Washing machine

Abstract

A direct drive washing machine is disclosed which is capable of performing a washing operation by efficiently converting electric energy supplied into an electric motor (10) into mechanical energy or with less vibration and noise. When a washing operation is carried out with efficient energy conversion, an acceleration time and a deceleration time of an agitator (8) rotated by the motor (10) are controlled on the basis of a measured value of a vibration sensor (25) or a measured value of clothes weight so that vibration of a water-receiving tub (4) becomes maximum. On the other hand, when a quiet washing operation with less vibration is carried out, the acceleration time and the deceleration time of an agitator (8) rotated by the motor (10) are controlled on the basis of the measured value of the vibration sensor (25) or the measured value of clothes weight so that vibration of the water-receiving tub (4) becomes minimum.

Description

TECHNICAL FIELD

The present invention relates to a washing machine with a construction that an agitator and a rotating tub are rotated directly by a brushless motor.

BACKGROUND ART

Full automatic washing machines have conventionally been used as means for removing soil adherent to clothes at home. The full automatic washing machine is provided with mechanisms for automatically carrying out sequential steps of wash, rinse and dehydration in the same tub.

An agitator is turned alternately in the positive and negative directions in each of the wash and rinse steps, whereas the agitator and the rotating tub serving as a wash tub and a dehydration tub are rotated at high speeds in the same direction. In order that these two driving manners may be carried out, recent full automatic washing machines employ a direct drive system transmitting torque developed by a motor rotor only via a clutch mechanism directly to the agitator or rotating tub without provision of reduction gears. No reduction gears are provided between the motor and the agitator or between the motor and the rotating tub in the direct drive system. Accordingly, the motor necessitates the performance of driving the agitator and the motor rotor at low speeds in the wash step thereby to develop a large torque. Further, the motor also necessitates, in the dehydration step, the performance of driving the agitator and the rotating tub at lower speeds than those by a drive system provided with a reduction mechanism so that a larger torque is developed than that developed by the drive system with the reduction mechanism. Different rotational speeds are required in the wash, rinse and dehydration steps.

Thus, the motor for the washing machine of the direct drive system needs to meet the conditions of low speeds, large torque and variable speed. In order that the conditions may be met, a large size brushless DC motor has recently been employed and a control system has been employed to control torque developed by the brushless DC motor by means of inverter control such as a vector control system.

However, in the conventional washing machine employing the direct drive system, vibrating characteristics of various mechanisms of the washing machine are not sufficiently considered for the wash step. In most cases, only a maximum rotational speed and a rotating time of the motor are controlled according to clothes. Accordingly, torque developed by the motor is not efficiently transmitted to rotating objects including the motor rotor, the agitator, wash liquid and clothes. Thus, electric energy supplied to the motor is not effectively used in many cases. Further, even when a quiet operation with less vibration is desired, for example, an outer or water-receiving tub resonates to produce noise, resulting in problems concerning noise in many cases.

The present invention was made in view of the foregoing circumstances and an object thereof is to provide a washing machine which can perform an operation in which torque developed by the motor is efficiently transmitted to wash liquid and clothes when an efficient washing operation is desired, and which can perform an operation resulting in low vibration and low noise when a quiet operation with less vibration is desired, for example, in the night.

DISCLOSURE OF THE INVENTION

A washing machine of the present invention which comprises a water-receiving tub elastically suspended in an outer cabinet, a rotating tub provided in the water-receiving tub, an agitator provided in the rotating tub, an electric motor provided on an underside of the water-receiving tub for direct driving the agitator, and a control device controlling the motor and the overall washing machine, is characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that vibration of the water-receiving tub becomes maximum. Consequently, electric energy supplied to the motor can efficiently be converted to mechanical energy for the wash liquid and clothes in the washing operation.

Further, a washing machine of the present invention is characterized in that the control device detects a weight of clothes put into the rotating tub prior to the washing operation and subsequently reads an acceleration time corresponding to a detected weight value from a chart storing relationship between weight of clothes and an acceleration time required for the vibration of the water-receiving tub to become maximum corresponding to the weight of clothes and that the control device controls either one or both of the acceleration time and the deceleration time of the motor in the washing operation so that the acceleration time and/or the deceleration time corresponds to the read time. Consequently, electric energy supplied to the motor can efficiently be converted to mechanical energy for the wash liquid and clothes in the washing operation.

Further, a washing machine of the present invention which comprises a water-receiving tub elastically suspended in an outer cabinet, a rotating tub provided in the water-receiving tub, an agitator provided in the rotating tub, a vibration sensor detecting vibration of the water-receiving tub, an electric motor provided on an underside of the water-receiving tub for direct driving the agitator, and a control device controlling the motor and the overall washing machine, is characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that a value of vibration detected by the vibration sensor during the wash operation becomes maximum. Consequently, electric energy supplied to the motor can efficiently be converted to mechanical energy for the wash liquid and clothes in the washing operation.

Further, a washing machine of the present invention which comprises a water-receiving tub elastically suspended on an outer cabinet, a rotating tub provided in the water-receiving tub, an agitator provided in the rotating tub, an electric motor provided on an underside of the water-receiving tub for direct driving the agitator, and a control device controlling the motor and the overall washing machine, is characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that vibration of the water-receiving tub becomes minimum. Consequently, a noise-reduced operation with less vibration can be realized in the washing operation.

Further, a washing machine of the present invention is characterized in that the control device detects a weight of clothes put into the rotating tub prior to the washing operation and subsequently reads an acceleration time corresponding to a detected weight value from a chart storing relationship between weight of clothes and an acceleration time required for the vibration of the water-receiving tub to become maximum corresponding to the weight of clothes and that the control device controlling either one or both of the acceleration time and the deceleration time of the motor in the washing operation so that the acceleration time and/or the deceleration time corresponds to the read time. Consequently, a noise-reduced operation with less vibration can be realized in the washing operation.

Further, a washing machine of the present invention which comprises a water-receiving tub elastically suspended in an outer cabinet, a rotating tub provided in the water-receiving tub, an agitator provided in the rotating tub, a vibration sensor detecting vibration of the water-receiving tub, an electric motor provided on an underside of the water-receiving tub for direct driving the agitator, and a control device controlling the motor and the overall washing machine, is characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that a value of vibration detected by the vibration sensor during the washing operation becomes minimum. Consequently, a noise-reduced operation with less vibration can be realized in the washing operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section of the washing machine in accordance with the present invention;

FIG. 2 is an example of electric circuit arrangement applicable to a manner in which no vibration sensor is used in the present invention;

FIG. 3 illustrates changes in the motor speed in the washing operation with lapse of time;

FIG. 4 shows a simplified model of washing machine for the purpose of analyzing vibration;

FIG. 5 shows a model of vibration system to set up an equation of motion of the vibration;

FIG. 6 shows an equation of motion of the vibration in the case where the washing machine is divided into three portions;

FIG. 7 shows an example of frequency characteristics of the amplitude of the vibration caused by the water-receiving tub;

FIG. 8 shows waveforms of torque developed by the motor in the washing operation;

FIG. 9 illustrates magnitude of amplitude corresponding to frequency component contained in the torque waveform in the acceleration;

FIG. 10 is a longitudinal section of the washing machine in which the vibration sensor is mounted on the water-receiving tub in accordance with the present invention;

FIG. 11 is an electric circuit arrangement applicable to a manner in which the vibration sensor is mounted on the water-receiving tub in the present invention;

FIG. 12 is a chart showing an example of optimum acceleration time t1 corresponding to put clothes weight when HARD WASHING COURSE has been selected; and

FIG. 13 is a chart showing an example of optimum acceleration time t1 corresponding to put clothes weight when QUIET WASHING COURSE has been selected.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described with reference to the accompanying drawings in order to be disclosed in more detail.

