JP5730650B2 - Conveyor scale load cell - Google Patents

Description

  The present invention relates to a load cell for a conveyor scale that is used in a conveyor scale and in which a load cell main body that receives a load of an object to be weighed and a measurement circuit that calculates a digital load signal are integrated.

  There are a track scale and a conveyor scale as a measuring instrument in which a display operation device for monitoring a measured value in a measuring unit and adjusting a zero point is remotely installed on the main unit of the measuring unit. Of these, the truck scale is often used so that the four corners of the weighing platform are supported by four load cells. The conveyor scale also supports the weighing section with a plurality of load cells, more specifically. Specifically, a configuration in which a conveyor transport roller is supported by a plurality of load cells is often used.

  As load cells used for these, a substrate having an A / D conversion circuit and an arithmetic circuit is integrally installed in the vicinity of the strain generating body, and an analog load signal corresponding to a predetermined load is set to a predetermined magnitude by A / D conversion. A load cell configured to convert the digital load signal into a serial line and output the digital load signal to a serial line is preferable. That is, if the display operation device is remotely arranged with respect to the main body of the measuring unit, the number of wirings between them is increased and the cost is increased. Therefore, input / output signals for a plurality of load cells are used as serial signals, A single serial line is provided, and the weighing unit main body in which a plurality of load cells are installed is connected to the display operation device through the single serial line, and the plurality of load cells and the display operation device are polled by the display operation device. It is preferable to adopt a method of communicating with each other.

  When multiple load cells are used in one weighing unit, the output signal of one load cell is compared with the output signal of another load cell, so that the output error of the load cell during operation of the weighing instrument can be detected. It has a great effect that it can be discovered and the failure can be dealt with early (see Patent Document 1). Of course, it goes without saying that the weight of the object to be weighed can be accurately measured.

In order to provide a failure detection function, basically, an output signal for each load cell must be sent to the display / operation device. In this case, since the conventional load cell for outputting an analog load signal has to individually send output signals to the display / operation device, a large number of wirings are required, but the above-described digital load cell does not have such a problem.
In addition, when the load cell is easily inspected or when the load cell is replaced, the load cell for analog load signal output requires span adjustment on the main body. However, in the case of a digital load cell, there is an advantage that it can be easily replaced because the built-in arithmetic circuit has only to store the span coefficient specific to the load cell at the time of the single adjustment.

  In order to take advantage of this digital load cell, as shown in FIGS. 6 and 7 of Patent Document 2, a single serial line common to a plurality of load cells supporting the platform scale is provided to communicate with an external unit. Such a structure is known. However, when the input / output signals of a plurality of load cells are connected by a single common serial line as described above, it takes a long time for communication and a long time for controlling the communication, and the weight signal is sent to the display operation device at high speed. There is a problem that can not be.

  The conveyor scale is equipped with a pulse transmitter that emits a pulse at every predetermined distance, and the weight of the object to be weighed conveyed on the conveyor is measured according to the pulse transmitted from this pulse transmitter and integrated. However, since the objects to be weighed conveyed on the conveyor are distributed in a complicated shape, a pulse is transmitted at the smallest possible movement distance to transmit accurately. Measurement and calculation operations for calculating the weight at a speed (time interval) corresponding to the applied pulse are required. For example, if the moving speed of the conveyor is fast, the frequency of the transmission pulse is about 500 Hz, and a speed within 2 msec may be required for the weight measurement for each predetermined moving distance.

  In this case, there is no problem in measuring the load signal with a period of about several milliseconds in the digital load cell, but communication control is performed by the arithmetic circuit of the display operation device, and the short period of the plurality of digital load cells changes. Even when trying to read the load signal, the display operation device used with the normal communication controller and CPU does not catch up with the reading speed, so the load signal cannot be read reliably. There is a problem that can not be.

JP-A-5-264375 Japanese Patent Laid-Open No. 1-250028

  The present invention has been made in view of the above-described problems. By inputting the pulse signal output from the pulse transmitter and calculating the transport amount, one serial line is shared with other load cells. It is an object of the present invention to provide a conveyor scale load cell that can accurately calculate an integrated transport amount by reading an accurate transport amount into a display / operating device even if it is used.

In order to achieve the above object, a conveyor scale load cell according to the present invention comprises:
In a load cell for a conveyor scale in which a load cell main body that receives a load of an object to be weighed and a measurement circuit that calculates a digital load signal are integrally provided.
The conveyor scale load cell includes a pulse signal input line for inputting a pulse signal transmitted from a pulse transmitter to the measurement circuit every time a conveyor constituting the conveyor scale moves a predetermined distance,
The measurement circuit is connected to an external device of the conveyor scale load cell by a serial line for serial signal communication,
The measurement circuit calculates a transport amount for each predetermined movement distance for each load cell of the object to be weighed conveyed on the conveyor based on the pulse signal and a load signal detected by the load cell main body. The data is output to the serial line (first invention).

  In the present invention, in response to a measurement mode switching signal from the outside of the conveyor scale load cell, a first measurement mode for calculating and outputting a transport amount for each predetermined movement distance of the object to be weighed, and the object to be weighed It is preferable that the second measurement mode for calculating and outputting a load signal for each predetermined time for an object can be switched (second invention).

  In this case, it is preferable that the transport amount for each predetermined movement distance or the load signal for each predetermined time is output to the serial line in accordance with the measurement mode switching signal (third invention).

  According to the first aspect of the present invention, the conveyor scale load cell includes a pulse signal input line for inputting a pulse signal transmitted from the pulse transmitter, and each time the conveyor moves a predetermined short distance during the operation of the conveyor. Each time a generated signal is input and the conveyor moves a predetermined distance, a load signal detected by the load cell body and a pulse signal output from the pulse transmitter are used to convey the object conveyed for a predetermined distance. The transportation amount of the weighing object is calculated, and this transportation amount is output to, for example, a serial line. Therefore, even if the reading cycle of the conveyor scale load cell from an external device (such as a display operation device) is slow, the conveyor moving distance in the time interval corresponding to the period or more is set in advance, and the moving distance within the load cell is set. If a single serial line is commonly used for many digital load cells, the accurate transport amount can be read into the external device and accurately integrated in the external device. Transport volume can be determined.

  Also, the load cell needs to be able to adjust the span as a single unit, and even when it is installed on the conveyor scale body and adjusted, accurate zero adjustment is necessary to recognize the span being used and the amount of zero fluctuation. It is necessary to avoid variations in the load signal and to allow the operator to easily recognize the value when the load signal is displayed. In response to this problem, according to the second aspect of the invention, unlike the first measurement mode that continuously calculates and outputs the accumulated transportation amount in a predetermined section, for example, the load signal changes in a long cycle time of 100 msec or more. Since the second measurement mode is also provided and the two measurement modes can be easily switched from the outside as required, a digital load cell capable of executing the measurement mode according to the external request can be obtained.

