1. Field of the Invention
Aspects of the present invention relate to an electrographic image forming device, and more particularly, to a method and apparatus to control power supplied to a paper transfer belt (PTB) unit and a laser scanning unit (LSU) according to whether a cover of an image forming device is open or closed and whether the PTB unit is installed within the image forming device.
2. Description of the Related Art
In an image forming device, when a paper jam, in which printing paper fed by a paper transfer belt (PTB) unit is jammed in a transfer belt, occurs, a user generally cannot remove the jammed paper until after opening an outer cover of the image forming device. Similarly, when the transfer belt, which is a replaceable part, must be changed, a user cannot replace the transfer belt until after separating the PTB unit from the image forming device. As illustrated in FIG. 1, if a laser scanning unit (LSU) which scans a laser beam onto a photosensitive medium faces the outer cover of the image forming apparatus, a laser beam may be irradiated on the eyes of the user when the user opens the outer cover of the image forming device or separates the PTB unit from the image forming device.
In order to prevent this problem whereby a laser beam scanned by the LSU is irradiated on the eyes of the user, the conventional image forming device generally includes a device to block the laser beam so that the laser beam is not exposed to the user. In particular, if a laser beam is irradiated on the eyes of the user, various problems may occur, such as the laser beam distracting the user. Thus, various kinds of standards require image forming devices to include a device which double blocks the laser beam irradiated by the LSU.
FIG. 1 is a side view of an image forming device having a conventional power control apparatus. The image forming device in FIG. 1 may be a copier, a facsimile machine, a multi-function unit, etc. Referring to FIG. 1, an LSU 100 scans light to form an electrostatic latent image onto a photosensitive medium 110. A PTB unit 120 feeds a recording medium, such as printing paper, into the image forming device and transfers a developed latent image onto the recording medium. An outer cover 130 allows a user to open or close the image forming device from the outside so that the user can remove jammed recording media from the PTB unit 120 and/or separate the PTB unit 120 from the image forming device by allowing access to the inside of the image forming device.
A first micro-switch 140 and a second micro-switch 150 are devices to cut off power supplied to the LSU 100 in response to the opening of the outer cover 130. The LSU shutter 160 is a device which blocks a laser beam scanned by the LSU 100 in response to the opening of the outer cover 130.
FIGS. 2A and 2B are block diagrams of conventional power control apparatuses. These conventional power control apparatuses are generally housed within conventional image forming devices, such as the conventional image forming device shown in FIG. 1.
In the conventional power control apparatus illustrated in FIG. 2A, a power controller 170 receives electrical power of +24V and +5V generated by a power supply unit 180 and transmits the received electrical power of +24V and +5V to the LSU 100 via the first micro-switch 140 and the second micro-switch 150, respectively. The first micro-switch 140 and the second micro-switch 150 are both turned on when the outer cover 130 is closed, and are both turned off when the outer cover 130 is opened. Thus, when a user opens the outer cover 130, the first micro-switch 140 turns off, thereby cutting off the electrical power of +24V supplied to a motor 102 of the LSU 100, and the second micro-switch 150 also turns off, thereby cutting off the electrical power of +5V supplied to a laser diode (LD) 104 of the LSU 100. The power controller 170 generates electrical power of +3.3V using the electrical power supplied by the power supply unit 180 and provides the generated electrical power of +3.3V to various kinds of sensors and memory units included in the PTB unit 120.
Unlike the conventional power control apparatus illustrated in FIG. 2A, which has two micro-switches 140 and 150, the conventional power control apparatus illustrated in FIG. 2B has only one micro-switch 140 and an LSU shutter 160 which blocks a laser beam scanned by the LSU 100. Since the components of the conventional power control apparatus illustrated in FIG. 2B are the same components as the components of the conventional power control apparatus illustrated in FIG. 2A except for the LSU shutter 160, only the LSU shutter 160 will be described. As shown in FIG. 1, the LSU shutter 160 is installed next to the LSU 100 near an opening through which a laser beam is irradiated. When a user opens the outer cover 130, a lever operating in conjunction with the opening and closing of the outer cover 130 causes the LSU shutter 160 to block the laser beam. Thus, when a user opens the outer cover 130, the LSU shutter 160 blocks a laser beam from irradiating outside of the image forming device.
As described above, the conventional power control apparatus illustrated in FIG. 2A has a first micro-switch 140 and a second micro-switch 150. The first micro-switch 140 and second micro-switch 150 are both turned on when the outer cover 130 is closed, and are both turned off when the outer cover 130 is opened, in order to support double blocking of a laser beam according to a specification. The conventional power control apparatus illustrated in FIG. 2A has several drawbacks. Since a plurality of micro-switches must be installed, the space required to install the plurality of micro-switches is large, the manufacturing costs of the conventional power control apparatus are high, and the mechanical embodiment is complicated.
Furthermore, the conventional control apparatus illustrated in FIG. 2B also has drawbacks. Although the design of the conventional power control apparatus illustrated in FIG. 2B reduces the number of micro-switches to only one, this design additionally requires the LSU shutter 160. For an image forming device using a single path method, since laser beams to which yellow, magenta, cyan, and black images are exposed must all be blocked, the conventional power control apparatus illustrated in FIG. 2B must have at least four LSU shutters 160, resulting in a spatial problem and high manufacturing costs.
Moreover, in the conventional power control apparatuses illustrated in FIGS. 2A and 2B, even though electrical power supplied to the LSU 100 is cut off when the outer cover 130 (FIG. 1) is opened, electrical power is continuously supplied to the PTB unit 120. This continuous supply of electrical power to the PTB unit 120 causes glitch noise to occur due to an instantaneous unstable contact when the outer cover 130 is closed, causing malfunctions of the various kinds of sensors and memory units included in the PTB unit 120.