GB2087103A

GB2087103A - Electric motor speed controller

Info

Publication number: GB2087103A
Application number: GB8129613A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-10-17
Filing date: 1981-10-01
Publication date: 1982-05-19
Also published as: FR2492608A1; FR2492608B1; GB2087103B; IT8124346A0; IT1139496B; DE3039315C2; DE3039315A1

Abstract

Speed control means for an electric motor (eg a spin dryer motor) (1) which rotates a mass having a changeable centre of gravity, comprises a motor current regulating circuit (2), which controls the supplied motor current in dependence on a predetermined target value and which is arranged in the motor current supply circuit. A sensor is arranged to detect the eccentricity of the mass and, in dependence on the detected eccentricity the target value for the speed of the motor (1) is variable in the regulating circuit (2) by way of a control circuit (4). <IMAGE>

Description

SPECIFICATION Electric motor speed controller The present invention relates to speed control means for a variable speed electric motor for rotationally driving a mass having a changeable centre of gravity.

Speed control means of that kind is usable in conjunction with the current supply of the drive motor of the drum of a washing machine. In a washing machine, the highest rotational speed at which spinning can be carried out without danger to the machine is dependent on the degree of imbalance of the loaded drum. This led to the situation whereby maximum allowable speeds for spinning are limited in such a manner that the machine will not suffer damage when loaded with the maximum permiss- ible quantity of laundry when the laundry is distributed to provide maximum eccentricity of the centre of gravity of loaded drum. This means that the most unfavourable distributed spinning mass is utilised as a criterion for maximum permissible spinning speed, even though this distribution of the laundry is not encountered in the majority of cases. On the other hand, it is also known that high spinning speeds are prerequisite to optimum centrifugal discharge of water from the spinning laundry.

It has become known, particularly in washing machines in which the washing drum is also used for spinning of the washed laundry, to interrupt the spinning operation after a short spinning phase in order to allow the then somewhat loosened laundry the possibility of distributing itself more uniformly within the spinning drum. As a result, the danger of an extreme eccentricity of the centre of gravity of the mass is reduced.

There is accordingly a need for motor speed control means able to determine the maximum speed of an electric motor in such a manner that damage to an appliance due to imbalance of a drum of appliance is avoided, while allowing an optimum rate of spinning of a mass driven by the motor.

According to the present invention there is provided speed control means for a variable speed electric motor for rotationally driving a mass with a changeable centre of gravity, the speed control means comprising detecting means for detecting the degree of any eccentricity of the centre of gravity of such mass relative to the axis of rotation thereof.

determining means for determining an optimum motor speed in dependence on the detected degree of any such eccentricity, and regulating circuit means for regulating the supply of operating current to such motor in dependence on the determined optimum speed.

In speed control means embodying the present invention a current regulating circuit, which controls the supplied motor current in dependence on a predetermined target value, is arranged in the motor current circuit and a sensor is arranged to detect the eccentricity force of the centre of gravity of the mass to be driven by the motor, so that in dependence on the detected measurement result the target value for the speed of the motor Is variable in the regulating circuit through a control circuit.

Such a sensor determines the eccentricity force of the centre of gravity of the mass and feeds it as a control value to the control circuit, which in its turn delivers the target value to the regulating circuit. As a result, the maximum rotational speed of the mass, for example a loaded laundry drum, is optimally selected in correspondence with the eccentricity conditions.

It is particularly advantageous to provide, as the control circuit, a microprocessor circuit programmed according to the relationship between eccentricity force and maximum rotational speed. Through this measurement, a highly accurate and fine matching of the eccentricity force to the permissible maximum speed of the drum can be achieved. If the eccentricity force of the loaded drum exceeds a predetermined value, then the drive of the drum can be interrupted so that the laundry can redistribute itself more favourably within the drum in readiness for a further spinning phase.

Preferably, a sensor detecting the motor current is provided for the measurement of the eccentricity force of the centre of gravity of the mass. The inflowing motor current can thus be utilised as a direct control criterion for the imbalance of the mass to be driven.

In conjunction with this preferred feature, it is expedient to arrange a resistance measurement track, through which the pick-up for the control circuit is applied as sensor, in one of the current paths to the electric motor. A measurement circuit of that kind is of particularly simple and economic construction.

Preferably, a further sensor, delivering a control value analog of the mass set into rotation, is connected to the motor regulating circuit. This sensor makes available a control value for the actual speed of the motor, which control value, interlinked with the control value derived from the determined eccentricity, performs the motor current regulation.

An embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a schematic block circuit diagram of motor speed control means according to the said embodiment, and Fig. 2 is a diagram showing speed/time relationship for control of such motor to drive a laundry drum of a washing machine.

Referring now to the drawings, there is shown in Fig. 1 an electric motor 1 which serves for the drive of the washing/spinning drum of a washing machine which is not described in detail. The motor 1 drives the drum in phases, as illustrated in the diagram of Fig. 2. During a washing and rinsing phase W, the drum is driven at about 50 revolutions per minute alternately in opposite directions. Thereafter, the spinning operation starts. This is initiated through a stimulating spinning phase Sa, during which the drum has a spinning speed of about 85 revolutions per minute. In that case, any imbalance within the drum is measured. If this imbalance exceeds a predetermined permissible value, then the spinning operation is interrupted and restarted so that the laundry can redistribute itself more evenly. If tolerated values of imbalance are not exceeded, then the spinning speed of the drum is increased to about 400 revolutions per minute for a so-called preliminary spinning phase Sb. During this spinning phase Sb, an examination of the imbalance in the drum again takes place, from the measurement result of which is derived the final speed for the spinning phase Sc.

This value usually lies between 600 and 1400 revolutions per minute according to the actual imbalance.

If the imbalance of the entire system changes during the spinning operation in the phase Sc due to reduction of the mass (expulsion of water from the laundry) which would normally lead to an improvement in the conditions, then a further regulation of the speed can be performed.

The speed control of the electric motor 1 is effected through a motor current regulating circuit 2.

This is supplied with an actual speed value which is derived by a speed meter 3 coupled with the electric motor 1. A target speed value is delivered to the regulating circuit 2 from an electronic control circuit 4, for example a microprocessor circuit. This target speed value is determined through the control circuit 4 by detection of the current flowing through the motor 1, namely through a pick-up of the voltage across a resistance 5 in the motor current path.

The voltage picked up across the resistance 5 and thereby the current fed to the motor 1 represents a direct measure of the imbalance of the drum.

In the control circuit 4, a certain permissible speed is associated with the ascertained motor current, representing a measurement value for the imbalance of the spinning drum, from empirical values in the form of a table. This enables the target value to be derived, which is then fed to the regulating circuit 2. Since the current fed to the motor 1 can be determined continuously through the resistance 5, the control circuit 4 is also capable of continuously adapting the target speed value to the obtaining conditions.

Claims

1. Speed control means for a variable speed electric motor for rotationally driving a mass with a changeable centre of gravity, the speed control means comprising detecting means for detecting the degree of any eccentricity of the centre of gravity of such mass relative to the axis of rotation thereof, determining means for determining an optimum motor speed in dependence on the detected degree of any such eccentricity, and regulating circuit means for regulating the supply of operating current to such motor in dependence on the determined optimum speed.

2. Speed control means as claimed in claim 1, the determining means comprising a microprocessor programmed with a predetermined relationship between degrees of eccentricity and maximum motor speeds.

3. Speed control means as claimed in either claim 1 or claim 2, the detecting means comprising a sensor responsive to the motor current.

4. Speed control meants as claimed in claim 3, wherein the sensor comprises resistance means arranged in a current path of the motor.

5. Speed control means as claimed in any one of the preceding claims, comprising means for applying to the regulating circuit means control signals indicative of the mass driven by the motor.

6. Speed control means for a variable speed electric motor for rotationally driving a mass with a changeable centre of gravity, the speed control means being substantially as hereinbefore described with reference to the accompanying drawings.

7. A washing machine comprising a laundry drum, a variable speed electric motor for rotationally driving the drum, and speed control means as claimed in any one of the preceding claims.