Patent Publication Number: US-2006010936-A1

Title: Apparatus for detecting a vibratory movement of a laundry drum

Description:
BACKGROUND OF THE INVENTION  
     Field of the Invention  
      The invention relates to an apparatus for detecting a vibratory movement of the rotary shaft of an internal unit, which is suspended such that it can vibrate, of a washing machine having a laundry drum which is driven by an electric motor.  
      The internal unit of a washing machine or spin-dryer contains a washing container, which has a laundry drum which is mounted in the container such that it can rotate, and a drive unit in the form of an electric motor that usually drives the laundry drum via a reduction gear or a transmission. The internal unit is suspended in a machine housing such that it can vibrate and constitutes an overall system which can vibrate in a damped manner and which is subject to unbalance-dependent resonance phenomena in specific regions of the rotational speed of the laundry drum, this speed being lower than the rotational speed of the motor. The causes of the resonance phenomena are vibratory movements due to momentary unbalances in the load in the laundry drum.  
      Vibratory movements such as these, which are the result of unbalances, can be countered in the program sequence of a washing machine or spin-dryer by a specific laundry distribution phase. For this purpose, the control program for driving the drum advances to a higher rotational speed for removing moisture and spin-drying the laundry in the laundry drum only when, in the course of a laundry distribution phase of this type, the unbalances have been compensated for or have been reduced at least to a level which is suitable for introducing higher rotational speeds.  
      In order to detect such an unbalance in the laundry drum, German patent DE 37 41 791 C3 and European patent EP 0 349 789 B1 (corresponding to U.S. Pat. No. 5,098,224) disclose the use of a so-called tachogenerator as a rotary encoder. This is connected to the motor shaft and produces a signal voltage which corresponds to the respective rotational speed of the laundry drum and whose frequency is proportional to the rotational speed. The signal provided by the tachogenerator thus virtually represents the actual rotational speed of the laundry drum, the speed fluctuating as a function of the unbalance of the laundry in the laundry drum. A tachogenerator of this type as a rotary encoder thus detects those components of a vibratory movement of an internal unit, which is suspended such that it can vibrate, of a washing machine that lead to a corresponding angular acceleration or torque fluctuation about this axis of rotation.  
     SUMMARY OF THE INVENTION  
      It is accordingly an object of the invention to provide an apparatus for detecting a vibratory movement of a laundry drum that overcomes the above-mentioned disadvantages of the prior art devices of this general type.  
      With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for detecting a vibratory movement of a rotary shaft of an internal unit of a washing machine. The washing machine has a laundry drum driven by an electric motor, and the internal unit is suspended for allowing the internal unit to vibrate. The apparatus contains a sensor part and a measured-value detector connected to the rotary shaft and provides a measured variable varying periodically with a rotational speed of the rotary shaft and periodically with the vibratory movement in at least one direction parallel to an axis of rotation of the rotary shaft or in at least one radial direction.  
      For this purpose, provision is made first of a sensor part and second of a measured-value detector which is also referred to below as an actuator part and is connected to the rotary shaft. The measured-value detector and the sensor part provide a measured variable which varies periodically with the rotational speed of the rotary shaft and periodically with the vibratory movement in at least one direction (x, y, z), that is to say in the axial direction (x) and/or in a radial direction (y, z). In this case, the actuator part and/or the sensor part can expediently move axially or radially, for example are/is supported such that they/it can move.  
      The invention is in this case based on the idea that a vibratory movement of the rotary shaft and thus of the overall system or internal unit of a washing machine can be detected particularly reliably when, in addition to a vibratory movement about the rotary shaft which is reflected in the directly detectable change in rotational speed, a vibratory movement about at least one further axis is also detected, this axis not coinciding with the rotary shaft defined by the bearing shaft of the motor or of the laundry drum. Therefore, as is known, with an unbalanced load of laundry, the laundry drum rotates not only about this axis of rotation which is defined by the bearing shaft of the laundry drum, but, as a function of the position and the size of the unbalanced load, also follows vibratory movements in the or about the axes which are orthogonal to the axis of rotation and represent the y- and z-axes based on a Cartesian coordinate system with the axis of rotation on the x-axis.  
