`
`
`
`EXHIBIT
`
`EXHIBIT
`1002
`
`1002
`
`

`

`Dec. 2, 1969
`
`R . .M. ZOOT
`F.M. LASER CONTOUR MAPPER
`
`3,481,672
`
`Filed Jan. 3, 1967
`
`4 Sheets-Sheet 1
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`Dec. 2, 1969
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`Filed Jan. 3, 1967
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`R. M. ZOOT
`F.M. LASER CONTOUR MAPPER
`
`3,481,672
`
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`

`United States Patent Office
`
`3,481,672
`Patented Dec. 2, 1969
`
`1
`
`3,481,672
`F.M. LASER CONTOUR MAPPER
`Robert M. Zoot, Thousand Oaks, Calif., assignor to
`Hughes Aircraft Company, Culver City, Calif., a
`corporation of Delaware
`Filed Jan. 3, 1967, Ser. No. 616,996
`Int. Cl. GOlb 11100; G01c 3/08
`U.S. Cl. 356-167
`
`8 ·Claims
`
`ABSTRACT OF THE DISCLOSURE
`A non-contacting distance gauge and contour mapping
`apparatus utilizing a high intensity light source. A single
`light beam from the source is split into a plurality of
`separate beams by an appropriate transmitter reticle struc(cid:173)
`ture. The beams are then focused on the object, the dis(cid:173)
`tance to which, or contours of which, are being measured.
`At object-focal point coincidence, the beams merge to
`form a single spot. When the object surface does not
`coincide with the focal point, multiple spots are pro(cid:173)
`duced. Light reflected from the object is caused to sweep
`across a receiving reticle placed in front of an optical
`detector. The harmonic content of the optical detector
`output is indicative of the object focal plane coincidence.
`A servomechanism used in conjunction with drive mech(cid:173)
`anisms serve to keep the beams focused on the object
`no matter how its contour changes. Readout information
`is obtained from the in-out motion of the transmitter.
`
`This invention relates to electro-optic measuring meth(cid:173)
`ods and apparatus and more specifically to methods and
`apparatus for quickly and accurately determining dis(cid:173)
`tances and contours.
`In the past, countless methods and devices have been 35
`employed to measure relatively short distances. Depend(cid:173)
`ing upon the particular requirement of the job at hand,
`direct measurements have been made with rulers, calipers,
`micrometers and gauges of innumerable types. Frequently, 40
`it is advantageous or necessary to measure the distance
`between a reference point and an object without touching
`or disturbing the object. The requirement for noncontact(cid:173)
`ing measurement may arise because of the nature of the
`object or because of its position. Oftentimes, in such 45
`instances, optical techniques, including those which utilize
`precision instruments and associated hardware, have been
`employed. In general, such techniques require highly
`skilled operators to perform manual adjustments and
`set-up operations. Depending upon the application, these 50
`operations can comprise positioning aligning, leveling and
`establishing reference targets. It is obvious, therefore, that
`such measuring techniques are both complex and time(cid:173)
`consuming.
`Accordingly, it is one object of the present invention 55
`to simplify optical measuring techniques.
`It is another object of the present invention to provide
`improved noncontacting apparatus for accurately measur(cid:173)
`ing the distance between a reference point and an object.
`One application of precision measurements in modern 60
`industry is in conjunction with automatic machining and
`tooling processes. In these applications, it is frequently
`advantageous to construct a model of an article of manu(cid:173)
`facture or structure from which patterns, dies or drawings
`can be made. It is common practice in these processes to 65
`utilize a master model or template, together with auto(cid:173)
`matic machine tools, to form large quantities of similarly
`finished articles.
`In manufacturing or construction practices which utilize
`this technique the contours of the model must be trans- 70
`lated into a form by which the mass-produced articles
`may be manufactured. This process may involve time-
`
`2
`consuming hand measurements or the construction of
`templates at successive cross-sections of the object. It is
`therefore advantageous to utilize contour or profile map(cid:173)
`ping means which enable the contours of the object to be
`5 determined quickly, precisely and preferably automat(cid:173)
`ically. It is also advantageous if the contour mapper is
`capable of yielding an output in the form of digital or
`analog signals which can be utilized to program auto(cid:173)
`~atic machine tools for die forming or machining opera-
`10 tions.
