Patent Description:
In general a washing machine includes a drum to be loaded with clothes and a motor to rotate the drum and perform a series of phases in a washing cycle such as washing, rinsing and spinning phases.

When the laundry is not uniformly distributed in the drum and a certain mass is concentrated in a part of the drum, during the rotation of the drum in the spinning phase, vibrations and noise occur due to eccentric rotation of the drum. If such eccentric rotation becomes severe, some parts of the washing machine, such as the drum, the bearings supporting the drum, or the tub may be damaged.

Normally to prevent the above listed damages an unbalance measurement check is implemented, that before spinning measures the unbalance level. In case of excessive unbalance the appliance control tries to better redistribute the laundry in the drum and, if after several attempts, the unbalance level is still to high, it performs the spinning at reduced rpm.

The unbalance has several negative effects on the customer satisfaction because of the generated noise and vibrations, the longer washing/drying cycle duration due to the re-balancing attempts and the poor drying performance when, in case of excessive unbalance level the spinning rpm speed is reduced.

Moreover the generated mechanical vibrations cause a significant stress to the mechanical structure reducing the appliance reliability that is partially compensated in the washer design by the use of bigger, more robust and expensive parts.

Therefore in the washing machine design it is beneficial the use of a balancer, which offsets unbalanced load generated from inside of the drum, to stabilize the drum rotation.

The known balancer systems make use of a balancer ring with a hollow space where are positioned some masses, typically spherical shaped that are free to move in the balancer ring. Often the balancer ring is filled with a fluid to limit the speed of the movement of the balancing masses. Even if this known balancer systems help to reduce the unbalance level they suffer of several drawbacks:.

In order to improve the balancing process active balancers are revealed. In particular <CIT> reveals a balancer ring with balancing units receiving wireless power from a transmission coil provided at the tub. The transmitter coil is wound centered with respect the drum axis while the receiver coils in the balancing unit have their winding axis parallel to the radial direction defined by the drum axis.

The orthogonal configuration between the transmitter coil winding axis and the receiver coil winding axes ensures a constant power transfer to the balancing units when they rotate with the drum facing the transmitter coil winding.

In addition <CIT> reveals a detection coil positioned on the transmitter coil winding that allows, during the drum rotation, the detection of the balancing units passage at its position. The appliance controller, to balance the drum load, exploits the action of gravitational and inertial forces acting on the balancing units. It enables their movement with a proper timing, based on their positions and the unbalance amplitude and position.

Previous art disclosures use electromagnetic actuators having moving parts that can brake a balancing unit wheel or can act interacting directly with the housing walls.

The actuators based on moving parts are more complicated to build, are expensive to integrate into the complete system and have a response time that depends on the moving part mass.

A first invention objective is to provide an active balancing system that uses an improved actuator solution without moving parts that is cheaper, has faster reaction time, a high reliability while ensuring a low friction force for the balancing unit. It permits a large rpm range where the balancing unit can be moved under the action of the gravitational and inertial that includes the wash unit resonance frequency.

It allows the possibility to cross the resonance frequency with a balanced drum and to perform balancing adjustment above the resonance frequency compensating the laundry unbalance changes due to the water extraction when the drum spinning speed is increased.

To solve the problem the invention disclose an electromagnet in the balancing unit that interacts with a ferromagnetic race of the housing channel.

A simple application of an electromagnet in the balancing unit due to its sliding friction coefficient would give a limited the rpm range where it is possible to move it.

According to the invention there is a wheel that transfers to the outer race the largest part of the acceleration force acting on the balancing unit; while the electromagnet transfers the remaining much smaller part of the acceleration force. It is obtained by having the balancing unit centre of gravity on one side very close the wheel shaft while on the opposite side, at the end, there is the electromagnet.

The small force transferred by the electromagnet surface is enough to ensure it a mechanical contact with the ferromagnetic outer race of the housing.

This configuration ensures a low friction between the balancing unit and the housing as the large part of the force is transferred through the wheel, which has a low rolling friction coefficient. The smaller remaining part of the force is transferred through the electromagnet surface which has a higher sliding friction coefficient, but its contribution is limited by the low percentage of the transferred force.

Being the housing outer race made of ferromagnetic material the controllable magnetic force acting between the electromagnet surface and the housing outer race generates an additional friction force that acts on the balancing unit.

