Bleaching and dyeing; fluid treatment and chemical modification – Fluid treatment – Manipulation of liquid
Reexamination Certificate
1999-06-24
2002-07-16
Stinson, Frankie L. (Department: 1746)
Bleaching and dyeing; fluid treatment and chemical modification
Fluid treatment
Manipulation of liquid
C068S012060, C068S012020, C068S012160
Reexamination Certificate
active
06418581
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to the field of laundry washing machines. More specifically, the invention comprises a method and apparatus for measuring load imbalance in the spinning drum of a washing machine, and then using the value of the load imbalance to calculate the maximum safe spinning speed during the water extraction cycle.
BACKGROUND
2. Description of Prior Art
Laundry washing machines typically use a rotating drum to agitate the clothes being washed. Turning to
FIG. 1
, which contains cutaways to aid visibility, washing machine
10
has drum
12
, which rotates around horizontal axis
14
. Clothing load
18
is contained within drum
12
. After clothing load
18
has been taken through the washing and rinsing cycles, it is necessary to remove excess water before the clothes can be removed and placed in a dryer. This goal is typically accomplished by rotating drum
12
at a relatively high speed, so that centrifugal acceleration forces clothing load
18
against the interior surface
20
of drum
12
. As the rotation of drum
12
is continued, the water within clothing load
18
flows out through perforations in interior surface
20
, and is removed via channeling means within drum
12
(not shown).
While many methods are employed to ensure even distribution of clothing load
18
, load imbalance is a frequent problem. If clothing load
18
is not evenly distributed, the resulting imbalance will cause a vibration while drum
12
is spinning. If the imbalance is significant, this vibration can cause the rotating drum
12
to strike chassis
16
, resulting in damage to the machine. Thus, the detection of an imbalanced load is important for safe operation of washing machine
10
.
Several methods have been previously used to detect an unbalanced condition. First, mechanical limit switches (“trembler” switches) can be mounted on chassis
16
to detect an unbalanced load. If sufficient vibration builds, the “trembler” switch will make contact and the resulting circuit is used to trigger a shut-down of the machine.
The same result can be accomplished with an electrical accelerometer switch. This type of device measures oscillating acceleration (vibration) by measuring the mechanical force induced in a load cell. Like the trembler switch, it sends a shut-down signal if a fixed vibration threshold is exceeded.
Yet another method of detecting load imbalance is to monitor the variation in drive motor load when drum
12
is rotated at low speed.
FIG. 2
shows a simplified rear view of washing machine
10
. Drum pulley
22
is attached to the rear of drum
12
. Drive motor
28
is mounted to chassis
16
, in the area below drum
12
. Drive motor
28
has motor pulley
24
, which drives drive belt
26
. Drive belt
26
, in turn, drives drum pulley
22
, which drives drum
12
. An imbalanced load in drum
12
, will therefore cause a variation in the load experienced by drive motor
28
. In order to understand this phenomenon, the reader's attention is directed to FIG.
3
.
FIG. 3
shows a front view of washing machine
10
, again in simplified form. The imbalanced load is represented by a single unbalanced mass
30
. Drum
12
is spinning in the direction indicated by the arrow. When unbalanced mass
30
is in the position depicted in
FIG.3
, the gravitational force on unbalanced mass
30
(Fw), opposes the driving torque of drive motor
28
, thereby increasing the load. When unbalanced mass
30
is in the position depicted in
FIG. 4
, the gravitational force acts in the same direction as the driving torque, thereby decreasing motor load. The result is a sinusoidal variation in motor load, resulting from the raising and lowering of unbalanced mass
30
within the earth's gravitational field. The reader will appreciate that this phenomenon is only observed in washing machines having an off-vertical spin axis. For a machine having a purely vertical spin axis, there will be no load variation caused by gravity.
The magnitude of the load variation within drive motor
28
is proportional to the magnitude of unbalanced mass
30
. Thus, if the load variation can be accurately sensed, the magnitude of the imbalance can be determined. The variation in motor load will cause a small variation in motor speed. If drive motor
28
is equipped with an accurate tachometer, it is possible to measure this variation in speed, and it is therefore possible to calculate the magnitude of the imbalanced load. This magnitude is then used to determine whether the load is sufficiently well balanced to initiate the spin cycle. This method is typically employed at a relatively low spin speed in order to detect any imbalance before the vibration has built to a dangerous level. If the load is sufficiently well balanced, drum
12
would then be accelerated to the speed normally used during the spin cycle.
All of these methods, consisting of the trembler switch approach, the accelerometer approach, and the motor load sensing approach, traditionally result in a “GO/NO-GO” decision on the spin cycle. If clothing load
18
is sufficiently balanced, the machine will proceed to the spin cycle. If clothing load
18
is not sufficiently balanced, several things may occur. Many machines are programmed to stop and then begin a series of motions intended to redistribute the load. Other machines will simply shut down and await operator intervention. Even for those machines with provisions for an attempted redistribution, the redistribution will only be attempted a few times before the machine shuts down. The result is that a significantly imbalanced load will cause the machine to shut down before the spin cycle, meaning that clothing load
18
will be left soaking wet. The operator often discovers the machine in a seemingly inoperative condition and, unaware that it needs to be reset, places a needless service call. Additionally, the three approaches described require the use of an extra sensor or sensors, thereby adding cost and reliability concerns.
A more sophisticated solution is described in U.S. Pat. No. 5,161,393 to Payne et. al. (1994). The Payne device seeks to calculate the load imbalance, and then use this value to select among several available terminal spin speeds in order to ensure that a maximum permissible vibration is not exceeded. It calculates the load imbalance in a two-step process. First, the device applies a fixed torque to the spinning drum at relatively low speed (approximately 30 to 50 rpm) and measures the time interval required to accelerate the drum to 250 rpm. This time measurement is used to calculate the moment of inertia of the load within the drum, and thereby obtain an approximate value for its mass. The reader should note that, over this relatively low speed range, the time interval is not significantly sensitive to load imbalance; i.e., an imbalanced load will accelerate at nearly the same rate as a balanced one. Thus, the first time interval is measured to determine mass, irrespective of imbalance.
As the drum is accelerated past 250 rpm, a significant load imbalance will retard the acceleration of the drum. This phenomenon is illustrated by
FIG. 29
in the Payne et.al. disclosure. An unbalanced load will take longer to accelerate from 250 to 600 rpm, as shown by the diverging angular velocity curves. This information, when used in conjunction with the total load information obtained during the acceleration from low speed to 250 rpm, is used to determine the imbalance. The magnitude of the imbalance is then used to determine what maximum spin speed will be selected from among several discrete available speeds.
The Payne et.al. invention does require reasonably accurate measurement of drum speed and elapsed time. These requirements do not necessarily necessitate additional sensors, however. The reader will note from the Payne et.al. disclosure that the spinning drum is directly coupled to an electric drive motor. The motor controller would typically have time and motor speed sensing means. Thus, by monitoring existing functions of the motor contro
Adcock Albert Ford
Bruce Mats Gunnar
Oswald Christopher Andrew
Adams, Schwartz & Evans P.A.
Ipso-USA, Inc.
Stinson Frankie L.
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