JP2577975B2 - Monitoring system - Google Patents

Description

The present invention relates to a monitoring system including a plurality of imaging devices,
In particular, the present invention relates to a monitoring system for preventing a screen of a monitor television from being disturbed when a video signal from an imaging device is selectively switched.

(Prior Art) In a monitoring system that supplies images from an imaging device such as a plurality of television cameras to one monitor television to monitor the images, usually, a video signal switch is used to switch from a desired image-capturing device to a desired image-capturing device. Is selectively extracted and supplied to a monitor television. In this case, since the screen of the monitor television is disturbed at the time of switching, it is necessary to synchronize the video signals output from the respective imaging devices in order to prevent the disturbance.

For example, in a monitoring system that does not employ a method of supplying power via a video signal cable, as one method for synchronizing video signals in a plurality of imaging devices, in addition to video signal wiring, each imaging device On the other hand, a method of wiring for supplying a synchronization pulse, that is, an external synchronization method has been adopted. This will be briefly described with reference to FIG. 5. The imaging devices 50, 51, 52 are connected to a monitor television 57 via video signal cables 53, 54, 55 and a changeover switch 56, respectively. On the other hand, a synchronization pulse generator 58 for generating in-phase synchronization pulses is provided, and each of the imaging devices 50, 5
Lines 59, 60, and 61 are connected between 1, 52 and the synchronization pulse generator 58 to supply in-phase synchronization pulses to the imaging devices 50, 51, and 52, respectively.

In this external synchronization method, since each imaging device operates based on the supplied synchronization pulse, the video signal output from each imaging device is synchronized, and even if the video signal switch is operated, the monitor television There is no disturbance on the screen.

Another method is a power supply synchronization method. Usually, each imaging device in the monitoring system is installed in or around the same building, and power is supplied to each imaging device through the same AC commercial power line, so that all imaging devices are the same. Operates on phase AC commercial power. Therefore, the frequency (50 Hz or 60 Hz) of the AC commercial power supply is equivalent to the frequency of the vertical synchronization signal of the video signal.
A vertical synchronizing signal is generated in each imaging device based on a commercial power signal. Even in this case, it is possible to prevent the screen from being disturbed at the time of switching.

(Problems to be Solved by the Invention) However, the above-described external synchronization method requires a dedicated line for supplying a synchronization pulse to each imaging device by the number of imaging devices, separately from the video signal wiring. The system must be complicated and expensive.

Further, since the above power supply synchronization method uses AC commercial power supply, it cannot be used in an area (for example, East Japan) where the frequency of the vertical synchronization signal is different from the frequency of the AC commercial power supply. In addition, since the vertical synchronization frequency of the NTSC color television system is 59.94 Hz, the above power supply synchronization system cannot be applied to a monitoring system of the NTSC color television system.

In view of the above problems, the present invention provides a monitoring system that does not require a dedicated line for supplying a synchronization pulse to each imaging device and can be installed anywhere regardless of the frequency of an AC commercial power supply. The purpose is to do.

(Means for Solving the Problems) In order to achieve the above object, a plurality of imaging devices that create and output a video signal based on a synchronization signal, and a video that transmits a video signal output from each of the imaging devices A monitoring system according to the present invention, comprising: a signal cable; a changeover switch for selecting one of the video signal cables; and a monitor television to which an output of the changeover switch is supplied. A coupling means for coupling a synchronization pulse having a frequency related to the frequency of the synchronization signal to each of the video signal cables; and a coupling means provided between the coupling means and the changeover switch, and coupled to the video signal cable. Erasing means for erasing the synchronized pulse, provided in each of the imaging devices, and sent from the video signal cable. A synchronization pulse extraction unit that extracts the synchronization pulse that comes in, a synchronization signal generation unit that is provided in each of the imaging devices and that generates the synchronization signal based on the synchronization pulse extracted by the synchronization pulse extraction unit; And synchronizing the video signal output from the imaging device so as not to cause disturbance on the screen of the monitor television when the changeover switch is operated.

