Image forming apparatus and image forming method

1 . An image forming apparatus comprising:

a photosensitive drum that rotates about a rotation axis direction;

an exposure head including a plurality of light-emitting units that emit light on a basis of an image data signal for exposure of the photosensitive drum and are arranged in a number of rows n in a direction that intersects the rotation axis direction; and

a control unit that controls a rotational speed of the photosensitive drum and light emission of the light-emitting units,

wherein the control unit

can execute a first mode in which the photosensitive drum is rotated at a first rotational speed and a second mode in which the photosensitive drum is rotated at a second rotational speed that is slower than the first rotational speed and that is a/b times (a and b are integers) of the first rotational speed, and

in order to perform exposure for forming an image of one line along the rotation axis direction on a sheet in the second mode,

controls a cycle of a light emission timing of the light-emitting units at a cycle of b/a times of a cycle of the first mode,

sets c/d (c and d are integers) so that n×(c/d) is an integer and controls the light-emitting units to cause, from among the number of rows n, the light-emitting units of a number of rows (n×(c/d)) to emit light and to cause the light-emitting units of a number of rows (n×((d−c)/d)) to not emit light, and

sets a drive current of the light-emitting units so that an amount of light of the plurality of light-emitting units matches (a×d)/(b×c) times of an amount of light in the first mode.

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

the control unit sets c/d to a value closest to a/b and equal to or greater than a/b times from among values that make n×(c/d) an integer.

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

the control unit sets c/d to a value closest to a/b and equal to or less than a/b times from among values that make n×(c/d) an integer.

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

the control unit sets c/d to a value closest to a/b from among values that make n×(c/d) an integer.

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

the control unit

sets a drive current of the plurality of light-emitting units in the first mode to a value that is not a maximum value or a minimum value in a range between the maximum value and the minimum value, and

sets the drive current in the second mode in a range between the maximum value and the minimum value.

6 . An image forming apparatus comprising:

a photosensitive drum that rotates about a rotation axis direction;

an exposure head including a plurality of light-emitting units that emit light on a basis of an image data signal for exposure of the photosensitive drum and are arranged in the rotation axis direction and in a plurality of rows in a direction that intersects the rotation axis direction; and

a control unit that controls a rotational speed of the photosensitive drum and light emission of the light-emitting units,

wherein the control unit

can execute a first mode in which the photosensitive drum is rotated at a first rotational speed and a second mode in which the photosensitive drum is rotated at a second rotational speed that is slower than the first rotational speed and that is a/b times (a and b are integers) of the first rotational speed, and

in order to perform exposure for forming an image of one line along the rotation axis direction on a sheet in the second mode,

in a case where a minimum value of an amount of time for enabling transmission of an image data signal of one line is Tmin, calculates a division coefficient e corresponding to an integer that satisfies b/(a×e)≥Tmin and controls a cycle of light emission timing of the light-emitting units at a cycle of b/(a×e) times of a cycle in the first mode,

controls the plurality of light-emitting units so that, of e times an image data signal of one line is being transmitted, the plurality of light-emitting units are caused to emit light f times and the plurality of light-emitting units are caused to not emit light (e−f) times, and

sets a drive current of the light-emitting units so that an amount of light of the plurality of light-emitting units matches (a×e)/(b×f) times of an amount of light in the first mode.

7 . The image forming apparatus according to claim 6 , wherein

the control unit sets the f to an integer closest to a value of (a×e)/b and equal to or greater than a value of (a×e)/b.

8 . The image forming apparatus according to claim 6 , wherein

the control unit sets the f to an integer closest to a value of (a×e)/b and equal to or less than a value of (a×e)/b.

9 . The image forming apparatus according to claim 6 , wherein

the control unit sets the f to an integer closest to a value of (a×e)/b.

10 . The image forming apparatus according to claim 6 , wherein

the control unit

sets a drive current of the plurality of light-emitting units in the first mode to a value that is not a maximum value or a minimum value in a range between the maximum value and the minimum value, and

sets the drive current in the second mode in a range between the maximum value and the minimum value.

11 . An image forming apparatus comprising:

a photosensitive drum that rotates about a rotation axis direction;

an exposure head including a plurality of light-emitting units that emit light on a basis of an image data signal for exposure of the photosensitive drum and are arranged in the rotation axis direction and in a number of rows n in a direction that intersects the rotation axis direction; and

a control unit that controls a rotational speed of the photosensitive drum and light emission of the light-emitting units,

wherein the control unit

can execute a first mode in which the photosensitive drum is rotated at a first rotational speed and a second mode in which the photosensitive drum is rotated at a second rotational speed that is slower than the first rotational speed and that is a/b times (a and b are integers) of the first rotational speed, and

in order to perform exposure for forming an image of one line along the rotation axis direction on a sheet in the second mode,

in a case where a minimum value of an amount of time for enabling transmission of an image data signal of one line is Tmin, calculates a division coefficient e corresponding to an integer that satisfies b/(a×e)≥Tmin and controls a cycle of light emission timing of the light-emitting units at a cycle of b/(a×e) times of a cycle in the first mode,

controls the plurality of light-emitting units so that, of e times an image data signal of one line is being transmitted, the plurality of light-emitting units are caused to emit light f times and the plurality of light-emitting units are caused to not emit light (e−f) times,

sets a multiplying factor g equal to or less than 1 so that n×g is an integer and controls the light-emitting units to cause, from among the number of rows n, the light-emitting units of a number of rows (n×g) to emit light and to cause the light-emitting units of a number of rows (n×(1−g)) to not emit light, and

sets a drive current of the light-emitting units so that an amount of light of the plurality of light-emitting units matches (a×e)/(b×f×g) times of an amount of light in the first mode.

