Voltage switch and electrophotographic color image forming apparatus using the same

A voltage switch for connecting a power supply with a plurality of development units in sequence, and an electrophotographic color image forming apparatus using the voltage switch. In the voltage switch, a first terminal is arranged on a circuit board and is connected to the power supply, and a plurality of second terminals are arranged in a circle on the circuit board and are connected with the plurality of development units, respectively. A rotor is rotatably coupled with the circuit board of the switch and is provided with a lead, such that as the rotor rotates about the circle, the first terminal can be electrically connected with the plurality of second terminals in sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2004-0077722, filed in the Korean Intellectual Property Office on Sep. 30, 2004, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic color image forming apparatus. More particularly, the present invention relates to a voltage switch of an electrophotographic color image forming apparatus wherein the voltage switch can sequentially apply a development voltage to each color development unit, such that each of the color development units can apply its toner to an electrostatic latent image of a photoconductor for developing the latent image.

2. Description of the Related Art

An electrophotographic image forming apparatus is a device in which an electrostatic latent image is formed on an outer circumference of a photoconductor charged to a predetermined electric potential by scanning light onto the photoconductor. A toner which is a developing agent is applied onto the electrostatic latent image and is developed as a black-and-white or color image, and the image is then transferred and fixed onto a paper so that an image is printed. A typical electrophotographic image forming apparatus capable of color printing includes a light scanning unit for emitting light beams that correspond to an image data, a photoconductor on which the emitted light beams are projected to form an electrostatic latent image, and four development units having yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively, to apply these toners to the electrostatic latent image of the photoconductor for developing the latent image into a visible toner image.

During the developing by the development units, the four kinds of toners can be applied from the development units to the photoconductor by a force resulting from a potential difference between the development units and the photoconductor. To form the potential difference, a high voltage must be applied to the four development units in sequence.

FIG. 1is a schematic view of a conventional voltage switch of an electrophotographic color image forming apparatus.

Referring toFIG. 1, a voltage switch10includes a solenoid12and a circuit board20. The circuit board20includes a first terminal21connected to a power supply1for supplying high voltages up to 3 kV, a second terminal22connected to a cyan development unit5C containing a cyan (C) toner, and a leaf spring17having ends17aand17b, the end17abeing fixed to the circuit board20for an electrical connection with the second terminal22and the other end17bbeing spaced apart from the first terminal21but being capable of contacting the first terminal21.

The solenoid12is securely installed to the circuit board20by a bracket15and is provided at one end with a holder13that is coupled with the end17bof the leaf spring17. Though the four development units containing the yellow (Y), magenta (M), cyan (C), and black (K) toners, require four solenoids, only the solenoid12for the cyan development unit5C is illustrated inFIG. 1as an example, and the remaining solenoids each have substantially the same structure.

When the solenoid12of the voltage switch10is switched on, the holder13coupled with the end17b, moves toward the first terminal21such that the end17bcomes into contact with the first terminal21. The power supply1supplies power to the first terminal21such that a development bias voltage is applied to the cyan development unit5C to cause a potential difference between the cyan development unit5C and the photoconductor (not shown). The potential difference ensures that the cyan (C) toner can move from the cyan development unit5C to the photoconductor for developing a cyan (C) toner image. When the solenoid12is off and the power supply1is off, the developing of the cyan (C) toner image is completed. In the same manner, each solenoid provided for the magenta (M), yellow (Y), and black (K) development units, is sequentially operated to supply power from the power supply1to the development units.

However, the voltage switch10of the conventional electrophotographic color image forming apparatus is not suitable for a small color image forming apparatus because of its size. Though there are other types of conventional voltage switches using a relay or a solid stator instead of the solenoid, these kinds of voltage switches cannot be used at a high voltage of about 3 kV. Further, conventional voltage switches that can be used at high voltages are too big and expensive to be used in a small-sized, low-priced color image forming apparatus.

Accordingly, a need exists for a system and method for providing a lower cost, smaller sized voltage switch that can operate safely at higher voltages.

SUMMARY OF THE INVENTION

The present invention provides a voltage switch requiring a smaller space for installation owing to its small size, and an electrophotographic color image forming apparatus using the voltage switch.

According to an aspect of the present invention, a voltage switch is provided comprising a first terminal connected to a power supply, a plurality of second terminals arranged in a circle and connected with a plurality of development units, respectively, wherein each of the plurality of development units holds a different color toner, and a rotor for rotating about the circle to allow the first terminal to be electrically connected with the plurality of second terminals in sequence.

The rotor can comprise a lead to connect the first terminal and the plurality of second terminals, wherein the lead comprises a ring-shaped portion being in contact with the first terminal regardless of the rotation of the rotor, and a linear portion connected with the ring-shaped portion to contact the second terminals in sequence by the rotation of the rotor.

The voltage switch can comprise a step motor to drive the rotor.

The voltage switch can also comprise a sensing element to detect an angular displacement of the rotor.

The voltage switch can further comprise a stopping element to stop the rotation of the rotor when the first terminal and any one of the second terminals are connected.

The first terminal and the plurality of second terminals can be sufficiently spaced apart from one another to prevent a leakage (that is, sparking, arcing or any other undesired conductance), of electricity.

The voltage switch can still further comprise a motor to drive the rotor, wherein the motor is sufficiently spaced apart from the first terminal and the plurality of second terminals to prevent a leakage of electricity.

The sensing element can comprise a sensor, wherein the sensor is sufficiently spaced apart from the first terminal and the plurality of second terminals to prevent a leakage of electricity.

According to another aspect of the present invention, an electrophotographic color image forming apparatus is provided comprising a photoconductor on which an electrostatic latent image is formed, a plurality of development units each containing different color toner to apply the toner to the photoconductor in order to develop a visible toner image, a power supply for supplying development voltages to the plurality of development units, and a voltage switch for connecting the power supply with the plurality of development units in sequence. The voltage switch comprises a first terminal connected to the power supply, a plurality of second terminals arranged in a circle and connected with the plurality of development units, respectively, wherein each of the plurality of development units holds a different color toner, and a rotor for rotating about the circle to allow the first terminal to be electrically connected with the plurality of second terminals in sequence.

The rotor can comprise a lead to connect the first terminal and the plurality of second terminals, wherein the lead comprises a ring-shaped portion being in contact with the first terminal regardless of the rotation of the rotor, and a linear portion connected with the ring-shaped portion to contact the second terminals in sequence by the rotation of the rotor.

The voltage switch can comprise a step motor to drive the rotor.

The voltage switch can also comprise a sensing element to detect an angular displacement of the rotor.

The voltage switch can further comprise a stopping element to stop the rotation of the rotor when the first terminal and any one of the second terminals are connected.

The first terminal and the plurality of second terminals can be sufficiently spaced apart from one another to prevent a leakage of electricity.

The voltage switch can still further comprise a motor to drive the rotor, wherein the motor is sufficiently spaced apart from the first terminal and the plurality of second terminals to prevent a leakage of electricity.

The sensing element can comprise a sensor, wherein the sensor is sufficiently spaced apart from the first terminal and the plurality of second terminals to prevent a leakage of electricity.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A voltage switch and an electrophotographic color image forming apparatus using the same will now be described in greater detail with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown.

FIG. 2is a sectional view of an electrophotographic color image forming apparatus according to an embodiment of the present invention,FIG. 3is an exploded perspective view of a voltage switch according to an embodiment of the present invention, andFIGS. 4 and 5are plan views illustrating a circuit board in which an operation of an electrophotographic color image forming apparatus depicted inFIG. 3is illustrated. Specifically,FIG. 4is a view when one of development units is applied with a voltage, andFIG. 5is a view when no development unit is applied with a voltage.

Referring toFIG. 2, an electrophotographic color image forming apparatus100comprises a case101comprising a photoconductor111, a charge roller115, a light scanning unit105, a cyan development unit160C, a magenta development unit160M, a yellow development unit160Y, a black development unit160K, and a transfer belt151.

The photoconductor111comprises a metal drum and a photoconductive layer formed on the outer surface of the metal drum by using a deposition or similar method. The charge roller115is one example of a charger that can be provided, which charges the photoconductor111to have a uniform potential. The light scanning unit105is installed under the photoconductor111to apply light beams to the uniformly charged photoconductor111, thereby forming an electrostatic latent image corresponding to an image data.

