US3670226A

US3670226A - Device for the controlled actuation of the basket of a washing machine

Info

Publication number: US3670226A
Application number: US37104A
Authority: US
Inventors: Lamberto Mazza
Original assignee: Industrie Zanussi SpA
Current assignee: Industrie Zanussi SpA
Priority date: 1969-05-17
Filing date: 1970-05-14
Publication date: 1972-06-13
Anticipated expiration: 1989-06-13
Also published as: AT304420B; ES379784A1; GB1273086A; DE2023715A1; NL7007063A; DE2023715B2; FR2047821A5; SE367524B

Abstract

A speed governing device for washing machines for overcoming the defect of generating radiofrequency noises without using any filter. In addition, the device exploits the advantages of DC motors in general without suffering from the inconveniences thereof. The arrangement essentially comprises a DC motor fed through a constant current transformer and a rectifier having rectifying elements whose opening is controlled by a device which delivers opening pulses synchronized with the zeros of the AC feeding current until the speed of the motor is below a predetermined value, while the delivery of pulses is discontinued as the predetermined value aforementioned is exceeded.

Description

United States Patent Mazza [4 1 June 13, 1972 [54] DEVICE FOR THE CONTROLLED 3,475,670 10/1969 Warren et a1. ..318/341 X ACTUATION OF THE BASKET OF A 3,309,602 3/1967 Euvino et ..323/25 WASHING MACHINE 3,526,791 9/1970 Codichini .323/22 SC 3,460,017 8/1969 Eggleston et a1. ..318/345 Inventor Llmberto Mam, Pordenone. Italy 3,335,291 8/1967 Gutzwiller .323/25 Assignee: lndustrie A. SJLA" Pordenont Schaeve t x Italy 2,814,012 11/1957 Swanson... ....318/345 X 3,307,094 2/1967 Ogle ..318/345 X [22] Filed: May 14, 1970 [21 App]. Na: 37 04 Primary Examiner-William H. Beha, J1.

Attorney-Holman & Stern [30] Foreign Application Priority Data 57 ABsTRA-CT May 17, 1969 Italy ..l6948 A/69 A speed governing device for hi hi for aing the defect of generating radiofrequency noises without [52] U.S. CI. ..318/345, 68/12, 307/252 UA, using any filter In addition, the device exploits the advantages 321/18 323/22 SC of DC motors in general without suffering from the incon- [51] Int.Cl. ..H02p,DO6f33/O0,H02m H03 veniences thereof The arrangement essentially comprises a [58] Field ofSearch ..32l/l6, 18, 323/22 SC, 6, 25, DC motor fed through a consmm current transformer and a 318/345 281; 307/146 252 UA; 68/12 rectifier having rectifying elements whose opening is controlled by a device which deliversopening pulses synchronized [56] References Cited with the zeros of the AC feeding current until the speed of the UNITED STATES PATENTS motor is below a predetermined value, while the delivery of pulses is discontinued as the predetennined value aforemen- 593,050 11/1897 Hull ..323/6 tioned is exceeded 3,293,889 12/1966 Cobb et a1... ..68/12 R 3,369,381 2/1968 Crane et a1 ..3l8/281 X 3 Claims, 7 Drawing Figures (WASHING BASKET PATENTEDJUN 13 m2 SHEET 10F 2 Gang v n.

m N am ONOOOOQOOGOOOO Dow on H

u amm .3 am aw DEVICE FOR THE CONTROLLED ACTUA'I'ION OF THE BASKET OF A WASHING MACHINE BACKGROUND OF THE INVENTION This invention relates to a device for actuating, at a controlled speed, the washing basket of a washing machine.

As is well known, the two elements which particularly characterize an actuating device for a washing machine, are the motor and the speed governor.

