JP2740033B2 - Load measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load measuring device that converts a weighing signal into a digital signal and outputs the result.

2. Description of the Related Art Even if the load is detected by a load converter having an analog output, the load is often converted into a digital signal for signal processing in a subsequent stage. With a general electronic scale,
As shown in FIG. 3, an object 1 is loaded on a load cell 2, and an output signal of the load cell 2 is applied to an unknown input of a double integration type A / D converter 5 via an amplifier 3 and a low-pass filter 4 so as to be digitalized. Has been converted.

Problems to be Solved by the Invention The double integral type A / D converter 5 is widely used for electronic scales, but in the field of measuring the load of a weighing object during high-speed transportation by a belt conveyor, Since high-speed digital conversion cannot be realized, it is very difficult to use a conventional double integrating A / D converter.

Furthermore, even if high-speed digital conversion can be realized,
In order to obtain the peak value of the weighed value, it is necessary to perform repeated arithmetic calculations.

The present invention can measure the load of the object to be weighed during high-speed transportation even if the overall operation speed is slow, and furthermore, when trying to find the peak value of the weighed value, it is not necessary to perform repeated arithmetic calculations. An object is to provide a load measuring device.

Means for Solving the Problems A load measuring apparatus according to the present invention compares a first comparator with a first comparator which determines the level of an analog weighed signal by comparing an analog weighed signal level with a reference signal level. A second comparator for detecting that the level difference between the two signals falls within a specified range, a reversible counter for selecting a down-count of a clock up-count based on a determination of the first comparator, A D / A converter that converts the digital output of the counter into an analog signal, and control that is controlled by the output of the second comparator and that inhibits the count value updating operation of the reversible counter when the level difference between the two signals falls within a specified range. Unit, the analog output of the D / A converter is connected to the first comparator as a reference signal, and the digital output of the reversible counter is counted. It is characterized by obtaining a digitally converted output of a heavy signal.

According to this configuration, when the level difference between the two signals compared by the first comparator is large and does not fall within the specified range, the level of the analog weighed signal and the current count value of the reversible counter are calculated by D / The reversible counter counts up the clock when the first comparator determines that the level of the analog weighed signal is larger than the reference signal level by comparing the analog weighed signal with the reference signal level converted by the A converter. When the first comparator determines that the level is lower than the reference signal level, the reversible counter counts down the clock. Therefore, the content of the reversible counter at each time becomes a digital value corresponding to the weighed value.

If the level difference between the two signals compared by the first comparator is small and falls within the specified range, the second comparator inhibits the counting operation of the reversible counter via the control unit and outputs the analog weighed signal. In the state where the level change amount per unit time is small, the content of the reversible counter sometimes does not fluctuate.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a main part of a weight integrator for a belt conveyor employing the present invention. The load received by the weighing conveyor 8 interposed between the conveyors 6 and 7 is detected by the load cell 2,
Is compared to the level V _R of the reference signal 10 is applied to the non-inverting input of the first comparator 9 via an amplifier 3 and a low-pass filter 4 (+). Assuming that the output level of the low-pass filter 4 is V _S , the output side T ₁ of the first comparator 9 is inverted to the logic level “H” when “V _R > V _S ”, and the output side T ₂
Inverted to a logic level "H" in the case of the "V _R <V _S". Here, the output side T1 of the _first comparator 9 is a reversible counter 11
It is connected to the instruction to the + terminal to perform up-counting of the control terminal of the output side T ₂ instructs the execution of the down-counting of the reversible counter 11 - is connected to the terminal.

The reversible counter 11 is a clock that is repeatedly output from the pulse oscillator 12 when the + terminal is at the logic level “H”.
CK is counted up, and the clock CK is counted down when the-terminal is at the logic level "H".

The count content of the reversible counter 11 is converted into an analog signal by the D / A converter 13 and applied to the inverted input (−) of the first comparator 9 as the reference signal 10.

A weighed signal having a fluctuation period t as shown in FIG. 2 is applied to the non-inverting input (+) of the first comparator 9,
Assuming that the repetition frequency of CK is f and the resolution of the load integrator is a, the following is set.

f ≧ (a / t) Further, the clock CK is supplied to the reversible counter 11 from the pulse oscillator 12 via the gate 14 as a control unit for inhibiting the counting operation. The gate 14 is controlled by a second comparator 15. Second comparator 15
Is configured such that when the level difference | V _S −V _R | between the weighed signal level V _S and the output level of the D / A converter 13 is smaller than the reference signal level, the output is inverted. When | V _S −V _R | is large, the output signal of the pulse oscillator 12 is supplied to the reversible counter 11 via the gate 14, and when the level difference between the two becomes small, the gate 14 is turned off and the reversible counter 11 is turned off. Is not supplied with clock CK.

