JP2012154823A - Weighing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a weighing device which easily and precisely identifies which load cell has an abnormal span during usual weighing operation, and which easily makes it return to a normal state.SOLUTION: A weighing device includes half bridge load signal calculating means for arithmetically processing an applied load to load cells in such a manner that each of load signals Wa1, Wa2 output from two terminals becomes the load signals with the same magnitude. A load cell having an abnormal span is detected among the load cells by comparing the two half bridge load signals.

Description

  The present invention relates to a weighing device that determines which of the load cells that support the four corners of the weighing table has an abnormal span and recovers from the failure.

  When the load cell, which is the core part of the weighing device, fails, the function to easily and accurately determine the failure state and easily return it to the normal state is the time until replacement with a new load cell. It can be said that this is an important function in that the weighing operation can be continued. Here, the factors that cause the load cell output to fluctuate from the normal value are that the zero point fluctuation amount becomes abnormally large and the span fluctuation amount becomes abnormally large. These zero point fluctuation amount and span fluctuation amount abnormality can be determined without requiring any special operation during normal measurement work, and if there is an abnormality, it is required to issue an alarm. It is required to return the weighing device to a normal state without requiring any special operation.

  Among the above failure factors, the variation of the zero point is not due to the failure of the load cell itself, but is also caused by foreign matter adhering to the weighing platform, and while the amount is small, the operator can switch the zero adjustment switch during normal weighing work Since it can be easily returned to the normal state by operating, etc., it is not considered to be in an abnormal state and no special alarm is given. In other words, if a zero point abnormality alarm is issued with a small zero point variation that can easily return to the normal state, it becomes difficult to use as a weighing device. Therefore, although the zero point abnormality can be restored to normal by repeating the zero adjustment operation when the zero point continuously fluctuates in one direction, it is abnormal when the accumulated zero point fluctuation amount becomes a large value. Be alerted as.

  On the other hand, a span abnormality cannot be easily corrected during normal work, and the abnormality must be determined even if the absolute value of the load cell output fluctuation amount is small. For example, if the accuracy of the weighing device is 1/2000, and if it is strictly determined that the span is abnormal, the weight measurement value of the object to be weighed even if the object to be weighed is a load substantially corresponding to the rated load. If the fluctuation amount is 1/2000 or more, an allowable value is set so as to warn of a span abnormality. However, since this value is small, simply judging the magnitude of the fluctuation amount of the weight measurement value and giving an abnormality alarm, an unnecessary abnormality alarm due to zero point fluctuation is output as described above, and the weighing device It becomes difficult to use. On the other hand, if the determination is based on a large allowable value ignoring a small output fluctuation, a span abnormality cannot be accurately detected or alarmed.

  Conventionally, there are devices disclosed in Patent Documents 1 and 2 as devices for diagnosing a failure of a weighing device in which four corners of a weighing table are supported by load cells.

JP 2006-162252 A JP 2006-226916 A

  In the failure diagnosis devices disclosed in Patent Documents 1 and 2 described above, the failure detection device is configured to perform failure detection according to the magnitude of the fluctuation of the output signal of the individual load cell during use. However, the fluctuation factor is zero fluctuation. Even if there is a span fluctuation, failure detection is performed without distinction. Therefore, if an allowable alarm value is set for a small fluctuation amount in order to accurately determine the span abnormality, the fluctuation will occur for each individual load cell. An alarm is immediately issued by the zero point, and the weighing device becomes difficult to use. On the other hand, if a large allowable value is set, a span abnormality cannot be accurately detected.

  Since each output signal of each load cell includes a zero point fluctuation amount component individually, it is necessary to provide a means for removing the zero point movement amount in each load cell in order to accurately evaluate the span fluctuation. In the cases of 1 and 2, no consideration is given to the removal processing method for the zero point fluctuation of the individual load cell during normal use.

  In addition to the above-described problems, there is a problem that accurate abnormality determination cannot be performed as described below even if the zero-point fluctuation component is removed from the output signal of the load cell.

As shown in FIG. 1A, if load cells 1A, 1B, 1C, and 1D are respectively installed at four corners a, b, c, and d of a weighing platform 5 having a quadrilateral shape, the following formula ( 50) holds. However, in the actual machine, it is difficult to accurately arrange the load cells supporting the weighing platform 5 at the four corners of the quadrilateral according to the dimensions (it is not easy to reduce the installation dimension accuracy to 1/1000). , B, c, d points are arranged as shown in FIG. In this case, for example, when the gravity center position G of the object to be weighed moves along the x axis on the line y = B / 2, the load distributed to the load cells 1A and 1B of the load Wx of the object to be weighed at the gravity center position G The ratio and the ratio of the load distributed to the load cells 1D and 1C differ depending on the value of the x coordinate, that is, the x coordinate value of the gravity center position G of the object to be weighed. Therefore, the ratio W1 / W2 and the ratio W4 / W3 differ depending on the value of the x coordinate, that is, the placement position of the object to be weighed on the weighing platform 5. The same applies to the movement in the y-axis direction.
W1 = {(A−x) · (B−y) / A · B} Wx
W2 = {x · (B−y) / A · B} Wx
W3 = {x · y / A · B} Wx
W4 = {(A−x) · y / A · B} Wx
W1 / W2 = W4 / W3 = (A−x) / x
W1 / W4 = W2 / W3 = (B−y) / y (50)

  Accordingly, as described below in paragraph [0046] of Patent Document 1, an object to be weighed is an arbitrary one on the weighing table with reference to the placement position of the object to be weighed at a certain point on the weighing table at the time of adjustment. Even if an attempt is made to evaluate a span abnormality during normal weighing placed at a position, it cannot be accurately evaluated.

  Similarly, since the equations (5) to (8) in paragraph [0031] of Patent Document 1 are not accurately established, in the method described in paragraph [0033] and below, x = x0, x = x1 The difference Wad between the output values of the load cells cannot be accurately expressed as shown in the equation (10) described in the same document 1, and it is accurately determined that one of the load cells has an abnormal span. Can not. Moreover, if a small abnormality cannot be found, a load cell abnormality cannot be found at an early stage.

  Furthermore, in order to detect which one of the load cells has an abnormal span and which one of the load cells has an abnormal span, in Patent Document 1, the weight of the object to be weighed is measured on the weighing table. Two weighing operations are required from the normal weighing time point to measure at a certain position and then move to a predetermined position different from that position. It cannot be easily identified automatically.

  The present invention has been made in view of the above-described problems, and in a weighing apparatus including a weighing table supported at four corners by a load cell, the span of any load cell becomes abnormal during a normal weighing operation. It is a first object of the present invention to provide a weighing device capable of easily and accurately detecting whether or not the device is in the early stage. A second object of the present invention is to provide a weighing device that can easily return the weighing device to a normal state after a load cell having an abnormal span is specified.

In order to achieve the first object, the weighing device according to the first invention comprises:
A half bridge load signal is generated based on output signals from two terminals in a Wheatstone bridge circuit composed of at least four strain gauges affixed to the strain generating portion of the load cell, and four corners are formed in the load cell. In a weighing device in which an object to be weighed is placed on a weighing platform that is supported and the weight of the object to be weighed is measured.
A half-bridge load signal calculation means is provided for calculating the load load on the load cell so that each half-bridge load signal becomes a load signal having the same magnitude.

  According to a second aspect of the present invention, in the first aspect of the invention, a span abnormality detecting means for detecting a load cell having an abnormal span among the load cells by comparing two half bridge load signals output from the half bridge load signal calculating means. It is characterized by providing.

  According to a third invention, in the first invention or the second invention, at least one of the two half bridge load signals output from the half bridge load signal calculating means varies from a zero point. It is characterized by comprising zero-point variation identifying means for identifying.

  According to a fourth invention, in any one of the first to third inventions, zero point adjusting means for manually or automatically adjusting the zero points of the two half bridge load signal output from the half bridge load signal calculating means. It is characterized by providing.

