JPS60211318A - Electronic metering device - Google Patents

Abstract

PURPOSE:To perform proper sampling at any oscillation period and to perform metering with high precision at a high speed by setting the current sampling interval at every time on the basis of the last sampled value. CONSTITUTION:This metring device consists of a metering conveyor provided with a load cell 12, the sampling interval measuring device consisting of a CPU15, ROM16, and RAM11, etc. When a conveyed body to be measured is placed on the conveyor, the metered value varies greatly and then the variation attenuates. For the purpose, the relation between the weight and natual oscillation of this body to be measured is stored previously, the oscillation period is calculated on the basis of the storage contents and last sampled value, and the next sampling interval is set to an integral (Nb) submultiple of the oscillation period. The number NA (integer) of sample values to be averaged finally is so set that Na/Nb is an integer. Consequently, when the frequency and amplitude of the oscillation are constant, the mean value is the center value of the oscillation without fail and a high-precision measurement of weight is taken.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic weighing device that measures true weight from vibrating weighing values.

Immediately after the article is placed on the weighing pan, the measured value oscillates greatly, but after that it becomes a damped oscillation that converges toward the true value.

Generally, measurements are performed after the measured value stabilizes, but a measuring device has been developed that samples several vibration values during a transient period and averages the sampled values to arrive at the true value.

According to this Sugi device, it is possible to know the true value without waiting for the measurement to stabilize, so it is possible to speed up the measurement, and even when the measurement device itself is vibrating due to external vibrations, etc. However, you can effectively calculate the true value.

By the way, in conventional munoseed measuring devices, the sampling interval of measured values is a constant value set in advance.
Depending on the period of vibration, the sampling values could become inappropriate. That is, the sampled value may be biased toward either the peak or the valley of the vibration waveform, and in such a case, the average value naturally deviates from the true value. Furthermore, since the vibration period changes depending on the weight of the object to be weighed, the measuring accuracy of conventional weighing devices ultimately changes depending on the weight of the object to be weighed, resulting in low reliability of measured values. .

In view of the above-mentioned circumstances, the present invention provides an electronic weighing device that can perform appropriate sampling at any vibration period, thereby achieving high accuracy and speeding up weighing. The feature is that the current sampling interval is set each time based on the previous sampling value.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1M1 is a plan view showing a schematic configuration of an embodiment of the present invention. This embodiment is an example in which the present invention is applied to an automatic weighing, packaging, and pricing machine, and an automatic weighing, packaging, and pricing machine is a machine that performs a series of automatic processes to package, weigh, and price products. It is.

In FIG. 1, 1, 2, and 3.4 #i are conveyors, and each one runs to the right in the drawing and conveys the product to the right. A roller conveyor 5 conveys the products to the right in the same way as conveyors 1 to 4. M and ~M4 are motors that drive the roller conveyor 5 and conveyors 2 and 3゜4, respectively.◎Also, the offset belt conveyor 6&~6ah installed between the rollers of the roller conveyor 5 guides the products passing above. It is moved to the plate 7 side and brought into contact with this guide plate 7. Therefore, the product conveyed on the roller conveyor 5 comes into contact with the guide plate 7vc by the width shifting belts 6&~6o, and then moves to the guide plate 7&C? Ej is transferred onto conveyor 2. 5
Each of la-84a is a light projector, and the irradiated light thereof is received by light receivers stb to 54bK arranged facing each other. In this case, each of the light receivers Sl'b-84b detects a product passing in front of it. 9t;j A console consisting of an operation section 9& (see Fig. 3) such as a keyboard and a display section 9b, and 10 is a console for attaching labels (
This is a printer that affixes the product weight and price (on which the product weight and price are printed). In this case, the conveyor 3 constitutes a weighing conveyor that performs weighing while conveying, and as shown in FIG. 2, a Ko-do cell 12 is provided below the conveyor 3. The load cell 12 bears the weight of the conveyor 3, motor MS, pulley, belt, etc., and its right end is fixed to a support base 13. Note that products that have already been packaged (packed, etc.) by a packaging section (not shown) are transferred to the conveyor 1 shown in FIG.

