GB2124662A - Controlling spin-dry drum speed according to drum imbalance - Google Patents

Abstract

A washing machine or spin dryer has a spin-dry drum (I, Figure 1), a motor (5) for rotating the drum, a control system for controlling the speed of rotation of the motor, and sensing means (15, 16, Figure 2) responsive to the degree of imbalance of the drum during rotation thereof and operable to cause the control system to select a motor speed for rotating the drum (1) that is determined by the degree of imbalance. The sensing means may sense stress imposed on a component by imbalance, or sense changes in motor speed. <IMAGE>

Description

SPECIFICATION Improvements in or relating to washing machines and spin dryers This invention relates to washing machines that include a spin sequence as part of a washing program and to spin dryers.

In order to limit the loading of certain critical components of such equipment to ensure that the components have an acceptable working life, it is usual to select the speed of rotation at which spinning takes place to a value ensuring that working life. However, high spin speeds are desirable because at such speeds a higher proportion of moisture can be extracted than is the case with presently used speeds.

It is possible to use high spin speeds by increasing the ability of the components to withstand such higher forces as result from the higher spin speeds but this is expensive and it limits the extent to which it is possible to standardise components for a range of equipment.

The loading of the components is determined in part by the degree of "out-of-balance" of the rotating parts and it has been suggested that means be incorporated which respond to an excessive out-of-balance and stop the rotation of the drum. Excessive in this context is that degree of out-balance which will cause unacceptable movement of the machine or internal parts of the machine during the early part of the acceleration to spin speed, and which might cause damage either to itself or adjacent objects, and is often alarming to the user. The user may then rearrange the articles in the drum with a view to achieving better distribution before again trying to spin.

It has also been suggested that instead of stopping rotation, a reversion to a tumble speed is effected in an attempt to achieve a better distribution of articles to be spun after which spinning is attempted again.

It has also been proposed to employ a speed control system for the motor driving the drum which, during the acceleration of the drum to the spin speed provides a slight pause in the rate of acceleration at what is called "distribute" speed to allow the contents of the drum to distribute themselves in a reasonably balanced formation inside the drum. The "distribute" speed is a speed above the normal "wash-tumble" speed and just below the "sticking" speed at which articles in the drum are held, by centrifugal force, against the inner surface of the drum and cannot move relatively to that surface.With such a control, it is found that in a high proportion of cases, spinning will take place with only a small out-of-balance although in a small proportion of cases relatively large out-of-balance loads will still persist, and the maximum spin speed has always to be limited so that on these occasions the forces created are kept within the limits that the machine can withstand.

In all the proposals just mentioned, the maximum spin speed is preset and is calculated, on the basis of the maximum out-of-balance load that will occur in practice even though this may happen very infrequently.

It is an object of the present invention to overcome the disadvantage just mentioned.

According to the present invention, a washing machine or spin dryer having a container for spinning articles to extract moisture therefrom has a control system for controlling the speed of rotation of a motor driving the container, and sensing means responsive to the degree of out-of-balance of the container during rotation thereof and operable to cause the control system to select a motor speed for carrying out a spinning of the container that is determined by the degree of out-of-balance detected by the sensing device.

Sensing the degree of out-of-balance may be effected by sensing the stress occurring at one or more selected locations in the mechanical structure of the machine. Preferably, sensing is effected by one or more transducers located where they can respond to stresses experienced by critical components of the mechanical structure. For example if the critical components are the bearings that support the shaft of the rotatable drum of the machine, then the transducer or transducers are so located that they respond to loads on the bearings or loads on components which are stressed proportionally to the bearings by the out-of-balance condition in the rotating drum.

The transducer may be of the strain gauge or pressure type.

The transducer or transducers are arranged to provide a control signal that is used to determine the maximum spin speed that the drum will be allowed to reach. For example, the acceleration of the motor to reach the spin speed may be controlled by an integrated circuit which may be that known as the TDA 101 so and in this case, the control signal after suitable processing in a micro-processor for example will result in a control voltage applied to the speed control input of the integrated circuit.

Sensing the degree of out-of-balance by sensing the stress in some component may conveniently be done at a sensing speed that is above distribute speed and above any critical resonant frequency of the tub on the suspension system, and well below any final spin speed. This may be at a drum speed of around 200-300 r.p.m. The drum would be accelerated as fast as is practicable from distribute speed to this speed so as to get through the resonant speed or speeds as fast as possible and the speed would then be held at sensing speed giving time for the measurements to be taken. The drum would then be accelerated in the normal way to the final spin speed which would be determined by the degree of out-of-balance sensed.

