The present invention relates to a method for estimating the moment of inertia of the rotating unit of a washing machine, and to a washing machine implementing said method.
In particular, the present invention relates to a method that is able to estimate the moment of inertia in a washing machine or in a washing-and-drying machine of the type comprising: a box-like frame, and a washing unit set within the frame and comprising a tub fixed within the frame by means of a suspension equipment and a rotating unit, which is, in turn, provided with a laundry drum housed in an axially rotatable way within the tub, and a driving device able to set the laundry drum in rotation about its longitudinal axis inside the tub itself.
Methods are known that are able to determine the unbalancing of the washing unit of a washing machine in order to control the speed of rotation of the laundry drum so as to prevent possible conditions of collision of the washing unit with the frame and at the same time reduce vibrations and/or phenomena of bouncing of the washing machine caused by said unbalancing.
Some of the aforesaid methods determine the unbalancing of the washing unit through calculation of the moment of inertia of the “total rotating load” associated to the mass of the rotating unit plus the mass of the laundry housed inside the laundry drum.
In particular, the aforesaid methods calculate the moment of inertia via an energy-balance function, which necessarily requires both a measurement of the torque and a measurement of the speed of rotation of the laundry drum in a condition of “stability” of the rotating unit, which is reached only when, thanks to the centrifugal force, the laundry is substantially stuck to the internal wall of the laundry drum in a state of immobility.
If the energy-balance function used in the aforesaid methods on the one hand enables precise calculation of the moment of inertia of the rotating unit plus the laundry contained in the drum, on the other hand it is constrained to a condition of “stability” of the rotating unit being reached, which occurs when the speed of rotation of the washing drum reaches the so-called “sticking speed”, which, as is known, is the minimum speed of rotation of the drum at which the laundry remains completely stuck to the wall of the drum.
The sticking speed referred to above can reach relatively high values and consequently, in the case of non-uniform distribution of the laundry inside the drum, can determine an uncontrolled unbalancing of the rotating unit so causing a collision of the washing unit with the frame.
There consequently exists, on the one hand, the need to eliminate the risk of collision of the washing unit with the frame in any condition of operation of the washing machine and, on the other hand, the need to have available an estimate of the moment of inertia of the rotating unit plus laundry present in the laundry drum even when the speed of rotation is maintained around small values, i.e., lower than the sticking speed.
The aim of the present invention is consequently to provide a method that will be able to estimate the moment of inertia even at speeds lower than the aforesaid sticking speed in such a way as to be able to maintain control of unbalancing at any speed, hence eliminating any condition of collision between the washing unit and the frame of the washing machine.
According to the present invention, a method for estimating the moment of inertia of the rotating unit of a washing machine is consequently proposed, as specified in claim 1 and preferably, but not necessarily, in any one of the claims depending either directly or indirectly upon claim 1.
According to the present invention, a device for estimating the moment of inertia of the rotating unit of a washing machine is moreover provided as specified in claim 9 and preferably, but not necessarily, in any one of the claims depending either directly or indirectly upon claim 9.
According to the present invention, moreover provided is a software product as specified in claim 17.
According to the present invention, moreover is provided a washing machine as specified in claim 18 and preferably, but not necessarily, in any one of the claims depending either directly or indirectly upon claim 18.
The present invention will now be described with reference to the annexed drawings, which illustrate a non-limiting example of embodiment thereof and in which:
With reference to
The electrical household appliance 1 further comprises a motor unit, such as, for example, an electric motor 5, which is connected to the laundry drum 4 through a drive member 6 for transmitting the motion for driving the laundry drum 4 in rotation about its axis of rotation A.
The laundry drum 4, the drive member 6, and the rotor of the electric motor 5 together define a rotating unit 7 of the washing machine 1.
The washing machine 1 further comprises a control unit 8, designed to govern the electric motor 5, and a calculation device 9, which is designed to estimate the total moment of inertia Je of the rotating unit 7 plus the laundry contained inside the drum 4.
In the case in point, in the example shown in
In detail, the estimator module 11 calculates the moment of inertia Je through a linear combination FL(Ki(ωi),Ti(ωi)) comprising one or more torque values Ti(ωi) multiplied by respective pre-set linear parameters Ki(ωi), and in which each torque value Ti(ωi) is measured at a pre-set speed ωi lower than a sticking speed ωa.
In particular, in the example illustrated in
Je=FL(Ki(ωi),Ti(ωi); i.e.
Je=Ko+K1(ω1)*T1(ω1)+K2(ω2)*T2(ω2)+K3(ω3)*T3(ω3)+K4(ω4)*T4(ω4)+K5(ω5)T5(ω5)+K6(ω6)*T6(ω6)
The linear parameters Kiwi) can be estimated experimentally through laboratory tests in which there are measured the real inertia and the torque values Ti provided to the rotating unit 7 in pre-set conditions of speed ωi. The calibration of the parameters is done collecting data with different laundry loads (starting from the minimum up to the maximum load) and performing several test cycles with the specific speed profile selected for the machine under analysis.
