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1. a housing having dimensions suitable for being hand held during operation a power source positioned within said housing and providing a high voltage output and a low voltage output as required to other components a laser rangefinder system disposed within said hous ing and constructed to fire a laser pulse of short duration at a selected target to detect an RX re turn pulse of laser light reflected from said se lected target and to produce count data reflective of an elapsed time of flight between firing of said laser pulse and receipt of said return pulse a vertical angle sensor for sensing a vertical angle between said target and said housing and con structed to output an electrically readable vertical angle signal reflective thereof a magnetic compass constructed to output a direction reading in electronically readable form a sighting scope attached to said housing having apparent width measuring means for measuring the apparent width of a target and operably associated with said laser rangefinder said vertical angle sen sor and said magnetic compass such that when a user sights on a target with said sighting scope said laser rangefinder light detector and magnetic compass are simultaneously aimed at said target and said vertical angle sensor outputs a signal re flective of the vertical angle to said target trigger means mounted to said housing for manipula tion by a user to trigger operation of said survey2. JOVLTOA 3ON3H3d3H XV 39V L10A Sheet 6 of 7 5 291 262 Mar 1 1994 U S Patent H3sviL 6 062 Z62 NIWL 123135 9 014 09 H3TIOHINOJOHOIN woud 22889 Ho XXn 212 1109419 9NILV5 8rz 209 NOHJ NOILY TOdH31NIQ OL 06 992 1109419 NOLLVTOdH3JINI O OL oor HOLVHVdWOO 209 092 H31Nn 02 M9019 Ol 009 019 5 291 262 Sheet 7 of 7 Mar 1 1994 U S Patent mola T f DS T1 JEN yaran bos 1 Lun 1 0 of WOW 1 2 5 291 262 1 LASER SURVEYING INSTRUMENTRelated Applications This application is a continuation in part of applica tion Ser No 07 489 720 filed Feb 26 1990 whichisa continuation of application Ser No 07 329 303 filed Mar 27 1989 both abandoned FIELD The invention relates generally to surveying devices and more particularly to a laser surveying device STATE OF THE ART Surveying devices are available to serve various pur poses including topographical mapping surveying to determine property boundaries etc Such devices usu ally include a sight a compass and an inclinometer for ascertaining the direction and the angle of inclination from the surveyor s position of the landmark whose location is being determined Typically two persons are
3. Mar 1 1994 U S Patent 26 0L 34025 02 4 YANOLLIGNOD TVN9IS HOLVHJN39 3S Id Alddns HJMOd JOVLTOA MOT YOSNAS ZHNLVHIdMIL HOSN3S LLL OLA104197113 SISATVNV ov we HOSS320Hd sng viva be SSS eee ISQNVWNOO 1 FAD I AVidsia 1uvn SSVdWOO 8 Sheet 2 of 7 5 291 262 1 1994 U S Patent 11420 Luv OVdADI o 01 WOH 082 r b 17 1 t 1 86 2 won U S Patent Mar 1 1994 Sheet 3 of 7 5 291 262 DATA BUS t FROM 1CONTROL LINES REFERENCE FROM MICRO THRESHOLD CONTROLLER COMPARATOR 216 300 COUNTER 302 CLOCK GK SIGNAL TIMING CLOCK LOGIC RESET GATE CONTROL SIGNAL 332 310 RX PULSE PULSE 206 FROM 330 COMPARATOR O 208 RX PULSE 232 TO TIMING LOGIC 242 U S Patent 1 1994 Sheet 4 of 7 5 291 262 S1 FROM TIMING LOG C OUTPUT TOA I 402 FROM TO TIMING START LOGIC PULSE OUTPUT INTER POLATION COUNTER 5 291 262 Sheet 5 of 7 Mar 1 1994 U S Patent S big HO3 INdLNO HOLVHVd 4 YASVIL HOF LINdLNO HOLVUVd NIALL HO 140 41 00 HOLVHVd 2190 21901 43SVU 21907 ONIWIL WOU 0 doya JDVLIOA 4
4. by REF interpolation circuit 246 A corresponding REF interpolation count is acquired by REF interpola tion counter 250 from which it can be read by mi crocontroller 60 An RX interpolation pulse is similarly produced and processed by RX interpolation circuit 248 and interpolation counter 252 All of the TMIN REF TMAX REF TMIN RX TMAX RX REF and RX count values acquired by interpolation counters 250 252 as well as the integral clock count of main counter 260 can be read by microprocessor 60 from the count ers when so directed by the internal configuration stored in ROM 282 In the embodiment illustrated in FIG 6 TMIN has a duration equal to exactly one cycle of timing clock 242 and TMAX has a duration equal to exactly two cycles of timing clock 242 However alternatively TMIN and TMAX may vary between any convenient integral or half integral number of clock periods for example be tween and 14 clock periods or between 1 and 3 clock periods so long as TMIN is not zero The latter restric tion is important because electronic circuits do not op erate instantaneously and there would be nonlinearity 15 20 25 30 35 45 50 55 65 12 as the interpolation pulse width approached zero Also as the pulse width of a REF or RX interpolation pulse approached zero considerable ringing and distortion would occur on the capacitor wave form when the current switch in the pulse stretcher type interpolation circuit
5. device when said survey device is aimed at the target and control means including a microcontroller having memory means for storing instructions and data said microcontroller being communicatively inter connected to said power source said laser range finder said vertical angle sensor and to read said horizontal direction signal from said magnetic compass said control means being configured to calculate the time of flight of said laser pulse from said count data calculate a distance to said target from said time of flight and the speed of light 5 291 262 17 calculate a vertical height from a pair of vertical angle signals each corresponding to a different target or different points on said selected target operate said magnetic compass to produce a com pass reading indicative of the direction from said survey device to said selected target and receive said apparent width reading and to com pute from said apparent width reading and said distance an actual width of said target 2 The survey device of claim 1 wherein said width measuring means comprises a split image prism dis posed for viewing in said sighting scope and dividing a target seen through said sighting scope into two adja cent portions means for adjusting the positions of said adjacent portions relative to each other and an electri cal encoder operably associated with said adjustment means for detecting said adjustment and providing an adjustment sign
6. required a first positioned at the landmark itself and a second at a known distance from the landmark taking readings The second person sights on the first person and takes readings from the compass and inclinometer The necessary calculations are based on the known distance between the landmark and the surveyor the compass heading and the inclination The first person then moves to another location and the process 15 re peated Readings from at least three different locations are needed to establish the location of the landmark More recently survey devices utilizing laser light have been designed In some instances a laser light spot is projected against a target which may be an inanimate target placed by the surveyor who then takes readings from a known distance for example see U S Pat Nos 4 029 415 to Johnson 4 873 449 to Paramythioti and 4 673 287 to Rickus Proper sighting by the surveyor may be established by receipt of a reflected pulse from the target by visual observation of laser light on the target or by a signal provided by the target upon its being struck by the laser beam In a further improvement the distance between the surveyor and the target is established from laser light reflected by the target and received by a detector in the surveyor s unit Such laser distance measurements have also been employed for surveying determining the speed of objects or vehicles etc as illustrated in U S Pat Nos 3 464
7. the incli nation from the horizontal of target 90 In the present preferred embodiment vertical angle sensor 40 is an electrolytic type tilt sensor such as the model L 211 U which is commercially available from Spectron Glass and Electronics Inc Hauppage New York also avail able through G G Technics AG CH 4419 Lupsin gen BL Switzerland The indicated electrolytic sensor is obtained from the company without attached means for generating the desired vertical angle data signal Therefore a signal conditioner 44 processes the raw signal to produce a vertical angle signal readable by microprocessor 60 Signal conditioning circuitry 44 drives the electrolytic sensor with a square wave drive signal in a balanced bridge configuration Signal conditioning circuitry 44 also includes a voltage to frequency V F converter which converts the electrolytic sensor output signal 46 to a frequency signal which is sent to a counter timer port on microprocessor 64 Microprocessor 64 sets a known sampling period so that the count received at the counter timer port is directly proportional to the vertical angle sensed by the electrolytic sensor Many other types of vertical angle sensors are known and these may be substituted for the electrolytic tilt sensor with appropriate changes in signal condi tioner 44 In particular other fluid type vertical angle sensors for example capacitive fluid type sensors may be equally suitable as the elect
