JP2002243562A - Digital load cell and multi-load cell type weighing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital load cell and a multi-load cell type weighing machine capable of organizing easily a system as a weighing machine by being connected to existing external equipment, and reducing a load on the external equipment side. SOLUTION: In this digital load cell, a mass value conversion means for converting a digital signal outputted from an A/D conversion means 5 into a mass value, an evaluation means for executing at least one evaluation relative to the mass value, a mass value memory 13 for storing the mass value, a mass value fluctuation detection means for reading out the mass value from the mass value memory 13, and acquiring the change with time of the mass value, and a processing means for executing at least one from among zero set processing relative to the digital signal before conversion into the mass value or to the mass value, zero tracking processing, and processing except a tare, or the like, are installed on a strain element 40 or disposed near it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital load cell which is a load cell (load detector) capable of digitally outputting a detection result, and to a multi-load cell scale which receives a load on an object to be weighed by a plurality of digital load cells.

[0002]

2. Description of the Related Art Conventionally, a circuit board having a function of converting an analog output signal of a bridge circuit affixed to a flexure element into a digital signal is directly attached to the flexure element, or disposed near the flexure element. There is a digital load cell in which a strain body and a circuit board are configured as one unit.

FIGS. 6 and 7 show an example of the digital load cell. The circuit board 1 is attached to the substantially columnar flexure element 40 shown in FIG. 7 and the digital load cell 20 shown in FIG.
Is configured. The circuit board 1 is attached by screwing a screw 41 a into a screw hole 41 b formed in the strain body 40. Four strain gauges (two in the figure, but two on the rear side) are attached to the peripheral surface of the small diameter portion 40c at the center of the strain body 40. These are electrically connected to form a bridge circuit 2. Flexure element 40
When a load acts on both end surfaces 40a and 40b of the small diameter portion 40,
c is a strain, which is detected by the strain gauge 42, and a voltage corresponding to the magnitude of the strain is applied to the bridge circuit 2.
Output.

FIG. 8 is a block diagram showing a configuration of the digital load cell 20. An amplifier 3 is connected to an output side of the bridge circuit 2, a low-pass filter 4 is connected to an output side of the amplifier 3, and an A / D converter 5 is connected to an output side of the low-pass filter 4. A reference voltage generator 8 is connected to the bridge circuit 2 and the A / D converter 5. The reference voltage generator 8 supplies an excitation voltage to the bridge circuit 2 and supplies a reference voltage to the A / D converter 5. give.

[0005] The A / D converter 5 is connected to the CPU 6. A two-way communication control circuit 7 having a transmitting circuit and a receiving circuit is connected to the CPU 6, and an indicator, a personal computer (P
C; Personal Computer), programmable logic
Controller (PLC; Programmable Logic Controlle)
r) Signal transmission / reception with external devices such as is possible.

The above described amplifier 3, low-pass filter 4,
A / D conversion means 5, a reference voltage generation circuit 8, a CPU 6, a bidirectional communication control circuit 7, and the like are formed on the circuit board 1.

In the digital load cell 20 configured as described above, when a load acts on the strain element 40 and the resistance of the strain gauge 42 attached to the strain element 40 changes, the balance of the bridge circuit 2 is lost. A voltage proportional to the resistance change of the gauge 42 is output. This analog output is amplified by an amplifier 3 and a low-pass filter 4
To enter. Then, high-frequency components (noise) are removed by the low-pass filter 4, and further converted to digital signals by the A / D converter 5.

The digital signal output from the A / D conversion means 5 is corrected by the CPU 6 in a span adjustment (sensitivity adjustment) in which the output is adjusted to a rated value under a rated load, and a variation in the output value due to a temperature change is corrected. Temperature correction, output value correction according to the difference in gravitational acceleration at the weighing place, etc.
The data is transmitted to an external device such as an indicator via the bidirectional communication control circuit 7.

