GB2073257A - Improvements in or relating to washing machines and spin-driers - Google Patents

Abstract

A washing machine is provided with a moving-magnet accelerometer 6 which is fixed to an end wall of a wash drum assembly and used to detect excessive vibration during the spin cycle. A programme or control circuit 24 responds to the output of the accelerometer 6 and, in the event of an excessive degree of vibration being detected, temporarily de- energises the spin winding 26 of the drive motor and energises its tumble winding 25 so that a distribute cycle takes place during which clothes are redistributed within the wash drum. The accelerometer 6 comprises a magnet 10 and a coil wound on a bobbin 7 relatively movable to generate a signal in the coil dependant upon the degree of vibration. <IMAGE>

Description

SPECIFICATION Improvements in or relating to washing machines and spin-driers The present invention relates to spin-driers and to washing machines having a spin-drying function, in particular but not exclusively to front loading washing machines capable of spin-drying clothes.

During spinning the wet clothes are rotated at high speed within the drum and if they are unevenly distributed, large out-of-balance rotational forces arise which can cause vibrations which may damage the spin-drier or washing machine. Generally, the programmes for washing machines incorporate a "distribute" phase immediately prior to the spin phase, during which the drum of the machine is gradually accelerated to about 60 rpm with the aim of evenly distributing the clothes around the periphery of the drum. However, the desired even distribution of clothes is not always achieved by this technique.

Various method have previously been employed to detect any out-of-balance forces occurring during the spin stage and to correct the distribution of the clothes within the drum by slowing its rotation to return it to the distribute stage so as to provide an opportunity for the washing to re-position itself around the drum before returning to the spin cycle. Typical previous arrangements of this type have used microswitches and similar devices to detect vibration of the drum assembly.

According to the present invention there is provided a washing machine having a washing drum assembly, a drive arrangement operable for wash, distribute and spin operations, control circuitry for controlling the operation of the drive arrangement and an accelerometer comprising a magnet and a coil which are movable relative to one another due to inertia to generate a signal in the coil dependent upon vibration of the drum assembly, the control circuitry being arranged to respond to the output of the coil so that in the event of excessive vibration of the drum assembly, a distribute cycle occurs to redistribute clothes within the drum assembly. Thus if the maximum acceptable degree of vibration is exceeded, the machine re-enters the distribute phase so that the articles in the drum are tumbled and given an opportunity to re-distribute in a more satisfactory manner.

In one embodiment of the present invention we provide a spin-drier or a washing machine having a spin-drying function and comprising a resiliently mounted drum assembly comprising inner and outer co-axial drums, the inner drum being rotatably mounted relative to the outer drum, with the accelerometer arranged to detect vibration of the drum assembly resulting from an out-ofbalance condition of rotation of the inner drum during spinning caused by washing being unevenly distributed around the periphery of the inner drum.

The present invention is described below with reference to its application to a front loading washing machine but it will be appreciated that it can also be applied to top loading washing machines although in such a case, there would be no distribute phase normally preceding the spin~ the distribute phase would only occur following excessive vibration during spinning.

The invention will be further described with reference to the accompanying drawings, in which:~ Figure 1 is a very schematic vertical crosssection of a front loading washing machine embodying the present invention; Figure 2 is a cross-section through the accelerometer of the washing machine of Figure 1; Figure 3 is a diagram in block form of part of vibration sensor circuitry of the machine shown in Figure 1; Figure 4 shows part of the circuitry of an alternative embodiment of the present invention; Figure 5 shows the variation of demanded speed with time in the embodiment of Figure 4; and Figure 6 shows in block form control circuitry which may be used in association with the circuitry of Figure 3.

Figure 1 shows a front loading washing machine having a casing 1 within which is positioned a drum assembly comprising inner and outer co-axial drums 2 and 3, the inner, perforated drum 2 being mounted for rotation relative to the outer drum 3 by means of a shaft 4. The drum assembly is resiliently and dampingly mounted within the casing 1 by conventional means (not shown).

