JPH0251121B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moving object detection device for accurately detecting the timing at which a predetermined portion of an object moving at a relatively high speed, such as printing paper in a rotary printing press, passes a predetermined position.

In a rotary printing press or the like, printing operations can be performed at a fairly high speed, and a large number of printed materials can be obtained in a short period of time. Therefore, it is desirable to be able to inspect the printed matter in real time during the printing operation.

Therefore, devices have been proposed that use image sensors or the like to automatically inspect printed matter while it is running. It is necessary to detect the timing of the moment when the object passes through the position with high precision.

Therefore, in order to detect such timing,
A device that uses a photoelectric detector to detect the passage of a predetermined part of a pattern on a running printing paper, or the passage of a detection mark printed along with each pattern. has traditionally been used.

An example of such a detection device is shown in FIG.

In the figure, 1 is a light source, 2 and 3 are lenses, 4,
5 is a photoelectric conversion element, 6 and 7 are amplifiers, 8 is a slice circuit, 9 is a slice level correction circuit, and P
is a printing paper (hereinafter referred to as a web), M is a detection mark printed on a margin such as the side edge of the web P, and S is an illuminance reference plane.

The light source 1 serves to maintain a predetermined illuminance between the portion of the web P where the mark M is printed and the illuminance reference surface S, and is composed of, for example, an incandescent lamp.

The lens 2 functions to form an image of the mark M on the photoelectric conversion portion of the photoelectric conversion element 4, and the lens 3 functions to cause reflected light from the illuminance reference surface S to enter the photoelectric conversion element 5.

The photoelectric conversion elements 4 and 5 are composed of photodiodes and the like, and each detects the amount of incident light and generates a signal, and serves to generate a detection signal a and a reference signal b at the outputs of the amplifiers 6 and 7.

The slice circuit 8 consists of a comparator etc. that receives the level signal l as a comparison input, and detects the detection signal a at the slice level SL set by the level signal l.
It functions to generate the timing detection signal T only when the timing exceeds the threshold.

The slice level correction circuit 9 functions to generate a reference level signal l and to correct the level of this level signal l in accordance with the level of the reference signal b.

Next, the operation of this device will be explained.

The detection signal a is configured to have a maximum value when the amount of light incident on the photoelectric conversion element 4 is 0, and its level decreases as the amount of incident light increases.

Therefore, when the web P is traveling in the direction of the arrow and the mark M has not reached the optical axis part of the lens 2, the light from the margin part of the web P is incident on the photoelectric conversion element 4, so that the detection signal a is The level does not reach the slice level SL caused by the signal l, and the timing detection signal T is not output from the slice circuit 8. However, when the mark M passes through the optical axis portion of the lens 2 due to the running of the web P, the timing detection signal T is not output from the slice circuit 8. The amount of incident light is greatly reduced and the detection signal a
increases to near the maximum level and exceeds the slice level SL, so the timing detection signal T is output, and the timing of the passage of the mark M can be detected.

By the way, at this time, if the amount of light incident on the photoelectric conversion element 4 changes in an accurate stepwise manner as the mark M passes, it would be possible to detect the correct timing, but from a practical point of view, A certain area is required for the light-receiving part of the photoelectric conversion element 4, and therefore, a certain slope is given to the change in the amount of incident light due to the passage of the mark M, and the rising and falling parts of the detection signal a are also sloped. is given.

Therefore, in the conventional example described above, if the slice level SL in the slice circuit 8 is kept constant, the amount of illumination light from the light source 1 changes, and the level change range of the detection signal a, that is, from the minimum value to the maximum value, changes. When the width changes, due to the slope given to the rising or falling portion of the detection signal a described above, the timing at which the detection signal a is sliced changes even when the passing timing of the mark M remains constant. This will cause a detection error.

Therefore, in the above conventional example, a light reference surface S is provided which is illuminated together with the web P by the light source 1, and the reflected light from this is made to enter the photoelectric conversion element 5, and is approximately directly proportional to the amount of light incident thereon. A reference signal b of the same level is taken out, and the level signal l is corrected using this signal b, so that the slice level SL with respect to the detection signal a is corrected by the illuminance of the reference surface S.

