US3640098A

US3640098A - Clothes-washing and spin-drying machines

Info

Publication number: US3640098A
Application number: US834686A
Authority: US
Inventors: Martin Harold Eastall
Original assignee: British Domestic Appliances Ltd
Current assignee: British Domestic Appliances Ltd
Priority date: 1968-06-20
Filing date: 1969-06-19
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: GB1266691A; FR2011348A1; CA937659A

Abstract

A clothes-washing and spin-drying machine having a drum rotatable about a nonvertical axis at a relatively slow speed for washing and at a much higher speed for spin drying, including control means for accelerating the driving motor, and hence the drum, relatively slowly through a speed at which the centrifugal force on the clothes within the drum equals the force due to gravity, to produce a uniform distribution of the clothes within the drum, and subsequently more rapidly towards the spin-drying speed.

Description

[45] Feb. 8, 1972 United States Patent Eastall ...68/24 X Mellinger...............................68/24 X [54] CLOTHES-WASHING AND SPIN- 3,055,203

DRYING MACHINES 3,293,889 12/1966 Cobb et al.. [72] Inventor: Martin Harold Eastall, Peterborough, En- 3,346,115 10/1967 gland [73] Assignee: British Domestics Appliances Limited,

Primary Examiner-Marvin A. Champion Assistant Examiner-Robert A. Hafer Peterborough England Anamey-Larson, Taylor and Hinds June19,l969 V V.

Appl. No.: 834,686 g [22 Filed:

ABSTRACT A clothes-washing and spin-drying machine having a drum [30] Foreign Application Priority Data June 20, 1968 Great rotatable about a nonvertical axis at a relatively slow speed for .29,412/68 washing and at a much higher speed for spin drying, including control means for accelerating the driving motor. and hence .68/12 R, 68/24 the drum, relatively slowly through a speed at which the cen- 33/00 trifugal force on the clothes within the drum equals the force .68/12, 24; 318/398, 416 due to gravity, to produce a uniform distribution of the clothes within the drum, and subsequently more rapidly towards the References Cited spin-drying speed.

UNITED STATES PATENTS 3,003,090 10/1961 Neyhouse et 11 Claims, 2 Drawing Figures F Ii. .l... s? s i|.l!|i|.|.| |i|. Ii. 1 88 Tm w N w, a .74 I I I.L e Q Fest Acceleration -Slow Acceleration 1 l l I l I l l m oeqm L226 CLOTHES-WASHING AND SPIN-DRYING MACHINES This invention relates to clothes-washing and spin-drying machines and relates especially though not exclusively to such machines of the type in which clothes can be washed in a drum by means of a tumbling action effected by rotating the drum about a horizontal or at least inclined axis at a relatively low speed in the presence of washing liquid and can subsequently be dried by a spinning operation achieved by rotating the drum about the same axis at a comparatively high speed.

A problem associated with such washing and spin-drying machines is the prevention of excessive out of balance forces on the drum during high-speed spinning clue to clothes accumulating at one point in the drum. With lower spinning speeds the problem can be overcome by incorporating a suspension for the outer container of such a design that out of balance forces are absorbed. However, at higher spinning speeds, which are, in any event, desirable for the successful drying of the clothes, this solution is not practicable and arrangements must be made to ensure that the clothes drum is not excessively out of balance during such high-speed rotation. This may be achieved by making the clothes drum such that it is selfbalancing-but that reduces the possible size and hence the capacity of the drum. Alternatively it can be arranged that whenever the clothes drum is required to rotate at a high spinning speed this operation is preceded by rotation of the drum at a low washing speed in the same direction. This solution is not entirely satisfactory, however, as the speed for washing the clothes must be low enough to cause the clothes to tumble and not cling to the drum wall, i.e., the centrifugal force on the clothes must be less than the gravitational force, and as a result the clothes are not evenly distributed around the drum wall, as is desired, if the drum is to be in a balanced condition for the subsequent high-speed spinning operation.