      In this case, the particularly critical vibratory movements about the axes perpendicular to the bearing shaft or rotary shaft of the drum and also pitching and yawing movements of the washing container or tub are detected and thus identified. At an increased amplitude, the yawing movements may therefore lead to the tub and thus the internal unit of the washing machine striking its side walls, while pitching movements may lead to the front face of the washing machine being struck. Accordingly, if at least one of these vibratory movements about the y- or z-axis, which runs orthogonal to the axis of rotation and thus to the x-axis, is separately or additionally detected, unbalances can be comparatively precisely determined and changes in the rotational speed can be comparatively exactly controlled for reliable and effective operation of the washing machine.  
      In one variant of the apparatus for detecting a vibratory movement of the rotary shaft of a laundry drum, the sensor part and the measured-value detector are part of an acceleration sensor whose measured-value detector is expediently connected to the rotor of the electric motor or to the drum bearing shaft. As a result, the acceleration sensor can assume the functions of a rotational-speed sensor or detector. Otherwise, at least some of the supply and/or signal lines of the acceleration sensor are common lines of an existing rotary encoder. This considerably reduces at least the cabling complexity.  
      In one advantageous refinement, the measured-value detector of the acceleration sensor is expediently sensitive in the axial direction or the sensor part is expediently sensitive in the axial and/or radial direction, and the measured-value detector and sensor part are formed in such a way that they influence the rotary-encoder signal, which is proportional to the rotational speed or represents the rotational speed, by modulating the pulse width, the frequency or the amplitude. For this purpose, the measured-value detector and/or the sensor part can move axially or radially with respect to the motor or drum-bearing shaft and thus with respect to the axis of rotation.  
      In addition, superimposition of the ability to move axially and radially and also an apparatus having two measured-value detectors or sensor parts, and sensor parts and measured-value detectors associated with each of these and with the ability to move axially and/or radially in relation to the axis of rotation, may be provided.  
      In one expedient embodiment, the acceleration sensor together with a measured-value detector, which is borne such that it can move axially and whose ability to move is expediently limited by two stops, and together with a sensor part is in the form of a fixed-position forked light barrier. Instead of this optical embodiment, it is also possible to detect changes in other physical variables that vibrate periodically with the laundry drum. Therefore, by way of example, a reflective, photoelectric, electromagnetic or piezoelectric embodiment of the acceleration sensor may be provided.  
      The common basic principle of these is that the ratio of an expediently toothed or perforated division that is predefined by the measured-value detector changes as a result of a vibratory movement. For example, in an embodiment having two stops, a different division ratio is therefore produced at each of these stops on account of an axial or radial movement, resulting from a vibratory movement, of the measured-value detector or of a part thereof in relation to the fixed-position sensor part. These changes in the division ratio vary periodically with the vibratory movement of the washing tub. In the case of an in particular digitally regulated or controlled washing-machine drive, this is in turn reflected in a change in the mark/space ratio and therefore in the clock rate of the rotational-speed or rotary-encoder signal which is generated during detection of the rotational speed.  
      Other features which are considered as characteristic for the invention are set forth in the appended claims.  
      Although the invention is illustrated and described herein as embodied in an apparatus for detecting a vibratory movement of 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.  
