GB2271837A

GB2271837A - Balancing a washing machine drum before spinning

Info

Publication number: GB2271837A
Application number: GB9321744A
Authority: GB
Inventors: Wolfgang Schuwerk; Roland Morent
Original assignee: AKO Werke GmbH and Co KG
Current assignee: AKO Werke GmbH and Co KG
Priority date: 1992-10-22
Filing date: 1993-10-21
Publication date: 1994-04-27
Anticipated expiration: 2013-10-21
Also published as: DE4235614A1; ITMI932182A0; ITMI932182A1; GB9321744D0; FR2697332A3; IT1270884B; FR2697332B3; DE4235614C2; GB2271837B

Abstract

To determine the unbalance of the loaded drum of a washing machine, an unbalance measurement is effected after a load distribution phase prior to spinning. After a load distribution phase the setpoint rotational speed is suddenly increased. Overshoot of the actual rotational speed over the setpoint rotational speed is measured and from this a correction value for the unbalance measurement is determined.

Description

2271837 Method of determining the unbalance of a loaded washing machine

drum The invention relates to a method of determining the unbalance of the loaded drum of a washing machine, with an unbalance measurement being effected after a load distribution phase prior to a spinning process.

DE 30 39 315 Al describes a rotational speed control device for an electric motor which sets in rotation a mass of differing mass eccentricity (washing machine drum). The control device controls the motor current in dependence upon a setpoint value. A sensor which detects the force of mass eccentricity influences the setpoint value of the rotational speed. The sensor detects the motor current. The unbalance measurement is effected during an application spinning process (load distribution phase). If the measured unbalance is too great, said process is interrupted. If the unbalance lies within acceptable values, the rotational speed of the drum is increased to around 400 rpm. An unbalance measurement is effected particularly during said pre-spinning phase. From the result of said measurement the final spinning speed is derived. Depending on the unbalance actually arising, said spinning speed lies, for example, between 600 and 1400 rpm.

Unbalance detection in dependence upon the prevailing motor current is also described in EP 0 275 862 B1 and in DE 26 20 464. Neither case, however, provides an adjustment of the final spinning speed in dependence upon the unbalance. What is proposed, at a limit value of unbalance, is to discontinue spinning or return to the washing rotational speed.

US 3 152 462 describes a control device for the motor of a washing machine, wherein the rotational speed of the motor is detected by a tachogenerator and an unbalance sensor detects 2 the mechanical impulses of the unbalance of the drum and supplies corresponding signals to a computer control system. In the event of unbalance, the rotational speed is reduced.

US 3 674 419 likewise describes a washing machine control device. An unbalance switch is provided to prevent an acceleration of the rotational speed up to the intended value.

Mechanical unbalance detection of the kind described in US 3 152 462 and US 3 674 419, for example, is in practice expensive and unreliable.

In DE 29 15 815 Al, a device for detecting the rotational speed and the unbalance of a unit mounted in rockers in a housing (washing drum) is described. Provided on the driving pulley of the washing drum are markings which are optically scanned for unbalance detection. It is therefore possible to detect the rotational speed and the unbalance, with the result that the spinning speed is adaptable to prevailing conditions. Owing to the need to apply markings, however, said device appears expensive and requires maintenance.

GB 2 124 626 A likewise describes a motor control device of a washing machine. According to one construction (cf. Fig.4), load determination in terms of weight by means of weightdependent sensors is provided. Such sensors are expensive and in continuous operation are susceptible to faults. The construction according to Fig.6 is provided with a tachogenerator which. by means of one assembly group, detects the variations in rotational speed. The basic unit regulates the desired rotational speed.

In methods of the type described initially, different spinning speeds are adjusted depending on the measured unbalance. Lower spinning speeds are adjusted for greater unbalances than for smaller unbalances. The known unbalance measurement gives a very accurate result, assuming a specific load weight r 3 - (clothes plus as yet unextracted water). In practice, however, the drum will not always be loaded with said weight; often the load is lighter or heavier. The mass moment of inertia of the drum then varies correspondingly and the known unbalance measurement does not lead to the optimum spinning speed.

A method of measuring unbalance is described also in DE 40 38 178 Al. Here, the mass moment of inertia is measured by disconnection of the motor and purposeful acceleration. This results in uncontrolled operating phases.

The obj ect of the invention is to propose a method of the type described initially, which detects not only the unbalance caused by mass eccentricity in the case of a horizontal axis but also the load at any one time.

According to the invention, there is provided a method of determining the unbalance of the loaded drum of a washing machine, by measurement after a load distribution phase and prior to a spinning process, wherein after the said load distribution phase, a setpoint rotational speed value for control of the speed of a motor driving the drum is suddenly increased and the resulting actual rotational speed of the drum is compared with the increased setpoint value to derive a correction value related to the load of the drum for use in the unbalance measurement.

Conveniently, cyclical measurements of the difference between the actual rotational speed of the drum and the said increased setpoint value are summed within a measuring window to derive said correction value.

