Patent Application
20080112697
This application claims the benefit of Korean Patent Application No. 2006-111274, filed on Nov. 10, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
Aspects of the present invention relate to a motor controlling apparatus of an image forming apparatus and a method thereof, and more particularly, to an apparatus to control a direct current motor at low speed using a low resolution encoder and a method thereof.
2. Description of the Related Art
An image forming apparatus is an apparatus to print an image signal onto a printable medium. Examples of image forming apparatuses include printers, copying machines, facsimile machines, multifunction devices performing multiple functions (printing, scanning, copying, faxing, etc.), and the like. The image forming apparatus may include a scanner using a direct current (DC) motor as a driving force source in order to acquire an image. The image forming apparatus controls the movement of an image sensor to take a photograph of the image based on the operation of the DC motor.
In a system to control a DC motor, the speed of the DC motor is controlled according to the difference between a reference speed and a measured speed of the DC motor. Measuring the speed of the DC motor is carried out based on pulses of an encoder, which are generated during the rotation of the DC motor. However, when the DC motor rotates at a considerably low speed, the pulses of the encoder may not be detected within a sampling period, and due to this, the pulse period of the encoder is not detected until a next pulse is inputted. As a result, speed data may not be updated.
Japanese Unexamined Patent Application Publication No. Hei 7-015990 discloses a method of estimating a speed of a motor after assuming a motor is rotating at a speed lower than a previous speed or being stopped when information about the speed is not inputted. A shortcoming of this method is that a difference between the estimated speed and an actually measured speed is increased when the previous voltage applied to drive the motor is increased or a load ripple is generated by a gear transmitting the driving force of the motor.
Although a high resolution encoder can provide the speed information when driving the motor at low speed, high resolution encoders are more expensive, increasing the cost of the image forming apparatus.
Aspects of the present invention has been made in view of the above-mentioned problems, and an aspect of the invention is to provide a motor controlling apparatus of an image forming apparatus for controlling a direct current motor stably and reliably at low speed without a low resolution encoder and a method thereof.
According to an aspect of the present invention, a control apparatus for an image forming apparatus comprising an image device to take a photograph of an image, a moving unit in which the image device is installed, and a direct current motor to move the moving unit, the control apparatus controls the direct current motor and comprises: a speed sensor to output pulses corresponding to a speed of the direct current motor; a speed estimating unit to determine a necessity to estimate the speed of the direct current motor, and to estimate the speed of the direct current motor according to speed information measured by the speed sensor when the speed estimating unit determines a need for the estimation of the speed of the direct current motor; and a motor driving unit to drive the direct current motor based on the speed of the direct current motor estimated by the speed estimating unit.
According to another aspect of the present invention, the speed sensor is an encoder.
According to another aspect of the present invention, the speed estimating unit includes: a speed measuring unit to measure the speed and a position of the direct current motor according to the pulses of the speed sensor and to update and store information about the estimated speed and the position of the direct current motor for every controlling period; a controller to provide a control variable and a gain for the estimation of the speed of the direct current motor; a speed estimating device to estimate the speed of the direct current motor using the control variable provided by the controller and the speed and the position of the direct current motor provided by the speed measuring unit; and a speed controller to adjust the speed estimated by the speed estimating device using the gain provided by the controller.
According to another aspect of the present invention, the speed estimating device includes: a plant model to estimate the speed of the direct current motor using a formula model related to a plant of a controlling object in which an output speed is varied according to an input voltage; a ripple model to estimate the speed of the direct current model using a formula model due to a load ripple caused when driving the direct current motor; and an adder to add the speed of the direct current motor estimated by the plant model and the speed of the direct current motor by the ripple model to obtain the estimated speed of the direct current motor outputted by the speed estimating device.
According to another aspect of the present invention, the plant model uses the following formula to estimate the speed of the direct current motor:
y(n+1)=(ΔT/T)*K*r(n)+(1−(ΔT/T))*y(n)
In the formula, y (n+1) is the estimated speed of the direct current motor, r (n) is a previous voltage applied to the direct current motor, y (n) is a previous speed of the direct current motor, T is a time constant until an output speed of the direct current motor reaches 63% of a reference speed, ΔT is increase of the time constant, and K is a direct current gain with respect to an input and an output of the control of the direct current motor.
According to another aspect of the present invention, the ripple model uses the following formula to estimate the speed of the direct current motor:
estimated speed of ripple=(A+B*r(n))*sin(previous position of ripple peak+position of ripple peak−π)
In the formula, A and B are constants indicating a magnitude of the load ripple and the position of the ripple peak is a value corresponding to an initial position of the ripple peak.
