US20090165218A1

US20090165218A1 - Washing machine and method for controlling the same

Info

Publication number: US20090165218A1
Application number: US12/320,127
Authority: US
Inventors: Kweon Son; Yang Hwan No; Jung Hoon Kang; Hyo Sik Choi
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2004-02-27
Filing date: 2009-01-16
Publication date: 2009-07-02
Also published as: ES2401961T3; CN1661156B; US20050188473A1; EP1568813B1; CN1661156A; AU2004231244A1; AU2004231244B2; EP1568813A1

Abstract

Method for controlling a washing machine having a drum of which rotation speed is adjustable, including a first step for rotating the drum at a first rotation speed set at control unit, a second step for detecting whether resonance occurs or not at the drum rotating at the first rotation speed, and a third step for changing the rotation speed of the drum if the resonance is detected at the drum.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Application Nos. P2004-013268, and P2004-013269, both filed on Feb. 27, 2004, which are hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to washing machines, and more particularly, to method and device for preventing resonance from occurring in spinning of a washing machine.
2. Discussion of the Related Art
In general, the washing machine washes laundry by softening action of detergent, and friction of the laundry with water circulation caused by rotation of a pulsator or drum. Recently, demands for drum type washing machines increases day by day, which can reduce an entire height compared to a pulsator type washing machine, and prevent wrinkles from forming.
FIG. 1 illustrates a section of a related art drum type washing machine.
Referring to FIG. 1, the related art drum type washing machine is provided with a tub 3 inside of a cabinet 5 which forms an outer appearance of the drum type washing machine, and a drum 9 rotatably mounted on an inside of the tub 3. The cabinet 5 has a door 1 on a front for introduction of laundry, with a gasket 2 between the door 1 and the tub 3.
The tub 3 has springs 4 each with one end secured to an upper outside circumference thereof and the other end secured to the cabinet 5, and a friction damper 10 thereunder for damping vibration.
On a rear of the tub 3, there is a motor 6 directly coupled to the drum 9 with a rotation shaft 13. On front and rear portion of the rotation shaft 13, there are bearings 12 provided thereto, and on a rear surface of the tub 3, there is a bearing housing for supporting the bearing 12.
The motor 6 is provided with a stator 7 and a rotor 8, wherein the stator 7 is mounted to the rear surface of the tub 3, and the rotor 8 is fixed to the rotation shaft 13. Therefore, when the rotor 8 rotates, the drum 9 connected to the rotor 8 rotates at the same time.
There is a sensor (not shown) at one side of the motor 6 for detecting a rotation speed of the rotor 8, and on an upper portion of a front surface of the cabinet 5, there is a control panel having various buttons for controlling operation of the washing machine.
In the meantime, upon introduction of the laundry into the drum 9, and selecting a washing course, a washing cycle and a rinsing cycle are performed, and a spinning cycle is performed after above cycles are finished.
In the spinning cycle of the laundry, the rotation speed of the motor 6 is increased gradually until the rotation speed reaches to a preset speed when the preset speed is maintained for a preset time period. In this instance, even though a water extraction performance is proportional to the rotation speed of the motor 6, the rotation speed may vary with an extent of eccentricity of the laundry. That is, if the eccentricity of the laundry is great, the rotation speed of the drum 9 drops, or the rotation shaft 13 suffers from damage. Therefore, it is required to measure the eccentricity before the spinning of the washing machine starts.
In the meantime, during the spinning, there can be resonance occurred at the washing machine installed on a floor at a particular rotation speed of the motor 6. That is, if the rotation speed of the motor and the drum approaches close to a natural frequency of the frame, such as the cabinet and the like, the resonance occurs, and once the resonance occurs, vibration and noise become very heavy.
The heavy vibration and noise gives a feeling of inconvenience significantly in measuring the eccentricity of the laundry or in spinning the laundry, or damages the laundry. Moreover, the heavy vibration and noise drops reliability of user on the product.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a washing machine, and a method for controlling the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a washing machine for preventing resonance from occurring during spinning of the washing machine, and a method for controlling the same.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for controlling a washing machine having a drum of which rotation speed is adjustable includes a first step for rotating the drum at a first rotation speed set at control unit, a second step for detecting whether resonance occurs or not at the drum rotating at the first rotation speed, and a third step for changing the rotation speed of the drum if the resonance is detected at the drum.
The third step includes the step of storing the changed rotation speed in the control unit. The drum is rotated at the changed rotation speed when the washing machine is put into operation again after the washing machine is stopped.
The third step further includes the step of measuring eccentricity of laundry held in the drum rotating at the changed rotation speed. The step of decreasing the rotation speed of the drum again after increasing the rotation speed of the drum is repeated, if the eccentricity is greater than a preset value.