This frictional force is proportional to the magnetic force multiplied by the electromagnet surface sliding friction coefficient with the housing outer race. In this way it is possible to change the balance unit friction permitting or blocking its movement in the housing.

In a first embodiment the electromagnet has a coil that wound around ferromagnetic material and the current flowing in the coil generates the magnetic field. In this embodiment when both balancing units must stay in braked condition a multiplexing of two the two balancing unit resonance frequencies is used to supply a controlled average current to both balancing units electromagnets.

In a second embodiment a magnet generates the magnetic field in the electromagnet and in this case a coil generates an opposite magnetic field that can cancel the resulting magnetic field. It simplifies the wireless powering transfer to the balancing units. In this case both balancing units are normally braked by the magnetic material and only the one that must be moved needs to be powered by transferring power at its resonating frequency.

Other advantages and features of a balancing system for a laundry treating appliance, according to the present invention will be clear from the following detailed description, provided only as a non limitative example, in which:.

In the figures same parts are indicated with the same reference number.

In <FIG> it is shown a sectional view of the key structural parts of a horizontal axis washer <NUM>. In particular it is shown the wash unit consisting of the tub <NUM> on which is rotatably mounted a drum <NUM>. The wash unit is suspended to the cabinet <NUM> through springs <NUM> and dumpers <NUM>.

At the external perimeter of the drum <NUM> is fixed, centred with respect its axis <NUM>, a housing ring shaped <NUM> facing a transmitter coil <NUM>.

<FIG> shows a front view of the housing <NUM> channel internal content, where the internal sides in axial direction, parallel to the drum <NUM> axis <NUM>, form an outer race <NUM> and an inner race <NUM> for two balancing units <NUM>. In this document, if not differently specified, radial and axial directions are always defined with respect to the drum axis <NUM>.

<FIG> shows a detailed view of one balancing unit <NUM> in the housing <NUM>. The balancing unit has an arc shaped <NUM> body forming its exterior appearance and a driving wheel <NUM> configured to roll on the outer race <NUM>. The driving wheel <NUM> axis <NUM> is parallel to the drum axis.

The balancing unit body <NUM> dimensions radial and axial are smaller that the housing channel dimensions so that it can move in the housing channel. On Its side opposite to the driving wheel <NUM> there is a parking actuator <NUM> that interacting with an opening <NUM> on the inner race <NUM>, keeps the balancing unit blocked at its parking position when the drum is rotating at low rpm.

At one of the balancing unit <NUM> body ends there is an electromagnet <NUM> facing the outer race <NUM>. The electromagnet <NUM> sectional view is shown in detail in <FIG>. It includes the electric winding <NUM> wound around the central part of a ferromagnetic core <NUM>. The magnetic field, generated when the winding <NUM> is powered, is closed through the core <NUM> surfaces shown on the electromagnet <NUM> front view of <FIG> and the ferromagnetic outer race <NUM>.

The electromagnet <NUM> mechanical design and its position fixation on the balancing unit <NUM> body ensure a continuous contact between the surfaces of the electromagnet <NUM> core extensions <NUM> and the inner race <NUM>.

When the electromagnet winding is powered both its ferromagnetic core <NUM> and the inner race <NUM> contacted surface are magnetized. It generates an attraction force between the two surfaces that increases the friction force between the balancing unit <NUM> and the outer race <NUM>.

By changing the current flowing in the electromagnet winding <NUM> it is possible to brake in a controlled way the balancing unit movement.

<FIG> shows a sectional view of the parking actuator <NUM> it includes a movable ferromagnetic part <NUM> with an extension pin <NUM> and a winding <NUM>. A spring <NUM> pushes the movable part <NUM> keeping the pin <NUM> inside the opening <NUM> formed in the housing inner race <NUM>. It blocks the balancing unit <NUM> at its parking position when the drum <NUM> is rotating at low rpm.

When the parking actuator winding <NUM> is powered or when the drum <NUM> rotates at higher rpm, respectively the generated magnetic force and/or the centrifugal force retracts the pin <NUM> from the opening <NUM>, enabling the balancing unit <NUM> movement in the housing <NUM> channel.

The balancing unit <NUM> has its masses distributed so that the position of its centre of gravity is between the driving wheel <NUM> axis <NUM> and the electromagnet <NUM>, but much closer to the driving wheel axis <NUM>.

