ITTO20070501A1 - DEVICE AND METHOD TO BLOCK AND UNLOCK THE DOOR OF A HOUSEHOLD APPLIANCE - Google Patents

Abstract

The present invention relates to a method for locking and unlocking a door of a household appliance, wherein door locking means are actuated by an electric actuator when the latter receives a voltage exceeding a preset value. The method comprises a household appliance safety locking step wherein the locking means are set to a door locking position and a positive temperature coefficient thermistor arranged in series with the actuator is heated for the purpose of increasing its resistance up to such a value that, when the full power voltage of the household appliance is applied across the actuator- thermistor pair, a voltage drop below said preset value will be generated across the actuator. A device capable of implementing said method is also described.

Description

Description of the Industrial Invention entitled:

"DEVICE AND METHOD FOR LOCKING AND UNLOCKING THE DOOR OF A APPLIANCE"

SUMMARY

The present invention relates to a method for locking and unlocking a door of an electrical appliance, in which door locking means are operated by an electric actuator by applying to the latter a voltage higher than a predetermined value.

The method involves a phase of securing the appliance in which the locking means are positioned in a door lock position and a positive thermal coefficient thermistor is heated, placed in series with the actuator, in such a way as to increase its resistance up to a value such that, by applying the entire power supply voltage of the household appliance to the ends of the thermistor actuator pair, a voltage drop lower than said predetermined value is generated at the ends of the actuator. A device capable of implementing the method is also described.

DESCRIPTION

The present invention relates to a method for locking and unlocking the door of a household appliance according to the preamble of claim 1 and to a relative door locking device.

The present invention relates in particular to the sector of washing and drying machines, in which it is necessary to ensure the closing of the loading door during some phases of the treatment of the garments which are considered dangerous.

As an example, it is important to ensure that, during spinning operations, the user cannot open the door because any contact with the drum moving at high speed can be dangerous.

For this reason, washing and / or drying machines are equipped with devices for locking and unlocking the door.

Among the known solutions used, there are locking and unlocking devices which use an electric actuator to control the locking and unlocking of the door.

Since the electric actuator has very short reaction times, of the order of a few tens of milliseconds, these devices are said to be of the "instantaneous" type.

Safety regulations provide that any disturbance or failure, such as a short circuit or "diode mode" operation of the triac that generates the actuator command pulses, must not be sufficient to allow the door to be unlocked.

For this reason, there are various solutions that involve the use of at least two impulses to unlock the door.

Solutions of this type are known from patents EP0808935 and 1156,334,637. In the patent EP0808935, the electric actuator consists of a solenoid inside which a movable element is mounted sliding in the axial direction. By applying pulses to the solenoid, the moving element moves to a position which depends on the number and polarity of the pulses applied. The actuator is then controlled in such a way that the movable element extends into at least two locking positions and can move backward within the solenoid into a door unlock position.

In US6,334,637 the electric actuator is constituted by a solenoid inside which a ferromagnetic core is slidingly mounted which is moved by applying an alternating voltage to the solenoid for short intervals of time.

Each voltage pulse applied to the solenoid causes the movement of the mobile element which engages in a mechanical transmission capable of cyclically assuming three positions, two for locking and one for unlocking the door.

The safety required by the regulations is therefore obtained by means of the aforementioned mechanical transmission, which requires two pulses to be given to the solenoid to pass from a locked to an unlocked position.

The object of the present invention is to present an alternative method and device for controlling the locking and unlocking of the door of a household appliance, in particular of a washing machine and / or dryer.

This object is achieved by means of a method and a device incorporating the characteristics of the attached claims, which form an integral part of the present description.

The general idea behind the present invention consists in using a thermistor, in particular a PTC (Positive Temperature Coefficient), placed in series with the solenoid of the electric actuator, as a safety device against the involuntary unlocking of the door due to disturbances or faults such as short circuits. or the "diode mode" operation of the triac which controls the energizing of the solenoid.

