Patent Publication Number: US-2007101511-A1

Title: Washing machine and method for detecting unbalanced state of laundry therein

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of Korean Patent Application No. 2005-106000, filed Nov. 7, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a washing machine and a method for detecting an unbalanced state of laundry therein More particularly, to a washing machine, which determines whether laundry in a rotary tub is in an unbalanced state from an unbalance value calculated using the speed of the laundry and a variation of the unbalance value, and a method for detecting the unbalanced state of the laundry therein.  
      2. Description of the Related Art  
      Generally, conventional washing machines are apparatuses for removing various contaminants from laundry using emulsification of a detergent, friction between a rotary tub and the laundry placed therein due to the rotation of the rotary tub, and impact applied to the laundry due to the rotation of the washing tub.  
      In  FIG. 1A , a conventional washing machine  1  sequentially performs washing, rinsing, and dehydrating operations for a designated time after the supply of washing water and detergent. The washing and rinsing operations are performed by a rotation of a rotary tub  2  containing laundry  3  in a clockwise and counterclockwise directions. After the above operations, as shown in  FIG. 1A , the laundry  3  may be gathered on one side of the rotary tub  2 , thereby causing the rotary tub  2  to become unbalanced. The unbalanced state of laundry  3  as shown in  FIG. 1A  does not cause trouble in the washing and rinsing operations, in which the rotary tub  2  is rotated at a comparatively low speed, but causes severe vibration of the rotary tub  2  and heavy noise and damages the washing machine  1  in the dehydrating operation, in which the rotary tub  2  is rotated at a high speed. In order to prevent the noise and vibration, after the rinsing operation the laundry  3  is uniformly positioned as shown in  FIG. 1B , and then the dehydrating operation is performed.  
      Conventionally, in order to determine whether the laundry is in the unbalanced state, a vibration of the speed of a washing motor is used.  FIG. 2  is a graph illustrating the speed of a motor for illustrating a conventional method for sensing an unbalanced state of laundry in a rotary tub of a washing machine. In the conventional method, whether the laundry in the rotary tub is in the unbalanced state is determined by detecting the deviation of the speed of the rotary tub under the condition that the speed of the rotary tub is uniformly maintained. However, when it is determined that the laundry in the rotary tub is in the unbalanced state under the condition that the rotary tub is rotated at a low speed as shown in  FIG. 2 , the laundry moves and the motor is rotated at a speed shown by a slide line. The actual mean speed of the motor is shown by a dotted line. The calculated mean speed of the motor is shown by a one-dot chain line. When a variation of the speed of the motor is calculated using the calculated mean value of the speed of the motor, a value different from an actual value is obtained, thereby causing an error in determining the unbalanced state of the rotary tub.  
      Further, as shown in  FIG. 1C , when laundry  3  in the rotary tub  2  is in a conical unbalanced state, i.e., when laundry  3  around an entrance and an inner part of the rotary tub  2  at symmetric positions is unbalanced, the deviation of the rotating speed of the rotary tub  2  cannot be easily detected.  FIG. 3  illustrates the moving state of a rotary shaft when vibration due to the conical unbalanced state occurs. Since the conical unbalanced state occurs at symmetrical positions of the rotary tub, the deviation of the rotating speed of the rotary tub is small at a low rpm. Accordingly, in order to sense the conical unbalanced state, the washing motor is calmly driven at a speed close to a resonance rpm. However, when the conical unbalanced state is detected at a high rpm, noise due to vibration caused by the conical unbalanced state is increased, and may cause mechanical damage to the washing machine.  
      When the rotating speed of the rotary tub is lowered so as to prevent vibration and noise due to the conical unbalanced state, the deviation of the rotating speed of the rotary tub is reduced, thereby causing a difficulty in sensing the unbalanced state and generating noise due to vibration during the dehydrating operation caused by an error in sensing the unbalanced state.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an aspect of the present invention to provide a washing machine which precisely detects an unbalanced state of laundry so as to reduce vibration and noise, and a method for detecting the unbalanced state of laundry therein.  
      It is another aspect of the present invention is to provide a washing machine, which precisely detects an unbalanced state of laundry, particularly a conical unbalanced state of the laundry, even at a low rpm so as to reduce vibration and noise and to shorten a time taken to perform a total washing operation, and a method for detecting the unbalanced state of laundry therein.  
      Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.  
