JP2856066B2 - Ultrasonic detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic detecting device for detecting an end position of a web carried between a transmitter and a receiver of an ultrasonic wave and a thickness of the web.

[0002]

2. Description of the Related Art To detect the end position of a web, light is applied to the end of the web, and the end position (edge position) is detected based on the amount of light shielding. In the case of a light-transmitting object or a light-sensitive object, air is blown onto the upper surface of the web edge, and the position of the web edge is detected from the amount of change in air pressure on the lower surface of the web edge. Also, a method of arranging an ultrasonic transmitter and a receiver facing each other, and detecting a position of a web edge from a change in a reception signal of the receiver when a web edge enters between the two. Is disclosed in Published Patent Publication No. 62-501520. According to this method, when an ultrasonic pulse train is intermittently transmitted from a transmitter, a direct wave and a reflected wave reflected by a web or a receiver are received by a receiver. Sampling is performed with the range limited, and the peak value is extracted as an electric signal. This eliminates the influence of the reflected wave from the electric signal.

[0003]

The edge position detection method using light cannot be used when the web is transparent. In addition, when air is used, the web is often contaminated by the cleanliness of the air or the entrainment of dust around it. It changes and becomes less stable. In the case of Japanese Patent Publication No. Sho 62-501520, a sampling signal synchronized with the transmission timing of the transmitter is sampled in order to sample a limited area not including the reflected wave in the electric signal converted by the receiver. After storing the sampled electric signal in the memory, the reset signal needs to be set to the 0 level to input the next sampled data. Therefore, a circuit for generating the sampling signal and the reset signal is required.

[0004] As an effect of the reflected wave, there is a case where a so-called beat phenomenon occurs due to interference with a direct wave. The standing wave is such that waves having the same amplitude and traveling in opposite directions overlap and do not travel. When the standing wave is generated, the received signal fluctuates and measurement becomes impossible. However, the duration t
Is transmitted at an interval T, t is set shorter than the reciprocating time between the ultrasonic transmitter and the receiver, and T is received after the reflected wave of the previous pulse train has almost disappeared. It has been experimentally confirmed that a standing wave is not generated if it is determined to reach the wave device. If the generation of the standing wave can be prevented in this way, even if the direct wave and the reflected wave overlap, it does not hinder detection of the overlap (change in thickness) at the edge position of the web or the seam position of the web. This is because the direct wave having a large peak value is usually received first, and the peak value of the reflected wave received thereafter is often smaller than that of the direct wave, so that the peak value of the direct wave occupies a large weight in the detection data. This is because the amplitude of the reflected wave also changes in accordance with the magnitude of the amplitude of the direct wave, so that the case where the direct wave and the reflected wave overlap has the same tendency as the case of the direct wave.

The present invention has been made on the basis of such knowledge, and in detecting the edge position and thickness of the web, the apparatus has simplified the apparatus without continuously taking in received data and sampling or resetting the sampled data. It is an object to provide an ultrasonic detection device.

[0006]

In order to achieve the above object, in an ultrasonic detecting apparatus for detecting a web carried between an ultrasonic transmitter and a receiver, an ultrasonic pulse train is intermittently transmitted. A transmitter for transmitting, and a receiver for receiving the pulse train provided to face the transmitter and converting the pulse train to an electric signal,
A peak hold circuit connected to the receiver for holding a peak value of the electric signal; discharge means connected to the peak hold circuit; and a smoothing circuit for smoothing an output of the discharge means. The wave generator sets the transmission duration of the pulse train shorter than the time that the ultrasonic wave reciprocates between the transmitter and the receiver, and sets the transmission interval of the pulse train to the next after the reflected wave of the previous pulse train has almost disappeared. To reach the receiver.

[0007]

When a pulse train is transmitted from a transmitter, an electric signal corresponding to the degree to which the web between the transmitter and the receiver interrupts the pulse train is output from the receiver. The electrical signal for one pulse train first shows a large peak value of the direct wave,
Thereafter, a reflected wave whose peak value becomes smaller continues. The peak value is held by the peak hold circuit, but the peak value is gradually reduced by the discharging means. When the peak value of the reflected wave during the decrease becomes larger than this decrease curve, the peak value is held and gradually decreases again.
By smoothing the output of the discharge means, an average value of the discharge curve is obtained. Since this average value indicates the amount of the pulse train that passes without being interrupted by the web, it indicates the edge position or thickness of the web. The transmitter sets the transmission duration of the pulse train shorter than the reciprocating time of the ultrasonic wave between the transmitter and the receiver, and sets the transmission interval of the pulse train to the next pulse train after the reflected wave by the previous pulse train has almost disappeared. Is set to reach the receiver, so that generation of a standing wave is prevented. Since the peak value of the peak hold circuit is reduced by the discharging means, the peak value generated by the next pulse train can be held. This eliminates the need for sampling and resetting of the sampled values, so that these circuits become unnecessary.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment. The oscillation circuit 1 has a cycle of a pulse train of an ultrasonic wave to be transmitted,
Oscillation is performed with an amplitude, a pulse train duration t, and a pulse train interval T determined. The power amplification circuit 2 power-amplifies the pulse train generated by the oscillation circuit 1. The ultrasonic transmitter 3 converts the power-amplified signal into an ultrasonic wave and transmits the ultrasonic wave. The ultrasonic wave receiver 4 converts a direct wave and a reflected wave transmitted from the ultrasonic wave transmitter 3 and reaching the web 10 without being interrupted, into an electric signal. The preamplifier circuit 5 amplifies this electric signal, and the peak hold circuit 6 has a discharging means, holds the peak value of the amplified electric signal and discharges this peak voltage, and the signal of the next pulse train comes. To a predetermined value by
The peak value of the signal of the next pulse train is held. The low-pass filter circuit 7 is a smoothing circuit that smoothes the output of the peak hold circuit 6 and outputs the average value.

