Force sensor assembly
A force sensor assembly 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 assembly has a housing in which force sensing circuitry is mounted. The force sensing circuitry is configured for receiving an input force to be sensed and converting the input force into an output signal indicative of the input force. A coupling transmits the input force to the force sensing circuitry. The coupling has an inner section that applies the input force to the load bearing member, an outer section that receives the contact force on the nib and a collapsible section that allows the outer section to move relative to the inner section when the contact force exceeds a threshold. The relative movement of the outer section is limited by an abutment on the housing so that the input force on the force sensing circuitry never exceeds the threshold. This protects the force sensing circuitry from damage by sharp impact loads such as dropping the stylus on its nib.
1. A force sensor assembly comprising:
force sensing circuitry for receiving and input force and converting the input force into an output signal indicative of the input force; and,
a coupling having an inner section for transmitting the input force to the force sensor circuitry, an outer section for receiving an applied contact force and a collapsible section for allowing the outer section to move relative to the inner section when the contact force exceeds a threshold; such that,
the input force never exceeds the threshold.
2. A force sensor assembly according to claim 1 wherein the collapsible section has a deformable structure.
3. A force sensor assembly according to claim 2 wherein the deformable structure deforms plastically when the contact force exceeds a threshold.
4. A force sensor assembly according to claim 3 wherein the deformable structure is a series of struts extending between the inner section and the outer section such that the struts buckle when the contact force exceeds their combined buckling loads.
5. A force sensor assembly according to claim 4 wherein the struts are inclined to the direction of the contact force in order to promote buckling at a lower threshold.
6. A force sensor assembly according to claim 2 wherein the deformable structure deforms elastically when the contact force exceeds a threshold.
7. A force sensor assembly according to claim 6 wherein the deformable structure has a pair of abutting slip surfaces biased against each other by a resilient member, such that the slip surfaces slide relative to each other if the input force exceeds the threshold created by friction between the slip surfaces.
8. A force sensor assembly according to claim 7 wherein the resilient member is an elastic sleeve tightly fitted around the two components that respectively define the slip surfaces, the slip surfaces being inclined relative to the direction of the input force.
9. A force sensor assembly according to claim 1 wherein the coupling is biased against the load bearing member.
10. An electronic stylus comprising:
an elongate body;
a nib extending from one end of the elongate body;
a force sensing circuitry mounted to the elongate body for receiving an input force caused by contact on the nib and converting the input force into an output signal indicative of the input force;
a coupling having an inner section for applying the input force to the force sensing circuitry, an outer section for receiving the contact force on the nib and a collapsible section for allowing the outer section to move relative to the inner section when the contact force exceeds a threshold; wherein,
the relative movement of the outer section is limited by an abutment on the elongate body such that the input force never exceeds the threshold.
11. An electronic stylus according to claim 10 wherein the collapsible section has a deformable structure.
12. An electronic stylus according to claim 11 wherein the deformable structure deforms plastically when the contact force exceeds a threshold.
13. An electronic stylus according to claim 12 wherein the deformable structure is a series of struts extending between the inner section and the outer section such that the struts buckle when the contact force exceeds their combined buckling loads.
14. An electronic stylus according to claim 13 wherein the struts are inclined to the direction of the contact force in order to promote buckling at a lower threshold.
15. An electronic stylus according to claim 11 wherein the deformable structure deforms elastically when the contact force exceeds a threshold.
16. An electronic stylus according to claim 15 wherein the deformable structure has a pair of abutting slip surfaces biased against each other by a resilient member, such that the slip surfaces slide relative to each other if the input force exceeds the threshold created by friction between the slip surfaces.
17. An electronic stylus according to claim 16 wherein the resilient member is an elastic sleeve tightly fitted around the two components that respectively define the slip surfaces, the slip surfaces being inclined relative to the direction of the input force.
18. An electronic stylus according to claim 10 wherein the coupling is biased against the load bearing member.
19. 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.
20. An electronic stylus according to claim 10 wherein the output signal from the circuitry support a hand writing recognition facility.