      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  
       FIG. 1  is a diagrammatic, plan view of a washing machine having an internal unit which is suspended such that it can vibrate, an electric motor which drives a laundry drum, and an apparatus for detecting vibratory movements and disposed on the electric motor;  
       FIG. 2  is a diagrammatic, sectional view of the detection apparatus with a measured-value detector and a fixed-position sensor part;  
       FIGS. 3A and 3B  are diagrammatic, sectional views of detail III from  FIG. 2  on an enlarged scale with a toothed and, respectively, perforated actuator ring;  
       FIG. 4  is a sectional view through the measured-value detector of the detection apparatus taken along the line IV-IV shown in  FIG. 2 ;  
       FIG. 5  is a diagrammatic, plan end view of the measured-value detector according to  FIG. 2  with two mutually orthogonal sensor parts;  
       FIG. 6  is a detailed, sectional view of the measured-value detector according to  FIG. 5  in an illustration as shown in  FIGS. 3A and 3B ;  
       FIG. 7  is a diagrammatic, sectional view of a first embodiment of a radially moving sensor part in an illustration as shown in  FIG. 5 ; and  
       FIG. 8  is a diagrammatic, plan view of a second embodiment of the radially moving sensor part in an illustration as shown in  FIG. 6 .  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a schematic view, from an end and towards the rear face (which is opposite a loading opening) of a machine housing  1 , of an internal unit  2 , also referred to as an overall system below, of a washing machine or of a spin-dryer. The internal unit  2  is suspended in the machine housing  1  by springs  3  and friction dampers  4  such that it can vibrate. The internal unit  2  contains a washing tub  5 , which is suspended such that it can therefore vibrate and is elastically damped, and a washing or laundry drum  6 , which is mounted in particular in the rear wall of the washing tub  5  such that it can rotate, and also an electric motor  7  that drives the drum  6 . A bearing shaft of the electric motor or motor shaft  8 , also referred to as rotary shaft below, runs at least approximately parallel to a drum shaft or bearing shaft and thus to a rotary shaft  9  of the laundry drum  6 , the rotary shafts  8 ,  9  running in the x-direction with respect to the illustrated Cartesian coordinate system.  
      In the exemplary embodiment, an apparatus for detecting vibratory movements, referred to below as an acceleration sensor  10  and in which the functions of a rotational-speed sensor are expediently also integrated or implicit, is provided on the rotary or bearing shaft  8  of the electric motor  7 . As an alternative, the acceleration sensor  10  can also be disposed analogously in the region of the rotary shaft  9  of the laundry drum  6 . In this case, the, for example electronic, acceleration sensor  10  can be fitted at any defined angle relative to a top surface of the washing machine, irrespective of the inclination of the laundry drum  6  which, for example, may be inclined by up to 15° with respect to the horizontal.  
      A rotary-encoder or sensor signal S I , which is provided by the acceleration sensor  10  and expediently also represents the rotational speed of the motor or drum, can be supplied to an evaluation or control device  11 . Further measured variables and/or control variables, in particular a rotational-speed setpoint value S S , can in turn be supplied to the evaluation or control device  11 . The device  11  can, for its part, output a control variable or a control signal S D  to the electric motor  7  in order to set or control the rotational speed. When the laundry drum  6  is not rotating, the sensor signal S I  or the change in it can also be used to detect the degree of loading in the drum, since the sensor or quiescent signal from the acceleration sensor  10  changes as the laundry drum  6  is filled.  
      According to FIGS.  2  to  4 , the acceleration sensor  10  contains a measured-value detector  12 , also referred to below as an actuator, and a sensor part  13 . The sensor part  13  is fixed in position in relation to the measured-value detector  12  and, in this case, can be mounted on a fixed part of the electric motor  7 . The sensor part  13  can also move in a tangential direction (y, z)—in the z-direction here. This is expedient in particular in the case of a motor configuration without a separate tachogenerator and with a motor  7  without any sensors and in which the actual rotational-speed information is obtained from the motor current and, if appropriate, the sensor is used for deflection on a further axis.  
      The sensor part  13 , which is in the form of a forked light barrier in the present case, surrounds an actuator ring  14  of a first actuator part  15  of the measured-value detector  12  by the limbs of the fork light barrier. The first actuator part  15  coaxially surrounds a second actuator part  16 , which is connected to the drive or bearing shaft  8  of the electric motor  7  and thus to the rotary shaft such that it is fixed in terms of rotation, and can move with respect to the second actuator part parallel to the axis of rotation  8 ,  9 .  
