JP2008058725A5 - - Google Patents

Claims (9)

A heating means including a heating element that generates heat upon receiving power from a power source;
A first protection means for protecting the heating element in response to the temperature of the heating element exceeding a temperature threshold , wherein a predetermined response time elapses after the temperature of the heating element exceeds the temperature threshold; First protection means for protecting the heating element by restricting the supply of power to the heating element;
When the heating rate of the heating element is faster than a predetermined heating rate, the heating element is not supplied in time for the response time by the first protection means. And a second protection means for protecting the heating element by limiting for a predetermined time or more. The second protection means includes
Current detecting means for detecting a value of a current passed through the heating element;
Limiting means for limiting the supply of power to the heating element when the detected current value exceeds a first current threshold;
The supply restarting means for restarting the supply of electric power to the heating element when the detected current value is equal to or less than a second current threshold value smaller than the first current threshold value. The fixing device described. The second protection means includes
A comparing means for comparing the detected current value with a preset current threshold;
Setting means for setting the current threshold value compared by the comparison means to either the first current threshold value or the second current threshold value;
The setting means sets the current threshold used by the comparison means to the second current threshold when the current detection means detects a current exceeding the first current threshold, and detects a current equal to or lower than the second current threshold. The fixing device according to claim 2, wherein a current threshold value used by the comparison unit is set to the first current threshold value. The comparison means includes
Voltage value corresponding to the value of the current detected by said current detecting means exceeds a first voltage threshold value corresponding to the first current threshold outputs High, the voltage value is, the less the first voltage threshold value It includes a comparator that outputs Low,
The setting means includes
An energization control circuit for energizing the heating element when the output from the comparator becomes High, and interrupting the current to the heating element when the output from the comparator becomes Low;
When the output from the comparator becomes Low, the voltage threshold input to the comparator is switched from the first voltage threshold to the second voltage threshold corresponding to the second current threshold, and the output from the comparator is High. The fixing device according to claim 3, further comprising a switching circuit that switches from the second voltage threshold value to the first voltage threshold value. Voltage value corresponding to the value of the detected current by said current detecting means, outputs a Low exceeds a first voltage threshold value corresponding to the first current threshold, wherein the voltage value is, the less the first voltage threshold value A first comparator that outputs High;
Voltage value corresponding to the value of the current detected by said current detecting means exceeds a second voltage threshold value corresponding to the second current threshold outputs High, the voltage value is, the less the second voltage threshold value A second comparator that outputs Low,
A third comparator including a first terminal to which an output from the first comparator and an output from the third comparator are input; and a second terminal to which an output from the second comparator is input. 3 comparators,
When the first comparator becomes High, the output of the third comparator is switched to Low, and even if the first comparator is switched to Low again, the second comparator is Low. 4. The fixing device according to claim 3, wherein the current to the heating element is interrupted by continuously outputting Low until the mode is switched. 3. The first current threshold value is less than a current value that may damage the heating element, and is equal to or greater than a current value required for the fixing device to operate. 6. The fixing device according to any one of items 5 to 5. It said second current threshold, fixing according to any one of claims 2 to 6, characterized in that said first protection means is a prescribed value so as to operate prior to the heating element is damaged vessel. An image forming apparatus,
An image forming unit that forms an image using a developer;
Wherein the image formed by the image forming unit is heated and fixed to the recording material, the image forming apparatus characterized by comprising a fixing device according to any one of claims 1 to 7. A method of protecting a heating element included in a fixing device of an image forming apparatus,
A first protection step for protecting the heating element in response to the temperature of the heating element exceeding a temperature threshold, and when a predetermined response time elapses after the temperature of the heating element exceeds the temperature threshold; A first protection step for protecting the heating element by restricting the supply of power to the heating element;
When the heating rate of the heating element is faster than a predetermined heating rate, the heating element is not supplied in time for the response time in the first protection step. And a second protection step of protecting the heating element by limiting for a certain time or more.