In the conventional digital load cell 20, FIG.
As shown in FIG.
Only the digital value "0000" was output, and the external device 30 converted the digital value "300000" into a mass value in response to the output. And a combination example of the weighing capacity and the scale weight as shown in Table 1 are stored in the memory.

[0010]

[Table 1]

For example, the rated capacity of the digital load cell 20 is 300 kg, and the rated output value at this time is “60000”.
0 ", and it is assumed that" 150 kg of weighing capacity / 0.05 kg of graduation "is specified from the combinations in Table 1. In this case, a digital value “300000” corresponding to 150 kg
Divided by 3000 (= 150 kg / 0.05 kg) 1
00 count is equivalent to 0.05 kg, and the external device 30 sets the digital output value of the digital load cell 20 to 100
Convert to mass values (in 0.05 kg increments) in count increments.

Further, with respect to the mass value obtained therefrom,
Various comparative evaluations are performed according to the purpose of use of the digital load cell 20. For example, when the digital load cell 20 is used for a hopper scale, the mass value
On the 0 side, by comparing with various comparison reference values, it is determined whether the contents in the hopper are excessive or insufficient. Further, a process of storing the mass value in the memory of the external device 30 for a predetermined period and obtaining a temporal change of the mass value in the predetermined period is also performed. Furthermore, a zero value for adjusting the mass value at the time of no load or the digital value before mass value conversion to zero,
The external device 30 also performs various processes such as zero tracking for compensating for the fluctuation of the zero-set value due to temperature change and the like, and taring for subtracting the mass of the mounting table and hopper.

In the case of a multi-load cell type balance in which a plurality of digital load cells support one loading table or hopper, the indicator receives the detected values (digital values) of the plurality of digital load cells and sums them. Later, mass value conversion and various comparative evaluations on the mass value are performed.

[0014]

Conventionally, a mass value conversion program and a comparative evaluation program must be incorporated in an external device such as an indicator, a personal computer, and a programmable logic controller connected to a digital load cell. Did not. With this, whenever you change the use purpose or place of use of the digital load cell,
It is necessary to create and incorporate various programs in a language and a format suitable for the intended use and in the external device installed at the place of use, which is troublesome and costly. In other words, existing personal computers and the like could not be used immediately as indicators, and their usability was poor.

Many programs are incorporated in existing personal computers and the like to perform various functions in addition to the above-described various processes related to the digital load cell, and are not necessarily used exclusively for various processes of the digital load cell. Therefore, depending on the external device to be used, the load applied to the CPU and the memory is increased by performing the above-described various processes by being connected to the digital load cell, and the process is delayed.

The present invention has been made in view of the above-described problems, and provides a digital load cell and a multi-load cell type scale that can be easily connected to existing external equipment to construct a system as a scale and can reduce the load on the external equipment. The task is to

[0017]

According to a first aspect of the present invention, there is provided a digital load cell, wherein a mass value conversion means for converting a digital signal output from an A / D conversion means into a mass value is attached to or near a strain body. It is arranged and configured. That is,
Each digital load cell that is a load detection sensor itself has a mass value conversion function, the digital load cell itself outputs as a scale, and the external device only needs to have a display function. And reduce the load on the external device.

According to a second aspect of the present invention, there is provided a digital load cell, comprising: a processing unit for performing at least one of a zero set process, a zero tracking process, and a tare process on a digital signal output from the A / D conversion unit. , Attached to or near the flexure element. This eliminates the need to provide the external device with the above-described processing functions, thereby improving the usability of the external device and reducing the load on the external device.

In the multi-load cell scale according to the third aspect of the present invention, any one of the plurality of digital load cells receives a digital signal output from the A / D conversion means of another digital load cell. The sum of the received digital signal and the digital signal output from the A / D converter is calculated. In other words, since the digital load cell itself has a function of adding the detection value of the other digital load cell and the detection value of the digital load cell itself that constitute a multi-load cell scale, the usability of the external device is improved and the external device side Such a load is reduced.