According to another aspect of the present invention, the control apparatus further includes a switch to selectively connect an output of the speed measuring unit to one of the speed estimating device and the speed controller, and the speed measuring unit connects the output of the speed measuring unit to the speed estimating device when the pulses of the speed sensor are not generated within the controlling periods, and applies a switching signal for connecting the output of the speed measuring unit to the speed controller to the switch when the pulses of the speed sensor are generated within the controlling periods.
According to another aspect of the present invention, a control apparatus for an image forming apparatus is provided comprising an image device to take a photograph of an image, a moving unit in which the image device is installed, and a direct current motor to move the moving unit, to the control apparatus controlling the direct current motor, and comprising: an encoder to output pulses corresponding to a speed of the direct current motor; a speed measuring unit to measure the speed and a position of the direct current motor according to the pulses of the encoder generated within controlling periods and to provide information about a previous speed and a previous position of the direct current motor that is required to estimate the speed of the direct current motor, when the speed and the position of the direct current motor are 0 (zero) as a result of the measurement according to the pulses; a controller to a control variable and a gain for the estimation of the speed of the direct current motor based on the pulses of the encoder; a speed estimating unit to apply the control variable provided by the controller, and the previous speed, the previous position, and a previous voltage of the direct current motor provided by the speed measuring unit to a formula model to estimate the speed of the direct current motor; a speed controller to adjust the speed of the direct current motor estimated by the speed estimating unit using the gain provided by the controller; and a motor driving unit to drive the direct current motor based on a motor driving voltage adjusted by the speed controller.
According to another aspect of the present invention, the speed estimating unit adds a speed of the direct current motor, estimated using a formula by adding a speed of the direct current estimated using a formula model with respect to a plant of a controlling object and a speed of the direct current motor estimated using a formula model with respect to the load ripple, to estimate the speed of the direct current motor.
According to another aspect of the present invention, a method of controlling a direct current motor of an image forming apparatus, including an image device to take a photograph of an image, a moving unit in which the image device is installed, and the direct current motor to move the moving unit, the method comprising: measuring a speed and a position of the direct current motor according to pulses corresponding to the speed of the direct current motor; estimating the speed of the direct current motor according to a formula model when the pulses are not generated within controlling periods; outputting a motor driving voltage adjusted using a gain and a difference between the estimated speed of the direct current motor and a reference speed; outputting a motor driving voltage adjusted using the measured speed of the direct current motor and the reference speed when the pulses are generated within the controlling periods; and controlling the speed of the direct current motor based on the outputted motor driving voltage.
According to another aspect of the present invention, the estimating includes estimating a first estimated speed of the direct current motor using a formula model due to a plant of a controlling object in which an output speed is varied according to an input voltage; estimating a second estimated speed of the direct current motor using a formula model due to a load ripple caused when driving the direct current motor; and adding the first estimated speed and the second estimated speed.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.
Although aspects of the present invention are applicable to any apparatus employing a direct current (DC) motor, use of a DC motor with a contact image scanner as illustrated in
In order to control a DC motor of an image forming apparatus, a speed of the DC motor is controlled in two ways. First, when the speed of the DC motor is fast and pulses of an encoder are generated within a controlling period, the speed of the DC motor is controlled according to a speed estimated using only an output of the encoder. Second, even when the speed of the DC motor is very slow and the pulses of the encoder are not generated within the controlling period, the speed of the DC motor is controlled according to a motor speed estimated using the output of the encoder and a formula model. According to other aspects of the invention, any speed sensor may be used to measure the speed of the DC motor.
As illustrated in
A first switch 20 is connected to an output side of the speed measuring unit 10. The first switch 20 selectively contacts one of a first contact a and a second contact b. The contacting operation of the first switch 20 is carried out by a switching signal of the speed measuring unit 10. When the encoder pulses are generated within the controlling period, the first switch 20 contacts the first contact a according to the switching signal of the speed measuring unit 10. When the encoder pulses are not generated within the controlling period, the first switch 20 contacts the second contact b according to the switching signal of the speed measuring unit 10.
When the first switch 20 contacts the first contact a, a speed controller 30 adjusts a speed difference signal and outputs a motor driving voltage to drive the DC motor to a motor driving unit 70 according to the adjustment. The speed difference signal corresponds to a difference between a motor speed measured by the speed measuring unit 10 and a reference speed set by a user using a gain to be provided from a controller 100.