In one embodiment of the present invention, the coupling means includes a synchronization pulse generator that generates a synchronization pulse, and a superimposition circuit that receives the synchronization pulse and couples the synchronization pulse to each of the video signal cables. The erasing means includes an erasing pulse generator for generating an erasing pulse, and an erasing circuit for receiving the erasing pulse and erasing the synchronization pulse from a video signal transmitted through the video signal cable.

In the monitoring system of the present invention, the synchronization signal is generated in synchronization with the synchronization pulse or the AC commercial power frequency. When the synchronization pulse has the same frequency as the vertical synchronization signal, the synchronization pulse extracting means is connected to the synchronization signal generation means via a selection switch. The synchronizing signal generating means includes a phase comparison circuit forming a PLL circuit, an electric control oscillator, and a synchronizing signal generator, and is configured to synchronize one of the fixed contacts of the selection switch with the same frequency as the vertical synchronizing signal from the synchronizing pulse extracting means. A pulse is supplied, an AC commercial power signal is supplied to another fixed contact of the selection switch, a movable contact of the selection switch is connected to one input of the phase comparison circuit, and a signal from the synchronizing signal generator is A vertical synchronization signal is applied to another input of the phase comparison circuit, and the switching of the selection switch causes the synchronization signal generation means to output the synchronization pulse or the AC signal.
Generates a synchronization signal synchronized with commercial power.

When the synchronization pulse has the same frequency as the horizontal synchronization signal, the synchronization signal generation unit includes a first phase comparison circuit that receives the synchronization pulse from the synchronization pulse extraction unit at one input; The first fixed contact
A selection switch that receives the output of the phase comparison circuit, a voltage-controlled oscillator having an input connected to the movable contact of the selection switch, a synchronization signal generator that receives the output of the voltage-controlled oscillator, and a vertical signal from the synchronization signal generator. A second receiving synchronization signal at one input and receiving an AC mains signal at another input
A horizontal synchronizing signal from the synchronizing signal generator to another input of the first phase comparing circuit, and an output of the second phase comparing circuit to another fixed of the selection switch. Connect to contacts. In this case, by operating the selection switch, a synchronization pulse or a synchronization signal synchronized with the AC commercial power signal can be generated.

(Operation) In the present invention, the in-phase synchronization pulse is supplied to all the imaging devices via the video signal cable, and the imaging device generates a synchronization signal based on the synchronization pulse. Is generated. On the other hand, the synchronization pulse transmitted to the monitor television by the video signal cable is erased by the erase pulse. Thus, even if the video signal is switched by operating the changeover switch, the screen of the monitor television is not disturbed.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of a monitoring system according to the present invention, in which three imaging devices are installed.
In the figure, video output terminals 4, 5, and 6 of three imaging devices 1, 2, and 3 are connected to video signal cables 7, 8, and 9, respectively.
Via the corresponding input terminal 1 of the synchronizing signal combiner / eliminator 10
Connected to 1,12,13. The synchronizing signal combiner / eliminator 10 has output terminals 14, 15, 16 corresponding to the input terminals 11, 12, 13,
These output terminals 14, 15, 16 are connected to fixed contacts 18, 19, 20 of a video signal switch 17, respectively, and a movable contact 21 of the video signal switch 17 is connected to a monitor television 22.

Each of the imaging devices 1, 2, and 3 has a synchronization pulse detection circuit 23 connected to the corresponding video output terminals 4, 5, and 6, respectively.
The synchronizing signal combiner / eliminator 10 includes a synchronizing pulse generator 25 and an erasing pulse generator 26. The synchronizing signal generator 24 receives an output from the synchronizing pulse detecting circuit 23. Synchronous pulse generator 25 is 59.94 Hz, PAL
In the case of the specification, a synchronization pulse of 50.00 Hz having the same frequency as the vertical synchronization signal is output, and the erase pulse generator 26 outputs an erase pulse.

