JPS6277760A - Heater control system in original reader - Google Patents

Abstract

PURPOSE:To keep tube wall temperature constant by controlling a heater current in response to an output of a comparator to which a reference value is inputted depending on the heater detection temperature and ambient temperature to control the heater under the optimum condition at any ambient temperature. CONSTITUTION:When power is applied, a microprocessor 10 turns on transistors (TRs) Tr1, Tr2 to monitor the output of a comparator 8 thereby obtaining a time (t) changed from logical 1 to 0. When the time (t) is a prescribed time t1 or below, it is recognized that the ambient temperature is high to turn on the Tr1, Tr2 and to bring the original reader to the readable state. When the temperature (t) is larger than the temperature t1 and less than a prescribed temperature t2, it is recognized that the ambient temperature is room temperature, only the Tr1 is turned on and the output of the comparator 8 is changed from logical 1 to 0 again to bring the state into the read enable state. When the temperature (t) is larger than the temperature t2, it is recognized that the ambient temperature is low, both the Tr1, Tr2 are turned off, the output of the comparator 8 is changed from logical 1 to 0 again to bring the state into the read enable state.

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 temperature detected by the detector and a reference value. a comparator that outputs the difference between the two; and means for controlling the current flowing through the converter according to the output of the comparator;
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 an ambient temperature detection device that detects whether the ambient temperature is low, room temperature, or high temperature. and means for changing the reference value according to the temperature detected by the ambient temperature detecting means.

[Industrial application field]

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

[Conventional technology and problems]

FIG. 5 is a diagram showing a heater control method in a conventional document reading device. In FIG. 5, ■ is a thermistor, 2 to 7 are resistors, 8 is a comparator, 9 is a human powered boat, 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, when the output of the comparator 8 changes from logic "1" to logic "0", the microprocessor 1O puts the document reading device into a readable state. Further, the output of the comparator 8 is sent to the 5SR 12 via the inverter 11.

5SR12 is turned on when the input signal is logic "0" to flow current to the heater 14, and is turned off when the input signal is logic "1" to cut off the current flowing to the heater 14.

FIG. 6 is a diagram showing the arrangement of a fluorescent lamp and a heater.

In FIG. 6, 15 indicates a fluorescent lamp. If the tube wall temperature of the fluorescent lamp is low, the amount of light from the fluorescent lamp decreases, 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. 5, the voltage at the junction between resistors 3 and 4 is constant. However, as shown in FIG. 6, 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 fifth
In the conventional device shown in the figure, especially at low temperatures, the comparator 8
Even if the output of the fluorescent lamp 15 changes from logic "1" to logic "0" to indicate that the document can be read, the temperature of the tube wall of the fluorescent lamp 15 has not reached a sufficiently stable state, and the amount of light may be insufficient.

[Purpose of the invention]

The present invention is based on the above consideration, and an object of the present invention is to optimally control a heater installed in order to stabilize the amount of light from a fluorescent lamp used as a light source of a document reading device.

[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;
It is characterized by comprising an ambient temperature detecting means for checking whether the ambient temperature belongs to a low temperature, a normal temperature, or a high temperature, and a means for changing the reference value according to the temperature detected by the ambient temperature detecting means. It is something.

[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 Figure 1,
4-1 and 4-2 are resistors, 16 is the output port, 7'rl
and Tr indicate transistors, respectively. In addition,
The same reference numerals as in FIG. 5 indicate the same parts.

FIG. 2 is a diagram showing the relationship between the temperature of the heater, that is, the temperature detected by the thermistor 1, and the tube wall temperature of the fluorescent lamp. When the ambient temperature is high, the difference between the temperature detected by the thermistor and the tube wall temperature of the fluorescent lamp is small; when the ambient temperature is room temperature, the difference between the temperature detected by the thermistor and the tube wall temperature of the fluorescent lamp is small. is moderate, and when the ambient temperature is low, the difference between the temperature detected by the thermistor and the tube wall temperature of the fluorescent lamp is large.

FIG. 3 is a diagram showing the rise of the heater temperature and the tube wall temperature of the fluorescent lamp under the recognized ambient temperature. For example, when the ambient temperature is recognized to be low, the low temperature reference voltage is applied to the lower input of the comparator 8, the heater temperature rises like curve HL, and the tube wall temperature of the fluorescent lamp increases. rises like curve TL. In addition, when the ambient temperature is recognized as normal temperature, the reference voltage for normal temperature is applied to the lower side of the comparator 8, the temperature of the heater rises like curve HM, and the temperature of the tube wall of the fluorescent lamp increases. is the curve T. -L rises like this. Furthermore, if the ambient temperature is recognized to be high,
A high-temperature reference voltage is applied to the lower input of the comparator 8, the temperature of the heater rises as shown by curve H□, and the tube wall temperature of the fluorescent lamp rises as shown by curve TH.

FIG. 4 is a flowchart showing the ambient temperature recognition process performed by the microprocessor 10. When the microprocessor 10 is powered on, it performs the following processing.

(2) Turn on both transistors Tr and 'l'rz.

■ Monitor the output of comparator 8.

(2) Check whether the output of the comparator 8 has changed from logic "1" to logic "0-1". If YES, perform the process (2); if NO, return to the process (2).

■ Find the time t (based on when the power is turned on) when the logic changes from logic "1" to logic "0".

(2) If t is less than or equal to t1, it is recognized that the ambient temperature is high, and the transistors Tr and Tr2 are kept in the on state, so that the document reading device is immediately ready for reading.

t is 1. If the temperature is greater than t2 and less than t2, it recognizes that the ambient temperature is room temperature, turns on only the transistor Tr, and waits for the output of the comparator 8 to change from logic "1" to logic "0" again. When the change occurs, the document reading device is set to a readable state.

If t is greater than t2, it is recognized that the ambient temperature is low, transistors 'l'rl and Tr are both turned off, and the output of the comparator 8 changes from logic rlJ to logic "0" again. Wait until it changes, and then set the document reading device to a readable state.

〔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 the relationship between the heater temperature and the tube wall temperature of a fluorescent lamp, and FIG. 3 is a diagram showing the relationship between the heater temperature and the tube wall temperature under the recognized ambient temperature. FIG. 4 is a flowchart showing the ambient temperature recognition process performed by the microprocessor 10; FIG. 5 is a diagram showing the heater control force formula in a conventional document reading device; FIG. The figure shows the arrangement of fluorescent lights and heaters. 1...Thermistor, 2 to 7...Resistor, 8...
Comparator, 9... Input port, 10... Microprocessor, 11... Inverter, 12... Solid
State relay, 13... AC source, 14... Heater, 15... Fluorescent lamp, 16... Output boat, 4-1
and 4-2...resistor, Tr, and Tr2...transistor.

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 comparison means for controlling the current flowing through the heater according to the output of the heater;
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 an ambient temperature detection device that detects whether the ambient temperature is low, room temperature, or high temperature. , means for changing the reference value according to the temperature detected by the ambient temperature detecting means.