Sensing of the degree of out-of-balance of the load in the drum, in the case of a washing machine, may also take place during the so-called "distribute" phase that occurs as the drum is accelerated to the spin speed, the speed of rotation during that phase being below the critical speed. At a speed below the critical speed and above the speed at which the clothes are stuck in the drum, the rotating out-of-balance load will cause the drum rotation to speed up as the load falls and to slow down as the load is lifted, and this speed variation will have a relationship to the degree of out-of-balance. If there is no "distribute" phase, it will be necessary to provide for some arbitrary period of constant speed during which sensing can take place.

The concept is suitable for use in washing machines and spin dryers in which the drum is rotated by a series wound motor whose speed is controlled by a control system receiving signals from a tacho-generator driven by the motor. Although the control system ordinarily incorporates a speed control function that ensures a constant speed of drum rotation irrespective of the load in the drum, the speed control function must be so arranged that it will not react to the small, and relatively rapidly occurring, speed changes resulting from an out-of-balance condition of the drum. Part of the normal speed control function is concerned with the maintenance of a constant rotational speed irrespective of the load on the motor to ensure, for example, that the load of articles within the drum does not affect the motor speed provided that the load is within allowed limits.The rate at which the speed control responds to a change in load is known as the "stiffness" of the control. A "stiff" control is one which reacts very quickly to a change in load to maintain a constant speed and it is necessary that the stiffness of the control is carefully designed so as not to react during one drum revolution so quickly as to eliminate speed variation and yet still perform its necessary function of maintaining a sufficiently constant speed in relation to variation of load in the drum.

The concept just described is especially applicable to washing machines and spin dryers in which the container or drum is mounted for rotation about a horizontal axis. In such form, it is found that at speeds below the critical speed of rotation of the drum, i.e. at speeds below that equivalent to the resonant frequency of the resilient system supporting the tub of the machine, variations in motor speed occur during each revolution of the drum because for part of the revolution any out-of-balance is being lifted whereas during another part, that load is falling. Thus, the drum will tend to turn more slowly while the out-of-balance load is being lifted and more quickly when that load is falling.

Such variations in speed are detected, for example by a tacho-generator, to produce a control signal that is used to select a spin speed appropriate to the degree of out-of-balance detected.

The washing machine or the spin dryer may be microprocessor controlled in which case the microprocessor will be programmed to select the appropriate spin speed. For example, the microprocessor may be programmed to average over several drum revolutions the difference between maximum drum speed and minimum drum speed. For particular bands of difference, predetermined maximum spin speeds will have been programmed into the microprocessor which will select the appropriate spin speed in accordance with those bands.

The concept is also suitable for washing machines and spin dryers in which permanent magnet d.c.

motors are used to drive the drum. In this case, out-of-balance can be detected by sensing variations during each revolution of the motor current.

Both sensing concepts are suitable for embodiments in washing machines with a drum rotatable about a horizontal or near horizontal axis loaded either from the top or the front, but the concept where a calculation is made based on imposed stresses at a particular low drum spin speed above the critical speed of the suspension system, or where the spin speed acceleration is stopped when a predetermined stress is achieved for a particular spin speed, are also applicable to washing machines and spin dryers where the drum is rotatable about a vertical axis.

By way of example only, embodiments of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure I is a vertical section in diagrammatic explanatory form of a washing machine, Figure 2 is a view partly in section of a part of a washing machine, Figure 3 is an explanatory flow chart, Figure 4 shows part of a control circuit in block schematic form, Figure 5 is another explanatory flow chart, and Figures 6 and 7 show parts of other control circuits in block schematic form.

Figure 1 is a vertical section in diagrammatic explanatory form of a domestic washing machine to which the invention may be applied.

The washing machine is of the horizontal axis, front loading type and comprises a drum 1 mounted within a tub 2. The tub 2 is resiliently mounted or suspended or both on a damped spring system so that it is relatively free to orbit about the horizontal rotational axis of the drum 1 in relation to the base 3 and casing 4 of the machine.