According to a fifth aspect of the present invention, in the second aspect of the invention, stable weight value generation is performed for determining stability of two half bridge load signals output from the half bridge load signal calculating means and generating a stable weight value of the load cell. Each load cell with the difference between the latest stable weight value generated by the means and the stable weight value generating means and the stable weight value generated at the timing immediately before the latest stable weight value as a stable load change amount. A load change amount calculating means for calculating each time,
The span abnormality detection means detects an abnormality in the span of the load cell by comparing the stable load change amounts of the two half bridges calculated by the load change amount calculation means.

  According to a sixth aspect of the present invention, in the second or fifth aspect of the present invention, the present invention further comprises a span change rate calculating means for calculating a span change rate in a half bridge of a load cell in which a span abnormality is specified by the span abnormality detecting means. It is what.

  Further, according to a seventh invention, in any one of the second invention, the fifth invention, or the sixth invention, any half bridge of two half bridges in a load cell in which a span abnormality is specified by the span abnormality detection means. It is characterized by comprising a span abnormal half-bridge specifying means for specifying whether or not is abnormal.

  In order to achieve the second object, the eighth invention outputs the output signal at the time of normal span for the load cell in which the span abnormality is specified in the seventh invention to the remaining three load cells. It is characterized by comprising a normal output signal estimating means for estimating by calculating a signal.

  According to a ninth aspect of the invention, in the eighth aspect of the invention, the normal output signal estimating means outputs an output signal of one load cell having a half bridge with an abnormal span to an arbitrary center of gravity position on the weighing platform of the object to be measured. It is characterized in that it is estimated by the calculation of the conversion coefficient calculated based on the above and the output signals of the remaining three load cells.

  The tenth invention is the load cell according to the eighth or ninth invention, wherein the output signal of one load cell having a half bridge with an abnormal span is replaced with the output signal estimated by the normal output signal estimating means. Output signal replacement means is provided.

  According to an eleventh aspect of the invention, there is provided the load cell span correction means for correcting the span of the half-bridge output signal having an abnormal span with the output signal estimated by the normal output signal estimation means. It is what.

  In a twelfth aspect of the invention according to the eleventh aspect, the load cell output signal replacing means replaces the span when the weight measurement value of the object to be weighed on the weighing platform is calculated at the timing when the load cell having an abnormal span is detected. And an automatic return means for automatically switching between a mode for replacing the output signal of the abnormal load cell and a mode for executing an operation for correcting the output signal of the load cell having an abnormal span by the load cell span correction means. To do.

  According to a thirteenth aspect, in the eleventh aspect, when calculating a weight measurement value of an object to be weighed on a weighing table at a timing when a load cell having an abnormal span is detected, the load cell output signal replacing means performs a span measurement. And a manual return means for switching between a mode for replacing the output signal of the abnormal load cell and a mode for executing an operation for correcting the output signal of the load cell having an abnormal span by the load cell span correction means. To do.

  According to a fourteenth aspect of the invention, there is provided the display device according to the second aspect of the invention, further comprising display means for displaying the load cell in which a span abnormality is specified by the span abnormality detecting means and the contents of the abnormality by an identification code. .

  According to a fifteenth aspect of the invention, there is provided the display device according to the sixth aspect, further comprising display means for displaying the value of the span change rate calculated by the span change rate calculating means together with an identification code of an abnormal load cell of the span. is there.

  Further, in a sixteenth aspect of the invention according to the twelfth or thirteenth aspect of the invention, the automatic return means or the manual return means displays that the output signal of the load cell having an abnormal span is being corrected or replaced with a normal value. Means are provided.

According to the first to seventh inventions, the fourteenth invention, and the fifteenth invention, it is possible to accurately detect only the span fluctuation by removing the zero fluctuation from the output of each half bridge, and determine the span abnormality. Can be done accurately. Moreover, this span abnormality determination can be carried out while continuing normal measurement work without requiring any special work.
In addition, according to the eighth to thirteenth and sixteenth inventions, after the span abnormality is determined, the weighing device is easily returned to a normal state, so that the weighing is performed until it is replaced with a new load cell. Work can be continued.

Schematic diagram of a weighing platform in a weighing device according to an embodiment of the present invention. The use state diagram of the load cell used in the weighing device of the present embodiment, the state diagram used for the compression type load cell Schematic system configuration diagram of a failure diagnosis device in the weighing device of the present embodiment Block diagram showing the configuration of the arithmetic circuit The figure explaining the method of calculating | requiring a span evaluation coefficient by proportional distribution by x, y coordinate Schematic system configuration diagram of a failure diagnosis apparatus according to another embodiment of the present invention

  Next, specific embodiments of the weighing device according to the present invention will be described with reference to the drawings.

  1A and 1B are schematic views of a weighing table in a weighing device according to an embodiment of the present invention. FIG. 2 is a use state diagram of a load cell applied to the weighing device of the present embodiment, and a state diagram used for the compression type load cell is shown. FIG. 3 shows a failure diagnosis in the weighing device of the present embodiment. A schematic system configuration diagram of the apparatus is shown.

As shown in FIG. 1A, the weighing platform 5 has a quadrilateral shape, and the four corners a, b, c, and d are supported by load cells 1A, 1B, 1C, and 1D, respectively. On the plane including the article placement surface of the weighing platform 5, the point a is the origin, the direction of the straight line connecting the points a and b is the x axis, and the direction of the straight line connecting the points a and d is the y axis. Set the xy coordinates. The coordinates of the center of gravity G of the object placed on the weighing platform 5 are (x, y), the load at the center of gravity G of the object to be weighed is Wx, and each load cell 1A, 1B, The output signals of 1C and 1D are W1, W2, W3, and W4. The dimensions of the weighing platform 5 are ab = A and ad = B.
Actually, it is difficult to accurately place the load cells 1A, 1B, 1C, and 1D at the four corners of the quadrilateral, and the points a, b, c, and d that are the positions of the load cells are extremely small. In other words, the arrangement is as shown in FIG.

  As shown in FIG. 2, each of the load cells 1A, 1B, 1C, 1D is a compression type load cell, and includes a support portion 2, a strain generating portion 3 provided on the support portion 2, and the strain generating portion 3. It comprises a force receiving part 4 provided at the upper part, and is configured such that when the receiving part 4 receives a force F, the strain generating part 3 is compressed. Strain gauges 11 and 13 are attached to the strain generating part 3 in parallel to the axial direction of the strain generating part 3, and strain gauges 12 and 14 are attached to the strain generating part 3 at right angles to the axial direction of the strain generating part 3. When the strain gauges 11 and 13 contract, the resistance value decreases to detect the compressive force, and when the strain gauges 12 and 14 extend, the resistance value increases to detect the tensile force.

  As shown in FIG. 3, the strain gauges 11, 12, 13, and 14 are connected to each other so as to constitute a full bridge circuit 15. Here, in the full bridge circuit 15, if both the strain gauges 12 and 14 constituting the opposite sides are tensile forces, the tensile force is obtained, and both the strain gauges 11 and 13 constituting the opposite sides are both compressive forces. Then, it is wired to receive the same type of force as compression force.

  In the full bridge circuit 15, excitation direct current voltage is applied to two opposing connection points 16 and 17, and force or load is detected from the connection points 18 and 19 positioned at right angles to these connection points 16 and 17. The voltage is taken out.

  A fault diagnosis device 20 is provided for the above-described full bridge circuit 15. The fault diagnosis apparatus 20 includes two voltage reference fixed resistors 21 and 22, an analog adder circuit 23, and two analog-digital converters (hereinafter referred to as “A / D converters”) 24, 25 and an arithmetic circuit 26. Here, the fixed resistors 21 and 22 are connected in series to each other and are connected to connection points 16 and 17 of the full bridge circuit 15. The fixed resistors 21 and 22 and the strain gauges 12 and 13 form a half bridge circuit 15a, and the fixed resistors 21 and 22 and the strain gauges 11 and 14 form a half bridge circuit 15b.