In this way the radial force acting on the balancing unit <NUM> is transferred to the outer race <NUM> mostly through the driving wheel <NUM>, while the remaining force fraction is transferred by the electromagnet <NUM> contacting surface <NUM>. The resulting friction coefficient between the balancing unit <NUM> and the outer race <NUM> can be calculated as the sum of the wheel <NUM> rolling friction and the electromagnet sliding friction.

Because the largest part of the centrifugal force is transferred through the wheel <NUM>, it can be configured to minimise its rolling friction coefficient keeping the balancing unit friction at high drum speed as low as possible.

For example the driving wheel <NUM> could be made of hardened steel and the outer race <NUM> could be formed by a steel sheet providing a possible coefficient of rolling friction c=<NUM>,<NUM>. While the electromagnet sliding friction Ks, assuming steel material for its core <NUM>, could have a range of values Ks=<NUM>,<NUM>-<NUM>,<NUM>.

Moreover the position the balancing unit <NUM> could be designed to have its resulting centre of gravity at a position that ensures that the centrifugal force transferred by the electromagnet <NUM> to the outer race <NUM> is much smaller, for example <NUM>/<NUM> smaller, than the force transferred by the driving wheel <NUM>.

The resulting balancing unit friction coefficient could be, calculated the weighting the force sharing Fc= <NUM>,<NUM>*Kr +<NUM>,05Ks given by the contributions of the wheel <NUM> rolling friction Kr and the maximum actuator static friction Ks.

On the basis of the above assumptions, if the driving wheel <NUM> has <NUM> radius, we could have Kr=<NUM>,<NUM>/<NUM>=<NUM>,<NUM> and the resulting balancing unit friction coefficient would be Kc=<NUM>,<NUM>*<NUM>,<NUM>+<NUM>,<NUM>*<NUM>,<NUM>=<NUM>,<NUM>+<NUM>,<NUM>=<NUM>,<NUM>.

The friction force F acting between the balancing unit <NUM> and outer race <NUM> could be F=Kc*Fc+Ks*Fm, where Fc is the radial force acting on the balancing unit and Fm is the magnetic force acting between the outer race <NUM> and the electromagnet <NUM> when its coil <NUM> is powered.

At low rpm in order to block the balancing unit movement the the magnetic force must be grater than the gravitational force. It means that enough current must be supplied to the electromagnet <NUM> to ensure that the balancing stays attached to the outer race <NUM> and it does not slide on its surface. Assuming a worst case Ks=<NUM>,<NUM> it would require <NUM>,<NUM>*Fm>M*g where M is the balancing unit mass and g is the gravity acceleration constant, i.e. Fm><NUM>*m*g, a magnetic force <NUM> times higher than the gravitational force. In this condition the balancing unit is blocked at its position.

During the drum <NUM> rotation period by stopping, with a proper timing, the supplied current to the electromagnet <NUM>, the gravitational force can move the balancing unit in the desired direction.

The balancing unit <NUM> is equipped inside the body <NUM> with receiver coils <NUM>. The balancing unit receiver coils <NUM> are wound around a cylindrical ferrite core extending in radial direction, perpendicular to the drum axis <NUM>.

A front view of the transmitter coil <NUM> is shown in <FIG>, it is fixed to the tub <NUM> with a support element <NUM> and has its winding <NUM> wound around the drum <NUM> axis <NUM>.

The position configuration between the transmitter coil <NUM> and the balancing unit receiver coils <NUM> ensures a constant magnetic coupling when the drum <NUM> is rotating or the balancing units <NUM> move in the housing <NUM> facing the transmitter coil <NUM> winding. The constant magnetic coupling ensures a continuous wireless electric power transfer from the transmitter coil <NUM> fixed on the tub <NUM> to the balancing units <NUM> in the housing <NUM>.

On the transmitter coil winding <NUM>, as shown in <FIG>, there are two detection coils <NUM> and <NUM>. The two detection coils <NUM> and <NUM> are identical, having an elliptical shape with the minor axis aligned to the radial direction. They are positioned with respect to the radial direction to ensure a zero flux coupled to the transmitter coil <NUM>. It is achieved positioning them approximately opposite with respect the transmitter coil <NUM> winding average radial dimension.