FIG. 1 is a longitudinal section of the overall washing machine comprising a rotating tub serving as a wash tub and a dehydration tub and directly driven by an inverter-controlled brushless motor. A washing machine body 1 in FIG. 1 roughly comprises a rectangular box-shaped outer cabinet 2 and a top cover 3 provided on the top of the outer cabinet 2. An outer tub or water-receiving tub 4 receiving dehydrated water is elastically supported by an elastic suspension mechanism 5 in the outer cabinet 2. A rotating tub 6 serving as a wash tub and a dehydration tub is rotatably provided in the water-receiving tub 4. The rotating tub 6 has a circumferential wall formed with a number of dehydration holes 6a. Water dehydrated from clothes is discharged through the dehydration holes 6a into the water-receiving tub 4 in the dehydration. Further, a balancing ring 7 is provided along an upper end of the rotating tub 6 in order to maintain the rotating tub 6 in the balanced state during the dehydration. Further, an agitator 8 is rotatably provided on a bottom of the rotating tub 6.

A driving mechanism section 9 is provided on an underside of the water-receiving tub 4. The driving mechanism section 9 includes a brushless motor 10 of the outer rotor type and a clutch mechanism (not shown). The motor 10 includes a stator 10a fixed to the water-receiving tub 4 with a driving mechanism section base 9a interposed therebetween and a rotor 10b coupled directly to the agitator 8. Only the agitator 8 is rotated alternately in the normal and reverse directions by the motor 10 in wash and rinse steps. The rotating tub 6 is coupled to the rotor 10b by a clutch so as to be rotated at high speeds together with the agitator 8 only in one direction.

The water-receiving tub 4 has a bottom formed with a drain hole 11. A drain valve 12 is mounted in the drain hole 11 and has an outlet to which a drain hose 13 is connected. An air trap 14 is further provided to be adjacent to the drain hole 11. Pressure in the air trap 14 is introduced via an air tube 15 to a water level sensor 16 (shown in FIG. 2). The water level sensor 16 detects a water level in the water-receiving tub 4 and is disposed inside the top cover 3.

A lid 17 is mounted on the top of the top cover 3 and an operation panel 18 is mounted on the upper front of the top cover 3. A control device 19 is mounted on the inside of the top cover 3. Further, a water supply valve 22 (shown in FIG. 2) is mounted on the rear inside of the top cover 3 for controlling water supply into the rotating tub 6.

An electrical arrangement of the aforesaid washing machine will be described with reference to FIG. 2. A control device 19 is principally comprised of a microcomputer. The control device 19 includes a memory storing a control program required to control the operation of the overall washing machine. The control device 19 also has a function of executing control computation required for inverter control of the motor 10. The results of control computation for the control of torque developed by the motor 10 or rotational speed thereof are delivered to a motor drive circuit 23 comprising a PWM forming circuit and a PWM inverter circuit. Output of the PWM inverter circuit is supplied to the motor 10 so that the latter is driven. A brushless motor is used as the motor 10. A rotational position of the rotor 10b is detected by a Hall IC 10c. Pulse signals detected by the Hall IC 10c are supplied to the control device 19 and the motor drive circuit 23. The rotational position of the rotor 10b may be detected and the motor 10 may be controlled by a sensorless vector control system, instead of detection using the Hall IC 10c.

To the control device 19 are supplied ON/OFF signals from switches 20 mounted on the operation panel 18, a water level signal from the water level sensor 16, and rotational position signal pulses from the Hall IC 10c. Further, output signals include signals supplied to the valve drive circuit 21 for opening and closing the drain valve 12 and water supply valve 22 and display signals supplied to the displays 20 mounted on the operation panel 24 as well as a control signal supplied to the motor drive circuit 23.

The following describes the controlling operation in a wash step under the foregoing electrical arrangement and mechanical construction. Clothes to be washed are put into the rotating tub 6 which has not been filled with water, and the lid 17 is then closed. Thereafter, the wash step starts when a start switch of the switches 20 is depressed.

