Method for balancing a washing machine

Abstract: The washing machine (1) has a drum (3) rotating about a horizontal axis (3a) and is equipped with at least three water chambers (4a,4b,4c) distributed through the internal periphery of the drum to which chambers a flow of water (13) is provided selectively from the chambers' respective solenoid valves (10a,10b,10c) to compensate for the unbalance, while the drum is accelerated at a gradual rate by means of a T/F speed variator (6) of the motor (5), and the magnitude of the vibration (12) and its position (11) are measured by a vibration sensor (8) and a position sensor (9). The measured values are compared to a preset threshold value which changes with drum rotation speed until the maximum spinning speed is reached.

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a washing machine whose drum rotates about a horizontal axis, and more particularly to the prevention of vibrations in the clothes-laden drum when it rotates at high speed during the spinning stage. PRIOR ART US 5,280,660 describes a method for balancing a washing machine whose drum rotates about a horizontal axis, wherein the washing machine is equipped with at least three water chambers distributed peripherally inside the drum, which chambers selectively receive a preset amount of water from their respective solenoid valves depending upon the result of the vibration measured by a vibration sensor and the drum unbalance position measured by means of a proximity sensor, the signals from both sensors being combined to select the water supply that will compensate for the unbalance, and a motor that accelerates the drum to maximum spinning speed during the compensation process. US 4,517,695 describes a method for balancing a washing machine whose drum rotates about a horizontal axis, wherein the drive motor is connected to a rotation speed control device that controls drum acceleration from an initial spinning speed to a final speed, depending upon the force exerted by the unbalance of the clothing and the comparison thereof with a preset value calculated for the final spinning speed. In known methods, drum rotation is accelerated from a low initial value to a high final maximum spinning value, in spurts by means of various abrupt speed increases, and maintaining constant velocity in each spurt, in intervals whose length depends upon the result of the measurement of vibration at each constant speed value. During the course of the interval at constant drum speed, a preset quantity of water is placed in the selected compensation chamber, and this action is repeated until the measured vibration value falls below a certain reference value. With known methods, the acceleration time that transpires until the maximum speed for carrying out the compensation method is reached is excessive, because the water is added to the compensation chambers in ever-equal given doses, and because the drum undergoes successive accelerations after acceleration-free intervals. DISCLOSURE OF THE INVENTION The object of the invention is a method for balancing the drum of a washing machine equipped with three or more hollow water chambers distributed through its internal periphery by means of compensating for unbalance while the drum accelerates from a low initial speed to a high final maximum spinning speed, while combining the addition of water to the selected water chamber, which is situated diametrically opposite the unbalanced position. The addition of compensating water is continuous, by means of a given flow; acceleration is likewise continuous in gradual fashion, while vibration is measured continuously, and only the rate of acceleration is dependent upon the result of the vibration measurement. With the method according to the invention, smooth rotation is achieved without exceeding an admissible washing machine vibration value by means of drum acceleration at a gradual rate until reaching a maximum speed, while the unbalance of the clothes is compensated for in a shorter total process time. In order to carry out drum acceleration at a gradual rate, the drum drive motor is controlled through a voltage/frequency speed variator governed by the washing machine's electronic controller to regulate the rate of drum acceleration as a function of the result of the vibration measurement and its comparison with a preset reference value. One characteristic of the invention is that the vibration reference value for comparison with the real value is changing throughout the range of spinning speeds and is reduced as the drum accelerates to maintain the unbalanced mass of the drum always below a constant value, inasmuch as vibration increases at a square rate with the drum speed. The speed variator also allows the torque of the drum drive motor to be raised at a speed as low as 10 r/min, to effect full water chamber emptying before beginning a new balancing process. The vibration sensor used to execute the method has the advantages of lower economic cost and easier installation than the accelerometers of known methods, as well as the fact that the result of measurement is not affected by the mass of the washing machine's structure, as occurs with an accelerometer, but only by the unbalance of the clothing, thus also gaining time in the execution of the compensation process until final compensation is achieved. DESCRIPTION OF THE DRAWINGS FIG. 1 shows two views of the washing machine with the system for carrying out the method for balancing the washing