CA1155538A - Device for the detection of sheet-like objects - Google Patents
Device for the detection of sheet-like objectsInfo
- Publication number
- CA1155538A CA1155538A CA000369134A CA369134A CA1155538A CA 1155538 A CA1155538 A CA 1155538A CA 000369134 A CA000369134 A CA 000369134A CA 369134 A CA369134 A CA 369134A CA 1155538 A CA1155538 A CA 1155538A
- Authority
- CA
- Canada
- Prior art keywords
- receiver
- oscillator
- source
- output
- sheet
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Controlling Sheets Or Webs (AREA)
- Length Measuring Devices Characterised By Use Of Acoustic Means (AREA)
Abstract
A B S T R A C T
Ultrasonic double-sheet detecting system in which the frequency of the ultrasonic source is tuned to the natural frequency of the total system in the circumstances as things are. When no sheet-like object is present in the detecting system this system is in a situation compar-able with proximities between microphone and loud speaker, and the frequency of the oscillator is tuned thereto. When a sheet-like object is present that situation is replaced by a comparator situation between the phases of the oscillator and of the ultrasonic signal receiver.
Ultrasonic double-sheet detecting system in which the frequency of the ultrasonic source is tuned to the natural frequency of the total system in the circumstances as things are. When no sheet-like object is present in the detecting system this system is in a situation compar-able with proximities between microphone and loud speaker, and the frequency of the oscillator is tuned thereto. When a sheet-like object is present that situation is replaced by a comparator situation between the phases of the oscillator and of the ultrasonic signal receiver.
Description
~ ~ 5553~
DEVICE FOR T~IE DETECTION OF S~IEET-LIKE OBJECTS
_ .. .. .... _ _ _ This invention rela-tes to a system for detecting -the presence of and dis-tinguishing be-tween superimposed and single sheet-like objec-ts moving along a transport path.
A sritish Patent No. 1,533,630 discloses a device for this purpose which comprises an ul-trasonic signal source and an ultrasonic signal receiver arrangecl on opposite sides of a transpor-t path so tha-t a signal from the source passes through the transport path to the receiver, with an oscillator and a phase comparator connected in the system so that the outputs of -the oscillator and the receiver form the inputs of the phase comparator. For -the operation of this known device the oscillator is set to a cer-tain frequency which is applied to the ultrasonic source. When superimposed sheets instead of a single sheet appear in the gap between the source and the receiver, an increased phase displacement is -to be detected between the respective sig-nals of the oscillator and the receiver. This phase shift is related to an initial phase displacement to be detected when no sheet is present in the gap. The initial phase displacement, however, varies in magnitude with variations in the characteristics of the source and the receiver and with variations in temperature and/or humidity, which alter the properties of the air in the gap between the source and receiver. Furthermore, any change in the distance between the source and the receiver will bring about a different phase displacement.
The result of all this is that the known device does not serve its purpose reliably under all circumstances.
.~ ~
1 ~5553~
The object oE the present invention is to provide a system for the stated purpose which avoids the disadvantages of the known device mentioned above.
It has been found that -this object can be achieved by a method which comprises passing ultrasonic vlbrations through a gap across the transpo.rt path from an ultrasonic source to an ultrasonic receiver that produces a signal out-put representing characteristics of the vibrations received;
when no sheet-like object is present in the gap connecting the source with the receiver in a feedback circuit whereby the vibrations in the gap acquire a certain natural frequency determined by then existing characteristics of the elements of the circuit and tuning an oscillator to a frequency corresponding to that natural frequency; and when a sheet-like object is present in the gap applying to the source the tuned frequency of the oscillator and comparing the phase of the vibrations resulting at the receiver with the phase of the oscillator vibrations, thereby producing a signal representing the phase displacement effected by the object.