When the washing machine 1 is a full automatic washing machine, the weight of clothes is generally detected first. The control device 19 delivers a predetermined speed command signal to the motor drive circuit 23 so that the rotational speeds of the rotating tub 6 and the agitator 8 are increased to respective predetermined values. Thereafter, electric supply to the motor 10 is interrupted so that the drive torque of the motor 10 is decreased to zero or is under the condition of free running. The speed of the motor 10 is then reduced by the mechanical friction and air resistance such that the motor 10 is stopped. The reduction ratio of the motor 10 is influenced by the weight of clothes to be washed. Accordingly, the weight of clothes is obtained by predetermined calculation from changes in the frequency of the rotational position pulses detected by the Hall IC 10c or the results of rotor rotational position detection by the sensorless vector control.

Upon completion of detection of clothes weight, an “OPEN” signal is supplied to the water supply valve 22 so that water supply starts. An amount of water supplied is a predetermined amount of water determined according to the weight of clothes and is supplied to the rotating tub 6 also serving as the wash tub.

Upon completion of water supply, the washing operation starts. In the washing operation, the rotating tub 6 is fixed to the drive mechanism section base 9a serving as a stationary portion by the operation of the clutch, whereupon the rotating tub 6 is not rotated by the operation of the clutch. The agitator 8 directly connected to the rotor 10b is rotated alternately in the normal and reverse directions by the motor 10, so that washing liquid and clothes in the rotating tub 6 are rotated alternately in the normal and reverse directions, whereby the washing operation is carried out.

The agitator 8 is rotated along a speed curve as shown in FIG. 3 during the washing operation. More specifically, in the normal rotation, the motor 10 applies constant torque to the rotor 10b during an acceleration time t1, so that the rotational speed of the rotor 10b and agitator 8 is increased approximately at constant acceleration, thereby reaching a predetermined revolution N. Thereafter, torque developed by the motor is adjusted so that the predetermined revolution N is maintained.

The acceleration time t1 is usually set to an extraordinarily short time so that a time required for the wash step is shortened. In order that the rotational speed of the rotor 10b and agitator 8 may be increased to the predetermined revolution N within the short acceleration time t1, the motor 10 is required to develop an extraordinarily large torque. On the other hand, torque required to maintain the predetermined revolution N takes a smaller value as compared with torque required to maintain the predetermined revolution N. Further, a time period for which the predetermined revolution N is maintained is extraordinarily longer than the acceleration time t1. When thus rotated, the agitator 8 results in complex rotational motion of wash liquid and clothes, whereupon soil is removed from the clothes.

After the predetermined revolution N is maintained for a predetermined time, the agitator 8 is transferred to a deceleration stage and then stopped. Torque developed by the motor 10 is controlled so that the deceleration time becomes equal to the acceleration time t1. The torque developed by the motor 10 in the deceleration stage has a waveform which has the same magnitude as and the reverse polarity to the torque in the acceleration stage.

The agitator 8 is stopped for a predetermined time and thereafter rotated in the reverse direction. The motor 10 is controlled so that the agitator 8 is rotated along the same speed curve as but in the opposite direction to that for the normal rotation.

Analysis is carried out for vibration at various sections of the washing machine. For the purpose of simplification in vibration analysis calculation, it is assumed that the washing machine is composed of three separate portions as shown in FIG. 4. The first portion is stationary and includes the water-receiving tub 4, rotating tub 6 and stator 10a of the motor. The second portion is directly rotated by the motor 10 and includes the rotor lob of the motor and agitator 8. The third portion is driven by rotation of the agitator 8 and includes wash liquid and clothes. Torque developed by the motor acts between the first and second portions.

FIG. 5 shows a model of rotational vibration system concerning the foregoing three portions in order that motion of the rotational vibration system may be represented by an equation of motion. FIG. 6 shows the equation of motion representative of the rotational vibration system. In FIGS. 5 and 6, reference symbol m1 designates a total moment of inertia of the first portion, namely, the water-receiving tub 4, rotating tub 6 and stator 10a of the motor. Reference symbol m2 designates a total moment of inertia of the second portion, namely, the rotor 10b of the motor and agitator 8. Reference symbol m3 designates a total moment of inertia of the third portion, namely, the wash liquid and clothes. Reference symbols K1 and K2 designate spring constants. Reference symbols c1 to c4 designate damping constants. Reference symbols x1 to x3 designate rotation angles of the first, second and third portions respectively. Reference symbol T designates torque developed by the motor. Sinusoidal torque changing at frequency f is considered as torque T and the equation of motion of FIG. 6 is solved for x1. FIG. 7 shows the frequency characteristic of the magnitude (amplitude) of the rotation angle x1. The axis of abscissas represents frequency f and the axis of ordinates represents a ratio of amplitude of rotation angle at the frequency to a reference frequency in dB in FIG. 7. The rotation angle x1 has resonant frequencies f1 and f3 and an antiresonant frequency f2 as shown in FIG. 7. The amplitude at the lowest resonant frequency is taken as the reference amplitude for the divisions of the axis of ordinates.

On the other hand, FIG. 8 shows rough waveform of torque developed by the motor 10 only in the normal rotation in order that the agitator 8 may be driven along the speed curve as shown in FIG. 3. The axis of abscissas represents time and the axis of ordinates represents developed torque. Usually, the time period for which the motor 10 maintains the constant speed N is sufficiently longer than the accelerating and deceleration times t1. Further, torque required for the rotation at the constant speed N is sufficiently smaller than torque in each of acceleration and deceleration. Accordingly, assume the case where torque with the waveform as shown in FIG. 8 is applied as the drive torque T in the equation of FIG. 6. In this case, it is considered that relatively large vibration of each portion produced during the acceleration time is damped thereby to become smaller during rotation at the constant speed N. Constant torque T is applied when the motor is in rotation at the constant rotational speed N. As stated in the last part of the description of BACKGROUND ART, the present invention resides in provision of the washing machine which can perform an operation in which torque developed by the motor is efficiently transmitted to wash liquid and clothes when an efficient washing operation is desired, and which can perform an operation resulting in low vibration and low noise when a quiet operation with less vibration is desired, for example, in the night. Accordingly, when the motor 10 is under rotation for a long time with the constant rotational speed N maintained, this state does not so much relate to the torque transmission efficiency and noise production. What affects the object of the invention most is considered to be an operation of the vibration system in the acceleration and deceleration. Consequently, analysis can be carried out with attention only to the behavior of the vibration system in the case where the torque at the time of acceleration as shown in FIG. 8 is applied thereto. The same behavior can also be seen at the time of deceleration with rotational direction reversed.

In order that the aforesaid behavior may be examined, consider the case where the torque waveform as shown in FIG. 8, namely, the torque waveform with constant amplitude and duration t1 is applied once in a single-shot manner. The single-shot waveform is transformed by means of the Fourier transform to be graphed in order that the frequency characteristic of the torque component contained in the single-shot pulse may be examined. FIG. 9 shows the resultant graph. The axis of abscissas represents the frequency component contained in the single-shot pulse and the axis of ordinates represents a relative value in dB representative of magnitude (amplitude) of the torque corresponding to the frequency relative to the value in the case where the frequency is at zero. The frequency component of torque contains a frequency at which the torque component becomes a minimum. When symbols f4 and f5 designate two lower frequencies of the frequency at which the torque component becomes a minimum, it is known that there is the following relationship between the values f4 and f5 and the acceleration (or deceleration) time t1 in FIG. 3 or 8:f4=1/t1 andf5=2/t1.

