Digitizing stylus having capacitive pressure and contact sensing capabilities

• US 5,438,275 A
• Filed: 01/03/1994
• Issued: 08/01/1995
• Est. Priority Date: 01/03/1994
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Wong, Tin-Lup, Kowalewski, Paul D., Fado, Francis, Donaldson, Robert L., Verrier, Guy F.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): Do, Diep
• Application Number:
  US08/177,106
• Time in Patent Office: 575 Days
• Field of Search: 324/661, 324/662, 324/686, 324/690, 324/71.1, 73/865.4, 73/862.626, 361/181, 361/283.1, 361/283.2, 361/283.3
• US Class Current: 324/662
• CPC Class Codes: G06F 3/03545 Pens or stylus

Abstract

A stylus assembly in which a stylus is mounted in a housing for movement relative thereto. An electrical circuit is provided for sensing contact of the stylus with a writing surface and measuring the pressure exerted on the surface by the stylus.

Claims

1. An assembly for sensing pressure applied to a contact surface, said assembly comprising:

a housing;

a stylus mounted in said housing for movement relative thereto;

an electrical circuit associated with at least one of said housing and said stylus for detecting and quantifying pressure exerted on said stylus as a result of said stylus engaging said contact surface, said electrical circuit comprising a capacitor having one plate mounted on said stylus and another plate mounted on said housing so that movement of said stylus as a result of said stylus engaging said contact surface varies a capacitance of said capacitor;

spring means normally applying a predetermined pressure against said one capacitor plate to urge said one capacitor plate in a direction towards said other capacitor plate and opposite the direction of said pressure exerted on said stylus by said contact surface; and

means for varying said predetermined pressure on said spring to vary an initial contact threshold and an operating range of said electrical circuit.

2. The assembly of claim 1 wherein said electrical circuit comprises means responsive to movement of said stylus relative to said housing for generating an output signal.

3. The assembly of claim 2 wherein said movement responsive means comprises a variable reactive component associated with one of said housing and said stylus.

4. The assembly of claim 3 wherein said variable reactive component is a capacitor having one plate mounted on said stylus and another plate mounted on said housing so that movement of said stylus as a result of said stylus engaging said contact surface varies a capacitance of said capacitor.

5. The assembly of claim 4 further comprising spring means normally applying a predetermined pressure against said one capacitor plate to urge said one capacitor plate in a direction towards said other capacitor plate and opposite the direction of said pressure exerted on said stylus by said contact surface.

6. The assembly of claim 5 wherein said spring means urges said one capacitor plate to a predetermined position relative to said other plate to establish a finite capacitance between said plates, said movement of said one plate varying said capacitance.

7. The assembly of claim 1 wherein said housing has a circular cross section, and wherein said stylus is coaxially disposed in said housing and is adapted for movement along the axis of said housing.