Apparatus and method for detecting laundry weight in washing machine employing sensorless BLDC motor

[00002] 1. Field of the Invention

[00003] The present invention relates to an apparatus and method for detecting a laundry weight in a washing machine employing a sensorless BLDC motor, and more particularly, to an apparatus and method for detecting a laundry weight in a washing machine employing a sensorless BLDC motor that is capable of detecting a laundry weight in a dry state by using a motor speed difference according to a laundry weight.

[00004] 2. Description of the Background Art

[00005] Recently, in order to improve a washing degree of the laundry and reduce a noise and an energy of a washing machine, an inverter unit which is able to variably control freely a motor speed has been adopted to a washing machine, and in addition to this, in order to adjust a water level and a detergent amount, a method for detecting a laundry weight (a weight of the laundry) in a washing machine has been adopted.

[00006] FIG. 1 is a circuit diagram showing a driving device of a BLDC motor in accordance with a conventional art.

[00007] As shown in FIG. 1, the driving device includes a rectifying unit 11 for rectifying and smoothing an AC power, an inverter unit 12 for applying the rectified and smoothed voltage and current to a BLDC motor 13 and controlling the speed of a rotor (not shown) of the motor; a position detector 14 for detecting a position of a rotor of the motor 13 by using a hall unit 17 attached at the motor 13; a microcomputer 15 for receiving a position detect signal from the position detector 14 and controlling the speed of the motor 13; and a pulse width modulator 16 for receiving a control signal from the microcomputer 15, modulating an output pulse width and controlling the inverter unit 12.

[00008] The conventional driving device of the BLDC motor constructed as described above will now be explained.

[00009] When the rectifier 11 rectifies and smoothes an input AC power and applies it to the inverter unit 12, the inverter unit 12 receives a drive signal from the pulse width modulator 16 and applies a three-phase voltage to the motor 13.

[00010] Accordingly, the motor 13 starts rotating. At this time, the position detector 14 detects a position of the rotor of the motor 13 by using the hall unit 17 attached at the motor 13, and inputs a voltage value according to the detected position value to the microcomputer 15.

[00011] The microcomputer 15 computes the speed of the motor 13 with the voltage value, compares it with a pre-set reference speed, and outputs a control signal for rotating the motor 13 at a desired speed to the pulse width modulator 16.

[00012] Upon receipt of the control signal from the microcomputer 15, the pulse width modulator 16 converts a level of the control signal and outputs it to the inverter unit 12.

[00013] There are two methods for detecting a laundry weight by using the BLDC motor.

[00014] The first one is a method that the motor 13 is accelerated to a certain speed for a predetermined time period and then a power is cut off so as to check a rate at which the speed of the motor 13 is decelerated, to thereby measure a laundry weight. That is, in this method, the inertia of the motor 13 according to the laundry weight is measured to detect the laundry weight. This method is mostly adopted to a washing machine in which a pulsator (not shown) reduces a rotational force of the motor 13 or changes a direction of the motor by a clutch and a gear.

[00015] The second one is a method that time during which the motor 13 reaches a certain speed is measured. In this method, since the motor 13 is directly connected to the pulsator (not shown) or an inner tub (not shown) and driven, this method is useful for a washing machine adopting a direct driving method.

[00016] The laundry weight detecting method adopted to a washing machine of the direct driving method will now be described with reference to FIGS. 2A through 2E.

[00017] After the motor 13 is aligned at a certain position at the initial stage, the size of the voltage applied to the motor 13 is regularly increased.

[00018] That is, as shown in FIG. 2A, a duty ratio (an ON/OFF ratio of 6 transistor switches of the inverter unit 12) is controlled so as to be proportionate to the size of a voltage corresponding to each phase, thereby increasing the size of the voltage.

[00019] Thereafter, when the microcomputer 15 regularly increases the phase voltage applied to the motor 13, the speed of the inner tub directly connected to the motor 13 or the pulsator is gradually increased.