Examination by the inventors shows that when the acceleration time t1 is controlled so that the frequency f4 at which the torque component becomes a minimum corresponds to the antiresonant frequency f2 in FIG. 7, electric energy supplied to the motor 10 is efficiently converted to kinetic energy of wash liquid and clothes. Further, the examination also shows that vibration of the water-receiving tub 4 in the rotation direction is increased when the frequency f4 at which the torque component becomes a minimum corresponds to the antiresonant frequency f2. The reason for this is that when the frequency f4 at which developed torque component becomes a minimum corresponds to the antiresonant frequency f2 in FIG. 7, namely, the frequency f2 at which vibration scarcely occurs, the vibration system is vibrated to a large degree by the torque component due to the frequency other than f4, whereupon torque developed by the motor 10 is efficiently converted to mechanical energy or, first of all, the mechanical energy of wash liquid and clothes.

On the other hand, when a quiet operation with less vibration is desired, the acceleration time t1 is controlled so that the frequency f4 at which the minimum torque component in FIG. 9 is reached corresponds to the resonant frequency f1 of the lowest order in FIG. 7. Consequently, it is found that a quiet operation can be carried out even when torque developed by the motor 10 is relatively large. The reason for this is that it is hard to cause resonance since drive torque component (torque component of frequency f4) corresponding to frequency f2 causing resonance is a minimum value.

Thus, it is proved that the object is achieved when the acceleration or deceleration time t1 is controlled so that the frequency f4 corresponds to the resonant frequency f2 when energy conversion efficiency is of much importance and the frequency f4 corresponds to the resonant frequency f1 of the lowest order.

Next, the following is the description of manners of controlling the acceleration or deceleration time t1 so that the frequency f4 (=1/t1 ) corresponds to the resonant frequency f1 or the antiresonant frequency f2. Changing the acceleration or deceleration time t1 is achieved by delivering, as a target value, constant torque developing time t1 in the waveform of a torque command value supplied from the control device 11 to the motor drive circuit 23. However, how the acceleration time t1 corresponding the frequency f4 to frequency f1 or f2 can be found is a problem. The inventors have found the following two manners.

In the first manner, a vibration sensor 25 is mounted on the water-receiving tub 4 to detect its vibration as shown in FIGS. 10 and 11. The vibration of the water-receiving tub 4 contains a number of frequency components. Accordingly, in order that the magnitude of the vibration may be determined, for example, voltage signal indicative of the vibratory waveform during the acceleration time t1 is rectified and then converted to DC voltage, so that the magnitude of vibration is determined by the magnitude of obtained DC voltage. In this arrangement, the acceleration time t1 is changed at the intervals of 0.2 to 1.0 sec., for example, 0.1 sec. and the magnitude of vibration at the time of change of the acceleration time t1 is measured in an initial stage of the washing operation. When the washing operation is carried out with the priority given to energy transmission efficiency, the acceleration time t1 is determined so that the measured vibration becomes maximum. On the other hand, when a quiet operation with less vibration is carried out, the acceleration time t1 is determined so that the measured vibration becomes minimum. Consequently, the washing operation can be carried out so that each purpose is achieved.

In the second manner, the acceleration times t1 at which maximum transmission efficiency and minimum vibration are reached are obtained. The obtained acceleration times t1 correspond to the weight of clothes put into the rotating tub and an amount of water supplied are obtained. A correspondence table is previously stored in a memory of the control device 19. The weight of clothes is measured and the acceleration or deceleration time t1 are read from the correspondence table to be used for the control.