Next, FIG. 3 is a block diagram showing the electrical configuration of this embodiment, and parts corresponding to those in FIGS. 1 and 2 are given the same reference numerals.

In the figure, 15 is a CPU (central processing unit) that controls each part of the device, 16 is a ROM in which programs used by the CPU 15 are stored, and 17 is a RAM in which calculation results and various data of the CPU 15 are temporarily stored. be. In this case, the CPU 5 creates drive/stop signals for the motors Ml to M4 based on the light reception signals of the light receivers 5tb-84b supplied via the sensor interface 18, and transfers the drive/stop signals to the motor control interface. 19 to the motors M1 to M. And this CP
The motor control of U15 prevents more than one product from being placed on the conveyor 3 at a time. Therefore, the weight of each product can be detected using the load cell 120 weight multiplier. The weight multiplier of the load cell 120 is amplified by an amplifier 20 and then converted into a digital signal by an integral type A/D converter (hereinafter simply referred to as an A/D converter) 21 and supplied to the CPU 15. Also, A/D
The converter 21 has an interface 22 from the CPUI 5.
From the moment when the conversion start signal ST is supplied via A/
The D conversion operation is started. The output timing of the signal ST in this case will be described in detail later. C
The PU 15 calculates and measures the weight of the product based on the output signal of the Φ converter 21, and supplies weight data obtained from the calculation result to the printer 10 via the printer control interface 24f7r. The printer 10 prints the product weight and price on an internally stored label based on the supplied weight data. Further, the CPU 15 sends a label pasting signal to the printer control interface 24 after a predetermined period of time has elapsed since the product passed in front of the light receiver S4b.
is supplied to the printer 10 via. In this case, during the predetermined time period, the product being conveyed on the conveyor 4 is exactly
It is set to the time to reach the 0 pasting position.

Next, the operation of this embodiment with the above-mentioned configuration will be explained, but first, the principle of weight detection in this invention will be explained.

FIG. 4 is a diagram showing changes in the weight signal of the load cell 120 immediately after the product is transferred onto the conveyor 3. Note that the weight signal of the load cell 12 includes the weight C of the motor M, conveyor 3, pulley, belt, etc. (this weight is referred to as initial load α), but this figure shows the weight signal after subtracting the initial load α. It shows. In addition, in this example, since weighing is performed while being transported as described above, the vibrations of the transport system are actually superimposed on the waveform shown in the figure, but this is omitted here for the sake of simplifying the explanation. .

Now, as shown in FIG. 4, immediately after the product is transferred from the conveyor 2 to the conveyor 3, the measured value oscillates greatly, and thereafter becomes a damped oscillation that converges toward the true value W0. The period of this vibration is disordered immediately after being placed, but as the amplitude attenuates, it becomes a certain period. This constant period is determined by the weight of the product and is generally known to be expressed by the following equation.

T=1/1JkXj:=1/M in agony...(1
1vW However, k: Spring constant g: Gravitational acceleration W: Product weight By the way, in order to measure the true weight from the vibrating weighing value, #'i, after the vibration enters a certain period, It is desirable to sample several points at uniform intervals within one period of , and average the sampled values. Therefore,
In this invention, the above-mentioned formula (1), corresponding formulas, tables, etc. are stored in advance, and the vibration period is determined based on the stored contents and the previous sampling value, and the next sampling interval is an integer of the vibration period. Set it so that it is 1. In addition, the solid line e shown in the M5 diagram indicates the curve corresponding to the equation (11) described above, and the polygonal line 1@a, It B* 1m is the interval α+0 to α
+Wk, α10Wk~α+2 Wk, α+2 Wk
A broken line I shows the case where equation (1) is linearly approximated at ~α+gWk (Wk is a weight appropriate for segmentation).

shows the case where (equation 11 is linearly approximated) in the entire interval.And to calculate the vibration period using the graph, @5
Solid line el shown in the figure, broken line 1 *a * l *b *
ho or dashed line 1. Either of these methods may be used, and an appropriate one may be selected depending on the required accuracy and calculation time.