      In order that the moving first actuator part  15  can move along the axis of rotation  8 ,  9  in the x-direction with as little friction as possible on the (second) actuator part  16  which is fixed in terms of rotation, the two actuator parts  15 ,  16  are connected using balls  19  which run in grooves  17  and  18 . In this case, the length of the groove  17  formed in the moving actuator part  15  is expediently greater than the length of the groove  18  formed in the actuator part  16  that is fixed in terms of rotation.  
      In particular, the length of the groove  17  formed in the moving actuator part  15  is greater than or equal to the sum of two end spacing gaps  20 ,  21  between the two actuator parts  15  and  16 . At least two grooves  17 ,  18  filled with balls  19  are preferably disposed, in particular symmetrically, about the center of the axis of rotation  8 ,  9 . The balls  19  also indirectly increase the inert mass of the moving actuator part  15  since the balls assume its direction of movement (x-direction) during acceleration and effectively push the moving actuator part  15 , if the groove  17  in the moving actuator part  15  is smaller than the corresponding groove  18  in the fixed actuator part  16 .  
      The actuator ring  14  that extends in the axial direction (x-direction) is integrally formed on the end of the moving actuator part  15 . According to  FIG. 3A , the actuator ring  14  can be formed with sawtooth-like teeth as a toothed profile  22  which can taper from the base of the ring to the free end of the tooth. As an alternative, the actuator ring  14  according to  FIG. 3B  can also be formed with hole cutouts as a perforated profile  23 . The essential feature when forming the actuator ring  14  is that one profile side  22   a,    23 A is made to be variable while the other profile side  22   b  or, respectively,  23 B runs parallel to the axis of rotation  8 ,  9  so that a sawtooth profile, for example, is created overall. This shaping of the actuator ring  14  fixes the timing of a signal transition of the acceleration sensor  10  irrespective of the position of the moving actuator part  15 .  
      The forked light barrier as the sensor part  13  protrudes beyond the actuator ring  14 , the opening width of the forked light barrier being wider than the thickness of the actuator ring  14  and its opening depth being greater than the sum of the two spacings or spacing gaps  20  and  21 . In this case, the forked light barrier  13  is disposed in such a way that its active components likewise centrally illuminate the actuator ring  14  in the center position of the moving actuator part  15 . The illustrated parts of the acceleration sensor  10  can at least partially be surrounded by a housing (in a manner not shown in any more detail) in order to protect the actuator or measured-value detector  12  and the sensor part  13  from contamination.  
      During operation of the washing machine, both the actuator part  16  which is fixed in terms of rotation and also, by the balls  19  acting as drivers, the rotating actuator part  15  rotate when the electric motor  7  is running. The beam path of the forked light barrier  13  is in this case periodically interrupted by the toothed profile  22  ( FIG. 3A ) or the ring webs  25  ( FIG. 3B ) of the perforated profile  23  which are present between the hole cutouts  24 . The rotational speed act  of the motor  7  is obtained from the light and dark changes detected at the forked light barrier  13  per unit time divided by the number of ring teeth  26  or hole cutouts  24  on the circumference of the actuator ring  14  which cause these light and dark changes.  
      If the motor  7 , which is itself fixedly connected to the washing tub  5 , now accelerates in the axial direction (x-direction) on account of non-uniform loading of the laundry drum  6 , the moving actuator part  15  of the acceleration sensor  10  will follow this movement between stops  27   a  and  27   b  shown in  FIG. 2  until the maximum speed is reached in the axial, or x-, direction. The axial movement of the motor  7  and of the overall system  2  is at least approximately sinusoidal if the deflection of the internal unit  2  and thus of the overall system is smaller than its free spacing from the housing parts of the machine housing  1 . In this case, the period of this harmonic vibration corresponds to the rotational speed act  of the drum.  