The motors as conventionally used are those operated by alternating current, more exactly tri-phase AC, since the DC motors, which should be preferred from a number of standpoints, and more particularly due to their greater versatility and adaptability to an extremely fine and sophisticated speed adjustment, cannot be employed inasmuch as the humidity of the environment in which they are required to operate, may cause them to short-circuited, with the result that very high currents are drawn in, which are susceptible to cause damage to the rectifying elements which feed the motors or at least impede the rectifying elements being properly controlled.

The most commonly used speed governors, in turn, are the so-called wave train governors and the phase-splitting governors." The former governors are based on the presence of an assembly of electronic components having a controlled opening (SCR diodes, thyratrons, etc.) which are controlled so as to cutoff the feed to the motor whenever the motor speed exceeds a predetermined value and to reinstate it, at any instant of time, as the motor speeds go below a certain preselected value. The latter governors are based on the presence of a number of electronic components having a controlled opening, which are controlled in such a way as to cut off the feeding for a certain portion of a half-wave of the feeding voltage and to reinstate it for the remaining portion, with the ratio of one of the times relative to either of the portions aforementioned to the other portion being automatically varied as a function of the speed of the motor being controlled.

Both types of governors as mentioned above suffer from the drawback of originating intense radiofrequency noises on account of the steep voltage fronts which are present when passing from the feeding cut off stage to the feeding reinstatement stage. The noises are always and at any rate undesirable, but are particularly disturbing in the case of washing machine motors, since RF noises directly involve the users. It is possible to suppress them or at least to reduce them to negligible proportions by using suitable filters: however, the large size of these render the implementations both bulky and expensive.

The object of the invention is to provide a devicefor the controlled actuation of the basket of a washing machine which is capable of exploiting the advantages of DC motors without suffering the drawbacks thereof, and in which the speed adjustment is carried out in such a way as not to originate the above mentioned RF noises.

SUMMARY OF THE INVENTION The object of the invention is achieved by means of a device characterized in that it comprises a DC motor fed through a transformer of the constant-current type and a rectifier comprising rectifying elements whose opening is controlled by an adjustment device adapted to deliver opening pulses which are synchronized with the zeros of the feed AC current until the speed of the motor is below a predetermined value, and to stop the delivery as the predetermined value is exceeded.

The particular combination of elements composing the present actuating device is the origin of a number of advantages. More particularly, the use of a DC motor (preferably of the independent excitation type so as to limit the breakaway torques produced while dispensing with a tacheometric generator to take speed readings) permits a finer and more linear control of the speed, the presence of a transformer of the constant current type (that is of the type as commonly used for the electric welding machines) permits limiting the currents which flow through the controlled rectifying elements in the case of shortcircuiting of the motor and thus impede damage for the controlled rectifying elements and, lastly, the use of a governor capable of causing the instants of opening of the controlled rectifying elements (and thus it can be defined as a governor which suppresses whole half-waves) to coincide with the zeroes of the feeding voltage, avoids the presence of steep voltage fronts at the instant in which one passes from a cut off condition to a feeding condition and thus eliminate the RF noise mentioned above in connection with wave train governors and phase splitting governors.

Further features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof. In this detailed description, given by way of example only, reference will be had to the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuitry diagram, in detail, of the preferred embodiment of the actuation device according to the invention.

FIGS. 2 to 7 are plots which show the trends, as a function of time, of a few signals which have a quite particular meaning for indicating the operation of the device of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION With reference to FIG. 1, a DC motor 2, of 'the collector type and having an independent excitation (permanent magnet or field windings) is inserted in a branch of a bridge circuit 1 having in the other three branches as many resistors 3, 4 and 5. The bridge 1 is fed, in correspondence with two of its terminals 6 and 7, by the output of a rectifying bridge 8 which comprises two diodes 9 and 10 and two SCR diodes l1 and 12. The two terminals 13 and 14 of the rectifier bridge 8, in addition to being connected to one another by an additional circulation diode 64 (intended to prevent the inductive load consisting of the motor 2 from causing the delayed extinction of the SCR diodes) are connected to the terminals 6 and 7 of the bridge circuit 1, whereas the remaining two

terminals

15 and 16 of the rectifying bridge 8 are connected to a secondary winding 17 of a constant-current transformer 18, whose primary windings receives a conventional AC feed from the main at two terminals 20 and 21. A selector switch 22 can selectively engage five different taps of the secondary winding 17 and thus cause the input voltage to the rectifier bridge 8 to be varied among five different magnitudes.

