JP2603645B2 - Light intensity control circuit for fluorescent light for document surface illumination - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document surface illumination device that controls a light amount for illuminating a document when a fluorescent lamp is used as a light source for optically illuminating the document. The present invention relates to a light quantity control circuit for a fluorescent lamp.

(Prior art)

Until now, incandescent lamps and the like have been widely used as light sources in electronic copiers, but incandescent lamps use a cooling fan or other complicated and expensive heat treatment circuit to process a large amount of heat emitted from the lamp. In order to avoid this problem, an electronic copying machine using a fluorescent lamp as a light source for illuminating a document surface has already been proposed.

By the way, when a fluorescent lamp is used as a light source for illuminating a document surface, the above-mentioned problem is solved, but the amount of light of the fluorescent lamp itself also fluctuates considerably due to a change in the tube surface temperature due to the influence of the ambient temperature. Therefore, in order to perform stable electronic copying, it is necessary to suppress the influence of light amount fluctuations due to a change in tube surface temperature.

Therefore, in the related art, a heating device is provided so that even when the ambient temperature fluctuates, the surface temperature of the fluorescent lamp is maintained at a constant temperature value so that the amount of light from the fluorescent lamp becomes constant. Was.

However, the stabilization of the amount of light from a fluorescent lamp by such a heating device has little substantial effect unless the power of the electronic copying machine itself is constantly turned on and the power is constantly supplied to the heating device. Conversely, if power is always supplied to the electronic copying machine, not only is there a problem that the power consumption is increased, but also from the viewpoint of safety of the electronic copying machine.

[Object of the invention]

The present invention has been made in view of the above problems, and controls the application time of the tube current in accordance with the tube surface temperature of a fluorescent lamp so that the tube surface temperature fluctuates with a change in ambient temperature. However, the purpose is to always keep the amount of light of the fluorescent lamp constant.

[Configuration of the invention]

In order to achieve such an object, the present invention has the following configuration.

That is, the present invention relates to a fluorescent lamp for document surface illumination, in which a fluorescent lamp provided for illuminating a copy original is driven by supplying a high-frequency tube current based on a lighting command to drive the fluorescent lamp. A temperature detection sensor that detects a surface temperature, a comparison unit that obtains a difference between a temperature detection value obtained by the temperature detection sensor and a reference value corresponding to a reference temperature, and a difference obtained by the comparison unit within a fixed period T. An output unit that outputs a signal having a pulse width corresponding to the above, and the high-frequency tube current is supplied to the fluorescent lamp at regular intervals T for a period determined by the pulse width output from the output unit. And a driving circuit.

[Action]

According to the above configuration, a lighting instruction of the fluorescent lamp is issued to illuminate the document. At this time, the tube surface temperature of the fluorescent lamp is detected by the temperature detection sensor. A difference between the detected temperature value and a reference value corresponding to the reference temperature is obtained by a comparing unit, and in accordance with the difference, a high-frequency driving operation of the fluorescent lamp is performed so that the light amount of the fluorescent lamp becomes a predetermined constant amount. Of the tube current is determined. Therefore, a signal having a pulse width corresponding to the difference obtained by the comparison unit within the fixed period T is output from the output unit. Thus, the high-frequency tube current is repeatedly supplied to the fluorescent lamp at regular intervals T for a period determined by the output pulse width. Therefore, the original can be illuminated with a fixed light amount regardless of the fluorescent lamp tube temperature at that time.

As a result, it is not only unnecessary to perform heating control of the tube surface temperature of the fluorescent lamp to a predetermined temperature, but also it is possible to reduce power consumption for heating. In particular, without delaying the start of document illumination when the fluorescent lamp tube temperature has not reached the predetermined temperature,
Driving can be started immediately by a lighting command.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic front sectional view of an electronic copying machine to which an embodiment of the present invention is applied, and FIG. 2 is a fluorescent lamp for illuminating a document surface incorporated in the electronic copying machine and a tube of the fluorescent lamp. FIG. 3 is a main part configuration diagram of an embodiment showing a control circuit for controlling a current to control the amount of light. FIG. 3 is a diagram showing a specific circuit of the output means of FIG. 2 together with a thermistor. a)
FIG. 4B is an output waveform diagram from the output means, and FIG. 4B is a current waveform diagram of the tube current of the fluorescent lamp.

In the copying machine 2 shown in FIG. 1, 4 is a photosensitive drum, 6 is a developing device, 8 is a transfer charger, 10 is a cleaner, 12 is a charger, 14 is a paper cassette, 16 is a timing roller, 18 is paper, Reference numeral 20 denotes a fixing roller, 22 denotes a document table, and 24 denotes a range array.

Reference numeral 25 denotes a reflecting mirror, 26 denotes a fluorescent lamp provided in the reflecting mirror 25 as a light source for illuminating a document surface, and 28 denotes a thermistor as a temperature detection sensor attached to the fluorescent lamp 26. As is well known, the fluorescent lamp 26 is turned on when a lighting drive command is output based on the start of a document copying operation, and illuminates the document on the document table 22.

