Washing machine

Abstract

In any type of washing machine, an amount of laundry introduced into the washing machine may be measured in a short time with high accuracy. A washing machine includes a rotational spin tub into which laundry is introduced; a driving unit including a motor for rotating the spin tub; and at least one processor configured to control the driving unit to rotate the spin tub at first rotational speed, control the driving unit to rotate the spin tub at second rotational speed, and identify weight of the laundry based on acceleration at the time of changing of rotational speed of the spin tub from the first rotational speed to the second rotational speed and the second rotational speed.

Claims

1. A washing machine comprising: a spin tub configured to be rotatable and into which laundry is introduced; a driving system including a motor and configured to rotate the spin tub; and at least one processor configured to: control the driving system to apply a first torque to rotate the spin tub at a first rotational speed, after rotation speed of the spin tub is stabilized to the first rotational speed, control the driving system to apply a second torque greater than the first torque during an acceleration period to rotate the spin tub at a second rotational speed higher than the first rotational speed, identify acceleration of the spin tub while rotational speed of the spin tub increases from the first rotational speed to the second rotational speed, after rotation speed of the spin tub is stabilized to the second rotational speed, identify a value of the second rotational speed, and identify a weight of the laundry based on the second rotational speed and the acceleration.

2. The washing machine of claim 1, further comprising: at least one memory, wherein the at least one memory stores base information including linear relationship information between the acceleration and the second rotational speed associated with a size of a load applied to the spin tub, and wherein the at least one processor is configured to identify the weight of the laundry based on the acceleration, the second rotational speed, and the base information.

3. The washing machine of claim 1, wherein: the motor is an asynchronous motor, and the at least one processor is configured to: control the driving system to drive the motor with a first voltage and a first frequency such that the spin tub is rotated at the first rotational speed, and control the driving system to drive the motor with a second voltage and a second frequency such that the spin tub is rotated at the second rotational speed.

4. The washing machine of claim 3, wherein: the driving system comprises an inverter for controlling the motor, and the at least one processor is configured to obtain the acceleration and the second rotational speed based on a current output from the inverter to the motor.

5. The washing machine of claim 1, wherein: the motor is a synchronous motor, and the at least one processor is configured to control the driving system to drive the motor with a first current such that the spin tub is rotated at the first rotational speed, and control the driving system to drive the motor with a second current such that the spin tub is rotated at the second rotational speed.

6. The washing machine of claim 1, further comprising: at least one memory, wherein the memory stores temperature correction information including linear relationship information between each of the acceleration and the second rotational speed, and a temperature of the motor, and wherein the at least one processor is configured to correct the acceleration and the second rotational speed based on the temperature correction information.

7. The washing machine of claim 6, wherein the at least one processor is configured to identify the temperature of the motor based on a resistance of a coil of the motor and resistance information stored in the memory.

8. The washing machine of claim 7, wherein the at least one processor is configured to control the driving system to apply a predefined direct current (DC) voltage to the coil, and measure the resistance of the coil.

9. The washing machine of claim 1, wherein the at least one processor is configured to: identify a measurement of the weight of the laundry at multiple times, and identify the weight of the laundry based on multiple measurement results.

10. The washing machine of claim 9, wherein the at least one processor is configured to control the driving system to rotate the spin tub at a different speed for each of the multiple times.

11. The washing machine of claim 1, wherein the driving system comprises a clutch for switching between a connected state in which the motor and the spin tub are connected and a disconnected state in which the motor and the spin tub are disconnected, and wherein the clutch switches the spin tub from the connected state to the disconnected state when the spin tub is decelerated.

