Plotter pen presence and type identification system

Abstract

An improvement to graphics pen plotters including a pen gripping mechanism for gripping a cylindrical bodied pen in a generally vertical orientation for sensing the presence and type of a pen in the gripping mechanism with a single sensor. There is a multi-channel sensor adapted for producing and sensing a plurality, 'n+1', of parallel light beams disposed one above the other to produce a binary number at an output thereof indicating the ones of the light beams sensed by the sensor. The sensor is disposed to shine the light beams at a position past which the pen is moved by the gripping mechanism. There is also a cylindrical reflective surface disposed about a portion of the body of the pen so as to be struck by the light beams when the pen is being gripped by the gripping mechanism at the position and reflect the light beams back towards the sensor to be sensed thereby. The reflective surfce has 'n' cylindrical strip positions disposed to be struck by 'n' of the light beams for selectively containing non-reflective strips to indicate a binary indication of the pen type whereby one digit of the binary number output indicates the presence or absence of a pen at the position and the remaining 'n' digits of the binary number designate one of 2.sup.n possible pen types. Particular size relationships are disclosed providing preferred error-free operation in a low tolerance environment.