Abstract:
The laundry in a rotating, obliquely mounted drum falls in the direction of action of gravitational force and therefore is no longer perpendicularly with respect to the axis of rotation of the drum, which results in an uneven distribution over the axial length of the drum, this leading to wobbling movement during the rotation of the drum that cannot be measured by conventional rotational sensor systems with their rigid attachment. In order to be able to counteract such movements on the drive side, these two further components of inertia have to be sensed orthogonally with respect to the main axis of inertia. For this purpose, the output signal of the rotational sensor, which signal indicates the rotational speed of the drum, experiences a variation in its output signal, the variation being dependent on the additional pitching and yawing movements of the laundry drum.

Description:
BACKGROUND OF THE INVENTION  
     FIELD OF THE INVENTION  
       [0001]     The invention relates to a method and a device for sensing unbalance-dependent movement phenomena in a laundry drum that is equipped with a rotational sensor as an instrument for measuring the rotational speed.  
         [0002]     Such generic measures are disclosed, for example, in European Patent EP 0 349 798 B1. In accordance therewith, the laundry drum, which rotates in a domestic washing machine about its horizontal axis, is driven through a reduction gear, in this case a transmission, by an electric motor that can be controlled in its rotational speed and is equipped with a tachogenerator as a rotational sensor. Its rotor, functioning as an actuator, resolves in a rotationally rigid manner together with the motor shaft while its stator, functioning as a sensing element, is fixed rigidly to the motor housing which, for its part, is fitted on the tub, within which the drum, which is mounted in the end wall of the tub, rotates. The output voltage or the output frequency of the rotational sensor is a measure of the rotational speed of the motor at a particular instant and thus also for the rotational speed of the drum, which is reduced in relation to the rotational speed of the motor, at a particular instant. The rotational speeds experience unbalance-dependent fluctuations, with the result that the signal fluctuation at the output of the rotational sensor is a measure of the unbalance at a particular instant in the loading of the laundry drum. An unbalance of this type can be encountered in the program sequence of a washing machine or spin-dryer by a laundry distributing phase before the program for driving the drum is switched on to a significantly higher rotational speed for extracting the moisture from the laundry and, finally, for spin-drying the laundry in the drum.  
         [0003]     Such measures have become thoroughly well-established in the case of current washing machines and spin-dryers whose laundry drums have an essentially horizontal axis of rotation. However, rotational sensor systems sense only the rotational speed or the angular acceleration about the axis of the drum, which substantially coincides with the main axis of inertia. On the other hand, in the case of a nonsymmetrical loading with respect to the center point of the axis of rotation of the drum, acceleration components also occur on the drum and result in wobbling movements of the drum in the pitching and yawing direction and in corresponding movement components of the tub, in which the drum is mounted. Such movements cannot be sensed by a sensor whose sensing element is connected rigidly to the tub, since such movements are not orientated centripetally with respect to the axis of rotation about the axis of inertia of the rotation of the drum, but rather are based on unbalance-induced oscillations about the Y-axis and about the Z-axis of a three-dimensional Cartesian coordinate system, if the X-axis thereof is the axis of rotation of the laundry drum. Such unbalance-induced oscillations in addition to those about the X-axis occur, in particular, if the laundry is distributed nonuniformly in the axial direction within the drum. This occurs, for example, in the case of higher cost machines, in which the axis of the laundry drum runs at an inclination to the rear from the engagement opening to make it easier to see in and to make the loading and unloading process much more convenient. As a result, the laundry which, after being lifted up in the drum, drops back in the direction of gravitational force and therefore vertically, is not distributed here to a greater or lesser extent symmetrically with respect to the center point of the axis of the drum. This leads increasingly to unbalance-induced loads about axes of inertia transversely with respect to the axis of rotation, and therefore to the wobbling stresses on the drum and on the tub surrounding it. This results in the risk of the tub striking, in particular laterally, against the inner walls of the appliance housing surrounding it. Although this can be encountered by a greater clear distance between the housing and tub, this brings about, however, a reduction in the drum diameter and thus a reduced loading volume and therefore works against the higher machine price.  
