JPH023450B2 - - 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) Prior art and its problems Conventionally, this type of load cell scale has the output terminals of multiple load cells connected in parallel to take out the load cell output, which is amplified by an amplifier and then converted to an A/D converter. A device that converts into count data is known, but such a device requires an A/D converter with a wide input-output conversion range, that is, one that can sufficiently digitally convert even high input voltages. However, there was a problem with poor economic efficiency. Furthermore, the amplifier used must have relatively high allowable input and output levels, which also poses the problem of poor economic efficiency.

(3) Purpose of the invention This invention is an input of an A/D converter used.
It is an object of the present invention to provide a load cell type scale that can narrow the output conversion area, keep the allowable input and output levels of the amplifier used low, and improve economic efficiency.

(4) Structure of the Invention This invention detects the load dividedly using a plurality of load cells, extracts the divided load output in a time-divisional manner by controlling a switch element, amplifies it with an amplifier, and sequentially converts it into digital data using an A/D converter. The weight data is obtained by converting the data and adding the digital data.

(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 a phototransistor 6Tr, 7 of a photocoupler 6, 7, 8, 9.
It is connected to the negative terminal of the battery 5 via Tr, 8Tr, and 9Tr. Further, the load cell 1,
2, 3, and 4 respectively connect one of the other opposing contacts in the bridge to the amplifier 1 via analog switches 10, 11, 12, and 13 as switch elements.
It is connected to the input terminal of No. 4, and the other end is grounded. The amplifier 14 includes an operational amplifier element 15 and resistors 16 and 17, and the operational amplifier element 1
The non-inverting input terminal (+) of No. 5 is used as an input terminal, and the resistor 16 is connected between the output terminal of the operational amplifier element 15 and the inverting input terminal (-).

Further, a reference voltage generation circuit 18 is connected to the battery 5.
are connected. The reference voltage generating circuit 18 is composed of a series circuit of buffer amplifiers 19 and 20, a differential amplifier 21, a resistor 22, a variable resistor 23, and a resistor 24, and the non-inverting input terminal (+) of the buffer amplifier 19 is connected to the positive terminal of the battery 5. The non-inverting input terminal (+) of the buffer amplifier 20 is connected to the negative terminal of the battery 5. The output terminal of the buffer amplifier 19 is connected to the non-inverting input terminal (+) of the differential amplifier 21 via a resistor 25 and is further grounded via a resistor 26. The output terminal of the buffer amplifier 20 is connected to the differential amplifier 21 via a resistor 27.
Connected to the inverting input terminal (-) of the The output terminal of the differential amplifier 21 is connected to its own inverting input terminal (-) via a resistor 28, and is grounded via the resistor 22, variable resistor 23, and resistor 24 in series. The movable terminal of the variable resistor 23 is used as the output terminal of the reference voltage generating circuit 18. A reference voltage outputted from the output terminal of the reference voltage generation circuit 18, that is, the movable terminal of the variable resistor 23 is supplied to the A/D converter 29 and also to the zero point setting circuit 30. The zero point setting circuit 30 consists of a series circuit of buffer amplifiers 31, 32, a resistor 33, a variable resistor 34, and a resistor 35, and uses the non-inverting input terminal (+) of the buffer amplifier 31 as an input terminal and also as the output terminal of the buffer amplifier 31. Resistor 33, variable resistor 3
4. Grounded through a resistor 35 in series. The buffer amplifier 32 has its non-inverting input terminal (+)
The movable terminal of the variable resistor 34 is connected to.
The zero point setting circuit 30 uses the output terminal of the buffer amplifier 32 as the output terminal of the circuit, and connects the output terminal to the low resistor 16 via the resistor 17 of the amplifier 14.
It is connected to the inverting input terminal (-) connection end of the operational amplifier element 15. The amplifier 14 includes a resistor 16,
The connection point 17 is used as a voltage signal output terminal, and the output terminal is connected to the signal input terminal of the A/D converter 29. The A/D converter 29 is of a double integral type, for example, and converts the voltage signal input from the amplifier 14 into count data according to the level by using the reference voltage from the reference voltage generation circuit 18. I have to. The count data output from the A/D converter 29 is taken in by a control device 36. The control device 36 includes an arithmetic circuit therein and adds the count data from the A/D converter 29, and calculates the count data Z obtained by addition based on the predetermined minimum scale value X _g =Y count.
By calculating Z/Y.X, weight data in grams is obtained, and the data is displayed on the display 37. 38 is a switch element control circuit, and this control circuit 38 is controlled by the control device 36 to turn on each of the analog switches 10, 11, 12, and 13 at the timings indicated by A, B, C, and D in FIG. 2, respectively. While controlling the operation, the light emitting diodes 6D, 7D, 8 of the photocouplers 6, 7, 8, 9
The light emitting operations of D and 9D are controlled at the timings indicated by E, H, G, and H in FIG. 2, respectively. The A/D converter 29 performs a conversion operation at the timing shown by the arrow in FIG.
6 takes in count data from the A/D converter 29 at that timing. That is, the control device 36 controls timings T ₁ , T ₂ , . . .
...The count data is taken in from the A/D converter 29 at T _i , and the count data taken in at timing T ₁ is subtracted from the count data taken in at timing T ₂ to obtain the load data from load cell 1, and thereafter at timing T _{i +} The count data imported at timing T _i is subtracted from the count data imported at _{step 1} to obtain the load data from each load cell, and when the load data for 4 load cells is obtained, it is added to obtain the weight data. . Note that 39 is a keyboard, which is used for setting zero points, tare weight subtraction, etc.