`Recently, and as a consequence of advances in laser
`technology, automatic contour mapping systems have been
`proposed which offer greater accuracy than heretofore
`available. Two such systems are mentioned briefly in
`15 an article appearing in Electronics, vol. 39, No. 17, dated
`August 22, 1966, at pages 209-210. According to this
`article, both systems are based on the fundamental con(cid:173)
`cept of keeping a laser beam continuously focused on the
`model or object being measured, no matter how its con-
`20 tour changes. That is, as the optical system is moved
`laterally across the model the laser head is moved toward
`and away from the object, thereby maintaining the dis(cid:173)
`tance constant. Readout information representative of the
`in-and-out motion of the laser head thereby furnishes an
`25 accurate measure of the variation of contours of the
`model. This readout information can then be processed
`and stored on tape or cards for later utilization or can
`be fed as input information to automatic machine tools.
`It is apparent that the dimensional readout information
`30 can be scaled up or down in any desired manner by elec(cid:173)
`tronic or mechanical means.
`Although the two above-mentioned systems share a
`common principle of operation, they differ in the manner
`in which this principle is implemented. Specifically, al(cid:173)
`though both use a laser beam which is focused on the
`model, one system utilizes a triangulation method to main-
`tain the laser beam in focus. That is a continuous wave
`laser is used in one leg of a triangl~ and an optical de(cid:173)
`tector in another leg. The distance separating the laser
`and ~etector forms the third leg of the triangle. By virtue
`of this arrangement, the greatest accuracy is achieved only
`for contour changes in the direction normal to the plane
`of the triangle.
`The second system utilizes a laser beam focused on
`the object by means of a lens arrangement which is also
`used for receiving the reflected image. By virtue of the
`coaxial laser transmitter and receiver optics a much
`greater range of contours can be measured. In keeping
`with this system, the image of the beam reflected from
`the object is projected onto an optical detector. A small
`pin hole interposed in the light path between the object
`and the detector at the focal point, or point of least con(cid:173)
`fusion, is caused. to oscil~ate by means of a tuning fork,
`thereby. modulatmg the mtensity of the detected image.
`A lock-m detector coupled to both the tuning fork oscil-
`lator and the optical detector provides a measure of the
`dista~ce between th~ laser transmitter and the object.
`. It IS a further O?Ject of the present invention to pro(cid:173)
`VIde an el~ct:o-optic contour mapping system operating
`on the pnnc1ple of frequency modulation.
`In keeping with the principles of the present invention
`the above-mentioned objects are accomplished with ~
`beam of high intensity monochromatic light such as that
`provided by a continuous wave laser. The light beam is
`transmitted through a beam splitting reticle in the trans-
`mitting optical system. When the beam is focused on the
`?bject, the distance to which is to be determined, an image
`m the form of a single spot is produced. As the distance
`between the light source and object increases or decreases
`so that the image is out of focus, the image produced
`on the object separates into a plurality of spots. By
`
`

`

`3 481672
`'
`'
`3
`optical path between object 11 and detector 17 is the
`utilizing a receiving optical system which includes a ro(cid:173)
`tating nutating plate and a receiving reticle in front of
`receiving objective lens 16, reflecting members 18 and
`an optical detector, a fluctuating detector output signal is
`19, a nutating plate 20, a receiving reticle' 21 and an op-
`obtained. The harmonic content of the detector output
`tical filter 22.
`In operation, a high-intensity light beam provided by
`signal provides a measure of the amount by which the 5
`object surface· is out of focus.