In the ROM 16 in this embodiment, broken lines 1. A table corresponding to is stored.@Next, the operation of this embodiment will be explained.

First, when the product to be transported enters the conveyor 3, the C
PTJ15 detects this from the change in the output signal of photoreceiver s3b and starts weighing measurement operation (step sp in Figure 6).
. Then, the time △to (this Δt
(0 is a fixed value stored in advance in the ROM 16), the CPU 15
A conversion start signal 5Tt- is supplied to the /D converter 21 (step sp,).

SPj )o As a result, the A/D converter 21 converts the point νP
At o (see FIG. 4), the A/D conversion operation is started. The A/D converter 21 in this embodiment is a so-called dual slope type integral type A/D converter, and steps SP4 to S shown in FIG. 6 (portions surrounded by broken lines) are as follows.
The processing process of this A/D converter 21 is shown. Then, step sp4°SP corresponds to period T shown in FIG. 7, and steps sp, , sp, , sp correspond to period T [corresponding to step SP, . ,sp, corresponds to period T. In this case, the offset processing period T increases or decreases depending on the length of the second integration period T, and the total time TAD during which the human/D conversion sum is increased remains constant regardless of the magnitude of the converted analog signal -ix <There's a lot of pressure. When this A/D conversion process is completed, the CPU 15 moves to step 8P and reads the count value (V conversion result) of the A/D converter 21. Then, the read count value is stored in the area @lK of the memory block 17& set in the RAM 17. This memory block 17 aFi multiple areas 1~on(
n is about 4°6.8), and CPt
When new data is supplied from J15, area e →
The data are sequentially shifted and stored in the order of . . . → en. Further, the CPU 15 performs step SP
1. When the count value is read in, the vibration period corresponding to this count value (i.e. weight value) is stored in the ROM 16.
Calculate with reference to the inner 'ff-pull (corresponding to broken line e in Figure 5) (step SP, a).

Then, based on the calculated vibration period, the waiting time until the next sampling point is calculated, and the timer setting time corresponding to this waiting time is calculated.

Note that the timer in this case is a timer configured by a program. And step SB.

A timer is set at step SP, and the timer is reset at step SP, when the timer time has elapsed.

When the processing of steps sp, , is completed, step S
The process moves to P, and the next sampling process (the same process as described above) is started. Here, the timer setting time sum calculated in steps SP, . . . will be explained.

Now, let's consider the case of sampling in terms of the vibration period.

First, suppose that the point P0 at which the first sampling was performed was time t, and the imaging period obtained at step SP1' was TIL, then the next sampling was performed from time 1m to T a / 2 (Δ1 .) You will know what to do later. By the way, in step SP, the A/D conversion time TAD has elapsed since time t, and
In step sp, , for setting the tie Yt, step sp, .

The computation time at SP, , continues to elapse. Therefore, if the time used from step sp, , to step sp, , < is t-T4, then TAD+T4
=T&/2...It must be C1!1. Then, if the time required for performance IE&C is ΔT4, the timer setting time T4I becomes T&T;=-1ΔT,-,TAI)...song (8).

In step SP1 described above, the time TI shown in equation (8) is calculated.

According to the above process, the sampling point is
As shown in FIG. 4, two points are taken at approximately equal intervals within one cycle of vibration. Note that if sampling is performed in % of the vibration period, four points will be equally spaced within one period, which is clear from the above.

As shown in FIG. 6, it is possible to sample evenly from the peaks and valleys of the vibration waveform by following the flow shown in FIG.

Then, during the sampling process, steps 70- shown in FIG. 6 are cycled through, and step SP.

The count value read in is sequentially shifted and stored in block 17aK shown in FIG.

