Note: Descriptions are shown in the official language in which they were submitted.
94
BACKGROUND OF THE INVENTION
Radar systems may suffer from a variety of limitations including
masking of radar beams by physical obstructions, degraded operation in poor
weather and poor resolution, particularly with low frequency radar. Radar
problems and limitations become even more important when radar signals are
employed to operate collision avoidance systems and thus the present inven-
tion is primarily described herein with respect to this application although
the invention is not limited to any particular application.
Collision avoidance systems for automatically warning of possible
collision between ships, for example, are known in the art and a highly
successful system is described in my U.S. Patent Application ~o. 3,660,846.
The general background of collision warning and avoidance systems and the
purpose and advantages thereof are set forth in the above-noted patent.
'J` -2~
11~0794
1¦ One of the problems with shipboard radar employed with
21 collision avoidance system is masking of radar search areas by
3 ¦obstruction on the ship, such as funnels, cranes and the like.
4 ¦Many ships have structures which obstruct radar signals so that
5 ¦one or more sectors of the horizon are "hidden" from the radar
6 ¦antenna. This produces blind spots or areas from which no target
7 ¦information may be obtainea and thus introduces an uncèrtainty into
8 the overall system which is undesirahle. Another problem is the
9 ¦poor perEormance of high frequency radar, i.e. poor target
10 ¦detection of small targets that are in areas of precipitation.
11 ¦Low frequency radar is affected less by precipitatlon, however,
12 ¦it has poorer short range resolution. With respect to common ship
13 ¦radar practice, the terms "high frequency" refers to an operating
14 ¦wavelength of approximately 3 centimeters and the term "low
15 ¦frequency" refers to an operatin~ wavelength of approximately
16 ¦10 centimeters~
17 ¦ Modern radar requirements for large ships may include
18 ¦the provision of a back-up ràdar set r however, singals from the
¦main and back-up sets are not compatible and are not combined with
20 each othex. Theoretically, an analogue combination of signals
21 ¦from a pair of separate radar sets might be accomplished by the
22 ¦use of analogue delays, but only with great complexity of equipment
23 ¦which has effectively precludea such combination for practical
26¦ap lication.
28
29
31
32
1 1~)7~
1 The present invention br~adly comprises a system for
2 combinin~ information from two or more radar sets that may operate
3 at different frequencies and may have the antennas thereof
4 physically separated.
The present invention overcomes the problem of radar
ff masking by employing signals from spaced-apart radar antennas
7 connected to separate radar sets whose outputs are converted to
8 numerical form for interchangeable utilization to thus ensure
9 searching of the entire horizon for di~play andJor warning of
10 possible collision between a ship, for example, carrying the
~ ¦system and her o~jects.
2~611
2~
30 . . .
321 - 4 - .
,.. ,. : :
~ ...... . . .
'.,. ~ sn7~l
1 SU~U~ARY O~ INV~NTION
3 l
5 1
6 ¦ The present invention is directed to the solution of a
7 practical problem arising particularly on ships equipped with
8 collision warning and/or avoidance systems incorporating radar
¦equipment, but not limited to shipboard use. Structural elements
1a lon shipboard are often necessarily located in positions to
11 intercept~radar signals over some part of the radar scan so as to
12 1block effective radar searching in one or more azimuth sectors.
13 ¦The present invention overcomes the foregoing problem by employing
14 1two or more radar sets transmitting and receiving from separate
antennas which are physically separated and located to un-
16 ¦obstructedly scan any and all blind spots of the other(s). The
17 ¦present invention is hereinafter described with respect to a pair
18 If radar sets although it will be appreciated that additional sets
19 ¦may be incorporated in the same manner as may be required for
20 ¦particular application~.
21
22
23
24
27
28
29
31
32 _ 5 _
~ .
~ 1~07~
1 Radar echo signals or target signals from the separate
2 radar sets are herein converted into numerical form identifying
3 the boundaries of targets and such information may be interrogated
4 to determine the target centers in terms of range and azimuth or
5 employed directly. These target signals in numerical form are
6 converted to a common coordinate system of the"addition"of ali~nmen
7 a~ta determined by separation of radar antennas,rates of antennas,
¦rotation and time delays in the circuitry of sëparate radar sets
9 Iso that they may be correlated and employed interchangeably and
10 ¦compared to establish coincidences of targets. The correlated
11 ¦numerical-target information either sinyly or in combination may be
12 ¦employed to operate a collision avoidance system that includes
13 ¦automatic warning means and may also include tracking and display
14 ¦means.
15 ¦ The present invention provides the capability of
16¦ electronically comparing targets from separate radar sets which are
17 ¦not otherwise comparable in order to additionally verify the
18¦ existence of true targets. Thus~ for example, detection of a
19¦ target by one set only may be treated as a probably target which
201 detection of the same target by two sets may be treated as a
2~1 verified target. Alternatively, the correlator may adjustably
22¦ determina the level~of target signals required for target
231 identification by either or both inputs to the correlator and
241 apply same in the correlation process. Ad~itionally, the separate
251 radax sets may be operated at quite different fre~uencies to
26¦ obtaln the combined advantage of high resolution and all weather
271 operation.
281
29
311
~ 32 - 6 -
.. . ' .
' ' .
07~4
1 1 ~SCRI~TION OF FIGUR~S
4 The present invention is illustrated with regard to a
5 preferred embodiment of the present invention in the accompanying
6 drawings wherein:
Fi~ure l is a schematic side elevational view of a
8 container ship that may advantageously employ the present invention
9 Figure 2 is a schematic plan view of the ship of Figure l
10 illustrating the efect of obstructions in the "field of view" of
11 a radar set on such ship;
12 Figure 3 is a schematic perspective view of another
13 vessel illustrating a common type of radar obstruction;
14 Figure 4 is a plan view illustrating zones.that are
15 masked from the radar of the vessel of Figure 3;
16 Figure 5 is a block diagram of a collision avoidance
17 system; and ~
18 Figure 6 is a block diagram of a.multiple radar
19 combini.ng system in accordance with the present invention and
ZZ ¦ havi/~g disp ay and/or c-llision avoi4an~e outvuts.
32 . - 7 - .
. ~ . ' 1,~807~ '
1 DESCRIPTIOM OF PREFERRED EMFsODIMENT
4 The present invention is adapted to a wide variety of
S applications, however, the invention is ~articularly advantageous
6 in connection with shipboard radar and the preEerred embodiment
7 thereof is thus illustrated and described in connection with this
8 ¦application. It is first noted that a collision warning and/or
9 ¦avoidance system is adapted to cooperate with or incorporate a
10 ¦conventional radar set having an antenna from which radar signals
~1 ¦are propagated and echo si~nals from targets are received. These
12 ¦radar echo signals or target signals are employed in the coIlision
13 ¦avoidance system to warn of possible collisions and to provide
14 information to prevent same and thus it is clearly necessary for
15 ¦the radar set to accurately detect and locate objects in the
1 16 ¦field of scan.
17 ¦ Although the present invention has many applications, it
18 ¦is hereinafter described primarily with respect to the combination
19 ¦of signals from two or more physically separated radar antennas
20 ¦and utilization of the output in a collision avoidance system with
221notations of ther applioations.
24
26
27
2~
29
31
32 ~ 8 -
.,
.. . .
,. '
~ 18()7~ `
l Many ocean-going vessels have physical obstructions that
.interfere Wi.t~l the propagation and reception of radar signals. Thus
3 reference is made to Figure l of the arawings schematically
4 illustrating a container vessel ll having a mast 12 atop the bridge
5 with a rotating radar antenna 13 thereupon. ~his radar antenna is
6 normally mounted upon a high point on the surface structures or
7 ship, however, it will be appreciated that various structures or
.~ elements may also extend upwardly from the deck of the ship, such
as, for example, a cargo of containers 14 stack~d on the deck
lO of the ship.
11 At least certain of the upwardly extendin~ objects may
12 well lie in the path of the radar beam as it is swept through an
. 13 arc of 360~ This will then cause the radar beam to be blocked :
l4 f~om some areas of the horizontal scan. Referring to Figure 2,
15 there is schematically illustrated masking of the radar signals
16 that may occurl for example, by cargo containers 14 loaded on the
17 deck of the ship. It will be seen that the shaded area i6 is
18 màsked from the radar antenna 13 by portions o the cargo 14.
21
22 . ..
23 . . :
24 . . .
26
2~
29
3~ .
