Compact laser-based distance measuring apparatus

A light-weight, hand-held range finding apparatus of the present invention includes signal emitting circuitry and lens for emitting signals, and signal receiving circuitry and lens for receiving reflected signals, which are positioned within a chamber of a housing. The housing includes an upper section to which a sighting device is attached, a front end through which the emitted signals are emitted and the reflected signals are received, a back panel having a display device attached to said housing for displaying operational selections and range findings. An actuator is mounted adjacent the upper section and is operably connected to the signal emitting circuitry. The actuator is used to select desired operational selections displayed on the display device and actuating the signal emitting circuitry.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to range finding equipment, especially to 
laser-based range finding and distance measuring apparatus. More 
particularly, this invention relates to a measuring apparatus which may be 
held, aimed, and operated with one hand by a user to determine measurable 
parameters such as distance, elevation, inclination and range. This 
invention also relates to an electronic filtering feature in a laser-based 
range finding apparatus, wherein the electronic filter, when enabled by 
the user, rejects spurious reflected signals from the ranging calculation. 
2. Description of the Related Art 
A laser-based distance and ranging measuring device is described in U.S. 
Pat. No. 5,359,404 entitled "Laser-based Speed Measuring Device," the 
disclosure of which applicants expressly incorporate by reference herein. 
Other recently issued U.S. Patents relating to laser based measuring 
devices, assigned to the assignee of the present invention, include U.S. 
Pat. Nos. 5,612,779 and 5,652,651, the disclosures of which applicants 
also expressly incorporate by reference herein. 
Distances, as measured in a laser-based ranging device, are generally 
determined by calculating the time of flight of a laser pulse to and from 
a desired target. An elapsed time measurement is calculated based on, 
among other things, a clock signal, a counter triggered on by transmission 
of a laser pulse and triggered off by the receipt of a reflected pulse 
signal from the target. The reflected pulse signal is detected by the 
ranging device using a light sensing receiver. The distance may then be 
determined based on the clock pulse width using the number of pulses 
counted between transmission and reception or by using methods such as the 
precision timing technique described in the above identified patents. 
The accuracy of the desired ranging measurement in a laser range finding 
device can be compromised if reflective obstacles exist between the 
ranging device and the desired target. For instance, if the ranging device 
is being used to measure an outdoor distance between the ranging device 
and a wall, it is possible that the ranging device may detect reflected 
pulses from objects in the line of sight, such as reflections off of 
shrubbery and trees, etc. In prior ranging devices, it is understood that 
optical filters have been used to distinguish between noise signals and 
the desired signal reflected from the target. However, these filters are 
somewhat cumbersome to carry, install and remove. What is needed is a 
laser range finding device having a built in feature whereby the user of 
the device in the field can simply exclude such unwanted reflections. For 
example, what is needed is a means to selectively adjust the sensitivity 
of the receiver of the device, so that when the user attempts to measure a 
distance or range to an object where other reflective objects exist 
between and in the line of sight of the object and the ranging device, the 
ranging device will ignore the spurious reflections from the non-target 
objects. 
In addition, because prior art devices can weight six pounds or more, such 
devices are preferably tripod mounted. An operator typically needs both 
hands to both hold and operate a conventional range finding device. When 
the device is operated while hand held, the operator soon fatigues, 
especially when the unit is operated at arms length. Thus, there is a 
continuing need for range finding and distance determining equipment which 
can be used without causing fatigue to the operator and which can be 
operated by a user in the field having only one free hand to hold, aim and 
operate the apparatus. 
Thus there remains a need for a distance measuring apparatus which includes 
a simply selectable user actuated capability to discriminate between true 
target reflections and spurious reflected signals, and such equipment 
which may be used with one hand and without the necessity for the operator 
to continually need to obtain operational instructions from a manual or 
instruction book. It is against this background that the significant 
improvements and advancement of the present invention have taken place in 
the field of laser based distance measuring apparatuses. 
SUMMARY OF THE INVENTION 
A primary object of the invention is to provide a distance measuring 
apparatus which is light weight and designed to be held, aimed, and 
operated by an individual using only one hand. 