8. 770 to Schmidt et al 4 902 889 to Sodi and 3 698 811 to Weil Such improved laser distance measuring devices eliminate the need for the surveyor to physically measure the distance to the target However such devices require the surveyor to re cord the readings on the inclinometer and the compass The surveyor further must either perform the necessary calculations by hand or enter the measured values of inclination and compass heading into a computer in the device in order to arrive at the location coordinates of the target An electronic surveying system is disclosed in U S Pat Nos 4 146 927 and 4 205 385 both to Erickson et al The system includes a theodolite which provides data in a digital output form an electronic distance find ing device a tilt sensor and computing means interfac ing with these elements to make survey calculations However the electronic distance finder is a phase shift analysis type of instrument which requires a reflective marker attached to the survey target to achieve ade 5 10 20 25 30 35 40 45 50 55 60 65 2 guate return signal strength for the phase analysis Moreover a theodolite must be fixedly mounted for example on a tripod and referenced to two known survey points in order to make measurements Thus it is very cumbersome to make measurements at numerous different and remote locations However for some purposes it is extremely inconve nient to mount a
9. and TLAS ER RX from said interpolation means and calculates said time of flight from said calibration values said number of whole clock pulses and said REF and RX values 14 The survey device of claim 10 wherein said laser rangefinder further includes a first collimator operably disposed for directing a major portion of said laser pulse toward a target and said reference pulse means is a second collimator operably disposed for directing a minor portion of said laser pulse to said light detection means to produce said reference pulse and wherein said light detection means includes a first light detector having operably associated focussing means for focus sing and receiving said reflected laser light and in re sponse producing said RX pulse and a second light detector disposed for detection of said minor portion of said laser pulse and producing said reference pulse in response thereto 15 The survey device of claim 1 wherein said self calibrating interpolation is performed at least once each time said trigger is operated to initiate firing of said laser pulse 16 The survey device of claim 1 wherein said laser rangefinder includes gating means operably associated with said return pulse detector and said control means for selecting an RX pulse received within an adjustable time window and transmitting only said selected RX pulse to said control means for computation of said time of flight said gating means and said microcon
10. and the speed of light 11 The survey device of claim 10 wherein said tim ing analysis circuitry defines an interpolation interval equal to an integral number of said clock periods and further includes a reference pulse interpolation circuit for interpolating a value TLASER REF representing a fractional time within a said clock period at which said reference pulse arrived at said detector and an RX returned pulse interpolation circuit for interpolating a fractional value TLASER RX of a fractional time within a later said clock period at which said RX pulse arrives at said detector said values TLASER RX AND TLASER REF being determined with respect to said interpolation interval 12 The survey device of claim 11 wherein said tim ing analysis circuitry is further constructed to generate a pair of calibration pulses respectively referred to as TMIN and TMAX and spaced to define said interpola tion interval wherein said timing analysis circuitry subjects said calibration pulses to a said reference inter polation circuit to produce a pair of calibration values TMIN REF TMAX REF and wherein said timing analysis circuitry further subjects said calibration pulses to said RX interpolation circuit to produce a second pair of calibration values TMIN RX TMAX RX 13 The survey device of claim 12 wherein said con trol means reads a number of whole clock pulses from said main counter reads TMIN REF TMAX REF TLASER REF TMIN RX TMAX RX
11. is fur ther narrowed for the fourth REF pulse and so on When the window is narrowed it may also be re cen tered the delay time changed on the average of the receipt times of specified detector pulses These steps of widening and narrowing the window are repeated as indicated until microprocessor 60 determines that a window which appropriately defines the arrival of the true RX pulses has been established Such a window may for example be determined as the window within which a desired high proportion of the detector pulses falls within the window The gating circuit with the microcontroller config ured as described to vary independentiy the opening and closing times of the RX window and to iteratively narrow and widen the RX window causes the range finder to effectively lock on to a target and avoid errors due to detector or circuit noise or readings made from non target objects adjacent the selected target Also jamming of the laser return signal is very difficult with the survey device so designed As seen in FIG 3 gating circuit 212 has 2 identical counters 300 302 which are connected to microcon troller 60 by both logic control lines 122 and the main data buss such that counters 300 302 can be selectably set to desired values by microcontroller 60 Counters 300 302 are also connected to receive a clock signal from clock 242 The REF pulse 218 is sent from thresh old comparator 216 into both counters 300
12. surveys the microcontroller may be configured to collect height and or width data for a series of trees in a selected sector to estimate the board footage or number of logs per tree from the height and width data etc The useful ness of the survey system extends to many other types of survey measurements as well THE DRAWINGS In the drawings which illustrate what is presently regarded as the best mode for executing the invention like reference numbers indicate like elements and FIG 1 is a block diagram of a working embodiment of the laser surveying device of the invention 10 20 25 30 35 45 50 55 65 4 FIG 2 is a block diagram detailing the laser range finder system of FIG 1 FIG 3 is a functional schematic of the gating cir cuitry of the timing logic of FIG 2 FIG 4A is a functional schematic of an embodiment of a pulse stretcher circuit useful as interpolation circuit 250 or 252 FIG 4B is a functional schematic of an alternate embodiment of a charge pump circuit useful as interpo lation circuit 250 or 252 FIG 5 is a waveform diagram for pulse stretchers 250 252 FIG 6 is a functional schematic of a timing logic circuit 240 FIG 7 is a block diagram of an alternate embodiment wherein interpolation circuit 250 is the charge pump circuit of FIG 4B DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS FIG 1 depicts a working embodiment of the laser surveying device This embo
13. switches These noted effects would contribute significant errors if TMIN were zero FIG 6 depicts a working embodiment of a timing logic circuit 240 in greater detail A periodic clock signal from clock 242 is received at input 600 reference pulse 218 from comparator 216 enters at input 602 and RX pulse 232 at input 604 Input 600 from timing clock 242 is connected to a three input and gate 606 which opens when reference pulse 218 arrives at input 602 to transmit clock signals to output 610 to main counter 260 Timing logic circuit 240 has an associated crystal controlled timing clock 242 which is desirably of high stability and high accuracy Timing clock 242 provides a periodic clock signal 243 comprising a series of pulses equally spaced at a preset time period Timing logic circuit 240 with interpolation circuits 246 248 interpo lation counters 250 252 and main counter 260 produces timing data representing the elapsed time between a selected point on reference signal 218 and an equivalent selected point on RX signal 232 in terms of the number of pulses of clock signal 243 In the instant embodiment the selected points are the rising edge of reference pulse 218 and the rising edge of RX pulse 232 However the period of timing clock 242 is too large to offer good resolution Therefore interpolation cir cuit circuits 246 248 are operably associated with tim ing logic 240 for expanding the time duration of the fractional portion