The perspective view explaining the structure of the conveyor scale which concerns on one Embodiment of this invention. Front view (a), side view (b) and partial enlarged view (c) showing a state in which a reference weight roller is loaded in the conveyor scale of the present embodiment. The perspective view of the load cell used for the conveyor scale of this embodiment Block diagram showing the configuration of the load cell Overall system configuration diagram of conveyor scale of this embodiment Overall system configuration diagram of conveyor scale according to another embodiment of the present invention

  Next, a specific embodiment of a conveyor scale load cell according to the present invention will be described with reference to the drawings.

<Overview of Conveyor Scale Load Cell According to this Embodiment>
If the load cell output abnormality can be detected easily and early during the operation of the conveyor scale load cell, it is determined which load cell output is abnormal, and the determined abnormal load cell is replaced. During this period, normal weighing 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. It is desirable to determine these zero point fluctuation amount and span fluctuation amount without requiring any special operation during normal measurement work, and to alert or display if there is any abnormality.

  In most cases, failure occurs from one load cell among multiple load cells. Therefore, in order to measure the transport amount (transport weight) of the objects to be transported on the conveyor, The following is a description of a system that can easily and accurately determine whether a zero point and / or span abnormality has occurred in one of the two load cells provided at both ends of the supporting weighing roller during the weighing operation. I decided to.

  By the way, as a diagnostic device for determining an abnormality in the output of a load sensor in a conventional case where a plurality of load sensors are provided in a weighing unit for measuring the load of an object to be measured, Japanese Patent Laid-Open No. 5-264375 (hereinafter referred to as “ Patent Document 1 ”) and Japanese Patent Laid-Open No. 9-280939 (hereinafter referred to as“ Patent Document 3 ”).

  Usually, in a weighing device, a weight measurement value is obtained from the sum of the outputs of a plurality of load sensors that support the weighing unit, and the weight measurement value is displayed on a display. If any weight measurement value is displayed on the display unit even though the object to be weighed is unloaded, zero adjustment is performed by zero adjustment means such as a zero adjustment switch provided in the weighing device.

  Since the output signal of multiple load sensors includes the zero point fluctuation component of different factors individually, zero point fluctuation and span fluctuation can be evaluated for each individual load sensor. A means to adjust is needed. In addition, for example, each load sensor fluctuates due to non-abnormal factors such as foreign matter adhering to the measuring section. Therefore, fluctuations including zero fluctuations for each load sensor generated after zero adjustment of zero fluctuations that are not abnormal must be taken into account. Don't be.

  However, in Patent Documents 1 and 3, the zero point adjusting means for each individual load cell is not clarified. That is, in Patent Document 1, as described in paragraph [0011], the load of the weighing unit is expressed by the sum of outputs of a plurality of load sensors, but the sum of outputs of the load sensors is displayed. When the displayed value fluctuates from zero, the output sum is only adjusted to zero. On the other hand, as described in paragraph [0014] of Patent Document 3, there is means for displaying the measured value of each load sensor, but when the zero point of the output of the load sensor fluctuates individually However, the means for individually adjusting the zeros is not disclosed. Therefore, in these patent documents 1 and 3, the magnitude of the fluctuation from the normal state of the output of each load sensor cannot be accurately detected by comparing the outputs of the load sensors with each other.

Further, in these Patent Documents 1 and 3, even if the zero point fluctuation component is removed from the output signal of the individual load sensor, there is a problem described below, and accurate span abnormality determination cannot be performed.
(1) The load sensor that supports the weighing unit cannot be arranged to receive the load of the object to be measured accurately and evenly in the actual machine. For this reason, in weighing the object to be weighed, a fixed deviation specific to the structure of the weighing device is generated between the outputs of the two load sensors.
(2) The weighing object is hardly conveyed on the conveyor with a completely uniform load distribution. The distribution of the apparent specific gravity of the object to be weighed is not completely uniform in each weighing. The conveyor also meanders on the metering roller. Therefore, the load sensor output varies in each weighing. In Patent Documents 1 and 3, the weighing unit is a weighing hopper, but does not deal with variations in load distribution to the load sensor due to variations in the accommodation state of the objects to be weighed.
Therefore, it is unavoidable to make an abnormality determination with a boundary value that roughly estimates variation, and an accurate determination cannot be made. In other words, the alarm is not issued until the degree of abnormality becomes large, and failure detection is performed only when temporary use is not possible until the abnormal load cell is replaced with another load cell. Can not.

  Further, as a method of returning the weighing device to normal weighing when a faulty load sensor is detected, as disclosed in paragraph [0024], the method of Patent Document 1 has failed with the output of the normal load sensor. It replaces the load signal of the load sensor and represents the load load of the entire weighing unit. The method disclosed in Patent Document 3 uses the same method as described in paragraph [0017]. However, since the objects to be weighed are not uniformly distributed on the weighing unit each time and the density is not uniform, the distribution to each load sensor is different even if the weight of the objects to be weighed is the same in each weighing. Even if the output signal of the faulty load sensor is excluded by prescribing the load distribution in advance and only the output signal of the normal load sensor is estimated, the weight value of each time cannot be expressed accurately.

  In order to cope with the problems described above, in the present embodiment, both ends of the weighing roller of the conveyor scale are supported by two digital load cells, and zero point adjusting means capable of adjusting the zero point for each load cell, and any one of the digital load cells Or when all of the values change from the value set by the zero adjustment means, the display means for displaying it, and when any output of the digital load cell is changed to an abnormal size, Regardless of the magnitude of the load load, regardless of the load distribution to the load cell of the object to be weighed, the influence of uneven distribution of the object to be weighed and density distribution on the conveyor is reduced, and an abnormality occurs. It is configured so that it is accurately detected. In addition, abnormal load cells are inspected after normal operation is stopped. This inspection can identify abnormal load cells, correct spans and / or zeros, and perform normal weighing until the abnormal load cells are replaced. It is what I did.

<Overview of conveyor scale>
FIG. 1 is a perspective view illustrating a structure of a conveyor scale according to an embodiment of the present invention. As illustrated, the conveyor scale body 1 is a conveyor belt (hereinafter referred to as “conveyor”). 2, one of the transport rollers 3, 4, 5 is composed of a metering roller (hereinafter referred to as “metering roller 4”). It has been done. The weighing roller 4 is supported at both ends a and b by load cells 6 and 7, respectively, and the weight of the object to be weighed conveyed on the conveyor 2 by these load cells 6 and 7 (hereinafter referred to as “transport amount”). ) To measure. Here, the load cells 6 and 7 include various types such as a strain gauge type, a magnetostrictive type, and a string vibration type, and any type may be used. In this embodiment, as load cells 6 and 7, a robotic load cell in which a strain gauge is attached to a stretchable strained portion provided on a metal elastic body (a parallelogram having two strained portions provided on two beams) An example in which a type load cell) is used is shown.

  The transport rollers 3, 4 and 5 are installed with a distance L (m) therebetween. The weights of the objects to be weighed on the conveyor 2 are distributed in the distance p from p to q in the distance of L / 2 from the left and right of the weighing roller 4 at the points a and b. (The range of p to q is called working length). Further, a pulse transmitter 8 is connected to the transport roller 3 via a connection mechanism (not shown) so as to transmit a pulse number proportional to the moving distance of the conveyor 2, that is, the transport distance of the object to be measured. Yes.

  FIG. 2 shows a state in which the reference weight roller 11 for checking the output of the load cells 6 and 7 is loaded. L-shaped reference weight support fittings 9 and 10 are supported by the load cells 6 and 7, respectively, and both ends of a reference weight roller (reference weight article) 11 are supported by horizontal portions of the reference weight support fittings 9 and 10. Here, the engaging portion between the reference weight support brackets 9 and 10 and the reference weight roller 11 includes a positioning mechanism including a protrusion 12a on the reference weight support bracket 9 and 10 side and a notch 12b on the reference weight roller 11 side. 12 is provided. The reference weight roller 11 has a known weight, and is used for specifying a faulty load cell and correcting an output when a load cell abnormality is detected.

  In place of the reference weight roller 11, a weight having a known weight is used, and a support bar for connecting the left and right reference weight support brackets 9 and 10 is provided, and a positioning mechanism is provided near the center of the support bar. The weight can be configured to be suspended.

<Description of load cell>
As shown in FIG. 3, the load cells 6 and 7 are robust load cells having a strain-generating portion forming a robust (parallelogram) on the tip side of the attachment portion 13. In the present embodiment, for waterproofing and dustproofing, a strained body 14 including a strained portion is covered with a cover (not shown) made of a metal bellows. Further, a strain circuit (corresponding to the “load cell main body” in the present invention) 14 is integrally mounted with a measurement circuit board (hereinafter referred to as “measurement circuit”) 15 described below, so that the digital load cell It has a configuration.

  The strain generating portion has two beams (beams) 14a and 14b. Strain gauges 16 and 17 are provided on the beam 14a, and strain gauges 18 and 19 (not shown in FIG. 3) are provided on the beam 14b. , 14b are attached along the longitudinal direction. Further, a load support portion (applying portion) 20 for suspending and supporting the measuring roller 4 is coupled to the distal end side of the strain generating body 14. Thus, when an object to be weighed is placed on the conveyor 2, a load corresponding to the weight of the object to be weighed acts on the strain generating portion 14, and the strain gauges 17 and 19 are bent in a direction in which the gauge adhesion surface extends. Under the stress, the strain gauges 16 and 18 are subjected to a bending stress in a direction in which the gauge bonding surface contracts.

  As shown in FIG. 4, the strain gauges 16, 17, 18, and 19 are connected to each other so as to constitute a Wheatstone bridge circuit 21. A voltage for excitation is applied from the power source 31 to the two opposing terminals 22 and 23 of the Wheatstone bridge circuit 21, and force or load is applied from the terminals 24 and 25 positioned in a direction orthogonal to the terminals 22 and 23. The detected voltage is taken out and input to the measurement circuit 15.

  The measurement circuit 15 includes an operational amplifier 26, an analog-digital converter (hereinafter referred to as “A / D converter”) 27, an input / output circuit (I / O) 28, and a central processing unit (CPU). 29, a memory block (MEM) 30, and a power source 31. Thus, the detected voltage taken out from the terminals 24 and 25 of the Wheatstone bridge circuit 21 is converted into an analog load signal eo1 through the operational amplifier 26, and this analog load signal eo1 is converted into a digital load signal by the A / D converter 27. Converted to Wa1 ′. The digital load signal Wa1 ′ is read into the memory block 30 from the input / output circuit 28 via the central processing unit 29. Further, the pulse from the pulse generator 8 is input to the input / output circuit 28 through the pulse signal input line, and the pulse is received by the central processing unit (CPU) 29 via the input / output circuit 28, so that a predetermined number of pulses is obtained. The integrated weight value for each predetermined section to be determined is obtained as the section transportation amount, and the transportation amount is output to the serial line c for each section. Here, the memory block 30 is composed of a storage element (semiconductor element) such as a RAM that primarily stores data for input, output, and calculation, an EEPROM that continuously stores setting data, and a PROM that continuously stores predetermined programs. is there.

<Description of circuit configuration of conveyor scale and display operation device>
As shown in FIG. 5, each load cell 6, 7 of the conveyor scale body 1 is connected to the pulse transmitter 8, and through a common serial line c for serial signal communication with the arithmetic circuit of the display operation device 40. The display operation device 40 side is a master controller, the load cells 6 and 7 are slave controllers, and data is communicated bidirectionally by polling from the display operation device 40 side. More specifically, the serial line c outputs a transportation amount of a basic section, which will be described later, to the display / operation device 40, and also stores a zero point at the time of zero adjustment, initial weight storage, and calculation of a span coefficient from the display / operation device 40. The operation command signal (code) is transmitted.

  The display / operation device 40 includes an input / output circuit (I / O) 41, a central processing unit (CPU) 42, a memory block (MEM) connected to the load cells 6 and 7 of the conveyor scale body 1 via the serial line c. ) 43 and a power source 44. The input / output circuit 41 is connected to a display (DIS) 45, a key switch (KEY) 46, and the like. The weight value and the like are displayed on the display 45, and operations such as data setting and zero adjustment are performed. This is performed by the key switch 46.

<Description of dynamic measurement and stationary measurement mode of digital load cell>
The display operation device 40 is set to ON or OFF by the key switch 46. When the operation operation ON is set by the key switch 46 in the weight measuring device, the display / operation device 40 enters the dynamic measurement mode, and the dynamic measurement mode (first measurement mode) command signal is sent to the load cell 6 of the conveyor scale body 1. 7 is sent. When the operation operation OFF is set by the key switch 46, the display / operation device 40 enters the stationary measurement mode, and a stationary measurement mode (second measurement mode) command signal is sent to the load cells 6 and 7 of the conveyor scale body 1. .

  The output signal Wa1 ′ from the A / D converter 27 shown in FIG. 4 has a time interval Δt (for example, Δt = 1 msec) that is sufficiently shorter than one pulse period transmitted from the pulse transmitter 8, as will be described later. It is a digital signal obtained by A / D sampling the analog load signal eo1, and is subjected to smooth filtering processing to attenuate mechanical vibrations caused by the movement of the conveyor by an arithmetic circuit, and is sequentially output from the smoothing filter. The above arithmetic operation is performed in any of the dynamic / stationary measurement modes.

  When the dynamic measurement mode is specified for the load cells 6 and 7 by the display operation device 40, the load cells 6 and 7 are in the dynamic measurement mode together with the display operation device 40. In this dynamic measurement mode, W1, which is calculated for each pulse, every time the number of transmitted pulses reaches the number of pulses N0 determined as a basic section to be described later, according to the transmitted pulses from the pulse transmitter 8. Based on W2, the transport amount of the objects to be transported on the conveyor 2 between the number of pulses N0 is calculated as the basic section transport amount W1mn, W2mn, and the calculated basic section transport amount is measured in the basic section. Each time it is completed, it outputs through the serial line c. When the operation operation is ON, based on the transport amount of the basic section output from the load cells 6 and 7 while continuing the dynamic measurement mode, the display / operating device 40 detects any abnormal load cell output fluctuation as will be described later. If there is, issue an alarm.

  On the other hand, when the operation operation OFF is set by the key switch 46 in the display operation device 40, the load cells 6 and 7 enter the stationary measurement mode together with the display operation device 40. In the static measurement mode, the digital load signal output from the smoothing filter during the time interval of one pulse given from the pulse transmitter 8 to the arithmetic circuit via the input / output circuit 28 is, for example, T1 = 100 · Δt. = A moving average or an average value of M is calculated every 100 msec, and given to an expression for obtaining output signals W1 and W2 described later as adjustment and display digital load signals Wa1, and a load signal is calculated. The load cell output load signals W1 and W2 in the static measurement mode are transmitted to the display operation device 40 through the serial line c and displayed.

<Explanation of adjustment in load cell unit>
Regarding the load cell abnormality determination process, first, span adjustment is performed for the load cell alone. The outputs of the load cells 6 and 7 are single and are calculated by the following equations.
W1 = K1. (Wa1-Wi1 ')
W2 = K2 · (Wa2-Wi2 ')
Here, K1, K2: Span coefficient, Wa1, Wa2: A / D converter, digital load signal that has passed through the filter, Wi1 ′, Wi2 ′: initial zero point amount of the load cell. It is assumed that the span coefficients K1 and K2 are adjusted so that the output changes by the same amount with respect to the load.
The load cells 6 and 7 are set alone in the load test apparatus, the serial line c of the load cells 6 and 7 is connected to the serial line c of the load cell adjusting device, and the span coefficients K1 and K2 are adjusted as described above. The power supply to the load cells 6 and 7 is supplied from the load cell adjusting device.

When the stationary measurement mode for adjustment is designated in the load cell adjusting device, the stationary stationary measurement mode command code is transmitted to the load cells 6 and 7 through the serial line c, and the load cells 6 and 7 are for the stationary measurement mode. Specified in the static measurement mode.
As described above, Wa1 is generated every T1 time in the static measurement mode. In the still measurement mode, W1 is calculated by the following equation.
W1 = K1. (Wa1-Wi1 ')

  At the start of the adjustment, the span coefficient is set to K1 = 1 in the arithmetic circuit of the load cell, and the content of the initial load storage memory Wi1 ′ is zero. As for the value of W1, every time the contents of Wa1 are updated (every T1), M moving average values or average values for each M unit are calculated and sent as a display value to the load cell adjusting device with a code. Displayed on the adjustment device.

  When the operator makes the load cell 6 unloaded and presses the initial zero storage key while observing the display value, an initial zero storage operation designation signal is sent to the arithmetic circuit of the load cell 6. At this time, W1 is the zero point movement when the load cell 6 is not loaded. Further, the display value of W1 is stored in the load storage memory Wi1 ′ in the memory block 30 of the load cell 6 as the initial zero point amount. Here, since Wi1 ′ = Wa1, W1 changes to W1 = 0 in the above formula.

The known load value Ms is set in advance in the load cell adjusting device. When the value of Ms is set and the reference value storage key is pressed, it is sent to the load cell 6 with a code indicating the reference weight Ms.
Next, a known reference load is applied to the load cell 6. Then, W1 increases and changes by the reference load, and the display value also increases accordingly. When the operator operates the span storage switch with the load cell adjusting device while observing the display value of W1, the span coefficient storage command code is transmitted to the load cell 6, and K1 = Ms / (Wa1- Wi1 ′) and the value of K1 is calculated as a span coefficient. The calculated span coefficient K1 is registered in the memory block 30 in the load cell 6 as the span coefficient of the load cell. In this way, the display value of W1 is replaced with K1 from 1 as the span coefficient, and becomes the value of Ms.
Thereafter, if the load cell is designated as the adjustment stationary measurement mode, the value of W1 = K1 · (Wa1−Wi1 ′) in which the value of the span coefficient K1 is determined is updated from the load cell to the contents of Wa1, and W1 is updated. Is output each time

<Explanation of adjustment after load cell installation>
Next, the digital load cell adjusted as a single unit as described above is attached to both ends of the conveyor-scale weighing roller 4, and the serial lines c of the load cells 6 and 7 are serially connected to the display operation device 40 as shown in FIG. 5. Connected to the line c, the power supply to the load cells 6 and 7 is also given from the power supply 44 of the display operation device 40. It is assumed that the load cells 6 and 7 are normal outputs at the time of adjustment.

When connected to the display / operation device 40, the operation operation is turned off when the power supply is turned on, and a stationary measurement mode command is transmitted to the load cells 6 and 7 in response to the operation operation being turned off. When the stationary measurement mode command is received, the following expression (1) is set as a processing expression for the outputs W1, W2 of the load cells 6, 7, depending on the contents of the zero point storage memories Wz1, Wz2 and the new initial load memories Wi1, Wi2.
W1 = K1. (Wa1-Wi1) -Wz1
W2 = K2 · (Wa2−Wi2) −Wz2 (1)

Next, an operation for storing an initial load value as a conveyor scale is performed. At that time, it is assumed that the conveyor 2 is separated from the measuring roller 4 as a work standard.
First, in the load cell designated in the stationary measurement mode, Wa1 and Wa2 are generated every T1 time as described above and transmitted to the display / operation device 40, and a plurality of Wa1 and Wa2 are received by the central processing unit 42 of the weight measuring device. The average value is calculated and put into the above formula (1), and the moving average value or the average value for each M unit is calculated as the values of W1 and W2, and is displayed as a display value to the display operation device 40. Is transmitted and displayed on the display 45.

  Next, the display / operation device 40 sets the initial load storage mode ON. When the initial load storage mode ON is instructed, 0 is set in the zero point storage memories Wz1 and Wz2 and the initial load memories Wi1 and Wi2 in W1 and W2 of Expression (1). In the initial load storage mode, a value of 1 is used as K1 and K2. Thus, when the initial load storage switch of the display operation device 40 is pushed in a state where the conveyor 2 is detached from the measuring roller 4, M average values of W1 and W2 at the time when the switch is operated in the display operation device 40. Thus, the initial loads Wi1 and Wi2 of the load cell main body are determined and registered in the initial load memory of the memory block 30 in the arithmetic circuit of the load cells 6 and 7, respectively.

  Next, the display operation device 40 sets the initial load storage mode to OFF. Then, as K1 and K2 in the above formula (1), values registered in the memory block 30 at the time of adjusting the load cell alone are called and replaced with the values of 1. Further, the data is called from the zero-point storage memories Wz1 and Wz2, and an operation of substituting W1 and W2 into Expression (1) is performed.

  After storing the initial loads Wi1 and Wi2 of the main body, W1 of the display 45 of the display operation device 40 in a state where the conveyor 2 is detached from the measuring roller 4 due to foreign matter adhesion to the measuring roller 4 or a large change in the ambient temperature. , W2 when a numerical value other than 0 appears, it is regarded as a zero fluctuation, and when the zero adjustment switch of the display operation device 40 is pressed, a zero adjustment command is transmitted from the display operation device 40 to the load cells 6 and 7 through the serial line c. When the arithmetic circuit of the load cells 6 and 7 receives the zero adjustment command signal code, the load cells 6 and 7 individually adjust the zero by adding the current values of W1 and W2 to Wz1 and Wz2, respectively, in equation (1). Is done. The operation of the zero adjustment switch is effective only when the operation operation is OFF.

  Next, an operation for loading the reference weight roller 11 onto the load cells 6 and 7 and examining the change in the span of the output of each load cell is performed. As shown in FIG. 2, the reference weight roller 11 is stacked at a predetermined position in a predetermined stacking direction. At this time, it is desirable to have the positioning mechanism 12 as strict as possible. However, even in such a case, a load equal to the load cells 6 and 7 is not always applied depending on the distributed load and the loading position of the reference weight roller 11.

  In order to store the output value of the load cells 6 and 7 by loading the reference weight roller 11 as a reference weight reference value, a reference weight reference value storage memory (“reference weight reference” in the present invention) is stored in the memory block 30 of the load cell arithmetic circuit. Corresponding to "value storage means") Ws1 and Ws2 are prepared. As the values of the outputs W1 and W2 of the load cells 6 and 7, M average values ws1 and ws2 are displayed on the display 45. When the operator confirms the display and presses the reference weight registration switch of the display operation device 40, those values are registered as reference values when the spans of the load cells 6 and 7 are normal. , Ws2. When the reference weight reference value call switch of the display / operating device 40 is pressed, a reference weight reference value call command is output to the calculation circuit of the load cells 6 and 7 and the reference value is referred to from the calculation circuit receiving the command. Values registered in the value storage memories Ws1 and Ws2 are called out, transmitted to the display / operation device 40, and displayed on the display 45. Note that, when the weight of the reference weight roller 11 is stored, the work reference is to remove the conveyor 2 from the measuring roller 4 as in the zero point adjustment. When registration of the reference weight reference value is completed, the conveyor 2 is brought into contact with the measuring roller 4.

<Explanation about output during operation>
The pulse transmitter 8 outputs one pulse every time the conveyor 2 advances by ΔL (m), the working length is L (m), and the conveyor moving distance ΔL per one pulse and the working length L are displayed and operated. Set to device 40. When the load of W (kg) is loaded on the conveyor working length of L (m), the weight of the conveyor, etc. is subtracted as the initial load. If the output by the load is W1, and the output of the load cell 7 is W2, the load applied to the load cells 6 and 7 per unit length of the conveyor 2 is W1 / L and W2 / L (kg / m), respectively.

  During the operation of the conveyor scale, the outputs W1 and W2 of the load cells 6 and 7 are measured every time one pulse is transmitted from the pulse transmitter 8. Since the conveyor 2 advances ΔL (m) per pulse, the load per pulse is W1 · (ΔL / L) (kg) for the load cell 6 and W2 · (ΔL / L) for the load cell 7 (Kg), and the number of pulses is proportional to the conveyor travel distance. That is, obtaining the transportation amount with a predetermined number of pulses means obtaining the transportation amount at a predetermined movement distance of the conveyor 2.

  In order to prescribe the transport amount of a relatively short distance in the display / operation device 40, the basic section is set as the value of the pulse number N0, and the unloaded transport amount of the conveyor 2 (the object to be weighed is not loaded on the conveyor 2) The conveyor movement distance for calculating the transport amount in the state) is set as the pulse number Nz (Nz> N0). The values of N0 and Nz are registered in the memory block 43 of the display / operation device 40, transmitted to the arithmetic circuits of the load cells 6 and 7, and registered in the memory block 30 of each arithmetic circuit.

  When the operation switch is turned on in the display operation device 40 and the display operation device 40 is set to the dynamic measurement mode and the dynamic measurement mode command is sent to the load cells 6 and 7, the arithmetic circuits of the load cells 6 and 7 perform dynamic measurement. Switch to dynamic measurement mode in response to a mode command. Also in this dynamic measurement mode, the analog load signals of the load cells 6 and 7 are A / D converted, and digital load signals Wa1 and Wa2 are continuously generated through a filter at a time interval of Δt = 1 msec. Note that the time interval of one pulse of the pulse transmitter 8 is set to a specification that is at least longer than Δt = 1 msec, that is, a cycle slower than 1 kHz.

  In this dynamic measurement mode, for each pulse received from the pulse transmitter 8, Wa1 and Wa2 detected during one pulse are added to calculate an average value, and the result is Wa1 and Wa2 in the equation (1). Is assigned to In this way, the process of obtaining the values of W1 and W2 for each pulse is continuously performed. Even in the dynamic measurement mode, the conveyor speed is extremely slow, and the time interval of one pulse may be extremely long. Therefore, the number of additions is counted by the counter and the arithmetic circuits of the load cells 6 and 7 are preliminarily stored. The number of addition saturation is set.

ここで、走行時のコンベヤ無負荷による基本区間輸送量（＝コンベヤ無負荷輸送量）を記憶させるメモリを、ロードセル６においてＷ１ｄｚ、ロードセル７においてＷ２ｄｚとすると、基本区間におけるコンベヤ２上を輸送される被計量物のロードセル６，７についての輸送量Ｑ１０，Ｑ２０は、次式（３）にて求められる。
Ｑ１０＝Ｑ１０′−Ｗ１ｄｚ
Ｑ２０＝Ｑ２０′−Ｗ２ｄｚ ・・・・・（３）
これらＱ１０，Ｑ２０の値はパルス数Ｎ０毎にロードセル６，７から表示操作装置４０へ伝送される。一方、コンベヤ２としての基本区間輸送量Ｑ１２０は、表示操作装置４０内の演算回路で次式（４）にて演算され、Ｑ１０，Ｑ２０，Ｑ１２０の値が表示器４５に表示される。
Ｑ１２０＝Ｑ１０＋Ｑ２０ ・・・・・（４） Since the basic section transportation amounts Q10 'and Q20' in the operation operation are the number of pulses q = N0, as described above, each time Wa1 and Wa2 are obtained by the arithmetic circuit of the load cells 6 and 7 for each pulse, W1 Are calculated as W11, W12, W13,... And W2 is calculated as W21, W22, W23,.

