Image forming apparatus which changes time period for masking detection of period of rotation synchronous signal

An image forming apparatus, which is configured to form an image on a recording medium at an image forming speed that is selectively set from a plurality of image forming speeds, the image forming apparatus comprising:

• a photosensitive member;
• a light source configured to emit a light beam;
• a rotary polygon mirror configured to deflect the light beam emitted from the light source so that the light beam scans a surface of the photosensitive member;
• a drive motor configured to rotate the rotary polygon mirror;
• a signal generation unit configured to generate a rotation synchronous signal including a pulse that is generated in a period corresponding to a rotation speed of the rotary polygon mirror;
• and
• a rotation control unit configured to control the rotation speed of the rotary polygon mirror, the rotation control unit being configured to selectively set, based on a set image forming speed, a rotation speed from a plurality of rotation speeds including a first rotation speed and a second rotation speed which is lower than the first rotation speed, to control the drive motor based on the period of the pulse included in the rotation synchronous signal so that the rotary polygon mirror is rotated at a set rotation speed,
• wherein the rotation control unit executes a masking processing of masking the rotation synchronous signal received in a time period from when a pulse is generated in the rotation synchronous signal to when a next pulse is generated in the rotation synchronous signal, and the rotation control unit does not execute a rotation control of the drive motor based on the rotation synchronous signal in the time period in which the masking processing is executed, and the rotation control unit releases the time period, in which the rotation synchronous signal is masked, in synchronization with generation of the next pulse, the masking processing being enabled in synchronization with generation of the pulse,
• wherein a time period in which a first masking processing set with respect to the first rotation speed is enabled is shorter than a time period in which a second masking processing set with respect to the second rotation speed is enabled, and
• wherein, in a sequence of switching the rotation speed of the rotary polygon mirror from the first rotation speed to the second rotation speed without stopping the rotary polygon mirror, the rotation control unit is prevented from executing the masking processing from when reduction of the rotation speed of the rotary polygon mirror is started to when the rotation speed of the rotary polygon mirror reaches the second rotation speed.

An image forming apparatus, comprising:

• a photosensitive member;
• a light source configured to emit a light beam;
• a rotary polygon mirror configured to deflect the light beam emitted from the light source so that the light beam scans a surface of the photosensitive member;
• a drive motor configured to rotate the rotary polygon mirror;
• a signal generation unit configured to generate a rotation synchronous signal including a pulse that is generated in a period corresponding to a rotation speed of the rotary polygon mirror, wherein mask processing is executed on the rotation synchronous signal so as to mask the rotational synchronous signal in a period of the rotation synchronous signal;
• and
• a rotation control unit configured to receive the rotation synchronous signal, configured to control the rotation speed based on the rotation synchronous signal, and configured to change a mask processing time period,
• wherein, in a case in which the rotation control unit executes a deceleration of the rotation speed, the rotation control unit changes the mask processing time period after the deceleration of the rotation speed is started.