JPS58198766A - Detecting circuit of life of exposure lamp - Google Patents

Abstract

PURPOSE:To detect the life of an exposure lamp, by detecting a current value required for making the quantity of light constant. CONSTITUTION:When the quantity of light of an exposure lamp 4 is larger than a prescribed value, the base potential of a transistor TR 205 is higher than a ordinary value, and therefore, a capacitor 206 is charged gradually, and a time tA required for the output of a pulse voltage from a timer circuit 208 is relatively longer. The pulse voltage of the timer circuit 208 is outputted to the secondary winding of a pulse transformer 213, and a triplepole AC controlling element 214 is turned on. From this time t1 or t4, power is supplied from a power source 1 to the exposure lamp 4 through the first choke coil 6, and a capacitor 5 is charged simultaneously. When the voltage of the power source 1 becomes 0V, the element 214 is turned off, and the discharge of the capacitor 5 is started. That is, while the element 214 is turned on, the lamp 4 is lit to perform dimming. In this device, the lamp current is detected by the voltage between both ends of the choke coil 6 and is displayed on a meter 12 to discriminate the degradation of the exposure lamp quantitatively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for detecting the lifespan of a fluorescent lamp for exposure, whose light intensity is kept constant by a dimmer.

2. Description of the Related Art Fluorescent lamps (hereinafter referred to as exposure lamps) used for exposure in document reading sections of copying machines, facsimile machines, and the like are often kept constant in luminous flux or light amount using a dimming device.

FIG. 1 shows an exposure apparatus for such electronic equipment. Dimmer device 2 connected to power source 1 with this device
The switch element in the light control device 2 controls the opening and closing of the power supply 1 according to the photovoltaic current of the photodiode 3, and adjusts the tube current of the exposure lamp 4 to keep the amount of light constant. The capacitor 5 is charged when the tube current is flowing from the current m1 to the exposure lamp 4 via the first choke coil 6, and is discharged when the power source 1 is cut off, and the second choke coil 7 is charged. It plays the role of allowing the tube current to flow through the tube.

Generally, the lifespan of a fluorescent lamp is defined by the decrease in light intensity with use. For example, a normal 40W fluorescent light is about io,
After ooo hours of use, the amount of light decreases to about 85% compared to the initial amount, and this may be defined as the end of its life.

However, in an exposure lamp using a light control device as described above, the light amount is kept constant, so even if changes in the amount of light are measured, the lifespan cannot be predicted. Special exposure lamps used in copying machines and the like have a relatively short lifespan compared to ordinary fluorescent lamps, and when this reaches the end, it becomes impossible to adjust the amount of light with a dimmer, and the amount of light suddenly decreases. This, of course, reduces the quality of the copy and the quality of the transmitted image.

For this reason, maintenance workers of electronic equipment have traditionally counted the usage time of exposure lamps and the number of copies, etc., and have used this as a standard to replace exposure lamps before their service life. However, the lifespan of an exposure lamp varies greatly depending on (1) usage conditions such as the number of lighting times, (2) usage environment such as temperature, and (2) slight differences in manufacturing process. Therefore, some items recovered during periodic inspections as being near the end of their service life,
While some items were sufficient to be replaced at or after the next periodic inspection, others reached the end of their service life between periodic inspections and needed urgent replacement.

In this way, the lifespan of the exposure lamp could not be determined accurately, which resulted in many uneconomical aspects.

The present invention was made in view of the above circumstances, and includes: 1)
The above purpose is achieved by focusing on the fact that a fluorescent lamp using a dimmer increases the tube current as it deteriorates, and by detecting the end of the life of the fluorescent lamp using a tube current measuring means. .

The present invention will be described in detail below with reference to Examples.

FIG. 2 shows an exposure apparatus equipped with an exposure lamp life detection circuit. When the exposure lamp 4 of this device is turned on, the photodiode 3 generates a photovoltaic current depending on the illuminance. This photovoltaic current is subjected to current-voltage exchange by the first operational amplifier 201 in the light control device 2 . A voltage proportional to the illuminance is input to the Φ terminal of the second operational amplifier 202. The e terminal of the second operational amplifier 202 has a power supply voltage v
A predetermined reference voltage obtained by dividing 1 by resistors 203 and 204 is applied. The second operational amplifier 202 outputs a zero level voltage when the voltage applied to the terminal (2) is lower than this reference voltage, and amplifies the voltage accordingly when it is higher than the reference voltage. The output voltage of the second operational amplifier 202 is determined by the current control transistor 205.
is applied to the base of A capacitor 206 is connected to the collector of the transistor 205, and the lower the voltage applied to the base, the more current is supplied to the capacitor 206 from the power supply line 207. The resulting voltage change on the capacitor 206 is supplied to the input terminal IN of the timer circuit 208.