The drum may be rotated in regular/reverse directions alternately for a plurality of times, if the eccentricity exceeds a preset value.
In a case the eccentricity is below the preset value, the third step further includes the steps of rotating the drum at the set second rotation speed for extracting water from the laundry, detecting whether the resonance occurs at the drum rotating at the second rotation speed or not, changing the rotation speed of the drum, if the resonance is detected at the drum, and storing the changed rotation speed in the control unit.
The method further includes the step of measuring the eccentricity of the laundry held in the drum, if no resonance occurs in the second step. The step of decreasing the rotation speed of the drum again after increasing the rotation speed of the drum is repeated, if the eccentricity is greater than a preset value. The drum is rotated in regular/reverse directions alternately for a plurality of times, if the eccentricity exceeds a preset value.
In a case the eccentricity is below the preset value, further includes the steps of rotating the drum at the set second rotation speed for extracting water from the laundry, detecting whether the resonance occurs at the drum rotating at the second rotation speed or not, changing the rotation speed of the drum, if the resonance is detected at the drum, and storing the changed rotation speed in the control unit.
The rotation speed of the drum increases in the third step. The rotation speed of the drum decreases in the third step. The rotation speed of the drum changes by predetermined magnitudes each greater than 50 rpm in the third step.
The resonance of the drum is detected by a resonance detecting device automatically in the second step. The third step is performed automatically by the control unit which receives a signal from the resonance detecting device.
The second step includes the step of sounding alarm through a speaker if the resonance of the drum is detected. The steps are performed in a state a test mode is selected.
In another aspect of the present invention, a method for controlling a washing machine having a drum of which rotation speed is adjustable for extracting water from laundry, includes a first step for rotating the drum at a second rotation speed set at a control unit, a second step for increasing the rotation speed from the second rotation speed by predetermined magnitudes of rpm in succession, and whether resonance occurs or not at every rotation speed section is detected, a third step for changing the rotation speed of the drum when resonance of the drum is detected, and a fourth step for storing the changed rotation speed in the control unit.
The first step includes the steps of selecting one of course relevant to a kind of laundry, and rotating the drum at the second rotation speed for the selected course.
The rotation speed of the drum increases in the third step. The rotation speed of the drum may decrease in the third step. The rotation speed of the drum changes by predetermined magnitudes each greater than 50 rpm in the third step.
The steps are performed in a state a test mode is selected. The drum is rotated at the changed rotation speed when the washing machine is put into operation again after the test mode is finished.
Not the changed rotation speed, but the second rotation speed is displayed on a display, when the washing machine is put into operation again after the washing machine is stopped. The fourth step includes the step of sounding an alarm from a speaker when the changed rotation speed is stored.
The third step is performed automatically by the control unit having the signal received from a resonance detecting device. The second step includes the step of automatic detection of resonance occurrence at the drum by the resonance detecting device.
The second step further includes the step of storing a preset maximum rotation speed in the control unit in a case no resonance occurs until the drum rotates up to the preset maximum speed. The second step further includes the step of sounding an alarm from a speaker if the resonance of the drum is detected.
In the meantime, in another aspect of the present invention, a washing machine includes a motor for generating rotating force, a drum for being rotated upon receiving driving force from the motor, a sensor for sensing rotation speed of the drum, a vibration detecting device for transmitting a signal if vibration greater than a preset value is detected at the drum, and a control unit for adjusting the rotation speed of the motor to prevent the resonance of the drum from occurring upon reception of the signal.
The washing machine further includes a rotary key electrically connected to the control unit for a user to turn to change the rotation speed of the drum. The washing machine further includes a selection button connected to the control unit for selecting a course for a kind of laundry. The washing machine further includes a storage button connected to the control unit for storing an adjusted rotation speed.
The washing machine further includes a test mode button connected to the control unit for performing a test mode to search a rotation speed at which the resonance of the drum occurs. The washing machine further includes a speaker connected to the control unit for sounding an alarm when a working rotation speed is stored. The washing machine further includes a display for displaying a rotation speed of the drum sensed at the sensor.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings;

