Communications: radio wave antennas – Antennas – With means for moving directive antenna for scanning,...
Reexamination Certificate
2000-09-29
2001-11-06
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With means for moving directive antenna for scanning,...
C343S882000
Reexamination Certificate
active
06313805
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wide range azimuth (AZ) driving system for a satellite communication antenna which is set at an earth station of a satellite communication system, and more particularly, to a wide range azimuth (AZ) driving system for an antenna in view of driving at a low speed for tracking of a geostationary satellite and driving at a high speed for re-positioning.
2. Description of the Related Art
Hitherto, the wide range azimuth (AZ) driving system for the antenna is used as a wide range azimuth (AZ) driving system for a satellite communication antenna which is set at an earth station of a satellite communication system using, for example, a geostationary satellite shown in FIG.
1
.
Systems such as INTELSAT (Internal Telecommunications Satellite Consortium) and INMARSAT (International Maritime Satellite Organization) are well known as satellite communication systems to which the antenna is applied.
As shown in
FIG. 1
, a wide range azimuth (AZ) driving device
13
for an antenna as the above-mentioned system is disposed at a base portion of a yoke for supporting an antenna
9
and drives the antenna
9
in the azimuth (AZ) direction.
As an example of the outline of a size in a system which is put into practical use, an aperture diameter D
1
of the antenna
9
is within a range of approximately 3.6 (m) as one of a small size to 18 (m) as one of a maximum size and a main body of the antenna
9
is approximately 16 (t) in weight at the maximum. A diameter D
2
of a large gear
10
is approximately 1.8 (m).
As one example of the size in antennas which are widely used, the aperture diameter D
1
of the antenna
9
is approximately 10 (m), the main body of the antenna
9
is approximately 4 (t) in weight, and the diameter D
2
of the large gear
10
is approximately 1.2 (m).
The antenna in the satellite communication system is driven in the azimuth (AZ) direction by the following two operations.
According to a first operation, an antenna is azimuthally (AZ) driven by switching geostationary satellites which communicate data. The geostationary satellite communication system comprises a plurality of geostationary satellites and data which is communicated every satellite is different. As shown in
FIG. 1
, the antenna
9
which communicates data with an A geostationary satellite
14
-
1
is azimuthally (AZ) driven in a direction (shown by reference numeral
9
′ in
FIG. 1
) of a B geostationary satellite
14
-
2
so as to communicate another data. The operation is called as wide range driving.
The wide range driving requires that a target satellite is acquired as quickly as possible. Therefore, the antenna
9
also requires driving at a high speed throughout a wide range.
According to a second operation, an antenna is azimuthally (AZ) driven so as to track a satellite which the antenna acquires. The position of the geostationary satellite which is seen from the earth always changes by the deviation from an orbit.
FIG. 2
shows a state of the change in the position of the satellite which is seen from the earth. This is called as 8-shaped movement of the satellite, the satellite draws an 8-shaped locus on one-day cycle while the position at which the satellite should inherently remain stationary is central. As one example, an azimuth (AZ) tracking range (azimuth range) of the 8-shaped movement is approximately 6° in the azimuth (AZ) direction at the maximum.
However, a range of directional characteristics (azimuth range) of the aforementioned antennas which are generally used is 0.024°, that is, remarkably narrow, as one example of the systems which are put into practical use.
Therefore, if the antenna acquires the satellite once, the satellite deviates from the orbit by the 8-shaped movement and, thus, deviates from the range of the directional characteristics of the antenna and cannot maintain a predetermined antenna gain continuously.
Then, the antenna is driven in the azimuth (AZ) direction in accordance with the 8-shaped movement of the satellite and tracks the satellite. The operation is called as tracking driving.
The tracking driving requires that the azimuth of the antenna is accurately controlled. Accordingly, it is necessary to suppress backlash of a gear of a driving system.
Incidentally, referring to
FIG. 2
, the 8-shaped movement of the satellite includes not only the displacement of the azimuth (AZ) direction but also the displacement in the elevation (EL) direction. However, the present invention includes no driving of tracking in the elevation (EL) direction and the description is omitted.
FIG. 3
is a structural diagram illustrating one example of wide range azimuth (AZ) driving systems for an antenna according to a conventional technique which is used for the operations.
Referring to
FIG. 3
, the wide range azimuth (AZ) driving system for the antenna according to the conventional technique comprises one large gear
10
, an A small gear
1
and a B small gear
3
for driving the large gear
10
, two gear reducers of an A small gear
15
-
1
and a B small gear
15
-
2
, two motors of an A motor
16
-
1
and a B motor
16
-
2
, two clutches of an A clutch
5
-
1
and a B clutch
5
-
2
for connecting/disconnecting the A gear reducer
15
-
1
and the B gear reducer
15
-
2
to the A motor
16
-
1
and the B motor
16
-
2
, an antenna control unit (ACU)
19
, a torque bias adding circuit (TB)
17
, and two servo amplifies of an A servo amplifier
18
-
1
and a B servo amplifier
18
-
2
.
The ACU
19
is instructed on the azimuth to which the antenna
9
is directed from the outside, and instructs the A servo amplifier
18
-
1
and the B servo amplifier
18
-
2
on the rotational direction, rotational speed, and stop of the A motor
16
-
1
and the B motor
16
-
2
. The ACU
19
also detects the azimuth (AZ) direction to which the antenna
9
is directed. As one example of the systems which are put into practical use, the ACU
19
has performance for detecting the azimuth (AZ) direction with precision of a level ranging from {fraction (1/100)}° to {fraction (1/1000)}°. Specifically speaking, the azimuth (AZ) direction is determined every system in accordance with the range of the directional characteristics of the antenna (azimuth range).
The TB
17
measures consumption currents of the two motors of the A motor
16
-land the B motor
16
-
2
, thereby detecting loads of the A motor
16
-
1
and the B motor
16
-
2
and controlling the A servo amplifier
18
-
1
and the B servo amplifier
18
-
2
so as to cause torque biases in the two motors.
The torque bias will be simply described. According to the structure shown in
FIG. 3
, the A motor
16
-
1
and the B motor
16
-
2
suppress backlash which is caused among the A small gear
1
, the B small gear
3
, and the large gear
10
by causing a torque bias when the azimuth of the antenna is maintained and the tracking by the antenna
9
is driven.
When the azimuth (AZ) direction of the antenna
9
is maintained, the ACU
19
controls the A servo amplifier
18
-
1
and the B servo amplifier
18
-
2
so as to stop the A motor
16
-
1
and the B motor
16
-
2
. The TB
17
controls the A servo amplifiers
18
-
1
and the B servo amplifier
18
-
2
so that the A motor
16
-
1
and the B motor
16
-
2
generate driving forces having a predetermined intensities which are mutually directed in the opposite direction. Thus, the A servo amplifier
18
-
1
drives the A motor
16
-
1
that, for instance, the A motor
16
-
1
rotates in the right direction and the B servo amplifier
18
-
2
drives the B motor
16
-
2
that, for instance, the B motor
16
-
2
rotates in the left direction. The TB
17
detects the loads of the motors and controls the motors so that the mutual driving forces are balanced. Accordingly, the backlash is suppressed and the azimuth of the antenna
9
is precisely maintained. The driving force is called as a torque bias.
Incidentally, the A clutch
5
-
1
and the B clutch
5
-
2
are provided for purpose of disconnecting a trou
NEC Corporation
Nguyen Hoang
Ostrolenk Faber Gerb & Soffen, LLP
Wong Don
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