The reference voltage generator 2
2 uses the movable terminal of the potentiometer 27 as an output terminal, and applies a reference voltage generated from the output terminal to the A/D converter 33 and to the zero point setting circuit 34. The zero point setting circuit 34 includes two buffer amplifiers 35 and 36 and a resistor 3.
7, a potentiometer 38, and a resistor 39 in series, and inputs a reference voltage to the input terminal of a buffer amplifier 35. The buffer amplifier 35 has its output terminal grounded through a series circuit of a resistor 37, a potentiometer 38, and a resistor 39. The buffer amplifier 36 has its non-inverting input terminal (+) connected to the movable terminal of the potentiometer 38, and its output terminal connected to the inverting input terminal (-) of the operational amplifier 21 via a resistor 40. .
The operational amplifier 21 has a resistor 41 connected between its output terminal and its inverting input terminal (-).

The operational amplifier 21 inputs its output to the input terminal of the A/D converter 33 via a low-pass filter 42. The A/D converter 3
3 is of a double integral type, for example, and by using the reference voltage from the reference voltage generator 22, the voltage signal inputted from the operational amplifier 21 via the low-pass filter 42 is converted into count data according to its level. I try to do that. Said A/D
The count data output from the converter 33 is taken into a control device 44 incorporating an arithmetic circuit 43. The control device 44 receives count data from the A/D converter 33, operates the arithmetic circuit 43, and calculates a predetermined minimum scale value.
Based on the relationship of Xg=Y count, the count data Z is converted to weight data in grams by calculating Z/Y.X, and the weight data is displayed on the display 45. The light emitting diode 6D of the photocoupler 6 and the analog switch 20 are operated at predetermined timing by a switch control circuit 46. That is, the switch control circuit 46 turns on the light emitting diode 6D for a certain period of time at the timing shown in FIG. 2A, and turns on the analog switch 20 for a certain period of time at the timing shown in FIG. 2B. Note that 47 is a keyboard, and this keyboard 47 is provided with keys for determining the zero point, keys for taring, and the like.

In the embodiment of the present invention configured in this way, each load cell 1, 2, 3, 4 detects the load on the tray by dividing the load. The switch control circuit 46 controls the light emitting diode 6D of the photocoupler 6 at timings T ₂ , T ₄ ,
. . . is turned on for a certain period of time, and the analog switch 20 is turned on at timings T ₁ , T 3 , and T ₃ shown in FIG.
T ₅ , ... turns on for a certain period of time. However, at timings T ₁ , T ₃ , T ₅ , ..., each load cell 1, 2, 3, 4 is not connected to the battery 5, so no output is generated from each load cell 1, 2, 3, 4. . On the other hand, since the analog switch 20 is turned on at this timing, one end of the capacitor 19 is grounded. Therefore, when an offset voltage is generated at the output terminal of each of the buffer amplifiers 7, 8, 9, and 10, the offset voltage is added in the adder 11, and the offset voltage of the operational amplifier 21 of the adder 11 is also added to the output terminal of the adder 11. and is stored in the capacitor 19.
Also, at timings T ₂ , T ₄ , ..., the photocoupler 6 is turned on and each load cell 1, 2, 3,
4 is connected to battery 5. On the other hand, the analog switch 20 is turned OFF, and one end of the capacitor 19 is disconnected from the ground. In this state, each load cell 1, 2, 3, 4 outputs a voltage corresponding to the respective load, and the buffer amplifier 7, 8,
The signals are amplified by 9 and 10, added by an adder 11, and input to an operational amplifier 21 via a capacitor 19. At this time, the offset voltage applied to the output of the adder 11 is canceled by the offset voltage stored in the capacitor 19, and the offset voltage is applied to the output of the operational amplifier 2.
Only voltage signals corresponding to the output voltages of the load cells 1, 2, 3, and 4 are inputted to the load cells 1. Then, in the operational amplifier 21, the adder 11
The input voltage from the zero point setting circuit 34 is subtracted from the input voltage from the zero point setting circuit 34, and is input as a load output voltage to the A/D converter 33 via the low-pass filter 42. It operates and converts the input voltage into count data. This count data is then taken into the control device 44, converted into weight data in grams by the arithmetic circuit 43, and displayed on the evaluator 45.
In this way, the weight in grams corresponding to the load is displayed.

