Time measuring apparatus and image forming apparatus
The present invention teaches and claims an image forming apparatus using a time measuring apparatus to accurately measure the time in which the image forming apparatus stays in one or more modes. The image forming apparatus comprises a first CPU which outputs a pulse signal to a receiving second CPU. The second CPU calculates, by using the received pulse signal, a timer error of a second clock signal. The time measuring apparatus measures time in one or more modes based on the second clock signal and then corrects the measured time using the calculated timer error.
1. An image forming apparatus operating in at least two modes including a normal mode and a power-saving mode comprising:
a first CPU configured for controlling operations performed by the image forming apparatus in the normal mode and configured to suspend its operation in the power-saving mode, the first CPU including an oscillator for generating and outputting a first clock signal;
a second CPU connected to the first CPU and configured for controlling operations performed by the image forming apparatus in the power-saving mode and for controlling the amount of time the image forming apparatus operates in the power-saving mode, the second CPU including a timer for generating and outputting a second clock signal having a timer error larger than the timer error of the first clock signal, and the second CPU configured for measuring a time period based on the second clock signal; and
a detection unit configured to detect a remaining amount of paper;
wherein the second CPU has a receiving unit that receives the first clock signal and a correction unit that corrects the time period measured based on the second clock signal by using the first clock signal received by the receiving unit, and controls the detection unit so as to detect a remaining amount of paper in response to the second CPU measuring a predetermined time period in the power-saving mode.
2. The image forming apparatus according to claim 1 , wherein the image forming apparatus switches from the power-saving mode to the normal mode in response to an image forming job request and the first CPU controls the execution of the image forming job request.
3. The image forming apparatus according to claim 1 ,
wherein a predetermined time period within which image formation can be enabled is longer in the power-saving mode than in the normal mode; and
wherein the second CPU measures the time when the image forming apparatus is in the power-saving mode.
4. The image forming apparatus according to claim 1 , wherein a power consumed by the image forming apparatus operating in the normal mode is larger than a power consumed by the image forming apparatus operating in the power-saving mode.
5. The image forming apparatus according to claim 1 , wherein the oscillator is a crystal oscillator.
6. The image forming apparatus according to claim 1 , wherein the image forming apparatus switches from the power-saving mode to the normal mode based on the second CPU measuring a predetermined time period in the power-saving mode.
7. The image forming apparatus according to claim 1 , wherein the correction unit corrects the time period measured based on the second clock signal by using the first clock signal received by the receiving unit when the image forming apparatus is powered on.
8. The image forming apparatus according to claim 1 , wherein said second clock signal is generated without use of crystal oscillator.