Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-12-13
2003-08-26
Nguyen, Judy (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06609781
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to printer systems employing encoders for providing positioning information regarding printhead carriages and, more particularly, to a printhead firing control system including an encoder signal filtering arrangement and method for reducing high frequency errors in the encoder output signal.
BACKGROUND OF THE INVENTION
Thermal ink jet printer mechanisms which utilize printheads having heater resistors for effecting the ejection of small ink droplets from the printhead are well known. The ejection of a large number of small ink droplets at controlled locations on a printing medium produces a desired printed image. In such printer mechanisms the printhead typically moves with a carriage across a paper path and firing pulses are produced to position the ejected ink droplets at desired locations on the paper. However, the digital output signal produced by the encoder can include high frequency error components which result in reduced accuracy in controlling the positioning of ejected droplets.
Accordingly, it would be advantageous to provide a printhead firing control system which accounts for such high frequency error components in order to increase printing accuracy.
SUMMARY OF THE INVENTION
In one aspect of the invention, a printhead firing control system for an inkjet printer includes a printhead mounted for movement across a paper path and an encoder for producing a digital output signal indicative of movement of the printhead. A filter circuit is connected to receive the digital output signal for filtering the digital output signal to remove frequency variations which meet at least one predetermined parameter, thereby providing a filtered digital signal. A fire-pulse generation circuit receives the filtered digital signal from the filter circuit and produces printhead heater resistor drive pulses based at least in part upon the filtered digital signal. This arrangement provides for improved printing accuracy by eliminating frequency changes in the digital encoder signal which may erroneously be caused by mechanical vibrations or other noise within the printer.
In another aspect of the present invention, a method for providing increased printing accuracy in an inkjet printer system involves providing an encoder for producing a digital output signal indicative of movement of a printhead across a paper path and monitoring the digital output signal. Frequency changes in the digital output signal which occur at a rate faster than a threshold change rate are eliminated to produce a filtered digital signal. Printhead firing pulses are then produced based at least in part upon the filtered digital signal.
One type of filter which may be utilized in the subject system and method is a digital phase-locked loop filter (DPLL). In this regard, a further aspect of the invention provides a digital oscillator, which may be used in the DPLL in place of a traditional analog voltage controlled oscillator. The digital oscillator includes a period resolution circuit and a frequency generator circuit. The period resolution circuit includes an input for receiving a digital frequency selection input value, a digital multiplier for multiplying the input value by a gain value and outputting a resultant value, a digital adder for adding a minimum frequency value to the resultant value and outputting a summed value, and a digital divider for dividing a digital clock frequency value by the summed value, the digital divider outputting a count value indicative of a number clock frequency pulses occurring during one half of a period of a desired oscillator output frequency. The frequency generator circuit is connected to receive the count value from the period resolution circuit and includes a digital counter for receiving count value s from the period resolution circuit, and a digital toggle circuit associated with the digital counter for producing an oscillating output signal, the toggle circuit responsive to the digital counter to vary the oscillating output signal between high and low levels.
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Adkins Christopher Alan
Barkley Lucas David
Marra, III Michael Anthony
Huffman Julian D.
Lexmark International Inc.
Nguyen Judy
Thompson Hine LLP
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