With said method it is advantageous that the prevailing mass moment of inertia of the drum is directly determined. the mass moment of inertia being a function of the weight of the clothes and the water held by the clothes and their distribution in the drum. What is measured is the "overshoot" of the actual rotational speed over the suddenly increased setpoint rotational speed, said overshoot being dependent upon the prevailing mass moment of inertia.

Since, to determine the mass moment of inertia at any one time, its influence upon the rotational speed of the drum is used and a rotational speed detection device is in any case provided, there is no need for an additional sensor for detecting the load.

In a refinement of the invention, the first measuring window starts, when after the sudden increase of the setpoint rotational speed the actual value of the rotational speed overshoots the setpoint value, and is set at a fixed length of time.

In a development of the invention, after a dwell time, which is selected so as to be long enough for the setpoint rotational speed to be reached, the unbalance measurement is effected in a second measuring window in that the unbalancedependent variations in the rotational speed are detected. The second measuring window preferably comprises a constant time fraction and a variable time fraction and the variable time fraction is adjusted in dependence upon the correction value. By said means, a correction of the unbalance measurement in dependence upon the prevailing load or the prevailing mass moment of inertia is easily achieved.

Further advantageous developments of the invention are indicated in the sub-claims and the following description. The drawings show:

Figure 1 a block diagram of a washing machine, Figure 2 a timing diagram of the drum rotational speed, and Figure 3 a graph with test results, diagrammatically f or comparison.

A washing machine comprises a washing drum (2) driven by a motor (1). Coupled to the drive shaft of the motor (1) is a tacho-generator (3). The tacho-generator supplies an alternating voltage whose frequency is proportional to the rotational speed of the motor. The frequency of said alternating voltage, estimated with the motor-to-washing drum transmission ratio, therefore represents the actual rotational speed of the drum. Variations in the rotational speed as a result of an unbalance of the washing drum (2) lead to corresponding variations in the output voltage of the tachogenerator (3).

The frequency of the alternating voltage of the tachogenerator (3) is applied to microprocessor-controlled. digital rotational speed electronics (4). Stored in the rotational speed electronics (4) are the setpoint rotational speeds of the drum which are required for the various washing programs. These are compared with the actual rotational speeds of the drum and the motor (1) is actuated accordingly via power electronics (5). The desired program may be called by means of a program selection switch (6).

The timing diagram (cf. Fig.2) shows the transition area between a washing phase and a spinning phase (not shown).

Curve I shows the actual rotational speed characteristic when the washing drum (2) contains a load of 10 kg. Curve II shows the characteristic of the actual rotational speed for an unloaded washing drum (2), with the load in practice comprising the weight of the clothes plus the water held in the clothes. The loads 10 kg and 0 kg are limit values. They were chosen for the sake of simplicity. In practice, the load values lie between said quantities. Curve I I I shows the setpoint characteristic.

Figure 2 in particular shows the following:

A washing phase (A) is followed by a load distribution phase (B). During the latter. the rotational speed of the drum is increased up to around 82 rpm (U1). During the load distribution phase, the clothes are to be applied in a stable manner against the inner periphery of the washing drum (2). on reaching the clothes application speed U1, af ter a brief phase (C) the setpoint rotational speed is suddenly increased to U2.. e.g. 120 rpm. With a 10 kg load, owing to the greater mass moment of inertia the motor (1) takes a little longer to accelerate up to the setpoint rotational speed but then reaches a greater maximum actual rotational speed U3 (cf. curve I) than with no load (cf. curve II, with maximum actual rotational speed U4).

After a specific time, the setpoint rotational speed drops back to the value US, e.g. 100 rpm. said value is higher than the clothes application speed U1 because the clothes should not detach themselves from the drum. The time during which the setpoint rotational speed U2 is preset is so selected that, even given the maximum anticipated mass moment of inertia, the actual rotational speed reliably comes up to the setpoint rotational speed U2.

After the jump from U2 to U5, the drum (2) decelerates faster without a load than with a load on account of its mass moment of inertia then being lower.

A first measuring window (D) is provided. Said window starts when the actual value of the rotational speed exceeds the setpoint value U2. The duration of the measuring window (D) is set at a f ixed value. It is around 4 seconds. The measuring window is, say, as long as the duration of the setpoint rotational speed U2. Fig.2 shows the measuring window for the curve II. In the case of curve I, the measuring window (D) is displaced slightly to the right. The first measuring window (D) ends in any case before the actual rotational speed has reached the setpoint rotational speed US.

In the first measuring window (D), the system deviation of curve I or curve II from the setpoint value U2 is integrated correctly as regards sign. This is ef f ected by cyclical measurement of the rotational speed differences in the overshoot of the rotational speed characteristics of curve I or curve II compared to the setpoint rotational speed U2. In principle, the area (a) or (b) of the respective overshoot is acquired. The value obtained from the difference of the areas b minus a is a measurement of the prevailing mass moment of inertia of the possibly loaded washing drum (2) and is further processed as a correction value in the manner described below. The areas (c, d) of the curves I and II lying in the measuring window (D) above the setpoint value US may also be included in the integration.

Following the first measuring window (D) is a dwell time (E) at the setpoint rotational speed US. The dwell time (E) is experimentally determined in such a way that within the dwell time (E), even given the maximum anticipated mass moment of inertia, the setpoint rotational speed US f or the unbalance measurement is reliably reached.