12. The washing machine of claim 1, wherein the driving system comprises a variable belt interposed between the motor and the spin tub for transmitting a driving power of the motor to the spin tub.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:

(2) FIG. 1 illustrates a schematic cross-sectional view of a primary structure of a washing machine, according to an embodiment of the disclosure;

(3) FIG. 2 illustrates a schematic diagram of a structure of a driving unit;

(4) FIG. 3 illustrates a control block diagram of a washing machine, according to an embodiment of the disclosure;

(5) FIG. 4 illustrates a graph representing linear relationships that exist between acceleration and rotational speed;

(6) FIG. 5 illustrates a graph representing relationships between acceleration and motor temperature;

(7) FIG. 6 illustrates a graph representing changes in rotational speed of a spin tub, which are used in measuring the weight of laundry;

(8) FIG. 7 is a flowchart illustrating a control method of a washing machine, according to an embodiment of the disclosure;

(9) FIG. 8A and FIG. 8B are flowcharts illustrating a method of determining the weight of laundry, according to an embodiment of the disclosure; and

(10) FIG. 9A and FIG. 9B are flowcharts illustrating a method of determining the weight of laundry, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

(11) FIGS. 1 through 9B, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

(12) Embodiments of the disclosure will now be described in detail with reference to accompanying drawings. The embodiments are merely examples, without being limited thereto.

(13) FIG. 1 illustrates a schematic cross-sectional view of a primary structure of a washing machine, according to an embodiment of the disclosure. Referring to FIG. 1, a washing machine 1 is a full automatic top load washing machine. A series of courses, such as washing, rinsing spin-drying, etc., are automatically performed under an instruction of the user. The washing machine 1 may include a main body 2 shaped like a vertically long box, and an operator 3 with switches or buttons arranged thereon provided on the top and rear of the main body 2. The instruction of the user is received through the operator 3.

(14) An opening covered by a door 2a that may be opened or closed are formed on the main body 2 in front of the operator 3. Laundry such as clothing is introduced into the main body 2 through the opening. A fixed tub 4 that may store water is installed in the main body 2. The fixed tub 4 is a cylindrical container with the bottom. An inlet 4a is formed on the top of the fixed tub 4 to face the opening. A drain system 5 and a driving system 6 are provided under the fixed tub 4. The driving system 6 may be called a driving unit 6.

(15) The fixed tub 4 may fluctuate because the fixed tub 4 is suspended from the main body 2 by the wire 7. A water supply system 8 connected to an external water source is provided in an upper portion of the main body 2. The water supply system 8 includes a water supply valve 8a and a water supply pipe 8b. When the water supply valve 8a is opened, water is automatically supplied into the fixed tub 4.

(16) A spin tub 9 is accommodated in the fixed tub 4. The spin tub 9 may be rotated around a vertical axis A. The spin tub 9 is shaped like a cylindrical container with the bottom, and an entrance 9a is formed on the top of the spin tub 9. The spin tub 9 is accommodated in the fixed tub 4 so that the entrance 9a of the spin tub 9 faces the inlet 4a. Accordingly, the laundry is introduced into the spin tub 9 through the inlet 4a and the entrance 9a.

(17) A plurality of through holes 9b are formed on the side of the spin tub 9. A ring-shaped balancer 10 is installed on the top of the spin tub 9 to keep the spin tub 9 balanced during high speed rotation. A disc-shaped pulsator 11 is installed on the bottom of the spin tub 9.

(18) The drain system 5 includes a drain valve 5a, a drain pipe 5b, etc., and the drain system 5 is connected to a drainage hole formed at the bottom of the fixed tub 4. When the drain valve 5a is opened for draining, the water contained in the fixed tub 4 is released out of the washing machine 1 by natural drainage due to gravity.

(19) The driving system 6 includes a motor 60, an inverter 61, a power transmitter 62, etc. The driving system 6 may be called a driving unit 6. The driving system 6 rotates the pulsator 11 and the spin tub 9 by using the motor 60 as a power source. As shown in FIG. 2, the motor 60 is connected to an external power source PS through the inverter 61. In general, the external PS is a commercial alternate current (AC) power source, and the inverter 61 may include a converter in an embodiment of the disclosure. Accordingly, the inverter 61 may be connected to a direct current (DC) PS or AC PS and may perform voltage conversion.