With such a configuration, the count value of the reversible counter 11 at any time can be changed to the change of the weighed signal shown in FIG. 2 without executing high-speed sampling as in the conventional double integration type A / D converter. A digital output of a weighing signal is obtained from the output of the reversible counter 11, and a subsequent signal processor (not shown) measures the transported weight based on the count value of the reversible counter 11 and integrates this. And the total transport volume is calculated.

Further, since the gate 14 is controlled by the second comparator 15, it is possible to reduce a situation where the count value of the reversible counter 11 repeats up and down little by little when the level V _{S of the} weighed signal is stable. And a stable digital output can be provided at the subsequent stage.

Further, when the peak values P ₁ , P ₂ ,... Shown in FIG. ₂ are obtained, the output side T ₁ or T ₂ of the reversible counter 11 is monitored, and the reversible counter 11 at the timing when the logical level is inverted is monitored. It is only necessary to read the count value of, and there is no need to arithmetically compare the digital output values as in the conventional case.

In the above embodiment, the case of a weight integrator has been described as an example.However, a product that needs to be sorted is conveyed at a high speed, compared with the reference weight value in the middle of the conveyance, and the product is compared with the reference weight value. This is effective for objects that need to measure a moving object, such as a weight checker configured to switch the discharge path.

In the above embodiment, the control unit for turning on / off the clock CK at the gate 14 to inhibit the count value updating operation of the reversible counter 11 is configured. However, the control terminal of the reversible counter 11 is directly connected to the output of the second comparator 15. The same applies to a configuration in which a data holding state in which neither counting up nor counting down is performed even when the clock CK is input is performed.

Second comparator 15 in the above embodiment, the level difference between the reference signal level and the input signal | V _S -V _R | is compared with the count value updating operation of the reversible counter 11 the reference signal level as a boundary on / off the, which is a dead zone width is provided around the reference signal level, the level difference between the input signal | V _S -V _R | count update reversible counter 11 when Do even slightly greater or less than the dead band level The same applies to a configuration in which the operation is turned on / off.

As described above, according to the present invention, the first comparator that determines the level of the analog weighed signal by comparing the analog weighed signal level with the reference signal level and the first comparator that determines the level of the analog weighed signal are used. A reversible count in which clock up-counting and down-counting are selected, and a D / A converter for converting the digital output of the reversible count into analog are provided, and the reversible counter is controlled by the output of the first comparator. Even if the overall operation speed is reduced, the load value of an object moving at a high speed can be converted into a digital value.

Further, a second comparator for detecting that the level difference between the two signals compared by the first comparator falls within a specified range, and a level difference between the two signals controlled by an output of the second comparator. And a control unit for prohibiting the count value updating operation of the reversible counter when the signal enters the inside, so that it is possible to eliminate the slight fluctuation of the output digital value when the analog weighed signal level becomes stable. it can.

Also, when trying to find the peak value of the weighed value,
It is only necessary to monitor the output side of the reversible counter and read the count value of the reversible counter at the timing when the counting operation switches from counting up to counting down or vice versa, and it is necessary to arithmetically compare the digital output value as in the past. And the configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a weight integrator for a belt conveyor as one embodiment of a load measuring device of the present invention, FIG. 2 is a waveform diagram of the main portion of the device, and FIG. It is a block diagram. 2 ... Load cell, 9 ... First comparator, 10 ...
Reference signal, 11 ... reversible counter, 13 ... D / A converter, 14 ... Gate [control unit], 15 ... Second comparator.

Claims (1)

(57) [Claims] A first method for comparing an analog weighed signal level with a reference signal level to determine a level of the analog weighed signal.
, A second comparator for detecting that the level difference between the two signals compared by the first comparator falls within a specified range, and counting up and down of the clock based on the judgment of the first comparator. Is selected, a D / A converter for converting the digital output of the reversible counter into analog, and the reversible when the level difference between the two signals is controlled by the output of the second comparator and falls within a specified range. A control unit for inhibiting the count value updating operation of the counter is provided, an analog output of the D / A converter is connected as a reference signal to the first comparator, and a digital conversion output of a weighed signal is obtained from the digital output of the reversible counter. Load measuring device.