JPH0629863B2 - Defect detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a defect detection device, and more particularly to an analog image signal of an object to be inspected captured by an image pickup means such as a CCD (charge coupled device) in the defect detection device. It relates to a circuit for transmitting.

<Prior Art> Conventionally, in the case of transmitting an analog image signal of an object to be inspected, which is picked up by a CCD or the like, to a control panel having a defect signal processing unit, a method using a shield wire or a coaxial cable,
A PCM method using a pulse transformer and a photo coupler, and a method of transmitting only by a pulse transformer are known.

<Problems to be Solved by the Invention> However, the method using a shield wire or a coaxial cable has a problem that the transmission / reception circuit is not separated and is vulnerable to noise, and the PCM method has a complicated circuit and requires a device. There is a problem that it becomes expensive.

On the other hand, the method of transmitting only by the pulse transformer has a problem that when a square pulse is input, the output waveform causes overshoot or sag to cause waveform distortion, and a signal having a wide pulse width cannot be accurately transmitted.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional example, it is an object of the present invention to provide a defect detecting device having a simple circuit configuration and capable of accurately transmitting an image signal of an object to be inspected to a control panel.

<Means for Solving Problems> In order to solve the above problems, the present invention includes means for imaging an object to be inspected, and a sample hold circuit for converting a pulsed video signal from the imaging means into an envelope waveform. , A filter for removing a DC component from the signal of the sample and hold circuit, a circuit for differentiating the signal from the filter, a pulse transformer for transmitting the differential signal from the differentiating circuit, and a signal transmitted by the pulse transformer. It is characterized in that it has a circuit for performing inverting amplification and integration, and a circuit for clamping the signal from the integration circuit to a reference potential during the blank period of the video signal.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings. First
FIG. 1 is a circuit diagram of a defect detecting device according to the present invention, and FIG.
FIG. 3 is a schematic configuration diagram of the device shown in FIG. 3, which is a timing chart of main signals of the circuit shown in FIG.

As shown in FIG. 2, the apparatus of this embodiment is of a transmission type in which the inspection object 1 is arranged between the light source 2 and the detection section 3, that is, the imaging section, and the inspection object detected by the detection section 3 is shown. The video signal 1 is transmitted to the control unit 5 having the receiving unit 4.

Returning to FIG. 1, an image pickup means such as a CCD 12 for picking up an image of the object 1 to be inspected through the lens 11 is connected to a sample hold circuit (S / H) 14 through an amplifier 13, and the sample hold circuit 14 receives an image. The signal S ₁ (Fig. 3) is input. The CCD 12 and the sample hold circuit 14 are driven by the signal of the drive circuit 15 by the start signal S ₂ generated for each scanning.

The sample and hold circuit 14 is a bandpass filter (BP
Through F) 16 is connected to one end of the capacitor C _1, the capacitor C ₁ is connected to the input terminal at one end and buffer amplifier 17 of the resistor R _1, the other end of the resistor R ₁ is grounded. The capacitor C ₁ , the resistor R ₁ and the buffer amplifier 17 constitute a differentiating circuit 18.

The output terminal of the buffer amplifier 17 of the differentiating circuit 18 is connected to the input terminal of the pulse transformer 19, and the output terminal of the pulse transformer 19 is connected to the input terminal of the pulse transformer 21 via a twisted pair 20. . r is an output stabilizing resistor. The pulse transformers 19 and 21, the twisted wire pair 20, and the resistor r form a transmission line 22.

The lens 11, the CCD 12, the amplifier 13, the sample and hold circuit 14, the bandpass filter 16, the differentiating circuit 18 and the pulse transformer 19 described above constitute the detecting unit 3, that is, the transmitting side circuit in FIG. It constitutes the receiving unit 4 in FIG.

The output terminal of the pulse transformer 21 is connected to the (−) terminal of the operational amplifier 23 via the resistor R _2, and the (+) terminal of the operational amplifier 23 is grounded. The output terminal of the operational amplifier 23 is connected to the (−) terminal of the operational amplifier 24 via the capacitor C ₂ and the resistor R _{3 and also} to the (+) terminal of the operational amplifier 24. The (-) terminal of the operational amplifier 24 is grounded, and the output terminal is connected to the (-) terminal of the operational amplifier 23 via the switch SW. The switch SW is turned on by the clamp pulse from the clamp pulse generation circuit 24. These resistors R ₂ ,
R ₃ , the capacitor C ₂ , the operational amplifiers 23 and 24, and the switch SW form a reproducing circuit 26. The resistor R ₂ and the capacitor C ₂ are selected to have the same time constant as that of the differentiating circuit 18 (R ₂ C ₂ = R ₁ C ₁ ).

