Patent Publication Number: US-2011056028-A1

Title: Washing machine and control method thereof

Description:
BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to a washing machine and a control method thereof to alleviate high-frequency noise generated during rotation of a motor. 
     2. Description of the Related Art 
     Generally, washing machines may be classified into a drum washing machine, a pulsator washing machine, and an agitator washing machine. The drum washing machine washes clothes using collision force between wash water and the clothes as the clothes drop by rotation of a drum. The pulsator washing machine washes clothes by friction between the clothes and wash water as a pulsator is rotated at a bottom surface of a drum. The agitator washing machine washes clothes by friction between the clothes and wash water as an agitator mounted in a washtub forcibly generates water streams. 
     The above-described various kinds of washing machines performs a washing operation in such a manner that the drum, the pulsator, or the agitator is rotated forward or reverse at a low speed to rotate the wash water or to agitate the clothes. Also, a dehydration operation is performed in such a manner that the drum, in which all of the clothes are received, is rotated at a high speed to apply centrifugal force to the clothes, causing water remaining on the clothes to be removed by the centrifugal force. 
     Meanwhile, a motor of these washing machines is generally rotated by a Pulse Width Modulation (PWM) control method. In the PWM control method, a specific form of PWM signal is output by inputting a sinusoidal reference signal and a triangular wave carrier signal into a comparator and comparing them with each other. The PWM signal controls switching of an inductor. A motor drive signal output from the inductor is input to each coil of the motor, inducing rotational force of the motor. The PWM control method serves to change a rotational speed of the motor by, e.g., changing frequencies of triangular and sinusoidal waves. 
     SUMMARY 
     Therefore, it is an aspect of the present invention to provide a washing machine and a control method thereof to alleviate high-frequency noise generated during a constant-speed period of a dehydration operation. 
     Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with one aspect of the present invention, a control method of a washing machine includes confirming whether to enter a constant-speed period upon progress of a dehydration operation, and repeatedly raising or lowering a speed of a universal motor within a predetermined magnitude range if it is confirmed to enter the constant-speed period, so as to alleviate high-frequency noise. 
     The repeated raising or lowering of the speed of the universal motor within the predetermined magnitude range may include adjusting a command speed of the universal motor to repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range. 
     The adjustment of the command speed of the universal motor may include repeatedly raising or lowering the command speed of the universal motor within a predetermined magnitude range. 
     The repeated raising or lowering of the speed of the universal motor within the predetermined magnitude range may include adjusting a voltage applied to the universal motor to repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range. 
     The adjustment of the voltage applied to the universal motor may include repeatedly raising or lowering the voltage applied to the universal motor within a predetermined magnitude range. 
     The repeated raising or lowering of the voltage applied to the universal motor within the predetermined magnitude range may include adjusting a duty ratio of the voltage to repeatedly raise or lower the voltage applied to the universal motor within the predetermined magnitude range. 
     The repeated raising or lowering of the voltage applied to the universal motor within the predetermined magnitude range may include adjusting a phase of the voltage to repeatedly raise or lower the voltage applied to the universal motor within the predetermined magnitude range. 
     The repeated raising or lowering of the speed of the universal motor within the predetermined magnitude range may include periodically repeatedly raising or lowering the speed of the universal motor within the predetermined magnitude range. 
     The repeated raising or lowering of the speed of the universal motor within the predetermined magnitude range may include aperiodically repeatedly raising or lowering the speed of the universal motor within the predetermined magnitude range. 
     In accordance with another aspect of the present invention, a washing machine includes a universal motor, and a control unit to repeatedly raise or lower a speed of the universal motor within a predetermined magnitude range if it is confirmed to enter a constant-speed period upon progress of a dehydration operation, so as to alleviate high-frequency noise. 
     The control unit may repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range by adjusting a command speed of the universal motor. 
     The control unit may repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range by adjusting a voltage applied to the universal motor. 
     The control unit may repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range by repeatedly raising or lowering the voltage applied to the universal motor within a predetermined magnitude range. 
     The control unit may repeatedly raise or lower the voltage applied to the universal motor within the predetermined magnitude range by adjusting a duty ratio of the voltage. 
     The control unit may repeatedly raise or lower the voltage applied to the universal motor within the predetermined magnitude range by adjusting a phase of the voltage. 
     The control unit may periodically repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range. 
