Patent Description:
A laser printer typically includes an optical scanning unit for exposing a photosensitive member. The optical scanning unit emits laser based on image data. The laser is reflected by a rotating polygon mirror, and reflected laser light is then transmitted through a scanning lens. Transmitted light irradiates a photosensitive drum to expose the photosensitive drum. As the polygon mirror rotates, a laser spot formed on the surface of the photosensitive drum continuously moves to achieve scanning, thereby forming a latent image on the photosensitive member.

An existing scanning lens may have F-θ characteristics. The lens with F-θ characteristics may cause the laser spot to move on the surface of the photosensitive member at a uniform linear velocity when the polygon mirror rotates at a uniform angular velocity. The scanning lens with F-θ characteristics may be configured to perform proper exposure.

However, the scanning lens with F-θ characteristics may have relatively large size and high cost. Therefore, in order to reduce the size and cost of an image-forming apparatus, the scanning lens without F-θ characteristics may be configured.

Patent document <CIT> refers to an image forming apparatus performing correction of scanning deviation due to inaccuracy of the optical system. Patent document <CIT> refers to an image forming apparatus performing correction of scanning deviation due to absence or over/under-correction of an F-Theta lens arrangement.

In the existing technology, electrical correction may be performed to change an image clock frequency during a scanning operation, such that when the laser spot does not move at a uniform speed on the surface of the photosensitive member, no pixel deviation may be in the laser spot formed on the surface of the photosensitive member.

However, in above-mentioned existing technology, due to the change in the clock frequency, the exposure amounts of the pixels at an end region and a central region of the photosensitive member along a main scanning direction may also change, and such difference in exposure amounts may cause image degradation.

One aspect of the present disclosure provides an image-forming apparatus. The image-forming apparatus includes a photosensitive member; a scanning unit, configured to perform laser scanning on the photosensitive member at a non-constant linear speed along a main scanning direction to form an electrostatic latent image; and a controller, configured to make a scanning period T1 corresponding to a first pixel at a central region of the photosensitive member to be not equal to a scanning period T2 corresponding to a second pixel at a non-central region of the photosensitive member. The first pixel and the second pixel are each configured with a light-emitting time period and a non-light-emitting time period; the light-emitting time period satisfies that a light-emitting time length of the light-emitting time period of the first pixel is same as a light-emitting time length of the light-emitting time period of the second pixel; and for printing a fixed page, a light-emitting power of the scanning unit is a preset fixed value.

In an alternative embodiment, the controller is configured to make T1 greater than T2 or T1 smaller than T2.

In an alternative embodiment, the light-emitting time period is configured continuously or discontinuously in a scanning period.

In an alternative embodiment, the light-emitting time period is at a middle section of a scanning period; and the non-light-emitting time period is at a first section and a last section of the scanning period.

In an alternative embodiment, a quantity of the light-emitting time period is at least <NUM>; and/or a quantity of the non-light-emitting time period is at least <NUM>.

In an alternative embodiment, the controller is configured to control the scanning unit to emit light or not to emit light through a video signal.

In an alternative embodiment, a proportion of the light-emitting time period to a total time of the scanning period is not higher than <NUM>/<NUM>.

In an alternative embodiment, the non-central region further includes an end region and at least one transition region, wherein a scanning period of a pixel in the end region is shorter than a scanning period of a pixel in the transition region.

In an alternative embodiment, the scanning unit includes a rotating polygon mirror capable of reflecting a laser, the laser reflected by the rotating polygon mirror is applied to the photosensitive member through an image-forming lens, and the image-forming lens is not capable of correcting the laser along the main scanning direction to be linear.