`light source 10 is directed through primary lens 12. The
`light beam, indicated by the dashed arrows, diverges after
`By employing three-axis mechanical drive means for
`passing through lens 12 and is directed toward composite
`the laser transmitter-optical detector assembly, noncon(cid:173)
`lens-re'ticle structure 13. The central portion of the diverg(cid:173)
`tacting contour mapping is achieved. The harmonic com(cid:173)
`ponents of the detector output can be passed through 10
`ing light beam is intercepted by the back of reflector 18.
`a tuned high Q filter, for example, to provide an error
`The annular outer portion of the diverging light beam
`passes through transmitting objective lens 14 and is split
`signal to a servomechanism for automatic tracking. As
`the beam is scanned across the object, the in-out motion
`into four somewhat pie-shaped segments by transmitting
`reticle 15 and focused on object 11. It is noted that re-
`of the servo drive mechanism provides a direct measure
`15 fleeting member 18 is preferably of substantially e'llipti(cid:173)
`of object contour changes.
`In order that the invention may be clearly understood
`cal shape so that when it is oriented at an angle as shown
`and readily carried into effect, it .will now be described
`in FIG. 1, it presents a circular cross-section to the light
`with reference by way of example to the accompanying
`beam source 10. In this manner, receiving objective lens
`drawings, in which:
`16 is masked from the transmitted light beam. In prac(cid:173)
`FIG. 1 is a view, partially in schematic and partially 20
`tice, the back of reflecting member 18 can be absorptive
`in cross-section, of a preferred embodiment of the present
`or reflective of the light beam from source 10 so long as
`it is nontransmissive. This is important in order to insure
`invention.
`FIG. 2 is a cross-sectional view of the composite lens(cid:173)
`that the light pattern formed on object 11 is entirely due
`reticle structure utilized in the embodiment of FIG. 1.
`to the light beam passing through the transmitting objec(cid:173)
`FIG. 3 is a plan view of the receiving reticle structure 25
`tive lens 14 and is not distorted, blurred or "fogged" by
`utilized in the embodiment of FIG. 1.
`other light reaching the object which does not pass through
`FIGS. 4A, 4B, 4C and 4D are sequence views illus(cid:173)
`the transmitting reticle 15.
`trating the operation of the embodiment of FIG. 1 for an
`As mentioned above, the transmitted light is split by
`object having a surface which is coincident with the focal
`transmitting reticle 15 into four segments and focused on
`plane of the transmitting optical system.
`30 object 11. In the embodiment of FIG. 1, the region of
`FIGS. 5A, 5B, 5C and 5D are sequence views illus(cid:173)
`object 11 on which the transmitted light beam is focused
`trating the operation of the embodiment of FIG . 1 for
`coincides with the focal point of the primary lens-trans(cid:173)
`an object having a surface which is slightly displaced
`mitting objective lens combination. When object 11 is so
`situated, the transmitted light beam appears as a spot on
`from the focal plane of the transmitting optical system.
`the surface of object 11. The diameter of the spot is ex(cid:173)
`FIGS. 6A, 6B, 6C and 6D are sequence views illustrat- 35
`tremely small and is determined primarily by the quality
`ing the operation of the embodiment of FIG. 1 for an
`of the optical path including lens 12 and 14.
`object having a surface which is substantially displaced
`Reflected light from the spot imaged on object 11
`from the focal plane of the transmitting optical system.
`passes through the receiving objective lens 16 which
`FIG. 7 is a simplified pictorial view of an embodiment
`of the present invention adapted for automatic contour 40
`causes the beam to converge. The converging beam is re(cid:173)
`flected by reflecting members 18 and 19 and directed
`mapping use; and
`through nutating plate 20. In passing through nutating
`FIG. 8 is a block diagram of a portion of an electro(cid:173)
`plate 20, the converging light beam is displaced from the
`mechanical system for implementing contour mapping
`optical axis. By rotating nutating plate 20 by means of
`operation.
