Abstract:
An image forming apparatus having a main body and optional trays and a communication method between the main body and the optional trays, the apparatus including: the main body having a main controller; at least one optional tray detachably set up in the main body and having a tray controller for communicating with the main controller to transmit and receive data; and communication lines forming a communication channel connecting the main controller and the tray controllers, for data exchange, and for informing the main controller that the data is provided from tray controllers to the main controller. Since the main body and the optional trays communicate through a single UART communication channel, the number of communication channels is decreased thereby saving time and simplifying protocol as well as reducing costs and simplify circuits. Also, it is possible to assign IDs rapidly and simply, prevent generation of errors in ID assignment, and make use of the image forming apparatus convenient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2005-56804 filed Jun. 29, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     An aspect of the present invention relates to an image forming apparatus and a communication method with trays thereof; and, more particularly, to an image forming apparatus that can communicate with trays through a single communication channel and assign an identification (ID) to each tray simply and accurately, and its communication method with its trays. 
     2. Description of the Related Art 
     Recently, functions of image forming apparatuses are diversified such as a function of a printer and a function of a copier, and the image forming apparatuses are connected through a network. This has increased the required quantity of recording media and thus the image forming apparatuses should be equipped with many optional trays. Therefore, image forming apparatuses with a plurality of optional trays stacked in multiple steps are widely used these days. Each optional tray of an image forming apparatus communicates with the main body of the image forming apparatus through a communication channel. Herein, a one-to-one communication UART is usually used as the communication scheme. 
       FIG. 1  is a schematic diagram showing a conventional communication scheme between the main body of an image forming apparatus and its optional trays. According to the UART communication scheme shown in the drawing, the main body  10  of the image forming apparatus is assigned in advance with as many communication channels as the number of available optional trays  20 ,  30  and  40  and, when each optional tray  20 ,  30  or  40  is mounted in the main body  10 , it is connected to the main body  10  to be able to communicate through a one-to-one communication channel. Therefore, since the main body  10  uses a separate communication channel to communicate with each optional tray  20 ,  30  or  40  one-to-one, it requires as many communication channels as the number of optional trays  20 ,  30  and  40 . 
     A first optional tray  20  is connected to the main body  10  through a first UART communication channel, and a second optional tray  30  is connected to the main body  10  through a second UART communication channel. Likewise, a third optional tray  40  is connected to the main body  10  through a third UART communication channel. Thus, the image forming apparatus transmits a control command through the first UART to operate the first optional tray  20  and transmits a control command through the second UART to operate the second optional tray  30 . For example, when the main body  10  transmits a feeding command to the second optional tray  30  through the second UART, the second optional tray  30  drives a feeding motor for operating a feeding roller (not shown) to feed a recording medium. 
     Since the conventional image forming apparatus performs one-to-one communication between its main body  10  and each optional tray  20 ,  30  or  40  through a UART communication channel, it has an advantage that communication protocol is simple. However, it requires as many communication channels as the number of optional trays it can have in the main body  10  and it takes a high amount of costs to form the main body  10  to be connected with a plurality of communication channels. Moreover, since many communication channels are applied to the main body  10 , the conventional image forming apparatus has a shortcoming that a Central Processing Unit (CPU) of the main body  10  suffers much load. 
     In order to reduce the amount of load applied to the CPU, a method of connecting the main body and optional trays through a UART communication channel and then connecting a first optional tray and a second optional tray through a UART communication channel has been suggested. However, although the method can reduce the amount of load applied to the CPU, it still requires as many UART communication channels as the number of optional trays because it needs a UART communication channel between the main body and the first optional tray and a UART communication channel between the first optional tray and the second optional tray separately. Therefore, there are problems that it takes much cost for building up a plurality of UART communication channels and that the circuit is complex. 
     Since the conventional image forming apparatus needs as many UART communication channels as optional trays, the number of optional trays that can be used in the image forming apparatus is limited. 
     To solve the problem, a method that can reduce costs and complexity in the circuit by using a single communication channel between the main body and the optional trays should be sought. 
