Force sensor with dilatant fluid stop

• US 20070070053A1
• Filed: 07/31/2006
• Published: 03/29/2007
• Est. Priority Date: 08/19/2005
• Status: Active Grant

• Current Assignee: Livescribe Incorporated (Anoto Group AB)
• Original Assignee: Silverbrook Research Pty Limited
• Inventors: Silverbrook, Kia, Lapstun, Paul
• Granted Patent: US 7,898,532 B2
• Time in Patent Office: Days
• US Class Current: 345/179
• CPC Class Codes: B43K 23/12 for pens caps co-operating with retractable nibs B43K5/165
• CPC Class Codes: B43K 23/126 with clips
• CPC Class Codes: B43K 25/022 attached to a pen cap
• CPC Class Codes: B43K 29/00 Combinations of writing implements with other articles
• CPC Class Codes: B43K 29/003 with optical equipment, e.g. magnifier, viewer
• CPC Class Codes: B43K 29/004 with more than one object
• CPC Class Codes: B43K 29/08 with measuring, computing or indicating devices
• CPC Class Codes: B43K 29/093 with calculators
• CPC Class Codes: B43K 29/10 with illuminating devices
• CPC Class Codes: B43K 7/005 Pen barrels
• CPC Class Codes: B43K 7/02 Ink reservoirs; Ink cartridges B43K7/01 takes precedence
• CPC Class Codes: G01L 1/26 Auxiliary measures taken, or devices used, in connection with the measurement of force, e.g. for preventing influence of transverse components of force, for preventing overload
• CPC Class Codes: G01L 5/162 of piezoresistors
• CPC Class Codes: G06F 3/0321 by optically sensing the absolute position with respect to a regularly patterned surface forming a passive digitiser, e.g. pen optically detecting position indicative tags printed on a paper sheet constructional details of pen-shaped pointing devices G06F3/03545, G06F3/03542, G06F3/037
• CPC Class Codes: G06F 3/03545 Pens or stylus

Abstract

A force sensor particularly suited for use in an electronic stylus that senses the contact force on its nib for recording pen strokes and handwriting recognition. The sensor has a housing for a load bearing member for receiving an input force to be sensed and associated circuitry for converting the input force into an output signal indicative of the input force. A coupling transmits the input force to the load bearing member and, a compressible reservoir containing dilatant fluid mounted between the housing and the coupling restricts the input force to the load bearing member caused by shock loading to the coupling. This protects the force sensor from damage by sharp impact loads such as dropping the stylus on its nib.

Claims

1. A force sensor assembly comprising:

a housing;

a load bearing member for receiving an input force to be sensed;

circuitry for converting the input force into an output signal indicative of the input force;

a coupling for transmitting the input force to the load bearing member; and

,

a compressible reservoir containing dilatant fluid mounted between the housing and the coupling to restrict the input force to the load bearing member caused by shock loading to the coupling.

2. A force sensor assembly according to claim 1 wherein the compressible reservoir of dilatant fluid maintains a gap between the load bearing member and the coupling when the input force is not applied, and the compressible reservoir compresses to allow the coupling to directly engage the load bearing member with a steady application of the input force.

3. A force sensor assembly according to claim 2 wherein the compressible reservoir is secured to the housing and the coupling, and the coupling is biased away from the housing to maintain the gap between the coupling and load bearing member when the input force is not applied.

4. A force sensor assembly according to claim 1 wherein the load bearing member has a protrusion with round end for engagement with the coupling.

5. A force sensor assembly according to claim 4 wherein the coupling has a similar protrusion extending centrally from a flange such that the distal end of the protrusion engages the rounded end of the protrusion from the load bearing member, and the compressible reservoir of dilatant fluid is positioned between the housing and the flange.

6. A force sensor assembly according to claim 5 wherein the housing defines a recess for the circuitry, the rounded end of the protrusion from the load bearing member extends proud of the recess for engaging the coupling.

7. A force sensor assembly according to claim 6 wherein the compressible reservoir has an annular shape and is positioned around the opening to the recess and around the central protrusion from the flange of the coupling.

8. A force sensor assembly according to claim 1 wherein the output signal from the circuitry support a hand writing recognition facility.

9. A force sensor assembly according to claim 1 wherein the load bearing member can move up to 100 microns relative to the housing.

10. An electronic stylus comprising:

an elongate body;

a nib extending from one end of the elongate body; and

,

a load bearing member mounted to the elongate body for receiving an input force caused by contact on the nib;

circuitry for converting the input force into an output signal indicative of the input force;

a coupling for transmitting the input force to the load bearing member; and

,

a compressible reservoir containing dilatant fluid mounted between the housing and the coupling to restrict the input force to the load bearing member caused by shock loading to the coupling.

11. An electronic stylus according to claim 10 wherein the load bearing member has a protrusion with round end for engagement with the coupling.

12. An electronic stylus according to claim 11 wherein the coupling has a similar protrusion extending centrally from a flange such that the distal end of the protrusion engages the rounded end of the protrusion from the load bearing member, and the compressible reservoir of dilatant fluid is positioned between the housing and the flange.

13. An electronic stylus according to claim 12 wherein the elongate body defines a recess for the circuitry, the rounded end of the protrusion from the load bearing member extends proud of the recess for engaging the coupling, and the compressible reservoir has an annular shape and is positioned around the opening to the recess and around the central protrusion from the flange of the coupling.

14. An electronic stylus according to claim 10 wherein the the compressible reservoir of dilatant fluid maintains a gap between the load bearing member and the coupling when the input force is not applied, and the compressible reservoir compresses to allow the coupling to directly engage the load bearing member with a steady application of the input force.

15. An electronic stylus according to claim 14 wherein the compressible reservoir is secured to the housing and the coupling, and the coupling is biased away from the housing to maintain the gap between the coupling and load bearing member when the input force is not applied.

16. An electronic stylus according to claim 10 wherein the nib of the electronic stylus is a ball point writing nib with a tubular ink cartridge extending from the nib toward the load bearing member such that the coupling is a detachable boot that fits over the end of the cartridge opposite the nib.

17. An electronic stylus according to claim 16 wherein the input force can be up to 5 Newtons.

18. An electronic stylus according to claim 10 wherein the circuitry is a piezoresistive bridge circuit.

19. An electronic stylus according to claim 10 wherein the load bearing member can move up to 100 microns relative to the housing.

20. An electronic stylus according to claim 10 wherein the output signal from the circuitry support a hand writing recognition facility.