      The foregoing and/or other aspects of the present invention are achieved by providing a washing machine including a rotary tub containing laundry therein, a washing motor rotating the rotary tub, a motor speed detecting unit detecting a speed of the washing motor and outputting a motor speed signal, and a controller calculating an unbalance value of the laundry and a variation of the unbalance value using the motor speed signal, determining the unbalanced state of the laundry in the rotary tub using the unbalance value and a variation of the unbalance value, and controlling the washing motor according to determination results.  
      The controller calculates the unbalance value of the laundry and the variation of the unbalance value using a speed ripple extracted from the motor speed signal.  
      The controller calculates the unbalance value of the laundry and the variation of the unbalance value by detecting the speed ripple in real time.  
      The controller calculates the unbalance value of the laundry and the variation of the unbalance value using the speed ripple extracted from the motor speed signal during a change of the speed of the washing motor.  
      The controller includes a motor speed processing unit detecting a speed ripple from the motor speed signal and calculating an absolute value of the detected speed ripple, and calculating the unbalance value and the variation of the unbalance value using the absolute value of the speed ripple.  
      The controller further includes an unbalance value detecting unit calculating the unbalance value using the absolute value of the speed ripple. The unbalance value detecting unit is a low-pass filter (LPF).  
      The controller determines the unbalanced state of the laundry in the rotary tub by respectively comparing the unbalance value and the variation of the unbalance value to predetermined first reference values and by comparing another unbalance value of laundry, obtained by increasing an rpm of the washing motor, to a predetermined second reference value.  
      The unbalance state of the laundry is determined by comparing a conical unbalance value to the predetermined first and second reference values.  
      It is another aspect of the present invention to provide a method for detecting an unbalanced state of laundry in a washing machine having a rotary tub containing the laundry and a washing motor rotating the rotary tub, the method including detecting a rotating speed of the washing motor and outputting a motor speed signal, calculating an unbalance value of the laundry contained in the rotary tub and a variation of the unbalance value using the outputted motor speed signal, and determining the unbalanced state of the laundry by comparing the unbalance value and the variation of the unbalance value to respective reference values.  
      The calculation of the unbalance value of the laundry and the variation of the unbalance value includes extracting a speed ripple from the outputted motor speed signal; and calculating the unbalance value and the variation of the unbalance value using the extracted speed ripple.  
      The unbalance value of the laundry and the variation of the unbalance value is calculated in real time using the speed ripple extracted in real time.  
      The unbalance value of the laundry and the variation of the unbalance value is calculated using the speed ripple extracted during a change of the speed of the washing motor.  
      The calculation of the unbalance value of the laundry and the variation of the unbalance value further includes calculating an absolute value of the extracted speed ripple, and the unbalance value of the laundry and the variation of the unbalance value is calculated using the absolute value.  
      The determination of the unbalanced state of the laundry includes respectively comparing the unbalance value and the variation of the unbalance value to predetermined first reference values, increasing the rpm of the washing motor, and comparing a newly obtained unbalance value to a predetermined second reference value.  
      The unbalance state of the laundry is determined by comparing a conical unbalance value to the predetermined first and second reference values. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:  
       FIG. 1A  is a sectional view illustrating an unbalanced state of laundry in a rotary tub of a conventional washing machine;  
       FIG. 1B  is a sectional view illustrating a balanced state of laundry in the rotary tub shown in  FIG. 1A ;  
       FIG. 1C  is a schematic view illustrating a conical unbalanced state of laundry in the rotary tub shown in  FIG. 1A ;  
       FIG. 2  is a graph illustrating the speed of a motor for illustrating a conventional method for sensing an unbalanced state of laundry in a rotary tub of a washing machine;  
       FIG. 3  is a schematic view illustrating the moving state of a rotary shaft when vibration due to a conical unbalanced state occurs in a conventional washing machine;  
       FIG. 4  is a schematic control block diagram of a washing machine in accordance with an embodiment of the present invention;  
       FIG. 5  is a block diagram illustrating a detailed configuration of a controller of the washing machine in accordance with the embodiment of the present invention;  
       FIG. 6  is a graph illustrating waveforms for processing a motor speed signal of the washing machine in accordance with an embodiment of the present invention;  
       FIG. 7  is a graph illustrating a driving pattern of a washing motor for sensing a conical unbalanced state of laundry in a rotary tub of the washing machine in accordance with an embodiment of the present invention;  
       FIG. 8  is a graph illustrating waveforms of unbalanced state detecting signals to various conical unbalance values according to rpm; and  
       FIG. 9  is a flow chart illustrating a dehydrating operation of the washing machine in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to an embodiment of the present invention, an example of which is illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiment is described below to explain the present invention by referring to the figures.  