Each buffer amplifier 7, 8, 9, 1 in this operation
The canceling of the offset voltage in the adder 11 and the offset voltage in the adder 11 will be explained in detail. Each buffer amplifier 7, 8,
The offset voltages of 9 and 10 are respectively ν _ps1 , ν _ps2 ,
ν _ps3 and ν _ps4 , the offset voltage of the operational amplifier 16 of the adder 11 is ν _ps5 , and each variable resistor 12,
The resistance values of 13, 14, and 15 are R ₁₂ , R ₁₃ , R ₁₄ ,
If R ₁₅ and the resistance value of the resistor 17 are R ₁₇ , the adder 1 at timings T ₁ , T ₃ , T ₅ , ...
The output E ₅₍₁₎ of 1 is E ₅₍₁₎ = R ₁₇ /R ₁₂・ν _ps1 +R ₁₇ /R ₁₃・v _ps2 +R ₁₇ /R ₁₄・ν _ps3 +R ₁₇ /R ₁₅・ν _ps4 +ν _ps ...
... becomes. Here, ν _ps5 is ν _ps5 = R ₁₇ /R ₁₂・ν′ _ps5 +R ₁₇ /R ₁₃・ν′ _ps5 +R ₁₇ /R ₁₄・ν _ps5 +R ₁₇ /R ₁₅・ν′ _ps5 …
..., so the above equation ends up being E ₅₍₁₎ = R ₁₇ /R ₁₂ (ν _ps1 + ν′ _ps5 ) +R ₁₇ /R ₁₃ (ν _ps2 +ν′ _ps5 ) + R ₁₇ /R ₁₄ (ν _ps3
+ν′ _ps5 )+ R ₁₇ /R ₁₅ (ν _ps4 +ν′ _ps5 )... This E ₅₍₁₎ is then stored in the capacitor 19.

Also, the output of each load cell 1, 2, 3, 4
Assuming E ₁ , E ₂ , E ₃ , E ₄ , timing T ₂ , T ₄ ,...
The output E ₅₍₂₎ of the adder 11 at ... is E ₅₍₂₎ = R ₁₇ /R ₁₂ (ν _ps1 + ν′ _ps5 +E ₁ ) +R ₁₇ /R ₁₃ (ν _ps2 +ν′ _ps5 +E ₂ ) +R ₁₇ / R ₁₄ (ν _ps3 + ν′ _ps5 + E ₃ ) + R ₁₇ /R ₁₅ (ν _ps4 + ν′ _ps5 + E ₄ )... Therefore, the voltage V _io input to the operational amplifier 21 is V _io =E ₅₍₂₎ −E ₅₍₁₎ =R ₁₇ /R ₁₂・E ₁ +R ₁₇ /R ₁₃・E ₂ +R ₁₇ /R ₁₄・E ₃ +R ₁₇ /R ₁₅・E ₄ ..., and the offset voltage is canceled.

Therefore, the resistance values of resistors 40 and 41 are R ₄₀ ,
When R ₄₁ and the output of the zero point setting circuit 34 are E ₆ , the output V _put of the operational amplifier 21 is V _put = (1 + R ₄₁ /R ₄₀ ) (R ₁₇ /R ₁₂・E ₁ +R ₁₇ /R ₁₃・
E ₂ +R ₁₇ /R ₁₄・E ₃ +R ₁₇ /R ₁₅・E ₄ )−R ₄₁ /R ₄₀・E ₆ …
... becomes. And this V _put is A/D converter 33
It will be converted into count data by .

In this way, the output of each load cell 1, 2, 3, 4
E ₁ , E ₂ , E ₃ , and E ₄ are utilized without being reduced, and each load cell can be used efficiently. Further, the offset voltages of each buffer amplifier 7, 8, 9, 10 and the offset voltage of adder 11 can be canceled, allowing accurate measurement corresponding to the load.

In the above embodiment, four load cells were used, but the present invention is not limited to this, and it is sufficient to use a plurality of load cells.

Further, in the above embodiment, a photocoupler was used as the switch element, but it is needless to say that the present invention is not limited to this.

(6) Effects of the Invention According to the present invention, in a device using a plurality of load cells, the output of each load cell can be taken out without decreasing, so each load cell can be used efficiently. It is possible to provide a load cell type scale that can perform accurate weighing because the offset voltage of the weighing device can be canceled.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of this invention, Fig. 2 is a circuit diagram showing an embodiment of the present invention;
The figure is a waveform diagram showing the operation timing of each part in the same embodiment. 1, 2, 3, 4...Load cell, 5...Battery, 6...Photocoupler, 7, 8, 9, 10...
Buffer amplifier, 11...Adder, 19...Capacitor, 20...Analog switch, 33...A/D
Converter, 43... Arithmetic circuit, 44... Control device, 46... Switch control circuit.

Claims (1)

[Claims] 1. A DC power supply, multiple load cells each connected to this power supply via a switch element and outputting a voltage according to the load, multiple buffer amplifiers that amplify each of these load cell outputs, and the summation of each amplifier output. an analog switch connected between the output terminals of the adder via a capacitor, a switch control circuit that alternately controls ON/OFF of the switch element and the analog switch for a fixed period of time;
An A/D converter that receives the output of the adder via the capacitor when OFF and outputs count data corresponding to the input level; and an arithmetic circuit that receives the output of the A/D converter and obtains data in weight units. A load cell scale characterized by comprising: