JPH0423727B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for calculating a weight value in a continuous weighing device that weighs an object while conveying it.

A continuous weighing device consists of a weighing unit that is integrated with a transport conveyor (for example, a belt conveyor) that transports objects to be weighed, a motor that drives this transport conveyor, etc., and a load cell that measures the total weight of this weighing unit. , and a weighing section that calculates the weight of the object to be weighed from the weighing results.
The weight of the object to be weighed is determined by subtracting the total weight of the weighing unit when there is no object to be weighed (no load) from the total weight of the weighing unit when the object is being transported.

By the way, the motor in the above-mentioned measuring unit,
Or the rollers that drive the conveyor belt, etc.
Due to eccentricity of the shaft, etc., the load cell always has a unique vibration that is synchronized with the rotation period, although there are differences in degree, and for this reason, the output of the load cell under no load fluctuates as shown in FIG. 1. As a result, as the no-load weight of the weighing unit, for example, point P shown in FIG.
1 or when using the value of point P2,
A large error occurs in the measured value of the object to be weighed.

In view of the above circumstances, the present invention provides a method for calculating measured values in a continuous weighing device that corrects errors caused by vibrations of a weighing unit and enables highly accurate weighing. a weighing unit having a conveying means for transporting an object to be weighed, a weighing means for measuring the total weight of the weighing unit, and a determining means for determining whether or not there is an object to be weighed on the weighing unit; In a continuous weighing device that measures the weight of an object while conveying it, the period (sampling period) TS for sampling the measured value from the weighing means is set to 1/N (N is the period T of the natural vibration of the weighing unit). Positive integer)
, and the determination means determines that there is no object to be weighed on the weighing unit (at no load)
N consecutive sampled measurement values (one period T of the natural vibration of the measurement unit)
is stored in the storage means, and when the judgment means judges that there is an object to be weighed on the weighing unit (when a load is applied), the N pieces stored in the storage means are calculated from the sampled weight values. calculating the weight value of the object to be measured by subtracting the weight value of the object to be measured by subtracting one of the weight values at the time of no load, and updating the weight value stored in the storage means when there is no load; This update process is performed by comparing the currently sampled measured value and the already stored measured value for items that have the same phase with respect to the period T of the natural vibration, and if the difference is less than a predetermined value, the updated value is updated. It is characterized in that sampled measurement values are stored, and if the difference between them is greater than a predetermined value, the stored measurement values are maintained as they are. In addition, in this invention, the period of natural vibration of the weighing unit means the period of vibration that is a combination of these vibrations when the entire weighing unit vibrates due to the rotation of rotating parts such as motors, pulleys, rollers, etc. It is used in

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a schematic diagram showing the configuration of a continuous measuring device according to an embodiment of the present invention. In this diagram,
Reference numeral 1 is a conveyor belt that conveys the object to be weighed L;
2 and 3 are rollers that drive the belt 1, 4 is a motor that drives the roller 2, 5 and 6 are pulleys, and 7 is a V-belt, and a measuring unit 8 is constituted by these. Note that the diameter ratio between the pulley 5 and the pulley 6 is 1:2 in this embodiment, and therefore the ratio between the number of rotations of the motor 4 and the number of rotations of the roller 2 is 2:1. Moreover, the diameters of roller 2 and roller 3 are the same. Reference numeral 9 is a load cell unit that measures the total weight of the weighing unit 8, and is fixed to the base 10. 11 is an entry sensor that detects that the object to be weighed L has reached the entrance of the conveyor; 12 is a discharge sensor that detects that the object to be weighed L has reached the outlet of the conveyor;
Each is composed of a photoelectric detector and the like.

When the apparatus configured as described above is in operation, the motor 4 and the roller 2 each have a natural vibration as described above. Then, motor 4 and roller 2
Since the ratio of the rotational speeds is 2:1, the ratio of the periods of each natural vibration is 1:2. FIGS. 3A and 3B are diagrams showing examples of vibration waveforms of the motor 4 and roller 2, respectively, and the period T2 in these diagrams is T2=2×T1 (1). When vibrations as shown in this figure occur in the motor 4 and roller 2, the entire weighing unit 8 generates vibrations with a waveform that is a combination of the waveforms A and B in Figure 3, that is, the waveform shown in C in Figure 3. Occur. The period of this composite waveform is the least common multiple of the periods of each waveform in Figure 3 A and B (T2 in the example in Figure 3)
Further, in the load cell in the load cell unit 9, a voltage waveform substantially similar to the waveform shown in FIG. 3C is generated in the no-load state.

Next, FIG. 4 is a block diagram showing the configuration of a measured value calculation section in the above-mentioned continuous measuring device. In this figure, 15 is a load cell provided in the load cell unit 9 in FIG.
is the sample hold signal from the calculation control section 17
An A/D (analog/digital) converter that holds the output voltage of the load cell 15 based on SH and converts the held voltage into digital data (hereinafter referred to as load cell data DR) and outputs it; 17 is the object to be measured; 18 is a memory, 11 and 12 are an entry sensor and an ejection sensor shown in FIG. 2, and 19 is a roller 2.
This is a synchronous switch that turns on once every time the switch rotates once.

Next, the operation of the above circuit will be explained. First, the period (sampling period) TS of the sample and hold signal SH having the following relationship is set in advance in the arithmetic control section 17 (see FIG. 3D).

TS=T2/N (2) However, N is a positive integer.The period TS must be set to be longer than the A/D conversion time in the A/D converter 16. The device is then powered on and
When the rotation of the motor 4 reaches a steady state (at this time, the object to be weighed L has not yet reached the conveyor), the arithmetic control unit 17 outputs the sample hold signal SH (period TS) after the synchronization switch 19 is turned on. )
are sequentially output and N load cell data DR are sequentially fetched, and the area 18a of the memory 18 shown in FIG.
Write the sample number inside.

Here, the sample number refers to the synchronization switch 19.
The sample number of the load cell data DR that is first captured after turning on is set to 1, and from then on,
This is a number that increases sequentially up to N every time the load cell data DR is sampled. Further, by the above sample operation, one period of no-load load cell data (hereinafter referred to as zero point data) of the vibration waveform shown in FIG. 3C is sampled. That is,
Each sample number corresponds to a phase difference when dividing the vibration waveform with period T2 into 1/N, and data with the same sample number is data at the same phase position of the vibration waveform with period T2.

Thereafter, the calculation control section 17 continuously samples the load cell data DR in the same manner as described above, but before the object L to be weighed reaches the conveyor, the following processing is performed. In other words, if you first import the load cell data DR of sample number 1,
The load cell data of the corresponding sample number 1 is read from the memory 18, and the read data and the sampled data are compared. If the difference between the two is less than a certain value, the newly sampled load cell data is written into the area of sample number 1 of the memory 18, and if the difference is more than the certain value, the above writing is not performed.

This means that a significant change above a certain value cannot be considered a change in the normal state of the zero point data.
This is the result of external disturbances such as vibrations,
This is because if the measured value is calculated using this value as zero point data, a large error will occur. Hereinafter, the above process is performed every time each load cell data DR of sample numbers 2, 3, . . . is sampled. Through the above processing, the zero point data in the memory 18 is constantly updated.

Next, when the object L to be weighed reaches the position of the entry sensor 11, the calculation control section 17 performs the following processing. That is, for example, assume that the sample number of the load cell data DR sampled at the time when the detection signal from the entry sensor 11 is supplied to the arithmetic control unit 17 is "5". In this case, when the calculation control unit 17 samples the load cell data DR of the next sample number "6", it first
The zero point data of the sample number "6" is read out from the area 18a of the memory 18, and then the zero point data is subtracted from the sampled load cell data DR.
Write in area 18b-1 of b. In this case, the data previously stored in area 18b-1 is transferred to area 18b-2, the data stored in area 18b-2 is transferred to area 18b-3, and the data stored in area 18b-2 is transferred to area 18b-3.
The data stored in 8b-3 is stored in area 18b.
-4 respectively and stored. Next, when the load cell data DR of sample number "7" is sampled, the zero point data of sample number "7" is read from the memory 18 in the same way as above, this zero point data is subtracted from the sampled data DR, and the result of this subtraction is is written to area 18b-1 of area 18b, and the area 18 is written as in the above case.
Rewrite b-2, 18b-3 and 18b-4. The same process is repeated and the memory 18
The four latest subtraction results are always stored in the area 18b. Then, when the detection signal of the discharge sensor 12 is output, the arithmetic control unit 12 reads each data in the area 18b, averages it, and displays the data obtained by this average as the weight value of the object L to be weighed. Output to each department. As is clear from the above process, in the embodiments shown in FIGS. 2 and 4, the weight value is calculated based on four sample data immediately before the object L is discharged from the conveyor. However, the number of samples to be averaged is not limited to four, and the number of samples to be averaged is arbitrary.

Further, in the above-mentioned embodiment device, only the latest piece of zero point data corresponding to each sample number is stored in the area 18a of the memory 18, and based on this stored piece of data, the zero point data is Although this configuration performs rewriting and calculation of measured values, the present invention is not limited to this. For example, the seventh
As shown in the figure, areas 18a-1, 18a-2, 18a-3, 18a- are stored in the area 18a of the memory 18.
4, and store the latest multiple pieces of zero point data corresponding to the sample numbers in this area (for example, 4
), and determine whether or not to rewrite the current zero point data based on these average values (i.e., if the difference between the current zero point data and the average value is less than a certain value) It is also possible to write the data sampled this time, and if it is above a certain value, write the previous zero point data as the current zero point data), and to calculate the measured value. In this way, by storing a plurality of pieces of zero point data corresponding to each sample number, it is possible to further improve the precision of measurement.

In the above-described embodiment, there are three parts in the weighing unit 8 that have natural vibrations: the motor 4 and the rollers 2 and 3, and when the diameters of the rollers 2 and 3 are the same and the motor rotates twice, the roller 2 This is a case in which the rotation occurs once, but the invention is not limited to this. For example, the rotation synchronization of rollers 2 and 3 is caused by motor 4.
is not set to an integral multiple of the rotational synchronization, or if the diameters of rollers 2 and 3 are not the same,
Alternatively, if there are three or more parts having natural vibrations with different frequencies, the least common multiple of the vibration periods of each part may be found, and the sample period TS may be found by dividing this found value by N.

Furthermore, if the natural frequency of the weighing unit changes when transmitting the driving force using a V-belt, as in the case of the above embodiment, the driving force may be transmitted using a timing belt or gears, and the motors may be synchronized. By using a motor, it is possible to accurately define the natural frequency of the weighing unit, allowing for more accurate weighing. In addition, in the above embodiment, the sample period of the load cell data during no-load and the sample period of the load cell data under load were set to the same period TS, but the sample period of the load cell data during load was made to be different from the sample period TS during no-load. Good too. In this case, as the no-load load cell data in the memory 18 when calculating the measured value, data closest to the load sampling point may be used.

As explained above, according to the present invention, the sampling period is determined based on the period of the natural vibration of the weighing unit, and the weight of the weighing unit under no load is measured at the determined sampling period. The weighing value of the object to be weighed is calculated based on the actual weight of the object to be weighed, so even if the weight under no load vibrates and is unstable, the weighing value of the object to be weighed can be calculated with extremely high accuracy. There are potential benefits.

[Brief explanation of drawings]

Fig. 1 is a diagram showing changes in the output voltage of a load cell during no-load in a continuous measuring device, Fig. 2 is a schematic configuration diagram of a continuous measuring device according to an embodiment of the present invention, and Fig. 3 A to C are the same. Figure 5 shows the vibration waveforms of the motor 4, roller 2, and weighing unit 8 in the continuous weighing device; Figures 4 and 6 are respectively
FIG. 7 is a diagram showing the storage area provided in the memory 18 in the figure, and FIG. 7 is a diagram showing the storage state in the area 18a of the memory 18 when a plurality of zero point data are stored. 1... Conveyor belt, 2, 3... Roller, 4
...Motor, 15...Load cell, 16...A/
D converter, 17... Arithmetic control unit, 18... Memory.

Claims (1)

[Scope of Claims] 1. A weighing unit having a conveyance means for continuously transporting an object to be weighed, a weighing means for measuring the total weight of the weighing unit, and whether or not there is an object to be weighed on the weighing unit. In the continuous weighing device which measures the weight of the object to be weighed while conveying the object, the weighing unit determines a sampling period (sampling period) TS for sampling the measured value from the weighing means. When the determining means determines that there is no object to be weighed on the weighing unit (when no load is applied), the continuous N sampled measurement values (one period T of the natural vibration of the weighing unit) are stored in a storage means, and when the judgment means judges that there is an object to be weighed on the weighing unit ( When a load is applied), among the N measured values stored in the storage means at the time of no load, those having the same phase with respect to the period T of the natural vibration are subtracted from the sampled measured values to calculate the measured value of the object to be measured. In addition to calculating the measured value of The measured value is compared with the stored measured value, and if the difference is less than a predetermined value, the currently sampled measured value is stored, and if the difference is greater than the predetermined value, the stored measured value is maintained as is. A method for calculating a measured value in a continuous measuring device, characterized in that: