Bistable actuator device

An actuator device varies its functional condition from a state of rest to a working state, both stable and has a body receiving a thermal actuator, an electric heater, electric contacting elements and a transmission shaft for the thrust generated by the actuator. A bistable kinematic mechanism uses inclined planes and/or cams.

SPECIFICATION 
FIELD OF THE INVENTION 
The present invention relates to a bistable actuator, i.e. an actuator 
device capable of assuming two states, both of which are stable, and in 
which the commutation between the two different states is commanded by 
external intervention. In other words, a bistable actuator device is 
capable, during its first functional cycle, to reach a determined working 
condition and to maintain it, to then return to the previous working 
condition, in following a successive functional cycle. Such actuator 
systems therefore have actuator means and means for maintaining the 
condition reached on termination of the first functional cycle. The 
actuator devices of the cited type contrast with those without means for 
maintaining the position when their energy supply is stopped (monostable 
actuator systems). 
BACKGROUND OF THE INVENTION 
Bistable actuator systems in practice are utilized for numerous 
applications. For example they are used for blocking systems of the doors 
of electrical household appliances, so as to avoid dangerous operations 
for the user. 
Thermal bistable actuator systems are known, in which the maintaining of 
the position reached is assured by way of a couple of bimetallic elements. 
Such known systems however lack appropriate functional control means, so 
that their way of operating, which is based on ambient temperature, easily 
results in being affected by external sources of heat. 
Electromagnetic bistable actuator systems are also known, that depend upon 
complex circuitry for controlling the polarity inversion or the electric 
commutation. 
Another typical problem of the known art is that of the complexity of the 
components making up the bistable devices, and their arrangement. For 
example the use of electromagnets makes the actuator devices complex, 
bulky and expensive. 
A further problem of known thermal or electric bistable systems if the 
reduced stroke available, together with the high forces to be used. 
Normally, with the purpose of obtaining greater forces with devices of 
contained dimensions, the electric actuator means of devices in use must 
be sized for a very brief supply time. In such cases there is however the 
risk that accidental extended times of supply cause the destruction of the 
actuator device. 
OBJECT OF THE INVENTION 
The principal object of the invention is to overcome the aforementioned 
drawbacks and to provide a bistable actuator that is simple, economical 
and reliable in the most varied conditions of use. 
Another object of the invention is a bistable actuator that, even being of 
very contained dimensions, is able to generate great forces and strokes, 
and which is able to work with long or short periods of supply and/or 
insertion. 
SUMMARY OF THE INVENTION 
These objects are attained according to the present invention by way of an 
actuator device capable of varying its functioning conditions between a 
state of rest and a working state, both of which being stable, comprising 
an actuator element capable of carrying out, by way of an external 
command, the commutation between the two functional states of the device, 
and holding means, able to hold the device in the working state. According 
to the invention, the actuator element is a monostable actuator, in 
particular of the thermal type, and in that an adapter is provided which 
makes the actuator a bistable device by way of kinematic motion that 
assures the holding of the working state even without supply to said 
monostable actuator.

SPECIFIC DESCRIPTION 
The bistable actuator device 1 a body 2 in which a monostable type actuator 
is housed and a substantially tubular shaped body 3 within which kinematic 
means are housed. The diameter of the body 3 is extremely limited 
(approximately 17 mm). 
As can be seen from FIG. 2, a chamber 4 is defined in the body 2 which 
houses: 
a thermal actuator, or thermoactuator 5, 
an electric heater 6, for example a positive temperature coefficient 
registor PTC, arranged in contact with the thermoactuator 5; and 
two electric supply terminals 7, exiting the body 2. 
The thermoactuator 5 comprises a conductive body 8, which is thermally and 
electrically connected to the heater 6 supplied by two electric terminals 
7. 
The two terminals 7, the thermoactuator 5 and the heater 6 constitute an 
electrical heating circuit that, due to the effect of the PTC heater, is 
self-regulating in its temperature. 
In the body 8 of the thermoactuator 5 a sealed chamber is defined, filled 
with a thermal expandable material 9, for instance wax. In this sealed 
chamber a small piston 10 is arranged, the extremity 10A of which exits 
the body 8 of the thermoactuator 5; the expansion of the material 9, when 
subjected to an increase in temperature (induced by the heater 6 
electrically supplied by way of the terminals 7) induces a thrust on the 
piston 10, and therefore a linear movement of the same, so as that the 
extremity 10A is spaced from the body 8. 