After the dwell time (E), a second measuring window (F) begins. The measuring window (F) comprises a constant time fraction (Fl) and a variable time fraction (F2). In the measuring window (F), the prevailing unbalance of the loaded washing drum (2) is measured. Uneven distribution of the clothes generates an additional torque, as a result of which the actual rotational speed of the drum periodically varies about the setpoint rotational speed US. The amplitude of said variations is directly proportional to the extent of the unbalance but inversely proportional to the mass moment of inertia of the washing drum (2) relative to the axis of rotation. In Fig.2, such unbalance-related variations are illustrated in the measuring window (F). said unbalance variations are superimposed on the curves I and II in the previously described time ranges also. The period of the unbalance variations is much smaller than even the constant time fraction (Fl) of the measuring window (F). The unbalance is determined by integration of the amount of said periodic variations about the setpoint rotational speed.

The duration of the variable time fraction (F2) of the measuring window (F) is adjusted as a function of the correction value determined in the measuring window (D). The variable time fraction (F2) is therefore approximately proportional to the increment of the mass moment of inertia caused by the load. A proportionality factor may be determined experimentally. Extending the measuring window (F) by the variable time fraction (F2), which is dependent on the prevailing mass moment of inertia, corresponds to multiplication of the measuring result obtained within the constant time fraction (F1) by a factor greater than 1.

The measuring result determined in the measuring window (F) therefore also takes into consideration the prevailing mass moment of inertia. Using said measuring result it is possible to adjust the setpoint rotational speed appropriate to the prevailing load and unbalance conditions for a spinning process (G) following to the measuring window (F).

In Fig.3, for various cases, the measured unbalance (M) is plotted against various inserted unbalanced weights (U). The curves I and I I are shown f or the case according to the invention, in which the measuring window (F) has a variable time fraction (F2). The curves III and IV were determined for the case of prior art, in which the measuring window (F) has only a constant time fraction (Fl). Curve I is for a 10 kg load. Curve II is f or no load. Curve III is for no load. Curve IV corresponds to a 10 kg load. It is apparent that, in the case of the curves III and IV according to prior art, the unbalance measuring results (M) diverge increasingly one from the other as the unbalanced weight (U) increases while, on the other hand, the unbalance measuring results (M) of the curves I and II lie much closer to one another as the unbalanced weight (U) increases. This means that the unbalance measuring result (M) in the case of the invention is much less dependent upon the prevailing load than in the case of prior art.

The accuracy of measurement may be improved by synchronizing the start of measurement of the mass moment of inertia with the position of the unbalance. For said purpose it is possible to use the angle of rotation of the washing drum at which the system deviation of the rotational speed changes from a positive to a negative value, or vice versa.

The overall effect achieved by the described correction of the unbalance measurement by measurement of the mass moment of inertia is that it is possible to operate at very high spinning speeds without any risk of excessive loading of the bearings of the washing drum.

Claims

Claims

A method of determining the unbalance of the loaded drum of a washing machine, by measurement after a load distribution phase and prior to a spinning process, wherein after the said load distribution phase, a setpoint rotational speed value for control of the speed of a motor driving the drum is suddenly increased and the resulting actual rotational speed of the drum is compared with the increased setpoint value to derive a correction value related to the load of the drum f or use in the unbalance measurement.
A method according to claim 1, wherein cyclical measurements of the difference between the actual rotational speed of the drum and the said increased setpoint value are summed within a measuring window to derive said correction value.
3. A method according to claim 1 or 2, wherein the setpoint rotational speed suddenly increased after the load distribution phase is lower than a spinning rotational speed.
A method according to any preceding claim, wherein the setpoint rotational speed after the increase is reduced to a compensating rotational speed.
5. A method according to claim 4, wherein the compensating rotational speed is equal to or higher than a clothes application speed whereby the load remains applied against the drum's inner periphery.
A method according to any one of the preceding claims, wherein the measuring window starts, when after the sudden increase of the setpoint rotational speed the 1 -1 actual value of the rotational speed overshoots the setpoint value, and is set at a fixed length of time.
A method according to any one of the preceding claims, characterized in that the duration of the measuring window is maintained f or at least as long as the setpoint rotational speed remains increased.
8. A method according to any one of the preceding claims, wherein after a dwell time which is selected so as to be long enough for the actual rotational speed to reach the setpoint compensating rotational speed, the unbalance measurement is effected in a second measuring window by detecting unbalance-dependent variations in the rotational speed.
9.

A method according to claim 8, wherein the second measuring window comprises a constant time fraction and a variable time fraction and that the variable time fraction is adjusted as a function of the correction value.
10. A method according to any one of the preceding claims, wherein the moment of changing the setpoint rotational speed is synchronized with the angle of rotation of the drum at which the unbalance lies.
11. A method according to claim 10, wherein by detecting a change from a first sense of rotational acceleration to an opposite second sense, the angle of rotation at which the unbalance lies is found.
12. A method as claimed in claim 1, substantially as described herein.
13. A washing machine programmed to carry out the method of any one of claims 1 to 11.