         [0004]     In recognition of these circumstances, the present invention is based on the technical problem of sensing, with the laundry drum loaded, also those unbalance phenomena which result in wobbling stresses on the drum that cannot be detected as a consequence of fluctuations in the rotational speed about the axis of the drum, but which it should also be possible to counteract by control technology so as to avoid critical, unbalance-induced deflections of the tub by the drive of the drum. In particular, the intention of the present invention is therefore to be able to sense unbalance-induced oscillations of the drum that cannot be sensed using a rotational sensor coupled in the conventional manner rigidly to the machine.  
       SUMMARY OF THE INVENTION  
       [0005]     It is accordingly an object of the invention to provide a method and a device for sensing unbalance-dependent movement phenomena in a laundry drum that overcomes the above-mentioned disadvantages of the prior art devices of this general type.  
         [0006]     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for sensing unbalance-dependent movement phenomena in a laundry drum. The method includes measuring a rotational movement of the laundry drum, and sensing angular accelerations occurring about an axis of inertia transversely with respect to an axis of rotation of the laundry drum, as a fluctuation in a measured value of a rotational speed through a displacement of a sensing element or actuator of a rotational sensor system.  
         [0007]     Accordingly, use is no longer made of a sensing element of the rotational sensor that is coupled rigidly to the appliance, in which the laundry drum rotates, but rather the sensing element can be displaced tangentially (preferably counter to an elastic restoring force and/or against one or two stops) or about the axis of rotation of the actuator, which revolves together with the drum. As a result, the rotational sensor additionally senses an angular acceleration about one of the two other main axes of inertia, which are perpendicular with respect to the axis of rotation of the laundry drum and may therefore result in a wobbling movement of the drum.  
         [0008]     It will normally suffice to derive a measure for the wobbling movement just from the angular acceleration about one of the two axes of inertia which are perpendicular with respect to the axis of rotation of the drum; or in the case of a horizontal axis of rotation, preferably about the vertical axis in order to avoid the wobbling drum striking laterally against the bucking tub surrounding it or to avoid this tub striking laterally against the lateral appliance walls by prompt counter control of the motor in antiphase on the drive side. If, however, in the plane transverse with respect to the axis of rotation of the drum, two rotational sensors having sensing elements which are coupled, according to the invention, elastically to the machine, are disposed orthogonally with respect to each other, continuously updated information about the angular acceleration can be obtained from them for each of the two main axes of inertia transverse with respect to the axis of rotation of the drum.  
         [0009]     This is of particular interest in the case of obliquely mounted laundry drums that are substantially for the user easier to load and unload and offer an easier visual view of the drum contents. The laundry in a rotating, obliquely mounted drum continues, of course, to fall in the direction of action of gravitational force and therefore no longer perpendicularly with respect to the axis of rotation of the drum, in which case an uneven distribution over the axial length of the drum is more probable. This can lead to wobbling movements during the high-speed rotation of the drum, which movements cannot be sensed by conventional rotational sensor systems with their rigid attachment to the appliance. In order to be able to counteract all such possible wobbling movements, for example via an activation of the driving motor of the drum in proper phase, both angular accelerations about the axes of inertia have to be sensed orthogonally with respect to the main axis of inertia X. For this purpose, the output signal of the rotational sensor, which signal indicates the rotational speed of the drum, experiences a variation as a function of the additional pitching or yawing movements of the laundry drum because the particular sensing element of the rotational sensor is, according to the invention, no longer fixed rigidly, but rather can be displaced in the transverse plane to the axis of rotation of the drum counter to the elastic force of a restoring device under the influence of the wobbling forces which occur. Two possibilities according to the invention of displacing rotational-sensor sensing elements, which possibilities are provided orthogonally with respect to each other in this transverse plane, therefore supply separate effects on the results of the continuous measurements of rotational speed on the drum, namely in accordance with the pitching and the yawing stresses on the laundry drum.  
