Image formation apparatus and heater control method

1. An image formation apparatus comprising:

an image formation unit that forms an image on a recording medium by using a developer;

a fixation device including a first heater and a second heater, wherein the first heater generates heat with a first heater electric power and the second heater generates heat with a second heater electric power smaller than the first heater electric power;

a first switch comprising a first triac configured, based on a first control signal, to supply a power supply signal to the first heater;

a second switch comprising a second triac configured, based on a second control signal, to supply the power supply signal to the second heater; and

a heater controller that generates the first control signal and the second control signal to the first switch and the second switch to supply the power supply signal to the first heater and the second heater, wherein the first control signal comprises a first on-voltage that turns on the first triac and a first off-voltage that turns off the first triac, and the second control signal comprises a second on-voltage that turns on the second triac and a second off-voltage that turns off the second triac, wherein

upon a first operation to transition from a state where the first and second switches are off to a state where the first and second switches are on, the heater controller:

at a first timing, turns on the second switch from an off-state thereof;

at a second timing at which a first length of time equal to or longer than a predetermined time length has elapsed from the first timing, turns off the second switch from an on-state thereof;

at a third timing after the second timing, turns on the first switch from an off-state thereof; and

at a fourth timing at which a second length of time equal to or longer than the predetermined time length has elapsed from the third timing, turns on the second switch from the off-state thereof.

2. The image formation apparatus according to claim 1 , wherein

upon a second operation to transition from the state where the first and second switches are off to a state where the first switch is on and the second switch is off, the heater controller:

at a fifth timing, turns on the second switch from the off-state thereof;

at a sixth timing at which a third length of time equal to or longer than the predetermined time length has elapsed from the fifth timing, turns off the second switch from the on-state thereof; and

at a seventh timing after the sixth timing, turns on the first switch from the off-state thereof.

3. The image formation apparatus according to claim 1 , wherein

upon a third operation to transition from a state where the first switch is off and the second switches is on to the state where the first and second switches are on, the heater controller:

at an eighth timing, turns off the second switch from the on-state thereof;

at a ninth timing after the eighth timing, turns on the first switch from the off-state thereof; and

at a tenth timing at which a fourth length of time equal to or longer than the predetermined time length has elapsed from the ninth timing, turns on the second switch from the off-state thereof.

4. The image formation apparatus according to claim 1 , wherein

upon a fourth operation to transition from the state where the first and second switches are on to the state where the first and second switches are off, the heater controller:

at an eleventh timing, turns off the second switch from the on-state thereof;

at a twelfth timing at which a fifth length of time equal to or longer than the predetermined time length has elapsed from the eleventh timing, turns off the first switch from an on-state thereof;

at a thirteenth timing after the twelfth timing, turns on the second switch from the off-state thereof; and

at a fourteenth timing at which a sixth length of time equal to or longer than the predetermined time length has elapsed from the thirteenth timing, turns off the second switch from the on-state thereof.

5. The image formation apparatus according to claim 1 , wherein

the predetermined time length is equal to or longer than 30 milliseconds.

6. The image formation apparatus according to claim 1 , wherein

the third timing is a timing when not more than 30 milliseconds has been elapsed from the second timing.

7. The image formation apparatus according to claim 2 , wherein

the sixth timing is a timing when not more than 30 milliseconds has been elapsed from the fifth timing.

8. The image formation apparatus according to claim 3 , wherein

the ninth timing is a timing when not more than 30 milliseconds has been elapsed from the eighth timing.

9. The image formation apparatus according to claim 1 , wherein

the first triac is transitioned from the on-state to the off-state when a polarity of the power supply signal is inverted for the first time after the first control signal is transitioned from the first on-voltage to the first off-voltage, and

the second triac is transitioned from the on-state to the off-state when a polarity of the power supply signal is inverted for the first time after the second control signal is transitioned from the second on-voltage to the second off-voltage.

10. The image formation apparatus according to claim 9 , wherein

upon the first operation, the heater controller:

at a fifteenth timing before the second timing, changes the second control signal from the second on-voltage to the second off-voltage; and

at the third timing after a timing at which a predetermined stand-by time has elapsed from the fifteenth timing, changes the first control signal from the first off-voltage to the first on-voltage.

11. An image formation apparatus comprising:

an image formation unit that forms an image on a recording medium by using a developer;

a fixation device including a first heater and a second heater, wherein the first heater generates heat with a first heater electric power and the second heater generates heat with a second heater electric power smaller than the first heater electric power;

a first switch comprising a first triac configured, based on a first control signal, to supply a power supply signal to the first heater;

a second switch comprising a second triac configured, based on a second control signal, to supply the power supply signal to the second heater; and

a heater controller that generates the first control signal and the second control signal to the first switch and the second switch to supply the power supply signal to the first heater and the second heater, wherein the first control signal comprises a first on-voltage that turns on the first triac and a first off-voltage that turns off the first triac, and the second control signal comprises a second on-voltage that turns on the second triac and a second off-voltage that turns off the second triac, wherein

upon an operation to transition from a state where the first and second switches are on to a state where the first and second switches are off, the heater controller:

at a first timing, turns off the second switch from an on-state thereof;

at a second timing at which a first length of time equal to or longer than a predetermined time length has elapsed from the first timing, turns off the first switch from an on-state thereof;

at a third timing after the second timing, turns on the second switch from an off-state thereof; and

at a fourth timing at which a second length of time equal to or longer than the predetermined time length has elapsed from the third timing, turns off the second switch from the on-state thereof.

12. A heater control method comprising:

a first operation to transition from a state where first and second switches are off to a state where the first and second switches are on, wherein the first switch comprises a first triac which is configured, based on a first control signal, to supply a power supply signal to a first heater that generates heat with a first heater electric power and the second switch comprising a second triac which is configured, based on a second control signal, to supply the power supply signal to a second heater that generates heat with a second heater electric power smaller than the first heater electric power, and wherein the first control signal comprises a first on-voltage that turns on the first triac and a first off-voltage that turns off the first triac, and the second control signal comprises a second on-voltage that turns on the second triac and a second off-voltage that turns off the second triac, wherein

the first operation comprises:

at a first timing, turning on the second switch from an off-state thereof;

at a second timing at which a first length of time equal to or longer than a predetermined time length has elapsed from the first timing, turning off the second switch from an on-state thereof;

at a third timing after the second timing, turning on the first switch from an off-state thereof; and

at a fourth timing at which a second length of time equal to or longer than the predetermined time length has elapsed from the third timing, turning on the second switch from the off-state thereof.