JPH0410978B2 - - Google Patents

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 thereafter becomes a damped oscillation that converges toward the true value. Generally, measurement is performed with stable measured values, but a measuring device has been developed that samples several vibration values during a transient period and averages the sampled values to obtain the true value. With this type of device, it is possible to know the true value without waiting for the weighing to stabilize, so it is possible to speed up the weighing, and even when the weighing device itself is vibrating due to external vibrations, etc. The true value can be found effectively.

By the way, in this type of conventional measuring device, since the sampling interval of the measured value is a preset constant value, the sampling value may become inappropriate depending on the period of vibration. 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. Moreover, since the vibration period changes depending on the weight of the object to be weighed, in the end, in conventional weighing devices,
The disadvantage is that the measurement accuracy changes depending on the weight of the object to be measured, and the reliability of the measured value is low.

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 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. 1 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 system that performs packaging, weighing, and pricing of products through a series of automatic processes. It is a machine that does.

In FIG. 1, 1, 2, 3, and 4 are conveyors, each of which runs to the right in the drawing and conveys products to the right. A roller conveyor 5 conveys the products to the right in the same way as conveyors 1 to 4. _M1 ~
_M4 is roller conveyor 5, conveyor 2, 3,
This is the motor that drives 4. In addition, the width belt conveyors 6a to 6c installed between the rollers of the roller conveyor 5 transport the products passing above to the guide plate 7.
Move it to the side and bring it into contact with this guide plate 7. Therefore, the products conveyed on the roller conveyor 5 come into contact with the guide plate 7 by the width adjustment belts 6a to 6c, and then are transferred onto the conveyor 2 along the guide plate 7. S1a to S4a are each a light projector, and a light receiver S1b is arranged opposite to each of them.
~S4b receives the irradiated light. In this case, each of the light receivers S1b to S4b detects a product passing in front of it. 9 is a console consisting of an operating section 9a (see Fig. 3) such as a keyboard and a display section 9b, and 10 is a label on the transported product (the weight and price of the product are printed on this label).
It is a printer that applies adhesive. In this case, the conveyor 3 constitutes a weighing conveyor that performs weighing while conveying, and as shown in FIG. 2, a load cell 12 is provided below the conveyor 3. The weight of the conveyor 3, motor M ₃ , pulley, belt, etc. are all applied to the load cell 12, and its right end is fixed to a support base 13. Note that the conveyor 1 shown in FIG.
Products that have already been packaged (packed, etc.) are transferred by a packaging section (not shown).

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 CPU 1
The calculation results and various data in step 5 are temporarily stored.
It is RAM. In this case, the CPU 15 uses the light receiver S1 supplied via the sensor interface 18.
~ Based on each light reception signal of S4b, motor M ₁ ~ _{M 4}
drive/stop signals are generated, respectively, and the drive/stop signals are supplied to the motors M ₁ to _{M 4} via the motor control interface 19 . And this CPU1
5 motor control, two at a time on the conveyor 3.
The following products are no longer available. Therefore, the weight of each product can be detected using the weight signal of the load cell 12. The weight signal from the load cell 12 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.
It is supplied to the CPU 15. In addition, A/D converter 2
1, from the time when the conversion start signal S _T is supplied from the CPU 15 via the interface 22, the A/
The D conversion operation is now started. The output timing of the signal _ST in this case will be described in detail later. When the CPU 15 calculates and measures the weight of the product based on the output signal of the A/D converter 21,
Weight data, which is the result of this calculation, is supplied to the printer 10 via the printer control interface 24. The printer 10 prints the product weight and price on an internally stored label based on the supplied weight data. Further, the CPU 15 supplies a label pasting signal to the printer 10 via the printer control interface 24 after a predetermined period of time has passed since the product passed in front of the light receiver S4b. In this case, the predetermined time is set to the time when the product conveyed on the conveyor 4 just reaches the sticky position of the printer 10.

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 12 immediately after the product is transferred onto the conveyor 3. Note that the weight signal of the load cell 12 includes the weight of the motor M ₃ , conveyor 3, pulley, belt, etc. (hereinafter this weight is referred to as initial load α), but this figure shows the weight signal after subtracting the initial load α. It shows. Furthermore, in this embodiment, since the 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 purpose of simplifying the explanation.