The respective input terminals 11, 1 of the synchronization signal combiner / eliminator 10
2 and 13 are connected to a superimposing circuit 27 to which a synchronizing pulse is supplied from a synchronizing pulse generator 25, and an output signal of each superimposing circuit 27 passes through an erasing circuit 28 to which an erasing pulse is supplied from an erasing pulse generator 26. And connected to the corresponding output terminals 14, 15, 16.

Next, the operation of the embodiment shown in FIG. 1 will be described. The video signals output from the video output terminals 4, 5, 6 of the respective imaging devices 1, 2, 3 are input to video signal cables 7, 8, 9 and input terminals 11, 12, 13 of a synchronizing signal combiner / eraser 10. The synchronization pulse generated by the synchronization pulse generator 25 is supplied to each of the superimposition circuits 27 via a corresponding one of the superimposition circuits 27. Therefore, in each superimposing circuit 27, the synchronizing pulse generator 25 is added to the video signals from the imaging devices 1, 2, and 3.
The composite signal (FIG. 2) including the synchronization pulse is output to the erasing circuit 28 during the vertical blanking period of the video signal. At the same time, the synchronizing pulse from the synchronizing pulse generator 25 is transmitted from the superimposing circuit 27 to the video signal cable 7,
The signals are also transmitted to the video output terminals 4, 5, 6 of the respective imaging devices 1, 2, 3 via 8, 9 and are added to the synchronization pulse detection circuit 23 together with the video signal.

The synchronization pulse detection circuit 23 in each of the imaging devices 1, 2, and 3 detects and separates synchronization pulses from signals supplied from the video output terminals 4, 5, and 6. Since the separated sync pulse has the same frequency as the vertical sync signal, each sync signal generating circuit 24 generates a sync signal necessary for horizontal / vertical scanning in each camera based on this sync pulse. Thereby, the synchronization signals of all the imaging devices 1, 2, and 3 are oscillated in synchronization, and the video signals output from the imaging devices 1, 2, and 3 are synchronized with each other.

On the other hand, the erase circuit 28 applies an erase pulse from the erase pulse generator 26 to the composite signal output from the superposition circuit 27 and given to the erase circuit 28. Thus, the synchronizing pulse added to the video signal by the superimposing circuit 27 is erased. This is for transmitting a video signal satisfying the standard to the monitor television 22 via the video signal switch 17.

Thus, the fixed contacts 18, 19 of the video signal switch 17
20 is supplied with a video signal according to the standard synchronized with the synchronization pulse generated by the synchronization pulse generator 25,
Even if the video signal switching unit 17 switches the connection between the fixed contacts 18, 19, 20 and the movable contact 21 to select the video signal from the imaging devices 1, 2, and 3, the screen of the monitor television 22 is disturbed at the time of switching. Does not occur.

In the above description, a pulse having the same frequency as the vertical synchronizing signal is used as the synchronizing pulse from the synchronizing pulse generator 25. Instead, a pulse having the same frequency as the horizontal synchronizing signal (15.734KHz in the case of the NTSC system) is used. The same effect can be obtained by using a pulse.

FIG. 3 and FIG. 4 are block diagrams showing another embodiment of the present invention, in which an external synchronizing signal generating circuit in the imaging devices 1, 2, 3 is synchronized by a synchronizing pulse from a synchronizing pulse generator 25. The synchronous operation can be performed by either a synchronous method or a power synchronous method that synchronizes with an AC commercial power signal. Which imaging device 1,
Since the configurations and operations of 2 and 3 are also the same,
Will be described as an example.

FIG. 3 shows an example in which a synchronizing pulse having the same frequency as the frequency of the vertical synchronizing signal is generated by the synchronizing pulse generator 25 and added to the synchronizing pulse detecting circuit 23 as described in the embodiment of FIG. The output terminal of the synchronous pulse detection circuit 23 whose input terminal is connected to the video output terminal 4 of the imaging device 1
It is connected to a synchronization signal generation circuit 24 via a selection switch 29 for selecting a synchronization method. One fixed contact 30 of the selection switch 29 is connected to the output terminal of the synchronous pulse detection circuit 23, the other fixed contact 31 is connected to an AC commercial power supply, and its movable contact 32 is connected to the synchronous signal generating circuit 24.

