Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~L~49634
1 The present invention relates to equipment capable
of measuring linear, angular, or combined linear and angular dis-
placement. In particular, it relates to such devices ~1hich are
operated on a digital basis and wherein the magnitude of such dis-
placement is directly displayed or recorded in a prearranged
digital code through suitable read-out and output means. The need
for such systems, and in particular for such systems wherein the
read-out is carried out without possibility of ambiguity and in a
reliable manner, is very wide. A particular field of application
to be discussed herein is the field of aerial and photogrammetry
and of the taking of forest ~nventories. The system is, of course,
in no respect limited to these applications.
As regards the taking of forest inventories, it has
been found that the efficiency of such inventories can be increased ~-
by minimizing the tedious and expensive ground work required to
correlate photo and ground estimates. Current research, therefore,
is aimed at developing methods which will increase the reliability
of photogrammetric measurements and estimates of tree characteris-
tics. One technique which is becoming established is forest sampling
by air photography from low altitudes (typically at scales betwéen
1:1000 and 1:3000), which provides sufficient detail for accurate
photo measurements of tree height and tree-crown diameters which
permit the estimation of tree diameter, volume and other statistics.
But the conversion of these measurements to actual values requires
exact knowledge of the photographic scale. Conventional methods
based on ground controls are inefficient.
A radar altimeter has been developed which is capable
of measuring distance between aircraft and the ground with a pre-
cision of ~ 1%, regardless of intervening vegetation. This con-
tinuous measurement is recorded on each photographic frame through-
. ,:
.
1109L9634
1 out the secondary optics of the camera. From -the aircraft-to-
ground distance and the focal leng-th of the camera, the true
dimensional relatlonship between the object and its image can be
computed, provided the camera was vertical at the time of the
exposure. Unfortunately, this is seldom the case and serious
errors can be introduced by tilt, for example, when using small ~ -
format (70 mm) cameras and lenses of long focal length, a longitudi-
nal tilt difference of only one degree between successive frames
might cause a base deformation and height error of more than 20%.
To overcome this difficulty, an airborne gyrostabilizer system can
be used to continuously measure and record aircraft pitch and roll
angles and the corresponding angles on the aerial camera which is
rigidly mounted to the airframe. The longitudinal and lateral tilt
angles measured at the gimbals of the gyroscope are recorded on each
photographic frame through the secondary optics of the camera.
- Thus, the angles at which each exposure was made are immediately
known. With the system of the present invention wherein a lack of ~;
arnbiguity in the read-out is accomplished even at very high resolu-
tion, the required degree of accuracy of the tree measurements men-
tioned above can readily be achieved.
The present invention can, of course, find application
also in conjunction with airborne gyrostabillzer systems wherein it
is merely required to furnish an indication of the longitudinal and
lateral tilt angles to the pilot. In this case, these angles are
not recorded by a camera, but are displayed directly for the pilot's
information.
The present invention comprises displacement measuring
apparatus for measuring displacement in a predetermined direction of
a first element relative to a second element. It comprises code
display means coupled to said first element, said code display means
... . . .
-
963~
1 ha~ing digital code markings representing predetermined units of
displacement, spaced at predetermined intervals from each other in
said predetermined direction. It further comprises control markings
on said code display means, said control markings being arranged in
predetermined posi-tions relative to said code markings. ~he in-
vention further comprises read-out means including at least one
code read-out means and one control read-out means for reading,
respectively, code markings and control markings passing in opera-
tive proximity thereto and furnishing corresponding data and con-
trol signals. The invention further comprises output circuitmeans connected to said read-out means for furnishing output signals
corresponding to sa~ data signals only upon receipt of said control
signals, whereby said output signals are furnished only when said
read-out means is in predetermined positions relative to said code
markings.
More specifically, when said code markings are arranged
side-by-side, each of said control markings are positioned relative
to said code markings in such a manner that said control markings
indicate the center of said code markings in said predetermined
direction. In this way, the output signals are furnished only when
the read-out means are substantially in the center of the code
markings in the displacement direction, thereby preventing ambiguities
which might occur when the read out means are in a position wherein
two code markings may be overlapped or wherein slight oscillations
might cause a change from one code marking to the next.
It should be noted that the term "center" in the
present application is used in a broad sense for indicating any po-
sition along said width of said code markings where no read-out
ambiguity can occur. It thus includes, but is not limited to, the
geometric center of the code markings in said predetermined position.
