Note: Descriptions are shown in the official language in which they were submitted.
CA 02302517 2000-03-28
IMPROVEMENTS IN OR RELATING TO LAUNDRY MACHINES
AND/OR METHODS OF CONTROLLING THE SAME
This application is a division of Canadian Patent
Application Serial No. 2,029,025 filed 27 August 1990.
CA 02302517 2000-03-28
This invention relates to laundry machines and/or
methods of controlling the same.
It is an object of the present invention to provide a
laundry machine and/or methods of controlling the same
which will at least provide the public with a useful
choice.
Accordingly in one aspect the invention consists in a
a method of providing a desired level of washing liquid in a laundry machine
having
a cabinet, a washing container within said cabinet, a rotatable assembly
having a
spin tub within said container and an agitator within said spin tub, a motor
driving
said agitator conjointly with said spin tub or separately on disconnection of
said spin
tub from said agitator as required, and washing liquid level control means to
control
washing liquid level in said washing container, the method comprising:
with a load of clothes in said spin tub, initiating supply of washing liquid
to
said container and energizing said motor intermittently to produce changes in
the
rotational speed of said rotatable assembly as washing liquid is being
supplied to
said container; sensing the changes in speed of said rotatable assembly
relative to
energy input to said motor with a sensing means being indicative of the
resistance to
rotation of said agitator; passing signals indicative of the resistance to
rotation of
said agitator to said control means which resistance to rotation is a measure
of the
2 0 viscosity of the mixture of clothes and washing liquid in said container;
comparing
the viscosity of said mixture with a desired viscosity; controlling the supply
of
further washing liquid to said container with said control means until said
viscosity
is equal to said desired viscosity to provide a required level of washing
liquid; and
causing continuous washing action to commence when said required level is
reached.
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CA 02302517 2000-03-28
In a further aspect the invention consists in
control means for a laundry machine having a cabinet, a washing container
within
said cabinet, a rotatable assembly comprising a spin tub within said container
and an
agitator within said spin tub, and a motor driving said agitator conjointly
with said
spin tub or separately on disconnection of said spin tub from said agitator as
required, and washing liquid admission means, said control means comprising:
sensing means to sense the changes in speed of said rotatable assembly
including the mass of clothes load in said assembly relative to energy input
to said
motor; and washing liquid level control means arranged to control washing
liquid
level in said washing container in response to signals passed by said sensing
means
to said control means, the construction and arrangement being such that said
control
means energize said motor intermittently to sense the resistance to rotation
of said
agitator relative to energy input to said motor, receive signals indicative of
the
resistance to rotation of said agitator from said sensing means which signals
are a
measure of the viscosity of the mixture of clothes and washing liquid in said
container, compare the viscosity of said mixture with a desired viscosity,
control the
supply of further washing liquid to said container until said viscosity is
equal to said
desired viscosity to provide a desired level of washing liquid and cause
continuous
2 0 washing action to commence when said desired level is reached.
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CA 02302517 2000-03-28
In a still further aspect the invention consists in a laundry machine
comprising:
a laundry machine comprising:
a cabinet; a washing container within said cabinet; a rotatable assembly
comprising a spin tub within said container and an agitator within said spin
tub; a
motor driving said agitator conjointly with said spin tub or separately on
disconnection of said spin tub from said agitator as required; control means
comprising sensing means to sense the changes in speed of said rotatable
assembly
including the mass of clothes load in said assembly relative to energy input
to said
motor; and washing liquid level control means arranged to control washing
liquid
level in said washing container in response to signals passed by said sensing
means
to said control means, the construction and arrangement being such that said
control
means energize said motor intermittently to sense the resistance to rotation
of said
agitator relative to energy input to said motor after sensing said
disconnection,
receive signals indicative of the resistance to rotation of said agitator from
said
sensing means which signals are a measure of the viscosity- of the mixture of
clothes
and washing liquid in said container, compare the viscosity of said mixture
with a
desired viscosity, control the supply of further washing liquid to said
container until
said viscosity is equal to said desired viscosity to provide said desired
level of
washing liquid and cause continuous washing action to commence when said
desired
level is reached.
?0 To those skilled in the art to which the invention relates, many changes in
construction and widely differing embodiments and applications of the
invention
will suggest themselves without departing from the scope of the invention as
defined
in the appended claims. The disclosures and the descriptions herein are purely
illustrative and are not intended to be in any sense limiting.
_a_
CA 02302517 2000-03-28
The invention consists in the foregoing and also
envisages constructions of which the following gives
examples only.
One preferred form of the invention will now be
described with reference to the accompanying drawings, in
which;
Figure 1 is a cross sectional elevation of one form of
laundry machine to which the invention is applicable,
Figure 2 is a flow chart of one form of control means
incorporated in the laundry machine of Figure 1,
Figure 3 is a flow chart of a further form of control
means,
Figure 4 is a flow chart of a further form of control
means,
Figure 5 is a flow chart of a part of the control means
of Figures 2 to 4, and
Figures 6 and 7 are graphs of rotational velocity vs
time of the rotatable assembly of the laundry machine of
Figure 1.
Referring to the drawings, Figure 1 illustrates a cross
section of a preferred form of laundry machine, a full
description of which appears in published U.S. patent
specification No.4,813,248 and the description of that
laundry machine in that specification is incorporated
herein by reference.
- S -
CA 02302517 2000-03-28
For the purposes of the present invention the laundry
machine comprises a cabinet 1 within which there is a fixed
container 2 and within that container is a rotatable spin
tub 3 and within the spin tub is an agitator 4. An
interengagement mechanism is provided to enable the spin
tub 3 and the agitator 4 to be raised and lowered when
washing liquids hereinafter referred to as water enters the
container 1 and such mechanism includes an air chamber
shown generally by the reference 5 and is described in the
said specification. The agitator 4 is driven by an
electronically commutated motor 10, driving a shaft 11
carried in bearings 12. This construction is fully
described in the above New Zealand patent specification
which is incorporated herein by reference, including a
reference to parts of a dog clutch or inter engagement
mechanism 13.
A control means 15 is provided preferably associated
with the stator of the motor 10 and such control means
include starting means arranged so that on appropriate
operation of manually operable controls in a console 16 by
an operator, starting up of a washing cycle is commenced
and water is admitted into the container 2 through a valve
17. Motor controls 19 including sensing means t~ sense
changes in speed and energy input to said rotatable
assembly are also provided and the sensing means pass
signals indicating these parameters to the control means.
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CA 02302517 2000-03-28
The washing machine has washing liquid level detection
means which comprise the spin tub 3, the disengagement of
which from the agitator which is caused by its floating and
the air chamber in liquid in the container disengaging the
parts of the dog clutch mechanism 13 and also lifts the
spin tub 3 and this is sensed by sensing means. The
washing machine container 2 also has an auxiliary washing
liquid level detection means comprising for example a
pressure transducer 18 which provides the control means 15
with a signal indicative of the level of water in the
container 2.
It has been found that there are three main methods by
which the control means may determine the load in a washing
machine and therefore control the supply of water or
washing liquid to the level which provides the most
effective wash performance.
In each method, the operator places a load e.g. of
clothes in the spin tub 3 and appropriately operates the
manual controls to give a desired wash.
In one form of the invention relating to a first
control method, the control equipment includes a
microprocessor programmed in accordance with a flow chart
shown in Figure 2, and referring to that flow chart, the
operator operates the appropriate controls in the console
15 such that the microprocessor enters the flow chart at
the start, block 20. The microprocessor causes the
CA 02302517 2000-03-28
agitator and spin tub to rotate to a suitable speed e.g.
approximately 100 rpm and the supply of power to the motor
is controlled by the microprocessor to provide such a
speed. Thus a certain amount of energy is imparted to the
motor rotor, spin tub, and agitator which together comprise
the rotatable assembly of the washing machine, and which,
with the load of clothes, provide the initial resistence to
rotation. Thus energy is imparted to the clothes in the
spin tub. Changes in the velocity of the rotatable
assembly correspond to changes in kinetic energy of the
rotatable assembly and clothes load. Therefore if
electrical energy is provided to the motor such that a
certain velocity (and rotational kinetic energy) is
attained, the time taken for the motor to coast to zero
velocity will be a measure of the mass of the rotatable
assembly and the load of clothes in the spin tub. The
changes or rates of change of kinetic energy of the spin
tub and contents are a measure of the mass of clothes
therein. In Figure 2 the load size is determined at block
22 before water is supplied to the washing container.
Referring now to Figure 5 which a flow chart applicable
to all three methods. This figure is a flow chart showing
the steps involved in the preferred form of load
determination according to the present iwention.
The methcd of Figure 5 determines the changes in
kinetic energy of the rotatable assembly comprising the
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CA 02302517 2000-03-28
motor, drive shaft, interconnecting means, spin tub,
agitator and clothes by supplying a minimum amount of
energy to the motor such that the rotatable assembly
approximates a predetermined velocity e.g. 40 rpm. The
motor and motor controls referred to in the specification
are of the same form as those described in the
specification of our New Zealand patent application No.
213489/213490 filed 16 September 1985, {US Patent
No.4,857,814) which is incorporated herein by reference.
i0 The predetermined velocity is stored in an information
storage means comprising a memory of the microprocessor
which controls the motor and is compared with the
instantaneous velocity of the motor, which as described in
the above specification is constantly calculated by the
15 microprocessor as part of the motor control system
function. The motor control system thus provides sensing
means which sense the kinetic energy of the rotatable
assembly and provide signals indicating the mass of the
rotatable assembly and the rotatable contents {clothes
20 load) thereof to the microprocessor. To enable the
rotatable assembly to reach the predetermined velocity the
pwm period is controlled, effectively controlling the
current input to the motor as it is being commutated so
that the velocity of the rotatable assembly slowly
25 increases. Referring to Figure 5, the algorithm there
illustrated begins at the start block 50. Power is
_q _
CA 02302517 2000-03-28
supplied to the motor winding stages at block 51, as
- described above. It has been found that supplying a
minimal amount of energy to the rotatable assembly is
desirable, since large amounts of energy in the rotatable
assembly mean measurements take a longer time to obtain.
When power is supplied to the motor windings, the velocity
of the motor and rotatable assembly is then monitored by
the motor controller at block 52. A predetermined motor
velocity e.g. 40 rpm is stored in the memory of the
microprocessor and this predetermined velocity is compared
at block 53 with the instantaneous motor velocity measured
in block 52. When the motor velocity is equal to the
predetermined motor velocity, power is removed from the
windings and a timer begins at blocks 54 and 55. At this
stage the motor velocity is still being measured. After
power is removed from the windings the motor speed will
gradually decrease until it eventually stops. The point at
which the motor velocity reaches zero is determined at
block 56 and at this point the timer is stopped at block 57
and the elapsed time is stored in the memory of the
microprocessor. This cycle is repeated, the motor being
energised and de energized intermittently.
Referring now to Figure 6 a graph of velocity vs time
is shown, the origin representing the point at which the
motor velocity is zero, before power is applied to the
motor windings. The point 58 on the vertical velocity axis
- I 0-
CA 02302517 2000-03-28
represents the predetermined velocity and the point 59 on
- the horizontal time axis is a measure of the time taken to
reach the predetermined velocity. When the rotatable
assembly reaches the predetermined velocity 58 the pwm
period is adjusted by means of the motor control system
such that the predetermined velocity is maintained. The
period for which this is maintained is shown as the time
between points 59 and 60 in Figure 6. The points 59 and 60
could be substantially coincidental. The motor is then
turned off at time 60 and allowed to coast. As soon as
power is removed from the motor windings a timer is
activated in the microprocessor and the back emf induced in
the motor windings or the output of hall effect sensors
mounted on the stator is monitored, so that the speed of
rotation of the motor is known. When the rotatable
assembly stops rotating the timer in the microprocessor
records the time taken for the motor to decelerate to zero.
This time may be for example, time 61 or 62 shown in Figure
6 and this time is representative of the inertia of the
rotatable assembly. For example, if there is a large mass
of clothes in the spin tub then the inertia of the
rotatable assembly will be greater and the time taken for
the rotational velocity of the rotatable assembly to reach
zero will be significantly longer than the time taken if
the spin tub had no clothes therein, for example. Since at
this point in the wash cycle the agitator and spin tub are
CA 02302517 2000-03-28
interconnected and the inertia of this apparatus is
. constant, the only factor which will change the time taken
for the motor speed to ramp down will be the load of
clothes in the spin tub and therefore the load is known.
However, due to some spurious variables such as the
changing position of the clothes within the spin tub, any
one reading of the time taken for the speed of the motor to
reach zero will not necessarily be precisely representative
of the load of clothes in the spin tub. Therefore it has
been found that a number of readings e.g. at least one
reading in each direction of rotation is desirable in order
to obtain a true indication of the load of clothes in the
machine. If the readings in each direction provide times
which are within acceptable tolerances of each other, then
these times are compared with time values stored in look up
tables in the memory of the microprocessor which provide
the control system with an indication of the load of
clothes in the machine and therefore the water level which
will be required for the wash routine for that load to
commence. Once the appropriate water level is known by the
control system the wash profile of agitation stroke time,
desired speed of rotation and acceleration is selected in
accordance with the specification of our New Zealand patent
application No.213489/213490.
Although in this form of the invention load measuring
may be carried out with the load of clothes dry, the
' -12-
CA 02302517 2000-03-28
accuracy of load measurements may also be increased by
dampening the clothes before taking the measurements. Such
dampening is effected by rotating the spin tub slowly while
spraying water from the outlet of valve 17 over the clothes
in the spin tub.
Once the load size check has been carried out at block
22 of Figure 2 the microprocessor causes valve 17 to be
opened by a signal from the "water on" block 23. Slow
stirring with reversals or with intermittent supply of
power is carried on at block 24 as has been described
above. At this point the load comprises clothes and water.
The change in kinetic energy is continuously checked as
shown by the circuit 25 containing the slow stir routine at
24. The declutch and disconnection of the agitator 4 from
the spin tub 3 is detected by the air chamber or float 5
interrogation at 26. The spin tub and the agitator are
connected together by the mechanism 13 and initially a
relatively large inertia is present in the associated spin
tub agitator and load of clothes. The inertia of the
rotatable assembly and load is measured as a change in
kinetic energy when the power to the motor is cut off and
the motor is allowed to slow to zero speed after being
maintained at a predetermined velocity as described above.
The water level in the container increases until the float
5 floats the spin tub upwardly in a manner such as to
disconnect the interconnecting means between the agitator
-13-
CA 02302517 2000-03-28
and the spin tub. When this disconnection occurs there is
a sudden decrease in the inertia of the rotatable assembly
which is detected by the sensing means. Referring again to
Figure 6, the disconnection is seen by the sensing means as
a sudden decrease in the time taken for the rotatable
assembly to decelerate from the predetermined velocity to
zero. The time taken for the rotatable assembly to
decelerate after disconnection may for example be only one
tenth that taken prior to disconnection. Thus the time
between points 60 and 62 in Figure 6 may represent the time
taken for the rotatable assembly to decelerate when the
spin tub and agitator are interconnected and the time
between points 61 and 60 may represent the time taken for
the rotatable assembly to decelerate after declutching has
occurred. Thus it can be seen that there is a clear
indication provided to the sensing means that disconnection
has occurred.
It should be noted that the time taken for the
rotatable assembly to accelerate to the predetermined speed
may also be used as an indication of the inertia of the
rotatable assembly and water and clothes therein. The
change in the time required to accelerate the rotatable
assembly is not shown in Figure 6 in order to simplify the
diagram.
Referring now to Figure 7, the time required for the
rotatable assembly of clothes load to reach the
_14_
CA 02302517 2000-03-28
predetermined velocity 58 prior to disconnection is the
time between the origin and point 63. If the same torque
is applied to the motor after disconnection the time taken
to reach velocity 58 is that between the origin and point
59. Again the disconnection of the spin tub from the
agitator is sensed, the signal change indicated to the
control means where, by reference to the look up tables, a
water level for the load is selected. The ramp down times
are not shown for simplicity.
Thus when declutching occurs a further timer commences
operation, allowing the water supply to remain on for a
desired water on overrun time, which is either a
predetermined period, or is of say 10-20~ of the time to
fill the container 2 to declutch. The water on overrun
time is operated in block 27 and when that time has elapsed
at block 28 the "water off" signal operates at 29 causing
' valve 17 to close. The load measured from block 22
indicates the washing profile at block 30 and washing
started at block 31. The washing profile control is
described in the specification of our New Zealand patent
application No. 213489/213490.
Thus in this first method the water level is determined
by adding water after declutching for a period of time
which is either a proportion of the time to fill to
declutching or a fixed further period of time dependent on
the sensed load in the machine.
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CA 02302517 2000-03-28
Referring again to Figure 1, water pressure indicator
l8senses pressure of water in the base of the washing
container and therefore also provides an indication of the
water level in the container 2. If the pressure indicator
18 is present, the routine to time further water supply in
block 27 is not necessary and a branch may be taken from
block 26 to block 32 (dashed lines) which checks the water
level indicator and compares this at block 33 with the
desired water level which has been obtained from look up
tables relating to the load size stored in information
storage means which comprise the memory of the
microprocessor. If the correct water level has been
reached the water off block is returned to at 29, the wash
profile is set by reference to the look up tables and the
wash begins.
