KR102457410B1 - Method for controlling washing machine - Google Patents

Abstract

The present invention provides a tub containing water, a drum rotatably provided in the tub, at least one nozzle for spraying water into the drum, a washing motor rotating the drum, and at least one of water discharged from the tub. In the control method of a washing machine including a pump for pumping to a circulation nozzle, (a) after accelerating the washing motor so that, in a state in which water is contained in the tub, the cloth on the inner circumferential surface of the drum rises while in contact with the drum by centrifugal force , braking the washing motor so that the cloth falls from the inner circumferential surface of the drum, and (b) accelerating the pump motor constituting the pump to spray water through at least one nozzle, and then starting from the braking point of the washing motor It relates to a control method of a washing machine, comprising the step of initiating deceleration of the pump motor after a time period.

Description

How to control washing machine {METHOD FOR CONTROLLING WASHING MACHINE}

The present invention relates to a control method of a washing machine having a circulation pump for circulating wash water.

In general, a washing machine is a device that separates contaminants from clothes, bedding, etc. (hereinafter abbreviated as 'laundry') by using a chemical decomposition action of water and detergent and a physical action such as friction between water and laundry. it will be called

Such a washing machine includes a tub containing water and a drum rotatably provided in the tub to accommodate laundry. Recent washing machines are also configured to circulate the water discharged from the tub using a circulation pump, and spray the circulated water into the drum through a nozzle.

Recently, new technologies for controlling the rotation of the drum have been developed in order to give variety to the flow of laundry put into the drum. On the other hand, techniques for changing the water pressure sprayed through the nozzle according to the rotation of the drum and improving the washing effect are also being developed.

However, in order to further improve the washing effect, there is a need for an improved method of controlling the water pressure sprayed through the nozzle according to the rotation control of the drum.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling a washing machine in which a washing effect is improved during a washing motion causing a fall.

The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, a control method of a washing machine according to an embodiment of the present invention includes a tub containing water, a drum rotatably provided in the tub, and at least one nozzle for spraying water into the drum; , a washing motor rotating the drum, and a pump for pumping water discharged from the tub to the at least one circulation nozzle, wherein the control method of the washing machine comprises: (a) water in the tub In this contained state, after accelerating the washing motor so that the cloth on the inner circumferential surface of the drum rises while in contact with the drum by centrifugal force, braking the washing motor so that the cloth falls from the inner circumferential surface of the drum; and (b) accelerating the pump motor constituting the pump to spray water through the at least one nozzle, and then starting the deceleration of the pump motor after a first time from the braking time of the washing motor. includes ;

The details of other embodiments are included in the detailed description and drawings.

The control method of the washing machine according to the present invention provides a time delay between the starting point of decelerating the rotational speed of the washing motor and the starting point of decelerating the rotational speed of the circulation pump motor in the fall-inducing motion to reduce the water pressure of the water stream sprayed from the nozzle. It has the effect of effectively washing laundry. That is, with respect to laundry falling from the top of the drum to the lowest point when the washing motor starts decelerating (or braking), the rotation speed of the circulation pump motor is maintained at a high speed and the water sprayed from the nozzle exerts a physical impact on the laundry with strong water pressure. It can improve the washing effect.

The effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

1 is a perspective view illustrating a washing machine according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the washing machine shown in FIG. 1 .
3 is a block diagram illustrating a control relationship between main parts of a washing machine according to an embodiment of the present invention.
4 schematically shows the main components of a washing machine according to an embodiment of the present invention.
5 schematically shows the drum viewed from the front, and the spraying range of each nozzle is shown.
6 is a schematic view of the drum viewed from the side, and the spraying range of each nozzle is shown.
7 is a view showing drum driving motions that can be implemented by a washing machine according to an embodiment of the present invention.
8 is a graph comparing washing power and vibration level of drum driving motions.
9 is a diagram referenced for explaining the injection motion in each drum driving motion of the present invention compared with the conventional one.
10 is a flowchart illustrating a method of controlling a washing motor and a pump motor in a drum driving motion.
11 is a view showing the entire washing procedure applied to the washing machine of the present invention.
12 is a graph showing the speed (a) of the washing motor and the speed (b) of the pump motor in rolling motion and tumbling motion.
13A is a graph for explaining operations of a washing motor and a pump motor in swing motion, scrub motion, and step motion according to an embodiment of the present invention.
13B and 13C are graphs illustrating a speed (a) of a washing motor and a speed (b) of a pump motor in swing motion, scrub motion, and step motion according to another embodiment of the present invention.
14 is a view illustrating a change in the rotational speed of the drum (a) and a change in the rotational speed of the pump (b) during filtration motion according to an embodiment of the present invention.
15 shows the arrangement of laundry in the drum while the filtration motion is being performed.
16 is a graph comparing the speed of the pump motor in each drum driving motion, when the laundry amount belongs to the first laundry weight range (I) and when the laundry weight belongs to the second laundry weight range (II).

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, the present invention will be described with reference to the drawings for explaining the configuration and control method of a washing machine according to embodiments of the present invention.

<configuration>

1 is a perspective view illustrating a washing machine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the washing machine shown in FIG. 1 . 3 is a block diagram illustrating a control relationship between main parts of a washing machine according to an embodiment of the present invention. 4 schematically shows the main components of a washing machine according to an embodiment of the present invention.

1 to 4 , the casing 10 forms the exterior of the washing machine, and an inlet 12h through which laundry is put is formed on the front side. The casing 10 includes a cabinet 11 having an open front side, a left side, a right side, and a rear side, and a front panel 12 coupled to the open front of the cabinet 11 and having an inlet 12h formed therein. can The bottom and top surfaces of the cabinet 11 are open, and the horizontal base 15 supporting the washing machine may be coupled to the bottom surface. In addition, the casing 10 may further include a top plate 13 covering an open upper surface of the cabinet 11 , and a control panel 14 disposed above the front panel 12 .

The control panel 14 includes an input unit (eg, a button, a dial, a touch pad, etc.) for receiving various settings for operation of the washing machine from a user, and a display unit (eg, LCD, LED display, etc.).

The door 20 for opening and closing the inlet 12h may be rotatably coupled to the casing 10 . The door 20 may include a door frame 21 having an open substantially central portion, rotatably coupled to the front panel 12 , and a window 22 installed in the open central portion of the door frame 21 . .

A tub 31 containing water may be disposed in the casing 10 . The tub 31 has an inlet formed on the front so that laundry can be put in, and the inlet is communicated with the inlet formed in the casing 10 by a gasket 60 .

The gasket 60 is to prevent the water contained in the tub 31 from leaking. The front end is overlapped with the front (or front panel 12) of the casing 10, the rear end is coupled to the inlet of the tub 31, and a tubular shape extends between the front end and the rear end. The gasket 60 may be made of a flexible or elastic material. The gasket 60 may be made of natural rubber or synthetic resin.

The gasket 60 includes a casing coupling part 61 coupled around the inlet of the casing 10 , a tub coupling part 62 coupled around the inlet of the tub 31 , and a tub coupling from the casing coupling part 61 . It may include an extension 63 extending to the portion 62 .

A flat portion 64 extending flatly (evenly) from the casing coupling portion 61 to the tub coupling portion 62 is formed in the extension portion 63 , and between the flat portion 64 and the tub coupling portion 62 . A foldable portion 65 may be formed on the .

The folding part 65 is folded or unfolded when the tub 31 moves in an eccentric direction. The folded portion 65 may be formed over the entire circumference of the gasket 60 .

The nozzles 83a and 83b may be installed on the flat portion 64 . According to an embodiment, the nozzles 83a and 83b may be integrally formed with the flat portion 64 , but the present invention is not limited thereto, and a nozzle fastener (not shown) is formed on the flat portion 64 , and the gasket 60 is not limited thereto. ) and an inlet pipe (not shown, a pipe through which water pumped by a pump flows in) formed as a separate part may be inserted/fixed to the nozzle fastener. In either case, preferably, the outlet of the nozzle for spraying water toward the drum 40 is located on the inside surrounded by the gasket 60 , and the circulating water guide pipe 18 is located on the outside of the gasket 60 . connected to the inlet pipe.

The front panel 12 has the periphery of the inlet rolled outward, and the casing coupling portion 61 is fitted in the concave portion formed by the outer circumferential surface of the rolled portion. An annular groove in which a wire is wound is formed in the casing coupling part 61, and after the wire is wound along the groove, both ends of the wire are bound, so that the casing coupling part 61 is connected to the front panel 12 around the inlet. is firmly fixed on

A drum 40 in which laundry is accommodated is rotatably provided in the tub 31 . A plurality of through holes 47 communicating with the tub 31 may be formed in the drum 40 . In addition, a lifter 45 for lifting laundry when the drum 40 rotates may be provided on the inner peripheral surface of the drum 40 .

The drum 40 accommodates the laundry, is disposed so that the inlet into which the laundry is put is located in the front, and rotates about a substantially horizontal center line C of rotation. However, "horizontal" herein is not a term used in a mathematically strict sense. That is, when the rotation center line C is inclined at a predetermined angle (for example, 5 degrees or less) with respect to the horizontal as in the embodiment, it is also close to the horizontal, so it can be said that it is approximately horizontal.

The tub 31 may be supported by a damper 16 installed on the bottom of the casing 10 . The vibration of the tub 31 induced when the drum 40 rotates is attenuated by the damper 16 .