(20) In the inverter 61, there is a common electric circuit including a plurality of switching devices such as insulated gate bipolar transistors (IGBTs), a plurality of free wheeling diodes connected in anti-parallel with the switching devices, three arms on which the switching devices and free wheeling diodes are arranged, etc. The inverter 61 converts a DC voltage converted by turning on and off the switching device of each arm to three AC voltages of different phases U, V, W, and outputs the AC voltages.

(21) In an embodiment, the motor 60 is an inductive motor (asynchronous motor). The motor 60 includes a cylindrical stator 60b equipped with a plurality of coils 60a and a cargo-shaped rotor 60c rotationally arranged inside the stator 60b. FIG. 2 illustrates a simplified version of the motor 60.

(22) When different phases of AC currents flow in the coil 60a, different phase magnetic fields are produced around the stator 60b. Due to an inductive current resulting from the magnetic field, the rotor 60c is rotated at a speed slower than a synchronous speed. That is, the motor 60 produces ‘slip’ while being rotated.

(23) In an embodiment, the motor 60 is a three-phase motor. In this case, three-phase AC currents output from the inverter 61 are input to the motor 60. The motor 60 is driven by the three-phase AC currents. As shown in FIG. 1, a main pulley 63 is coupled to an output shaft of the motor 60.

(24) A power transmission system 62 includes a sub-pulley 620, a clutch 621, a conversion mechanism part 622, etc. The power transmission system 62 is installed under the fixed tub 4 so that the center of the power transmission system 62 is aligned with the vertical axis A. The conversion mechanism part 622 includes an input shaft 622a protruding downward, a first vertical power shaft 622b penetrating the bottom of each of the fixed tub 4 and the spin tub 9 and having a front end fixed to the pulsator 11, and a second vertical power axis 622c fixed to the bottom of the spin tub 9.

(25) The sub-pulley 620 is installed at the input shaft 622a. The sub-pulley 620 and the main pulley 63 are coupled by a variable belt 64. Accordingly, the driving power of the motor 60 is transmitted to the power transmission system 62 through the variable belt 64.

(26) The conversion mechanism part 622 may switch between a “washing/rinsing mode” in which to decouple the input shaft 622a from the second vertical power shaft 622c and couple the input shaft 622a to the first vertical power shaft 622b, and a “spin-dry mode” in which to decouple the input shaft 622a from the first vertical power shaft 622b and couple the input shaft 622a to the second vertical power shaft 622c. That is, when the motor 60 is rotated in the washing/rinsing mode, the pulsator 11 is rotated, and when the motor 60 is rotated in the spin-dry mode, the spin-tub 9 is rotated.

(27) The clutch 621 is interposed between the input shaft 622a and the second vertical power shaft 622c for switching the state of connection between the input shaft 622a and the second vertical power shaft 622c. Specifically, the clutch 621 switches between a connected state (‘connected’) in which the input shaft 622a and the second vertical power shaft 622c are connected so that the motor 60 and the spin tub 9 are connected, and a disconnected state (‘disconnected’) in which the input shaft 622a is decoupled from the second vertical power shaft 622c so that the motor 60 and the spin tub 9 are separated.

(28) The clutch 621 is pressed by elastic force of a spring to be in the connected state when the spin tub 9 is rotated at constant speed or acceleration. When the spin tub 9 slows down, the clutch 621 automatically switches the spin tub 9 into the disconnected state (a spring clutch method).

(29) A control system 20 is installed in an upper portion of the main body 2. The control system 20 controls general operation of the washing machine 1. The control system 20 includes hardware components such as a processor, e.g., a central processing unit (CPU), a memory, etc. The memory stores software such as a control program or different types of data. The processor included in the control system may create a control signal to control operation of the washing machine 1 based on the control program and data stored in the memory. The processor and the memory may be implemented in separate chips or in a single chip. Furthermore, the control system 20 may include at least one processor and at least one memory.