Although the load of clothes in the spin tub may be
sensed before water is added to the spin tub by the method
previously described, a second method of determining the
load of clothes in the spin tub is to start the washing
machine motor from a stand still as previously described
but in addition, substantially simultaneously or earlier
admitting water to the container, increasing the rotational
velocity of the motor up until a predetermined velocity is
obtained and then measuring the time taken for the
rotational velocity to drop to zero, as the water is being
allowed to enter the washing container. When a certain
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CA 02302517 2000-03-28
known quantity of water is present in the container, float
will rise and the spin tub will be disconnected from the
agitator such that the spin tub is stationary. As with the
first method since the spin tub comprises a significant
proportion of the.mass of the rotatable assembly, the
inertia of the assembly will suddenly decrease and after
the predetermined velocity is reached, the time taken for
the rotatable assembly to come to a halt will suddenly
decrease by a significant time period. The microprocessor
has in its memory a figure representative of a sufficiently
large time period such that if the measured time period
decreases by an amount which is equal to or greater than
the value stored in a memory of the microprocessor, the
microprocessor will signal that disconnection of the spin
tub from the agitator has occurred. The amount of water
necessary for disconnection to occur will vary depending on
the load of clothes in the spin tub. The microprocessor
has stored the time value indicative of the total load of
the rotatable assembly from the last iteration prior to
disconnection. Thus the load of clothes and water in the
machine is known just prior to disconnection. Since the
time from when water was first introduced to the container
to the time at which disconnection occurs is a relative
measure of the load of clothes in the spin tub depending on
the rate of water flow into the machine, the microprocessor
may now refer to a look up table in order to obtain a value
-17-
CA 02302517 2000-03-28
of the time required to fill the container to a desired
water level. The look up table in the microprocessor
provides a further "water on" time after disconnection
which is a percentage overrun time based on the time taken
to fill the container to declutch.
In the routine of Figure 3, as stated above, operating
the controls causes a routine to start at 20 and the
microprocessor causes the valve 17 to be opened by a signal
from the "water on" block 21. Before load measurement
begins the spin tub may be rotated slowly such that the
outlet of valve 17 sprays water on top of the clothes in
the container in order to ensure that the clothes are
uniformly wet before load measurement begins. In addition
slow stirring is commenced by a signal from block 35, such
slow stir includes acceleration and deceleration sequences
during which there are changes in kinetic energy and the
' speed changes and the mass of the load can be indicated by
sensing means which sense the changes in kinetic energy
over a predetermining timer or between predetermined
speeds. As explained above with reference to Figures 5 and
6, signals indicating the changes in kinetic energy are
then passed from block 36. The spin tub and the agitator
are connected together by the mechanism 13 and initially a
relatively large inertia is present in the associated spin
tub agitator and load of clothes. This inertia is measured
for example as a change in )cinetic energy when the power to
-1$-
CA 02302517 2000-03-28
the motor is cut off and allowed to slow to zero speed as
. previously described. The water level in the container
increases, until the float 5 floats the spin tub upwardly
in a manner such as to disconnect the interconnecting means
between the agitator and spin tub. At this point there is
a sudden decrease in the inertia of the rotatable assembly
and this decrease in inertia is detected by the sensing
means and instead of the microprocessor indicating that the
slow stir is to continue, causes at 37 a signal to be
passed by block 36 indicating that disconnection has
occurred as indicated by the block 38. The momentum or
kinetic energy signal reached in the final stages before
declutching is recorded at block 38 and is passed to block
42. The mass of the clothes load in the spin tub has been
found by experiment to be directly proportional to the
quantity of water, required to float the spin tub. The
water or washing liquid is supplied to the container at a
fixed rate and therefore the time between turning the water
valve "on" and disconnection is also an indication of the
2p load of clothes in the container. Since the water level at
disconnection is known from pressure indicator 18 the load
of clothes is known and the control means can supply tile
appropriate water level for washing. If water pressure
indicator 18 is not present the mass of the clothes load
and the desired washing water level may be calculated by
the control means eg. by the look up tables in the
-lq-
CA 02302517 2000-03-28
microprocessor since the relationship between water level
. at disconnection and clothes load is known and the total
load of water and clothes is known at disconnection. The
operator will have selected a desired degree of
vigorousness of wash and this vigorousness is affected by
the momentum of the spin tub, agitator, clothes and water
contained at the declutch level. Accordingly a desired
rotary stroke of the agitator during washing is set up
according to the momentum figure stored in block 42 as is
described in New Zealand patent specification No.