Another aspect of the present disclosure provides a controller, applied to an image-forming apparatus, where an image-forming lens of the image-forming apparatus is not capable of correcting a laser along a main scanning direction to be linear. A controller is configured to make a scanning period T1 corresponding to a first pixel at a central region of a photosensitive member to be not equal to a scanning period T2 corresponding to a second pixel at a non-central region of the photosensitive member, where the first pixel and the second pixel are each configured with a light-emitting time period and a non-light-emitting time period; the light-emitting time period satisfies that a light-emitting time length of the light-emitting time period of the first pixel is same as a light-emitting time length of the light-emitting time period of the second pixel; and for printing a fixed page, a light-emitting power of the scanning unit is a preset fixed value.

Other aspects of the present disclosure may be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure.

To clearly describe technical solutions of various embodiments of the present disclosure, the drawings which need to be configured for describing various embodiments are described below. Obviously, the drawings in the following description are merely some embodiments of the present disclosure. For those skilled in the art, other drawings may be obtained in accordance with the drawings without creative efforts.

In order to better understand the technical solutions of the present disclosure, embodiments of the present disclosure are described in detail below with reference to accompanying drawings.

It should be understood that described embodiments are only some of embodiments of the present disclosure, rather than all of embodiments. According to embodiments in present disclosure, all other embodiments obtained by those skilled in the art without making creative efforts should fall within the protection scope of present disclosure.

<FIG> illustrates a schematic of a laser-type image-forming apparatus provided by exemplary embodiments of the present disclosure. A laser driving unit <NUM> included in an optical scanning device <NUM> as an optical scanning unit may be configured to generate scanning light (i.e., laser) <NUM> in response to an image signal outputted from an image signal generation unit <NUM> and a control signal outputted from a control unit <NUM>. A photosensitive drum <NUM> that the surface of the photosensitive drum is charged may be scanned by the laser <NUM>, such that a latent image may be formed on the surface of the photosensitive drum <NUM>. A developing unit (not shown) may apply toner to the latent image to form a toner image corresponding to the latent image. The toner image may be transferred to a recording medium (such as paper), thereby completing a forming process of one image. An example of a controller mentioned in the present disclosure may be a single piece including the image signal generation unit <NUM> and the control unit <NUM>. An example of the scanning unit mentioned in the present disclosure may be the optical scanning device <NUM> in <FIG> which may function as the scanning unit.

<FIG> illustrates a cross-sectional view of the optical scanning device <NUM> along a main scanning direction. The main scanning direction may be a direction in parallel with the surface of the photosensitive drum <NUM> and orthogonal to a moving direction on the surface of the photosensitive drum <NUM>. In one exemplary embodiment, the scanning light (e.g., laser) <NUM> emitted from a light source <NUM> may be reflected by a reflective surface of a rotating polygon mirror <NUM> after passing through an optical lens assembly (not shown). The light (e.g., light beam) reflected by the reflective surface may be configured as the scanning light <NUM>, and the scanning light <NUM> may irradiate onto a scanning surface <NUM> to form a spot image. In the scenario where the rotating polygon mirror <NUM> is rotated by a driving unit (not shown) at a constant angular velocity along the direction indicated by an arrow A, the light spot may move on the scanning surface <NUM> along the main scanning direction, such that the electrostatic latent image may be formed on the scanning surface <NUM>.

It may be seen that when the rotation angular speed of the rotating polygon mirror <NUM> is constant, the linear speed of the light spot moving along the main scanning direction may be not constant, that is, the linear speed at the end may be faster than the linear speed at the center. Such linear velocity inconsistency may lead to scanning deviation. Such deviation problem may be solved by designing an image-forming lens <NUM> as the lens with F-θ characteristics. The F-θ lens may achieve linear scanning with incident light of constant angular velocity. However, the lens with F-θ characteristics may be relatively large and expensive and require more space inside the printer; or in some image-forming apparatuses using the F-θ lens, the characteristics of the F-θ lens may be not sufficient to completely correct the laser along the main scanning direction to be linear. Therefore, a method of adjusting control period to reduce the scanning deviation is disclosed in the existing technology. For the principle of such method shown in <FIG>, the control period T2 corresponding to image pixels at the end region may be shorter than the control period T1 corresponding to image pixels at the central region. However, it can be seen from <FIG> that, due to different lengths of the control periods, when the output power of the laser remains unchanged, actual exposure amounts of all pixels at the end region and the central region may be inconsistent. Such exposure inconsistency may result in different toner densities at the end region and the central region (i.e., P1 and P2 in <FIG>), which may reduce image quality. In order to solve such problem, a technology solution of adjusting exposure amounts according to the positions may be provided; that is, the laser output power when the end region is scanned may be lower than the laser output power when the central region is scanned. Although such configuration can theoretically overcome above-mentioned problem, relatively high accuracy of the control signal may be needed, and the controller may need to at least ensure that a VIDEO signal and a brightness control signal are maintained to be highly synchronized, which may increase development cost of the image-forming apparatus and increase the types of failures such as signal desynchronization.

