JPH10228207A5 - - Google Patents

Description

[Title of Invention] Image forming apparatus

[0001]
[Technical Field to which the Invention Belongs]
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that controls energization to apply thermal energy to a fixing roller that fixes a toner image on a recording material.

[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide an image forming apparatus that solves the above problems.

Claims (6)

An image forming apparatus comprising: a thermal energy generating means for converting electrical energy into thermal energy; a heat generation control means for controlling generation of the thermal energy by energizing the thermal energy generating means; and a fixing roller for melting a toner image formed on a rotating body based on an image signal by the thermal energy and fixing the toner image onto a recording material,
a variable impedance element having impedance characteristics according to temperature and disposed opposite the fixing roller;
a parameter generating means for generating an electrical parameter according to the impedance of the variable impedance element;
an electric current control means for comparing the electrical parameter with a predetermined reference value and controlling the electric current supplied by the heat generation control means in accordance with the comparison result; In claim 1,
the variable impedance element is a thermistor having a negative temperature coefficient;
the parameter generating means includes first and second constant impedance elements having different impedances, the variable impedance element, and switch means for selectively connecting either the first or second constant impedance element to the variable impedance element, and generates first and second electrical parameters according to the switching state of the switch means when power is supplied;
an electric current supply control means for supplying the electric current to the heat energy generating means by the heat generation control means based on the comparison results of the first and second comparison means; a first comparison means for comparing the first electrical parameter with a first reference value indicating an abnormality in the temperature of the fixing roller; a second comparison means for comparing the second electrical parameter with a second reference value indicating an abnormality in the variable impedance element; and an electric current supply stop means for controlling the heat generation control means to stop supplying electric current to the heat energy generating means based on the comparison results of the first and second comparison means. In claim 1 or 2,
the variable impedance element is disposed at a position where its temperature changes depending on the position where the recording material passes through the fixing roller,
An image forming apparatus characterized by comprising a reference value changing means for changing the first reference value in accordance with the dimension of the recording material in the axial direction of the fixing roller, and making the first reference value larger when the dimension is small than when the dimension is large. In claim 1 or 2,
the variable impedance element is disposed at a position where its temperature changes depending on the position where the recording material passes through the fixing roller,
An image forming apparatus characterized by comprising a reference value changing means for changing the first reference value in accordance with the number of times the recording material passes through the fixing roller within a predetermined time, and making the first reference value larger when the number of times the recording material passes through the fixing roller than when the number of times the recording material passes through the fixing roller is small. In any one of claims 2 to 4,
the parameter generating means has the variable impedance element and the switch means connected in series to the power supply, and the power supply is alternately supplied to both series circuits of the first or second constant impedance element and the variable impedance element, to generate a first detection voltage as the first electrical parameter corresponding to a first voltage division ratio based on the impedances of the variable impedance element and the first constant impedance element, and a second detection voltage as the second electrical parameter corresponding to a second voltage division ratio based on the impedances of the variable impedance element and the second constant impedance element;
an image forming apparatus characterized in that the power supply stopping means stops power supply to the thermal energy generating means when the first detected voltage is greater than the first reference value and when the second detected voltage is smaller than the second reference value. In any one of claims 2 to 4,
the parameter generating means has the variable impedance element and the switch means connected in parallel to the power supply, and the power supply is alternately supplied to both parallel circuits of the first or second constant impedance element and the variable impedance element, to generate a first detection current as the first electrical parameter corresponding to a first division ratio based on the impedances of the variable impedance element and the first constant impedance element, and a second detection current as the second electrical parameter corresponding to a second division ratio based on the impedances of the variable impedance element and the second constant impedance element;
an image forming apparatus characterized in that the power supply stopping means stops power supply to the thermal energy generating means when the first detected current is greater than the first reference value and when the second detected current is smaller than the second reference value.