Typewriting machines – Sheet or web – For feeding sheet from stack or pack holder
Reexamination Certificate
2000-01-05
2001-09-25
Eickholt, Eugene (Department: 2854)
Typewriting machines
Sheet or web
For feeding sheet from stack or pack holder
C400S629000, C347S104000
Reexamination Certificate
active
06293718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to printers, and more particularly, to an ink jet printer having two motors, each driving one of two sets of rollers of a drive paper mechanism.
2. Related Art
Digital set-top boxes (e.g., cable television boxes, Internet terminal boxes etc.) are being used increasingly with consumer home entertainment equipment such as television sets, video cassette recorders, digital video disc (DVD) players and the like. In many cases, it may be desirable for users to obtain a hard copy of information displayed on the screen of their television sets. Specifically, users typically want to print e-mail messages, maps, recipes and information-rich content, such as still or captured scenes from live broadcasts, DVD players, movie cameras, video recorders etc.
Currently, if a user wants to have a hardcopy of the displayed information, the user has to use a conventional printer. Most conventional printers, however, are bulky, and thus require large amounts of space in users' home entertainment units. Hence, a printer specifically designed for use in home entertainment units is needed (i.e., a living room printer).
The living room printer should be of low height (i.e., low profile) and relatively narrow in width to blend in with other home entertainment equipment. In addition, since home entertainment equipment is usually stacked one atop another in home entertainment units, user access to the living room printer should preferably be through a front plane of the printer.
Designing a low profile, narrow width printer with user front plane access presents some technical difficulties. For example, some conventional ink jet printers use a two-roller paper drive mechanism. One roller (i.e., a pick roller) is used to pick print media from an input paper tray and to propel the print media to a second roller (i.e., a feed roller). The feed roller forwards the print media to a print zone where the print media is printed upon by an ink jet printhead. For ease of explanation, the channel within which the print media travels from the pick roller to the print zone will be referred to as a paper path.
The feed roller is typically placed in close proximity to the print zone. This configuration minimizes paper advance errors. Paper advance errors occur when one part of the print media (the part in the print zone) moves slower than another part of the print media (the part closest to the feed roller). One reason for this occurrence is due to a combination of print media flexibility, inertia and a friction force that develops as the print media moves along the paper path. This friction force acts in opposite direction to the direction of travel of the print media. As such, paper advance errors typically occur more frequently with increased distances between the print zone and the feed roller. Thus, placing the feed roller close to the print zone diminishes the likelihood of paper advance errors.
When a print media is skewed (i.e., when the print media is at an angle greater than zero degree in relation to the paper path) as it is picked up by the pick roller, it usually remains skewed as it reaches the print zone, thereby creating a slanted printout. In addition, both right and left margins of the print media may be offset. The extent to which the margins will be offset depends on the length of the paper path and the angle at which the print media is picked up by the pick roller.
Consequently, typical printers are designed to have a short paper path to minimize the offset of the margins of a skewed print media. However, since low-profile living room printers require front access and have stringent height requirements, a short paper path is undesirable. As such, current low-profile printers require longer paper paths, which necessitate longer gear trains to drive the rollers. A longer gear train increases the complexity of the paper drive mechanism. For example, if the teeth of one gear do not perfectly mesh with the teeth of another gear from which power is being transferred, a delay may be introduced. The delay will be equal to the elapsed time between when the motor is actuated and when the roller actually begins to move. Additional gears in the gear train equate to longer delays.
Although high precision gear trains are typically used to avoid this problem (a high precision gear train is a gear train that has the teeth of one gear that tightly interlocks with the teeth of another gear from which it receives power), they increase the complexity of assembling the paper drive mechanism of the printer which in turn increases the cost of the printer.
Therefore what is needed is a living room printer with a longer paper path that utilizes an efficient gear train. What is also needed is a printer with a gear train that has a low number of gears to transfer power from the motor to both the pick roller and the feed roller for reducing the complexity of assembling the paper drive mechanism without significantly reducing printer throughput.
SUMMARY OF THE INVENTION
To overcome the limitations of the systems and methods described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a low-profile and narrow-width printer having two rollers, a pick roller and a feed roller, and two roller motors. Each one of the two roller motors is used to drive one of the two rollers. Due to this configuration, a very short gear train can be used. For example, only two gears can be used to drive each one of the rollers, one from a motor and one from a roller.
Driving the pick roller by one motor and the feed roller by another motor allows the pick roller to pick a print media from the input tray while another print media is being printed upon by the ink jet printhead. This, then, minimizes the delay that normally occurs between two pages when a multi-page document is being printed, and thus, enhances the throughput of the printer.
Another advantage of having the two rollers driven by different motors is that skewed print media may be straightened out. The feed roller of the printer of the present invention is placed at a distance away from the pick roller that is chosen to be less than the length of the print media. When the leading edge of the print media reaches the feed roller, the feed roller is stationary. Thus, as the pick roller continues to push the print media forward, the print media is forced to form an arch. When the print media is arched, the leading edge of the print media is straightened out. Thus, when the motor driving the feed roller is actuated, the feed roller will forward a straightened print media to the print zone.
The printer of the present invention uses two sensors to pinpoint locations of paper jams. One sensor is preferably located near the pick roller and the other near the feed roller. If the sensor by the pick roller does not detect the print media after the print media is picked up by the pick roller, then there is a paper jam at the entrance of the paper path. If the sensor by the pick roller detects a print media but the sensor by the feed roller never detects the print media, then there is a paper jam in the paper path. If the sensor by the feed roller continues to detect the presence of the print media well after when the media should have cleared the print zone, there is a paper jam somewhere near or at the print zone. When it is detected that a paper jam exists either at the entrance of the paper path or in the paper path, the motor driving the pick roller is automatically run in reverse to clear the paper jam.
The present invention as well as a more complete understanding thereof will be made apparent from a study of the following detailed description of the invention in connection with the accompanying drawings and appended claims.
REFERENCES:
patent: 4270860 (1981-06-01), Tsuda et al.
patent: 5223858 (1993-06-01), Yokoi et al.
patent: 5462373 (1995-10-01), Chia
patent: 5500659 (1996-03-01), Curran et
Eickholt Eugene
Hewlett--Packard Company
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