This application claims priority from Korean Patent Application No. 10-2008-0104484, filed on Oct. 23, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
The present disclosure relates generally to an image forming apparatus and a velocity control method of a rotating body thereof, and more particularly to an image forming apparatus which reduces a velocity fluctuation of a rotating body and a velocity control method of a rotating body thereof.
An image forming apparatus may generally operate to form an image on a print medium. Depending on an image forming method, the image forming apparatus may generally be classified as an electrophotographic printer, which forms an image on a print medium through a series of processes, including charging, exposing and developing an electrostatic latent image, and transferring and fusing of the developed image onto a print medium; an inkjet printer, which forms an image by jetting ink through a nozzle; or a thermal transferring printer, which uses a thermal print head.
An image forming apparatus may generally require the use of a rotating body, such as, for example, an image bearing body and a transfer roller, to form an image on a print medium. To secure uniform image quality, the rotating velocity of a rotating body should desirably be kept consistent (i.e., without any fluctuation).
An image forming apparatus may generally include driving power transmitting mechanisms, such as a gear, a belt, a chain, and the like, to transmit rotating power of a rotating shaft of a driving motor to the rotating body. However, unfortunately, even if a driving shaft of the driving motor rotates at a consistent rate, the rotating velocity of the rotating body may fluctuate due to the deviations, due to the allowed fabrication/assembly tolerance, of the power transmitting mechanisms themselves. An image forming apparatus with improved velocity control of the rotating body is thus desired.
According to an aspect of the present disclosure, an image forming apparatus may be provided to include an image bearing body, a driving motor and a controller. The image bearing body may have a toner image form on the surface thereof. The driving motor may be configured to drive the image bearing body according to an input signal. The controller may be configured to provide the input signal to control the driving motor so as to cause the driving motor to output a motor output velocity at a period equal to that of an AC velocity component of the image bearing body.
According to an embodiment, the motor output velocity and the AC velocity component of the image bearing body may have a phase difference of approximately 180°.
The controller may supply a discrete motor input signal to the driving motor to output the motor output velocity, in which the discrete motor input signal is generated as an input signal by sampling a continuous motor input signal at predetermined sampling time, which may be, according to an embodiment, 0.05 seconds or less.
The continuous motor input signal may be provided to correspond to a sinusoidal wave that approximates a rotating velocity of the image bearing body having the AC velocity component.
The continuous motor input signal may include a sinusoidal wave which has a phase angle that minimizes an amplitude of the AC velocity component. The phase angle, according to an embodiment, may be 270°. According to an embodiment, the phase angle may differ by the sampling time and/or may increase as the sample time becomes longer.
The image forming apparatus may further include a memory for storing therein the continuous motor input signal and other data and/or information related to the image forming apparatus.
According to another aspect, a method of controlling a velocity of a rotating body of an image forming apparatus may include: sampling a continuous motor input signal at a period equal to an AC velocity component of a rotating velocity of the rotating body to obtain a sampled discrete motor input signal; and providing the sampled discrete motor input signal to a driving motor that drives the rotating body.
Driving the rotating body may include outputting a motor output velocity having a phase difference of approximately 180° with respect to the AC velocity component of the rotating body according to the sampled discrete motor input signal; and rotating the rotating body according to the outputted motor output velocity.
The sampling time may be 0.05 seconds or less, according to an embodiment.
The continuous motor input signal may correspond to a sinusoidal wave that approximates a rotating velocity of the rotating body having the AC velocity component.
The continuous motor input signal may include a sinusoidal wave which has a phase angle minimizing an amplitude of the AC velocity component. The phase angle, according to an embodiment, may be 270°. According to an embodiment, the phase angle may differ by the sampling time.
The method may include reading the continuous motor input signal from a memory component of the image forming apparatus.
According to an embodiment, the method may further include measuring an AC velocity component of the rotating body and generating the continuous motor input signal corresponding to the measured AC velocity component.
According to yet another aspect, a method of controlling a rotating body of an image forming apparatus may comprise: inputting an input control signal to a motor device; and driving the rotating body to rotate at a rotational velocity with the motor device operating according to the input control signal. The input control signal may satisfy the relationship, Hz=B+Am·sin(wmt+θm). Hz is the input control signal in pulse per second (PPS). B corresponds to an average number of pulses per second input to achieve a desired rotational velocity of the rotating body. Am proportionally corresponds to an amplitude of fluctuation from the desired rotational velocity of the rotating body. wm corresponds to an angular velocity of the fluctuation expressed as 2πf, f representing an inverse of a period of the fluctuation. θm represents a phase angle of the input control signal.
