Electricity: magnetically operated switches – magnets – and electr – Permanent magnet-actuated switches – Plural magnets
Reexamination Certificate
2000-12-12
2001-11-06
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Permanent magnet-actuated switches
Plural magnets
C335S205000
Reexamination Certificate
active
06313724
ABSTRACT:
FIELD OF INVENTION
This invention relates to a magnetic proximity sensor with novel features. It is based on a magnetic pole array, which exhibits a balanced magnetic field in one state and unbalanced magnetic field in the opposite state. The transition from one state to the other is accomplished with a minimal sized ferromagnetic substance(s) (magnetic shunt) either added or removed from strategic places on the magnetic pole array. The sensors may perform logical functions, primarily when multiple shunts are used.
DESCRIPTION OF PRIOR ART
Magnetic proximity sensing has been used for many years. There are many different magnetic proximity sensor concepts in use today including static threshold, transient, electromagnetic, and solid-state. The list of prior art for magnetic proximity sensing applications is very long and includes security systems, automation, instrumentation, etc.
The magnetic proximity sensor category of the instant invention is best characterized as the static threshold type using a magnet as part of the mechanism. Typically in this sensor category, a sensing device such as a reed switch, coil, Hall effect or other solid-state device is used for sensing the strength of the magnetic field or the resulting magnetic flux flow.
Most proximity sensors require two devices, one attached to each of the two elements (physical entities) whose relative proximity to each other is being sensed. These devices typically comprise a permanent magnet opposite a reed switch as is commonly used in home security systems. These devices are substantial in size and are therefore undesired for some applications. U.S. Pat. No. 4,745,383 (Zovath et al.) houses the magnet and switch in one device and responds to the proximity of a ferromagnetic shunt-like element. The flux follows two independent paths, one through each side of the pivoting armature. The ferromagnetic external element attenuates the flux through the latched side of a pivoting armature and allows the force in the other side of the armature to tilt the armature to the other position. The limitations of this approach include that the pivoting armature is a moving part, that there is the necessity of forming several relatively precise parts, and that it requires alignment during fabrication. U.S. Pat. No. 4,858,622 (Osterweil) also consolidates both the permanent magnet and the reed switch in one device and a small ferromagnetic shunt constitutes the other device. This proximity sensor overcomes the problem of both devices being bulky and allows a small and unobtrusive device (the shunt) to be attached to the mobile element in a given application. However, U.S. Pat. No. 4,858,622 (Osterweil) is based on employing a magnetic shunt for attenuation of the magnetic field in the area where a magnetic field sensor (reed switch) is located. While the magnet generating the magnetic field and the sensor are fixed in space relative to each other, the removal or replacement of the shunt determines the sensor's response. The shunt is made of a high permeability (&mgr;) ferromagnetic material, usually soft iron, and is placed across the magnet poles. As long as the ferromagnetic material is sufficiently large to completely shunt the magnetic flux, the remaining external field emanating from these poles will be negligible and undetectable by a common sensor such as a reed switch. When the shunt is removed, the magnetic field is restored in the air gap between the poles and the magnetic sensor (the reed switch) is activated. In the existing art, the reed switch is activated when the shunt positioned between the magnet's poles and the reed switch is removed. For repeatable production and reliable performance, the shunt is placed against the magnet in a space between the magnet and the reed switch. One embodiment of U.S. Pat. No. 4,858,622 (Osterweil) shows the reed switch and the magnet on the same side of the shunt. However, this embodiment is very sensitive as to the relative position of the magnet and the switch and will require a complicated alignment procedure in the course of production. U.S. Pat. No. 5,929,731 (Jackson) requires a magnetic element in both devices of the proximity sensor and a multitude of switching elements. It does not meet the objective of having one of the two devices small and unobtrusive. U.S. Pat. No. 5,877,664 (Jackson) is another magnetic field sensing device and can be implemented in the instant invention instead of the reed switch or other sensors.
SUMMARY OF THE INVENTION
The concepts of existing art are based on employing two devices of significant size that encumber the moving element whose proximity to another element is being monitored. Other approaches, like U.S. Pat. No. 4,858,622 (Osterweil), have the deficiency of inactive sensing of the proximity sensor's normal state, as well as inconvenient shunt access.
The instant invention applies the properties of magnetism in a novel manner. A magnetic pole array is constructed in a manner that defines a balanced zone in which all magnetic field vectors of the individual poles of the magnetic pole array substantially cancel each other out. A reed switch is placed in the balanced zone. While the balance is maintained, the sensor is inactive. At least one shunt placed in designated locations of the balanced magnetic pole array disrupts the balance and causes a magnetic field aggregate vector to reach a finite value and activate the sensor. If a balanced magnetic pole array already includes shunts, removal of at least one shunt from the magnetic pole array will also disrupt the balance. When the balance is disrupted, the reed switch is activated.
The primary objectives of the instant invention is to allow a small device (a shunt) to be attached to a moving element whose proximity to the element containing the magnetic pole array and reed switch is being monitored and the sensor (reed switch) is active in its normal state. This novel approach to proximity sensor design in its category offers several advantages. The cancellation of the magnetic field aggregate vector in the balanced zone offers a large field strength ratio between the balanced and the unbalanced state which allows the use of a very sensitive switch, offers a robust design for moderate component tolerances, and reduces the shunt size and mass. The active mode feature in the normal state offers essentially a self-test for the proximity sensor, as well as a more dependable system approach for security and safety uses. The ability to apply multiple shunts to a single magnetic pole array with logical functional relationships between them opens the possibility of a variety of new applications for single proximity sensor usage. For example, a double door using a single magnetic pole array and reed switch on or in the doorframe and with one small shunt on each door, can activate an alarm when either door is opened (OR function), when both doors are open simultaneously (AND function), or when one door is open while the other is closed (Exclusive OR function). An additional advantage of the balanced magnetic pole array approach is the ability to offset the balance in a controlled manner and change the threshold of activation position.
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patent: 3560846 (1971-02-01), Bessko
patent: 4319712 (1982-03-01), Bar
patent: 4331013 (1982-05-01), Jaulmes
patent: 4837537 (1989-06-01), Nakada et al.
patent: 5128641 (1992-07-01), Posey
patent: 5233322 (1993-08-01), Posey
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