Electromagnetic position transducer having active transmitting stylus

• US 5,122,623 A
• Filed: 03/08/1991
• Issued: 06/16/1992
• Est. Priority Date: 11/01/1990
• Status: Expired due to Term

• Current Assignee: Logitech, Inc. (Logitech International SA)
• Original Assignee: Gazelle Graphic Systems, Inc.
• Inventors: Gilano, Michael N., Zank, Anthony E., Gold, Kenneth S., France, H. Maurice
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/667,604
• Time in Patent Office: 466 Days
• Field of Search: 178/18, 178/19, 340/706
• US Class Current: 178/19.04
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/046 by electromagnetic means
• CPC Class Codes: G06F 3/047 using sets of wires, e.g. crossed wires

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 tablet coil with tap nodes spaced between its end extremities. In one configuration, an oscillator drives the tablet coil for simultaneously producing oppositely directed currents 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 from a stylus coil. Analog and digital versions of the integrator are disclosed. In another configuration, the oscillator drives the stylus coil for variably coupling magnetic flux to the tablet coil, a receiver signal that is coupled from the end extremities being responsive to the position of the stylus coil and the taps selected. A preferred configuration of the tablet coil has separate oppositely wound coil components.

Claims

1. A position transducer comprising:

(a) helical electrically conductive tablet 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) selector means for sequentially addressing selected ones of the coil tap nodes;

(c) a transducer body movable in a first transducer direction relative to the tablet coil and having a stylus coil fixedly mounted thereto; and

(d) oscillator means for producing a coil drive current in one of the tablet coil and the stylus coil;

(e) circuit means connected to the selector means and responsive to the stylus 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.

2. The transducer of claim 1, wherein the oscillator means is connected to the tablet coil, the coil drive current flowing in opposite directions on opposite sides of each selected tap node.

3. The transducer of claim 1, wherein the tablet coil comprises a pair of oppositely helically wound coil components, each of the components having a plurality of the coil tap nodes, the selector means sequentially connecting the coil components at corresponding ones of the coil tap nodes.

4. The transducer of claim 3, wherein the tablet coil comprises first and second trace layers, the first trace layer having a parallel spaced array of front coil portions, the second trace layer having a parallel spaced array of rear coil portions, alternate ones of the coil portions forming equally spaced portions of each of the oppositely wound coil components, each front coil portion being aligned with a rear coil portion of an oppositely wound coil component.

5. The transducer of claim 4, further comprising an array of conductive elements connecting each front coil portion to a corresponding rear coil portion of the same coil component, the conductive elements forming side coil portions of each of the coil components.

6. The transducer of claim 5, wherein adjacent pairs of the conductive elements comprise corresponding tap nodes of the oppositely wound coil components.

7. The transducer of claim 1, wherein the oscillator means is connected to the stylus coil for magnetically coupling a stylus field to the tablet coil, and the circuit means comprises a receiver node electrically coupled to the end extremities of the tablet coil, a receiver signal at the receiver node being responsive to the magnitude of the stylus field at the tablet coil.

8. The transducer of claim 7, wherein the tablet coil comprises a pair of oppositely helically wound coil components, each of the components having a plurality of the coil tap nodes, the selector means sequentially connecting the coil components at corresponding ones of the coil tap nodes.

9. The transducer of claim 8, wherein the circuit means comprises a balanced differential input amplifier, end extremities of the tablet coil components being coupled to complementary counterparts of the receiver node for feeding the amplifier, the amplifier rejecting stray electrical noise.

10. The transducer of claim 9, wherein the counterparts of the receiver node are coupled to respective end extremities of the coil components by corresponding diodes.

11. The transducer of claim 8, comprising a pair of the transmitter coils for dual-axis position measurements in alternating axis intervals, the end extremities of the coils being coupled to the differential amplifier through diode isolators.

12. The transducer of claim 7, further comprising an auxiliary coil proximately enclosing the tablet coil for providing an auxiliary signal in response to magnetic coupling from the stylus field.