14. target device or sensor on the target for example if it is desired to determine the compass headings and distances to a number of different targets from a given user s position Additionally one may wish to estimate the height and or width of distant objects For the above purposes it is time consuming and tedious for the user to have to enter by hand multi ple values of compass heading and inclination under such circumstances Thus a need remains for a laser survey device which is accurate conveniently portable and does not require known reference points for calibration of distance or compass heading or mounting on a fixed structure such as a tripod A need further remains for such a device which does not require attachment of a target sensor or other device to the target whose distance is to be deter mined Desirably such a system would measure and digitally input directly to an internal computer readings of distance compass heading and inclination SUMMARY OF THE INVENTION The invention comprises a laser survey instrument including at least the following components a laser rangefinder a magnetic compass module constructed to produce an electronically readable compass signal a vertical angle sensor module which is constructed to produce an electronically readable vertical angle signal and a microprocessor based microcontroller which is controllingly and communicatively interconnected to the foregoing components In a hi
15. troller being mutually configured to permit selectable and independent setting of an opening time and a clos ing time of said adjustable time window 10 20 50 55 60 65 20 17 The survey of claim 16 wherein said gating means is a digital logic gating circuit 18 The survey device of claim 16 wherein said con trol means is configured to iteratively adjust said adjust able time window from larger to smaller and smaller to larger to thereby focus said adjustable time window to distinguish a detector signal resulting from laser pulse light returned from said chosen target from a false detector signal resulting from other causes 19 A laser surveying device comprising a housing constructed to be hand held during opera tion 1 a power source positioned within said housing and providing a high voltage output and a low voltage output as required to other components a laser rangefinder system disposed within said hous ing and constructed to fire a laser pulse of short duration at a selected target to detect an RX re turn pulse of laser light reflected from said se lected target and to produce count data reflective of an elapsed time of flight between firing of said laser pulse and receipt of said RX pulse trigger means mounted to said housing for manipula tion by a user to trigger operation of said survey device when said survey device is aimed at said selected target vertical angle sensor for sensing a vert
16. 302 The output of counter 302 is sent through an inverting am plifier 304 and in turn goes to an and gate 306 along with the output of counter 300 And gate 306 outputs a gate control signal 310 which is active logical 1 when gate open counter 300 finishes counting the delay the first time period Gate control signal 310 becomes inac tive logical 0 when the second preset time period in gate close counter 302 elapses The detector pulse 206 from threshold comparator 208 is connected both to the clock input CLK of an edge clocked J K flip flop 314 and to an inverting am plifier 316 Gate control signal 310 is sent to the J input of flip flop 312 Flip flop 312 is configured so that it will only respond to a rising edge at clock input 312 when gate control signal 310 is active Also J K flip flop 312 only changes state on the first clock edge that occurs during the active period all other clock edges will be ignored When gate control signal 310 is active flip flop 314 outputs the rising edge of the RX pulse 232 at the Q output RX pulse 232 is then sent to timing logic 240 and also to an and gate 330 which also receives input from the not Q output of a second J K flip flop 332 Flip flop 332 receives detector pulse 206 at its CLK input after de tector pulse 206 has been passed through inverting am plifier 316 Flip flop 332 also receives gate control sig nal 310 at the J input Thus when gate control signal 310 is acti
17. 65 8 interpolation counters 250 252 and main counter 260 operates to determine the arrival times of the respective rising edges of reference and RX pulses 218 232 in terms of the number of cycles of clock 242 These count times are temporarily stored in main counter 260 and interpolation counters 250 252 Microcontroller 60 reads and stores the clock count times from the counters and from these values computes the time of flight of the laser pulse The time of flight is divisible by twice the speed of light to give the distance from the survey de vice to the target A significant feature of the design of timing analysis circuitry 114 is its mutual configuration with micro controller 60 to provide self calibrated interpolated values of the respective fractional portions of the arrival times within the corresponding clock periods in which reference REF and reflected light RX pulses 218 and 232 are received That is the arrival times of the REF and RX pulses generally fall somewhere within a clock period Thus the true elapsed time between the REF and RX pulses comprises the number of whole clock periods elapsed plus the fractional portion of the clock period occurring just after the receipt of the REF pulse and the fractional portion of the clock period occurring just prior to receipt of the RX pulse These two frac tional portions will be referred to as REF fractional portion and RX fractional portion respectively The self c
18. United States Patent m9 Dunne AAA AKAY AK AA US005291262A 11 Patent Number 4 Date of Patent 5 291 262 Mar 1 1994 1544 LASER SURVEYING INSTRUMENT 76 Inventor Jeremy Dunne 2686 E Otero PI 11 Littleton Colo 80122 21 Appl No 914 764 22 Filed Jul 15 1992 Related U S Application Data 63 Continuation in part of Ser No 489 720 Feb 26 1990 abandoned which is a continuation of Ser No 329 303 Mar 27 1989 abandoned 51 Int CLS s G91C 3 08 GO1P 3 36 52 UIS CL EREM YEN R 356 5 356 28 368 120 58 Field of Search 356 5 28 152 141 368 120 56 References Cited U S PATENT DOCUMENTS 3 464 770 9 1969 Schmidt 3 680 958 8 1972 VonBose 356 141 3 698 811 10 1972 Weil 356 5 4 346 989 8 1982 Gort et al 356 5 4 527 894 7 1985 Goede et al 356 28 4 569 599 2 1986 Bolkowetal 356 5 4 620 788 11 1986 Giger eee 356 5 4 732 472 3 1988 Konigetal 356 152 4 948 246 8 1990 Shigematsu 356 5 COMPASS v2 i SERIAL DATA amp COMMANDS 24 8L 1 MAGNETIC i 5 SUPPLY 2 vi 54 CIRCUITRY 1 TEMPERATURE VOLTAGE SENSOR POWER t t i 42 1 1 l Low 1 i 1 Vi VOLTAGE 1 t t 1 Eh
19. a reflective thereof to said control means and wherein said control means is further opera ble to compute an apparent width of said target from said adjustment signal 3 The survey device of claim 1 wherein said laser rangefinder system includes a laser pulse generator connected to receive high voltage from said power source reference pulse means for generating an REF refer ence pulse representative of the time of firing of said laser pulse light detection means for receiving and detecting light reflected from said target and in response producing an RX return pulse and timing analysis circuitry connected to receive said RX pulse and said REF pulse and operable to produce said count data relating to the elapsed time between said REF and RX pulses wherein said count data comprise REF count data and RX count data and wherein said timing analysis cir cuitry is further constructed to produce self cali bration pulses and to process said self calibration pulses in the same manner as said REF and RX pulses to produce calibration count values and wherein said microcontroller is further configured to read said calibration count values and to calculate said time of flight from said calibration count val ues said REF and RX count data and the speed of light 4 The survey device of claim 3 wherein said timing analysis circuitry comprises a clock providing a periodic series of clock pulses spaced by a known time period
20. a main counter for counting the number of said clock pulses occurring between a start time correspond ing to said REF pulse and an end time correspond ing to said RX pulse interpolation means connected to receive said REF and RX pulses for interpolating respective frac tional portions of said start time and said end time within said preset period of said clock signal said interpolation means including a start time interpo lation counter providing a start time interpolation count reflective of a fraction of a first said preset period at which said start time occurs and an end time interpolation counter providing an end time interpolation count reflective of a fraction of a second said preset period at which said end time Occurs and a timing logic circuit constructed to generate first and second self calibration pulses which differ by an 20 25 30 40 45 50 55 65 18 integral number of said preset periods to process said REF and RX pulses to produce respective REF and RX interpolation signals comprising the corresponding fractional portions of the arrival times of said REF and RX pulses and to send said self calibration pulses and said REF and RX pulses to said interpolation means thereby producing a set of calibration values and a REF interpolation count and said RX interpolation count which are defined with respect to said calibration values and wherein said microcontroller is configured to read said calibr
