This invention relates to controlled devices having an electrically operated mechanism and a scanner for sensing indicia of how the mechanism is positioned or aligned. The invention has special application to printer devices, e.g., high speed printer devices, having an electrically operated print head which is movable relative to record media on which printing is to occur, and a scanner for sensing indicia of alignment or position of the print head relative to the record media.
High speed line printers of the dot-matrix type, for example, typically include a print head which is movable across a paper document in a reciprocating manner for serial printing of selected dot positions in a dot column or row. The print head may be moved by cable and pulley arrangement, a lead screw, or a cam drive or like drive mechanism. A typical print head is mounted for movement on a carriage, and has one or more electrically operated print elements which are actuated or energized at high speed to cause printing of dots by jet-like ejection of ink droplets or movement of print wires attached to solenoids for impact against the paper. In the case of a thermal printer, the print elements are actuated to provide highly localized sources of heat for thermal printing of dots on record media which is heat-sensitive.
The print elements may be arranged in a row for printing a single horizontal line of dots at a time so that a line of printed characters is completed by plural horizontal passes of the print head across the record media. Alternatively, the print elements may be arranged in one or more vertically oriented groups of elements for printing a line of dot-matrix characters with a single print head pass.
When printing begins, the print head is normally moved to the lefthand margin position on the paper document and the print head is then moved from left to right across the document at a substantially constant speed while successively printing dots at selected positions until reaching the righthand margin of the paper to complete a line of print. The print head may then be moved in the reverse direction, that is from right to left, back to the lefthand document margin whereupon the paper document will be advanced in readiness for printing of the next line. In the case of a bi-directional printer, the document is advanced at the conclusion of each print line and printing occurs in both directions of print head movement.
A timing or registration strip with slots or like indicia has been commonly used in high-speed printers to determine rate of movement and position of the print head with respect to the record media for purposes of controlling the printer operation. As the print head is moved, the indicia are sensed by a scanner which provides related electrical feedback signals to control electronics which trigger energization of the print elements with proper timing, and which are sometimes also used to control the speed of the print head movement. Scanner feedback has also been used to signal the left and righthand margin home positions of the print head to time reversals in direction of the print head movement, document advancement and related controlled printer operations.
Various types of scanners are known, and the known scanners include magnetic readers and optical scanners. Optical scanners generally use a light source such as a light-emitting diode, and light detection means such as a photodiode or a phototransistor. For a reflective type of optical scanner, the light source and the light detection means are positioned on the same side of the timing strip, and the light detection means detects light from the light source which indicia on the timing strip reflect back. A reflective type optical scanner may be used with a timing strip having indicia such as a bar code, where the light detection means is used to detect variations in light which the timing strip reflects. A transmissive type of optical scanner may be used with a timing strip provided with indicia such as a series of slots or like transparent areas, and the light detection means is in that case used to detect variations in light which is transmitted through the timing strip upon being emitted by the light source. The output of a typical scanner is often an analog current signal which can be converted to a voltage signal and amplified and digitized to produce a digital voltage signal for processing by control electronics according to known means.
Examples of U.S. patents which describe printer devices having movable electrically operated print heads, and timing strips, scanners and related control electronics, are U.S. Pat. No. 3,970,183, issued July 20, 1976, to Robinson et al.; U.S. Pat. No. 4,050,563, issued Sept. 27, 1977, to Menhennett; U.S. Pat. No. 4,204,777, issued May 27, 1980, to Jen; and U.S. Pat. No. 4,208,137 issued June 17, 1980 to Liu; and the descriptions and drawings in these patents are hereby fully incorporated herein by reference for informational purposes. U.S. Pat. No. 3,849,632 issued Nov. 19, 1974, to Eckert, Jr., et al., describes a reflective type optical scanner and related circuitry, and the description and drawings in this patent are likewise hereby fully incorporated herein by reference.
In a typical printer device having a movable print head, the print elements which are part of the print head are electrically actuated by signals carried by an electrical conductor which is operatively connected at one end to the print head. The other end of the electrical conductor is operatively connected to control electronics which may be in a fixed position with respect to the printer device frame. Since the movement of the print head is relative to the frame, it is common to provide the required electrical conductor in the form of a flexible circuit. The flexible circuit may comprise a number of electrically conductive runs made of copper or copper alloy arranged adjacent one another in parallel spaced-apart relationship and supported by a plastic electrically-insulative material. Common insulative materials for this purpose are Mylar and Kapton type plastics, which are known for their flexibility, flex life and resistance to heat.
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