The SCR diodes l1 and 12 of the rectifier bridge 8 are controlled by a regulating device adapted to supply them with opening pulses synchronized with the AC main voltage until exceeding a value which is predetermined by the c.e.m.f. of the motor 2. The regulator device comprises a rectifier 23 consisting of a bridge circuit defined by four

diodes

24, 25, 26 and 27 and having two

terminals

28 and 29 connected to the terminals 20 and 21, respectively, and two terminals 30 and 31 connected to one another by a series of a resistor 32 and a Zener diode 33 and a series of two

resistors

34 and 35.

the terminal 13 of the rectifier bridge 8 by an arrangement of the resistor 41 and another resistor 43 and by a series arrangement of the resistor 42 and another resistor 44; the

resistors

41 and 42 must consequently be equal to one another and the same is true of the

resistors

43 and 44.

The control electrode of the SCR diode 39 is connected to the emitter of an NPN transistor 45, whose collector is connected through a resistor 46 to a point of a conductor 47 which connects the cathode of the diode 38 to the corresponding plate of the capacitor 40. The base of the transistor 45, in

turn, is connected to the collector of an NPN transistor 38, with such collector being also connected to the conductor 47 via a resistor 49. Conversely, the emitter of the transistor 48 is directly connected to a point of the conductor 50 which connects the other plate of the capacitor 40 to the terminal 31 of the rectifier 23, whereas the base of the same transistor 48 is connected to the conductor 50 via the resistor 35.

The base of the transistor 48 is connected also via a Zener diode 51 to the collector of a transistor 52 having its emitter directly connected to the conductor 50 and the collector connected also to the conductor 47 through a resistor 53. The base of the transistor 52, in addition to being connected to the collector and the emitter, respectively, of the same transistor 52 through a capacitor 54 and a diode 55, is directly connected to a point or node 56 with the latter being connected to a terminal 57 of the bridge circuit through a resistor 58, and to the conductor 47 through a resistor, to be selected from time to time, of five resistors 59' to 59 whose selection is carried out by a selector switch 60. The circuit is then completed by the direct connection between the conductor 50 and the terminal 61 of the bridge 1.

The operation of the device shown in FIG. 1 is as follows: the AC voltage V which is present at the terminals 20-21 (FIG. 2) is converted by the rectifier 23 into a pulsatory voltage V,(FIG. 3) between the terminals 30 and 31 and thus, even with a different amplitude, to the ends of the resistor 35. At the ends of the Zener diode 33, instead, a voltage is established which is of the type of FIG. 4 V which, through a diode 38, charges the capacitor 40 by keeping the voltage constant at the ends thereof (V FIG. 5

The pulsatory trend of the voltage at the ends of the resistor 35 causes the transistor 48 to be cut off whenever said voltage crosses the zero point, to be reinstated to the conducting condition immediately after. The cutoff of the transistor 48 causes the voltage at the point 62 to be raised and thus the transistor 45 is switched to its conducting condition. This conducting condition has an extremely short duration since, as the voltage at the ends of the resistor 35 returns to values other than zero, the transistor 48 is brought back to conducting condition, lowering the potential of the point 62 and cutting off thereby the transistor 45. The collector-emitter output current of the transistor 45 has thus a pulse-like trend with a pulse at every zero crossing of the feed voltage as drawn at the terminals 20 and 21.