In particular, before the operating phases of the machine considered dangerous, the invention provides for a safety phase of the household appliance in which the door is locked and the thermistor is heated in such a way as to increase its resistance up to a value such that even by applying the entire power supply voltage of the household appliance to the ends of the thermistor actuator pair, a voltage drop lower than the voltage value is generated at the ends of the actuator, beyond which the electric actuator activates the locking and unlocking means.

This solution causes any disturbances or faults to affect the thermistor rather than the solenoid, which consequently does not unlock the appliance door.

Furthermore, this solution makes it possible to avoid unlocking the door in the event of electrical disturbances or breakdowns without necessarily providing a double pulse for unlocking or a particular transmission that achieves the safety conditions imposed by the standard.

Further objects and advantages of the present invention will become clearer from the following description and from the annexed drawings, in which:

Figure 1 shows a locking device according to the present invention;

Figure 2 shows a detail of the device of Figure 1 in the unlocked door position;

Figure 3 shows a detail of the device of Figure 1 in the locked door position;

Figure 4 is a time diagram of the voltage applied to the door locking device according to a first embodiment of the method according to the present invention;

figure 5 is a time diagram of the voltage applied to the door locking device according to a second embodiment of the method according to the present invention;

figure 6 is a time diagram of the voltage applied to the door locking device according to a third embodiment of the method according to the present invention;

- figure 7 shows a first curve of increase of the voltage applied to the device according to the present invention during an operating phase which anticipates dangerous cycles of the household appliance, and

Figure 8 shows a second curve for increasing the voltage applied to the device according to the present invention during an operating phase which anticipates dangerous cycles of the household appliance.

Figure 1 schematically shows a locking device according to the present invention.

The device has a pair of terminals (L and N) for connection to the conductors (respectively phase and neutral) of a single-phase AC power supply line.

The device comprises an electric actuator 1 comprising a solenoid 2 connected to the phase and to the neutral through a PTC thermistor 3 and a triac 4.

The triac 4 is substantially a switch controlled by a control unit 5 (in particular a microcontroller) which regulates its opening and closing, thus regulating the passage of current through the solenoid 2 and the thermistor 3.

Preferably, the microcontroller 5 performs a phase control of the triac 4 in such a way as to apply to the thermistor solenoid pair an alternating voltage having an effective value between zero and a maximum value which is obtained by keeping the triac constantly closed.

In the case of figure 1, by closing the triac 4 the thermistor solenoid pair is connected between the phase and neutral terminals of the power supply, therefore this maximum value corresponds to the effective value of the power supply voltage.

A ferromagnetic core 6 is axially mounted inside the solenoid 2, which constitutes a movable element capable of engaging with the locking means 7, described below, in such a way as to cause it to pass from a locked position to a different one. unlocking the door.

In the preferred embodiment, the locking means 7 comprise a movable rod 8 capable of engaging in an opening 9 in such a way as to block the movement of a slider 10 and consequently block the opening of the door.

The rod 8 bears on one side a metal contact 11, for example a copper plate, of a general switch 12 whose closure allows to power the loads 13 of the household appliance, for example motor, pumps, etc.

On another side, the rod 8 has a projection 14 which engages under the teeth 15 of a toothed wheel 16.

The wheel 16 then has an upper indentation 19 on which a lever 17 acts which causes the wheel 16 itself to rotate.

In particular, at each stroke the lever 17 rotates the wheel 16 so that the projection 14 of the rod 8 engages alternately under a tooth 15 (position pi of fig. 2) and inside the space between two consecutive teeth 15 (position p2 of fig. 3).

The lever 17 is mounted slidingly in a direction parallel to the longitudinal axis (x) of the solenoid 2, in such a way that the mobile element 6, engaging on the lever 17, causes the wheel 16 to rotate.

A pawl 18 acts on the indentation 19 preventing the wheel 16 from rotating in the opposite direction with respect to the motion imparted by the lever 17.

The pawl 18 is held against the wheel by a spring 20 which acts between the pawl ratchet and the lever 17.

Through the lever 17, the spring 20 exerts a force on the movable element 6 which pushes it inside the solenoid 2.

To make the wheel 16 rotate, it is therefore necessary that the movable element is pushed out of the solenoid with a force such as to overcome the resistance of the spring 20.