.,
104963~ ~
1 In a preferred embodiment of the present invention,
the output signals furnished at the occurrences of one control
signal are stored and continue to be displayed until receipt of
the next subsequent control signal.
The novel features which are considered as charac-
teristic for the invention are set forth in particular in the
appended claims. The invention itself, however, both as to its
construction and its method of operation, together with additional
objects and advantages thereof, will be best understood from the
following description of speci.fic emhodiments when read in connec-
tion with the accompanying drawing.
FIG. 1 shows the code display means of the present
invention mounted for measurement of angular displacement;
FIGS. 2a, 2b and 2c show preferred embodiments of code
display means including control markings;
FIG. 3 shows a block diagram of the overall system of
the present invention;
FIG. 4 (located on the same drawing page as FIG. 1)
is a schematic diagram of the code read-out means of the present in-
vention;
FIG. 5a is a schematic diagram of the control read-out
means of the present invention;
FIG. 5b shows ~aveforms at various points of the cir-
cuit of FIG. 5a;
FIG. 6 iS a schematic diagram showing a gyroscope with
digital tilt angle pickoffs;
FIG. 7 shows the arrangement for furnishing the
shutter signal utilized in FIG. 3; and
FIG. 8 (located on the same drawing page as FIG. 6)
shows the pulse sequences generated by the code and control read-
-5-
63~ ~
1 out means.
A preferred embodiment of the present invention will
now be described with reference to the drawings.
In FIG. 1, an arrangement for measuring angular-dis-
placement is shown. Shaft 1 rotates in direction a-a. Attached
to shaft 1 is an armature 2 which at its rim is fitted with the
code display means, here a perforated or otherwise encoded screen
3 suitably curved in a circular curve concentric with the axis of
shaft 1.
The embodiment shown in FIG. 1 is a photoelectric
embodiment, which is a preferred embodiment of the present inven-
tion. For this embodiment a light source, here a light-emitting
diode 4, is placed on one side of a screen and a photosensor, here -
phototransistor 5, is placed on the other side. As shaft 1 ro-
tates, the angular position of armaturs 2 changes accordingly and,
if the angular change is sufficient, the light beam emitted by
diode 4 will be interrupted, causing a change in the light impin~-
in~ upon phototransistor 5, thereby changing the output of said
phototransistor. Thus the angular rotation of the shaft is digni-
tized in a sequence of pulses which, in the simplest case may be
counted to constitute a measure of the total angular displacement.
- Arrangements using the single pulse line described
~ are known. However, the arrangement of FIG. 1 may utilize code
-~- .
display means according to the present invention such as show~ in
FIGS. 2a, 2b and 2c which differ from the above-described singl~
line arrangements in two respects. First, because in actual prac-
; tice a single pulse line is impractical, a multi-line code is used
as represented by lines D1-D4. This allows each displacement angle
to be represented by a predetermined code combination. Thus, if
a light source is used whose width in the direction in which the
--6--
- ' ' ' ' ' ' ' . . ' ' ~ ;
:. .. . .
~9gi3~
1 displacemen-t is to be measured is equal to the width of one digit
and whose length encompasses four lines and, if further, four
phototransistors are used arranged in a single vertical line, the
simultaneous read-out of all four phototransistors would result
in a digital count for every angular position. The total actual
digit count for the disk shown in fifteen and the resolution is the
angular displacement represented by the width of one digit. The
digit count may, of course, be extended by additional lines,
depending upon the total angular rotation to be measured and the
resolution requirements.
However, the above technique suffers from the draw-
back that it is virtually impossible to obtain a perfectly aligned
array of phototransistors or a perfectly aligned light source.
Any slight misalignment will, of course, produce ambiguity in the
read-out if the angle that is measured is close to the line sepa-
rating two digits. Further, of course, if the shaft rotates or
oscillates by very small angular amounts around the digit separa-
tion line, a superimposed display may occur which may completely
change the angular reading. For example, in the code display
shown in FIG. 2, oscillation between the values of 7 and 8 may
result in a read-out of 15.
To prevent the above-mentioned ambiguities and in-
accuracies, in accordance with the present invention a control
line marked K is added. This control line comprises a plurality
of control markings each of which has a predetermined position
relative to the code markings. It is the purpose of these code
markings to furnish control signals` after suitable processing,
which control signals allow the data signals resulting from the
read-out of the code markings to become effective only when the
read-out means (photosensors) are in a predetermined position
--7--
~ ~ .
