Method and apparatus for calibrating delay lines to create gray levels in continuous tone printing

• Main Authors: WADE, THOMAS CAMPBELL, OVERALL, GARY S
• Format: Patent
• Language: English
• Published: 11.07.2000
• Edition: 7
• Subjects: CORRECTION OF TYPOGRAPHICAL ERRORS; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; LINING MACHINES; PERFORMING OPERATIONS; PICTORIAL COMMUNICATION, e.g. TELEVISION; PRINTING; SELECTIVE PRINTING MECHANISMS; STAMPS; TRANSPORTING; TYPEWRITERS

An improved printer is provided which includes a series of analog delay elements that operate at a very fast speed, and therefore, can be used in an enhanced mode to further subdivide the slice clock to create a greater variety of gray levels that can be used in continuous tone printing. By using this enhanced mode of continuous tone printing , a full ""on"" slice can be immediately preceded or followed by a partial slice, under the control of the series of delay elements. The delay elements are automatically calibrated at the beginning of each page to be printed by placing the delay line chain circuit into a ""calibrate mode"", during which time a clock pulse is provided to the delay line chain so that the chain is repeatedly tested, in increments of one additional delay element at a time, to determine the number of delay elements that are required to cause a time delay that is greater than or equal to the period of the slice-based clock. Once that quantity is determined, the calibrated delay elements will be used to print the entire next page to be output from the laser printhead. As the printer desires various gray levels for continuous tone printing, the number of whole slices and partial slices for a particular pel or group of pels will be determined by the desired gray level, and when a partial slice is to be printed. The printer will select the appropriate number of delay elements that will be used to control a flip-flop that outputs the 'video output"" signal to the laser printhead. When the asynchronous ""reset"" input of the flip-flop has a control signal applied, the output of the flip-flop will immediately change state to truncate the ""on time"" of the slice that was currently being output to the laser printhead. By use of the asynchronous reset flip=flop, the slice can be subdivided into smaller time intervals, completely under the control of the delay line chain without regard to the frequency or phase angle of the pel clock or the slice-based clock.