This is obtained by applying to the solenoid a voltage with an effective value higher than a predetermined value.

When the switch 4 is opened, the voltage across the solenoid drops to zero and therefore the spring 20 brings the movable element 6 back inside the solenoid.

As can be seen from Figure 1, the teeth 15 of the wheel 16 are spaced so that with each stroke of the lever 17, the wheel moves by an angle corresponding to a tooth 19, with the projection 14 being alternately held in a position pi (shown in Figure 2) which corresponds to a situation of unlocking the door and switch 12 open, and in a position p2 (shown in Figure 3) in which the projection 14 is inserted between two teeth 15 allowing the rod 8 to go up again engaging the cursor 10 and closing the switch 12.

Figure 4 shows a time diagram from which the control carried out by the microcontroller 5 in order to ensure the safety of the machine is visible.

Figure 4 shows the effective value of the voltage applied across the thermistor solenoid pair of figure 1.

At time t, the washing cycle is started which lasts up to time t1 and foresees, in a known way, different phases with movement of the drum in an alternating direction.

In the example described here, the washing cycle foresees that the drum is rotated at rather low speeds, of the order of 45-55 rpm, and with little water in the tank, for this reason the washing phase is considered not dangerous.

The details of the washing cycle are not relevant for the purposes of the present invention and for this reason they will not be treated in greater detail.

From time ti to time t2, on the other hand, there is the rinsing phase, in which the drum is rotated at high speeds (higher than 60 rpm) and the quantity of water in the tub is higher than in the washing phase; this phase is instead considered dangerous and therefore it is necessary for the door to remain blocked for the whole phase.

In the example of embodiment of figure 4, at the start of the washing cycle the microcontroller closes the triac so that the entire power supply voltage of the appliance is applied to the ends of the thermistor solenoid pair, which in the example we assume to be the mains voltage available in homes, in Europe this mains voltage is equal to 220V rms @ 50Hz, while in the USA the voltage is 110V rms @ 60Hz.

The solenoid and the thermistor remain powered for the entire washing and rinsing phase.

At the time to the impedance of the solenoid and of the thermistor is substantially equal and of a few tens of Ohms, therefore the drop across the solenoid is of several tens of Volts and such as to exceed the predetermined value described above, such that the element mobile 6 is pushed out of the solenoid by an amount and with a force such as to overcome the resistance of the spring 20 and cause the wheel to snap.

The rod 8 thus engages in the opening 9 and the door is locked (position p2 of Figure 3).

Over time, the thermistor heats up due to losses (a phenomenon known as self-heating) and its resistance increases in value.

After a few seconds the resistance of the thermistor becomes much larger than that of the solenoid, therefore the voltage drop across the solenoid is reduced due to the solenoid thermistor resistive divider.

Under these conditions, the force of the spring 20 exceeds that exerted on the movable element 6, which thus re-enters the interior of the solenoid while the rod 8 remains in the position of engagement with the slider 10.

Given the difference in resistance between the solenoid and the heated PTC thermistor, any disturbances or faults affect the thermistor and only minimally on the solenoid, therefore they are not able to generate a voltage drop on the solenoid such as to cause a new activation of the means. lock (rotation of wheel 16) which would unlock the door.

It is therefore clear how this solution advantageously allows to keep the door locked substantially during the whole period to-t2.

At the end of the rinses, the washing machine carries out a series of movements necessary to remove the clothes, otherwise glued to each other on the periphery of the drum due to the spin effect carried out during the rinses.

During this phase, the method according to the invention provides for the voltage to be removed from the solenoid 2 and the thermistor 3, which takes place by means of a command from the microcontroller 5 which opens the triac 4.

The thermistor cools and thus reduces its impedance.

After a short period, the duration of which depends on the characteristics of the thermistor (but typically it can be 10-15 seconds), the impedance of the solenoid and the thermistor return to be comparable.

At this point (instant t3), the microcontroller 5 can apply to the ends of the thermistor solenoid pair a voltage pulse capable of causing the release of the lever 17 and of the wheel 16, thus causing the passage of the rod 8 from position p2 to position pi where the door is unlocked.