The phase angle θm of the input control signal may be empirically determined by selecting an angle that minimizes the amplitude of fluctuation.
The empirical determination of the phase angle may comprise inputting a plurality input control signals each having a respective phase angle different from that of other ones of the input control signals; and selecting as the phase angle a selected angle that produces a standard deviation in the rotational velocity of the rotating body below a threshold value.
The phase angle θm may range between 210° and 320°.
Various features and advantages of the disclosure will become more apparent by the following detailed description of several embodiments thereof with reference to the attached drawings, of which:
Reference will now be made in detail to several embodiment, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. While the embodiments are described with detailed construction and elements to assist in a comprehensive understanding of the various applications and advantages of the embodiments, it should be apparent however that the embodiments can be carried out without those specifically detailed particulars. Also, well-known functions or constructions will not be described in detail so as to avoid obscuring the description with unnecessary detail. It should be also noted that in the drawings, the dimensions of the features are not intended to be to true scale and may be exaggerated for the sake of allowing greater understanding.
With reference to
The driving motor 120 may include a driving shaft (not shown) configured to rotate according to a motor input signal supplied by the controller 130, and a pinion (not shown) connected to the driving shaft in the same axis. The driving motor 120 may include a brushless direct-current (BLCD) motor, for example.
If the image forming apparatus 100 includes multiple image bearing bodies 110, the driving motor 120 may include a plurality of driving motors 120 to correspond to the plurality of image bearing bodies 110 to drive each of the plurality of image bearing bodies 110.
A gear (not shown) may be installed in a rotating shaft (not shown) of the image bearing body 110 to receive driving power from the pinion of the driving motor 120. Driving power transmitting parts such as a coupler, a chain, a belt, and the like may be provided to transmit the driving power of the pinion to the image bearing body 110.
A visible image including developer, e.g., toner, may be formed on the surface of the image bearing body 110. Broadly speaking, and by way of an example, the visible developer image may be formed by uniformly charging the surface of the image bearing body 110, which surface may be exposed to a light corresponding to a desired image by an exposing unit (not shown) to create potential differences defining an electrostatic latent image across the surface of the image bearing body. The electrostatic latent image is then developed with developer, such as, for example, toner particles, to form the visual developer image on the surface of the image bearing body 110.
The image bearing body 110 may include a plurality of photo conductors for forming different colored developer images, for example, in yellow, magenta, cyan and black (YMCK). Forming a color image with the plurality of image bearing bodies 110 may be accomplished by utilizing a so-called a tandem type or a single path type process. In some cases, however, the image bearing body 110 may include a single photo conductor. An intermediate transfer belt unit (not shown) may be provided to face the single image bearing body 110 to form a color image. Each time an intermediate transfer belt (not shown) rotates a complete loop, a visible image in one color that had been formed on the surface of the image bearing body 110 is transferred to the belt. Accordingly, in four rotations of the belt, four color images of YMCK are transferred to the belt overlapping one another to form a color image. Such a method is generally referred to as a multi-path type.
According to an embodiment, the controller 130 may operate in a general control mode to control the driving motor 120 to rotate a driving shaft (not shown) of the driving motor 120 at consistent RPM and/or a constant velocity control mode to control the driving motor 120 to output a motor output velocity at a period equal to that of an AC velocity component, thereby reducing the AC velocity component of the image bearing body 110.
A mode conversion between the general control mode and the constant velocity control mode may be performed manually at a user's request or automatically if, for example, a color registration of a color image formed on a print medium by the image bearing body 110 is determined to be poor or to not meet certain requirements.
In the plots shown in
As shown in
Thus, when the driving shaft of the driving motor 120 is controlled in the general control mode to rotate at consistent RPM, a velocity fluctuation, such as the AC velocity component D, is incorporated in the rotating velocity of the image bearing body 110.