machine drum according to the invention. FIG. 2 is a wiring diagram of the sensor used to measure vibration. FIG. 3 is a diagram of the measurement of the vibration generated by the drum unbalance combined with the measurement of the unbalance position. FIG. 4 is a diagram of the different drum accelerations depending upon the unbalance, in an embodiment of the invention. FIG. 5 is the diagram of the steps included in the embodiment of the balancing method, according to fig. 4. PREFERRED EMBODIMENT OF THE INVENTION With reference to figures 1 to 3, the washing machine 1 for executing the method according to the invention is comprised of a tub 2 fixed to the washing machine structure, the drum 3 rotating about a horizontal drive axis 3 a through whose internal periphery are distributed three water chambers 4 a ,4 b ,4 c , a housing 2 a holding the bearings of the axis 3 a which is fixed to the rear of the tub 2, the induction motor 5 for driving the drum 3, the washing machine's electronic controller 6, the voltage-frequency converter speed variator 7, the device 8,9 for detecting vibration and position, and the solenoid valves 10 a ,10 b ,10 c activated individually by the controller 6 to compensate for the unbalance by means of selectively filling the chambers 4 a ,4 b ,4 c by means of water streams according to the arrows 13 in figure 1. The drum drive motor 5 shown in figure 1 has two windings 14,15 powered separately to achieve two ranges of drum rotation speed N, the low 35-to-55 r/min speed for clothes washing and the high spinning speed between 200 and 900 r/min, these latter two speeds being referenced respectively as Nini and Nmax. Both windings of the motor 5 are powered through the speed variator 7, the low-speed winding 14 to reduce the speed N to a very low value such as 10 r/min when the chambers 4 a ,4 b ,4 c are to be emptied, and the winding 15 to bring the speed N up gradually to spinning speed during the unbalance compensation process. The unbalance detection device 8,9 includes a vibration magnitude sensor 8, shown in figure 2, and a position sensor 9 to measure the position of the unbalance, shown in figure 3, which rotates of a piece with the drum axis 3 a . The vibration sensor 8 used for the execution of the compensation method, shown in fig. 2, is preferably constructed using a strain gauge 8 a and an associated circuit 8 b for filtering, amplifying and processing the output signal. The gauge 8 a is fixed through a substrate to the bearing-holding housing 2 a where it is easily accessible and in a place to which all radial drum vibration is transmitted. The circuit 8 b faithfully reproduces the oscillation of the vibration through its signal 11 of electrical voltage V oscillating between two alternating peak values +Vc and -Vc which is almost a sine function, shown in figure 3, and the numerical result of the measurement is the Vc peak to peak amplitude. The sensor 9 sensing the unbalance position in relation to the water chambers 4 used preferably for the execution of the method is an optic sensor where the photoelectric transmitter not shown in the figures is associated with a rotating disk fixed to the axis 3 a and perforated with a number of orifices 9 b distributed uniformly over its periphery indicating the angle rotated by the drum. The position sensor 9 could also be a magnetic proximity or Hall effect sensor. One of the perforations in the disk in sensor 9 is a long groove 9 a whose position relative to one of the chambers 4 is recorded in the controller 6, serving as a zero reference of the angle rotated by the drum 3. The photoelectric transmitter provides an electrical signal 12 associated with the position of the groove 9 a , and the controller 6 combines the two electrical signals 11 and 12 to measure the phase angle p hi, as shown in figure 3, between the said groove 9 a and the peak value +Vc of the vibration signal 11, to select one or two of the three chambers 4 a , 4 b , 4 c , diametrically opposite the location of the mass causing the unbalance. Figure 4 depicts the acceleration of the drum 3 by means of the variator 7 in an embodiment of the method 40 for balancing the drum 3 according to the flow diagram in figure 5. The acceleration of the drum 3 takes place smoothly, from the initial spinning speed Nini and gradually up to the maximum speed Nmax, by means of tiny successive "delta N" increments, for example increments of 50 r/min or less at a time, yielding different rates of acceleration Na as a function of the initial unbalanced mass. Vibration magnitude is measured between the two opposing peak values Vc of the signal from sensor 8 shown in figure 3. The vibration value Vum is a threshold value admissible for each actual speed value N according to an exponential function found by experiment, examples being Vum = 600 mV at 200 r/min and Vum = 150 mV at 900 r/min, and the safety limit value Vlim is for example 2000 mV. The preferred embodiment 40 of the balancing method, according to the step diagram in figure 5, includes prior steps 41 to 44, the balance compensating sequence of steps 45 to 50, and final steps 51 to 53, which include: step 41, identification of one of the chambers 4 a ,4 b ,4 c with the zero position of groove 9 a of position sensor 9, and identification of each of the solenoid valves 10 a ,10 b ,10 c with its respective chamber 4, which stage is performed only once, when the washing machine is installed on its site. The respective solenoid valve 10 a ,10 b ,10 c is