Fluid handling – Systems – Programmer or timer
Reexamination Certificate
2001-04-06
2003-07-29
Lee, Kevin (Department: 3753)
Fluid handling
Systems
Programmer or timer
C137S066000, C251S065000, C310S015000, C310S023000
Reexamination Certificate
active
06598621
ABSTRACT:
FIELD OF INVENTION
This invention concerns magnetic drives, particularly but not exclusively for valves for controlling gas flow or fluid flow and for opening and closing electrical switch contacts.
BACKGROUND TO THE INVENTION
Magnetic attraction and repulsion is commonly employed as a motive force to operate devices such as valve closure members, pistons in cylinders to achieve a pumping action, and contactors and switches for opening and closing electrical circuits.
Such drives may have a bistable or monostable characteristic, and often employ a spring force to provide a restoring force and create a monostable operating characteristic.
Magnetic fields to achieve the operation are usually generated by causing an electric current to flow in a winding surrounding a ferromagnetic core or the like, which if the magnetic field is to collapse when the current flow ceases (as is usually required), is usually constructed from a magnetisable material having a low magnetic permanence.
Where valves control the flow of inflammable or poisonous gases or fluids, it is usual to design the magnetic drive therefor to be monostable and to have a so-called fail-safe characteristic in the event of a power failure. By fail-safe is meant that the valve will revert to a closed condition in the event that there is an electrical power failure.
The invention seeks to obviate the need to provide electric current continuously to maintain the operational state of a monostable device.
It is a particular object of the present invention to provide a bistable magnetic drive which does not require a continuous current flow to maintain it in either of its stable states.
Another object of the present invention is to provide a magnetic drive having a bistable characteristic, which can be readily modified to possess a monostable characteristic so that it will revert to (or remain in) one of its two states in the event of a power failure.
It is a further object of the invention to provide a mechanical device for altering the characteristics of a bistable magnetic device, to those of a monostable device.
It is a still further object of the invention to provide a digital fluid flow controlling valve, particularly for controlling the flow of gas or air.
It is a still further object of the invention to provide a digitally controllable gas flow control valve with a safety characteristic which reverts to a closed state in the event of the failure of a monitored source of energy such as an electrical current flow, a source of heat, or a source of light.
A further object of the invention is to provide pneumatic devices in which air or gas flow is under the control of valves controlled by such improved magnetic drives.
PRIOR ART
From U.S. Pat. Nos. 4,554,610, 4,386,823 and 3,772,540 are known magnetic drive devices having permanent magnet means, an armature displaceable between air gaps and an electromagnetic winding for driving the armature. In all cases, the axis of the winding lies parallel to the path of movement of the armature.
SUMMARY OF THE INVENTION
According to one aspect of the invention a magnetic drive device comprises a permanent magnet means generating magnetic flux, an armature mounted for movement enabling it to occupy either a first air gap in which the flux is in one direction, or a second air gap in which the flux is in the opposite direction, with a region of flux cancellation between the two air gaps, and at least one electromagnet winding having an axis generally perpendicular to the path of movement of the armature coil to which current can be supplied to adapt said at least one winding when energised to produce a magnetic flux in said one direction or the other, depending on the direction of the current, the flux from the winding increasing the flux density in the other air gap, thereby effectively shifting the flux cancellation region towards or into one of the two air gaps so as to produce a flux density gradient extending from one air gap to the other which will cause the armature to move into (or remain in) the air gap having the higher flux density, wherein the armature will continue to remain after the current flow ceases.
According to another feature of the invention, in use the winding both polarises the armature and changes the magnetic flux in the air gaps.
According to another aspect of the invention in a magnetic drive device as aforesaid further includes low reluctance flux concentrating means external to the electromagnet winding which provides a low reluctance external path for returning flux from one end to the other thereof when the winding is energised, thereby to increase the flux produced by the winding when energised, so as to magnify the magnetic flux available to effect movement of the armature.
The external flux concentrating means conveniently comprises at least one elongate member of magnetisable material which extends parallel to the magnetic flux in the air gap and generally perpendicular to the direction of movement of the armature and beyond the extent of its travel.
A magnetic drive device as aforesaid, (with or without the external flux concentrating means) may comprise four similar elongate magnetisable pole pieces arranged symmetrically in pairs, each pair occupying one of the two magnetic fields, wherein the air gap between the pole pieces in each pair defines the air gaps at the two extremes of the armature travel, and the two pairs of pole pieces serve to concentrate the internal magnetic flux into the two air gaps at opposite ends of the armature travel.
The combination of internal and external flux concentrating elements assists in defining the two stable positions of the armature and also assists in effecting the movement of the armature from one end to the other.
A pair of electrical contacts may be provided at one end of the armature travel which are electrically joined by being bridged by the armature, or by conductive means or a coating on the armature, when the latter is located at that end of its travel.
Likewise a pair of electrical contacts may be provided at the other end of the travel as well, and if required second conductive means or a coating is provided on the armature to ensure that the said other contacts are also bridged when the armature is at the other end of its travel.
By providing electrical contacts at either one or both ends of the armature travel, the drive is converted into an electrical switch in which one pair of contacts are bridged when the armature is at one end of its travel and the other pair are bridged when it is at the other end of its travel. The converted drive is therefore equivalent to an electromagnetic relay or contactor.
According to a further aspect of the invention a magnetic drive device as aforesaid may be contained within a sealed chamber and where electrical contacts are involved, at least part of the wall of the chamber may be formed from electrical insulating material to provide a region for conductive feedthroughs to terminals external of the chamber to allow electrical connection to be made to the contacts therein which, when the armature is in an appropriate position, are bridged thereby.
The chamber for example may be formed from plastics or glass or quartz.
According to another aspect of the invention, a magnetic drive device as aforesaid may include a further flux concentrator which is movable relative to the drive, so as to adopt a first position relatively close to the drive to reduce the flux density at one end of the armature travel, thereby causing the device to assume a monostable characteristic when the further concentrator is in that position, and is movable out of the first position into a second position where it has little or no influence on the flux density in the drive, to reinstate the bistable characteristic of the drive.
In an alternative arrangement, the said further flux concentrator may be permanently located very close to one end of the armature travel so as to produce a drive having a permanent monostable characteristic.
In one embodiment of the invention, a single permanent magnet
Barnes & Thornburg
Camcon Ltd.
Lee Kevin
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