. _ g _
1 18079-1
1 Although fringin~ effects of the raaar propagation may reduce the
2 actual size of this area, it will be appreciated that there does
3 exist an area ahead of the vessel which is not viewed by the radar
set so that targets that are in this area mav not be detected by
the radar. ~he presence of such blind spots or the masked areas in
6 the horizontal scan of the radar systems will introduce
7 uncertaintiesr such as lost tracks or target swap in information
8 supplied to a collision avoidance or warning system which is
9 undesirable from the view point of protection against possible
collision.
11 In Figure 3 there is.illustrated another common physical
12 obstruction to radar on a container ship in the form of a massive
13 crane structure 18. A radar antenna 13 located, for example, on
14 a mast atop the bridge of the ship would be masked from portions
of the horizon by such structure and in Figure 4, there are
16 illustrated shaded zones 18a and 18b lying behind vertical portions
17 of the crane 18 from the antenna 13 so as to be masked from the
18 radar beam. In these areas or zones, a target such as a small
19 vessel would not be detected by a radar beam transmitted from the
21 antenna 13.
22
23
241
27
28
2g
.
31
32 - 10 -
' ' , ' ~ 1~07g~ i
1 ¦ The present invention provides a solution to the
2 ¦foregoing problem by the incorporation of one or more additional
3 ¦radar sets in the system employed on a vessel 11, for example.
4 ¦The antenna of the additional set is physically spaced from antenna
5 ¦13 and located so as to have an unobstructed scan of any or all
¦masked oE blind areas that are in the scan of the set connected to
7 ¦the antenna 13. Thus, for example, a further antenna 19 may be
8 ¦mounted adjacent to the bow of the vessel 11 so as to un- .
9 ~obstructively sweep the area~ 16 with a radar beam therefrom so as
10 ¦to provide information as to the presence of targets therein.
11 Quite clearly the field of view or scan of the antenna 19 will be
12 lobstructed rearwardly of the ship, however, these areas are
13 ¦covered without obstruction by the beam from the antenna 13.
14 ¦With this arrangement of the present invention, it will be seen
15 ¦that the entire 350 of the horizon is unobstructively swept by a
16 ¦radar beam from one or the other of the set~ connected to the
17 ~antennaS 13 and 19.
i8 ¦ Individual radar sets connected to antennas 13 and 19,
19 ¦for example, individually produce coherent and highly useful
20 ¦information as to range and bearings of targets, however, the
21 ¦signals from these separate sets are not compatible nor are they
22¦ related in any manner that will allow their normal combination or
23 utili2ation in combination. The present invention.~ro~ides for
24 combining signals from two or more radar sets to thus facilitate
26 ¦problems r lated to radar masking and the like.
28
30j
32 ~
': I
,
: . .
1181\79~ ~
1 Reference is now made to Figure S of the drawings
2 illustrating in block form/ a collislon avoic1ance system employing
3 a single radar set. Radar set 21 propagate~s a na~row beam of hi~h
4 frequency electroma~netic radiation from an antenna 22 which is
5 rotated to scan the horizon and this antenna Z2 receives radar
6 signals reflected from objects as echo signals or target signals. I
7 The radar output, which is herein taken to include video, trigger
8 and a~mitth signals, i5 applied from the radar set 21 to electronic
9 circuitry herein termed a target extractor 23, wherein a variety of
10¦1~unctions could be conventionally performed, such as verifying
11 the si~e and existence of an actual traget. It is recognized
12 that various conditions may produce false target indications,
13 such as re1ections caused by atmospheric conditions. In all
14 circumstances, so called "sea clutter" results from the reflection
15 of some radar signals -from the sea surface so as to produce a noise
16 level or the like which may be sufficiently high to mask physical
17 objects comprising targets of interest. Thus the taryet extractor
18 separates target identification information from sea clutter as by
19 counting the number of reflected pulses out of some predetermined
20 number of transmitted pulses to distinguish between random
21 xeflections and target reflections. Additionally, the circuitry
22 may count the number of scans in which a particular target is
23 identified and compare this to a predetermined number as a further
24 verification of target existence. Nu~ ous manners of target
25 verification are known in the art including the "m" out of "n"
26 detection and at least many of these are applicable to the
27 present invention. Also the amplitude of reflected pulses may be
28 compared to a predetermined amplitude level as a further manner of
29 verifying target existence.
31 - 12 -
, .