     Korean Patent No. 10-378172 entitled “Tray recognizing apparatus and method,” discloses a structure where each of a plurality of optional trays is assigned an ID. According to this technology, a power supplier of the main body supplies power to a controller of a first optional tray, and the first optional tray transmits the power to a second optional tray. In short, the power is supplied from the main body to the optional trays sequentially. Herein, since each optional tray has a resistance set up therein, the level of power is decreased as the power passes through each resistance. Thus, the main body can assign an ID to each optional tray based on the voltage value of power applied to each optional tray. However, since a contact resistance may be generated by a connector, the voltage value applied to each optional tray can be different from an expected level and the voltage difference between the optional trays can be diverse. Therefore, an error may occur when the main body communicates with each optional tray or when an ID is assigned to each optional tray. 
     Other than the above-described method, there is a method of providing a switch for manually setting each optional tray. According to this method, a user turns on a switch after mounting each optional tray. Then, each optional tray recognizes its own ID and transmits its ID to a main controller. This method, however, has a drawback in that a user has to manually manipulate the switch and, if the same ID is set for a different optional tray due to a mistake of the user, data can be entangled during data transmission and reception. 
     Therefore, a method that can relieve users from manually setting up an ID and assigning an ID to each optional tray rapidly and accurately is needed. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an aspect of the present invention to provide an image forming apparatus that can simplify a circuit and reduce costs by using a single communication channel between a main body and optional trays, and a communication method with optional trays thereof. 
     It is another aspect of the present invention to provide an image forming apparatus that can relieve users from the trouble of setting up an ID for themselves and assign an ID to each optional tray rapidly and accurately, and a communication method with optional trays thereof. 
     In accordance with an aspect of the present invention, there is provided an image forming apparatus, which includes: a main body having a main controller for controlling the image forming apparatus to output image; at least one optional tray which is set up in the main body detachably and has a tray controller for communicating with the main controller to transmit and receive data; and communication lines that form one communication channel connecting the main controller and each tray controller, make the main controller and the tray controller exchange data, and inform the main controller that data are provided from at least one tray controller to the main controller. 
     In accordance with another aspect of the present invention, the communication lines include a TXD line for providing data from the main controller to each tray controller, an RXD line for providing data from the tray controller to the main controller, and a busy line for informing that data are provided from at least one tray controller to the main controller through the RXD line. 
     In accordance with another aspect of the present invention, each line for connecting the RXD line with each tray controller includes an open connector set up therein for preventing collision between signals from different tray controllers, and a line for connecting the RXD line and the main controller includes a pull-up resistance for turning on the open collector. 
     In accordance with another aspect of the present invention, a line for connecting the busy line with each tray controller includes an open collector set up therein for preventing collision between signals transmitted from different tray controllers, and a line for connecting the busy line and the main controller includes a pull-up resistance for turning on the open collector. 
     In accordance with another aspect of the present invention, data from each tray controller can go through wired-OR in each open collector and a result obtained from the wired-OR is transmitted to the main controller. 
     In accordance with another aspect of the present invention the communication lines can adopt a UART communication scheme. 
     In accordance with another aspect of the present invention, there is provide an image forming apparatus, which includes: a main body having a main controller for controlling the image forming apparatus to output an image; at least one optional tray which is set up in the main body detachably and has a tray controller for communicating with the main controller to transmit and receive data; communication lines for forming at least one communication channel for communication between the main controller and tray controllers; and a plurality of reset lines for connecting the main controller of the main body and a tray controller of an optional tray closest to the main body, and connecting the tray controllers of adjacent optional trays together sequentially. 
     Preferably, but not necessarily, each reset line includes a pull-down resistance for pulling down voltage to maintain a reset mode. 
     The tray controllers of optional trays can be revoked from the reset mode sequentially from the tray controller of an optional tray closest to the main controller based on a reset revocation signal transmitted form the main controller. 