A water supply hose (not shown) for guiding water supplied from an external water source, such as a faucet, to the tub 31, and a water supply valve 94 for controlling the water supply hose may be provided.

A dispenser 35 for supplying additives such as detergent and fabric softener into the tub 31 or the drum 40 may be provided. In the dispenser 35 , additives may be classified and accommodated according to their type. The dispenser 35 may include a detergent accommodating part (not shown) for accommodating detergent and a softener accommodating part (not shown) for accommodating the fabric softener.

At least one water supply pipe 34 for selectively guiding the water supplied through the water supply valve 94 to each receiving part of the dispenser 35 may be provided. The at least one water supply pipe 34 may include a first water supply pipe for supplying water to the detergent accommodating part and a second water supply pipe for supplying water to the fabric softener accommodating part. In this case, the water supply valve 94 is It may include a first water supply valve that regulates the first water supply pipe, and a second water supply valve that regulates the second water supply pipe.

On the other hand, the gasket 60 may be provided with a direct water nozzle 57 for spraying water into the drum 32 , and a direct water supply pipe 39 for guiding the water supplied through the water supply valve 94 to the direct water nozzle 57 . ) may be provided. The water supply valve 94 may include a third water supply valve that controls the direct water supply pipe 39 .

Water discharged from the dispenser 35 is supplied to the tub 31 through the water supply bellows 37 . A water supply port (not shown) connected to the water supply bellows 37 may be formed in the tub 31 . The tub 31 has a drainage port for discharging water, and the drainage bellows 17 is connected to the drainage port. can A circulation pump 36 for pumping the water discharged to the drain bellows 17 to the circulation water guide pipe 18 may be provided.

The circulation pump 36 may include an impeller (not shown) for pumping water, a pump housing (not shown) in which the impeller is accommodated, and a circulation pump motor 92 for rotating the impeller. The pump housing has an inlet port (not shown) through which water flows through the drain bellows 17, and a circulating water discharge port (not shown) for discharging the water pressurized by the impeller to the circulating water guide pipe 18. can be formed. An inlet of the circulating water guide pipe 18 is connected to a circulating water discharge port, and an outlet is connected to nozzles 83a and 83b to be described later.

When the user inputs settings (eg, washing course, washing, rinsing, spin-drying time, spin-drying speed, etc.) through the input unit provided on the control panel 14 , the control unit 91 operates the washing machine according to the input settings. control to drive. For example, control algorithms such as the water supply valve 94, the washing motor 93, the circulation pump motor 92, and the drain valve 96 are pre-stored in a memory (not shown) for each course selectable through the input unit. In addition, the controller 91 may control the washing machine to be operated according to an algorithm corresponding to the setting input through the input unit.

A drain pump 33 for pumping water discharged from the tub 31 to the drain pipe 19 may be provided. The drain pump 33 pressurizes the water introduced through the drain bellows 17 to the drain pipe 19 . The drain pump 33 may include an impeller (not shown) for pumping water, a pump housing (not shown) in which the impeller is accommodated, and a drain pump motor 98 for rotating the impeller. The drain pump motor 98 may be configured substantially the same as the circulation pump motor 92 . An inlet port (not shown) through which water flows through the drain bellows 17 and a drain outlet port (not shown) for discharging the water pressurized by the impeller to the drain pipe 19 may be formed in the pump housing. .

Under the control of the controller 91 , the circulation pump 38 may be operated (eg, during washing) or the drain pump 33 may be operated (eg, during drainage) according to a preset algorithm.

On the other hand, the circulation pump motor 92 is a variable speed motor whose rotation speed is controlled. According to an embodiment, when the circulation pump is provided separately from the drain pump, the pump motor constituting the circulation pump may be a variable speed motor. The circulation pump motor 92 is a BLCD motor (Brushless Direct Current Motor) is suitable, but is not necessarily limited thereto. A driver for controlling the speed of the circulation pump motor 92 may be further provided, and the driver may be an inverter driver. The inverter driver converts AC power to DC power and inputs it to the motor at a target frequency.

A control unit 91 for controlling the circulation pump motor 92 may be further provided. The controller 91 may include a proportional-integral controller (PI controller), a proportional-integral-derivative controller (PID controller), and the like. The controller receives an output value (eg, output current) of the circulation pump motor 92 as an input, and based on this, the rotation speed (or rotation speed) of the circulation pump motor 92 is set at a preset target rotation speed (or , the target rotation speed) may be controlled to control the output value of the driver.

On the other hand, the control unit 91 may control not only the circulation pump motor 92 but also the drain pump motor 98 and further control the overall operation of the washing machine. Even if not mentioned, it will be understood that the control is performed by the control unit 91 .

At least one nozzle (83a, 83b) for injecting the circulating water pressurized by the circulation pump (36) into the drum (40) may be provided. In the embodiment, the nozzles 83a and 83b respectively provided on the left and right sides of the gasket 60 are configured to spray water upward from the lower side than the center of the drum 40 , but this is not necessarily limited thereto. That is, the number or position of the nozzles can be variously modified. However, in any case, in the washing machine according to an embodiment of the present invention, as the supplied water pressure increases (that is, the water pressure and discharge of the pump 36 ) As the flow rate, rotational speed or rotational speed increases), it is preferred to include one or more nozzles configured to spray water further upwards.

The outlet of each of the nozzles 83a and 83b may be opened upwardly toward the inside of the drum 40 . Therefore, when water is supplied above a certain water pressure, spraying through each of the nozzles 83a and 83b is made in an upwardly inclined direction to the inside of the drum 40 , and the sprayed water is sprayed to the depth of the drum 40 . This can be achieved.

On the other hand, when the water pressure of the water supplied to the nozzles 83a and 83b is not sufficient, the water sprayed through the outlets of the nozzles 83a and 83b does not sufficiently proceed upward and is easily lowered by gravity, so the drum 40 ) does not reach deep inside.

In FIG. 4, the spraying form when water is supplied by the pump 36 with sufficient water pressure is indicated by "a", and the case where the water pressure is lower than that is indicated by "b". That is, as the rotational speed of the pump 36 is varied, the shape of the water flow injected through the nozzles 83a and 83b may be varied between a and b.

5 schematically shows the drum viewed from the front, and the spraying range of each nozzle is shown. 6 is a schematic view of the drum viewed from the side, and the spraying range of each nozzle is shown.

Referring to FIG. 5 , when quadrants Q1 , Q2 , Q3 , and Q4 are defined by dividing the drum 40 viewed from the front, the first nozzle 83a is disposed in the third quadrant Q3 , and the second The nozzle 83b is disposed in the fourth quadrant Q4. 5, the lower limit (b) of the water flow injected through each nozzle (83a, 83b) shows when the circulation pump motor 92 rotates at 2600 rpm, and the upper limit (a) is the circulation pump motor 92 at 3000 rpm. Shows a poem that will be rotated to .

Depending on the rotational speed of the circulation pump motor 92 , the first nozzle 83a is configured to spray water into an area extending to the third quadrant Q3 and the second quadrant Q2 . That is, as the speed of the circulation pump motor 92 increases, water is gradually sprayed upward through the first nozzle 83a, and when the circulation pump motor 92 rotates at the maximum speed, the first nozzle 83a The water flow jetted from the drum 40 reaches the second quadrant Q2 on the rear surface 41 of the drum 40 .

Depending on the rotational speed of the circulation pump motor 92 , the second nozzle 83b is configured to spray water into the area extending to the fourth quadrant Q4 and the second quadrant Q1 . That is, as the speed of the circulation pump motor 92 increases, water is gradually sprayed upward through the second nozzle 83b, and when the circulation pump motor 92 rotates at the maximum speed, the second nozzle 83b The water flow sprayed from the drum 40 reaches the first quadrant Q1 on the rear surface 41 .

6, if the drum 40 viewed from the side is divided into thirds to define the first region, the second region, and the third region in order from the front, as the rotational speed of the circulation pump motor 92 gradually increases, It can be seen that the water flow injected from the nozzles 83a and 83b reaches a deeper position of the drum 40 . As exemplarily shown in the figure, when the rotational speed of the circulation pump motor 92 is 2200 rpm, the water flow injected from the nozzles 83a and 83b reaches the first area of the inner peripheral surface 42 of the drum 40, In the case of 2500 rpm, it reaches the second region, and in the case of 2800 rpm, it reaches the third region. When the rotation speed of the circulation pump motor 92 is further increased, the water flow reaches the rear surface 41 of the drum 40, and at 3000 rpm, the water flow reaches 1/3 of the height H of the drum 40, 3400 rpm The water flow reaches 2/3 of the height H of the drum 40 . When the rotational speed of the circulation pump motor 92 reaches 3400 rpm, the height at which the water flow reaches the maximum, and on the structure of the nozzles 83a and 83b, thereafter, the injection height does not rise any more, only the intensity of the water flow is strengthened

<Control method>

7 is a view showing drum driving motions that can be implemented by a washing machine according to an embodiment of the present invention. Hereinafter, the drum driving motions will be described in detail with reference to FIG. 7 .

The drum driving motion means a combination of the rotational direction and the rotational speed of the drum 40, and the laundry positioned inside the drum 40 by the drum driving motion changes the falling direction or the falling time, and as a result, the drum 40 ), the flow of laundry inside is different. The drum driving motion is implemented by controlling the washing motor 93 by the control unit 91 .