It is therefore desirable that the drum be rotated at a speed intermediate the tumbling speed and the spinning speed for a short time prior to spinning the drum at high speed in order to ensure that the clothes distribute themselves equally around the internal periphery of the drum in a balanced manner. This has been achieved, for example, by providing a drive motor for the drum capable of energization at three speeds, these speeds being selected by a control arrangement for the machine such that, on termination of a tumbling action provided by rotation of the motor at its lowest speed the spin action provided by the motor rotating at its highest speed is precededvby a short period of rotation at an intermediate speed where the weight of the clothes is just balanced by the centrifugal force on the clothes at this speed, the desired result being that the clothes cease to tumble within the drum and contact the inner peripheral wall of the drum in a balanced manner. The drive motor is then accelerated to its highest (spinning) speed. A problem inherent in this arrangement is that there is no certainty that the clothes will distribute themselves in a balanced manner in the drum during the period of rotation at the intermediate speed, as the comparatively rapid acceleration of the drum from tumbling speed to this intermediate speed tends to fling the clothes abruptly outwards to the wall of the drum in the pattern of distribution which they adopt for the previous tumbling operation (which is very rarely uniform). As a result of this the acceleration to spinning speed results in large out of balance forces on the drum.

The object of the present invention is to reduce the difficulty indicated in the preceding paragraph.

According to the present invention there is provided a clothes-washing and spin-drying machine or a spin-drying machine, having a clothes drum rotatable about a nonvertical axis, and an electric motor for rotating the drum both at a relatively slow speed and also at a much higher speed for spin drying, wherein there is provided control means for the motor capable of accelerating the motor relatively slowly through a critical speed at which the centrifugal force on the clothes within the drum equals the force-due to gravity, and sub-- uequently accelerating the motor more rapidly until said higher speed is attained.

Such an arrangement results in a more uniform distribution of the clothes within the drum before the latter attains full spin-drying speed, thereby reducing the possibility of excessive out of balance forces being created, and as a result particularly high drum speeds are rendered possible.

In a preferred form of the invention design for a combined washing and spin-drying machine a common DC series electric motor is provided for driving the clothes drum both for washing and for spin drying, and the control means includes a motor speed control circuit having means for generating a series of electric pulses of which the conduction angle or mark to space ratio determines the power supply to, the motor, and said control means includes time-dependent means for varying said conduction angle or mark to space ratio in such a way as to produce said different accelerations.

Conveniently a controlled semiconductor rectifier device such as a thyristor is provided in series with the electric motor with respect to input terminals which are arranged to be connected to an alternating current supply, electric pulses being arranged to be applied to the gate of the device in appropriate half-cycles of the alternating current supply to fire the device and cause driving power to be supplied to the motor.

The control means in such a case is conveniently formed with solid state control elements, in particular transistors, so connected and arranged as to control the conduction angle or mark-to-space ratio of the pulses applied to the motor from the semiconductor rectifier device.

The control means preferably also includes feedback means which normally tend to maintain the motor rotating with a selected constant slow speed, said time-dependent means being arranged to override the feedback means when a spin drying operation is initiated. i

It will be understood that the invention also includes within its scope control units for controlling the speed of an electric motor driving the clothes drum of a clothes-washing and spindrying machine or a spin-drying machine in accordance with the invention. I

In order that the present invention may be clearly understood and readily carried into effect it will now be described with reference to the accompanying drawings in which:

FIG. 1 illustrates diagrammatically the program control circuit for a combined washing and spin-drying machine according to one example of the invention, and

FIG. 2 is a graph representing the relationship of the rotational speed with time for the clothes drum during the period of controlled acceleration from washing speed to spinning speed.

The machine itself is not illustrated in the figures but typically it can comprise a drum mounted on a shaft in bearings so as to be rotatable on a horizontal axis within a liquid containing cylinder which is suspended by means of cooperating springs and dampers within an outer cabinet. A DC electric drive motor of the series-type is secured to the liquid containing cylinder and is drivingly connected by means of a V or multi-V belt-drive system to a pulley wheel secured to the drum shaft outside the liquid cylinder. The system is such thatthe drum is rotated at a speed below the motor speed and in a fixed relationship of say l:l0 or thereabout. Liquid may be supplied to the cylinder through an electromagnetically actuated inlet valve and removed by an electric motor-driven pump. Liquid in the cylinder may be heated by an electric sheathed wire heating element mounted in a lower wall of the cylinder, the heating element being disposed within the cylinder.

in operation of the washing machine its various functions are sequentially controlled by a program controller comprising a synchronous electric timer motor actuating, via a stepping linkage, a number of cams and hence switches which control the supply of electrical power to the various parts of the machine in sequence so as to cause a particular program of operations to be performed on clothes placed in the drum. and a solid state switching circuit, also controlled by the timer motor for the drive motor of the machine, which controls the speed and acceleration of the drum motor.