Then, when the product being weighed is sent out from conveyor 3,
(The ll'PU 15 detects this from the change in the output signal of the light receiver S4b, and at this point, the sampling process (the process shown in FIG. 6) ends. When the sampling process ends, the CPU 15 stores The data in each area . If four are provided, the data to be averaged will be the four data immediately before the product is sent out (a period in which the vibration cycle is approximately constant).

Thereafter, new products are weighed one after another in the same manner as described above. Note that the number Nm of sampling values to be finally averaged is set so that N''I is an integer value when the sampling interval is 1/Nb ([number)] of the natural frequency period.For example, If Nb = 2 as in the above example, then FiNa = 4, i.e. 1., - = 2 (integer)
Make it so that With this configuration, when the frequency is constant and the amplitude is constant, the average value will always be the center value of the vibration. In this way, in this embodiment, extremely high precision can be achieved in conveyance weighing. It is possible to measure weight, and the measurement time is short (no need to wait for the weight to stabilize).
In high-speed conveyance and weighing, there is an advantage that accuracy does not deteriorate even if the product is delivered from the conveyor before the weighing becomes stable.

In this embodiment, a strain gauge or other device that outputs an analog weight signal was used as the load cell, but instead, for example, a weight detector that outputs a digital weight signal using vibration preload may be used. You can. An example of this type of weight detector is shown in FIG. 30 in the figure
is a parallel beam structure vibrator, and this vibrator is excited by a piezoelectric vibrating element 31 from one side, and a vibration wave number is detected by a piezoelectric vibrating element 32 from the other side. Then, when a load F is applied to the vibrator 30 in the direction shown by the arrow, corresponding to the magnitude of the load F,
The frequency of the vibrator 30 changes, and as a result, a weight frequency signal can be extracted from the piezoelectric vibrating element 32. When such a weight detector is used, an A/D converter is not required, so the output signal of the piezoelectric vibrating element 32 may be supplied to the CPU 1BK via an appropriate interface.

The structure of the vibrator 30 is the parallel beam structure shown in the drawing.
A summer type structure or a ring structure that can be used for running is also considered.

As explained above, according to the present invention, since the current sampling interval is set each time based on the previous sampling value, sampling can be performed evenly from the peaks and valleys of the vibration waveform. This makes it possible to perform extremely accurate weighing at high speed. Therefore, transport weighing can be carried out at a higher distance, and even in normal stationary weighing, accurate weight can be measured during the transition period before the weighing becomes stable.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a schematic configuration of an embodiment of the present invention;
Figure 2 is a side view showing the configuration near the conveyor 3, Figure @3 is a block diagram showing the electrical configuration of the same embodiment, and Figure 4 is the weight signal of the load cell 12 immediately after the product is transferred onto the conveyor 3. A waveform diagram showing waveforms, Fig. 5 is a graph showing the relationship between weight and natural vibration stored in the same embodiment, Fig. 6 is a flowchart showing the operation of the same embodiment, and Fig. @7 is an integral type A.
/T') A waveform diagram showing an integral operation in the converter 21, FIG. 8 is a conceptual diagram showing a storage block that stores sampling values, and FIG. 9 is a schematic diagram showing another example of the weight detector. 15...CPU (Central Processing Unit), 16...
・ROM. 17...RAM (15 to 17 are sampling interval setting means).

Claims (1)

[Claims] 1. In an electronic weighing device that samples vibrating measured values and averages the sampled values to calculate the weight, the relationship between the weight of the object to be weighed and the natural vibration corresponding to this weight is stored in advance. An electronic weighing device characterized by comprising a sampling interval setting means for setting a current sampling interval based on the stored content and the previous sampling value. 2. The electronic weighing device according to claim 1, wherein the sampling interval setting means stores the relationship between weight and natural vibration as a mathematical formula. (v) The sampling interval setting means sets the current sampling interval to be 1/Nb (integer) of the specific imaging period, and uses the average value of pJ a (integer) of one sampling value as the measured value. An electronic weighing device according to claim 1, characterized in that: 4. The electronic weighing device according to claim 1, wherein the integer values N& and Nb are each set such that Na/Nb is an integer value.