Electrical generator or motor structure – Dynamoelectric – Reciprocating
Reexamination Certificate
1998-12-29
2001-06-12
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Reciprocating
C318S118000
Reexamination Certificate
active
06246132
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to magnetostrictive actuators which provide position control over very small, or larger, distances, and which provide force control.
BACKGROUND OF THE INVENTION
Cryogenic shape and force actuators are required for NASA's Next Generation Space Telescope (NGST). The shape control actuator must provide a small stroke in a rigid structure whereas the force control actuator must provide a controlled force through a small displacement, imposed on a somewhat compliant optical surface. Solenoids can only pull, and thus require a separate return mechanism. Also, since solenoids have moving parts, they are not sufficiently reliable, repeatable, or precise.
SUMMARY OF THE INVENTION
The design of the inventive actuators of this invention incorporate cryogenic magnetostrictive materials. The preferred magnetostrictive material has the highest strains at cryogenic temperatures. These strains, which approach 0.63%, exceed that available from piezoelectric materials at the design operating temperatures for the NGST of between 20 and 60 K. Also, the invention employs electrical coils for providing the controlled strength magnetic field applied to the magnetostrictive material, to cause elongation of the material, and resultant desired movement. In an embodiment for low temperature operation in an environment in which heat dissipation and power use must be minimized, as in the NGST, high temperature superconducting wire is used to apply the magnetic field to the magnetostrictive materials. At the operating temperatures specified, superconducting wire exhibits zero resistance and therefore generates no heat in the actuator during activation. This minimizes any thermal interference with the optical surfaces to which the actuators will be attached in the NGST. The only source of heat generation is found in the internal resistance of the drive electronics.
The current flowing to the actuator is the most critical aspect of the ability to control the precision shaping and positioning of the optical surfaces of the NGST. In order to meet this requirement, a unique actuator control system based on industry standard electronics, operated at cryogenic conditions, is utilized. This cryogenic operation reduces internal resistance by a factor of between 15-30 and provides the actuators with a high efficiency current source with a 10-ppm accuracy.
It is therefore an object of this invention to provide a magnetostrictive actuator.
It is a further object of this invention to provide such a magnetostrictive actuator which can be used as a shape controller.
It is a further object of this invention to provide such a magnetostrictive actuator which can be used as a linear motor.
It is a further object of this invention to provide such a magnetostrictive actuator which can be used as a force applicator.
It is a further object of this invention to provide such a magnetostrictive actuator which can move in very small increments, but across a relatively large distance.
It is a further object of this invention to provide such a magnetostrictive actuator which is very reliable.
It is a further object of this invention to provide such a magnetostrictive actuator which is very repeatable.
It is a further object of this invention to provide such a magnetostrictive actuator which is very precise.
It is a further object of this invention to provide such a magnetostrictive actuator which does not have moving parts.
This invention features a magnetostrictive actuator comprising a magnetostrictive member which elongates upon application of a magnetic field, and a translating member mechanically coupled to the magnetostrictive member, for translating the change in length of the magnetostrictive member into a desired action. There is further included a means for selectively applying a magnetic field to the magnetostrictive member, to selectively change the length of the magnetostrictive member and thereby cause the translating member to create the desired action.
The magnetostrictive member may be a rod with a desired cross-sectional shape (e.g. round or rectangular), which may be accomplished in a number of rod sections which are rigidly coupled together. This allows the use of a rod which is longer than a single rod which can be fabricated by current magnetostrictive material production techniques, in order to produce larger motions.
The actuator preferably includes a means for applying a compressive force to the magnetostrictive member, to align the magnetic moments in the member. This means may be accomplished with a compressed spring or any other similar device which applies force to the member.
The means for selectively applying a magnetic field may itself be accomplished with an electrical coil (such as a superconducting coil) surrounding the magnetostrictive member, and a means for applying a selected current to the coil, to generate an electromagnetic field with a selected field strength. The device may also include a magnetic return path structure substantially surrounding the coil, and coupled to the magnetostrictive member, to increase the magnetic coupling between the coil and the magnetostrictive member. The magnetic return path structure may contain material having a permanent magnetization.
This invention may be used to accomplish a linear motor, which can move in discrete steps of variable size. To accomplish this, the actuator includes a mechanical member coupled to the magnetostrictive member, which moves when the magnetostrictive member changes in length. Some means for holding this mechanical member in place (relative to the outside world) is also included. Such may be accomplished with a releasable clamp. A discrete movement of the mechanical member is accomplished by immersing the magnetostrictive member in a magnetic field while the clamp is released, and then closing the clamp before removing the magnetic field. In a preferred embodiment of a linear motor, the translating member is accomplished with rods or other protruding mechanical members coupled to each end of the magnetostrictive member. These protruding mechanical members translate a change in length of the magnetostrictive member into a change in their position. To accomplish maximum linear motion, these mechanical members are axially aligned, and are aligned along the major axis of motion of the magnetostrictive member.
The clamps can themselves be magnetostrictively actuated, and adapted to grip and release a protruding mechanical member as they are operated from a clamping position which holds the mechanical member in place, to a released position which allows the mechanical member to move. In this embodiment, the clamps can be adapted to grip when they are in the “power off” mode.
This invention also features a translating member which includes means for translating the change of length of the magnetostrictive member into a force output. This may be accomplished with a spring member such as a flat spring, which translates displacement into force. The flat spring may include a plurality of spring arms emanating from a central spring body. There may further be included a means for mechanically coupling the magnetostrictive member to the distal ends of these spring arms. In this case, the force translation may be provided with a mechanical member coupled to the central spring body. The force actuator may further include means for controlling the magnetostrictive member to provide a desired force. This may be accomplished with a means for sensing the force output, and means, responsive to such sensing, for controlling the field strength of the magnetic field applied to the magnetostrictive member, to control the change in length of the magnetostrictive member.
REFERENCES:
patent: 4754441 (1988-06-01), Butler
patent: 5249117 (1993-09-01), Greenough et al.
patent: 5281875 (1994-01-01), Kiesewetter et al.
patent: 5693154 (1997-12-01), Clark et al.
patent: 5739601 (1998-04-01), Tsodikov
Bent Bruce R.
Joshi Chandrashekhar H.
Dingman Brian M.
Energen, Inc.
Jones Judson H.
Ramirez Nestor
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