Calibration of a system for tracking a writing instrument with multiple sensors

• US 6,492,981 B1
• Filed: 11/21/2000
• Issued: 12/10/2002
• Est. Priority Date: 12/23/1997
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Angelo, Michael, Wolff, Gregory J., Stork, David G.
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Bell, Paul A.
• Application Number:
  US09/721,045
• Time in Patent Office: 749 Days
• Field of Search: 334/31, 73/17.5, 73/17.8, 73/17.9, 737/67, 318/582, 701/200, 701/207, 701/213, 701/216, 701/300, 340/988, 342/76, 116/209, 345/158, 702/150, 702/151, 702/152, 702/153, 702/154, 178/18.01
• US Class Current: 345/179
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device
• CPC Class Codes: G06V 30/228 of three-dimensional handwriting, e.g. writing in the air

Abstract

One embodiment of the writing instrument described herein comprises a pen-like device containing three accelerometers and three gyroscopes. Data from these sensors are processed via an Euler transform. Prior to using the writing instrument, the user holds the writing instrument in multiple predefined positions and sensor readings are taken. The sensor readings are mapped to the corresponding predefined positions. In addition, the sensor readings are compared to expected sensor readings to compensate for environmental variations such as altitude or temperature as well as for the possible tilt of a writing surface. The sensor readings are interpolated to map sensor readings other than those at the predefined positions to other writing instrument positions. When the user writes with the writing instrument, sensor outputs are used to track the writing instrument to define strokes made by the user. The data describing the strokes may be stored or processed to accomplish a variety of tasks including faxing a message, recording information, etc.

Claims

1. An apparatus for tracking movement of an input device comprising:

means for obtaining sensor readings for each of a plurality of predefined positions of the input device with respect to a writing surface;

means for generating a mapping of possible sensor outputs to possible input device positions based on the sensor readings at the predetermined positions;

means for mapping a first voltage output by a first sensor when the input device is in a first predetermined position with respect to the writing surface;

means for mapping a second voltage output by a second sensor when the input device is in a second predetermined position with respect to the writing surface; and

means for mapping sensor output voltages between the first voltage and the second voltage to positions of the input device between the first predetermined position and the second predetermined position.

2. The apparatus of claim 1 further comprising:

means for mapping a third voltage output by a third sensor when the input device is in a third predetermined position with respect to the writing surface; and

means for interpolating sensor output voltages between the second voltage and the third voltage to positions of the input device between the second predetermined position and the third predetermined position.

3. An apparatus, comprising:

means for obtaining sensor readings for each of a plurality of predefined positions of a writing instrument;

means for generating a mapping of sensor outputs to writing instrument positions based, at least in part, on the sensor readings at the plurality of predefined positions with respect to the writing surface; and

means for generating a mapping of possible sensor outputs to possible writing instrument positions comprising means for determining a polynomial approximation of future writing instrument positions corresponding to future sensor outputs based on sensor outputs at the predetermined positions, wherein the polynomial approximation includes the sensor outputs for each predefined position.

4. The apparatus of claim 3, further comprising means for changing the mapping of possible sensor outputs to possible writing instrument positions to compensate for an angle of a writing surface.

5. The apparatus of claim 3, further comprising means for changing the mapping of possible sensor outputs to possible writing instrument positions based on measurable deviations of a mapped position to a known position.

6. A machine readable medium having stored thereon instructions, which when executed by a processor, cause the processor to perform the following comprising:

obtaining sensor readings for each of a plurality of predefined positions of the input device with respect to a writing surface;

generating a mapping of possible sensor outputs to possible input device positions based on the sensor readings at the predetermined positions;

mapping a first voltage output by a first sensor when the input device is in a first predetermined position with respect to the writing surface;

mapping a second voltage output by a second sensor when the input device is in a second predetermined position with respect to the writing surface; and

mapping sensor output voltages between the first voltage and the second voltage to positions of the input device between the first predetermined position and the second predetermined position.

7. The machine readable medium of claim 6, wherein the processor further performs the following comprising:

mapping a third voltage output by a third sensor when the input device is in a third predetermined position with respect to the writing surface; and

interpolating sensor output voltages between the second voltage and the third voltage to positions of the input device between the second predetermined position and the third predetermined position.

8. A machine readable medium having stored thereon instructions, which when executed by a processor, cause the processor to perform the following comprising:

obtaining sensor readings for each of a plurality of predefined positions of a writing instrument;

generating a mapping of sensor outputs to writing instrument positions based, at least in part, on the sensor readings at the plurality of predefined positions with respect to the writing surface; and

generating a mapping of possible sensor outputs to possible writing instrument positions comprising means for determining a polynomial approximation of future writing instrument positions corresponding to future sensor outputs based on sensor outputs at the predetermined positions, wherein the polynomial approximation includes the sensor outputs for each predefined position.

9. The machine readable medium of claim 8, wherein the processor further performs the following comprising changing the mapping of possible sensor outputs to possible writing instrument positions to compensate for an angle of a writing surface.

10. The machine readable medium of claim 8, wherein the processor further performs the following comprising changing the mapping of possible sensor outputs to possible writing instrument positions based on measurable deviations of a mapped position to a known position.