[0001] The present invention relates to a washing machine.
[0002] As is known, when loaded inside the drum of a front-loading washing machine, the
laundry accumulates on the bottom of the cylindrical lateral wall of the drum, and
is subsequently distributed dynamically and randomly over the whole lateral wall of
the drum during all the stages in the wash cycle in which the drum rotates about its
longitudinal axis, with the exception of the spin stage, in which the fast rotation
speed of the drum stabilizes and freezes distribution of the laundry on the lateral
wall.
[0003] Almost invariably, the laundry is obviously not distributed perfectly evenly over
the whole lateral wall of the drum, so that, as the drum rotates, and particularly
at the spin stage, mechanical vibration is produced which increases as a function
of the extent to which the laundry is distributed unevenly, instant by instant, inside
the drum.
[0004] To eliminate this drawback, the entire wash assembly of the machine is normally suspended
in floating manner from the machine casing by a system of springs and shock-absorbers
designed to absorb at least part of the vibration.
[0005] Since mechanical vibration produced by rotation of the drum is mainly responsible
for the noise level of the machine and reaches its peak during the spin stage, over
the past few years, motor control strategies have been devised which, by rapidly inverting
the rotation direction of the drum at the start of the spin stage, attempt to distribute
the laundry evenly inside the drum to further reduce mechanical vibration transmitted
to the casing, and so reduce the noise level.
[0006] Unfortunately, in recent years, the maximum rotation speed of the drum during the
spin cycle has increased considerably, so that current solutions for reducing mechanical
vibration of the drum are now inadequate. In an attempt to solve the problem, washing
machine manufacturers have inserted inside the machine casing one or more oscillating-mass
vibration dampers designed to reduce mechanical vibration in the most critical machine
operating conditions, i.e. during the spin cycle.
[0007] The introduction of oscillating-mass vibration dampers and other devices for reducing
mechanical vibration transmitted to the casing has obviously increased the manufacturing
cost of washing machines, with all the problems this entails.
[0008] BE 1012788A6 discloses a washing machine comprising a drum provided with at least three tanks
which may be filled with water before the rinsing phase, and which may be emptied
during the rotation of the drum, so as to balance the imbalance of the drum due to
the presence of the laundry.
[0009] It is an object of the present invention to eliminate at the source mechanical vibration
produced by the drum rotating about its longitudinal axis.
[0010] According to the present invention, there is provided a washing machine, as claimed
in Claim 1 and preferably, though not necessarily, in any one of the dependent Claims.
[0011] A non-limiting embodiment of the present invention will be described by way of example
with reference to the accompanying drawings, in which:
Figure 1 shows a view in perspective, with parts in section and parts removed for
clarity, of a washing machine in accordance with the teachings of the present invention;
Figure 2 shows a schematic section of the Figure 1 washing machine, with parts in
section and parts removed for clarity;
Figure 3 shows a larger-scale detail of Figure 2;
Figure 4 shows a schematic equivalent kinematic model of the washing machine drum.
[0012] Number 1 in Figure 1 indicates as a whole a washing machine, which is particularly
advantageous for home use, and substantially comprises a casing 2 resting on the floor;
a preferably, though not necessarily, cylindrical wash tub 3 suspended in floating
manner inside casing 2 by means of a number of coil springs 4 (only one shown in Figure
1) preferably, though not necessarily, combined with one or more known shock-absorbers
5; a rotary drum 6 housed, to rotate axially about its longitudinal axis A, inside
wash tub 3; and a drive unit 7 connected mechanically to drum 6 to rotate it about
its longitudinal axis A inside wash tub 3.
[0013] Wash tub 3, drum 6, and the other component parts of washing machine 1 suspended
from casing 2 by coil springs 4 form the wash assembly of the washing machine.
[0014] With reference to Figures 1 and 2, washing machine 1 also comprises a laundry weight
detecting device 8 for determining the weight of the laundry currently inside drum
6, and for communicating the weight value to the electronic central control unit 9
of washing machine 1, which in turn optimizes the wash cycle parameters in known manner
as a function of the actual weight of the laundry inside drum 6.