FIG. 1 illustrates a section of a related art drum type washing machine;

FIG. 2A illustrates a frontal perspective view of a washing machine;

FIG. 2B illustrates a graph showing variation of rotation speed during progress of spinning of a washing machine;

FIGS. 3A˜3C illustrate control systems of a washing machine in accordance with preferred embodiments of the present invention;

FIG. 4 illustrates a flow chart showing the steps of a method for controlling spinning of a washing machine of the present invention;

FIG. 5 illustrates a flow chart showing the steps of a method for controlling spinning of a washing machine in accordance with a preferred embodiment of the present invention; and

FIG. 6 illustrates a flow chart showing a method for controlling spinning of a washing machine in accordance with another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Embodiments of the washing machine of the present invention will be described with reference to FIGS. 2A˜6.
FIG. 2A illustrates a perspective view of a washing machine, having a control panel 100 on a front. The control panel 100 includes various buttons, a rotary key 200, and a display 300. The rotary keys 200 and buttons are connected to a control unit 103. As the user rotates the rotary key 200, rotation speeds of the motor and the drum are adjusted.
The buttons include a selection button 101, and a storage button 102. The selection button 101 is provided for selecting one of courses operative in various speeds depending on kinds of laundry, and the storage button 102 is provided to store the adjusted speed in the control unit. Moreover, a test mode button 110 is provided additionally, for selecting a test mode in which the rotation speed is set separately to avoid the resonance of the drum.
FIG. 2B illustrates a graph showing variation of rotation speed during progress of spinning of a washing machine.
Referring to FIG. 2B, the spinning step of the washing machine includes an eccentricity detecting step, additionally. That is, in the spinning step, the eccentricity of the laundry and a foam quantity are detected. It is preferable that the detection of the eccentricity is performed at a rotation speed in the vicinity of 108 rpm at which the laundry starts to be in close contact with an inside surface of the drum.
In this instance, the eccentricity is detected by detecting variation of the rotation speed. The eccentricity is small when the rotation speed of the drum is uniform, and the eccentricity is great if the rotation speed of the drum varies sharply and periodically.
It is preferable that the eccentricity is detected, and corrected before performing the spinning step. The spinning of the drum in a state the eccentricity of the laundry is great might give damage to the drum and the rotation shaft.
In the meantime, if a resonance occurs between the drum and the rotation shaft, which spin, and the cabinet which supports them, the detection of the eccentricity is difficult. That is, when the rotation speed of the drum is the same with the natural frequency of the frame, the resonance occurs. In this instance, since the vibration and noise produced from the drum increase sharply, and the rotation speed of the drum becomes erratic, accurate measurement of the eccentricity is not possible.
Therefore, it is required to know a rotation speed of the drum at which the resonance occurs in advance, for measuring the eccentricity in a range outside of the rotation speed at which the resonance occurs.
FIGS. 3A˜3C illustrate control systems of a washing machine in accordance with preferred embodiments of the present invention.
Referring to FIG. 3A, the washing machine includes a control unit, a motor 104, a sensor 105, a selection button 101, a storage button 102, a rotary key 200, a display 300, and a speaker 400.
The selection button 101 is connected to the control unit 103, for selecting an operation of desired course according to a kind of laundry. Therefore, if one of courses is selected with the selection button 101, the motor 104 rotates at a rotation speed set to meet a course requirement. The rotation speed of the motor 104 is measured at the sensor 105, and provided to the control unit 103, and displayed on the display 300. The rotary key 200 is provided for the user to change the rotation speed.
If the resonance occurs at the drum, vibration or noise increases sharply. In this instance, for avoiding the resonance, the user turns the rotary key 200 to adjust the rotation speed, and presses the storage button 102, to store the adjusted rotation speed in the control unit 103.
In the meantime, the washing machine further includes the speaker 400 connected to the control unit 103, so that the speaker 400 sounds an alarm when the resonance of the drum is detected, or the adjusted rotation speed is stored.
In the meantime, referring to FIG. 3B, the washing machine can detect the resonance at the drum by means of a resonance detecting device 150, automatically.
The resonance detecting device 150 includes a spring and a grounding part. If the spring vibrates more than a preset level, the spring comes into contact with the grounding part, when a signal indicating that the resonance is occurred is generated.
That is, if the resonance occurs at the drum, an amplitude of the vibration becomes great suddenly, and the resonance detecting device 150 provides the signal that the resonance occurs to the control unit 103 in a case a vibration value exceeds a preset value. In this instance, the control unit 103 having received the signal adjusts the rotation speed of the drum, automatically. Of course, the adjustment of the rotation speed may be made by the user manually by turning the rotary key.
In the meantime, the speaker 400 connected to the control unit 103 sounds alarm when resonance of the drum is detected, or the adjusted rotation speed is stored. It is preferable that the adjusted rotation speed is stored automatically by the control unit 103.
In the meantime, referring to FIG. 3C, the washing machine further includes test mode buttons 110 connected to the control unit 103.
