JPH023451B2 - - 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. This method converts the data into count data and calculates weight data from the count data, but with this method, the weight data is calculated with the offset voltage of the amplifier added, making it difficult to obtain correct weight data according to the load. I had a problem that I couldn't solve.

(3) Purpose of the Invention This invention was made to solve the above-mentioned problems, and it is possible to cancel the offset voltage of the amplifier and obtain correct weight data according to the load. The purpose is to provide a load cell type scale.

(4) Structure of the Invention This invention operates a plurality of load cells sequentially and cyclically at fixed time intervals by controlling a switch element, and outputs a voltage corresponding to the load sequentially from each load cell to an amplifier. The amplifier output at fixed time intervals and the amplifier output when each load cell is operating are input to the A/D converter alternately and converted into digital data sequentially.The arithmetic circuit converts the A/D converter output when the load cell is operating to the load cell. The A/D converter output when stopped is subtracted to obtain data for each load cell, and the data is added to obtain weight 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 serving as a DC power source, and the other to a photocoupler 6, 7, 8, and 9 serving as a switch element. It is connected to the negative terminal of the battery 5 via transistors 6Tr, 7Tr, 8Tr, and 9Tr. Each of the load cells 1, 2, 3, and 4 has one of the other opposing contacts in the bridge connected to the input terminal of the amplifier 14 via analog switches 10, 11, 12, and 13, and the other is grounded. are doing. The amplifier 14 is made up of an operational amplifier element and resistors 16 and 17, and has the non-inverting input terminal (+) of the operational amplifier element 15 as an input terminal, and a circuit between the output terminal of the operational amplifier element 15 and the inverting input terminal (-). The resistor 16 mentioned above is connected.

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 the resistor 22, variable resistor 23, and resistor 24 are connected in series. The movable terminal of the variable resistor 23 is used as the output terminal of the reference voltage generating circuit 18. The 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
It is supplied to the D converter 29 and also to the zero point setting circuit 30. The zero point setting circuit 3
0 consists of a series circuit of buffer amplifiers 31, 32, a resistor 33, a variable resistor 34, and a resistor 35, and the non-inverting input terminal (+) of the buffer amplifier 31 is used as an input terminal, and the buffer amplifier 31
Connect the output terminals of resistor 33, variable resistor 34, and resistor 35
are connected in series to ground. The buffer amplifier 32 has its non-inverting input terminal (+) connected to the movable terminal of the variable resistor 34. The zero point setting circuit 30 uses the output terminal of the buffer amplifier 32 as an output terminal of the circuit, and the output terminal is connected to the output terminal of the amplifier 1.
The resistor 16 is connected to the inverting input terminal (1) connection end of the operational amplifier element 15 via the resistor 17 of No. 4. The amplifier 14 uses the connection point between the resistors 16 and 17 as an output terminal for a voltage signal, and its 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, adds the count data from the A/D converter 29, and calculates the count data Z obtained by the addition from the predetermined minimum scale value X _g =Y count by Z/ By calculating Y and X, weight data in grams is obtained and displayed on the display 37. Reference numeral 38 denotes a switch element control circuit, and this control circuit 38 is controlled by the control device 36 to control the analog switches 10, 11, 12, and 13, respectively, as shown in FIG.
The ON operation is controlled at the timings indicated by B, C, and D, and the light emitting diodes 6D, 7D, 8D, and 9D of the photocouplers 6, 7, 8, and 9 are controlled at the timings indicated by E, H, G, and J in FIG. 2, respectively. The light emitting operation is controlled by The A/D converter 29 performs a conversion operation at the timing indicated by the arrow in FIG. 2, and the control device 36 takes in count data from the A/D converter 29 at that timing. That is, the control device 36
is the load from the load cell 1 by taking in the count data from the A/D converter 29 at timing T ₁ , T _{2 ,} ...T _i , and subtracting the count data taken in at timing T ₁ from the count data taken in at timing T 2 After that, the count data taken at timing T _i is subtracted from the count data taken at timing T _{i +1} to obtain the load data from each load cell, and when the load data for 4 load cells is obtained, it is added. I'm trying to get 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 way, each load cell 1, 2, 3, 4 separates and detects the load on the tray. Then, each analog switch 10, 11, 12, 13 is controlled by the switch element control circuit 38 as shown in FIG.
The photocouplers 6, 7, 8, and 9 are turned on at the timings indicated by B, C, and D, and the photocouplers 6, 7, 8, and 9 are turned on at the timings indicated by B, C, and D.
The ON operation is performed at the timings shown in F, G, and G.
Thus, each load cell 1, 2, 3, 4 is connected to the battery 5 and operated at the timing shown by R, N, R, W in FIG. Therefore, at timing _T1 , analog switch 10
is operating on, but since the photocoupler 6 is off, the load cell 1 is not operating at this time, and an offset voltage is generated at the output terminal of the amplifier 14.
This voltage is converted into count data by the A/D converter 29 and taken into the control device 36. At the next timing _T2 , analog switch 10
Since both the load cell 1 and the photocoupler 6 are turned ON, the load cell 1 is operated at this time, and the voltage whose output is amplified by the amplifier 14 is converted into count data by the A/D converter 29 and taken into the control device 36. Then, in the control device 36, the timing
The count data at timing T ₁ is subtracted from the count data at time T ₂ to obtain load data of the load cell 1. 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 up the obtained load data for each load cell, converts it into grams, and displays it on the display 37. 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 ν _ps , the output E ₅₍₁₎ of the amplifier 14 at timing T ₁ , that is, when the load cell 1 is stopped, is E ₅₍₁₎ = R ₁₆ /R ₁₇・(v _ps +E ₀ ) ...(1) becomes. Further, when the output of the amplifier 14 at timing T ₂ , that is, when load cell 1 is operating, is E _{5 (2)} and the output of load cell 1 is E ₁ , E _{5 (2)} = R ₁₆ /R ₁₇・(E ₁ + ν _ps + E ₀ ) ...(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 ν _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, 4, etc.

