GB2048314A - Improvements In and Relating To Electrical Machines - Google Patents

Abstract

A control system of a washing machine or spin dryer is described, in which operation of the motor 1 driving the washing machine or dryer drum is controlled by a microprocessor 4. To ensure that the door of the drum can not be opened when the motor 1 is operating, a changeover switch 13 is provided, through which either the motor 1 is energized (to rotate the drum) or a door locking means e.g. a solenoid 11, is energized (to permit the door to be opened) but not both: if the locking means 11 is not energized the door can not be opened. Operation of the changeover switch 13 is effected by a bimetallic element carrying a movable contact 13c heated, under the control of the microprocessor 4, when the motor is operating. When the motor is de-energized, the heat is removed and the bimetallic element cools down: the locking means 11 is not energized until the bimetallic element has cooled and the time delay thus introduced ensures that the door can not be opened until the drum has slowed down. <IMAGE>

Description

SPECIFICATION Improvements in and Relating to Electrical Machines The increasing cost of producing mechanical and electro-mechanical control equipment for electrical machinery and the increasing availability of highly sophisticated and versatile electronic control circuits has caused many manufacturers to use electronic control circuits where previously they would have used mechanical or electro-mechanical equipment.

This is so in respect of domestic washing machines where a single microprocessor integrated circuit and its associated interface circuitry can be used to provide the automatic washing sequence, switch the speed of the motor between the "spin" and "wash" speeds, and give several additional features not previously available, e.g. digital clock.

Microprocessors are low voltage, low current devices but the electrical components to be switched in a washing machine run on mains voltage.

The microprocessor is arranged to produce appropriately timed pulses which are fed to triacs connected in series with the respective electrical components. In this way not only can the components be turned on and off but a continuously, variable control is possible by varying the proportion of the mains cycle for which the component is energised. In a washing machine continuous control of heater power and/or motor speed is possible if required.

A washing machine manufacturer, if he wishes to sell his machines internationally must comply with the international safety standards. These provide (inter alia) that the door of a washing machine be locked when the water is above 5000 and its level is above the level of the door aperture and when the drum is revolving at a speed in excess of 60 r.p.m. The usual way of meeting this requirement is to provide a timed delay at the end of the programme after the normal washing sequence. After the period of the delay the door lock is released and the door can be opened. The delay is arranged to be sufficient to ensure that the motor is no longer rotating.

To comply with the international standards, the washing machine must not only be safe in normal operation but it must remain safe under certain fault conditions. In the case of equipment containing electronic components the equipment must remain safe in the event of individual component becoming open circuit or short circuit one at a time.

In a centrally controlled washing machine such as one where every control function is performed by a micro-processor failure of the microprocessor can result in simultaneous energisation of the motor and unlocking of the door and thus cause a potentially dangerous situation.

Similarly short-circuit failure of the motor triac can cause the motor to be driven at full speed even though the microprocessor has run through the washing sequence and unlocked the door. A purely electronic interlock between the motor energising circuit and the door lock energising circuits will not make the machine more safe as a fault in either of the energising circuits may disable the interlock.

It is an object of this invention to produce an electrical machine in which the problems similar to or identical to those described above in respect of a washing machine are at least to some extent alleviated.

According to the present invention there is provided an electrical machine including a motor, electronic circuit means for controlling energisation and de-energisation of the motor, a door affording access, when open, to apparatus driven by the motor, door locking means operable to prevent opening of the door, a changeover switch operable by the electronic circuit and having a first position in which the motor only is energisable and a second position in which the door locking means only is energisable to permit the door to be opened, and a time delay mechanism for preventing energisation of the door locking means until the expiry of a time delay sufficient to allow the apparatus to slow down to a predetermined speed.

The electrical machine may be a washing machine in which case the driven apparatus is the washing machine drum. The door lock may be operated by a solenoid so that when the solenoid is energised the door is unlocked.

The delay mechanism may be thermally operated, for example it may comprise a bimetallic strip.

The delay mechanism may be incorporated in the changeover switch in such manner that the time delay occurs between operation of the switch from its first to its second position. In its first position, the changeover switch may complete a power supply path for the motor whilst in its second position, the switch may complete a power supply path for the solenoid.

The electronic circuit means may include a microprocessor.

A washing machine embodying the invention may also include a water level sensing device arranged also to interrupt the solenoid power supply path when the washing machine drum is full of water so as to prevent the door from being unlocked.

A clothes washing machine embodying the invention will now be described, by way of example only, making reference to the accompanying drawing which is a circuit diagram of part of the control system of a washing machine.

Referring to the drawing, a washing machine has a main motor 1 for rotating a clothes drum (not shown), a main heating element 2 for heating water in the drum and a pump 3 for expelling water from the drum. Energisation of each of these components is controlled by an appropriate control signal from a microprocessor unit 4. The main motor 1 and the pump 3 have respective triacs 5 and 6 connected in series with them. The gate terminal of each of the triacs 5 and 6 is connected to the microprocessor unit 4 via respective control conductors 7 and 8. The heating element 2 is connected in series with the switch of a thermal switch unit 9, the heating element of which is coupled to the microprocessor unit 4 via a control conductor 10.

The washing machine of the drawing also has a door (not shown) affording access to the drum.

