Typewriting machines – Sheet or web
Reexamination Certificate
2000-01-25
2001-11-13
Hilten, John S. (Department: 2854)
Typewriting machines
Sheet or web
C400S709000
Reexamination Certificate
active
06315473
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to printers and printing systems, and more particularly to a system for automatically detecting and measuring the size of print media loaded in a print media supply bin for printing.
BACKGROUND OF THE INVENTION
Present day imprinting mechanisms, for example, electrophotographic copiers, laser printers, inkjet printers and the like, are generally capable of handling more than a single size of print media. An automatic manner of sensing the size of print media which has been loaded in a supply bin for inputting to a printing mechanism is the subject to be addressed herein. The print media may be any type of substantially flat material, such as plain paper, specialty paper, card-stock, fabric, transparencies, foils, mylar and the like, but the most common type or print media is paper. For convenience, I will discuss printing on paper as a representative example of these various types of print media. The media may be supplied to the printing mechanism in a variety of different sizes. For instance, in desktop inkjet or laser printers, paper is typically supplied in a stack of cut-sheets, such as letter size, legal size, or A-4 size paper, which are loaded or placed in a supply bin or input tray for subsequent input to the printing mechanism. Smaller sized envelopes or postcards or other media sizes may also be used for printing. Typically, the media sheets, cards or envelopes are sequentially pulled from the top of the stack and printed on, after which the printed sheets are deposited in an output tray.
It is desirable to have a printer which can measure and communicate what size media has been loaded in the input tray to the printer controller and to a host computer, particularly when the printer is not within sight of the computer user, such as when several computer users on a networked system share a printer or printers. Even when a printer is located on the users desktop, it may be helpful to provide the user with a warning if the wrong size media is loaded for a particular print job. This would tell the user to load the proper size media, or to adjust the print job parameters to fit the size of the loaded print media.
Automatic media size sensing must be highly accurate to be useful. In order to avoid toner contamination in the mechanism, this is particularly true for printing mechanisms which are capable of printing to the edges or near the edges of the sheets of print media. Sensing of media length and width is a feature often found in high-end printers and plotters for business and industrial use. However, these size sensing devices are typically quite cost-sensitive and general application sensing devices of the quality required can be very costly. Typically, for the small business and home markets where there is much more price sensitivity, automated media type detection has not been economically viable.
In the past, various methods have been used for media size determination. For example the use of a retroflective photo diode or a capacitance sensor mounted at some point in the printer paper path or on the print carriage to detect leading and trailing or side edges of the media sheet. However, retroflective and capacitive sensors are themselves expensive with the added direct and indirect costs incurred due to where within the printer the sensors are mounted and operate. Linear variable resistive and capacitive sensors mounted within the input paper tray tend to be less expensive than other methods, but, nevertheless, sensors of the required accuracy and sensitivity are expensive.
For example, one method of print media size detection utilizes a linear potentiometer mounted in the input paper tray. While this method provides a continuous output (i.e., a smooth function of output versus position), it can be either expensive, using large sensor components, or have lower accuracy due to scaling down the traverse with gears, levers or the like, and using smaller potentiometers. Another method is to use absolute encoders (optical, magnetic, etc, for example) to measure the true position of a movable member. In a printing mechanism supporting sizes of A-5 ledger media (222 mm of travel), an encoder would require 8 bits of resolution for 1 mm accuracy. Again, this can be expensive.
Accordingly there is a need for a sensor for determining what size print media is loaded in a printer input or supply tray having sufficient accuracy to be useful yet inexpensive enough to be utilized for low-end applications such as small business and home use.
SUMMARY OF THE INVENTION
In a preferred embodiment, the present invention provides a sensor assembly that measures the displacement of one member with respect to another member with a high degree of accuracy and at a low cost. A sensor assembly embodying the present invention utilizes multiple low cost, smaller sensor components to provide a less expensive and more accurate sensor assembly that a single, larger sensor performing the identical task.
In one embodiment the present invention provides a sensor assembly for measuring the displacement of a movable member. The sensor assembly utilizes two or more smaller, less accurate sensors to perform the function of a single, larger sensor. Each sensor includes a movable portion and a stationary portion, each sensor generating an output signal in response to movement of the movable portion with respect to the stationary portion. In one embodiment, the sensors are attached to a movable member while the movable portion of each sensor is in contact with a contoured surface of a stationary member. Movement of the moveable member causes the moveable portion of each sensor to move along and follow the contoured surface of the stationary member, which, in turn, causes movement of the movable portion of each sensor relative to the stationary portion of the sensor. The amount of movement of the movable portion of the sensor is proportional to the displacement of the movable member with respect to the stationary member. The portion of the contoured surface each sensor movable portion is in contact with has a different profile. As a result, for a given displacement of the movable member, the movable portion of each sensor will have a different amount of travel with respect to the sensor stationary portion, and thus produce a different output signal. The contoured surface of the stationary member is profiled to reverse the direction of motion of each of the movable portions with respect to the stationary portions at least once over the range of movement of the movable member. The output signals of the two or more sensors then form a set which uniquely identifies the displacement which produced the set of output signals.
In a preferred embodiment, the present invention is embodied in a printer to provide an apparatus for measuring the size of print media sheets loaded in a print media supply bin. The supply bin (i.e., input paper tray) includes a movable member which serves as a print media fence or stop mounted and disposed at a variable position within the supply bin. The position of the movable member is adjustable to allow print media sheets of differing sizes to be loaded in the supply bin. At least two sensors are mounted on the movable member. Each sensor includes a movable portion and a stationary portion, the movable portion of each sensor contacting an associated contoured surface of the supply bin. In response to displacement of the movable member with respect to the supply bin, the movable portion of each sensor follows its associated contoured surface thereby producing movement of the movable portion with respect to the stationary portion. The stationary portion of each sensor includes a variable electrical element which is responsive to movement of the movable portion with respect to the stationary portion to generate an output signal indicative of the displacement of the movable member with respect to the supply bin. The output signals generated by the at least two sensors are indicative of a unique position of the movable member wi
Hewlett--Packard Company
Hilten John S.
Murray Leslie G.
Nolan, Jr. Charles H.
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