166
`
`Sensors for Mobile Robots
`
`Lewis, RA, Johnson, A.R., "A Scanning Laser Rangefinder for a Robotic
`Vehicle.” 5th International Joint Conference on Artificial Intelligence, pp.
`762-768, 1977.
`Massa, “E-201B & E-220B Ultrasonic Ranging Module Subsystems Product
`Selection Guide." Product Literature 891201710M. Massa Products
`Corporation. Hingham, MA. undated.
`Moravec. H. P.. Eifes, A., “High Resolution Maps from Wide Angle Sonar,"
`IEEE lntemational Conference on Robotics and Automation, St. Louis, MO,
`pp. 116-121, March. 1985.
`NASA. “Fast. Accurate Rangefinder, NASA Tech Briefi NFC-13460, Winter,
`1977.
`
`National, “LM1812 Ultrasonic Transceiver.” Special Purpose Linear Devices
`Datebook. National Semiconductor Corp.. Santa Clara, CA, Section 5. pp.
`l03-110. I989.
`National, “Electrostatic Transducers Provide Wide Range Ultrasonic
`Measurement." Linear Applications Handbook, National Semiconductor
`Corp, Santa Clara, CA, pp. “72-1173, 1991.
`Olson, R.A., Gustavson, R1... Wangler. R.J., McConnell. RE... “Active Infrared
`Overhead Vehicle Sensor.” [BEE Transactions on Vehicular Technology.
`Vol. 43, No. 1, pp. 79-85, February, 1994.
`Pin. F. (3.. Watanabe. Y., “Using Fuzzy Behaviors for the Outdoor Navigation of
`a Car with Low-Resolution Sensors," IEEE Lntemational Conference on
`Robotics and Automation, Atlanta, GA, pp. 548-553. 1993.
`Pletta. .I.B.. Amai, W.A.. Klarer. R, Frank, D.. Carlson, J.. Byrne, R.. “The
`Remote Security Station (RSS) Final Report," Sandia Report SAND92-l947
`for DOE under Contract DE—AC04—76DPOO789. Sandia National
`Laboratories, Albuquerque, NM, October, 1992.
`Polaroid, “Polaroid Ultrasonic Ranging System User‘s Manual." Publication No.
`P1834B. Polaroid Corporation, Cambridge, MA, December, 1981.
`Polaroid, “Technical Specifications for Polaroid Electrostatic Transducer,“ 7000-
`Series Product Specification ITP—64. Polaroid Corporation, Cambridge, MA.
`June, 1987.
`Polaroid, "6500-Series Sonar Ranging Module," Product Specifications PID
`615077, Polaroid Corporation, Cambridge. MA, ll October. l990.
`Polaroid. “Polaroid Ultrasonic Ranging Developer’s Kit." Publication No.
`PXW6431 6/93. Polaroid Corporation, Cambridge. MA, June. 1993.
`RIEGL, “Laser Distance, Level, and Speed Sensor LD90-3." Product Data Sheet
`3194, RlEGL Laser Measurement Systems, RIEGL USA, Orlando, FL. Match.
`1994.
`
`SEO, "LRF-X Laser Rangefinder Series.", Product Literature, Schwartz Electro-
`Optics. Inc.. Orlando. FL. October, l99la.
`SEO, “Scanning Laser Rangefinder,". Product Literature, Schwartz Electro-
`Optics, Inc., Orlando. FL. October. l991b.
`
`
`SilverStar Exhibit 1016 - 181
`SilverStar Exhibit 1016 - 181
`
`

`

`Chapter 5 Time of Flight
`
`16'!
`
`SEO, "Helicopter Optical Proximity Sensor System". Product Literature,
`Schwartz Electro—Oplics, 1110.. Orlando, FL, October, 19919.
`SEO, Process Report for US Army Contract DAAJ02-9l-C-0026, Schwartz
`Electro—Optics, Inc.. Orlando, FL, December. l991d.
`Siuru, B., “The Smart Vehicles Are Here," Popular Electronics, Vol.
`pp. 41—45, January. 1994.
`Vuylsteke, R, Price, C.B., Oosterlinck, A., “Image Sensors for Real-Time 3D
`Acquisition, Part I,“ ," in Traditional and Non-Traditional Robotic Sensors,
`T.C. Henderson, ed., NATO ASI Series, Vol. F63, Springer—Verlag, pp. 187-
`210, 1990.
`
`1 1, No. 1,
`
`SilverStariE;hibit 1016 - 182—
`SilverStar Exhibit 1016 - 182
`
`

