GB2266996A - Antenna support providing movement in two transverse axes. - Google Patents

Abstract

An elevation-over-azimuth platform, e.g. for controlling the positioning of a dish antenna 6, includes an antenna mounted on a shaft 7 which is rotatable about elevation axis 14 and is supported by a yoke 12 which is freely rotatable about azimuth axis 22 by means of bearing 20 on base plate 18, and shaft 62 which is rotatable about its axis parallel to the azimuth axis 22 and is movable along a path concentric with the azimuth axis 22, the shaft 62 being driven so that when it rotates about its own axis only the elevation of the antenna is controlled and when it moves along the path without rotating on its own axis the movement of the antenna about the azimuth axis is controlled. As shown, inner and outer ring gears 30 and 32 are rotatable concentrically about azimuth axis 22 by means of wheels (e.g. 38, 42, 44) engaging grooves in the outside and inside respectively of ring gears 30 and 32. Spur gear 60, rigidly connected to shaft 62, engages gear tracks on the facing surfaces of the ring gears, and shaft 62 itself passes rotatably through the yoke and is drivingly connected to the shaft 7 via bevel gears 72. When ring gears 30 and 32, driven by respective motors, rotate in the same direction with the same angular velocity, the spur gear and shaft 62 move bodily around the azimuth axis without rotation and carry the yoke with them; azimuthal positioning results. When ring gears 30 and 32 are rotated in opposite directions, but again at the same angular velocity, spur gear 60 and shaft 62 are rotated about their own axis but do not move bodily. Elevational positioning then takes place. <IMAGE>

Description

PROVIDING MOVEMENT IN TWO TRANSVERSE AXES The invention relates to the providing of movement in two transverse axes. In various applications, a device is required to be supported so as to be movable in space about two transverse or orthogonal axes so as to achieve a desired spatial position and, by way of example, the invention is applicable to the provision of such movement. An example of such an application is an elevation-over-azimuth platform. However, the invention has many other applications.

According to the invention, there is provided apparatus supporting an element for angular movement about first and second predetermined axes which are transverse to each other, comprising a structure mounted on a base for angular movement relative thereto about the first axis and supporting the element for angular movement relative to the structure about the second axis, a rotary drive member carried by the structure so as to move therewith along a path concentric with the first axis and rotatable about a third axis parallel to the first axis and intersecting the said path, drive means mounted on the base for moving the drive member along the said path without angular movement about the third axis and for angularly moving the drive member about the third axis without moving it along the path, and a mechanical interconnection for angularly moving the element about the second axis in response to angular movement of the drive member about the third axis.

According to the invention, there is further provided an elevation over azimuth platform, comprising a base, a yoke mounted on the base to be rotatable about the azimuth axis and carrying, between arms of the yoke, an element rotatable about the elevation axis, a rotary shaft carried by the yoke and rotatable about a third axis parallel to but spaced from the azimuth axis and connected by a transmission on the yoke to cause angular movement of the element about the elevation axis as the shaft rotates, and drive means carried by the base for rotating the shaft about the third axis and for independently permitting the shaft to move bodily in a circular path in a plane perpendicular to and around the azimuth axis, without rotation about the third axis, as the yoke turns about the azimuth axis.

An elevation over azimuth platform embodying the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of the platform; Figure 2 is a cross-section on the line II-II of Figure 1; and Figure 3 is a side view of Figure 2 but partially sectioned along the line III-III of Figure 2.

Figure 1 shows a platform comprising a radio antenna arrangement 6 in the form, in this example, of a dish antenna such as for receiving transmissions from a satellite. The antenna 6 is supported on a shaft 7 rotatable between the arms 8 and 10 of a yoke 12 and is angularly movable with the shaft about an elevation axis 14.

The base 16 of the yoke 12 is supported from a base plate 18 by a hub 20 so that the yoke is rotatable about an azimuth axis 22.

Therefore, movement of the dish 6 about the axis 14 determines the elevational position of the antenna arrangement while movement of the yoke 12 about the axis 22 determines the azimuthal position of the antenna arrangement.

The base plate 18 may be fixed on the ground.

Alternatively, it may be mounted on a ship or an aircraft but other applications are of course possible.

In order to position the dish 6 in elevation and azimuth, respective drives are required and these will now be described with particular reference to Figures 2 and 3.

