Three-axis force measurement stylus

• US 4,896,543 A
• Filed: 11/15/1988
• Issued: 01/30/1990
• Est. Priority Date: 11/15/1988
• Status: Expired

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Gullman, Larry S.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US07/271,254
• Time in Patent Office: 441 Days
• Field of Search: 73/862.04, 73/862.05, 73/826.06, 73/862.54, 73/865.4, 382/3, 382/59, 401/194
• US Class Current: 73/862.041
• CPC Class Codes: B43K 8/22 with electrically or magnetically activated writing-points
• CPC Class Codes: G01L 5/161 using variations in ohmic resistance
• CPC Class Codes: G01L 5/167 using piezoelectric means
• CPC Class Codes: G06F 3/03545 Pens or stylus

Abstract

A three-axis force measurement stylus includes a housing and a cartridge and an interface between the housing and the cartridge wherein the interface comprises a plurality of pressure sensitive sheets, preferably of variable resistance pressure sensitive Mylar films which sense the force between the cartridge and the housing. The cartridge and the housings are disposed at a skew angle relative to the axis of the stylus to be able to sense forces in three dimensions. In a specific embodiment, the cartridge forms a conical section which mates with a complimentary conical section of the housing. Membranes of the force sensitive material are provided along three fingers from an apex of the conical section. The cartridge is preloaded against the conical section by a spring between the housing and the cartridge. Alternatively to the force sensitive film, a sheet of a piezoelectric pressure-sensitive material may be substituted. In each instance, direct pressure between the conical section of the cartridge and the conical section of the housing is sensed by the sensor mounted therebetween.

Claims

1. An apparatus for generating signals representing direction and magnitude of force on a shaft in a stylus comprising:

a housing, wherein said housing comprises a funnel portion;

a pickup, wherein said pickup comprises a cone portion; and

means disposed between said housing and said pickup and abutting said housing and said pickup at an interface skewed from said shaft for sensing pressure between said housing and said pickup in a plurality of directions wherein said sensing means further comprises a first pad, a second pad and a third pad constructed on a common elastomeric backing material, each said pad including at least a pair of conductive traces having a surface exposed for electrical connection thereto and a coating of conductive material over said traces, said conductive material being in contact with said traces varying conductivity between said traces in proportion to pressure between said coating and said traces.

2. The apparatus according to claim 1 wherein said pickup further comprises an ink-carrying cartridge, said cartridge being removably mounted to said cone portion.

3. The apparatus according to claim 2 further including means for biasing said funnel portion against said cone portion.

4. The apparatus according to claim 1 further including means for biasing said funnel portion against said cone portion.

5. An apparatus for generating signals representing direction and magnitude of force on a shaft in a stylus comprising:

a housing, wherein said housing comprises a funnel portion;

a pickup, wherein said pickup comprises a cone portion; and

means disposed between said housing and said pickup and abutting said housing and said pickup at an interface skewed from said shaft for sensing pressure between said housing and said pickup in a plurality of directions, wherein said funnel portion and said cone portion abut one another in a complementary relationship forming said interface, and wherein said sensing means comprise planar pads which are disposed at said interface between said funnel portion and said cone portion and which are distributed around a central axis through said cone portion for sensing directionality of force.

6. The apparatus according to claim 5 wherein said pickup further comprises an ink-carrying cartridge, said cartridge being removably mounted to said cone portion.

7. The apparatus according to claim 6 further including means for biasing said funnel portion against said cone portion.

8. The apparatus according to claim 5 further including means for biasing said funnel portion against said cone portion.

9. An apparatus for generating signals representing direction and magnitude of force on a shaft in a stylus comprising:

a housing, wherein said housing comprises a first pressure means;

a pickup, wherein said pickup comprises a second pressure means; and

a sensing means disposed between said housing and said pickup and abutting said housing and said pickup at an interface wherein said first and second pressure means exert pressure on said sensing means for sensing pressure of said pickup abutting said housing in a plurality of directions, wherein said first pressure means comprises a funnel portion and wherein said second pressure means comprises a cone portion, said cone portion abutting said funnel portion in a complementary relationship forming said interface, and wherein said sensing means comprises planar pads which are disposed at said interface between said funnel portion and said cone portion and which are distributed around a central axis through said cone portion for sensing directionality of force.

10. The apparatus according to claim 9, wherein said sensing means further comprises a first pad, a second pad and a third pad constructed on a common elastomeric backing material, each said pad including at least a pair of conductive traces having a surface exposed for electrical connection thereto and a coating of conductive material over said traces, said conductive material being in contact with said traces varying conductivity between said traces in proportion to pressure between said coating and said traces.

11. The apparatus according to claim 10, wherein said pickup further comprises an ink-carrying cartridge, said cartridge being removably mounted to said cone portion.

12. The apparatus according to claim 11, further including means for biasing said funnel portion against said cone portion.

13. The apparatus according to claim 10, further including means for biasing said funnel portion against said cone portion.

14. The apparatus according to claim 9, wherein said pickup further comprises an ink-carrying cartridge, said cartridge being removably mounted to said cone portion.

15. The apparatus according to claim 14, further including means for biasing said funnel portion against said cone portion.

16. The apparatus according to claim 9, further including means for biasing said funnel portion against said cone portion.