Therefore, according to this conventional example, it is possible to obtain a timing detection signal T in which timing detection errors due to changes in illuminance of the light source 1 are compensated for.

In this conventional example, the lens 3 does not need to be used, and a blank space on the web P where the mark M is not made may be used instead of the illuminance reference surface S.

However, in this conventional example, if the density of the object to be detected, such as the mark M, changes, the slice level is not corrected, which causes errors in timing detection, and If a blank area of the web P is used for the detection, an error may also occur when the density of a background area of the object to be detected, such as a blank area of the web P, changes.

Therefore, the conventional device described above has the disadvantage that it is not possible to detect the passing timing of a moving object with sufficient accuracy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a moving object detection device that can always detect timing with sufficient accuracy in any case, while eliminating the drawbacks of the prior art described above.

In order to achieve this object, the present invention obtains a difference signal between signals sequentially detected at different positions along the passing direction when a moving object passes a predetermined position, and detects the movement of the moving object based on the peak timing of this difference signal. It is characterized by detecting the timing of the passage of the body.

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

FIG. 2 is a block diagram generally showing one embodiment of the present invention, in which 10A and 10B are paired photodetectors, 20A and 20B are amplifiers, 30 is a difference signal detection circuit, 40 is a differential circuit, 50 is a gate signal generation circuit, 60 is a zero cross detection circuit, 70 is a gate circuit, 80 is a pulse shaping circuit, lens 2,
The web P, mark M, etc. are the same as in the conventional example shown in FIG.

The paired photoelectric detectors 10A and 10B are composed of photoelectric conversion elements such as photodiodes, and as shown in FIG.
pa and pb are slit-like, and they are
For example, they are arranged with an extremely narrow gap g of 100 μm or less in between, and the image of the mark M on the web P is formed on the light receiving portions pa and pb by the lens 2, and the web P is When moving in the direction of the arrow, the mark M is displayed at these light-receiving parts pa and pb.
The image is oriented so that it moves in the direction of the arrow in Figure 3.

These photoelectric detectors 10A and 10B output a signal that shows a positive predetermined level for the light from the margin part of the web P, and changes to approximately 0 level only when the light from the mark M is detected. The operation of this embodiment will be explained below with reference to the waveform diagram of FIG.

Now, at time _t1 in FIG. 4, the front end of the image of mark M in the traveling direction reaches the light receiving portion pa of the photoelectric detector 10A, and then at time _t2 , the front end of the image of the mark M reaches the light receiving portion pa of the photoelectric detector 10B.
Suppose that pb is reached, and then the trailing edge passes through at times t ₃ and t ₄ , respectively.

Then, a first detection signal a1 as shown in FIG. 1 appears at the output of the amplifier 20A, and a second detection signal a2 as shown in FIG. 2 is obtained at the output of the amplifier 20B. Note that these amplifiers 2
0A and 20B are amplifiers 6 in the conventional example shown in FIG.
It has a function similar to that of the photoelectric detector 10A, 10B, and has the function of amplifying the output signals from the photoelectric detectors 10A and 10B to a predetermined level.

These first and second detection signals a1 and a2 are respectively supplied to comparison inputs of the difference signal detection circuit 30,
At its output, a signal c representing the difference between the first detection signal a1 and the second detection signal a2 is generated as shown in FIG. 4.

This difference signal c is supplied to the differentiating circuit 40 and the gate signal generating circuit 50. First, the differentiating circuit 40
Then, the difference signal c is differentiated and the output is the fourth
A differential signal d as shown in FIG. 4 is extracted and supplied to the zero-cross detection circuit 60.

This zero cross detection circuit 60 is a circuit that operates so that the output becomes level 0 when the level of the input signal to it changes from positive to negative, and conversely, the output becomes level 1 when the level of the input signal changes from negative to positive. Therefore, when the differential signal d is input to this zero-cross detection circuit 60, a zero-cross signal f as shown in FIG. 4 is taken out as its output.