(30) FIG. 3 illustrates key components of the control system 20. The control system 20 is electrically connected to a current sensor 12, a voltage sensor 13, the operator 3, the driving system 6, the water supply valve 8a, the drain valve 5a, etc. The current sensor 12 measures a current output from the motor 60, and sends the measured value to the control system 20. The voltage sensor 13 measures a voltage output from the motor 60, and sends the measured value to the control system 20. The operator 3 sends information instructing a start of operation, a selection of operation mode, etc., to the control system 20. The control system 20 controls the driving system 6, the water supply valve 8a, the drain valve 5a, etc., based on the measured values and the instruction information.

(31) The control system 20 includes a default processor 21, a laundry weight measurer 22, a temperature corrector 23, and an information memory 24. The default processor 21 carries out a series of courses such as washing, rinsing, spin-drying, etc., under an instruction. The laundry weight measurer 22 measures and/or identifies the weight of the laundry introduced into the spin tub 9 in the beginning of the washing course (a laundry weight measurement process). The temperature corrector 23 performs a temperature correction process corresponding to a temperature of the motor 60 for the laundry weight measurement process. The information memory 24 stores base information, temperature correction information, etc., which will be described later, and sends the information to the laundry weight measurer 22, the temperature corrector 23, etc. The information memory 24 corresponds to a memory. The processes carried out by the default processor 21, the laundry weight measurer 22, and the temperature corrector 23 may be performed by at least one processor.

(32) Water is automatically supplied in each of washing and rinsing courses. To gain an adequate washing effect and efficiently save water, an adequate amount of water needs to be determined depending on the weight of the laundry. For this, the laundry weight measurer 22 performs the laundry weight measurement process by measuring and/or determining the weight of the laundry introduced into the spin tub 9 in the beginning of the washing course.

(33) As the spin tub 9 slows down, the spin tub 9 is automatically decoupled from the motor 60 and goes into a free state. Because the mechanical load differs during acceleration and deceleration, and it is difficult to measure rotational speed and acceleration during the deceleration, the washing machine 1 may not measure the weight of the laundry using a change in rotational state during deceleration.

(34) In an embodiment, the washing machine 1 may measure the weight of laundry with high accuracy without using the change in rotational state during deceleration. For example, the washing machine 1 turns the spin tub 9 loaded with the laundry (also called a laundry-loaded spin tub 9) by applying torque to the spin tub 9, and measures the weight of the laundry based on acceleration and rotational speed during constant-speed rotation of the laundry-loaded spin tub 9.

(35) When the laundry-loaded spin tub 9 is rotated under a certain torque by driving of the motor 60, the laundry-loaded spin tub 9 is engaged with the output of the motor 60 and accelerated, and then rotated at a constant speed corresponding to the torque. In this case, the acceleration and rotational speed of the laundry-loaded spin tub 9 are affected by a mechanical loss, such as a friction occurring in the driving system 6.

(36) Hence, when the weight of the laundry is measured based on the acceleration and rotational speed without reflecting the mechanical loss, the measurement may turn out to be inaccurate. The acceleration and the rotational speed, which are affected by the mechanical loss, have a predefined linear relationship associated with the size of a load applied to the spin tub 9.

(37) FIG. 4 illustrates an example of a linear relationship that exists between acceleration and rotational speed. The vertical axis represents acceleration and the horizontal axis represents rotational speed. Straight lines L1 to L4 represent linear relationships between acceleration and rotational speed for different sizes of load applied to the spin tub 9. The load of L1 is 4 kg, L2 is 2 kg, L3 is 1 kg, and L4 is 0 kg.

(38) The acceleration and the rotational speed, which are affected by the mechanical loss, have a linear relationship defined as a (acceleration)=k (coefficient)×ω(rotational speed)+Z, depending on the size of a load applied to the spin tub 9.

(39) As shown in FIG. 4, the load applied to the spin tub 9 and Z have a proportional relationship. That is, Z(α-k.Math.ω) is proportional to the load applied to the spin tub 9. Accordingly, based on this relationship, the load applied to the spin tub 9 may be calculated.

(40) For example, each load Z shown in FIG. 4 and Z calculated from the measurement are compared in value. Accordingly, it is determined whether the load applied to the spin tub 9 is in a range of 0 to 1 kg, 1 kg to 2 kg, 2 kg to 4 kg, or 4 kg or more, and based on the determination, the weight of the laundry is identified.

(41) The coefficient k varies depending on the driving voltage or frequency. The information about the linear relationship is experimentally obtained, and stored in the information memory 24 as base information.

(42) Detection of the acceleration is easily affected by temperature. Especially, as for an inductive motor, the acceleration and rotational speed vary by the temperature at the time of rotation, which might influence the measurement accuracy. In an embodiment, the washing machine 1 may even make a temperature correction in the laundry weight measurement process.

(43) FIG. 5 illustrates relationships between acceleration and motor temperature. The acceleration and the motor temperature have also a linear relationship associated with the size of the load applied to the spin tub 9. Straight lines L5 to L7 represent linear relationships between acceleration and motor temperature for different loads applied to the spin tub 9. The load of L5 is 4 kg, L6 is 2 kg, and L7 is 1 kg. Although not shown, a similar linear relationship exists between the rotational speed and the temperature of the motor 60.

(44) The information about the linear relationship is experimentally obtained, and stored in the information memory 24 as temperature correction information. A temperature corrector 23 corrects the acceleration and rotational speed (second rotational speed) of the laundry-loaded spin tub 9 depending on the temperature of the motor 60 based on the temperature correction information. Accordingly, an accurate laundry weight measurement process is possible.

(45) Motor temperature may be measured by e.g., a temperature sensor installed at the motor 60. In this case, however, the need for newly setting up the temperature sensor may cause increasing product cost or increasing number of manufacturing processes. In an embodiment of the disclosure, the washing machine 1 measures the temperature of the motor 60 indirectly without using the temperature sensor.

(46) For example, the temperature of the motor 60 is measured by using a linear relationship between temperature and resistance of the coil 60a. Specifically, the information memory 24 stores information (resistance information) about a linear relationship between temperature and resistance of the motor 60 in advance. The resistance information may be experimentally obtained. In the laundry weight measurement process, the control system 20 controls the inverter 61 to perform a temperature measurement process that applies a predefined DC voltage to the coil 60a.

(47) Resistance R of the coil 60a, a DC current I flowing in the coil 60a, and a DC voltage V applied across the coil 60a have such a relationship as R=V/I. When performing the temperature measurement process, the control system 20 identifies the resistance of the coil 60a by substituting the measurements obtained from the current sensor 12 and the voltage sensor 13 in the equation. The control system 20 identifies a motor temperature by comparing the identified resistance with resistance information.

(48) Acceleration and rotational speed of the motor 60 may be measured by an instrumentation device, such as e.g., a resolver or a rotary encoder installed at the motor 60. In this case, however, the need for newly setting up the instrument device may cause increasing product cost or increasing number of manufacturing processes. Hence, in an embodiment of the disclosure, the washing machine 1 indirectly measures the acceleration and rotational speed of the motor 60.

(49) For example, the control system 20 obtains current values Id and Iq by performing αβ conversion and dq conversion over the current values Iu of phase U, Iv of phases V, and Iw of phases W, received from the current sensor 12 while the motor 60 is rotated. The rotation frequency ωs due to slip is obtained by calculating Iq/Id. The rotational speed ω of the spin tub 9 is obtained by subtracting the rotation frequency ωs due to the slip from the frequency ωi of a voltage for driving the motor 60 (ωi-ωs).

(50) As such, the control system 20 obtains the acceleration and rotational speed of the motor 60 by performing arithmetic operations based on the values received from the current sensor 12 without the need for an instrumentation device.

(51) FIG. 6 illustrates changes in rotational speed of the spin tub 9 over time, which are used in measuring the weight of laundry.

