Optics: measuring and testing – By light interference
Reexamination Certificate
2000-02-16
2002-03-19
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
C356S482000, C250S227240
Reexamination Certificate
active
06359690
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to an apparatus, system and method for determining wear and the rate of wear of an article such as for example a carbon brush, a brake pad or tire.
BACKGROUND OF THE INVENTION
Dynamoelectric machines such as direct current (DC) motors use carbon brushes to provide a means for transferring current from an external source to a rotating armature of the motor. The brushes are typically made of a carbon particulate such as graphite and a binder material and may also include metallic particles.
These brushes are typically spring loaded to maintain good electrical contact with a commutator (i.e., slip ring) of the motor. A follower spring is employed to apply a biasing force against the rear end of the brush to cause the other end of the brush to be pushed into contact with the commutator. Since the commutator is in motion with the brushes in contact therewith, the brushes wear down over time. Consequently, these brushes must be replaced before they are completely worn in order to protect the commutator of the motor against damage. Alternating current (AC) machines may similarly employ brushes and commutators for the transfer of electric power and have similar brush wear problems.
Because the operating life of carbon brushes depends, respectively, upon the type of operation and environmental conditions of the installed motor and the desire to utilize the brushes to the maximum possible extent without risk to the commutator, it is good practice to monitor the carbon brushes for a predetermined amount of wear.
Cut-off carbon brushes are occasionally employed which automatically switch off a motor drive when a predetermined amount of wear of the carbon brushes has been reached. However, in the absence of expensive and time-consuming intermediate inspections, it is unforeseeable when the motor drive will be switched off. As a result, a process incorporating such a device must take into account the risk of unexpected shutdown of the motor drive due to brush wear.
Carbon brushes with alarm devices which provide an early warning of the failure due to wear are available. These devices typically include an alarm contact provided by an electrical conductor (e.g., a copper strand) baked into the upper end of the carbon brush by the commutator. When the brush wears by a predetermined amount, the electrical conductor contacts the commutator (or slip ring) which serves to complete an electric circuit or, as by wearing through a loop at the end of the conductor, break an existing circuit. A problem with such a device is that the electrical conductor may cause some damage to the commutator surface if exposed to it for an extended period of time as a result of metal to metal contact. Furthermore, such devices only alert a user that the brush has reached a particular level of wear - such alarm system does not provide a user with the rate of wear of the carbon brush or any type of intermediate evaluation.
Another type of article that is prone to frictional wear is a brake pad. Brake pads in automobiles, for example wear through usage and require periodic replacement. Inspection of brake pads requires the removal of the wheel from the vehicle so that a visual examination may be performed. Many individuals are unwilling and/or unable to perform the inspection or not skilled enough to know what to look for when the wheel is removed.
Many vehicle owners may rely on a dashboard trouble light to indicate when brakes need replacement. However, this trouble light is present to monitor the hydraulic braking system through brake fluid pressure and does not monitor brake pad wear. A squeal from the brakes may be a warning, or may indicate that the rivets holding the brakepad to its backing are contacting a rotor or drum which can cause scoring of the rotor or drum. Should the pad be totally worn out, the noise would be from the pad backing contacting the rotor or drum, which would cause considerable damage to the rotor or drum.
Another article which is prone to wear is a tire for use in an automobile, for example. Tires wear as a result of frictional contact with road surfaces. Furthermore, tires are prone to other problems in connection with pressure and temperature. An improperly inflated tire or worn tire may be manifested as reduced efficiency in gas mileage, reduced performance in ride and handling, reduced performance in vehicle braking, reduced cornering ability, and potential blowout or other catastrophic failure.
Additionally, conventional techniques for monitoring pressure and temperature information relating to an article and/or an environment such as, for example, in a carbon brush or pump chamber often prove to be expensive and/or cumbersome.
In view of the above, there is a strong need in the art for an improved apparatus, system and/or method for determining wear and the rate of wear of an article such as a carbon brush, brake pad or tire, for example. Furthermore, it would be highly desirable to have such an apparatus, system and/or method which can also determine pressure and/or temperature information relating to the article.
SUMMARY OF THE INVENTION
The present invention employs an optical fiber to facilitate the measure of wear and the rate of wear of an article that the optical fiber is embedded in. By embedding at least one optical fiber into the article, information relating to the wear and rate of wear of the article can be obtained. For example, in the case of a carbon brush of a dynamoelectric machine, an optical fiber is embedded into the carbon brush in order to obtain such wear data. As the article (i.e., carbon brush) wears so does the optical fiber which has its length direction disposed substantially parallel to the direction of wear of the article.
A light beam is directed into one end of the optical fiber and the light is transmitted through the optical fiber to the surface of a commutator which the brush is in contact with. The light is reflected off the surface of the commutator and transmitted back through the optical fiber. The present invention employs interferometric techniques to analyze the transmitted light signal (i.e., measurement signal) and a reference signal. From the interferometric techniques, information relating to the wear and rate of wear of the fiber optic cable can be determined. Since the optical fiber is substantially weaker than the article it is disposed in, the wear and rate of wear of the optical fiber is substantially that of the article. Thus, wear and rate of wear of the article can be conveniently determined. Wear and rate of wear may be determined extremely accurately with a precision of a fraction (e.g. {fraction (2/10)}) of the wavelength of the transmitted light beam. Furthermore, most dynamoelectric machines employ a multitude of brushes (perhaps 8 or more). The present invention affords for sharing a common light source and some sensing devices.
The aforementioned technique may be employed to analyze wear and rate of wear of a variety of articles including brake pads and tires. For example, an optical fiber may be embedded in a brake pad such that as the brake pad wears so does the optical fiber in its length direction. By using interferometric techniques as discussed herein, the amount of wear and the rate of wear of the brake pad can be determined. Likewise, the amount of wear and the rate of wear of a tire can be determined employing a similar technique.
Additionally, the present invention provides for determining other information such as that relating to surface assessment, article related temperature and/or environmental pressure, motor speed, and article related pressure and/or environmental related pressure.
Light reflected off a surface of something the article is in contact with will have encoded therein data relating to the condition of the surface. Thus, if the article is in contact with a commutator surface for example, the light reflected off the surface of the commutator will change in intensity relative to the passing of the commutator bars and slots and to the condition
Discenzo Frederick M.
Harris James S.
Amin Himanshu S.
Font Frank G.
Gerasimow Alexander M.
Lee Andrew H.
Reliance Electric Technologies LLC
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