Now, as shown in Figure 4, the product is placed on the conveyor 2.
Immediately after being transferred to the conveyor 3, the weighing value oscillates greatly, and after that, the true value W ₀
It becomes a damped vibration that converges toward . The period of this vibration is disordered immediately after being placed, but as the amplitude attenuates, it becomes a certain period. This fixed period is determined by the weight of the product,
It is generally known that it is expressed by the following formula.

However, K: spring constant g: gravitational acceleration W': product weight By the way, in order to measure the true weight from the weighing value that vibrates in this way, after the vibration enters a certain period, It is desirable to sample several points at uniform intervals and average the sampled values. Therefore, in this invention, the above (1)
Equations and corresponding equations, 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 set to be one integer fraction of the vibration period. In addition, the solid line l ₁ shown in FIG. 5 shows the curve corresponding to the above-mentioned equation (1), and the polygonal lines l ₂ a, l ₂ b, l ₂ c are the sections α+0 to α+Wk,
α + Wk ~ α + 2Wk, α + 2WK ~ α + 3Wk (Wk
indicates the case where equation (1) is linearly approximated at the weight appropriate for dividing into sections), and the broken line _l3 shows the case where equation (1) is linearly approximated over the entire section. Therefore, to calculate the vibration period using a graph, use the solid line shown in Figure 5.
Any of l ₁ , broken lines l ₂ a, l ₂ b, l ₂ c, or broken lines l ₃ 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, a table corresponding to the broken line _l3 is stored.

Next, the operation of this embodiment will be explained.

First, when the product to be transported enters the conveyor 3, the CPU 15 detects this from a change in the output signal of the light receiver S3b, and starts weighing and measuring operation (6th
Figure step SP ₁ ). Then, when a time △t ₀ (this △t ₀ is a fixed value stored in advance in the ROM 16) has elapsed since the product entered the product, the CPU 15 starts conversion via the interface 22 to the A/D converter 21. Supply signal _ST (steps SP ₂ , SP ₃ ).
As a result, the A/D converter 21 converts the point P ₀ (fourth
(see figure), the A/D conversion operation is started.
The A/D converter 21 in this embodiment is a so-called dual-slope integral type A/D converter, and steps SP ₄ to _{SP 11} (portion surrounded by broken lines) shown in FIG. The processing process of the converter 21 is shown. Steps SP ₄ and SP ₅ correspond to the period T ₁ shown in FIG. 7, and steps SP ₆ and SP 5 correspond to the period T 1 shown in FIG.
SP ₇ and SP ₈ correspond to period T ₂ , and steps SP ₁₀ and
SP ₁₁ corresponds to period T ₃ . In this case, the offset processing period _T3 increases or decreases depending on the length of the second integration period _T2 , and the total time _TAD required for A/D conversion
is made constant regardless of the magnitude of the analog signal to be converted. When this A/D conversion process is completed, the CPU 15 moves to step _SP12 and reads the count value (AD conversion result) of the A/D converter 21. Then, the read count value is stored in RAM 17.
Area e ₁ of memory block 17a set in
Store in. This memory block 17a is a block consisting of a plurality of areas e ₁ to e _o (n is about 4, 6, 8), and when new data is supplied from the CPU 15, the areas e ₁ →e ₂ ...→e It is designed to be stored by shifting sequentially in the order of _o . Also,
When the CPU 15 reads the count value in step _SP12 , the CPU 15 reads the count value (i.e., the weight value).
The vibration period corresponding to is calculated with reference to the table in the ROM 16 (corresponding to the broken line _l3 in FIG. 5) (step _SP13 ). Then, based on the calculated vibration period, a waiting time until the next sampling point is calculated, and a timer setting time corresponding to this waiting time is calculated. Note that the timer in this case is a timer configured by a program. Then, in step SP ₁₅ , a timer is set,
At step _SP16 when the timer time has elapsed, the timer is reset. When the process of step _SP16 is completed, the process moves to step _SP3 , and the next sampling process (the same process as described above) is started.
Here, the timer setting time calculated in step _SP14 will be explained.

Now, let's consider the case of sampling at 1/2 of the vibration period.