It is preferable that the step of adjusting the rotation speed for avoiding the resonance of the drum is made before a regular spinning operation of the washing machine. Therefore, the step of adjusting the rotation speed is performed after the user selects the test mode button 110. The adjusted rotation speed is stored in the control unit before the test mode is finished.
Accordingly, when the regular spinning operation is performed again after the test mode is finished, the drum rotates at the adjusted rotation speed.
A method for controlling spinning of the washing machine will be described.
FIG. 4 illustrates a flow chart showing the steps of a method for controlling spinning of a washing machine of the present invention.
A method for controlling a washing machine of the present invention will be described, with reference to FIG. 4.
At first, the drum is rotated at a first rotation speed set at the control unit (S1). In order to detect the eccentricity of the laundry, it is preferable that the first rotation speed is in the vicinity of 108 rpm. As described before, it is preferable that the detection of the eccentricity is made in a state no resonance occurs at the drum.
Therefore, occurrence of the resonance at the drum rotating at the first rotation speed is detected (S2). If the resonance is detected at the drum, the rotation speed of the drum is changed, automatically, or manually (S3). It is preferable that an alarm sounds from the speaker if the resonance occurs at the drum for the user to know.
It is preferable that the rotation speed is increased or decreased, by a preset unit greater than 50 rpm. This is, since a resonance range of the drum varies a certain level with a small variation of the eccentricity of the laundry, for changing the rotation speed of the drum greater than a variation range. That is, for securer avoidance of the resonance occurrence, the rotation speed is changed by predetermined magnitudes each greater than a certain rpm.
In the meantime, even if the user can know the occurrence of resonance at the drum from sudden increase of vibration and noise in the step (S2) of detecting resonance of the drum, it is preferable that the occurrence of resonance is detected automatically by the resonance detecting device.
The resonance detecting device provides the signal that the resonance is occurred to the control unit, automatically. It is preferable that the rotation speed is changed by the control unit which received the signal for avoiding the resonance, and the changed rotation speed is stored in the control unit as a new first rotation speed. Accordingly, when the washing machine is put into operation again after the washing machine is stopped, the drum is controlled to rotate at the changed rotation speed.
After change of the rotation speed, a step (S5) for measuring eccentricity of the laundry held in the drum is performed.
In a case the eccentricity is greater than a preset value, a step for decreasing the rotation speed of the drum after increasing the rotation speed of the drum is repeated. That is, by repeating the step of varying the rotation speed, the laundry is made to be spread evenly on an inside surface of the drum, by which the eccentricity of the laundry is corrected to an appropriate level.
Alternatively, for correcting the eccentricity to a desired level, the drum may be rotated in regular/reverse directions alternately for a plurality of times. In cases the eccentricity is corrected to a value below the preset level, or the detected eccentricity is below the preset level, the rotation speed of the drum is increased, to progress the spinning.
Opposite to this, in a case no resonance occurs at the drum rotating at the first rotating speed, instead of changing the rotation speed of the drum, a step (S6) for measuring eccentricity of the laundry held in the drum is progressed, directly.
In this instance, as described before, if the measured eccentricity is greater than the preset value, the step of decreasing the rotation speed of the drum after increasing the rotation speed of the drum is repeated, or the drum is rotated in regular/reverse directions alternately for a plurality of times.
In cases the eccentricity is corrected to a value below the preset level, or the detected eccentricity is below the preset level, the rotation speed of the drum is increased, to progress the spinning.
It is preferable that the step (SA) for changing the rotation speed for avoiding the resonance, and the detection (S5, and S6) of eccentricity of the laundry are performed in a state the test mode is selected.
As described before, after finish of detection and correction of the eccentricity of the laundry held in the drum, the spinning step is progressed.
In the meantime, FIG. 5 illustrates a flow chart showing the steps of a method for controlling spinning of a washing machine in accordance with a preferred embodiment of the present invention.
Referring to FIG. 5, the drum is rotated at a constant speed of a preset second rotation speed for extraction of water from the laundry (S7).
The second rotation speeds corresponding to kinds of laundry, such as lingerie, blue jeans, general clothes, and blanket, are set at the control unit. Therefore, once a desired course is selected by the user by pressing the selection button according to kind of the laundry initially, the drum is rotated at the second rotation speed of the selected course. It is preferable that the second rotation speed is higher than 600 rpm for smooth extraction of water from the laundry.
Referring to FIG. 2B, it is preferable that a step is further performed, for detecting a volume of foam inside of the drum while rotating the drum at a constant speed of a third rotation speed (W12) before the rotation speed is increased from the first rotation speed W1 to the second rotation speed W2.
Then, if resonance occurs at the drum rotating at the second rotation speed W2 is detected (S8), if the resonance is detected, the rotation speed of the drum is changed (S9). The changed rotation speed is stored in the control unit (S10).
It is preferable that the change of the rotation speed is made by predetermined magnitudes each greater than 50 rpm. This is for changing the rotation speed of the drum greater than a change range of a resonance range of the drum caused by a minute change of the eccentricity of the laundry.