With reference now to FIG. 1, which shows such a circuit, the drum of the washing machine (not shown) is rotatably driven by a DC electric series motor 1. The machine is connected to a source of AC supply through a main isolating switch (not shown) the motor being supplied through a thyristor 2 and a low value resistor 3. A diode 4 connected in parallel with the motor acts as a flywheel diode in known manner to provide a smoothing effect on the motor current supply, and a series combination of a resistor 38 and capacitor 39 is also connected across the motor to suppress commutator sparking.

The thyristor 2 is fired by a pulse-producing circuit (indicated by chain-dotted lines A) whose output (to the thyristor) is controlled by a negative feedback circuit 8,, sensitive to rising motor speed, a positive feedback circuit 8,, sensitive to rising motor current and a time dependent circuit C, these control circuits acting to vary the pulses produced by circuit A and hence the pulses of DC power supplied to the motor from the thyristor. The circuits A, B,, B and C are supplied with low voltage DC by means of a voltage dropping resistance 61, a diode 40, a smoothing capacitor 41 and a zener diode 17.

The time dependent circuit C is switched into operation, when required, by means of a switch 5 actuated by a cam in a program controller driven by a synchronous motor 6. The motor 6 also determines the condition of other cam actuated switches 7 and 8 in the electrical supply to a heater 9 and a pump motor 10.

A further cam actuated switch 29 is arranged to reverse position at regular intervals throughout the washing action in order to periodically reverse the drive motor and hence the wash drum in a manner to be described.

In operation the program controller selects, by sequential operation of the switches, one of several operations to suit the clothes being processed. A complete washing and drying cycle may, for example, comprise the following steps:

Prewash, spin, wash, spin, rinse and spin.

During the prewash, wash and rinse functions the drum is rotated at low speeds (say 50 r.p.m.) in one direction for a short period of time (say seconds) and then rotated in the opposite direction for an equal period of time. Since the speed of rotation during these operations is low, the centrifugal force on the clothes is not sufficient to hold them in contact with the wall of the drum as they are carried round and as a result they tumble within the drum. The spin action is achieved by rotating the drum at a high speed (say 1,000 r.p.m.) in one direction only, the centrifugal force on the clothes being sufficiently large to retain them in contact with the wall of the drum and to extract any contained liquid from them.

The low speed of rotation of the drum is determined by the pulse-producing circuit A and the feedback circuits B, and B The time dependent circuit C is, at this time, switched off by the switch 5, which is closed so as to provide a biassing voltage zero with respect to its emitter to the base of the transistor 11 within the time dependent circuit, so as to .switch it off, the circuit then being isolated from the pulse producing circuit A.

Thus, during a washing (or rinsing) operation, the drive motor speed is determined entirely by circuits A, B, and B which are set so as to maintain the motor speed at substantially 500 rpm, corresponding to a drum speed of 50 rpm, irrespective of normal variations in load on the motor.

The pulse producing circuit A comprises, essentially a capacitor 12, a complementary pair of transistors 13 and 14, a further transistor 19 and a differentiating circuit comprising resistor 43 and a further capacitor 44. The circuit A is supplied with a pulse of approximately rectangular form during each positive half cycle of the AC supply, the negative halfcycle being suppressed by a zener diode 17. During each said positive half-cycle the capacitor 12 becomes charged via diode 45 at a rate dependent upon the voltage applied to the base of the transistor 19 and the value of the resistor 42, and

governed by the differentiating circuit, the transistor 19 being conductive at this time, due to the voltage at its emitter being below that at its base, this base voltage being normally made up of an adjustable reference voltage derived from a potentiometer network P and modified by the two feedback circuits B, and B as will subsequently be described.