Since the laundry is raised by the lifter 45 provided on the inner circumferential surface of the drum 40 when the drum 40 rotates, the impact applied to the laundry can be varied by controlling the rotation speed and direction of the drum 40 do. That is, it is possible to vary the mechanical force such as friction between laundry, friction between laundry and washing water, and the impact of falling of laundry. In other words, the degree of tapping or rubbing the laundry for washing can be varied, and the degree of dispersing or turning over the laundry can be varied.

On the other hand, in order to implement these various drum driving motions, the washing motor 93 is preferably a direct motor. That is, it is preferable that the stator of the motor has the tub 31 fixed to the rear, and the drive shaft 38 rotated together with the rotor of the motor directly drives the drum 40 . This is because, by controlling the rotation direction, torque, etc. of the motor, it is possible to immediately control the drum driving motion by preventing time delay or backlash as much as possible.

On the other hand, in the form of transmitting the rotational force of the motor to the rotating shaft through a pulley, etc., a drum driving motion of a type that allows a time delay or backlash, for example, a tumbling driving or a spin driving is possible, but various other drum driving motions It is not suitable for implementing Since the driving method of the washing motor 93 and the drum 40 is obvious to those skilled in the art, a detailed description thereof will be omitted.

7A is a view showing a rolling motion. In the rolling motion, the washing motor 93 rotates the drum 40 in one direction (preferably, one or more rotations), and the laundry on the inner circumferential surface of the drum 40 moves in the direction of rotation of the drum 40 by less than about 90 degrees. It is a controlled motion to fall from position towards the lowest point of the drum 40 .

For example, when the washing motor 93 rotates the drum 40 at about 40 RPM, the laundry located at the lowest point of the drum 40 rises to a predetermined height along the rotational direction of the drum 40, and then It flows toward the lowest point of the drum 40 as if it rolls at a position less than about 90 degrees from the lowest point in the rotational direction. Visually, when the drum 40 rotates clockwise, the laundry continuously rolls in the third quadrant of the drum 40 .

In the rolling motion, laundry is washed through friction with washing water, friction between laundry, and friction with the inner peripheral surface of the drum 40 . At this time, the laundry is turned over sufficiently to obtain the effect of gently rubbing the laundry.

Here, the rotational speed (rpm) of the drum 40 is determined in relation to the radius of the drum 40 . As the rotational speed of the drum 40 increases, the centrifugal force acting on the laundry in the drum 40 also increases. The flow of laundry in the drum 40 is changed due to the difference in magnitude between the centrifugal force and gravity. Of course, the rotational force of the drum 40 and the frictional force between the drum 40 and the laundry should also be considered. As such, when considering various forces acting on the laundry, the rotational speed of the drum 40 in the rolling motion is determined in a range in which the sum of the centrifugal force and the frictional force is smaller than the gravity (1G).

7 (b) is a view showing a tumbling motion. In the tumbling motion, the washing motor 93 rotates the drum 40 in one direction (preferably, one or more rotations), and the laundry on the inner circumferential surface of the drum 40 is rotated by about 90 degrees to 110 degrees in the direction of rotation of the drum 40 . It is a controlled motion to fall from position to the lowest point of the drum 40 . The tumbling motion is a drum driving motion generally used for washing and rinsing because mechanical force is generated only by controlling the drum 40 to rotate in one direction at an appropriate rotation speed.

That is, the laundry put into the drum 40 is positioned at the lowest point of the drum 40 before the washing motor 93 is driven. When the washing motor 93 provides torque to the drum 40 , the drum 40 rotates, and the laundry is removed by friction with the lifter 45 provided on the inner circumferential surface of the drum 40 or the inner circumferential surface of the drum 40 . It rises from the lowest point in the drum 40 to a predetermined height. For example, when the washing motor 93 rotates the drum 40 at about 46 rpm, the laundry falls from the lowest point of the drum 40 to the lowest point of the drum 40 at about 90 to 110 degrees in the rotational direction. do.

The rotational speed of the drum 40 in the tumbling motion may be determined in a range in which centrifugal force is generated larger than in the case of rolling motion, but is generated less than gravity.

Visually, the tumbling motion is, when the drum 40 rotates clockwise, the laundry rises from the lowest point of the drum 40 to a 90 degree position or a second quadrant, and then is separated by the inner circumferential surface of the drum 40 and the lowest point of the drum 40 It is in the form of falling towards

Therefore, in the tumbling motion, laundry is washed by friction with washing water and impact force caused by falling, and in particular, it is washed by a greater mechanical force than in the case of the rolling motion. In particular, the tangled laundry is separated during the tumbling motion, and there is an effect that the laundry is dispersed.

7C is a view showing a step motion. In the step motion, the washing motor 93 rotates the drum 40 in one direction (preferably, less than one rotation), but the laundry on the inner peripheral surface of the drum 40 is near the highest point of the drum 40 (preferably). , about 146 to 161 degrees in the rotational direction of the drum 40, but it is not necessarily limited thereto, and an angular position greater than 161 degrees is possible within a range not exceeding 180 degrees.) of the drum 40 Motion controlled to fall towards the lowest point.

That is, the step motion is the speed at which laundry does not fall from the inner circumferential surface of the drum 40 due to centrifugal force (that is, the speed at which laundry is rotated together with the drum 40 while attached to the inner circumferential surface of the drum 40 due to centrifugal force) This is a motion that maximizes the impact force on the laundry by rapidly braking the drum 40 after rotating the furnace drum 40 .

For example, when the washing motor 93 rotates the drum 40 at about 60 rpm or more, the laundry rotates without falling by centrifugal force (that is, the drum 40 in a state attached to the inner circumferential surface of the drum 40) In this process, when the laundry is located near the highest point (180 degrees in the rotational direction) of the drum 40, the torque in the opposite direction to the rotational direction of the drum 40 is applied to the washing motor ( 93) can be controlled.

After the laundry rises from the lowest point of the drum 40 in the direction of rotation of the drum, the drum 40 stops and falls to the lowest point of the drum 40, so that the laundry has a maximum fall, and thus the impact force acting on the laundry is also maximized. Mechanical force (eg, impact force) generated by such a step motion is greater than the aforementioned rolling motion or tumbling motion.

Visually, the step motion is, when the drum 40 rotates clockwise, the laundry located at the lowest point of the drum 40 moves to the highest point (180 degrees) of the drum 40 through the third and second quadrants and then suddenly the drum (40) It is separated from the inner peripheral surface and falls toward the lowest point of the drum (40). Therefore, the step motion provides the greatest mechanical force as the laundry has the largest drop and the smaller the laundry amount is.

On the other hand, as a control method of the washing motor 93 for braking the drum 40, reverse-phase braking is preferable. Reverse phase braking is a method of braking by generating a rotational force in a direction opposite to the direction in which the washing motor 93 is rotating. The phase of the power supplied to the washing motor 93 may be reversed in order to induce a rotational force opposite to the direction in which the washing motor 93 is rotating, and in this way, sudden braking is possible. Therefore, reverse-phase braking is suitable for step motion.

After the washing motor 93 is braked, the washing motor 93 again applies torque to the drum 40 to raise the laundry at the lowest point of the drum 40 to the highest point. That is, after applying a torque to rotate in the forward direction, a torque is applied to instantaneously rotate in the reverse direction to make a sudden stop, and then, a torque is applied to rotate in the forward direction again to implement step motion.

In the step motion, when the drum 40 rotates, the washing water introduced through the through hole 47 formed in the drum 40 rubs against the laundry to wash, and when the laundry is located at the highest point of the drum 40, it is dropped and applied to the impact force. It can be called the motion of washing by

7 (d) is a view showing a swing motion. In the swing motion, the washing motor 93 rotates the drum 40 in both directions, but at a position less than about 90 degrees in the rotational direction of the drum 40 (preferably, about 30 to about 30 in the rotational direction of the drum 40 ). It is a motion controlled so that the laundry falls at the 45 degree position, but is not necessarily limited thereto, and an angular position greater than 45 degrees is possible within a range not exceeding 90 degrees). For example, when the washing motor 93 rotates the drum 40 counterclockwise at about 40 rpm, the laundry located at the lowest point of the drum 40 rises to a predetermined height in the counterclockwise direction. At this time, the washing motor 93 stops the rotation of the drum 40 before the laundry reaches the position of about 90 degrees in the counterclockwise direction. moves toward the lowest point of

After the drum 40 stops rotating in this way, the washing motor 93 rotates the drum 40 clockwise at about 40 RPM this time so that the laundry moves in the rotation direction of the drum 40 (ie, clockwise). to rise to a predetermined height. And, before the laundry reaches the position of about 90 degrees in the clockwise direction, the washing motor 93 is controlled so that the rotation of the drum 40 is stopped, so that the laundry is moved to the drum 40 at a position less than about 90 degrees in the clockwise direction. falls towards the lowest point of

That is, the swing motion is a motion in which the forward rotation/stop of the drum 40 and the reverse rotation/stop of the drum 40 are repeated. After ascending to the quadrant, it gently falls, passes through the fourth quadrant of the drum 40 again, rises to the first quadrant, and then gently falls. That is, visually, the swing motion becomes a form in which laundry flows in a figure 8 shape lying on its side across the third and fourth quadrants of the drum 40 .

In this case, power generation braking is suitable for braking the washing motor 93 . The power generation braking minimizes the load generated on the washing motor 93 , and minimizes mechanical wear of the washing motor 93 , and at the same time makes it possible to control the impact applied to the laundry.