FIG. 2 is a diagram showing a means used to reduce the influence of the reflected wave. FIG. 2A shows an ultrasonic pulse train transmitted from the ultrasonic transmitter 3 to the ultrasonic receiver 4. On the other hand, the web 10 is arranged obliquely so that the reflected wave does not enter the ultrasonic wave transmitter 3 and the ultrasonic wave receiver 4.
(B) shows a configuration in which the receiving surface of the ultrasonic receiver 4 is inclined with respect to the pulse train transmitted from the ultrasonic transmitter 3 so that the reflected wave does not enter the ultrasonic transmitter 3. By taking such measures and setting the pulse oscillation conditions in the oscillation circuit 1 so as not to generate a standing wave described later, the influence of the reflected wave can be sufficiently reduced.

FIG. 3 is a circuit diagram of the peak hold circuit 6. A rectifier 11 and a capacitor 12 constitute a peak hold circuit, and a leak resistor 13 is coupled to discharge continuously,
Decrease the charge voltage. The operational amplifier 14 is used as a voltage follower, and holds and outputs a charge voltage.
The signal is continuously discharged by the leak resistor 13 so that the signal of the next pulse train can be held.

FIG. 4 is a diagram showing output waveforms of each circuit shown in FIG. The waveforms a to d represent the waveforms at the positions a to d in FIG. a is the output waveform of the power amplifier circuit 2, t is the duration of the pulse train, and T is the pulse train interval. t and T are set to values that do not generate a standing wave due to the direct wave and the reflected wave. t is set to be shorter than the time required for the ultrasonic wave to reciprocate between the ultrasonic wave transmitter 3 and the ultrasonic wave receiver 4 and to make the pulse train several pulses or more. T is determined so that the reflected wave from the previous pulse train has almost disappeared before the next pulse train reaches the ultrasonic wave receiver 4. In this embodiment, the distance between the ultrasonic wave transmitter 3 and the ultrasonic wave receiver 4 is 35 mm.
When t = 0.15 ms, the number of pulses in the pulse train was 32, and T = 1.5 ms, no standing wave was detected.

The waveform b is the output waveform of the ultrasonic wave receiver 4, and a direct wave having a large amplitude appears first, followed by a reflected wave whose peak amplitude decreases. After the reflected wave has almost disappeared, a direct wave is generated by the next pulse train.

C is an output waveform of the peak hold circuit 6,
In the capacitor 12 shown in FIG. 3, a large peak value of the first direct wave is accumulated, discharged by the leak resistor 13, and the charge voltage of the capacitor 12 is attenuated. When the peak value of the reflected wave larger than this attenuation voltage appears, the charge voltage becomes that voltage, and attenuation from that voltage is performed. The slope of the attenuation is determined by the CR values of the capacitor 12 and the leak resistor 13.

D represents the output waveform of the low-pass filter circuit 7. d indicates a value obtained by smoothing the curve c, and this value is determined by the held peak value if the slope of the attenuation of the curve c is constant. In other words, since it is determined by the peak value of the direct wave input first, the degree of shielding of the ultrasonic wave receiver 4 by the web 10 and the degree of transmission can be determined.
Can be measured from the degree of shielding, and the thickness can be measured from the degree of transmission.

FIG. 5 shows the relationship between the degree of shielding of the ultrasonic wave receiver 4 by the web 10 and the curves c and d. Since the slope of the peak value decay due to discharge is constant,
The output signal of d is proportional to the peak value of c. Since the peak value of the direct wave is larger than the peak value of the reflected wave, the influence of the reflected wave is not shown.

[0016]

As is clear from the above description, the present invention prevents generation of a standing wave by setting the oscillation condition of the ultrasonic wave, and holds the peak value of the output of the ultrasonic wave receiver. Since the discharge is attenuated and the average value of the attenuated voltage is obtained to obtain the edge position and thickness of the web, a circuit for sampling data that is not affected by the reflected wave and a circuit for resetting the sampled data are unnecessary. The circuit configuration is simplified. Further, this can reduce the cost.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first exemplary embodiment.

FIG. 2 is a diagram illustrating a means used to reduce the influence of a reflected wave.

FIG. 3 is a circuit diagram of a peak hold circuit.

FIG. 4 is a diagram showing an output waveform of each circuit.

FIG. 5 is a diagram showing a position of a web and outputs of a peak hold circuit and a low-pass filter circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillation circuit 2 Power amplifier circuit 3 Ultrasonic wave transmitter 4 Ultrasonic wave receiver 5 Preamplifier 6 Peak hold circuit 7 Low pass filter circuit 11 Rectifier 12 Capacitor 13 Leakage resistance 14 Operational amplifier

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01V 1/00 B65H 43/00-43/06 G01B 17/00-17/06

Claims (1)

(57) [Claims] 1. An ultrasonic detector for detecting a web carried between an ultrasonic transmitter and a receiver, comprising: a transmitter for intermittently transmitting an ultrasonic pulse train; A receiver for receiving the pulse train and converting the pulse train into an electric signal, a peak hold circuit connected to the receiver for holding a peak value of the electric signal, and connected to the peak hold circuit And a smoothing circuit for smoothing the output of the discharging means, wherein the transmitter sets the transmission duration of the pulse train to the time that the ultrasonic wave reciprocates between the transmitter and the receiver. An ultrasonic detection apparatus, wherein the transmission interval of the pulse train is shorter, and the next pulse train reaches the receiver after the reflected wave of the previous pulse train has almost disappeared.