Image forming apparatus, image forming method, and computer program product

An image forming method implemented by an image forming apparatus that includes

• a transfer-sheet conveying member that rotates to convey a transfer sheet;
• a first image forming unit that directly transfers a single-color image or images in a plurality of colors onto the transfer sheet that is in a process of being conveyed;
• an intermediate transfer member that rotates while an image, which is to be transferred onto the transfer sheet that is in the process of being conveyed, is being transferred thereon;
• a second image forming unit that transfers, onto the intermediate transfer member, images in a plurality of colors except for a color of the image directly transferred by the first image forming unit;
• and
• a secondary transfer unit that transfers the images transferred onto the intermediate transfer member onto the transfer sheet that is in the process of being conveyed,
• the image forming method comprising:
• measuring, by a measuring unit, a surface velocity of each of the transfer-sheet conveying member and the intermediate transfer member for at least one cycle;
• and
• performing, by a control unit, phase matching control by accelerating or decelerating at least one of the transfer-sheet conveying member and the intermediate transfer member so as to match a phase of fluctuation of the measured surface velocity of the transfer-sheet conveying member and a phase of fluctuation of the measured surface velocity of the intermediate transfer member.

A computer program product comprising a computer usable medium having computer readable program codes embodied in the medium that when executed causes a computer to execute an image forming method for an image forming apparatus that includes

• a transfer-sheet conveying member that rotates to convey a transfer sheet;
• a first image forming unit that directly transfers a single-color image or images in a plurality of colors onto the transfer sheet that is in a process of being conveyed;
• an intermediate transfer member that rotates while an image, which is to be transferred onto the transfer sheet that is in the process of being conveyed, is being transferred thereon;
• a second image forming unit that transfers, onto the intermediate transfer member, images in a plurality of colors except for a color of the image directly transferred by the first image forming unit;
• and
• a secondary transfer unit that transfers the images transferred onto the intermediate transfer member onto the transfer sheet that is in the process of being conveyed,
• the program codes when executed causing a computer to execute:
• measuring a surface velocity of each of the transfer-sheet conveying member and the intermediate transfer member for at least one cycle;
• and
• performing phase matching control by accelerating or decelerating at least one of the transfer-sheet conveying member and the intermediate transfer member so as to match a phase of fluctuation of the measured surface velocity of the transfer-sheet conveying member and a phase of fluctuation of the measured surface velocity of the intermediate transfer member.