(52) The control system 20 (the laundry weight measurer 22 in particular) controls the inverter 61 from a state in which the laundry-loaded spin tub 9 is stopped (torque control). Because a certain magnitude of torque (first torque) is applied to the laundry-loaded spin tub 9, the laundry-loaded spin tub 9 is gradually accelerated and stabilized at a highest rpm that may be reached by the first torque, and rotated at a constant speed of the rpm (the first rpm) (a first constant speed rotation process). The first rpm refers to a first rotational speed.

(53) The control system 20 applies an AC current with a first voltage and first frequency to the motor 60. For example, an AC current with 120 V and a frequency that aims at 250 rpm is applied to the motor 60. The laundry-loaded spin tub 9 is accelerated accordingly, and then rotated at a constant speed of the first rotational speed, which is about 200 rpm.

(54) The control system 20 applies second torque to the spin tub 9, the second torque being greater than the first torque, in order for the spin tub 9 rotating at the first rotational speed to be rotated at the second rotational speed that is higher than the first rotational speed (a second constant speed rotation process).

(55) In FIG. 6, in about 6 seconds for which the first constant speed rotation becomes stabilized, the frequency of the AC current is changed to a second frequency that aims at 500 rpm, and the second torque is applied to the laundry-loaded spin tub 9. For second constant speed rotation, the second voltage applied to the motor 60 may be equal to the first voltage. Accordingly, the spin tub 9 is accelerated and then rotated at a constant speed of the second rotational speed, which is about 490 rpm.

(56) The control system 20 obtains the acceleration at the changing moment from the first rotational speed to the second rotational speed, and the second rotational speed for the second constant speed rotation.

(57) The acceleration may be obtained by using an acceleration section 1a (about 2 seconds) having high linearity. For example, the acceleration may be obtained by measuring the speeds at the beginning and at the end of the acceleration period 1a and dividing them by the elapsed time. A plurality of speeds in the acceleration period 1a may be measured, and the acceleration may be obtained by a first approximation.

(58) Furthermore, the second rotational speed may be obtained when the spin tub 9 is somewhat stabilized. In FIG. 6, the second rotational speed is measured in a stabilized section 1v (about 1 second) in 10 minutes after the second constant speed rotation process begins. The second rotational speed may be obtained by performing measurement several times and averaging the measurements.

(59) As the motor 60 is an asynchronous motor, the control system 20 drives the motor 60 at a predefined voltage and frequency to apply certain torque to the laundry-loaded spin tub 9. The second voltage for the second constant speed rotation process may be higher than the first voltage for the first constant speed rotation process. This attains higher acceleration, and a time required for measurement may be reduced. In this case, the second frequency for the second constant speed rotation process may be equal to the first frequency for the first constant speed rotation process.

(60) As such, the control system 20 obtains the acceleration and rotational speed of the motor 60. Subsequently, the control system 20 may make temperature correction and mechanical loss correction for the obtained acceleration and rotational speed, and measure the weight of the laundry.

(61) FIG. 7 illustrates a flowchart of a control method of a washing machine, according to an embodiment of the disclosure, and FIG. 8A and FIG. 8B illustrate flowcharts of a method of determining the weight of the laundry, according to an embodiment of the disclosure.

(62) Referring to FIG. 7, laundry is introduced into the spin tub 9 first when a washing course is performed, in S1. A detergent is put into the washing machine 1 along with the laundry. An instruction to start washing is input through the operator 3, in S2. The control system 20 (the default processor 21 in particular) automatically carries out a series of washing, rinsing, and spin-drying courses under the instruction.

(63) In the beginning of the washing course, the control system 20 (the laundry weight measurer 22 in particular) performs the laundry weight measurement process to determine an appropriate amount of water supply, in S3. FIG. 8A and FIG. 8B show details of the method.

(64) The control system 20 (the temperature corrector 23 in particular) performs a temperature measurement process, in S301. Specifically, as described above, the control system 20 controls the inverter 61 to apply a predefined DC voltage to the coil 60a and measures actual resistance of the coil 60a. The control system 20 identifies the temperature of the motor 60 by comparing the measured actual resistance with resistance information.