A mobile rod 11 has an extremity 11A extending out of the body 2. The rod 
11 is subjected to the contrary reaction of an elastic element, for 
instance a coil spring 12. The spring 12 acts upon the seat 11B to cause 
the re-entry of the piston 10 in the thermoactuator 5 upon termination of 
the heating cycle of the latter. 
The thermoactuator 5, the heater 6, the electrical contacts 7, the rod 11, 
the spring 12 and the body 2 constitute as a whole a thermoelectric 
monostable actuator device DA, i.e. capable of thrust operating only when 
electrically supplied, but not able to maintain the position reached once 
supply is withdrawn. 
The body 2 of the thermoelectric actuator device is mechanically coupled to 
the body 3, being two flanges 13, 14 of the bodies 2 and 3, equipped with 
a bayonet type hooking system for their mutual joining. Coaxial holes 15, 
16 are present in the flanges for fixing the device 1 to another device. 
The distance between the hooks 15, 16 visible in the upper and lower part 
of the figure is approximately 26 mm. 
The body 3 is internally equipped with a bistable kinematic mechanism, i.e. 
capable motion, i.e. apt at of maintaining the working position reached, 
determined by the activation of the thermoactuator 5, even upon 
termination of the supply to the latter. The body 3 and the said internal 
kinematic mechanism therefore constitute a bistable adapter CB, apt at 
transforming the monostable actuator DA in the bistable actuator device 1. 
The bistable kinematic motion comprises a sliding cursor element 20 
linearly slidable within the body 3, and restrained in its movement by a 
pair of appropriate guides 21A and 21B obtained as protrusions on the 
internal wall of the body 3. A mobile element 22 also linearly slidable 
within the body 3, is caused to rotate by the thrust of the sliding cursor 
20. An elastic element 23 such as a spiral spring acts between the 
extremity of the body 3 and the rod 24, partially inserted in the mobile 
element 22. 
The guides 21A and 21B, the sliding cursor and the element 22 have a system 
of inclined planes and/or cams able to transform the linear movement of 
the piston 10, of the rod 11 and of the sliding cursor 20 in a rotary 
movement of the mobile element 22. 
The sliding cursor 20, of a circular section, has at one of its extremities 
a seat 20A capable of receiving the extremity 11A of the rod 11. On the 
edge of the opposite extremity of the sliding cursor 20 small teeth 25 are 
provided (FIG. 1), that therefore create a series of inclined planes 26. 
On the external surface of the sliding cursor 20 four radial contours are 
also defined. As seen in FIG. 4, these contours 27 cooperate with the 
guides 21A and 21B of the body 3 for permitting only a linear movement of 
the sliding cursor 20. As can be seen in FIG. 2, the two guides 21A also 
have an edge provided with inclined planes, indicated with 28 and 29. 
The mobile element 22 has in its lower part a circular section of a 
diameter being less than that of the sliding cursor 20, from which four 
radial teeth 30 are obtained (see FIG. 3), of a length being less than 
that of the overall mobile element 22; the extremity 30A of such teeth 30 
pointing towards the sliding cursor 20 is not flat, but inclined. 
As can be seen from FIGS. 1, 2 and 5, the mobile element 22 is capable of 
being partially inserted in the sliding cursor 20. To the mobile element 
22 an extremity of the said rod 24 is then introduced. Its other extremity 
exits from the body 3. 
The forms and dimensions of the details 20 and 22, the guides 21A and 21B 
and of the body 3 are calculated so as that the sliding cursor 20 is 
guided, by way of the guides 21A-21B and contours 27, to slide for all its 
linear movement, and the mobile element is guided, by way of the guides 
21A-21B and teeth 30, only for a limited section of its path. 
The functioning of the device subject of the present invention is described 
in the following; to such purposes it is to be noted that the initial 
condition of the device is that as illustrated in FIG. 5. 
The thermoactuator 5, when not electrically supplied by way of the 
terminals 7, is subject to the reaction of the spring 12, the force of 
which is greater than the thrust exercised on the piston 10 by the 
material 9, when this is not heated. In such condition the extremity 10A 
of the piston 10 is in a withdrawn position. 