     The control unit may aperiodically repeatedly raise or lower the speed of the universal motor within the predetermined magnitude range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a view schematically illustrating an overall configuration of a washing machine according to an exemplary embodiment of the present invention; 
         FIG. 2A  is a schematic view illustrating a universal motor according to the embodiment of the present invention; 
         FIG. 2B  is a perspective view illustrating a configuration of a rotor of the universal motor according to the embodiment of the present invention; 
         FIG. 2C  is a front view of the rotor of the universal motor according to the embodiment of the present invention; 
         FIG. 3  is a schematic circuit diagram illustrating a drive unit in the washing machine according to the embodiment of the present invention; 
         FIGS. 4A and 4B  are speed control graphs of a motor in the washing machine according to the embodiment of the present invention; 
         FIGS. 5A and 5B  are speed control graphs of the motor in the washing machine according to the embodiment of the present invention; 
         FIGS. 6A and 6B  are graphs illustrating a noise waveform depending on an operation frequency of the washing machine according to the embodiment of the present invention; 
         FIG. 7  is a control flow chart of the washing machine according to the embodiment of the present invention; and 
         FIG. 8  is a control flow chart of the washing machine according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  is a view schematically illustrating an overall configuration of a washing machine according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , the washing machine  10  includes a housing  20  defining an outer appearance of the washing machine  10 , a control panel  30  provided at an upper end of a front surface of the housing  20 , a drum  40  mounted in the housing  20 , a tub  50  surrounding the drum  40 , and a universal motor  29  to rotate the drum  40  so as to perform a washing operation, a rinsing operation, and a dehydration operation. 
     The housing  20  defines the outer appearance of the washing machine  10 . The housing  20  receives a variety of devices required to operate the washing machine  10 . The front surface of the housing  20  has an opening  22 , to which a door  25  is hinged to open or close the opening  22 . The door  25  is centrally provided with an observation window  27 , to allow a user to observe the progress of washing from the outside without opening the door  25 . 
     The control panel  30  includes a variety of operating buttons (not shown) required by the user to operate the washing machine  10  and a display window (not shown) to show the progress of washing. The control panel  30  is coupled to the upper end of the front surface of the housing  20  via hook fastening or screwing. A controller (not shown) is installed at a rear end of the control panel  30  and generates control signals required, e.g., to determine the supply amount of water, to adjust the amounts of wash water and rinse water, to control the progress of washing and rinsing, and to change a rotational speed of the universal motor  29 . 
     The drum  40  mounted in the housing  20  has a cylindrical shape and receives laundry therein to provide a space in which washing of the laundry is actually performed. In consideration of the fact that the drum  40  comes into direct contact with wash water, the drum  40  is made of, e.g., rustproof stainless steel. The drum  40  is rotated clockwise or counterclockwise upon receiving rotational force from the universal motor  29 , causing washing of the laundry. 
     The tub  50  is configured to surround the drum  40  and provides a space to receive wash water therein. An inlet channel  52  is connected at one end thereof to an upper end of the tub  50  to introduce the wash water into the tub  50 . The other end of the inlet channel  52  is connected to a water source at the outside of the housing  20 . A detergent box  53  is located on a portion of the inlet channel  52 . Detergent received in the detergent box  53  is dissolved in the wash water as the wash water passes through the detergent box  53 . The resulting detergent dissolved wash water is introduced into the tub  50  through the inlet channel  52 . An outlet channel  54  to discharge the wash water is connected to a lower end of the tub  50  out of the tub  50 . Specifically, the outlet channel  54  serves to discharge contaminated wash water generated during washing out of the washing machine  10  based on a control signal of the controller. If the drum  40  undergoes eccentricity due to the laundry or the wash water, the tub  50  linked to the drum  40  is vibrated. To alleviate vibration of the tub  50 , the tub  50  is connected to the housing  20  by use of a supporting device (not shown). A door packing  58  is fitted between the tub  50  and the opening  22  of the housing  20 . The door packing  58  is made of a flexible material and thus, acts to prevent vibration of the tub  50  from being directly transmitted to the housing  20 . 
     The universal motor  29  rotates the drum  40 , to perform a washing operation, a rinsing operation, and a dehydration operation. Specifically, if commercial alternating current (AC) power output from a power source unit  60  whose a duty ratio or phase is controlled is transmitted to the universal motor  29 , rotational force of the universal motor  29  is changed, causing the drum  40 , in which the laundry is received, to be rotated at a predetermined speed. 
       FIG. 2A  is a schematic view illustrating a universal motor according to the embodiment of the present invention.  FIG. 2B  is a perspective view illustrating a configuration of a rotor of the universal motor according to the embodiment of the present invention, and  FIG. 2C  is a front view of the rotor of the universal motor according to the embodiment of the present invention. 