Here, assuming that the memory for storing the basic section transportation amount (= conveyor unloaded transportation amount) due to no load on the conveyor at the time of travel is W1dz in the load cell 6 and W2dz in the load cell 7, it is transported on the conveyor 2 in the basic section. The transport amounts Q10 and Q20 for the load cells 6 and 7 of the objects to be weighed are obtained by the following equation (3).
Q10 = Q10'-W1dz
Q20 = Q20'-W2dz (3)
The values of Q10 and Q20 are transmitted from the load cells 6 and 7 to the display operation device 40 every number of pulses N0. On the other hand, the basic section transportation amount Q120 as the conveyor 2 is calculated by the following expression (4) by an arithmetic circuit in the display operation device 40, and the values of Q10, Q20, and Q120 are displayed on the display unit 45.
Q120 = Q10 + Q20 (4)

引き続き、ロードセル６，７について基本区間のコンベヤ無負荷輸送量Ｗ１ｄｚ，Ｗ２ｄｚが次式（６）にて算出され、メモリＷ１ｄｚ，Ｗ２ｄｚの内容がそれら算出値に置き換えられる。

この操作によって、基本区間輸送量Ｑ１０，Ｑ２０，Ｑ１２０は、コンベヤ２上が無負荷であれば、ほぼ零の値を表示するようになる。上記基本区間輸送量Ｑ１０，Ｑ２０はパルス数がＮ０に到達する度に算出される。そして、算出されたＱ１０，Ｑ２０は図４の入出力回路（Ｉ／Ｏ）２８内に設けたシリアル通信コントローラ内の送信メモリへ送られる。ここで、これらのデータは表示操作装置４０の演算処理事情で決まる時間間隔で読み取られるが、新たなＱ１０，Ｑ２０によって通信コントローラ内の送信メモリが更新される前に読み取られるように、表示操作装置４０の最長読み取り時間間隔を考慮し、それより長くなるようにＮ０の値が予め設定される。なお、コンベヤ２としての被計量物の積算輸送量は、表示操作装置４０にロードセル６，７毎の基本区間輸送量Ｑ１０，Ｑ２０が伝送され、Ｑ１２０がＱ１０，Ｑ２０によって算出される度に、言い換えれば基本区間パルス数Ｎ０の度にＱ１２０の値を積算することによって求められ、表示される。 Since W1dz and W2dz = 0 at the beginning, the transport amount due to the load of the conveyor 2 when the conveyor is running is displayed as Q10, Q20, and Q120. When the no-load transport amount storage mode switch is pressed in the display / operation device 40, the transport amounts Q10 ″ and Q20 ″ in the basic section where the number of pulses q = Nz is calculated by the following equations (5) in the arithmetic circuit of the load cells 6 and 7, respectively. Sought by.

Subsequently, the conveyor unloaded transport amounts W1dz and W2dz of the basic section for the load cells 6 and 7 are calculated by the following equation (6), and the contents of the memories W1dz and W2dz are replaced with the calculated values.

By this operation, the basic section transportation amounts Q10, Q20, and Q120 display a value of almost zero when the conveyor 2 is unloaded. The basic section transportation amounts Q10 and Q20 are calculated every time the number of pulses reaches N0. The calculated Q10 and Q20 are sent to a transmission memory in the serial communication controller provided in the input / output circuit (I / O) 28 of FIG. Here, these data are read at a time interval determined by the calculation processing circumstances of the display operation device 40, but the display operation device is read before the transmission memory in the communication controller is updated by the new Q10 and Q20. Considering the longest reading time interval of 40, the value of N0 is preset so as to be longer. The accumulated transport amount of the objects to be weighed as the conveyor 2 is paraphrased every time the basic section transport amount Q10, Q20 for each load cell 6, 7 is transmitted to the display operation device 40 and Q120 is calculated by Q10, Q20. For example, it is obtained by integrating the value of Q120 every time the number of basic section pulses is N0 and displayed.

  When only load signals are calculated in the two load cells, transmitted to the display / operation device 40 by serial communication, and a transmission pulse is given to the display / operation device 40 to obtain the transport amount, the two load cell load signals are calculated. Due to the time required for communication and the overhead time for switching, the load signal that changes due to the change in the distribution state of the objects to be weighed on the conveyor cannot be sent reliably. Depending on the situation, it becomes intermittent and the transport volume cannot be determined accurately.

On the other hand, as in the present embodiment, the load cell is provided with a pulse signal input line, the transmission pulse is read into the load cell, and the basic section transportation amount corresponding to the required time longer than the communication required time is obtained. By doing so, an accurate transportation amount without loss is obtained in the arithmetic circuit of the load cell and can be reliably transmitted to the display / operation device 40, so that an accurate transportation amount measuring device can be configured.
In addition, even if the transportation amount is output during operation, adjustment of the load cell alone or adjustment at the time when the load cell is installed on the conveyor scale body requires reading of the static weighing value. A measurement mode for outputting and a mode for measuring and outputting a stationary weight are provided, and it is necessary for the digital load cell for conveyor scale to be able to easily switch between these modes.

<Description of load cell output abnormality detection>
Next, a calculation process for detecting an output abnormality of the load cell performed during the operation will be described. Hereinafter, the basic section transportation amount for the load cell 6 is Q10 = W1mn, and the basic section transportation amount for the load cell 7 is Q20 = W2mn. These basic section transportation amounts W1mn and W2mn are transmitted to the display operation device 40 through the serial line c each time they are calculated. In order to detect an abnormality, the following arithmetic operation is executed in the arithmetic circuit of the display operation device 40.

By the way, even if the load to be weighed on the conveyor 2 has a uniform distribution with a uniform density, the load on the conveyor 2 has a positional relationship between the conveyor 2 and the measuring roller 4. Therefore, W1mn ≠ W2mn is basically not distributed to the load cells 6 and 7 at 1: 1. Actually, since the distribution and density of the objects to be weighed are different, W1mn and W2mn vary. Therefore, if the ratio R of the basic section transportation amount of the objects to be measured for the load cells 6 and 7 is set as the following equation (7), this ratio R will not change even if the transportation weight of the objects to be weighed increases or decreases. Absent.
R = W1mn / W2mn (7)

Here, it is assumed that the load on the working length is distributed to the load cells 6 and 7 at k1: k2 (≠ 1: 1), and the density (apparent specific gravity) of the objects to be weighed on the conveyor 2 is uniform and completely distributed. Is uniform, the following equation holds.
R = k1 / k2 (8)
When the output of the load cell 6 changes by e, R becomes the following equation.
R = (k1 / k2) · (1 + e) = (k1 / k2) + (k1 / k2) · e
(9)

In equation (9), the value of k1 / k2 is unknown, and therefore when R = k1 / k2 is compared with the reference value 1 when the output change rate e is 0, the value is different from 1. It is unclear whether this was caused by load cell output fluctuations. Therefore, R = Ri when the load cell is in a normal state is obtained, R = Rv during operation is obtained, and the amount of change therebetween is expressed as follows: E = Rv−Ri = (k1 / k2) · e 10)
If the change amount (k1 / k2) · e is evaluated as follows, since k1 / k2 ≠ 1, this change amount is not equal to e, but k1 / k2 is about 1, so it is almost equal to e. Close variation can be evaluated.

  If the accuracy of abnormality determination is not required, the amount of change of only Rv from 1 or the loads ws1 and ws2 when the above-described standard weight roller 11 is measured from the standard weight reference value storage memories Ws1 and Ws2. It may be called to derive k1 / k2 = ws1 / ws2 = kws and determine the amount of change from this kws.

