Device for determining position coordinates of points on a surface

A device for determining position coordinates of points on a surface, comprising:

• a plurality of equally spaced driver windings, each of said driver windings having a pair of parallel conductors laid in an X-direction and mutually connected at one end, said X-direction being fixed to a surface of a tablet;
• a plurality of equally spaced sense windings, each of said sense windings having a pair of parallel conductors laid in a Y-direction and mutually connected at one end, said y-direction being perpendicular to said X-direction so that there is no appreciable magnetic coupling from any one of said driver windings to any one of said sense windings;
• a driver winding scanner which connects a driver winding successively selected from said plurality of driver windings to an output of an amplifier of an alternating signal current;
• a cursor having a coil which forms a closed circuit and is magnetically coupled to both the driver windings and the sense windings, wherein the coupling coefficient between the cursor coil and either of said windings is a function of the distance of the cursor coil from said winding;
• a sense winding scanner which connects a sense winding successively selected from said plurality of sense windings to a receiving amplifier;
• a plurality of auxiliary sense windings, composed of a plurality of equally spaced conductors laid in the Y-direction and end-connected to form a serial circuit, said plurality of auxiliary sense windings being arranged with a mutual shift in the X-direction such that at least one of said auxiliary sense windings has a sufficiently large magnetic coupling to said cursor coil at any position of the cursor coil on said tablet;
• and
• a processor which controls said driver winding scanner in a first mode of measurement wherein the sum of the amplitudes of voltages of said auxiliary sense windings induced by the current in said cursor coil when said alternating current signal is flowing in a driver winding is detected to determine the Y directional position coordinate of said cursor based on the values of the sum of the detected amplitudes for all the driver windings and which controls said sense winding scanner in a second mode of measurement wherein said driver winding supplies said alternating current signal to the driver winding which gives the maximum sum of the amplitudes of the voltages on said auxiliary sense windings, and wherein the amplitude of the voltage on a sense winding induced by the current in said cursor coil is detected for determining the X directional position coordinate of said cursor coil from the values of the detected amplitude for all sense windings.