JPS6277759A - Heater control system for original reader - Google Patents

Abstract

PURPOSE:To stabilize the light emitting quantity by controlling a heater current in response to an output of a comparator of a reference value decided by a detection temperature of a fluorescent lamp heater and ambient temperature to make the fluorescent lamp tube wall temperature constant independently of the ambient temperature. CONSTITUTION:When power is applied, a microprocessor MPU 10 reads a value of an A/D converter 16 to obtain an optimum slice level to a read value from a table stored in a ROM of a MPU 10. Then the slice level obtained in this way is set to a D/A converter 17, the output is amplified and fed to a lower side input terminal of the comparator 8. Thus, even when the ambient temperature is in any sate, the heater is controlled under the optimum condition to keep the tube wall temperature of the fluorescent lamp constant independently of the ambient temperature.

Description

[Detailed Description of the Invention] [Summary] A fluorescent lamp as a light source, a heater that warms the fluorescent lamp, a detector that detects the temperature of the heater, and a difference between the temperature detected by the detector and a reference value. a comparator that outputs; a means for controlling the current flowing through the heater according to the output of the comparator;
Heater control in a document reading device comprising: a control device that enables a document reading operation when the output of the comparator changes from a predetermined value to another predetermined value; and means for changing the reference value according to ambient temperature. It is a method.

[Industrial application field]

The present invention relates to a heater control method for warming a fluorescent lamp serving as a light source of a document reading device.

[Prior art and problems]

FIG. 4 is a diagram showing a heater control method in a conventional document reading device. In FIG. 4, 1 is a thermistor, 2 to 7 are resistors, 8 is a comparator, 9 is an input board, 10 is a microprocessor, 11 is an inverter, 12 is a solid state relay (hereinafter referred to as SSR), 13 14 indicates an AC source, and 14 indicates a heater. The thermistor 1 has a negative resistance, and the resistance value decreases as the temperature increases. The voltage divided by thermistor 1 and resistor 2 and the voltage divided by resistors 3 and 4 are connected to comparator 8.
is input. When the former is smaller than the latter, the comparator 8 outputs a high level (logic "1") signal. resistance 5 and 6
is for giving a hysteresis characteristic to the output of the comparator 8. Microprocessor 10 can read the output of comparator 8 via an input port. Then, the microprocessor 10 enables the document reading device to operate when the output of a comparatively hot day changes from logic "1" to logic "0". Further, the output of the comparator 8 is sent to the SSR 2 via an inverter 11. 5SR12 turns on when the input signal is logic "0" and causes current to flow to the heater 14, and turns off when the input signal is logic "1" to cut off the current flowing to the heater 14.

FIG. 5 is a diagram showing the arrangement of a fluorescent lamp and a heater.

In FIG. 5, 15 indicates a fluorescent lamp. If the tube wall temperature of the fluorescent lamp is low, the sight of the fluorescent lamp will be reduced, so it is necessary to warm up the fluorescent lamp of the document reading device when the ambient temperature is low.

The heater 14 is for that purpose. The heater 14 is sheet-shaped, and its temperature is detected by the thermistor 1.

In the conventional device shown in FIG. 4, the voltage at the junction between resistors 3 and 4 is constant. However, as shown in FIG. 5, the thermistor 1 is attached to the heater 14;
Since the temperature of the fluorescent lamp 15 and the tube wall temperature of the fluorescent lamp 15 do not match, the fourth
In the conventional device shown in the figure, especially at low temperatures, the output of the comparator 8 changes from logic "1" to logic "0", indicating that the document can be read, but the tube wall temperature of the fluorescent lamp 15 is insufficient. [Objective of the Invention] The present invention is based on the above consideration, and aims to stabilize the light intensity of a fluorescent lamp used as a light source of a document reading device. The purpose is to optimally control the heater installed in order to

[Structure of the invention]

Therefore, the heater control method in the document reading device of the present invention includes a fluorescent lamp serving as a light source, a heater that warms the fluorescent lamp, a detector that detects the temperature of the heater, and a temperature detected by the detector. a comparator that outputs the difference between the temperature and a reference value; a means for controlling the current flowing through the heater according to the output of the comparator; a control device that enables read operations;
The invention is characterized by comprising means for changing the reference value according to the ambient temperature.

[Embodiments of the invention]

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In FIG. 1, 16 is an A/D converter, 17! t
A D/A converter and a buffer amplifier 18 are respectively shown. Note that the same reference numerals as in FIG. 4 indicate the same parts.

The A/D converter 16 converts an analog voltage value at the junction of the thermistor 1 and the resistor 2 into a digital voltage value. The D/A converter 17 converts the digital slice level output from the microprocessor 10 into an analog slice level.

Buffer amplifier 18 amplifies the output of D/A converter 17. The output of buffer amplifier 18 is at slice level Vr*f. slice level■,
.

, are supplied to the lower input terminal of the comparator 8.

FIG. 2 shows slice level setting processing by the microprocessor. When the power is turned on, the microprocessor 10 performs the following processing.

■ Read the value of A/D converter 16.

■ Bring the best slice level for the reading from the table. This table is microprocessor 1
0 ROM (not shown).

■ Set the obtained slice level in the D/A converter 17.

FIG. 3 is a diagram showing the relationship between the ambient temperature T and the slice level. The ambient temperature T1 can be considered to match the temperature measured by the resistance of the thermistor when the power is turned on. As can be seen from FIG. 3, the higher the temperature, the lower the optimum slicing level.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to optimally control the heater no matter what the ambient temperature is, and this makes it possible to control the tube wall temperature of the fluorescent lamp in relation to the ambient temperature. can be kept constant without

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing slice level setting processing by a microprocessor, and FIG. 3 is a diagram showing the relationship between the ambient temperature T and the slice level. FIG. 4 is a diagram showing a heater control system in a conventional document reading device, and FIG. 5 is a diagram showing the arrangement of a fluorescent lamp and a heater. 1...Thermistor, 2 to 7...Resistor, 8...
Comparator, 9... Input board, 10... Microprocessor, 11... Inverter, 12... Solid
State relay, 13... AC source, 14... Heater, 16... A/D converter, 17... D/A converter, 18... Hasophia amplifier.

Claims (1)

[Claims] A fluorescent lamp as a light source, a heater that warms the fluorescent lamp, a detector that detects the temperature of the heater, a comparator that outputs the difference between the temperature detected by the detector and a reference value, and a comparator that outputs the difference between the temperature detected by the detector and a reference value. means for controlling the current flowing through the heater according to the output;
A document comprising: a control device that enables a document reading operation when the output of the comparator changes from a predetermined value to another predetermined value; and means for changing the reference value according to ambient temperature. Reader heater control method.