Pen carousel, pen sensing and indexing

Abstract

In a multi-position graphics plotter pen carousel system employing a pen capping mechanism therein at each pen position for capping and uncapping pens held by the carousel, an improvement for allowing the sensing of pen presence at the pen positions and the indexing of the carousel with a single sensor. Each pen capping mechanism is adapted to assume a first position with a pen in the pen position and assume a second position with no pen in the pen position. A plurality of first sensible attributes are associated with respective ones of the pen capping mechanisms for exhibiting a first characteristic when a pen is contained at the associated pen position and for exhibiting a second characteristic when no pen is contained at the pen position. A plurality of second sensible attributes are associated with respective ones of the pen positions for constantly exhibiting the first characteristic. There is a single sensor for sensing the first and second characteristics and for developing a sensible signal at an output thereof indicating whether the first or second characteristic is presently being sensed. The plotter logic is adapted to sense the first sensible attributes and step the carousel between respective ones of the first sensible attributes when sensing pen presence with the sensor and to sense the second sensible attributes and for step the carousel between respective ones of the second sensible attributes when indexing the carousel with the sensing attributes whereby the sensible signal at the output of the sensor indicating the first characteristic indicates the presence of a pen at a pen position of the carousel when sensing the first sensible attributes and indicates the passage of a pen position when sensing the second sensible attributes to count pen positions to index the carousel.