Power generation braking is a braking method using that the washing motor 93 acts as a generator due to rotational inertia when the current applied to the washing motor 93 is turned off. When the current applied to the washing motor 93 is turned off, the direction of the current flowing through the coil of the washing motor 93 is opposite to the direction of the current before the power is turned off. Fleming's right hand rule) acts to brake the washing motor 93 . Unlike reverse-phase braking, the power generation braking does not rapidly brake the washing motor 93 and allows the rotation direction of the drum 40 to be smoothly switched.

7 (e) is a view showing a scrub motion (scrub motion). The scrub motion is a motion in which the washing motor 93 alternately rotates the drum 40 in both directions, and the laundry is controlled so that the laundry falls at a position of about 90 degrees or more in the rotational direction of the drum 40 .

For example, when the washing motor 93 rotates the drum 40 in the forward direction at about 60 rpm or more, the laundry positioned at the lowest point of the drum 40 rises to a predetermined height in the forward direction. At this time, the washing motor 93 is a position corresponding to the set angle of the laundry in the forward direction of about 90 degrees or more (preferably, 139 to 150 degrees, but is not necessarily limited thereto, and 150 degrees or more is possible.) A reverse torque is provided to the drum 40 to temporarily stop the rotation of the drum 40 . Then, the laundry on the inner peripheral surface of the drum 40 falls rapidly.

Thereafter, the washing motor 93 rotates the drum 40 at about 60 rpm or more in the reverse direction to raise the dropped laundry to a predetermined height of 90 degrees or more in the reverse direction. When the laundry reaches a set angle of 90 degrees or more in the reverse direction (for example, a position corresponding to 139 to 150 degrees), the washing motor 93 provides a reverse torque to the drum 40 again to temporarily stop the rotation of the drum 40 At this time, the laundry on the inner peripheral surface of the drum 40 falls toward the lowest point of the drum 40 at a position of 90 degrees or more in the reverse direction.

The scrub motion washes the laundry by causing the laundry to fall rapidly from a predetermined height. At this time, it is preferable that the washing motor 93 is reverse-phased to brake the drum 40 .

Since the rotation direction of the drum 40 is rapidly changed, the laundry does not deviate significantly from the inner circumferential surface of the drum 40 , so that a very strong rubbing effect can be obtained.

In the scrub motion, laundry that has moved forward through the third quadrant to the second quadrant falls rapidly, and in the reverse direction, it passes through the fourth quadrant and moves to a part of the first quadrant, and then falls repeatedly. Therefore, visually, it can be said that the laundry rises and then descends along the inner circumferential surface of the drum 40 repeatedly.

7(f) is a view showing a filtration motion. In the filtration motion, the washing motor 93 rotates the drum 40 so that the laundry does not fall off the inner circumferential surface of the drum 40 by centrifugal force, and in this process, the washing water enters the drum 40 through the nozzles 83a and 83b. It is a motion that sprays

After the laundry is unfolded, the wash water is sprayed into the drum 40 while it is rotated in close contact with the inner circumferential surface of the drum 40. ) to exit through the tub (31).

By the filtration motion, the surface area of the laundry is widened, and since the wash water permeates the laundry, there is an effect that the laundry is evenly wetted.

7 (g) is a view showing a squeeze motion (squeeze motion). In the squeeze motion, the washing motor 93 rotates the drum 40 so that the laundry does not fall off the inner circumferential surface of the drum 40 by centrifugal force, and then lowers the rotation speed of the drum 40 to remove the laundry from the inner circumferential surface of the drum 40 This is a motion of repeating the separation operation and spraying wash water into the drum 40 through the nozzles 83a and 83b while the drum 40 is rotating.

In the filtration motion, the laundry continues to rotate at a speed that does not fall off the inner circumferential surface of the drum 40, but the squeeze motion changes the rotational speed of the drum 40 so that the laundry adheres to and separates from the inner circumferential surface of the drum 40 repeatedly. There is a difference in

8 is a graph comparing washing power and vibration level of drum driving motions. In FIG. 8 , the horizontal axis represents the washing power, and as it goes to the left, it is easier to separate the dirt contained in the laundry. The vertical axis indicates the level of vibration or noise, and as it goes upward, the level of vibration increases, but the washing time for the same laundry decreases.

The step motion and scrub motion have excellent washing power, so they are suitable for a case where the laundry is heavily contaminated and for a washing course to shorten the washing time. In addition, step motion and scrub motion are motions with high levels of vibration and noise. Therefore, it is an undesirable motion when the laundry is sensitive clothing or in a laundry course in which noise and vibration need to be minimized.

Rolling motion is characterized by excellent washing power, low vibration level, minimal damage to laundry and low motor load. Therefore, it is applicable to all washing courses, but in particular, it is a motion suitable for dissolving detergent and wetting laundry at the initial stage of washing. However, the rolling motion has a disadvantage in that it takes longer to wash the washing to the same level as compared to the tumbling motion instead of the low vibration level.

In the tumbling motion, the cleaning power is lower than that of the scrub motion, but the vibration level is intermediate between the scrub motion and the rolling motion. The tumbling motion is applicable to all washing courses, but it is particularly useful in the step for dispersing the fabric.

In the squeeze motion, the washing force is similar to that of the tumbling motion, and the vibration level is higher than that of the tumbling motion. The squeeze motion is useful for rinsing because the washing water passes through the laundry and is discharged to the outside of the drum 40 in the process of repeating the adhesion and separation of the laundry to the inner circumferential surface of the drum 40 .

In the filtration motion, the cleaning power is lower than that of the squeeze motion, and the noise level is similar to the rolling motion. The filtration motion is a useful motion to wet the laundry or to apply detergent water to the laundry at the beginning of washing because the washing water passes through the laundry and is discharged to the tub 31 while the laundry is in close contact with the inner circumferential surface of the drum 40 .

Swing motion is the motion with the lowest vibration level and cleaning power. Therefore, the swing motion is a motion useful for a low-noise or low-vibration washing course, and is a motion suitable for washing sensitive clothes (gentle care).

9 is a diagram referenced for explaining the injection motion in each drum driving motion of the present invention compared with the conventional one. 9 (a) is a graph showing the rotational speed of the drum 40 or the washing motor 93 for each drum driving motion, (b) is a conventional washing machine having a constant speed pump, at the time of each drum driving motion It is a graph showing the rotation speed of the pump motor, (c) is a graph showing the rotation speed of the circulation pump motor 92 in each drum driving motion in the washing machine according to an embodiment of the present invention, (d) In the washing machine according to an embodiment of the present invention, (e) shows the movement of laundry in each drum driving motion, and (e) is a spraying form (hereinafter, “ It is referred to as "injection motion.") is shown.

Referring to FIG. 9 , since the conventional washing machine cannot change the speed of the pump motor, even if the drum driving motion is changed, the pump motor has no choice but to rotate at a constant speed. Therefore, in the conventional washing machine, the water flow sprayed through the nozzle could not effectively respond to the movement of the cloth induced by the type of drum driving motion, and it was difficult to manage power consumption, washing performance, wetness performance, and the like. The present invention aims to solve the above problems by appropriately controlling the rotational speed of the circulation pump motor 92 according to the drum driving motion, and further, by considering the amount of laundry in this process.

In particular, it rises in a state of being attached to the inner circumferential surface 42 of the drum 40 by the rotating drum 40, and when it reaches a predetermined height, it is separated from the inner circumferential surface 42 by braking of the drum 40 and falls In the case of drum driving motions (hereinafter, referred to as "fall-inducing motion by braking". For example, swing motion, step motion, or scrub motion), the rotational speed of the circulation pump motor 92 is variable within a predetermined range. However, the range is set according to the amount of laundry.

And, in the case of the rolling motion, the tumbling motion, and the filtration motion, in a section in which the rotation speed of the circulation pump motor 92 is kept constant, the rotation speed is set according to the amount of laundry.

Meanwhile, referring to FIG. 9C , in the case of a rolling motion, a swing motion, a step motion, a scrub motion, and a filtration motion, the rpm of the pump motor 92 may be controlled in a different way. In the figure, the rpm of the pump motor 92 when the amount of laundry is large is shown by a solid line, and the rpm of the pump motor 92 when the amount of laundry is small is shown by a dotted line. In the case of the tumbling motion, the rpm of the pump motor 92 may be controlled in the same way regardless of the amount of laundry.

In each of the drum driving motions shown in FIG. 9, the operations of the washing motor 93 and the circulation pump motor 92 are interlocked with each other. Hereinafter, a method in which the washing motor 93 and the circulation pump motor 92 are controlled will be described with reference to FIG. 9 . In FIG. 9 , A1 to A6 indicate control steps of the washing motor 93 , and B1 to B6 indicate control steps of the circulation pump motor 92 .

When a preset drum driving motion is performed while the washing machine operates, the controller 91 controls the washing motor 93 and the circulation pump motor 92 according to a method determined for each drum driving motion.

Specifically, the control unit 91 starts driving the washing motor 93 (A1) and accelerates the washing motor 93 (A2). A sensor for detecting the rotation angle of the drum 40 may be provided, and the rotation angle of the drum 40 sensed through the sensor is a value determined for each drum driving motion (θ, hereinafter referred to as “motion angle”). When it reaches (A3), the controller 91 may control the washing motor 93 to be decelerated (A4).

