Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2002-03-07
2004-05-25
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S087000, C345S212000, C345S213000
Reexamination Certificate
active
06741239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive power source of a liquid crystal display in an image forming apparatus, that is, an LCD power source control method for controlling a drive voltage and a control circuit thereof, and an image forming apparatus having the control circuit.
2. Description of the Prior Art
Hitherto, in an image forming apparatus of a copying machine or the like, for example, there is one in which fine toner particles are used to copy an image of an original document onto a copy paper.
According to this image forming apparatus, the image of the original document is optically read by an image reading device and then the read image is formed as an electrostatic latent image on a photoreceptor such as a photosensitive drum. Fine toner is adhered to the electrostatic latent image of the photoreceptor so that the image is formed (developed) by the toner.
Moreover, in the image forming apparatus, a sheet feed roller draws a copy paper from a paper tray or the like and the drawn copy paper is conveyed to a position of the photoreceptor by a number of sheet feed rollers, whereby the image formed on the photoreceptor is copied on the copy paper. The copy paper having the image copied thereon in such manner is transferred by the sheet feed roller to a portion of a fixed roller which will be heated by a heater. After being heated by the heat of the fixed roller, the copy paper is then discharged therefrom. The image transferred on the copy paper is fixed thereon due to heating.
Such an image reading device, a sheet feed roller, a photosensitive drum, fixed roller, and the like are operated by a power source circuit that is provided in a main body of the image forming apparatus.
Further, various operation buttons or switches are provided on an operation panel in such an image forming apparatus, and an LCD (liquid crystal display) for displaying the present situation of the apparatus and the displays corresponding to the operation is normally provided as display means therein as well.
A liquid crystal display such as an STN-LCD (Super Twisted Nematic Liquid Crystal Display) is often used for the operation panel. A drive voltage from a power source circuit is applied to a logic circuit, whereby operation control of a liquid crystal display such as the STN-LCD is performed based on a timing signal generated from the logic circuit. For example, a frame signal is used as the timing signal. A low voltage drive power source of a +5V system, a +3.3V system, or the like is necessary in order to control the operation of the logic circuit, and a drive power source of a relatively high voltage such as +24V or −12V is necessary for driving the liquid crystal display as well. It should be noted that, in order to discern the low voltage drive power source of the logic circuit from the drive power source for driving the liquid crystal display, the drive power source for driving the liquid crystal display is explained herein as a high voltage drive power source.
These drive power sources are provided in an LCD module, that is, inside the module of the liquid crystal display, whereby the drive voltage of the logic circuit and the liquid crystal display may be increased and generated inside the module.
Since the power source circuit for driving the image reading device and the movable parts such as the sheet feed roller, the photosensitive drum, and the fixed roller is disposed in the main body of the apparatus as mentioned above in the aforementioned image forming apparatus. The present situation is that a low voltage drive power source for the LCD module is provided in the power source circuit of the main body of the apparatus in order to reduce costs.
Further, it is necessary to set input and interruption timing of the power source of the main body of the apparatus as follows in the image forming apparatus in order to prevent deterioration of the liquid crystal of the liquid crystal display when performing input/interruption of the power source thereof. In other words, there is a demand that at the time of the power source input, the high voltage drive power source of the liquid crystal display rises at the same time as or later than the low voltage drive power source of the logic circuit. Also, at the interruption of the power source, it is demanded that the high voltage drive power source of the liquid crystal display falls earlier than or at the same time as the low voltage drive power source of the logic circuit.
However, in practice, it is difficult to fall the high voltage drive power source of the liquid crystal display faster than the low voltage drive power source of the logic circuit at the interruption of the power source. The reasons for this are enumerated as follows:
(1) Under the state in which the power source can be interrupted, because the drive of the image reading device, the motor, or the like for driving the movable parts such as the sheet feed roller, the photosensitive drum, and the fixed roller are not in operation, an amount of a consumed current of the power source circuit is small, and therefore the power source circuit is rendered into a stand-by mode;
(2) In addition, when the drive of the image reading device, the motor, or the like for driving the movable parts such as the sheet feed roller, the photosensitive drum, and the fired roller are in operation, power source capacity of the high voltage drive power source is made large so that ample power can be supplied to the motor or the like for driving the movable parts, and hence a voltage drop of the power source circuit at the time of power source interruption is slow; and
(3) Still further, because the electricity consumed by the low voltage drive power source of the logic circuit during the stand-by mode is almost equivalent to that during operation, the voltage thereof drops relatively faster at the time of power interruption.
Regarding a drive voltage control device of a liquid crystal display, there is one disclosed in, for example, Japanese Patent Application Laid-open No. Heisei 11(1999)-282427. The drive voltage control device of the liquid crystal display disclosed in this publication has a control circuit as shown in FIG.
13
.
As shown in
FIG. 13
, the drive voltage control device of the liquid crystal display has a power source circuit
1
, which outputs voltages such as a stand-by voltage (+5VE) and a drive voltage (+24V), as well as switching means
2
inserted in a drive voltage supply line. A control voltage (+5V) thereof and the drive voltage (+24V) are to the applied to the liquid crystal display.
The drive voltage control device of the liquid crystal display includes timing control means (timing circuit) made up of a reset circuit
3
, flip-flop circuits
4
and
5
, an inverter
6
, resistors
7
and
8
, or the like.
According to this timing control means, the aforementioned switching means
2
is in a conductive state after the rise of the aforementioned control voltage (+5V) when changing to a power-saving mode OFF and when changing to a power-saving mode ON, the aforementioned switching means
2
is in a nonconductive state at the point where the aforementioned control voltage (+5V) starts to fall. The control voltage (+5V) and the drive voltage (+24V) are thus outputted when the power-saving mode is OFF. Further, when the power-saving mode is ON, output of the control voltage and the drive voltage are stopped. It should be noted that reference symbol
1
a
denotes a main power source switch and reference symbol
1
b
denotes a switch which will be shut when in the power-saving mode OFF.
According to this structure, the control voltage (+5V) is applied to the control circuit of the liquid crystal display (LCD) and the drive voltage (VEE=+24V) is applied to the liquid crystal display (LCD) after the control circuit starts operating. Therefore, when the power source circuit
1
is switched to the power-saving mode OFF, the liquid crystal display (LCD)
Nguyen Kimnhung
Oblon, Spivak, McCelland, Maier & Neustadt, P.C.
Ricoh & Company, Ltd.
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