In the meantime, it is preferable that the rotation speed change for avoidance of the resonance is made in a state the test mode is selected. After finish of the rotation speed change, the test mode is finished automatically, and, then, the spinning step proceeds for a preset time period by spinning the drum.
For an example, if the initially set second rotation speed is 700 rpm in a selected course, and the resonance occurs at the rotation speed, the rotation speed is changed by turning the rotary key, or automatically by the control unit. Then, the rotation speed is changed to 650 rpm, and stored in the control unit. Thereafter, when the test mode is finished, and the washing machine is put into operation again, the drum performs the spinning at the 650 rpm which is newly stored second rotation speed.
In this instance, the rotation speed of the drum is displayed on the display 300, wherein, even if the spinning is progressed at 650 rpm actually, it is preferable that the rotation speed is displayed on the display as 700 rpm as set initially. That is, at a time the washing machine is put into operation again after the washing machine is stopped, not the changed rotation speed, but the second rotation speed set initially is displayed on the display 300. This is for preventing the user from confusing on the rotation speed.
In the meantime, the display may display the changed rotation speed and the initially set second rotation speed alternately at regular time intervals.
FIG. 6 illustrates a flow chart showing a method for controlling spinning of a washing machine in accordance with another preferred embodiment of the present invention.
A method for controlling a washing machine will be described with reference to FIG. 6, in which a rotation speed of a drum is controlled for extraction of water from laundry.
At first, the drum is rotated at the second rotation speed set at the control unit (S12). In the spinning step, it is preferable that the second rotation speed is set different from each other according to kinds of laundry. For this, the spinning step further includes a step for selecting one of courses corresponding to a kind of the laundry, and a step for rotating the drum at a second rotation speed relevant to the selected course.
That is, second rotation speeds are set at the control unit for various kinds of laundry, such as lingerie, blue jeans, general clothes, and blanket, respectively. Therefore, once the user selects a desired course by pressing the selection button according to kind of the laundry, the drum is rotated at the second rotation speed of the selected course.
The rotation speed is increased in succession by predetermined magnitude of rpm from the second rotation speed (S15, and S17), and whether the resonance occurs at the drum or not is detected at every rotation speed section (S14, S16, and S18). It is preferable that the predetermined magnitude of rpm is 50 rpm or 1000 rpm.
That is, if the resonance is detected at any one section of the rotation speed, the rotation speed of the drum is changed (S20), and if no resonance is detected, after the rotation speed is increased by predetermined magnitudes of rpm, whether the resonance occurs or not is detected, again.
For an example, a case is assumed in which the drum rotates at 500 rpm which is initially set second rotation speed. If no resonance occurs, the rotation speed is increased to 600 rpm. If the resonance occurs at the increased rotation speed, the rotation speed is decreased to 650 rpm or increased to 700 rpm.
In a case resonance is detected at the drum, the rotation speed of the drum is increased or decreased, preferably by predetermined magnitudes each greater than 50 rpm. According to this, occurrence of the resonance at the changed rotation speed can be prevented, securely.
Thus, the rotation speed is adjusted for preventing occurrence of the resonance at the drum, and the adjusted rotation speed is stored in the control unit. If the resonance of the drum is detected, an alarm sounds form the speaker, by which the user can know occurrence of the resonance, easily.
In the meantime, the control unit has a maximum rotation speed set therein, and, in a case no resonance occurs until the drum rotates up to the set maximum rotation speed, the maximum speed is stored in the control unit.
It is preferable that the detection of resonance at the drum S14, S16, and S18, the change of the rotation speed S20, and the storage of the changed rotation speed S21 are performed in a state the test mode is selected S21.
Since the changed rotation speed is stored as a newly set second rotation speed in the control unit, when the washing machine is put into operation again after the test mode is finished, the drum is rotated at the changed rotation speed directly, instead of increasing the rotation speed gradually.
In the meantime, an alarm sounds from the speaker when the changed rotation speed is stored in the control unit, and the storage of the change rotation speed is performed automatically by the control unit in response to the signal from the resonance detecting device. Moreover, it is preferable that the occurrence of the resonance at the drum is detected by the resonance detecting device, automatically.
It is preferable that the washing machine is provided with a reset button for returning the rotation speed to the initialed set second rotation speed, for making the next operation by the user in performing the test mode easy.
As has been described, the washing machine and the method for controlling the same have the following advantages.
First, the method for controlling a washing machine of the present invention permits more accurate measurement of an eccentricity by detecting resonance and adjusting the rotation speed in measuring eccentricity of the laundry held in the drum.
Second, the detection of resonance at a rotation speed of the drum and adjustment of the rotation speed to avoid the resonance in the spinning step permits to enhance reliability of the product.
The foregoing method for controlling spinning in a washing machine is applicable not only to the drum type washing machine, but also other general washing machines, such as a pulsator type washing machine.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1-18. (canceled)