As described above, the weight of clothes put into the rotating tub is detected at an initial stage of wash step in the full automatic washing machines. An amount of water to be supplied is previously determined for every combination of the measured weight of clothes and a washing course selected by the switches 20, for example, “careful washing course” or “quiet washing course.” Water supply is carried out according to the combination of the clothes weight and the washing course. More specifically, a total mass of the weight of clothes and amount of washing liquid can be grasped by the control device 10. Accordingly, previous calculation or experiment is carried out so that the acceleration time t1 corresponding to the total mass and provides maximum energy efficiency is grasped and so that the acceleration time t1 at which minimum vibration and noise are reached is grasped. Correspondence tables are formed and stored in a memory. Consequently, a purposeful washing operation can be carried out. FIGS. 12 and 13 illustrate examples of such correspondence charts. FIG. 12 is an example of chart showing the relationship between optimum acceleration or deceleration time t1 corresponding to the weight of clothes and the antiresonant frequency f2 in the case where the careful washing course (efficient washing course) has been selected. FIG. 13 is an example of chart showing the relationship between optimum acceleration or deceleration time t1 corresponding to the weight of clothes and the resonant frequency f1 of the lowest order in the case where the quiet washing course (washing course with less vibration) has been selected.

In the foregoing description, the acceleration time and the deceleration time are equal to each other. The reason for this is that effect corresponding to the purpose most is obtained. When the effect may be sacrificed more or less, either one of the acceleration or deceleration time may be controlled in the aforesaid manner and the other of the acceleration and deceleration time may be set to a different value.

INDUSTRIAL APPLICABILITY

As described above, the washing machine in accordance with the invention is suitable for the execution of the washing operation according to the purpose when the washing operation most efficiently converting electric energy to the mechanical energy of wash liquid and clothes. Further, the washing machine is suitable for the execution of the washing operation according to the purpose when a quiet washing operation with less vibration is desired.

Claims

1. A washing machine which comprises: a water-receiving tub elastically suspended in an outer cabinet; a rotating tub provided in the water-receiving tub; an agitator provided in the rotating tub; an electric motor provided on an underside of the water-receiving tub for direct driving the agitator; and a control device controlling the motor and the overall washing machine, characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that vibration of the water-receiving tub becomes maximum.

2. A washing machine according to claim 1, characterized in that the control device detects a weight of clothes put into the rotating tub prior to the washing operation and subsequently reads an acceleration time corresponding to a detected weight value from a chart storing relationship between weight of clothes and an acceleration time required for the vibration of the water-receiving tub to become maximum corresponding to the weight of clothes, and that the control device controls either one or both of the acceleration time and the deceleration time of the motor in the washing operation so that the acceleration time and/or the deceleration time corresponds to the read time.

3. A washing machine which comprises: a water-receiving tub elastically suspended in an outer cabinet; a rotating tub provided in the water-receiving tub; an agitator provided in the rotating tub; a vibration sensor detecting vibration of the water-receiving tub; an electric motor provided on an underside of the water-receiving tub for direct driving the agitator; and a control device controlling the motor and the overall washing machine, characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that a value of vibration detected by the vibration sensor during the wash operation becomes maximum.

4. A washing machine which comprises: a water-receiving tub elastically suspended in an outer cabinet; a rotating tub provided in the water-receiving tub; an agitator provided in the rotating tub; an electric motor provided on an underside of the water-receiving tub for direct driving the agitator; and a control device controlling the motor and the overall washing machine, characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that vibration of the water-receiving tub becomes minimum.

5. A washing machine according to claim 4, characterized in that the control device detects a weight of clothes put into the rotating tub prior to the washing operation and subsequently reads an acceleration time corresponding to a detected weight value from a chart storing relationship between weight of clothes and an acceleration time required for the vibration of the water-receiving tub to become maximum corresponding to the weight of clothes, and that the control device controls either one or both of the acceleration time and the deceleration time of the motor in the washing operation so that the acceleration time and/or the deceleration time corresponds to the read time.

6. A washing machine which comprises: a water-receiving tub elastically suspended in an outer cabinet; a rotating tub provided in the water-receiving tub; an agitator provided in the rotating tub; a vibration sensor detecting vibration of the water-receiving tub; an electric motor provided on an underside of the water-receiving tub for direct driving the agitator; and a control device controlling the motor and the overall washing machine, characterized in that the control device controls either one or both of an acceleration time and a deceleration time of the motor in a washing operation so that a value of vibration detected by the vibration sensor during the wash operation becomes minimum.