JPS5817407B2 - Zero adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zero adjustment device using an electronic servo system used in electronic scales and other measuring instruments.

In general, electronic measuring instruments such as load cells are widely used in industrial applications, using a load cell or the like as a sensor.

With this kind of load cell, even if the load of the object to be measured is zero,
For example, a certain detection output is generated from the sensor due to the weight of the object to be measured, etc., and a certain certain value is indicated to the indicator even though the load is originally zero.

Therefore, a zero adjustment device is required to adjust this indicated value to the original zero load.

By the way, this type of measuring instrument conventionally used a mechanical servo system using a servo amplifier, servo motor, and potentiometer, but in recent years these have been replaced by comparators, up/down counters, and digital-to-analog converters. (hereinafter D
An electronic servo system consisting of a /A converter) has come into use.

Electronic servo systems are characterized by the fact that they have no mechanical parts.
It is superior in terms of reliability compared to mechanical types.

However, when used as a zero adjustment circuit, if the controlled object exceeds a predetermined range and zero adjustment becomes impossible, since a counter is used, the target output will vibrate during operation, and the target position will be reached when the operation stops. There is a possibility that it will stop far away.

This is more likely to have an adverse effect on a system using this device than on a system using a mechanical servo system.

FIG. 1 is a block diagram showing the configuration of a conventional zero adjustment device using an electronic servo system element 2. As shown in FIG.

In FIG. 1, reference numeral 1 denotes an amplifier which inputs a voltage V in detected by a sensor (not shown) and amplifies it to produce an output Vout.

This output Vout is sent to an indicator (not shown), such as a voltmeter.

2 is an electronic servo system element which is the main body of the zero adjustment device, and is composed of the following elements.

That is, 3 is a comparator which inputs the output of the amplifier 1 as a signal e+ to be controlled, compares it with a reference value e-, and determines the magnitude relationship.

Note that the input terminal for the reference value e- is connected to ground (zero point).

5 is an up/down counter whose counting direction is controlled by the determination signal from the comparator 3.

That is, the judgment signal from the comparator 3 is e + > e-
If so, count in the upward direction, and if e+<e-, count in the downward direction.

4 is a clock pulse generator, which is operated by the zero adjustment finger/S>A applied from the outside to generate a clock pulse C;
Add this to up/down counter 5.

6 is an I)/A converter which inputs the output Dout of up blanker rank 5 and outputs an analog output e.

occurs. This analog output e. becomes the inverting input to amplifier 1.

The input/output relationship of the servo system element 2 is as shown in FIG.

a is the input voltage e+, e- of comparator 3, e + > e-
The analog output voltage e of the D/A converter 6 in the case of

The waveform I] is a similar waveform when e + < e-.

All of these are generated when the clock pulse C from the clock pulse generator 4 is applied to the up/down counter 5.

The generation and stop of the clock pulse C can be controlled by the zero adjustment finger 4>A.

Therefore, when the clock pulse C is generated by the zero adjustment finger GA (hereinafter this state is referred to as zero adjustment), the comparison input voltage e+
, i.e. the output voltage of amplifier 1.

Vout operates so as to approach e-, that is, the zero point, and zero adjustment is performed.

When the zero adjustment is completed, the zero adjustment finger /S>A is turned off and the clock pulse C is stopped (hereinafter, this state will be referred to as a steady state).

Now, the output voltage Vout, which is the target of zero adjustment, is the output type.

Pressure e.

It does not reach zero within the range (for example, Vout > e-)
Suppose that the state is .

If zero adjustment is performed at this time, the output will be e.

vibrates as shown in Figure 2a. The resulting output Vout
also vibrates in the same way, but in the opposite direction.

Also, when the steady state is established, the output e. Hato. Since it is uncertain whether it will be held at this position, Vout will not necessarily be in a steady state close to zero.

Furthermore, these devices need to output to the outside that the target has exceeded a predetermined range and zero adjustment has become impossible.

In general, it is possible to detect the analog output using a comparator or the like, but the circuit becomes complicated.

The present invention eliminates the above drawbacks, detects whether or not zero adjustment is not possible when performing zero adjustment operation using a simple circuit that does not use a comparator, and prevents vibration when zero adjustment is not possible. Another object of the present invention is to obtain a zero adjustment device that can stop the target output in a direction close to zero when the zero adjustment operation is stopped.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 3 is a diagram showing an embodiment of the present invention, in which the configuration of the servo system element 2 in FIG. 1 is used in the same manner, and the up/down counter 5
Carry up or down output (hereinafter referred to as carry output) B
is the human power of one of the conditional circuits (for example, ANT) circuit 8 for operating the clock pulse generator 4.

The zero adjustment finger /S>A is calculated as the other manual power of the AND circuit 8.

The zero adjustment finger 4>A is connected to a reset pulse generation circuit 7 using a monostable multi-bi-break or the like, and its output is applied to the load terminal of the up/down counter 5.

Explanation in FIG. 3: The top-up down count 5 is 4 bits, starting from the least bit (LSB) to the maximum bit (MSB).
B) counter output as A.

, Bo, Co, D. shall be.

The control power S of the clock pulse generator 4 generates clock pulses at F level.

Zero tone finger 4 again? It is assumed that A operates at H level.

Now, the output Vout is the output e.

It is assumed that zero adjustment becomes impossible in a state where Vout > e- regardless of the value of .