Mounted upon the tub 2 is a drive motor 5 which rotates the drum about its horizontal axis via a driving belt 6 and a pulley 7 fixed to a drive shaft 8 upon which the drum 1 is mounted and which constitutes the horizontal rotational axis of the drum 1. The shaft 8 supports the drum 1 in cantilever fashion and is rotatably supported in ball or roller bearings 9, 10 spaced along the drive shaft 8 and fitted in a rigid housing which constitutes or is secured to the rear wall 11 of the tub 2.

The machine shown in Figure 1 is of the front loading type, the drum 1 and tub 2 being open at their front ends as shown. A conventional flexible sealing collar 12 secures the front of the tub 2 to the casing 4 which has a front loading aperture fitted with a door 13.

As is well known, to carry out a washing operation, the drum 1 is rotated slowly within the tub 2 which is partially filled with water for washing, the drum being rotated at higher speeds for extracting water from articles within the drum, the extracted water being removed from the tub 2 by a pump (not shown).

During spinning, any loads imposed by the centrifugal force created by an out-of-balance condition of the load within the drum 1 are transferred to, and the reaction force is provided by, the drum mass via the bearings 9, 10. It will be seen that the loads on either or both of the bearings will be directly proportional to the extent of the out-of-balance of the drum mass, and that the stresses produced in the drum rear wall 8, the bearings and their housings will be proportional to those loads.

Such stresses can be gauged by one or more transducers appropriately located, the condition of the transducers indicating the extent of the stresses.

Figure 2 shows, on an enlarged scale, part of the tub 2 including the rear wall 11 thereof. At the centre of the wall is formed a housing 14forthe bearings 9 and 10 carrying the shaft 8. Figure 2 also shows part of the pulley.

Two possible transducer locations are shown in Figure 2. The first of these locations is indicated at 15 and here the transducer is responsive to stresses set up in the rear wall 11 of the tub 2. A second suitable location is indicated at 16 and in this location the transducer is responsive to stressing of the bearing 9.

The type of transducer employed will obviously depend upon the nature of the stress occurring at the transducer location. Thus, a strain gauge transducer will be employed at location 15 but a pressure type transducer, for example a piezo-electric transducer, will be employed at location 16.

The transducer location selected may depend upon location of the component whose acceptable working life represents the critical factor determining the maximum spin speed. If that factor is the acceptable working life of the bearings 9 and 10, then location 16 is suitable.

The output of a piezo-electric transducer at location 16 is used to determine the maximum spin speed to be permitted during the spinning of a load in the drum. The output of the tranducer is used to control the maximum spin speed by means of a speed control associated with the motor 5.

For example, Table 1 shows, for a typical washing machine the relationship between the out-of-balance load at mid-drum position, speed variation produced by the particular out-of-balance loads at a nominal drum speed of 84 r.p.m., the load sensed by the transducer at location 16, the maximum permissible load sensed by the transducer at a particular maximum calculated spin speed, and the maximum permitted spin speed allowed for particular out-of-balance loads.

TABLE 1 Out-of Speed Load Maximum Maximum balance variation sensed permissible permissible load at at 84 rpm on front load sensed spin speed mid drum nominal bearing on front position {max-min) at 300 rpm bearing at full spin speed 0.145 kg 0-4 rpm 13.3 kg 332.5 kg 1500 0.190 kg 4-5 rpm 17.5 kg 380.0 kg 1400 0.256 kg 5-6 rpm 23.5 kg 441.0 kg 1300 0.500kg 5-10 rpm 46.0kg 618.0kg 1100 0.899 kg 10-15 rpm 82.7 kg 829.0 kg 950 1.787 kg 15-26 rpm 164.0 kg 1166.0 kg 800 A flow chart depicting the sequence followed during a washing program involving a spinning cycle at the end thereof is shown in Figure 3.

At the end of the washing sequence, i.e. when articles in the drum have been washed and are ready for spinning, there is preliminary agitation of the articles at a drum speed of 50 rpm, after which the drum speed is increased to the distribute speed of 84 rpm to attempt to distribute the articles in a reasonably balanced orientation within the drum after which the drum speed is increased to 300 rpm. At that speed, the transducer in location 16 is energised or otherwise brought into use and the stress on bearing 9 is assessed.

Depending upon that assessment, the maximum spin speed that the drum will be accelerated to is determined.