~180~g~
1 The extractor 23 additionally and primarily converts the
2 data from the radar set into numerical form. This may convenientl
3. comprise the generation of four binary words identifying the
4 azimuth and range limits of the detected targets. This conversion
is normally carried out in collision avoidance system of the type
6 herein conte~plated as being connected to the output of the present
7 invention, This data in numerical form may then be operated upon
by a center finder 24 to determine the range and bearing of the
9 center of the target and target information as to target limits or
10 center is commonly fed to a collision avoidance computer 26 which
11 may include tracking means for producing a variety of information
12 such as closest point of approach time to closest point of
13 approach. In addition to the ~oregoing, the collisison avoidance
14 system includes an alarm 27 and one or more displays 28 which
15 visually indicate protected areas established by the system and the
16 location of targets therein in analogue form and also in digital
17 form if desired. At least a part of the visual display be be
18 provided on the display of the raaar set, as indicated by the
22 ¦dasled line Figu~e 5.
241
26
~8
29
31
32 - 13 -
': '
. ~ . ... . .. ~ ..
t1807g4
1 The present invention may incorporate a collision avoidance
2 system, such as that illustrated in Figure 5 and briefly described
3 above. Referring to Figure 6, there will be seen to be illustrated
4 a pair of radar sets 31 and 41 separately connected to radar
antennas 32 and 42, respectively, which may be physically separated
6 and located as noted above) so as to unobstructedly scan any and
7 all blind spots of the other antenna. Each of these radar sets 31
8 and 41 generate data as to the bearing, range and extent of objects
9 causing reflected signals. The radar output date from the radar
sets 31 and 41, as defined above, are separately fed into separate
1l target extractors 33 ana 43, respectively, wherein such data is
12 converted into numerical or binary form and tar~et information may
13 be verified as noted above. Each of the target extractoxs 33 and
14 43 may, if desired, feed center finders 34 and 44, respectively,
15 wherein there is produced a numerical signal indicative of the
16 center of the target information or data rom the separate radar
I7 sets. It is noted that the target data, i.e., range and bearing
18 limits,-may be directly employed in the remainder of the system
19 without locating target centers, however, sophisticated systems
20 normally include identification of target centers.
21
22
26
28
29
31
32 - 14 -
,~"' .
I 1807g~
I The present invention provides an alignment data unit 51
2 which contains inEormation for converting numerical data from the
3 radar sets into data related to a common coordinate system. The
4 foregoing may either comprise information for converting the data
5 of one radar set into the coordinate system of the other or for
6 converting the data of both radar sets into a convenient separate
7 coordinate system. The term coordinate system is herein defined as
8 a reference from which range and bearing are measurea, so that
9 correction is made for physical separation of antennas, and it is
I0 noted that different time delays in separate radar sets produce an
II apparent shift of coordinate systems. The foregoing may be best
12 understood by considering an example of a target A located at
13 relative bearing of 0 or 360, i.e. dead ahead of the vessel 11
I4 ~n Figure 2. With the radar antennas 32 and 42 of Figure ~
I5 located at the points 13 and 19 of Figure 2J it will be seen that
16 ~oth radar sets 31 and 41 will identify the target at bearing ~,
17 ~owever~ each set will identify the target at a different range,
18 ~ith the difference in rangè being the diskance between the points
I9 3 and 19 on the vessel. Assuming that the data from the radar `
20 ets is to be converted into information relative to the position
21 f antenna 32, the alignment data unit 51 would then add a constant
22 to the range from radar set ~1, wi~h this constant being equal
23 to the dist nce between the points 13 and I9 in the vesseI.
28
29
31
32 - 15 -
., . .
4 ~1)794
1 Alternàtively, a target located at point B of Figure 2 lying on a
? perpendicular bisector of a chord between points 13 and 19 would
3 cause each o~ the radar sets 31 and 32 to produce equal ran~e
4 signals, but different bearing si~nals. These azimuth si~nals
might, for example, comprise 150 for radar set 31 and a bearing
6 indication of 30 for radar set 41~ These readings, o course,
7 depend not only upon the bearing, but also range, because of the
8 physical separation of the radar antennas and thus the alignment
9 data unit 51 contains a substantial number of constants related
to range and bearing of target data from radar set 31, for example
11 which, when added to target data from radar set 41 would compensat~
12 the latter for the physical separation of the radar antennas.