The drive unit 24 comprises two ring gears 30 and 32 which are concentrically positioned relative to the axis 22. As shown in Figure 3, ring gear 30 has a groove 34 running around its outer periphery, and ring gear 32 has a similar groove 36 running around its inner periphery. These grooves are used to support the ring gears. Thus, ring gear 30 is supported by three support wheels 38,40 and 42 which engage the groove 34 and are freely rotatably supported from the base plate 18. They thus support the ring gear 30 so that it is freely rotatable about the axis 22. Similarly, ring gear 32 is supported by three support wheels 44,46 and 48 which are also freely rotatably carried by the base plate 18. Ring gear 32 is thus freely rotatable about axis 22. Therefore, neither ring gear is supported from a central hub.

Although there is no centre hub for the ring gears, the mechanism includes the central hub 20 (see also Figure 1) which supports the base 16 of the yoke 12, the base 16 being shown dotted in Figure 2. Hub 20 is freely rotatably supported on the base plate 18 and thus permits the base 16 to rotate about the axis 22 (and independently of the ring gears 30 and 32).

The inner periphery 52 of the ring gear 30 carries gear teeth (omitted from the Figures for clarity) and the outer periphery 54 of the ring gear 32 carries similar gear teeth (also omitted), and these two sets of gear teeth mesh with a spur gear 60 which is fixed to a shaft 62 rotatably mounted in and carried by the base 16 of the yoke 12.

In addition, the outer periphery of the ring gear 30 carries gear teeth at 63 and the inner periphery of the ring gear 32 carries similar gear teeth at 64 (see Fig.

3). These gear teeth respectively mesh with drive pinions 66 and 68. These drive pinions are rotatable about respective axes fixed in relation to the base plate 18 and are driven by respective electric motors (not shown) carried on the base plate. Thus, energisation of each of these drive motors causes the respective ring gear 30 or 32 to be rotated about the axis 22 in a direction and at a speed dependent on the energisation of the motor.

The shaft 62 carrying spur gear 60 rises parallel to the arm 8 of the yoke 12 and is connected to the shaft 7 carrying the dish 6 via bevel gears 72 (see Figure 1).

The operation will now be described.

In order to control the azimuthal position of the platform 5, the two drive motors are energised so as to drive the pinions 66 and 68 in opposite rotary directions at such relative speeds that the two ring gears 30 and 32 are rotated (in the same angular direction) about axis 22 with the same angular velocity. The result is therefore that the spur gear 60 is carried bodily along a circular path around the axis 22 but without any rotation of the gear about its own axis. This bodily movement of spur gear 60 carries the base 16, and thus the whole yoke 12, around the axis 22, thus achieving azimuthal movement. However, because spur gear 60 does not rotate, shaft 62 does not rotate either; therefore shaft 7 does not rotate and there is no elevational adjustment.

In order to achieve elevational positioning, pinions 66 and 68 are driven in the same angular direction by their respective electric motors and at such relative speeds that the gear rings 30 and 32 again rotate at the same angular velocity but, this time, in opposite angular directions. The result of this is that spur gear 60 is rotated about its own axis but does not move bodily relative to axis 22. The base 16 of the yoke 12, and thus the yoke 12 itself, remain stationary. However, shaft 62 is rotated by spur gear 60 and, through the intermediary of bevel gears 72 (Fig. 1), adjusts the elevational position of platform 5.

It will be apparent that the relative rotational speeds of the gears 66 and 68 which are necessary in order to achieve the elevational and azimuthal positioning described above are determined by the ratio of the diameters of the ring gears 30 and 32. Thus, if the diameter of the outer ring gear 30 is D1 and the diameter of the inner ring gear is D2, the rotational speed of pinion 68 is related to the rotational speed of pinion 66 in the ratio D2:D1.

In a practical case, a re-positioning of the antenna arrangement 6 from a current position to a new position is likely to require both azimuthal and elevational movements. It will be apparent that the speeds and directions of rotation of the pinions 66 and 68 can be controlled in a compound manner so as to achieve simultaneous azimuthal and elevational re-positioning.

The mechanism described is Such that the drive motors for the pinions 66 and 68 are spatially fixed in relation to each other and are carried by the base plate 18. Simple and direct electrical connections may therefore be made to them. This therefore contrasts with mechanisms which require the motor for adjusting the elevational position to be mounted on the yoke itself and which thus require sliprings to feed electrical energisation to such a motor. Sliprings are disadvantageous because of their potential unreliability. In such other arrangements, feedback signals may also have to be passed through the sliprings for controlling the elevation drive motor. In the mechanism illustrated, however, feedback signals for the elevational position can be derived directly from the spur gear 60, if allowance is made for backlash in the gears 72.

In addition, the design of the mechanism is such that a very compact arrangement is provided and of generally "flat" form - the mechanism is little thicker than the thickness (along axis 22) of the inner and outer ring gears 30 and 32.

Various modifications may be made to the mechanism illustrated.