In the case in point, it is possible to determine the linear parameters Ki(ωi) through an estimation method, preferably, but not necessarily, the least-squares method. The least-squares method is a known optimization technique, which enables a linear combination of specific functions to be found that, by means of linear parameters, approaches as closely as possible an interpolation of a set of data, which, in this case, are constituted by the torque values Ti(ωi) measured at the various speeds ωi.
With reference to
It should be pointed out that the present invention is related to a low speed measuring procedure to evaluate an approximated value of the inertia without reaching the sticking speed. A speed profile used for the inertia estimation is showed in the
With reference to
In this step, the calculation device 9 measures the total torque T1(ω1) (block 110), and then (block 120) the temporary value of the moment of inertia Je is updates by adding the value K1(ω1)*T1(ω1), thus implementing the following relation:
Je=Je+K1(ω1)*T1(ω1)
At this point, a check is made to see whether the counter i has reached its maximum value Nmax (i=Nmax) (block 130), corresponding to the maximum number of terms envisaged by the linear combination FL(Ki,Ti(ωi)) and, if it has not reached said value (output NO from block 130), the counter is incremented (i=i+1) and at the same time the speed is varied, i.e., ω=ωi (block 140).
Once the speed ω=ωi is reached, the method envisages measuring the total torque Ti(ωi) (block 110), and then (block 120) updating again the temporary value Je by adding the value Ki(ωi)*Ti(ωi) via the relation:
Je=Je+Ki(ωi)*Ti(ωi)
If, instead, the counter has reached its maximum value i=Nmax (output YES from block 130), the method provides the final value of the moment of inertia Je by adding the pre-set constant. K0 correlated to the friction torque of the rotating unit 7.
The method explained above estimates therefore the moment of inertia Je by measuring the torque values Ti provided by the motor over some steps performed at substantially constant speed for a certain time interval.
In general, the method for estimating the moment of inertia Je measures and elaborates the torque values Ti provided to the rotating unit and drives the motor 5 in such a way to generate a stepwise pattern of pre-determined speeds, or else a ramp of speed.
It should moreover be pointed out that the measurements of torque can be performed by rotating the drum alternately in opposite directions at pre-set speeds ωi, as shown in the example of
It should moreover be pointed out that, in the case where the sticking speed ωa has a value higher than approximately 75 rpm, the pre-set measurement speeds ωi of the aforesaid method can be conveniently comprised in a range of approximately 45-70 rpm.
The calculation device 9 further comprises an estimation module 12, which receives at input the moment of inertia Je and supplies at output an estimate of the weight of the laundry B contained in the drum. In the case in point, the estimation module 12 can implement a function P=G(Je), determined, for example at an experimental stage, which enables unique determination, for each value of the moment of inertia Je, of a corresponding weight P of the laundry contained in the drum 4. Said function can correspond, for example, to a curve (not indicated) obtained experimentally via laboratory tests indicating the evolution of the moment of inertia Je as the weight P of the laundry B varies.
Estimation of the moment of inertia Je is performed on the basis of the measurement of a series of torques Ti, the main component of which is the lifting torque Ts.
As above disclosed the aforesaid estimation of the moment of inertia Je is substantially based upon the fact that, in conditions of low speed, i.e., lower than the sticking speed ωa, the measured torque Ti basically comprises two components, i.e., the lifting torque Ts deriving from the action of lifting of the laundry, which, since it is not stuck to the wall, tends to shift by gravity towards the bottom part of the drum 4, and a friction torque Ta correlated to the friction encountered by the rotating unit 7.
Laboratory tests have, in fact, shown that at low speeds, i.e., in conditions of non-sticking of the laundry, the lifting torque Ts has a relevant effect in comparison with the friction torque.
In the case in point, laboratory tests have shown that, if a mass present inside the drum is completely stuck into over the pre-set speed profile (for example when the drum speed is higher then the sticking speed or when some fixed masses is used for simulating an increase in the drum inertia), the aforesaid method estimates a moment of inertia Je substantially constant even if the load varies.
In this case, in fact, the contribution of the lifting torque on the torque Ti measured is substantially zero in so far as the laundry is completely stuck to the internal wall of the drum 4. Consequently, the torque applied corresponds to the one necessary to overcome the friction torque of the rotating unit and the inertia estimation procedure doesn't work properly.
The device described above presents the advantage of being extremely simple to produce and hence of being particularly inexpensive.
In addition, the method is able to estimate the moment of inertia of the rotating unit and the weight of the laundry B even at low speeds hence enabling a timely evaluation of the unbalancing before the sticking speed is reached. In this way, any condition of unbalancing of the washing unit that may cause collision of the washing unit with the frame is consequently conveniently eliminated.
Finally, it is clear that modifications and variations may be made to the calculation device, the method, and the washing machine described above, without thereby departing from the scope of the present invention, as defined by the annexed claims.
Number | Date | Country | Kind |
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08153788.8 | Mar 2008 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP09/02245 | 3/27/2009 | WO | 00 | 9/29/2010 |