When the terminals 7 are connected to a source of electrical supply, the 
heater 6 (PTC) heats, thermo-adjusting automatically its temperature. The 
heat thus created is transferred by contact to the body 8 of the 
thermoactuator 5, and therefore to the expandable material 9 contained 
within the sealed chamber. 
The increase of temperature of the thermoactuator 5 determines an increase 
in volume of the expandable material 9 and therefore a thrust on the 
piston 10; it is to be noted that the temperature and the relation between 
the volume of the sealed chamber and the volume of the expandable material 
9 is appropriately calculated, so as to allow a precise increase in 
pressure and to enable movement of the piston 10 and the rod 11 without 
exceeding in thrust. 
The extremity 10A of the piston 10 pushes the rod 11, which in turn 
operates a thrust on the sliding cursor 20. This sliding element 20 
therefore linearly slides in the guides 21A and 21B, integral with the 
body 3, and thrusts, with its inclined planes 26, the inclined extremity 
30A of the teeth 30 of the mobile element 22. 
The mobile element 22 also slides in a linear manner, restrained by the 
guides 21A-21B and contours 30, but only for a brief section (for example 
during the first phase of the actuation cycle), also moving linearly the 
rod 24 in contrast to the action of the spring 23. The resulting force on 
the rod 24 corresponds therefore to the difference between the force of 
the thermoactuator 5 and the contrary forces of the springs 12 and 23. 
The mobile element 22 moves in a linear manner until is not pushed by the 
sliding cursor 20 over the extremity of the guides 21A and 21B, or better 
until its teeth 30 are no longer restrained by the guides 21. 
Thus, in the terminal part of its run (i.e. some instants before the 
interruption of supply to the thermoactuator) the mobile element 22 is no 
longer restrained by the guides 21A and 21B; at this point, the thrust 
between the inclined planes 26 of the sliding cursor 20 and the inclined 
extremity 30A of the teeth 30 of the mobile element 22 generates on the 
latter a transversal component no longer affected by the guides 21A and 
21B. This transversal component causes a rotary motion of the mobile 
element 22, with an angular movement of 15.degree.: such rotary movement 
brings the inclined planes 20A of the two teeth 30 opposite to rest on the 
inclined planes 28 of the two guides 21A and 21B. 
Upon termination of the electrical supply, the heater 6 and the 
thermoactuator 5 cool down, the consequent reduction of the pressure 
inside the sealed chamber and the interruption of the thrust on the piston 
10. The force of reaction of the spring 12 therefore determines a return 
of the rod 11 in the withdrawal position, that in turn ceases the thrust 
on the sliding cursor 20. As a consequence the thrust on the mobile 
element is also ceased, and thus on the rod 24. 
At this point the reaction of the spring 23, that operates on the rod 24, 
determines a contrary thrust on the mobile element 22; the inclined 
extremity of the teeth 30 push therefore on the inclined planes 28 of the 
guides 21. 
Such pressure causes the sliding of the inclined extremity of the teeth 30 
on the inclined plane 28 (that therefore functions as a slide), i.e. a 
second rotary movement of the mobile element 22, with its one further 
angular movement of approximately 30.degree., until it arrives at the 
point visible in FIG. 2. In the condition illustrated in FIG. 2 (also in 
FIG. 1), therefore, the device is no longer electrically supplied, but the 
working position reached by the rod 24 is maintained. 
The commutation, i.e. the change of the balancing state of FIG. 2, is 
obtained with a successive electrical supply of the device. 
Such new supply determines, in a way similar to that already described, a 
new thrust of the sliding cursor 20, that freely slides along the guides 
21 until it contacts the inclined planes 26 on the inclined extremities 
30A of the two teeth 30; in particular such two teeth 30 are those which 
for the moment are not employed on the extremities of the guides 21A and 
21B. 
The relative thrust permits the extremities 30A of the other two teeth 30 
to free themselves from the inclined planes 28 of the guides 21A and 21B, 
that generates a new traversal component capable of causing a rotary 
motion of the mobile element 22; in this way an angular movement of 
approximately 15.degree. is obtained that permits the inclined extremities 
30A of the teeth 30 to reach in support the inclined planes 29 of the 
guides 21A and 21B. 