FIG. 2 shows the fluorescent lamp 26 of FIG. 1, the thermistor 28 attached to the fluorescent lamp 26, and the tube current of the fluorescent lamp 26.
The fluorescent lamp 26 is controlled according to the detection output from the thermistor 28.
FIG. 3 is a diagram showing a control circuit 30 for controlling the amount of light of FIG. The thermistor 28 outputs a detection output corresponding to a temperature change of the tube surface of the fluorescent lamp 26. The control circuit 30 includes a thermistor 28
Output means 32 for outputting a pulse width modulation (PWM) signal having a duty ratio in accordance with the detection output from the CPU, and a driving circuit for driving the fluorescent lamp 26 by applying a high-frequency tube current to the fluorescent lamp 26 And an inverter 34 that controls the application time of the tube current in accordance with the duty ratio of the PWM output provided from the output means 32.

FIG. 3 is a specific circuit diagram of the thermistor 28 and the output means 32. The output means 32 is provided with a first
And a second series circuit 42 composed of a thermistor 28 and a resistor 40.
44 is connected to the common connection of the resistors 35 and 36 in the first series circuit 38, and the comparison voltage input 46 is connected to the common connection of the second thermistor 28 and the resistor 40 in the second series circuit 42. And a PWM circuit 48. The PWM circuit 48 constituting the output means uses the above-described reference voltage input to both the input units 44 and 46, that is, the reference value corresponding to the reference temperature, and the comparison voltage, that is, the voltage corresponding to the temperature detected by the thermistor 28. It is composed of a comparison unit for obtaining a voltage difference from a certain detection value and A / D converting the difference, and an output unit for outputting a PWM output from the terminal 50 according to the A / D conversion value. This PWM output corresponds to a change in the resistance value of the thermistor 28 corresponding to a change in the tube surface temperature of the fluorescent lamp 26.

Next, the operation will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4 (a) is a waveform diagram of the PWM output, and FIG. 4 (b) is a waveform diagram of the tube current of the fluorescent lamp 26.
As shown in FIG. 4A, the PWM output has a constant period T
PW occupying the period T within (for example, 1 millisecond)
The ratio (duty ratio) of the M output pulse changes according to the change in the resistance value of the thermistor 28. This PWM output is given to the inverter 34.

The inverter 34 drives the fluorescent lamp 26 by supplying a high-frequency (for example, 30 to 40 kHz) tube current as shown in FIG. 4B to the fluorescent lamp 26. The tube current is applied by the PWM output from the PWM circuit 48. Time is controlled.

In this embodiment, the fluorescent light is used to start the copying operation of the original.
For example, when the tube surface temperature of the lamp 26 rises, the light quantity of the fluorescent lamp 26 tends to increase, but in this case, the resistance value of the thermistor 28 decreases, and as a result, the duty ratio of the PWM output from the PWM circuit 48 in the output means 32 , The application time t of the tube current in the fixed period T from the inverter 34 to the fluorescent lamp 26 is shortened, and the light amount of the fluorescent lamp 26 is reduced. Therefore, by controlling the light quantity of the fluorescent lamp 26 to be always constant, the copying machine can perform a stable copying operation.

〔effect〕

As described above, according to the present invention, when there is a lighting instruction for a fluorescent lamp, the supply period of the high-frequency tube current according to the fluorescent lamp tube temperature at that time is controlled. The fluorescent lamp can be driven by the amount of light. for that reason,
Control such as keeping the temperature of the fluorescent lamp constant becomes unnecessary, and unnecessary power consumption at that time can be eliminated.

In addition, since the fluorescent lamp can be turned on immediately regardless of the temperature, the waiting time required for image formation can be eliminated.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings relate to an embodiment of the present invention, FIG. 1 is a schematic front view of a copying machine to which the embodiment is applied, FIG. 2 is a circuit diagram of a main part of the embodiment, FIG. Circuit diagram,
Fig. 4 (a) is a PWM output waveform diagram of the PWM circuit, Fig. 4 (b)
7 is a waveform diagram of a tube current for a fluorescent lamp. 26: fluorescent light, 28: thermistor (temperature detection sensor),
30 control circuit, 32 output means, 34 inverter.

Claims (1)

(57) [Claims] A fluorescent lamp for illuminating a document to be copied, wherein a fluorescent lamp for document surface illumination is driven by supplying a high-frequency tube current based on a lighting command to drive the fluorescent lamp. A temperature detecting sensor for detecting a temperature, a comparing unit for calculating a difference between a temperature detected by the temperature detecting sensor and a reference value corresponding to a reference temperature, and a constant period T
And an output unit that outputs a signal having a pulse width corresponding to the difference obtained by the comparison unit, and a pulse width output from the output unit at regular intervals T to the fluorescent lamp. And a drive circuit for supplying the high-frequency tube current during the period.