In the case of the rolling motion, the tumbling motion, and the filtration motion, since the rotation of the drum 40 is continuous by one or more rotations, the motion angle θ has a value of 360 degrees or more.

On the other hand, in the case of a fall-inducing motion by braking such as swing motion, step motion, scrub motion, etc., the motion angle θ is within 180 degrees so that the fore can be induced to fall within 180 degrees. set to a value. For example, the motion angle θ may be a value between 30 and 45 degrees in the case of a swing motion, a value between 146 and 161 degrees in the case of a step motion, and a value between 139 and 150 degrees in the case of a scrub motion. .

As the drum 40 is decelerated and stopped, the drum driving motion is completed once, and the drum driving motion is performed again (A5). The control unit 91 repeats steps A2 to A5 until the execution of the drum driving motion reaches a preset number of times, and when the preset number of times is reached, the operation of the washing motor 93 is stopped (A6).

On the other hand, when the driving of the washing motor 93 is started in step A1, the control unit 91 applies the start signal SG1 to the circulation pump motor 92, and in response to the start signal SG1, the circulation pump motor ( 92) is started (B1). Thereafter, the control unit 91 accelerates the circulation pump motor 92 according to a setting determined for each drum driving motion based on the motion information (that is, information on the currently implemented drum driving motion) (B2).

Meanwhile, in step A3 , when the rotation angle of the drum 40 reaches the motion angle θ, the control unit 91 applies the angle control completion signal SG2 to the circulation pump motor 92 .

In the case of a fall-inducing motion by braking, the circulation pump motor 92 at B2 responds to the angle control completion signal SG2, and the rotational speed reaches the upper limit Pr(V, H) determined for each drum driving motion. After that, acceleration is stopped (or braking of the circulation pump motor 92 ), and the speed is decelerated according to a setting determined for each drum driving motion (B4, B5).

Thereafter, in step A5 , when the washing motor 93 is again started to be driven, the controller 91 applies the restart signal SG3 to the circulation pump motor 92 , and the circulation pump motor 92 receives the restart signal In response to (SG3), when the rotational speed reaches the lower limit (Pr(V, L)) determined for each drum driving motion, the deceleration is stopped (B5), and steps B2 to B5 are repeated.

On the other hand, in the case of swing motion, tumbling motion or filtration motion, when the angle control completion signal SG2 is applied to the circulation pump motor 92, the circulation pump motor 92 maintains the rotation speed determined for each drum driving motion, is being rotated Accordingly, in the case of these motions, in response to the angle control completion signal SG2, deceleration of the circulation pump motor 92 is performed (B4).

On the other hand, in the case of any drum driving motion, when the washing motor 93 is stopped in step A6, the controller 91 applies a stop signal SG4 to the circulation pump motor 92, and receives the stop signal SG4. Accordingly, the circulation pump motor 92 is stopped.

As shown in FIG. 11 , the washing machine may be configured to sequentially perform a water supply/soak cycle, a spin cycle, a cycle, and a spin cycle. The watering/soaking administration is the administration of watering with detergent to wet the cloth.

The washing cycle rotates the drum 40 according to a preset algorithm to remove contamination from the laundry, and a rolling motion and a tumbling motion may be performed.

The dewatering process is a process of draining water and removing water from the fabric while rotating the drum 40 at high speed.

The rinsing process is a process of removing detergent adhered to the fabric, and water is supplied, and rolling motion and tumbling motion may be performed, and then, a dehydration process may be performed again.

Hereinafter, a control method for the washing motor 93 and the circulation pump motor 92 for each drum driving motion will be described in more detail.

<Rolling motion/Tumbling motion>

12 is a graph showing the speed (a) of the washing motor and the speed (b) of the pump motor in rolling motion and tumbling motion. 16 is a graph comparing the speed of the pump motor in each drum driving motion when the laundry amount falls within the first laundry weight range (I) and when the laundry weight falls within the second laundry weight range (II).

In the method of controlling a washing machine according to an embodiment of the present invention, the drum 40 is moved in one direction so that laundry on the inner circumferential surface of the drum 40 falls from an elevated position to a position corresponding to a rotation angle of the drum 40 less than approximately 90 degrees. The first step of rotating the drum 40, and the first step of rotating the drum 40 in one direction so that the laundry on the inner circumferential surface of the drum 40 falls from a position raised to a height higher than a position corresponding to a rotation angle of less than 130 degrees of the drum 40 It involves two steps. The second step may be performed after the first step, but is not limited thereto, and the second step may be performed before the first step.

While the first step is performed, the rotation speed of the pump 36 is controlled to a preset first rotation speed, and during the second step, the rotation speed of the pump 36 is higher than the first rotation speed. Controlled by 2 revolutions.

The driving motion of the drum 40 in the first step may correspond to a rolling motion. The driving motion of the drum 40 in the second step may be a rolling motion or a tumbling motion, but is preferably a tumbling motion. That is, the second step may be a step of performing a tumbling motion in which the drum is rotated in one direction so that the laundry on the inner circumferential surface of the drum 40 falls from a position corresponding to a rotation angle of approximately 90 degrees to 110 degrees of the drum 40. .

Hereinafter, it is exemplified that the first step is a rolling motion, and the second step is a tumbling motion.

12 and 16 , the rolling motion and the tumbling motion are performed in a state in which water is contained in the tub 31 so that the water flow can be sprayed through the nozzles 83a and 83b. Referring to FIG. 12 , in the rolling motion, the controller 91 controls the washing motor 93 to move the laundry on the inner peripheral surface of the drum 40 to a position corresponding to the rotation angle of the drum 40 less than approximately 90 degrees. The drum 40 is rotated in one direction to fall from the raised position. During the rolling motion, the washing motor 93 or the drum 40 may be rotated while maintaining Dr(R) for a predetermined time after being accelerated to the rotational speed Dr(R). The rotational speed Dr(R) is preferably 37 to 40 rpm, but is not necessarily limited thereto.

While the rolling motion is being performed, the rotation speed of the circulation pump motor 92 is controlled to a preset rotation speed Pr(R). In FIG. 12 , t(SG1) is the generation time of the start signal (SG1, see FIG. 10), t(SG2) is the generation time of the angle control completion signal (SG2, see FIG. 10), and t(SG4) is the stop It is the generation time of the signal SG3 (refer to FIG. 10). Hereinafter, other examples are also displayed in the same manner.

The rotation speed Pr(R) may be set according to the amount of laundry. Before the drum driving motion is implemented, the control unit 91 may rotate the washing motor 93 and detect the amount of laundry in this process. The amount of laundry may be determined based on the principle that the rotational inertia of the drum 40 varies depending on the amount of cloth put into the drum 40 . For example, the laundry amount may be It is obtained based on the time it takes to reach the target speed, or it is obtained based on the acceleration slope of the washing motor 93 , or it is obtained based on the time taken from braking the washing motor 93 to stop, or the deceleration slope It can be obtained based on , or it can be obtained based on the back electromotive force at the time of power generation braking. However, various methods for calculating the amount of laundry are already known in the washing machine technology field, and it goes without saying that these known techniques can be applied. Hereinafter, although not described, it is assumed that the step of detecting the amount of laundry is performed before each drum driving motion is executed.

The control unit 91 may set the rotation speed Pr(R) according to the laundry amount range to which the detected laundry weight belongs. For example, the laundry amount may be subdivided into a first level to a ninth level, and the laundry weight range is divided into a small amount (or the first laundry weight range (I), see FIG. 16) and a large amount (or a second laundry weight range ( II), see FIG. 16.), the detected laundry amount may be classified as a small amount when the first to fourth levels are detected, and as a large amount when the detected laundry amount is from the fifth to the ninth level. However, the present invention is not limited thereto, and it is also possible to classify the laundry weight range for each level.

In the embodiment, the rotational speed Pr(R) is set higher in the case of a large amount of laundry than in the case of a small amount. For example, when the amount of laundry is small, the rotation speed Pr(R) may be set to 2800 rpm, and when the amount of laundry is large, it may be set to 3100 rpm. In particular, when the amount of cloth is small, since most of the cloth moves in the front portion of the drum 40 , the water flow sprayed from the nozzles 83a and 83b does not have to touch the rear surface 41 of the drum 40 . (2800rpm or less. See Fig. 6.)

Conversely, when the amount of cloth is large, since the cloth fills up to the center of the drum 40, the water flow sprayed from the nozzles 83a and 83b must be able to reach a height higher than the center of the drum 40, so that the water flow is It is preferable to reach the first quadrant (Q1, see FIG. 5) and the second quadrant (Q2, see FIG. 5), and for this, the rotational speed of the circulation pump motor 92 is approximately 3000 rpm or more, preferably 3100 rpm is set to

In the case of the tumbling motion, the washing motor 93 and the circulation pump motor 92 are controlled in a manner similar to the rolling motion. However, the rotation speed Dr(R) of the washing motor 93 is higher than that in the rolling motion, and the rotation speed Pr(T) of the circulation pump motor 92 is also higher than in the case of the rolling motion for the same amount of laundry. On the other hand, the rotation speed Dr(T) of the washing motor 93 is preferably 46 rpm, but is not necessarily limited thereto.