associated with the water chambers 4 a ,4 b ,4 c by means of successive activation and checking of the water chamber that causes the vibration Vc to vary; step 42, emptying of the water chambers 10 at a very slow speed N such as 10 r/min; step 43 checking of the records present in the controller 6 for the safety limit vibration Vlim, the balancing thresold vibration Vum at each actual speed N, the maximum rotation speed Nmax, and the maximum spinning time t max; step 44, acceleration of the drum to an initial spinning speed Nini, for example 200 r/min, and choising the actual acceleration rate N8 among said plurality of gradual rates, after measuring of the vibration Vc at the initial spinning speed Nini; the sequence of steps 45 to 50 comprising, measuring, step 45, of the vibration Vc and the unbalance position phi; the choice of chamber 4, step 46, to which the water stream 13 must be supplied and the activation of the corresponding valve 10; the increase "delta N", step 47, of the speed N, the comparison , step 48, of the actual speed N with the maximum speed Nmax; the comparison, step 49, of the measurement Vc with the balancing thresold value Vum (figure 3), which is changing with the real speed N of the rotation of the drum 3; and step 50, activation of solenoid valves 10 when Vc is greater than Vum; step 51, the comparison of the vibration measurement Vc with the safety limit value Vlim; The water flow 13 in this embodiment is supplied, step 50, to the selected chamber 4a-4c, or interrupted, step 52, according to the result of the comparison in step 49, and the result thus found conditions the activation and deactivation of the selected solenoide valves 10, since inasmuch the acceleration N8 is uninterrupted, when the measurement Vc is less than the value Vum, the valve is deactivated, step 52, and the selected chamber 4 is prevented from overloading, which could cause un unbalance in the position of the selected chamber 4 greater than the unbalance of the initial mass of clothes in the drum 3 in the opposite position. Thus the measurement Vc oscillates with the course of time arround the thresold value Vum, while the acceleration N8 is continuous. Finally, step 53, the elapsed time t is compared with the recorded maximum spinning time t max, and the drum 3 rotates at the maximum spinning speed Nmax until the maximum spinning time t max has expired.

Claims: Method for balancing a washing machine whose drum (3) rotates about a horizontal axis (3a), which washing machine is equipped with at least three water chambers (4a,4b,4c) distributed through its internal periphery for compensating for drum unbalance, a motor (5) equipped with means (7) for the controlled acceleration of the drum (3), a vibration (Vc) magnitude sensor (8), a position sensor (9) to measure the position of the unbalance on the periphery of the drum (3), an electronic washing machine controller (6) that combines the electrical signals (11,12) transmitted by the two sensors (8,9) to select at least one of the compensation chambers (4a,4b,4c) and supply it by means of a respective solenoid valve (10a,10b,10c) with a quantity of water (13) to compensate for the unbalance, while the drum is accelerated (47) between an initial and a final spinning rotation speed (Nini, Nmax), and the controller (6) repeats a sequence of operations (45-50) including measurement (45) of the vibration (Vc) and the unbalance position (phi), comparison (49) of the resulting measurement of the vibration (Vc) with a preset value (Vum), and comparison (48) of the actual drum speed (N) with the maximum spinning speed (Nmax), characterized by the steps an initial prior step (41) to identify one of the compensation chambers (4a,4b,4c) with a reference position (9a) for the position sensor (9), and the association of each of the compensation chambers (4a,4b,4c) with its respective solenoide valve (10a,10b,10c); an actual acceleration rate (Na) is chosen among a plurality of different rates (N5-N9) depending upon the resulting measurement of the vibration (Vc) at said initial spinning speed (Nini); while said sequence (45-50) of operation is executed repeatedly to compensate for the unbalance, the drum (3) is accelerated continuously at said rate (N5-N9), and simultaneously a flow (13) of water is supplied to the selected compensation chamber (4a,4b,4c); the continuous comparison (49) of the measured vibration value (Vc) with a preset vibration value (Vum), the latter changing with the actual drum speed (N). The method for balancing a washing machine of claim 1, wherein said actual acceleration rate (Na) is chosen among different constant rates (N5-N9) and the water flow (13) is supplied to the selected chamber (4) or interrupted depending upon the result of said comparison (49) of the measured vibration value (Vc) with said preset vibration value (Vum). The method for balancing a washing machine of claim 1, wherein the result of vibration measurement (45) is the measurement (Vc) of the peak to peak amplitude (+Vc,-Vc) of the alternating signal (12), produced by the vibration sensor (8) which is fixed to the casing (2a) of the drum bearing-holding, and that of the unbalance position is the measurement of the phase (phi) between one of said peaks (+Vc) and an electrical signal (11) from the position sensor (9).

Inventors: IRURETAGOIENA ETXANIZ MARCIAL, IRURETAGOIENA ETXANIZ, MARCIAL
Applicants: FAGOR S COOP, FAGOR, S.COOP
Application year: 1997
Main classification: D06F37
IPC codes: D06F37