For example, it may be advantageous to replace the drive pinions 66 and 68 by respective worm gears engaging worm gear teeth on the ring gears 30 and 32; this may produce a more compact arrangement.

It is also possible to dispense with the support wheels 44,46 and 48 and to support the inner ring gear 32 on the central hub 20.

Although the mechanism has been described as for use in an elevation over azimuth platform for an antenna arrangement, it is not limited in this way. There are many other applications in which it is desired to position a device or member of some type in both elevation and azimuth or otherwise in relation to two orthogonal axes.

It is also possible for the mechanism to be used (with modification) in the case where the axes are not necessarily orthogonal but merely transverse.

Claims (19)

1. Apparatus supporting an element for angular movement about first and second predetermined axes which are transverse to each other, comprising a structure mounted on a base for angular movement relative thereto about the first axis and supporting the element for angular movement relative to the structure about the second axis, a rotary drive member carried by the structure so as to move therewith along a path concentric with the first axis and rotatable about a third axis parallel to the first axis and intersecting the said path, drive means mounted on the base for moving the drive member along the said path without angular movement about the third axis and for angularly moving the drive member about the third axis without moving it along the path, and a mechanical interconnection for angularly moving the element about the second axis in response to angular movement of the drive member about the third axis.

2. Apparatus according to claim 1, in which the said path is defined by inner and outer surfaces concentric with the first axis, and in which the drive member is circular and in driving engagement with and between the two said surfaces whereby angular movement of the surfaces about the first axis in the same direction moves the drive element along the said path and angular movement of the surfaces in opposite directions rotates the drive member about the third axis.

3. Apparatus according to claim 2, in which the drive member is a rotary gear and the said surfaces define respective gear tracks engaging the rotary gear.

4. Apparatus according to claim 2 or 3, in which the means defining the outer surface comprises a ring supported from its outside for rotation about the first axis.

5. Apparatus according to any one of claims 2 to 4, in which the means defining the inner surface comprises a ring supported from its inside for rotation about the first axis.

6. Apparatus according to claim 4 or 5, in which the or each ring is supported by at least three rotary elements mounted on the base and engaging a groove in the respective side of the ring.

7. Apparatus according to any one of claims 4 to 6, in which the drive means comprises respective motor means for rotating the rings.

8. Apparatus according to claim 7, in which the motor means drive the respective rings through gears rotatable about axes parallel to the first axis and engaging gear tracks on the outside of the outer ring and on the inside of the inner ring.

9. Apparatus according to claim 7, in which the motor means drive the rings through respective worm gears.

10. Apparatus according to any preceding claim, in which the mechanical interconnection comprises gearing for transmitting angular motion of the drive member about the third axis into angular movement of the said element about the second axis.

11. Apparatus according to any preceding claim, in which the element is a radio antenna arrangement.

12. Apparatus according to any preceding claim, including control means responsive to a desired position in elevation and azimuth of the element for causing the drive means to simultaneously move the drive member along the said path and about the third axis by such extents and in such directions as to tend to establish the desired position for the element.

13. An elevation over azimuth platform, comprising a base, a yoke mounted on the base to be rotatable about the azimuth axis and carrying, between arms of the yoke, an element rotatable about the elevation axis, a rotary shaft carried by the yoke and rotatable about a third axis parallel to but spaced from the azimuth axis and connected by a transmission on the yoke to cause angular movement of the element about the elevation axis as the shaft rotates, and drive means carried by the base for rotating the shaft about the third axis and for independently permitting the shaft to move bodily in a circular path in a plane perpendicular to and around the azimuth axis, without rotation about the third axis, as the yoke turns about the azimuth axis.

14. A platform according to claim 13, in which the drive means comprises inner and outer rings mounted for concentric rotation relative to each other about the azimuth axis and defining between them the said circular path, the rings respectively defining inside and outside surfaces drivingly engaging a rotary member fast with the shaft, and drive means carried by the base for independently driving the rings about the azimuth axis at such relative angular velocities and in such relative directions that they rotate the rotary member, and the said shaft, about the third axis and move the rotary member, and the said shaft, bodily along the said path as necessary to achieve a desired azimuthal and elevational position for the said element.

15. A platform according to claim 14, in which the said surfaces of the rings carry gear tracks which drivingly engage the rotating member which is a gear wheel.

16. A platform according to claim 14 or 15, in which the drive means comprises respective motors for rotating the rings.

17. A platform according to any one of claims 13 to 16, in which the transmission comprises bevel gears.

18. A platform according to any one of claims 13 to 17, in which the element is a radio antenna.

19. An elevation over azimuth platform, substantially as described with reference to the accompanying drawings.