Measuring and testing – Vibration – Sensing apparatus
Reexamination Certificate
1998-11-20
2001-09-04
Moller, Richard A. (Department: 2856)
Measuring and testing
Vibration
Sensing apparatus
C068S023100
Reexamination Certificate
active
06282965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to clothes washing machines, and more particularly, to a method and system for detecting a tub imbalance condition in a washing machine.
2. Description of Related Art
Residential and commercial clothes washing machines are well known. A generally cylindrical tub or basket for holding the clothing and other articles to be washed is rotatably mounted within a cabinet. Typically, an electric motor drives the tub. During a wash cycle, water and detergent or soap are forced through the clothes to wash them. The detergent is rinsed from the clothes, then, during one or more spin cycles, the water is extracted from the clothes by spinning the tub.
One way of categorizing washing machines is by the orientation of the washing machine tub. Conventional, vertical-axis washing machines have the tub situated to spin about a vertical axis. Articles to be washed are loaded into the tub through a door, which is usually situated on the top of the washing machine. A vertical-axis washing machine tub includes an agitator situated therein, which cleans clothes by pushing and pulling them down into the water. A motor typically drives the agitator, in addition to spinning the vertically-oriented tub during spin cycles. The motor usually operates at a constant speed, and a series of gears or belts are configured to drive the proper component at the proper time during each washing machine cycle.
Horizontal-axis washing machines, having the tub oriented to spin about an essentially horizontal axis, do not include an agitator, and a variable-speed motor drives the tub. During wash cycles, the tub of the horizontal-axis washing machines rotates at a relatively low speed. The rotation speed of the tub is such that clothes are lifted up out of the water, using baffles distributed about the tub, then dropped back into the water as the tub revolves.
Both vertical and horizontal-axis washing machines extract water from clothes by spinning the tub, such that centrifugal force extracts water from the clothes. It is desirable to spin the tub at a high speed and extract the maximum amount of water from the clothes in the shortest possible time, thus saving time and energy. The distribution of the clothes about the periphery of the tub affects the washing machine's ability to spin the tub at a high speed.
Vertical-axis washing machines are especially susceptible to imbalance problems. Several factors contribute to this predicament. For instance, when a wash or rinse cycle completes and the water is drained from the tub, the clothes are gathered at the bottom of the tub, not distributed about the entire tub. In conventional washing machines, the tub typically is not perfectly cylindrical; but rather, includes a draft. When the tub spins, the clothes will “creep” up the sides of the tub. However, since a constant speed motor typically drives the vertically-oriented tub, the motor quickly ramps the tub up to the full spin speed. There is little chance for the clothes to distribute about the periphery of the tub, so they creep up the tub's sides in an unbalanced fashion.
The unbalanced, spinning tub vibrates within the cabinet. In conventional vertical-axis washing machines, if the vibration is too severe, the tub will trip a switch mounted inside the cabinet, stopping the tub's rotation and activating a tub-imbalance alarm. A user then manually redistributes the wet clothes within the tub, and restarts the spin cycle.
Horizontal-axis washing machines typically are less vulnerable to tub imbalances. As discussed above, the tub in a horizontal-axis machine is driven by a variable speed motor. This allows the inclusion of a “distribution” cycle, wherein the tub is rotated faster than the rotation speed of a wash cycle, but slower than in a spin cycle. The tub rotation speed is gradually increased, until the clothes begin to “stick” to the sides of the tub due to centrifugal force. The slower rotation speed allows the clothes to more evenly distribute about the sides of the tub. Once the clothes have been distributed about the tub, the speed is increased to a full spin speed to extract the water from the clothes.
Even though horizontal-axis washing machines may be less prone to tub imbalances, they are not immune to tub imbalance problems. If the clothes do not evenly distribute during the distribution cycle, the unbalanced load within the tub will cause unwanted vibrations as the tub rotates. Rather than applying all of the motor's power to spinning the tub at the highest possible speed, power is wasted in tub movement and cabinet vibrations.
Thus, it is desirable to detect the presence of an imbalance condition in a rotating tub, and take corrective action. However, prior art methods for detecting imbalance conditions have been largely unsatisfactory. The present invention addresses these, and other, shortcomings associated with the prior art.
SUMMARY OF THE INVENTION
In one aspect of the invention, a method of detecting an imbalance condition in a rotating washing machine tub includes receiving an indication of the actual tub rotation speed and comparing the actual tub rotation speed to a predetermined desired rotation speed to calculate a speed error. Maximum and minimum speed errors are determined, and the difference between the maximum and minimum speed errors is determined. A tub imbalance condition is detected based at least in part on the calculated difference.
In another aspect of the invention, a method of detecting an imbalance condition in a rotating washing machine tub includes receiving an indication of a power level required to achieve a given washing machine rotation speed and comparing the required power level to a predefined standard power level associated with the given rotation speed. A tub imbalance condition is detected in response to the comparison.
In yet another aspect of the invention, a system for detecting an imbalance condition for a rotating washing machine tub includes a processor and a memory accessible by the processor. The memory stores a rotation speed demand value. A speed detection device is adapted to indicate the rotation speed of the washing machine tub. The processor is programmed to compare the speed indicated by the speed detection device to the speed demand to calculate a speed error. The processor further is programmed to determine minimum and maximum speed errors, and calculate the difference between the maximum and minimum speed errors to detect an imbalance condition. In an alternative system, the memory stores a standard power level associated with a given rotation speed. The processor is programmed to calculate a power level required to achieve the given washing machine rotation speed indicated by the speed detection device, and compare the required power level to the predefined standard power level to detect a tub imbalance condition.
In a further aspect of the invention, a method of controlling a washing machine tub containing clothes being washed is presented. The method includes receiving an indication of a first tub rotation speed demand for a first operational cycle and receiving an indication of the actual tub rotation speed during the first operational cycle. The method further includes calculating a speed error by determining the difference between the first rotation speed demand and the actual rotation speed at predetermined points in at least one tub revolution of the first operational cycle and determining the range of speed errors. The tub rotation is affected in response to the range of speed errors.
In a still further aspect of the invention, a clothes washing machine includes a cabinet, a tub rotatably mounted within the cabinet, and a motor operably coupled to the tub for rotating the tub within the cabinet. The clothes washing machine further includes a memory storing a rotation speed demand value and a rotation speed detection device. A processor is programmed to detect an imbalance condition of the rotating tub, at least in part by comparing th
French Alan P.
Thorn John S.
Emerson Electric Co.
Howrey Simon Arnold & White , LLP
Moller Richard A.
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