On the other hand, the portion of the difference signal c supplied to the gate signal generation circuit 50 that is equal to or higher than the predetermined slice level is extracted, and a gout signal e as shown in FIG. Supplies gate signal input.

As a result, in the gate circuit 70, a predetermined portion of the zero cross signal f is extracted by the gate signal e, and a pulse signal h is generated at its output.
If the pulse shaping circuit 80 is triggered by this pulse signal h, a timing detection signal T having a predetermined pulse width τ can be obtained at its output, as shown in FIG. 4 and 8.

As is clear from the waveform diagram in FIG. 4, the rising point of the timing detection signal T is time _t2 , and the falling point of the second detection signal a2 shown in FIG. This corresponds exactly to the point in time when the front end of M reaches the light receiving portion pb of the photoelectric detector 10B.

Therefore, the timing detection signal T rises when the zero cross signal f (FIG. 6) rises from level 0 to level 1 within the period in which the gate signal e (FIG. 4, 5) exists, that is, the difference signal It is determined only by the timing at which the peak appears at c (FIG. 3), and is not affected at all by changes in the peak level. This is because even if the peak level of the difference signal c changes, the timing of the zero cross point at which the differential signal d changes from negative to positive does not change at all.

On the other hand, the timing at which the peak of this difference signal c appears is that the second detection signal a2 (Fig. 4 2) starts falling after the first detection signal a1 (Fig. 4 1) starts falling.
It is determined at the point when the first
and the second detection signals a1, a2. This is a natural result of creating a difference signal.

Therefore, according to the above embodiment, the first and second detection signals are changed due to a change in the illuminance of the light source 1 on the web P and the mark M, or a change in the density of the fabric of the web P or the density of the mark M. Even if a level change occurs in a1, a2, an accurate timing detection signal T that does not cause any timing error can be obtained, and the timing at which the mark M on the web P passes a predetermined position can be determined with sufficient accuracy. It can be detected stably.

Next, FIG. 5 shows a specific embodiment of the present invention.

The embodiment of FIG. 5 is a pair of photoelectric detectors 1
Photodiode with reverse bias of 0A and 10B
It consists of PD1 and PD2, and the photocurrent is converted into an operational amplifier.
Amplifiers 20A and 20B consisting of OP1 and OP2 convert it into voltage to obtain detection signals a1 and a2.

The difference signal detection circuit 30 is composed of an operational amplifier OP3, which supplies a detection signal a1 to its non-inverting input, a detection signal a2 to its inverting input, and a difference signal c to its output.
I'm starting to get more.

The differentiating circuit 40 is constructed by using an operational amplifier OP4 and connecting a capacitor C1 to its input.

The gate signal generation circuit 50 is a comparator OP
5, by supplying a comparison voltage to one input and a difference signal c to the other input, a gate signal e is obtained. ) can be arbitrarily selected to detect the passing of the mark M at its front end or at its rear end.
SW1, SW2, and SW3 are provided, and these will be described later.

The zero cross detection circuit 60 is composed of a comparator OP6 with one input kept at ground potential.
This allows the zero-crossing signal f to be extracted. Note that the inverter I will be described later.

The gate circuit 70 is composed of an AND gate, and the pulse shaping circuit 80 is composed of a monostable multivibrator MMV, a capacitor C2 for determining its time constant, and a resistor R1. Therefore, the pulse width τ of the timing detection signal T is determined by the capacitance of the capacitor C2 and the resistance value of the resistor R1.

Zener diodes ZD1 and ZD2 and variable resistors VR1 and VR2 create a comparison voltage for determining the pulse width of the gate signal e.

Therefore, when the switches SW1 to SW3 are switched to the state shown in the figure, they operate at the timing shown in the waveform diagram of FIG. 4, as in the case of FIG. 2, and the second detection signal a2 is When the fall started
The timing detection signal T that rises at _t2 is obtained, and the mark M is detected without being affected by changes in the light intensity of the light source 1 or changes in the density of the margins of the web P and the marks M.
It is possible to accurately detect the timing when the front end of the front end reaches a predetermined position. At this time, by adjusting the variable resistor VR1, the gate signal e
The pulse width of the oscillator can be varied, thereby allowing a stable operating point to be set.