     As shown in  FIGS. 2A to 2C , the universal motor  29  includes a stator  2  kept stationary inside a motor housing (not shown), and a rotor  200  rotatably installed inside the stator  2  while maintaining a predetermined air gap with an inner peripheral surface of the stator  2 . The universal motor  29  further includes a rectifier  5 , and brushes  7  installed at opposite sides of the rectifier  5  to come into elastic contact with an outer surface of the rectifier  5  so as to supply power to the rectifier  5 . The rotor  200  includes an armature core  110  and slot edge pieces  130 . The armature core  110  includes a base  111 , through the center of which a rotating shaft  4  is press-fitted, and a plurality of teeth  113  formed at an outer circumference of the base  111  for coil winding. The slot edge pieces  130  are installed between the respective neighboring teeth  113  to insulate the respective teeth  113  from one another. 
     In the above-described universal motor  29 , if AC power is applied to a coil of the stator  2 , electricity moving through the coil of the stator  2  is supplied to the rectifier  5  through one of the brushes  7 . The electricity supplied to the rectifier  5  is rectified into direct current (DC) and is supplied to a coil of the rotor  200 . The electricity moving through the coil of the rotor  200  is supplied to the coil of the stator  2  through an opposite one of the brushes  7 , escaping out of the motor  29 . A magnetic field created in the motor  29  upon the above-described movement of the power causes rotation of the rotor  200 . 
     With the above-described configuration of the universal motor  29 , the brushes  7  and the rectifier  5  may cause high-frequency noise due to mechanical friction when the universal motor  29  is rotated at a high speed. In addition, as shown in  FIG. 2C , air is introduced into and collides with stepped regions  9  between the respective teeth  113  and the slot edge pieces  130  during rotation of the rotor  200  of the universal motor  29 . This may further increase the strength of high-frequency noise, causing a user discomfort. 
       FIG. 3  is a schematic circuit diagram illustrating a drive unit in the washing machine according to the embodiment of the present invention. 
     As shown in  FIG. 3 , the drive unit of the washing machine  10  includes an operation manipulating unit  80  to allow the user to manipulate operation of the washing machine  10 , a speed sensing unit  90  to sense a speed of the motor  29 , a control unit  100  to control general operations of the washing machine  10 , a triac  72  having an On/Off operation by a speed control signal of the control unit  100 , first and second relays  74  and  76  to be switched so as to rotate the motor  29  forward or reverse, the power source unit  60  to supply power, a rectifying unit  78  to rectify and output commercial AC power, and the motor  29  to rotate the drum  40 . 
     The operation manipulating unit  80  outputs an electric signal corresponding to a user input command when the user selects a washing course (e.g., a washing operation and a rinsing operation). 
     The speed sensing unit  90  senses the speed of the universal motor  29  to output and transmit a corresponding sensed signal to the control unit  100 . For example, the speed sensing unit  90  may be a hall sensor. 
     The control unit  100  outputs a speed control signal to adjust the speed of the universal motor  29  (or a speed of the drum  40 ) and a switching control signal to rotate the universal motor  29  forward or reverse. Specifically, the control unit  100  receives key signals transmitted from the operation manipulating unit  80  and outputs the speed control signal for adjustment of the speed of the universal motor  29  to the triac  72  and the switching control signal for forward or reverse rotation of the universal motor  29  to the first and second relays  74  and  76 . 
     The control unit  100  repeatedly raises or lowers the speed of the universal motor  29  within a predetermined magnitude range by changing a command speed of the universal motor  29  during a high or low constant-speed period of a dehydration operation, to alleviate high-frequency noise. 
     In addition, the control unit  100  repeatedly raises or lowers the speed of the universal motor  29  within the predetermined magnitude range by changing a voltage applied to the universal motor  29  during the high or low constant-speed period of the dehydration operation, to alleviate high-frequency noise. 
     The control unit  100  repeatedly raises or lowers the voltage applied to the universal motor  29  within a predetermined magnitude range by adjusting a duty ratio of commercial AC power applied from the power source unit  60 . 
     The control unit  100  controls a phase of commercial AC power applied from the power source unit  60  to a Pulse Width Modulation (PWM) signal as the speed control signal, thereby repeatedly raising or lowering the voltage applied to the universal motor  29  within the predetermined magnitude range. The control unit  100  adjusts an input voltage applied to the universal motor  29  via the phase control, thereby changing the rotational force of the universal motor  29 . 