21. alcu late the height of a remote object such as a tree truck or the like 5 291 262 3 The magnetic compass is constructed to make a read ing of the compass heading based on magnetic fields without a reguirement for triangulation affixation 10 tripod or calibration to a known position Notably the magnetic compass is further constructed to provide an electronically readable data signal which can be read or modified for reading by the microcontroller The laser rangefinder has several notable features not necessarily listed in order of importance First a crystal clock based timing analysis circuit includes a gating circuit which is a digital logic edge sensitive gate for which both the opening and the closing of the time window can be selectably set by the microcon troller In a preferred embodiment the microcontroller is configured to alternately widen and narrow the win dow to selectively lock on RX pulses and ex clude pulses due to noise or other factors Second the timing analysis circuitry is constructed to generate self calibration pulses and to process them in the same manner as the REF and RX pulses thereby producing a set of calibration interpolation counts The controller uses these calibration interpolation counts along with the REF and RX interpolation counts to compute self calibrated values of the respective frac tional portions of the clock periods at which the REF and RX pul
22. alibrated interpolated arrival times are ob tained by 1 construction of timing logic circuit 240 to process the REF and RX pulses to produce correspond ing REF and RX interpolation pulses respectively com prising the REF fractional portion and the RX frac tional portion 2 construction of timing logic circuit 240 to generate a pair of self calibration pulses TMIN and TMAX which bracket a chosen interpolation width 3 sending the REF interpolation pulse through a REF interpolation circuit 246 and the RX interpola tion pulse through an RX interpolation circuit 248 to produce respectively REF and RX interpolated count values 4 sending both self calibration pulses TMIN and TMAX through each of interpolation circuits 246 248 thereby producing two respective sets of self cali bration values TMIN REF TMAX REF and TMIN RX TMAX RX and 5 configuration of microcon troller 60 to compute the REF and RX fractional por tions from the respective self calibration values and the appropriate REF or RX interpolated count values Mi crocontroller 60 is further configured to compute the time of flight from the number of whole clock periods acquired by main counter 260 through timing logic 240 and the REF and RX interpolated count values The design described in the preceding paragraph is particularly advantageous in that it substantially elimi nates errors resulting from drift in the interpolation circuits and timing logic or variability of c
23. ation values said start interpolation count and said end interpolation count from said interpolation counters to read said number of clock periods from said main counter and to calcu late said time of flight from said number of clock periods said start interpolation count said end interpolation count and said set of calibration val ues 5 The survey device of claim 4 wherein said timing analysis circuitry further includes gating means opera bly associated with said return pulse detector and said microcontroller for selecting RX pulses detected within an adjustable time window and transmitting only said selected RX pulses to said timing logic circuit for fur ther processing 6 The survey device of claim 5 wherein said gating means is a digital logic gating circuit in which the begin ning and the ending time of the window are indepen dently adjustable 7 The survey device of claim 6 wherein said digital logic gating circuit is an edge sensitive window con structed such that only a pulse whose rising edge falls within the window is accepted and transmitted 8 The survey device of claim 6 wherein said mi crocontroller and said digital logic gating circuit are mutually configured for selectable setting of either or both an opening time and a closing time of said adjust able time window 9 The survey device of claim 8 wherein said mi crocontroller is configured to adjust said adjustable time window in an iterative fashi
24. be changed with or without a change in the closing time and vice versa Additionally the gate is edge sensitive that is only a detector pulse whose rising edge falls within the win dow will be accepted and transmitted as an RX pulse If only the peak or the falling edge of a detector pulse falls within the window it will be rejected The use of edge sensitive gate components provides increased accuracy in the selection of RX pulses In a highly preferred embodiment microcontroller 60 is configured to iteratively and independently adjust the times of the opening and or closing of the gate for a series of laser pulses fired at a single target to establish a window which accurately defines true RX pulses from the target This adjustment is performed generally as follows 1 When the first REF pulse in the series arrives at the gate the window is opened very wide and the delay time is set to be short If a detector pulse is received within the first window then 2 when the second REF pulse arrives the window is narrowed and centered on the arrival time of the first detector pulse by shifting the opening and or closing time of the window as necessary If the second detector pulse is not received within the second window then 3 the window is widened again for the third REF pulse 20 25 35 40 45 50 60 65 10 However if the second detector pulse is received within the second window then 4 the window
25. comparator is always in the linear portion of the charge and discharge period and clear of any ringing and distortion When the voltage received by comparator 420 at the positive input from voltage follower 418 exceeds the reference voltage on the negative input the output from comparator 420 goes high This allows clock pulses from timing clock 242 to flow through to an input 450 to interpolation counter 250 since the output to the interpolation counter is the logical and of the output of comparator 420 and clock 242 When input 400 from timing logic 240 goes back to logic zero switch 51 again changes over so that 11 is diverted to ground Capacitor 410 now discharges at a much slower rate due to 12 When the voltage on capacitor 410 falls below the reference voltage the output of comparator 420 drops back to logic zero At this point in time interpolation counter 250 contains a count that relates to the width of the output pulse 450 Capacitor 410 continues to discharge until the initial conditions are again reached whereby D1 is conducting and balancing 12 The reference voltage is desirably set so that the threshold of comparator 420 is near the fifty percent point on the charging path for the TMIN pulse This gives maximum freedom from error effects due to ringing and non linearity at the switching points FIG 5 shows a pulse expansion for the TMIN TLASER and TMAX pulses wherein TMIN is one clock cycle in duration TMAX is
26. d detector signal exceeds the preset threshold of comparator 208 it is sent to a gating circuit 212 A second photodetector 21O which is here embodied as a PIN semiconductor photodetector is disposed to receive the redirected pulse portion 109 of the outgoing laser pulse 103 Upon receipt of the redirected pulse portion 109 PIN photodetector 210 generates an analog signal which is sent to amplification means 214 and in 20 25 30 35 40 45 turn to a threshold comparator 216 The output of 50 threshold comparator 216 constitutes a reference signal 218 which represents the time at which the outgoing laser pulse 103 was emitted Reference signal 218 is sent to timing analysis circuitry 114 A temperature sensor 270 is disposed to sense the temperature of APD 202 and to provide temperature readings to microcontroller 60 In response to these temperature readings microcontroller 60 consults a lookup table stored in memory 70 to determine the desired value of bias voltage to be applied to APD 202 and to control regulator 203 to adjust the bias voltage as needed to correspond to the desired value Optionally microprocessor 64 adjusts the firing voltage applied to laser diode 200 via regulator 201 in accordance with a firing voltage lookup table stored in memory 70 Timing analysis circuitry 114 which in the embodi ment of FIG 2 comprises gating circuit 212 timing logic 240 clock 242 interpolation circuits 246 248 60