The AC velocity component D may be approximated by a sinusoidal wave, and accordingly the rotating velocity V of the image bearing body 110, as shown in
V=V0+Aν sin(w0t+θ0) Formula (1)
According to this example, the DC component of the rotating velocity of the image bearing body 110 V0=161 mm/sec;
Aν=1 mm/sec;
w0=2πf=2.567π (f=1/T=1/0.78=1.28 Hz); and
θ0=Phase of the AC velocity component D
As shown in
The error of color registration refers to an error between a target location of dots of the developer and the actual location of the dots. The smaller the error of color registration, the better and clearer the color registration and the resulting color images become. The location error of the color registration is largest at the time of a semi-period T/2 of the AC velocity component D, as illustrated in
If the AC velocity component D of the image bearing body 110 is compensated for by the “velocity compensation” graph E, shown in
In the constant velocity control mode of the controller 130, a motor input signal is generated according to the following formula (2), and is provided to the driving motor 120 to compensate for the rotating velocity of the image bearing body 110, as in the “velocity compensation” graph E in
Motor input signal, Hz=B+Am sin(wmt+θm) Formula (2)
In the general control mode a value B (1268.4 PPS) is provided as a motor input signal, while in the constant velocity control mode, a fluctuation component of a sinusoidal waveform is included as well as the value B as the motor input signal.
In Formula (2) above:
B=Average PPS of motor input signal corresponding to V0 in the formula (1);
Am=Amplitude of fluctuation component of motor input signal corresponding to Av in formula (1);
wm=Angular velocity of the motor input signal, which is the same as the angular velocity w0 in the formula (1) (e.g., wm=w0); and
θm=Phase angle of the motor input signal (empirically determinable);
Thus, when B is 1268.4 PPS, the average PPS for a linear velocity of V0=161 mm/sec.
As shown in
161 mm/sec:1268.4 PPS=1 mm/sec(Aν):Am Formula (3)
Accordingly, Am is 7.9 PPS in this example.
With the phase angle θm as a test variable, the test result of the change in the AC velocity component of the image bearing body 110 is illustrated in
In this example, if the phase angle θm is 270°, the standard deviation σv is 0.21. At this phase angle θm, the AC velocity component D of the image bearing body 110 is at a minimum. Thus, to minimize the AC velocity component D of the magenta image bearing body 110, a motor input signal (motor input velocity) which satisfies the following formula (4) is applied to the driving motor 120.
Motor input signal=1268.4+7.9 sin(2.56π+270°)(PPS) Formula (4)
Similar to the formula (3), the motor input signal includes a fluctuation component Am sin(wmt+θm) to offset the AC velocity component D of the image bearing body 110.
The period (angular velocity) of the fluctuation component included in the motor input signal is the same as the period (angular velocity) of the AC velocity component D of the image bearing body 110.
The motor output velocity (angular velocity, RPM) output by the driving motor 120 according to the motor input signal also fluctuates at the same period as that of the AC velocity component D.
As illustrated in
As illustrated in
If the phase angle θm of the motor input signal is 270°, a phase difference between the AC velocity component D of the image bearing body 110 and the fluctuation component of the motor input signal is 180°. The two components may thus offset each other.
For example, in the illustrated example, it can be observed that, when a phase difference of 180°, exists between the phase angle θm of the motor input signal and the phase angle θ0 of the AC velocity component D of the image bearing body 110, the standard deviation is at its smallest.
As shown in
That is, if the motor input signal is provided to the driving motor 120 to make the phase difference between the phase angle θm of the motor input signal and the phase angle θ0 of the AC velocity component D of the image bearing body 110 exist in the range of approximately 130° to 230°, the standard deviation of the AC velocity component D of the image bearing body 110 is smaller than in the general control mode.
As shown in
As illustrated in the graph of frequency analysis, if the amplitude Am of the fluctuation component is 7.9 PPS, a dominant low frequency rises from 1.28 Hz to 2.56 Hz. In the remaining cases, the dominant low frequency remains at 1.28 Hz. The change in the dominant low frequency may positively contribute to an impact on the aspect of error of color registration.
If the driving power transmitting unit from the driving motor 120 to the cyan image bearing body 110 is the same as that from the driving motor 120 to the magenta image bearing body 110, a pattern of the rotating velocity may be the same or nearly the same. The standard deviation of the rotating velocity of the cyan image bearing body 110 in this case is 0.79 mm/sec, which is slightly larger than 0.75 mm/sec, the standard deviation of the rotating velocity of the magenta image bearing body 110 shown in
As shown in
If a motor input signal in the formula (4) is provided to the driving motor 120 to offset the AC velocity component D of the cyan image bearing body 110 shown in
In the general control mode, the standard deviation σv of the rotating velocity of the cyan image bearing body 110 is 0.79 mm/sec, as shown in
As illustrated in
As illustrated in
Since the motor input signal in the formulas (3) and (4) is a continuous, analog input signal as a function of time, it may be, according to an embodiment, sampled to be a discrete, digital input signal to be provided to the driving motor 120. For example, the test results in
The longer the sampling time Ts, the larger the phase angle θm of the motor input signal to minimize the standard deviation σv. Thus, if the sampling time Ts becomes longer, the phase angle θm of the motor input signal minimizing the amplitude of the AC velocity of the image bearing body 110 becomes larger. The shorter the sampling time Ts, the closer the discrete input signal is to an analog sine wave. Accordingly, time delay between the discrete input signal and output of the driving motor 120 may be reduced.
