Electricity: measuring and testing – Electrical speed measuring – Including speed analog electrical signal generator
Reexamination Certificate
1998-06-16
2001-12-04
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed analog electrical signal generator
C324S207130, C073S514390
Reexamination Certificate
active
06326777
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to sensing devices, and more particularly to devices for sensing changes in the velocity of a moving body.
There are many applications in science and industry for apparatus to measure velocity accurately and particularly to sense changes in velocity. Such velocity could be peripheral i.e. tangential or rectilinear.
One illustrative application in which such sensors could find great utility is in the aviation industry, and more particularly in the field of helicopter, or rotary wing, aviation. For the purposes of illustration, the following discussion will refer to the field of helicopter aviation but it should be noted that the invention is not limited to this particular field and that it may be employed in any industry or field of technology wherein it is desired to sense changes in the velocity of a moving body.
It has previously been proposed to employ sensors to monitor various components of rotary wing aircraft to enable mechanical problems to be spotted and dealt with before they pose a threat to the safety of the aircraft.
A number of recent air accidents have shown that the powertrain, and more particularly the geartrain, of an aircraft is particularly vulnerable to mechanical problems. To counter this threat, it has previously been proposed to install sensors to monitor the condition of the powertrain and gearboxes in particular. One such sensor which has previously been employed comprises an inertia device, such as a piezoelectric sensor, which is mounted on the geartrain housing, for example, of the aircraft.
It was previously postulated that an inertia device, such as a piezoelectric sensor, would be suitable for sensing the degradation of the gears within the housing, as any such degradation would give rise to vibrations that would cause the piezoelectric device to be subjected to inertia forces whereupon a signal would be generated that could be monitored. However, it has been noted by the present inventor that these inertial devices do not provide an accurate indication of the state of the gears within the housing. As a result of this, it is not uncommon for engineers to strip a gearbox, for example, in response to a detected problem only to find that the geartrain is in fact operating properly. In other instances, geartrains have failed without the sensors indicating that there is a problem to be addressed. It is apparent therefore that inertial sensors are not suitable when used to infer from a detected vibration the integrity of rotating, or otherwise moving, members of an aircraft component.
A number of alternative sensors have previously been proposed. For example, U.S. Pat. No. 4,751,459, European Patent Specification No. 0769700 and United Kingdom Specification No. 2257527 each disclose a sensing device comprising substantially U-shaped magnetic yoke which is fittable over the edge of a rotatable body to provide an indication of changes in the rotation velocity of the body. Whilst these sensing devices adequately enable the velocity changes of a moving body to be detected, they have their own set of associated problems and as such are generally unsuitable for use in certain applications.
For example, practical investigations have determined a number of problems associated with the use of these previously proposed sensors in the illustrative field of rotary wing aviation. A first problem is associated with the fact that the above mentioned systems are inordinately massive. In any device employed in an aircraft it is a requirement that the mass (weight) of the component should be reduced consistent with satisfactory formation.
A second problem is associated with the fact that all of the previously proposed mechanisms necessitate the provision of a magnetic circuit that extends from one face of the rotating component around the periphery of the component to the other face thereof. This is disadvantageous as the extension of the sensor beyond the periphery of the component requires the component casing to be enlarged in order to accommodate the sensor. It has also been noted that the portion of the magnetic circuit extending around the periphery of the sensor represents a large proportion of the total weight of the sensor, and thus that the weight of the sensor could be significantly reduced if this portion of the magnetic circuit could be removed.
SUMMARY OF THE INVENTION
It is an object of the invention to address these and other problems associated with previously proposed sensing devices.
According to the invention there is provided a device for sensing velocity variations in a conductive body moving through a magnetic gap between two discrete portions of a magnetic circuit, the magnetic circuit generating a magnetic flux in the gap to induce eddy currents in the body moving therethrough, the device comprising eddy current sensor means defining at least one further gap through which the body is also moved, and at least one sensor coil having a voltage induced therein by variations in the induced eddy currents, said voltage being detectable to provide an indication of variations, that is to say accelerations or decelerations, in the velocity of the moving body.
Thus a voltage is induced in the sensor coil only when variations occur in the eddy currents and variations occur in the eddy currents only when the velocity of the moving body varies. Accordingly, the sensor produces an analogue of the eddy currents which is an analogue not of velocity but, since it measures the variations in the flux from the eddy currents, of acceleration. If there is no rate of change in flux, no voltage will be induced in the sensor coil, that is to say in a steady state of no velocity changes there will be no output from the sensor coil.
Preferably, the two discrete portions of the magnetic circuit comprise a first permanent magnet having a north pole and a south pole, and a second permanent magnet having a north pole and a south pole, the first magnet being provided on one side of the moving body, and the second magnet being provided on the other side of the moving body such that the second magnet north pole opposes the first magnet south pole and the second magnet south pole opposes the first magnet north pole.
Alternatively, the two discrete portions of the magnetic circuit may comprise a permanent magnet provided on one side of the moving body and a body of soft magnetic material provided opposite the permanent magnet on the other side of the moving body.
As a further alternative, the two discrete portions of the magnetic circuit may comprise a first magnet having a north pole piece and a south pole piece interconnected by a body of soft magnetic material and provided on one side of the moving body, and a second magnet having a north pole piece and a south pole piece interconnected by a body of soft magnetic material and provided on the other side of moving body with the second magnet north pole piece arranged opposite the first magnet south pole piece and the second magnet south pole piece arranged opposite the first magnet north pole piece.
As a further alternative, the two discrete portions of the magnetic circuit may comprise a first magnet having a north pole piece and a south pole piece interconnected by a body of soft magnetic material and provided on one side of the moving body and a body of soft magnetic material provided opposite the first magnet on the other side of the moving body.
Alternatively, the two discrete portions of the magnetic circuit may comprise a first permanent magnet having a north pole and a south pole and provided on one side of the moving body, and a second magnet having a north pole piece and a south pole piece interconnected by a body of soft magnetic material and provided on the other side of the moving body, and first magnet north pole being provided opposite the second magnet south pole and the first magnet south pole being provided opposite the second magnet north pole.
Preferably, the magnetic flux is generated in a direction perpendicular to the plane of the moving body.
The eddy curr
Oda Christine
Penny & Giles International PLC
Schneck Thomas
Zaveri Subhash
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