JPS58162870A - Frequency detection circuit - Google Patents

Abstract

PURPOSE:To detect wide-range frequencies successively and precisely, by detecting the number N of pulses with specific time width T in a high frequency range, and detecting the T wit specific N in a low frequency range. CONSTITUTION:An encoder signal S2, after being frequency-divided to a double period by a counter 12 triggers a monostable multivibrator 14 and when the pulse width of a signal S4 is greater than the output pulse width of the monostable multivibrator 14, the output of an FF11 is 0, indicating the low frequency range. When the pulse width of the S4 is less, the output is 1, indicating the high frequency range l. In the high frequency range, the output S3 of an FF9 synchronizing with a signal S2 is a reference signal S7 whose pulse number is N, and supplied to a programmable timer element 8. In the low frequency range, on the other hand, the signal S4 is the N reference signal S7, and while N is constant, the time width T varies. At a raise of the output S8 of a counter 13, an interruption is caused and a microcomputer device calculates N/T on the basis of the N and T latched in timers #2 and #3 of the timer element T to detect the frequency.

Description

[Detailed Description of the Invention] The present invention relates to a frequency detection circuit for square wave pulses, and includes patents, patents, etc.
The present invention relates to a frequency detection circuit that detects the rotational speed of an ear'j motor for an incremental encoder 1i.

Conventionally, as a pulse frequency detection circuit, there is a method in which a high frequency pulse is used and the number of pulses input within a certain period of time is counted using a counter circuit tube. This is because as the frequency becomes lower, the number of noises that enter within a certain period of time decreases, so the accuracy of detecting the same wave number decreases.

In the case of low-frequency pulses, there is a method of counting the input pulse width T and detecting the frequency from f-〒, but at high frequency, the input pulse width T becomes smaller and the measurement type of T This has the drawback that the accuracy of frequency detection is poor and the precision of frequency detection is poor.

There is also a method that combines both of these, counting the number of input pulses in the high frequency range and counting the pulse width in the low frequency range, but this requires two circuits: a pulse number counting circuit and a pulse width counting circuit. However, the disadvantage is that the circuit becomes multi-axis, and it is difficult to continuously switch between the high frequency region and the low frequency region.

An object of the present invention is to provide a pulse frequency detection circuit that continuously and accurately detects frequency sounds in a wide range using a simple detection circuit.

The feature of the present invention is that in the high frequency region, the time width T is measured in synchronization with the rising edge of the input pulse, and the number of pulses N? entering the time width T? In the low frequency region, the input pulse number N is always constant, and the frequency detection circuit detects the time @T of the interval of the number N of pulses synchronized with the rising edge of the pulse. In addition, the discrimination signal between the high frequency region and the low frequency region is generated by operating the one-shot multi at the rising edge of the input pulse and comparing the output signal width with the input pulse width.

FIG. 1 shows a variable speed control device for an induction motor using a microcomputer as an example to which the present invention is applied. #li specified by potentiometer 1! [1 wave number f1
The information is input to the microcomputer device 2. On the other hand, the actual rotational speed fM of the electric conductor 3 is inputted to the microcomputer device from the output signal of the incremental encoder 4 directly connected to the electric current #dJm via the frequency detection circuit 5 of the present invention. Therefore, a gate signal is created by a microcomputer device so that f and fw match. Is this signal gate drive circuit 6? The signal is amplified through the power converter 7, which includes an inverter, etc., and as a result, the speed of the induction motor is controlled.

The NCf-posi system, which is an example of such a system, has a high speed ratio of 1000:1, and has high accuracy and
It is necessary to control the speed with high response, and the encoder signal must be detected accurately at every short sampling period from the low frequency region to the high frequency region. For this purpose, it is better to use an encoder with a large number of pulses at 1fOJ transition, but this has a limit due to the length of the signal cable, etc., and is mainly used for high-frequency encoders that detect the frequency from the count value of the number of input pulses. It is necessary to separate the detection into low frequency regions based on the region and input pulse width.

Next, FIG. 2 shows a wave number detection circuit according to the present invention.

This circuit is composed of a discrete circuit on the left and a programmable timer element 8, which is commercially available as a microcomputer peripheral element, shown on the right. This timer element 8 includes, for example, three timers φl, φ2 . φ3 is built-in, and φl has the function of generating square wave pulse 81.
÷2 is used as a function to detect the number Nt of pulses of the encoder signal S2 entering the reference signal S7 having a number N of pulses, and also as a function to detect Nt pulse width 'l.

The discrete circuits are connected as shown in FIG.
One-shot multi-f-14, (amplifier 15, 16, AND element 17, 18, OR element 19, resistor 20, 21
, capacitors 22 and 23. In this circuit, the N reference signal 83, which is a +2 gate signal in the daytime frequency region, is generated by inputting the square wave pulse signal Sl of φl to the encoder signal 83.
It is latched at eh of 2. As a result, the 83 signal is S2
It becomes a synchronized signal at the rising J position.

Next, the input signal 84 /ri of the one-shot multi 14, which becomes the φ2 gate signal in the low frequency region, and the encoder signal S
The frequency is divided to twice the period of 2, and the signal is synchronized at the rising edge of the 82 signal. On the other hand, the high frequency region and low frequency region discrimination signal 86 operates as a one-shot multi at the rising edge of S4.
If the pulse width of 84 is larger than the pulse width determined by the capacitor 22 and the resistor 20, the output will be 0, and it will be in the low frequency region.

