Minimum parallax stylus detection subsystem for a display device

• US 4,764,885 A
• Filed: 04/25/1986
• Issued: 08/16/1988
• Est. Priority Date: 04/25/1986
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Ruffino, Louis V., Greanias, Evon C., Schroeder, Karl F.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Ramirez, Ellis B.
• Application Number:
  US06/856,627
• Time in Patent Office: 844 Days
• Field of Search: 178/18, 178/19, 364/571, 364/709, 364/710, 340/709, 340/708, 250/216, 250/568
• US Class Current: 345/179
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06F 3/038 Control and interface arrangements therefor, e.g. drivers or device-embedded control circuitry
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0441 using active external devices, e.g. active pens, for receiving changes in electrical potential transmitted by the digitiser, e.g. tablet driving signals

Abstract

A minimum parallax stylus detection subsystem is disclosed for use with a graphic input grid overlay which is positioned on the viewing surface of a display device. The invention has a three phase operation wherein, during the first phase, the stylus is at a remote distance from the viewing surface of the display and therefore no representation of the stylus position is displayed. During a second phase, the stylus is brought within a first threshold distance from the viewing surface of the display, during which a cursor image is generated which is precisely positioned on the display corresponding to the detected position of the stylus. During a third phase of operation of the invention, the stylus is brought within a close proximity of the viewing surface of the display, during which the cursor image is removed from the display and an actual trace of the path of the stylus with respect to the graphic input grid overlay is shown. In this manner, the operator can focus attention on the displayed location of the cursor instead of on the physical location of the stylus, thereby minimizing the parallax error in the location of the stylus with respect to the displayed image.

Claims

1. In a data processing system including a display subsystem having a video buffer which stores a data representation of an image to be displayed, an image generator connected to the video buffer to convert the stored representation of the image into video signals and a display device connected to the image generator having a transparent viewing plate of finite thickness with a visual manifestation of the video signals being formed on one side of the plate for viewing through the plate, a stylus detection subsystem used in cooperation with the display subsystem, which minimizes the parallax between the apparent position of a stylus and the detected position thereof, data processing system comprising:

an array of horizontal and vertical signal wires disposed on said viewing plate, for radiating a signal from a radiative signal source for receipt by said stylus;

a decoder connected to said signal wires and said radiative signal source, for connecting selected ones of said signal wires to said signal source;

a counter having an output connected to said decoder, for cyclically outputting coordinate values to said decoder for energizing selected ones of said signal wires with a radiated signal;

a maximum signal detector having an input connected to said stylus, for outputting a triggering signal when a maximum value is detected in the strength of the radiated signal received by said stylus;

a cursor image generator having an input connected to said counter, an input connected to said minimum signal detector and an output connected to said display subsystem, for generating cursor image signals for display on said viewing plate at a location corresponding to coordinate values output from said counter when said signal strength is a maximum;

a low level signal detector, having an input connected to said stylus, a first output connected to said decoder and a second output connected to said cursor image generator, for outputting a first enabling signal to said decoder when said stylus is farther than a first distance from said viewing plate, said decoder in response thereto connecting selected ones of said wires to said signal source to radiate in a quiescent state pattern;

said low level detector terminating said first enabling signal when said stylus is closer to said viewing plate than said first distance but farther than a second distance, and outputting a second enabling signal to said cursor image generator, said cursor image generator in response thereto outputting cursor image signals for display on said viewing plate at a location corresponding to said coordinate values output from said counter;

a stylus trace generator having an imput connected to said counter and said maximum signal detector and an output connected to said display subsystem, for generating stylus trace signals for display on said viewing plate at a location corresponding to said coordinate values output from said counter when said radiated signal strength is a maximum;

a high level signal detector, having an input connected to said stylus and an output connected to said stylus trace generator, for outputting an enabling signal to said stylus trace generator when said stylus is closer to said viewing plate than said second distance, said stylus trace generator in response thereto outputting stylus trace signals for display on said viewing plate at a location corresponding to said coordinate values output from said counter;

whereby the operator can focus attention on the displayed location of said cursor instead of the stylus, to identify the location of the stylus as it is perceived by the stylus detection subsystem.

2. The apparatus of claim 1, wherein said low level detector terminates said second enabling signal when said stylus is closer to said viewing plate than said second distance, said cursor image generator terminating said display of said cursor image in response thereto.

3. In a system including a display subsystem having a display device with a transparent viewing plate of finite thickness, the visual manifestation of the image to be displayed being formed on one side of the plate for viewing through the plate, a stylus detection subsystem used in cooperation with the display subsystem, which minimizes the parallax between the apparent position of a stylus and the detected position thereof, data processing system comprising:

an array of signal wires disposed on said viewing plate, for radiating a signal from a radiative signal source for receipt by said stylus;

a decoding means connected to said signal wires and said radiative signal source, for connecting selected ones of said signal wires to said signal source;

a coordinate means having an output connected to said decoding means, for outputting coordinate values to said decoding means for energizing selected ones of said signal wires with a radiated signal;

a maximum signal detector having an input connected to said stylus, for outputting a triggering signal when a maximum value is detected in the strength of the radiated signal received by said stylus;

a cursor image generator having an input connected to said coordinate means, an input connected to said maximum signal detector and an output connected to said display subsystem, for generating cursor image signals for display on said viewing plate at a location corresponding to said coordinate values output from said coordinate means when said radiated signal strength is a maximum;

a low level signal detector, having an input connected to said stylus, a first output connected to said decoding means and a second output connected to said cursor image generator, for outputting a first enabling signal to said decoding means when said stylus is farther than a first distance from said viewing plate, said decoding means in response thereto connecting selected ones of said wires to said signal source to radiate in a quiescent state pattern;

said low level detector terminating said first enabling signal when said stylus is closer to said viewing plate than said first distance but farther than a second distance, and outputting a second enabling signal to said cursor image generator, said cursor image generator in response thereto outputting cursor image signals for display on said viewing plate at a location corresponding to said coordinate values output from said coordinate means;

a stylus trace generator having an input connected to said coordinate means and said maximum signal detector and an output connected to said display subsystem, for generating stylus trace signals for display on said viewing plate at a location corresponding to said coordinate values output from said coordinate means when said radiated signal strength is a maximum;

a high level signal detector, having an input connected to said stylus and an output connected to said stylus trace generator, for outputting an enabling signal to said stylus trace generator when said stylus is closer to said viewing plate than said second distance, said stylus trace generator in response thereto outputting stylus trace signals for display on said viewing plate at a location corresponding to said coordinate values output from said coordinate means;

whereby the operator can focus attention on the displayed location of said cursor instead of the stylus, to identify the location of the stylus as it is perceived by the stylus detection subsystem.

4. The apparatus of claim 3, wherein said low level detector terminates said second enabling signal when said stylus is closer to said viewing plate than said second distance, said cursor image generator terminating said display of said cursor image in response thereto.