It is another object of the invention to provide a hand held distance 
measuring apparatus which my be equally operated with either a user's 
right or left hand. 
It is a still further object of the invention to provide a hand held 
distance measuring apparatus which includes a user selectable filtering 
mode which alters the receive circuitry sensitivity for positively 
discriminating between spurious reflections and target reflections. 
A light-weight, hand-held range finding apparatus in accordance with the 
present invention includes signal emitting circuitry and lens for emitting 
and transmitting laser pulse signals, and signal receiving circuitry and 
lens for receiving reflected signals, and a signal processor, all of which 
are positioned within a chamber of a compact housing. The housing includes 
an upper section to which a sighting device is attached, a front panel 
through which the laser pulses are transmitted and the reflected signals 
are received, a back panel having a display device attached thereto for 
displaying operational mode selections and measured range values. An 
actuator comprising a pair of preferably identical control panels or 
keypads is incorporated into or mounted on the upper section of the 
housing such that one keypad, the primary keypad, is actuatable by the 
fingers of a user's hand while that hand is holding and aiming the 
apparatus. The other keypad may be configured to be the primary keypad 
when the user's other hand is used to hold and aim the apparatus. This 
actuator is operably connected to the signal emitting circuitry and 
processor control. The actuator is used to select desired operational 
modes and data selections displayed on the display device and to trigger 
the signal emitting circuitry to transmit laser pulse signals. Either 
keypad may be configured by the user as the primary keypad, depending on 
whether the user is right or left handed. The primary keypad is the only 
keypad necessary to be operated when taking any of the possible 
measurements with the apparatus. The secondary keypad provides support and 
calibration command functions that are not utilized while taking 
measurements. 
The apparatus in accordance with the present invention also includes an 
electronic filter mode, engagable via command from the keypads, which can 
reject spurious reflected signals from non-target objects, when engaged. 
The electronic filter mode of the present invention is designed for use 
with high reflectivity objects such as a mirror, and is ideally suited for 
use where the user mounts a reflector on the target so that the desired 
reflected signal from the target is known to have a substantially higher 
amplitude than the spurious reflections from non-target objects. 
The method of the present invention includes the steps of providing a range 
finding apparatus having a housing defining an internal chamber containing 
signal emitting circuitry for emitting signals and signal receiving 
circuitry for receiving reflected signals, and a sighting device mounted 
to the housing, holding the housing in one hand, making operational 
selections of one of a plurality of determinations to be made by the 
apparatus with the same hand, and actuating the signal emitting circuitry 
with the same hand while continuing to hold the apparatus. 
In the preferred embodiment, the operational selections made by the 
operator, i.e., the user, are displayed on a display screen mounted on the 
back panel of the apparatus, and the method further includes the steps of 
scrolling through a plurality of the display screens by actuating a screen 
display controller of the apparatus via the keypad with a finger of the 
same hand, while continuing to hold and aim the apparatus with that hand. 
The present invention is light weight, on the order of a couple of pounds, 
and is designed to be held and operated with one hand. Because of its 
light weight, and because the apparatus does not need to be held at arm's 
length, but rather is held close to the user's face, it can be operated 
for an extended time without causing undue operator fatigue. In addition, 
the apparatus of the present invention can be operated by a single user 
having only one hand free, either the right or the left, to operate the 
apparatus. The inclusion of the display with a plurality of selectable 
operational mode and option indicators in the preferred embodiment of the 
present invention obviates the need for keeping a manual or instruction 
book on hand when using the apparatus. Finally, the range finding 
apparatus of the present invention can selectably filter out spurious 
signals which otherwise might lead to inaccurate distance determinations. 
Other objects, features and advantages of the present invention will become 
apparent from a reading of the following detailed description when taken 
in conjunction with the accompanying drawing wherein a particular 
embodiment of the invention is disclosed as an illustrative example.