12 . The image forming apparatus according to claim 11 , wherein

the control unit sets the division coefficient e so that a light emission frequency of the light-emitting units in the second mode is different from a prohibited frequency band prepared in advance.

13 . The image forming apparatus according to claim 11 , wherein

the control unit sets a combination of the g and the f so that a value of (b×f×g)/(a×e) is closest to 1.

14 . The image forming apparatus according to claim 11 , wherein

the control unit

sets a drive current of the plurality of light-emitting units in the first mode to a value that is not a maximum value or a minimum value in a range between the maximum value and the minimum value, and

sets the drive current in the second mode in a range between the maximum value and the minimum value.

15 . An image forming method using an image forming apparatus provided with:

a photosensitive drum that rotates about a rotation axis direction;

an exposure head including a plurality of light-emitting units that emit light on a basis of an image data signal for exposure of the photosensitive drum and are arranged in a number of rows n in a direction that intersects the rotation axis direction; and

a control unit that controls a rotational speed of the photosensitive drum and light emission of the light-emitting units,

wherein the control unit

can execute a first mode in which the photosensitive drum is rotated at a first rotational speed and a second mode in which the photosensitive drum is rotated at a second rotational speed that is slower than the first rotational speed and that is a/b times (a and b are integers) of the first rotational speed, and

in order to perform exposure for forming an image of one line along the rotation axis direction on a sheet in the second mode,

controls a cycle of a light emission timing of the light-emitting units at a cycle of b/a times of a cycle of the first mode,

sets c/d (c and d are integers) so that n×(c/d) is an integer and controls the light-emitting units to cause, from among the number of rows n, the light-emitting units of a number of rows (n×(c/d)) to emit light and to cause the light-emitting units of a number of rows (n× ((d−c)/d)) to not emit light, and

sets a drive current of the light-emitting units so that an amount of light of the plurality of light-emitting units matches (a×d)/(b×c) of an amount of light in the first mode.

16 . An image forming method using an image forming apparatus provided with:

a photosensitive drum that rotates about a rotation axis direction;

an exposure head including a plurality of light-emitting units that emit light on a basis of an image data signal for exposure of the photosensitive drum and are arranged in the rotation axis direction and in a plurality of rows in a direction that intersects the rotation axis direction; and

a control unit that controls a rotational speed of the photosensitive drum and light emission of the light-emitting units,

wherein the control unit

can execute a first mode in which the photosensitive drum is rotated at a first rotational speed and a second mode in which the photosensitive drum is rotated at a second rotational speed that is slower than the first rotational speed and that is a/b times (a and b are integers) of the first rotational speed, and

in order to perform exposure for forming an image of one line along the rotation axis direction on a sheet in the second mode,

in a case where a minimum value of an amount of time for enabling transmission of an image data signal of one line is Tmin, calculates a division coefficient e corresponding to an integer that satisfies b/(a×e)≥Tmin and controls a cycle of light emission timing of the light-emitting units at a cycle of b/(a×e) times of a cycle in the first mode,

controls the plurality of light-emitting units so that, of e times an image data signal of one line is being transmitted, the plurality of light-emitting units are caused to emit light f times and the plurality of light-emitting units are caused to not emit light (e−f) times, and

sets a drive current of the light-emitting units so that an amount of light of the plurality of light-emitting units matches (a×e)/(b×f) times of an amount of light in the first mode.

17 . An image forming method using an image forming apparatus provided with:

a photosensitive drum that rotates about a rotation axis direction;

an exposure head including a plurality of light-emitting units that emit light on a basis of an image data signal for exposure of the photosensitive drum and are arranged in the rotation axis direction and in a number of rows n in a direction that intersects the rotation axis direction; and

a control unit that controls a rotational speed of the photosensitive drum and light emission of the light-emitting units,

wherein the control unit

can execute a first mode in which the photosensitive drum is rotated at a first rotational speed and a second mode in which the photosensitive drum is rotated at a second rotational speed that is slower than the first rotational speed and that is a/b times (a and b are integers) of the first rotational speed, and

in order to perform exposure for forming an image of one line along the rotation axis direction on a sheet in the second mode,

in a case where a minimum value of an amount of time for enabling transmission of an image data signal of one line is Tmin, calculates a division coefficient e corresponding to an integer that satisfies b/(a×e)≥Tmin and controls a cycle of light emission timing of the light-emitting units at a cycle of b/(a×e) times of a cycle in the first mode,

controls the plurality of light-emitting units so that, e times of an image data signal of one line is being transmitted, the plurality of light-emitting units are caused to emit light f times and the plurality of light-emitting units are caused to not emit light (e−f) times,

sets a multiplying factor g equal to or less than 1 so that n×g is an integer and controls the light-emitting units to cause, from among the number of rows n, the light-emitting units of a number of rows (n×g) to emit light and to cause the light-emitting units of a number of rows (n×(1−g)) to not emit light, and

sets a drive current of the light-emitting units so that an amount of light of the plurality of light-emitting units matches (a×e)/(b×f×g) times of an amount of light in the first mode.