13 The alignment data unit 51 also contains correction data for
14 different time delays in the circuitry of the separate radar sets
31 and 41 in order to fully convert radar output data into a
16 common coordinate system. The radar output data from radar set
17 31 is t~us fed into the alignment data unit 51 wherein the
18 appropriate conversion constants are chosen on the basis of this -
19 data and applied to a combiner 46 connected to the output of
the center finder 44 for the radar set 41. Under this
21 circumstance, the data of radar set 41 is modified to correct
22 for the physical displacement of the radar antennas 32 and 42
¦ and time di erences.
281
3l
32 - - 16 -
~ 07~ 1
1 Under the circumstances wherein it is desired to modify
2 the data from each of the radar sets to correct for displacement
3 of the antennas thereof from some central point such as the center
4 of the vessel 11, aata from radar set 41 is also applied to the
alignment data unit 51, so that the output thereof comprises a
6 correction or modification for the data from each of the radar
7 sets, and this is applied not only to the com~iner 46, but also to
8 a combiner 36 connected to the center finder 34 for the radar
9 set 31.
lO I As illustrated in Figure 6, the outputs of the combiners
il ~ 36 and 46 are applied to a correlator 52 wherein the data from the
l2 ¦ two sets are compared to determine, for example, whether or not
i3 ¦ both radar sets have identified the same target. Under certain
14 ¦ circumstances of operation, the present invention may be employea
l5 I to produce an output from the correlator 52 either upon a
16 ¦ coin~idence Gr target identification by both radar sets or upon
17 ¦ target identification by either radar sets. The separate target
18 ¦ signals applied to the correlato~ 52 from radar sets 31 and 41
19 ¦ are wholly compatible and thus a variety of operations may be
20 ¦ performed by the correlator which may include control means 53 for
21 ¦ selecting different modes of operation to accomplish different
22 functions. The correlator determines whether or not simultaneous
23 ¦ targets of separate radar sets are within a predetermined small
24 ¦ range and bearing limits so as to comprise the same target or
2S whether the single output of the correlator should identify two
26 ¦ targe~s. The correlator may also compare target quality informati( In
27 ¦ such as pulse amplitude carried by digital signals for each and-
28 I or both sets to some predetermined level for identif~ing or not
29 ¦ identifying a target.
31
32 - - 17 --
.
t 1~û7~
1 The target information from the correlator 52 may be applied to
2 collision avoidance computer 54 which may include a tracker as in
3 a conventional collision avoidance syskem wherein information as
4 to range, bearings~ speed and course of targets appearing within
the operating range of the systems are then applied to a display
6 56. It will, of course, be appreciated that collision avoidance
7 and warning systems often incorporate the capability o
8 establishing areas or guard zones oE determinahle range, range
9 depth and azimuth extent for the automatic production of warning
signals upon the verified ntrusion of objects within such zones.
11 Additionally~ the limits of such areas may be visually displayed
12 together with the identification of the location of targets
therein for ready utilization by operators or the like.
14 The system of the present invention has a range of
capabilities from the simple exclusion of blind spots or areas in
16 radar scanning to th~ verification of targets in a number of
17 different modes. Thus the output of the correlator 52 may
1~ comprise the identification of the range and bearing of a target
1g or targets detected by either radar set and may additionally
~ontain information as to whether or not the target is identified
21 by both radar sets. This information is, as noted above,
22 employed in the collision avoidance computer either in most
23 simple form, i.e. target identification, or in more complicated
24 ~orm as to whether it is a target identified by a single set or a
target identified by both sets. Some collision avoidance systems
26 provide a dlsplay bracket about each target being tracked and the
27 correlator output may also identify the size of targets for
28 assistance in establishing this bracket and for additional
29 information to the operator of the system.
31
32
- 18 -
, ~ ~
;. : .. . ..
~ lsn7s~
1 It is also noted that at least certain functions of the present
2 invention are capable of being performed in wholè or in part by a
3 computer and a collision avoidance computer may be employed for
4 this purpose when the present invention feeds a collision
5 avoidance system havin~ such a computer.