`

`SilverStar Exhibit 1016 - 183
`SilverStar Exhibit 1016 - 183
`
`

`

`6 P
`
`hase-Shift Measurement and
`
`Frequency Modulation
`
`6.1 Phase-Shift Measurement
`
`The phase-she)? measurement (or phase—detection) ranging technique involves
`continuous-wave (CW) transmission as opposed to the short-duration pulsed
`outputs used in the time-of-flight systems discussed in Chapter 5.
`(The
`transmission of short pulses may also be used if synchronized to a continuous-
`wave reference against which the phase of the returning signal is measured.) One
`advantage of continuous—wave systems over pulsed methods is the ability to
`measure the direction and velocity of a moving target, in addition to its range.
`In
`1842, an Austrian by the name of Johann Doppler published a paper describing
`what has since become known as the Doppler effect:
`the frequency of an energy
`wave reflected from an object in motion is a function of the relative velocity
`between the object and the observer. This subject will be discussed in more detail
`in Chapter 8.
`In practice, a beam of amplitude—modulated laser, RF, or acoustical energy is
`directed towards the target as illustrated in Figure 6-1. A small portion of this
`wave [potentially up to six orders of magnitude less in amplitude) is reflected by
`the object
`surface back to the detector
`(Chen. et al,
`1993).
`Improved
`measurement accuracy and increased range can he achieved when cooperative
`targets are attached to the objects of interest to increase the power density of the
`reflected signal. The returned energy is compared to 3 simultaneously generated
`reference that has been split off from the original signal, and the relative phase
`shift between the two is measured to ascertain the round—trip distance the wave
`has traveled. As with time‘ofrflight rangefinders, the paths of the source and the
`reflected beam are essentially coaxial. preventing the missing parts problem.
`For high-frequency RF— or laser»based systems. detection is usually preceded
`by heterodyning the reference and received signals with an intermediate frequency
`(the relative phase shift is preserved} to allow the phase detector to operate at a
`
`
`SilverStar Exhibit 1016 - 184
`SilverStar Exhibit 1016 - 184
`
`

`

`170
`
`Sensors for Mobile Robots
`
`more convenient lower frequency (Vuylsteke. 1990). The phase shift expressed as
`a function of distance to the reflecting target surface is (Woodbury, et 31.. 1993):
`
`where:
`
`q: 2 phase shift
`(1 = distance to target
`A = modulation wavelength.
`
`
`n-"i'
`
`1L“:
`_ it
`
`n=5
`
`n=5
`
`/..\/\/\/
`
` . \j/\/V\/
`
`
`
`Tarqel
`Suafoce
`
`Figure 6-1. Relationship between outgoing and reflected wavefom‘ts. where x is the distance
`corresponding to the differential phase it (adapted from Woodbury, et al.. 1993).
`
`The desired distance to target d as a function of the measured phase shift d: is
`therefore given by:
`
`where:
`
`c : speed of light.
`f: modulation frequency.
`
`The phase shift between outgoing and reflected sine waves can be measured by
`multiplying the two signals together in an electronic mixer. then averaging the
`product over many modulation cycles (Woodbury. et 8].. 1993). This integrating
`process can be relatively time consuming, making it difficult to achieve extremely
`rapid update rates. The result can be expressed mathematically as follows
`(Woodbury, et al., I993}:
`
`
`
`SilverStar Exhibit 1016 - 185
`SilverStar Exhibit 1016 - 185
`
`