[00020] In the case that the speed is increased, as shown in FIG. 2B, if there is much laundry weight compared to the reference laundry weight, the motor 13 should generate more torque, so that more time is taken for the motor 13 or the inner tub to reach the reference speed or the reference position than the reference time.

[00021] Thus, during the time when a certain torque is applied to the motor 13, if the laundry weight is more than the reference laundry weight, the motor 13 or the inner tub reaches the reference speed or the reference position after the reference time elapse.

[00022] Conversely, if the laundry weight is small, the motor 13 or the inner tub reaches the reference speed or the reference position in a shorter time than the reference time.

[00023] After a certain voltage is applied to the motor 13, the time during which the motor 13 or the inner tub reaches a certain speed or a certain position is computed, to thereby detect the laundry weight.

[00024] However, in the laundry weight detecting method, there are many factors affecting the accuracy of the detected laundry weight, including a mechanical factor such as a deviation of a bearing housing, a vibration difference of the inner tub, a deviation of a damper, a motor factor such as a resistance of the motor 13 or the inductance, and a control circuit factor such as a voltage detect circuit, a voltage variation or a temperature. Among them, the error in the voltage detection according to a power supply voltage variation is the factor that has the biggest influence on detecting of the laundry weight in a washing machine.

[00025] As shown in FIGS. 3A through 3D, if power is much used around the washing machine, the size of the power supply voltage inputted to the washing machine is reduced, and a DC link terminal voltage of the inverter unit 12 is varied depending on a limited capacity of a condenser according to the laundry weight and the operation speed in driving the washing machine.

[00026] Thus, it is difficult to detect the accurate number of rotation of the motor 13 at the initial stage. In addition, as shown in FIG. 3B, in detecting the laundry weight, if the power supply voltage is increased higher than the reference voltage, since the motor speed reaches the reference speed fast as much as Δt, than Δt₀, a laundry detection error occurs corresponding to the time Δt₁.

[00027] Conversely, if the power supply voltage is reduced lower than the reference voltage, since it reaches the reference speed as much as Δt₂, it is detected that there is more laundry corresponding to the time Δt₂.

[00028] Therefore, the method for detecting the laundry weight with the time during which the motor speed reaches the reference speed or the reference position has the following problem.

[00029] That is, in order to accurately compute the laundry weight, a certain voltage should be applied regardless of the laundry weight or the surroundings, but if a certain voltage fails to be applied to the motor due to the surroundings, a computed laundry weight may differ from an actual value.

[00030] Therefore, an object of the present invention is to provide a method for detecting a laundry weight that is capable of accurately measuring a laundry weight and effectively washing a laundry without a necessity of accurately detecting the number of rotation of a motor in an environment that a voltage is not regularly applied in detecting the laundry weight.

[00031] Another object of the present invention is to provide an apparatus for detecting a laundry weight that is capable of reducing a unit cost with a simple construction by not installing a hall sensor and its peripheral circuit in a washing machine employing a BLDC motor.

[00032] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for detecting a laundry weight in a washing machine employing a sensorless BLDC motor including the steps of: determining whether a first predetermined time elapses after a motor is initiated and reaches a certain speed; and controlling the motor in a torque control mode when the first predetermined time elapses and detecting a laundry weight on the basis of the motor speed after a second predetermined time elapses.

[00033] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

[00048] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[00049] FIG. 4 is a circuit diagram showing a driving apparatus of a sensorless BLDC motor in accordance with a preferred embodiment of the present invention.

[00050] As shown in FIG. 4, a driving apparatus of a sensorless BLDC motor includes: a rectifying unit 41 for rectifying and smoothing an AC power; an inverter unit 42 for applying the rectified and smoothed voltage and current to a BLDC motor 43 and controlling a speed of a rotor (not shown) of the motor 43; a position detecting unit 44 for detecting the current applied to the motor 43 and detecting a position of the rotor of the motor 43; a microcomputer 45 for receiving the position detect signal detected by the position detecting unit 44 and controlling the speed of the motor 43; a memory unit 47 for storing the speed value of the motor 43 output from the microcomputer 45; and a pulse width modulating unit 46 for receiving a control signal from the microcomputer, modulating an output pulse width and controlling the inverter unit 42.