The analog adder circuit 23 includes a first operational amplifier 31, a second operational amplifier 32, a third operational amplifier 33, and a fourth operational amplifier 34.
In the first operational amplifier 31, the input positive terminal 31 a is connected to the connection point 18 of the full bridge circuit 15, the input negative terminal 31 b is connected to the output terminal 31 c, and the output terminal 31 c is connected to the resistor 40.
In the second operational amplifier 32, the input positive terminal 32a is connected to the connection point 41 of the two fixed resistors 21 and 22, the input negative terminal 32b is connected to the output terminal 32c, and the output terminal 32c is connected to the resistors 42 and 43. It is connected.
In the third operational amplifier 33, the input positive terminal 33a is connected to the circuit ground 44, the input negative terminal 33b is connected to the resistors 40 and 42, and is connected to the output terminal 33c via the resistor 45, The output terminal 33c is connected to the A / D converter 24.
In the fourth operational amplifier 34, the input positive terminal 34 a is connected to the connection point 19 of the full bridge circuit 15, and the input negative terminal 34 b is connected to the resistor 43 and connected to the output terminal 34 c via the resistor 46. The output terminal 34 c is connected to the A / D converter 25.

  The A / D converters 24 and 25 convert the analog load signal from the analog adder circuit 23 into a digital load signal. The analog load signals eoa and eob output from the two sets of half-bridge circuits 15a and 15b are converted into analog load signals eoa 'and eob' through the analog adder circuit 23. These analog load signals eoa 'and eob' are represented by A / D converters 24 and 25 convert the signals into digital load signals. These digital load signals are input to the arithmetic circuit 26 to become digital load signals.

  The output signals Wa1 and Wa2 from the A / D converters 24 and 25 shown in FIG. 3 are digital signals obtained by A / D sampling the analog load signals eoa ′ and eob ′ with a relatively short time interval (for example, 5 msec). Thus, the natural vibration signal of the weighing device and the like are subjected to smooth filtering processing in the arithmetic circuit 26, and are given to the following output equation (1), for example, every time interval of several hundred msec. The output signals Wa1 and Wa2 corresponding to the half-bridge outputs of the load cells 1A, 1B, 1C, and 1D are expressed as Wa11, Wa21; Wa12, Wa22; Wa13, Wa23; Wa14, Wa24, respectively.

  As shown in FIG. 4, each load cell 1A, 1B, 1C, 1D (LC1, LC2, LC3, LC4) is for the strain generating body including the strain generating section 3 and the A / D conversion circuit shown in FIG. The component is configured as a digital load cell with a case surrounding the strain generating body, and is connected to the arithmetic circuit 26 of the weighing device of the present embodiment. Although the A / D conversion circuit can be provided on the weighing device side, it is more preferable to adopt a configuration of a digital load cell integrated with the strain generating body.

  The arithmetic circuit 26 includes an input / output circuit (I / O) 51, a central processing unit (CPU) 52, and a memory block (MEM) 53. Thus, the output signals of the A / D converters 24 and 25 are read from the input / output circuit 51 into the memory block 53 via the central processing unit 52. Here, the memory block 53 is composed of a storage element (semiconductor element) such as a RAM that primarily stores data for input, output, and computation, an EEPROM that continuously stores setting data, and a PROM that continuously stores predetermined programs. is there. The arithmetic circuit 26 is provided with a display device (DIS) 54, a key switch (KEY) 55, and the like. The weight value and the like are displayed on the display device 54, and operations such as data setting and zero adjustment are performed by the key. Implemented by switch 55.

(1) Determination / specification of load cell with abnormal span (1.1) Adjustment and processing of load cell half-bridge output signal Two sets of half-bridges (hereinafter referred to as “half-bridge 1” in each load cell 1A, 1B, 1C, 1D) The outputs of “Half Bridge 2” (see FIG. 3) are W11, W21; W12, W22; W13, W23; W14, W24, respectively. The processing of these output signals is independently provided with a span coefficient, a zero point weight storage memory, and an initial weight storage memory.

  First, the load cell alone is adjusted. In this adjustment, a weight measuring device similar to that shown in FIG. 4 is connected to the digital load cell. Here, the load measuring device for weight adjustment is provided with an initial load storage switch and a span coefficient setting switch. For example, when adjusting the half bridge 1 of the load cell 1A (LC1), first, the span coefficient K11 = 1 is set, the load cell is not loaded, the initial load storage switch is pressed, and the digital load signal Wa11 obtained from the half bridge 1 is set. Is stored in the initial load storage memory as the initial load Wi11.

The output of the half bridge 1 is calculated by the following processing expression in the calculation circuit 26.
W11 = K11 · (Wa11−Wi11)
At this time, since K11 = 1 and Wa11 = Wi11, W11 = 0 is displayed on the adjustment weight measuring device. The half bridge 2 is similarly adjusted. Note that W11 is set to have a resolution that is, for example, four times that of the display value as the weight measurement value of the object to be weighed in the weighing instrument.

  Next, a rated load is applied to the load cell, and a value WM obtained by converting the rated load with high resolution is set. When the span coefficient adjustment switch is pressed, the span coefficient K11 is determined so that the weight display indicates the value of WM. The span coefficient K21 of the half bridge 2 is determined in the same manner, and these span coefficients K11 and K21 are stored in the nonvolatile memory, and the adjustment of the single load cell is completed. In this way, the span coefficient of each half bridge in the single load cell is adjusted so as to have the same output change for the same load.

  Next, the load cell adjusted as described above is incorporated in the weighing platform 5 of the weighing device, and the output is connected to the weight measuring device for the weighing device. When the initial load storage switch of the weight measuring device is pressed in this state, for example, the load signal Wa11 which has been A / D converted and smoothed into the half bridge 1 of the load cell 1A enters the initial load storage memory and is stored at the time of single adjustment. The initial load value is changed.

During use as a weighing device, it is necessary to adjust the zero point fluctuation (adjusting the output to 0 when there is no object to be weighed on the weighing table 5), so the zero point weight storage memory Wz11 is provided and the output of the half bridge 1 is provided. Is set by the following processing formula (1). Similar processing formulas are set for the half bridge 2 and for the other load cells 1B, 1C, 1D.
-About load cell 1A W11 = K11 * (Wa11-Wi11) -Wz11
W21 = K21 · (Wa21−Wi21) −Wz21
W1 = (W11 + W21) / 2
-About load cell 1B W12 = K12- (Wa12-Wi12) -Wz12
W22 = K22 · (Wa22−Wi22) −Wz22
W2 = (W12 + W22) / 2
-About the load cell 1C W13 = K13- (Wa13-Wi13) -Wz13
W23 = K23 · (Wa23−Wi23) −Wz23
W3 = (W13 + W23) / 2
-About load cell 1D W14 = K14 * (Wa14-Wi14) -Wz14
W24 = K24 · (Wa24−Wi24) −Wz24
W4 = (W14 + W24) / 2 (1)
In the measurement circuit shown in FIG. 3, only a half-bridge output is provided. Therefore, during normal weighing, the full-bridge output used to obtain the weight measurement value of the object to be weighed is the half-bridge 1, 2. It is expressed by adding the outputs.
The weight value WT of the object to be weighed is expressed by the following equation with the outputs of the four load cells 1A to 1D.
WT = W1 + W2 + W3 + W4 (2)

  As a manual zero point adjustment operation during use of the weighing device, if the zero point adjustment switch is operated in the weight measuring device during use, the outputs of the half bridges 1 and 2 of the four load cells can be simultaneously adjusted to the zero point simultaneously. Is preferred. Here, the zero point adjustment is a process for adding W11 at the time of zero point adjustment to Wz11 for W11, for example, so that W11 = 0.

  Moreover, as an automatic zero correction function, the stable state of each load cell in the vicinity of the zero point weight of the half bridge output is individually determined, the output is stable, and the weight display value count level is 0 display. When the count level deviates from zero, the zero correction function is automatically executed for each half bridge of each load cell. In this case, each half-bridge output signal is processed with a high resolution so that it can be expressed with a count number that is at least four times larger than one count of the minimum display weight value as the weight value of the object to be weighed.