The pulses, synchronized with the feeding voltage cause the opening of the SCR diode 39 and, consequently, the opening of the SCR diodes 11 and 12. The feeding voltage, as transformed by the transformer 18 and applied between the

terminals

15 and 16 of the rectifier bridge 8, causes then a flow of current towards the bridge 1, with the result being the feeding of the motor 2. The current flow lasts as long as the SCR diodes 11 and 12 are open and thus for an entire half-wave of the feeding voltage. The intensity of the feeding current, and thus the nominal speed of the motor, are a function of the position of the selector switch 22 and, by appropriately designing the transformer 18 and, more particularly, the secondary winding 17 thereof, the speed can be maintain such as to keep low the breakaway torque of the motor and prevent damage to the SCR diodes 1 l and 12.

Should things always go in the manner described above, that is, more particularly, should the transistor 48 be cut off at every zero-crossing of the feeding voltage, the SCR diodes 11 and 12 would be fired at each zero-crossing of said voltage and thus a continuous sequence of pulsatory current half-waves would be experienced, having a frequency twice the one at the terminals 20 and 21 and in phase with the voltage therein, towards the motor 2, so that the latter would be constantly fed, In point of fact, this is just what happens until the speed of themotor does not exceed a certain predetermined limiting value. As a matter of fact, until the motor speed is low (or, more properly speaking, below said predetermined limiting value),the c.e.m.f. as produced is also low so that a proportion of the current which is caused to circulate by the constant voltage V, through a selected resistor of the resistors 59'-59" and towards the node 56, is guided towards the base of the transistor 52 (the resistor 58 and the capacitor 54 act as smoothing filter for the reactive component as caused by the inductance of the motor 2), thus causing the latter to conduct, with a collateral consequence being the potential at the point 63 being set below the value which is required to discharge the Zener diode 51.

Under these circumstances, the portion of the device which compares the fixed reference voltage V, with the signal which is a function of the c.e.m.f. and thus of the speed of the motor 2 does not influence the operation of the remaining portion of the device, and, more particularly, has no influence on the operation of the assembly formed by the pulse generator comprising the transistor 48 and that of the amplifier comprising the transistor 45, which continues to emit pulses at every zerocrossing of the feeding voltage. Thus, between the rectifier bridge 8 and the bridge circuit 1 whole half-waves of motorfeeding pulsatory current continue to flow.

If, however, the speed exceeds the predetermined limiting value cited above (to which an appropriate selection of the resistors 5959" corresponds), the current entering the node 56 is almost entirely forwarded through the resistor 58 (the capacitor 54 then absorbs the. reactive component of said current again), so that the transistor 52 is cut off or, at least, has so restricted a conducting conditions as to lift the potential of the point 63 above the threshold value of the Zener diode 51 thus causing the base of the transistor 48 to be fed by such a current as to keep it conducting in spite of the zero-crossing of the voltage supplied to the ends of the resistor 35 by the pulsatory voltage delivered by the rectifier 23. The result is now that, when the speed of the motor exceeds the limiting value predetermined therefor, the zero-crossings of the feed voltage do not cause any longer the cutoff of the transistor 48, so that the transistor 45 is non-conducting and consequently it does not deliver pulses to open the SCR diode 39. The SCR diodes 11 and 12 thus remain closed and consequently the feeding to the motor 2 is prevented.