     The main controller assigns an ID to each of the optional trays sequentially through the communication lines, when the optional trays are revoked from the reset mode. 
     Preferably, but not necessarily, when the tray controller of the optional tray closest to the main body is assigned with the ID, the tray controller of the optional tray closest to the main body transmits a reset revocation signal to the tray controller of a next closest optional tray. 
     In accordance with another aspect of the present invention, there is provided a method of communicating between a main body and trays in an image forming apparatus having a main body with a main controller, and at least one optional tray having a tray controller, the method including forming a single communication line connecting the main controller with the tray controllers; and transmitting data from the main controller to the tray controllers or from the tray controllers to the main controller through the communication line, wherein the main controller of the main body controls the image forming apparatus to output an image, and the optional tray is detachably set up in the main body and has the tray controller for data communication with the main controller. 
     In accordance with another aspect of the present invention, there is provided a method of communicating between a main body and trays in an image forming apparatus having a main body with a main controller and at least one optional tray having a tray controller, the method including forming a plurality of reset lines connecting the main controller of the main body with a tray controller of an optional tray closest to the main body and connecting tray controllers of adjacent optional trays; and setting up a pull-down resistance for pulling down voltage to maintain a reset mode for each reset line, wherein the main controller controls the image forming apparatus to output an image, and the optional tray is detachably set up in the main body and has the tray controller for communicating with the main controller to transmit and receive data. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantage of the invention will become more apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic diagram showing a conventional communication scheme between a main body of an image forming apparatus and its optional trays; 
         FIG. 2  is a circuit diagram illustrating a communication scheme between a main body of an image forming apparatus and its optional trays in accordance with an embodiment of the present invention; and 
         FIG. 3  is a flowchart describing a process of giving an identification (ID) to each optional tray in the image forming apparatus in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     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 in order to explain the present invention by referring to the figures. 
       FIG. 2  is a circuit diagram illustrating a communication scheme between a main body of an image forming apparatus and its optional trays in accordance with an embodiment of the present invention. As shown in the drawing, the image forming apparatus includes a main body  110  having a main controller  115 , and a plurality of optional trays  120  and  130  having tray controllers  125  and  135 , respectively. 
     The main body  110  and the optional trays  120  and  130 , which are a first optional tray  120  and a second optional tray  130 , respectively, are connected through three communication lines which form a single UART communication channel. Herein, the three communication lines include a TXD line  153  for transmitting data from the main body  110  to the optional trays  120  and  130 , an RXD line  151  for transmitting data from the optional trays  120  and  130  to the main body  110 , and a busy line  155  for notifying that an optional tray is in the middle of transmitting data to the main body  110 . 
     Among the lines, a line for connecting the main controller  115  of the main body  110  and the TXD line  153  includes a first buffer  116  set up therein, and a line connecting the TXD line  153  and the tray controllers  125  and  135  of the optional trays  120  and  130  includes a second buffer  126 . Through the TXD line  153 , the main controller  115  of the main body  110  transmits a control command to the optional trays  120  and  130 . For example, when the main controller  115  of the main body  110  generates a feeding command requesting the first optional tray  120  to feed a recording medium contained therein, the feeding command is transmitted from the main controller  115  to the tray controllers of all optional trays mounted in the main body  110  including not only the first optional tray  120  but also the second optional tray  130  through the TXD line  153 . Herein, the main controller  115  transmits a predetermined ID of the first optional tray  120  along with the feeding command. Thus, although the tray controllers  125  and  135  of all the optional trays  120  and  130  receive the feeding command, only the first optional tray  120  executes the feeding command and the other optional tray with a different ID is not operated. In short, only the first optional tray  120  drives a feeding motor to operate a feeding roller for feeding a recording medium. 