According to a fourth aspect of the present invention, the mass value conversion means for converting the sum value into a mass value is attached to or disposed near the flexure element to enhance the added value of the digital load cell.

According to claim 5 of the present invention, the mass value
An evaluation means for performing at least one evaluation is mounted on or near the flexure element to increase the added value of the digital load cell.

According to a seventh aspect of the present invention, a mass value memory for storing a mass value, and a mass value fluctuation detecting means for reading a mass value from the mass value memory and obtaining a temporal change of the mass value are provided. It is mounted on or near the body to increase the added value of the digital load cell.

According to an eighth aspect of the present invention, processing means for performing at least one of a zero set process, a zero tracking process, and a tare process on the mass value or the sum value is attached to or near the flexure element. To increase the added value of the digital load cell.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. The same components as those in the related art are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a block diagram showing a configuration of a digital load cell 10 according to an embodiment of the present invention. In the present embodiment, the CPU 6 'of the digital load cell 10 itself has functions as mass value conversion means, various evaluation means, mass value fluctuation detection means, zero set processing means, zero tracking processing means, and tare processing means. It has.

The CPU 6 'is connected to the A / D converter 5 and the bidirectional communication control circuit 7 on the circuit board 1 attached to the strain body 40, as in the prior art. In the CPU 6 ', arithmetic and logical operations, decoding and execution of instructions of various programs, A / D conversion means 5,
It exchanges signals with each of the memories 11 to 14 connected to the CPU 6 ′, external devices, and the like, and executes mass value conversion and various comparative evaluations. Various programs are stored in a main memory (not shown) (also formed on the circuit board 1 and the CPU 6 ′).
The signal is exchanged between the two.)

Next, each processing performed on the digital load cell 10 side will be described.

First, the mass value conversion will be described. In advance, the correspondence between the rated load and the rated digital value and a combination example of the weighing capacity and the weighing capacity as shown in Table 1 are written in the weighing capacity / weighing capacity memory 11 in advance. This is input to the bidirectional communication control circuit 7 from the external device side and written into the weighing / scale memory 11. When the combination of the weighing capacity and the scale is specified from the external device,
In the processing procedure according to the mass value conversion program executed by the CPU 6 ', the digital value (for example, "300000") output from the A / D conversion means 5 corresponds to the relationship between the rated load and the rated digital value. , And specified weighing capacity
It is converted to a mass value (for example, 150 kg) based on the scale interval,
The mass value is output to an external device via the bidirectional communication control circuit 7. The external device simply receives the mass value and displays it on the display unit.

Next, a case where the digital load cell 10 is applied to a hopper scale as shown in FIG. 3 will be described. Hopper 2 for storing materials such as powder and liquid
5 is supported by a plurality of digital load cells 10 via a bracket 25a attached to the outer peripheral wall. The material is introduced into the hopper 25 from above by a material introduction means (not shown), and the material is discharged from the discharge pipe 27 with the bottom valve 26 opened. The mass of the contents is obtained by summing the mass values (obtained by the above conversion) of the respective digital load cells 10, or by summing the digital values before mass value conversion, and then converting this to a mass value.

Various comparison reference values input from the external device and received by the bidirectional communication control circuit 7 are written in the comparison reference value memory 12 in advance. The mass value obtained by the above conversion is compared with various comparison reference values in a processing procedure according to a comparison evaluation program executed by the CPU 6 ′. Output to an external device via

As the comparison reference value, for example, the upper limit L1,
There are a fixed amount set value L2, a fixed amount set value L3, and a lower limit value L4.

The upper limit L1 is a value (mass value) indicating that the contents in the hopper 25 have reached or have reached the maximum capacity of the hopper 25. When the measured mass value reaches the upper limit value L1, the result is output to the external device side, and in response to this output, the external device notifies the operator by display or alarm and outputs a stop signal to the input means. Then, the charging of the material is stopped.

