CA2314955A1 - Thermal snap switch - Google Patents
Thermal snap switch Download PDFInfo
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- CA2314955A1 CA2314955A1 CA002314955A CA2314955A CA2314955A1 CA 2314955 A1 CA2314955 A1 CA 2314955A1 CA 002314955 A CA002314955 A CA 002314955A CA 2314955 A CA2314955 A CA 2314955A CA 2314955 A1 CA2314955 A1 CA 2314955A1
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- Prior art keywords
- shape memory
- snap
- electrical contact
- memory alloy
- alloy component
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H37/00—Thermally-actuated switches
- H01H37/02—Details
- H01H37/32—Thermally-sensitive members
- H01H37/323—Thermally-sensitive members making use of shape memory materials
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- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Thermally Actuated Switches (AREA)
Abstract
The present invention relates to thermal snap switch mechanisms and the like.
The thermal snap switch may for example be incorporated into fuse mechanisms.
The thermal snap switch may for example be incorporated into fuse mechanisms.
Description
This invention relates to elctrical switching devices that are used to interrupt or/and reestablish electrical connections under controlled conditions.
ABSTRACT
The innovation consists in a generic concept of bistable shape memory mufti-layer interrupters including methods of their manufacturing. The action of interrupting and reestablishing electrical contacts is assured by controlled heating and cooling of one or more shape memory layers assembled in a sandwich-like structure. The present invention includes three major types of devices, which can be used in three different kinds of applications. When electrical circuits must be protected thermally without having to reset afterwards the electrical connection, a One 13~a3~ Shape Memory Interrupter can be proposed. When the electrical connection should be restored after a fault, a Reset Shape Merrrory Interrupter can be used.
Finally, in order to perform alternate switching and resetting actions, a Two Way Sltape Memory Interrupter can be devised. All these devices make use of one or two layers of shape memory material, that can be provided in various shapes.
IN~1~RODUCT10N
To protect electrical circuits and avoid overheating of the conductors, it is necessary to severe an electrical contact in case of current overload as well as to reestablish the contact when the fault has passed. The actions of interrupting and reestablishing electrical contacts are commonly used in switching devices. In both cases, the switching action should be performed rapidly to prevent the formation of electrical arcs between contacts and minimize circuit disturbance.
S'fA'1'E OF THE ART
Thermally sensitive elements commonly used in these applications are bimetal or electromagnetic relays. Bimetal switches combining sensing and actuating functions represent an attractive choice when the space available is restricted, but an exact trigger temperature cannot be easily provided because of their proportional deflection-temperature switching behavior.
Shape Memory Alloys (SMA) possess a higher energy density comparatively to bimetal actuators ( 1-5 J/cm3 versus 0,02 J/cm3). Moreover, because of their stepwise deflection-temperature relationship, SMAs can be programmed with accuracy to a given trigger temperature about ~2°C (Figure 1 [1]). For example, a cantilever beam or a semi-spherical shape memory membrane represent compact examples of actuators severing the electrical contacts in case of overheating [2, 3).
I-iowever, neither thermo-bimetal nor SMA interrupters guarantee an instantaneous and definitive break-off operation. Thermo-bimetal interrupters providing a progressive switching action cause bouncing of the electrical connection, i.e., on and off switching, thus provoking potential disturbances in the system. SMA intcrrulUcrs arc also sensitive to contact flickering despite; the fact that the speed of the martcnsitic transformation is high enough to theoretically guarantee an instantaneous interruption of the current. (It is comparable with the speed of sound in metals, i.e., approximately 5000 mls). Practically, it is difficult to obtain a triggering time for SMA interrupters lower than 0.1 sec because the martensitic transformation is a thermally activated phenomenon and strongly depends on the heat transfer conditions between the actuator and the environment.
In order to avoid these problems, bistable bimetal active elements have been proposed [4, S, 6].
There are commonly designed in the shape of circular membranes or flexible beams having two stable shapes: one at high temperature and another one at low temperature, the second shape being a mirror reflection of the first one. These devices produce a snap effect during their activation, thus preventing contact flickering (or bouncing) during current switching (Figure 2 [7], Figure 3 [4]). The major deficiency of known bimetal bistable thermal interrupters lies in their sensitivity to impact or vibration, i.e., these switches can easily be moved out of their stable positions by simply knocking on the casing.
In order to avoid this problem and thus enhance the reliability of thermal interrupters, SMA
bistable thermal interrupters are proposed in this invention. These devices guarantee more precise triggering temperatures and provide more stable thrust positions than bimetallic thermal interrupters, because SMA possess a very marked difference (at least 10 times) in material rigidity between high and low temperatures.