To solve above-mentioned problem, embodiments of the present disclosure provide an image-forming apparatus. The image-forming apparatus may include a photosensitive member; a scanning unit, configured to scan the photosensitive member at a non-constant linear speed along the main scanning direction to form an electrostatic latent image on the photosensitive member; and a controller, configured to make the scanning period T1 corresponding to the first pixel at the central region of the photosensitive member to be not equal to the scanning period T2 corresponding to the second pixel at a non-central region of the photosensitive member. Both the first pixel and the second pixel may be configured with a light-emitting time period and a non-light-emitting time period; the light-emitting time period may satisfy that the light-emitting time length of the light-emitting time period of the first pixel may be same as the light-emitting time length of the light-emitting time period of the second pixel. For printing a fixed page, the light-emitting power of the scanning unit may be a preset fixed value.

The non-central region in the present disclosure may further include an end region and at least one transition region, where the scanning period of the pixel in the end region may be shorter than the scanning period of the pixel in the transition region. As shown in <FIG>, in one embodiment, the photosensitive member <NUM> may sequentially include a left end region A1, a left sub-end region B1, a left sub-central region C1 and a central region D from the left end to the center. The photosensitive member may sequentially include a central region D, a right sub-central region C2, a right sub-end region B2, and a right end region A2 from the center to the right end. The left sub-end region B1, the left sub-central region C1, the right sub-central region C2, and the right sub-end region B2 may be regarded as transition regions. In one embodiment, it assumes that scanning may be performed from left to right along the main scanning direction.

In one embodiment of the present disclosure, the scanning unit may have the following characteristics that the scanning speed of the end region on the scanning surface <NUM> may be higher than the scanning speed of the central region, which is because when the rotational angular velocity of the rotating polygon mirror (i.e., deflector) <NUM> is constant, the reflective surface may be further away from the end region of the photosensitive drum than from the central region of the photosensitive drum. Since the linear velocity is equal to the product of angular velocity and radius, it should be noted that the scanning linear velocity of the end region may be higher than the scanning linear velocity of the central region. That is, the scanning unit in one embodiment may perform laser scanning on the surface of the photosensitive member at a non-constant linear velocity. The image signal generation unit <NUM> may receive printing information from a computer and generate the VIDEO signal corresponding to image data; and the laser driving unit <NUM> may supply current to the light source <NUM> in response to the VIDEO signal to cause the light source <NUM> to emit light, such that the latent image corresponding to the VIDEO signal may be formed on the scanning surface. The image deviation problem caused by non-constant scanning speed may be solved by setting the period of the VIDEO signal. That is, the period T1 of the VIDEO signal corresponding to the pixel at the non-central region (such as the end region) may be shorter, and the period T2 of the VIDEO signal corresponding to the pixel at the central region may be longer. In one embodiment of the present disclosure, it may further configure the time of the VIDEO signal at an ON state (i.e., the laser emits light) in a period; and for remaining time of such period, the VIDEO signal may be at an OFF state (i.e., the laser does not emit light). That is, the VIDEO signal may be configured to control the scanning unit to emit light or not to emit light.

