GB2344223A

GB2344223A - Solenoid type electric motor with rotary output

Info

Publication number: GB2344223A
Application number: GB9826038A
Authority: GB
Inventors: John Rodgers
Original assignee: IMPAQ Ltd
Current assignee: IMPAQ Ltd
Priority date: 1998-11-28
Filing date: 1998-11-28
Publication date: 2000-05-31
Also published as: GB9826038D0

Abstract

An electric motor comprises a plurality of electric actuators (2) arranged radially about an axis of rotation, a cam surface (1) extending around the axis and engaged by the armatures (3,4) of the actuators to translate linear motion thereof into rotary motion, and control means for operating the actuators sequentially.

Description

ELECTRIC MOTOR Field of the Invention This invention relates to an electric motor, and in particular to a motor whose rotation can be controlled precisely.

Background to the Invention There are many applications which demand relatively high power from a motor, coupled with precise control of rotation. For example, remotely-controlled undersea vehicles used for construction, inspection or maintenance of undersea installations re- quire such motors, especially where power is supplie to the vehicle through a cable from the surface. At greater depths, the weight and drag of the cable itself adds significantly to the load on the motors. Another application for such motors is in the control of remote valves in pipelines.

A difficulty with the use of electric motors in such applications is that most high power motors are of high speed, and therefore require speed-reducing gearboxes where slow speed and precise control are needed. Such gearboxes are not only costly, but also add significantly to the weight of the vehicle, and therefore themselves add to the power requirement, hence requiring greater power input. This in turn requires greater electric power, and there are practical limits to the size of cable which can be employed from the ocean surface to the vehicle on the ocean floor. In addition, gearboxes introduce addition problems with sealing against water ingress and providing lubrication.

An alternative approach is to use hydraulic motors. Such motors can be relatively compact for a high output power, and can run at low speed, with the speed being controllable with reasonable precision. However, in order to generate hydraulic pressure to operate the motors, it is usually necessary to provide an electrically-powered hydraulic system on the vehicle itself, since it is generally impractical to supply hydraulic power along fluid lines of the sort of length required for sub-sea vehicles. Also, since the conversion of electrical power to hydraulic power involves some energy losses, the problems of supplying sufficient power from the surface via an electric cable still arise.

Summary of the Invention According to the invention, there is provided an electric motor comprising a plurality of electric linear actuators arranged with armatures directed radially about an axis of rotation, a cam surface extending around the axis and engaged by the armatures of the actuators to translate linear motion thereof into rotary motion, and control means for operating the actuators sequentially.

The motor may comprise a rotor carrying the actuators and a stator provided with the cam surface therearound, or a stator mounting the actuators and a rotor having a cam surface therearound. The rotor may surround the stator, or the stator may surround the rotor, with the actuators being arranged accordingly radially outwardly or inwardly therearound.

In a preferred arrangement, the stator has a plurality of sets of actuators, each set acting in a respective single plane on a respective cam surface, the sets being arranged parallel to each other, and the cam surfaces being provided on a common rotor.

Alternatively, the rotor has a plurality of sets of actuators, each set acting in a respective single plane on a respective cam surface, the sets being arranged in parallel to each other, and the cam surfaces being provided on a common stator.

The linear actuators are conveniently solenoid devices.

An advantage of the motor in accordance with the invention is that the motive power is derived from simple and relatively inexpensive standard actuators. The power output can be selected by combining an appropriate number of actuators. In addition, the failure of an individual actuator will not prevent the motor from operating, especially where the motor uses a larger number of actuators. The result of failure will simply be a proportional loss of power output. This is important where immediate repair is not possible, for example in sea-bed use, but continued operation of the device is essential.

Brief Description of the Drawings In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 is a diagrammatic end elevation of a motor according to one embodiment of the invention; Figure 2 is a diagrammatic end elevation of a motor according to another embodiment; and Figure 3 is a diagrammatic side elevation of a motor according to a third embodiment.

