Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2001-07-17
2004-11-16
Fureman, Jared J. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462010, C235S454000, C235S470000, C356S618000, C073S862324, C702S043000, C250S231160
Reexamination Certificate
active
06817528
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to measuring methods and systems. The present invention is also related to optical measuring methods and systems. In addition, the present invention is related to methods and systems for measuring the angular displacement and relative torque between two rotating shafts. The present invention is additionally related to non-invasive optical measuring techniques. The present invention is also related to optically sensing techniques for measuring relative mechanical characteristics between rotating members within a mechanical system.
BACKGROUND OF THE INVENTION
Torque Sensors
A variety of techniques for measuring torque in mechanical systems have been attempted. To date, however, none of these techniques have been completely satisfactory. Several methods of measuring torque within a shaft, strain or optical gauge have been described in the literature. As explained herein, such measuring techniques are generally limited in their scope and applications and are inherently unreliable in both their efficiency and accuracy.
Torque can be measured in a shaft by bonding strain gauges in a cross arrangement along helical lines of compression and tension. The strain gauges can be electronically configured via a balance-bridge and coupled to measuring electronics through slip rings or non-contacting rotary transformers. Generally, these cross arrangements are difficult to implement and usually require custom installation.
In optical torque transducers, light beams, code patterns and light sensors convert the differential angular displacement between two positions on a shaft into an output signal, due to applied torque. Specifically, identical patterns made of light reflecting strips can be arranged around the circumference of the shaft at two locations. The patterns may be illuminated by laser diodes and the reflected light sensed by a photocell. The output of each photocell can be configured as a pulse train wherein the phase difference is a measure of the torque. In a similar device, which is taught by Kawamoto, U.S. Pat. No. 4,767,925
, Optical Type Relative Rotation Measurement Apparatus
, a pair of light emitting and receiving elements produces an output dependent on the amount of light transmitted due to the relative rotation of two slotted disks. Levine, U.S. Pat. No. 4,433,585
, Device for Measurement of the Torsional Angular Deviation of a Loaded Rotating or Static Shaft
, discloses a technique for passing a beam of light through two diffraction gratings placed at different locations along a shaft and sensing the phase of the two resulting beams. Such techniques and devices thereof are not robust because they require precise alignment for optimal functioning.
U.S. Pat. No. 5,001,937
, Optically Based Torsion Sensor
to Bechtel et al., discloses an optically based torsion sensor that measures the phase displacement between two bands of alternating high and low reflectivity regions. A major drawback of this device is its dependence on the initial alignment of the two bands. In addition, minor differences in the rise time of detecting electronics will cause serious errors in measurement. U.S. Pat. No. 4,525,068
, Torque Measurement Method and Apparatus
to Mannava et al., discloses a torque sensor utilizing optical Doppler measurements. Since Doppler measures velocity only, this device suffers from a serious shortcoming in that it must infer torque from changes in instantaneous rotational velocity of two different sections of a shaft.
Two optical methods for measuring the strain of an object are noteworthy. U.S. Pat. No. 4,939,368
, Polychromatic Optical Strain Gauge
, to Brown, discloses an optical grating to measure strain in a stationary object. The device is complicated in that it requires two frequencies of light and has no provision for measuring a moving object such as a rotating shaft. U.S. Pat. No. 4,432,239
, Apparatus for Measuring Deformation
, to Bykov, discloses an apparatus for measuring the deformation of an object. The device utilizes an electro-optical frequency modulator to produce two components from an incident laser beam. A polarization splitter further splits the light into two different frequencies, which illuminate a diffraction grating on a stationary object. This device is also complicated and expensive and has no provision for measurement of a moving object such as a rotating shaft.
The literature discloses a capacitive torque sensor consisting of two encoders either mounted perpendicular to the shaft at each end or mounted along the circumference at two closely placed points along the shaft. For example, see
Interest in Misfire Detection Technology Grows
, Automotive Electronics Journal, Nov. 6, 1989, pg 12. Each encoder has two parts: a stator that consists of up to 256 radial fingers that are alternately charged; and a rotor that is generally mounted on the shaft. As the shaft turns, the rotor's potential switches between positive and negative at a frequency proportional to speed. A disk, at the center of the stator, electrically isolated from the charged fingers, collects the signal. Like the optical torque sensor, the twist of the shaft is determined by measuring the phase difference between the two encoders. Also, like the optical sensor, this device requires precise alignment.
Finally, magnetic torque sensors comprise much of the prior art. The magnetic properties of most ferromagnetic materials change with the application of stress to such an extent that stress may be ranked with field strength and temperature as one of the primary factors affecting magnetic charge. Magnetostriction is a measure of the stress sensitivity of a material's magnetic properties. Magnetic-based torque sensors take advantage of the magnetostrictive properties of ferromagnetic metals, such as carbon steel. See
Noncontact Magnetic Torque Transducer
, Sensors, November 1990, pp. 37-40. These sensors make a contact-less measurement of changes of magnetic permeability in shaft materials, which are caused by torsional stress.
In place of strain gauges, magnetic flux is directed into the shaft and along the helical lines of compression and tension. A positive magnetostriction shaft experiencing torsion will exhibit increased permeability along the line of tension and decreased permeability along the line of compression. At low stress levels the permeability is nearly linear with stress but varies dramatically at high stress. Another drawback of a magnetostrictive torque sensor is in the need for calibrating it individually with each shaft. This requirement is obvious because the torque measurement is made by means of the magnetostrictive properties of the shaft material and cannot be predetermined in the manufacture of the sensor by itself.
The variability in magnetostrictive properties is usually correlated with the variability of the mechanical hardness of the material. Hardness variability of shaft materials typically ranges from +10% to +40%. The shaft-to-shaft variability problem has been addressed in recent research by adding either a sleeve or coating of a well-defined and magnetically soft material, such as nickel, permalloy, or ferromagnetic amorphous alloys. While this approach shows promise, installation can not be made in situ, and all magnetic materials, even the softest, can retain some magnetism, leading to non-linearities and drift.
Each of the above-mentioned techniques for measuring torque falls short of the ideal due to a variety of shortcomings, which include high cost, inadequate resolution and sensitivity, extreme dependence on precise alignment, inability to be applied in situ, or susceptibility to environmental conditions. Therefore, there exists a need for an economical, accurate, simple, non-contact sensor for the measurement of relative torque.
Moirè Fringes and Talbot Self-Image Effect
When electromagnetic rays, including light rays, are impinged and reflected off a pattern contained within an encoded surface, such as a diffraction grating, a bar code or a grooved s
Abeyta Andrew A.
Fureman Jared J.
Honeywell International , Inc.
Ortiz & Lopez PLLC
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