DETAILED DESCRIPTION OF THE INVENTION 
A preferred embodiment of a compact laser-based distance-based measuring 
apparatus 10 of the present invention is shown in FIGS. 1-9. Although the 
apparatus 10 is referred to herein as a range finding apparatus, it should 
be understood that the term range finding apparatus is intended to include 
any device incorporating any combination of conventional 
surveying/measuring functions including, for example, range, azimuth, 
inclination, coordinate, height, and remote diameter or width 
determinations. 
The range finding apparatus 10 includes a compact housing 12 to which is 
mounted a sighting device 14. The housing 12 defines an internal chamber 
(not shown) in which signal emitting circuitry (not shown), a signal 
emitting lens 16, signal receiving circuitry (not shown) and a receiving 
lens 18 for receiving reflected signals, are positioned. As is shown in 
FIG. 1, the range finding apparatus 10 of the preferred embodiment is 
specially adapted to be held by a single hand 20 of an operator secured 
and steadied by the thumb 22 of the hand 20, and operatively controlled by 
movements of the fingers of the same hand 20. 
More particularly, the housing 12 of the preferred embodiment includes 
upper and lower sections 24 and 26, right and left side sections 28 and 
30, and front and back panels 32 and 34. The upper, lower, left and right 
side sections 24, 26, 28, and 30 are preferably portions of a one piece 
extruded aluminum tubular housing body. The front and back panels 32 and 
34 are conventionally fastened to the housing body to close and provide a 
moisture barrier for the housing 10. The upper section 24 includes an apex 
portion 36 to which is mounted the sighting device 14, preferably a red 
dot sighting scope. The sighting device 14 includes a viewing end 38 
adjacent the back panel 34. Positioned on the upper section 24 adjacent 
the right side section 28 is a right control panel 40 containing first set 
of control buttons 42a, 42b and 42c. Positioned on the upper section 24 
adjacent the left side section 30 is a left control panel 44 containing a 
second set of control buttons 46a, 46b and 46c. The control panels 40 and 
44 and the associated control buttons are preferably identical to each 
other. 
Mounted on the right side section 28 is a thumb rest 48 having a base 
portion 50, an outwardly projecting flange 51 extending from the base 
portion 50 and a strap retaining plate 53 fastened to the base portion 50 
via fastener 54. The retaining plate 53 has a slot 52 therethrough. The 
fastener screw 54 mounted through the retaining plate 53 and the base 
portion 50 attaches the thumb rest 48 to the right side section 28 of the 
housing 12 via a threaded bore 64 (not visible in the right side section 
28 as illustrated). 
The slot 52 is adapted to receive one end of an elongated strap 56. The 
opposing end of the strap 56 is received in a slot 58 formed in an anchor 
plate 60, which is mounted to the housing 12 by a fastener screw 62 in 
another threaded bore 64 in the right side section 28 adjacent the lower 
section 26, at a height which is lower than the attachment position of the 
thumb rest 48. 
Formed in the left side section 30 is a pair of threaded apertures 64 which 
are spaced directly opposite to the threaded bores or apertures 64 in the 
right side section 28. These apertures 64 are adapted to receive a 
left-handed thumb rest, (a mirror image of the thumb rest 48 shown in the 
Figures), the strap 56 and the anchor plate 60 so that a left handed user 
may operate the apparatus with only one hand. This left handed 
configuration is shown in phantom dashed lines in FIG. 7 and may be simply 
visualized by the reader by reversing the side location of the strap 56, 
the anchor plate 60, and installing a left thumb rest. 
The apertures 64 on the side section 28 or 30 not used to fasten the strap 
56 to the housing 12 may be used to mount a tripod mounting bracket 66 
(FIGS. 11 and 12), or attach a belt attachment clip 68 for mounting the 
range finding apparatus 10 on the belt of the operator when the apparatus 
is not in use. 
The front panel 32 is a generally flat aluminum plate member which supports 
the transmitting and receiving lenses 16 and 18. The front panel 32 is 
fastened to the housing 12 with four screws 71. The front panel 32 of the 
apparatus 10 has a signal emitting aperture 69 which is covered by the 
lens 16. Also formed in the front panel 32 is a signal receiving aperture 
70 which is covered by the receiving lens 18. 