[00051] An apparatus and method for detecting a laundry weight in a washing machine employing the sensorless BLDC motor 43 of the present invention will now be described on the basis of the driving apparatus of the sensorless BLDC motor (referred to as ‘motor’, hereinafter) with reference to FIGS. 4 through 6.

[00052] After a user puts the laundry in the inner tub (not shown), he or she depresses a washing start button. Then, the microcomputer 45 recognizes it and turns on a transistor of the inverter unit 42 to rotate the motor 43, in order to detect a laundry weight (steps S51˜S52).

[00053] When the motor 43 starts rotating, since an error is generated in a position detection and it is difficult to accurately control a torque, a laundry weight detecting time is divided into an interval that the motor 43 is driven at a certain speed (that is, time (T1) for which a position detection error can be disregarded) and an interval (T2) for accelerating the motor 43.

[00054] Thereafter, when it passes the interval at which the motor 43 is accelerated, an accurate laundry weight is determined on the basis of the difference of a speed according to a laundry weight.

[00055] In other words, when the motor 43 starts rotating, the microcomputer 45 periodically turns on and off the remaining transistors by means of the pulse width modulating unit 45 until the motor 43 reaches the certain speed (V1 RPM).

[00056] When the motor 43 reaches the certain speed (V1 RPM (revolutions per minute)), the microcomputer 45 drives the motor 43 at the certain speed (V1 RPM) for a predetermined time (T1) (step S53).

[00057] At the initial stage of driving the motor 43, substantially, an error may be generated in the position detection, and especially, an error in a current and a voltage applied to the motor 43 and a position detection error computed on the basis of the current and the voltage signal can be relatively large.

[00058] Then, the microcomputer 45 would fail to perform an accurate torque control, and even if it performs the torque control, it would fail to accurately measure the laundry weight according to the speed difference of the motor 43.

[00059] In addition, although the motor is driven at a speed that the position of the rotor of the motor 43 is stable, since the speed is not constant due to the acceleration characteristic of the motor 43, the speed needs to be maintained for a predetermined time to a degree that the position detection error can be disregarded (step S54).

[00060] In this respect, the certain speed (V1 rpm) and the predetermined time (T1) was 70 rpm and 6 sec according to an experiment result, but can be varied depending on the performance of the motor.

[00061] After the predetermined time (T1) elapses, the microcomputer 45 changes the control method of the motor 43 to a torque control method (a current control)(step S55).

[00062] Accordingly, in case that the motor 43 is accelerated with a certain torque, a speed difference would occur in a predetermined time (T2) according to the weight of the laundry, based on which the laundry weight is detected (steps S56˜S58). At this time, the predetermined time (T2) was 1˜2 sec, but can be varied depending on the performance of the motor.

[00063] Namely, after the predetermined time (T2) elapses, the speed of the motor 43 differs according to the laundry weight, and the microcomputer 45 stores each speed in the memory, detects the laundry weight on the basis of the stored speeds, accordingly sets an accurate water supply amount and washing time and performs washing, without exceeding or falling short of the washing time.

[00064] As another method for detecting the laundry weight in the predetermined, time (T2), the microcomputer 45 stores a laundry weight according to the speed of the motor as a look-up table in the memory and determines a laundry weight by referring to the look-up table in the predetermined time (T2).

[00065] As so far described, the method for detecting a laundry weight in a washing machine employing the sensorless BLDC motor has an advantage that a laundry weight can be accurately measured and the laundry can be effectively washed even in an environment that a voltage is not regularly applied.

[00066] In addition, since the laundry weight detecting apparatus of a washing machine employing the sensorless BLDC motor does not include a hall sensor and its peripheral circuit, its construction is simple and thus its price can be reduced.

[00067] As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, ace and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalence of such meets and bounds are therefore intended to be embraced by the appended claims.