As shown in the block diagram of <FIG>, a voltage generator <NUM> with a series capacitor <NUM> powers the transmitter coil <NUM>. It generates an electromagnetic field, which is coupled with the receiver coils <NUM> and the detection coils <NUM> and <NUM>. As said before the detection coils positions with respect the transmitter coil <NUM> ensures that at their series connection there is no voltage induced by the transmitter coil <NUM>. The voltage generator <NUM> output voltage amplitude and frequency are set by a local controller <NUM> that operates under the supervision of the appliance manager <NUM> (not shown).

The local controller <NUM> can also change the transmitter coil <NUM> resonance frequency by selecting compensating capacitors <NUM> with switches <NUM>.

In the balancing unit <NUM>, as shown in the block diagram of <FIG>, the receiver coils <NUM> primary winding are connected in series and form a resonant circuit with the capacitor <NUM>. Their secondary windings <NUM> are connected in series and perform an impedance adaptation function. Their series output voltage goes to a voltage rectifier block <NUM>, its dc output voltage <NUM>, filtered by conditioning block <NUM>, powers the electromagnet <NUM> and the parking actuator <NUM>.

The balancing units have receiver coils resonating at different frequencies. The local controller <NUM> by changing the generator <NUM> operating frequency can select the balancing unit resonance frequency to power its electromagnet <NUM> and the parking actuator <NUM>.

The local controller <NUM> can set the power transferred to the two balancing units by multiplexing the duration times tm1 and tm2 when the generator <NUM> output frequency operates at the two balancing units resonance frequencies. The multiplexing time frequency <NUM>/tm is much lower than the average resonance frequencies F1 and F2 of the balancing units receiver coils, <NUM>/tm<<(F1+F2)/<NUM>. For example F1=<NUM>, F2=<NUM> and <NUM>/tm=<NUM>. In each tm time slot the appliance controller can set within the time range tm>t><NUM> the times tm1 and tm2 lengths when the generator <NUM> is active for the selected frequencies F1 and F2.

The resonant current induced in the receiver coils <NUM> by the electromagnetic coupling with the transmitter coil <NUM> generates a voltage at the detection coils <NUM><NUM> series output when the balancing unit <NUM> is in their proximity. It allows the detection of the balancing units passage.

The appliance manager (not shown) through the local controller <NUM> can change the balancing units <NUM> positions based on unbalance sensors (not shown) information to effectively balance the drum <NUM>.

The appliance manager can leverage the action of the gravitational and inertial forces acting on the balancing units to change their positions. It can enable the selected balancing unit movement with a proper timing by stopping the power transferred to its electromagnet <NUM> that normally brakes it.

At low drum rpm, for example in washing, the balancing units parking actuators <NUM> movable parts have their extension pin <NUM> in the inner race openings <NUM>.

The appliance manager (not shown) to perform the spinning cycle first increases the drum speed until the laundry is satellized, said s1 this drum rpm speed. The parking actuators <NUM> springs <NUM> are configured to ensure that at this speed s1 their force is higher than the centrifugal force acting on the movable ferromagnetic part <NUM>.

The two balancing units <NUM> and <NUM> are kept opposite each other in the parking actuators defined positions as shown in <FIG>. In this condition the appliance manager (not shown) can estimate with its sensing elements (not shown) the laundry unbalance <NUM> amplitude and position.

In <FIG> are shown in time diagrams the steps executed by the appliance manager to change one balancing unit position.

The balancing process changing the balancing units positions is performed keeping the drum <NUM> first rotation speed s1 constant.

The first time diagram <NUM> shows the detection pulses <NUM> and <NUM> associated to the balancing units passage at the detection coils <NUM><NUM> position. The appliance manager receives a reference periodical pulse <NUM> generated each drum turn rotation time period <NUM> when a reference point on the drum is aligned with a reference position on the tub.

The appliance manager based on this timing information can calculate the balancing units positions with respect to the drum reference position and knows the unbalance position from his interna sensing function.

The appliance manager knowing the relative positions of the balancing units with respect to the unbalance <NUM> can calculate the new balancing units positions that can balance the drum <NUM>.

At the satellization speed s1 the gravitational force acts to move the balancing units each drum rotation turn back and forward with respect the drum rotation direction.

