Coded data generation or conversion – Phase or time of phase change – Synchro or resolver signal
Reexamination Certificate
1999-09-01
2001-09-18
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Phase or time of phase change
Synchro or resolver signal
C358S001500
Reexamination Certificate
active
06292117
ABSTRACT:
TECHNICAL FIELD
This invention relates to printer paper positioning systems. More particularly, the invention relates to an integrated adjustable current to voltage converter and digital quadrature generator in a printer paper positioning system.
BACKGROUND
Computer technology is continually advancing, expanding the need for computers in the personal, business, and academic fields. As the need for computers has grown, so too has the need for various peripheral devices for use with computers, such as printing devices. A wide variety of printing devices exist that operate in a wide range of manners, however all share the same fundamental purpose of generating a “hard copy” of data, whether it be on paper, on transparencies, etc.
Most printers rely on accurate control and positioning of the printing medium (e.g., paper). The paper should be accurately fed through and positioned in the printer in order for the data to be printed accurately. If the paper is not aligned properly in the printer, then various user-perceivable errors in printing can occur, such as inconsistent spacing between lines, parts of characters or other images not being lined up properly, etc.
One way to ensure such accurate control is to include a disc that rotates as the paper is fed through the printer, such as by affixing the disc to a shaft that also controls rollers to feed the paper through the printer. The disc includes markings that are read by an optical encoder, which in turn generates analog current signals as the disc rotates. These signals are then provided to a controller in the printer to use in determining the location of the paper.
One problem that can be encountered in such systems is that the optical encoder generates an analog signal whereas the controller requires input in digital form. Thus, the analog signal from the encoder needs to be converted to digital signals that can be interpreted by the controller.
Furthermore, problems can arise from variances in the optical encoder and the disc, which can be caused by a variety of circumstances. Mechanical variances from the manufacturing process of the optical encoder and/or the disc can result in the optical encoder generating different than expected values. Other variances can also manifest themselves over time, such as a light emitting diode (LED) used by the optical encoder gradually dimming over time, dirt and/or ink accumulating on the disc over time, the temperature of the encoder changing due to frequent use, etc. As these variances can alter the signals generated by the optical encoder, it would be beneficial to provide a mechanism that is tolerant of these variances, allowing accurate paper positioning and paper control despite these variances.
The invention described below addresses these and other disadvantages of the prior art, providing an improved integrated adjustable current to voltage converter and digital quadrature generator.
SUMMARY
In a printer, a paper positioning system is used to control feeding a printing medium, such as paper, through the printer. An optical encoder is used to generate analog current waveforms as the paper is fed through the printer. An integrated adjustable current to voltage converter and digital quadrature generator are used to convert waveforms received from the optical encoder into a digital form and then selectively converted to digital form for use by the paper positioning system.
According to one aspect of the invention, the current to voltage converter includes a current to voltage conversion stage and a gain stage. The current to voltage conversion stage includes an adjustable current source, and the gain stage includes switched resistors. This adjustability in the current to voltage converter allows the converter to be adjusted to account for variances encountered by the optical encoder.
According to another aspect of the invention, two comparisons are made (based on two waveforms received from the optical encoder) to generate digital quadrature encoding signals. These two comparisons are: 1) comparing the two waveforms and generating an output based on which has a greater value; and 2) comparing one waveform with the inverse of the other waveform and generating an output based on which of these has a greater value.
According to another aspect of the invention, a multiplexer is used to select one of various analog signals, based on the waveforms received from the optical encoder, to be converted to digital form. The multiplexer includes an “auto select” setting that causes one of the various analog signals to be selected for conversion based on digital quadrature encoding signals input to the multiplexer.
REFERENCES:
patent: 4282515 (1981-08-01), Patterson, III
patent: 4949306 (1990-08-01), Nakagome et al.
patent: 5729493 (1998-03-01), Morton
Hewlett--Packard Company
Jean-Pierre Peguy
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