  Although the above equation (8) is set so that the density (apparent specific gravity) of the objects to be weighed on the conveyor 2 is uniform and the distribution is completely uniform, the density of the objects to be weighed on the conveyor 2 is actually Since it is not uniform and the distribution is not uniform, it includes variations. On the other hand, since the value of R is the transport amount in the basic section, if a sufficiently long moving distance is set as the evaluation section, the distribution state and density are averaged and the variation is attenuated. However, if the moving distance is long, it takes a long time to obtain the measurement value, and there is a problem that the timing of abnormality determination is delayed. In addition, the variation in R cannot be finally reduced to 0, In order to determine the boundary value for performing the abnormality determination, it is necessary to perform the determination based on the actual amount of variation.

  Therefore, v shift registers are prepared, and the transport amount of the basic section (= added value of N0 measurement data) W1mn, W2mn is obtained in this shift register, and the ratio R is calculated each time the ratio R is calculated. The ratio R of the v basic intervals and the square value thereof are stored. The reason why the square value is stored is to calculate the standard deviation of v stored values later.

  Abnormality determination is performed as follows for each transport amount in the basic section. Note that load cell failures often occur as the gauge or strained part gradually deteriorates and rarely appear suddenly, but it is desirable to warn as soon as abnormal fluctuations exceed a predetermined value. .

The basic section transportation amount transmitted from the load cell is stored in the shift register of the display operation device 40 in the order of transmission. When v values of R are first stored in the v shift registers after the start of the operation operation, the average value Ra is calculated with the stored R and registered as the initial value Rai. At the same time, the standard deviation σi is obtained from the v R values. The standard deviation σai of the average value Rai is expressed by the following equation (11).
σai = v ^1/2 · σi (11)
Thus, when the average value Rai and the standard deviation σai are stored, these values are used as a reference value in a normal state of the load cell, and the fluctuation amount between the two load cells 6 and 7 is detected by the subsequent transport amount. It shall be.

Subsequently, every time the ratio R of the basic section is newly obtained, the oldest R in the shift register is discarded and a new R is inserted, and the average value Rav and the standard deviation σv are obtained from the latest v pieces of transportation. The standard deviation σav of the average value Rav is expressed by the following equation (11).
σav = v ^1/2 · σv (12)
Here, the change amount Ea from the initial value of the average ratio Ra is expressed by the following equation (13), and the standard deviation σae of the change amount Ea is expressed by the following equation (14).
Ea = Rav−Rai (13)
σae = (σai ² + σav ² ) ^1/2 (14)
Rav and Rai are v values obtained by adding the measured weight values corresponding to the number of pulses N0 in the basic interval, and are expressed as average values. Therefore, the change amount Eas of the relative ratio R and its standard deviation σaes are calculated by the following equations.
Eas = Ea
σaes = σae (15)

Assuming that the allowable value due to zero point fluctuation or span fluctuation in the output measurement value of the load cell is e, in order to reliably alarm when the fluctuation exceeds this allowable value e, judgment is made based on the change amount Eas from the initial value. In the case, the boundary value Rhe of the abnormality alarm is
Rhe = e + 2 · σaes (16)
And the automatically set boundary value is displayed on the display 45 of the display operation device 40. The standard deviation (variation amount) described above is calculated in a variation amount determination unit (corresponding to “variation amount determination means” in the present invention) in the central processing unit 42.
Further, when the basic load distribution is considered to be uniform for both load cells and can be ignored in terms of abnormality determination accuracy, the determination is made based on the magnitude of the amount of change from 1 of the relative ratio R in which the variation is attenuated. .

Or, as mentioned above,
R1 = k1 / k2 = ws1 / ws2 = kws (17)
As such, the amount of change from kws may be obtained. That is, the amount of change Ea from kws of the average relative ratio Ra is obtained by the following equation (18).
Ea = Rav-kws (18)
The standard deviation of the change amount Ea is that σav and kws are constant values, so the boundary value Rhr of the abnormality alarm is
Rhr = e + 2 · σav (19)
Is automatically set, and the magnitude comparison between Eas and the boundary value Rhr or the magnitude comparison between Rav-kws and the boundary value Rhr is performed.
1) If Eas> Rhe, it is determined that the output of the load cell 6 fluctuates with an abnormal magnitude in the increasing direction, or the output of the load cell 7 fluctuates with an abnormal magnitude in the decreasing direction. . In addition, if 2) Eas <−Rhe, it is determined that the output of the load cell 6 fluctuates with an abnormal magnitude in the decreasing direction or the output of the load cell 7 fluctuates with an abnormal magnitude in the increasing direction. To do.

<Explanation on how to return to normal weighing>
The return to the normal weighing operation when any of the load cells is determined to be abnormal is performed manually as described below.

  When an abnormality alarm is issued, first, in order to determine the zero point abnormality, the conveyor 2 is stopped as soon as possible, the objects to be weighed are removed from the working length of the conveyor 2, and then the conveyor 2 is lifted from the measuring roller 4 ( Look at the display of W1, W2 (without contact). At this time, if the zero point of the load cell fluctuates from the zero point determined before the initial operation, a numerical value other than 0 appears as a fluctuation amount during the operation operation. A load cell in which the fluctuation amount is larger than the allowable value is determined to be zero point abnormality. The load cell determined to be abnormal needs to be replaced. However, if there is a situation where the load cell cannot be replaced immediately, the zero adjustment is performed by operating the zero adjustment switch even if the zero fluctuation is larger than the allowable value. At this time, the zero point of the normal load cell is adjusted at the same time.

Next, the magnitude of the span fluctuation is examined. For the span inspection, as shown in FIG. 2, the reference weight roller 11 is loaded at a predetermined position of the reference weight support brackets 9 and 10 according to the positioning mechanism 12, and the output W1 = ws1 ′ of the load cells 6 and 7 , W2 = ws2 ′.
When the reference weight reference value call switch of the display / operation device 40 is pressed, a reference weight reference value call command is output to the arithmetic circuit of the load cells 6 and 7, and the reference weight reference value storage memories Ws1 and Ws2 are received from the arithmetic circuit receiving the command. The registered reference weight values ws1 and ws2 are called, transmitted to the display / operation device 40, and displayed on the display 45. In this way, the display value is compared with the reference value, and if the spans of both load cells 6 and 7 are normal, ws1 ′ = ws1 and ws2 ′ = ws2 are established, so that the abnormality of the span can be determined.

  If the load display value of the current reference weight roller 11 is different from the reference weight values ws1 and ws2 stored in the normal state for either or both of the load cells so that correction is necessary, span correction for the load cell to be subjected to span correction is performed. Press the switch. Then, the span correction command for the specified load cell is transmitted to the load cell (the span correction command is transmitted to both load cells, but the command to be processed by its own arithmetic circuit according to the load cell number attached to the command code. Determine if or not.)