`

`Chapter 6 Phase-Shift Measurement and Frequency Modulation
`
`IT]
`
`T
`
`.
`
`1.
`
`lim i Isin [zit +fl] sin [a] d:
`
`K
`
`it
`
`it
`
`T I]
`T —> m
`
`which reduces to:
`
`where:
`
`t: time
`
`4M
`
`Acos —l t l
`
`T = averaging interval
`A = amplitude factor from gain of integrating amplifier.
`
`the quantity actually
`it can be seen that
`From the earlier expression for til,
`measured is in fact the casing of the phase shift and not the phase shift itself
`(Woodbury. et 31., 1993). This situation introduces a socalled ambiguity interval
`for scenarios where the round-hip distance exceeds the modulation wavelength A.
`(i.e.. the phase measurement becomes ambiguous once (it exceeds 360 degrees).
`Conrad and Sampson (1990) define this ambiguity interval as the maximum range
`that allows the phase difference to go through one complete cycle of 360 degrees:
`
`where:
`
`Ru = ambiguity range interval.
`
`Referring again to Figure 6-[‘ it can be seen that the total round—trip distance
`2:! is equal
`to some integer number of wavelengths n}. plus the fractional
`wavelength distance x associated with the phase shift.
`Since the cosine
`relationship is not single-valued for all of ti), there will be more than one distance
`of corresponding to any given phase—shift measurement (Woodbury, et al.. 1993):
`
`eos¢ = cos [%J = cos [EFT—m]
`
`where:
`
`d = (x + 1270/2 = true distance to target
`x = distance corresponding to differential phase 4)
`n = number of complete modulation cycles.
`
`Careful re-examination of Figure 6-1. in fact. shows that the cosine function is
`not single—vaiued even within a solitary wavelength interval of 360 degrees.
`
`
`SilverStar Exhibit 1016 - 186
`SilverStar Exhibit 1016 - 186
`
`

`

`WE
`
`Sensors for Mobile Robots
`
`the ambiguity
`Accordingly, if only the cosine of the phase angle is measured,
`interval must he further reduced to half the modulation wavelength, or 180
`degrees (Scott, 1990).
`In addition. the slope of the curve is such that the rate of
`change of the non—linear cosine function is not constant over the range of 0 S 4; S
`180 degrees, and is in fact zero at either extreme. The achievable accuracy of the
`phase-shift measurement technique thus varies as a function of target distance,
`from best-case performance for a phase angle of 90 degrees to worst case at O and
`ISO degrees. For this reason. the useable measurement range is typically even
`further limited to 90 percent of the ISO-degree ambiguity interval (Chen, et 31.,
`1993).
`A common solution to this problem involves taking a second measurement of
`the same scene but with a 90-degree phase shift introduced into the reference
`waveform.
`the net effect being the sine of the phase angle is then measured
`instead of the cosine. This additional information (i.e., both sine and cosine
`measurements) can be used to expand the phase angle ambiguity interval to the
`full 360 degree limit previously discussed (Scott,
`|990). Furthermore, an overall
`improvement in system accuracy is achieved. as for every region where the cosine
`measurement
`is
`insensitive
`(i.e.,
`zero
`slope).
`the
`complementary
`sine
`measurement will be at peak sensitivity (Woodbury, et al., 1993).
`Nevertheless, the unavoidable potential for erroneous information as a result of
`the ambiguity interval
`is a detracting factor in the case of phase-detection
`schemes. Some applications simply avoid such problems by arranging the optical
`path in such a fashion as to ensure the maximum possible range is always less
`than the ambiguity interval (Figure 6-2). Alternatively, successive measurements
`of the same target using two different modulation frequencies can be performed,
`resulting in two equations with two unknowns. allowing both .3; and n (in the
`previous equation) to be uniquely determined. Kerr (1938) describes such an
`implementation using modulation frequencies of 6 and 32 MHz.
`
`
`
`
`
`Security
`
`\.
`
`a huge
`
`—%®
`
`Figure 6-2. By limiting the maximum distance measured to be less than the range ambiguity
`interval R", erroneous distance measurements can be avoided.
`
`the relatively low frequencies typical of
`For square—wave modulation at
`ultrasonic systems (201200 KHz), the phase difference between incoming and
`outgoing waveforms can be measured with the simple linear circuit shown in
`Figure 6—3 (Figueroa & Barbieri, 1991a). The output of the exclusive-0r gate goes
`high whenever its inputs are at opposite logic levels, generating a voltage across
`capacitor C:
`that is proportional to the phase shift. For example, when the two
`
`SilverStar Exhibit 1016 - 187
`Silvers—tar Exhibit 1016 - 187
`
`