It will be observed that, if the transducer indicates an out-of-balance load greater than that allowed at the lowest permitted spin speed, the drum speed is dropped to the "agitate" speed and a second attempt is made to distribute the articles within the drum in a more balanced manner. A third attempt may be made but if this is unsuccessful, the program is terminated and possibly a visual warning energised to indicate to a user that a manual re-distribution of the articles is required.

In one particular embodiment a series wound electric motor is used to rotate the drum and the acceleration of the motor up to spin speed is controlled by an integrated circuit of the type known as the TDA 1085A. The transducers are employed to provide a control signal that is applied to the speed control input of the TDA 1085A.

Figure 4 shows in block schematic form part of a control circuit suitable for an embodiment of the invention employing transducers as just described.

The control circuit employs a microprocessor components of which are indicated in the drawing by functional blocks. A motor driving the washing machine drum is shown as block 17 connected in series with a current flow control device for example a triac shown as block 18 across mains supply terminals L, N.

Driven by motor 17 is a tacho-generator (not shown) the amplitude or frequency of whose output is proportional to the speed of the motor. The tacho-generator output is applied via an interface unit 19 to a comparator 20. Interface unit 19 converts the analogue output of the tacho-generator into a form, for example a digital form, suitable for the comparator 20.

Analogue signals from the load transducer are applied to a load sensor interface represented by block 21.

The transducer is responsive to bearing loads or tub loads as described above. Interface 21 converts the analogue signals into, for example, digital form for presentation to a load comparator represented by block 22 and in which the output of interface 21 is compared with a series of bands of loads from which is determined the variation from a minimum or a maximum spin speed that is required to allow the drum to be spun at a safe speed. A digitally encoded signal representing the variation is applied by comparator 22 to unit 23 to which is also fed an input representing "requested speed" which is preferably the maximum spin speed for the drum, shown in Table 1 as 1500 r.p.m., but which could be the minimum drum spin speed of 80 r.p.m.In unit 23, the requested speed signal is modified to produce an output signal, representing the permitted spin speed as determined by the sensed load, is applied to comparator 20.

As a result of the comparison in comparator 20 of the actual motor speed and the permitted spin speed, output signals are produced by comparator 20 which determine the positioning of the gate firing angle of the triac 18 and hence the motor speed.

The output signals from comparator 20 are applied to unit 24 together with a reference signal indicating instants of zero mains voltage to ensure that the traic 18 is turned on at instants of zero mains voltage. Triac 18 is actuated from unit 24 via a gate firing circuit indicated by block 25.

The "requested speed" input may be derived directlyfrom a controller that progresses the washing machinehrough the stages of a selected wash program or from an electronic control circuit performing the same function and forming part of the microprocessor.

As has been indicated above, the degree of out-of-balance can also be sensed by detecting changes in the rotational speed of the motor at speeds below the critical speed.

Figure 5 is a flow chart setting out the steps involved in a system for sensing changes in rotational speed or speed swings.

As the chart indicates speed swings above a predetermined value cause the machine to revert to "agitate" speed and repeat the sensing steps. After an unsuccessful third attempt the washing program is terminated and, if desirable, a warning signal is given.

The steps indicated in Figure 5 will be carried out by a microprocessor which may be programmed to average the speed swing over one or several drum revolutions and to select, in accordance with the averaged value a maximum spin speed appropriate to that value.

Figure 6 shows in block schematic form part of a control circuit suitable for an embodiment of the invention employing the sensing of changes in rotational speed of the motor, i.e. speed swings, these being detected by a tacho-generator driven by the motor.

In Figure 6, functional units identical with certain of those in Figure 5 have been given identical reference numbers and will not be described in detail.

The digitally encoded representations of actual motor speed appearing on the output of interface 19 are applied to unit 26 in which speed swing is determined. From the determined speed swing can be obtained a signal representing the variation from the "required speed" that is required to allow the drum to be spun at a safe speed.

The speed swing may be obtained by checking the actual motor speed at selected time intervals during a single revolution of the motor or at intervals during several revolutions and then averaging the values obtained. A comparison is then made to determine within which of a number of different bands of speed swing the averaged value lies, that band then determining the variation from the "requested speed" that is needed.

Figure 7 shows in block schematic form part of a control circuit suitable for an embodiment of the invention employing the detection of speed swings by sensing changes in motor current. Again, functional components of Figure 7 identical with those of Figure 4 have the same reference numerals and will not be described in detail.

