GB2131372A

GB2131372A - Actuator

Info

Publication number: GB2131372A
Application number: GB08234969A
Authority: GB
Inventors: Richard Cresswell
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1982-12-08
Filing date: 1982-12-08
Publication date: 1984-06-20
Also published as: GB2131372B

Abstract

The actuator mechanism which is suitable for controlling the vanes of an underwater torpedo consisting of an electric motor 12 which rotates a shaft 14 which engages with a ball screw nut 17. As the nut travels along the shaft it causes rotation of the vane to which it is coupled by linkage 20, 21. The mechanism can be configured in an extremely compact form and can be mounted within a streamlined pod which is spaced apart from the body of the torpedo by a vane. Typically four independently suitable vanes are mounted in two mutually perpendicular axes. <IMAGE>

Description

SPECIFICATION Actuator The invention relates to an actuator which is suitable for operating the steering mechanism of a vessel travelling through a fluid medium. It is particularly applicable to underwater torpedos, but in principle it could be applied to aircraft and the like vessels or craft. It is usual to steer such a body by altering the angle of one or more inclined vanes whose principle of operation is analogous to that of a rudder on a ship. Difficulties arise in providing an actuator which must have a very fast response, particularly where the space available to accommodate the actuator mechanism itself is extremely limited. The present invention seeks to provide an improved actuator.

According to this invention an actuator which is coupled to a vane so as to cause rotation of the vane about a predetermined axis includes an electric motor arranged to rotate a shaft lying perpendicular to said axis; a member mounted on said shaft and arranged to travel along it in response to rotation thereof, the direction of travel being dependent on the sense of rotation; and a pivoted linkage coupling said member to the vane so as to cause rotation thereof.

The invention is particularly applicable to an underwater torpedo which carries four independently controllable vanes arranged in two mutually perpendicular axes, in which separate mechanisms are provided to produce the required rotation of each of the four individual vanes.

Conveniently the mechanisms are housed in pods which are spaced apart from the rear body of the torpedo itself with the respective vane being positioned between the pod and the torpedo body.

Preferably the rotatable shaft is provided with a helical screw thread which cooperates with a ball screw nut. It is much preferred that the axis of the shaft and said predetermined axis both lie in a single plane, as this permits the space occupied by the actuator mechanism to be minimised, and allows the electric motor to be positioned symmetrically about the same plane as the one in which the predetermined axis lies.

The invention is further described by way of example with reference to the accompanying drawings in which Figure 1 is a plan view of the rear end of a torpedo incorporating the present invention, and Figures 2 and 3 are respectively side and elevation views of the actuator mechanism.

Referring to Figure 1 the rear end of a torpedo body is tapered in conventional manner. It is provided with four fins (of which only three fins 2, 3, and 4 are visible) to provide the necessary degree of stability to the motion of the torpedo. In order to permit the torpedo to be steered with the required degree of accuracy, two pairs of movable vanes are provided, the axes of which lies in two mutually perpendicular planes. In Figure 1 only two vanes 5 and 6 are shown, and in practice the two further vanes would be mounted at right angles to these. The mechanisms which actuate the vanes are mounted within four separate pods, one of which is associated with and located closely adjacent to a respective vane. Three pods 7, 8, and 9 are shown in Figure 1.It is not possible to mount the actuator mechanisms within the housing of the torpedo body itself, as insufficient space is available for this purpose. Typically the rear of the torpedo body houses the propulsion means which drive the torpedo through the water, but these means are not shown. It is therefore necessary to mount the actuators at a distance from the torpedo body itself, and their profile is shaped so as to be reasonably streamlined. They are conveniently mounted at the trailing surfaces of the four fins, of which only fins 2, 3, and 4 are shown.

Referring to Figures 2 and 3 the actuator mechanism which is located within only one pod 7 of the four pods is illustrated in greater detail, as the other three mechanisms are identical. The pod consists of an outer water tight housing which contains the mechanism which is used to rotate the movable vane 5 about an axis 10. The vane itself is securely mounted on a shaft 11 which is supported by a water tight bearing 29 and which is secured at its end remote from the pod by means of a water tight bearing located in the body of the rear end of the torpedo itself. Rotational movement is transmitted to the vane from a small but powerful, electric motor 12 having its axis of rotation 1 3 at right angles to the axis 1 0. Both axes lie in the same plane.The motor 12 carries a shaft 14, one end of which is supported at a bearing 1 5 and the other end of which carries a helical threaded portion 1 6 which engages with a ball screw nut 17. The nut 1 7 is constrained to slide along guides 1 8, 1 9 as it is forced to move along the length of the shaft 14 by the rotation of the shaft 14. The bearing 1 5 is designed to withstand the thrust load from the ball screw.