`

`Chapter 6 Phase-Shin Measurement and Frequency Modulation
`
`173
`
`the gate output stays low and V is zero;
`signals are in phase 0.3.. q: = 0),
`maximum output voltage occurs when 4: reaches 130 degrees. While easy to
`implement. this simplistic approach is limited to very low frequencies and may
`require frequent calibration to compensate for drifts and offsets due to component
`aging or changes in ambient conditions (Figueroa & Lamancusa. 1992).
`
`
`‘I H
`Reletence
`
`R
`
`
`_Tm_fib VV :c.“
`
`
`.
`—=l s—
`Phase Difference
`
`
`
`XOR Cele
`
`_:
`
`low frequencies typical of ultrasonic systems. a simple phase-detection circuit
`Figure 6-3. At
`based on an ext‘fust've-or gate will generate an ana]og output voltage proportional to the phase
`difference seen by the inputs (adapted from Figueroa 3t Barbieri. l99la).
`
`report an interesting method for
`(1991a; 1'991b)
`Figueroa and Barbieri
`extending the ambiguity interval in ultrasonic phase-detection systems through
`frequency division of the received and reference signals.
`Since the span of
`meaningful comparison is limited (best case) to one wavelength, A, it stands to
`reason that decreasing the frequency of the phase detector inputs by some
`common factor will increase it by a similar amount. The concept is illustrated in
`Figure 64 below. Due to the very short wavelength of ultrasonic energy lie.
`about 0.25 inches for the Polaroid system at 49.! KHz). the total effective range is
`still only 4 inches after dividing the detector inputs by a factor of 16. Due to this
`inherent range limitation, ultrasonic phase-detection ranging systems are not
`extensively applied in mobile robotic applications, although Figueroa and
`Lamancusa ([992) describe a hybrid approach used to improve the accuracy of
`TOF ranging for three-dimensional position location (see Chapter 15).
`Transmitted
`TTL Sinr
`
`Trrir-smillrr
`
`"
`l
`
`{
`l
`
`l
`
`-
`l U
`
`Function
`Genewlcr
`
`
`
`lililllil
`
`Receiver
`
`Received
`ill.
`trove
`
`’
`
`J
`
`l
`
`Frequency
`Vulls
`Divider
`— mm 5 I 3 Phase
`
`
`Phase
`11
`211
`Detection
`
`
`7_|
`l WEEK-m “an?
`
`
`Figure 11-4. Dividing the input frequencies to the phase comparator by some common integer
`value will extend the ambiguity interval by the same factor, at the expense of resolution (adapted
`from Figueroa St Barbieri. 19913.}.
`
`
`
`laser-based continuousrwave ranging originated out of work performed at the
`Stanford Research Institute in the 19705 (Nitaan, e1 31., 1977'). Range accuracies
`
`
`SilverStar Exhibit 1016 - 188
`SilverStar Exhibit 1016 - 188
`
`

`

`|T4
`
`Sensors for Mobile Robots
`
`approach those achievable by pulsed laser TOF methods. Only a slight advantage
`is gained over pulsed TOF rangeflnding, however. since the time-measurement
`problem is replaced by the need for fairly sophisticated phase-measurement
`electronics (Depkovich & Wolfe, 1984).
`In addition. problems with the phase
`shift measurement approach are routinely encountered in situations where the
`outgoing energy is simultaneously reflected from two target surfaces at different
`distances from the sensor. as for example When scanning past a prominent vertical
`edge (Hebert & Krotkov, 1991). The system electronics are set up to compare the
`phase of a single incoming wave with that of the reference signal and are not able
`to cope with two superimposed reflected waveforms. Adams (1993) describes a
`technique for recognizing the occurrence of this situation in order to discount the
`resulting erroneous data.
`
`6.1.1 ERIM 3-D Vision Systems
`
`The Adaptive Suspension Vehicle {AS‘V} developed at Ohio State University
`(Patterson. et al., 1984) and the Autonomous [and Vehicle (ALVJ developed by
`Martin Marietta Denver Aerospace were the premier mobile robot projects
`sponsored by the Defense Advanced Research Projects Agency (DARPA) in the
`[9805 under the Strategic Computing Program.
`In support of these efforts, the
`Environmental Research Institute of Michigan (ERIM) was tasked to develop an
`advanced three-dimensional vision system to meet the close—in navigation and
`collision avoidance needs of a mobile platform. The initial design, known as the
`Adaptive Suspension Vehicle Sensor (Figure 66). operates on the principle of
`optical radar and determines range to a point through phasevshift measurement
`using 3. CW laser source (Beyer. et 111.. 1987).
`The ranging sequence begins with the transmission of an amplitude—modulated
`laser beam that illuminates an object and is partially reflected back to the detector,
`generating a representative signal that is amplified and filtered to extract the 16-
`MHz modulation frequency. The amplitude of the signal is picked off at this
`point to produce a reflectance video image for viewing or for two-dimensional
`image processing. A reference signal is output by the modutation oscillator; both
`the detector and reference signals are then sent to the comparator electronics. The
`resulting phase difference is determined by a time—measurement technique, where
`the leading edge of the reference signal
`initiates a counting sequence that
`is
`terminated when the ieading edge of the returned signal enters the counter. The
`resulting count value is a function of the phase difference between the two signals
`and is converted to an 8—bit digital word representing the range to the scene.
`Three-dimensional images are produced by the ASV sensor through the use of
`scanning optics. The mechanism consists of a nodding mirror and a rotating
`polygonal mirror with four reflective surfaces as shown in Figure 6-6. The
`polygonal mirror parts the transmitted laser beam in azimuth across the ground.
`creating a scan line at a set distance in the front of the vehicle. The scan line is
`
`
`SilverStar Exhibit 1016 - 189
`SilverStar Exhibit 1016 - 189
`
`

