JPS61159649A - Heat development controller - Google Patents

Abstract

PURPOSE:To hold the temperature of a heat development photosensitive material constant by providing a deviation detecting circuit for the deviation of the resistance value of the heat development photosensitive material from a specific resistance value and a control circuit for electric power supplied to a feed heating body according to the output of said circuit. CONSTITUTION:When the temperature of the feed heating body 1 is low and its resistance value Rt is smaller than a desired value, a phase control circuit 8 increases the firing angle of a triac 3 to increase the level of a current which flows through the feed heating body 1. When the temperature of the feed heating body 1 is high and its resistance value Rt is larger than the desired value, on the other hand, the firing angle of the triac 3 is decreased to decrease the current level. When an AC power source 2 is determined,a voltage V1 is constant, so when the resistance value Rt of the feed heating body 1 is held constant, a voltage V2 is also constant, and consequently the output voltage Vf of an operational amplifier 5 is held nearly as high as a reference voltage Vr.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a thermal development control device that is capable of heat-developing a photothermographic material provided with one current-carrying heat generating layer at a constant temperature.

(Technical Background of the Invention and Other Points) A photothermographic material is known in which a photosensitive layer is formed on the front surface and an energized heating layer is provided on the back surface. Such heat-developable photosensitive materials undergo heat development after image exposure! Itr+ is conveyed while being sandwiched between two sets of drive rollers and pressing rollers, and a voltage is applied to the energized heating element of the photothermographic material through these rollers, so that the energized heating element is heated by energization. It was heat developed by
Resistance value R of the current-carrying heating element provided on the surface of the photothermographic material
changes non-linearly with respect to the heat generation temperature T, as shown in FIG. When the ambient temperature changes even when a constant voltage is applied to the heating element, or when the heat capacity of the heat-developable photosensitive material changes due to water content, the heating temperature of the SgL photosensitive material must be kept constant. It was difficult to control this.

Therefore, in the past, no control was carried out to maintain the resistance of the heat-developable photosensitive material constant in a heat-developing apparatus.

(Object of the invention) This invention was made under the above circumstances,
The purpose of this invention is to maintain the temperature of the photothermographic material at a constant level by always controlling the resistance value of the photothermographic material at a constant level using the temperature characteristics of the current-carrying heating element of the photothermographic material. The purpose of the present invention is to provide thermal development control*i that allows for improved thermal development control*i.

(Summary of the Invention) The heat development control device of the present invention detects the resistance value of the energized heating element of the heat-developable photosensitive material and performs feedback control to detect changes in ambient temperature or change the resistance of the energized heating element of the heat-developable photosensitive material. The resistance value of each energized heating element is kept constant regardless of variations in heat capacity, thereby making it possible to keep the heating temperature for heat development constant and to always perform heat development under the same conditions.

(Embodiment of the Invention) FIG. 1 is a diagram showing an embodiment of a heat development control device of the invention.

The current-carrying heating element of the heat-developable photosensitive material loaded in the thermal development apparatus and to be thermally developed is connected to form a bridge circuit with resistors R1, R2, and field effect transistor 4. The current-carrying heating element l is a resistor. It has a value Rt, and the source-drain resistance of the field effect transistor 4 is Rf. And the field effect transistor 4 is the 3rd v! It has the characteristic of voltage VF - resistance Rf as shown in J, and when the bridge circuit is in a balanced state, R1@R2=Rt・
The revision is established. The alternating current power supply 2 supplies power to the bridge circuit mentioned above through a bidirectional three-terminal thyristor, that is, a switch 3, which is made conductive to the gate G by a gate trigger current. Therefore.

By adjusting the pulse phase of the pulse signal applied to the gate G of the triac 3, the firing angle or conduction angle of the triac 3 can be adjusted, and the amount of current flowing between the main electrodes of the triac 3 can be controlled. The voltage Vl at the connection point between the resistor R1 and the field effect transistor 4 and the voltage V2 at the connection point between the 1-current heating element l and the resistor R2 are each operationally amplified! 1
5 is entered. Also, operational amplification! I5. Reference voltage source 6 and comparison! I7 constitutes the deviation detection circuit 9.

The operational amplifier 315 operates linearly and differentially, and after determining the difference between the two input voltages vl and input voltage v2, amplifies the difference to provide an output voltage Vf. This output voltage Vf is applied to the gate G of the field effect transistor 4 and is also input to the comparison base 7. Compare! ! 7 compares the output voltage vf of the operational amplifier 7 and the reference voltage Vr from the reference voltage source 6, and outputs a positive or negative phase control voltage vb that determines the deviation of the output voltage vf with respect to the The output PS of the 0-phase control circuit 8, which is input to the 1-phase control circuit 8, is fed back to the gate G of the triac 3.

In such a configuration, the 1-phase control circuit 8 outputs an output signal PJ for controlling the firing phase angle of the triac 3 according to the positive or negative value and magnitude of the voltage vb inputted from the deviation detection circuit 9. , this is returned to gate G of Try 7 Fuku 3. In other words, in the one-phase US circuit 8, when the temperature of the current-carrying heating element l is low and its resistance value Rt is smaller than a desired value, the firing angle of the trier 7 is increased to increase the amount of current flowing through the current-carrying heating element l. increase.

Conversely, if the temperature of the energizing heating element 1 is high and its resistance (1Rt) is larger than the desired value, the firing angle of the triac 3 is made smaller and the amount of current is reduced.The voltage Vl remains constant once the AC power source 2 is determined. Therefore, if the resistance value Rt of the energized heating element l is held constant, the voltage v2 will also be held constant, and as a result, the output voltage vr of the operational amplifier 5 will also be held approximately equal to the reference voltage Vr. The heating temperature of the developing photosensitive material 1 is maintained at a temperature corresponding to the reference voltage Vr, and when changing the heating temperature, the value of the reference voltage Vr may be changed.

(Effects of the Invention) The heat development control device of the present invention always heats the photothermographic material at a constant temperature even if the ambient temperature of the photothermographic material changes or the water content of the photothermographic material changes. This has the effect of improving the thermal development image quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the heat development control device of the present invention, FIG. 2 is a diagram showing an example of the resistance-temperature characteristics of a heat-developable photosensitive material, and FIG. 3 is a diagram showing an example of the characteristics of a field effect transistor. FIG. ! ... Current-carrying heating element, 2 ... AC power supply, 3 ... Bidirectional 3-terminal sirisk, 4 ... Field effect transistor, 5 ... Y4 arithmetic amplifier, 6 ... Reference voltage source, 7・・・
- Comparison judge, 8... Phase control circuit, 9... Deviation detection circuit.

Claims (3)

[Claims] (1) a power supply that supplies power to the current-carrying heating element of the heat-developable photosensitive material provided with the current-carrying heat-generating layer; a deviation detection circuit that detects the deviation of the resistance value of the photothermographic material from a predetermined resistance value;
A thermal development control device comprising: a power control circuit that controls power supplied to the energizing heating element in accordance with the output of the deviation detection circuit. (2) A patent claim characterized in that the power control circuit comprises a bidirectional three-terminal thyristor connected in series to the power source, and a phase control circuit that controls the firing angle of the bidirectional three-terminal thyristor. The thermal development control device according to item 1. (3) an operational amplifier in which the deviation detection circuit takes and amplifies an output voltage difference of a bridge circuit including the energized heating element;
Claim 1, characterized in that it comprises a reference voltage source that provides a predetermined reference voltage, and a comparator that detects a deviation of the output voltage difference from the reference voltage and outputs it to the power control circuit. Thermal development control device.