The synchronization signal generation circuit 24 includes a phase comparison circuit 33 constituting a PLL circuit, a voltage controlled oscillator 34, and a synchronization signal generator 35, and one input terminal of the phase comparison circuit 33 is a selection switch 29.
Is connected to the movable contact 32. The synchronization signal generator 35 outputs a vertical synchronization signal and a horizontal synchronization signal based on the signal from the voltage controlled oscillator 34, and the vertical synchronization signal
It is applied to 33 other input terminals. In this example, since the frequency of the synchronization pulse generated by the synchronization pulse generator 25 is equal to the frequency of the AC power signal, the synchronization pulse or the switching of the switch 29 provided in front of one phase comparison circuit 33 is performed.
A synchronization signal synchronized with the AC power signal can be created.

When the horizontal synchronizing signal is used for the phase comparison, it is desirable to appropriately synchronize the time relationship with the vertical synchronizing signal.

FIG. 4 shows an example in which the synchronizing pulse generator 25 generates a synchronizing pulse having the same frequency as the horizontal synchronizing signal, and the synchronizing pulse is applied from the video output terminal 4 of the imaging device 1 to the synchronizing pulse detecting circuit 23. In the synchronization signal generation circuit 24 of this example, a first phase comparison circuit that receives the output of the synchronization pulse detection circuit 23
36, a selection switch 37, a voltage controlled oscillator 38, and a synchronization signal generator 39 are connected in this order to form a PLL circuit.

The output terminal of the first phase comparison circuit 36 is connected to the input terminal of the voltage controlled oscillator 38 via one fixed contact 40 and the movable contact 41 of the selection switch 37, and the other fixed contact 42 of the selection switch 37 is connected to the second Is connected to the output terminal of the phase comparison circuit 43. The synchronizing signal generator 39 generates a vertical synchronizing signal and a horizontal synchronizing signal based on the signal supplied from the voltage controlled oscillator 38, and outputs the horizontal synchronizing signal to the input terminal of the first phase comparator 36 and the vertical synchronizing signal It is supplied to the input terminals of the second phase comparison circuit 40, respectively. Another input terminal of the second phase comparison circuit 43 is connected to an AC commercial power supply. In the example of FIG. 4, the synchronization pulse generator 25 generates a synchronization pulse having a frequency significantly different from that of the AC commercial power supply signal, so that two phase comparison circuits are required. Therefore, it can be said that the example of FIG. 3 in which the number of the phase comparison circuits is small is practically more advantageous.

In the above description, the frequency of the synchronization pulse is the same as the frequency of the vertical synchronization signal or the horizontal synchronization signal. However, the frequency of the synchronization pulse is not limited thereto. Any value may be set as long as the value can determine the frequency of the signal.

(Effects of the Invention) As described so far according to some embodiments, the present invention supplies a synchronization pulse to each imaging device via a video signal cable connecting each imaging device and a monitor television, and performs all imaging operations. Since the oscillation operation of the synchronization signal generation circuit in the device is synchronized, the screen of the monitor television is not disturbed even when the video signal from the imaging device is selectively switched. Moreover, since there is no need to provide a dedicated line for supplying a synchronization signal to the imaging device, the configuration of the entire monitoring system can be simplified.

Moreover, in the invention of the present application, the erasing means is provided between the coupling means and the changeover switch, so that the erasing means and the coupling means can be integrated, for example, housed in one housing, and can be integrated. Therefore, it is possible to simplify wiring and prevent wiring errors. Further, since the erasing means and the coupling means can be accommodated in one case, it is easy to synchronize the synchronization pulse with the erasing pulse.

