JP2013036806A - Measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring device in which high-precision measuring can be performed even without using expensive components and also costs can be reduced remarkably.SOLUTION: In a measuring device 1, a load cell bridge circuit 42 to which an AC voltage is supplied and a reference bridge circuit 44 are connected in parallel, output signals of the load cell circuit 42 and the reference circuit 44 are switched alternately on the basis of a cycle of the AC voltage by switch means 57, and the output signal of the load cell circuit 42 is corrected on the basis of the output signal of the reference circuit 44 by correction means 60. The output signals of the load cell circuit 42 and the reference circuit 44 are obtained alternately and compared constantly and a measured value is determined after correcting a path error that may occur in the output signals of the reference circuit 44 and the load cell circuit 42, thereby obtaining a high-precision measured value. Further, the measuring device 1 which is made inexpensive can be provided by eliminating the need to use expensive components for output sides of the circuits 42 and 44.

Description

  The present invention relates to a weighing device, and more particularly to a weighing device that obtains a measured value by data processing of a signal generated by a load of an object to be weighed.

  This type of weighing device is operated by a DC power supply, outputs a load signal according to the amount of strain due to the load of the object to be weighed, an amplifier that amplifies the load signal from the load cell, and its analog load signal is digital It consists of an A / D converter (hereinafter referred to as ADC) that converts it into a signal, applies a DC voltage to the bridge circuit for the load cell, amplifies the output voltage signal by an amplifier, converts it to a digital signal by the ADC, and outputs it However, it is generally known that a metric value is obtained based on data obtained by arithmetic processing of such a digital signal (see, for example, Patent Document 1).

JP-A-6-174664 (FIG. 1, paragraphs 0018 to 0030)

  However, in the above-described conventional weighing device, the digital signal drifts due to a thermoelectromotive force due to a temperature change, an offset drift of an amplifier, an ADC, or the like. In order to reduce this, it is necessary to use an amplifier with good temperature characteristics, a highly stable ADC, etc., but these parts are very expensive, and there is a problem that it is difficult to reduce the cost of the weighing device. .

  The present invention has been made in view of the above-described problems of the prior art, and provides a weighing device that can perform high-precision weighing without using expensive parts and can also realize a significant cost reduction. It is.

  In order to achieve the object, in the weighing device according to claim 1, a load cell bridge circuit to which an AC voltage is supplied, and a reference bridge to which the AC voltage is supplied are connected in parallel to the load cell bridge circuit. A switching means for alternately switching an output signal of the load cell bridge circuit and an output signal of the reference bridge circuit based on a cycle of the AC voltage, and the load cell based on the output signal of the reference bridge circuit And a correction means for correcting the output signal of the bridge circuit.

  (Operation) While applying an AC voltage instead of a DC voltage to the load cell, an AC voltage is supplied not only to the load cell bridge circuit but also to the reference bridge circuit, and an output signal from each bridge circuit is supplied by the switching means. Since switching is performed according to the cycle of the AC voltage, the output signal of the load cell bridge circuit and the output signal of the reference bridge circuit can be obtained alternately.

  According to a second aspect of the present invention, in the weighing device according to the first aspect, the switching unit is connected to two or more output channels so that the load cell bridge circuit and the reference bridge circuit can be connected to the output channels. In addition, the output channels to be connected are alternately switched.

  (Operation) Since two or more output channels for outputting the output signal from each circuit are provided and the output channel connected to each circuit is alternately switched based on the cycle of the AC voltage, the output channel is always set to one of the output channels. , Either a load cell or a reference circuit is connected.

  According to a third aspect of the present invention, in the weighing device according to the second aspect, the correcting means connects the output signals of the load cell bridge circuit obtained alternately in the respective output channels and is a continuous load cell side output signal. Data coupling means for obtaining data; and data correction means for correcting the load cell side output signal data using a correction coefficient calculated from the output signal data of the reference bridge circuit.

  (Operation) In the correcting means, the output signal obtained by alternating the load cell and the reference signal in each output channel is converted into the load cell side output signal data in which the load cell side output signal is continuous by the data connecting means. The correction coefficient is calculated by comparing the reference side output signal data in each output channel by the data correction means, and the path error generated in the load cell side output signal data is corrected using the correction coefficient.

  According to a fourth aspect of the present invention, in the weighing apparatus according to any one of the first to third aspects, the switching unit performs switching every cycle of the AC voltage.

  According to a fifth aspect of the present invention, in the weighing apparatus according to any one of the first to fourth aspects, the weighing apparatus is a weight checker that performs weighing while conveying an object to be weighed.

  According to the first aspect of the present invention, when the output signals from the load cell bridge circuit and the reference bridge circuit are output separately, the amplifiers and A / There is a possibility that an error may occur in the measurement value due to various factors such as a difference in sensitivity drift of D converter (hereinafter referred to as ADC) (individual difference of elements on the path). The load cell bridge circuit and the constant output reference bridge circuit output signal are obtained alternately, and the reference bridge circuit and the load cell bridge circuit are constantly compared to output the reference bridge circuit and the load cell bridge circuit. Since the measurement value is obtained after correction to reduce the path error that occurs in the output signal, it is possible to obtain a highly accurate measurement value. That.

  In addition, since each bridge circuit is supplied with an AC voltage instead of a DC voltage, the measurement value is calculated using the amplitude value, thereby eliminating the effect of temperature drift of each element on the path of the amplifier or the like. Also from this point, a highly accurate measurement value can be obtained.

  Furthermore, since it is not necessary to use an expensive amplifier with good temperature characteristics, a highly stable ADC, or the like on the output side of each bridge circuit, an inexpensive weighing device can be provided because it is not necessary to use expensive parts.

  According to the second aspect of the present invention, the output signal of the load cell bridge circuit and the output signal of the reference bridge circuit can be obtained in all time periods of measurement. In other words, both data of the output signals of the load cell bridge circuit and the reference bridge circuit can be obtained continuously. This further facilitates subsequent digital processing and improves the S / N ratio. Further, since the number of data samples obtained within a predetermined measurement time is doubled compared to the case where each circuit is connected to one output channel, the response speed can be shortened accordingly.

  According to the third aspect of the invention, the load means side output signal data in a continuous form is obtained by the correcting means, and the path caused by the path difference between the output channels (individual difference of elements on each path, etc.) Since the load cell side output signal data in which the error is eliminated is obtained, a highly accurate measurement value can be obtained.

  According to the fourth aspect of the present invention, since switching is performed every cycle, it is possible to quickly cope with temperature drift in a short time.

  According to the invention of claim 5, the present invention is particularly suitable for a weight checker that is frequently used continuously for a long time and is easily influenced by temperature.

Schematic equipment configuration diagram of weighing device in this embodiment The block diagram which shows the circuit structure of the control system and the principal part of the measuring device Weighing flow diagram It is a figure explaining the process of a correction process, and is a figure which shows the output signal waveform after A / D conversion It is a figure explaining the process of a correction process, and is a figure which shows the output signal waveform after a data connection process It is a figure explaining the process of a correction process, and is a figure which shows the output signal waveform after a data correction process

  An embodiment of a weighing device according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic equipment configuration diagram of a weighing device in the present embodiment, and FIG. 2 is a block diagram showing a control system of the weighing device and a circuit configuration of a main part. The weighing device according to the present embodiment is a so-called weight checker 1 that measures a material to be weighed W such as meat, fish, processed food, and pharmaceuticals while carrying it, and includes a carry-in conveyor 2, a weighing conveyor 3, and a carry-in detection sensor 8. A load cell 4, a control unit 5 of the apparatus, an operation unit 6 of the apparatus, and an apparatus main body unit 10 that integrally accommodates the display unit 7 of the apparatus for displaying a measured value.

  The carry-in conveyor 2 is driven by a motor (not shown) controlled by a CPU 56 described later, and conveys the workpiece W to the weighing conveyor 3.

  The weighing conveyor 3 measures the object to be weighed W while being transferred on the weighing conveyor 3.

  The load cell 4 is a load sensor that supports the weighing conveyor 3 downward, and is a full bridge type composed of a strain generating body that generates strain according to a loaded mass and four strain gauges 43 attached to the strain generating body. The load cell bridge circuit 42 and the reference bridge circuit 44 having the same configuration with the strain gauge 45 are included. The load cell bridge circuit 42 and the reference bridge circuit 44 are connected in parallel between a voltage output terminal and a reference potential terminal of a DAC 501 that generates an AC voltage signal described later. The load cell bridge circuit 42 outputs a load signal and load cell side output signal based on each resistance value that changes in accordance with the strain amount of the strain gauge 43. The reference bridge circuit 44 outputs a reference signal and a reference-side output signal having a constant output based on, for example, the resistance value of the strain gauge 45 when a load rating is applied to the load cell 4.