27. diment incorporates the following basic components a sighting scope 10 for a user to visually select a target a keypad 20 and trigger 24 which together comprise user operation means a laser rangefinding system 30 a vertical angle sensor 40 with an associated temperature sensor 42 and signal processor 44 a magnetic compass 50 a microcontroller 60 including a microprocessor 64 and a communica tively associated memory unit 70 and data output means 80 which is here shown to comprise a display 82 and a UART 84 connectible to provide data to an exter nal computer or data logger Microcontroller 60 is communicatively interfaced to send logic commands and to read and store data from laser rangefinder 30 vertical angle sensor 40 and mag netic compass 50 The operations which microcon troller 60 is configured to supervise include sending a laser pulse toward the target to determine its distance making a compass reading and determining the angle and direction of tilt Modes which microcontroller 60 may be configured to control are described in greater detail later herein In the illustrated embodiment selec tion of an operating mode is made by operation of ap propriate buttons or the like on keypad 20 which is communicatively connected to the microcontroller Microcontroller 60 is also configured to perform vari ous computations with readings acquired from range finder subsystem 30 vertical angle sensor 40 and com pass 50 Relevant de
28. enerator 102 to fire a number of pulses at successive equal time intervals towards target 90 The respective distances for each of the pulses are temporarily stored in memory 70 and microcontroller 60 computes from these distances and the time between readings the velocity of the target using the method of least squares In this speed detecting embodiment the electronic vertical angle sensor and the magnetic com pass are optional The disclosed laser survey instrument has numerous advantages It is very compact lightweight easy to use and can be used to perform a wide range of surveying tasks These include nearly any task requiring some combination of one or more distance measurements one or more inclination measurements one or more com pass measurements and or one or more width measure ments Various readings and computed values may be displayed as appropriate on the display sent to the UART to be downloaded to other computational de vices or the like The keypad in conjunction with the microcontroller is provided for a user to select and initiate any automatic measuring modes which the mi crocontroller is configured to control For example a user could take measurements of the height and width of all of the trees visible at a selected distance and or within a selected directional sector from a given observation point The microcontroller may be configured to compute the diameter of a cylin drical object such as a tree using
29. er than the time to receive the reflected pulse light and averaging the elapsed time between REF and RX pulses for most or all of the plurality of fired pulses Specific circuits embodying various elements of tim ing analysis circuitry 114 are functionally depicted in FIGS 3 4A 4B and 6 Gating circuit 212 depicted in greater detail in FIG 3 ensures that only detector pulses produced by APD 202 within a selected time window following emission of laser pulse 103 are accepted as representing returned laser pulse light 105 and sent to the timing logic 240 as RX return pulse signal 232 for analysis A detector pulse 206 arriving before or after the selected window is not transmitted by gating circuit 212 to timing logic 240 and does not receive further processing Gating circuit 212 also outputs a digital pulse width signal 233 which is reflective of the width of the RX pulse RX pulse width signal 233 is sent to microcontroller 60 via a pulse width measuring circuit 235 and an A D converter 234 where it is used to derive a correction factor to compen sate for saturation of APD 202 and or the amplification means 204 Gating circuit 212 is a digital logic operated gate in which both the delay time the time at which the win dow opens and the time at which the window closes can be independently selectably set via micro processor 60 as directed by a user or by a program stored in memory 70 That is the delay time can
30. ghly preferred embodiment the instrument is small enough to be easily hand held and further in cludes a trigger and a sighting scope for a user to visu ally select a target and to trigger operation of the device upon the selected target Desirably the sighting scope includes means for measuring the apparent width of the target The survey device determines the distance to a re mote target by measuring the time of flight of a very short duration pulse of infrared light The laser range finder fires the laser pulse detects reflected laser light and provides count values reflective of the respective arrival times of a REF reference pulse representing the firing time of the laser pulse and an RX pulse repre senting reflected laser pulse light The microcontroller is configured to read these count values and to compute from them the time of flight of the laser pulse and in turn the distance to the target The vertical angle sensor is presently embodied as a commercially manufactured electrolytic tilt sensor which in combination with appropriate signal condi tioning circuits outputs an inclination signal reflective of the vertical angle to the target However any other type of vertical angle sensor or inclinometer which provides an electronic ally readable data output signal may be used The micro controller is operable to use the vertical angle signals in conjunction with the dis tance data signals provided by the rangefinder to c
31. ical angle between said target and said housing and con structed to output a vertical angle signal reflective thereof magnetic compass mechanically associated with said housing and constructed to output compass readings in electronically readable form and control means including a microcontroller communi catively interconnected to said power source said laser rangefinder said vertical angle sensor and said magnetic compass said control means being configured to calculate the time of flight of said laser pulse from said count data calculate a distance to said target from said time of flight and the speed of light calculate a vertical height from a pair of vertical angle signals each corresponding to a different target or different points on said selected target operate said magnetic compass to produce a com pass reading for a selected target and to read said compass reading from said magnetic compass and gating means operably associated with said laser rangefinder and said microcontroller for selecting an RX pulse received within an adjustable time window and transmitting only said selected RX pulse to said control means for computation of said time of flight said gating means and said mi crocontroller being mutually configured to permit selectable and independent setting of an opening time and a closing time of said adjustable time window 20 The survey device of claim 19 wherein said con trol means is configured to i
32. ies Inc 1991 Power for magnetic compass 50 is supplied by connection to the V2 low power output of power supply 100 Basi cally the fluxgate compass comprises a sensor coil as sembly having a floating magnetic ring core surrounded by a toroidal drive coil and two orthogonally disposed detection coils A processing board contains all the components needed to drive the sensor detect the re turn signals and derive a magnetic compass bearing Desirably the compass module has an auto calibration mode which allows a user to correct for errors in com pass readings introduced by stray magnetic fields within the survey device Laser rangefinder system 30 determines a distance 92 from the survey device to target 90 distance 92 is sche matically depicted along the sightline from sighting scope 10 to target 90 Rangefinder system 30 includes a high voltage power supply 100 connected to power a laser pulse generator 102 and to provide bias voltage to a light detector 104 A first collimator 106 is operably associated with laser pulse generator 102 for directing a major portion of an outgoing laser pulse 103 generated by laser pulse generator 102 towards a target 90 A second collimator 108 is disposed to redirect a minor portion 109 of each outgoing laser pulse 103 to generate a timing reference signal In the embodiment of FIG 1 the redirected portion 109 is sent to the APD light detector 104 which outputs an analog signal con taining infor
