Insulative contact sensor

Details Insulative contact sensor Insulative contact sensor

2001-03-02

2002-12-24

Oda, Christine (Department: 2858)

Electricity: measuring and testing

Determining nonelectric properties by measuring electric...

Semiconductors for nonelectrical property

C340S686300

Reexamination Certificate

active

06498470

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to electronic sensors and, more particularly, to apparatus for remote electronic monitoring and detection of imminent failure of high speed rotating equipment such as for aerospace applications where power, weight, and electrical supply are severely restricted.
In various machine structures with high-speed relative moving parts it is of utmost importance to detect imminent component failure. Such failure could lead to costly damages and/or catastrophic loss of life and equipment, as would be the case for many aerospace applications. The simplest techniques for detection of imminent component failure are by means of periodic visual inspections, manual measurements, or by detection of secondary phenomena such as noise levels, temperature variations, or the like. These detection methods are accomplished at considerable effort and expense, frequently produce questionable or unreliable results, and are of no use whatsoever to warn of imminent failure when the machinery is operational, and in flight as would usually be the case for aerospace applications.
Electrical and temperature detection means have been used widely in the past in an effort to monitor operating performance of machine structures with relative moving parts. Most have involved monitoring and detection of bearing wear. Of particular interest in this regard are the following references and examples:
U.S. Pat. No. 3,102,759, Sept. 3, 1963, for Journal Bearing Wear Detector, involves the use of an insulated wire embedded in the bearing material as a wear detector in railroad car journal bearings. When the bearing material has worn to expose the wire, an applied current will short circuit through the bearing and an appropriate indicator will expose the short circuit.
U.S. Pat. No. 3,108,264, Oct. 22, 1963, for Bearing Wear Sensor, employs a bearing wear monitor device incorporating small diameter wires connected to a normally energized holding coil. The wear monitor device is installed at very close proximity to a shaft such that when the shaft bearing wears a predetermined amount, the wire insulation rubs off and the holding coil short-circuits.
U.S. Pat. No. 3,775,680, Nov. 27, 1973, for Device for the Detection of Wear, discloses placement of an electrical resistor on the wear surface of a machine element, such as a bearing. The current carrying cross section of the resistor is reduced as a function of wear, the extent of which is measurable with suitable electrical circuits.
U.S. Pat. No. 3,824,579, Jul. 16, 1974, for Apparatus for Monitoring Bearing Temperature and for Protecting Bearing from Overtemperature, involves placement of a temperature responsive thermistor at close proximity to a bearing. As the bearing changes in temperature, the thermistor experiences a corresponding change in resistance, which is sensed by a protection circuit. Upon overheating, a switch is actuated either to shut down the associated equipment or to energize an indicator alarm.
U.S. Pat. No. 3,897,116, Jul. 29, 1975, for Bearing Wear Detector, provides for a bearing wear detector comprised of an element carried by a shaft and another similar element, which incorporates an insulating coating, fixed to the shaft housing. As the shaft moves excessively due to bearing wear, the two elements contact each other, wear through the insulating coating, and activate an alarm circuit.
U.S. Pat. No. 4,063,786, Dec. 20, 1977, for Self-Lubricating Auxiliary Bearing With a Main Bearing Failure Indicator, discloses an auxiliary bearing, which engages upon main bearing failure thus providing for temporary continued operation until the associated equipment can be shut down. An electrical alarm circuit is also activated when the auxiliary bearing engages, causing the abrading of insulation from an electrical probe.
U.S. Pat. No. 4,584,865, Apr. 29, 1986, for Device and Method for Testing for Motor Bearing Wear, discloses use of a conductive ring element fixed to a rotor stator, while another similar ring element is attached to the rotating rotor. One of the elements is coated with non-conductive material, and means are provided for measuring the resistance between the two ring elements. As the motor bearings wear, displacement of the rotating ring element causes wear of the non-conductive coating, causing a corresponding decrease in resistance.
U.S. Pat. No. 5,017,912, May 21, 1991, for Electrical Detection of Shear Pin Operation, relates to a shear pin with electrical resistance characteristics, the status of which is monitored by an electrical detection circuit which can identify anomalous conditions. Corrective or preventive action is possible based on signals indicating that the shear pin has been sheared or crushed by excess mechanical loads.
U.S. Pat. No. 5,701,119, Dec. 23, 1997, for Linear Bearing with Wear Sensors, relates to a bearing liner equipped with electrically isolated electrical conductors. The liner is positioned between inner (rotatable) and outer (fixed) bearing rings, and is fixed to the stationary ring. Wear on the bearing liner causes the inner ring to contact and electrically connect the electrical conductors, a condition which is detected by an electrical circuit, thereby warning of excessive wear.
Other conventional sensors, such as Bentley probe, monopoles, and contact switches have been used to detect various failure modes of rotating equipment. Bently probes are Proximity sensors/probes, and are used for measurement of the gap or “proximity” on rotating equipment. The usual applications of these devices require employment of substantial structural supporting elements, significant external electrical power sources, and the sensors are only able to detect the occurrence of major performance anomalies, rather than imminent failures.
These references and examples, however, suffer from one or more of the following disadvantages:
a) The rotating speed is lower then normally encountered in aerospace applications.
b) Many of the cited devices are designed to indicate gradual wear rather then imminent failure.
c) An external electrical source must be applied to detect wear or failure.
d) An independent electrical monitoring system and electrical supply system is required to obtain the desired measurements.
e) Excessive weight prevents use of the system for aerospace applications.
f) Temperature changes are measured to indicate wear, and such changes are unduly slow to detect high-speed aerospace failure modes.
g) The detection system requires excessively high electrical power sources.
h) The weight of the detection system is excessive for aerospace applications.
For the foregoing reasons, there is need for a light-weight device capable of operating under conditions where power and electrical supply are severely limited, and be able to detect and provide a timely warning when high speed rotating equipment is in danger of imminent failure.
SUMMARY OF THE INVENTION
A sensor is provided to detect imminent failure of rotatable equipment that has lost centerline control and is near catastrophic failure. The sensor system is comprised of a linear stainless steel tube, the inner surface of which is tightly lined with a non-metallic tube. Permanently potted within the combined tube element is a thin gage insulated input wire with a fuse connected in series, and thin gage insulated return wire. The end of the input wire, the contact wire, is placed in direct contact with a disk made of a semiconductor material. Bonded to the semiconductor disk is another disk made of an abradable material. The return wire is connected between the fuse and the semiconductor disk and provides an electrical return path for detection of a change in electrical continuity.
The complete sensor system is placed at close proximity to the rotatable equipment being monitored. The abradable and semiconductor disks, between the contact wire and the rotatable equipment, act as insulators from errant grounding. Loss of rotatable equipment centerline control will cause physical contact between the contact wire

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