Movement of the nut 1 7 towards or away from the motor 12 is determined by the sense of rotation of the shaft 14. Suitable ball screw nuts of this kind are well known, and exhibit a very low degree of friction and mechanical backlash as engagement with the shaft 14 is via rows of precision ball bearings.

A block 33 in the form of a lever is rigidly mounted on the inner end of the shaft 11, and the block 33 is provided with a central cut out 34 through which the shaft 14 passes. The nut 17 is linked to the block 33 by two similar arms 20 and 25 which have precision pivot joints lying on the axes 30 and 31. Those portions of the block 33 lying on either side of the cut out 34 represent lever arms 21 and 24.

It will be appreciated that the pitch of the threaded portion 1 6 and the length of the arms 21 and 24 both determine the reduction ratio by means of which rotational movement produced by the electric motor is converted to a much slower rate of rotation of the shaft 11. This reduction ratio enables a relatively high torque to be applied to the shaft 11; typically the mechanism gives a reduction ratio of 50:1.

The angular position of the shaft 11 is of great importance since it determines the inclination of the vane 10 which steers the torpedo. A position sensor 22 is mounted on an extension 23 of shaft 11, and the extension 23 is supported by a bearing 35.

The layout of the mechanical linkage and the electric motor permits the actuator to be mounted in an extremely small space which is compatible with the streamlined shape of the pod.

Furthermore the nature of the linkage enable the angular position of the vanes to respond very rapidly indeed to electrical signals applied to the motor 12 with a minimum of mechanical backlash.

Claims

1. An actuator which is coupled to a vane so as to cause rotation of the vane about a predetermined axis including an electric motor arranged to rotate a shaft lying perpendicular to said axis; a member mounted on said shaft and arranged to travel along it in response to rotation thereof, the direction of travel being dependent on the sense of rotation; and a pivoted linkage coupling said member to the vane so as to cause rotation thereof.

2. An actuator as claimed in claim 1 and wherein said member includes a ball screw nut which cooperates with a portion of said shaft which carries a helical screw thread.

3. An actuator as claimed in claim 2 and where in the axis of said shaft and said predetermined axis both lie in a single plane.

4. An actuator as claimed in claim 3 and where in said pivoted linkage consists of two arms, one on either side of said shaft, coupled between said ball screw nut and a lever which is rigidly connected to said vane, the lever having a cut-out through which said shaft freely passes.

5. An actuator as claimed in claim 3 or 4, and where in an angular position sensor is mounted on said predetermined axis, the sensor being driven by a shaft extension of an actuator output shaft on which the vane is mounted, so that the position sensor and the vane lie on mutually opposite sides of said shaft.

6. A torpedo incorporating four independently controllable vanes arranged symmetrically around the rear end of the torpedo body and mounted so as to be movable about two mutually perpendicular axes, each vane being as claimed in any of the preceding claims.

7. An actuator substantially as illustrated in and described with reference to Figures 2 and 3 of the accompanying drawings.

7. A torpedo as claimed in claim 6 and wherein the electric motor, ball screw nut and pivoted linkage associated with each of the four vanes, are housed in four separate pods which are spaced apart from the rear body of the torpedo itself, with the respective vane being positioned between the pod and the body.

8. An actuator substantially as illustrated in and described with reference to Figures 2 and 3 of the accompanying drawings.

Superseded claims 1 to 8 New or amended claims

1. An actuator which is coupled to a vane so as to cause rotation of the vane about a predetermined axis including an electric motor arranged to rotate a shaft lying perpendicular to, and in the same plane as, said axis; a member mounted on said shaft and arranged to travel along it in response to rotation thereof, the direction of travel being dependent upon the sense of rotation; and a pivoted linkage coupling said member to the vane so as to cause rotation thereof.

2. An actuator as claimed in claim 1 and wherein said member includes a ball screw nut which co-operates with a portion of said shaft which carries a helical screw thread.

3. An actuator as claimed in claim 2 and wherein said pivoted linkage consists of two arms, one on either side of said shaft, coupled between said ball screw nut and a lever which is rigidly connected to said vane, the lever having a cut-out through which said shaft freely passes.

4. An actuator as claimed in claim 3, and wherein an angular position sensor is mounted on said predetermined axis, the sensor being driven by a shaft extension of an actuator output shaft on which the vane is mounted, so that the position sensor and the vane lie on mutually opposite sides of said shaft.

5. A torpedo incorporating four independently controllable vanes arranged symmetrically around the rear end of the torpedo body and mounted so as to be movable about two mutually perpendicular axes, each vane being as claimed in any of the preceding claims.

6. A torpedo as claimed in claim 5 and wherein the electric motor, ball screw nut and pivoted linkage associated with each of the four vanes, are housed in four separate pods which are spaced apart from the rear body of the torpedo itself, with the respective vane being positioned between the pod and the body.