33. in FIG 4B However for the pulse width circuit 235 some of the component values differ from those used in the charge pump circuits 700 702 used as interpolation circuits see FIG 7 This difference is because the range of pulse widths found for RX pulse 232 differs as compared to the REF and RX interpolation pulses from the timing logic Timing logic circuit 240 depicted in greater detail in FIG 6 is configured to perform the following func tions First it gates the signal from the clock 242 to the main counter 260 between the respective rising edges of the REF and RX pulses 218 232 Main counter 260 then counts the number of complete cycles of REF pulse 218 and RX pulse 232 Second timing logic 240 uses the signal from clock 242 to generate calibration pulses TMIN and TMAX which are separated by a known integral number of periods of clock 242 with neither TMIN nor TMAX being equal to 0 TMIN and TMAX together define an interpolation width e g an interval which is defined with respect to the known clock per iod in which the precise fraction of the clock period at which a pulse such as REF or RX pulses 218 232 ar rives can be determined Calibration pulses TMIN and TMAX are both sent to interpolation circuits 246 248 for processing to produce calibration values TMIN REF TMAX REF and TMIN RX TMAX RX re spectively Finally timing logic 240 derives a REF interpolation pulse from REF pulse 218 and sends it to be processed
34. keypad 20 Microcon troller 60 is configured to use the reticle marking data in conjunction with the target distance determined by laser rangefinder 30 to compute the actual width of the target by computations which will be apparent to those skilled in the art of surveying Optionally the inclina tion as measured by vertical angle sensor 40 may be included in the computation An alternate embodiment of width measuring means for sighting scope 10 is a split prism lens arrangement similar to those used as focussing aids for cameras The split prism lens is connected to an adjustment knob associated with a rotary encoder In this embodiment the user operates the adjustment knob to visually align one edge of the target in the upper half of the split image to the opposite edge in the other lower half of the image The rotary encoder generates an encoder signal comprising a series of pulses proportional to the angle through which the knob is turned The encoder signal is fed to a counter port of microprocessor 64 The rotary encoder also generates a clockwise anticlockwise sig nal and the latter in combination with the encoder sig nal allows microcontroller 60 to accurately calculate the knob rotation and thereby the horizontal angle subtended by the target object The actual width may then be computed as described for the reticle embodi ment Vertical angle sensor 40 generates a vertical angle signal reflective of the detected vertical angle
35. l arts Microcontroller 60 may be configured to perform these and any other operations and computations based on the four basic readings of width horizontal angle subtended horizontal distance inclination vertical angle and compass direction 10 45 55 65 16 Furthermore the timing analysis circuitry of the laser rangefinder portion offers considerably improved accu racy to the distance measurement This improved accu racy is especially due to the self calibrating interpola tion feature The rangefinder also has a high capability to discriminate between noise and or false return sig nals generated by structures near the target by effec tively locking on to signals returned from the true selected target This locking on capability is due to the incorporation of a digital logic gating circuit pro viding adjustment of both the beginning and the end of the time window plus the configuration of the micro processor to independently vary the beginning and end of the window and to alternately widen and narrow the window until the window which most accurately de fines the true return pulse from the target is established Although a preferred form of the invention has been herein disclosed many substitutions are possible with out departing from the concept of the invention The claims themselves define the scope of that which is regarded as the invention What is claimed is 1 A laser surveying device comprising
36. mation both as to the timing reference pulse and the subsequently received reflected light pulse In an alternate embodiment depicted in FIG 2 the redi rected portion 109 is sent to a separate light detector specifically a PIN photodetector 210 which provides a second detector signal constituting the timing reference signal Returning to FIG 1 focussing optics 110 are opera bly associated with light detector 104 for focussing received light thereon A bandpass filter 112 is desirably associated with focussing optics 110 for ensuring that detector 104 only receives light of wavelengths near the expected wavelength based on the emitted laser pulse In the working embodiment bandpass filter 112 is a narrow band interference filter Light detector 104 is 5 291 262 7 also connected to detector signal processing circuitry 113 Operation of the laser rangefinding subsystem 30 is controlled by a microcontroller 60 via logic control lines 122 which are connected to laser pulse generator 102 and the detector signal processing circuitry 113 The detector signal processing circuitry 113 is further connected to provide detector signals reflective of laser light received by light detector 104 to micro controller 120 and associated elements including a memory 70 display 82 and UART 84 Memory 70 includes both nonvolatile and volatile components and is configured for nonvolatile storage of instructions for the microcon troller semipermanent
37. mr GENERATOR 90 SIGNAL H COND T ONER i 11 5 a 5 046 839 9 1991 Krangle 356 5 Primary Examiner Stephen Buczinski Attorney Agent or Firm Trask Britt amp Rossa 57 A laser survey instrument is described which includes laser rangefinder which determines the time of flight of an infrared laser pulse to a target a magnetic compass module which produces an electronically readable com pass signal a vertical angle sensor module which pro duces an electronically readable inclination signal and a microprocessor based microcontroller The device is small enough to be easily hand held and includes a trigger and a sighting scope for a user to visually select a target and to trigger operation of the device upon the selected target The sighting scope preferably has means for measuring the apparent width of the target The laser rangefinder includes self calibrating interpo lation circuitry a digital logic operated gate for re flected laser pulses in which both the opening and the closing of the gate can be selectably set by the mi crocontroller and dual collimation of the outgoing laser pulse such that a minor portion of the outgoing laser pulse is sent to means for producing a timing refer ence signal The instrument is capable of performing numerous kinds of surveying operations 22 Claims 7 Drawing Sheets iu 103 102 106 30 5 291 262 Sheet 1 of 7
38. n the art FIG 4 depicts a single pulse stretcher circuit interpola tion circuits 246 and 248 would each be such a pulse stretcher circuit and equivalent in all respects except that REF interpolation circuit 246 receives REF pulse output from timing logic 240 and provides the interpo lated REF output to REF interpolation counter 250 5 291 262 13 while interpolation circuit 248 receives the RX pulse output and provides the stretched RX pulse signal to end interpolation counter 252 At the start of a measurement cycle the input 400 from timing logic 240 is at logic zero and current 11 is switched to ground The current 12 into constant cur rent sink 408 discharges capacitor 410 until diode D1 conducts and balances current 12 The voltage on ca pacitor 410 is then the clamp voltage minus the voltage drop across D1 Thus when the timing input 400 goes high capacitor 410 is charged by the current difference 11 12 The circuit component values are selected such that capacitor 410 charges rapidly when current 11 flows to output 404 The voltage across capacitor 410 is buffered by a voltage follower 418 and is sent to the positive input of a comparator 420 Comparator 420 in turn sends its output to an and gate 424 And gate 424 also receives clock signals from clock 242 and in turn provides an output 450 to interpolation counter 250 Desirably the reference voltage to comparator 420 is set to ensure that the switching point of the