       FIG. 4  is a schematic block diagram of a control system of a washing machine in accordance with an embodiment of the present invention. The washing machine comprises components in relation to the detection of an unbalanced state of laundry. That is, as shown in  FIG. 4 , the washing machine of the present invention comprises an input unit  40 , a controller  42 , a motor driving unit  44 , a motor speed detecting unit  46 , and a washing motor  45 . The washing machine of the present invention may further comprise other components in relation to other operations, such as washing and rinsing operations.  
      The washing machine of the present invention is driven by various operating instructions inputted through the input unit  40  by a user. The controller  42  analyzes the operating instructions inputted by the user, and outputs a control signal to the motor driving unit  44 . The motor driving unit  44  receives the control signal, and outputs an operating signal, such as a PWM signal, to the washing motor  45 . The washing motor  45  is driven at a proper rpm according to the inputted operating signal. The motor speed detecting unit  46  detects the rotating speed of the washing motor  45 , and outputs a motor speed signal to the controller  42 . The motor speed detecting unit  46  is a hall sensor or an encoder, for example. However, the motor speed detecting unit is not limited thereto, and may vary, as necessary.  
       FIG. 5  illustrates a detailed configuration of the controller  42 . Hereinafter, with reference to  FIGS. 5 and 6 , a process for calculating an unbalance value will be described. A motor speed signal (Y 1 ) outputted from the motor speed detecting unit  46  is inputted to a motor speed signal processing unit  50  of the controller  42 . The motor speed signal processing unit  50  extracts a speed ripple (Y 2 ) from the inputted motor speed signal (Y 1 ), and calculates an absolute value (Y 2 *Y 2 ) of the speed ripple (Y 2 ) so as to convert the extracted speed ripple (Y 2 ) into a RMS value. The extraction of the speed ripple (Y 2 ) from the motor speed signal (Y 1 ) is achieved by a high-pass filter (HPF) or a band-pass filter (BPF). When the washing motor  45  is operated at a constant speed, a direct current component corresponding to the constant speed has no relation with the unbalanced state, and is thus removed by the HPF or the BPF. Further, since mechanical noise having no relation with the unbalanced state is removed by the HPF or the BPF, it is possible to precisely determine the unbalanced state of laundry. The speed ripple (Y 2 ) having passed through the filter is squared, thereby producing the absolute value (Y 3 ). The calculation of the absolute value (Y 3 ), i.e., a RMS value, which is used to provide convenience in comparison and to obtain a precise unbalance value.  
      The speed ripple absolute value (Y 3 ) is inputted to an unbalance value detecting unit  52 , and then the unbalance value detecting unit  52  outputs a current unbalance value (Y 4 ). The unbalance value detecting unit  52  comprises a low-pass filter (LPF), and receives the speed ripple absolute value (Y 3 ) and outputs the current unbalance value (Y 4 ), which is easily compared. Further, since noise having no relation with the unbalanced state is removed by the LPF, it is possible to precisely determine the unbalanced state of laundry.  
      The unbalance value (Y 4 ) outputted from the unbalance value detecting unit  52  is inputted to an unbalance value variation calculating unit  54 . The unbalance value variation calculating unit  54  performs sampling of unbalance values (Y 4 ) for a designated time and divides the sum of the total of the unbalance values (Y 4 ) by the time, thereby producing a variation of the unbalance values (Y 4 ) according to time. The unbalance values (Y 4 ) and the variation of the unbalance values (Y 4 ) according to time are inputted to an unbalanced state determining unit  56 . The unbalanced state determining unit  56  compares the unbalance values (Y 4 ) and the variation of the unbalance values (Y 4 ) according to time to reference values, thereby determining the unbalanced state of laundry. When it is determined that the laundry is in an unbalanced state, a motor control unit  58  stops the operation of the washing motor, and appropriately controls the washing motor  45  so as to perform a laundry winding operation again. When it is determined that the laundry is in a balanced state, the motor control unit  58  increases the rpm of the washing motor to start a high-speed dehydrating mode.  
