Rangefinding system
First Claim
1. A system for measuring the duration of a first pulse sequence, said first pulse sequence including a first pulse and n subsequent pulses, comprising:
- A. delay means for delaying said first pulse sequence to provide a second pulse sequence corresponding to said first pulse sequence but delayed by a predetermined period,B. first counting means responsive to said first pulse sequence to count the pulses of said first pulse sequence,C. second counting means responsive to said second pulse sequence to count the pulses of said second pulse sequence,D. first detection means to detect the occurrence of the first pulse in said second pulse sequence,E. second detection means and associated gate means, said second detection means being responsive to said first and second counting means to provide an enabling signal when said second counting means has counted the first n--1 of said subsequent pulses of said second pulse sequence, and said gate means being responsive to said enabling signal and said second pulse sequence to pass only the last pulse of said second pulse sequence, andF. interval timing means responsive to said first detection means to begin timing the duration of said second pulse sequence in response to said detected occurrence of said first pulse in said second pulse sequence, and responsive to said last pulse passed by said gate means to terminate timing, the duration of said second pulse sequence being representative of the duration of said first pulse sequence.
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Accused Products
Abstract
A system for determining the range between a reference point and a target by transmitting a pulse toward the target and measuring the time until receipt of a pulse reflected by the target. In an airborne laser altimeter configuration, the reference point may be located on an aircraft and a pulsed laser is directed along a vertical path to the ground. The system measures the duration of a pulse sequence including a first (or start) pulse, representing a pulse transmitted from the reference point, and the last of one or more associated subsequent return pulses, where the return pulses represent reflections of the transmitted pulse from both the ground and interfering objects located between the reference point and the ground. The system generates a replica of the start pulse and subsequent pulses, with the replica being delayed by a predetermined period from the start pulse and associated subsequent return pulses. The undelayed pulse sequence is processed to determine the number of return pulses in that sequence, and this detected number of pulses is utilized to enable a gate which passes only the last return pulse in the delayed pulse sequence. A time interval measurement is performed by a single precision time interval counter which is initiated by the start pulse of the delayed pulse sequence and is disabled by the gated last, or stop, pulse of the delayed pulse sequence.
17 Citations
15 Claims
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1. A system for measuring the duration of a first pulse sequence, said first pulse sequence including a first pulse and n subsequent pulses, comprising:
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A. delay means for delaying said first pulse sequence to provide a second pulse sequence corresponding to said first pulse sequence but delayed by a predetermined period, B. first counting means responsive to said first pulse sequence to count the pulses of said first pulse sequence, C. second counting means responsive to said second pulse sequence to count the pulses of said second pulse sequence, D. first detection means to detect the occurrence of the first pulse in said second pulse sequence, E. second detection means and associated gate means, said second detection means being responsive to said first and second counting means to provide an enabling signal when said second counting means has counted the first n--1 of said subsequent pulses of said second pulse sequence, and said gate means being responsive to said enabling signal and said second pulse sequence to pass only the last pulse of said second pulse sequence, and F. interval timing means responsive to said first detection means to begin timing the duration of said second pulse sequence in response to said detected occurrence of said first pulse in said second pulse sequence, and responsive to said last pulse passed by said gate means to terminate timing, the duration of said second pulse sequence being representative of the duration of said first pulse sequence. - View Dependent Claims (2, 3)
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4. A system for measuring the duration of a first pulse sequence, said first pulse sequence including a first pulse and n subsequent pulses, comprising:
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A. gating means for generating a gated pulse sequence including a gated first pulse and gated subsequent pulses respectively corresponding to said first pulse and ones of said n subsequent pulses occurring within a first time interval, said first time interval having a predetermined length L1 and including the last of said subsequent pulses, B. delay means responsive to said gating means, said delay means for generating a delayed pulse sequence including a delayed first pulse and delayed subsequent pulses respectively corresponding to said gated first pulse and said gated subsequent pulses but delayed by a delay period Δ
equal to or greater than the length L1 of said first time interval,C. first counter means operative during said first time interval to count said gated subsequent pulses, D. second counter means operative during a second time interval having a length L2 equal to or greater than the length L1 of said first time interval and including points in time displayed by Δ
from the beginning and end of said first time interval, said second counter means including means to count said delayed subsequent pulses,E. first detection means responsive to said delay means to detect the occurrence of said delayed first pulse and to generate a start control signal representative thereof, F. second detection means and associated gating means responsive to said first and second counter means to provide an enabling signal when said second counter means has counted the first n-1 of said delayed subsequent pulses, and said associated gating means being responsive to said enabling signal and said delay means to detect the occurrence of the last of said delayed subsequent pulses and to generate a stop control signal representative thereof, G. interval timing means responsive to said start control signal to begin timing the duration of said second pulse sequence and to said stop control signal to terminate timing the duration of said second pulse sequence, the duration of said second pulse sequence being representative of the duration of said first pulse sequence. - View Dependent Claims (5, 6, 7, 8, 9)
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10. Laser rangefinding system comprising:
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means to transmit at least one laser pulse from a reference point to a target, means to detect at said reference point a first pulse sequence including a first pulse, said first pulse corresponding to said laser pulse, and further including n subsequent pulses, said subsequent pulses being reflections of said laser pulse, and means for measuring the duration of said first pulse sequence comprising; A. gating means for generating a gated pulse sequence including a gated first pulse and gated subsequent pulses respectively corresponding to said first pulse and ones of said n subsequent pulses occurring within a first time interval, said first time interval having a predetermined length L1 and including the last of said subsequent pulses, B. delay means responsive to said gating means, said delay means for generating a delayed pulse sequence including a delayed first pulse and delayed subsequent pulses respectively corresponding to said gated first pulse and said gated subsequent pulses but delayed by a delay period Δ
equal to or greater than the length L1 of said first time interval,C. first counter means operative during said first time interval to count said gated subsequent pulses, D. second counter means operative during a second time interval having a length L2 equal to or greater than the length L1 of said first time interval and including points in time displaced by Δ
from the beginning and end of said first time interval, said second counter means including means to count said delayed subsequent pulses,E. first detection means responsive to said delay means to detect the occurrence of said delayed first pulse and to generate a start control signal representative thereof, F. second detection means and associated gating means responsive to said first and second counter means to provide an enabling signal when said second counter means has counted the first n-1 of said delayed subsequent pulses, and said associated gating means being responsive to said enabling signal and said delay means to detect the occurrence of the last of said delayed subsequent pulses and to generate a stop control signal representative thereof, G. interval timing means responsive to said start control signal to begin timing the duration of said second pulse sequence and to said stop control signal to terminate timing the duration of said second pulse sequence, the duration of said second pulse sequence being representative of the duration of said first pulse sequence. - View Dependent Claims (11, 12, 13, 14, 15)
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Specification