`

`Chapter ti Phase-Shift Measurement and Frequency Modulation
`
`ITS
`
`deflected by the objects and surfaces in the observed region and forms a contour
`of the scene across the sensors horizontal field of View. The third dimension is
`
`added by the nodding mirror which tilts the beam in discrete elevation increments.
`A complete image is created by scanning the laser in a left-to-right and bottom-to-
`top raster pattern.
`
`
`
`Figure 6-5. The Adaptive Suspension Vehicle Sensor [courtesy Environmental Research Institute
`of Michigan).
`
`The returning signals share the same path through the nodding mirror and
`rotating polygon (actually slightly offset) but are split through a separate glass
`optical chain to the detector. The scan rate of IBO lines per second is a function of
`the field of view and desired frame rate. determined by the vehicle's maximum
`forward veiocity (IOI feet/second in this case). The size, weight, and required
`velocities of the mirrors precluded the use of galvanometers in the system design;
`the rotating and nodding minors therefore are servo driven.
`An SZO—nanometer gallium arsenide (GaAs) laser diode with coliimating and
`expansion optics is used to produce a 6-inch diameter laser footprint at 30 feet.
`The detector is a silicon avalanche photodiode. optically filtered to match the laser
`wavelength. The laser source. detector. scanning optics, and drive motors are
`housed in a single enclosure situated at a height of 8 feet. looking down upon the
`field of view. The scanning laser beam strikes the ground between 2 and 30 feet
`in front of the vehicie. with a 22—foot wide horizontal scan line at the maximum
`distance of 30 feet. {The major factor limiting the useful range of the system is
`the measurement ambiguity that occurs when the phase difference between the
`reference and returned energy exceeds 360 degrees.) The 2—Hz system update rate
`creates a new image of the scene for every 5 feet of forward motion at
`the
`vehicle's maximum speed of 10 feeUsecond.
`
`SilverStar Exhibit 1016 - 190
`SilveirStar Exhibit 1016 T190
`
`

`

`176
`
`Sensors for Mobile Robots
`
`Needing Mirror
`
`. Beam
`
` Output
`
`Raceiver
`
`Transmitter
`
`Figure 6-6. Scanning and nodding mirror arrangement in the ERIM laser rangefinder for the
`Adaptive Suspension Whit-i: (courtesy Environmental Research Institute of Michigan).
`
`Following the design and fabrication of the ASV sensor, ERl'M undertook the
`task of developing a similar device known as the ALV sensor for DARPA'S
`autonomous land vehicle. The two instruments were essentially the same in
`configuration and function but with modified performance specifications to meet
`the needs of the individual mobile platforms (Table 6-[).
`
`the Adapn’ve Suspension Vekide and
`for
`Selected specifications
`Table 6-1.
`Autonomous Land Vehici'e scanning laser rangefindcrs.
`
`Parameter
`
`ASV
`
`ALV
`
`Horizontal FOV
`Vertical FOV
`Beamwidth
`Frame rate
`
`Scan lines per frame
`Pixels per scan line
`Maximum range
`Vertical scan
`Wavelength
`Power
`
`80
`60
`l
`2
`
`128
`128
`32
`[0
`820
`24
`450
`
`80
`30
`0.5
`2
`
`64
`256
`64
`20
`820
`24
`450
`
`Units
`
`degrees
`degrees
`degrees
`Hz
`
`feet
`degrees
`nanometers
`volts
`watts
`
`Size
`Weight
`
`14 by 26 by 22
`85
`
`14 by 29 by 22
`85
`
`inches
`Rounds
`
`An advanced ranging device known as the Muttispectru! ALV Sensor was later
`developed for exterior applications addressing rugged cross—country traversal as
`opposed to the relatively uniform road surfaces seen in the initial tests of the
`autonomous land vehicle concept. The variations in terrain, surface cover, and
`vegetation encountered
`in off-road scenarios require an effective means to
`distinguish between earth. rocks. grass, trees. water. and other natural features.
`
`
`SilverStar Exhibit 1016 - 191
`SilverStar Exhibit 1016 - 191
`
`