An LCD display panel 72 is mounted to the back panel 34. As is described in 
further detail below, when the apparatus 10 is actuated, the display panel 
72 displays a series of menus options containing instructions and 
selections for the operator, as well as displaying indications of 
measurements and determinations made by the apparatus 10. Beneath the 
display panel 72 on the back panel 34 is a battery cap 74 threaded into 
corresponding threads in a bore (not shown) through the back panel 34 
which circumscribes a cylindrical compartment (not shown) extending into 
the internal chamber (not shown). The cylindrical compartment holds a 
power supply, such as a pair of AA batteries (not shown) mounted end to 
end, which provides power to the apparatus 10. Adjacent the battery cap 74 
on the back panel 34 is a connector 76, such as preferably an RS232 serial 
output port, mounted through another bore through the back panel 34 
through which data can be downloaded from the apparatus 10 via an 
appropriate cable, to a remote device such as a computer, a data-logger, 
or printer. 
Also formed in the back panel 34 above the display screen 72 is an aperture 
78 which surrounds a stainless steel grill of a diaphragm speaker 80. The 
speaker 80 is adapted to emit a predetermined tone from a plurality of 
predetermined tones, each of which corresponds to a predetermined 
frequency of vibration of the speaker 80. During operation of the 
apparatus 10, the speaker 80 emits a predetermined audible tone in 
response to certain events, such as target acquisition by the receiver 
circuitry. A different audible tone may be provided for different events 
so that the user can tell, without actually looking at the display panel 
72, what mode of operation the apparatus 10 is in or what measuring 
function is anticipated as being performed, such as direct distance or 
horizontal distance, or inclination measurement. 
In the preferred embodiment of the apparatus 10, the housing 12 is a 
one-piece aluminum housing. The end panels 32 and 34 are gasketed to the 
housing 12 to make the structure water proof. The sides 28 and 30 have a 
non-slip grip surface. The aluminum construction contributes to the light 
weight of the apparatus 10, which preferably weighs at most approximately 
2.2 pounds. The apparatus 10 is compact in size, have preferred dimensions 
of approximately 6 inches from front panel to back panel 34, approximately 
5 inches in height from the lower section to the top of the sighting 
device, and approximately 2.5 inches in width measured across the front 
panel 32 from right side section 28 to left side section 30. 
The upper section 24 of the housing 12 is divided into three straight, 
axially extending portions: the apex portion 36, left control panel 
portion 44 and right control panel portion 40. These portions are joined 
together to form an overall curved upper section shape which has an 
overall larger radius of curvature than the lower section. The lower 
section 26 is rounded, with has a radius of curvature optimized to allow 
the lower section of the apparatus 10 to comfortably fit in the hand of 
the typical user. The upper section right and left control panels 44 and 
40, the apex portion 36 of the upper section 24, and the right and left 
side sections 28 and 30 join together forming faceted surfaces between 
their respective intersecting edges. 
Preferably, the apparatus 10 has a maximum range of at least 500 meters, a 
range resolution of up to 0.01 meters, and an inclination limit of plus or 
minus 180 degrees with an inclination accuracy of about .+-.0.1 degrees. 
In accordance with its most preferred embodiment, the range finding 
apparatus 10 of the present invention also includes a user selectable 
electronic filter which can reject spurious reflected signals from 
non-target objects. The electronic filter of the present invention is 
designed for use with high reflectivity objects, and is ideally suited for 
use where the user mounts a reflector on the target so that the desired 
reflected signal from the target is known to have a substantially higher 
amplitude than the spurious reflections from non-target objects. 
More particularly, the user of the ranging device 10 of the present 
invention can be visually prompted using the display 72 as to enable or 
disable the electronic filter. Based on the user input received through 
the user control of the ranging device 10, the processor enables or 
disables the electronic filter in the received section of the ranging 
device 10. 