     The triac  72  performs an On/Off operation by the speed control signal transmitted from the control unit  100 . With the On/Off operation of the triac  72 , the commercial AC power of the power source unit  60  is supplied to the rectifier  78  or is intercepted. The triac  72  controls the applied commercial AC power to a firing angle based on the PWM signal as the speed control signal, so as to change a magnitude of output voltage and consequently, to change the rotational speed of the universal motor  29 . That is, the triac  72  controls phase or duty ratio of commercial AC power so as to supply the controlled power to the universal motor  29 . 
     The first relay  74  and the second relay  76  are switched by the switching control signal of the control unit  100 , causing forward or reverse rotation of the universal motor  29 . For example, if the switching control signal switches the first relay  74  to an A terminal and the second relay  76  to a D terminal, the voltage is supplied to a rotor  29   a  and a stator  29   b  of the universal motor  29  via the A terminal of the first relay  74  and the D terminal of the second relay  76 , causing forward rotation of the universal motor  29 . With the forward rotation of the universal motor  29 , the drum  40  is rotated forward, performing the dehydration operation. On the other hand, if the switching control signal switches the first relay  74  to a B terminal and the second relay  76  to a C terminal, the universal motor  29  is rotated in reverse. 
     The power source unit  60  supplies the commercial AC power required to drive the washing machine  10 , and the rectifying unit  78  rectifies and outputs the commercial AC power supplied from the power source unit  60 . 
     The universal motor  29  is driven upon receiving a predetermined voltage output from the rectifying unit  78  and includes the rotor  29   a  and the stator  29   b.    
       FIGS. 4A and 4B  are speed control graphs of the motor in the washing machine according to the embodiment of the present invention. 
     In  FIG. 4A , considering change in the RPM of the universal motor during the dehydration operation of the washing machine, the dehydration operation is divided into a first acceleration period in which the speed is accelerated at a fixed rate to a first speed V 1 , a low constant-speed period in which the first speed V 1  is kept for a predetermined time, a second acceleration period in which the speed is accelerated at a fixed rate to a second speed V 2 , and a high constant-speed period in which the second speed V 2  is kept for a predetermined time. The universal motor  29  generates high-frequency noise due to mechanical friction between the brushes and the rectifier during rotation thereof. The mechanical frictional noise of the universal motor  29  is mainly generated during the high or low constant-speed period. Accordingly, controlling the speed of the universal motor  29  to be changed within a high or low speed range during the high or low constant-speed period may alleviate the high-frequency noise. 
     To alleviate the high-frequency noise, the control unit  100  repeatedly raises or lowers the command speed of the universal motor  29  within a predetermined magnitude range (for example, 20 rpms). When the command speed of the universal motor  29  is repeatedly raised or lowered within the predetermined magnitude range, an actual speed of the universal motor  29  is repeatedly raised or lowered within a predetermined magnitude range. It may be seen from  FIG. 4A  that the actual speed of the universal motor  29  is repeatedly raised or lowered within the predetermined magnitude range with a slight time difference when the command speed of the universal motor  29  is periodically repeatedly raised or lowered within the predetermined magnitude range (for example, 20 rpms) during the high or low constant-speed period. 
       FIG. 4B  illustrates that the actual speed of the universal motor  29  is aperiodically repeatedly raised or lowered within the predetermined magnitude range when the command speed of the universal motor  29  is aperiodically repeatedly raised or lowered within the predetermined magnitude range (for example, 20 rpms). 
       FIGS. 5A and 5B  are speed control graphs of the motor in the washing machine according to the embodiment of the present invention. 
       FIG. 5A  is a graph illustrating that the actual speed of the universal motor  29  is repeatedly raised or lowered with a certain period within the predetermined magnitude range according to the magnitude of voltage applied to the universal motor  29 . The control unit  100  keeps the command speed of the universal motor  29  at a predetermined speed (for example, 1000 rpms) and periodically repeatedly raises or lowers the voltage applied to the universal motor  29  within a predetermined magnitude range (for example, 2V). When the voltage applied to the universal motor  29  is periodically repeatedly raised or lowered within the predetermined magnitude range, the actual speed of the universal motor  29  is periodically repeatedly raised or lowered within the predetermined magnitude range (for example, 20 rpms). The control unit  100  may adjust the voltage applied to the universal motor  29  by controlling the phase of commercial AC power to the PWM signal as the speed control signal. The control unit  100  may also adjust the voltage applied to the universal motor  29  by controlling the duty ratio of commercial AC power. 
       FIG. 5B  is a graph illustrating that the actual speed of the universal motor  29  is aperiodically repeatedly raised or lowered within the predetermined magnitude range according to the magnitude of voltage applied to the universal motor  29 . The control unit  100  keeps the command speed of the universal motor  29  at the predetermined speed (for example, 1000 rpms) and aperiodically repeatedly raises or lowers the voltage applied to the universal motor  29  within the predetermined magnitude range (for example, 2V). When the voltage applied to the universal motor  29  is aperiodically repeatedly raised or lowered within the predetermined magnitude range, the actual speed of the universal motor  29  is aperiodically repeatedly raised or lowered within the predetermined magnitude range (for example, 20 rpms). 