On the other hand, in the case of the tumbling motion, it is important to apply a stronger mechanical force to the cloth than in the case of the rolling motion, so the water flow pressure sprayed through the nozzles 83a and 83b needs to be sufficient regardless of the amount of cloth. Accordingly, in the case of the tumbling motion, the circulation pump motor 92 may be rotated at a constant speed having a value between 3400 and 3600 rpm regardless of the amount of laundry. However, the present invention is not limited thereto, and it is of course possible to set the rotational speed Pr(T) higher than when the amount of laundry is large, compared to when the amount of laundry is small. For example, when the amount of laundry is small, the rotation speed Pr(T) may be set to 3400 rpm, and when the amount of laundry is large, it may be set to 3600 rpm.

The steps of controlling the pump 36 while performing the rolling motion and the tumbling motion described above are suitable for a washing cycle and/or a rinsing cycle among the series of washing cycles of FIG. 11 .

<Step motion/Scrub motion/Swing motion>

13A, 13B, and 13C are graphs for explaining operations of a washing motor and a pump motor in swing motion, scrub motion, and step motion according to an embodiment of the present invention.

13A and 16 , in the case of a fall-inducing motion caused by braking, the controller 91 controls the rotation speed of the pump motor 92 to vary while the drum 40 is rotating.

The fall-inducing motion by braking is performed in a state in which water is contained in the tub 31 so that the water flow can be sprayed through the nozzles 83a and 83b. During the fall-inducing motion due to braking, the controller 91 controls the washing motor 93 so that the laundry (cloth) on the inner circumferential surface 42 of the drum 40 is in contact with the drum 40 by centrifugal force. It is possible to accelerate the washing motor 93 to rise. The control unit 91 accelerates the washing motor 93 so that the drum 40 is rotated at a speed that rises without falling from the inner circumferential surface 42 of the cloth drum 40 , and then the cloth falls from the inner circumferential surface 42 . The washing motor 93 is braked. That is, during the fall-inducing motion by braking, the washing motor 93 rises to a preset rotation speed Dr(V), and then decelerates until it stops.

The rotation speed Dr(V) may be set differently for each drum driving motion. Since the rotational speed Dr(V), that is, the maximum rising height of the cloth increases in the order of swing motion, scrub motion, and step motion, a greater centrifugal force must act in the order of the motions, and, therefore, the rotational speed Dr (V)) may also be set to a larger value in the order of the motions.

However, the maximum rise height of the forearm in the fall-inducing motion caused by braking is also determined by the rotation angle at which the drum 40 is braked (or the motion angle θ), and the rotation speed Dr(V) Even if the swing motion, scrub motion, and step motion are all set the same, if the motion angle (θ) in each motion is set differently, the maximum rise height (or the height at which the fabric starts to fall) can also vary. have. In any case, the motion angle θ is preferably set to be high in the order of swing motion, scrub motion, and step motion. Within the range that satisfies this premise, for example, the motion angle θ is 30 to 45 degrees in the case of a swing motion, 139 degrees to 150 degrees in the case of a scrub motion, and 146 degrees to 161 degrees in the case of a step motion. It can be set to a value.

Meanwhile, while the fall-inducing motion by braking is being performed, the control unit 91 may increase the rotational speed of the pump motor 92 while the laundry is rising (or while the washing motor 93 is being accelerated). have.

While the fall-inducing motion by braking is being performed, the control unit 91 may reduce the rotation speed of the pump motor 92 while the laundry is falling (or when the washing motor 93 is braked and decelerated). have.

That is, the controller 91 may control the pump motor 92 to accelerate in response to the acceleration of the washing motor 93 and to decelerate in response to the braking of the washing motor 93 .

The pump motor 92 may be varied within a rotational speed range set for each drum driving motion. 13 shows the upper limit of the rotation speed range as the highest rotation speed Pr(V, H), and the lower limit value as the lowest rotation speed Pr(V, L).

The maximum rotation speed of the circulation pump motor 92 to be described below is defined as a preset value as the upper limit of the rotation speed of the circulation pump motor 92, not the speed at which the circulation pump motor 92 can rotate at the maximum. can be

Before the drum driving motion is implemented, the control unit 91 may rotate the washing motor 93 and detect the amount of laundry in this process. The method for detecting the amount of laundry may be configured as described above in the description of the rolling/tumbling motion, or other methods may be used.

The rotation speed range can be set according to the amount of laundry. That is, the controller 91 may set the maximum rotation speed Pr(V, H) and the minimum rotation speed Pr(V, L) according to the amount of laundry. In each drum driving motion, the rotational speed range may be set to a higher band as the amount of laundry increases.

For example, in the case of scrub motion, when the detected laundry amount is in a small amount (or the first laundry amount range (I), see FIG. 16), the rotation speed of the pump motor 92 is the lowest rotation speed Pr(V). , L)) of 2800 rpm and the maximum rotational speed (Pr(V, H)) of 3100 rpm. And, when the sensed laundry amount is a large amount (or the second laundry amount range (II), see FIG. 16 ), the rotation speed of the pump motor 92 is 3400 rpm, which is the minimum rotation speed Pr(V, L), and 3400 rpm, which is the maximum amount. The rotation speed Pr(V, H) may be varied between 3600 rpm.

In the case of step motion, when the detected laundry amount belongs to a small amount (or the first laundry amount range (I), see Fig. 16.), the rotation speed of the pump motor 92 is the minimum rotation speed Pr(V, L). It can be varied between 2200 rpm which is phosphorus and 2500 rpm which is the maximum rotation speed (Pr(V, H)). And, when the sensed laundry amount is a large amount (or the second laundry amount range (II), see FIG. 16 ), the rotation speed of the pump motor 92 is 3400 rpm, which is the minimum rotation speed Pr(V, L), and 3400 rpm, which is the maximum amount. The rotation speed Pr(V, H) may be varied between 3600 rpm.

Meanwhile, even in the case of the swing motion, a range in which the rotational speed of the pump motor 92 is variable may be set according to the amount of laundry in the same manner as in the scrub motion or step motion.

In the case of swing motion, when the detected laundry amount is in a small amount (or the first laundry weight range (I), see FIG. 58.), the rotation speed of the circulation pump motor 92 is the lowest rotation speed Pr(V, L) ), which is 1700 rpm, and the maximum rotation speed (Pr(V, H)) of 2200 rpm. And, when the sensed laundry amount is a large amount (or the second laundry weight range (II), see FIG. 58), the rotation speed of the circulation pump motor 92 is 2300 rpm, which is the minimum rotation speed Pr(V, L)). The maximum rotation speed (Pr(V, H)) can be varied between 2800rpm.

At this time, the pump motor 92 is set within a range in which the water flow injected from the nozzles 83a and 83b does not touch the rear surface 41 of the drum 40 (eg, 2200 to 2800 rpm, see FIG. 6). it is preferable

However, in the case of the swing motion, since the drop of the cloth is not large compared to the scrub motion or the step motion, the rotational speed range of the pump motor 92 can be set constant regardless of the amount of cloth, for example, In both small and large amounts, the pump motor 92 may be varied between 2200 rpm, which is the lowest rotational speed Pr(V, L), and 2800 rpm, which is the highest rotation speed Pr(V, H). .

Hereinafter, with reference to FIGS. 10, 13A, 13B, 13C and 16 , the operation of the washing motor and the pump motor in swing, scrub, and step motion according to an embodiment of the present invention will be described in more detail. do.

Referring to FIGS. 10 and 13A , the control unit 91 drives the pump motor 92 when the washing motor 93 is driven (A1) and a start signal SG1 is generated (t(SG1)). can be initiated (B1).

The control unit 91 may accelerate the washing motor 93 to the set maximum rotation speed Dr(V) (A2). The maximum rotational speed Dr(V) may be defined as a preset value as the upper limit of the rotational speed of the washing motor, not the maximum rotational speed of the washing motor.

When the pump motor 92 starts driving, the controller 91 may control the pump motor 92 to be accelerated based on the motion information (B2).

The control unit 91 may accelerate the pump motor 92 to the maximum rotational speed Pr(V, H). When the pump motor 92 reaches the target RPM (Pr(V, H)), the controller 91 may stop the acceleration to limit the speed (B3).

The controller 91 may rotate the washing motor 93 up to a set motion angle θ. The control unit 91 controls the washing motor ( 93) can be controlled.

The control unit 91 completes the control of the washing motor 93 up to the motion angle θ (A3), and when the angle control completion signal SG2 is generated (t(SG2)), based on the motion information, the pump It is possible to decelerate the motor 92 (B4).

That is, the control unit 91, the pump motor 92 reaches the target RPM (Pr(V, H)) in the state in which the speed is limited (B3), when the angle control completion signal (SG2) is generated ( A3), the pump motor 92 can be decelerated (B4).

On the other hand, referring to FIG. 13A , the control unit 91 controls a time point at which the washing motor 93 reaches the maximum rotation speed Dr(V), and the pump motor 92 at the maximum rotation speed Pr(V, H). It is possible to control the washing motor 93 and the pump motor 92 so that the timing of reaching .

However, in reality, when the washing motor 93 completes the control up to the motion angle θ (or reaches the maximum rotation speed Dr(V)) (A3), the angle control completion signal SG2 is generated ( t(SG2)) and the time when the pump motor 92 starts to decelerate based on the generated angle control completion signal SG2, the time taken for the control unit 91 to process or the time the signal is transmitted The same delay may occur.