  By performing signal processing for each half bridge in this way, the zero point fluctuation for each half bridge output of each load cell at the time of normal weighing work is removed, and what accurately corresponds to the magnitude of the load load can be obtained. Therefore, it is possible to cope with the detection of a span abnormality.

  As described above, in the present embodiment, the calculation processing in which the half bridges 1 and 2 have the same output signal with respect to the load applied to the load cell is performed by the half bridge load in the central processing unit 52. It is executed in a signal calculation unit (corresponding to “half-bridge load signal calculation means” in the present invention). In addition, the arithmetic processing for detecting a load cell having an abnormal span among the load cells by comparing the output signals from the two half bridges 1 and 2 is a span abnormality detecting unit (the present invention). This corresponds to “span abnormality detecting means” in FIG.

(1.2) Reliable span abnormality determination process The weight display of the weighing device is displayed by converting the value of WT, which is the weight value of the object to be weighed on the weighing platform 5, into the display level resolution. The operator performs the weighing work while looking at the displayed value. Therefore, for example, when the zero points of the half bridges 1 and 2 of the load cell 1A fluctuate in the positive and negative directions by the same large value, the output as the load cell 1A becomes zero. If the outputs of the other load cells 1B to 1D are also 0, the zero point as the added value WT becomes 0, so the display value becomes 0, and the zero point adjustment switch is not pressed.

  In this embodiment, the load cell span abnormality detection is performed by comparing the outputs of two half bridges in the same load cell. Even if the minutes are the same, the difference remains and it is determined that the span is abnormal. For example, when foreign matter is attached to the weighing platform 5, the zero point of both half bridge outputs fluctuates by the same amount, so the comparison result is not affected, but the ambient temperature is changing. The two half bridges are affected by different temperatures and a difference occurs between the zero points of both half bridge outputs.

  In view of this point, in order to accurately detect a span abnormality, a means capable of recognizing that the zero point of the half bridge output is individually adjusted or a means capable of individually recognizing the zero point fluctuation (provided in the central processing unit 52). It is necessary to provide zero point fluctuation identification means). Therefore, in this embodiment, when any one of the half bridge outputs is not zero, or when all the half bridge outputs of all the load cells are zero, the half bridge zero point display that displays the lamp or characters to that effect The means is provided in the display device 54. In this way, when any one of the zero points of the half bridge output is moving, the operator can easily recognize this by the half bridge zero point display means, and press the zero point adjustment switch. Thus, the zero adjustment of all the half bridge outputs can be performed simultaneously. Here, the zero point adjustment switch is preferably used also as a normal weight display zero point adjustment switch.

  Regarding the sign display of the half bridge zero point display means, a lower limit value Wzl and an upper limit value Wzu are determined as boundary weight values for determining that the half bridge output is in the region near the zero point, and any one of all the load cells is set. When the half-bridge output is not in the zero-point vicinity area, or when all the half-bridge outputs are in the specified zero-point vicinity area, a sign indicating that is displayed (zero fluctuation sign), and the operator adjusts the zero adjustment switch. It is configured to be able to recognize whether or not there is a need to press, and in some cases to prompt the user to press the zero adjustment switch. In this case, the upper limit value Wzu and the lower limit value Wzl are set to values in front of which the value of the minimum display amount (minimum scale value) of the weight value display of the object to be measured converted from the WT is displayed. It is preferable.

  Next, a description will be given of countermeasures in the case of a weighing device that cannot rely on the operator's zero adjustment operation or when the operator forgets the zero adjustment operation for the half-bridge output. As a countermeasure, by providing load fluctuation amount detection means that calculates only the fluctuation amount due to load load for the half-bridge output signal of each load cell as follows, the span abnormality can be automatically and accurately detected. To do.

  For example, for the output W11 of the half bridge 1 of the load cell 1A, this W11 is generated at a time interval of, for example, Ta = several 100 msec after smoothing the load signal read from the A / D converter 24. The latest M W11s are always stored in the prepared M shift registers in order, and the maximum value-minimum value in the stored M W11s is within the preset allowable limit of the stability limit. Is determined to be in a stable state. In this way, stability determination is sequentially performed for each time interval Ta with respect to the half-bridge outputs of all the load cells, and the average value of the shift register is calculated to determine the current weight measurement W11, that is, the stable weight value of the load cell. To do. This calculation processing is executed in a stable weight value generation unit (corresponding to “stable weight value generation means” in the present invention) in the central processing unit 52.

  If an object to be weighed is placed on the weighing platform 5, the shift register data may deviate from the allowable value due to the value of W11 read at a certain timing, and the stable condition may not be satisfied. However, since the latest value that entered the shift register at the timing just before the stability condition is usually the limit value of the allowable range, it is necessary to calculate the value of W11 as the stable weight value. It is appropriate to exclude the most recently entered value and obtain the average value with M-1.

  In order to detect a span abnormality automatically and accurately, a load change amount calculating means for calculating only a variation amount due to a load load is provided for the half bridge outputs of all load cells as follows.

If one stable weight value storage register for storing the stable weight value immediately before becoming unstable (latest stable weight value) is prepared and stable weight values are continuously generated at every time interval Ta, the stable Each time the weight value is generated, the contents of the stable weight value storage register are updated with the latest stable weight value W11 as the previous stable weight value W1u. In this way, the latest stable weight value is always stored in the stable weight value storage register and updated to the latest value for the half bridge outputs of all the load cells 1A to 1D, and the respective values are changed to W11u, W21u; W12u, W22u; W13u, W23u; W14u, W24u. Then, when the stable weight values of the half-bridge outputs W11 to W24 of each load cell are generated together, the following load change amounts W11p to W24p are obtained from the stable weight values of all the load cells and the currently stored stable weight values. calculate.
W11p = | W11−W11u |
W21p = | W21−W21u |
W12p = | W12−W12u |
...
W14p = | W14-W14u |
W24p = | W24−W24u | (3)

The change width Wh of the stable weight value is set in advance, and when all the load change amounts exceed the change width Wh, that is, when the following formula is satisfied at the same time, the load change large enough to determine the span abnormality in each load cell The span abnormality between the half bridges 1 and 2 of each load cell is determined on the assumption that the amount is W11p to W24p. Here, as the value of Wh, a load of maximum Ws / 4 is normally applied to each load cell with respect to the rated load Ws of the weighing device, so that Wh = Ws / 16 as 1/4 of the value. Etc. are set.
W11p-W24p> Wh (4)

For example, for the load cell 1A, the span change rate R1 is expressed by the following equation based on the difference in load change between the half bridge 1 and the half bridge 2.
R1 = | W11p−W21p | / {(W11p + W21p) / 2} (5)
Equation (5) does not include the zero-point fluctuation of each half bridge output, and can be accurately expressed as the rate of change of the half bridge span on either side with respect to the half bridge span on the other side. . The change rates R2 to R4 of other load cells can be obtained in the same manner. This calculation processing is executed in a span change rate calculation unit (corresponding to “span change rate calculation means” in the present invention) in the central processing unit 52.

Thus, in each load cell LCn (n = 1 to 4), the inequality Rn> Rh (6) with respect to the allowable value Rh in which the span change rate Rn is set.
If there is one that satisfies the condition, it is determined that the span of the load cell LCn is abnormal. That is, it is possible to automatically and accurately identify which load cell span is abnormal among the load cells 1A to 1D supporting the four corners of the weighing platform 5 during normal weighing work.

  In this judgment method, the zero point fluctuation is removed, so the difference in load change is due to the fluctuation of the span, but because it is a comparison of the half bridge output in the same load cell, Even if the output fluctuates between load cells depending on the position on the table, it is not affected. Therefore, since a minute difference can be detected, a span abnormality can be accurately determined. Further, during normal weighing work, if an object to be weighed to a certain extent is placed on the weighing table 5 so that the load distribution of the load cell is not extremely biased, that is, Equation (5) is established. For example, the span abnormality determination mechanism can be operated during normal measurement work.