-contiiever eeam -Frte Length SO mm Thitkn~ss 1mm E
E_ z v w J
Figure 1 Temperature/deflection curves for a shape memory Cu-Zn-A1 actuator and a bimetal TB 1577A actuator [1].
ABSTRACT
The innovation consists in a generic concept of bistable shape memory mufti-layer interrupters including methods of their manufacturing. The action of interrupting and reestablishing electrical contacts is assured by controlled heating and cooling of one or more shape memory layers assembled in a sandwich-like structure. The present invention includes three major types of devices, which can be used in three different kinds of applications. When electrical circuits must be protected thermally without having to reset afterwards the electrical connection, a One 13~a3~ Shape Memory Interrupter can be proposed. When the electrical connection should be restored after a fault, a Reset Shape Merrrory Interrupter can be used.
Finally, in order to perform alternate switching and resetting actions, a Two Way Sltape Memory Interrupter can be devised. All these devices make use of one or two layers of shape memory material, that can be provided in various shapes.
IN~1~RODUCT10N
To protect electrical circuits and avoid overheating of the conductors, it is necessary to severe an electrical contact in case of current overload as well as to reestablish the contact when the fault has passed. The actions of interrupting and reestablishing electrical contacts are commonly used in switching devices. In both cases, the switching action should be performed rapidly to prevent the formation of electrical arcs between contacts and minimize circuit disturbance.
S'fA'1'E OF THE ART
Thermally sensitive elements commonly used in these applications are bimetal or electromagnetic relays. Bimetal switches combining sensing and actuating functions represent an attractive choice when the space available is restricted, but an exact trigger temperature cannot be easily provided because of their proportional deflection-temperature switching behavior.
Shape Memory Alloys (SMA) possess a higher energy density comparatively to bimetal actuators ( 1-5 J/cm3 versus 0,02 J/cm3). Moreover, because of their stepwise deflection-temperature relationship, SMAs can be programmed with accuracy to a given trigger temperature about ~2°C (Figure 1 [1]). For example, a cantilever beam or a semi-spherical shape memory membrane represent compact examples of actuators severing the electrical contacts in case of overheating [2, 3).
I-iowever, neither thermo-bimetal nor SMA interrupters guarantee an instantaneous and definitive break-off operation. Thermo-bimetal interrupters providing a progressive switching action cause bouncing of the electrical connection, i.e., on and off switching, thus provoking potential disturbances in the system. SMA intcrrulUcrs arc also sensitive to contact flickering despite; the fact that the speed of the martcnsitic transformation is high enough to theoretically guarantee an instantaneous interruption of the current. (It is comparable with the speed of sound in metals, i.e., approximately 5000 mls). Practically, it is difficult to obtain a triggering time for SMA interrupters lower than 0.1 sec because the martensitic transformation is a thermally activated phenomenon and strongly depends on the heat transfer conditions between the actuator and the environment.
In order to avoid these problems, bistable bimetal active elements have been proposed [4, S, 6].
There are commonly designed in the shape of circular membranes or flexible beams having two stable shapes: one at high temperature and another one at low temperature, the second shape being a mirror reflection of the first one. These devices produce a snap effect during their activation, thus preventing contact flickering (or bouncing) during current switching (Figure 2 [7], Figure 3 [4]). The major deficiency of known bimetal bistable thermal interrupters lies in their sensitivity to impact or vibration, i.e., these switches can easily be moved out of their stable positions by simply knocking on the casing.
In order to avoid this problem and thus enhance the reliability of thermal interrupters, SMA
bistable thermal interrupters are proposed in this invention. These devices guarantee more precise triggering temperatures and provide more stable thrust positions than bimetallic thermal interrupters, because SMA possess a very marked difference (at least 10 times) in material rigidity between high and low temperatures.
-contiiever eeam -Frte Length SO mm Thitkn~ss 1mm E
E_ z v w J
Figure 1 Temperature/deflection curves for a shape memory Cu-Zn-A1 actuator and a bimetal TB 1577A actuator [1].
TEMPERATURE ('C 1 y O
Figurz ? Temperatureldel7ection characteristics of a himetal snap action disc [?].
Figure 3 US Patent 5,670,930, Temperature-dependent switch [4].
rower Upper Snepping ~pmparature 10~
~F
STATEMENT OF INVENTION
The present invention in one aspect provides a snap thermal switch comprising a first electrical contact element a second electrical contact element and a snap element for providing temperature dependent electrical contact between said first and second electrical contact elements said snap element comprising a primary contact component and a shape memory alloy component, said primary contact component being in electrical contact with said second electrical contact element, said shape memory alloy component being configured and disposed such that said shape memory alloy component has a first (e. g. working) configuration wherein said shape memory alloy component is in electrical contact with said first electrical contact element and a second (e. g. non-working) configuration wherein said shape memory alloy component is electrically disconnected from said first electrical contact element, said shape memory alloy component being configured and disposed such that when said shape memory alloy component is subjected to a predetermined snap temperature, said shape memory alloy component is able to pass with snap action from said first configuration to said second configuration.