Accordiny to a further feature of the invention, when a sheet-like object ceases to be present in the gap between the source and the receiver a resultant sudden increase in the amplitude of the vibrations at the receiver is detected, and in response to -this change of amplitude the ultrasonic source is switched from connection with the oscillator to connection with the receiver in the feedback circuit and the oscillator is tuned to the resultant natural frequency of the vibrations in the gap.
i "
1 .11 ~55~8 - 2a -For carrying out the invention, a detecting device or system is provided which comprises an ultrasonic signal source and an ultrasonic signal receiver arranged at opposite sides of the transport path so that the source will transmit ultrasonic signals through the transport path to the receiver, which then forms an output representing characteristics of the signals received, an oscillator having an input to control the frequency of i-ts oscillations, and a phase comparator having inputs connected respectively with the output of the oscillator and the receiver output, together with a first switching means for connecting the output of the phase comparator with the control input of the oscillator, a changeover switching means which in a first position thereof connects the source with the output of the oscillator and in a second position thereof connects the source with the receiver output, and a control circuit including means rendered operative in a period when no sheet-like object is present between the source and the receiver to actuate the first switching means and to dispose the changeover switching means in its second position.
By means of this combination, when no sheet-like obiect is present in the ultrasonic signal gap the source and the receiver are contained in a "free oscillator" feedback circu.it comparable to that occurring with proximities between a microphone and a loud speaker. As a result, a certain natural frequency is set up at a value dependent solely on the elements in the feedback chain, and at the same time the oscillator is tuned to this natural frequency so that ,,1~, ...
~ 155538 - ~b -when the oscillator ls switched over to connection with -the source and a sheet-like object is present the phase displace-ment between the respective vibrations at the source and the receiver is only that which the object itself produces.
Furthermore, with this combination the distance between the source and the receiver is no longer critical; so consider-able variation of that distance can be tolerated without rendering the detecting system unreliable.
The control circuit of a device according to the inven-tion comprises an amplitude detector connected with the receiver, which detector by reacting to changes in the amplitude of the vibrations at the receiver ensures that the changeover switch will be in its second position only when no sheet-like object is present in the ultrasonic signal gap.
The above-mentioned and other characteristics and advantages of the invention will be apparent from the following description and the accompanying drawing of a preferred embodiment of the invention.
The drawing is a schematic diagram of an electrical circuit for carrying out the invention.
The diagram illustates a device, or system, according to the invention for de-tecting doubled or otherwise super-imposed sheets and distinguishing them from single sheets moving along a transport path. Such a device can be employed to advantage, for example, in a copying machine.
Here the sheets mo~e along a transport path, schematically t ` ., ",r 5 ~ 8 - 2c -5 indicatecl by the arrows A. A sheet detector 1 is located by this transport path and cornprises a signal source 2 for the generation of ultrasonic vibrations and a receiver 3 for these vibrations, the source 2 and the receiver 3 being arran~ed opposite each other on either side of the transport path. The input of the source 2 is connected 10 via a changeover s~itch ~ with the output of an oscillator 5, in the embodiment shown this being a voltage-controlled oscillator ~V.CØ).
The control input for the oscillator 5 is connected via a switching element 6 with the output of a phase comparator 7. The control input of the oscillator 5 is at the same time connec-ted via a capacitor 9 15 to earth. In the embodiment illustrated the integrated circuit type 9046 has been employed for the oscillator 5 and the phase comparator 7.
~ ;~ 55538 The first input of the phase comparator 7 -is connected with the output of oscillator 5. Via an amplifier 8 the second inpu-t of the phase comparator 7 is connected with the receiver output. By means of changeover element 4 it is possible, as required, for source 2 to be 5 connected with the oscillator 5 or with receiver 3. In the first case the source then transmits signals at the frequency of oscillator 5.
In the output of phase comparator 7 a direct voltage signal is now generated which is proportional to the phase displacement between the input signals. The direct voltage signal can furthermore be compared 10 with a reference voltage from which it is possible to then derive the presence of a single sheet or a double sheet between the source and the receiver. In the second case a feed back circuit Forms which starts to oscillate at a preferred frequency. This frequency depends on a number of factors such as the temperature of the air, characteristics 15 of the electrical components in the chain, the distance between source and receiver, etc. The oscillator is now regulated to exactly the same frequency via switch 6 and phase comparator 7.
When changeover switching takes place frorn the second to the first position, there is always a defined phase difference of 0 between the 20 s;gnal offered to the source and the signal from the receiver, regardless of the tolerances in components and the distance between source and receiver. As a result the device can operate re~iably under all circumstances and adjustments are superfluous.