      At the points at which the motor  7  or the overall system  2  reaches its highest axial speed, and from which the motor or overall system is again decelerated to the reversal points, the moving actuator part  15  will maintain the instantaneous or current direction of movement and pass through the spacing gaps  21 ,  22 , continuing at the maximum speed. As a result, the beam path of the forked light barrier  13  moves into the illustrated regions a and b in the toothed profile  22  as shown in  FIG. 3A . In an analogous manner, the beam path of the forked light barrier  13  moves into the illustrated regions a′ and b′ in the perforated profile  23  as shown in  FIG. 3B . At a constant rotational speed act  of the motor  7  and, respectively, of the rotary shaft  8 ,  9  and thus with a constant number of light/dark changes, these shifts in region cause a change in the time periods in which the beam path of the forked light barrier  13  is interrupted or is not interrupted by the profiles  22  and  23  and thus becomes dark or light.  
      In the case of an electrical output or sensor signal S I  measured at the forked light barrier  13 , the mark/space ratio changes at a constant frequency. Forming the actuator ring  14  as a sawtooth profile  22 ,  23  results in that, depending on the direction of rotation about the axis of rotation  8 ,  9 , one of the two profiled edges  22   b,    23 B will remain constant while the other profiled edge  22   a,    23 A changes in relation to the movement of the moving actuator part  15 . It is therefore possible to measure by electrical measures whether and, if appropriate, at which stop  27   a,    27   b  the moving actuator part  15  is currently present and in which direction parallel to the axis of rotation  8 ,  9  the laundry drum  6 , together with the washing tub  5 , is currently moving.  
      Constant timing or time detection therefore provides information about that point in time at which the moving actuator part  15  was last at one of the two stops  27   a  or  27   b.  The moving actuator part  15  will provide a constantly changing mark/space ratio at the forked light barrier  13  as long as it has not reached the opposite stop  27   b  or, respectively,  27   a.  Upon reaching the opposite stop  27   b  or  27   a,  the detected mark/space ratio becomes constant again. At this point, the time is recorded or detected for a second time. The difference between the two times or time intervals measured or detected here, together with the distance or the travel between the two stops  27   a  and  27   b,  give the maximum speed of the moving actuator part  15 . This speed is identical to the maximum speed of the motor  7  and of the overall system or internal unit  2  in the axial or x-direction. The deflection of the overall system or internal unit  2  can be determined or calculated from this using the rotational speed act  of the drum.  
      The important factors here are the deflections or vibratory movements in the axial direction (x-direction) of the internal unit  2  which is suspended by the springs  3 , is damped by the friction dampers  4  and has the washing container  5 , the laundry drum  6  and also the motor  7 . This is true in particular close to or in the resonance region, where severe deflections or vibratory movements may lead to mechanical destruction. At comparatively high or relatively high rotational speeds act , an unbalanced overall system causes vibration which, although no longer leading to the internal unit  2  striking the machine housing  1 , is however just as undesirable. For a rotational speed act  in the region above resonance, the apparatus according to the invention therefore provides for the rotating actuator part  15  to be fixed with respect to the actuator part  16  which is fixed in terms of rotation. This can take place, in particular, in the manner of a centrifugal brake which increases the friction between the two parts  15 ,  16  as a function of the rotational speed until they are completely fixed. In this case, in one refinement of the actuator or measured-value detector  12  and in a manner not shown in any more detail, the moving actuator part  15  may have a groove in the radial direction, in which groove the centrifugal brake latches and thus holds the moving actuator part  15  in a defined central position.  
      In one variant of the apparatus according to the invention that is not shown in any more detail, the moving actuator part  15  is not fixedly connected to the actuator part  16  that is fixed in terms of rotation. Instead, the moving actuator part  15  can be located on a fixed motor part such that it can move with the forked barrier and thus with the fixed-position sensor part  13 . This may be advantageous for installation, in particular to compensation for manufacturing tolerances.  