(65) Subsequently, the control system 20 controls the power transmission system 62 to switch the conversion mechanism part 622 into a spin-drying mode, in S302. As the motor 60 is driven accordingly, the spin tub 9 is rotated as well.

(66) As shown in FIG. 6, the control system 20 controls the inverter 61 to apply the first torque to the spin tub 9, thereby driving the motor 60 with the first voltage and first frequency, in S303. When the rotational speed of the spin tub 9 is stabilized at the first rotational speed in a certain time in S304, the control system 20 controls the inverter 61 to apply the second torque to the spin tub 9, thereby driving the motor 60 with the second voltage and second frequency in S305. The second voltage may be equal to the first voltage, and the second frequency may be higher than the first frequency. Alternatively, the second voltage may be higher than the first voltage, and the second frequency may be equal to the first frequency. As such, the voltage and frequency applied to the motor 60 may be separately controlled.

(67) The control system 20 detects acceleration using an acceleration section, in S306 and S307. When the spin tub 9 is stabilized at a second rotational speed in a certain time, in S308, the control system 20 detects the second rotational speed (terminal velocity), in S309.

(68) The control system 20 estimates an amount of laundry based on the temperature, acceleration, and rotational speed of the motor 60, in S310.

(69) The control system 20 compares the estimated amount of laundry W with a weight distinction value stored in the information memory 24 (herein, there are three weight distinction values A, B, and C based on the relationship of FIG. 4. C≥B≥A).

(70) When the estimated amount of laundry W is less than weight distinction value A in S311, the control system 20 identifies that the amount of laundry is 0 kg in S312.

(71) When the estimated amount of laundry W is equal to or greater than the weight distinction value A in S311, the control system 20 compares the estimated amount of laundry W with the weight distinction value B in S313. When the estimated amount of laundry W is less than the weight distinction value B in S313, the control system 20 identifies that the amount of laundry is 1 kg in S314.

(72) When the estimated amount of laundry W is equal to or greater than the weight distinction value B in S313, the control system 20 compares the estimated amount of laundry W with the weight distinction value C in S315. When the estimated amount of laundry W is less than the weight distinction value C in S315, the control system 20 identifies that the amount of laundry is 2 kg in S316, and when the estimated amount of laundry W is equal to or greater than the weight distinction value C in S315, the control system 20 identifies that the amount of laundry is 4 kg in S317.

(73) Once the control system 20 identifies the amount of laundry, water supply begins in S4, as shown in FIG. 7.

(74) The information memory 24 stores water supply information that enables an amount of water supply corresponding to the amount of laundry to be set. The control system 20 selects an appropriate amount of water supply by comparing the identified amount of laundry with the water supply information. The control system 20 controls the water supply valve 8a to supply as much water as the selected amount of water supply to the fixed tub 4.

(75) When the water supply is done, the control system 20 starts the washing course, in S5. In the washing course, the conversion mechanism part 622 switches the washing machine 1 from the spin-drying mode to the washing/rinsing mode. The pulsator 11 is driven to be rotated at low speed for a predefined time to agitate the laundry. After this, the drain valve 5a is controlled to release the water from the fixed tub 4 and the washing course is ended.

(76) When the washing course is ended, the control system 20 starts the rinsing course, in S6. Even in the rinsing course, as in the washing course, water supply, agitation, and drain are performed. The rinsing course may be performed several times.

(77) When the rinsing course is ended, the control system 20 starts the spin-drying course, in S7. In the spin-drying course, the conversion mechanism part 622 switches the washing machine 1 from the washing/rinsing mode to the spin-drying mode. The spin-tub 9 is driven to be rotated at high speed for a predefined time to dewater the laundry. The water collected into the fixed tub 4 due to the spin-dry is discharged through the drain system 5.