`a motor assembly, indicated generally by windings 23,
`Referring more specifically to the drawings, FIG. 1 45
`the converging light beam can be made to trace a cir-
`is a view, partially in schematic and partially in cross(cid:173)
`cular path. The rotating nutated light beam is then di(cid:173)
`section of a preferred embodiment of the present inven(cid:173)
`rected toward receiving reticle 21. By virtue of the ge(cid:173)
`tion. In FIG. 1 there is shown a light source 10 which
`ometric configuration of receiving reticle 21, the converg(cid:173)
`is capable of emitting a continuous beam of high-intensity,
`ing light beam is periodically interrupted so that it passes
`highly-directional, substantially monochromatic light. As 50
`through optical filter 22 to detector 17 only four times
`used herein, the term "light" is understood to include not
`per revolution of nutating plate 20. Optical filter 22 serves
`only those portions of the electromagnetic wave spectrum
`to pass only those wavelengths near the operating wave(cid:173)
`lying in the visible region but also those in the infrared
`length of light source 10, thereby reducing the "noise" to
`and ultraviolet regions. By way of example, light source
`detector 17.
`10 can comprise a laser oscillator of the continuous wave 55
`In order to more fully understand the operation of
`type.
`the embodiment of FIG. 1, reference is made to the cross(cid:173)
`An object 11, the distance to which is to be measured, is
`sectional view of FIG. 2 which is taken through the cen(cid:173)
`located away from light source 10. In the optical path
`ter of composite lens-reticle structure 13. In FIG. 2,
`between light source 10 and object 11 there is disposed
`transmitting reticle 15 is indicated as a cross which masks
`a primary lens 12 and a composite lens-reticle structure 60
`most of transmitting objective lens 14 with the exception
`13. The composite lens-reticle structure 13, in turn, com(cid:173)
`of the four substantially pie-shaped sections indicated as
`prises an annular transmitting objective lens 14, an an(cid:173)
`14a, 14b, 14c and 14d. The receiving objective lens 16
`nular transmitting reticle 15 and a receiving objective
`as indicated hereinabove is disposed coaxially within the
`lens 16, which is located within the central region of an(cid:173)
`center of the transmitting objective lens and is held in
`nular transmitting lens 14. Although transmitting reticle 65
`place by suitable mounting or bonding means well known
`15 is shown as a thin centrally located member sand(cid:173)
`in the art. Although the composite lens-reticle structure is
`wiched between two halves of the transmitting objective
`indicated as comprising two separate lenses, it is obvious
`lens, other arrangements are possible. For example, if a
`that one single lens can be used, together with an ap-
`more economical structure is desired, the reticle can
`propriate reticle which leaves a circular opening in the
`simply be painted upon one of the surfaces of the' trans- 70
`central region to form the receiving objective lens.
`mitting objective lens 14.
`FIG. 3 is an illustration of receiving reticle 21 viewed
`An optical detector 17, which is capable of generating
`from the direction of the optical axis indicated by arrows
`an electrical output signal, the magnitude of which varies
`3-3. Receiving reticle 21 comprises four opaque quad(cid:173)
`in response to the intensity of the light incident upon it,
`rants 21a, 21b, 21c and 21d which are held in place by
`is also incorporated in the embodiment of FIG. 1. In the 75
`
`

`

`3,481,672
`
`5
`a suitable mounting ring 30. Between the quadrants there
`is a transparent dielectric gap or air space in the form
`of a cross. Receiving reticle 21, therefore, has a geometric
`configuration which can be described as the inverse of
`the configuration of transmitting reticle 15. That is, the
`transparent region of the receiving reticle forms a cross,
`whereas in the transmitting reticle, the opaque region
`forms a cross.
`Continuing the description of the operation of the em(cid:173)
`bodiment of FIG. 1, reference is now made to FIGS. 4,
`S, and 6 which represent the conditions of the embodi(cid:173)
`ment of FIG. 1, wherein the illuminated region of object
`11 is coincident with the focal plane, slightly out of the
`focal plane, and substantially out of the focal plane, re(cid:173)
`spectively. Specifically, FIG. 4A is an enlarged view of
`the object 11, showing the converging transmitted light,
`indicated by arrows 40, illuminating a region of object
`11 which lies in the focal plane. The image thus produced
`is shown in the partial view of object 11 shown in FIG.