When the voltage across the capacitor 12 becomes large enough, this will cause the transistor 13 to conduct. The transistor 13 then supplies base current to transistor 14 turning it on so as to supply more base current to transistor 13. This cumulative action leads to rapid saturation of these transistors with the result that the lower end of capacitor 12 is effectively connected to the H.T. rail via transistors 13 and 14, resulting in a voltage pulse which is now positive with respect to the H.T. rail being applied to the gate of the thyristor 2. Diode 45 now prevents capacitor 12 from short circuiting directly through transistors 13 and 14 and as a result the thyristor switches on, supplying the motor with a pulse of DC power.

Control of the conduction angle or mark to space ratio for the motor current waveform is effected by varying the rate at which capacitor 12 charges which is in turn affected by varying the voltage at the base of the transistor 19. As this voltage rises the rate of charge of the capacitor 12 increases, with the result that the firing pulse to the gate of the thyristor is applied earlier in the half-cycle with the result that the conduction angle of the supply to the drive motor is increased giving a faster motor speed.

Similarly if the rate of the charge of the capacitor 12 decreases as a result of the base voltage of the transistor 19 being reduced the firing pulse to the gate of the thyristor is applied later in the half-cycle causing the conduction angle of the supply to the drive motor being decreased and reducing the motor speed.

As previously pointed out the voltage at the base of the transistor 19 is controlled by the feedback circuits B, and B The negative feedback circuit B, comprises a tachogenerator 18 (mechanically connected to the driving motor 1) which applies a voltage, decreasing with increasing motor speed, to the base of a transistor 19. As the voltage applied to the base of transistor 19 decreases the power supplied to the motor and hence the motor speed decreases.

The positive feedback circuit B comprises resistors 3, 20 and 21 and diode 46, the arrangement being such that as the motor load, and hence the current required for the motor, increases, the positive feedback voltage applied to the base of the transistor 19 also increases so that the power input to the motor increases to maintain the motor speed.

The feedback circuits B, and B and the value of the reference voltage are chosen so as to maintain the motor speed at approximately 500 r.p.m. at this time, i.e., with circuit C isolated.

At the end of a washing (or rinsing) period the timer motor 6 closes the switch 16 so as to energize the electric motor driven pump 23 to remove all the free washing liquid from the machine. Simultaneously the timer opens switch 5 which controls the time dependent circuit C. When switch 5 is opened a capacitor 24 commences to discharge through a high value adjustable resistor 25. As a result the voltage at the base of the transistor 11 increases slowly over a period of time (which can be determined by adjustment of the high value resistor 25). The transistor 11 is then switched on and thereafter the current through the transistor (from collector to emitter) increases slowly thus increasing the control voltage applied at the base of transistor 19 so that the motor speed, and hence the drum speed, slowly increases, as shown in FIG. 2.

During this slow acceleration from washing speed the centrifugal force on the clothes gradually increases until it exceeds the gravitational force on the clothes. This gradual increase in speed has the effect of slowly moving the clothes outward to contact the wall of the drum in a balanced manner.

As a transistor 11 becomes more conductive the voltage at the base of a further transistor 27 rises this causing the transistor 27 to start conducting and the voltage at the base of the transistor 19 to rise rapidly to a maximum determined by the transistor 27 reaching a stable conducting condition.

As this base current further increases the transistor 19 turns on harder more rapidly, the conduction angle of the rectified supply to the motor similarly increasing rapidly to its maximum, and the motor is supplied with maximum power and rapidly accelerates the clothes drum to high speed thereby spinning the clothes as shown by F in FIG. 2; the point of conduction of the transistor 27 is represented in FIG. 2 by T. The capacitor and resistor values can readily be selected, in dependence upon the transistors employed, to obtain the appropriate time intervals. A capacitor 60 primarily prevents the voltage at the base of thetransistor 19 from changing too rapidly and giving an excessively fast change in motor speed and also serves to absorb any transient surges. For terminating the spinning operation (or washing operation) the timer closes a switch S thus reducing the voltage at the base of the transistor 19 to a value such that it is switches off, gate pulses no longer being applied to the thyristor 2.

In some cases for example when spin drying delicate materials a shorter spinning time may be required. This is achieved by closure of switch SS, causing a capacitor 31 to charge up via a resistor 50 and diode 51 and this takes place before transistor 27 starts to conduct, i.e., during the slow acceleration period-see FIG. 2. When transistor 27 breaks over the voltage at its collector decreases and diode 51 is now reverse biassed thus preventing further charge to capacitor 31.