As shown in the time chart of FIG. 4, the up/down counter 5 is reset by the reset pulse R8 due to the zero adjustment finger 4>A.

Therefore, carry output B from up/down counter 5
does not occur (becomes H level), the control human power S is applied from the AND circuit 8 to the clock pulse generator 4, and the clock pulse generator 4 supplies the clock pulse C to the up/down counter 5.

Up/down counter 5 receives this clock pulse C and outputs e from A/D converter 6.

Tracking begins in the direction of increasing power, that is, in the direction of up-counting.

Then, just before the output Dout of the up/down counter 5 overflows, a carry output B is output.

In other words, the carry output B becomes L level and the AND circuit 8
The output S becomes L level and the clock pulse C stops.

Therefore, this carry output B is the clock pulse generator 4.
Acts as a stop signal.

Therefore, it is held in this state until the next zero adjustment command is issued.

Note that depending on the counter, the carry logic may change in the up/down direction, so when using it in such a state, the output of comparator 3 should be connected to the clock pulse C.
It is necessary to use a circuit, for example a data flip-flop, that latches at

As can be seen from FIG. 3, this carry output B can also be used to indicate a state in which zero adjustment is not possible.

Additionally, as shown in the figure, at the start of the zero adjustment command, if the counter is loaded to the intermediate value of the digital value, that is, only the maximum bit is 1 and the others are 0, the maximum zero adjustment time can be halved. .

FIG. 5 shows an example in which a flip-flop 10 is separately provided for indicating that zero adjustment is disabled.

That is, the carry output terminal of the up/down counter 5 is connected to the terminal S of the cell 1 of the flip-flop 10 via the NOT circuit 9, and the output terminal of the reset pulse generation circuit 7 is connected to the reset terminal H. do.

Further, the reset output terminal Q of the flip-flop 10 is connected to one input terminal of the circuit A, NI) circuit B0).

In this case, the A-N I) circuit 8 for directly stopping the carry output and the clock pulse C as shown in FIG.
Since it is not used as an input, there is no need to reset the up/down counter 5.

In other words, in general, when zero adjustment becomes impossible, amplifier 1
The input voltage Vin is changed and the zero adjustment finger 4> and A are issued again to perform the zero adjustment, but in the circuit shown in Fig. 3, the clock pulse stop signal F is canceled by the carry output B. It is necessary to reset the up/down counter 5.

However, in the circuit shown in Figure 5, the zero-tune finger 4? A reset pulse I (S) resets the flip-flop 10, and its output B' (H level) makes the A/ND circuit 8 conductive, so there is no need to reset the up/down counter 5.

Each operation is the same as described above, but at the start of the zero adjustment command, the reset pulse R8 is activated as described above.

The flip-flop 10 is reset and the clock pulse stop signal is released to enable the clock pulse generator 4 to operate.

Also, when zero adjustment is not possible, the output Do of the up/down counter 5
Since carry output B becomes L level immediately before ut overflows, this sets flip-flop 10, and output B, which becomes L level at that time, causes clock pulse C to be stopped.

That is, the output B' at L level functions as a clock pulse stop signal.

In any case, when zero adjustment is possible, the up/down counter 5 does not overflow (including when the down count exceeds), so no carry occurs.

As explained above, the present invention is capable of detecting failure of zero adjustment using an analog circuit without using a complicated circuit such as a comparator, does not cause vibration even when zero adjustment is impossible, and clamps the output toward the side closer to zero. Therefore, the possibility of adverse effects on the system using this device is reduced.

[Brief explanation of the drawing]

Fig. 1 is a basic diagram of a zero adjustment device using a conventional electronic servo system, Fig. 2 is an explanatory diagram showing the outputs of servo elements and the controlled object, and Fig. 3 is a diagram of a zero adjustment device according to the present invention. FIG. 4 is a block diagram showing one embodiment of the present invention, FIG. 4 is a quimchard for explaining the present invention, and FIG. 5 is a block diagram showing another embodiment of the present invention. 1...Amplifier, 2...Servo system element,
3... Comparator, 4... Clock generation circuit, 5... Up/down counter, 6...
...D/A converter, 7...Reset pulse generation circuit, 8...Condition circuit, 9...NOT
Circuit, 10...Flip-flop, Vout
......Amplifier output voltage, e+, e-...
Comparator input terminal, e□...J)/A converter output voltage, A...Zero adjustment command, B, B......
Carry and zero adjustment disabled output, C...clock pulse, R, S...reset pulse, DoutA
o, Bo, Co, Do... Counter output, Di
n...Counter preset manually.

Claims (1)

[Claims] 1 Signal e+ and reference signal e to be controlled by the comparator
-, determine the counting direction of the up/down counter based on the magnitude relationship, add the output of this up/down counter to a digital-to-analog converter, and add the analog output to the control target that performs zero adjustment to the electronic servo system. A zero adjustment device configured with a clock pulse generator that provides clock pulses to the up/down counter, and a condition that when a zero adjustment command is input, no carry or carry output is generated from the up/down counter. A conditional circuit that activates the clock pulse generator and stops the clock pulse generator when a carry or carry-down output occurs from an up-down counter, and a condition circuit that operates the clock pulse generator based on the carry or carry-down output upon input of a zero adjustment command. A zero adjustment device comprising: a reset pulse generation circuit for canceling a clock pulse generator stop signal to the condition circuit.