This door has an electrically operated lock having a solenoid 1 The door can be opened only when the solenoid 11 is energised. One terminal of the solenoid 11 is connected to the line mains conductor 12 via a thermally-operated changeover switch 13, and a switch 1 a which is user operated. To open the door the switch 1 1 a is operated to close the solenoid circuit and enable the solenoid to release the door lock. A second switch 1 1 b is operated by the door so that switch 1 ib is closed when the door is properly closed, and thus enabling the electrical power to be fed to the microprocessor 4, after the main machine switch has been closed. With the door opened, switch 1 b is opened and there is no power input to the microprocessor.The changeover switch 13 has a first and a second stationary contact 1 3a and 1 3b, a movable contact 1 3c carried by a bimetallic strip, and a heating element 1 3d. When the bimetallic strip is cool the movable contact 1 3c is in a second position where it touches the second stationary contact 136. As the element 1 3d heats the bimetallic strip the movable contact gradually moves to a first position where it touches the first stationary contact 1 3a. Hence there is a time delay between the "break" of one set of contacts and the "make" of the other set.

The other terminal of the solenoid 1 1 is connected to the neutral mains conductor 14 via a pneumatic water level sensing switch 18. The changeover thermal switch 13 is also in series with the conductor which runs between the motor 1 and the line mains conductor 12 The changeover thermal switch 13 interconnects the line mains conductor with the motor 1 or with the solenoid 1 1 but never both.

The heating element of the changeover thermal switch 13 is connected to the microprocessor unit 4 via a control conductor 15. The microprocessor unit 4 also has control conductors 17 to operate water valves and a number of sense inputs designated collectively by reference numeral 16.

These inputs are connected to devices to sense conditions such as water temperature, the positions of the front panel controls and whether the soap drawer is closed, etc..

In operation, and assuming the access door is correctly shut, switch 1 1 b is closed, the microprocessor 4 is powered thereby energising the solenoid 1 1 and allowing the access door to be opened after the switch 1 a has been operated by the user. The machine is then loaded with articles to be washed. The door is then closed and a programme selected and initiated.

The microprocessor unit 4 energises the water valves, the motor 1, heating element 2, and pump 3 in a sequence appropriate to the programme selected. Throughout the programme the microprocessor unit keeps the element in the thermal switch 13 heated via the control conductor 15 5 to connect the line conductor 12 to the motor and not to the door lock solenoid. There is an initial delay due to the heating of the element, but it is of no consequence, as the motor is not required until the drum has filled with water.

The pneumatic water sensing switch 18 prevents the solenoid 11 from unlocking the door by interrupting the neutral mains conductor to the solenoid when the drum is full of water. Another switch 19, also sensing water level is provided which prevents flooding of the machine by switching on the pump 3 if the water level ever exceeds a predetermined maximum.

Thus not only is the door prevented from being opened when the motor is running but also it cannot be opened when the drum is full of water.

The washing machine also remains safe despite failure of the major electronic components. For example suppose the triac 5 becomes short circuit. The drum would rotate at full speed until the end of the programme. At the end of the programme, the microprocessor unit would stop heating the element 1 3d of the thermal changeover switch thus breaking the connection between the motor and the line mains conductor 12. After a delay during which the bimetallic strip which carries the moving contacts in the switch cools down, the connection between the lock solenoid and the line mains conductor is made. In the meantime the motor slows down and stops. Failure of the microprocessor unit similarly cannot create a dangerous condition because the thermal changeover switch ensures a delay between the switching off of the motor and the unlocking of the door.

While the invention is particularly useful in a washing machine employing a microprocessor, it is also applicable to other machines where a similar problem exists. For example, in gaurded factory machinery it is essential that the machinery is not in motion when the guard is opened. The use of a central control unit to control all the functions in such machinery could under failure conditions allow the guard to be opened while the machinery is still in motion. The central control unit need not include a microprocessor.

The invention can also be applied to spin dryers.

Claims (12)

Claims

1. An electrical machine including a motor: electronic circuit means connected to control energization and de-energization of the motor: a door affording access, when open, to apparatus driven by the motor; locking means which prevents opening of the door unless said locking means is energized; a changeover switch operable by the circuit means and having a first position in which the motor is energizable but not the locking means and a second position in which the locking means is energizable but not the motor, and a time delay mechanism operable to prevent energization of the locking means until a predetermined time interval has elapsed following de-energization of the motor, the time interval being sufficient to allow the said apparatus to slow down to a predetermined speed.

2. An electrical machine as claimed in claim 1, in which the delay mechanism is operable, upon operation of the chageover switch out of the first position, to prevent the changeover switch takingup the second position until the said time interval has elapsed.

3. An electrical machine as claimed in claim 1 or claim 2, in which the delay mechanism is thermally-operated.

4. An electrical machine as claimed in claim 3, in which the delay mechanism comprises a thermally-responsive member controlling operation of the changeover switch between the first and second positions, and a heater forthe thermally-responsive member, and in which the electronic circuit means is connected to control energization and de-energization of the heater.

5. An electrical switch as claimed in claim 4, in which, when the thermally-responsive member is cool, the changeover switch is in the second position and, when the thermally-responsive member is hot, the changeover switch is in the first position, and in which the said time interval is the time taken for the thermally-responsive member to cool following de-energization of the heater.

6. An electrical machine as claimed in claim 4 or claim 5, in which the thermally-responsive member is a bimetallic strip.

7. An electrical machine as claimed in any one of the preceding claims, in which locking means includes a solenoid energizable to release the door for opening.

8. An electrical machine as claimed in claim 7, in which the changeover switch, in the first position, prepares a power supply path for the motor and, in the second position, prepares a power supply path for the solenoid.

9. An electrical machine as claimed in any one of the preceding claims, in which the electronic circuit means includes a microprocessor.

10. A washing machine as claimed in any one of the preceding claims, in which the apparatus driven by the motor is the washing machine drum.

1 A washing machine as claimed in claim 10, including a device responsive to the water level in the drum to prevent energization of the locking means when the water level exceeds a predetermined height.

12. An electrical machine substantially as described herein with reference to, and as illustrated by, the accompanying drawing.