GB2146664A

GB2146664A - Vibration detector for washing machine

Info

Publication number: GB2146664A
Application number: GB08325153A
Authority: GB
Inventors: Stephen John Newton
Original assignee: Thorn EMI Domestic Appliances Ltd
Current assignee: Thorn EMI Domestic Appliances Ltd
Priority date: 1983-09-20
Filing date: 1983-09-20
Publication date: 1985-04-24
Also published as: GB8325153D0

Abstract

A vibration sensing device (11) for use in a washing machine (9) or other similar domestic appliance, which device (11) is caused to oscillate when the machine (9) is subjected to vibrational movement caused by an unevenly-distributed load, for example. The device (11) includes a piezoelectric crystal (1), which generates a voltage signal indicative of the amplitude of the vibrational movement. If the monitored amplitude exceeds a predetermined threshold value, thereby indicating that the machine (9) is being subjected to excessive vibrational movement, a microprocessor (13) causes the machine (9) to go into a re-distribute mode to attempt to re-distribute the uneven load of the machine. <IMAGE>

Description

SPECIFICATION A vibration sensing device This invention relates to a vibration sensing device and in particular, though not exclusively, to such a device for use in a washing machine or other similar domestic appliances.

Known devices of this kind, such as accelerometers which may consist of a solenoid having a resiliently mounted magnetic core which is caused to oscillate in accordance with detected vibrations, may be incorporated within a washing machine, for example, so as to detect excessive vibrations during a spin cycle of the wash programme. Such vibrations may be caused by an unevenly distributed load within the drum of the machine and a signal generated by the device may be used to stop the spin cycle of the machine, if such vibrations are detected.

It is an object of the present invention to provide a vibration sensing device for use in a washing machine or other similar domestic appliance, which is simpler, less expensive to manufacture and more robust than those devices known heretofore.

According to the invention there is provided a vibration sensing device for use in a washing machine or other similar domestic appliance comprising piezoelectric means for sensing vibrational movement of said appliance and for generating a voltage signal indicative of the amplitude of said movement, said appliance including means for causing operation of the appliance to be inhibited when said voltage signal indicates that said amplitude has exceeded a threshold value, for initiating re-distribution of a load disposed therewithin, and for subsequently re-commencing said inhibited operation.

The piezoelectric means is preferably a piezoelectric crystal, such as a ceramic disc, which may be disposed at, or adjacent to, a suitable location within the appliance which is sensitive to the vibrational movement during operation thereof.

The piezoelectric crystal is preferably rigidly mounted at one side thereof, whilst an opposing side is free to flex and is preferably weighted so that movement of the free side produces a relatively predictable response to the amplitude of the vibrational movement of the appliance.

The invention will now be further described by way of example only with reference to the accompanying drawings wherein: Figure 1 shows a side view of one embodiment of the present invention, Figure 2 shows a view in the direction of arrow A and shown in Figure 1, and Figure 3 shows a schematic view of the embodiment shown in Figures 1 and 2 incorporated within a washing machine.

Figure 1 shows a vibration sensing device consisting of a piezoelectric crystal 1, which may be, for example, a piezoelectric disc, which is mounted on a metallic membrane 1 a, which in turn is mounted to a vertical chassis face, shown in part at 3, by a suitable mounting clamp 4, so that side 2 of the crystal 1 is held rigid. Opposing side 5 of the piezoelectric crystal 1 is however free to move and is weighted by a suitable weight 6, which is mounted on metallic membrane 1 a by a second clamp 14. Wires 7 and 8 are electrically connected respectively to opposing faces of the crystal 1, via metallic membrane la and clamp 4.

Grommet 15 provides a resilient limit stop against walls 16 and 17 to prevent overstress in the piezoelectric crystal 1.

It may therefore be envisaged that, if the device is subjected to vibrational movement, the free side 5 would be caused to oscillate, or flex, in the directions shown by arrows B, in response to the vibrational movement, the amplitude of the oscillations, or flexures, being indicative of the amplitude of the vibrational movement.

An electrical polarisation would thus be established within the crystal, thereby generating a voltage signal indicative of the amplitude of the vibrational movement, this signal being subsequently transferred from the crystal 1, via wires 7 and 8, to a microprocessor, which is referred to hereinafter.

Figure 2, which is a view in the direction of arrow A shown in Figure 1, indicates the preferred circular shape of the piezoelectric crystal 1 and the supporting metallic membrane la.

Figure 3 shows a schematic view of a washing machine 9, within which the device is preferably employed, although it may be utilised in other similar domestic appliances, such as tumble dryers or spin dryers, for example.

The washing machine 9 includes a drum 10, which, during use of the machine, accommodates a load of clothing, or other items, to be washed. The device, in accordance with the present invention, as shown at 11, is mounted to a chassis member 12 of the machine 9.

Wires 7 and 8 are connected to a microprocessor 13, which controls the operation of the machine 9.

During operation of the machine, particularly during a spin cycle of the wash programme therefor, the machine 9 is generally subjected to a certain amount of vibrational movement which is consequently imparted to the device 11, due to the device being mounted at a location within the machine 9 which is sensitive to vibrational movement.

The device, which is thus caused to oscillate, generates a voltage signal indicative of the amplitude of the vibrational movement of the machine 9, this signal being passed to the microprocessor 13, via wires 7 and 8. The device 11, in conjunction with the microprocessor 13, therefore monitors the amplitude of the vibrational movement throughout the whole or any part of the wash programme of the machine 9.

The amplitude of the vibrational movement is most likely to increase substantially during the spin cycle of the programme, particularly if the load within the drum is unevenly distributed therewithin.

Consequently, should the monitored amplitude of the vibrational movement exceed a predetermined threshold value, thereby indicating that the machine is being subjected to excessive vibrational movement, the microprocessor 13 will cause the drum 10 to stop spinning and will initiate a re-distribute mode of the programme, so as to attempt to re-distribute the load within the drum 10. Once this mode has been completed, the microprocessor 13 will recommence the spinning cycle of the programme. If, during the spinning cycle so recommenced, excessive vibration is sensed again, the procedure of inhibition of the spin cycle, re-distribution of clothing and recommencement of the spin cycle is repeated.

The weight 6 is provided on the free side 5, so as to cause the side 5 to perform more definite oscillations, which are more accurately indicative of the amplitude of the vibrational movement than they would be if side 5 was not so weighted.

The piezoelectric crystal 1 may be mounted at any suitable location within the machine 9 where it is susceptible to the vibrational movement of the machine.

As an alternative to the utilisation of a microprocessorto control the operation of the washing machine, a motor control circuit may be employed.

In accordance with the present invention, the piezoelectric crystal 1 may be of any suitable shape or configuration, for example rectangular or a cantilevershape, rather than circular.

As an alternative to the implementation of a piezoelectric ceramic disc, a naturally-occurring piezoelectric crystal, such as quartz, or a synthetical ly-produced piezoelectric material, such as polyviny lidene fluoride (PVDF), may be utilised in accordance with the present invention.

Claims

1. A vibration sensing device for use in a washing machine or other similar domestic ap pliance comprising piezoelectric means for sensing vibrational movement of said appliance and for generating a voltage signal indicative of the amplitude of said movement, said appliance including means for causing operation of the appliance to be inhibited when said voltage signal indicates that said amplitude has exceeded a threshold value, for initiating a re-distribution of a load disposed therewithin and for subsequently re-commencing said inhibited operation.

2. A vibration sensing device as claimed in claim 1 wherein said piezoelectric means comprises a piezoelectric crystal.

3. Avibration sensing device as claimed in claim 2 wherein said crystal is a ceramic disc.

4. Avibration sensing device as claimed in any one of claims 1, 2 or 3 wherein said piezoelectric means is disposed at, or adjacent to, a location within the appliance which is sensitive to said vibrational movement.

5. Avibration sensing device as claimed in any preceding claim wherein said piezoelectric means is mounted adjacent one side thereof, an opposing side thereof being substantially free to flex.

6. A vibration sensing device as claimed in claim 5 wherein said opposing side is weighted.

7. Avibration sensing device substantially as herein described with reference to the accompany ing drawings.

8. A washing machine or other similar domestic appliance having a vibration sensing device as claimed in any preceding claim incorporated therein.