213489/213490.
Once disconnection or declutching has occurred
according to signals from block 36, (and the timing of such
disconnection depends on the size of the clothes load) the
microprocessor continues to check the load which is still
influenced by the filling of water into the container 2 as
' is indicated in block 39 and the microprocessor determines
at block 40 as to whether a desired water level and load
measurement has been reached. This is achieved by means of
the water pressure indicator 18 from which the
microprocessor has determined the water level at
disconnection. Knowing the water level at this point means
that the load of clothes in the spin tub is known and the
microprocessor then refers to a look up table to determine
the desired water level. The water level may then be
monitored by checking the pressure indicator at block 39.
-20.-
CA 02302517 2000-03-28
Also, once the time to declutch is known the correct water
level may be reached by timing the further water supply as
shown in the block 44 with dashed lines, this time being an
empirically decided percentage overrun time from the time
taken for declutch to occur. When the correct water level
has been reached in block 45 the water valve 17 is turned
off in block 41 and the wash begins in block 43.
Referring now to Figure 4, a third method of
determining the load in the washing machine is shown. As
with Figures 2 and 3 the routine starts at block 20 and
water is turned on at block 21. The slow stir with changes
in speed of the rotatable assembly and corresponding
changes in kinetic energy as described with reference to
Figures 5 and 6 is initiated in block 58. The load
measurement is updated in block 59 and declutching is
detected in block-60. When the water is turned on in block
21 and before the slow stir begins in block 58 the spin tub
is rotated slowly for a brief period so that the water
coming in through valve 17 is sprayed onto the clothes in
the spin tub to ensure that the clothes are substantially
uniformly wet before load measurements are taken. Thus
initially, there are wet clothes about the agitator and
between the agitator and the walls of the spin tub. when
disconnection occurs there will be some water in the
container 2 and there will still be clothes between the
agitator and the spin tub such that the agitator movement
-2(-
CA 02302517 2000-03-28
is restricted by the clothes. As more water is introduced
into the container, the clothes in the spin tub will begin
to float free from the agitator and thus the increased
water in the container reduces the friction between the
agitator and the walls of the spin tub. Therefore if the
agitator is rotated to a certain low velocity and power is
removed from the motor, allowing the motor and agitator to
coast, the time taken for the agitator to reach zero
velocity will gradually increase as more water is
introduced into the container. Therefore the measurements
that began as measurements of the mass of the rotatable
assembly, clothes and water before disconnection become
measurements of the friction between the agitator and spin
tub due to the clothes and water in the container. These
measurements may also be thought of as measurements of the
"viscosity" of the mixture of clothes and water in the
' washing container. When the time taken for the agitator to
reach zero velocity is sufficiently long then the optimum
water level has been reached for good wash performance.
The load measurement on the agitator is compared with the
optimum stored in the microprocessor at block 61 and if the
load measurement is satisfactory the water valve 17 is
switched off at block 62. The load measurement obtained in
block 59 may be passed to block 63 to give a measure of the
load size to set the initial wash profile. Alternatively,
the water pressure indicator 18 may be monitored in order
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CA 02302517 2000-03-28
to determine the water level reached and from this water
level the desired initial wash profile may be determined.
The wash then begins in block 64.
After the washing container has been filled to the
desired level and before the wash begins the clothes in the
washing container will often have a number of air bubbles
therein and when agitation begins these will be expelled
and the water level in the container may drop
significantly. Therefore in each of the methods described,
in machines which are provided with a water pressure
indicator 18, before the wash is started the agitator is
rotated back and forth a small number of strokes in order
to expel the air trapped in the clothes in the spin tub.
Once the air is removed the water valve 17 is turned on
again in order to refill the water container 2 to the
desired level.
From the foregoing it will be seen that methods of
providing an optimum water level for a load of clothes in a
washing machine are provided which are performed
automatically by the machine without any necessary
information or decisions being supplied by the operator,
other than decisions regarding vigourousness of wash.
_23_
