Electro-optical ranging apparatus having scanning circuitry and servoloop processor for resolving separation of images on photoelectric detector arrays

• US 4,589,770 A
• Filed: 10/25/1982
• Issued: 05/20/1986
• Est. Priority Date: 10/25/1982
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Storey, Moorfield Jr., Jones, Philip, Jones, William R.
• Primary Examiner(s): Buczinski, S. C.
• Assistant Examiner(s): Issing, Gregory C.
• Application Number:
  US06/436,600
• Time in Patent Office: 1,303 Days
• Field of Search: 356/1, 356/4, 354/402-409
• US Class Current: 356/3.14
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves

Abstract

In an optical ranging apparatus, especially designed for measuring the range to a source of infrared radiation, a narrow band time-shift servoloop processor is used to resolve the offset (separation distance) of images of the infrared source that are projected onto first and second, juxtaposed photooptical detector arrays. The range (distance) to the infrared source is functionally related to the measured offset of the infrared images. To enable the servoloop processor to measure this offset, the outputs of the first and second detector arrays are automatically scanned by electronic scanning circuitry to develop first and second time-variable signals that represent the relative positions of the infrared images on the respective arrays. These time-variable signals are substantially overlapping, and the slight phase or time separation between these signals is related to the offset of the images on the detector arrays. The servoloop processor receives the substantially overlapping time-variable signals from the scanning circuitry and resolves the time difference therebetween as a continuously variable time shift Δt signal. The measured offset is then fed to a ranging processor to produce a signal representing the range (R) to the distant infrared source.

Claims

1. An electro-optical apparatus for measuring the range R to a distant source of light, comprising:

first and second optical/detector assemblies, each of which comprises optics having an optical axis, a field of view FOV and frame length l_f, and an array of photoelectric detector elements arranged at a center-to-center distance l_d along a predetermined scanning direction on a focal plane normal to said optical axis and upon which an image of said source is focused by said optics, said first and second assemblies being arranged with said optical axes parallel and spaced apart by a predetermined distance d along a baseline that in turn defines a perpendicular bisector, said assemblies adapted for being oriented so that said perpendicular bisector defined by said baseline points generally in the direction of a distant source of light such that images of the source are focused by said optics on said arrays at relatively different positions with respect to corresponding points on said arrays wherein such difference in the image positions is defined by an image offset Δ

x;

scanning circuitry means connected to said detector elements of said arrays of said first and second assemblies for electrically, sequentially sampling output signals at a predetermined sampling interval τ

from said array of said detector elements of said first assembly, and in unison therewith sequentially sampling output signals at said interval τ

from said array of detector elements of said second assembly so as to produce a first time/amplitude-varying signal t₁ representing the image position on said array of said first optical/detector assembly and so as to produce, in concert therewith, a second time/amplitude-varying signal t₂ representing the image position on said array of said second optical/detector assembly wherein said signals t₁ and t₂ exhibit a phase difference referred to as time-shift Δ

t that in turn represents said offset Δ

x of images on said arrays, said scanning circuitry means comprising the subcombination of;

a first channel having a first plurality of preamplifiers individually connected to said detector elements of said first optical/detector assembly, and a first plurality of signal control gates connected individually in series between said first plurality of preamplifiers and a first, signal-combining junction;

a second channel comprising a second plurality of preamplifiers connected individually to said detector elements of said second optical/detector assembly, and a second plurality of signal-controlled gates connected individually in series between said second plurality of preamplifiers and a second signal-combining junction;

gate signal sequencer means having a plurality of gate-controlling output leads connected to corresponding ones of said first and second plurality of gates such that said sequencer means actuates a set of corresponding gates from said first and second channels simultaneously and operates different gates in said first and second channels sequentially to sample the output signals through said first and second pluralities of preamplifiers and associated detector elements from both said first and second optical/detector assemblies in unison, whereby the sampled signals from said first and second assemblies appear at said first and second signal-combining junctions, respectively; and

output means for communicating said first and second signal-combining junctions to first and second outputs of said scanning circuitry at which time/amplitude-varying signals are produced representing the positions of the source image on said optical/detector assemblies, said output means comprising the subcombination of;