On the other hand, when the 84 pulse width is small, it becomes l, which is the − frequency region. The flip-flop circuits 10 and 11 are designed to handle high frequencies, considering the transient state when switching from low frequency to high frequency.
It is provided so that the low frequency discrimination signal S6 is switched at the rising edge of the encoder signal S2. Further, a filter consisting of a resistor 21 and a capacitor 23 is provided in a round shape to absorb minute width pulses generated when the switch 86 is switched. FIG. 3 shows a signal time chart of the above-described circuit in the high frequency region in a steady state, and FIG. 4 shows a signal time chart of the low frequency region. From FIG. 3, since the discrimination signal S6 is low in the high frequency region, the S3 signal synchronized with the rise of the encoder signal S2 becomes the reference signal S7 with the number of pulses N. In this case, the time 1[T is approximately determined by the period of the reference signal S1 of the +1 timer, and the number N of pulses of the encoder signal S2 changes.

On the other hand, in the low frequency region shown in FIG. 4, the discrimination signal S6 is 0.
Therefore, 2 synchronized with Tateoka of encoder signal S2
The double period signal S4 is Nl! becomes a single signal S7. In this case, N is always constant and the time width T changes.

Next, FIG. 5 shows a time chart of a transient state in which the high frequency region is switched to the low frequency region. In this case as well, all the signals are always synchronized with the rising edge of the encoder signal S2 and switched continuously. Time chart of transient axis switching from low frequency to high frequency? It is shown in FIG. Similarly, in this case,
All signals are continuously switched in synchronization with the rising edge of the encoder signal 82. - Next, the operation of the programmer grouper 1 will be explained with reference to FIG. The reference signal S7 with the number N of encoder pulses and the reference signal S8 with the cycle FIT of the N pulse section are always synchronized with the rising edge of the encoder signal S2,
'7.88? $2 In the case where 101 shown in the figure is input, the number of pulses N is 87. Encoder signal S2 that enters from the falling edge of the signal to the next falling edge is counted.

On the other hand, 19115 FUT is counted during the 0 interval of the 88 signal, and the time width is T. The time width is T. As a result, an interrupt is generated at the rising edge of the $8 signal, and the programmable timer is launched. Input the N and T information on the microcomputer, and then convert the N/T to the computer.
This becomes the frequency detection value f.

According to this embodiment, since the frequency detection value is obtained from the pulse dN and the N pulse time width T in synchronization with the rising edge of the encoder signal S2, highly accurate detection is possible. Furthermore, detection is performed using a method divided into a high frequency region and a low frequency region, and this switching is performed continuously, which has the effect of greatly increasing the frequency detection range.

Furthermore, by increasing the oscillation period ti of the timer l in the high frequency region, the sampling synchronization of detection can be changed.

According to the present invention, it is possible to continuously detect the number of pulses N and N/<pulse time width T1 in synchronization with the encoder signal with a simple circuit, so that the detection accuracy is high and the detection range is expanded.

[Brief explanation of drawings]

Fig. 1 is a block diagram of variable speed control of an induction motor to which the present invention is applied, Fig. 2 is a frequency detection circuit diagram showing an embodiment of the present invention, and Fig. 3 is a signal of the inventive circuit in a high frequency region. 4 is a signal time chart of the present invention in the low frequency region. FIG. 5 is a signal time chart of the present invention when switching from the high frequency region to the low frequency region. FIG. 7 is a signal time chart of the present invention when switching to a high frequency region, and is an explanatory diagram of the operation of the programmable timer element of the present invention. 8...programmable timer element, 9,10.11.
...Flip-flop, 12.13...Counter,
14... One-shot multi, 15.16... Inno(-ta, 17.18... Logical product element, 19... Brass logic and sum element ¥ 3 figure Brown 4 figure

Claims (1)

[Scope of Claims] 1. In a square wave pulse frequency detection circuit, a discrimination circuit for generating signal tubes for discriminating each of the high frequency region and low frequency region, and a reference signal tube for detecting the number N of pulses for each of the high frequency region and the low frequency region are provided. The circuit for generating the pulses and the number of pulses N
and a circuit for counting the N pulse time width Tar, and in synchronization with the edge of the input pulse, the two discrimination signals ? At the same time, in the high frequency region, the N%T? is synchronized with the edge of the input pulse. means for detecting the frequency from N/T; and means for detecting the frequency from N/T in the low frequency region in synchronization with the edge of the input pulse in the N constant state, and detecting the frequency from N/T. A frequency detection circuit characterized by: 2. In claim I41, the number of pulses N
and N The circuit that counts the Hals time width Tfr is a programmable timer element, and the two-set discrimination signal is a signal set by comparing the input pulse width with the one-shot multi output width synchronized with the edge of the input pulse. , the reference signal for detecting the Norkle number N in the high frequency region is an output signal launched at the edge of the input pulse by inputting a signal in which a detection bumping time is set, and A frequency detection circuit characterized in that a reference signal for detecting the number N of pulses in a region is a frequency-divided signal of the input pulse.