JPS6047720B2 - How to avoid scanning discharge lamp electrophoresis - Google Patents

Description

TECHNICAL FIELD The present invention relates to image transmission techniques, such as original scanning techniques using discharge lamps operated with direct current.

Basic level of technology In image transmission devices, copying devices, facsimile devices, reading devices, etc., linear illumination of the original using arc tubes is often used for scanning.

In order to avoid undesirable brightness fluctuations, the lamp is advantageously operated with direct current. The filling of this lamp consists of a heavy gas, generally mercury vapor, which is excited by the discharge and emits radiation primarily in the ultraviolet range.

This light beam strikes a coating applied to the inner wall of the discharge vessel.
The coating has the property of emitting light in the visible region when irradiated with ultraviolet rays. When such a discharge lamp is operated with direct current, mercury atoms ionized by impact ionization move toward the cathode by so-called electrophoresis and remain there, so that after a certain operating time, the arc tube becomes A phenomenon occurs in which mercury vapor around the anode decreases.
As a result, an unexcited mercury field around the anode
The number of children, and thus the probability of impact ionization, decreases. Furthermore, the UV radiation generated therein and thus the excitation of the luminescent substance is reduced. In this case, the anode side end of the arc tube becomes dark, and the requirement of uniformly illuminating the image line for scanning cannot be met. The above-mentioned disturbances are time-dependent and occur suddenly after a certain operating period of constant brightness. The prevention of this phenomenon by alternating the polarity has been known for a long time and is also applied in the manufacture of lamps (for example in 1-luminescent lamps and their uses [1j.ucht
st0ff1ampenundihreA11wend
Ung]! Dr. W. Elenbaasl Phillips ◆Technicsier Bibliotheque, 1962, pages 111-162.

) Manually performing this polarity switching by an operator after a certain period of time is not suitable for image scanning devices.

This is because operators often forget this operation. Furthermore, a simple polarity reversal method using a time switch cannot be used in image scanning devices. This is because there is a high probability that the switching will take place during the image transmission, which means that during the switching (even for a very short time) the lamp may go out completely and disrupt the image transmission. . Furthermore, the number of transmissions while the lamp is in use is extremely large, and the transmission time each time varies greatly.
Even if, in principle, polarity reversal always takes place before image transmission, the entire life of the lamp is not necessarily divided equally between the two polarities. Therefore, only one polarity is likely to be used frequently, resulting in the above-mentioned phenomenon. DISCLOSURE OF THE INVENTION The basic problem of the present invention is to automatically reverse the polarity before the brightness distribution along the tube becomes non-uniform due to electrophoresis, and to reverse the polarity during image transmission. Providing a method of switching polarity such that reversal does not occur and therefore, over the life of the lamp, each hour of operation in one polarity is equal to the amount of time it is operated in the other polarity. It is to be.

The present invention solves the above problems as follows.

That is, the lamp lighting time is measured and stored in the first polarity during the first image transmission. Before the second image transmission begins, the polarity is reversed and the lamp lighting time at the second polarity is similarly measured and stored. The difference between the first and second lighting times is then formed and stored. In this way, whenever the third and subsequent image transmissions are performed, a carryover value of the total lighting time is formed, taking into account the polarity. This carry-over time is compared with the lamp lighting time of the last transmission, and only when the last lighting time is longer than the stored carry-over time, the polarity of the voltage applied to the lamp is changed before the next image transmission. Invert.

[Brief explanation of the drawing]

Next, the present invention will be explained in detail with reference to FIGS. 1 and 2. FIG. 1 is a principle diagram of an embodiment of the present invention, and FIG. 2 is a float chart for explaining the present invention. A preferred embodiment of the invention assumes that the device is connected and ready for image transmission. When the start key 1 is operated, the small computer 2 (for example, Intel's 8748) starts transmission. The small computer 2 is used for controlling mechanical movements, activating scanning electronic equipment, etc., and also lights up a light-emitting lamp 3 that illuminates the original image in a line when photoelectric scanning is performed. 3
is switched on via a transistor 5 by a corresponding output signal present at the output 4 of the microcomputer 2.
The light emitting lamp 3 is operated using direct current for the reasons mentioned above. Illumination takes place in the usual manner by means of a starter 6 and a choke 7 connected upstream. When operating with direct current, the choke 7 cannot act as a sufficiently large preresistance, so a current limiting resistor 8 is inserted in the current path. The flowchart in FIG. 2 makes it clear how the small computer 2 functions. The lamp 3 is turned on by the first control of the start key 1, and counting processing begins in the small computer. The counting process stops at the end of image transmission. At this time, the count value becomes the reference for the lighting time of the lamp 3, and is stored in the small computer 2. When the start key 1 is controlled for the next transmission, after the polarity of the operating voltage of the lamp 3 is reversed, it is stored again in the small computer 2. Counting process begins. The counting process stops when the current transmission ends, and is stored in the same way as the previous one. Thereafter, the small computer 2 calculates the difference in the lighting times during the two scans and stores the carryover value of the detected time difference. When the third image transmission starts, a new counting process starts and ends when the third image transmission ends. Thereafter, the small computer 2 compares this final lighting time with the stored time difference and outputs the output side 9 and the driver stage 10.
A criterion for determining whether or not the polarity reversal relay 11 should be energized is obtained through the . The polarity reversal relay reverses the polarity of the lamp voltage whenever the final lighting time is longer than the stored lighting time difference of previous scans. This operation is repeated whenever a subsequent image transmission is performed, and the final lighting time is always compared with the stored carryover value of all previous lighting times, taking into account the polarity.
Polarity reversal is performed via relay electrodes 12,13.
Although the individual transmission times are very different, the method described above allows the two polarities to equally divide the total lamp life and thus extend the lamp life under given operating conditions. It is clear that a corresponding circuit can also be constructed from conventional counting and storage units.

Claims (1)

[Claims] 1. In a method of avoiding electrophoresis of a scanning discharge lamp operated with direct current, which irradiates parts of the original image in a non-point manner, the lighting time of the lamp in the first polarity during the first image transmission is measured. , memorize and invert the polarity before the second image transmission begins, measure and store the bulb lighting time in the same way with the second polarity, and form the difference between the first and second lighting times. In this way, for all subsequent image transmissions, a carry-over value for the total lighting time is formed taking into account the polarity, and this carry-over time is used as the lamp lighting time for the last image transmission. By comparison, a scanning discharge operated with direct current is characterized in that the polarity of the lamp voltage is reversed before the start of the next transmission only when this final lighting time is longer than the stored carryover time. How to avoid lamp electrophoresis.