      In one expedient development, in addition to the actuator ring  14 , extending in the axial direction (x-direction), for detecting the pitching movement on the moving actuator part  15 , according to  FIGS. 5 and 6 , a further actuator ring or collar  28 , extending in a radial direction (y- and/or z-direction), can be provided on the actuator or measured-value detector  12 . The further actuator ring or collar is used to detect the so-called yawing movement, that is to say a rotary movement of the overall system or internal unit  2  about an imaginary vertical through its centre point, and thus a movement in the z-direction illustrated in  FIG. 6 .  
      The actuator collar  28  which is likewise expediently toothed or perforated has an associated further forked light barrier  29  as sensor part. In this embodiment, the second forked light barrier  29  is located on a moving part that can move in the radial direction. In this embodiment too, the mark/space ratio of an electrical signal S I  measured at the second forked light barrier  29  changes analogously as a function of the yawing movement. It should be taken into account here that, in the case of combined measurement of the pitching and yawing movements, the opening width of the second forked light barrier  29  also has to record the movement of the actuator collar  14  which moves in the axial direction.  
      In the embodiment according to  FIGS. 7 and 8 , the sensor part or the forked light barrier  13  is not fixed in position but is mounted such that it can move in the radial direction y. For this purpose, the sensor part  13  is attached to a holding apparatus  30  that, for its part, is held on the motor housing for example. To this end, the holding apparatus  30  is composed of the light barrier or the sensor part  13 , a holding arm or a holder  31 , and a counterweight  32 , the holding apparatus being mounted at a bearing point  33 . The bearing is the result of two different variants.  
      Therefore, in a first variant, the light barrier  13  is fixed in the x-direction. If the actuator part  15  moves in the x-direction, the mark/space ratio and therefore the light and dark periods at the light barrier  13  change. When the holder or holding apparatus  30  moves in the y-direction, that is to say in the direction perpendicular to the plane of the drawing of  FIG. 7 , the frequency of the light and dark changes varies in such a way that the measured frequency is lower when the moving actuator part  15  is rotated in the clockwise direction and the holding apparatus  30  moves out of the plane of the drawing—that is to say with the same direction of rotation as the moving actuator part  15 —and the measured frequency is higher with the opposite direction of rotation. The holding apparatus  30  thus oscillates about an (imaginary) extension of the center of the motor shaft.  
      In a second variant, the actuator part  15  is fixedly connected to the actuator part  16  that is fixed in terms of rotation. In this case, the holder  30  and the light barrier  13 , together with the counterweight  32 , have to produce both movements in the x- and in the y-direction. In this case, the functional principle remains the same, while the holder  30  now has to move with only two degrees of freedom. The bearing or the bearing point  33  should therefore effectively be in the form of ball bearings.  
      If the washing container or tub  5  of the washing machine now accelerates in a radial direction y and/or z, the light barrier  13  which is mounted such that it can move rotates in or counter to the respective direction of rotation of the washing container  5 . The rotary movement of the motor  7  generates a square-wave signal, which is proportional to the rotational speed, at the light barrier  13  on account of the beam path being interrupted. The frequency, that is to say the mark/space ratio of the square-wave signal resulting from the light/dark changes, decreases or increases when the moving light barrier  13  is deflected in or counter to the current direction of rotation.  
      According to the illustration shown in  FIG. 8 , the pendulum weight or counterweight  32  is formed by the light barrier  13  itself. In this embodiment too, two stops  34  limit the deflection of the radial movement. In this case, the illustrated stops  34  cannot be overcome by an oscillating light barrier  13  and/or an oscillating holding apparatus  30 . The acceleration and therefore the deflection of the washing container  5 —in the radial direction y here—can in turn be determined from the duration of the frequency change.  
      This application claims the priority, under 35 U.S.C. § 119, of German patent application No. 10 2004 029 625.1, filed Jun. 18, 2004 and German patent application No. 10 2004 053 216.8, filed Nov. 4, 2004 the entire disclosure of the prior application is herewith incorporated by reference.