`4B. Under the condition of object-focal plane coinci(cid:173)
`dence, the image formed is a highly illuminated point of
`light 41.
`The reflected light from the illuminated point 41 is
`transmitted back through the receiving objective lens 16
`as explained hereinabove. The reflected image is there(cid:173)
`after nutated in a circular path around the axis of receiv(cid:173)
`ing reticle 21 as indicated in FIG. 4C. The speed of rota(cid:173)
`tion of the nutated reflected image is, of course, deter(cid:173)
`mined by the rotational speed of nutating plate 20. In
`each traversal of its circular path around receiving reticle
`21, the reflected image passes through the open portions
`thereof and reaches detector 17. By virtue of the ge(cid:173)
`ometric configuration of receiving reticle 21, the reflected
`light beam passes therethrough four times during each
`revolution. Thus, the detector output signal shown graph- 35
`ically in FIG. 4 consists of a series of pulses having a
`frequency equal to four times the nutating frequency.
`FIGS. SA, 5B, 5C and 5D illustrate the same sequence
`as described above but for the case in which the object
`11 is slightly behind the focal plane. As seen from FIGS. 40
`SA and 5B, the image produced on the object is larger
`and consists of four quadrants of light produced by the
`masking effect of the transmitting reticle. After the re(cid:173)
`ceived image is nutated about the receiving reticle 21
`shown in FIG. SC, it is transmitted to the detector. The 45
`detector output illustrated in FIG. 5D comprises a broad(cid:173)
`ened waveform with a slight second harmonic compo(cid:173)
`nent. The harmonic content of the detector output is in(cid:173)
`creased further as the object 11 moves further from the
`focal plane. The sequence views of FIGS. 6A, 6B, 6C and 50
`6D illustrate the condition for an object substantially out
`of the focal plane of the transmitting lens. As indicated in
`FIG. 6D, the detector output signal is substantially a total
`second harmonic signal.
`It is apparent that the detector output can be utilized 55
`to determine the condition wherein the object is in the
`focal plane of the transmitting lens. This is done by
`moving either the object or the optical structure, herein(cid:173)
`after termed the "sensing head," so as to minimize the
`harmonic content of the detector output. As will be de- 60
`scribed hereinbelow, this can be accomplished by means
`of a servomechanism in which an error signal derived
`from the hormonic content of the detector output serves
`as a control signal which adjusts the object-transmitter
`distance to the point of minimum detector harmonic con- 65
`tent. A reference point can be established for the sensing
`head-to-object distance which results in object-focal plane
`coincidence. With a reference position thus established,
`a micrometer dial or linear displacement transducer
`coupled to the drive mechanism can be utilized to indicate 70
`the distance between the reference point and object.
`In FIG. 7 there is shown a simiplified block diagram
`view illustrating a preferred use of the present invention.
`In FIG. 7, the sensing head which comprises the ele(cid:173)
`ments shown in FIG. 1 is indicated generallY by block 70. 75
`
`6
`The sensing head 70 is adapted by mechanical means
`such as a gantry for selective and controlled three-dimen(cid:173)
`sional motion. Drive mechanism indicated by blocks 71,
`72 and 73 provide the power means for moving the
`5 optical system in the x, y and z directions respectively. In
`accordance with the arbitrarily assigned nomenclature
`of FIG. 7, the x and y axes correspond to the horizontal
`and vertical directions respectively, and the z axis corre(cid:173)
`sponds to the direction perpendicular to the x-y plane
`10 toward the object 74.
`In FIG. 7, object 74 is shown as comprising a model
`of an automobile body, the contour of which is to be
`measured. It is obvious, of course, that other models
`such as buildings, airframes, or other objects or works of
`15 art of substantially limitless scope may be adapted for
`contour mapping by this method.