         [0010]     The sensing according to the invention of wobbling movements by measuring the fluctuations which are combined with the current measured value of rotational speed in the case of a displaceable rotational-sensor sensing element can be used not only with an axis of rotation of the drum that is horizontal or that is slightly inclined with respect to the horizontal, but in any desired spatial angular position of the axis of rotation and therefore also in the case of a vertical X-axis or axis of rotation of the drum, as in the case of the “actuator washing machines”. Whereas for the basic explanations above, and also in the description of examples which follows below, the starting point for making comprehension easier is that the actuator of the rotational sensor system is coupled in a rotationally rigid manner to the drum and its sensing element can be pivoted (preferably counter to an elastic restoring force), the reverse assignment can also be realized within the context of the present invention, i.e. a, for example, rotationally elastic coupling of the rotor or similar actuator to the drum with a conventional, rigid coupling of the coil system or similar sensing element to the appliance part which supports the drum. A crucial factor, according to the invention, is that the wobbling stresses on the rotating drum enable the rotational-speed signal supplied by the rotational sensor system to correspondingly intensively fluctuate.  
         [0011]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0012]     Although the invention is illustrated and described herein as embodied in a method and a device for sensing unbalance-dependent movement phenomena in a laundry drum, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0013]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a diagrammatic illustration of a stator of a tachogenerator functioning as a rotational sensor, the stator being coupled elastically to a drum tub according to the invention;  
         [0015]      FIG. 2  is a perspective view of an elastically displaceable light barrier of a pulse-repetition-frequency generator being the rotational sensor; and  
         [0016]      FIG. 3  is a perspective view showing a development of the rotational sensor according to  FIG. 2  in order to be able to sense angular accelerations about two axes of inertia, which are perpendicular to an axis of rotation of the drum, and therefore detecting the complete wobbling stress on the laundry drum about the Y and Z-axes. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a rear view being opposite to the loading opening view, of a laundry drum  11  of a domestic washing machine or a domestic spin-dryer, which is mounted rotatably here in a rear wall of a tub  12  (sketched in cubic form). The tub  12  is suspended in an oscillable, but elastically damped manner, in a machine housing  13 . In the simplified illustrations of the drawing, a motor, which is coupled directly or by a gear mechanism to the laundry drum  11 , for the rotational movement of the laundry drum  11  about its axis of rotation  14  that is inclined, for example, with respect to the horizontal has been omitted. However,  FIG. 1  does illustrate a transmission  15  for the rotationally rigid coupling of a permanent-magnet-type rotor of a rotational sensor  18  in the form of a tachogenerator  18  to the laundry drum  11 , which is driven by the electric motor. An axis of rotation  20  of the rotor of the rotational sensor  18  is oriented substantially parallel to the axis of rotation  14  of the laundry drum  11  which, for its part, shall be defined in the three-dimensional Cartesian coordinate system (as indicated in  FIG. 1 ) as the X-axis. This is the main axis of inertia of the rotating system of the loaded laundry drum  11  in the event of an accumulation of masses that is distributed approximately axially symmetrically with respect to its center point.  
         [0018]     Like the laundry drum  11 , a rotor of the rotational sensor  18  is also mounted rotatably via its stator on the tub  12 . Driven by the drum  11 , the rotor rotates within the coil system of its stator. The rotor therefore functions as an actuator  16  and the coil system functions as a sensing element  17  of the rotational sensor  18 . As a tachogenerator  18 , the rotational sensor  18  supplies an output voltage, which is dependent on rotational speed, or as a frequency generator, the rotational sensor  18   c  supplies a pulse sequence, as a function of the rotational speed, to an evaluation circuit which can be provided separately (not taken into consideration in the drawing), but in practice is preferably realized in a microprocessor control of the driving motor for the operation of the laundry drum  11 .  