In the embodiment of the present invention configured in this manner, each of the load cells 1, 2, 3, and 4 detects the load on the tray by dividing the load. Then, each analog switch 10, 11, 12, 13 is controlled by the switch element control circuit 38 as shown in FIG.
The ON operation is performed at the timings shown by c and d, and each photocoupler 6, 7, 8, and 9 is turned on at the timings shown by c and d.
The ON operation is performed at the timing shown by G and H. Therefore, each load cell 1, 2, 3, 4 is
It will be connected to the battery 5 and operated at the timings indicated by nu, ru, and wo. Therefore, at timing _T1 , the analog switch 10 is ON, but the hot coupler 6 is OFF, so at this time an offset voltage is generated at the output terminal of the amplifier 14, and this voltage is applied to the A/D converter 29.
The data is converted into count data and taken into the control device 36. At the next timing _T2 , both the analog switch 10 and the photocoupler 6 turn on, so at this time the voltage amplified by the amplifier 14 from the output of the load cell 1 is applied to the A/D converter 29.
The data is converted into count data and taken into the control device 36. Then, in the control device 36, timing T ₁ is determined from the count data at timing T ₂ .
The count data at the time is subtracted and the load cell 1
Load data can be obtained. Similarly timing T ₃ ,
Load data of the load cell 2 is obtained from the count data from the A/D converter 29 at timing T ₄ , load data of the load cell 3 is obtained from the count data from the A/D converter 29 at timings T ₅ and T ₆ , and load data of the load cell 3 is obtained from the count data from the A/D converter 29 at timing T ₇ . , _T8 , the load data of the load cell 4 is obtained from the count data from the A/D converter 29. Then, when the processing from timing T ₁ to T ₈ is completed, the control device 36 adds the obtained load data for each load cell, converts it into units of grams, and displays the result on the display 37.
to be displayed. Note that the voltage from the zero point setting circuit 30 is always added to the input voltage to the A/D converter 29.