Therefore, the load W that the control device 36 finally obtains is W= ₄ 〓 ⁿ⁼¹ E _L(o) (5).

In this way, before taking in the output of the load cell 1, the operation of the load cell 1 is stopped for a certain period of time, and the A/D converter 2 is converted by the output of the amplifier 14 at that time.
The count data from the A/D converter 29 is taken in from the A/D converter 29 based on the output of the amplifier 14 while the load cell 1 is operating. The count data of load cell 1 is obtained by subtracting the count data of load cell 1, and then the same process is continued for load cells 2, 3, and 4, thereby obtaining the count data of load cells 2, 3, and 4, respectively. Then, the count data of each load cell 1 to 4 is added and converted into grams to obtain weight data, so the change in count data due to the offset voltage of the amplifier 14 is always canceled and the output of each load cell is Correct and correct count data can be obtained. Therefore, correct weight data corresponding to the load can always be obtained.

Incidentally, although the above embodiment has been described using four load cells, it is needless to say that the present invention is not limited to this.

Further, in the above embodiment, a photocoupler was provided corresponding to each load cell, but the invention is not limited to this. One photocoupler is provided in common for each load cell, and this photocoupler is connected to the timing T ₂ , T ₄ , T ₆ , T ₈ ...
It may be configured to operate every time.

Further, in the above embodiments, a photocoupler is used as the switch element, but the switch element is not limited to this, and for example, a transistor or the like may be used.

(6) Effects of the Invention According to the present invention, since it is possible to cancel changes due to the offset voltage of the amplifier for each of a plurality of load cells, correct weight data can always be obtained by adding count data corresponding to each load cell output. It is possible to provide a load cell type scale that can perform

[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, 6, 7, 8, 9... Photocoupler, 14...
Amplifier, 29... A/D converter, 36... Control device, 38... Switch element control circuit.

Claims (1)

[Claims] 1. A DC power supply, a plurality of load cells each connected to this power supply via a switch element and outputting a voltage according to the load, and each load cell is sequentially cycled after a certain stop time by controlling the switch element. a switch element control circuit that operates the switch element control circuit, an amplifier that sequentially amplifies the voltage sequentially output from each of the load cells by this control circuit, and an amplifier that sequentially amplifies the voltage that is sequentially output from each of the load cells; A/A/
D converter and this A/D converter output are sequentially taken in, and the A/D converter output when the load cell is stopped is subtracted from the A/D converter output when the load cell is operating to obtain data for each load cell.
A load cell type scale characterized by comprising an arithmetic circuit that adds the weight data to obtain weight data.