Now, both ends of the commercial i oov power supply 1 are connected to rectifiers 209.
The full-wave rectified output is supplied to a light emitting diode 211 constituting a photocoupler. The photodiode 212 in the photocoupler is turned on while the light emitting diode 211 emits light. At this time, the potential appearing at its collector is kept at L (low) level.

Further, at the moment when the light emitting diode 211 does not emit light, it is turned off and the potential is changed to H (high) level. Therefore, as shown in FIG. 3, there is a zero cross point t where the voltage of the power supply 1 becomes zero. and at t3, the phototransistor 21
The potential on the collector side of No. 2 becomes H level. This signal change is supplied to the reset terminal R of the timer circuit 208, which is reset. That is, time t. and t3, the capacitor 206 is discharged, and the voltage applied to the input terminal IN is monitored starting from these times.

When the voltage applied to the input terminal IN reaches a predetermined level, the timer circuit 208 outputs a pulse voltage from the output terminal OUT at time t1 or t4.

Suppose now that the amount of light from the exposure lamp 4 is greater than a specified value.

In this case, the base potential of the transistor 205 becomes higher than the normal value, so the capacitor is charged with a gentle curve of 8A as shown in FIG. The time (to~t1 or t3~j+) is a relatively long time t^. On the other hand, when the light amount of the exposure lamp 4 is below the specified value, the capacitor is rapidly charged as shown by the curve 8B, and the above-mentioned time becomes a relatively short time t8.

When a pulse voltage is output from the timer circuit 208 at such timing, the pulse transformer 21 that inputs the pulse voltage
A pulse voltage is output to the secondary winding No. 3, and the three-pole AC control element 214 is turned on.

From this time t1 or t4, the first choke coil 6
Power source 1 is supplied to exposure lamp 4 through.

At this time, the capacitor 5 is also charged at the same time.

When the voltage of the power supply 1 becomes O■, the time t3 or t.

At this point, the AC control element 214 is turned off. At the same time, the capacitor 5 starts discharging.

That is, the time t when the AC control element 214 is next turned on.
4 or tl, the exposure lamp 4 is turned on by the capacitor 5. Thereafter, the exposure lamp is dimmed by the same circuit operation.

In such exposure control, times t1 to t3 and t
4 to 'to', a current (lamp current) flows through the first choke coil 6. FIG. 5 shows the temporal change in lamp current for the exposure lamp 4 of this embodiment. A straight line 9A shown by a one-dot chain line in the figure shows the case where the light is turned on and off at a rate of 5 times per minute while keeping the amount of light constant in an environment with a temperature of 20 degrees Celsius.

in this case. Initially, the lamp current is about 1 ampere or more, but increases to 2 ampere after about 200 hours of use. On the other hand, a straight line 9B indicated by a two-dot chain line indicates a case where the light is repeatedly turned on and off at a rate of twice per minute under the same environment.

In this case, the lamp current increases to the same value after about 300 hours of use. If the exposure lamp 4 reaches the end of its life when the lamp current slightly exceeds 2 amperes, detecting and displaying a lamp current of 2 amps or around this can indicate that the life is nearing the end. .

In this exposure apparatus, an amplifier 11 amplifies the change in potential that occurs across the first choke coil 6 due to the lamp current, and a meter 12 displays the amplified change.

Since the meter 12 has a scale, the maintenance work involves quantitatively determining the degree of deterioration of the exposure lamp 4 during periodic inspections, and replacing the exposure lamp with a new one if necessary.

Of course, a display means such as a display lamp or a buzzer may be used in place of the meter, and the indicator may be used to indicate when the life span has reached or is approaching. In addition to the choke coil, it is also possible to use a resistor, a current transformer, or the like as a means for detecting the lamp current.

As described above, according to the present invention, the lifespan of an exposure lamp using a dimming device can be accurately determined with a simple circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional exposure apparatus, and FIGS. 2 to 5 are for explaining an embodiment of the present invention.
Figure 2 is a circuit diagram of an exposure apparatus equipped with an exposure lamp life detection circuit, Figure 3 is a power supply waveform diagram to explain the timing of on/off operations of AC control elements, and Figure 4 is an exposure lamp circuit diagram. FIG. 5 is a characteristic diagram showing changes in capacitor voltage due to changes in the amount of light. FIG. 5 is a characteristic diagram showing changes in lamp current over time depending on the number of times the exposure lamp is lit. 2... Dimmer device 4... Exposure lamp (
Fluorescent lamp) 6...First choke coil 11...Amplifier 12...Meter Applicant: Fuji Xerox Co., Ltd. Agent Patent attorney Umeo Yamauchi 9- 337 8-

Claims (1)

[Claims] In an exposure apparatus equipped with a light control device that adjusts the tube current so as to keep the light intensity of the fluorescent lamp constant, the exposure apparatus includes a measuring means for measuring the tube current, and a tube current measured by the means until the tube current reaches a predetermined value. 1. A life detection circuit for an exposure lamp, comprising display means for indicating that a fluorescent lamp has reached or is approaching the end of its life when the life of the fluorescent lamp increases.