Next, when switches SW1 to SW3 are switched to the contacts opposite to those shown in the figure, the difference signal c and the comparison voltage for comparator OP5 are exchanged, and the AND gate is switched from comparator OP6 for zero-cross detection.
Since the zero-crossing signal f supplied to AND passes through inverter I, the operation at the timing shown in the waveform diagram of FIG. 6 is performed at this time.
Timing detection signal T (FIG. 6, 8) rises at time _t4 when second detection signal a2 (FIG. 6, 2) starts rising
is obtained, and the timing when the rear end of the mark M reaches a predetermined position can be accurately detected.

Note that the waveform diagrams in FIGS. 4 and 6 are mainly intended to show the timing relationship for the embodiment in FIG. 5, so the polarities of the signals do not necessarily match. According to the embodiment of FIG. 5, the polarities of waveform diagrams 1, 2, and 3 of FIGS. 4 and 6 are reversed.

Next, the effects of the above embodiment are enumerated as follows.

Because timing information is extracted by taking the difference between the outputs of two paired photoelectric detectors and differentiating the signal of the difference, the illuminance of the illumination system and the density of the detection target and its background change, causing the above-mentioned Even if the difference signal undergoes amplitude changes or level shifts, timing detection is not affected at all, and highly accurate timing detection is always possible.

Since an illuminance reference surface is not required, the detection head becomes compact and requires less installation space.

You can detect either the front end or the rear end of the object to be detected by simply operating the switch. Therefore, the front and rear ends of the detection target can be detected when the reflectance of the detection target is low compared to the background, and the front and rear ends of the detection target can be similarly detected even when the detection target has high reflectance compared to the background. The front and rear ends can be detected.

There is almost no effect from fluctuations in power supply voltage,
High accuracy is always maintained.

Not only marks provided on the web but also parts where contrast exists, such as the edges of paper, can be detected at any desired and accurate timing.

It can also be applied to accurate measurement of rotation angle timing of rotating objects.

In the conventional example shown in FIG. 1, even if there is no change in the illuminance of the light source 1 or the density of the web P and mark M, due to the response speed and drift of the amplifiers 6, 7, slice level correction circuit 9, etc. Since the slope characteristics and level of the signal change, which causes detection errors, high-performance devices are required for these, which increases costs. Since it is less susceptible to accuracy, it is easy to reduce costs.

As explained above, according to the present invention, the detection area is completely unaffected by changes in illuminance in the detection area, changes in the density of the detected object, and changes in the density of its background.
Since the timing at which the detection object passes a predetermined position can be detected, it is possible to eliminate the drawbacks of the prior art and easily provide a moving object detection device that can always detect timing with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example of a moving object detection device, FIG. 2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a front view of a photoelectric detector in the above embodiment, and FIG. FIG. 5 is a waveform diagram for explaining the operation, and FIG. 5 is a circuit diagram of an embodiment further embodying the present invention.
The figure is a waveform diagram for explaining the operation. 10A, 10B... Paired photoelectric detectors, 2
0A, 20B...Amplifier, 30...Difference signal detection circuit, 40...Differential circuit, 50...Gate signal generation circuit, 60...Zero cross detection circuit, 70...Gate circuit, 80...Pulse shaping circuit.

Claims (1)

[Claims] 1. A moving object detection device that detects the timing of passage of a moving object to a predetermined position by optically detecting at least one of a predetermined mark added to an end of the moving object and a predetermined portion thereof, an optical system that projects an optical image of a predetermined portion of the movable body onto a predetermined image-forming plane; a means for extracting a difference signal from the first and second detection signals obtained from the first and second photoelectric conversion elements, and a signal of the difference. means for obtaining a gate signal by slicing the signal at a predetermined level, means for obtaining a differential signal of the difference signal, and means for obtaining a zero-cross signal of the differential signal, and gates the zero-cross signal with the gate signal. A moving object detection device characterized in that it is configured to obtain a signal representing the timing of passage of the moving object to a predetermined position.