Apparatus for measuring the relative speed of handwriting in a predetermined writing area on a writing support surface, comprising:
- a writing instrument having therein a longitudinal axis, a writing tip at one end thereof, and means for providing a magnetic flux directed substantially parallel and adjacent to the axis;
- a first electrically conductive winding comprising a plurality of turns below the writing support surface having a selected portion in which the conductors are substantially in a plane adjacent and parallel to the writing area, extend in substantially straight lines across the writing area in a first direction, and are substantially evenly distributed across the writing area in a second direction that is substantially perpendicular to the first direction, with the rest of the winding extending away from the vicinity of the writing area;
- a second electrically conductive winding comprising a plurality of turns below the writing support surface having a selected portion in which the conductors are substantially in a plane adjacent and parallel to the writing area, extend in substantially straight lines across the writing area in the second direction, and are substantially evenly distributed across the writing area in the first direction, with the rest of the winding extending away from the vicinity of the writing area;
- the selected portions of first and second windings thus forming a substantially rectangular grid adjacent and parallel to the writing area and substantially coextensive therewith;
- so that, when the writing tip is moved in the proximity of the writing area, voltages are induced in the windings by the variations in magnetic flux across the selected portions of the windings responsive to the speed of the movement;
- means responsive to the voltage across each winding for indicating the relative speed of the writing tip, the magnetic flux providing means comprising an annular magnet positioned substantially coaxial with the writing tip around the longitudinal axis of the writing instrument;
- and
- a third electrically conductive winding comprising a plurality of turns below the writing support surface substantially in a plane adjacent and parallel to the writing area and extending around the writing area;
- so that, when the writing tip is moved in the proximity of the writing area in a direction having a component of movement perpendicular to the plane of the third winding, voltage is induced in the third winding by the variation in magnetic flux across it responsive to the speed of the movement component perpendicular to the plane of the writing area;
- and means for connecting the voltage across the third winding to the voltage responsive means, in opposition to the voltage across the first winding, and in opposition to the voltage across the second winding.