JPS5832381B2 - CRT brightness control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a CRT brightness control method, and more particularly to a CRT brightness stabilization method suitable for stabilizing the brightness of a CRT display device.

In general, CRT devices have poor brightness stability when used for long periods of time. For example, when a CRT device is used in the latent image area of an electrophotographic device, a problem arises in that print density fluctuates.

For this reason, in the past, drivers and others checked the density at a timely manner and manually operated the CRT each time to ensure that the optimum density was obtained.
The brightness was being adjusted.

However, this adjustment is troublesome and has the disadvantage that it is not possible to efficiently operate an electrophotographic apparatus or the like.

The present invention aims to eliminate the above-mentioned drawbacks, and this purpose is achieved by using a light receiving element, a means for comparing an output voltage from the light receiving element with a reference voltage, and a comparison result by the comparing means. A brightness correction means is provided, which includes means for generating a correction voltage that increases or decreases, and a feedback means for adding the correction voltage from the correction voltage generation means to the brightness voltage, so that the output voltage from the light receiving element and the reference voltage are It is distantly related to this method by generating a correction voltage to match the voltage.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, for example, a photodiode 2 is connected to a CRT 1
It is a figure which shows the Example mounted|worn on the tube surface of.

As shown in the front view of FIG. 1, the photodiode 2 is mounted outside an area A used for display on the CRT 1.

Further, as shown in the side view of FIG. 1a, before normal illumination of characters, for example, the beam (cathode ray) BM is deflected to the mounting position of the photodiode 2, and the mounting position is illuminated. ing.

Therefore, as shown in detail in Figure 2, the amount of luminous light at this time is determined by the photodiode 2 first passing a photocurrent proportional to the incident luminous flux, and the photoamplifier 3 converting this photocurrent into voltage, which changes the CRT luminance. A proportional detection voltage Vint is obtained.

The present invention performs a brightness correction operation using the detection voltage V int to maintain a constant print density in, for example, an electrophotographic device or a phototypesetting device. will be explained in detail.

In FIG. 3, 100N is a video signal based on print data; 4 is a video amplifier that adds a correction voltage DAO (described later) to the video signal to obtain a brightness signal VID; 5 is a detection voltage Vint from the photoamplifier 3 and a reference voltage VC1. When the detection voltage Vint is equal to II □ ++
, 11 in the opposite case, a comparator that obtains a comparison output COMP of +1: SAMP is a clock pulse that is sent from an oscillator (not shown) only during the correction period, that is, outside the character display period: 9 is a certain period of time δ from the clock pulse. A monostable multi-high inflator (hereinafter referred to as mono-multi) that obtains a pulse DLSP with a delayed timing: 6 is synchronized with the pulse DLSP, and the comparison output COMP is ++,
The flip-flop nearer outputs the amplifier down signal U/D, which has a high potential U when ++ and a low potential when "lo" 1, is synchronized with the clock pulse SAMP, and counts up (count value) when the high potential U arrives. 8 is a digital-to-analog converter (hereinafter referred to as D) that outputs a correction voltage DAO proportional to the count value of counter 7.
/A converter).

Next, according to the time chart shown in Figure 4 and Figure 3,
The brightness correction operation will be explained.

Now, the detection voltage Vint proportional to the brightness is the reference voltage VC
When it is lower than 1, the comparison output COMP becomes II I ++, and the up-down signal U/D becomes a high potential U.

Therefore, first, the counter 1 continuously counts up, and the correction voltage DA output from the D/A converter 8
O increases sequentially, the brightness of CRTl increases, and eventually the detection voltage Vint increases.

On the other hand, the detection voltage Vint raised in this way eventually becomes higher than the reference voltage VC1.

Then, the comparison output COMP changes from II II+ to II □ ++, and then, after a delay of a certain period (this is equal to t-δ, where t is the period of the clock pulse SAMP), the up-down signal U/D changes to a high potential. It becomes low potential from U.

Finally, with a delay of one clock, the correction voltage DAO falls by one count.

In this case, the detection voltage Vint becomes lower than the reference voltage ■C1 again.

Therefore, it is clear that the corrected voltage DAO rises by one count after one clock elapses, and falls to the original voltage after one more clock elapses, as in the case of falling. This correction operation is stabilized when rising and falling are repeated alternately.

Moreover, even if the detection voltage Vint is initially higher than the reference voltage VC·1, this stable state is still reached.

By the way, it can be seen that the difference between the detected voltage Vint and the reference voltage VC1 in this stable state is at most the difference of one count.

Further, this difference can be reduced to a practical level by selecting the comparator 5, the counter 7, and the D/A converter 8.

Next, how the brightness correction operation described above is applied to this embodiment, that is, a phototypesetting apparatus, will be explained with reference to FIG.

First, the operating period of a CRT used in a phototypesetting apparatus is divided into a printing period and a correction operation period.

During this printing period, for example, during the printing (latent image) of pages n-1 and (n is a natural number), the video signal 1
00N fluctuates in a pulse shape according to the print data, clock pulse 5AIVIP stops the vibration, and the correction voltage DA
O becomes a constant value due to the stop of this clock pulse SAMP.

