Machine element or mechanism – Elements – Flywheel – motion smoothing-type
Reexamination Certificate
2001-04-30
2003-08-19
Kim, Chong H. (Department: 3682)
Machine element or mechanism
Elements
Flywheel, motion smoothing-type
C700S279000
Reexamination Certificate
active
06606922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to systems and methods for enhancing the operation of rotating machinery. More specifically, the present invention relates to an imbalance compensator and an associated method of operation, by which an eccentric load on a driven shaft can be balanced to reduce vibrations and enhance the consistency of loading on the shaft.
2. The Relevant Technology
Rotating parts are common in many different types of machines. For example, most electric motors, internal combustion engines, transmissions, and the like include one or more rotating parts. Although rotating parts are often designed to be symmetrical, machining defects, wear, deformation, and the like often cause the center of gravity of the rotating part to be located some distance away from the axis of rotation. Thus, an eccentric load, or an imbalance, is created.
Eccentricity is often measured in terms of the magnitude of the eccentric load multiplied by the distance of the load from the rotational axis. Thus, eccentricity, or imbalance, may be stated in terms of foot pounds, gram centimeters, or the like.
Imbalanced loads are problematic for a number of reasons. They create vibrations that can cause noise, expedite wear, and potentially even result in failure of the machine, particularly where the frequency of vibration happens to match the natural frequency of some part of the machine. Additionally, imbalanced loads increase the mass moment of inertia of the rotating member, thereby placing a greater load on the driving mechanism. Furthermore, imbalanced loads can induce reciprocating stresses, or “fatigue” stresses in the machine. Fatigue stresses also tend to accelerate wear and failure of machine parts.
Imbalanced loads are particularly problematic for mechanized tools and other machines in which wear of a rotating member occurs rapidly. For example, mills, lathes, drill presses, grinders, and the like rotate tools or workpieces that will experience wear during the machining process. Unfortunately, wear may not necessarily occur evenly about the circumference of the tool or workpiece. Thus, even if the machine is well made and balanced prior to use, imbalanced loads will rapidly appear.
In response to these problems, a number of balancing devices have been created. Although known devices have been helpful in reducing load imbalances in some cases, known balancing devices tend to fall short in a number of ways. For example, many known balancing devices are somewhat complex, and are therefore expensive to manufacture and maintain.
Additionally, many known balancing devices have a somewhat limited range of compensation capability. Thus, they can only be effectively used in applications in which the magnitude of the imbalance is known to be within a certain range. Some balancing devices can be adjusted prior to use, for example, by installing additional weights or removing weights. Such devices cannot dynamically cover a wide range; rather, once an out of-spec imbalance occurs, the machine must be stopped so that the necessary adjustments can be made.
Some known balancing devices provide compensation by moving a gas, for example, through the use of thermal gradients. Unfortunately, gases are not very dense; consequently, a large volume of gas must be moved to provide compensation. The temperature gradients required to keep such volumes in place are difficult to maintain because the temperature within the balancing device tends to even itself out over time through heat transfer from heated parts of the device to those that must remain unheated to maintain the temperature gradient.
A further problem with known balancing devices is that many are simply too large to fit within the space constraints of certain machines. The amount of imbalance a given device can compensate for is dependent upon the size of the device. Some machines simply have a load imbalance/available space ratio that is too high to permit the use of existing balancing devices.
Yet further, many known devices have a limited resolution. For example, some devices have only a limited number of positions in which weights can be moved to provide compensating weight. Thus, the balancing device is unable to fully compensate for any load imbalance that falls between the levels the device is designed to counteract. Hence, the device's ability to fine tune the load balancing is severely limited.
Still further, many known devices are quite heavy. The weight of the balancing device adds to the overall weight of the machine, and also adds to the rotational inertia of the entire rotating system. Consequently, the system cannot start or stop rotation as rapidly as would be possible without the balancing device.
Accordingly, a need exists for an imbalance compensator capable of compensating for comparatively large load imbalances, without requiring a great deal of space around the rotating shaft. A further need exists for an imbalance compensator that is capable of such large scale correction without sacrificing the resolution required for fine tuning. Yet further, a need exists for an imbalance compensator that adds comparatively little weight and rotational inertia to the rotating machine. Still further, a need exists for an imbalance compensator that is comparatively simple in design and manufacture, so that the imbalance compensator can be inexpensively produced and easily adapted to different rotational systems.
BRIEF SUMMARY OF THE INVENTION
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available balancing devices. The present invention provides an imbalance compensator with enhanced compensation range and resolution, with a comparatively lightweight, compact, and simple design.
According to one configuration, the imbalance compensator comprises a balancing ring positioned around a rotating shaft, and attached to rotate with the shaft. The balancing ring may be controlled by a ring controller positioned near the balancing ring to provide control signals and power through magnetic transmission. The ring controller, in turn, may be connected to a control console that contains circuitry pertinent to the operation of the imbalance compensator and provides a user interface. The control console may also be connected to a vibration sensor mounted at a location near the shaft and oriented to measure the shaft's vibration.
The balancing ring may be embodied in several different forms. In certain embodiments, the balancing ring has a housing with a generally annular shape. An interior opening of the housing is large enough to fit around the shaft with clearance. The housing contains a receiving coil positioned near the outer diameter of the housing. The receiving coil is connected to a processor to transmit control and power signals to the processor. Additionally, a phase sensor and a vibration sensor are also connected to the processor to relay data concerning the rotational orientation and vibration of the shaft and balancing ring to the processor.
The processor processes the vibration and phase data to determine which direction the center of gravity of the balancing ring must move to compensate for the load imbalance. The center of gravity of the ring should be moved in a direction substantially opposite that of the load imbalance, with respect to the axis of rotation of the shaft.
According to one embodiment, the processor is connected to a plurality of actuators installed in the housing. Each actuator is connected to a solid compensation mass, in the form of a compensation ring, to apply a force tending to push the solid compensation mass in a certain direction with respect to the axis of rotation of the shaft. The actuators may be axisymmetrically arrayed around the compensation ring to impinge against the compensation ring from opposing directions, thereby providing the capability to relatively move the com
Case Wayne A.
Penswick Laurence B.
Kim Chong H.
Schmitt Measurement Systems, Inc.
Stoel Rives LLP
Thompson John R.
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