Now, the resistance value of the resistor 16 is R ₁₆ , the resistance value of the resistor 17 is R ₁₇ , the output voltage of the zero point setting circuit 30 is E ₀ ,
If the offset voltage of the amplifier 14 is v _ps , the output E ₅₍₁₎ of the amplifier 14 at timing _T1 is E ₅₍₁₎ = R ₁₆ /R ₁₇・(v _ps +E ₀ )...(1) Become. Also, amplifier 1 at timing T _2:00
When the output of the load cell 1 is set to E1, the output E5( _{2 )} of the load cell 1 becomes E5 ₍₂₎ = _R16 / _R17・( _E1 + _vps + _E0 )...(2). Therefore, the voltage component E _L(1) of the load data from the load cell 1 finally obtained by the control device 36 is E _L(1) = E ₅₍₂₎ −E ₅₍₁₎ = R ₁₆ /R ₁₇・E ₁ ...(3), and the offset voltage v _ps of the amplifier 14 is canceled. In this way load cell 1
The count data corresponding to the output voltage _E1 from can be used as the load data. This process is performed similarly for other load cells 2, 3, and 4, so the above formula (3) is E _L(o) = E _5(i+1) − for all load cells 1, 2, 3, and 4. E _5(i) =R ₁₆ /R ₁₇・E _o ...(4) However, i=1, 2, 3, ...i, n=1, 2,
It will be expressed as 3 and 4. Therefore, the load W finally obtained by the control device 36 is W= ₄ 〓 ⁿ⁼¹ E _L(o) (5).

In this way, the load on the plate is divided and applied to the four load cells 1, 2, 3, and 4, and the output from each of the load cells 1 to 4 corresponding to the divided load is amplified by the amplifier 14, and the A/D converter 29 Since each load cell 1 to 4 is converted into count data for each load cell 1 to 4 and added by the control device 36 to finally obtain weight data corresponding to the load, each input to the A/D converter 29 The voltage for each load cell is relatively small, and as the A/D converter 29, an inexpensive one with a narrow input-output conversion range can be used, and as the amplifier 14, an inexpensive one with a small allowable input/output level can be used, making it economical. You can improve.

In addition, in order to adjust the sensitivity of each load cell 1 to 4 to be constant, for example, the sensitivity correction coefficients a ₁ , a ₂ , a ₃ , and a ₄ for each load cell 1 to 4 are preset, and the control device 1
It is sufficient to multiply the load data for each load cell by a coefficient when calculating the weight in step 6. In this case, the above formula (5) is W= ₄ 〓 ⁿ⁼¹ a _o・E _L(o) ……(6 ).

In addition, if the load remains on the control device 36 for t seconds or more after the load returns to zero, the control circuit 38 controls each analog switch 10 to 13 and each photocoupler 6 to 9 for a period of time (timing T ₁
~ _T8 ) If a control function is provided to repeat at a certain time interval instead of repeating continuously, each photocoupler 6 to 9 will be
Since it remains OFF, load cells 1 to 4
It is possible to reduce the power consumption of the device, resulting in power saving.

In addition, although the said Example described the thing which used four load cells, it is needless to say that it is not necessarily limited to this.

(6) Effects of the Invention This invention detects a load by dividing it by a plurality of load cells, extracts the divided load output from each load cell in a time-divisional manner by controlling a switch element, and amplifies it with an amplifier to generate an A/ Since weight data is obtained by sequentially converting data into digital data using a D converter and adding the digital data obtained from an A/D converter, an A/D converter with a relatively narrow input-output conversion area can be used, and the allowable input・
It is possible to provide a load cell type scale that can use an amplifier with a relatively low output level and can improve economic efficiency.

[Brief explanation of drawings]

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, 10, 11, 12, 13... Analog switch, 14... Amplifier, 29... A/D converter, 36... Control device, 38... Switch element control circuit.

Claims (1)

[Claims] 1 DC power supply and each connected to this power supply,
A plurality of load cells that output a voltage according to the load, a switch element control circuit that controls a switch element to take out the output of each load cell in a time-sharing manner, and the output of each of the load cells taken out by this control circuit sequentially. A load cell type weigher comprising: an A/D converter that performs digital conversion; and an arithmetic circuit that sequentially takes in and adds the outputs of the A/D converter to obtain weight data.