High resolution light pen for use with graphic displays

Claim 2

A high resolution light pen for sensing light rays emitted from a pixel on a video screen comprising: an elongated cylindrical housing having opposed front and rear ends; a collimation tube mounted within the housing and projecting outwardly from the front end thereof, said collimation tube having a cylindrical channel extending along the longitudinal axis thereof, with the inner surface of said channel being nonreflective; photodetector means fixedly mounted within said housing to the rear of said collimation tube and axially aligned with the channel thereof; and lens means disposed within the channel of the collimation tube adjacent the front end thereof, said lens means having a focal length equal to the distance defined between the lens means and the virtual image of the pixel on the video screen when the front end of the collimation tube is placed against the outer surface of the screen, whereby all light rays emanating from a pixel axially aligned with the channel and passing through the lens means are refracted axially along the channel and directed to said photodetector, while light rays passing through the lens means from a displaced source are refracted at an angle and absorbed by the walls of the channel such that only light rays from an aligned pixel are sensed by said photodetector.

Claim 3

A light pen as recited in claim 1 further including a second lens means disposed adjacent the rear end of said channel for focusing said axially directed light rays within said channel directly onto said photodetector means.

Claim 4

A light pen as recited in claim 2 wherein said second lens means is fixedly mounted to said photodetector means.

Claim 5

A light pen as recited in claims 1, 2 or 3 wherein said collimation tube is slidably mounted within said housing and wherein said light pen further includes a switch means operatively connected to said photodetector, said switch means being disposed behind said collimation tube in a manner such that when the front end of said tube is pressed against the video screen it is moveable rearwardly, relative to said housing, to actuate said switch means.

Claim 6

A light pen as recited in claim 4 wherein said collimation tube includes a recess for receiving a stop pin fixedly mounted on said housing, said recess and stop pin combination for restricting the movement of said collimation tube in an axial direction.

Claim 7

A high resolution light pen system including a light pen for sensing light rays emitted from a pixel on a video screen and generating input pulses which are tested for validity by a discrimination circuit to reduce jitter, said system comprising: a collimation tube mounted within the housing and projecting outwardly from the front end thereof, said collimation tube having a cylindrical channel extending along the longitudinal axis thereof, with the inner surface of said channel being nonreflective; photodetector means fixedly mounted within said housing to the rear of said collimation tube and axially aligned with the channel thereof, said photodetector means generating input pulses in response to the reception of light rays; lens means disposed within the channel of the collimation tube adjacent the front end thereof, said lens means having a focal length equal to the distance defined between the lens means and the virtual image of the pixel on the video screen when the front end of the collimation tube is placed against the outer surface of the screen such that all rays emanating from a pixel axially aligned with the channel and passing through the lens means are refracted axially along the channel and received by the photodetector; first comparator means operatively connected to and receiving the input pulses generated by the photodetector means, said first comparator means for generating a first signal whenever the voltage of an input pulse exceeds a first threshold level; second comparator means operatively connected to and receiving the input pulses generated by the photodetector means, said second comparator means for generating a second signal when the voltage of an input pulse exceeds a second threshold level, said second threshold level being lower than said first threshold level; delay means connected to said second comparator means for delaying said second signal a fixed amount; and gate means operatively connected to said first comparator means and said delay means, said gate means generating an output pulse whenever said gate means receives the first and second signals from said delay means and said first comparator means simultaneously, to reduce the difference in time at which output pulses are generated by input pulses of different amplitudes all exceeding the first threshold, thereby also reducing jitter.