The lower limit L4 is a value (mass value) indicating that the contents are disappearing from the hopper 25. When the measured mass value reaches the lower limit value L4, the result is output to the external device side, and when the output is received, the external device side notifies the operator by display or alarm, etc., and the valve (for example, solenoid valve) 26 Is switched to closed, and a charging signal is output to the charging means to replenish the material in the hopper 25.

The set value L2 is, for example, 100 kg, and the set value L3 before quantification is, for example, 80 kg. If the measured mass value is less than the pre-quantification set value L3, the material is supplied at a large input amount per unit time, and the pre-quantification set value L3
Is reached, the result is output to the input means, and the input amount per unit time is made smaller than when the value is less than the pre-quantification set value L3. When the set value L2 is reached, this result is output to the input means and the input is stopped. Thereby, a fixed amount of material of 100 kg can be put into the hopper 25 in a short time and with high accuracy.

As another comparison reference value, when measuring an object whose mass value is known to some extent before weighing, set values 1 to 3 for evaluating the accuracy of the measured mass value. There is. This is because, when the condition of set value 1 ≦ measured mass value ≦ set value 2 has continued for a predetermined time (set value 3), weighing is now performed stably without being affected by vibration or the like. Thus, the result that the measured mass value is accurate and the mass value are output to the external device.

A certain mass value is set as another comparison reference value, and the number of times of weighing which is equal to or larger than the certain mass value is stored in the count value memory 14 at the time of weighing. Then, if the count value is output to the external device based on a command from the external device side, the accumulated load status on the digital load cell 10 up to the present time can be known. Then, when the digital load cell 10 breaks down, by checking whether the count value is within the range of durability, the quality of the digital load cell 10 can be determined.

Next, a description will be given of a process for obtaining a temporal change of the measured mass value in a certain set period.

When a measurement start command is input from the external device, the mass value memory 13 stores mass values measured at a timing by a clock signal generator (not shown). This is continued until a measurement end command is input from the external device. Then, the mass value stored in the mass value memory 13 is read out by the processing procedure according to the mass value variation detection program executed by the CPU 6 ′, and is set for a set period (from the measurement start command to the measurement end command). ) Is obtained as a graph in which the horizontal axis is the time axis and the vertical axis is the mass value, and the result is output to the external device via the bidirectional communication control circuit 7.

The functions described above are required, for example, when the digital load cell 10 is used for a tensile test of a material, and the material is broken (at this time, the mass The maximum value immediately before the value becomes 0) is obtained as the maximum tensile strength of the material. In addition, a function for determining a temporal change in the mass value is required even in a compression test or the like.

The digital load cell 10 having such a function can also be applied to the case where materials on a belt conveyor are weighed. FIG. 4 shows an example of the configuration of the belt conveyor. A belt conveyor including a belt 31 and a driving roller 32 and a driven roller 33 around which the belt 31 is wound is supported by a movable frame 34. Drive roller 3
2 is driven at a constant speed by a motor 35 via a belt 36, so that the belt 31 runs at a constant speed in the direction of the arrow A. A blade receiver 37 is fixed to a lower portion of the movable frame 34, and a blade 38 fixed to a base 39 is engaged with the blade receiver 37. Digital load cell 1 is on base 39
0 is fixed, and the movable frame 34 is
In this case, the rotating force is received with the blade 38 as a fulcrum. A dash pot 44 is fixed to the left end of the base 39, and functions to apply a brake to the rotational movement of the movable frame 34. Stoppers 45a and 45b are provided at the front end portion and the rear end portion of the movable frame 34 to restrict the rotation of the movable frame 34 by a predetermined amount or more so that an excessive load is not applied to the digital load cell 10.

The material cut out from a material supply hopper or the like (not shown) is transferred on the belt 31 in the direction of arrow A, and its mass value is detected by the digital load cell 10. Then, by observing the temporal variation of the detected mass value, if there is an extremely large value or a small value, it is determined that some abnormality may have occurred on the cut side of the material, for example. Can be performed.