Capacitor 31 now discharges via variable resistor 32 over a period of time (e.g., l5 seconds) preset by the variable resistor 32.

As capacitor 31 discharges the voltage at the junction of diode 51 capacitor 31 and variable resistor 32 decreases and a point is reached when transistor 33 turns off. The voltage at the collector of transistor 33 increases and since this is connected to the base of the transistor 13 in the pulse producing circuit A the latter will be prevented from firing and hence will prevent the application of a firing pulse to the thyristor 2, thus terminating the spinning operation.

Conveniently a further normally open switch 30 may be provided associated with a part of the suspension of the liquidcontaining cylinder. The switch 30 is so positioned that in the event of the drum becoming out of balance during the spinning operation (or in the event of the drum being loaded with a single heavy article, such as a blanket, which may require a considerable time to distribute itself correctly within the drum) the excessive movement of the drum on high-speed rotation momentarily closes the switch.

The out-of-balance switch 30 is arranged to turn on a transistor 34 having its collector connected to the base of the transistor 11, permitting the capacitor 24 to charge up and reducing the base voltage of the transistor 11 which cuts off, also cutting off the transistor 27 and thereby reduces the voltage at the base of the transistor 19. This lowers the motor speed to a value appreciably below the critical speed. The capacitor 53 will start to charge (having been discharged previously by 30) when the switch 30 is opened and the transistor 34 will cut off, recommencing the controlled acceleration from slow speed, to effect a redistribution of the clothes up towards spinning speed in the manner already described, this operation being repeated if this is necessary until the clothes are distributed in a manner which avoids excessive out of balance. Capacitor 52 and associated circuitry also provides a soft start facility when the motor is initially energized.

It will also be appreciated that if for any reason the motor is switched off in any running condition by interrupting the main power supply the capacitors 24, 26, will discharge completely. On restoring the supply with the switch 5 open the capacitor 24 will ensure that a gradually increasing voltage will be applied to the base of the transistor 11 causing the emitter voltage to increase slowly and the controlled acceleration will thus recommence from the slow-speed condition as in the manner above described, thus avoiding restarting of the motor at full power which would inflict a severe shock load on the machine transmission. Diode 53 provides the discharge path for capacitor 52 in the event of the supply being interrupted as described. 7

The control arrangement conveniently includes safety means for switching off the motor 1 in the event of the motor temperature rising to an excessively high value. Such a safety means may, for example, incorporate (not shown) a negative temperature coefficient of resistance resistor (an N.T.C.R. resistor) associated with the motor stator windings such that if the motor temperature rises unduly the current supply to the motor 1 is reduced, an excessively high rise cutting off the motor current completely. A further N.T.C.R. resistor 35 connected to the emitter of transistor 19 is included as a means of providing temperature stability for the electronics circuit in known manner. A

Similarly a further safety means is provided to limit any excessive rise in motor current. This incorporates a further transistor 36 which is normally conducting but which in the event of an excessive rise in motor current, resulting in a corresponding rise in the voltage across the resistor 3, cuts off thereby lowering the voltage at the base of the transistor 19, with the result that the thyristor firing angle is modified thereby limiting the motor current to a safe value. The value at motor current reached before the transistor 36 switches off is set by an adjustable resistor 37.

Although the invention has been described in relation to a combined washing and spin-drying machine it can also be applied to a machine designed solely for the spin drying of clothes in which the clothes drum is arranged to start at a very low speed and then accelerated to a much higher spin drying speed.

I claim:

1. A clothes-washing and spin-drying machine or a spin-drying machine including:

a. a clothes drum arranged torotate about an nonvertical axis;

b. a DC electric motor for rotating the clothes drum at a relatively slow speed and also at a substantially higher speed for spin drying;

c. a controlled semiconductor device, connected in series with the electric motor with respect to input terminals which are arranged to be connected to a source of alternating current for controlling said motor; and

d. a motor speed control circuit for controlling the operation of the semiconductor device such that, for carrying out a spin-drying operation, the motor is caused to accelerate relatively slowly through a critical speed at which the centrifugal force on the clothes within the drum equals the force due to gravity and is subsequently caused to accelerate more rapidly until said higher speed is attained.