  As the degree of abnormality of the load cell increases, the subsequent progress of the degree of abnormality increases and becomes faster. As a result, the load cell is not in time for output compensation and needs to be replaced quickly. However, if the load cell to be replaced is not at hand, the other three load cell outputs must replace the abnormal load cell output. However, in this case, the weight value varies depending on the position of the object to be weighed on the weighing table, and the weighing accuracy is lowered. In the present invention, since an abnormal degree can be detected at an early stage while being small, it can be dealt with by output compensation of an abnormal load cell.

  Here, if the weight measuring device is not equipped with a function for returning to normal weighing, when the abnormality is determined, the load cell and the content of the abnormality such as a sign that the span is abnormal and the number of the failed load cell are displayed by the weight measuring device. Each is displayed on the display device 54 by an identification code, and the span change rate (see equation (5)) is also displayed together with the identification code of the load cell having an abnormal span. The alarm signal is output by means such as lamp display, character display, and voice. On the other hand, in the case of having a function for returning to normal weighing, as described below, the above-described alarm display or the like is performed after the specific processing as to which half bridge is abnormal is performed.

(2) Overview of Returning Method to Normal Weighing Operation of Weighing Device (2.1) Returning Method There are the following two methods for returning the weighing device to the normal state after specifying the fault load cell.
1) A method for obtaining a weight measurement value by using the outputs of the remaining three load cells without using the output of the load cell having an abnormal span. This method is used to load the load cells 1A to 1D that support the four corners of the quadrilateral weighing platform 5. Based on the relationship between the output of one specific load cell derived from the ratio and the output of the remaining three load cells, the output of the specific one load cell determined to be a span abnormality is determined by the output of the remaining three load cells. It is a method to substitute.
In Japanese Patent Laid-Open No. 2006-162252 (Patent Document 1), a method of specifying a faulty load cell by moving the position of an object to be weighed on a weighing table is performed, and then the weighing device is in a normal state by the method. What was made to return to is disclosed. On the other hand, in the present embodiment, the load cell having the span abnormality is specified by the span comparison by the half bridge and by surely removing the zero point variation from the load cell output. The load cell can be specified more accurately and easily.

2) Method to compensate and use the output of a load cell with an abnormal span This method identifies a half bridge with a normal span and substitutes the full bridge output of the load cell with a normal half bridge output for a failed load cell. This is a method for obtaining a weight measurement value. It is also possible to correct an abnormal half-bridge output span with a normal half-bridge output span and obtain a weight measurement value by a full-bridge output using the corrected half-bridge output.

  According to the present embodiment, since the rate of change of the span can be obtained more accurately, the output of the load cell in which the span has changed abnormally can be corrected to the original span, and the output of the load cell is the same as before the failure. Can be used for Thus, the position of the center of gravity of the object to be weighed on the weighing table 5 is greatly deviated, or a concentrated load is applied depending on the type of the object to be weighed. If the distribution does not meet the specified ratio, the load cell output with the corrected span can participate in the calculation of the weight measurement value, and it can be measured with four load cells, thus obtaining a highly accurate measurement value. Can do.

(2.2) Recovery process from abnormality determination To recover from abnormality determination, 1) a method of automatically returning the weighing device to a normal state by the above-described recovery method, and 2) manual recovery means such as a return switch. There is a method to check the output of the span abnormality alarm and manually return the weighing device to the normal state.

(3) Measures for returning to normal weighing operation If the weight measuring device has a function for returning to normal weighing, perform the following processing to return to the normal state.
When a fault load cell whose span has abnormally changed is identified by comparing the half bridges, it is next determined which side of the half bridges 1 and 2 of the fault has a span fault. To make this determination, one load cell output identified as having an abnormal span is accurately represented by the remaining three load cell outputs, regarded as a temporary normal output of the fault load cell, and the half bridge 1 of the fault load cell. , 2 compared. Then, it is determined that the half bridge having the larger comparison difference has a span abnormality, and the failed half bridge is specified. This arithmetic processing is executed in a span abnormal half-bridge specifying unit (corresponding to “span abnormal half-bridge specifying means” in the present invention) in the central processing unit 52.

(3.1) Load cell output signal used for return determination Similar to the load cell abnormality determination, the load on the half bridges 1 and 2 of each load cell determined above so that the zero bridge fluctuation is not included in the half bridge output. The change amounts W11p, W21p, W12p, W22p, W13p, W23p, W14p, and W24p are used and expressed as the full bridge output using the following equation.
W1p = (W11p + W21p) / 2
W2p = (W12p + W22p) / 2
W3p = (W13p + W23p) / 2
W4p = (W14p + W24p) / 2 (7)
When the load cell output of an abnormal span is expressed by the remaining three normal load cell outputs, the display method is determined as follows in consideration of the load cell installation conditions. The calculation process for estimating the normal output signal of the span for the load cell in which the abnormality of the span is specified is the normal output signal estimation unit in the central processing unit 52 (“normal output” in the present invention). Corresponding to "signal estimation means").

(3.2) When the load cell is accurately arranged at the four corners of the quadrilateral (see FIG. 1A)
(3.2.1) Identification of half bridge with span abnormality Full bridge outputs not including zero fluctuations of load cells 1A, 1B, 1C, and 1D are denoted as W1, W2, W3, and W4, respectively. It is preferable to use the above W1p to W4p for these W1 to W4.
If the load cells 1A to 1D are accurately arranged at the four corners of the quadrilateral, from FIG.
W1 = W2 · (W4 / W3) (8)
Therefore, if the span of any half bridge of the load cell 1A is specified to be abnormal by the above method, W2 · (W4 / W3) based only on the normal load cell output is used instead of W1. The weight measurement value WT of the weighing object is calculated by the following formula.
WT = W1 + W2 + W3 + W4 = W2 / (W4 / W3) + W2 + W3 + W4
... (9)

Similarly, when it is determined that the span of any one of the load cells 1B, 1C, and 1D is abnormal, any one of W2, W3, and W4 is replaced with the following formula to obtain WT: Return to a state where normal weighing can be performed. Thus, the abnormal load cell output is not used.
W2 = W1 · (W3 / W4)
W3 = W4 · (W2 / W1)
W4 = W3 · (W1 / W2)

If the load cell 1A is specified as an abnormal load cell, the outputs W11 and W21 of the half bridges 1 and 2 (both outputs that do not include the zero fluctuation) and W2 (W4 / W3) are based on the equation (7). Comparison is made and it is determined that the span of the half bridge having the larger absolute value of the difference is abnormal. That is,
| W11-W2 (W4 / W3) |> | W21-W2 (W4 / W3) | ... (10)
Is established, it is determined that the output of the half bridge 1 is a span abnormality, and conversely,
| W11-W2 (W4 / W3) | <| W21-W2 (W4 / W3) | ... (11)
If is established, it is determined that the output of the half bridge 2 has a span abnormality.

  When an abnormal load cell is identified in this way, it is subsequently determined which half-bridge output in the load cell is abnormal, and at this time, the above-mentioned sign, alarm output, etc. are performed. By this alarm or sign, the operator presses a normal return switch (manual return means) in the case of manual return, and returns to normal as described below. In the case of automatic return, the automatic return means automatically returns to normal weighing. However, when returning to normal weighing, a sign of “forcibly returning” is displayed on the display device (display means) 54. This display is performed in order to notify the operator of the state in which the span abnormality has occurred and to formally investigate the span abnormality state after the end of the work or to prompt the arrangement of the load cell to be replaced.

(3.2.2) Return to normal weighing 1) Method using only the normal half-bridge output For example, for the load cell 1A, the normal half-bridge output W21 is used instead of W1 in the formula for obtaining the weight measurement value WT. Using the following formula.
WT = W21 + W2 + W3 + W4

2) Method of correcting and using the span of the abnormal half-bridge output Since the span change rate R1 of the half-bridge is calculated, R1 is applied to the output W11 of the half-bridge 1 having an abnormal span.
W11 / R1 (12)
The span changed is corrected, and the full bridge output is calculated by the following formula to return to the normal weighing operation.
W1 = (W11 + W12) / 2 = {(W11 / R1) + W21} / 2 (13)
The same applies to the half-bridge outputs of other load cells.