In order to detect an out-of-balance rotational condition of the inner drum 2, an accelerometer 6 is bolted on to the outside of the rear end wall of the outer drum 3.

The accelerometer 6 is shown in more detail in Figure 2 and comprises a bobbin 7 around which is wound a coil, of course, for example, 10,000 turns of suitable fine gauge wire. A magnet 10 is positioned within the bobbin 7 by means of two springs 1 1 and 12, the lower end of the spring 12 being supported by a member 8 fixed to the bobbin 7. The upper spring 1 1 engages with an end wall 13 fixed to the bobbin 7.

In use, vibration caused by damp clothing being unevenly distributed around the periphery of the inner drum 2 during the spin mode of operation is transmitted to the non-rotating outer drum 3 via the shaft 4 and is detected by the accelerometer 6. The inertia of the magnet 10 causes it to move relative to the coil 9 so that its lines of flux cut the turns of the coil 9 and cause a signal to be generated in the coil. As indicated in Figure 3, this signal is amplified by an amplifier 20, rectified by diode 21 and smoothed by a parallel RC combination 22 and then applied to one input of a comparator 23.A reference signal representing the desired maximum degree of vibration of the drum assembly is applied to the other input of comparator 23 and the output of this comparator is delivered to the programmer 24 which controls the energisation of the tumble and spin windings, 25 and 26 respectively, of the drive motor of the washing machine. The time constant of the RC combination 22 is chosen as a compromise between speed of response of the circuitry to an out-of-balance vibrational condition and avoidance of spurious operation.

The programmer 24 may include a conventional cam timer arrangement or may be in integrated circuit form, and controls the sequential operation of the washing machine in accordance with a programme selected by the user and appropriate to the articles to be washed. Prior to the spin phase of operation, the programmer 24 energises the tumble winding 25 of the drive motor so that the drum is gradually accelerated towards 90 rpm. During this time the clothes distribute themselves around the periphery of the drum and any excess water is sprayed out of the drum. The programmer 24 then de-energises the tumble winding 25 and energises the spin winding 26 whereupon the drum accelerates rapidly towards 400 rpm to spin water out of the clothes.

During this period, the programmer 24 is responsive to the output of the accelerometer so that if an unacceptable out-of-balance condition is detected, the spin winding is temporarily deenergised, the tumble winding 25 energised briefly so that the clothes re-distribute themselves within the drum and the spin winding is subsequently re-energised. According to the selected programme, the normal, 400 rpm, spin phase may be followed immediately by a fast, 800 rpm, spin phase; during this time the accelerometer and associated circuitry will be disabled, it being assumed that the clothes will have satisfactorily distributed themselves around the drum either before or during the 400 rpm spin phase.

The programme of 24 is arranged so that it automatically times out the spin phase after the length of time allotted in the selected programme to the spin phase. This avoids the machine repeatedly re-entering the distribute phase in the event that a particular wash load cannot be satisfactorily distributed around the inner drum.

Figure 4 shows part of the circuitry of a front loading washing machine embodying the invention in which a series-wound motor is used in place of the conventional induction motor as the drive motor of the machine. This change is desirable as more precise control of the speed of the drive motor can be achieved. In Figure 4, the desired speed of the motor at any particular instant is represented by the voltage across a capacitor 30, the charging and discharging of which is controlled by a programmed current source and sink 31, this being programmed so that the desired speed of the drive motor as represented by the voltage across capacitor 30 varies in a manner appropriate to the various sequential phases of machine operation during a particular wash programme.The voltage across capacitor 30 is monitored by a phase control circuit 32 which controls the energisation of the drive motor to carry out either closed or open loop control of its speed.

Figure 5 shows one hypothetical programmed variation of the voltage across capacitor 30 during the distribute, normal and fast spin phases of operation. During the normal spin phase, a control input 33 of the programmed current source and sink 31 is enabled, this control input being connected to an output of a comparator corresponding to the comparator 23 of Figure 3. In the event that the comparator output changes state, the capacitor 30 is discharged so that the distribute phase is re-entered.

Figure 6 shows one possible form of the control circuitry which may be incorporated in or associated with the programmer 24 to initiate the 'redistribute' function when the output of comparator 23 in Figure 3 indicates that an outof-balance condition of the drum exists.

Respective zero-crossing detectors 41 and 42 produce pulses as the voltages across the tumble and spin windings 25, 26 across zero and drive pulse generates 43, 44 which produce output pulses which are delayed by appropriate amounts, having regard to the inductances of the coils 25, 26, so that the pulses are timed to coincide with the zero crossovers of the currents through the coils. The outputs of the pulse generators 43, are applied to two inputs of control logic 45, which has complementary outputs to gates 50 and 51.

Control logic 45 comprises a suitable gating arrangement so that only one of the two gates 50 and 51 can produce a "high" output at a time.

The vibration sensing circuitry of Figure 3, generally designated 46 in Figure 6, drives a pulse generator 47 which when activated produces a pulse of a length equal to the desired duration of the redistribute phase. The output of this pulse generator is applied to two comparators 48, 49 where it is compared with a reference voltage V REF. When the pulse generator 47 is not operating i.e. no vibration has been detected, the output of comparator 48 is high and that of comparator 49 is low, whereas while the pulse generator 47 is operating (i.e. in the period following the detection of vibration) the output of 49 is high while that of 48 is low. The outputs of these two comparators are applied to respective inputs of the gates 50, 51 which also receive the complementary outputs of the control logic 45; the gates 50, 51 drive respective pulse generators 52, 53 which in turn drive the gates of triacs respectively associated with the spin winding 26 and the tumble winding 26. The effect of control logic 45 is to ensure that the spin and tumble triacs are not turned on concurrently.

The overall operation of the circuitry of Figure 6 is that in normal operation during a spin cycle, the pulse generator 52 appropriately gates on the spin-winding triac. If and when an out of balance condition is detected by the sensor circuitry 46, the pulse generator 47 starts operating so that the pulse generator 52 is disabled thus turning off the spin winding while the pulse generator 53 is enabled thus energising the tumble winding and thus causing the articles in the drum to redistribute themselves as described above.

Numerous modifications and variations of the above described embodiments will be apparent to those skilled in the art. For example, the sensitivity of the accelerometer could be made to be adjustable by varying the force exerted on the magnet via the springs 11 and 12. This could be achieved, for example, by providing an end cap threadedly engaged with the bobbin which could be screwed down to increase the compressive force of the springs.

The motion of the magnet 10 could be electrically damped by passing an appropriate current through the coil 9.

The speeds quoted for the distribute, spin and fast spin are purely exemplary~obviously other values might be used.

Claims (7)

1. A washing machine having a washing drum assembly, a drive arrangement operable for wash, distribute and spin operations, control circuitry for controlling the operation of the drive arrangement and an accelerometer comprising a magnet and a coil which are movable relative to one another due to inertia to generate a signal in the coil dependent upon vibration of the drum assembly, the control circuitry being arranged to respond to the output of the coil so that in the event of excessive vibration of the drum assembly, a distribute cycle occurs to redistribute clothes within the drum assembly.

2. A machine according to claim 1 wherein the accelerometer is of the moving magnet type.

3. A machine according to claim 2 wherein the accelerometer comprises a housing supporting the coil and containing the magnet.

4. A machine according to any one of the preceding claims wherein the washing drum assembly is resiliently mounted in the machine and comprises inner and outer co-axial drums, the inner drum being rotatably mounted relative to the outer drum and the accelerometer being fixed to the exterior of the outer drum.

5. A machine according to claims 3 and 4 wherein the housing of the accelerometer is secured to an end wall of the outer drum.

6. A machine according to any one of the preceding claims wherein the control circuitry is arranged to produce a signal defining a demanded rotational speed, with the demanded speed progressively increasing during the distribute cycle.

7. A washing machine constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.