In accordance with the present invention, two general modes of operation 
are disclosed herein. In a high-reflectivity or "filter-on" mode, the 
laser-based ranging device 10 rejects spurious reflections from non-target 
objects through the use of either an adjustment of sensitivity or gain of 
the receive section of the ranging device 10, or by raising the signal 
threshold point to where the processor recognizes a valid reflected signal 
received. In the high-reflectivity mode, the present invention can utilize 
any of these filtering methods in any combination which is preferably 
determined by software. A reflector can be optionally mounted on the 
desired target to ensure that the reflected signal from the desired target 
is of sufficient power to be detected and processed by the receive section 
of the ranging device operating in high-reflectivity mode. In a 
non-high-reflectivity mode, the laser based ranging device 10 of the 
present invention disables the electronic filter mode thereby placing the 
ranging device in a normal mode of operation. 
In operation, when the ranging device is placed in high-reflectivity mode 
by the user, the processor activates one or more control lines from the 
processor to the circuits in the receive section of the ranging device. 
Specifically, these control lines initiate a decrease in the receive diode 
sensitivity by changing the diode bias voltage and/or by a decrease in 
gain of the receiver amplifier which decreases the sensitivity of the 
receive section. Additionally, the processor can increase the minimum 
required signal threshold level for processing any received signal pulse. 
In this manner, only reflected signals with sufficient magnitude will be 
processed, thereby increasing the likelihood that the reflected pulse used 
in the ranging calculation corresponds to the reflected pulse from the 
desired target. Further, the software can include a pre-set lookup limit 
to fine tune the level of acceptable reflected pulses. 
FIG. 10 illustrates a block diagram of one embodiment of the apparatus 10 
of the present invention. The laser-based range finder 10 has a 
microprocessor 112 coupled to the display 72, the control keypads 40 and 
44 for user input, a precision timing circuit 114, a laser pulse receiver 
116 and a laser pulse transmitter 118. The microprocessor 112 is also 
coupled to a power supply 120, a memory 122 and serial communications port 
connector 76. 
The laser pulse receiver 116 includes a laser diode 124 connected diode 
operating circuit 126 which is in turn connected to a receiver amplifier 
128 and then to a comparator 130. The comparator 130 in turn provides its 
output to the precision timing circuit 114. The comparator 130 receives a 
threshold control signal via line 132 from the microprocessor 112. The 
receiver amplifier 128 receives a gain control signal also from the 
microprocessor 112 via line 134. The receiver diode operating circuit 126 
receives a diode bias control signal via line 137 from a receiver 
regulator 136 which in turn receives a control signal via line 138 from 
the microprocessor 112. 
The laser pulse transmitter 118 includes a laser transmit diode 140 and 
receives a fire command via line 142 from the processor 112. The laser 
pulse transmitter 118 sends a timing reference signal via line 144 to the 
precision timing circuit 114 and also receives a transmitter bias control 
signal via line 146 from a transmit regulator 148. The transmit regulator 
148 is in turn controlled by the microprocessor 112 via line 150. 
The filter function of the present invention is introduced in the high 
reflectivity mode selected by the user from a visual prompt on display 72. 
The filter function in accordance with the present invention is 
implemented via software and involves one or more of four elements. The 
first element is the receiver bias control provided via line 137 to the 
receive diode circuit 126. The bias on this line may be increased or 
decreased by the microprocessor to change the sensitivity of the receiver 
diode 124 directly. For example, when using an APD detector, its gain can 
be altered simply by changing the diode operating bias. However, if a pin 
diode is being used, another method is required as the gain is fixed. The 
second element is the amplifier gain control signal provided on line 134 
to the amplifier 128 from the microprocessor 112. Simply adjusting the 
amplifier gain for the signals fed into the comparator 130 will change the 
overall sensitivity of the receiver 116. The third element is provided by 
the threshold control signal on line 132 from the microprocessor 112. The 
threshold below which amplified reflection pulse signals will be stopped 
is changed by the voltage provided on line 132. Changing this threshold 
voltage on line 132 will change the overall sensitivity of the receiver 
Finally, the software has the ability of accepting and processing only 
those received pulses which exceed a predetermined signal threshold 
magnitude. The high reflectivity mode of operation may be programmed to 
utilize any one of these elements either alone or in any combination to 
provide an overall sensitivity change so as to only be responsive to high 
reflectivity signals. Conversely, when the user de-selects 
high-reflectivity mode, processor 112 disables the gain and/or threshold 
selection elements discussed above so that the settings of receiver 116 
gains and thresholds are restored to normal. 