`

`Chapter 6 PhasevShift Measurement and Frequency Modulation
`
`1??
`
`The scanner mechanism for the multispectral sensor was essentially identical to
`the scanners developed for the earlier AS V and ALV sensors. the only significant
`difference being the substitution of a hexagonal rotating mirror instead of a square
`mirror
`for panning the beam in azimuth.
`This configuration caused the
`transmitted and returned signals to impinge on separate mirrored surfaces,
`resulting in reduced crosstalk and simplified sensor alignment (Figure 6—7). The
`nodding mirror for tilting the beam in elevation remained largely unchanged.
`
`tfi 9
`F—--"—'—"'l
`lrunsmrllzr Brunt
`E’P‘W’"
`
`‘
`
`a
`
`.
`
`< \h
`.' .'
`
`'
`
`
`
`
`
`
`
`Mirror
`
`Elevnlrnn
`Mirror
`
`S
`
`lam
`menu
`
`Figure 6-7. Hexagonal rotating minor used in the multispectral scanner reduces crosstalk and
`simplifies mirror alignment (courtesy Environmental Research Institute of Michigan).
`
`The mass of the scanning mechanism plus the plurality of lasers. optics. and
`detectors made the multispectral sensor large (12 by 3 by 2 feet) and heavy (600
`pounds). increasing the complexity of the control and analysis required to produce
`results. The multiple frequency sources. corresponding detectors. detector cooling
`system, and scanner resulted in significant power consumption: 15 kilowatts!
`
`6.1.2 Perceptron [ASAR
`
`Perceptron Corporation. Pennington Hills, MI. has developed and is currently in
`production of IASAR. the AM—modulated 3-9 laser scanner shown in Figure 6-8.
`Intended for industrial machine vision applications. versions of this device have
`already been used in navigational guidance, bin-picking. hazardous inspection.
`and mining scenarios. The sensor employs a nodding mirror in conjunction with a
`rotating—polygon assembly to achieve a 4S-degree symmetrical field of view. At
`ful|~frame (1024 x 1024) resolution. a single update takes 6.4 seconds. with
`increased frame rates possible at lower resolutions. The maximum operating
`range of the LASAR system is around 40 meters. with an advertised single—frame
`range accuracy of i2 millimeters at a distance of 2 meters. Frame rates up to 10
`Hz and operating ranges in excess of 100 meters have been demonstrated in
`specially configured versions of the device.
`
`
`
`SilverStar Exhibit 1016 - 192
`SilverStar Exhibit 1016 - 192
`
`

`

`li'B
`
`Sensors for Mobile Robots
`
`
`
`Figure 6-8. The MSAR 37D scanner achieves a range-measurement accuracyr of 2 millimeters
`over a 45— by 45-degree field of View at a stand—off distance of 2 meters (caurtesy Perception
`Com).
`
`6.1.3 Odetics Scanning Laser Imaging System
`
`Odetics, Inc., Anaheim, CA. developed an adaptive and versatile scanning laser
`rangefinder in the early [9803 for use on ODEX i, the six-legged walking robot
`shown in Figure 6-9 (Binger & Harris. 1987', Byrd & Dth-ies. 1990). The system
`determines distance by phase-shift measurement. constructing three-dimensional
`range pictures by panning and tilting the sensor across the field of View. The
`phase-shift measurement technique was selected over acoustic-ranging. stereo-
`vision. and structured-light alternatives because of the inherent accuracy and fast
`update rate.
`The imaging system is broken down into the two major subelernents depicted
`in Figure 6—10:
`the scan unit and the electronics unit. The scan unit houses the
`laser source, the photodetector, and the scanning mechanism. The laser source is
`a GaAlAs laser diode emitting at a wavelength of 820 nanometers. with power
`output adjustable under software control between 1 to 50 milliwatts. Detection of
`the returned energy is achieved through use of an avalanche photodiode whose
`output is routed to the phase—measuring electronics.
`The second subelement. the electronics unit. contains the range calculating and
`video processor as well as a programmable frame buffer interface. The range and
`video processor is responsible for controlling the laser transmission. activation of
`the scanning mechanism. detection of the returning energy. and determination of
`range values. Distance is calculated through a proprietary phase-detection
`
`
`
`SilverStar Exhibit 1016 - 193
`SilverStar Exhibit 1o1é-193i
`
`