6 The multiple radar combining system of the present
7 invention produces output signals, as noted ahove, that may be
8 employed or a variety of purposes. Thus these signals may be
9 converted into "analogue" signals suitable for operating a
conventional radar display, for e~ample. In Figure 6 there is
11 shown a converter 57 receiving output signals from the correlator
12 52 and converting these signals into suitahle form for operating
13 a display 58. Although the original radar signals need not be
14 fully recreated, the conversion is herein termed as being to
analogue form as distinguished from straight digital which is
16 normally unsuited for operating most analogue display systems.
17 This display of the output of the present invention may be quite
18 advantageous for situations, as aboard a large seagoing vessel
19 wherein separate radar sets and antennas are provided, for
example, on opposite wings of ~he briage.
21
26
2~
31
32 - l9 -
: :
~ .
11~07~
1¦ The present invention provides for the combination of
21 radar outputs from separate radar sets and the situation of spaced
31 apart radar antennas has been described above as an example.
41 Many other examples also exist and note is particularly made of
51 circumstances wherein scanning is carried out with two radar sets
6 1 operating one at hiyh frequency and one at low frequency. The
7 ¦ antennas of such sets may be mounted on the same mast so that ther~
8 ¦ is no appreciable physical separation, however, diff~rences in
9 ¦ rate of rotation of the antennas, heading of antennas and time
10 ¦ delays in circuitry of the separate sets will cause the same
11¦ target to be located at different times by separate set.s. This
12 ¦ has the effect of different coordinate systems which is equivalent
13 ¦ to physical separation of antennas.
14 ¦ The present invention is equally applicable to and
15 1 advantageous in the combination of radar outputs under the above-
16 ¦ noted circumstances even though no physical separation of
17 1 antennas exist. The advantages of good resolution with high
18 ¦ frequency radar and good long range and all weather performance
19 ~ of low frequency radar may thus be obtained with the present
20 ¦ invention. Such a combination of high and low frequency radar
21 1 may also be employed with spaced antennas.
22 ¦ It will be appreciated that no attempt is made in the
23 1 block diagram of Figure 6 to illustrate all electronic connections
24 ¦ or components that may be employed in an overall system, but
instead, the blocks are intended as function blocks rather than
26 ¦ circuit blocks. Convention electronic circuitry may be employed
27 ¦ for the individual functions of the present invention, and one
28 ¦ skilled in the art may design circuitry for accomplishing the
29 ¦ functions ~f the separate blocks of the present invention.
32 - 20 -
.
~ ~ ()7~
In one example set forth above, the radar sets were
2 ¦ stated to be operated at a relatively high frequency for one,
3 ¦ and a relatively low frequency for the other, although it will
4 ¦ be appreciated that this is not necessary. There are,
51 however, certain advantages to employing substantially different
6 ¦ frequencies for the sets inasmuch as a low frequency radar set
7 ¦ provides relatively poor resolution, but does provide superior
8 ¦ operation in rain and for distant targets. A high frequency
9 radar set, on the other hand, provides good resolution but
10 I degraded operation in bad weather. Thus the present invention
11¦ may be employed not only to overcome the problems of
12 ¦ obstructions to the propagation and receipt of radar signals at
13 ¦ radar antennas, but also to overcome problems of atmospheric
14 conditions.
16
17
Z~
2Z
27
28
29
3~
32 - 21 -
:'' .
'
7~
; The components and operatlon of collision avoidance and warning
systems in general are only briefly described above, inasmuch as same are
known in the art. It is, however, desired to emphasize the overall purpose
and function of collision avoidance systems which are designed to automatic-
ally activa~e audio-visual alarms upon the location by radar of a target or
obJect that may present a threat of collision for the purpose of requiring
an operator to take some positive action either to turn off the alarm or
possibly to change the course or speed of the vessel to prevent collision.
The various capabilities of a collision avoidance system may also be employ-
ed for other purposes such as harbor control of vessels with radar antennas
widely separated but feeding a central display, oil drilling platforms with
radar antennas on separate corners, surveilance monitoring, and many others.
The present invention will be seen to provide a relatively simple,
; but highly advantageous system that may, for example, be employed to achieve
; a marked improvement in collision avoidance systems. Although the invention
has been described with respect to particular preferred embodiments thereof,
it is not intended to limit the invention to the precise terms of descrip~
tion or details of illustration inasmuch as it will be apparent to those
skilled in the art that numerous modifications and variations may be made
within the spirit and scope of the invention.
, ~ ~
-2~-
~;: t