The span fluctuation rate is calculated as follows. That is, the span variation rate E1 for the load cell 6 and the span variation rate E2 for the load cell 7 are obtained by the following equations, respectively.
E1 = (ws1 ′ / ws1) −1
E2 = (ws2 ′ / ws2) −1 (20)
If it is a span correction command of the load cell 6, the value of E1 is registered in the span fluctuation rate memory Me1 in the arithmetic circuit, and after receiving this command, in the arithmetic circuit of the load cell 6 in W1 of the expression (1) The output is calculated by the following equation with the span coefficient K1 being E1. The load cell 7 is similarly calculated by the following equation.
W1 = K1 (1-Me1). (Wa1-Wi1) -Wz1
W2 = K2 (1-Me2). (Wa2-Wi2) -Wz2 (21)

When the span correction amount for the load cell 6 is to be reset, when the span correction value reset switch for the load cell 6 is pressed on the display / operation device 40, the load correction command for the span correction value for the load cell 6 is transmitted to the load cell 6, and the contents of Me1 Is reset.
The calling of the reference weight reference value and the span correction operation may be performed by stopping the operation of the conveyor 2 at an arbitrary time regardless of the presence or absence of an abnormality detection alarm.

<Description of the usefulness of digital load cells>
In the present embodiment, the digital load cell is used as the dedicated load cell for the conveyor scale, but instead of using this digital load cell, as shown in FIG. 6, load cells 6A and 7A for outputting analog load signals are provided. An embodiment is also possible in which the display operation device 40A is directly connected, and all digital operations are performed by the operation circuit in the display operation device 40A.

  However, in the configuration shown in FIG. 6, when adjusting the span of the load cell, it is necessary to connect the load cell installed on the conveyor scale body to the display operation device 40A. Therefore, when the load cell breaks down and is replaced, it is necessary to mount a new load cell on the conveyor scale main body, apply a reference weight load to the main body, and adjust the span. The main body is configured so that the span of the load cell can be temporarily temporarily adjusted by a temporary reference load (reference weight roller). However, in order to precisely adjust the span with the reference weight, the reference weight is used. It is necessary to prepare a special load state, which takes time.

  In the above-described embodiment, it is necessary to measure the load signals of a plurality of load cells individually and compare their outputs, instead of simply measuring the weight of an object to be weighed on the conveyor and measuring the transport amount. is there. Therefore, the analog load signals of a plurality of load cells cannot be added, and the load signals of the load cells must be individually wired to the display operation device. When a load signal is individually required for a plurality of load cells in a display operation device installed remotely from the conveyor scale body, the number of wires between the load cell and the display operation device should be reduced as much as possible. For these reasons, the load signal measurement circuit, A / D conversion circuit, and arithmetic circuit are mounted integrally on the load cell body or its vicinity, and can be handled as an integrated product, and the digital load signal is output on the serial line. Use of a load cell is preferred.

With respect to the above-mentioned problem, since the span characteristics with respect to the load can be adjusted by adjusting the load cell by applying the digital load cell, it is not necessary to adjust the span even if the load cell is replaced in the case of failure. The load signal can be output via a serial line.
However, if a serial line is provided at the output as a digital load cell for a conveyor scale, and in particular, if serial lines from a plurality of load cells are shared, the number of wires is reduced, but communication delay becomes a problem. In addition, in order to accurately calculate the transport amount according to the change in the distribution of the objects to be transported on the conveyor, the weight is measured at every short distance and a pulse is sent at every short distance so that every short distance is possible. It is necessary to add up the weight.

  On the display / operation device side, processing other than communication is also required, and communication speed is limited, so weight measurement values at short distance intervals from the load cell side, that is, weight measurement values at short time intervals cannot be transmitted. It can only be sent intermittently. Then, there is a problem that an accurate transportation amount cannot be obtained even if the weight value transmitted by receiving the transmission pulse on the display operation device side is added.

  In this embodiment, a digital load cell is used as a dedicated load cell for the conveyor scale, and the pulse signal from the pulse transmitter 8 is input to the digital load cells 6 and 7 through the pulse signal input line as described above, and the stationary measurement mode is used as the measurement mode. And the dynamic measurement mode, these modes are specified by the display / operation device. In the static measurement mode, display signals for zero adjustment and span adjustment are output to the display operation device. In the dynamic measurement mode, pulses are transmitted. The pulse from the container 8 is read, and in accordance with the read pulse, the transport amount of the object to be weighed conveyed on the weighing conveyor for each predetermined section is calculated in the load cell, and is output to the display operation device through the serial line. It is configured.

  With this configuration, even if the weighing unit is composed of a plurality of load cells or a system configuration in which the number of weighing rollers is two or more on one conveyor scale, a plurality of conveyor scales are used on a plurality of conveyor scales. Even if a weighing roller is used, the transport amount calculated for each predetermined section can be sent to the display / operation device, so there is enough transmission time and the transport amount output from multiple load cells can be displayed and operated. If it adds with the apparatus 40, there exists an effect that the transport amount of the to-be-measured object on the conveyor 2 can be calculated correctly.

  The stationary measurement mode is a mode in which a digital load signal is output from the load cell at a predetermined time interval by an operation of the load cell itself. In response to ON / OFF of the conveyor operation, when the display operation device instructs each load cell to turn on the conveyor operation, the load cell enters the dynamic measurement mode, and when OFF is instructed, the load cell enters the stationary measurement mode. Become. Also, when adjusting the span of a single load cell, a command to turn off the conveyor operation is sent. This makes it easy to adjust the span of the load cell alone or to attach and adjust the load cell on the conveyor scale body.

  The conveyor scale load cell of the present invention allows an accurate amount of transport to be read by an external device even when a single serial line is commonly used for many digital load cells. Since the amount can be obtained, the implementation effect is great.

1 Conveyor scale body 2 Conveyor (belt)
4 Weighing rollers 6, 7 Load cell (load cell)
DESCRIPTION OF SYMBOLS 8 Pulse transmitter 9,10 Reference | standard weight support metal fitting 11 Reference | standard weight roller 12 Positioning mechanism 14 Strain body 16-19 Strain gauge 20 Load support part 21 Wheatstone bridge circuit 28 Input / output circuit 29 Central processing unit 30 Memory block 40 Display operation device 41 Input / output circuit 42 Central processing unit 43 Memory block 45 Display 46 Key switch

Claims (3)

In a load cell for a conveyor scale in which a load cell main body that receives a load of an object to be weighed and a measurement circuit that calculates a digital load signal are integrally provided.
The conveyor scale load cell includes a pulse signal input line for inputting a pulse signal transmitted from a pulse transmitter to the measurement circuit every time a conveyor constituting the conveyor scale moves a predetermined distance,
The measurement circuit is connected to an external device of the conveyor scale load cell by a serial line for serial signal communication,
The measurement circuit calculates a transport amount for each predetermined movement distance for each load cell of the object to be weighed conveyed on the conveyor based on the pulse signal and a load signal detected by the load cell main body. A conveyor scale load cell that outputs to the serial line .   In response to a measurement mode switching signal from the outside of the conveyor scale load cell, a first measurement mode for calculating and outputting the transport amount for each predetermined movement distance of the object to be weighed, and a predetermined value for the object to be weighed The load cell for a conveyor scale according to claim 1, wherein the second measurement mode for calculating and outputting a load signal for each time can be switched.   The conveyor scale load cell according to claim 2, wherein a transport amount for each predetermined movement distance or a load signal for each predetermined time is output to a serial line in accordance with the measurement mode switching signal.

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