       FIG. 7  is a graph illustrating a driving pattern of a washing motor for sensing a conical unbalanced state of laundry of the washing machine in accordance with an embodiment of the present invention. As described above, since the deviation of the rotating speed of a rotary tub is small at a low rpm in the conical unbalanced state, it is difficult to sense whether the laundry is in the conical unbalanced state. With reference to a graph shown in  FIG. 8  illustrating wave forms of various conical unbalance values according to rpm, in order to sense the conical unbalanced state, the rpm must be increased close to a resonance frequency band. This increase of the rpm causes the increase of a dehydrating time and the increase of noise and vibration. In the present invention, the conical unbalanced state is sensed through unbalance values at an rpm of approximately 100 and variations of the unbalance values according to time. Preferably, the rpm for sensing the conical unbalanced state is set a point where the unbalance value is greatly varied according to time. The rpm may be reset by tests.  FIG. 8  illustrates one example of the tests, and shows that variations of the unbalance values according to time used to sense the unbalanced state is well expressed at approximately 100 rpm.  
      In the present invention, since the unbalanced state of laundry is sensed using the variation of the unbalance value according to time, it is possible to precisely sense a common unbalanced state as well as the conical unbalanced state at a comparatively low rpm. That is, when an unbalance value detected at a low rpm and the variation of the unbalance value according to time are obtained, an unbalance value at a designated resonance frequency band is calculated, and thus it is possible to precisely and effectively sense the unbalanced state of laundry.  
      Further, since the detection of a pure unbalance value is achieved by removing noise using the extracting of the speed ripple, it is possible to calculate the unbalance value during the changing of the speed in real time and thus to calculate the variation of the unbalance value according to time.  
      Accordingly, the determination of the unbalanced state is achieved by calculating unbalance values and the variation of the unbalance values according to time under the condition that the speed of the washing motor is increased from 100 rpm to 400 rpm, as shown in  FIG. 7 , and, when it is determined that the laundry in the washing machine is in the unbalanced state, the speed of the washing motor  45  is decreased and a laundry winding operation is performed again. Thereby, it is possible to shorten a time taken to perform the total washing operation of the washing machine.  
       FIG. 9  is a flow chart illustrating a dehydrating operation of the washing machine in accordance with the present invention. In operation  810 , A dehydrating operation is started after washing and rinsing operations are performed by operating instructions inputted by a user. From operation  810 , the process moves to operation  820  where a laundry winding operation for uniformly positioning of laundry in a balanced state is performed so as to prevent noise and vibration due to the unbalanced state of laundry. After the laundry winding operation is performed for a designated time in operation  820 , in order to sense the unbalanced state as shown in  FIG. 7 , the process moves to operation  830  where unbalance values of laundry contained in a rotary tub and the variation of the unbalanced values according to time are sensed in real time under the condition that the rotating speed of the washing motor is adjusted. From operation  830 , the process moves to operation  840  where an unbalance value for determining the unbalanced state and the variation of the unbalance value according to time at an rpm where the variation of unbalance value according to time is well expressed are respectively compared to first reference values (first limit condition) for detecting the conical unbalanced state. When the unbalance value and the variation of the unbalance value according to time are respectively lower than the first reference values in operation  840 , the process moves to operation  850  where the rotating speed of the washing motor is increased. Although the unbalanced state can be precisely sensed by the comparison using the first limit condition, unbalance values are continuously detected under the condition that the rotating speed of the washing motor is increased to a designated rpm in operation  860 , and from operation  860 , the process moves to operation  870  where the detected unbalance value is compared to a second reference value (second limit condition). Since the unbalance values are detected using the speed ripple, it is possible to determine whether or not the laundry is in an unbalanced state during the changing of the rotating speed of the washing motor. As comparison results, when the detected unbalance value is lower than the second reference value, it is determined that the laundry is uniformly positioned in the rotary tub, and in operation  880  a high-speed dehydrating mode is started. On the other hand, when the obtained values do not satisfy the first or second limit condition, the laundry winding operation is performed again.  
      As apparent from the above description, the present invention provides a washing machine, which determines whether laundry in a rotary tub is in an unbalanced state using an unbalance value and a variation of the unbalance value according to time using a speed ripple of a washing motor so that the unbalanced state of the laundry in the rotary tub can be precisely sensed, and a method for detecting the unbalanced state of the laundry therein.  
      Since the unbalanced state of the laundry in the rotary tub of the washing machine is sensed using the variation of the unbalance value according to time as well as the unbalance value, it is possible to precisely sense the unbalanced state of the laundry at a low rpm.  
      Further, the washing machine of the present invention precisely senses a conical unbalanced state of laundry at a low rpm.  
      Since the unbalanced state of the laundry is sensed at a low rpm, a time taken to perform the total washing operation of the washing machine is shortened.  
      Although an embodiment of the invention has been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.