Because the operation of the filtering of the present invention is under to 
control of processor 112, it is understood that each of the four disclosed 
methods of filtering could be implemented singly or in any combination by 
a software routine operating within processor 112. 
The calibration for the range finding device 10 may be modified between the 
filtered and unfiltered modes. Calibration is necessary to compensate for 
the return signal power variations, which affect the determined distance 
(range) values. The surface of the desired target affects the pulse width 
of the return signal, which in turn, results in a timing difference at the 
leading edge of the pulse where the counter is initiated, which further 
affects the calculated flight time, and thus distance. Since the filter on 
mode or high reflectivity on mode adjusts some of the circuit 
characteristics as described above, the calibration values to apply to the 
filtered return signals may be different than the calibration values to be 
used for the filter off mode. To generate the calibration table for either 
mode (filter on or filter off), the device is tested by targeting the 
signal at a prism at a fixed distance to get a wide range of return signal 
power variance or, the return signal power variance can be simulated with 
filters. This testing generates the calibration table values which are 
then compared to actual distance values inputted by the user. 
Referring back now to FIGS. 5 and 7, the keypads 44 and 40 each have three 
buttons. One panel is designated via software as the primary panel. The 
other is the secondary panel. The primary panel is the only panel used 
during measurement operations. The secondary panel is only used for 
control editing, calibration functions, and power on/off operations of the 
sighting device and the display. 
The button nearest the rear panel (42a, 46a) is termed the "fire" button. 
The middle button (42b, 46b) typically scrolls forward through the 
operating modes or options. The front button (42c, 46c) scrolls the 
operator backwards through the various available modes and/or options. For 
example, different measurement modes may include slope distance, height, 
horizontal distance, inclination, vertical distance, and multiple 
measurements. Selectable options may include measurement gating, range 
offsets, pivot offsets, and filtering. The current mode or option is 
indicated on the display 72 as the buttons are depressed. In addition, the 
display preferably indicates such conditions as battery, laser firing, and 
indications for which measurements the instrument is set to take, such as 
a base measurement when in the height measurement mode or a first 
measurement during tilt calibration. 
Each keypad 44 or 40 may be configured as the primary keypad with the other 
being configured as a secondary keypad, depending on whether the user is 
right or left handed. This is done via software in processor 112. The 
primary keypad is configured by simply toggling one of the system software 
system settings via the current primary control panel Fire, Back and 
Forward buttons. 
Because the three buttons of the primary control panel 44 or 40 and the 
three buttons of the secondary control panel select and/or scroll through 
options and modes, and these modes and options are visually indicated on 
the display 72, the user need not continually refer to an instruction 
manual to operate the apparatus 10. The user can simply and conveniently 
select which mode and option to utilize, take the indicated measurements 
with one hand, and record or download the measured data. 
The present invention may be practiced otherwise than as specifically 
described above. Many changes, alternatives, variations, and equivalents 
to the various structures shown and described will be apparent to one 
skilled in the art. For example, the two apertures 16 and 18 in the front 
panel may be combined in a single aperture with the transmitted and 
reflected signals traveling the same path. The control panels or keypads 
40 and 44 may be arranged with four buttons rather than three as shown in 
the figures. The buttons may also be arranged other than in a straight 
line as shown. For example, they may be arranged along a curve 
approximating a normal reach of each of three or the four fingers on one's 
hand. Accordingly, the present invention is not intended to be limited to 
the particular embodiments illustrated but is intended to cover all such 
alternatives, modifications, and equivalents as may be included within the 
spirit and broad scope of the invention as defined by the following 
claims. All patents and patent applications referred to herein are hereby 
incorporated by reference in their entirety.