`

`Chapter 6 Phase-Shift Measurement and Frequency Modulation
`
`179
`
`scheme, reported to be fast, fully digital. and self-calibrating with a high signal—to-
`noise ratio. The minimum observable range is [.5 feet, while the maximum range
`without ambiguity due to phase shifts greater than 360 degrees is 30.74 feet.
`
`
`
`Figure 6-9 The Scanning Later imaging System was initialiy deveioped for use on the Ode:
`Series of sixrlegged walking robots (courtesy Odetics. 1:10.).
`
`The scanning hardware consists of a rotating polygonal mirror that pans the
`laser beam across the scene and a planar mirror whose back-and—forth nodding
`motion tilts the beam for a realizable field of View of 60 degrees in azimuth and
`60 degrees in elevation. The scanning sequence follows a raster—scan pattern and
`can illuminate and detect an array of 128 by 128 pixels at a frame rate of 1.2 Hz
`(Boltinghouse. et al.. 1990).
`
`Scan Uml
`Electronics Unit
`
`
`I
`'
`'
`
`7 _
`Range]
`W190
`Processor
`
`50 Degree
`PM
`Rosier
`Benn
`
`_‘
`
`'
`
`'
`
`'
`
`l‘wolnnchc
`
`P’IUEWlodc
`1
`'
`sec" 7 [9:413
`,
`Loser
`Mechanism
`
`Phuheluck
`.._
`Prat-asset
`
`
`
`
`
`
`
`
`
`
`
`
`Run 9
`
`.
`Vldeo
`
`Programmable
`Frnme
`Burr“
`lnlerlace
`
`
`
`l
`
`Figure 6-10. Block diagram of the Odetics scanning laser rangefinder {courtesy Odetics. lnc.).
`
`
`SilverStar Exhibit 1016 - 194
`SilverStar Exhibit 101—6 - 194
`
`

`

`ISO
`
`Sensors for Mobile Robots
`
`
`
`Figure 6-11. The Odetics Scanning Laser Imaging System captures a ['28- by 128-pixel image
`every 835 milliseconds [courtesy Odeties, Inc.).
`
`For each pixel. the processor outputs a range value and a video reflectance
`value. The video data are equivalent to that obtained from a standard lilatzlcandw
`white television camera. except
`that
`interference due to ambient
`light and
`shadowing effects are eliminated.
`The reflectance value is compared to a
`prespecilied threshold to eliminate pixels with insufficient return intensity to be
`properly processed.
`thereby eliminating potentially invalid range data: range
`values are set to maximum for all such pixels (Boltinghouse & Larsen, 1989). A
`three—by—three neighborhood median filter is used to further filter out noise from
`data qualification,
`specular
`reflection,
`and impulse
`response
`[Larson &
`Boltinghouse. 1988).
`The output format is a 16-bit data word consisting of the range value in either 8
`or 9 bits. and the video information in either 8 or 7 bits. respectively. The
`resulting range resolution for the system is 1.44 inches for the 8-bit format, and
`0.72 inch with 9 bits. A buffer interface provides interim storage of the data and
`can execute single—word or whole-block direct-memoryaccess
`transfers
`to
`external host controllers under program control.
`Information can also be routed
`directly to a host without being held in the buffer. Currently.
`the interface is
`designed to support VAX. VME-an, Meltibus. and lBM-PC/AT equipment. The
`scan and electronics unit together weigh 31 pounds and require 2 amps at 28 volts
`DC.
`
`6.1.4 Sandie Scanner-less Range [wager
`
`Originally conceived as an active seeker head for smart weapons. the Scannerle.s's
`Range lmager
`(Figure 6—i2} developed at Sandia National Laboratories.
`Albuquerque. NM. computes three-dimensional range information without need
`
`SilverStar Exhibit 1016 - 195
`SilverStar Exhibit 101—6 -195—
`
`

