Multiple Axis Actuator

The field of this invention relates generally to linear motor and rotational motor structures. More specifically, this invention relates to linear and rotational actuators utilized in the isolation of platforms in inertial stabilization systems. Prior art attempts at producing actuators for such stabilizing systems have been directed primarily to rotational motor systems as well as single axis actuator systems which utilize a very narrow gap magnetic element. This resulted in a cumbersome structure which required numerous individual linear actuators, one for each translational axis of motion desired and additional combinations thereof if rotational motion is desired.

Since it is the object of isolation platforms to isolate translational as well as rotational motions caused by vibration of the mounting platform which supports the isolation platforms, the primary concern becomes one of eliminating short stroke motions. Accordingly, actuators used may be short stroke actuators of the linear or rotational variety. The armature of the actuator of the instant invention is mounted on a platen which in turn is mounted to the vibrating structure. Wide gap magnets for interaction with said platen are mounted to the structure to be isolated. Such magnets may be either electromagnets or permanent magnets. It should be noted that reverse mounting does not affect the operation.

The novel structure provides windings on a platen disposed between the poles of such magnets which generate magnetic fields which in turn attract or repel portions of such platen from said poles in a controlled manner. Specifically, the platen contains a double winding arranged in a spiral configuration lying in a plane substantially parallel to the pole faces. Current driven through such windings in a controlled manner is used to generate force along an axis perpendicular to current flow. The individual spirals of said double winding are displaced from one another by a predetermined distance and lie in parallel planes adjacent one another. When a voltage is applied to said windings current passes through a first spiral in one direction and generates a first resultant magnetic field normal to the plane of the winding. The current continues through the second winding in a direction opposite its direction of travel in said first winding and generates an opposing resultant magnetic field also normal to the plane of the winding. The incremental spacing or the difference in position of the two windings prevents the total cancellation of either of the resultant magnetic fields, thereby creating a residual magnetic field. When viewed external of said windings the magnetic field from either side of the windings appears to be of one polarity. This will cause attraction of one side of the windings towards one pole of said magnet and a repulsion of the opposite side from the opposite pole, thereby causing the platen upon which the windings are mounted to be attracted to one pole of the magnet and repelled from the other. Hence force is generated along a line substantially parallel to the magnetic field flux lines of the magnets. Force in the opposite direction is accomplished by simply reversing the direction of current in the windings. When the spiral configuration is combined with a two axis platen, force along three translational axes is accomplished. A plurality of such spirals lying in the same plane but adjacent one another may be used to cause rotational force of the platen relative to the magnetic poles by causing adjacent pairs of said windings to generate apparent magnetic fields of opposite polarity, thereby attracting one side of said platen to one magnetic pole and the opposite side of said platen to the opposite pole. Disposing said adjacent pairs of such windings at 90 degrees to one another as viewed along a line normal to the plane of such windings adds additional rotation force about a second axis disposed 90 degrees from the first axis of rotation. Thus, a platen having two linear windings disposed at 90 degrees to one another for providing two translational axes of force, a single double winding spiral lying in a plane parallel to the plane of the first two axes for a third translational axis of force perpendicular to the first two translational axes, and two pairs of double spiral windings disposed at 90 degrees to one another for providing two rotational axes of force, allows force to be applied over five or more controlled axes, three translational and two rotational axes.

Having thus described the invention, it is an object thereof to provide an actuator operable over both translational and rotational axes. It is a further object of this invention to provide a translational type actuator operating on a rotational axis. It is a further object of this invention to provide a linear actuator which operates on short stroke motions parallel to magnetic lines of force. When used herein "perpendicular" means disposed 90 degrees from one another when veiwed along a line normal to the surface of the planes within which the various elements lie and does not require actual intersection. Principles and advantages of this invention may be more fully understood by reference to the drawings and specific description hereinafter set forth.

FIG. 1 is an objective view of the double spiral winding in space.

FIG. 2a is a pictorial view of a single current carrying winding disposed between magnetic poles.

FIG. 2b is a pictorial view of a double winding carrying current in opposite directions disposed between magnetic poles.

FIG. 3a and b are a planar views of two pairs of windings adjacent one another in both vertical and horizontal dispositions.

FIG. 4 is a pictorial view of a platen having multiple windings disposed between magnetic poles.

FIG. 5 is a pictorial view of an isolation system utilizing the actuator of the instant invention.