(78) When the spin-dry course is ended, the control system 20 notifies the user that the laundry is done e.g., through a buzzer.

(79) In an embodiment, it is assumed that the motor 60 is an asynchronous motor. However the disclosure is also applicable to a synchronous motor. In an embodiment, it is assumed that the motor 60 is a synchronous motor.

(80) Except that the motor 60 is a synchronous motor, the structure of the washing machine 1 is the same as in a previous embodiment. Accordingly, description of the same parts will be omitted or simplified, and different parts will be described.

(81) The motor 60 is e.g., a permanent magnet-type motor (synchronous motor). The rotor 60c includes a plurality of permanent magnets that constitute a plurality of magnetic poles. As for the motor 60, when an AC current of a different phase flows in each coil 60a, the rotor 60c is rotated at a (synchronous) speed in sync with the AC current (without occurrence of slip).

(82) Accordingly, the control system 20 controls the inverter 61 to apply particular torque to the spin tub 9, thereby regulating the current to drive the motor 60. In other words, the control system 20 may drive the motor 60 with a predefined current.

(83) FIG. 9A and FIG. 9B are flowcharts illustrating a method of determining the weight of laundry, according to another embodiment of the disclosure. The embodiment of FIG. 9A and FIG. 9B overlap some of the previous embodiment of FIG. 8A and FIG. 8B. Accordingly, description of the overlapping parts will not be repeated or will be simplified by using the same reference numerals.

(84) The control system 20 performs the temperature measurement process in S301, and then switches the conversion mechanism part 622 into a spin-drying mode in S302.

(85) The control system 20 controls the inverter 61 to apply the first torque to the spin tub 9, thereby driving the motor 60 with the first current, in S401. When the rotational speed of the spin tub 9 is stabilized at the first rotational speed in a certain time in S304, the control system 20 controls the inverter 61 to apply the second torque to the spin tub 9, thereby driving the motor 60 with the second current in S402.

(86) Subsequent steps (S306 to S317) are the same as in FIG. 8A and FIG. 8B. The disclosure is applicable both to the asynchronous motor and the synchronous motor by replacing the target subject to be controlled to apply certain torque to the spin tub 9.

(87) The disclosure is not limited to the aforementioned embodiments but includes other various embodiments. For example, the washing machine is not limited to the top-load washing machine. The washing machine may also be a drum washing machine whose rotational axis is horizontal or inclined.

(88) Types of the washing machine 1 are not limited to the type in which the motor drives the spin tub indirectly like the washing machine 1 that employs the aforementioned spring clutch method. The disclosure may also be applied to a direct-drive type washing machine in which the motor drives the spin tub directly.

(89) Furthermore, the disclosure is suitable to a simple belt-driven washing machine rather than the spring-clutch type washing machine. Specifically, in a washing machine that transmits driving power of the motor to the spin tub through a variable belt, the motor rpm and the spin tub rpm may not correspond to each other due to e.g., slip of the variable belt. The technology of the disclosure is thus effective even for the belt-driven washing machine.

(90) The laundry weight measurement process may be performed several times, and the weight of the laundry may be identified based on the plurality of measurement results. This enables more accurate determination of the weight of the laundry. In this case, the torque applied to the spin tub may vary. Furthermore, the rotational speed may use the first rpm instead of the second rpm.

(91) In the case of performing the laundry weight measurement process several times, the same procedure may be repeated, or different procedures in which acceleration and rotational speed may be measured by gradually increasing the rpm i.e., sequentially performing the first constant speed rotation process, the second constant speed rotation process, the third constant speed rotation process, etc.

(92) The motor temperature may be measured by a temperature sensor. Acceleration or rotational speed of the spin tub may be actually measured by a sensor. The motor may be a two-phase motor or a one-phase motor as well as the three-phase motor.

(93) According to embodiments of the disclosure, in any type of washing machine, an amount of the laundry introduced into the washing machine may be measured for a short time with high accuracy. As a result, more effective water-saving may be expected.

(94) Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.