       FIGS. 6A and 6B  are graphs illustrating a noise waveform depending on an operation frequency of the washing machine according to the embodiment of the present invention. 
       FIG. 6A  illustrates a noise waveform depending on an operation frequency band of 2 kHz to 4 kHz when the universal motor  29  is rotated at 970 rpms. It may be appreciated that this causes a pointed noise waveform and the maximum noise strength is 56 dB. 
       FIG. 6B  illustrates a noise waveform depending on an operation frequency band of 2 kHz to 4 kHz when the universal motor  29  is rotated at 970 rpms under the assumption that a noise removal algorithm according to the embodiment of the present invention (for example, phase control, duty ratio control, and command speed control) is used. It may be appreciated as compared to  FIG. 6A  that the noise waveform becomes relatively gentle and the maximum noise strength is lowered to 50 dB. 
       FIG. 7  is a control flow chart of the washing machine according to the embodiment of the present invention. 
     As shown in  FIG. 7 , once a dehydration operation is initiated, the control unit  100  confirms whether the universal motor  29  enters the high or low constant-speed period in which the universal motor  29  is rotated at a high or low speed for a predetermined time. The dehydration operation is divided into the first acceleration period in which the speed is accelerated at a fixed rate to the first speed V 1 , the low constant-speed period in which the first speed V 1  is kept for a predetermined time, the second acceleration period in which the speed is accelerated at a fixed rate to the second speed V 2 , and the high constant-speed period in which the second speed V 2  (V 2 &gt;V 1 ) is kept for a predetermined time (S 10  and S 20 ). 
     Next, if it is confirmed to enter the high or low constant-speed period, the control unit  100  repeatedly raises or lowers the speed of the universal motor  29  within the predetermined magnitude range by adjusting the command speed of the universal motor  29 . To alleviate the high-frequency noise, the control unit  100  repeatedly raises or lowers the command speed of the universal motor  29  within the predetermined magnitude range (for example, 20 rpms). When the command speed of the universal motor  29  is repeatedly raised or lowered within the predetermined magnitude range (for example, 20 rpms), the actual speed of the universal motor  29  is repeatedly raised or lowered within the predetermined magnitude range (S 30 ). 
     Next, the control unit  100  confirms whether the dehydration operation is terminated, e.g., by the lapse of a dehydration operation time. If the termination of the dehydration operation is confirmed, the control unit  100  changes the command speed of the universal motor  29  to a command speed depending on a following operation (S 40  and S 50 ). 
       FIG. 8  is a control flow chart of the washing machine according to the embodiment of the present invention. 
     As shown in  FIG. 8 , once the dehydration operation is initiated, the control unit  100  confirms whether the universal motor  29  enters the high or low constant-speed period in which the universal motor  29  is rotated at a high or low speed for a predetermined time (S 100  and S 110 ). 
     Next, if it is confirmed to enter the high or low constant-speed period, the control unit  100  repeatedly raises or lowers the speed of the universal motor  29  within the predetermined magnitude range by adjusting the voltage applied to the universal motor  29 . To alleviate the high-frequency noise, the control unit  100  repeatedly raises or lowers the voltage applied to the universal motor  29  within the predetermined magnitude range (for example, 2V). When the voltage applied to the universal motor  29  is repeatedly raised or lowered within the predetermined magnitude range (for example, 2V), the actual speed of the universal motor  29  is repeatedly raised or lowered within the predetermined magnitude range (for example, 20 rpms). The control unit  100  adjusts the voltage applied to the universal motor  29  by controlling the phase of commercial AC power to the PWM signal as the speed control signal. The control unit  100  also adjusts the voltage applied to the universal motor  29  by controlling the duty ratio of commercial AC power (S 120 ). 
     Next, the control unit  100  confirms whether the dehydration operation is terminated, e.g., by the lapse of the dehydration operation time. If the termination of the dehydration operation is confirmed, the control unit  100  changes the voltage applied to the universal motor  29  to a voltage depending on a following operation (S 130  and S 140 ). 
     As is apparent from the above description, according to the embodiment of the present invention, a speed of a universal motor is repeatedly raised or lowered within a predetermined magnitude range if the motor enters a high or low constant-speed period of a dehydration operation, resulting in alleviated high-frequency noise. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that varies may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.