     Meanwhile, a line connecting the RXD line  151  and the main controller  115  of the main body  110  includes a third buffer  117  and a first pull-up resistance  118  for supplying power for operating a first open collector  127 , and a line connecting the RXD line  151  and the tray controllers  125  and  135  of the optional trays  120  and  130  includes the first open collector  127  set up therein. Herein, the first open collector  127  is used to prevent a short-circuit which can be caused when a plurality of outputs are connected in a Complementary Metal Oxide Semiconductor (CMOS) device or a TTL circuit performing a complementary operation. It performs a wired-OR function when a plurality of outputs are connected through the first open collector  127 . According to the wired-OR function, each open collector  127  connected to each RXD line  151  sends out an ‘L’ signal to the main controller  115  when data outputted from each optional tray  120  or  130  has both a ‘high (H)’ state and a ‘low (L)’ state, that is, when data outputted from each optional tray  120  or  130  have at least one ‘L’ state. 
     The RXD line  151  transmits data from the tray controllers  125  and  135  of the optional trays  120  and  130  to the main controller  115  of the main body  110 , and the data is mainly composed of data of the state of the optional trays  120  and  130  which is sensed by sensors. Most of the transmitted data is concerned with whether there is a recording medium jam, whether there is a recording medium, the remaining quantity of the recording medium, whether the recording medium is in the right position for being picked up, the size of the recording medium, and whether a pickup roller is driven. 
     Similar to the RXD line  151 , a line connecting the busy line  155  and the main controller  115  of the main body  110  is connected to a fourth buffer  112  and a second pull-up resistance  113 . Also, a line connecting the busy line  155  and the tray controllers  125  and  135  of the optional trays  120  and  130  is connected to a second open collector  128 . The busy line  155  prevents collision between data caused when a plurality of optional trays  120  and  130  share one communication channel. When even one of the optional trays  120  and  130  transmits data to the main controller  115  through the RXD line  151 , the busy line  155  transmits a busy signal to the main controller  115 . In short, even when one ‘L’ signal is inputted from the optional trays to the main controller  115 , the main controller  115  determines that the RXD line  151  is in use. 
     In the above-described structure of the UART communication channel, the main controller  115  of the main body  110  transmits such data as feeding commands to each optional tray  120  or  130  through the TXD line  153 , and the tray controllers  125  and  135  of the optional trays  120  and  130  transmit the data of the state of the optional trays  120  and  130  to the main body  110  through the RXD line  151 . Herein, the same data is transmitted to all the optional trays  120  and  130  through the TXD line  153 . However, since the data includes an ID of an optional tray  120  or  130 , only the corresponding optional tray is operated according to the data. Also, if any one of the optional trays  120  and  130  is in the middle of transmitting data to the main body  110 , that is, if any one is in the ‘L’ state, the busy line  155  transmits data indicating that the RXD line  151  is in use to the main body  110  according to the wired-OR function of the second open collector  128 . 
     Meanwhile, the main body  110  and the optional trays  120  and  130  are connected to each other through reset lines  160 ,  170  and  180  in order to assign an ID to each optional tray  120  or  130 . First, the main body  110  and the first optional tray  120  are connected through a first reset line  160 , and the first optional tray  120  and the second optional tray  130  are connected through a second reset line  170 . The second optional tray  130  and yet another optional tray are connected through a third reset line  180 . 
     Herein, the first reset line  160  is connected to pull-down resistances  163  and  167  and buffers  161  and  165  on the part of the main body  110  and on the part of the first optional tray  120 , respectively. Likewise, the second reset line  170  is connected to pull-down resistances  173  and  177  and buffers  171  and  175  on the part of the first optional tray  120  and on the part of the second optional tray  130 , respectively. Herein, the pull-down resistances  163 ,  167 ,  173  and  177  force the voltage to fall down in order not to generate output in the reset mode, that is, in order to output an ‘L’ signal. 
     A process of giving an ID through each reset line will be described herein with reference to  FIG. 3 . 