Detailed Description of the Illustrated Embodiments Referring first to Figure 1, a motor comprises a circular frame 1 on which are mounted eight electrical linear actuators 2 spaced equally around the frame and directed radially inwardly. It will be appreciated that the final number of actuators may be greater or smaller than eight, being determined by the desired power output, the size of the motor, and the sizes of the actuators, for example. Each actuator 2 has a roller 3 mounted on the end of its armature 4, the rollers 3 all engaging a cam 5 mounted around a drive shaft 6. The frame 1 is fixed and so constitutes a stator. The cam 5 is shaped so that, as the actuators are energised in sequence, it is caused to rotate, turning the drive shaft 6. The precise shape will need to be determined according to the number of actuators and the force that each is capable of exerting. The shape of the cam in Figure 1 does not represent the final choice of shape, but is included merely to illustrate the principal of operation. A power supply (not shown) switches power to the actuators in a pre-determined sequence, either simply pulsing the voltage or varying it in a sine wave of variable frequency to control the movement of the armatures in conjunction with the desired movement of the cam. Thus, the actuators may be driven in both directions, applying force inwardly to drive the cam, and then withdrawing the armature at a rate such that the roller keeps in contact with the cam without inhibiting rotation of the cam. This arrangement is necessary to avoid bouncing the rollers on to and off the cam, leading to increased wear and noise. An alternative arrangement would be to use springs biasing the armatures sufficiently to maintain light contact in the return movement, driven by the cam itself.

It will be appreciated that Figure 1 could also represent another configuration, in which the shaft 6 is fixed and the frame 1 rotates about it, drive being transferred from the rotating frame by external gearing, for example. A rotary contact arrangement for the power supply will be necessary in this embodiment.

Figure 2 illustrates a motor in which an annular cam surface 10 surrounds a set of radially-directed actuators 11 mounted on a rotor 12 carried by a shaft 13. Each actuator has a roller 14 on its armature in contact with the cam surface 10. In this embodiment, the power supply to the actuators will need to be by way of rotary contacts, for example a multi slip-ring device so that each can be operated independently of the others. As with the embodiment of Figure 1, operating the actuators in a predetermined sequence causes the rotor 12 to turn relative to the cam surface, thereby rotating the drive shaft 13.

An alternative arrangement can also be represented by Figure 2, in which the rotor 12 and shaft 13 are f xed, and the cam surface then rotates about them when the actuators are operated. In this arrangement, the need for rotary contacts is avoided.

Drive can then be transferred by gearing external to the cam member, for example.

It will be appreciated that the sequencing of the actuators can be done in a number of different ways, and will be determined by factors such as the cam shape and the number of lobes thereon. For example, where a large number of actuators is used, it might be possible to operate them in opposed pairs, thereby balancing the forces on the shaft, as well as increasing the power output.

Figure 3 shows a motor in which a number of motors of the type illustrated in Figure 1 or Figure 2 are stacked together in parallel to operate on the same central drive shaft, thereby increasing further the power output. It might be possible to form the motors as modules which simply link together by way of co-operating elements on the drive shafts. Thus, the desired power output could be achieved by stacking the appropriate number of modules, and controlling the power supply accordingly. While Figure 3 shows gaps between the motors 30, it will be appreciated that the modules may readily be designed with mating surfaces enabling them simply to be stacked and secured together.

Claims

1. An electric motor comprising a plurality of electric linear actuators arranged with armatures directed radially about an axis of rotation, a cam surface extending around the axis and engaged by the armatures of the actuators to translate linear motion thereof into rotary motion, and control means for operating the actuators sequentially.

2. An electric motor according to Claim 1, comprising a stator mounting the actuators and a rotor having a cam surface therearound.

3. An electric motor according to Claim 2, wherein the rotor surrounds the stator and the actuators are directed radially outwardly of the stator.

4. An electric motor according to Claim 2, wherein the stator surrounds the rotor and the actuators are directed radially inwardly of the stator.

5. An electric motor according to Claim 1, comprising a rotor carrying the actuators and a stator provided with the cam surface therearound.

6. An electric motor according to Claim 5, wherein the rotor surrounds the stator and the actuators are directed radially inwardly of the rotor.

7. An electric motor according to Claim 5, wherein the stator surrounds the rotor and the actuators are directed radially outwardly of the rotor.

8. An electric motor according to any of Claims 2 to 4, wherein the stator has a plurality of sets of actuators, each set acting in a respective single plane on a respective cam surface, the sets being arranged parallel to each other, and the cam surfaces being provided on a common rotor.

9. An electric motor according to any of Claims 5 to 7, wherein the rotor has a plurality of sets of actuators, each set acting in a respective single plane on a respective cam surface, the sets being arranged in parallel to each other, and the cam surfaces being provided on a common stator.

10. An electric motor, substantially as described with reference to, or as shown in, the drawings.