.' , . '
~496i;~
1 relative to the code markings and more specifically are at the
center of such code markings where the term "center", as previ-
ously mentioned, includes, but is not limited to, the geometric
center. As will be described in detail below, the processing in-
cludes differentiation of the signals derived from the phototran-
sistors constituting control read-out means. The control signals
derived by such differentiation, of course, occur substantially
at the geometric center of each of the code markings for the em-
bodiments shown in FIGS. 2a, 2b and 2c.
It will be noted that FIGS. 2 and 2b show embodiments
of the code display means of the present lnvention used for measur-
ing angular rotation and FIG. 2c shows an embodiment of the code
display means for measuring of linear displacement, all three of
the code display means having additional control lines which pre-
vent ambiguity of the read-out mentioned above.
In the embodiments shown in FIGS. 2a, 2b and 2c, the
read-out means for the control line and code line are assumed to
be positioned in a straight line perpendicular to the direction
in which displacement is to be measured. The control markings
could of course be aligned with the code markings in the direction
of displacement if the control read-out means were displaced half ;~
the width of a code marking from the code read-out means. For the
purpose of the present invention, it is only important that the
control pulse is furnished when the code read-out means are cor-
rectly positioned relative to the code markings.
The overall system utilizing the code display means
described above will now be discussed with reference to FIG. 3.
Light and dark inputs are received at terminals Cl-C4 in dependence
on the code markings in lines Dl-D4, respectively, of FIG. 2. The
code read-out means each comprise a phototransistor which forms
3~ :
1 the input -to a circui-t such as shown in FIG. 4. The output of
each of the code read-out circuits is applied to the inverters
labelled 21-24, respectively. The data signals appearing at the
input and output of each of these inverters are applied to the J
and K inputs of flip-flops 31-34, respectively. By applying a
data signal (for example a "1") to the J input and its inverse
("0") simultaneously to the K input of any one flip-flop, a reli-
able setting of the flip-flop in accordance with the data signal
is assured. The signals are transferred from the inputs of the
flip-flops to the outputs (labelled Ql-Q4 in the Figure) only
upon occurrence of a clock signal at the clock input, which is so
labelled in the Figure. Thus, any signal which is applied at the
input of each of the flip-flops remains at the input until receipt
of the clock signal, at which time it is transferred to the-output.
It is stored at the output until receipt of the next subsequent
clock signal.
In the simplest embodiment of the present invention
the clock signal would be derived directly from the output of the
control read-out circuitry. The control read-out circuitry is re- ~
sponsive to the light change generated by control line K as described ;
above. Details of this circuitry are shown in FIG. 5.
However, when the present invention is utilized in
the arrangement for measuring camera tilt, and when it is desired
to record the tilt angles at the instant of each exposure, further
circuitry is required as shown in the block diagram of FIG. 3.
Before this circuitry is discussed, it should be noted that in the
aerial photography system in which this invention is to be utilized,
the reference is provided by a conventional vertical gyroscope with
two bu~t-in optoelectronic sensing units 100 and 101. (See FIG. 6.)
The gyroscope is compensated for drift and utilizes an electrical
_g_
. : , , :
,
9~3~
1 caging facility to rest the gyro. The sensing units are, of
course, used for measuring and displaying the angles o~ forward and
lateral tilt of the camera lens axis at the instant of exposure.
Thus, two rigid structures are firmly attached to the gimbals of
the gyroscope, on the longitudinal and lateral axes, respectively.
Each holds a suitably mounted encoded mask specifically designed
for opto-electrical read-out. These masks may, for example, be
the masks shown in FIG. 2. Two code read-out units, each consisting
of a series of light-emitting diodes constituting a light source
and opposed by an equal number of phototransistors are mounted on
the gyroscope main chassis and the longitudinal axis gimbal, re-
spectively. A gap between the light sources and the corresponding
phototransistors allow free movement of the code display as a
function of aircraft attitude change. Thus, the code display - ~
means are rigidly related to the roll and pitch axes of the ver- ~ ;
tical gyroscope (constituting first elements) whereas the code read-
out units are correspondingly related to the roll and pitch axes
of the camera lens (second elements). Any change in the relative
positions of the stakle gyr~cope axes and that of the camera lens
induces a change in the data read-out. The use of the control
read-out, of course, eliminates any ambiguity or overlap in the
read-out as mentioned above.