As shown in
As shown in
More specifically, if the sampling time is longer than 0.002 seconds, the phase angle θm of the motor input signal measured for the purpose of the testing shifts as much as the phase delay Δθm to reduce the standard deviation of the AC velocity component. As shown in
If the sampling time Ts is short, the phase delay Δθm may also be reduced. However, load to the system is greater and thus the sampling time Ts may not be unconditionally small. If the sampling time is longer, the phase delay Δθm is longer, as described above, and the actual discrete motor input signal has a phase different from that of the anticipated continuous input signal. Thus, the AC velocity component of the image bearing body 110 may not be removed effectively.
As illustrated in
As shown in
As shown in
As illustrated in
Accordingly, Max (AC) of the error of color registration AC is as follows:
It can be observed that the maximum value of the error of color registration Max(AC) is inversely proportional to the frequency of the AC velocity component, and is directly proportional to the amplitude of the AC velocity component.
As previously described above, in the constant velocity control mode, the amplitude of the AC velocity component of the image bearing body 110 is reduced by 75% while the error of color registration is also reduced. More particularly, as the dominant low frequency doubles, the error of color registration being inversely proportional thereto may be reduced to about half. Thus, in the above example, Aν=0.19 mm/sec, f=2.56 Hz, and Max(AC) is about 0.047 mm in the constant velocity control mode. The calculated continuous motor input signal may be stored in a memory, for example, the memory component 140 shown in
With reference to
At S10, a continuous motor input signal is sampled at a sampling period that is the same as the period of the AC velocity component of the rotating velocity of the rotating body.
The continuous motor input signal may be stored in the memory 140 of the image forming apparatus 100, for example. Accordingly, the continuous motor input signal stored in the memory 140 may be read and sampled. In an embodiment, the continuous motor input signal may be determined by empirically measuring an AC velocity component of the rotating body and generating a continuous motor input signal corresponding to the measured AC velocity component. If the continuous motor input signal is not stored in the memory 140, the controller 130 may generate the continuous motor input signal corresponding to the measured AC velocity component.
As would be readily understood by those skilled in the art, the controller 130 may be, e.g., a microprocessor, a microcontroller or the like, that includes a CPU to execute one or more computer instructions to implement the various control operations herein described and/or control operations relating to one or more other components of the image forming apparatus, and, to that end, may further include a memory device, e.g., a Random Access Memory (RAM), Read-Only-Memory (ROM), a flesh memory, or the like, in addition to or in lieu of the memory component 140 shown in
The continuous motor input signal may be calculated by the formula (2) as the phase angle θm in the formula (2) is determined to reduce the AC velocity component. The phase angle θm may be 270°, for example, according to an embodiment.
At S20, the sampled discrete motor input signal is provided to the driving motor 120 that is configured to drive the rotating body.
At S30, the driving motor 120 drives the rotating body according to the discrete motor input signal.
As described above, the rotating body may include the image bearing body 110, which has a toner visible image on a surface thereof. In some cases, the rotating body may include another rotating body for which a constant velocity is required other than the image bearing body 110. For example, the rotating body may include one of a transfer roller or a driving roller driving the belt.
According to aspects of the above-described embodiments, the velocity fluctuation of the rotating body, such as an image bearing body, can be reduced, allowing the rotating body may rotate at a consistent velocity. Furthermore, an AC velocity component of the rotating velocity of the image bearing body may be minimized. A constant velocity of the image bearing body for example improves the proper application of developers in different colors to the desired locations on a print medium or a transfer belt. Accordingly, color registration may improve, realizing a clearer image.
While the disclosure has been particularly shown and described with reference to several embodiments thereof with particular details, it will be apparent to one of ordinary skill in the art that various changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the following claims and their equivalents.
Number | Date | Country | Kind |
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10-2008-0104484 | Oct 2008 | KR | national |
Number | Name | Date | Kind |
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20070242980 | Kikuchi et al. | Oct 2007 | A1 |
Number | Date | Country |
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2006047920 | Feb 2006 | JP |
Number | Date | Country | |
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20100104321 A1 | Apr 2010 | US |