JPH0411831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a paper detection device suitable for detecting passage of paper in a copying machine or the like.

Conventionally, in copying machines, etc., the entry of copy paper,
There are optical and mechanical limit switch types for detecting passage, but it is not necessarily preferable to use light inside a copying machine, and limit switches have drawbacks such as a lack of high-speed response. For this reason, the present applicant has recently begun to consider the practical use of ultrasonic waves for detecting copy paper.

The present invention provides a paper detection device with a relatively simple configuration and excellent high-speed response and reliability by utilizing the ultrasonic blocking effect caused by the presence of paper in the space of an ultrasonic transducer. That is.

Embodiments of the paper detection device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. In this figure, a wave transmission system is composed of an oscillation circuit 1 and an ultrasonic transmitter 2, an ultrasonic receiver 3, a preamplifier circuit 4, a negative feedback amplifier circuit 5, an amplitude detection circuit 6, and a DC amplifier circuit. 7 and the output circuit 8 constitute a wave receiving system. The ultrasonic transmitter 2 and the ultrasonic receiver 3 face each other across the passage 11 of the paper 10.

The ultrasonic transmitter 2 and the ultrasonic receiver 3 are constructed by installing a surface sensing plate 21 such as an aluminum disk and an elastic layer 22 such as silicone rubber in the front opening of a resin case 20 having an opening at the front as shown in FIG. A piezoelectric element 23 is attached to the back surface of the front sensing plate 21, and each electrode of the piezoelectric element 23 is connected to pin electrodes 24A and 24B penetrating the bottom of the case 20. In this case, transmitter 2 and receiver 3
The front opening of the case 20 is sealed with a surface sensing plate 21 to prevent toner and paper dust from entering and adhering to the inside of the copying apparatus when the copying apparatus is installed. Furthermore, the resonant frequency of such a transmitter 2 and receiver 3 is determined by the piezoelectric element 2.
3 is 9.2 mm in diameter, 0.61 mm thick, with a radial vibration frequency of 300 kHz and a thickness direction vibration frequency of 2 kHz, and when it is attached to the surface sensing plate 21 of an aluminum disc with a diameter of 11 mm and a thickness of 1 mm, it will be around 100 kHz. Become.

Normally, the transmitter 2 and the receiver 3 are of the same structure, but the relationship between their resonant frequencies is as follows.
It looks like the picture. FIG. 3A shows the frequency characteristics of the impedance of the transmitter 2, and FIG. 3B shows the frequency characteristics of the impedance of the receiver 3.
Tr and Tar indicate the resonant frequency and anti-resonant frequency of the transmitter 2, respectively, and Rr and Rar indicate the resonant frequency and anti-resonant frequency of the receiver 3, respectively. And Tr is
It is set to be approximately midway between Rr and Rar. This uses the fact that transmitter 2 transmits maximum ultrasonic waves at point Tr, and receiver 3's maximum sensitivity is at a higher frequency than that, that is, above Rr + Rar - Rr / 2. This is to do so. If the resonant frequencies of the transmitter 2 and receiver 3 are set as shown in Fig. 3, the resonance characteristics of both will produce approximately
By being configured in a tuned manner with 20 dB selectivity, it is not only advantageous against jamming and interference, but also allows the output of the transmitting system to be lowered and the sensitivity of the receiving system to be lowered, making it possible to improve circuit design. It is advantageous. moreover,
Since the temperature characteristics are determined by the material of the piezoelectric element 23 and the like, it is characterized by high reliability.

Now, when used in a copying machine, it is necessary to take into account the intrusion and adhesion of toner and paper dust, and for this reason, as mentioned above, the transmitter 2 and the receiver 3 should be of a sealed structure. Although the sealing surface itself serves as an ultrasonic sensing surface, consideration must also be given to the ultrasonic frequency used. Curve A in FIG. 4 shows the paper cutoff attenuation frequency characteristic, and curve B in FIG. 4 shows the toner dust accumulation attenuation frequency characteristic. As can be seen from these curves A and B, at ultrasonic frequencies of 40kHz or less, which are conventionally used as ultrasonic propagation carriers for remote control, the amount of attenuation due to toner dust accumulation is greater than the amount of attenuation due to paper blocking. It can be seen that it is not suitable for the purpose of paper detection as it becomes large. On the other hand, ultrasonic frequencies in the range of about 60 kHz to 175 kHz, as shown by the arrow (c) further above this, are considered to meet the intended use because the paper cut-off attenuation is large and the toner dust accumulation attenuation is small.

Further, the material and thickness of the surface sensing plate 21, which serves as a wave transmitting surface or a wave receiving surface, also poses a problem. FIG. 5 shows the relationship between the plate thickness and the amount of attenuation when the surface sensing plate 21 is constructed of an aluminum disk. As can be seen from this figure, the amount of attenuation due to the use of the surface sensing plate 21 is extremely small within the range of plate thickness from 0.75 mm to 1.25 mm, and the amount of attenuation is quite large in other ranges. It can be seen that the efficiency decreases. Considering this point, in this embodiment, the surface sensing plate 2
1 is set to 1 mm, and the resonant frequency of the transmitter and receiver is set to approximately 100kHz.

FIG. 6 shows a specific circuit configuration of the oscillation circuit 1. In this figure, the collector of the switching transistor Q ₁ is connected to the tap of the pulse drive choke coil (transformer) CH ₁ , and the power supply voltage is applied to the collector via this choke coil CH ₁ .
VDD is applied. Also, transistor Q ₁
A bias current is passed through the base of the self-base bias resistor _R1 as a starter,
An input control diode _D1 is connected between the grounded emitter and the base. A series circuit of the piezoelectric element 23 of the wave transmitter ₂ and the feedback oscillation pickup coil L ₂ of the feedback tuning transformer IF is connected between the cheese yoke coil CH 1 and the ground.
The resonance point variable setting coil _L1 of the transformer IF constitutes a co-procuring circuit in series with the tuning capacitor _C1 , and is connected between the base of the transistor _Q1 and the ground. In this case, the resonant frequency of the series resonant circuit consisting of the variable resonance point setting coil L ₁ of the transformer IF and the tuning capacitor C ₁ is set to be approximately equal to the resonant frequency of the transmitter 2 in which the piezoelectric element 23 is provided. As a result, the transmitting circuit oscillates near the resonant frequency of the transmitter 2, and ultrasonic waves are emitted from the transmitter 2 toward the receiver 3 via the paper path 11.

Figure 7 shows the circuit configuration of the wave receiving system.
A preamplifier circuit 4 using a transistor Q ₂ , a two-stage directly connected negative feedback amplifier circuit 5 including transistors Q ₃ and Q ₄ , an amplitude detection circuit 6 using a diode D ₂ , and a DC amplifier including a transistor Q ₅ circuit 7
and an open collector output circuit 8 using a transistor _Q6 . where the power supply voltage
VDD is supplied to the collectors of each transistor via resistors _R2 to _R5 , and is connected between the output terminal 30 and the GND terminal 31, which are directly connected to the collector of the transistor _Q6 that constitutes the output circuit. Detection output is now output.

In the above configuration, when the paper 10 is not present in the paper path 11 or the wave transmitter 2 and the wave receiver 3 are not cut off, the wave transmitter 2 is driven by the oscillation circuit 1. As a result, 200mW at approximately 100kHz
An ultrasonic wave of about 1000 m is emitted toward the receiver 3, which receives it, and further amplifies and detects it in the amplifier circuits 4 and 5 and the amplitude detection circuit 6. As a result, the transistor Q ₅ of the DC amplifier circuit 7 A detection output corresponding to the received ultrasonic wave appears at the base of , which turns on transistor _Q5 and outputs output circuit 8.
Transistor _Q6 is turned off. As a result, the connection between the output terminal 30 and the GND terminal 31 is off,
This allows it to be known that the paper 10 does not exist or has not passed. On the other hand, paper aisle 1
When the paper 10 passes through the transistor Q ₅ and blocks the space between the transmitter 2 and the receiver 3, the ultrasonic wave reaching the receiver 3 becomes extremely weak.
Since the detection output applied to the base of is substantially zero, the transistor _Q6 of the output circuit 8 is turned on. That is, the connection between the output terminal 30 and the GND terminal 31 is turned on, which causes the transmitter 2 and the receiver 3 to
It is possible to detect that the paper 10 is present between the two. In this case, the following should be noted:
Even when the paper 10 is close to the space between the transmitter 2 and the receiver 3, the ultrasonic waves reaching the receiver 3 are attenuated, so the receiver is It is necessary to set the amplification degree of the system amplifier circuit. According to the first embodiment, the following effects can be achieved.

(1) The circuit configuration of the transmitting system and receiving system is relatively simple, and by appropriately setting the amplification degree of the receiving system, the space between the transmitter 2 and the receiver 3 can be reduced to a paper size. 10, it is possible to reliably detect complete interruption.

(2) The transmitter 2 and receiver 3 have a completely sealed structure, and the sealed surface serves as the surface sensing surface, which prevents toner and paper dust from entering the interior, making maintenance unnecessary and highly reliable. is high.

(3) Since the resonant frequencies of the transmitter 2 and receiver are set within the frequency range of 60kHz to 175kHz, which is suitable for paper detection, detection performance can be improved without being affected by adverse effects from toner and paper dust. can.

FIG. 8 shows a second embodiment of the invention. This second
In the embodiment, a logic circuit system is used in which the ultrasonic oscillation drive is intermittently driven by trigger oscillation drive, and the output of pulse synchronous detection is temporarily stored on the receiving side. In this figure, the wave transmission system is composed of a trigger generation circuit 40, an intermittent pulse drive circuit 41, and a wave transmitter 2.
The receiving side circuit includes a receiver 3, a selective tuning circuit 42, a logarithmic amplifier circuit 43, a synchronous detection differential shaping circuit 44, a waveform shaping delay circuit 45, and a flip-flop 46 as an output circuit. Here, it is used as a flip-flop 46 for temporarily storing information.
This shows the case when JK flip-flop is used.

In the configuration of the second embodiment described above, the trigger generation circuit 40 generates a trigger pulse as shown in FIG. The intermittent pulse drive circuit 41 drives the transmitter 2 only when a trigger pulse arrives, and the transmitter 2 emits ultrasonic waves in a pulsed manner as shown in FIG. 9B. The receiver 3 receives the incoming ultrasonic waves as shown in FIG. 9C. The received signal is amplified by a selective tuning circuit 42 and a logarithmic amplifier circuit 43, and further converted into a pulse waveform by a synchronous detection differential shaping circuit 44 as shown in FIG. 9D. This synchronous detection differential shaping circuit 4
The output of 4 is further shaped by a waveform shaping delay circuit 45 into a waveform as shown in FIG. added to. Here, when there is no paper, the trigger pulse is applied to the flip-flop 46.
Since the states of the J and K inputs do not change when they are applied to the CK input, flip-flop 4
The θ output of No. 6 does not change and remains at a low level as shown in FIG. 9F. Now, when a piece of paper passes through the space between the transmitter 2 and the receiver 3 and blocks it, the received signal of the receiver 3 becomes substantially zero, and the J input and K input of the flip-flop 46 are also inverted. do. As a result,
During the period when the paper is blocked, the θ output of the flip-flop 46 is at a high level as in the period W in FIG. 9F, so that the passage of the paper can be detected.

According to the configuration of the second embodiment, there is a large degree of freedom such as the spacing between the transmitter 2 and the receiver 3, and it is insensitive to the close structure and close movement of the space between them, so that it can be used as needed. This feature allows it to be used for multiple purposes other than paper detection.

As explained above, according to the present invention, by utilizing the ultrasonic blocking effect caused by the presence of paper in the space between transmitting and receiving ultrasonic waves, it is possible to achieve high-speed response and reliability with a relatively simple configuration. A paper detection device can be obtained, which is particularly effective when used for detecting passage of copy paper or paper jam in a copying device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of a paper detection device according to the present invention, FIG. 2 is a sectional view showing the structure of a transmitter and a receiver used in the first embodiment, and FIG. An explanatory diagram showing the mutual relationship between the resonant frequencies of the transmitter and the receiver. Figure 4 is a graph showing the frequency characteristics of the paper cut-off attenuation and the frequency characteristics of the toner dust accumulation attenuation. Figure 5 is the surface sensing plate. 6 is a circuit diagram showing a specific circuit example of the oscillation circuit in the first embodiment, and FIG. 7 is a graph showing the relationship between the plate thickness and the attenuation amount.
FIG. 8 is a block diagram showing a second embodiment of the present invention, and FIG. 9 is a waveform diagram for explaining the operation of the second embodiment. be. 1...Oscillation circuit, 2...Ultrasonic transmitter, 3...
Ultrasonic receiver, 4... Preamplifier circuit, 5... Negative feedback amplifier circuit, 6... Amplitude detection circuit, 7... DC amplifier circuit, 8... Output circuit, 10... Paper, 11...
Passageway, 20...Case, 21...Surface sensing plate, 2
2... Elastic layer, 23... Piezoelectric element, 30... Output terminal, 40... Trigger generation circuit, 41... Intermittent pulse drive circuit, 42... Selective tuning circuit, 43...
... Logarithmic amplifier circuit, 44 ... Synchronous detection differential shaping circuit, 45 ... Waveform shaping delay circuit, 46 ... Flip-flop, Q ₁ to Q ₆ ... Transistor.

Claims (1)

[Scope of Claims] 1. An ultrasonic transmitter and a receiver that face each other across a paper path, a drive circuit that drives the transmitter, and an amplifier that amplifies and detects the received wave output of the receiver. A paper detection device comprising a detection circuit and an output circuit that determines the presence or absence of paper in the paper path based on the output of the amplified detection circuit, wherein the transmitter and receiver include a surface sensing plate in a front opening of the case. and has a sealed structure in which a piezoelectric element is attached to the back surface of the front sensing plate, and the resonant frequency of the transmitter is set between the resonant frequency and the anti-resonant frequency of the receiver, and the transmitter A paper detection device characterized in that the device emits ultrasonic waves having a frequency within a range of 60kHz to 175kHz toward the receiver.