`For the sake of clarity, the mechanical details of the
`x-y-z drive mechanisms have eben omitted from the em(cid:173)
`bodiment of FIG. 7. Numerous suitable x-y plotters or
`20 gantries are known in the art. Mechanical x-y plotters
`can comprise, for example, a set of horizontal load-bear(cid:173)
`ing tracks which supports a framework, which in turn
`supports the drive motors, drive screws, and linear dis(cid:173)
`placement transducers. Control voltages to the drive
`25 motors can be programmed to cause the optical system
`70 to scan the x-y plane much as an electron beam scans
`the target of a cathode ray tube in a television receiver.
`In some instances, the scan can be performed in incre(cid:173)
`mental steps of a small fraction of an inch, depending
`30 upon the desired accuracy. If desired, the drive motors can
`also be programmed to scan continuously. In either event,
`the linear displacement transducers integral to each of
`the drive mechanisms provide the output which is indi-
`cative of the position of the sensing head along the x and
`y axes.
`For each x-y position at which contour or z informa(cid:173)
`tion is desired, the optical system, together with the z
`axis drive motor 73 which is coupled thereto by means
`of a servo loop, is caused to seek object-focal plane coin(cid:173)
`cidence. When this point of coincidence is reached, the z
`displacement information from a third linear displacement
`transducer coupled to the z axis drive mechanism is read.
`Since the focal length of the sensing head is known and
`remains fixed, the z distance to the object for any x-y
`position can be readily computed and recorded.
`In FIG. 8 there is shown in block diagram form a por(cid:173)
`tion of an electro-mechanical implementation of the pres(cid:173)
`ent invention. Block 80 represents the sensing head shown
`in FIG. 1. In practice, the light source, lenses, and as(cid:173)
`sociated components are structurally integrated in a
`single unit which can be moved about as shown in FIG.
`7 to track the contours of the object under measurement.
`In the present embodiment only the z drive mechanism
`is shown. As mentioned hereinbelow, the x and y drive
`mechanisms can comprise drive motors with screws or
`other mechanical means for transmitting the motion to
`the sensing head 80.
`In the present embodiment the z motion of sensing
`head 80 is imparted by a mechanically coupled hydraulic
`or pneumatic cylinder 81. A fluid or gas pressure source
`82 is coupled to cylinder 81 through an electrically con-
`trolled valve 83. Thus, by an electrical input signal to
`valve 83, the fluid or gas pressure to cylinder 81 is con(cid:173)
`trolled, thereby controlling the motion of sensing head 80.
`Tracking of the contours of the object being measured is
`accomplished by means of a servo loop by which the error
`signal from sensing head 80 is coupled to a first summing
`point 85 together with the output signal from a "dither"
`generator 86 and a stepping voltage generator 87. The sum
`of these three signals is then coupled to an electronic
`controller 88 which provides the control signal to valve
`83.
`The function of the "dither" generator 86 is to provide
`a relatively low level periodic signal which is superim(cid:173)
`posed on the error signal. This results in a very small
`
`

`

`3,481,672
`
`5
`
`7
`back and forth motion of the sensing head even for zero
`error signal position. The dithering motion thus serves to
`supply directional or phase information to the servo
`loop.
`Step generator 87, on the other hand, provides step
`voltages which serve to maintain sensing head 80 in the
`general position of desired operation. That is, it prevents
`the sensing head-to-object distance from becoming too far
`out of focus. Step generator 87, in tum, is activated by
`the sum of the signals from a step library 89 and a linear 10
`displacement transducer 84. Linear displacement trans(cid:173)
`ducer 84 is mechanically coupled to cylinder 81 and thus
`provides an output signal which is a function of the z
`axis displacement of sensing head 80. In addition to
`serving as an input signal to the step library 89, the output 15
`of transducer 84 is also coupled to data processor 91.
`The output signals from dither generator 86 and step
`generator 87 are also coupled to a data processing circuit
`91 which yields an output which is representative of the
`z direction displacement. This z+Llz signal is then cou- 20
`pled to a utilization means which, for example, can com(cid:173)
`prise storage means for recording x, y, z contour infor(cid:173)
`mation for later use. Alternatively, utilization means 92
`can comprise the input of an automatic machine tool as
`indicated hereinabove.