         [0019]     The particular feature of the rotational sensor  18  lies in the fact that the sensing element  17  in the form of a stator is no longer fixed in a rotationally rigid manner to the tub  12  or other appliance part rotatably holding the drum  11 , but rather can be pivoted about the axis of rotation  20  of the actuator  16  counter to an elastic restoring device  19 , with it being possible for the maximum pivotable deflection to be limited by two non-illustrated stops (one per pivoting direction) as an alternative or in addition to the elastic restoring device  19 . In this case, the sensing element  17  has an eccentric distribution of masses with respect to its axis of rotation  20 , which is illustrated in the sketch by an externally and locally applied, eccentric additional mass  21 . By this measure, in the case of an angular acceleration about the vertical Y-axis as a consequence of a wobbling movement of the drum  11 , a rotational-speed error is combined with the rotational-speed signal of the rotational sensor  18  as a fluctuation in the measured value of the rotational speed, the fluctuation serving, in the evaluation by control technology, as a measure of the current amplitude of the wobbling.  
         [0020]     A drive of the unbalanced laundry drum  11  at a moderate speed of rotation results in a relatively long period of duration for the fluctuating output signals of the rotational sensor  18 , with it being possible for any possible distortions of them as a consequence of slight oscillating movements of the sensing element  17  to be eliminated by measuring techniques, in so far as they cannot be entirely ignored in practice. However, the relative rotational-speed error rises with increasing rotational speed of the drum  11  owing to its tendency to then wobble more severely, and so, at high rotational speeds of the spinning operation, a rotational-speed error which is large enough to evaluate occurs at the output of the rotational sensor  18  owing to the correspondingly severe, wobbling-induced displacement of the sensing element  17 . This fluctuation, which is combined with the measurement of the rotational speed, is therefore in a direct interrelationship with the wobbling movement of the drum  11  as a consequence of angular accelerations about the axes of inertia Y and Z, which are perpendicular with respect to the axis of rotation X,  14 , particularly since, owing to the high potential energy of the loaded drum  11  at high rotational speeds, the rotational-speed fluctuations about the axis of rotation  14  themselves are still very small, even under unbalance effects, in comparison to the fluctuations in measured values caused by the wobbling stresses.  
         [0021]     According to the invention, the pivotably mounted rotational-sensor sensing element  17  thereby senses effects of forces which would not be able to be sensed if the rotational sensor were focused rigidly on the simple rotational movement of the laundry drum  11 , but can nevertheless have a considerable adverse affect on the operational reliability of the machine.  
         [0022]     In the variant according to  FIG. 2 , the laundry drum  11  is directly equipped with the actuator  16  of the rotational sensor  18 , with the result that the axis of rotation  14  of the drum and the axis of rotation  20  of the actuator coincide with the main axis of inertia X. A sensing element  17 ′ is secured here rigidly on the tub or housing ( 12  or  13  in  FIG. 1 ). The actuator  16 , which rotates together with the laundry drum  11 , has a structure with gaps, for example (as indicated in the enlargement of  FIG. 2 ) in the form of slots or apertures of, for example, approximately rectangular cross section which follow one another uniformly in the mark-space ratio of “1”. In this example, the gap-type structure of the actuator  16  is engaged over in a U-shaped manner along its outer edge by a forked light barrier as the sensing element  17 ′. Wherever the actuator  16  is transparent on account of its gap-type structure, the rotational sensor  18  responds because the sensing element  17 ′ connects through. The repetition frequency of the pulses triggered by the light barrier is a measure for the rotational speed at a particular instant of the laundry drum  11  about its axis  14 .  
         [0023]     In addition, the actuator  16 , which is in the form of the gap-type ring which rotates in a rotationally rigid manner together with the laundry drum  11 , is engaged over by the sensing element  17 , which is indeed also fitted to the tub  12  or the housing  13 , but is not secured rigidly, but rather again can be displaced counter to a restoring device  19  in and counter to the direction of movement of the actuator  16  to a structurally predefined degree. Here too, the maximum displacement of the sensing element  17  can be limited by one or two (for the sake of clarity not shown) stops (one per direction of movement of the sensing element  17 ) as an alternative or in addition to the restoring device  19 .  