On the other hand, during the correction period, for example between the two printing periods, the video signal 100N becomes a predetermined constant voltage, the clock pulse SAMP oscillates, and therefore the correction voltage DAO is adjusted according to the correction operation described above. Varies according to

The constant voltage of the video signal 100N at this time is set to an appropriate value that can be sufficiently detected by the photoamplifier 3 and does not saturate the comparator 5, counter 7, D/A converter 8, etc., and is kept constant for each page.

Furthermore, the oscillation of the clock pulse SAMP is stopped after the correction operation reaches the stable state described above.

In the embodiments of the present invention, only the basic correction operations have been described above, but the luminance can be more effectively stabilized in the following manner.

That is, FIG. 6 is a diagram showing an embodiment in which the correction operation can be monitored.

In this case, alarm circuits 10 and 12, a comparator 11, and a voltage source (DC) for obtaining the second reference voltage VC2 are added to the configuration shown in FIG.

The alarm circuit 10 is activated by the carry and borrow pulse outputs of the counter 7, and thereby generates a signal (referred to as an abnormal signal) ALM that lights up a lamp, for example.
This is a circuit that outputs l.

The alarm circuit 10 causes the counter 7 to
The detection voltage V is within the range where no carry or borrow is output from
By setting the difference between int and reference voltage VC1, abnormal operation, that is, abnormal increase or attenuation of brightness can be detected.

The alarm circuit 12 is activated by a pulse BEAM output from the comparator 11 when the detected voltage Vint is lower than the second reference voltage VC2, and outputs an abnormality signal ALM2 similar to the alarm circuit 10.

The second reference voltage VC2 at this time is set slightly lower than the detection voltage Vint when the beam BM successfully illuminates the device position of the photodiode 2.

Therefore, when the abnormality signal ALM2 is output, it can be seen that the beam BM was not deflected well or the amount of brightness was too small.

Further, at this time, the abnormality signal ALM1 is also outputted at the same time, but when only the abnormality signal ALM1 is outputted, it can be detected that the amount of bright light is excessive.

This simply means that the brightness control system and deflection system of the CRT are abnormal.

Note that these two alarm circuits are particularly useful in phototypesetting machines where the CRT is typically located in a dark room.

Although the embodiment has been described above in which the photodiode 2 is used in a phototypesetting device, the present invention is not limited thereto, and may be used in a display device or in which a photoelectric conversion element other than a photodiode is used. can do.

Further, the monomulti 9 is provided to compensate for the delay in the change in the detection voltage V int with respect to the correction voltage DAO, and therefore, other delay means can also be used.

In a more preferable case, as described above, the correction voltage DAO
Since the printing period is digitally held in a feedback loop, there is no fluctuation at all even over a long period of time compared to an analog type hold circuit, allowing highly accurate and highly stable correction.

As described above, according to the present invention, it is possible to detect variations in the brightness of a CRT and automatically make corrections to keep the brightness constant, which is an excellent effect.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the device position of photodiode 2;
The figure shows the photoamplifier 3, Figure 3 is a diagram illustrating the configuration according to the present invention, Figures 4 and 5 are time charts for explaining the operation, and Figure 6 is different from Figure 3. It is a figure showing an example. 1...CRT, 2...Photodiode, 3...Photoamplifier, 4...Video amplifier, 5, 11...Comparator, 6.
...Flip-flop, 7...Counter, 8...-D/A converter, 9...Mono multi, 100N...Video signal, VID・
...Brightness signal, DAO ...Correction voltage, S
AMP...Clock pulse, Vint...
...Detection signal, VCl...Reference voltage, DLSP
...Delayed pulse, COMP...
Comparison output, U/D...up/down signal, 10
, 12... Alarm circuit, ALMI. ALM2... Abnormal signal, C/B... Carry/borrow, VC2... Second reference voltage.

Claims (1)

[Scope of Claims] I A light-receiving element that detects the brightness of a CRT display device, means for comparing the output voltage from the light-receiving element with a reference voltage, and means for generating a correction voltage based on the result of the comparison means. and feedback means for adding the correction voltage from the correction voltage generation means to the brightness voltage, wherein the means for generating the correction voltage includes means for generating clock pulses, and feedback means for adding the correction voltage from the correction voltage generation means to the brightness voltage. It is characterized by having a counter that increases or decreases the count value based on the comparison result by the comparison means for each pulse, and a digital-to-analog converter that generates a correction voltage approximately proportional to the count value output from the counter. CRT brightness control method. 2. The CRT brightness control system according to claim 1, wherein abnormal increases and attenuations in brightness can be detected using pulses output as carry and borrow from the counter. 3. In addition to the brightness correction means, a comparator is provided for detecting that the output voltage from the light receiving element is smaller than a predetermined voltage,
3. The CRT brightness control system according to claim 1, wherein abnormalities in the CRT brightness control system and deflection are detected.