Coordinate position digitizing system

Claim 1

A coordinate position digitizing system comprising a cathode ray tube for displaying figures, beam deflecting means for causing an electron beam in said cathode ray tube to scan in synchronism with vertical and horizontal synchronizing signals, a position determining plate means juxtaposed with said cathode ray tube and having a plurality of conductors extending parallel with one another at regularly spaced intervals thereon, driving and controlling means for supplying a current selectively to the conductors of said plurality of on said position determining plate, one after another, consecutively within each horizontal scanning period of said cathode ray tube, magnetic flux detecting means juxtaposed with said position determining plate for detecting magnetic flux on said position determining plate and producing a signal in response to the detected magnetic flux, a band-pass filter means for extracting a signal component having a frequency higher than the frequency of a noise component obtained in response to the beam deflecting means of said cathode ray tube from the signal produced by said magnetic flux detecting means, and information producing means connected to said filter means for producing positional data defining a position of said magnetic flux detecting means on said position determining plate at a first instant during the operation controlled by said driving and controlling means between horizontal blanking periods and during a horizontal scanning period of said beam deflecting means and also at a second instant at which the signal component from said band-pass filter first crosses over a predetermined level in a predetermined direction in the same horizontal scanning period.