GB2273791A

GB2273791A - A control system for a washing machine

Info

Publication number: GB2273791A
Application number: GB9324975A
Authority: GB
Inventors: Pont Paolo Da
Original assignee: Elbi International SpA
Current assignee: Elbi International SpA
Priority date: 1992-12-24
Filing date: 1993-12-06
Publication date: 1994-06-29
Anticipated expiration: 2013-12-06
Also published as: FR2699939A1; GB2273791B; ES2074959B1; GB9324975D0; IT1258133B; ITTO921043A1; DE4344343A1; ES2074959R; FR2699939B1; ITTO921043A0; ES2074959A2

Description

2273791

DESCRIPTION

The present invention relates to a control system for a washing machine having a main alternating-current electric motor associated with the washing drum and comprising a rotor and a stator.

More specifically, the invention relates to a control system of the type comprising:

an electric speed sensor associated with the electric motor, a programmer (a timer)-with rotary cams for cooperating with associated electrical contacts to define one or more operating programmes or cycles of the machine, a switching device including two movable contacts which are controlled by the programmer and are connected to the rotor of the main motor, and which are intended, for predetermined periods of time, to adopt first and second working positions in which they cooperate, respectively, with first and second fixed contacts which are connected to supply terminals in order to supply the rotor of the main motor with a current flowing in one direction and in the opposite direction, respectively, in order correspondingly to rotate the motor in one sense and in the opposite sense, respectively, and control and operating means comprising a (first) Triac or the like arranged in series with the stator winding of the main motor between the supply terminals, and an electronic unit which is connected to the speed sensor, to contacts of the programmer, and to the control 2 terminal of the Triac, the arrangement being such that, when the Triac is conductive and the movable contacts are in one of the working positions, a current flows through the rotor and stator windings of the main motor which are connected between the supply terminals in series with each other and with the Triac.

A control system of this type is shown schematically in Figure 1 of the appended drawings.

In this drawing, the rotor and the stator winding of the main electric motor of the machine are indicated R and S, respectively. The rotor R is disposed between two movable contacts A and B, the positions of which are controlled in known manner by a programmer (a timer) T with rotary cams. The programmer generally comprises a plurality of cams, the profiles of which cooperate with associated electrical contacts in order to define one or more operating programmes or cycles of the washing-machine. In particular, the programmer T is arranged to cause the movable contacts A and B to adopt two different working positions in which they cooperate with respective fixed contacts al, bl and a2 and b2, respectively. The fixed contacts al, b2 are connected to a first supply terminal 3 and the fixed contacts a2, bl are connected each other and to the stator winding S. The control electrode (gate) of a Triac Tl interposed between this winding and a second supply terminal 4 is connected to an electronic control unit MP. A tachometric dynamo TA associated with the motor of the machine and a plurality of contacts Cl, C2... Cn controlled by the programmer T are also connected to the unit MP.

In order to cause the main motor of the machine to rotate in one sense or in the opposite sense in operation, the programmer T positions the movable contacts A and B in engagement with the f ixed contacts al, bl or a2, b2, respectively. The rotor R and the stator S are in series with each other in both of these working positions of the movable contacts (which will be defined below as position 1 and position 2, respectively). If the unit MP then makes the Triac Tl conductive, a current can flow through the rotor and the stator of the main motor of the machine, causing it to operate. The motor rotates in one sense or in the opposite sense according to whether the movable contacts A and B are in position 1 or in position 2.

In the system according to the prior art described above, in order to ensure that the movable contacts A and B do not switch from one working position to the t no voltW is applied tba-v--b, tte switdihg on and off of the Triac Tl is synchronised by (at least) one further contact C which is controlled by the programmer T and connected to the unit MP.

The cams of the programmer T which control the movable contacts A, B and the contact C are formed in a manner such that the switchings of the contacts are correlated in time in the manner which will now be described with reference to Figure 2.

The upper and lower graphs of Figure 2 show, by way of example, the positions of the movable contacts A, B and" of the synchronising contact C, respectively, as functions of the time t given on the abscissa. As can be seen, the cam which controls the synchronising contact C is formed in a manner such that the contact C closes with a delay tl after the contacts A, B have been positioned in the position 1 or 2, and it opens an interval t2 in advance of the departure of the movable contacts A, B from the working position 1 or 2.

The unit MP is arranged to switch the Triac Tl on and off in synchronism with the closure and opening of the contact C. This ensures that the contacts A, B are never switched from one working position to the other whilst a current is flowing through them.

The known solution described above has the disadvantage that it requires one or more synchronising contacts and respective control cams in the programmer T. Accordingly, an object of the present invention is to provide a control system for a washing machine of the type indicated above, in which synchronising contacts and respective control cams are not necessary.

Claims

These and other objects are achieved, according to the invention, by means

of a control system, the main characteristics of which are defined in Claim 1.