The appliance manager by enabling the balancing unit movements, with the proper timing within the drum turn, can change in steps their positions leveraging the action of the gravitational force.

The time diagrams <NUM> and <NUM> respectively shown the average power levels <NUM> and <NUM> transferred to the two balancing units <NUM>.

By transferring power to the two balancing units <NUM> the parking actuators <NUM> extension pins <NUM> are retracted from the inner race openings <NUM>. At the same time the attraction forces Fm between the electromagnets <NUM> and the outer race <NUM> keep the balancing units blocked at their positions. The attraction force depends on the average power supplied to the electromagnets coils <NUM> that can be regulated by changing within the multiplexing period tm, the time duration tm1 and tm2 when the generator <NUM> output frequency is respectively F1 and F2.

The appliance manager reduces the average transferred power <NUM> to the selected balancing unit to be moved. The parking actuator <NUM> is configured so that, once its ferromagnetic part <NUM> has moved retracting its pin <NUM>, a certain hysteresis behaviour and the reduced power are enough to keep the pin <NUM> in the retracted condition.

The power reduction pulse <NUM> starts at the time <NUM> until the time <NUM>, the time interval where the enabled balancing unit moves under the action of the gravitational force in the desired direction. To reduce the average power to the moved balancing unit, which has in this case the receiver coils resonant frequency F2, the time slot <NUM> duration associated to the frequency F2 is reduced. While the average power transferred to the balancing unit with resonance frequency F1 is kept constant not having changed its time slot duration.

The time diagram <NUM> shows in a zoomed time scale, in detail, the transition at the instant of the start of the average power reduction <NUM>. After the pulse reduction start <NUM> the F2 time slot duration <NUM> is reduced. The appliance manager after the pulse power reduction <NUM>, in the next drum turn, can evaluate the new balancing unit position using the pulse <NUM> detecting its passage at the detection coils <NUM><NUM> positions. Repeating iteratively the described positioning steps, the appliance manager, as shown in <FIG>, can position the balancing units <NUM> in the housing <NUM> canceling the unbalance <NUM> present in the drum created by the laundry.

A big advantage of using an electromagnet as brake is the possibility the adjust the resulting balancing unit movement changing the average power transferred that changes the braking force effect of the electromagnet current.

In a second embodiment the electromagnet <NUM> could have a permanent magnet (not shown) that magnetise its core <NUM>. The electromagnet with permanent magnet has also a coil <NUM> wound around the core <NUM>. The coil <NUM> magnetic field, when powered, generates an opposite magnetic canceling the permanent magnet field. In this embodiment when both electromagnets coils are not powered the magnetic force can keep the balancing units blocked at their positions.

It means that in washing the balancing units cannot move; if at the end of each spinning cycle the appliance manager position them opposite each other, the parking actuator (<NUM>) function is not needed. To move one balancing unit the appliance manager in this embodiment needs to power its electromagnet by transferring power at its receiver coils resonance frequency.

Claim 1:
A laundry treating appliance (<NUM>) comprising a tub (<NUM>), a drum (<NUM>) rotatably mounted inside the tub (<NUM>), at least one transmitter coil (<NUM>) wound around the drum (<NUM>) axis (<NUM>) configured to supply wireless electrical power; at least one ring shaped housing (<NUM>) mounted centred to the drum (<NUM>) on its perimeter, having an annular channel defined therein; at least two balancing units (<NUM>), each balancing unit having a body (<NUM>) forming its exterior permitting its movement in the said channel, said balancing unit (<NUM>) has at least, one receiver coil (<NUM>) having its winding axis perpendicular to the said transmitter coil (<NUM>) winding axis configured to receive wireless power from the said transmitter coil (<NUM>) and actuator means (<NUM>, <NUM>) powered by said receiver coil (<NUM>); unbalance sensors and an appliance manager controlling the complete laundry treating appliance (<NUM>) operation, configured to manage the positioning of said balancing units (<NUM>) and to drive the transmitter coil (<NUM>) based on the position of the balancing units (<NUM>), the drum (<NUM>) unbalance and the drum rotation speed, characterized in that the actuator means (<NUM>) is an electromagnet configured to create a friction force resulting of the magnetic attraction between its magnetising surface (<NUM>) and one ferromagnetic race (<NUM>) present on one of the housing (<NUM>) sides (<NUM>).