It may be understood that, in another embodiment of the present disclosure, the period T1 of the VIDEO signal corresponding to the pixel at the non-central region may be longer, and the period T2 of the VIDEO signal corresponding to the pixel at the central region may be shorter, which is due to "over-correction" of above-mentioned image-forming lens <NUM>. At this point, the scanning speed of the end region on the scanning surface <NUM> may be lower than the scanning speed of the central region on the scanning surface <NUM>. To solve such problem, the controller may be configured to make that T1 is smaller than T2.

The first VIDEO signal example is shown in <FIG>, where SubPixel refers to the light-emitting unit time of the laser. <FIG> may correspond to one control period in the A1 and A2 regions in <FIG>. In one embodiment, one control period may include <NUM> SubPixels; <NUM> SubPixels in the middle section of the control period may be configured to be at the ON state; and <NUM> SubPixels in the first section and last section of the control period may be configured to be at the OFF state.

The second VIDEO signal example is shown in <FIG> may correspond to one control period in the B1 and B2 regions in <FIG>. In one embodiment, one control period may include <NUM> SubPixels; <NUM> SubPixels in the middle section of the control period may be configured to be at the ON state; and <NUM> SubPixels in the first section and last section of the control period may be configured to be at the OFF state.

The third VIDEO signal example is shown in <FIG> may correspond to one control period in the C1 and C2 regions in <FIG>. In one embodiment, one control period may include <NUM> SubPixels; <NUM> SubPixels in the middle section of the control period may be configured to be at the ON state; and <NUM> SubPixels in the first section and last section of the control period may be configured to be at the OFF state.

The fourth VIDEO signal example is shown in <FIG> may correspond to one control period in region D in <FIG>. In one embodiment, one control period may include <NUM> SubPixels; <NUM> SubPixels in the middle section of the control period may be configured to be at the ON state; and <NUM> SubPixels in the first section and last section of the control period may be configured to be at the OFF state.

It may be seen from <FIG> that even if the control periods of different regions along the scanning direction change, the time lengths of the VIDEO signal at the ON state may remain unchanged. Therefore, when laser emission intensity at one scanning period is constant, the exposure amount of one pixel may be not changed, such that the image density may not change due to different regions along the main scanning direction. Furthermore, since the laser brightness is not adjusted and only the VIDEO signal is configured in one embodiment, there is no need to control the VIDEO signal and current signal simultaneously as in the existing technology which may increase signal control complexity. Therefore, the effect of simplifying control difficulty and adjustment difficulty may be achieved in one embodiment. It may be understood that in order to achieve above effect, it may only need to make different regions have same light-emitting time length, and there is no requirement for specific SubPixel positions that the VIDEO signal is at the ON state, that is, the positions that the VIDEO signal is at the ON state may be at the first section or last section of entire control period. Similarly, the SubPixels that the VIDEO signal is at the ON state may be continuous or non-continuous. For example, <NUM> SubPixels that the VIDEO signal is at the ON state may be continuous; or the SubPixels that the VIDEO signal is at the ON state may be configured to be spaced apart from the SubPixels that the VIDEO signal is at the ON state. In one embodiment, the number of light-emitting time periods may be at least <NUM>, and/or the number of non-light-emitting time periods may be at least <NUM>. Exemplarily, in the examples shown in <FIG>, the number of light-emitting time periods may be <NUM>, and the number of non-light-emitting time periods may be <NUM>. Under the condition that the exposure amount remains unchanged, the number of light-emitting time periods may also be configured to <NUM>, and the number of non-light-emitting time periods may be configured to <NUM>, which may not be limited in the present disclosure.

<FIG> illustrates a schematic of one embodiment of the present disclosure. L3 denotes a schematic of the light-emitting time period at the central region, L4 denotes a schematic of the light-emitting time period at the end region, the dotted box represents the control period, and T3 denotes actual light-emitting time period in the control period. It may be seen from <FIG> that although the control periods at the end region and the central region are different, actual light-emitting time periods may be same. Therefore, the toner density P3 at the central region and the toner density P4 at the end regions may be same without density difference.