Further characteristics and advantages of the control system according to the invention will become clear from the detailed description which follows with reference to the appended drawings andded purely by way of non-limiting example.

In the drawings:

Figure 1, which has already been described, shows a control system of the prior art, Figure 2, which has also been described already, shows examples of curves of the positions of the switching contacts and of a synchronising contact included in the system of Figure 1, as functions of the time t given on the abscissa, Figure 3 is a diagram of a control system according to the invention, Figure 4 is a diagram of a further control system according to the invention, Figure 5 is a series of graphs showing examples of curves of the positions adopted by the movable contacts of the switching device, and of the current correspondingly made to flow through the main motor of a machine having a control system according to the invention, as functions of the time t given on the abscissa, and Figure 6 is a series of graphs showing further examples of curves of the positions of the movable contacts of the switching device and of the current correspondingly made to flow through the motor as functions of the time t given on the abscissa in a variant of the control system according to the invention.

Figure 3 shows an embodiment of the system a ccording to the invention. In this drawing, parts and elements already described with reference to Figure 1 have again been given the same alphanumeric symbols.

A first substantial difference between the system according to the invention and the system of Figure 1 lies in the absence of the synchronising contact C and of the respective control cam in the programmer T. Instead, the system according to the invention 6 comprises means for supplying the electronic unit MP (formed, for example, by a microprocessor) with an electrical signal indicative of the passage of current through the main electric motor of the machine.

The base of a transistor, indicated TR, (of the npn type in the solution illustrated) is connected to the stator winding S by means of a resistor RO. A diode D, a capacitor CO, and a further resistor R10 are connected between the base and the emitter of TR. The collector of TR is connected to earth by means of a resistor Rll and its emitter is connected to a negative direct-current voltage supply VS.

In operation, when the movable contacts A, B are in the working position 1 or 2, a voltage (rectified by the diode D and smoothed by the capacitor CO) is applied to the base of TR so as to render the transistor conductive, thus enabling a current of a low intensity insufficient to operate the motor R, S to pass through the motor.

When the transistor TR becomes conductive, there is a change in the potential of its collector, which is connected to an input of the electronic unit MPt and thus supplies the unit with a signal indicative of the fact that the movable contacts A, B are (or are not) in one of the working positions.

In the alternative embodiment shown in Figure 4, a. resistor Rl is connected in a manner such that, in operation, a fraction of the current flowing through the motor passes through it. This resistor is connected to the unit MP.

7 In the system of Figure 4, the microprocessor unit MP is arranged to apply a signal to the Triac Tl to make it moderately conductive whilst the movable contacts A and B are switching between the working positions 1 and 2, so that the current which can flow through it is smaller than the minimum current which can operate the main motor of the machine. This low-intensity current (for example, of 1 mA) flows through the main motor only after the movable contacts A and B have actually reached a working position, as shown in the lower graph of Figure 5 which, moreover, also applies to the embodiment of Figure 3.

Thus, with reference to Figure 5 if, for example, the contacts A, B reach the position 1 at the time ti 01 starting from this time, a current of very low intensity starts to flow through the main motor of the machine.

The unit MP detects the passage of this small current by means of the collector of TR in the' version of Figure 3, and by means of Rl in the version of Figure 4.

The unit MP checks that this small current is flowing for a short period of predetermined duration A 1 (Fig. 5) at the end of which it makes the Triac Tl conductive to an extent such that the current flowing in the main motor of the machine can cause it to rotate. The time interval d!l 1 is predetermined so as to ensure that, when it ends, the movable contacts A, B are stably in the working position.

The Triac T1 is then switched off by the unit MP, after a subsequent time interval, indicated 21 2 in Figure 8 5, of predetermined duration such that the Triac is cut off before the subsequent switching of the positions of the contacts A, B. The Triac T1 is controlled in exactly the same manner in order to reach the new working position of the movable contacts A, B at the time indicated t2 in Figure 4.

with the system according to the invention, it is not therefore necessary to use synchronising contacts and respective programmer control cams.

The cams of the programmer T are rotated, in known manner, by a suitable electric motor indicated M in Figures 3 and 4. This motor is arranged in series with a second Triac T2 between the supply terminals 3 and 4. The control electrode of the Triac T2 is connected to an output of the unit MP.

This unit may conveniently be programmed to stop the motor M of -the programmer for predetermined time intervals whilst the movable contacts A, B are in one of the working positions, at certain stages of an operating cycle or programme of the washing machine defined by certain conditions of the contacts Cl... Cn.

The ability to stop the programmer is useful, for example, to allow for the so-called testing of thebalancing of the load in the washing drum, in particular, in order to determine the manner in which the spinning stages are carried out.