In the example of figure 4, this release pulse has an amplitude equal to the supply voltage and a duration t3-t4 of 40 ms, corresponding to two cycles of the supposed supply voltage at 50 Hz.

According to this embodiment, when the user wishes to open the door during the washing step, which is considered non-dangerous, the user must press a button or turn a knob, to signal the microcontroller to unlock the door.

The microcontroller receives the instruction from the user and opens the triac 4 so as to make the thermistor 3 cool, after which it transmits an unlock pulse like the one described above.

With reference to the example of Figure 5, an alternative solution is shown for controlling the device for locking and unlocking the door of a household appliance.

At time to a pulse of 220V and 40ms (to-ts) is applied across the thermistor solenoid pair; for what has been said above, this impulse causes the wheel 16 to snap and the rod 8 to move from the opening position pi to the door locking position p2.

During the washing phase, the solenoid remains de-energized until instant ts; so in the ts-te interval, the microcontroller, following an instruction from the user (and having verified that the appliance is not carrying out a dangerous operating phase), can instantly unlock the door by sending a new 220V impulse to the thermistor solenoid pair .

Before the rinsing phase (considered dangerous), the invention provides to put the machine in safe conditions in such a way that a possible disturbance or failure (such as a short circuit or a "diode mode" operation of the triac) is not able to unlock the appliance door during rinsing.

At time t6, prior to the dangerous rinsing phase, the microcontroller 5 acts on the triac 4 by increasing the voltage applied to the ends of the solenoid and thermistor pair, so that this increases without the voltage drop across the solenoid exceeding the value which the locking means are activated, which is made possible by the increase in the resistance of the thermistor.

In other words, the microcontroller 5 progressively increases the duty cycle of the triac 4 so as to increase the rms value of the voltage applied to the thermistor solenoid pair without thereby causing the locking means to operate because an insufficient voltage always falls across the solenoid. to actuation.

By increasing the voltage according to a ramp (or a series of steps) that is sufficiently slow, it is possible to heat the thermistor and increase its resistance while maintaining the voltage drop on the solenoid always below that limit value above which the element mobile 6 causes the wheel 16 to rotate.

At time 17, the voltage applied to the thermistor solenoid pair is maximum and the conditions described above with reference to Figure 4 are repeated, so that in the rinsing phase any disturbances are not such as to allow the door to be unlocked.

If during the washing phase there are disturbances or faults that cause the door to be unlocked without the user requesting it, the microcontroller 5 detects the opening of the main switch 12 and applies a new pulse to the thermistor solenoid pair. lock the door.

In case the fault was due to a short circuit or a "diode mode" operation of the triac, it would clearly not be possible to send the new block pulse, but the machine would be in a safe situation with the loads disconnected.

In the event that several dangerous operating phases are provided (for example rinsing and spinning) alternating with non-dangerous phases, in a preferred form the method according to the present invention provides that the thermistor solenoid pair is kept under voltage during all the dangerous phases, always maintaining the voltage drop on the solenoid below the operating value of the locking means.

The dangerous operating phases can also include the phases of the washing treatment in which the temperature of the washing liquid is higher than 50 ° C (even if they are not considered as such by the current legislation). The thermistor solenoid pair can therefore be suitably maintained under voltage, keeping the voltage drop across the solenoid below the operating value of the locking means, even when the temperature of the washing liquid is higher than 50 ° C.

This situation is shown in figure 6, where before a second dangerous phase (for example a centrifuge phase), the microcontroller makes the machine safe again by applying a voltage pulse (instants ts-tg) such as to position the rod 8 in the locked position.

Before the centrifuge phase (instants tio-tn) a heating phase of the PTC 3 thermistor is performed again (instants tVt'z), in which the resistance of the thermistor is increased in such a way as to make the electric actuator substantially "immune" to disturbances .

At the end of the spin cycle, the machine is in a non-dangerous situation. When the user gives a command to unlock the door, the microcontroller 5 generates a voltage pulse (instants ti2-ti3) which unlocks the door.

The heating phase of the PTC thermistor (with the purpose of increasing its resistance) can be carried out by increasing the voltage applied to the thermistor solenoid pair according to a strictly increasing monotonic curve, eg. a ramp (as in figure 5), or according to a non-decreasing monotonous curve, comprising, for example, step profiles.