It may be seen from above-mentioned principle that the maximum value of the light-emitting time period should not exceed total time length of one scanning period at the end region, otherwise the light-emitting time periods at the end region and other regions may be not consistent with each other. If the proportion of the light-emitting time period to total time of the scanning period is no more than <NUM>/<NUM>, the problem of inconsistent pixel widths may also be reduced. Pixel width refers to the product of exposure time of unit pixel and the scanning linear velocity. In the present disclosure, the light-emitting time periods in the scanning period of the pixels at the central region and the non-central region may be same, but the scanning linear velocities may be different, and theoretically the pixel widths may be different. If the proportion of the light-emitting time period to total time of the scanning period is reduced to less than <NUM>/<NUM>, the problem of inconsistent pixel widths may be no longer obvious and the impact on image quality may be reduced.

In an optional implementation manner, the scanning unit may include a rotating polygon mirror for reflecting laser. The laser reflected by the rotating polygon mirror may be applied to the photosensitive member through the image-forming lens, and the image-forming lens cannot correct the laser along the main scanning direction to be linear. That is, the image-forming lens used in one embodiment may have certain optical correction characteristics but may not completely correct the scanning light beam to be linear. In such case, above-mentioned manner for configuring the light-emitting time period and the non-light-emitting time period may also be used to solve such problem.

The present disclosure further provides a controller, applied to the image-forming apparatus. The image-forming lens used in the image-forming apparatus cannot correct the laser along the main scanning direction to be linear. The controller may be configured to make the scanning period T1 corresponding to the first pixel at the central region of the photosensitive member to be not equal to the scanning period T2 corresponding to the second pixel at the non-central region of the photosensitive member. Both the first pixel and the second pixel may be configured with the light-emitting time period and the non-light-emitting time period; the light-emitting time period may satisfy that the light-emitting time length of the light-emitting time period of the first pixel may be same as the light-emitting time length of the light-emitting time period of the second pixel. For printing a fixed page, the light-emitting power of the scanning unit may be a preset fixed value.

The controller used in exemplary embodiment two, same as the controller in exemplary embodiment one, may be applied to the image-forming apparatus without the F-θ lens and may also be applied to the image-forming apparatus including an optical correction lens that the correction characteristics of the lens are not sufficient to completely correct the scanning light beam to be linear. In one embodiment, the controller may include the image signal generation unit <NUM> and the control unit <NUM> as shown in <FIG>. The controller may control the scanning unit to emit light or not to emit light through the VIDEO signal. Parts of the controller in exemplary embodiment two same as those in exemplary embodiment one may not be described in detail herein.

Compared with the existing technology, the technical solutions provided by the present disclosure may achieve at least the following beneficial effects.

Compared with the existing technology, in embodiments of the present disclosure, the exposure amounts of the pixels at different regions along the main scanning direction may be same, which may reduce the problem of inconsistent image density at different regions which easily occurs in the existing technology, thereby improving image quality. Furthermore, the control logic of the present disclosure may be simple and easy to be configured and adjusted.

Claim 1:
An image-forming apparatus, comprising:
a photosensitive member;
a scanning unit, configured to perform laser scanning on the photosensitive member at a non-constant linear speed along a main scanning direction to form an electrostatic latent image; and
a controller, configured to make a scanning period T1 corresponding to a first pixel at a central region of the photosensitive member to be not equal to a scanning period T2 corresponding to a second pixel at a non-central region of the photosensitive member, wherein:
the first pixel and the second pixel are each configured with a light-emitting time period and a non-light-emitting time period;
characterized in that the light-emitting time period satisfies that a light-emitting time length of the light-emitting time period of the first pixel is same as a light-emitting time length of the light-emitting time period of the second pixel; and for printing a fixed page, a light-emitting power of the scanning unit is a preset fixed value.