The four development units160C,160M,160Y, and160K, include cyan (C), magenta (M), yellow (Y), and black (K) powder toners, respectively, and apply these toners to the electrostatic latent image formed on the photoconductor111to form visible toner images. The four development units160C,160M,160Y, and160K, include development rollers161C,161M,161Y, and161K, respectively, that are located to face the photoconductor111. The development rollers161C,161M,161Y, and161K, are spaced to form a development gap (Dg) of several tens to hundreds of micrometers apart from the outer surface of the photoconductor111. The toners move from the four development units160C,160M,160Y, and160K, to the photoconductor111due to a voltage difference between the photoconductor111and the development rollers161C,161M,161Y, and161K. The voltage difference is called a development voltage or development bias.

Cyan (C), magenta (M), yellow (Y), and black (K) toner images of the photoconductor111are sequentially transferred and overlapped on the transfer belt151to form a color image. Normally, the length of the transfer belt151is longer than or equal to that of a paper (S) on which the color image is finally transferred.

A transfer roller171faces the transfer belt151, and is spaced apart from the transfer belt151during the transferring of the toner images from the photoconductor111to the transfer belt151. The transfer roller171is then brought into contact with the transfer belt151to apply a pressure to transfer the color image from the transfer belt151to the paper (S).

To improve a transferring efficiency, a pre-transfer eraser107removes electric charge from a non-image area of the photoconductor111before transferring the toner image of the photoconductor111to the transfer belt151. Herein, the non-image area of the photoconductor111denotes an area where the toner image is not formed.

An erase lamp117is another example of such a charge eraser, and removes residual electric charge from the photoconductor111before charging the photoconductor111.

A power supply108provides the development bias to apply the toners from the four development units160C,160M,160Y, and160K, to the photoconductor111for forming the toner images. The power supply108also provides a first transfer bias to transfer the toner images of the photoconductor111to the transfer belt151for forming the color image, and provides a second transfer bias to transfer the color image from the transfer belt151to the paper (S). Further, the power supply108provides a charge bias to the charge roller115.

A fuser175fuses the toners of the color image onto the paper (S), and includes a pair of engaged rollers176and177. The pair of rollers176and177are provided with a heating element for heating the toners of the color image. While the paper (S) passes through the fuser175, the toners of the color image of the paper (S) are melted and securely adhered to the paper (S) by the heat and pressure of the fuser175, thereby completing a color image printing.

A first cassette180astores the paper (S) to be printed. There can also be a second cassette180band a third cassette180c. The third cassette180cis usually used for office head paper (OHP) paper or irregular paper.

A feed roller183conveys the sheets of paper (S) picked up one by one by a pick-up roller181a,181b, or181c. An eject roller184ejects the paper (S) from the case101. The electrophotographic color image forming apparatus100further comprises a feed passage185for feeding the paper (S) upwardly from the feed roller183to the fuser175, and also comprises a duplex path186for guiding the paper (S) downwardly for a duplex printing operation. After passing the fuser175, the paper (S) of which one side is printed, is ejected from the case101by the eject roller184. In a duplex printing operation, however, the eject roller184rotates in a reverse direction to direct the paper (S) to the duplex path186, and then the feed roller183conveys the returned paper (S) from the duplex path186to the feed passage185for printing on the other side of the paper (S). Herein, when the paper (S) is directed to the duplex path186by the eject roller184, the paper (S) is inverted for printing on the other side.

A first cleaning unit119removes the remaining toner from the outer surface of the photoconductor111after the transferring from the photoconductor111to the transfer belt151. Further, a second cleaning unit159removes the remaining toner from the transfer belt151after the transferring from the transfer belt151to the paper (S). The toners removed by the first cleaning unit119and the second cleaning unit159are conveyed to a waste toner collector (not shown).

An exemplary operation of the electrophotographic color image forming apparatus100will now be described in greater detail according to an embodiment of the present invention.

Color image data includes cyan (C), magenta (M), yellow (Y), and black (K) image data. In an embodiment of the present invention, cyan (C), magenta (M), yellow (Y), and black (K) toner images are sequentially transferred to the transfer belt151, such that the transferred toner images are overlapped on the transfer belt151to form a color image. The overlapped color image is then transferred and fused on the paper (S), thereby completing a printing operation.

