Calibration of a force sensing type of data input device

• US 4,745,565 A
• Filed: 01/21/1986
• Issued: 05/17/1988
• Est. Priority Date: 01/21/1986
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Garwin, Richard L., Levine, James L.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/821,177
• Time in Patent Office: 847 Days
• Field of Search: 364/571, 364/556, 364/558, 364/190, 178/18, 73/862.04, 73/1 R
• US Class Current: 702/95
• CPC Class Codes: G06F 3/04142 the force sensing means being located peripherally, e.g. disposed at the corners or at the side of a touch sensing plate

Abstract

The calibration of a force sensing type data input device through the use of at least one correction developed by minimization of differences between an actual location of a pattern of test forces and a calculated location of the test forces where the calculation is on the basis of the effect of the test forces on the equilibrium of the device.

Claims

1. An apparatus for introducing data into a data processing device said data being indicative of the position of a localized force applied to an area member supported with respect to a reference by at least three separate force sensors, the improvement comprising:

the data processing device provides at least one correction for the force sensed by each said force sensor in service, said correction being based on the minimization of the differences between coordinates of each of a plurality of known location test forces calculated with respect to the effect of said test forces on the equilibrium of said area member and actual coordinates of said test forces wherein said minimization is achieved mathematially through a procedure known as least squares.

2. The process of providing calibration information for a force sensitive input device that translates the location of a localized data input force applied to an area member coupled to a fixed member through a plurality of greater than two force sensors into data for machine computation comprising in combination the steps of:

establishing the no-load signal of each said force sensor,

providing serially a test force at each of a plurality of known location test force points, the number of said plurality being at least a quantity of half the quantity three times the number of said force sensors minus one,

correcting for each said test force applied to produce the output of each said force sensor by algebraically subtracting said no-load signal,

establishing an indicated x and y location coordinate for each said test force by the unbalancing effect of said force on the equilibrium of said area member,

establishing a difference between said indicated x and y location coordinates and the x and y coordinates of the known location of said test force, and

establishing at least one correction by a minimization of the differences for each said test force between said indicated and said actual coordinates through the mathematical technique known as least squares.

3. In a force sensitive input device for translating the location of a localized data input force applied to an area member into data for machine computation, wherein said area member is supported with respect to a reference at at least three points by separate force sensors,

the improvement for providing an in service essentially uniformly accurate data input force location signal independent of specific transducer response and location comprising in combination

means for application of a pattern of test forces, the number of said forces being at least half the quantity three times the number of said force sensors, minus one, each said test force being positioned at a separated known location,

means for determining the indicated point of application of each said test force by the effect on equilibrium conditions on said area member by sensing the output signal change from said force sensors responsive to said application of said test forces,

means for developing corrections for each said force sensor that minimize the differences between said indicated and said known locations for each test force in said pattern through the mathematical technique known as least squares and

employing said correction for each force location determination when said data input device senses a data input force in service.