  Specifically, assuming that the connection points in the load cell bridge circuit 42 are A, B, C, and D, and the connection points in the reference bridge circuit 44 are a, b, c, and d (FIG. 2), the load cell bridge circuit 42 The partial pressure at the connection point A (plus side output signal Vcell +) and the partial pressure at the connection point C (minus side output signal Vcell−) are output as load cell side output signals, and the reference bridge circuit 44 divides the partial pressure at the connection point a ( The plus side output signal Vref +) and the divided voltage at the connection point c (minus side output signal Vref−) are outputted as a reference side output signal and inputted to an analog switch 57 described later. The installation location of the reference bridge circuit 44 and the resistance value setting thereof are not limited to the above.

  The control unit 5 includes an analog switch 57, amplifiers 52 and 53, an audio IC 50, and a CPU 56 that are mounted on a wiring board that is electrically connected to the load cell 4.

  The audio IC 50 includes two output channels, L-ch and R-ch, and an L-ADC 504 and R-ADC 505 for each channel, and an AC wave generation circuit (hereinafter referred to as DAC) that generates an AC voltage signal. ) 501. Here, the audio IC 50 is adopted because it is an IC in which one DAC and two ADCs, which are the components necessary for the present invention, are combined into one package. The configuration may be such that two ADCs are provided as separate ICs, or another component on which each IC is mounted.

  Connected to the L-ch input side of the audio IC 50 is an L-side amplifier 52 that amplifies the load cell side output signals Vcell +, Vcell- or the reference side output signals Vref +, Vref- to a signal level optimum for data processing. Similarly, an R-side amplifier 53 is connected to the R-ch input side. On the other hand, the output side of the L-ch is connected to an L-ADC 504 that decomposes an analog signal input from the L-ch and converts it into a digital signal. Similarly, the output side of the R-ch is connected to the R-ADC 505. Has been.

  The L-ADC 504, the R-ADC 505, and the DAC 501 are connected to the CPU 56, respectively. The CPU 56 acquires the amplitude information and phase information of the digital signals from the ADCs 504 and 505, executes correction processing in the data connection means and data correction means (correction means 60) described later, calculates the measurement value, and the CPU 56 Based on the period of the AC voltage signal from the DAC 501, a switching signal is transmitted to the control terminal of the analog switch 57 described later. Further, it receives a signal from the carry-in detection sensor 8 and sends a command signal to the carry-in conveyor 2.

  The analog switch 57 is disposed between the load cell bridge circuit 42 and the reference bridge circuit 44 and the L side amplifier 52 and the R side amplifier 53, and is also connected to the CPU 56. Eight of the L-side input terminals TRef +, TCell +, TRef-, TCell- that can be connected to the L-ch and the R-side input terminals TRef +, TCell +, TRef-, TCell- that can be connected to the R-ch. Input terminal, plus side signal output terminal TL + and minus side signal output terminal TL- connected to the L side amplifier 52, plus side signal output terminal TR + and minus side signal output terminal connected to the R side amplifier 53 TR- and four output terminals, L side input terminals TRef +, TCell + and output terminal TL +, L side input terminals TRef-, TCell- and output terminal TL-, R side input terminals TRef +, TCell + and output It is composed of four control terminals T1 to T4 that alternately switch the connection between the terminals TR + and between the R-side input terminals TRef−, TCell− and the output terminal RL−.

  That is, the analog switch 57 has a configuration of 8 inputs and 4 outputs, and the connection points A and C of the load cell bridge circuit 42 and the connection points a and c of the reference bridge circuit 44 are set to L and R every two outputs. Switching means that enables connection to two output channels, and an output to which the load cell bridge circuit 42 and the reference bridge circuit 44 are connected by the operation of the control terminals T1 to T4 based on the period of the AC voltage signal. Switch channels alternately.