39. omponent tolerances The survey device so constructed can deter mine distances to a resolution of a few millimeters or less with very high accuracy The arrival times are here defined as the times at which the respective rising edges of REF and RX pulses 218 232 are transmitted through the respective threshold comparators 208 216 However it will be recognized that with appropriate modifications to com parators 208 216 and or gating circuit 212 any other point present on both REF and RX pulses 218 232 may be used to represent the arrival times of the pulses Microprocessor 64 is connected to set the select lines 294 296 into multiplexer MUX2 of timing logic 240 5 291 262 9 FIG 6 to control sending of calibration pulses TMIN TMAX to interpolation circuits 246 248 Generation of the calibration pulses by timing logic 242 is initiated at least once during each measurement cycle upon opera tion of the trigger by a user Preferably the self calibra tion cycle is performed a plurality of times perhaps 8 or more per measurement cycle Microprocessor 64 is also connected to reset all the logic elements in timing analy sis circuitry as necessary at the start of each measure ment and between production of the TMIN TMAX calibration pulses and the REF and RX interpolation pulses _Ina preferred embodiment each measurement cycle comprises the firing of a plurality of laser pulses at a preset interval which is significantly long
40. on from larger to smaller and smaller to larger to thereby focus said adjustable time window to distinguish a detector signal resulting from laser pulse light returned from said chosen target from a false detector signal resulting from other causes 10 The survey device of claim 1 wherein said laser rangefinder system includes a laser pulse generator connected to receive high voltage from said power source reference pulse means for generating an REF refer ence pulse representative of the time of firing of said laser pulse light detection means for receiving and detecting light reflected from said target and in response producing said RX pulse and timing analysis circuitry connected to receive said RX pulse and said REF pulse having a clock which produces a clock signal comprising periodic pulses separated by a known time interval and operable to produce said count data relating to the elapsed time between said REF and RX pulses wherein said count data comprise a whole number of said periodic pulses occurring between said REF and said RX pulses plus calibrated REF and RX interpolated values reflective of the fractional 5 291 262 19 portions of the respective clock periods during which said REF and RX pulses are received and wherein said microcontroller is further configured to read said calibration count values and to calculate said time of flight from said calibration count val ues said REF and RX count data
41. onverted to voltages that are proportional to the width of the pulses and sent to an A D converter This is in contrast to the embodiment of FIGS 2 and 4A in which the REF and RX interpo lation pulses are converted to stretched pulses and counted by counters 250 252 Otherwise the routing of the REF and RX interpolation pulses and the self cali bration pulses TMIN TMAX through the charge pump interpolation circuits 700 702 FIG 7 is the same as for the pulse stretcher interpolation circuits 246 248 FIG 2 The computations by microcontroller 60 are also the same as for the embodiment of FIG 2 The charge pump embodiment is preferred because it offers a much greater expansion factor up to 1000 fold expansion or more as compared to 150 fold for the pulse stretcher of FIG 4A In the embodiment of FIG 4B switch 51 is set to divert the current from constant current source 402 to ground Instead of a diode and a current sink a second switch CS2 is connected to the other position of switch 81 Switch 52 is closed so that capacitor 460 is dis charged and therefore the output voltage of buffer 462 is zero Before timing logic 240 sends a REF pulse 218 or an RX pulse 232 the logic reset signal received at input 464 is set inactive which opens switch 52 Upon receipt of a REF pulse or RX pulse from timing logic 240 switch S1 goes to the opposite position and sends current 11 to charge the capacitor 460 for the duration of the pul
42. or permanent storage of instru ment parameters look up tables and the like tempo rary storage of data readings made by the survey sys tem and a volatile working memory for initialization numerical manipulations and the like A working embodiment of rangefinding subsystem 30 is depicted in greater detail in FIG 2 In this embodi ment the laser pulse generator takes the form of a laser diode 200 having an operably connected driver while the light detector is a silicon avalanche photodiode detector 202 abbreviated hereinafter as APD 202 High voltage power supply 100 supplies power to laser diode 200 and APD 202 detector 104 via respective linear regulators 201 203 Regulator 201 controls the firing voltage of laser diode 200 and regulator 203 con trols the bias voltage applied to APD 202 Both regula tors 201 203 are connected via a D A converter 205 to microprocessor 64 which controls them to provide the appropriate respective voltages The firing voltage is adjusted so that the laser diode outputs the desired optical power The bias voltage is adjusted so that APD 202 is operated at the desired sensitivity APD 202 produces a signal current in response to the receipt of light passing through filter 112 This signal current is passed through amplification means 204 to be amplified and filtered to reject slowly varying interfer ence signals The amplified detector signal is then sent to a threshold comparator 208 If the amplifie
43. rolytic model selected here Also most fluid type sensors will have sensitivity and dynamics which are especially suited to a hand held 20 25 30 40 45 65 6 device However for a hand held survey device it is desirable that vertical angle sensor 40 be very compact Also the vertical angle sensor desirably has high resolu tion At present the electrolytic type tilt sensor selected appears to best meet these considerations Desirably the electrolytic tilt sensor has an associ ated temperature sensor 42 This is because the inclina tion signal produced by an electrolytic sensor is highly variable with variation in temperature Temperature sensor 42 communicates with microcontroller 60 which uses the temperature reading in conjunction with a look up table stored in memory 70 and other means for correcting the output of the electrolytic sensor Microcontroller 60 is further configured to compute the height of a remote target from a pair of inclination readings made respectively from the top and bottom of the target plus the distance to the target acquired via laser rangefinder 30 Magnetic compass 50 is here selected to be a mag netic fluxgate compass module model C100 commer cially available from KVH Industries Inc Middle town R I It is connected to provide a compass data signal to microprocessor 60 essentially as directed by the manufacturer C100 Electronic Compass Module User s Manual pub KVH Industr
44. s of the respective clock intervals at which the rising edge of the reference pulse and the rising edge of the RX pulse occur Each of interpolation circuits 246 248 takes an input pulse from the timing logic and generates an output pulse of longer duration Desirably the output pulse has been expanded by a factor of at least about 100 to 150 fold over the input pulse Interpolation circuit circuits 246 248 should be constructed such that the variation of duration of the output pulse is as nearly in exact propor tion to the variation of duration of the input pulse as possible The expanded output pulse is then sent to start interpolation counter 250 and end interpolation counter 252 providing them with a count reflective of the frac tional portions Interpolation circuits 246 248 may be constructed in various ways to accomplish the general purpose of accurately determining the precise fractional times of the clock period at which the REF and RX pulses ar rive Interpolation circuit 246 receives REF interpola tion pulse 400 from timing logic 240 while interpolation circuit 248 receives RX interpolation pulse 490 see FIG 6 FIG 4A depicts one embodiment of interpolation circuits which is a pulse stretching circuit The pulse stretching circuit is depicted in general functional form various resistors and like minor components are not shown as selection of the position and values of such components will be apparent to those skilled i
45. se After the pulse has passed switch 51 diverts current 11 back to ground Since the current 11 is effectively constant during the pulse the resulting voltage charged across capacitor 460 during the pulse is proportional to the width of the pulse The voltage across capacitor 460 is buffered by buffer 462 and sent to an A D converter see FIG 7 where it is converted to an integer value FIG 7 depicts an alternate embodiment of the laser rangefinder 30 having certain changes in timing analy sis circuitry 114 necessitated by the substitution of REF and RX charge pump interpolators 700 702 configured as in FIG 4B for the interpolation circuits 246 248 of FIG 2 In particular the interpolation counters 250 252 of FIG 2 are replaced by an A D converter 704 which receives the output from charge pump interpola tors 700 702 Also charge pump interpolators 700 702 do not require an input from clock 242 A D converter 234 which received the pulse width signal 233 from gating circuit 212 and the temperature signals from temperature sensor 270 is eliminated and the noted elements now are connected to A D converter 704 5 291 262 15 In another embodiment microcontroller 60 is further configured to determine the velocity of a moving target relative to a fixed observer or alternatively the veloc ity of a user relative to a fixed object In this embodi ment upon activation of trigger 24 microcontroller 60 causes laser pulse g