It is desired that the output signals be recorded
by the secondary optics of the camera. Thus, as shown in FIG. 3,
- a series of light-emitting diodes LEDl-LED4 is energized through
amplifiers Al-A4, respectively, by the output of flips-flops 31-34,
respectively. The light-emitting diodes are suitably mounted into
the data chamber of the camera. Also mounted within the camera
is a cutout disk 118 fixed concentrically on one of the camera
gears which is synchronized with the shutter. (See FIG. 7). An
~. --10--
.. "
-
9~34
l opto-electronic sensor 119, for example such as described with
reference to the cocle read~out means, is mounted to receive light
through this cutout disk and furnishes a signal when the shutter
is traveling across the field of the secondary optics. This
signal, after suitable processing in the shutter signal circuit
26, described in more detail with reference to FIG.`7, forms one
input to a NAND-gate 27 whose other input is furnished by control
read-out circuit 25. The output signal of NAND-gate 27 consti-
tutes the input to the clock inputs of flip-flops 31-34.
It is seen that by use of the gating means, namely
NAND-gate 27, the signals at the outputs ~l-Q4 of flip-flops FFl-
FF4 remain unchanged in the absence of the control signal and
when the shutter is passing across the field of the secondary
: optics in the camera. Thus, the display recorded on the camera will
not be subject to any ambiguity which might result if a change in
: read-out occurred during the shutter movement across the field of
the secondary optics. ~ :
The code read-out, control read-out and shutter sig-
nal circuits will now be described in greater detail.
The code read-out circuit shown in FIG. 4 includes
phototransistor 40, whose output is applied through an RC-filter
comprising a resistor 41 and a capacitor 42 to the base of tran-
sistor 43. Transistor 43 is connected as an emitter-follower stage, :.
the signal across its emitter resistor 44 being applied to the base .
. of transistor 45. The emitter of transistor 45 is connected to
ground potential through the parallel combination of capacitor 46
and resistor 47. It is further connected to the positive supply
line through resistor 48. The collector of transistor 45 is con-
nected to the base of transistor 49 through resistor 50. The base ~ .
of transistor 49 is further connected to ground potential through
. . .
-
.
~ 963~ ~
resistor 51, while its emitter is directly connected to the po-
sitive line and its collector is connected to ground potential
through a voltage divider comprising resistor 52 and resistor 53.
The output of the reading circuit is taken from the common point
of resistors 52 and 53.
The circuit operates as follows. Light falling on
phototransistor 40 causes a rise in voltage at the base of tran-
sistor 43. This rise in voltage is transmitted to its emitter and
therefore to the base of transistor 45. When transistor 45 becomes
; 10 conductive, current can flow through the emitter-base circuit of
transistor 49 causing this transistor to switch to the conductive
state. Thus, a positive voltage will appear at the terminal marked
"output" in Pigure 4.
The control read-out circuit is shown in Figure 5a.
This comprises a phototransistor 50 whose output is connected to
the base of a transistor 61 through a filtering network comprising a
resistor 62 and a capacitor 63. Transistor 61 is connected as an
-~ emitter-follower whose output controls the input to a Schmitt
trigger 64. The output of Schmitt trigger 64 is differentiated
by means of a differentiating circuit comprising a capacitor 65
and a resistor 66. Capacitor 65 is connected to the outputput of
the Schmitt trigger, while one terminal of the resistor 66 is
connected to ground potential. The other side of resistor 66
is connected through a diode 67 to an output terminal. The output
voltage of Schmitt trigger 6~ is further applied to the base of an
inverting transistor 68. The voltage at the collector of tran-
.
sistor 68 is differentiated by means of a differentiating circuit
comprising a capacitor 69 connected to the collector of transistor -~
68 and a resistor 70 connected between the other terminal of capa-
citor 69 and ground potential. The voltage at the common point of
capacitor 69 and resistor 70 is applied to the output terminal
::,
- 12 -
,
.
3~
1 mentioned above through a diode 71.