2. A machine according to claim 1, wherein the motor speed control circuit includes means for generating a series of electric pulses, the duration of which governs the power supply to the motor, and means for varying the duration of said pulses such as to produce said different accelerations.

3. A machine according to claim 2, wherein the electric pulses are arranged to be applied to a control electrode of the semiconductor device in appropriate alternate half-cycles of the alternating current supply so as to fire the device, whereby to cause driving power to be supplied to the motor.

4. A machine according to claim 3, wherein the motor speed control circuit includes feedback means which normally tends to maintain the motor rotating with a selected constant slow speed, and time-dependent means for overriding the feedback means when a spin-drying operation is initiated.

5. A machine according to claim 4, wherein the feedback means incorporates a first feedback circuit deriving from a tachometer coupled to the motor a first feedback signal varying with increasing motor speed and applied to said motor speed control circuit in such a sense as to reduce the motor speed, and a second feedback circuit deriving from the motor current a second feedback signal varying with increasing motor speed and applied to the motor speed control circuit in such a sense as to increase the motor speed, the feedback signals being so related as to stabilize the motor at said selected slow speed.

6. A machine according to claim including means for supplying a reference voltage to the motor speed control circuit to cause it to generate said series of pulses for driving the motor, the feedback signals being arranged to modify said reference voltage in the appropriate sense.

7. A machine according to claim 6, wherein the motor speed control circuit includes a capacitor, means for charging the capacitor during appropriate alternate half cycles of the supply voltage at a rate dependent upon the feedback signals, and means responsive to the charge on the capacitor for generating a said electric pulse when the charge on the capacitor reaches a predetermined value.

8. A machine according to claim 7 including a pair of transistors normally nonconducting one of which transistors is connected so as to become conducting when the charge on the capacitor reaches said predetermined value, and being so interconnected with the other by regenerative feedback connections that rapid saturation of both transistors takes place resulting in the generation of a said electric pulse.

9. A machine according to claim 6, wherein the time-dependent means is arranged to modify the reference voltage applied to the motor speed control circuit in such a sense as to produce a relative slow acceleration of the motor through said critical speed, and subsequently a relative rapid acceleration of the motor up to said higher speed.

10. A machine according to claim 9 wherein the time-dependent circuit includes a first transistor, capacitor means controlling the conductivity of the transistor so as to produce a relatively slow variation thereof following the actuation of the time dependent circuit, and means responsive to the conductivity of the transistor for modifying the reference voltage in such a sense as to produce said relative slow acceleration of the motor, and a second transistor connected so as to be switched on after the conductivity of the first transistor has reached a predetermined value and to rapidly attain a condition of maximum conduction, and means responsive to the conduction of said second transistor for further modifying the reference voltage in such a sense as to produce said relative rapid acceleration of the motor.

11. A machine according to claim 1 including means responsive to an out-of-balance condition of the drum following the acceleration of the motor past the critical speed, and the motor speed control circuit being responsive to the operation of the out-of-balance means in the event of an excessive out-of-balance condition to reduce the motor speed to a value significantly below the critical speed, and to repeat the relatively slow and relatively rapid acceleration of the motor towards said higher speed.

Claims

1. A clothes-washing and spin-drying machine or a spin-drying machine including: a. a clothes drum arranged to rotate about a nonvertical axis; b. a DC electric motor for rotating the clothes drum at a relatively slow speed and also at a substantially higher speed for spin drying; c. a controlled semiconductor device, connected in series with the electric motor with respect to input terminals which are arranged to be connected to a source of alternating current, for controlling said motor; and d. a motor speed control circuit for controlling the operation of the semiconductor device such that, for carrying out a spindrying operation, the motor is caused to accelerate relatively slowly through a critical speed at which the centrifugal force on the clothes within the drum equals the force due to gravity and is subsequently caused to accelerate more rapidly until said higher speed is attained.

6. A machine according to claim 5 including means for supplying a reference voltage to the motor speed control circuit to cause it to generate said series of pulses for driving the motor, the feedback signals being arranged to modify said reference voltage in the appropriate sense.