13. The transducer of claim 12, further comprising means for synchronizing the circuit means to the auxiliary signal.

14. The transducer of claim 12, wherein the oscillator means is located within the transducer body, the transducer further comprising:

(a) means for periodically driving the auxiliary coil at a power frequency;

(b) power receiver means in the transducer body for powering the oscillator means by magnetic coupling from the auxiliary coil; and

(c) means for periodically interrupting the power driver means for reception of the auxiliary signal.

15. The transducer of claim 14, wherein the power receiver means comprises:

(a) a power coil;

(b) rectifier means;

(c) filter means connected between the rectifier means and the oscillator means; and

(d) coupling means coupled between the power coil and the rectifier means, the coupling means being resonant with the power coil at the power frequency for canceling a reactance of the power coil at the power frequency.

16. The transducer of claim 14, wherein the power driver means comprises:

(a) a complementary pair of driver transistors for sequentially switching a power node between a power bus voltage and ground at the power frequency;

(b) a gated clock generator circuit for separately controlling the driver transistors, the generator circuit including means for delaying activation of each of the driver transistors for a predetermined delay period following deactivation of the other driver transistor; and

(c) a coupling capacitor connected between the coupling node and the auxiliary coil, the coupling capacitor being resonant with the auxiliary coil for canceling a reactance of the auxiliary coil at the power frequency.

17. The transducer of claim 14, wherein the power frequency is between approximately 10 KHz and approximately 10 MHz.

18. The transducer of claim 17, wherein the power frequency is between approximately 20 KHz and approximately 100 KHz.

19. The transducer of claim 17, wherein the power frequency is between approximately 25 KHz and approximately 50 KHz.

20. The transducer of claim 7, comprising 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 tablet coil.

21. The transducer of claim 20, wherein the oscillator circuit is operable in a burst mode having a burst duty cycle, the burst duty cycle being less than approximately 20 percent for conserving electrical power.

22. The transducer of claim 21, wherein the burst mode is terminated for at least a predetermined period of time upon occurrence of the valid signal.

23. The transducer of claim 7, wherein the circuit means further comprises:

(a) 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;

(b) latch means for latching a variable position signal, the position signal being representative of the location of the sequentially connected coil tap nodes along the tablet coil; and

(c) 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.

24. The transducer of claim 23, wherein the variable position signal is generated by an N-state counter, N being a multiple M of the number of the coil tap nodes of the tablet coil, the selector means decoding the N-state counter for connecting each of the coil tap nodes to the oscillator means during an interval group number of counter states, the interval group number corresponding to the multiple M.

25. The transducer of claim 23, wherein the integrator means comprises a bidirectional counter and a variable frequency oscillator, the frequency of the variable frequency oscillator being responsive to the magnitude of the receiver signal.

26. The transducer of claim 1, wherein the transducer coil is cylindrically helical about a coil axis and having front and back portions on opposite sides of the coil axis, the coil axis being parallel to the first transducer direction, the transducer further comprising means for guiding the body at a fixed probe distance t from the front portion of the coil.

27. The apparatus of claim 26, wherein the front and back portions of the transducer coil are spaced part by a winding distance d, the distance d being at least approximately 0.03 inches.

28. The transducer of claim 26, wherein the turns of the tablet coil are substantially uniformly spaced.

29. The transducer of claim 26, wherein the stylus coil is cylindrically symmetrical about a stylus axis, the transducer body defining a stylus point on the stylus axis, the stylus point moving at the probe distance t from the front portion of the coil.

30. The transducer of claim 29, wherein the tablet coil turns are spaced in the direction of the coil axis by a turn spacing l, the stylus coil having a diameter D and a length H, a central point within the stylus coil on the receiver axis being offset by a coil distance C from the stylus point, the coil distance C being approximately C=a complex function of (D, l, H, d and t) for permitting uniform operation of the transducer within a range of inclinations of the stylus axis relative to orthogonal alignment with the front portion of the coil.

31. The transducer of claim 30, wherein D≧

S≅

C.

32. The transducer of claim 30, further comprising means for gating the circuit means,

whereby the circuit means is responsive to the receiver coil during a sample interval only, a subset of the coil tap nodes being activated by the selector means during the sample interval for enhancing the uniformity of operation over the range of inclinations of the receiver axis.

33. The transducer of claim 32, wherein the duration of the sample interval is approximately equal to the time during which four of the coil tap nodes are selected by the selector means.