In accordance with the present invention a snap thermal switch as dedescribed herein may have a said snap element which has a disk shape and comprises a peripheral portion and a centrally disposed semi-spherical er partially-spherical protrusion or portion wherein the peripheral portion thereof defines said primary contact component and wherein said a central portion defines said shape memory alloy component.
DESCRIPTION OF THE INVENTION
The present invention includes three major types of devices, which can be used in three different kinds of applications. V~hen electrical circuits must be protected thermally without having to reset afterwards the electrical connection, a One lVa~~ Shape Memory Interrupter can be proposed. When the electrical connection should be restored after a fault, a Reset Shape ~Iemor~y~ Interr~rpter can be used. Finally, in order to perform alternate switching and resetting actions, a Two iVay Slrape Memory Interrrrpter can be devised. All these devices make use of one or two layers of shape memory material, that can be provided in various shapes.
One Way Shane Memory Interrupter The one-way SMA switch consists of the following main parts (Figure 4): the casing (1) that contains the isolated contact flat element (2) and the shape memory flexible element, called the snap (3). The shape memory element has two stable symmetric shapes: a low temperature shape (upward position) and a high temperature shape (downward position).
No power is required for it to stay in either position and it will remain so until activated to change position. Upon heating, the switch will move from the low temperature position to the high temperature one. However, in order to go from the high temperature position to the low temperature one, an external mechanical action is needed.
., i Figure 4 Schematics of the Shape Memory Active Single Layer Interrupter: (1) casing, (2) flat contact element and (3) flexible shape memory element (snap).
The proposed invention can be realized in the followin~way:
~ Plastic deformation of a shape memory film using conventional drawing procedure in order to obtain a semi-spherical (domed) shape (Figure 5, left).
Annealing of the deformed element in a clamping tool that retains its shape during the thermal treatment in order to memorize the high temperature shape (Figure 5, right).
~ Deformation of the shape memory element at ambient temperature in the direction opposite to that of stage 1 in order to obtain the low temperature shape.
~ Instal lation of the shape memory element in the casing.
~ The device presented in Figure 4 is normally closed. It means that in normal working conditions, an electrical connection is established between the shape memory element (3) and the contact element (2). When the temperature of the system and of the shape memory element (3) exceeds the phase transformation temperature of the shape memory material, the device tends to regain its initial downward shape. (This temperature elevation can be provoked by direct heating due to Joule effect as well as by convection, conductive or radiation heating.) However, the shape memory element (3) is maintained in its upward position as long as the energy of shape recovery accumulating in the material does not exceed tl~e energy that ensures the mechanical stability of the shape memory element (3).
When the energy of shape recovery becomes higher than the stability limit of the device, it will rock abruptly from the low temperature upward stable position to the high temperature downward position, thus interrupting the electrical connection.
Figure 5 Typical drawing process (left): (1) punch, (2) holding ring, (3) snap element, (4) die. ~1'hcrmal treatment crimping tool (right).
Reset Shane Memor-y Interrupter The electrical connection can be restored by moving the shape memory element back to its initial upward low temperature position. This resetting action can be performed using for example a two layer structure combining a shape memory layer and a superelastic layer bonded together instead a single shape memory element (Figure 6, left). These layers, because of their different phase states with respect to the service temperature range, will demonstrate different behaviors during heating or cooling.
Upon heating, the shape memory layer becomes more rigid than the superelastic one, thus forcing the whole system to rock into the opposite stable position (Figure 6, right). Upon cooling, the superelastic layer becomes more rigid and will reverse the shape of the device.
Therefore, alternate heating and cooling of the two layer SMA structure will provoke its motion from one stable position to another (Figure 6, right and left).
The proposed technolo~.y can be realized in the following way:
~ Plastic deformation of a shape memory and superelastic layers using conventional drawing procedure in order to obtain a dome shaped zone (Figure 5, left).
~ Annealing of the deformed layers in a clamping tool so that the shape memory and superelastic layers will retain and memorize their respective shapes during thermal treatment (Figure 5, right).
~ Assembly of the two layers with an adhesive film between their back (opposite to the protruded zones) surfaces (Figure 7a).
~ Bonding of the two layers by fixing them between two rigid plates (Figure 7b).