To reduce the duration of the heating phase of the thermistor, according to an embodiment of the invention the microcontroller controls the triac in such a way as to immediately apply a rather high voltage, e.g. 40 V rms, of a value in any case lower than that for which the force exerted on the mobile element is such as to overcome the resistance of the return means (eg the spring 20 of figure 1).

After this step, the microcontroller can increase the applied voltage according to a ramp, as shown in figure 7.

Figure 8 shows another possible curve for increasing the voltage applied to the thermistor solenoid pair, in which between time t6 and time t8 the voltage is increased according to a ramp having a different slope with respect to the ramp from t8 to tz.

It is also possible to foresee that, once an upper voltage limit value has been reached (for example equal to 80 V rms) through a ramp increase, the voltage is then brought to its maximum value (220 V rms) through a step increase.

It is now clear that many variants are possible for the man skilled in the art to realize a device and a method for locking a door of an electrical appliance.

In particular, the invention is not limited to the locking means described with reference to Figures 1-3: many other alternative mechanical solutions to the gear wheel described above and to the lever 17 can be used to carry out the transmission of the locking / unlocking command from the movable element to the locking means.

Furthermore, the triac 4 can be replaced by any other electromechanical or semiconductor switch.

The triac 4 and the microcontroller 5 can then be arranged on a printed circuit connected but independent of a module containing the solenoid, the thermistor and the locking and unlocking means.

Finally, in addition to self-heating, the resistance of the thermistor can be increased by means of external devices, such as heating elements, this further reduces the time of the heating phase.

Claims (30)