When the first switch 20 contacts the second contact b, the speed estimating unit 40 estimates the motor speed using the previous speed and the previous position of the DC motor, the driving voltage of the DC motor outputted from the speed controller 30, and a control variable provided from the controller 100. The speed estimating unit provides the estimated speed signal to the speed controller 30. The driving voltage outputted from the speed controller 30 may be a previous voltage of the DC motor. When the estimated speed signal is inputted through the speed estimating unit 40, the speed controller 30 adjusts the gain of the speed difference signal corresponding to the difference between the estimated speed signal and the reference speed set by the user and outputs the driving voltage of the DC motor in which the gain is adjusted.
The motor driving unit 70 drives the DC motor 80 in response to the driving voltage of the DC motor received through the speed controller 30. The encoder pulses outputted from the encoder 90 are provided to the controller 100 and the speed measuring unit 10 when driving the DC motor 80.
Operation of the speed estimating unit to estimate the speed of the DC motor based on the output information of the encoder will be described. The speed estimating unit 40, as illustrated in
The speed estimating unit 40 receives a required control variable, namely, information about K, T, ΔT, A, B, and a position of a ripple peak from the controller 100. As illustrated in
These control variables are obtained from experiments, and in this embodiment, the controller 100 is designed to provide them.
Kp=((2ωζ)−1)/K, Kir=(ω2T)/K Formula 1
Here, ζ and ω are design variables.
Then, the position of the DC motor is initialized (204). The initialization of the motor position may correspond to a starting position of an object moved by the DC motor. If a low resolution encoder does not generate pulses within the controlling period, the DC motor is controlled by the speed controller at low speed. The speed of the DC motor is controlled by a general method of controlling the speed of the DC motor according to the difference between the reference speed and the measured speed (206). After that, according to a result of controlling the DC motor at low speed, the position of the ripple peak is estimated (208). The estimation of the position of the ripple peak will be described in detail.
When controlling the DC motor at low speed, the motor speed is represented in the graph of
When the controlled result is plotted according to the positional variation, a graph such as that shown in
A formula model applied to the plant model 42 of the speed estimating unit 40 will be described. First, a formula of the output speed with respect to the input voltage of the DC motor within a Laplace domain is expressed by the following formula 2.
Y/R=K(Ts+1)
Y*(Ts+1)=K*R
(Y*Ts)+Y=K*R Formula 2
Here, Y is an output speed and R is an input voltage.
If formula 2 is transformed into a discrete domain, let s=(y(n+1)−y (n))/ΔT. Formula 3 is obtained from this substitution and transformation.
T*{(y(n+1)−y(n))/≡T}+y(n)=K*r(n) Formula 3
After a further transformation, formula 4 is obtained.
(T/ΔT)*y(n+1)−(T/ΔT)*y(n)+y(n)=K*r(n)
(T/ΔT)*y(n+1)=K*r(n)+((T/ΔT)−1)*y(n)
Y(n+1)=(ΔT/T)*K*r(n)+(1−(ΔT/T))*y(n) Formula 4
Here, y (n+1) is an estimated speed, r (n) is a previous voltage of the DC motor, and y (n) is a previous speed of the DC motor.
The ripple model 44 estimates the speed of the DC motor due to the load ripple according to the following formula 5.
Estimated speed of load ripple=(A+B*r(n))*sin(previous position of ripple peak+position of ripple peak−π)
Here, A+B*r(n) is the magnitude of the load ripple.
sin(previous position of ripple peak+position of ripple peak−π) is what the previous position is added to a certain position of a ripple peak provided by the controller 100 and is used to apply the increase to the speed estimation, since, as illustrated in
The adder 46 adds the speed estimated by the plant model 42 and the speed estimated by the ripple model 44 and outputs the added speed.
As illustrated in
Thus, although it may be misunderstood that the speed does not vary when the speed is based on only the encoder pulses, a more stable and more reliable motor control can be carried out when the DC motor is controlled at low speeds based on the actually estimated speed of the DC motor.
For reference, when the DC motor is controlled at low speeds by estimating the speed of the DC motor according to aspects of the present invention, as illustrated in
As described above, according to aspects of the present invention, since the estimated motor speed is used to drive the DC motor at low speed, the speed error can be reduced to achieve stable and reliable control of the DC motor. Since excellent control performance of the DC motor can be guaranteed using even a low resolution encoder, more expensive encoders need not be used. Moreover, since the controller is designed by applying the property of the DC motor due to the load ripple, the control apparatus according to aspects of the present invention strongly resists variation of load and has an excellent control performance.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-111274 | Nov 2006 | KR | national |
