Linear motor

Details Linear motor Linear motor

2001-08-28

2002-11-19

Tamai, Karl (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Linear

C310S026000, C310S328000, C310S323210

Reexamination Certificate

active

06483208

ABSTRACT:

This invention is concerned with motors, and relates in particular to novel varieties of linear motor and the mechanism for driving them.
Motors
The term “linear motor” is usually employed to describe a variety of electric motor. In a common type of conventional electric motor a rotating electromagnetic field is produced by a set of stationary coils (known as the stator) arranged to form a circle or cylinder, and this field interacts with a rotatably-mounted magnet or electromagnet (known as the rotor) mounted within the circle or cylinder of the stator, to drive the rotor round. In a linear motor, however, the stator coils are arranged in a line, and the field they produce advances along that line driving the “rotor”—in this case better described as a “translator”—along with it. Such a linear motor can be visualised as a conventional rotary motor the stator of which has been opened out and spread flat.
There are many other devices which produce propulsive force in a straight line rather than in a circle, and thus that might technically be considered as “linear” motors. Thus, steam, gas-driven, internal combustion, hydraulic and pneumatic reciprocating piston/cylinder engines are all non-electrical devices which fall into this category, while other electronic, electrical, electromagnetic devices are voice-coil motors, piezo-electric actuators, and some magnetostrictive devices (these last two have very short translator travel, measured in microns). Some types of linear motor—the so-called “inch worm” motors—use regions of physico-mechanical compression and expansion in the stator to push the translator along at the speed of propagation of those regions.
There are applicantions where very high speed, low force, long travel, high linearity and very low moving mass are required, but none of the known linear motors have all of these capabilities. This is a problem the present invention addresses, seeking to provide a linear motor that will enable long-travel high-linearity motion in either a straight or a curved line at very high speed with extremely small translator mass, and yet which is extremely simple in concept and can be manufactured from a very small number of components. To achieve this, the invention proposes the use of a mechanism that applies motive, displacing force not primarily in the direction along which translator movement is desired but instead approximately at right angles to that direction, the construction of the mechanism being such that the consequence is that there is a resultant force—a resolved component of the applied motive force—that is directed along the desired line of movement of the translator, and thus the translator is “squeezed” out in the required direction rather in the way that a cherry pip or plum stone can be shot out by being squeezed between finger and thumb. Another analogy would be trying to pick up a wet (and thus very slippery) curved-outline piece of soap with the palm of a wet hand (the harder the soap is “gripped” the faster it shoots out away approximately at right angles to the direction of grasp). In this latter case the “gripping” hand is nominally stationary (it is the stator) and provides the motive power, whilst the soap plays the part of the moving part or “translator”.
According to the present invention, there is provided a linear motor comprising a linearly-extensive stator supporting a translator in such a manner that the translator is able easily to move along the line, or axis, of the stator, and wherein the stator is made of piezoelectric material driven in operation by suitably-applied electrical voltages or a magnetorestrictive material driven in operation by suitably applied magnetic fields to provide a squeezing force across the translator in a direction approximately orthogonal to the line of the stator; and either the translator has along its movement direction a profile (either intrinsically or when so squeezed by the stator) that is slightly tapered or the translator is mounted on the stator by force-transmitting bearings that when so squeezed by the stator deform to become slightly tapered along the line of the stator such that in either case the effect of the squeezing is to produce a resultant force on the translator that is approximately orthogonal to the squeezing force, and thus along the line of the stator.
The linear motor of the invention comprises a linearly-extensive stator supporting a translator. The stator is linear in that it extends in a line rather than being arranged in a circle as in the case in most conventional electric motors. However, the line of the stator need not be straight—though most likely it is—but can be curved in several places and in one or two dimensions.
The stator may be of almost any shape and size. Basically, though, the stator may be constructed as to allow deformation of the bearing aperture within it from a nominally cylindrical internal outline to a nominally truncated conical form, it being possible to reverse which end of the aperture has the smaller internal diameter.
In the invention's linear motor the stator supports a translator. In this context a “translator” is simply a component that can be driven along the stator by the applied force so as to perform some desired operation. Examples of stators, as defined by what they are required to do, include:
a rod coupled to an external mechanism to provide useful mechanical movement therein;
a light self-contained radially-stiff piston effectively sealed against fluid flow within the stator (perhaps by the bearing structure) which acts directly on the air surrounding it, to act as an acoustic transducer;
a self-contained radially stiff piston effectively sealed against fluid flow within the stator (perhaps by the bearing structure) fluid-coupled to one or more external chambers so as to act as a pump in conjunction with fluid flow control valves;
a self-contained radially-stiff piston carrying one or more mirrors or mirror surfaces to act as a focusing or deflection component in an optical system;
a self-contained massive radially-stiff piston whose inertia, mechanically coupled to the bearing stator via the bearing member and thence to its supporting structure, is used to apply or dampen vibration to that structure.
The translator, whatever its detailed form, will normally (but now always) have length—that is, a significant size—in a direction along the intended line of movement, so that it necessarily has a front end and a rear end. This, as is explained hereinafter, is relevant to the manner in which the stator's squeezing forces can be applied.
The translator may be made as a very low mass item, the only requirement for adequate operation of the motor mechanism being that it can provide radial reaction to the squeezing forces of the stator (it is not required to remain totally rigid; indeed, some degree of deformability may be preferred, as noted below). In practice its nominal (undeformed) shape may be somewhat like a barrel, or alternatively it may be basically parallel-sided (parallel to the axis of the motor) but taking on a tapered form only when deformed under the influence of the squeezing forces applied by the stator. When used as an audio transducer the translator is to be coupled only to the surrounding air, and the constraints on its structure are further reduced; in order to provide the high accelerations required, minimal mass is the principal criterion (along with imperviousness to air). Very low mass translators for this purpose may be produced from expanded foamed plastic, thin-walled shells of expanded foam plastic (possibly with the addition of very thin high-tensile surface skins of metal or other material) or a silica (or other) aerogel. Another alternative for a translator for audio transducers is to inflate with pressurized gas a very thin-walled high-tensile cylinder of plastic or metal to achieve the desired radial stiffness with very low mass (similar to a pressurised thin-walled coke-can or plastic carbonated mineral-water bottle, where in both cases the stiffness produced is d

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