With reference to the drawings, FIG. 1 is an illustration of the manner in which the double spiral winding 30 is produced showing an upper winding 1 and a lower winding 2, produced from a single strand of wire which is looped at the center of the spiral to form loops having strands of wire adjacent to one another and concentric with each other. It is understood that the drawing is illustrative only and that the number of turns depends upon a particular magnitude of field desired, size of wire, and so on. With reference to FIG. 2, the spiral windings may be observed disposed equidistant between the poles of a magnetic member 50. Region 3 illustrates the distance between upper winding 1 and lower winding 2 which are here observed along a radial line of the spiral in cross section. Each of the sections shown illustrates the direction of current flow, using a dot to illustrate current flowing out of the page and an X to show current flowing into the page. Thus, it may be noted from the configuration shown, the windings generate magnetic fields which oppose one another. Since the windings are embedded in a rigid epoxy medium, they remain stationary relative to one another even though opposing fields are generated. External of this winding package, the spiral configuration appears to generate the same polarity magnetic field on either side of the windings. This is due to the fact that the spacing, region 3, prevents total cancellation of the magnetic fields beyond said windings. Thus, when a voltage is applied to said windings, current first passes through spiral 1 in one direction and generates a first magnetic field and since the spirals are composed of one strand of wire which is essentially folded back on itself, the current continues through winding 2 in a direction opposite its direction of travel in winding 1 and thereby causes the generation of opposing magnetic field. The displacement of these fields causes the appearance of residual magnetic fields external of said windings of one polarity. The force developed by the double spiral herein disclosed can be verified by considering first the force upon a single winding structure 40 as shown in FIG. 2a disposed between the poles of a magnetic member 50.

The force developed on the spiral axially is described in "Magnetic Circuits and Transformers" published by M.I.T. in 1957 as the force between magnetic poles and is given by the expression:

Where:

F=Force on the spiral

B.sub.a =Magnetic flux density in the air gap

A=Area of the air gap

.mu.a=Permeability of air

it is also known that:

Where:

.phi.=Total flux

mmf=Magnetomotive force

R=Reluctance of magnetic circuit

It is further known that:

Where

I=current in amps

NI=ampere turns

1=Length of gap

Therefore it follows that:

Since Area terms cancel equation 2.0 becomes:

Substituting equation 2.1 into equation 1.0 yields:

Therefore:

Where C.sub.1 is some constant.

Since there are two poles N and S as shown in FIG. 2a the net force on the winding is given by the expression:

For two windings spaced apart delta x as shown in FIG. 2b the net force is given by the expressions:

Resolving the terms of equation 4.1 yields: ##EQU2## Since the actuator may be of a wide gap type and the distance between windings is small i.e. on the order of one wire diameter, .DELTA.x terms which are orders of magnitude smaller than x.sub.n terms can be ignored and therefore equation 4.2 becomes:

Further where short stroke motion compensation is contemplated the distances x.sub.1 and x.sub.2 do not appreciably change and therefore F.sub.N is simply:

which illustrates that force is essentially a function of current and directly proportional thereto. This relationship allows excellent electronic control of actuators constructed in accordance with this invention. It is clear in the specific case shown in FIG. 2b that the winding will be attracted towards the south magnetic pole and repelled from the north magnetic pole, thereby generating force to the left. A reversal of the current will cause a reversal of the magnetic fields generated and thus will cause attraction of the winding to the north magnetic pole and repel it from south magnetic pole and thus cause force to the right. FIG. 3 is illustrative of pairs of smaller double windings disposed on the platen displaced from one another eight horiziontally as shown in FIG. 3a or vertically as shown in FIG. 3b. Actually, such windings may be positioned in any configuration depending upon the axis of force desired. These windings are identical to that shown in FIG. 1, although only one spiral winding 1 is shown. It is noted that the winding 2 is on the opposite side of said rigid epoxy medium and is not shown in the interest of simplicity. It may be readily noted in FIG. 3a that the application of current in one direction on winding 4 and the application of current in the opposite direction on winding 5 would cause one portion of the platen to be attracted to one pole and the other portion of the platen to be attracted to the opposite pole. This generates rotational force about an axis transverse to the line intersecting the center of the two windings. In the case of FIG. 3a, opposing currents will generate rotational force about a vertical axis through the platen, similarly in FIG. 3b, opposing currents through windings 6 and 7, respectively, will generate a torque or rotational force about a horizontal axis. In FIG. 4, a combination of windings as shown in FIG. 1 with the windings of both FIG. 3a and 3b allows the generation of rotation forces of platen 10 about at least two axes and one translational force of platen 10 parallel to lines of force between magnetic pole pieces 11. In an isolation system, as shown in FIG. 5, an illustrative system is shown having a platform 20 supported by linear decoupling member 22, angular decoupling members 24, a platen 26 having double winding 30 and adjacent windings 4 and 5 and 6 and 7 as illustrated in FIG. 4 disposed between the poles of magnetic member 28. It may be readily noted that in this configuration, the rotational forces as well as translational force parallel to the magnetic lines of force may be applied to the platform in order to stabilize the same. The size of the poles has been reduced so as to reveal the windings; however, it should be understood that good control is achieved by having pole faces very nearly equal in size to the winding distribution of the platen. It is also understood that the apparatus for motion detection may be any conventional system and that suitable control means are within the state of the art for providing controlled application of current to such windings.

Typically, sensors 32 are mounted on the platform 20 which detect relative motion of said platform, said platform being supported by mechanical ground 31. This motion may be either translational or rotational motions of various magnitudes. The sensors 32 may comprise a gyro which is able to detect relatively low frequency motion, such as change in attitude, and an angular accelerometer, which is able to respond to high frequency motions occasioned by shocks and vibrations. These sensors then generate signals which are proportional to the motion sensed, which are in turn applied to a controller. The controller after suitable calculation applies a current to the windings of the actuator sufficient to generate a magnetic field to interact with the field of the magnetic member in opposing the sensed motion, thereby cancelling the same.