With the successive termination of the electrical supply to the actuator 5, 
as described above, the return is determined of the withdrawal position of 
the rod 11 that ceases the thrust on the sliding cursor 20, and thus on 
the mobile element 22. As a consequence the reaction of the spring 23, 
that operates on the rod 24, a contrary thrust is applied to the mobile 
element 22. The thrust of the inclined extremity 30A of the teeth on the 
inclined planes 29 causes a rotary motion of the mobile element 22, with a 
further movement of 30.degree.. 
In such situation the teeth 30 return therefore to the initial position, 
i.e. of restraining the linear sliding by way of the guides 21A and 21B, 
in such a way that, under the thrust of the spring 23, the withdrawal of 
the rod 24 is permitted. 
We are therefore returned to the position illustrated in FIG. 5. 
It is to be noted that the particular configuration described, with an 
adapter CB equipped with the said system of inclined planes and/or cams, 
allows for obtaining a bistable system of greatly reduced dimensions. 
Moreover, in the case described, the power characteristics of the 
thermoactuator 5 allow for managing high loads. As a consequence the 
monostable actuator DA can therefore easily be transformed to a bistable 
actuator, in a simple and modular manner by way of said adapter, inasmuch 
the components illustrated DA and CB can be assembled and tested 
separately. 
In FIG. 6 the bistable actuator device of the present invention is 
represented in an embodiment being particularly advantageous, i.e. in an 
application to door blocking for electrical household appliances, such as 
washing machines and/or cooking ovens. This safety system is particularly 
useful in the case of washing machines for avoiding opening of the door 
during use, and in the case of cooking ovens for avoiding opening of the 
door for example during pyrolysis cleaning procedures. 
In FIG. 6, the door blocking device as a whole is indicated at 40, and body 
41, a door blocking element 42 and a micro-switch 43, for the detection of 
the various functional conditions. 
The device 1 according to the invention is mounted on a housing body 41 and 
its rod 24 operates, in the above described manner, on the blocking 
element 24, which is hinged at point 44 and limited by restraints at point 
45. The micro-switch 43, by way of its lever 46, detects the two working 
positions of the element 42. 
From the given description the characteristics of the device subject of the 
invention are clear, as are its advantages. 
In particular, in the described embodiment the use of a thermoactuator 5 
allows for developing considerable power with the aim of moving even heavy 
loads, for example in the order of 20 kg, even though being of greatly 
reduced dimensions. The body 23 of the illustrated device 1 has in 
particular the following dimensions: mm 17.times.18.5.times.71.5 (flange 
13 and 14, terminals 7 and rod 24 excluded). 
The use of an electric heater 6 of the PTC type allows thermo-adjustment of 
the actuator 5 without the addition of other control systems, and 
therefore yields a precise control of the actuation device at a low cost. 
The use of a thermoelectric actuator, comprising a thermoactuator 5 and a 
PTC electric heater 6, allows powering of the system independently from 
the voltage supply, while maintaining a low level of energy consumption. 
The bistable kinematic motion (CB) allows for a further saving in energy, 
during the long actuation cycles of the device 1, inasmuch it operates in 
working and/or rest conditions with short supply cycles. 
The particularly inclined planes and/or cam structure of the kinematic 
system provide a simple bistable mechanical system, of reduced dimensions 
and of high reliability, able to maintain the thrust on great loads, also 
in the case of sporadic increases of the forces exercised on the rod 24. 
The relatively slow insertion times, normally at several seconds, allow for 
eliminating vibrations or noise during the supply cycle. 
The modularity of the system allows production and separate testing of the 
actuator and bistable parts, with a reduction of costs due to production 
waste. 
The device according to the invention thus finds a field of application for 
greater than devices of the type known, in that it functions correctly in 
the most varied conditions of use, in small spaces, without sophisticated 
control systems, with great loads and however with both high and low 
voltage supplies. 
It is clear that numerous variants are possible by the man of the art to 
the device described as an example, without for this departing from the 
novelty principles inherent in the inventive idea. 
Furthermore it is clear that the bistable actuation device illustrated and 
described in an application of a door blocking systems for electrical 
household goods could advantageously be utilised for various uses, such as 
for example the opening/closing of air circulating flaps in no-frost 
refrigerators, or together with valves. In the second case, the device 
according to the invention allows for avoiding, due to its relatively slow 
insertion times, phenomena of turbulence normally known as "water 
hammering".