34. The transducer of claim 29, wherein the stylus coil comprises a pair of stylus coil components.

35. The transducer of claim 26, wherein the front coil portion is substantially planar, the means for guiding the body comprising a planar tablet surface for slidably supporting the body.

36. The transducer of claim 35, wherein the tablet coil is a first coil, the transducer comprising a second tablet coil, the second tablet coil being orthogonally supported relative to the first tablet coil.

37. The transducer of claim 35, further comprising an electronic graphic display unit, the display unit forming the tablet surface.

38. The transducer of claim 37, wherein the display unit is visually responsive to movement of the transducer body relative to the tablet surface.

39. The transducer of claim 26, wherein the tablet coil is a first tablet coil, the transducer comprising a second tablet coil, the second tablet coil being orthogonally supported relative to the first tablet coil, the front portions of the coils being substantially coplanar.

40. The transducer of claim 1, wherein the tablet coil includes a plurality of the turns between each of the coil tap nodes.

41. A position transducer comprising:

(a) electrically conductive first and second tablet 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, the tablet 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;

(b) selector means for sequentially addressing selected ones of the coil tap nodes for variably coupling the stylus field;

(c) a transducer body movable relative to the tablet coils and having a stylus 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;

(d) means for guiding the body at a predetermined probe distance from the front portions of the transducer coils;

(e) oscillator means in the transducer body for producing a coil drive current in the stylus coil for radiating a magnetic stylus field therefrom;

(f) circuit means connected to the selector means and responsive to the stylus coil for providing first and second position signals, the position signals representing position coordinates of the transducer body relative to the tablet coils, the circuit means comprising;

(i) a receiver node electrically coupled to end nodes of the tablet coils, a receiver signal at the receiver node being responsive to the stylus field at the selected tap node of the tablet coil; and

(ii) wireless means for synchronizing the circuit means to the oscillator means; and

(g) wireless means for periodically powering the oscillator means from the circuit means.

42. A method for measuring a coordinate position, comprising the steps of:

(a) providing a helical tablet coil having end extremities and a plurality of coil tap nodes spaced between the end extremities;

(b) providing a stylus coil in a movable transducer body;

(c) locating the stylus coil at the coordinate position for producing a receiver signal responsive to the magnetic coupling;

(d) driving an AC oscillator for producing a magnetic field between the tablet coil and the stylus coil;

(e) sequentially selecting a plurality of the coil tap nodes for variably magnetically coupling the tablet coil and the stylus coil; and

(f) detecting a centroid position of the receiver signal, the centroid position being representative of the coordinate position.

43. The method of claim 42, further comprising the steps of:

(a) periodically interrupting the AC oscillator;

(b) modulating a first timer interval during which the oscillator is interrupted in response to a movable member on the transducer body; and

(c) monitoring the first timer interval for detecting a position of the movable member.

44. The method of claim 43, wherein the movable member is a first movable member, the method including the further steps of:

(a) modulating a second timer interval during which the oscillator is operational in response to a second movable member on the transducer body; and

(b) monitoring the second timer interval for detecting a position of the second movable member.

45. The method of claim 43, including the further step of powering the AC oscillator by magnetic coupling to the transducer body during the first timer interval.

46. In a position transducer having a stylus that is wirelessly coupled to a tablet circuit, the tablet circuit being responsive to movement of the stylus relative thereto, the improvement comprising:

(a) timer means in the stylus; and

(b) means for synchronizing the tablet circuit in response to the timer means.

47. The transducer of claim 46, wherein the tablet circuit is operative for generating respective X and Y coordinate measurements of the position of the stylus in corresponding scan intervals, the scan intervals being sequentially initiated in response to the timer means.

48. The transducer of claim 46, the stylus further comprising auxiliary control circuit means, the timer means being responsive to the auxiliary control circuit means, the tablet circuit including means for generating at least one auxiliary output in response to the timer means, the auxiliary output corresponding to operation of the auxiliary control circuit means.

49. The transducer of claim 48, wherein the auxiliary control circuit means comprises at least one operator-controlled switch on the stylus.

50. The transducer of claim 49, wherein the stylus has a body and a stylus point, the operator-controlled switch being responsive to axial pressure against the stylus point.