`

`Chapter 6 Phase-Shift Measurement and Frequency Modulation
`
`lBi
`
`for mechanical or solid—state scanning. A laser diode or LED array is used to
`illuminate an entire scene in similar fashion to Robotic Vision System‘s pulsed
`TOF Long Optical Range and Detection System. described at
`the end of the
`previous chapter.
`The Sandia approach, however, employs an amplitude?
`modulated continuous-wave source in conjunction with a single CCD camera. and
`determines ranges to all pixel elements in essentially simultaneous fashion based
`on the perceived round-trip phase shift (Frazier, i994). Phase—shift measurement
`is rather elegantly accomplished by converting the phase difference to a more
`easily quantified intensity representation through use of a microchannei-pinte
`image intensifier as shown in the block diagram of Figure 6-13.
`
`
`
`Figure 6-12. The Sandia Scanneriesr Range imager employs an amplitude-modulated CW laser
`source in conjunction with a single CCD camera (courtesy Sandia National Laboratories).
`
`Reflected energy from the illuminated scene is focused by the receiver optics
`upon a photocathode element that creates a stream of electrons modulated in
`accordance with the amplitude variations of the incoming light. The sinusoidal
`laser-modulation signal fin is coupled to a thin conductive sheet (i.e.. analogous to
`the grid of a vacuum tube), as shown in the above figure, to control the flow of
`electrons from the photocathode into the microchanrtel plate (Scott. 1990). The
`electron stream is amplified through secondary emissions as it passes through the
`microchannel plate. and convened back to optical energy upon striking the
`phosphor screen as illustrated. Since the gain of the image intensifier stage is in
`this fashion modulated at the same frequency as the outgoing optical energy. the
`magnitude of phosphor radiance is thus a function of the cosine of the range—
`dependent phase angle (i.e., due to constructive and destructive interference). A
`ZlO-frarneslsecond Dalsa CCD camera is coupled to the phosphor screen by way
`of a coherent fiber-optic bundle to serve as an integrating 256-by—256 detector
`array (Weiss, 1994).
`
`
`SilverStar Exhibit 1016 - 196
`SilverStar Exhibit 1016 -196—
`
`

`

`[82
`
`
`
`Sensors for Mobile Robots
`
`
`fif—
`Henge
`Lnerqy {a
`Processor JW>{ inrqei
`
`
`
`
`
`Phosphor
`/ ,
`
`Tl'irl Flute
`Phoiacuth ode
`
`/
`
`iiich
`if
`Cuherew
`CCJJ'
`Chennai W { TEE:
`Fiber
`
`
`Plate
`u H I
`‘
`Bundle
`Figure 6-13. Range values are computed for all pixels in the CCD detector array based on the
`observed phase shift (adapted from Scott.
`|990).
`
`torn
`
`F
`
`To expand the phase ambiguity interval and improve resolution, a second
`image is obtained with the image intensifier modulated 90 degrees out of phase
`with respect to the light source. effectively measuring the sine of the phase angle.
`These “sine" and “cosine" images are processed together with a baseline image
`taken under conditions of no receiver or transmitter modulation in order to
`
`eliminate nonwrange-reiated intensity variations (Scott. 1990). The current system
`update rate using a 68040—based PC running at 40 MHz is one frame per second,
`but will be expanded to 8 Hz in the very near future through incorporation of TI-
`C40 digital signal processor (BS?) hardware.
`
`
`
`Figure 6-14. Resulting range image (left) and reflectance image {right} for atypical outdoor scene
`using an array offiGU—nunometer (red) LEDs (courtesy Sandia National Laboratories}.
`
`Due to its structural simplicity. relatively low cost. and demonstrated potential
`for high-bandwidth. medium—resolution range data. the Sandie Scanneriess Range
`[mager is being investigated for use on a number of robotic platforms. including
`the MDARS~Exterior system. One existing prototype of the sensor employs a 20-
`watt laser diode modulated at 5 MHz. resulting in a 90-foot ambiguity interval
`with a range resolution of 1 foot and a maximum range of 2.000 feet at night
`
`
`SilverStar Exhibit 1016 -19_7
`SilverStar Exhibit 1016 - 197
`
`

`

`Chapter 6 Phase-Shift Measurement and Frequency Modulation
`
`|83
`
`(Weiss, 1994). Nighttime operation using eye—safe LED emitxers has also been
`demonstrated out to 200 feet;
`representative range and reflectance images at a
`distance of approximately 60 feet are presented in Figure 6-14.
`Potential
`problems still being investigated include the significant power and cooling
`requirements for the laser source, and attainment of sufficient signal—to—noise ratio
`for reliable daytime operation.
`
`6.1.5 ESP Optical Ranging System
`
`The Optical Ranging System (ORS-IJ is a low-cost near-infrared rangefinder
`{Figure 6‘15} developed in 1989 by ESP Technologies, Inc, Lawrenceville, NJ.
`for use
`