These conditions last until the motor speed does not return below the fixed upper limit. At that stage, the current fed to the base of the transistor 52 is restored to a level which is sufficient to bring said transistor back to such a conducting conditions as to lower the potential of the point 63 below the threshold level of the Zener diode 51. The subsequent zerocrossing of the feeding voltage restores then to cutoff the transistor 48 and reinstates the original conditions. FIGS. 6 and 7 show, by way of example, the trends of the signals I and V which are present at the output of the transistor 45, and between the bridge 8 and the bridge 1, respectively, if the du ration time of the exceedingly high speed condition is such as to suppress only one of the pulses produced by the transistor 45 in synchronism with the zero-crossings of the feeding voltage. The voltage differential represented by the fourth halfwave of FIG. 7 corresponds to the value of the c.e.m.f. of the motor when the feeding voltage is cancelled. From the figures it can be inferred that, since the start and the stop of the cutoff stages of the feed of the motor 2 are determined by zeroes of the feeding voltage, entire half-waves are suppressed rather than portions of them, so that the several transitions from one condition to the other are never accompanied by undesirable voltage fronts. With an adjustment device of the kind described, no RF noises are experienced. At the same time, the use of a DC motor, which is pennitted by the presence of a constant-current transformer such as the transformer 18, permits a very fine and linear control to be carried out within a very wide speed range. It should be noticed thatthe device shown in FIG. 1 has been described herein by way of example only, since a number of changes may be introduced therein without therefor departing from the scope of the invention, whose limits are defined by the appended claims. For example, the assembly formed by the amplifier and which comprises the transistor 45 and the SCR diode 39 couldbe readily replaced by an assembly formed by a single shot multivibrator 100 and an amplifier 101 without varying the overall operation of the regulating device.

Similarly, the motor to be controlled could also be other than an independent excitation motor, and, possibly, a seriesexcitation motor: if so, the signal proportional to its speed could no more be drawn by a bridge 1 and an integrator, such as the resistor 58 plus the capacitor 54, but a tacheometric generator should be employed. This is one of the reasons, the others being the limitation of the breakaway torque, the possibility of using permanent magnets, the insensitivity to failures which lead directly to the motor the AC feeding current and so forth, why the most suitable of the DC motors which can be used for the device according to the invention is the independent excitation motor, especially on account of the fact that the subject device is intended for the actuation of the washing basket of a washing machine.

What is claimed is:

l. A device for the controlled actuation of the basket of a washing machine, including a DC motor, a control circuit therefor, a transformer having primary windings receiving AC and a secondary winding feeding constant current to the DC motor and control circuit, a rectifier circuit including rectifying elements, a regulating unit for controlling the opening of the rectifying elements, said unit being adapted to deliver opening pulses synchronized with the zero-crossings of the AC feeding voltage until the motor speed is below a predetermined value and to discontinue said delivery as said predetermined value is exceeded, said regulating unit comprising a pulse generator for delivering a pulse at each zero of its input signal, with said input signal being defined by the sum of a pulsatory signal having twice the frequency of, and in phase with, the feeding AC voltage, and a signal whose amplitude is other than zero only when the motor speed exceeds said predetermined value, the signal whose amplitude is other than zero only when the motor speed exceeds said predetermined value being composed by the discharge current of a Zener diode at whose ends a voltage is present which is a function of the difierence between a signal which is a function of the motor speed and a fixed reference signal.

2. The device according to claim 1, in which said motor is of the independent excitation type, or of the permanent magnet type of wound field type and said signal which is a function of the motor speed being drawn at the terminals of a bridge circuit, one branch of which includes the motor per se.

3. The device according to claim 2, including a smoothing filter for the signal drawn at the terminals of the bridge circuit.

I i l i

Claims

1. A device for the controlled actuation of the basket of a washing machine, including a DC motor, a control circuit therefor, a transformer having primary windings receiving AC and a secondary winding feeding constant current to the DC motor and control circuit, a rectifier circuit including rectifying elements, a regulating unit for controlling the opening of the rectifying elementS, said unit being adapted to deliver opening pulses synchronized with the zero-crossings of the AC feeding voltage until the motor speed is below a predetermined value and to discontinue said delivery as said predetermined value is exceeded, said regulating unit comprising a pulse generator for delivering a pulse at each zero of its input signal, with said input signal being defined by the sum of a pulsatory signal having twice the frequency of, and in phase with, the feeding AC voltage, and a signal whose amplitude is other than zero only when the motor speed exceeds said predetermined value, the signal whose amplitude is other than zero only when the motor speed exceeds said predetermined value being composed by the discharge current of a Zener diode at whose ends a voltage is present which is a function of the difference between a signal which is a function of the motor speed and a fixed reference signal.