46. ses arrived The self calibration pulses com prise a pair of pulses referred to for simplicity as TMIN and TMAX which differ by a known integral number of clock periods with neither TMIN nor TMAX being zero Together TMIN and TMAX define an expanded interpolation interval within which the fractional por tions of the RX and REF arrival times are interpolated This self calibrating interpolation provides greatly en hanced resolution and accuracy of distance measure ments based on elapsed time Third the laser rangefinder has a first collimator which directs a major portion of an outgoing laser pulse toward the selected target and a second collimator which redirects a minor portion of the laser pulse to produce a timing reference signal In one embodiment the minor portion of the laser pulse is sent to a second light detector separate from a first light detector here embodied as a silicon avalanche photodiode detector or APD which focusses and receives reflected laser light Alternatively the minor portion of the laser pulse is sent to the same detector which detects the returned laser light The microcontroller is constructed to direct a user s operation of the survey system according to various modes which include one or more of the following determination of range distance determination of loca tion coordinates of a target determination of the height and or width of a target object In an embodiment for use in forestry
47. standard trigonomet ric methods from the horizontal distance to the tree the inclination the vertical angle to the base of the tree the inclination at the point where the tree s diame ter is to be determined The microcontroller may further be configured to compute a conic projection useful to locate the height of the point on a tree where the diameter reaches the smallest usable diameter The conic projection may be computed from the horizontal distance the inclination to the base of the tree and selected width angles for the two points on the tree From these data the taper of the tree be computed and the diameter vs tree height projected until a desired minimum tree diameter is reached Or the instrument could be adapted by appropriate configuration of the microcontroller to be used in orien teering and searching A user could define her location relative to a visible remote object For example a user might walk to location away from a remote target ob ject determine her distance and compass direction from that object alter her course to travel on another course and recheck the new course by again determining her distance and compass heading from the target object Or the user could compare the distance and compass heading information for two or more remote targets and determine a travel course relative to those targets These and many other uses will be apparent to one skilled in surveying and related navigationa
48. tails of these computations are dis closed in a subsequent paragraph of this application Sighting scope 10 is provided for a user to select and aim the survey device at a selected target The sighting scope is operably associated with laser rangefinder 30 vertical angle sensor 40 and magnetic compass 50 such that when a user sights on target 90 with the sighting scope the laser pulse generator 102 light detector 104 and magnetic compass 50 are simultaneously aimed at the target and vertical angle sensor 40 outputs a signal reflective of the vertical angle to the target When the survey device is aimed at a target 90 the user then operates trigger 24 to initiate functioning of the survey device in a preselected mode Trigger 24 is communicatively connected to send a trigger signal to microprocessor 64 In response to receipt of the trigger signal microcontroller 60 initiates and supervises the performance of one or a series of operations by the 5 291 262 5 survey device according to which of a variety of oper ating modes has been selected In a highly preferred embodiment sighting scope 10 includes means for measuring the apparent width of target 90 In one embodiment the width measuring means is a reticle arranged in sighting scope 10 The user aims sighting scope 10 at the target 90 determines the number of reticle markings between the left and right edges of the target and enters these into mi crocontroller 60 by means of
49. teratively adjust said adjust able time window from larger to smaller and smaller to larger to optimize the duration and timing of said ad justable time window to more accurately distinguish a detector signal which is a true RX signal from a false detector signal resulting from other causes 21 The survey device of claim 19 further including a sighting scope attached to said housing having appar 5 291 262 21 ent width measuring means for measuring the apparent width of a target and operably associated with said laser rangefinder said vertical angle sensor and said mag netic compass such that when a user sights on a target with said sighting scope said laser rangefinder and said magnetic compass are simultaneously aimed at said 10 15 20 25 30 35 45 50 55 65 22 target and said vertical angle sensor outputs a signal reflective of the vertical angle to said target 22 The survey device of claim 21 wherein said con trol means is further configured to receive said apparent width reading and to compute from said apparent width reading and said distance an actual width of said target k
50. two cycles and TLASER varies between one and two cycles The variation in duration of output pulse 450 is pre cisely proportional to the variation in duration of the input pulse 400 Therefore TMAX REF minus TMIN REF represents exactly one clock period of clock 242 Similarly TLASER REF minus TMIN REF represents the fractional portion of the clock per iod following arrival of REF pulse 218 Therefore TLASER REF TMIN REF REF TMIN REF is a numeric fraction representing the REF fractional portion Since this fraction is a ratio of two numbers which were expanded in the same proportion the exact value of the pulse expansion is not important Also errors in determination of this fractional time due to 25 40 45 65 14 component tolerances or drift in the pulse stretcher circuit are substantially eliminated Similarly TMAX RX TLASER RX TMAX RX TMIN RX is the RX fractional portion The total number of elapsed clock periods between the REF and RX pulses is then equal to the sum of the two fractions above plus the number of whole clock periods An alternate and preferred embodiment of an interpo lation circuit is shown in FIG 4B This circuit operates generally as a charge pump but still performs essen tially the same interpolation function as the pulse stretching circuit depicted in FIG 4A In the charge pump embodiment of FIGS 4B and 7 the REF and RX interpolation pulses are c
51. ve flip flop 332 responds to the falling edge of the detector pulse 206 The NOT Q output of flip flop 332 is then sent to and gate 330 along with RX pulse 232 which is the signal from the Q output of flip flop 314 The output of and gate 330 is the RX pulse width signal 233 that is sent to a pulse width circuit 235 for determining its width The use of the second flip flop 332 ensures that only one pulse is passed to the pulse width circuit for each RX pulse 232 Pulse width signal 233 is processed by a pulse width measuring circuit 235 sent to A D converter 234 and 5 291 262 11 then to microcontroller 60 Microcontroller 60 com pares the pulse width value of signal 233 to a lookup table stored in EEPROM 284 to find the appropriate pulse width correction factor to correct for variations in the strength of the reflected laser light received by APD 202 That is detector efficiency is non linear and high power signals tend to saturate the detector and or the amplification circuitry causing a shift in the time at which the leading edge of the RX pulse exceeds the threshold of comparator 208 Most light detectors and amplifiers practicable for such apparatuses do have non linear detection efficiency The pulse width correc tion takes the form of an additive correction to the distance determined from the time of flight measure ment The RX pulse width measuring circuit 235 uses a charge pump circuit essentially identical to that shown
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