In a charging operation, the charge roller115uniformly charges the outer surface of the photoconductor111. In an exposing operation, the light scanning unit105applies a light beam corresponding to the cyan (C) image data to the uniformly charged photoconductor111that is rotating. The light beam causes the photoconductor111to have a lower resistance at an area where the light beam is applied, and this causes the area to discharge. Therefore, a voltage difference is generated between the light beam applied area and the remaining area of the photoconductor111, thereby forming an electrostatic latent image on the photoconductor111.

In a developing operation, when the rotating photoconductor111having the electrostatic latent image and the cyan development unit160C become closer, the development roller161C of the cyan development unit160C starts to rotate. The power supply108applies a development bias to the development roller161C to make the cyan (C) toner move across the development gap (Dg) and adhere to the electrostatic latent image of the photoconductor111, thereby developing a cyan toner image on the photoconductor111.

In a transferring operation, the cyan toner image on the photoconductor111reaches the transfer belt151by a rotation of the photoconductor111, and the cyan toner image is then transferred to the transfer belt151due to the first transfer bias or a contact pressure between the photoconductor111and the transfer belt151.

After the cyan toner image is completely transferred to the transfer belt151, magenta (M), yellow (Y), and black (B) toner images are sequentially transferred and overlapped to the transfer belt151through the same developing and transferring operations.

The transfer roller171is spaced apart from the transfer belt151until all four toner images are transferred to the transfer belt151to form the color image on the transfer belt151. The transfer roller171is then brought into contact with the transfer belt151to transfer the color image from the transfer belt151to the paper (S).

The paper (S) can be fed from the first cassette180a, second cassette180b, or third cassette180cto arrive at a contact line between the transfer belt151and the transfer roller171exactly at a time when a leading end of the color image of the transfer belt151arrives at the contact line. While the paper (S) passes between the transfer belt151and the transfer roller171, the color image is transferred to the paper (S) due to the second transfer bias. In a fusing operation, the transferred color image is securely bonded to the paper (S) by the heat and pressure of the fuser175. After these operations, the paper (S) is ejected from the case101to complete a printing operation.

Before the next printing operation, the first cleaning unit119and the second cleaning unit159remove the remaining toners from the photoconductor111and transfer belt151, respectively. The erase lamp117applies light to the photoconductor111to remove the residual charge.

A voltage switch for connecting the power supply108to the four development units160C,160M,160Y, and160K in sequence to apply a developing bias, will now be described in greater detail.

Referring toFIGS. 3,4, and5, a voltage switch200includes a circuit board201, a first terminal203, four second terminals205C,205M,205Y, and205K, and a rotor220. The first and second terminals are provided on the circuit board201, and the rotor220is rotatably installed on the circuit board201.

The first terminal203is electrically connected to the power supply108, and the four second terminals205C,205M,205Y, and205K are electrically connected to the four development units160C,160M,160Y, and160K, respectively. The four second terminals205C,205M,205Y, and205K, are arranged to form an imaginary circle C1and are preferably disposed on the circuit board201at an angle of 90° therebetween.

The rotor220has a circular plate shape and is installed to be rotatable about the center of the circle C1. A step motor210which can control a rotation angle, can be provided to drive the rotor220. The step motor210is mounted on one side of the circuit board201, with its shaft212inserted through the circuit board201at the center of the circle C1and protrudes from the other side of the circuit board201. The protruding shaft212is inserted into a hole222of the rotor220, thereby rotatably mounting the rotor220on circuit board201. The diameter of the rotor220C2is larger than that of the circle C1.

The rotor220is provided at one side such that a lead225is facing the circuit board201for electrically connecting the first terminal203to the four second terminals205C,205M,205Y, and205K, in sequence. The lead225can be comprised of a metal plate, and includes a ring-shaped portion226and a linear portion228connected with the ring-shaped portion226. The center of the ring-shaped portion226is located around the hole222, such that the ring-shaped portion226can contact the first terminal203regardless of the rotation of the rotor220. The linear portion228contacts the four second terminals205C,205M,205Y, and205K, in sequence by the rotation of the rotor220.