  When correcting the span, it is not corrected as soon as an abnormality is detected, but is measured with a substitute signal using the output of the remaining normal load cell other than the abnormal load cell as described above during multiple weighings. In the meantime, the span change rate Rna (n: span abnormal load cell LCn) is obtained multiple times by the equation (6), the average value is calculated, and the span of the abnormal half-bridge output with the average span change rate is calculated. It is more preferable to correct the above. Further, a correction switch may be prepared so that the average number of times and the correction timing are determined by the operator's intention when an abnormality occurs.

  The calculation process for replacing the output signal of the load cell having a half bridge with an abnormal span with the output signal estimated by the normal output signal estimation unit is the load cell output signal replacement unit in the central processing unit 52. (Corresponding to the “load cell output signal replacement means” in the present invention) and for correcting the span of the output signal of the half bridge having an abnormal span by the output signal estimated by the normal output signal estimation unit. The arithmetic processing is executed in a load cell span correction unit (corresponding to “load cell span correction means” in the present invention) in the central processing unit 52.

(3.3) When the load cell is not accurately arranged at the four corners of the quadrilateral (see FIG. 1B)
(3.3.1) Relationship that changes in response to changes in the x-coordinate of the position of the center of gravity of the object to be weighed If the load cells are accurately placed at the four corners of the quadrilateral, the relationship between the outputs of the four load cells is As expressed by equation (8), if the load cells are not accurately arranged at the four corners of the quadrilateral, the values of W1 / W2 and W4 / W3 are the same even if the output signals of all the load cells are normal. In addition to being not equal, it gradually changes according to the change in the center of gravity G of the object to be weighed on the weighing platform 5. If the object to be weighed (lorry vehicle) is to be weighed near the center line (CL) at the center of the weighing platform 5 as shown in FIG. / W2 and W4 / W3 are expressed as follows: W1 / W2 = r · (W4 / W3) (14)
Thus, it can be considered that the value of r (referred to as “span evaluation coefficient”) changes depending on the x coordinate of the gravity center position G of the object to be weighed placed on the weighing table 5. So r is a function of x,
r = f (x) (15)
It is expressed by the following formula.
r = f (x) = (W1 / W2) / (W4 / W3) (16)
Then, when W1 to W4 are respectively expressed by output expressions of the remaining load cells, the following expressions are obtained.
W1 = r · W2 · (W4 / W3)
W2 = (1 / r) .W1. (W3 / W4)
W3 = (1 / r) · W4 · (W2 / W1)
W4 = r · W3 · (W1 / W2) (17)

<Adjustment mode>
In the adjustment mode, a function r = f (x) relating r (span evaluation coefficient) and x when all the load cells have normal spans is obtained.

The position of the x, y coordinates of the object to be weighed obtained from the output signal of the load cell is as shown in the following equation from FIG.
x = [{W2 / (W1 + W2)} + {W3 / (W3 + W4)}] · A / 2
y = [{W3 / (W2 + W3)} + {W4 / (W1 + W4)}] · B / 2
... (18)

When there is some object to be weighed on the weighing platform 5 and a new object to be weighed is additionally placed, the load change amounts W1p to W4p are calculated and replaced with W1 to W4 as described above. Since the calculation is performed, the position of the center of gravity of the added object to be weighed is obtained.
The positions x and y of the objects to be weighed and the load change amount of each load cell are displayed on the display of the weight measuring device.

  In the adjustment mode of the weight measuring device, in the case of a weight or a truck scale, an object to be used as a test sample such as a freight car is placed near the center of the weighing platform 5 by x <(1/2) · A to x> ( While the display of the x-coordinate is confirmed, the distance is moved little by little around x = (1/2) · A.

  Here, an arbitrary load can be used as the load of the test sample, but it is preferable to use a load having a large value below the rated load of the weighing device. The display value of the x coordinate is preferably moved so as to change between x = A / 4 to (3/4) · A. Further, it is preferable to measure the test sample while moving it as much as possible along the center line represented by y = B / 2 in FIG. That is, it is preferable to move the y-coordinate so that y = B / 2 is displayed as much as possible.

  Each time the test sample is moved to several places around x = (1/2) · A, the x coordinate value is changed to an appropriate interval, and the stable weight value is obtained each time the position of the test sample is changed. When the load change amount of each of the load cells 1A to 1D is obtained, the display value of the load change amount is confirmed, and the measurement data storage switch provided in the weight measuring device is pushed. Then, each time the measurement data storage switch is pressed, the span evaluation coefficient r is calculated by the equation (14) from the load change amount of each load cell 1A to 1D, and the memory block 53 of the arithmetic circuit 26 of the weight measuring device together with the x coordinate value. Is remembered.

When span evaluation coefficients corresponding to a plurality of x coordinates are obtained on both sides of x = (1/2) · A as a center, when a span evaluation coefficient reference value setting switch provided in the weight measuring device is pressed, x Is divided into a range of x <(1/2) · A and a range of x ≧ (1/2) · A, and a reference value of a span evaluation coefficient for x is obtained for r by a method such as a method of least squares. As the functions fa (x) and fb (x), a linear expression or a multi-order expression is determined for each range and expressed in the form of the following expression, and this is expressed as a function relating to the x coordinate value of the span evaluation coefficient reference value. Are stored in the memory block 53.
ra = fa (x) (x <(1/2) · A)
rb = fb (x) (x ≧ (1/2) · A) (19)

  In this way, since the span evaluation coefficient reference values ra and rb for relating W1 / W2 and W4 / W3 can be determined according to the value of the center-of-gravity coordinate value x, the center-of-gravity position of the object to be weighed can be determined during normal operation. The span evaluation coefficient in the x coordinate can be used as a reference value when all the load cells are normal, and the span variation of any one of the load cells can be accurately determined. In the above description, two types of functions are set with x = (1/2) · A as a boundary. However, no range is provided for the value of x, and one type of function is set. Also good. Further, the range of the x coordinate may be subdivided, and the function of the span evaluation coefficient may be set in each range.

<During normal operation>
During normal operation (during normal weighing work), when an object to be weighed is placed on the weighing platform 5, the load change amounts W1 to W4 can be obtained for all the load cells. The x coordinate of the center of gravity position of the current object to be weighed can be obtained. Then, the span evaluation coefficient reference value ra (or rb) corresponding to the x coordinate value is represented by fa (x) (or fb (x)) from the equation (19) according to the determined x coordinate. Can be determined by substituting

For example, if the x coordinate value is x <(1/2) · A, the x coordinate value is substituted into ra = fa (x), and the span evaluation coefficient reference value ra for the current x coordinate value is calculated. By this ra, the output of one load cell is expressed by the following equation by the equation (17) by the output equation of the remaining three load cells.
W1 = ra · W2 · (W4 / W3)
W2 = (1 / ra) .W1. (W3 / W4)
W3 = (1 / ra) .W4. (W2 / W1)
W4 = ra · W3 · (W1 / W2) (20)
Therefore, if any of the half bridges of the load cell 1A is identified as having a span abnormality by the above half bridge output comparison determination,
| W11-ra · W2 (W4 / W3) | >> | W21-ra · W2 (W4 / W3) |
... (21)
Is established, it is determined that the output of the half bridge 1 is a span abnormality, and conversely,
| W11-ra · W2 (W4 / W3) | <| W21-ra · W2 (W4 / W3) |
(22)
If is established, it is determined that the output of the half bridge 2 has a span abnormality.

(3.3.2) Relations that change in response to changes in the x and y coordinates of the center of gravity of the object to be measured To obtain more accuracy, the x and y coordinates are divided into four quadrants according to the values of x and y. It is also possible to determine a function for obtaining a reference value of a span evaluation coefficient corresponding to the x and y coordinates in each quadrant. This method can be applied to a weighing device in which an object to be weighed is placed at an arbitrary position on the weighing table 5.

<Adjustment mode>
In the adjustment mode, the weighing table surface is divided into four equal parts by a straight line connecting x = (1/2) · A and y = (1/2) · B, and the center of gravity of the test sample is set to the first quadrant to the fourth quadrant, respectively. The coordinates are positioned in each quadrant, and the span evaluation coefficient reference value corresponding to the x and y coordinate values is obtained for each quadrant. The x and y coordinate values on the weighing table of the test sample are calculated by the equation (18) by measuring the output signal of each load cell and displayed on the weight measuring device. At the same time, the load change amount is displayed.

First, for the first quadrant: the test sample placement position is changed within the range of x <(1/2) · A, y <(1/2) · B, and the span evaluation coefficient reference value r1 is expressed by the following equation: r1 = (W1 / W2) / (W4 / W3) (23)
And the output signals of the load cells 1A to 1D are measured at a plurality of locations together with the x and y coordinate values. Thus, r1 corresponding to the coordinate values (x, y) at a plurality of measurement points in the first quadrant is obtained.

Next, the span evaluation coefficient reference value calculation formula for the first quadrant is expressed as follows: r1 = a1 · x + b1 · y + c1 (24)
Then, the values of a1, b1, and c1 are obtained by a method such as the least square method, and a calculation formula for the span evaluation coefficient reference value r1 for an arbitrary center of gravity (x, y) in the first quadrant is determined.

  Similarly, for the second quadrant: Formula for calculating the span evaluation coefficient reference value r2 for an arbitrary barycentric position (x, y) within the range of x ≧ (1/2) · A, y <(1/2) · B For the third quadrant: Formula for calculating the span evaluation coefficient reference value r3 for an arbitrary barycentric position (x, y) within the range of x ≧ (1/2) · A, y ≧ (1/2) · B For the fourth quadrant: x <(1/2) · A, y ≧ (1/2) · Calculation formula of span evaluation coefficient reference value r4 for an arbitrary center of gravity (x, y) within the range of B Determine. The formula for calculating the span evaluation coefficient reference value ri in the i quadrant (i = 1, 2, 3, 4) thus determined is stored in the memory block 53 of the arithmetic circuit 26 for each quadrant.

<During normal operation>
During normal operation (during normal weighing work), when an object to be weighed is placed on the weighing platform 5, when the load change amounts W1p to W4p of all the load cells are obtained for all the load cells, these are obtained. Are set to W1 to W4, the x and y coordinates of the center of gravity of the object to be weighed are calculated to determine what quadrant the loading position of the object to be measured is, and the functions corresponding to the determined quadrants are r1 to r4. The span evaluation coefficient reference value corresponding to the placement position of the object to be weighed is calculated by substituting x and y coordinate values into the selected function. Hereinafter, the process of determining which half-bridge of the load cell where the abnormality of the span is specified using the obtained span evaluation coefficient reference value is abnormal and returning to the normal measurement is the same as described above. .

  As another embodiment, there is the following method for obtaining a span evaluation coefficient by proportional distribution using x and y coordinates. In this method, when the weighing platform is smaller than a track scale or the like, in the adjustment mode, a weight is placed near the points e, f, g, h, and p shown in FIG. In this method, verification is performed, and the reference value of the span evaluation coefficient at an arbitrary position is determined using the measurement result of the four corner verification.

<Adjustment mode>
In the adjustment mode, the four-corner adjustment opportunity is used, and at the time of adjustment, the four-corner coordinate e point (A / 4, B) is determined by the combined value of the full-bridge output of one specific load cell and the full-bridge outputs of the other three load cells. / 2), f point ((3/4) · A, B / 2), g point (A / 2, (3/4) · B), h point (A / 2, B / 4) and the center As reference points for the span evaluation coefficients corresponding to the p points (A / 2, B / 2), the coefficients re, rf, rg, rh, and rp are obtained and stored in the memory block 53 of the arithmetic circuit 26.

For example, with respect to re, when the weight is placed so that the center of gravity of the object to be measured is near the point e in FIG. 5A, that is, in the adjustment mode, the x and y coordinate display values are x≈A / 4, y≈ In the vicinity of displaying B / 2, the coefficient storage switch is pressed to measure the load changes W1 to W4 of the load cells 1A to 1D, and re is obtained by the following equation.
re = (W1 / W2) / (W4 / W3) (25)
Similarly, rf, rg, rh, and rp are obtained for the f point, the g point, the h point, and the p point other than the e point. Then, the reference value of the span evaluation coefficient at these reference coordinate values is stored in the memory of the weight measuring device.

<During normal operation>
At the time of normal operation, the x and y coordinates of the center of gravity of the object to be weighed are calculated by the equation (18) when the load change amounts W1 to W4 can be obtained together as described above. Now, assuming that the coordinates of the center of gravity m of the object to be weighed on the weighing platform 5 are m (x, y) in FIG. 5A, the calculated x, y coordinate values and x = A / 2, y = The quadrant in which the m point is in the coordinates is determined by a comparison with B / 2. Then, the coordinates of the reference position and the corresponding reference value of the evaluation coefficient are selected according to the quadrant to which the m point belongs. The evaluation coefficient is a method that changes approximately linearly in a plane between the reference positions on the coordinate plane of the weighing table. This method can cope with the case where the evaluation coefficient of the entire weighing platform changes nonlinearly.

For example, as shown in FIG. 5B, when the m point is in the fourth quadrant, the span evaluation coefficient reference value of the m point is based on the span evaluation coefficient reference values of the p point, the g point, and the e point. (Same for other quadrants).
At this time, first, values of k1, k2, q1, and q2 are obtained. The reference value for the e ′ point is obtained from the following equation by using the ratio between k1 and k2 as the reference value for the e and p points.
re ′ = (k1 · rp + k2 · re) / (k1 + k2) (26)
Similarly, the reference value of the point g ′ is obtained by the following equation by using the ratio of q1 and q2 as the reference value of the point g and the point p.
rg ′ = (q2 · rp + q1 · rg) / (q1 + q2) (27)
The reference value rm of the m-point span evaluation coefficient is expressed by the following equation depending on the ratio of k2 and q1.
rm = (k2 · rg ′ + q1 · re ′) / (k2 + q1) (28)

  In this embodiment, when a load cell with an abnormal span is detected, when calculating a weight measurement value of an object to be weighed on the weighing platform 5, the automatic return means is used for a load cell having a half bridge with an abnormal span. The output signal is set to a mode in which the output signal estimated by the normal output signal estimation unit is replaced, or the span of the half-bridge output signal having an abnormal span is determined by the output signal estimated by the normal output signal estimation unit. It is preferable to have a function of switching between the modes for executing the correction operation. Similarly, with regard to the manual return means, a mode in which the output signal of the load cell having a half bridge with an abnormal span is replaced with the output signal estimated by the normal output signal estimation unit, or the half bridge with an abnormal span is used. It is preferable to have a function of switching whether to set a mode in which a calculation for correcting the span of the output signal is performed by the output signal estimated by the normal output signal estimation unit.

  Further, it is preferable to display that the output signal of the load cell having an abnormal span is being corrected or replaced with a normal value by the automatic return means or the manual return means.

<About a fault diagnosis apparatus according to another embodiment>
In the failure diagnosis apparatus 20 according to the present embodiment, as shown in FIG. 3, the load signal for each half bridge is obtained and the full bridge output is obtained by adding two half bridge outputs. Instead of such a system configuration, as shown in FIG. 6, it is also possible to adopt a system configuration in which the full bridge output is detected independently of the half bridge output. In the failure diagnosis apparatus 20A, the same or similar parts as those of the failure diagnosis apparatus 20 of the previous embodiment are given the same reference numerals in the drawing, and detailed description thereof is omitted. The description will focus on differences from the failure diagnosis apparatus 20 of the embodiment.

The failure diagnosis apparatus 20A of the present embodiment includes an analog adder circuit 57, an A / D converter 58, and an arithmetic circuit 26 that are provided for the full bridge circuit 15.
Here, the full bridge circuit 15 and the arithmetic circuit 26 are the same as those used in the failure diagnosis apparatus 20 of the previous embodiment.
In the failure diagnosis apparatus 20 of the previous embodiment, two A / D converters 24 and 25 are used, but in the failure diagnosis apparatus 20A of this embodiment, one A / D converter 58 is used. In the failure diagnosis apparatus 20A, three A / D converters may be used for each of two half-bridge outputs and one full-bridge output.
In the fault diagnosis apparatus 20 of the previous embodiment, a DC voltage is applied in which the potential at the connection point 16 in the full bridge circuit 15 is + V and the potential at the connection point 17 is zero. A DC voltage is applied such that the potential at the connection point 16 is + V and the potential at the connection point 17 is −V. In this case, the half-bridge circuits 15a and 15b using the voltage reference fixed resistors 21 and 22 that are required in the failure diagnosis apparatus 20 of the previous embodiment are not necessary.

The analog adder circuit 57 includes a first operational amplifier 61, a second operational amplifier 62, a third operational amplifier 63, a fourth operational amplifier 64, and a fifth operational amplifier 65.
In the first operational amplifier 61, the input positive terminal 61a is connected to the connection point 18 of the full bridge circuit 15, the input negative terminal 61b is connected to the output terminal 61c, and the output terminal 61c is connected to the resistors 66 and 67. .
In the second operational amplifier 62, the input positive terminal 62 a is connected to the connection point 19 of the full bridge circuit 15, the input negative terminal 62 b is connected to the output terminal 62 c, and the output terminal 62 c is the resistor 68 and the fourth operational amplifier 64. Each is connected to the input positive terminal 64a.
In the third operational amplifier 63, the input positive terminal 63a is connected to the resistor 68, and is connected to the circuit ground 70 via the resistor 69, and the input negative terminal 63b is connected to the resistor 66. The output terminal 63 c is connected to the A / D converter 58 via the analog switch 72.
In the fourth operational amplifier 64, the input positive terminal 64 a is connected to the output terminal 62 c of the second operational amplifier 62, and the input negative terminal 64 b is connected to the circuit ground 70 via the resistor 73 and the resistor 74. The output terminal 64 c is connected to the A / D converter 58 via the analog switch 75.
In the fifth operational amplifier 65, the input positive terminal 65 a is connected to the circuit ground 70 via a resistor 76, and the input negative terminal 65 b is connected to a resistor 67, and is also connected to a output terminal 65 c via a resistor 77. The output terminal 65 c is connected to the A / D converter 58 via the analog switch 78.

  In the failure diagnosis apparatus 20A of the present embodiment, the analog load signal for the weighing instrument is synthesized by the third operational amplifier 63. The output load signal of the half-bridge circuit 15a on the connection point 18 side is eob, the load signal of the half-bridge circuit 15b on the connection point 19 side is eoa, and only one A / D converter 58 is used for all signals. The input is switched by analog switches 72, 75, 78. Thus, the number of A / D converters used may be selected as appropriate.

If the full-bridge output exists independently as in the failure diagnosis apparatus 20A, the full-bridge output and the two half-bridge outputs have the same value for the same load when the load cell is adjusted. That is, the span coefficient is set so that Wn = Wan = Wbn, and an initial weight storage memory and a zero point weight storage memory are provided.
Independent of the half-bridge output, W1 to W4 are processed by the following equations.
W1 = K1. (Wa1-Wi1) -Wz1
W2 = K2 · (Wa2-Wi2) -Wz2
W3 = K3. (Wa3-Wi3) -Wz3
W4 = K4. (Wa4-Wi4) -Wz4

  The weighing device of the present invention can be suitably used for detecting an abnormality of a span generated in a strain gauge type load cell used in a weighing instrument such as a conveyor scale, a hopper scale, a track scale, a platform scale, a fee scale, or the like.

1A, 1B, 1C, 1D Load cell 5 Weighing table 15a, 15b Half bridge circuit 20, 20A Fault diagnosis device 26 Arithmetic circuit 52 Central processing unit 53 Memory block 54 Display device

Claims (16)

A half bridge load signal is generated based on output signals from two terminals in a Wheatstone bridge circuit composed of at least four strain gauges affixed to the strain generating portion of the load cell, and four corners are formed in the load cell. In a weighing device in which an object to be weighed is placed on a weighing platform that is supported and the weight of the object to be weighed is measured.
A weighing device, comprising: a half-bridge load signal calculation unit that performs calculation processing so that each half-bridge load signal becomes a load signal having the same magnitude with respect to a load applied to the load cell.   2. A span abnormality detection means for detecting a load cell having an abnormal span among the load cells by comparing two half bridge load signals output from the half bridge load signal calculation means. The weighing device described in 1.   And a zero point variation identifying unit for identifying that at least one of the two half bridge load signals output from the half bridge load signal calculating unit varies from the zero point. The measuring device according to claim 1 or 2.   4. A zero point adjusting means for manually or automatically adjusting the zero points of the two half bridge load signals output from the half bridge load signal calculating means. The weighing device described in 1. Stable determination of two half-bridge load signals output from the half-bridge load signal calculating means, and stable weight value generating means for generating a stable weight value of the load cell, and generated by the stable weight value generating means. Load variation calculation means for calculating for each load cell the difference between the latest stable weight value and the stable weight value generated at the timing immediately before the latest stable weight value as a stable load change amount. ,
The said span abnormality detection means detects the abnormality of the span of the said load cell by comparing the stable load change amount of two half bridges calculated by the said load change amount calculation means. The metering device described.   The measuring apparatus according to claim 2, further comprising a span change rate calculating unit that calculates a span change rate in a half bridge of the load cell in which a span abnormality is specified by the span abnormality detecting unit.   The span abnormality half-bridge specifying means for specifying which half bridge of two half bridges in a load cell in which a span abnormality is specified by the span abnormality detection means is abnormal. The weighing device according to 2, 5 or 6.   The normal output signal estimation means for estimating the normal output signal of the span for the load cell in which the abnormality of the span is specified by calculating the output signal to the remaining three load cells is provided. 7. The weighing device according to 7.   The normal-time output signal estimation means is configured to convert an output signal of one load cell having a half bridge with an abnormal span, a conversion coefficient calculated based on an arbitrary center of gravity position on the weighing table of the object to be measured, and the remaining The weighing apparatus according to claim 8, wherein estimation is performed by calculation with output signals of three load cells.   10. The load cell output signal replacing means for replacing the output signal of one load cell having a half bridge with an abnormal span with the output signal estimated by the normal output signal estimating means. The weighing device described in 1.   11. The measuring apparatus according to claim 10, further comprising: a load cell span correcting unit that corrects a span of an output signal of the half bridge having an abnormal span by the output signal estimated by the normal output signal estimating unit.   A mode for replacing the output signal of the load cell having an abnormal span by the load cell output signal replacing means when calculating the weight measurement value of the object to be weighed on the weighing platform at the timing when the load cell having an abnormal span is detected; 12. The weighing apparatus according to claim 11, further comprising automatic return means for automatically switching to a mode for executing an operation for correcting an output signal of a load cell having an abnormal span by the load cell span correction means.   A mode for replacing the output signal of the load cell having an abnormal span by the load cell output signal replacing means when calculating the weight measurement value of the object to be weighed on the weighing platform at the timing when the load cell having an abnormal span is detected; 12. The weighing apparatus according to claim 11, further comprising a manual return means for switching by a manual device to a mode for executing a calculation for correcting an output signal of a load cell having an abnormal span by the load cell span correcting means.   3. The weighing apparatus according to claim 2, further comprising display means for displaying a load cell in which a span abnormality is specified by the span abnormality detection means and the content of the abnormality by an identification code.   7. The measuring apparatus according to claim 6, further comprising display means for displaying a span change rate value calculated by the span change rate calculating means together with an identification code of a load cell having an abnormal span.   14. The display device according to claim 12, further comprising a display unit configured to display that the output signal of the load cell having an abnormal span is being corrected or replaced with a normal value by the automatic return unit or the manual return unit. Weighing device.

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