19. A method for controlling a washing machine having a drum of which rotation speed is adjustable for extracting water from laundry, comprising: a first step for rotating the drum at a second rotation speed set at a control unit; a second step for increasing the rotation speed from the second rotation speed by predetermined magnitudes of rpm in succession, and whether resonance occurs or not at every rotation speed section is detected; a third step for changing the rotation speed of the drum when resonance of the drum is detected; and a fourth step for storing the changed rotation speed in the control unit.

20. The method as claimed in claim 19, wherein the first step includes the steps of; selecting one of course relevant to a kind of laundry, and rotating the drum at the second rotation speed for the selected course.

21. The method as claimed in claim 19, wherein the rotation speed of the drum increases in the third step.

22. The method as claimed in claim 19, wherein the rotation speed of the drum decreases in the third step.

23. The method as claimed in claim 19, wherein the rotation speed of the drum changes by predetermined magnitudes each greater than 50 rpm in the third step.

24. The method as claimed in claim 19, wherein the steps are performed in a state a test mode is selected.

25. The method as claimed in claim 24, wherein the drum is rotated at the changed rotation speed when the washing machine is put into operation again after the test mode is finished.

26. The method as claimed in claim 25, wherein, not the changed rotation speed, but the second rotation speed is displayed on a display, when the washing machine is put into operation again after the washing machine is stopped.

27. The method as claimed in claim 19, wherein the fourth step includes the step of sounding an alarm from a speaker when the changed rotation speed is stored.

28. The method as claimed in claim 19, wherein the third step is performed automatically by the control unit having the signal received from a resonance detecting device.

29. The method as claimed in claim 19, wherein the second step includes the step of automatic detection of resonance occurrence at the drum by the resonance detecting device.

30. The method as claimed in claim 19, wherein the second step further includes the step of storing a preset maximum rotation speed in the control unit in a case no resonance occurs until the drum rotates up to the preset maximum speed.

31. The method as claimed in claim 19, wherein the second step further includes the step of sounding an alarm from a speaker if the resonance of the drum is detected.

32-38. (canceled)