The angular displacement of the rotor220is detected by a sensing element. The sensing element comprises a first slit231, second slit232, third slit233, and fourth slit234, that are formed at a peripheral portion of the rotor220, and also includes an optical sensor213for detecting the slits231through234.

The slits231through234are arranged around the hole222of the rotor220at an angle of 90° therebetween.

Referring toFIG. 4, when the fourth slit234passes through the optical sensor213during the rotation of the rotor220by the step motor210in the direction of the arrow, the optical sensor213detects the four slits of the fourth slit234and sends a corresponding signal to a controller (not shown) controlling the operation of the voltage switch200. The controller controls the step motor210to stop the rotor220when the linear portion228contacts the second terminal205K that is connected to the black development unit160K. In this manner, when the optical sensor213detects the single slit of the first slit231, the step motor210comes to a stop after a predetermined interval to maintain a contact between the linear portion228and the second terminal205C that is connected to the cyan development unit160C. When the optical sensor213detects the two slits of the second slit232, the step motor210comes to a stop after a predetermined interval to maintain a contact between the linear portion228and the second terminal205M that is connected to the magenta development unit160M. When the optical sensor213detects the three slits of the third slit233, the step motor210comes to a stop after a predetermined interval to maintain a contact between the linear portion228and the second terminal205Y that is connected to the yellow development unit160Y. The predetermined intervals are determined by an angular velocity of the step motor210, and the angles between the linear portion228and the second terminals205C,205M,205Y, and205K, that are pre-positioned to the linear portion228when the slits231,232,233, and234, pass through the optical sensor213.

When a motor, of which a rotation angle cannot be controlled, is used for driving the rotor220instead of the step motor210, a stopping element for stopping the rotor220can be required. Further, even when the step motor210is used as shown inFIGS. 3,4, and5, the employment of a stopping element increases reliability in the stopping of the rotor220. The stopping element comprises first, second, third, and fourth dents236,237,238, and239, and a stopper216that is capable of fitting into the dents for stopping the rotor220. The stopper216is provided with a lever217that is urged against the outer circumference of the rotor220by an elastic force. Also, the stopper216is provided with a solenoid218that is capable of retracting the lever217from the rotor220.

The dents236through239are placed around the hole222of the rotor220at an angle of 90 degrees therebetween. Referring again toFIG. 4, when the stopper216engages the dent239, the linear portion228comes into contact with the second terminal205K connected to the black development unit160K. In a similar manner, the other dents236,237, and238, are positioned to allow the linear portion228to contact the other second terminals205C,205M, and205Y, in sequence when the other dents236,237, and238, are sequentially engaged by the stopper216. Therefore, the development units160K,160C,160M, and160Y, can be sequentially connected with the linear portion228.

The controller (not shown) for controlling the voltage switch200also controls the stopper216. When one of the dents236through239is engaged by the lever217of the stopper216, the development bias is applied to a corresponding development unit to develop a corresponding toner image on the photoconductor111. At the end of the developing of the toner image, the solenoid218is supplied with a current to retract the lever217and thereby allow the rotor220to start to rotate. The developing of the toner image is suspended until the linear portion228contacts the next terminal.

To avoid sparks or arcing, the power supply108can be controlled to supply the development bias only after the linear portion228comes into contact with the second terminal205C,205M,205Y, or205K, and to stop the supply of the development bias just before the linear portion228leaves the second terminal.

A sufficient safety distance can be provided between the first terminal203and each of the second terminals205C,205M,205Y, and205K, to also prevent a leakage (that is, sparking, arcing or any other undesired conductance) of electricity. In one exemplary embodiment of the present invention, the safety distance can be about 5 mm when the power supply108supplies the development voltage of up to 3 kV. Also, a sufficient safety distance can be provided between the step motor210and the first terminal203, between the step motor210and the second terminals205C,205M,205Y, and205K, between the optical sensor213and the first terminal203, and between the optical sensor213and the second terminals205C,205M,205Y, and205K, in order to prevent a short circuit.

Since the voltage switch of the embodiments of the present invention has a smaller size than that of the conventional voltage switch, it requires a smaller space for installation, and thereby, the electrophotographic color image forming apparatus can be made to have smaller size.

Further, the voltage switch of the embodiments of the present invention is operated without the expensive solenoids and with fewer parts compared to the conventional voltage switch, thereby reducing cost.