     First, when the power of the main body  110  is turned on, the first reset line  160  enters a reset mode by the pull-down resistances  163  and  167  set up in the first reset line  160  connecting the main body  110  and the first optional tray  120 . Since the first optional tray  120  provides reset signals through the first reset line  160 , the tray controller  125  of the first optional tray  120  maintains the reset mode. Likewise, the tray controller  125  of the first optional tray  120  provides reset signals to the tray controller  135  of the second optional tray  130  through the second reset line  170 , the tray controller  135  of the second optional tray  130  maintains the reset mode as well. All the other optional trays including the first and second optional trays  120  and  130  maintain the reset mode. 
     At operation S 300 , when a reset revocation signal is transmitted to the tray controller  125  of the first optional tray  120  through the first reset line  160  by supplying an ‘H’ signal from the main controller  115  of the main body  110  to a first buffer  161  in the reset mode, i.e., in the ‘L’ state, at operation S 310 , the tray controller  125  of the first optional tray  120  is revoked from the reset mode. After the tray controller  125  of the first optional tray  120  gets out of the reset mode, the main controller  115  of the main body  110  communicates with the tray controller  125  of the first optional tray  120 . When the communication is not successful, the main controller  115  informs a user of information on the communication error with the first optional tray  120 . If the communication is made successfully, at operation S 320 , the main controller  115  assigns an ID to the first optional tray  120 , and the tray controller  125  of the first optional tray  120  acknowledges to the main body  110  that it has received the ID. Then, the first optional tray  120  waits for a signal indicating that the ID has been assigned successfully and the reset mode is switched into a normal operation mode from the main body  110 . Meanwhile, when there is another optional tray at operation S 330 , at operation S 340 , the first optional tray  120  transmits a signal for revoking the reset mode to the second optional tray  130  through the second reset line  170 . 
     Then, at operation S 350 , the second optional tray  130 , similar to the first optional tray  120 , is revoked out of the reset mode and, at operation S 360 , the main body  110  communicates with the second optional tray  130  to assign an ID to the second optional tray  130 . Herein, since the main controller  115  of the main body  110  has already assigned an ID to the first optional tray  120 , it assigns another ID that is not the same as that of the first optional tray  120  to the second optional tray  130 . Subsequently, the tray controller  135  of the second optional tray  130  acknowledges to the main controller  115  of the main body  110  that it has received the ID and waits for a sign indicating that its mode is switched into the normal operation mode from the main controller  115  of the main body  110 . 
     Through the above-described ID assigning process from operations S 330  to S 360 , another optional tray that can be provided to the main body can be revoked out of the reset mode and receive an ID assigned thereto. 
     According to the above-described ID assigning method, each of the optional trays receive an ID assigned thereto sequentially whenever the image forming apparatus is turned on. Therefore, users need not set up the IDs mechanically or electrically by using a switch for themselves. Therefore, this method makes the use of the image forming apparatus convenient. Also, it is possible to prevent an error form being generated due to a change in a resistance value during the ID assignment of each optional tray, which is a problem of conventional technology, by revoking each optional tray from the reset mode and assigning an ID sequentially. Therefore, each optional tray can be assigned with an ID more accurately and rapidly. 
     Meanwhile, since each optional tray and the main body communicate with each other through the RXD line  151 , TXD line  153  and busy line  155 , which form a single UART communication channel, the image forming apparatus according to an aspect of the present invention needs not a plurality of UART communication channels which are used in conventional technologies. Since the number of UART communication channels needs not be increased although the number of optional trays is increased, the circuit is simplified and costs are reduced. Also, since the entire optional trays can be controlled with one control command at the same time, it is possible to reduce time consumption for communication and simplify protocol. 
     The technology according to an aspect of the present invention described above can not only reduce costs and simplify the circuit but also reduces communication time and simplifies the protocol by making a communication between the main body and the optional trays through a single UART communication channel and reduces the number of communication channels. 
     Also, the technology according to an aspect of the present invention can prevent the generation of an error during the ID assignment and make the use of the image forming apparatus convenient as well as simplifying and rapidly generating the ID assignment by connecting the main body with an optional tray, and connecting the optional tray with another optional tray through reset lines, revoking the optional trays from the reset mode sequentially through the reset lines and assigning IDs. 
     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.