Claim 8

A high resolution light pen system including a light pen for sensing light rays emitted from a pixel on a video screen and generating input pulses which are tested for validity by a discrimination circuit to reduce jitter, said system comprising: a collimation tube mounted within the housing and projecting outwardly from the front end thereof, said collimation tube having a cylindrical channel extending along the longitudinal axis thereof, with the inner surface of said channel being nonreflective; photodetector means fixedly mounted within said housing to the rear of said collimation tube and axially aligned with the channel thereof, said photodetector means generating input pulses in response to the reception of light rays; lens means disposed within the channel of the collimation tube adjacent the front end thereof, said lens means having a focal length equal to the distance defined between the lens means and the virtual image of the pixel on the video screen when the front end of the collimation tube is placed against the outer surface of the screen such that all rays emanating from a pixel axially aligned with the channel and passing through the lens means are refracted axially along the channel and received by the photodetector; first comparator means operatively connected to and receiving the input pulses generated by the photodetector means, said first comparator means for generating a first signal whenever the voltage of an input pulse exceeds a first threshold level; second comparator means operatively connected to and receiving the input pulses generated by the photodetector means, said second comparator means for generating a second signal when the voltage of an input pulse exceeds a second threshold level, said second threshold level being lower than said first threshold level; delay means connected to said second comparator means for delaying said second signal a fixed amount; and gate means operatively connected to said first comparator means and said delay means, said gate means generating an output pulse whenever said gate means receives the first and second signals from said delay means and said first comparator means simultaneously, to reduce the difference in time at which output pulses are generated by input pulses of different amplitudes all exceeding the first threshold, thereby also reducing jitter.

Claim 9

A light pen system as recited in claim 6 further including a second lens means disposed adjacent the rear end of said channel for focusing said axially directed light rays within said channel directly onto said photodetector means.

Claim 10

A light pen system as recited in claim 7 wherein said second lens means is fixedly mounted to said photodetector means.

Claim 11

A light pen system as recited in claims 6, 7, or 8 wherein said collimation tube is slidably mounted within said housing and wherein said light pen further includes a switch means operatively connected to said photodetector, said switch means being disposed behind said collimation tube in a manner such that when the front end of said tube is pressed against the video screen it is movable rearwardly, relative to said housing, to actuate said switch means.

Claim 12

A light pen system as recited in claim 9 wherein said collimation tube includes a recess for receiving a stop pin fixedly mounted on said housing, said recess and stop pin combination for restricting the movement of said collimation tube in an axial direction.

Claim 13

A light pen system as recited in claim 6 wherein said gate means comprises a logical "and" circuit such that a positive output pulse is produced only when positive signals are simultaneously received from said first comparator means and said delay means.

Claim 14

A light pen system as recited in claims 6 or 11 further including an amplification means connected to both of said first and second comparator means, said amplification means for amplifying said input pulses prior to being supplied to both of said first and second comparator means.

Claim 15

A light pen having an end adapted to be abutted against a video screen for detecting the presence of an illuminated pixel located adjacent the abutting end of the pen, comprising: an elongated housing having opposed front and rear ends and formed with a hollow channel extending therethrough; a radiation detection device mounted in said housing adjacent the rear end of said channel; lens means mounted within said channel adjacent the front end thereof, said lens means having a focal length such that when the front end of said pen abuts against the screen, radiation from an illuminated pixel located near the axis of the channel is transmitted along the axis of the channel in a collimated beam to said detection device, while the radiation received from pixels displaced from the axis is directed by said lens towards the sides of the elongated channel and dissipated, whereby said detection device functions to detect the on-axis pixels to the exclusion of the off-axis pixels; and a second lens means disposed adjacent to the rear end of the channel for focusing the axially directed radiation directly onto said radiation detection device.

Claim 16

A light pen having an end adapted to be abutted against a video screen for detecting the presence of an illuminated pixel located adjacent the abutting end of the pen, comprising: an elongated housing having opposed front and rear ends and formed with a hollow channel extending therethrough; a radiation detection device mounted in said housing adjacent the rear end of said channel; lens means mounted within said channel adjacent the front end thereof, said lens means having a focal length such that when the front end of said pen abuts against the screen, radiation from an illuminated pixel located near the axis of the channel is transmitted along the axis of the channel in a collimated beam to said detection device, while the radiation received from pixels displaced from the axis is directed by said lens towards the sides of the elongated channel and dissipated, whereby said detection device functions to detect the on-axis pixels to the exclusion of the off-axis pixels; and a second lens means disposed adjacent to the rear end of the channel for focusing the axially directed radiation directly onto said radiation detection device.