Therefore, the meaning of the graph of FIG. 13A is that the washing motor 93 reaches the maximum rotation speed Dr(V)) t(SG1)), and the pump motor 92 indicates the maximum rotation speed Pr(V, H). )), the time point t(SG1)) at which the washing motor 93 reaches the maximum rotational speed Dr(V), without intention to artificially set a time difference, rather than being absolutely coincident, and the pump motor (92) can be interpreted as meaning that the control for the purpose of making the time of reaching the maximum rotation speed Pr(V, H) the same. In particular, 13b and 13a, which will be described later, are different from each other.

When the control of the washing motor 93 to the motion angle θ is completed (or the maximum rotation speed Dr(V) is reached) (A3), the control unit 91 may decelerate the washing motor 93. There is (A4). Alternatively, the controller 91 brakes the washing motor 93 when the control of the washing motor 93 up to the motion angle θ is completed (or the maximum rotation speed Dr(V) is reached) (A3). can do it

The controller 91 controls the washing motor 93 in the case of a motion in which acceleration and deceleration of the washing motor 93 are repeated a plurality of times based on the motion information (eg, step motion, scrub motion, swing motion). Returning to the step of accelerating (A2), steps A2 to A4 may be restarted (A5).

The control unit 91 may reduce the pump motor 92 to the lowest rotational speed Pr(V, L). When the pump motor 92 reaches the target RPM (Pr(V, L)), the control unit 91 may stop the deceleration to limit the speed (B5).

When the restart signal SG3 is generated, the controller 91 may return to the step B2 of accelerating the pump motor 92 and restart the steps B3 to B4 (B5).

Referring to FIG. 13A , when the pump motor 92 has completed braking (rpm=0) and a restart signal SG3 is generated (t=SG3), the pump motor 92 may be restarted.

That is, the control unit 91 controls the pump motor 92 when the restart signal SG3 is generated (t( SG3)), the pump motor 92 may be accelerated again (B2).

On the other hand, referring to FIG. 13A , the control unit 91 reaches a time point t(SG3) when the washing motor 93 is braked and the pump motor 92 reaches the minimum rotation speed Pr(V, L). The washing motor 93 and the pump motor 92 may be controlled so that the time point t(SG3) corresponds to each other.

However, between the time point t(SG3) at which the restart signal SG3 is actually generated and the time point at which acceleration of the pump motor 92 is started based on the generated restart signal SG3, the control unit 91 is There may be delays such as the time it takes to process or the time the signal is delivered. This may be understood as the same reason as the delay generated between the time when the angle control completion signal SG2 is generated and the time when the deceleration of the pump motor 92 is started, as described above.

When it is determined that the set operation is completed based on the motion information, the controller 91 may control the washing motor 93 to stop (A6).

When the washing motor 93 stops and the stop signal SG4 is generated (t(SG4)), the control unit 91 may control the pump motor 92 to stop (A6).

That is, the control unit 91 controls the pump motor 92 when the stop signal SG4 is generated (t( SG4)), the pump motor 92 can be stopped (B6). Here, stopping the pump motor 92 means starting control to stop the pump motor 92 or controlling the pump motor 92 to stop corresponding to the stopping point of the washing motor 93 . may include.

Referring to FIG. 13A , the control unit 91 is configured to wash the washing machine so that the time when the washing motor 93 stops (t(SG4)) and the time when the pump motor 92 stops (t(SG4)) correspond to each other. The motor 93 and the pump motor 92 may be controlled.

However, in reality, between the time point at which the stop signal SG4 is generated (t(SG4)) and the time point at which the pump motor 92 is stopped based on the generated stop signal SG4, the control unit 91 controls the processing. A delay such as the time required or the time the signal is transmitted may occur. This may be understood as the same reason as the delay generated between the time when the angle control completion signal SG2 is generated and the time when the deceleration of the pump motor 92 is started, as described above.

Hereinafter, a control method according to an embodiment of the present invention will be mainly described with reference to FIGS. 13B and 13C , focusing on parts different from those in FIG. 13A .

The steps (A1 to A2 and B1 to B2) of the controller 91 accelerating the pump motor 92 to correspond to the acceleration of the washing motor 93 may be described with reference to FIG. 13A and also be applied to FIG. 13B .

The controller 91 may control the deceleration of the pump motor 92 to start after the first time t1 from the braking time t(SG2) of the washing motor 93 .

The controller may provide a control signal to the circulation pump motor 92 so that the circulation pump motor 92 decelerates after a first time t1 has elapsed after the washing motor is braked.

The first time t1 may be a preset value as a time difference between the braking time t(SG2) of the washing motor 93 and the deceleration time t(H) of the pump motor 92 .

Alternatively, the control unit 91 may control the washing motor 93 to set the pump motor 92 to the maximum rotation speed Pr(V, H) after a second time from when the washing motor 93 reaches the maximum rotation speed Dr(V). ) can be controlled.

The second time is a time point (t(SG3)) at which the washing motor 93 reaches the maximum rotation speed Dr(V), and a time at which the pump motor 92 reaches the maximum rotation speed Pr(V, H). It may be the time difference between arrival times t(H).

The first time t1 and the second time may have the same value. That is, the control unit 91 may brake the washing motor 93 when the washing motor 93 reaches the maximum rotation speed Dr(V), and the pump motor 92 operates the maximum rotation speed Pr(V). When (V, H)) is reached, the pump motor 92 may be decelerated.

The control unit 91 completes the control of the washing motor 93 up to the motion angle θ (A3), and when the angle control completion signal SG2 is generated (t(SG2)), the pump motor 92 is the target Further based on whether the RPM (Pr(V, H)) has been reached, the pump motor 92 may be controlled.

13B, the control unit 91, when the angle control completion signal SG2 is generated (t(SG2)), before the pump motor 92 reaches the maximum rotation speed Pr(V, H) In this case, the pump motor 92 can be accelerated until it reaches the maximum rotational speed Pr(V, H).

That is, before the first time t1 elapses from the braking time t(SG2) of the washing motor 93, the control unit 91 may accelerate the pump motor 92 to the upper limit of the set rotation speed range. have.

Meanwhile, the control unit 91 controls the first rotation from the acceleration time of the pump motor 92 (or the acceleration time of the washing motor, t(SG1)) to the braking time of the washing motor 93 (t(SG2)). Accelerate the pump motor with the acceleration, and from the braking time t(SG2) of the washing motor 93 until the pump motor reaches the maximum rotation speed Pr(V, H), the pump motor ( 92) can be accelerated. The first rotational acceleration and the second rotational acceleration may have preset values, and the second rotational acceleration may be a value smaller than the first rotational acceleration.

Referring to FIG. 13C , the controller 91 controls the pump motor 92 to set the maximum rotation speed Pr( When it is determined that V, H)) is reached, the pump motor 92 may be controlled to maintain the maximum rotational speed Pr(V, H).

The control unit 91 controls the pump motor 92 at the maximum rotation speed Pr(V, H) before the first time t1 elapses from the braking time t(SG2) of the washing motor 93 . When it is determined that it has reached, the pump motor 92 may be decelerated after the first time t1 .

13B and 13C , the control unit 91 causes the washing motor 93 to rotate the lowest from a time point t(SG2) when the washing motor 93 reaches the maximum rotation speed Dr(V). In the section between the time when the speed is reached (or the time when it is stopped, t(SG3)), the washing motor 93 and the pump motor ( 92) can be controlled.

13B and 13C , the control unit 91 controls the pump motor 92 after a third time t2 from a time t(SG3) when the washing motor 93 is stopped and a restart signal is generated. can be controlled to reach the minimum rotational speed t(L). The third time t2 may be equal to or shorter than the second time t1.

Although not shown, the control unit 91 controls the washing motor 93 and the pump so that the pump motor 92 reaches the minimum rotation speed Pr(V, L) when the washing motor 93 stops. The motor 92 may be controlled. At this time, the third time t2 may be 0, and through this, the control unit 91 controls the pump motor 92 to spray water against the fabric rising while in contact with the drum 40 . can

13B and 13C , the controller 91 may repeatedly perform the above-described control of the washing motor 93 and the pump motor 92 . The control unit 91 may repeatedly perform the control of accelerating and decelerating the washing motor 93 as described above while changing the rotation direction of the drum 40 , and controlling the acceleration and deceleration of the washing motor 93 is performed. In response to the repetition, the control for accelerating and decelerating the pump motor 92 can be repeatedly performed. Through this, various drum driving motions can be implemented.

Meanwhile, the controller may perform the control operation of the circulation pump motor 92 with a delay of a preset time from the control operation of the washing motor. That is, the waveform of the time-rotation speed graph of the washing motor and the waveform of the time-rotation speed graph of the circulation pump motor 92 have only a difference in the rotational speed range, and the graph of the circulation pump motor 92 is preset It is delayed by time, and can be controlled in a shape that follows the graph of the washing motor. In this case, t1 and t2 shown in FIGS. 52B and 52C may be set to the same value.

When the control method of the washing machine configured as described above is used, water is more strongly sprayed on the cloth (laundry) falling within the drum 40 while the fall-inducing motion by braking is performed, thereby applying a physical impact to the washing effect. can increase

That is, in FIG. 13B , while the washing motor 93 is being accelerated, the cloth (laundry) rises while in contact with the drum 40, and when the washing motor 93 is braked (t(SG2)), the cloth is removed from the drum. It falls from the inner peripheral surface 42 of (40). At this time, the pump motor 92 rotates at the highest rotational speed Pr(V, H), and by spraying water with maximum intensity through the nozzles 83a and 83b, a physical blow to the falling fabric is possible.