The receiver 3 is also connected with an amplitude detection circuit 2510 which reacts to a sudden increase in the amplitude of the signal received by the receiver 3. The amplitude detection circuit 10 contains an oPerational amplifier~the output of which is connected with the base of a transistor 16 via a rectifier circuit consisting of a diode 13 and a capacitor 14 and a resistor15.The emitter of transistor 16 is connected ~o 30~arth and the collector is connected with a positive terminal of a voltage supply source.As soon as the amplitude of the receiver 3 signal exceeds a certain value the transistor 16 will conduct,so that the potentia1 in the collector will reduce.On each occasion when a change occurs in the detector from a condition in which a sheet-like ob~ject is present to a condition in 35which no sheet-1ike object is present a potential drop occurs in the collector.The collector of transistor 16 forms the output of circuit 10.
This outout is connected with the input of a monostable multivibrator11,the 5 ~ 8 output of which is connected with the changeover swi-tching element 4 and switching elernent 6. By this means it is ensured that when, via circuit 10, no sheet~like object is detected between source 2 and receiver 3, a signal is generated by the mono-s-table multivibrator 11 by means of which changeover switching element 4 connects the source 2 with receiver 3 and the switching element 6 is closed. This signal from the multivibrator 11 is generated for only a short period, after which the adjustment of oscillator 5 is performed by the capacitor 9 and the switch 6.
It is obvious that the invention is not restricted to the embodiment described and illustrated here, but that numerous modifications can be incorporated within the framewor~ of the following claims, particularly as regards the electrical components employed.
DEVICE FOR T~IE DETECTION OF S~IEET-LIKE OBJECTS
_ .. .. .... _ _ _ This invention rela-tes to a system for detecting -the presence of and dis-tinguishing be-tween superimposed and single sheet-like objec-ts moving along a transport path.
A sritish Patent No. 1,533,630 discloses a device for this purpose which comprises an ul-trasonic signal source and an ultrasonic signal receiver arrangecl on opposite sides of a transpor-t path so tha-t a signal from the source passes through the transport path to the receiver, with an oscillator and a phase comparator connected in the system so that the outputs of -the oscillator and the receiver form the inputs of the phase comparator. For -the operation of this known device the oscillator is set to a cer-tain frequency which is applied to the ultrasonic source. When superimposed sheets instead of a single sheet appear in the gap between the source and the receiver, an increased phase displacement is -to be detected between the respective sig-nals of the oscillator and the receiver. This phase shift is related to an initial phase displacement to be detected when no sheet is present in the gap. The initial phase displacement, however, varies in magnitude with variations in the characteristics of the source and the receiver and with variations in temperature and/or humidity, which alter the properties of the air in the gap between the source and receiver. Furthermore, any change in the distance between the source and the receiver will bring about a different phase displacement.
The result of all this is that the known device does not serve its purpose reliably under all circumstances.
.~ ~
1 ~5553~
The object oE the present invention is to provide a system for the stated purpose which avoids the disadvantages of the known device mentioned above.
It has been found that -this object can be achieved by a method which comprises passing ultrasonic vlbrations through a gap across the transpo.rt path from an ultrasonic source to an ultrasonic receiver that produces a signal out-put representing characteristics of the vibrations received;
when no sheet-like object is present in the gap connecting the source with the receiver in a feedback circuit whereby the vibrations in the gap acquire a certain natural frequency determined by then existing characteristics of the elements of the circuit and tuning an oscillator to a frequency corresponding to that natural frequency; and when a sheet-like object is present in the gap applying to the source the tuned frequency of the oscillator and comparing the phase of the vibrations resulting at the receiver with the phase of the oscillator vibrations, thereby producing a signal representing the phase displacement effected by the object.
Accordiny to a further feature of the invention, when a sheet-like object ceases to be present in the gap between the source and the receiver a resultant sudden increase in the amplitude of the vibrations at the receiver is detected, and in response to -this change of amplitude the ultrasonic source is switched from connection with the oscillator to connection with the receiver in the feedback circuit and the oscillator is tuned to the resultant natural frequency of the vibrations in the gap.
i "
1 .11 ~55~8 - 2a -For carrying out the invention, a detecting device or system is provided which comprises an ultrasonic signal source and an ultrasonic signal receiver arranged at opposite sides of the transport path so that the source will transmit ultrasonic signals through the transport path to the receiver, which then forms an output representing characteristics of the signals received, an oscillator having an input to control the frequency of i-ts oscillations, and a phase comparator having inputs connected respectively with the output of the oscillator and the receiver output, together with a first switching means for connecting the output of the phase comparator with the control input of the oscillator, a changeover switching means which in a first position thereof connects the source with the output of the oscillator and in a second position thereof connects the source with the receiver output, and a control circuit including means rendered operative in a period when no sheet-like object is present between the source and the receiver to actuate the first switching means and to dispose the changeover switching means in its second position.
By means of this combination, when no sheet-like obiect is present in the ultrasonic signal gap the source and the receiver are contained in a "free oscillator" feedback circu.it comparable to that occurring with proximities between a microphone and a loud speaker. As a result, a certain natural frequency is set up at a value dependent solely on the elements in the feedback chain, and at the same time the oscillator is tuned to this natural frequency so that ,,1~, ...
~ 155538 - ~b -when the oscillator ls switched over to connection with -the source and a sheet-like object is present the phase displace-ment between the respective vibrations at the source and the receiver is only that which the object itself produces.
Furthermore, with this combination the distance between the source and the receiver is no longer critical; so consider-able variation of that distance can be tolerated without rendering the detecting system unreliable.
The control circuit of a device according to the inven-tion comprises an amplitude detector connected with the receiver, which detector by reacting to changes in the amplitude of the vibrations at the receiver ensures that the changeover switch will be in its second position only when no sheet-like object is present in the ultrasonic signal gap.
The above-mentioned and other characteristics and advantages of the invention will be apparent from the following description and the accompanying drawing of a preferred embodiment of the invention.
The drawing is a schematic diagram of an electrical circuit for carrying out the invention.
The diagram illustates a device, or system, according to the invention for de-tecting doubled or otherwise super-imposed sheets and distinguishing them from single sheets moving along a transport path. Such a device can be employed to advantage, for example, in a copying machine.
Here the sheets mo~e along a transport path, schematically t ` ., ",r 5 ~ 8 - 2c -5 indicatecl by the arrows A. A sheet detector 1 is located by this transport path and cornprises a signal source 2 for the generation of ultrasonic vibrations and a receiver 3 for these vibrations, the source 2 and the receiver 3 being arran~ed opposite each other on either side of the transport path. The input of the source 2 is connected 10 via a changeover s~itch ~ with the output of an oscillator 5, in the embodiment shown this being a voltage-controlled oscillator ~V.CØ).
The control input for the oscillator 5 is connected via a switching element 6 with the output of a phase comparator 7. The control input of the oscillator 5 is at the same time connec-ted via a capacitor 9 15 to earth. In the embodiment illustrated the integrated circuit type 9046 has been employed for the oscillator 5 and the phase comparator 7.
~ ;~ 55538 The first input of the phase comparator 7 -is connected with the output of oscillator 5. Via an amplifier 8 the second inpu-t of the phase comparator 7 is connected with the receiver output. By means of changeover element 4 it is possible, as required, for source 2 to be 5 connected with the oscillator 5 or with receiver 3. In the first case the source then transmits signals at the frequency of oscillator 5.
In the output of phase comparator 7 a direct voltage signal is now generated which is proportional to the phase displacement between the input signals. The direct voltage signal can furthermore be compared 10 with a reference voltage from which it is possible to then derive the presence of a single sheet or a double sheet between the source and the receiver. In the second case a feed back circuit Forms which starts to oscillate at a preferred frequency. This frequency depends on a number of factors such as the temperature of the air, characteristics 15 of the electrical components in the chain, the distance between source and receiver, etc. The oscillator is now regulated to exactly the same frequency via switch 6 and phase comparator 7.
When changeover switching takes place frorn the second to the first position, there is always a defined phase difference of 0 between the 20 s;gnal offered to the source and the signal from the receiver, regardless of the tolerances in components and the distance between source and receiver. As a result the device can operate re~iably under all circumstances and adjustments are superfluous.
The receiver 3 is also connected with an amplitude detection circuit 2510 which reacts to a sudden increase in the amplitude of the signal received by the receiver 3. The amplitude detection circuit 10 contains an oPerational amplifier~the output of which is connected with the base of a transistor 16 via a rectifier circuit consisting of a diode 13 and a capacitor 14 and a resistor15.The emitter of transistor 16 is connected ~o 30~arth and the collector is connected with a positive terminal of a voltage supply source.As soon as the amplitude of the receiver 3 signal exceeds a certain value the transistor 16 will conduct,so that the potentia1 in the collector will reduce.On each occasion when a change occurs in the detector from a condition in which a sheet-like ob~ject is present to a condition in 35which no sheet-1ike object is present a potential drop occurs in the collector.The collector of transistor 16 forms the output of circuit 10.
This outout is connected with the input of a monostable multivibrator11,the 5 ~ 8 output of which is connected with the changeover swi-tching element 4 and switching elernent 6. By this means it is ensured that when, via circuit 10, no sheet~like object is detected between source 2 and receiver 3, a signal is generated by the mono-s-table multivibrator 11 by means of which changeover switching element 4 connects the source 2 with receiver 3 and the switching element 6 is closed. This signal from the multivibrator 11 is generated for only a short period, after which the adjustment of oscillator 5 is performed by the capacitor 9 and the switch 6.
It is obvious that the invention is not restricted to the embodiment described and illustrated here, but that numerous modifications can be incorporated within the framewor~ of the following claims, particularly as regards the electrical components employed.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of detecting and distinguishing between super-imposed and single sheet-like objects moving along a trans-port path, which comprises passing ultrasonic vibrations through a gap across the transport path from an ultrasonic source to an ultrasonic receiver that produces a signal output representing characteristics of the vibrations received; when no sheet-like object is present in said gap connecting said source with said receiver in a feedback circuit whereby the vibrations in said gap acquire a certain natural frequency determined by then existing characteristics of the elements of said circuit and tuning an oscillator to a frequency corresponding to that natural frequency; and when a sheet-like object is present in said gap applying to said source the tuned frequency of said oscillator and comparing the phase of the oscillator vibrations resulting at said receiver with the phase of the oscillator vibrations, thereby producing a signal representing the phase displace-ment effected by the object.
2. A method according to claim 1, and when a sheet-like object ceases to be present in said gap detecting the resul-tant increase in the amplitude of the vibrations at said receiver and in response thereto switching said source from connection with said oscillator to connection with said receiver in said feedback circuit and tuning said oscillator to the resultant natural frequency of the vibrations in said gap.
3. A device for detecting the presence of and distin-guishing between superimposed and single sheet-like objects moving along a transport path, comprising an ultrasonic signal source and an ultrasonic signal receiver arranged at opposite sides of the transport path so that said source will transmit signals through said path to the receiver, said receiver forming an output representing characteristics of the signals received, an oscillator having an input to control the frequency of its oscillations, a phase comparator having inputs connected, respectively, with the output of said oscillator and said receiver output, a first switching means for connecting the output of the phase comparator with said control input of the oscillator, a changeover switching means which in a first position thereof connects said source with the output of said oscillator and in a second position thereof connects said source with said receiver output, and a control circuit including means rendered operative in a period when no sheet-like object is present between said source and said receiver to actuate said first switching means and to dispose said changeover switching means in said second position.
4. A detecting device according to claim 3, said control circuit means comprising an amplitude detector connected with said receiver and which reacts to changes in the ampli-tude of said receiver output.
5. A detecting device according to claim 4, said amplitude detector comprising a transistor having its collector con-nected with a voltage source for producing an output signal when the amplitude of said receiver output exceeds a certain value, said control circuit further including a mono-stable multivibrator rendered operative by said output signal to close said first switching means and to dispose said change-over switching means in said second position.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000369134A CA1155538A (en) | 1981-01-23 | 1981-01-23 | Device for the detection of sheet-like objects |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000369134A CA1155538A (en) | 1981-01-23 | 1981-01-23 | Device for the detection of sheet-like objects |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1155538A true CA1155538A (en) | 1983-10-18 |
Family
ID=4118992
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000369134A Expired CA1155538A (en) | 1981-01-23 | 1981-01-23 | Device for the detection of sheet-like objects |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1155538A (en) |
-
1981
- 1981-01-23 CA CA000369134A patent/CA1155538A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |