Electromagnetic position transducer
First Claim
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1. A position transducer comprising:
- (a) helical electrically conductive transmitter coil having a plurality of coil turns and first and second end extremities, and a plurality of coil tap nodes thereon, the coil tap nodes being spaced between the end extremities;
(b) oscillator means for producing a coil drive current;
(c) selector means for sequentially connecting the oscillator means between the end extremities and selected ones of the coil tap nodes for producing a moving fringing field resulting from portions of the coil drive current flowing in opposite directions in the coil on opposite sides of each of the selected nodes;
(d) a transducer body movable in a first transducer direction relative to the transmitter coil and having a receiver coil fixedly mounted thereto; and
(e) circuit means connected to the selector means and responsive to the receiver coil for providing a first position signal, the first position signal representing the position of the transducer body relative to a first position reference, the first position reference being perpendicular to the first direction.
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Abstract
Disclosed is electromagnetic transducer that does not require complex analog to digital, digital to analog converters, microprocessors or large memory circuitry. The transducer has a helical transmitter coil with tap nodes spaced between its end extremities. An oscillator drives the coil for simultaneously producing oppositely directed current on opposite sides of selected taps, creating a moving fringing field that is compatible with modern graphic display tablet technology. A control circuit of the transducer has a closed-loop integrator for detecting the centroid of a received stylus signal. Analog and digital versions of the integrator are disclosed.
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Citations
38 Claims
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1. A position transducer comprising:
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(a) helical electrically conductive transmitter coil having a plurality of coil turns and first and second end extremities, and a plurality of coil tap nodes thereon, the coil tap nodes being spaced between the end extremities; (b) oscillator means for producing a coil drive current; (c) selector means for sequentially connecting the oscillator means between the end extremities and selected ones of the coil tap nodes for producing a moving fringing field resulting from portions of the coil drive current flowing in opposite directions in the coil on opposite sides of each of the selected nodes; (d) a transducer body movable in a first transducer direction relative to the transmitter coil and having a receiver coil fixedly mounted thereto; and (e) circuit means connected to the selector means and responsive to the receiver coil for providing a first position signal, the first position signal representing the position of the transducer body relative to a first position reference, the first position reference being perpendicular to the first direction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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37. A position transducer comprising:
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(a) electrically conductive first and second transmitter coils, each having a plurality of substantially uniformly spaced coil turns and opposite end extremities, and a plurality of coil tap nodes spaced between the end extremities, a plurality of the turns being included between adjacent ones of the coil tap nodes, the transmitter coils being cylindrically helical about respective first and second coplanar coil axes and having front and back portions on opposite sides of the coil axes, the coil tap nodes being located on the back portions of the respective coils; (b) oscillator means for producing a coil drive current simultaneously in opposite directions between opposite sides of a selected one of the coil tap nodes and the coil end extremities of the corresponding coil; (c) selector means for sequentially connecting the oscillator means to different selected ones of the coil tap nodes for producing a moving fringing field; (d) a transducer body movable relative to the transmitter coils and having a receiver coil cylindrically symmetrical about a receiver axis and fixedly mounted to the transducer body, the transducer body defining a stylus point on the receiver axis; (e) means for guiding the body at a predetermined probe distance from the front portions of the transducer coils; (f) circuit means connected to the selector means and responsive to the receiver coil for providing first and second position signals, the position signals representing position coordinates of the transducer body relative to the transmitter coils, the circuit means comprising; (i) a receiver node, a receiver signal at the receiver node being responsive to the magnitude of the fringing field at the receiver coil; (ii) integrator means for summing a first-polarity component of the receiver signal during a first cycle interval, the integrator means also summing an opposite-polarity component of the receiver signal during a second cycle interval; (iii) latch means for latching a variable position signal associated with each of the transmitter coils, each position signal being representative of the location of the sequentially connected coil tap nodes along the respective transmitter coil; and (iv) feedback means for activating the latch means in response to the integrator means, the first cycle interval terminating and the second cycle interval commencing upon activation of the latch means; (g) means for gating the circuit means, whereby the circuit means is responsive to the receiver coil during a sample interval only for each transmitter coil, a subset of the coil tap nodes being activated by the selector means during the sample interval for enhancing linearity of the position signal between the coil tap nodes; and (h) threshold means for detecting a predetermined magnitude of the receiver signal, the threshold means providing a valid signal when the transducer body is aligned within a predetermined distance from the first transmitter coil.
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38. A method for measuring a coordinate position, comprising the steps of:
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(a) providing a helical transmitter coil having end extremities and a plurality of coil tap nodes spaced between the end extremities; (b) driving the transmitter coil with an AC signal for producing electrical current in the coil simultaneously in opposite directions on both sides of a selected one of the coil tap nodes; (c) sequentially selecting a plurality of the coil tap nodes for producing a moving fringing field; (d) locating a receiver coil at the coordinate position for producing a receiver signal responsive to the fringing field; and (e) detecting a centroid position of the receiver signal, the centroid position being representative of the coordinate position.
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Specification