Further, the monitoring system of the present invention creates a synchronization pulse having a predetermined relationship with the frequency of the horizontal synchronization signal or the vertical synchronization signal and supplies it to each imaging device. Irrespective of the frequency of the device, it is possible to cope with any installation mode.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a monitoring system according to the present invention. FIG. 2 is a waveform chart for explaining the operation of the monitoring system of FIG. FIGS. 3 and 4 are block diagrams showing another embodiment of the present invention, showing different specific examples of the synchronization pulse detection / synchronization signal generator of the monitoring system of FIG. FIG. 5 is a block diagram showing a conventional monitoring system. 1.2.3: Imaging device, 7.8.9: Video signal cable, 10: Synchronous signal combiner / eliminator, 17: Video signal switcher, 22: Monitor television, 23: Synchronous pulse detection circuit, 24: Synchronous Signal generator circuit, 25: Synchronous pulse generator, 26: Erase pulse generator, 29/37: Select switch

Claims (5)

(57) [Claims] A plurality of image pickup devices for generating and outputting a video signal based on a synchronization signal; a video signal cable for transmitting a video signal output from each of the image pickup devices; and one of the video signal cables. A monitoring system comprising a changeover switch for selecting and a monitor television to which an output of the changeover switch is supplied, wherein a synchronization having a frequency related to the frequency of the synchronization signal is provided between the imaging device and the changeover switch. Coupling means for coupling a pulse to each of the video signal cables; erasing means provided between the coupling means and the changeover switch for erasing a synchronization pulse coupled to the video signal cable; A synchronization pulse pickup provided in each of the devices and for taking out the synchronization pulse sent from the video signal cable; Output means, and a synchronizing signal generating means which is provided in each of the imaging devices and generates the synchronizing signal based on the synchronizing pulse extracted by the synchronizing pulse extracting means, and is output from the imaging device. A surveillance system in which video signals are synchronized so as not to disturb the screen of a monitor television when the changeover switch is operated. 2. The synchronizing means according to claim 1, wherein said synchronizing means includes a synchronizing pulse generator for generating a synchronizing pulse, and a superimposing circuit for receiving the synchronizing pulse and coupling the synchronizing pulse to each of the video signal cables. Monitoring system. 3. The erasing means includes an erasing pulse generator for generating an erasing pulse, and an erasing circuit for receiving the erasing pulse and erasing the synchronization pulse from a video signal transmitted through the video signal cable. Item 2. The monitoring system according to Item 1. 4. The synchronizing pulse extracting means is connected to the synchronizing signal generating means via a selection switch, and the synchronizing signal generating means includes a phase comparison circuit forming a PLL circuit, a voltage controlled oscillator, and a synchronizing signal generator. A synchronization pulse having the same frequency as the vertical synchronization signal is supplied from the synchronization pulse extracting means to one fixed contact of the selection switch, and an AC commercial power signal is supplied to another fixed contact of the selection switch; Is connected to one input of the phase comparison circuit, and a vertical synchronization signal from the synchronization signal generator is applied to another input of the phase comparison circuit. The switching according to any one of claims 1 to 3, wherein the synchronization signal generation means generates the synchronization pulse or a synchronization signal synchronized with the AC commercial power supply. A monitoring system according to claim 1. 5. A synchronizing pulse having the same frequency as a horizontal synchronizing signal, wherein said synchronizing signal generating means receives a synchronizing pulse from said synchronizing pulse extracting means at one input; A selection switch for receiving an output of the first phase comparison circuit at a fixed contact, a voltage-controlled oscillator having an input connected to a movable contact of the selection switch, a synchronization signal generator for receiving an output of the voltage-controlled oscillator, A second phase comparison circuit that receives a vertical synchronization signal from one of the synchronization signal generators at one input and receives an AC commercial power supply signal at another input; and outputs the horizontal synchronization signal from the synchronization signal generator to the first input terminal. In addition to the other inputs of the phase comparator,
The monitoring system according to claim 1, wherein an output of the second phase comparison circuit is connected to another fixed contact of the selection switch.