`In operation, the sensing head ·80 is advantageously
`aligned with the z axis of the gantry as shown in FIG. 7.
`The x and y drive mechanisms are programmed to scan
`in the respective directions, either continuously or in
`incremental steps, depending upon the contour resolution 30
`desired. The x and y positions obtained from the x and
`y linear displacement transducers as indicated in FIG. 7
`are coupled to the utilization means 92. Thus, for each
`x, y position the sensing head is caused to maintain focal
`plane coincidence with the object as explained in connec- 35
`tion with FIG. 1. The information obtained from the data
`processor 91 is simultaneously applied to utilization means
`92. In this manner a z displacement which represents the
`distance to the object from the predetermined reference
`plane is obtained for each x, y position.
`In all cases it is understood that the above-described
`embodiments are merely illustrative of but a small num(cid:173)
`ber of the many possible specific embodiments which can
`represent applications of the principles of the present
`invention. Numerous and varied other arrangements can 45
`be readily devised in accordance with these principles by
`those skilled in the art without departing from the spirit
`and scope of the invention.
`What is claimed is:
`1. A non-contacting gauge for determining the distance
`between a reference plane and an object comprising, in
`combination:
`means for generating a beam of high intensity light;
`means for splitting said beam into a plurality of sec(cid:173)
`ondary beams;
`means for concentrating said secondary beams on the
`surface of said object, the images of said secondary
`beams on said surface being substantially coincident
`when the focal point of said concentrating means
`and the surface of said object are coincident, and 60
`separate when said focal point and said surface are
`not coincident;
`means for directing the reflected light from said images
`to an optical detector;
`nutating means and reticle means disposed in the light
`path between said object and said detector, said
`nutating means serving to sweep the reflected image
`over said reticle means to produce a pulsed output
`signal from said detector, the harmonic content of
`said output signal having a null indicative of said
`focal plane-object coincidence.
`2. The gauge according to claim 1 including servo
`means mechanically coupled to said beam generating
`means and responsive to the harmonic content of said
`output signal for varying the distance between said beam
`
`8
`generating means and said object to effect said coincident
`condition.
`3. A method for determining the distance between a
`reference point and an ·object comprising the ordered
`steps of:
`generating a beam of high intensity light;
`splitting said beam into a plurality of spatially sepa(cid:173)
`rated secondary beams;
`concentrating said secondary beams on the surface of
`said object, the images of said secondary beams on
`said surface being substantially coincident when said
`surface is in focus, and separate when said surface
`is out of focus;
`nutating the reflected light beams from said images
`over a receiving reticle;
`directing the nutated light beams passing through said
`reticle to an optical detector, the output of said opti(cid:173)
`cal detector having a pulsed waveform;
`measuring the harmonic content of said detector out(cid:173)
`put, said harmonic content having a null at said in
`focus condition;
`varying the distance between said light generating
`means and said object to produce said null; and
`observing the distance required to achieve said null.
`4. A non-contacting electro-optic distance gauge com(cid:173)
`prising:
`a source of high intensity light;
`means including 'a beam splitter for generating a plu(cid:173)
`rality of beams and for focusing said beams on a
`surface of an object;
`said beam splitter including a first reticle and being
`interposed between said source and said object in a
`light path;
`'an optical receiver including a second reticle and light
`responsive means interposed in the path of the beams
`reflected from the object;
`a nutating plate intermediate the object and said re(cid:173)
`ceiver for sweeping the beams reflected from said
`object surface over said second reticle and said light
`responsive means;
`said light responsive means providing an output signal
`indicative of the point at which the focal plane of
`said focusing means and the surface of said object
`coincide and to indicate the distance between said
`source of high intensity light and said object surface.
`5. The gauge according to claim 4 wherein said light
`source is a continuous wave laser.
`6. A non-contacting distance gauge for determining the
`distance between a reference point and the surface of an
`50 object comprising, in combination:
`means for producing a plur