Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-01-27
2003-04-29
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S207230, C324S207240
Reexamination Certificate
active
06556005
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to encoder apparatus, in general, and more particularly, to an encoder capable of resolving magnetically axial and/or rotational displacements independently and including a magnetic snap action switch.
Generally, encoder switches for use in avionics, like for controlling various functions of a display disposed on a cockpit panel, for example, are operative in a severe environment of shock and vibration while maintaining the intended accuracy and resolution, especially over a wide temperature range. As more and more avionic instruments are included on the cockpit panel to assist the pilot during flight, there is a continuing push to make the instruments and their corresponding control switches smaller while improving upon the accuracy and resolution thereof. In some instances, it may be desirable to combine functionality of two devices into one to reduce size and weight. This is no easy chore considering the stressful environment and wide temperature ranges over which these devices are intended to operate with high resolution and accuracy.
For example, well known AB switch encoders are used to control avionic instruments through rotational movement of the switch. These type encoder switches operate on a purely digital basis. Generally, two magnetic sensors are disposed within the switch in a quadrature orientation about either a cogged wheel or a multiple pole permanent magnet that is attached to the switch shaft and rotated past the magnetic sensors. Each sensor produces a pulsed train signal A and B in quadrature to the other in response to the shaft rotation. The angular position and direction of rotation of the switch is resolved by encoding the pulsed signal trains A and B. In order to improve the resolution of these type switches, more cogs, may be added to the wheel or more magnetic poles added to the permanent magnet. This may not result in a problem in and of itself, but to increase density and also reduce the size of the switch introduce alignment difficulties in sensing the angular position of the shaft at the desired resolution. In the environment of an aircraft, for example, the shock and vibration may cause a change in the alignment of the sensor with respect to the more closely spaced cogs or magnetic poles to render an error in angular position. Thus, improvement in this area is considered desirable.
Moreover, optical encoders are being proposed for use as an alternative sensing mechanism to their magnetic counterparts. While these optical devices may offer better resolution, they are much more sensitive to alignment and do not appear to be a viable alternative to magnetic sensing, especially over the wide operational temperature ranges of an aircraft not to mention the severe vibration and shock environments thereof. In addition, the packaging of these optical encoders are not currently designed to provide the necessary protection over the wide operating temperature ranges of an aircraft environment.
Devices that are used to detect axial displacement of the switch shaft, like push switches, for example, currently use a flexible domed element in the base of the switch to offer a “snap action” feel to the operator. When the switch is depressed, the bottom of the shaft makes contact with and flexes the top of the domed element and when the switch is released, the domed element flexes back to its original shape forcing the shaft to spring upward. Over time and with use, the mechanical domed element loses elasticity or collapses in shape, thus causing a loss in the “snap action” feel. This is another area where improvement appears desirable.
As has been indicated above, there is also a push to combine functionality in these avionic control switches and as a result of this push, it is desired to combine the functions of axial and rotational displacement in the same assembly with an improved resolution and accuracy. A muitfunctional encoder of this type with improved resolution would be considered an advance to the current state of the art of encode type switching and very desirable. Accordingly, the present invention intends to over come the aforementioned drawbacks of the current technology in the state of the art encoder and switching mechanisms and satisfy the packaging and performance demands for future applications, especially for avionic instruments.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a switch with magnetic snap action comprises a housing, at least one permanent magnet fixedly disposed with respect to the housing in a cavity of the housing, and a knob shaft including a top portion that is slideably disposed through an opening in the housing, and a bottom portion disposed in the housing cavity and including a member comprised of a magnetically attractive material. The knob shaft is held axially in a first position by a magnetic force between the shaft member and the at least one permanent magnet in the housing cavity. The knob shaft is displaced from the first position for as long as the magnetic force is overcome by an external force applied to the knob shaft, where upon release of the external force, the knob shaft snaps back to the first position by the magnetic force. A method of assembling the switch comprises the steps of: creating a first opening in a bottom side of the housing and a cavity within the housing into which the first opening extends, creating a second opening in a top portion of the housing which extends to the cavity, the second opening being smaller in width than the first opening, affixing a flux washer around an inner periphery of the cavity through the first opening, disposing a top portion of a bushing through the first opening, the cavity and through the second opening of the housing to render a bottom portion of the bushing within the flux washer, disposing a plurality of permanent magnets into cutouts around the periphery of the bottom portion of the bushing in an annular space between the bottom portion and the flux water, and disposing a top portion of a knob shaft though the first opening, the cavity and an opening in the bushing to render a disked shaped member of a bottom portion of the knob shaft comprised of a magnetic material in juxtaposition with the bottom portion of the bushing and form a magnetic connection with the plurality of permanent magnets thereof.
In accordance with another aspect of the present invention, a switch with magnetic snap action comprises a housing, a plate of magnetically attractive material fixedly disposed at an inside periphery of a cavity of the housing, and a knob shaft including a top portion that is slideably disposed through an opening in the housing, and a bottom portion disposed in the housing cavity and including a permanent magnet. The knob shaft is held axially in a first position with respect to the housing by a magnetic force between the permanent magnet and the plate. The knob shaft is slideably displaceable from the first position for as long as the magnetic force is overcome by an external force applied to the knob shaft, whereby upon release of the external force, the knob shaft snaps back to the first position by the magnetic force.
In accordance with yet another aspect of the present invention, an encoder apparatus comprises a housing, a knob shaft including an upper portion disposed through an opening in the housing, and a lower portion disposed in a cavity of the housing and including a permanent magnet magnetized with at least one set of north-south magnetic poles, the knob shaft and its permanent magnet being rotateably moveable in the housing cavity, a plurality of magnetic filled sensors disposed within the housing cavity in proximity to the permanent magnet and distributed angularly thereabout to sense the magnet field strength of the permanent magnet based on the orientation of the permanent magnet with respect to the sensors, each sensor for generating a signal representative of the magnitude of the magnetic field strength sense thereby, and a processor for proces
Calfee Halter & Griswold LLP
Goodrich Avionics Systems, Inc.
Patidar Jay
Rashid James M.
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