[0015] More specifically, laundry weight detecting device 8 determines the instantaneous
total weight of the current contents of drum 6, i.e. the total weight m
tot of the current amount of laundry inside drum 6. Unlike known solutions, laundry weight
detecting device 8 also extrapolates, from the total weight m
tot of the current amount of laundry inside drum 6, the balanced component and the unbalanced
component of the weight of the laundry inside drum 6. The balanced component represents
the weight of the amount of laundry distributed evenly inside drum 6, and the unbalanced
component represents the weight of the amount of laundry distributed unevenly, and
therefore in unbalanced manner, inside drum 6.
[0016] According to kinematic physics, in fact, the dynamic behaviour of the laundry distributed
randomly on the lateral wall of drum 6 rotating about longitudinal axis A may be represented
schematically as a combination of the dynamic behaviour of a balanced mass m
1 and an unbalanced mass m
2, both located inside the rotating drum 6. The balanced mass m
1 is distributed evenly on the lateral wall of drum 6, and, being perfectly balanced,
causes no mechanical vibration; whereas, the unbalanced mass m
2 is concentrated at one point on the lateral wall of drum 6, and causes vibration
which is absorbed by coil springs 4 and shock-absorbers 5 supporting the wash assembly.
[0017] The weight m
1 of the amount of laundry distributed evenly inside drum 6 obviously corresponds to
the balanced mass m
1 of the kinematic model, and the weight m
2 of the amount of laundry distributed unevenly inside drum 6 corresponds to the unbalanced
mass m
2 of the kinematic model.
[0018] The same obviously also applies to an empty drum 6 rotating about longitudinal axis
A, with the difference that, in this case, the equivalent kinematic model theoretically
only contemplates the presence of a sole balanced mass m
0, seeing as the body of drum 6 is intrinsically balanced.
[0019] In the kinematic laundry model, the weight of balanced mass m
1, the weight of unbalanced mass m
2, and the position of unbalanced mass m
2 on the lateral wall of drum 6 obviously vary from one instant to the next as a function
of the current distribution of the laundry inside drum 6, and are stabilized or frozen
when drum 6 reaches a rotation speed capable of immobilizing the laundry on the lateral
wall of drum 6.
[0020] On the basis of the above equivalent kinematic model, laundry weight detecting device
8 is therefore able to determine the total weight m
tot of the current contents of drum 6, i.e. the total weight m
tot of the current amount of laundry inside drum 6, and also to determine instant by
instant the weight of balanced mass m
1 and the weight and position of unbalanced mass m
2 of the equivalent laundry kinematic model, and to transmit these parameters to electronic
central control unit 9 of machine 1.
[0021] In the example shown, laundry weight detecting device 8 determines instant by instant
the total weight of the wash assembly weighing on coil springs 4, and then determines
the weight of balanced mass m
1 and the weight and position of unbalanced mass m
2 corresponding to the kinematic laundry model, by extrapolating them from the time
pattern, within a predetermined reference time interval and as drum 6 rotates, of
the weight weighing on coil springs 4 supporting the wash assembly. Laundry weight
detecting device 8 obviously also determines the total weight m
tot of the actual amount of laundry inside drum 6 by summing the weight of balanced mass
m
1 and the weight of unbalanced mass m
2.
[0022] With reference to Figures 1 and 2, in the example shown, laundry weight detecting
device 8 indirectly determines the instantaneous total weight of the wash assembly
weighing on coil springs 4, by determining the instantaneous length l of at least
one of coil springs 4 supporting the wash assembly inside casing 2.
[0023] More specifically, laundry weight detecting device 8 statistically processes the
time pattern l(t) of length l of coil spring 4 within a predetermined time interval
ΔT, in which drum 6 rotates at a predetermined rotation speed ω
0 high enough to freeze distribution of the laundry on the lateral wall of drum 6,
so as to determine the mean value l
m of length l of the reference coil spring 4 within the time interval ΔT in which drum
6 rotates at freezing rotation speed ω
0; and then calculates the total weight m
tot of the current amount of laundry inside drum 6 on the basis of the mean value l
m of length l of reference coil spring 4, and taking into account the weight of drum
6 and the way the total weight of the wash assembly of machine 1 is distributed between
coil springs 4 supporting wash tub 3.
[0024] Laundry weight detecting device 8 also statistically processes the time pattern l(t)
of length l of coil spring 4 within time interval ΔT to determine the deviation Δl
in the time pattern l(t) of length l of reference coil spring 4, and then extrapolates
from deviation Δl the actual weight of the mass of laundry theoretically concentrated
in one point on the lateral wall of drum 6, i.e. the weight of unbalanced mass m
2 of the kinematic model.
[0025] Finally, laundry weight detecting device 8 calculates the weight of the mass of laundry
theoretically distributed evenly over the whole lateral wall of drum 6, i.e. the weight
of balanced mass m
1 of the kinematic model, as the difference between the total weight m
tot of the laundry inside drum 6, and the weight of unbalanced mass m
2 of the kinematic model.
[0026] With reference to Figure 1, washing machine 1 also comprises a position sensor 10
for determining a predetermined reference angular position of drum 6 inside wash tub
3, and laundry weight detecting device 8 first compares the signals from position
sensor 10 with the time pattern l(t) of length l of reference coil spring 4 within
time interval ΔT to determine the time difference between the peaks in the time pattern
l(t) of length l of coil spring 4 and the signals from position sensor 10, and then
calculates the angular position of the point on the lateral wall of drum 6 at which
unbalanced mass m
2 of the kinematic model is theoretically concentrated, on the basis of the freezing
rotation speed ω
0 of drum 6 and the above time difference.
[0027] With reference to Figures 1, 2 and 3, washing machine 1 also comprises a drum balancing
device 11, which, under control of electronic central control unit 9, dynamically
balances the laundry inside drum 6 by temporarily forming inside drum 6 a number of
counterweights for compensating the effects of unbalanced mass m
2 of the kinematic model equivalent to the temporary distribution of the laundry on
the lateral wall of drum 6.
[0028] In other words, with reference to Figure 4, drum balancing device 11 temporarily
forms inside drum 6 a number of counterweights rotating with drum 6, and the weight
and position of which are determined so that the resulting dynamic behaviour can be
represented schematically by a kinematic model comprising a balanced mass m
3 and an unbalanced mass m
4, and in which the weight of unbalanced mass m
4 substantially equals the weight of unbalanced mass m
2 of the kinematic laundry model. Moreover, unbalanced mass m
4 and unbalanced mass m
2 of the kinematic laundry model are located at diametrically opposite points on the
lateral wall of drum 6.
[0029] More specifically, with reference to Figures 2 and 3, drum balancing device 11 comprises
a number of (at least three) wash water storage tanks 12 angularly spaced - preferably,
though not necessarily, equally spaced - on the lateral wall of drum 6, and which
are filled with a variable quantity of wash water; and a number of regulating valves
13 for controlling wash water flow to and from individual tanks 12.
[0030] Drum balancing device 11 also comprises a valve control assembly 14, which, under
control of electronic central control unit 9, opens regulating valves 13 on drum 6
independently of one another to adjust the amount of water inside individual tanks
12.
[0031] More specifically, on the basis of a mathematical model for determining, as a function
of the amount of water inside individual tanks 12, the weight of balanced mass m
3 and the weight and position of unbalanced mass m
4 of the kinematic model schematically representing the dynamic behaviour of the counterweights
defined by the masses of water inside tanks 12 rotating about longitudinal axis A,
electronic central control unit 9 of machine 1 calculates the amount of water required
inside each tank 12 to obtain an unbalanced mass m
4 of the same weight as unbalanced mass m
2 of the kinematic laundry model, and positioned diametrically opposite unbalanced
mass m
2 on drum 6, i.e. specularly with respect to the axis of rotation of drum 6, and then
operates valve control assembly 14 to achieve the calculated optimum distribution
of water inside tanks 12.
[0032] In the example shown, drum balancing device 11 comprises three wash water storage
tanks 12 defined by three vessels or cavities 12 formed directly, 120° apart, on the
lateral wall of drum 6; and each tank or vessel 12 is connected to wash tub 3 by a
controlled-release drain valve 13 fitted inside the lateral wall of drum 6 to connect
the inside of vessel 12 to the gap between wash tub 3 and drum 6. Controlled-release
drain valve 13 is designed to selectively and alternatively assume a first operating
configuration, in which it isolates tank 12 from wash tub 3 to prevent water flow
to or from tank 12, and a second operating configuration, in which it connects tank
12 to wash tub 3 to allow water flow to or from tank 12, depending on the position
of tank 12 inside wash tub 3.
[0033] More specifically, controlled-release drain valve 13 comprises a movable shutter
13a for controlling water flow from wash tub 3 to tank 12, and vice versa, by moving,
inside the body of valve 13 and in a direction preferably, though not necessarily,
perpendicular to the lateral wall of drum 6, between a closed position cutting off
water flow through valve 13, and a fully-open position allowing free water flow through
valve 13; and a coil spring 13b, or other elastic member, inserted inside the body
of valve 13 to hold movable shutter 13a in the closed position.
[0034] Valve control assembly 14 is designed to selectively open and close regulating valves
13 on command as the corresponding wash water storage tanks 12 travel through the
bottom portion 3a of wash tub 3, where the wash water normally accumulates during
normal operation of machine 1, or through the top portion of wash tub 3.
[0035] More specifically, in the example shown, movable shutter 13a of each drain valve
13 incorporates a permanent magnet (not shown) oriented with one pole inwards and
the other outwards of drum 6. And valve control assembly 14 substantially comprises
two coils 15 and 16 of electrically conducting material, which are fixed to the body
of wash tub 3, one at the bottom of bottom portion 3a of wash tub 3, and the other
at the top of top portion 3b of wash tub 3; and an electric power unit 17 for circulating
electric current through coils 15 and 16 independently of each other and under direct
control of electronic central control unit 9.
[0036] In the example shown, coil 16 occupies a larger portion of the wall of wash tub 3
than coil 15 underneath.
[0037] Each coil 15, 16 is oriented to generate, when supplied with electric current, a
magnetic field which interacts with the magnetic field of the permanent magnet in
movable shutter 13a of the valve 13 currently facing coil 15, 16, and moves movable
shutter 13a temporarily into the fully-open position in opposition to respective coil
spring 13b. Moving movable shutter 13a into the fully-open position obviously allows
water flow to or from tank 12, depending on the rotation speed of drum 6 about longitudinal
axis A and the position of coil 15, 16 on wash tub 3.
[0038] Operation of washing machine 1 will now be described, assuming wash tub 3 is filled
with water to a predetermined level W high enough to completely immerse tanks 12 moving
past coil 15, and that the selected wash cycle has finished the various stages preceding
the spin stage.
[0039] At this point, before rotating drum 6 at the maximum rotation speed of the selected
wash cycle, electronic central control unit 9 of washing machine 1 operates drive
unit 7 to move all of tanks 12 of drum balancing device 11 successively to the bottom
portion 3a of wash tub 3 and into position facing coil 15, and simultaneously activates
electric power unit 17 to power coil 15 and open the regulating valve 13 of the tank
12 stopped directly over coil 15.
[0040] Since the water level w inside wash tub 3 is high enough to completely immerse the
tank 12 stopped directly over coil 15, opening valve 13 allows wash water to flow
freely into and completely fill tank 12.
[0041] Once all the tanks 12 of drum balancing device 11 are filled, electronic central
control unit 9 operates drive unit 7 to rotate drum 6 at freezing rotation speed ω
0 and so freeze distribution of the laundry on the lateral wall of drum 6.
[0042] When drum 6 reaches freezing rotation speed ω
0, electronic central control unit 9 activates laundry weight detecting device 8, which,
by analysing the time pattern l(t) of length l of reference coil spring 4, determines
the weights of balanced mass m
1 and unbalanced mass m
2 corresponding to the actual distribution of the laundry inside drum 6, and the angular
position on the lateral wall of drum 6 of the point at which the whole unbalanced
mass m
2 of the kinematic laundry model is assumed to be concentrated.
[0043] More specifically, by analysing the time pattern l(t) of length l of reference coil
spring 4 and the signals from position sensor 10, laundry weight detecting device
8 calculates the weights of the balanced mass m
1' and unbalanced mass m
2' corresponding to the kinematic model of drum 6 rotating at rotation speed ω
0 together with the laundry and the masses of water stored in tanks 12.
