JPS6225397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal circuit that can prevent modulation of an output signal due to noise.

Conventionally, sewing machines used for sewing pockets, for example, have been known. This sewing machine uses a cloth feeding mechanism provided with a light reflecting section to transport a piece of pocket cloth held on the reflecting section from a first position to a second position sandwiching a sewing point of the sewing machine.

During this time, when the light emitted from the light detection device consisting of a light emitter and a light receiver arranged above the pocket cloth piece is no longer reflected from the reflecting part and the light receiver enters a light-blocking state. Detection related to.

In relation to this light shielding, the device determines when the front end of the pocket cloth matches the sewing point of the sewing machine, starts the sewing machine, and stops the sewing machine when the rear end matches the sewing point of the sewing machine. It is.

However, in such a light detection device, the light receiver generates a light reception signal in proportion to the intensity of light, and compares the level of this light reception signal with a constant comparison level voltage to determine whether the light reception is blocked or not. I am making this judgment.

Therefore, when there is no external noise, that is, when there is no light such as illumination, the light reception signal is always output as a constant pulse signal as shown in Figure 1A, but under normal usage conditions, external illumination, etc. is always required. Moreover, since the intensity of the light is not always constant, the received light signal is inevitably influenced by external lighting and the like and is modulated as shown in FIG. 1B.

Therefore, in the state shown in FIG. 1B, even though the light reception pulse signal is generated, the comparison level voltage L
If the sewing machine does not reach this point, there is a risk that the received light will be determined to be blocked, and the sewing machine will not be able to start or stop at the same timing as the front or rear edge of the pocket cloth, making it impossible to sew accurately. There was a drawback.

The present invention was made in view of these conventional drawbacks, and its purpose is to eliminate the possibility that the pulse input signal is affected by noise such as external lighting, which modulates the output signal. An object of the present invention is to provide a noise removal circuit that can remove noise without causing problems.

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

FIG. 2 shows an embodiment of the circuit according to the present invention.

In the figure, 1 is a peak hold circuit connected to the output terminal of a light receiver (signal generator) 2 that receives light from a light emitter and generates _a pulse at a level corresponding to the intensity of the received light.
It is composed of a transistor Tr, a resistor R ₁ , a capacitor C ₁ and an operational amplifier A ₂ for increasing the response speed of the output current amplifying circuit A ₁ .

3 is a high pass filter connected to the output terminal of the peak hold circuit 1, which is composed of a capacitor C ₂ and a resistor R ₂ .

4 is a subtraction circuit composed of operational amplifiers A ₃ , A ₄ , and A ₅ , and 4 of its two input terminals 4A and 4B
The A side is connected to the output terminal of the high-pass filter 3, and the 4B side is connected to the output terminal of the light receiver 2, and the difference between these two outputs is calculated so as to be generated as the output signal 5.

ASW is an analog switch interposed between the high-pass filter 3 and the subtraction circuit 4, and is provided to prevent malfunctions caused by noise such as external light.Although it is conductive only when light is received, it is not necessary. It's not a thing.

Furthermore, the peak hold circuit 1, high pass filter 3, and subtraction circuit 4 are not limited to the configurations shown in the drawings.

Next, the operation of one embodiment of the present invention will be explained.

Now, assume that a pulsed light is generated from a light emitter, and this light is received by a light receiver to generate a pulsed light reception signal (input signal) as shown in FIG. 1A.

At this time, if there is external light (noise) such as illumination, the received light signal will be modulated and become a modulated signal as shown in FIG. 1B.

When this modulated signal MW is input to the peak hold circuit 1, the AC of the modulated signal MW is
The output waveform EW is obtained by extracting only the components, that is, only the envelope is extracted.Moreover, since this output waveform EW passes through the peak hold circuit 1, there is no phase shift at all between it and the received light signal.

At this time, the slope of the discharge curve D between each pulse is the resistance
It is determined by the time constant of R ₁ and capacitor C ₁ , and this slope needs to be larger than the maximum rate of change of the envelope.

Then, when this output waveform EW is further passed through a high-pass filter 3, only the alternating current component of the output waveform modulated by the capacitor C ₂ and the resistor R ₂ is output, and the output waveform HW shown in FIG. 4 is obtained.

Then, by inputting this output waveform HW and the modulation signal MW to the subtraction circuit 4 and outputting the difference, a non-modulated output signal from which noise due to external light has been removed as shown in Figure 1A can be obtained as an output signal. .

As described above, according to the present invention, the difference signal between the signal obtained through the peak hold circuit and the high-pass filter and the pulse input signal that does not pass through these circuits is used as the output signal, so an output signal that is completely unaffected by noise can be extracted. This eliminates any risk of malfunctioning of the detection equipment or other machinery.

Further, according to the present invention, there is no phase shift between the input signal and the output signal due to the peak hold circuit, and in addition to the above-mentioned effects, malfunction of the equipment can be further prevented.

The present invention can be used not only for optical detection devices but also for noise removal in sound detection devices.

[Brief explanation of the drawing]

Figure 1A is a waveform diagram of a light reception signal in an unmodulated state, Figure 1B is a waveform diagram of a light reception signal in a modulated state, Figure 2 is a circuit diagram of an embodiment of the present invention, and Figure 3
The figure is a waveform diagram that extracts only the envelope of Figure 1 (b).
FIG. 4 is an output waveform diagram of the high-pass filter. 1...Peak hold circuit, 3...High pass filter, 4...Subtraction circuit.

Claims (1)

[Claims] 1. A peak hold circuit that holds the peak voltage of a pulse input signal from a signal generator until the next pulse input signal is generated and generates a signal that forms an envelope of the peak voltage; A high-pass filter that extracts only the modulated alternating current component of the generated signal and generates that signal, and a subtraction circuit that compares and calculates the pulse input signal and the generated signal from the high-pass filter and generates an output signal of the difference. noise removal circuit.