  The operation at the time of weighing of the weight checker 1 having the above configuration will be described with reference to the flowchart of FIG. In particular, correction processing in the correction means 60 will be described with reference to FIGS. FIG. 4 is a diagram for explaining the process of the correction process, showing the output signal waveform after A / D conversion, and FIG. 5 is a diagram for explaining the process of the correction process, showing the output signal waveform after the data connection process. FIG. 6 is a diagram for explaining the process of the correction process, and shows the output signal waveform after the data correction process.

  In the weight checker 1, first, in step 1, the object to be weighed W <b> 1 conveyed to the carry-in conveyor 2 is conveyed from the carry-in conveyor 2 to the weighing conveyor 3 due to the operation at the operation unit 6. When the object to be weighed W1 reaches the weighing conveyor 3, it is detected by the carry-in detection sensor 8, and a load is applied to the load cell 4 while the object to be weighed W1 is being transferred on the weighing conveyor 3. An AC voltage sine wave signal is generated from the DAC 501 and amplified by the amplifier 12. When the inspection object W1 is loaded on the load cell 4, the load cell bridge circuit 42 corresponds to the mass of the object W1. Load cell side output signals Vcell + and Vcell- are obtained. On the other hand, reference-side output signals Vref + and Vref− with constant outputs are obtained from the reference bridge circuit 44 (step 2).

  The generated load cell side output signal Vcell + is branched and input to the L side input terminal TCell + and the R side input terminal TCell +, and the load cell side output signal Vcell− is branched to the L side input terminal TCell− and the R side input terminal. The reference side output signal Vref + is branched and input to the L side input terminal TRef + and the R side input terminal TRef +, and the reference side output signal VRef− is branched and input to the TCell−. Is input to the side input terminal TRef-. At that time, the control terminals T1, T2, T3, and T4, which are controlled by the CPU 56, have the control terminal T1 as the L-side input terminal TRef + and the TCell +, and the control terminal T2 as the L-side input terminal. The control terminal T3 with the TRef− and TCell− switches the connection with the R side input terminals TRef + and TCell +, and the control terminal T4 switches the connection with the R side input terminals TRef− and TCell− alternately. Accordingly, the load cell side output signal and the reference side output signal are alternately input to the L side amplifier 52 and the R side amplifier 53 in units of one cycle of the AC voltage signal. In this way, by performing switching for every cycle of the AC voltage signal, it is possible to quickly cope with temperature drift in a short time.

  The output signals are amplified by the L-side amplifier 52 and the R-side amplifier 53, respectively, and then input to the L-ADC 504 and the R-ADC 505 to be converted into digital data. FIG. 4 shows the output signal waveform at this stage.

  At this time, output signal data cannot be compared because there is a path difference due to the influence of individual differences between amplifiers 52 and 53 and ADCs 504 and 505 in L-ch and R-ch. Since the circuit 42, 44 is supplied with an alternating voltage signal instead of a direct current, the measured value is calculated using this amplitude value, so the influence of the temperature drift of each element on the path (DC component) is Has been removed.

  Next, data processing by the correction means 60 is performed. In step 3, the output signal data obtained by alternating the load cell side output signal and the reference side output signal for each period in each of the L-ch and R-ch are connected together for each load cell, The load cell side output signal data Dc in a continuous form is obtained (data connection means). The same processing is performed on the reference side output signal to obtain continuous reference side output signal data Dr. FIG. 5 shows the output signal waveform at this stage.

  Next, in step 4, in order to correct the variation in the amplitude value due to the path difference between the output channels of L-ch and R-ch, the amplitude of the reference side output signal data Dr, that is, R- The correction coefficient α = A / B is calculated from the amplitude value A for ch and the amplitude value B for L-ch. Next, in step 5, the L-ch side output signal data is multiplied by a correction coefficient α to correct the amplitude value of the load cell side output signal data Dc (data correction means). The reference side output signal data Dr is similarly corrected. FIG. 6 shows the output signal waveform at this stage.

  On the reference side, as long as the correction coefficient α can be calculated by comparing L-ch and R-ch as in step 4, the data does not necessarily have to be connected in step 3, and the data in step 5 does not necessarily have to be connected. Need not be corrected.