The unit MP of the control systems described above'with 9 reference to Figures 3 and 4 may also be arranged to recognise (by the methods which will be described below) a short-circuit condition to the Triac Tl or a breakdown of the Triac such that it is permanently conductive. When the unit MP recognises such a condition, it activates the motor M of the programmer by means of the Triac T2 so as to move the contacts A and B to a position comprised between the positions l- and 2 and then to keep them there. This prevents the main motor of the machine from being activated until the short-circuit to the Triac T1 is eliminated or the Triac is replaced.

The unit MP may recognise a short-circuit condition to or within the Triac Tl essentially by two methods.

In a first method, the unit MP detects that the current flowing through the main motor of the machine during an interval 1 of Figure 5 is not the minimum current expected.

In a second method, the short-circuit condition may be recognised by the fact that the signal supplied to the unit MP by the tachometric dynamo TA is indicative of a speed of rotation of the motor of the machine which differs appreciably from the expected speed which is determined, at each stage of the operating cycle of the machine, by the state of one or more contacts C connected to the unit MP.

In the system according to the invention, it is also possible, by measures which will now be described, to arrange for the unit MP to be able to determine in which of the two working positions the movable contacts A, B are disposed and hence in which sense the main motor of the machine is rotating.

The working positions of the contacts A, B can generally be distinguished by the shaping andlor angular spacing of the cam profiles of the programmer which control the positioning of the movable contacts in the working positions, and by the analysis, by the unit MP, of some characteristics of the signal correspondingly supplied by the sensor means which detect the passage of current through the main motor of the machine.

In a first embodiment, the cam profiles which control the contacts A, B are formed in a manner such that switching from the position 1 to the position 2 takes place within a period of time which differs from the period required to switch from the position 2 to the position 1, as shown by the upper graph of Figure 5 in which these periods are indicated I1 and 12. In the embodiment of Figure 5, the switching period 11 is longer than the switching period 12.

The unit MP is correspondingly arranged to measure the intervals D1 and D2 during which there is no current flowing through the main motor of the machine. If the last interval during which current was not conducted was equal to II, the unit MP assumes that the movable contacts A, B are in the position 2.

A knowledge of the working positions of the contacts A, B and hence of the current sense of rotation of the main motor of the machine is useful, for example, in order to prevent a spinning (rapid rotation) stage from being activated when the main motor of the machine is not rotating in the sense envisaged for this operation.

11 A further method of distinguishing the working positions of the contacts A, B consists of controlling the contacts by means of different respective timer cam profiles. The cam profile associated with one of the contacts, for example the contact B, is formed in a manner such that. its portions corresponding to one of the two working positions (for example, the position 2) are of a shape such as to cause the contact to move away from that working position briefly during the period in which a small current is flowing through the main motor of the machine so as to cause a short break in the small current. Figure 6 shows the corresponding graphs of the positions of the contacts A and B and the corresponding curve of the current I flowing, detected by the unit MP. In the central graph of this drawing, an interval of duration d can be observed, in which, whilst the contact B is in the working position 2, it is moved momentarily away from that position and the current I detected by the unit MP is correspondingly interrupted.

The unit MP can thus distinguish the working position (position 2) of the movable contacts A, B by detecting this short break in the current.

The sense of rotation of the main Motor of the washing machine can also be distinguished by other methods generally based on the creation of anomalies which can be detected by the unit MP whilst the contacts A, B are in one of the two working positions, the anomalies. generally being brought about by alterations of the shapes of the cam profiles which control the movable contacts.

With reference to Figures 3 and 4, the data which reach 12 the microprocessor MP by means of the contacts Cl Cn of the programmer may conveniently be coded in binary form. This enables a large amount of data or a large number of commands to be transmitted to the unit MP by a limited number of programmer contacts.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the present invention.

4 13 CLAIMS 1. A control system for a washing machine having a main alternating- current electric motor associated with the washing drum and comprising a rotor (R) and a stator (S),. the system comprising:

an electric speed sensor (TA) associated with the electric motor (R, S), a programmer (a timer) (T) with rotary cams for cooperating with associated electrical contacts (A, B; Cl... Cn) to define one or more operating programmes or cycles of the machine, a switching device (A, B; al, a2, bl, b2) including two movable contacts (A, B) which are controlled by the programmer (T, M) and are connected to the rotor (R) of the main motor, and which are intended, for predetermined periods of time, to adopt first and second working positions (1; 2) in which they cooperate, respectively, with first and second fixed contacts (al, bl; a2, b2) which are connected to supply terminals (3, 4) in order to supply the rotor (R) of the main motor with a current flowing in one direction and in the opposite direction, respectively, in order to rotate the motor in one sense and in the opposite sense, respectively, and control and operating means (UC) comprising a (first)' Triac (T1) arranged in series with the stator winding (S) of the main motor between the supply terminals (3, 4) and an electronic unit (MP) which is connected to the speed sensor (TA), to contacts (cl...cn) of the programmer (T, M), and to the control terminal of the 14 Triac (T1), the arrangement being such that, when the Triac (T1) is conductive and the movable contacts (A, B) are in one of the working positions, a current (1) flows through the stator and rotor windings (R, S) of the main motor which are connected between the supply terminals (3, 4), in series with each other and with the Triac (T1), the system being characterized in that it also comprises current- conduction ct neans (TR, D; T1) vkdch are connected to the motor (R, S) and can enable a current of a low intensity, lower than the minimum current which -can operate the motor (R, S), to flow through the motor (R, S) when the movable contacts (A, B) are in one of the working positions (1, 2), and sensor means (TR; R1) which can supply the electronic unit (MP) with an electrical signal indicative of the passage of current through the motor (R, S), and in that the electronic unit (MP) is arranged for:

detecting, by means of the signal supplied by the sensor means (TR, R1), that the movable contacts (A, B) have reached one of the working positions, and. applying to the Triac (T1) a signal to make it conductive so as to operate the motor for a predetermined period of time ( A 2), and then cutting off the Triac (T1) before the subsequent switching of the movable contacts (A, B).

2. A system according to Claim 1, characterized in that the said ammntcaxiiaum ct me= comprise--- a transistor (TR) of which the base is connected to the motor (R, S) by means of a rectifier (D) and the collector-emitter is path is connected between earth and a direct-current voltage supply (V S), so that the transistor can become conductive when the small current is flowing through the motor (R, S); an output terminal of the transistor (TR), the potential of which can vary when the transistor (TR) becomes conductive, being connected to an input of the electronic unit (MP).

3. A system according to Claim 1, characterized in that tbe- said ammt-=xlntlan cu=t meam -canpruw the (first) Triac (T1) and in that the electronic unit (MP) is arranged to apply a signal to the Triac (T1), whilst the movable contacts (A, B) are switching between the working positions (1, 2), to make the Triac (R1) moderately conductive so that the current (I) which can flow through it is smaller than the minimum current which can operate the motor (R, S).

4. A system according to Claim 3, characterized in that the electronic unit (MP) is arranged to keep the Triac (T1) moderately conductive for a predetermined period of time ( 4 1) after the signal supplied by the sensor means (R1) indicates that the current (1) has started to flow.

5. A system according to one of the preceding claims, characterized in that the cam profiles of the programmer (T, M) which control the positioning of the movable contacts (A, B) in the first and second working positions (1; 2), respectively, are shaped andlor angularly spaced in a manner such that the electronic unit (MP) can determine in which working position the movable contacts (A, B) are disposed, and hence the sense of rotation of the motor, by analyzing characteristics of the signal supplied by the sensor 16 means (TR, R1).

6. A system according to Claim 5, characterized in that the cam profiles which control the movable contacts (A, B) of the switching device are formed in a manner such that the switching of the movable contacts from the first working position to the second takes place within a period of time (11) which differs from the period of time (12) required to switch from the second position to the first, and in that the electronic unit (MP) is arranged to distinguish the position of the movable contacts (A, B) by measuring the period of time (I1, 12) during which current is not conducted through the motor (R, S).

7. A system according to Claim 5, characterized in that the movable contacts (A, B) are controlled independently by respective cam profiles, the portions of the cam profile associated with one movable contact (B) which correspond to one (2) of the two working positions (1, 2) of the contact being of a shape such as to cause the contact (B) to move away from the working position (2) briefly during the period in which the small current is flowing through the motor (R, S) so as to cause a short break in the current correspondingly detected by the sensor means (TR, R1), and in that the electronic unit (MP) is arranged to distinguish the working position of the movable contacts (A, B) by detecting the short breaks in the current.

8. A system according to any one of the preceding claims, in which the programmer (T, M) comprises an electric motor (M) which rotates the cams (T), characterized in that the control and operating means 17 UC) comprise a second Triac (T2) or the like, arranged in series with the motor (M) of the programmer (T, M) and controlled by the electronic unit (MP), which is arranged to pilot the second Triac (T2) so as to stop the motor (M) of the programmer (T, M) whilst the movable contacts (A, B) of the switching device are in one of the working positions, for predetermined time intervals, at certain stages of an operating cycle or programme of the machine defined by the programmer.

9. A system according to any one of the preceding claims, characterized in that the electronic unit (MP) is arranged to recognise the occurrence of a short-circuit condition to or within the first Triac (T1).

10. A system according to Claims 8 and 9, characterized in that the electronic unit (MP) is arranged, upon recognition of a short-circuit to or within the first Triac (T1), to activate the motor (M) of the programmer (T, M) by means of the second Triac (T2) so as to move the movable contacts (A, B) to a position intermediate the working positions (1, 2).

11. A control system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.