         [0024]     An eccentric additional mass is not required here because this light-barrier sensing element  17  does not contain any distribution of masses concentric with respect to the X-axis. Its displacement occurs again if, owing to angular accelerations about the axis of inertia Y, forces act transversely with respect to the axis and therefore in the Z-direction to the movably mounted sensing element  17 . In the course of such a displacement of the elastically supported sensing element  17  in or counter to the direction of movement of the actuator  16 , again the pulse repetition triggered by the rotational sensor  18  varies significantly, at high rotational speed of the laundry drum  11 , in relation to the pulse repetition triggered by the sensing element  17 ′ which is fixed on the appliance and senses the rotational movement of the drum  11  about its axis X=14. This variable difference in pulse frequency is a measure for the yawing movement of the laundry drum  11 , i.e. its deflection about the vertical Y-axis in the horizontal Z-direction transversely with respect to the X-direction, the axis of rotation  14 , which is assumed for these exemplary embodiments as being essentially horizontal.  
         [0025]     The development according to  FIG. 3  involves, in principle, two rotational sensors  18 ,  18   a  having displaceable sensing elements  17  of the type as explained above in conjunction with  FIG. 2 . These two rotational sensors  18 ,  18 a are secured in a manner pivoted orthogonally in relation to each other in a plane which is oriented perpendicularly with respect to the axis of rotation  14  of the drum and therefore lies in the plane of coordinates of the Y and Z-axes. As a result, the one sensing element  17  is displaced again, as previously, owing to angular accelerations, about the Y-axis in the Z-direction, and the sensing element  17   a , which is orientated orthogonally with respect thereto, is displaced, owing to angular accelerations, about the Z-axis in the Y-direction. A comparison of the fluctuating output frequencies of these two rotational sensors  18 ,  18   a  with respect to the sensing element ( 17  in  FIG. 2 ) which is orientated rigidly with respect to the apparatus is now rendered superfluous because the pulse repetition frequencies of the two sensing elements  17  and  17   a , which can be displaced counter to their elastic restoring devices  19 ,  19   a , can be compared directly with one another. The relative changes in them are in each case a measure of the wobbling forces, which are now sensed separately in the two coordinate directions transversely with respect to the axis of rotation  14  of the drum.  
         [0026]     The invention thus takes into account that, in particular at higher rotational speeds of the laundry drum  11 , which is driven by an electric motor, not only do angular accelerations about its axis of rotation  14  as the main axis of inertia X occur, but, in addition, pitching and yawing forces which are dependent on the axially eccentric loading occur about the Z- and Y-axes, which are spatially orthogonal in each case with respect to the X-axis, on account of angular accelerations. These result in wobbling movements which cannot be sensed by a rotational sensor  18 , which is coupled rigidly to the machine in a conventional manner parallel to the X-axis, because they are also effective about other axes (Y, Z) than about the X-axis. They lead to a relative movement of the sensing element  17 , which is now mounted displaceably relative to the machine counter to elastic restoring forces, and therefore also relative to the rotational movement of the actuator  16 , with the result that the output signal of the rotational sensor  18  leads to rotational-speed fluctuations which can clearly be sensed by measuring techniques. These are a measure of the current wobbling movement of the laundry drum  11 , which can be actively counteracted by its drive, for example by starting up another rotational speed having smaller resonance-induced deflections of the drum, by changing the gradient of the rotational speed, in order to more rapidly pass through critical resonance frequencies, by redistributing the laundry or, in particular at low spinning speeds, by torque fluctuations of the drum drive combined in proper phase.  
         [0027]     This application claims the priority, under 35 U.S.C. § 119, of German patent application No. 103 45 591.4, filed Sep. 29, 2003, and German patent application No. 10 2004 028 365.6, filed Jun. 11, 2004; the entire disclosure of the prior applications are herewith incorporated by reference.