JPH0139537B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting that a weighing conveyor is not weighing articles, that is, is in a zero point state when automatically performing zero point correction on a weighing conveyor.

Conventionally, the above-mentioned device is equipped with an optical detector on the input side of the weighing conveyor, and a timer that is activated every time the detection output of the optical detector is supplied, even if the set time limit has not been reached. , when this timer reaches its set time limit (slightly longer than the time required to transport the article from the mounting position of the optical detector to the output side of the weighing conveyor) and generates a signal, the article is not on the weighing conveyor. There was one that judged this and automatically corrected the zero point. However, since this device uses an expensive optical detector, there is a problem that the product price is high, and there is also the problem that the optical axis of the optical detector's light source and receiver are misaligned during operation, causing malfunction. It was hot. In particular, if the weighing conveyor must be made waterproof, a waterproof type, which is even more expensive than an ordinary optical detector, must be used, and special consideration must be given to the wiring work. The need arose.

An object of the present invention is to provide a device that can automatically detect a zero point without using an optical detector. Hereinafter, the present invention will be explained in detail based on one embodiment shown in the drawings. In Figure 1, 1
2 is an incoming conveyor, 2 is an outgoing conveyor, and 3 is a weighing conveyor. The analog weighing signal from the weighing device 4 provided in the weighing conveyor 3 is a serial comparison type A/
The D converter 5 sequentially converts the signal into a digital measurement signal.

For example, when the weighing conveyor 3 finishes weighing an article and starts weighing the next article, the analog weighing signal of the weighing device 4 changes as shown by the solid line in FIG. Then, the A/D converter 5 converts the analog weighing signals W1 to Wn, shown as dots in the figure, to digital weighing signals D1 to Dn.
Convert to

These digital measurement signals D1 to Dn are sequentially supplied to the nth stage of the n-stage shift register 6.
The shift register 6 shifts the stored value of each stage to the next stage (to the right in this embodiment) every time a new digital weighing signal is supplied to the nth stage, so that the digital weighing signal Dn is shifted to the next stage (to the right in this embodiment). When stored in the eye, the first stage 61 of the shift register 6 contains
D1 is in the second stage 62, D2 is in the second stage 62, ...n-1st stage 6n-1
Dn-1 is stored in .

In addition, the digital measurement signals D1 to Dn are compared in the level comparator 7 with a digital level threshold, which is a digitized level threshold at which the analog measurement signal can be considered to be zero, as indicated by the dashed line in FIG. If the supplied digital measurement signals D1 to Dn are greater than the digital level threshold, an output "1" is generated, and if it is smaller, an output "0" is generated. 8 is a digital level threshold setter. The output “1” or “0” which is the level comparison result of the level comparator 7 is
It is supplied to the n-th stage 9n of the n-stage shift register 9. The shift register 9 shifts the stored value of each stage to the next stage every time a new output of "1" or "0" is supplied from the level comparator 7 to the n-th stage 9n, and also performs level comparison. Each output of the device 7 is synchronized with the digital weighing signals D1 to Dn, so when the level comparison result of the digital weighing signal Dn is stored in the nth stage, the output of the first stage 91 is synchronized with the digital weighing signals D1 to Dn.
The level comparison result of D1 is stored in the second row 92, the level comparison result of D2 is stored in the second row 92, and the level comparison result of Dn-1 is stored in the (n-1)th row 9n-1.

The stored values in each stage of the shift register 9 are
The analog weighing signal is supplied to the input NAND circuit 10, and when an item is not being weighed, the analog weighing signal is smaller than the level threshold as shown in FIG. 2, so the outputs of each stage of the shift register 9 are all "0". Yes, the input NAND circuit 10 generates an output "1".

In response to the output of the input NAND circuit 10, the average value calculation unit 11
The average value of the stored values of each stage from the stage 64 to the (n-3)th stage is calculated, and the zero point of the weighing device 4 is corrected based on the calculated value. Here, from the first row 61 to the third row
63, the stored values from the nth stage 6n to the n-2nd stage 6n-2 were removed and the average value was calculated using W1, W2, Wn-2, Wn-1 shown in Figure 2. , Wn, which are smaller than the level threshold, but are part of the falling or rising portions of the analog measurement signal, cannot be accurately corrected for the zero point. After the output of the input NAND circuit 10 generates "1" and the average value calculation command is output, all shift registers 91 to 93 or 9n are set to 1.
By setting this to , it is possible to prevent further calculation commands from being applied. The interval between zero correction calculations can be adjusted by the number of registers set to "1".

The zero point detection device according to the present invention uses an optical detector because it is configured to determine that the item is not being weighed and perform zero point correction when all of the digital weighing signals D1 to Dn are smaller than the digital level threshold. There's no need. Therefore, it is possible to reduce the price, prevent malfunctions, and is particularly effective when used in a weighing conveyor that must have a waterproof structure.

In the above embodiment, the first stage of the shift register 6
The average value was calculated by removing 61 to 3rd stage 63 and from n-2nd stage 6n-2 to nth stage 6n,
The number of stages to be removed can be arbitrarily changed depending on the speed of the weighing conveyor, the length of the article, etc., and depending on how the number of stages of the shift register 6 is selected, there is no need to remove the stages. Although the average value was calculated and the zero point was corrected using this, the zero point may also be corrected using the stored value of an appropriately selected stage.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a weighing conveyor incorporating a zero point detection device according to the present invention, and FIG. 2 is a diagram showing changes in analog weighing signals of the weighing conveyor. 3... Weighing conveyor, 5... A/D converter, 7... Level comparator, 8... Level setter, 9... Shift register, 10... Input NOT AND circuit (logic circuit).

Claims (1)

[Claims] 1. An A/D converter that sequentially converts analog weighing signals from the weighing conveyor into digital weighing signals;
A comparator that outputs a small display signal if each of the above-mentioned digital weighing signals is supplied in sequence and is close to the zero level and smaller than a predetermined level threshold, and a large display signal if it is large; A shift register to which the output of the device is sequentially supplied, and an AND circuit which receives the stored values of each stage of the shift register and generates a zero point detection signal when all of these stored values are the above-mentioned small display signals. Zero point detection device for weighing conveyor.