[0044] In this connection, it should be pointed out that, in theory, the weight of drum
6 is defined at the design stage, and drum 6 is balanced at the production stage and
so forms no part of the unbalanced mass of the kinematic model of drum 6.
[0045] On acquiring the parameters of the kinematic model of the laundry distributed inside
drum 6 rotating at rotation speed ω
0 - or, rather, the parameters of the kinematic model of the system comprising the
laundry and the water inside tanks 12 - electronic central control unit 9 calculates
the amount of wash water required in each tank 12 of drum balancing device 11 to compensate
the unbalanced mass m
2' formed by the laundry and the water in tanks 12 (as stated, drum 6 is balanced at
the production stage and forms no part of the unbalanced mass of the kinematic model
of drum 6), and then operates electric power unit 17 to power coil 16 synchronously
with the passage of individual tanks 12 past coil 16, and so selectively open regulating
valves 13 to drain surplus water from individual tanks 12.
[0046] If drum 6 is not perfectly balanced, by analysing the time pattern l(t) of length
l of reference coil spring 4 and the signals from position sensor 10, laundry weight
detecting device 8 calculates the weights of the balanced mass m
1' and unbalanced mass m
2' corresponding to the kinematic model of a mass system rotating at rotation speed
ω
0, wherein the mass system comprises drum 6 as it is, all the water inside drum 6 (both
inside and outside of tanks 12), and all laundry inside drum 6.
[0047] In this case, on acquiring the parameters of the kinematic model of the mass system
comprising drum 6 as it is, the laundry, and the water inside drum 6 (tanks 12 included),
electronic central control unit 9 calculates the amount of wash water required in
each tank 12 of the drum balancing device 11 to compensate the unbalanced mass m
2' formed by drum 6, the laundry and the water inside drum 6(tanks 12 included); and
then operates electric power unit 17 to power coil 16 synchronously with the passage
of individual tanks 12 past coil 16, and so selectively open regulating valves 13
to drain surplus water from individual tanks 12.
[0048] In both situations, the amount of wash water to be drained from each tank 12 of drum
balancing device 11 is calculated on the basis of the mathematical model, which, as
a function of the amount of water inside individual tanks 12, provides for determining
the weight of balanced mass m
3 and the weight and position of unbalanced mass m
4 of the kinematic model schematically representing the dynamic behaviour of the counterweights
defined by the masses of water inside tanks 12, assuming tanks 12 are all originally
filled completely with wash water, and therefore perfectly balanced, and so form no
part of unbalanced mass m
2'.
[0049] In other words, electronic central control unit 9 assumes the parameters of unbalanced
mass m
2' from laundry weight detecting device 8 depend solely on the uneven distribution
of the laundry on the lateral wall of drum 6 (i.e. unbalanced mass m
2' coincides with unbalanced mass m
2), and regulates the amount of water inside tanks 12 so that the unbalanced mass m
4 produced by optimum distribution of the water in tanks 12 of drum balancing device
11 compensates, and eliminates the effects of, the unbalanced mass m
2' of the kinematic model of drum 6 (i.e. the unbalanced mass m
2 produced by the laundry distributed randomly inside drum 6).
[0050] More specifically, on the basis of the mathematical model for determining the weight
of balanced mass m
3 and the weight and position of unbalanced mass m
4 on the basis of the water distribution inside tanks 12, electronic central control
unit 9 of washing machine 1 calculates the optimum distribution of water required
inside tanks 12 of drum balancing device 11 to obtain an unbalanced mass m
4 of the same weight as unbalanced mass m
2' and located diametrically opposite unbalanced mass m
2' on drum 6, and then operates regulating valves 13 to drain surplus water from individual
tanks 12 to achieve the calculated optimum distribution.
[0051] In the event the mathematical model supplies a number of possible optimum distributions
of water inside tanks 12 of drum balancing device 11, electronic central control unit
9 selects the optimum distribution resulting preferably, though not necessarily, in
the lightest balanced mass m
3, and then operates regulating valves 13 to drain surplus water from individual tanks
12 to achieve the selected optimum distribution.
