Abstract: A transparent disk with a round periphery is produced, for example, by a grinding operation, and a mark is placed at the geometric center of the disk. A coil is then wound about the periphery of the disk. As a consequence, the mark at the geometric center of the disk coincides with the electrical center point of the coil, thus obviating the need for a bobbin, or coil former, on which the coil can be wound.The transparent disk is first ground into a round shape, and a metallic film is deposited on a surface of the disk. The film is coated with a photosensitive resist material, and then exposed through a mask to define an image of a mark at the geometric center of the disk. The film is then etched to remove all but the mark from the disk.In manufacturing the coil, the disk is concentrically clamped between two plates of a winding jig, each plate having annular peripheral flanges that are radially larger than the disk and thus project beyond the periphery of the disk.

Abstract: A co-ordinate measuring system determines the position of a coil member relative to a grid member defined by a set of equidistant, parallel conductors associated with a co-ordinate axis of the system. The system includes a switching circuit that is constructed and arranged to produce a measuring signal in the form of a train of induced pulses in one of the members when a time variable current is applied to the other of the members. According to the present invention, a low pass filter at the front end of an evaluation circuit is responsive to the measuring signal for reducing frequency components therein due to operation of the switching circuit, and producing an output signal that is the first derivative of the envelope of the time variable magnetic flux. The second zero-axis crossing of the derivative of the output signal yields a representation of the co-ordinate of the coil relative to the grid member.

Abstract: A digitizer comprising a measuring table having a substrate on which a grid is mounted, and a movable coil inductively coupled to the grid. When a time variable current is applied, a variable magnetic flux produces a measuring signal in the form of an induced voltage. The grid is a plurality of side-by-side, parallel conductors, each having opposite axial ends and arranged in pairs. A bridge is provided between adjacent ends of a plurality of the pairs of conductors. Current flowing into the opposite end of one conductor of a pair of conductors, thus, produces oppositely directed magnetic fields around the conductors of the pair, or a changing magnetic flux produced by the coil and interacting with the conductors of a pair induces voltages of opposite polarity in the conductors of the pair.

Abstract: A transparent disk with a round periphery is produced, for example, by a grinding operation, and a mark is placed at the geometric center of the disk. A coil is then wound about the periphery of the disk. As a consequence, the mark at the geometric center of the disk coincides with the electrical center point of the coil, thus obviating the need for a bobbin, or coil former, on which the coil can be wound.The transparent disk is first ground into a round shape, and a metallic film is deposited on a surface of the disk. The film is coated with a photosensitive resist material, and then exposed through a mask to define an image of a mark at the geometric center of the disk. The film is then etched to remove all but the mark from the disk.In manufacturing the coil, the disk, is concentrically clamped between two plates of a winding jig, each plate having annular peripheral flanges that are radially larger than the disk and thus project beyond the periphery of the disk.

Abstract: A marking device for marking a sheet mounted on a digitizer board includes a measuring coil inductively coupled to the digitizer board when the coil is operatively positioned relative to the board. A switch on the marking device is operable to cause current pulses to be applied to the conductors on the digitizer board producing magnetic flux which couples the conductors on the board to the coil. A marker on the marking device is responsive to operation of the switch for marking a thermosensitive sheet on which the measuring coil is placed thereby marking on the sheet the position of the marking device when the switch was closed.