Although not shown, the controller may control the circulation pump motor 92 to decelerate to the third acceleration slope from the braking time t(SG2) of the washing motor until the first time t1 elapses. When the first time t1 has elapsed, the controller may control the circulation pump motor 92 to decelerate to a fourth acceleration slope steeper than the third acceleration slope. That is, the controller starts to gradually decelerate the circulation pump motor 92 when the washing motor brakes, and more rapidly decelerates the circulation pump motor 92 when the first time t1 elapses from the time the washing motor is braked. can do it

In this case, similarly, the washing effect can be enhanced by using the water pressure of the water flow sprayed from the nozzle for the falling cloth when the washing motor is braked (t(SG2)).

<Filtration Motion>

14 illustrates a change in the rotational speed of the drum (a) and a change in the rotational speed of the pump (b) according to an embodiment of the present invention.

15 shows the arrangement of laundry in the drum while the filtration motion is being performed, (a) is a case in which a small amount of laundry is put into the drum, and (b) is a case in which a large amount of laundry is put in.

The method of controlling a washing machine according to an embodiment of the present invention includes rotating the drum 40 in one direction so that laundry in the drum 40 does not fall on the inner circumferential surface of the drum 40 . This step corresponds to the aforementioned filtration motion.

14, 15 and 16, while the filtration motion is performed, the control unit 91 controls the drum 40 in one direction (preferably one rotation or more) while the drum 40 rotates in one direction (preferably one or more rotations), the circulation pump motor 92 Controls the rotation speed Pr(F) to increase. In the process of performing the filtration motion, when the rotational speed of the drum 40 starts to increase, the centrifugal force acting on the laundry is also increased, and the inner circumferential surface of the drum 40 sequentially from the laundry located close to the inner circumferential surface of the drum 40 . adhered to or adhered to. That is, during the filtration motion, the rotational speed of the drum 40 starts to increase and in the process of reaching the preset rotational speed Dr(F), in the beginning, sufficient centrifugal force is applied to the laundry located in the center of the drum 40. If the rotation speed of the drum 40 is sufficiently increased, the position of most of the laundry (preferably, all laundry) in the drum 40 with respect to the drum 40 is changed. is fixed

In particular, when the amount of laundry put into the drum 40 is below a certain level, the laundry generally gathers at the entrance of the drum 40 during the filtration motion (refer to (a) of FIG. 15 ). In this case, it is preferable to control the rotational speed of the pump 36 to be low so that the circulating water sprayed from the nozzles 83a and 83b falls in front of the drum 40 .

Conversely, when the amount of laundry put into the drum 40 is above a certain level, in the process of increasing the rotation speed of the drum 40, the empty space surrounded by the laundry expands backward from the entrance of the drum 40. , is eventually formed as shown in Fig. 15 (b).

Controlling the rotational speed of the pump 36 to increase while the filtration motion is performed is based on the mechanism of expansion of the empty space in the drum 40 as described above found in the process of performing the filtration motion. . That is, in the process in which the empty space is expanded to the rear of the drum 40, the injection pressure of the nozzles 83a and 83b is also increased in conjunction, so that the water flow can reach the deep inside of the drum 40. will be.

In the filtration motion, the control unit 91 accelerates the washing motor 93 until it reaches a preset rotation speed Dr(F), and when the rotation speed Dr(F) is reached, the rotation speed ( Control so that Dr(F)) is maintained. The rotational speed Dr(F) is determined within a range in which it is rotated in a powdered state depending on the inner circumferential surface of the cloth drum 40, and its value may vary depending on the amount of laundry, but is approximately set between 80 and 108 rpm.

In the filtration motion, the maximum rotational speed of the circulation pump motor 92 is set according to the amount of laundry. That is, the controller 91 may set the maximum rotational speed Pr(F) according to the sensed laundry amount. The pump motor 92 controls the maximum rotational speed Pr(Fs) when the sensed laundry amount belongs to a small amount (or the first laundry amount range I, see FIG. 16 ), compared to a large amount (or the second laundry amount). The maximum rotation speed Pr(Fm) in the case of belonging to the laundry amount range (II), see FIG. 16) may be set to a larger value.

At this time, the rotational speed of the pump 36 may be configured to start rising in response to the time t1 at which the rotation of the drum 40 starts to be accelerated. That is, the acceleration of the rotation of the drum 40 and the time of increasing the rotation speed of the pump 36 are linked (or synchronized).

The graph indicated by the solid line in FIG. 14(b) shows the change in the rotational speed of the pump 36 when the amount of laundry is greater than or equal to the reference value, and the graph indicated by the chain line is when the amount of laundry is less than the reference value, the pump ( 36) shows the change in rotational speed. As shown in these figures, the drum 40 may be braked when the rotation speed of the pump 36 reaches the preset maximum rotation speeds Pr(Fm) and Pr(Fs) (t=t2).

The method of controlling a washing machine according to embodiments of the present invention may further include detecting an amount of laundry in the drum 40 (hereinafter, referred to as “laundry amount”). Various methods for determining the laundry weight are already known. For example, the control unit 91 accelerates the drum 40 in a state in which laundry (or cloth) is loaded, and determines the amount of laundry based on the time taken for the rotation speed of the drum 40 to reach a preset rotation speed. can However, the present invention is not limited thereto, and the laundry weight may be obtained using other known methods.

The step of controlling the pump 36 while performing the filtration motion described above is suitable for a water supply/soaking stroke among a series of strokes according to FIG. 12 .

The present invention described above can be implemented as computer-readable code on a medium in which a program is recorded. The computer-readable medium includes all kinds of recording devices in which data readable by a computer system is stored. Examples of computer-readable media include Hard Disk Drive (HDD), Solid State Disk (SSD), Silicon Disk Drive (SDD), ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device, etc. There is also a carrier wave (eg, transmission over the Internet) that includes implementation in the form of. In addition, the computer may include a processor or a control unit.

In the above, preferred embodiments of the present invention have been illustrated and described, but the present invention is not limited to the specific embodiments described above, and in the technical field to which the present invention pertains without departing from the gist of the present invention as claimed in the claims. Various modifications may be made by those of ordinary skill in the art, and these modifications should not be individually understood from the technical spirit or perspective of the present invention.

10: casing 31: tub
40: drum 60: gasket
83a: first nozzle 83b: second nozzle
91: control unit 92: circulation pump motor
93: washing motor

Claims (10)

A tub containing water; a drum rotatably provided in the tub; at least one nozzle for spraying water into the drum; a washing motor rotating the drum; In the control method of a washing machine comprising a pump for feeding pressure with one nozzle,
(a) in a state in which water is contained in the tub, the cloth on the inner circumferential surface of the drum rises while in contact with the drum by centrifugal force, and after accelerating the washing motor, the cloth falls from the inner circumferential surface of the drum, the braking the washing motor; and
(b) accelerating the pump motor constituting the pump to spray water through the at least one nozzle, and then starting the deceleration of the pump motor after a first time from the braking time of the washing motor; including,
Step (b) is,
When the pump motor reaches the upper limit of the set rotation speed range before the first time elapses from the braking time of the washing motor, controlling the pump motor to maintain the upper limit of the set rotation speed range . The method of claim 1,
Step (b) is,
and providing a control signal to brake the washing motor and to provide a control signal to decelerate the pump motor after the first time has elapsed. The method of claim 1,
Step (b) is,
and accelerating the pump motor to an upper limit of a set rotational speed range from a braking point of the washing motor until the first time elapses. delete The method of claim 1,
Step (b) is,
and controlling the pump motor to rotate at a constant speed from a braking point of the washing motor until the first time elapses. 6. The method of claim 5,
The pump motor in step (b),
A control method of a washing machine, wherein the washing motor is controlled to rotate at a rotational speed at a braking time. A tub containing water; a drum rotatably provided in the tub; at least one nozzle for spraying water into the drum; a washing motor rotating the drum; In the control method of a washing machine comprising a pump for feeding pressure with one nozzle,
(a) in a state in which water is contained in the tub, the cloth on the inner circumferential surface of the drum rises while in contact with the drum by centrifugal force, and after accelerating the washing motor, the cloth falls from the inner circumferential surface of the drum, the braking the washing motor; and
(b) accelerating the pump motor constituting the pump to spray water through the at least one nozzle, and then starting the deceleration of the pump motor after a first time from the braking time of the washing motor; including,
Step (b) is,
accelerating the pump motor with a first rotational acceleration from an acceleration time of the pump motor to a braking time of the washing motor; and
accelerating the pump motor with a second rotational acceleration smaller than the first rotational acceleration from a braking time of the washing motor to a starting time of deceleration of the pump motor. The method of claim 1,
The pump motor in step (b),
In a section between the time when the washing motor reaches the upper limit of the set rotation speed range and the time when the washing motor reaches the lower limit of the set rotation speed range, deceleration of the pump motor is controlled to start. The method of claim 1,
The step (a) is repeatedly carried out while changing the direction of rotation of the drum,
The method of controlling a washing machine, wherein the step (b) is repeatedly performed in response to the step (a) being repeated. The method of claim 1,
(a-1) performing before step (a) and detecting the amount of laundry put into the drum; further comprising,
The pump motor in step (b),
The control method of a washing machine, wherein the control method is controlled to decelerate or accelerate within a rotation speed range set according to the amount of laundry detected in step (a-1).

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