reversing switching means coupling said first and second signal-combining junctions to said first and second outputs and having a first switching state in which said first signal-combining junction is coupled to said first output of said scanning circuitry and said second signal-combining junction is coupled to said second output of said scanning circuitry, and having a second state in which said signal-coupling relationship is reversed; and

reversing switching control means coupled to said sequencer means for changing said reversing switching means from said first state to said second state at predetermined times so that said time/amplitude-varying signals appearing at said first and second outputs of said switching circuitry means always exhibit the same leading-trailing phase relationship;

a servoloop processor having inputs connected to receive said signals t₁ and t₂ from said scanning circuitry means and having an output at which a signal is produced representing said time shift Δ

t measured from said input signals t₁ and t₂, said servoloop processor comprising the subcombination of;

variable delay means connected to a first input of said processor for variably delaying that one of said input signals t1 and t2 that leads the other input signal;

difference-taking means for receiving the variably delayed signal from said variable delay and the trailing signal from a second input to said processor for producing an error signal corresponding to the phase difference therebetween;

differentiator means connected to said second input of said processor for differentiating the signal thereat to produce a reference signal having substantially the same phase as said error signal;

multiplier means connected to said difference-taking means and to said differentiator for multiplying said error signal with said reference signal to produce a correction signal;

integrator means connected to said multiplier means for receiving and integrating said correction signal, said integrator means having an output producing an integrated correction signal that is connected to said variable delay means for controlling the amount of delay produced thereby; and

said output of said processor connected to said output of said integrator means for providing at said processor output said time-shift signal Δ

t as said integrated correction signal; and

a range processor having an input connected to said time-shift servoloop processor for receiving said signal representing said time shift Δ

t and having means responsive thereto for producing an output signal representing range R as a function of said time-shift signal Δ

t in accordance with the relationship;

space="preserve" listing-type="equation">R=(l.sub.f τ

d/(FOV) Δ

t l.sub.d).

2. An electro-optical apparatus for measuring the range R to a distant source of light, comprising:

first and second optical/detector assemblies, each of which comprises optics having an optical axis and an array of photoelectric detector elements arranged along a predetermined scanning direction on a focal plane normal to said optical axis and upon which an image of said source is focused by said optics, said first and second assemblies being arranged with said optical axes parallel and spaced apart by a predetermined distance d along a baseline that in turn defines a perpendicular bisector, said assemblies adapted for being oriented so that said perpendicular bisector defined by said baseline points generally in the direction of a distant source of light such that images of the source are focused by said optics on said arrays at relatively different positions with respect to corresponding points on said arrays wherein such difference in the image positions is defined by an image offset Δ

x;

scanning circuitry means connected to said detector elements of said arrays of said first and second assemblies for electrically, sequentially sampling output signals from said array of said detector elements of said first assembly, and in unison therewith sequentially sampling output signals from said array of detector elements of said second assembly so as to produce a time/amplitude-varying signal t₁ on a first output lead representing the image position on said array of said first optical/detector assembly and so as to produce, in concert therewith, a time/amplitude-varying signal t₂ on a second output lead representing the image position on said array of said second optical/detector assembly wherein said signals t₁ and t₂ exhibit a phase difference referred to as time-shift Δ

t that in turn represents said offset Δ

x of images on said arrays;

said scanning circuitry means including scan reversing switch means for sequentially sampling output signals from said arrays of said first and second assemblies in one direction and then in a reverse direction of scanning, and for reversing the connection of said output leads to said servoloop processor at each reversal of said direction of scanning so as to maintain a continuous leading-trailing relationship of said signals t₁ and t₂ at said inputs to said servoloop processor;

a servoloop processor having inputs connected to receive said signals t₁ and t₂ on said first and second output leads from said scanning circuitry means and having an output at which a signal is produced representing said time shift Δ

t measured from said input signals t₁ and t₂ ; and

a range processor having an input connected to said time-shift servoloop processor for receiving said signal representing said time shift Δ

t and having means responsive thereto for producing an output signal representing range R as a function of said time-shift signal Δ

t.