[0052] To safeguard against calculating errors caused by unequal filling of tanks 12 at
the start of the balancing process or by an unbalanced drum 6- which would result
in the water inside tanks 12 and/or in drum 6 forming part of unbalanced mass m
2' of the kinematic model of mass system -, electronic central control unit 9 of washing
machine 1 may keep track of the changes in individual parameters of the kinematic
model of the mass system as water is drained from tanks 12 of drum balancing device
11, and perform an interactive balancing process for reaching the minimum value of
the unbalanced component of the overall weight of drum 6 and its load.
[0053] In fact, due to the continuous variation of geometrical and constructive parameters
of the washing machine 1 and to non-accurate filling up and draining of the water
from tanks 12, electronic central control unit 9 can provide, at the beginning, a
rough distribution of the wash water in tanks 12. Then control unit 9 performs an
interactive "fine tuning" of the distribution of the wash water in tanks 12, regulating
step by step the water amount inside one or, maybe, two tanks 12 while monitoring
the evolution of the unbalanced component value. In other words, during the interactive
"fine tuning" control unit 9 repeats many times the calculation of the weights of
the balanced mass m
1' and unbalanced mass m
2' of the kinematic model, and the calculation of the optimum distribution of water
required inside tanks 12.
[0054] Obviously, electronic central control unit 9 of washing machine 1 discontinues the
interactive balancing process in the event of failure to gradually reduce the unbalanced
component of the overall weight of drum 6 and its load.
[0055] Dynamic balancing of drum 6 is terminated when electronic central control unit 9
succeeds in regulating the water inside individual tanks 12 of drum balancing device
11 to achieve the calculated/selected optimum distribution. The masses of water stored
inside tanks 12, in fact, define counterweights 12, which rotate about longitudinal
axis A integrally with drum 6, and which have a dynamic behaviour equivalent to the
sum of a balanced mass m
3 distributed evenly on the lateral wall of drum 6, and an unbalanced mass m
4 concentrated at a precise point on the lateral wall of drum 6, at which the weight
of unbalanced mass m
4 substantially equals the weight of unbalanced mass m
2' produced by the laundry distributed inside drum 6, and at which unbalanced mass
m
4 is located, on the lateral wall of drum 6, diametrically opposite the location point
of unbalanced mass m
2'.
[0056] Once drum 6 is balanced dynamically, and seeing as the distribution of the laundry
inside drum 6 remains unchanged as long as the centripetal force immobilizes the laundry
on the lateral wall of drum 6, electronic central control unit 9 of washing machine
1 operates drive unit 7 to increase the rotation speed of drum 6 gradually to the
maximum speed of the spin cycle, with no mechanical vibration being caused by rotation
of drum 6.
[0057] The advantages of the drum balancing method described are obvious: perfectly balancing
drum 6 at the spin stage eliminates the need for sophisticated, high-cost vibration-damping
systems, which have a far from negligible effect on the manufacturing cost of the
machine.
[0058] By eliminating mechanical vibration at the spin stage, the wash assembly suspension
system, i.e. coil springs 4 and shock-absorbers 5, can be designed to simply absorb
minor mechanical vibration produced by low-speed rotation of drum 6.
[0059] Clearly, changes may be made to the method of balancing drum 6 and to washing machine
1 implementing such a method, without, however, departing from the scope of the present
invention, which is defined by the appended claims.
[0060] For example, drain valves 13 may be conventional controlled-open-close solenoid valves.
In which case, valve control assembly 14 may comprise a central control unit fixed
to the casing; and wiring for electrically powering the solenoid valves on the lateral
wall of drum 6. In this case, the solenoid valve central control unit may obviously
be integrated in electronic central control unit 9 of washing machine 1.
[0061] In a further non-shown embodiment, valve control assembly 14 comprises only bottom
coil 15 which, in moving the movable shutter 13a into the fully-open position, can
selectively fill up tanks 12 with water, or drain surplus water from tanks 12. In
fact, when drum 6 reaches freezing rotation speed ω
0, the centrifugal force is high enough to push the water out of each tank 12 even
if said tank 12 faces the bottom portion 3a of wash tub 3 and is submerged in the
wash water.
[0062] In a further embodiment, the washing machine also comprises a second position sensor
10 for determining a predetermined angular position of the drum 6, and a second electronic
control unit 9 which compares the time pattern l(t) of the length l of the coil spring
4 within said reference time interval ΔT with the signals from said second position
sensor 10.