Schmitt trigger 64 shapes the signals supplied by
phototransistor 50 into substantially rectangular siynals, as shown
in line A of FIG. 5b. These rectangulax signals are differentiated
and the so-differentiated signals are applied through the above-
mentioned diode 67 to the output terminal. While both the positive-
and negative-going edges of the pulses of line A are differentiated,
the negative pulses at the differentiation circuit output are sup-
pressed by diode 67,~so that only the positive pulses shown on line
D appear at the output.
The inverted pulse sequence at the collector of tran-
sistor 68 (line B, FIG. Sb) is similarly differentiated, the re-
sulting signal at the cathode of diode 71 being shown in line C
of FIG. 5b. Of course, the signal at the output (FIG. 5a) com-
prises the signals of both lines C and D. Thus, the use of the in-
verting amplifier causes both the positive-going and the negative-
going edges of the output of the Schmitt trigger to be differenti-
ated and an output signal comprising a series of positive pulses,
each signifying one edge of the output waveform of the Schmitt
trigger 64 to be generated.
FIG. 7 shows the arrangement used to furnish the
shutter signal, that is an obturator disk 118 is shown passing be-
tween the light source LEDl and the phototransistor 119. As pre-
viously mentioned, disk 118 operates in synchronism with the
shutter. Specifically, light from LEDl is permitted to impinge
upon phototransistor 119 while an exposure takes place. Referring
now to FIG. 7, light falling on phototransistor 119 causes the
voltage at the base of transistor 123 to become more positive.
This causes transistor 123 to become conductive, causing the vol-
tage at the base of transistor 125 to become more negative, there-
- -13-
. . , ' : .~. ,
.. .
1C~49~3~ ~
1 fore causing transistor 125 to become conductive also. When
transistor 125 becomes conduc-tive, base-emitter current Elows
through transistor 127 causing this transistor to become aonduc-
tive, thereby changing the voltage at its collector from a voltage
substantially corresponding to the positive supply line voltage to
substantially ground potential.
The signal at the output of the collector of transistor
127 is the signal appearing at the output of the "shutter signal
circuit" of FIG. 3. As long as the voltage at the collector of
transistor 127 is high, any signals from the control read-out cir-
cuit 25 appearing at the second input of NAND-gate 27 are trans-
mitted through NAND-gate 27, since NAND-gate 27 is then conductive.
When the voltage at the collector of transistor 127 goes negative,
NAND-gate 27 is blocked, thereby preventing any signals from the
control read-out circuit 25 from reaching the clock input of flip-
flops 31-34. Thus, no change in the read-out can occur while the
shutter of the camera is open.
FIG. 8 shows the signals generated at the outputs of
the shutter signal and read-out circuits. Specifically, the line ~ -
labelled "Control Line Pulses" shows the output of the con-trol
; read-out circuits, while the lines labeled 1, 2, 4, and 8 consti-
tute the signals at the outputs of inverters 21-24 of FIG. 3.
Finally, FIG. 6 will be described in greater detail
in relation to a system wherein it i5 desired to display the air-
craft roll and pitch angles to the pilot. A gyroscope is used to
measure the pitch and roll angles of the aircraft. The gyroscope
has a spin motor 102 whose axis of rotation is indicated by "H
vector". The inner gimbal 105 rotates within bearings 101 and 104.
Rigidly connected to the outside of bearings 101 and 104 is the
outer gimbal 106 which, in turn, rotates within bearings 100 and 103.
-14-
. . :
~9634~
1 Code signals signifying the pitch and roll angles, respectively,
and the control signals which, as previously explained, assure
that the read-out takes place only when the read-out means are in
a predetermined position relative to the code markings, may be
derived from the inner and outer gimbal pickoffs, respectively.
The so-furnished signals from the inner gimbal pickoff are applied
to inputs K and Cl, C2, C3 and C4 of FIG. 3. Since it is desired
merely to furnish an indication of the pitch angle to the pilot,
NAND-gate 27 is eliminated, the output of control circuit 25 is
directly connected to the clock input of flip flops 31-34 and the
indications read on the light-emitting diodes LEDl-LED4 serves as
an indication of the pitch angle. The pickoffs from the outer
gimbal is, of course, similarly processed. Thus, pitch and roll
angles are indicates to the pilot.
While the preferred embodiment of the invention has
i~ been described as utilizing a photoelectric read-out, other types
-~ of read-outs such as magnetic and electromechanical read-outs may
also be used. The main distinguishing feature of the present in-
vention is the use of the control markings which prevent the am-
biguity in the digital read-out.
-15-
. .