First, the point at which the first sampling was performed
Assuming that P ₀ is time t ₁ and the vibration period determined in step SP ₁₃ is Ta, it is understood that the next sampling should be performed after Ta/2 (Δt ₁ ) from time t ₁ . By the way, in step _SP13 , the A/D conversion time _TAD has elapsed since time _t1 , and in step _SP15 for setting the timer, the calculation time in steps _SP13 and _SP14 is
More has passed. Therefore, the steps
If the time used from SP ₁₃ to step SP ₁₆ is T ₄ , then T _AD + T ₄ = Ta/2 (2) must be satisfied. Therefore, if the time required for calculation is △T ₄ , the timer setting time T′ ₄
becomes T′ ₄ =T _a /2−T ₄ −T _AD ……(3). In step _SP1 described above, time _T'4 shown in equation (3) is calculated.

If the above process is followed, the sampling points will be P ₁ , P ₂ , P _{3 .} . . shown in Figure 4, and two points will be taken at approximately equal intervals within one cycle of vibration. . Note that if sampling is performed at 1/4 of the vibration period, four points are taken at equal intervals within one period, which is clear from the above.
In this manner, by following the flow shown in FIG. 6, it is possible to sample evenly from the peaks and valleys of the vibration waveform.

During the sampling process, the flow shown in FIG. 6 is repeated, and step SP ₁₂
The count values read in are sequentially shifted and stored in block 17a shown in FIG. When the product being weighed is sent out from the conveyor 3, the CPU 15 detects this from a change in the output signal of the light receiver S4b, and at this point ends the sampling process (the process shown in FIG. 6). When the sampling is completed, the CPU 15 averages the data in each area e ₁ to _{e o} of the memory block 17a, uses this calculation result as a weight value, and displays it on the display 9.
a and the printer 10. In this case, for example, if four areas are provided in the memory block 17a, 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 Na of sampling values to be finally averaged is set so that Na/Nb becomes an integer value when the sampling interval is set to 1/Nb (integer) of the natural frequency period.

For example, when Nb=2 as in the above embodiment, Na=4, that is, Na/Nb=2 (integer). With this configuration, if 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, it is possible to measure weight with extremely high precision during conveyance weighing, and since the measurement time is short (weighing does not have stability), the weighing is stable during high-speed conveyance weighing. Even if the product is sent off the conveyor before the product is delivered, there is an advantage that accuracy does not deteriorate.

In this example, a strain gauge or other device that outputs an analog weight signal was used as the load cell, but instead of this, for example, a weight detector that outputs a digital weight signal using a vibrator may be used. May be used. An example of this type of weight detector is shown in FIG. In the figure, 30 is an average beam structure vibrator, and this vibrator is passed from one side to the piezoelectric vibrator 3.
1, and the piezoelectric vibration element 32 detects the vibration frequency from the other side. When a load F is applied to the vibrator 30 in the direction indicated by the arrow, the frequency of the vibrator 30 changes in accordance with the magnitude of the load F, and as a result, a weight frequency signal can be extracted from the piezoelectric vibrating element 32. I can do it. When such a weight detector is used, an A/D converter is not required, so the output signal of the piezoelectric element 32 may be supplied to the CPU 15 via an appropriate interface. In addition,
The structure of the vibrator 30 is not limited to the parallel beam structure shown in the drawings, but may also have a rhombic structure or a ring structure.

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 highly accurate weighing at high speed. Therefore, transport weighing can be carried out at a higher speed, and even in normal static weighing, accurate weight can be measured in 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, FIG. 2 is a side view showing the structure around the conveyor 3, FIG. 3 is a block diagram showing the electrical configuration of the embodiment, and FIG. The figure is a waveform diagram showing the weight signal waveform of the load cell 12 immediately after the product is transferred onto the conveyor 3, Figure 5 is a graph showing the relationship between weight and natural vibration stored in the same embodiment, and Figure 6 is a graph showing the same implementation. A flowchart showing an example operation, FIG. 7 is a waveform diagram showing an integral operation in the integral type A/D converter 21, FIG. 8 is a conceptual diagram showing a memory block that stores sampling values, and FIG. 9 is a weight detection diagram. It is a schematic block diagram which shows another example of a container. 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 calculates weight by averaging the sampled values, the relationship between the weight of an object to be weighed and the natural vibration corresponding to this weight is stored in advance. , set the current sampling interval so that it is 1/Nb (integer) of the natural vibration period obtained from this memory content and the previous sampling value, and measure the average value of Na (integer) sampling values. An electronic weighing device, comprising sampling interval setting means for setting the integer values Na and Nb such that Na/Nb is an integer 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.