CLAIMS 1. Method for locking and unlocking a door of an electrical appliance, in which means for locking the door are operated by an electric actuator by applying to said actuator a voltage higher than a predetermined value, characterized in that it comprises a step for securing the appliance in which said locking means are positioned in a locking position of the door and a thermistor is heated, placed in series with said actuator, in such a way as to increase its resistance up to a value such that, by applying the entire supply voltage of the appliance at the ends of the thermistor actuator pair, a voltage drop lower than said predetermined value is generated at the ends of the actuator. 2. A method according to claim 1, wherein said actuator comprises a solenoid adapted to move a movable element slidably mounted within said solenoid, and wherein said thermistor is connected in series to said solenoid and heated by a current flowing through said solenoid. Method according to claim 2, wherein said safety step comprises the following steps: - applying a voltage to the thermistor solenoid pair such that the voltage drop across the solenoid (2) has an effective value greater than said predetermined value so as to position said locking means (7) in said locking position (p2) of the door , - keep said solenoid pair (2) thermistor (3) under voltage Method according to claim 3, wherein said thermistor solenoid pair (2) is maintained under voltage until one of the following conditions is met: - a user of said household appliance gives a door release command, - ends at least one operating phase of the household appliance during which the door must not be allowed to open. Method according to claim 3 or 4, wherein said voltage applied to the thermistor (3) solenoid pair (2) is maintained until all the operating phases of the household appliance during which opening must not be allowed are completed of the door. Method according to claim 2, wherein said safety step comprises the following steps: - applying to the pair of solenoid (2) thermistor (3) a voltage pulse such that the voltage drop across the solenoid (2) has an effective value greater than said predetermined value so as to position said locking means (7) in said locking position (p2) of the door, - before an operating phase of the appliance during which the door must not be allowed to open, perform a thermistor heating phase in which the voltage applied to the thermistor solenoid pair is increased, so that the applied voltage increases up to to reach a maximum value without the voltage drop across the solenoid exceeding said predetermined value due to the increase in the resistance of said thermistor. - keep said solenoid pair (2) thermistor (3) under voltage. 7. A method according to claim 6, wherein the increase of said applied voltage follows a non-decreasing monotone curve. 8. Method according to claim 7, wherein said curve is strictly increasing monotone. Method according to claim 7 or 8, wherein said curve comprises a ramp. Method according to any one of claims 7 to 9, wherein said curve provides a first step in which the applied voltage reaches a value lower than said predetermined value. Method according to any one of the preceding claims, in which a microcontroller controls the opening and closing of a switch (4) adapted to connect said electric actuator (1) to the power supply voltage of the household appliance, so as to regulate the voltage applied to the thermistor actuator torque. Method according to claim 11, wherein said microcontroller receives a door release command from a user of said household appliance. 13. Method according to claim 12, wherein said microcontroller evaluates whether it is possible to unlock the door and if so opens said switch to cool said thermistor and subsequently applies to the thermistor actuator pair a voltage such that the voltage drop across said actuator it is such as to activate said locking means and bring them into an unlocked position. 14. Method according to claim 12, wherein said microcontroller evaluates whether it is possible to unlock the door and if so applies a voltage to the thermistor actuator pair such that the voltage drop across said actuator is such as to activate said locking means and bring them to an unlocked position. Method according to any one of the preceding claims, wherein said locking means (7) alternatively assume a locking position and an unlocking position of the door. Method according to any one of the preceding claims, wherein said thermistor is a positive temperature coefficient thermistor. 17. Device for locking and unlocking a door of a household appliance, characterized in that it is adapted to carry out the method according to any one of claims 1 to 16. 18. Device according to claim 17, comprising: - locking means adapted to assume at least one locking and one unlocking position of the door, - an electric actuator (1) comprising a movable element (6) sliding inside a solenoid (2) so as to assume at least one engaging position with said locking means (7) and to cause it to pass from the locked to the unlocked position when the voltage drop across said solenoid (2) exceeds a predetermined value, - a positive temperature coefficient thermistor (3) connected in series to said solenoid in such a way that the resistance of said thermistor increases following the passage of current through the solenoid (2), and - command and control means (4,5) adapted to control the voltage applied to said solenoid (2) and to said thermistor (3), characterized in that said command and control means (4,5) are adapted to position said locking means in a locking position (p2) of the door and to keep them in said locking position (p2) by heating said thermistor in such a way as to increase its resistance up to such a value that, by applying the entire supply voltage of said household appliance to the ends of the thermistor solenoid pair, a voltage drop lower than said predetermined value is generated at the ends of the solenoid. 19. Device according to claim 18, further comprising contrast means (20) adapted to generate a return force opposite to that of actuation which moves said movable element towards the locking means when a voltage is applied to said solenoid, in such a way that said movable element operates said locking means only when said actuation force is greater than a predetermined threshold. 20. Device according to claim 18 or 19, wherein said command and control means are adapted to: - applying to said solenoid (2) a voltage higher than said predetermined value so as to lock said door, - keep said solenoid (2) and said thermistor (3) powered 21. Device according to claim 20, in which said command and control means are operable - to receive an unlock command from a user of said appliance, - to check if said appliance is carrying out an operating phase during which the door must not be allowed to open, - to keep said solenoid (2) and said thermistor (3) under voltage until: - said door release command is not received, it is checked that at least one operating phase of the appliance has ended, during which the door must not be opened. Device according to claim 18, wherein said control and command means comprise a microcontroller (5) adapted to perform a phase control of a switch which connects said solenoid to the supply voltage of said household appliance. 23. Device according to any one of claims 18 to 22, in which said control and command means are adapted to increase the voltage applied across the solenoid and thermistor pair, so that said applied voltage increases without the voltage drop at the ends of the solenoid exceeds said predetermined value due to the increase in the resistance of said thermistor. 24. Device according to claim 23, wherein said control and command means are adapted to increase said voltage applied before a predetermined operating phase of said household appliance. A device according to claim 24, wherein the increase of said applied voltage follows a non-decreasing monotone curve. 26. Device according to claim 24, wherein said curve is strictly increasing monotone. 27. Device according to claim 25 or 26, wherein said curve comprises a ramp. 28. Device according to claim 25 or 26 or 27, wherein said curve provides a first step in which the applied voltage reaches a value lower than said predetermined value. 29. Device according to any one of claims 18 to 28, in which said locking means cyclically assume the closed position and the open position. 30. Household appliance comprising a door and a device for locking or unlocking the opening of said door according to any one of claims 17 to 29.