The output terminal of the operational amplifier 23 of the reproduction circuit 26 is connected to the (-) terminal of the operational amplifier 27 via the resistor r _2, and the (-) terminal and the output terminal of the operational amplifier 27 are connected via the variable resistor r _3. Has been done. On the other hand, the (+) terminal of the operational amplifier 19 is connected to the resistor r ₄
Grounded through. The operational amplifier 27 and the resistors r ₂ , r ₃ , r ₄ form an inverting amplifier circuit.

The operation of the embodiment according to the above configuration will be described with reference to FIG. 3. The video signal S ₁ of the DUT 1 amplified (inverted) by the amplifier 13 has a pulse waveform as shown in FIG. is there. In the figure, the signal has a hole a in the inspection object 1.

The video signal S ₁ is converted from a pulse-shaped waveform to an envelope waveform by the sample-hold circuit 14, and then the sample-hold noise and the DC component are removed by the bandpass filter 16 to obtain a rectangular pulse component (S ₃ in FIG. 3). The waveform includes the hole a).

When the signal S ₃ is differentiated by the differentiating circuit 18, as shown in FIG.
The differential signal as shown by S ₄ is obtained. In this case, since the differential signal S ₄ does not have a rectangular pulse component, the pulse transformer 19,
Even if the signal is transmitted via 21, no waveform distortion appears as shown at S ₅ in FIG.

Next, the transmitted signal S ₅ (level e ₅ ) is reproduced by the reproducing circuit 26.
Output signal (level e) when input to the operational amplifier 23 of
Is Becomes That is, this output signal is the signal Sa (-R ₃ e ₅ / R ₂ ) that has been inverted and amplified as shown at S ₆ in FIG.
(-1 / C ₂ R ₂ ∫e ₅ dt) is superimposed signal.

In the signal S ₆ , the switch SW is turned on during the period when there is no video signal due to the clamp pulse S ₇ from the clamp pulse generation circuit 24 because the operational amplifier offset occurs and the DC component due to the large one-way signal fluctuates. It is clamped to the electric potential (OV) and becomes the reproduction signal shown at S ₈ in FIG.

The reproduction signal S ₈ has the opposite polarity to the transmission signal S ₁ , and the transmission line 2
Since it is attenuated by 0 or the like, it is inverted and amplified (-r ₃ / r ₂ ) by the inverting amplifier circuit and becomes the same signal as the transmission signal S ₁ as shown by the signal S ₉ in FIG.

<Effects of the Invention> As described above, according to the present invention, a video signal of an object to be inspected is converted into a continuous signal by a sample and hold circuit, a direct current component is removed and differentiated, and then the signal is transmitted through a pulse transformer. Since the signal is inverted and amplified, integrated, and clamped to the reference potential while there is no video signal,
It is possible to perform signal transmission with good linearity and noise resistance with a simple and inexpensive circuit configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the defect detecting device according to the present invention, FIG. 2 is a schematic configuration diagram of the device of FIG. 1, and FIGS. 3 (a) to 3 (l) are the devices of FIG. It is a timing chart of the main signal of. DESCRIPTION OF SYMBOLS 1 ... Inspected object, 12 ... CCD, 14 ... Sample hold circuit, 16 ... Band pass filter, 18 ... Differentiation circuit, 1
9, 21 ... Pulse transformer, 25 ... Clamp pulse generating circuit, 26 ... Reproducing circuit.

Claims (1)

[Claims] 1. A means for imaging an object to be inspected, a sample and hold circuit for converting a pulsed video signal from the imaging means into an envelope waveform, a filter for removing a DC component from the signal of the sample and hold circuit, A circuit for differentiating the signal from the filter, a pulse transformer for transmitting the differential signal from the differentiating circuit, a circuit for inverting and amplifying the signal transmitted by the pulse transformer and integrating the signal, and a signal from the integrating circuit And a circuit for clamping the reference potential during a blank period of a video signal.