The concept of evaluating the mass value also includes a calculation process for the mass value performed on a counting scale that automatically counts the number of many parts of the same type. This means that, for example, one of a large number of parts (for example, bolts) of the same type whose number
Place 0 pieces on the plate and use the digital load cell 10
From the mass values (for example, 50 g) of these ten bolts, a mass value of 5 g per bolt is obtained. And this "5
g "is stored in the memory of the digital load cell 10, and then, when a large number of the above-mentioned bolts are put on the plate, and the mass value at this time is 8000 g, 8000 g /
When 5 g is calculated by the CPU 6 ', the number of bolts (1600) on the plate is obtained on the digital load cell 10 side, and the result (1600) is output to the indicator.

The digital load cell 10 is also provided with processing means for performing each of the processes of zero set, zero tracking, and tare so that the digital load cell 10 performs these processes. When a zero set command is received from the external device via the two-way communication control circuit 7 in a state where measurement is not being performed, a digital value output from the A / D conversion means 5 or a mass value obtained by converting the digital value from the digital value is output. Is set as the zero point. When a tare subtraction command is received from the external device via the bidirectional communication control circuit 7, the mass value measured at that time is stored in the memory of the digital load cell 10 as a tare mass value. Then, the digital value corresponding to the tare mass value is subtracted from the digital value before the mass value conversion. Each of the above processes is performed according to a processing procedure according to a predetermined program executed by the CPU 6 ′.

FIG. 2 shows the relationship between the digital load cell 10 and the external device 30 according to the present embodiment. As described above, the digital load cell 10 of the present embodiment has a mass value conversion function and various evaluation functions.
For 0, the mass value and the evaluation result are output. Therefore, the external device 30 only needs to have at least a function of displaying the results and input means such as a keyboard for setting a comparison reference value in the digital load cell 10 and giving various commands. It is not necessary for the external device 30 to create and install various programs in a language and format that can be recognized by the external device 30 (for recognizing the connected digital load cell 10 and exchanging signals). Program is required). Therefore, an existing personal computer or the like provided at the place where weighing is performed is replaced with the digital load cell 10.
To easily build a system as a scale,
We can start weighing work quickly without taking time and effort on the spot.

The digital load cell 10 is produced as a digital load cell having a mass value conversion function, a zero set processing function, a zero tracking processing function and a tare processing function in consideration of mass productivity. In order to be applicable to any purpose, various types of storage memories (one memory may be shared) may be provided, inputs from external devices may be received, and various programs may be stored. Incorporation and execution are possible, and the user incorporates various programs according to the application,
The digital load cell has a specific function. Alternatively, the problem may be dealt with by replacing the circuit board 1 created for each function. The digital load cell 10 can be applied to various uses other than those described in the above embodiments, and various comparison evaluation functions and processing functions are added according to the uses. The digital load cell 10 is a multi-function balance having these functions. The load cell itself can be configured.

Next, FIG. 5 shows each digital load cell 51 in the multi-load cell scale according to the present embodiment.
The connection relationship between a to 51d and the indicator 30 is shown. The multi load cell scale has four digital load cells 51a-
51d supports and supports a mounting table.

Each of the digital load cells 51a to 51d has the same configuration. In addition to the configuration of the digital load cell 10 described above, the detection value (digital value) of another digital load cell and the detection value of itself (digital value) are provided. Is provided. Then, any one of the four digital load cells 51a to 51d (in this case, for example, the digital load cell 51a) is used to detect each of the detection values (digital values) of the other three digital load cells 51b to 51d which together form a multi-load cell scale. ) Is received, and these three digital values and their own detected values (digital values) are summed by the summing means.

That is, the digital load cell 51a is used as a master load cell, and the addition processing in the multi-load cell scale is conventionally performed by the indicator 30.
The master load cell 51a performs the calculation, and the master load cell 51a converts the sum obtained by the summing means into a mass value, performs various evaluations on the mass value as described above, and displays the result as an indicator. Output to 30. Further, in the master load cell 51a, each processing of zero set, zero tracking, and tare for the sum value or the mass value is also performed. Therefore, the indicator 30 only needs to receive the output from the master load cell 51a and display it, and it is possible to prevent the indicator 30 from being overloaded and to speed up the processing. In addition, it is possible to use an inexpensive indicator having not so large processing capacity as the indicator. Also, even when a plurality of multi-load cell scales are connected to one indicator, it is not necessary to connect all the digital load cells to the indicator, and only the master load cell of each multi-load cell scale is connected to the indicator. Then, the indicator need only display the output.

[0049]

As described above, by using the digital load cell of the present invention, a digital output scale can be constructed simply and at low cost in combination with an existing personal computer. Also, in the case of a multi-load cell type scale, the load on the external device can be reduced and the processing speed can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital load cell according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a relationship between a digital load cell and an external device according to the present invention.

FIG. 3 is a schematic side view of a scale with a container.

FIG. 4 is a schematic side view of a belt conveyor with a load detection function.

FIG. 5 is a block diagram showing a connection relationship between each digital load cell constituting the multi-load cell scale according to the present embodiment and an external device.

FIG. 6 is a side view showing an example of a digital load cell.

FIG. 7 is a side view of a strain body constituting the digital load cell.

FIG. 8 is a block diagram showing a configuration of a conventional digital load cell.

FIG. 9 is a block diagram showing a conventional relationship between a digital load cell and an external device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 signal processing circuit board 2 bridge circuit 3 amplifier 4 low-pass filter 5 A / D conversion means 6 ′ CPU 7 bidirectional communication control circuit 10 digital load cell 30 external device 40 strain element 42 strain gauge 51 a master load cell

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koichi Segawa 2-35 Jinmucho, Yao-shi, Osaka F-term in Kubota Kuhoji Plant (reference) 2F049 BA01 CA04 CA11

Claims (8)

[Claims] 1. A flexure element having a bridge circuit attached thereto, and an A / D converter attached to or disposed near the flexure element to convert an analog signal output from the bridge circuit into a digital signal. Means for converting the digital signal into a mass value, wherein the mass value conversion means is attached to or near the strain body. 2. A flexure element having a bridge circuit attached thereto, and an A / D converter which is attached to or disposed near the flexure element and converts an analog signal output from the bridge circuit into a digital signal. Means for performing at least one of a zero set process, a zero tracking process, and a tare process on the digital signal, attached to the strain body or disposed in the vicinity thereof. A digital load cell characterized by: 3. A flexure element having a bridge circuit attached thereto, and an A / D converter attached to or disposed near the flexure element, for converting an analog signal output from the bridge circuit into a digital signal. Means for receiving a load on an object to be weighed by the plurality of digital load cells, wherein one of the plurality of digital load cells includes the digital load cell. Receiving the digital signal,
A multi-load cell scale, wherein the digital signal and its own digital signal are added to obtain a sum. 4. The multi-load cell scale according to claim 3, wherein mass value conversion means for converting the sum to a mass value is attached to or near the flexure element. 5. The digital load cell or claim according to claim 1, wherein an evaluation means for performing at least one evaluation on the mass value is attached to or near the flexure element. Item 4. A multi-load cell scale according to item 4. 6. A comparison reference value memory for storing a preset comparison reference value, a comparison means for reading the comparison reference value from the comparison reference value memory and comparing the comparison reference value with the mass value. 6. The digital load cell or multi load cell scale according to claim 5, further comprising: 7. A strain element, comprising: a mass value memory for storing the mass value; and a mass value variation detecting means for reading the mass value from the mass value memory to determine a temporal change of the mass value. The digital load cell according to claim 1 or a multi-load cell type balance according to claim 4, wherein the scale is mounted on or in the vicinity thereof. 8. A processing means for performing at least one of a zero set process, a zero tracking process, and a tare process on the mass value or the summed value is attached to or close to the strain body. The digital load cell according to claim 1, the multi-load cell scale according to claim 4, or the multi-load cell scale according to claim 3.