In series connection with the motor 17 is a motor current detector represented by block 27. The detector 27 may comprise a resister in series with the motor and means for detecting and encoding preferably in digital form changes in potential drop across the resister.

The encoded changes are then passed to unit 26 which functions in the manner of unit 26 in Figure 6.

Claims (20)

1. A washing machine or spin dryer having a drum for spinning articles to extract moisture therefrom and a motor for rotating the drum and also having a control system for controlling the speed of rotation of the motor, and sensing means responsive to the degree of imbalance of the drum during rotation thereof and operable to cause the control system to select a motor speed for rotating the drum to spin the articles that is determined by the degree of imbalance detected by the sensing device.

2. A washing machine or spin dryer as claimed in claim 1 in which the sensing means comprises a transducer responsive to stress imposed on a component of the machine or dryer by imbalance of the container.

3. A washing machine or spin dryer as claimed in claim 2 in which the transducer is so positioned that it responds to stress imposed on bearings supporting the drum for rotation.

4. A washing machine or spin dryer as claimed in claim 2 in which the transducer is so positioned that it responds to stress imposed on a component of a container in which the drum is mounted for rotation.

5. A washing machine or spin dryer as claimed in any one of claims 1-4 in which imbalance sensing is effected by detecting changes in motor speed.

6. A washing machine or spin dryer as claimed in claim Sin which changes in motor speed are detected by monitoring the output of a tacho-generator driven by the motor.

7. A washing machine as claimed in claim Sin which changes in motor speed are detected by monitoring changes in motor current.

8. A washing machine or spin dryer as claimed in any one of the preceding claims in which imbalance sensing is effected at a drum rotational speed greater than distribute speed but well below the minimum drum speed at which spinning can take place.

9. A washing machine or spin dryer as claimed in claim 8 in which the drum speed at which sensing is effected is also greater than the drum rotational speed correponding with the critical resonant frequency of a suspension of the machine or dryer.

10. A washing machine or spin dryer as claimed in claim 8 or 9 in which the drum speed at which sensing is effected is within the range of from 200-300 r.p.m.

11. A washing machine or spin dryer as claimed in any one of claims 1-7 in which imbalance sensing is effected at a drum speed substantially equal to the distribute speed.

12. Awashing machine or spin dryer as claimed in claim 11 in which the drum speed is about 84 r.p.m.

13. Awashing machine or spin dryer as claimed in any one of claims 8-12 in which the control system is adapted to hold the drum at sensing speed for a short period of time while sensing is effected.

14. A washing machine or spin dryer as claimed in any one of the preceding claims in which the control system includes a microprocessor programmed to select a spin speed determined by the sensed degree of out of balance.

15. Awashing machine or spin dryer as claimed in claim 14 in which the microprocessor is further programmed to average the sensed degree of imbalance over at least one drum revolution, the selected spin speed being determined by the averaged value of the imbalance.

16. Awashing machine or spin dryer as claimed in claim 15 in which the microprocessor is also programmed to determine the maximum and minimum drum speeds during the several revolutions, to average over the several drum revolutions the difference between the determined maximum and minimum drum speeds, and to ascertain within which one of several different bands of speed difference the average speed difference lies, the final spin speed being selected in dependence upon the ascertained band.

17. A washing machine or spin dryer as claimed in any one of the preceding claims in which the control system is adapted to reduce the drum speed to a preselected low value if the sensed degree of imbalance exceeds a preset value.

18. A washing machine or spin dryer as claimed in claim 17 in which the control system is also adapted to increase the drum speed from the preselected low value to a higher speed at which a further sensing of the degree of imbalance is carried out and in the event that the sensed degree does not exceed the preset value, the speed of rotation of the drum is increased to the determined spin speed.

19. Awashing machine or spin dryer as claimed in claim 17 in which the control system is also adapted to cycle the machine or dryer through a number of speed sequences in which the drum speed is reverted to the low value and is then increased to a higher speed at which the degree of imbalance is sensed, and, in the event that, in each seence, the sensed degree of imbalance exceeds the preset value, the drum is then brought to a standstill, but, in the event that in a sequence the sensed degree of imbalance is below the preset value, the drum speed is not reverted but is increased to the determined spin speed.

20. A washing machine substantially as herein described with reference to and as illustrated by Figures 1,2 and 3 or Figure 4 of the accompanying drawings.