  Finally, in step 6, the measured value is calculated using the corrected load cell side output signal data Dc, and the measured value is output from the CPU 56 and given to the display unit 7. The weighing of is finished. Such a process is repeated until all of the arbitrary number of objects to be weighed Wx have been weighed.

  According to this embodiment, an AC voltage, not a DC voltage, is applied to the load cell 4 and an AC voltage signal is supplied not only to the load cell bridge circuit 42 but also to the reference bridge circuit 44. The load cell side output signal and the reference side output signal are alternately obtained according to the cycle of the AC voltage signal, and by providing two output channels, the ADC connected to one of the output channels refers to the reference signal. When this is done, the ADC connected to the other output channel refers to the signal for the load cell, and this is performed alternately, so that either ADC constantly refers to the output signal on the load cell side. The output signals from the load cell bridge circuit 42 and the reference bridge circuit 44 are It can be obtained.

  Then, the correction means 60 can obtain an output signal obtained by alternating the load cell and reference signals in each output channel as continuous output signal data for each reference, particularly for each load cell (data connection). means). Further, the path error in the load cell side output signal data Dc and the reference side output signal data Dr caused by the different output channels is represented by the reference side output signal data Dr in each output channel (L-ch, R-ch). By calculating the correction coefficient α by comparing the amplitude values of the two and multiplying the load cell side output signal data Dc (data correction means), the load cell side output signal is continuously corrected with reference to the reference side output signal. Since the measurement value is obtained after the path error is eliminated, a highly accurate measurement value can be obtained.

  In addition, the bridge circuit 42, 44 is supplied with an alternating voltage signal instead of direct current, so that the influence of the temperature drift of each element on the path (DC component) is removed. A value can be obtained.

  Furthermore, since the number of data samples obtained within a predetermined weighing time is doubled compared with the case where each bridge circuit 42, 44 is connected to one output channel, the weighing response speed can be shortened accordingly. . Further, since the load cell side output signal data Dc can be obtained in a continuous form, the subsequent digital signal processing becomes smooth and the S / N ratio is improved.

  Since the configuration described above is adopted, it is not necessary to use an expensive amplifier having a good temperature characteristic, a highly stable ADC, or the like on the output side of each of the bridge circuits 42 and 44, so that expensive components are not used. Therefore, an inexpensive weighing device can be provided. In addition, by using the audio IC 50 in this embodiment, one DAC and two ADCs, which are necessary for the present invention, are replaced with one part, so that the number of parts is reduced and the cost is reduced. Since the amount of circulation is large, the cost can be reduced from this point.

  In the above embodiment, a sine wave is generated as an AC voltage, but a rectangular wave may be naturally used.

  Further, the switching in the switching means may be switched every two cycles or 1.5 cycles instead of one cycle of the AC voltage signal.

  The configuration of the present invention is often used continuously for a long time and is suitable for a weight checker that is easily affected by temperature. However, the weight checker is an example of the present invention, and the present invention is a weighing instrument other than this. Of course, it can also be applied to devices.

DESCRIPTION OF SYMBOLS 1 Weight checker which is a weighing device 4 Load cell 42 Load cell bridge circuit 44 Reference bridge circuit 57 Analog switch 60 which is switching means Correction means

Claims (5)

A load cell bridge circuit to which an alternating voltage is supplied;
A reference bridge circuit connected in parallel with the load cell bridge circuit and supplied with the AC voltage;
Switching means for alternately switching the output signal of the load cell bridge circuit and the output signal of the reference bridge circuit based on the period of the AC voltage;
Correction means for correcting the output signal of the load cell bridge circuit based on the output signal of the reference bridge circuit;
A weighing device comprising:   The switching means is connected to two or more output channels, enables the load cell bridge circuit and the reference bridge circuit to be connected to the output channels, and alternately switches the output channels to be connected. The weighing device according to claim 1.   The correction means includes a data connection means for connecting the output signals of the load cell bridge circuit obtained alternately in the output channels to obtain load cell side output signal data, and an output of the reference bridge circuit. The weighing apparatus according to claim 2, further comprising: a data correction unit that corrects the load cell side output signal data using a correction coefficient calculated from the signal data.   The weighing device according to claim 1, wherein the switching unit performs switching for each cycle of the AC voltage.   The weighing device according to claim 1, wherein the weighing device is a weight checker that performs weighing while conveying an object to be weighed.

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