~ Unce the contact forces are released, the superelastic layer being more rigid at low temperature than the shape memory layer will force the last one to follow the former in the high temperature position (Figure 7c).
~ If a two layer system is heated, the shape memory layer becomes more rigid than the superelastic one and will inverse the device position (Figure 7d). When heating is interrupted, the system wilt cool down and the contact element returns to its low-temperature position (Figure 7c).
Figure 6 Schematics of the Reset Shape Memory Interrupter: (1) casing, (2) flat contact element and (3) flexible shape memory element (snap); (1) casing, (2) and (S) flat contact elements, (3) aIld (4) bistable shape memory and superelastic elements bonded together.
Adhesive film Shape memory layer / / / l / /~l (b) Bonding (a) Assembling St~perelastic layer (c) Low temperature shape (d) High temperature shape ~~3 Figure 7 Assembly, bonding and testing of the Two Layer Shape Memory Interrupter.
Two Way Shape Memory Interrupter No power is required for the Reset Shnpe Memory Ir:terrr~pter presented above to reset the electrical connection (in case of a closed switch) or break this connection (in case of an open switch). however, to activate the system, i.e., io bring it into the high temperature position and maintain it in this position, a permanent heating of the shape memory layer is needed. In certain cases, especially for energy saving considerations, it can be important to ensure that external power is necessary only to activate the switching action so that any position of the switch can be retained without external power input.
O
i 'This principle can be realized using for example a three layer structure combining two shape memory layers separated by a polymer film. Upon heating the first shape memory layer, this layer becomes more rigid than the second one, thus forcing the whole system to rock into the opposite stable position. Upon heating the second layer, then in turn this layer becomes more rigid and hence the device will reverse its shape. Therefore, alternatively heating the first or the second shape memory layers will move the interrupter from one stable position to another.
The proposed technology can be realized in the followi~way:
~ Plastic deformation of shape memory layers using conventional drawing procedure in order to obtain a dome shaped zone (Figure 5, left).
~ Annealing of the deformed layers in a clamping tool so that the shape memory layers will retain and memorize their respective shapes during thermal treatment (Figure S, right).
~ Assembly of the two layers with a polymer film between their back (opposite to the protruded zones) surfaces (Figure 8a).
~ Bonding of the two layers by fixing them between two rigid plates (Figure 8b).
~ Once the contact forces are released, the whole system will not move because both layers have equal rigidity. However, if one of the shape memory layers is heated, it becomes more rigid at high temperature than another one and will force the last to move in the high temperature position of tire former (Figure 8c).
Pohm~er film 1" .Shane menrorv layer (b) Bonding (a) Assembly 2"" Shape memory layer (c) fiieating of the 2"d shape memory layer (d) Heating of the 1" shape memory layer Figure 8 Assembly, bonding and testing of the Two Way Shape Memory Interrupter.
'this three layer structure can be used in electro-mechanical matrix connection devices consisting of "n" inputs and "m" outputs giving the possibility of connecting each input to one or many outputs, and vice versa. This interconnection can be performed by means of an electrically driven mechanical actuator acting ars a micro-switch that connects interconnecting pads on a printed circuit board. This technology including micro-relays laid out in a matrix configuration is a natural extension of the single actuator tcchnologres presented beforehand.
In order to perform an actuation, the contact zone selected must be heated so that one shape memory layer becomes locally more rigid than the second one and hence the device will inverse its position. Once the second shape memory layer is heated, the system will switch back to the opposite position. Therefore, by alternatively heating or cooling each elementary micro-relay, it is possible to establish or interrupt electrical connections.
ADVANTAGES
The main advantages of Multi-Layer Shape Memory Interrupters are the following:
~ rapid action (contact separation time in the range of 0.1 millisecond);
~ stability of each contact position;
~ compactness (strokes of 0,6 - 0,8 mm);
~ high predictability and thermal accuracy (up to t2°C);
REFERENCES
1. P. Tautzenberger, Thermal actuators: a comparaison of shape memory alloys with tliern~ostatic bimetals and wax actuators, in Engineering Aspects of Shape Memory Alloys, Edit. T.W. Duerig, K.N. Melton and C.M. Wayman, Butterworth-Heinemann, 1990.
2. US Patent 5,747,187, Lithium Baitery having an over-loading preventing device May 1988.
3. US Patent 6,005,469, Thermal switch assembly, December 1999.
4. US Patent 5,670,930, Temperature-dependent switch, Sept. 1997.
Figurz ? Temperatureldel7ection characteristics of a himetal snap action disc [?].
Figure 3 US Patent 5,670,930, Temperature-dependent switch [4].
rower Upper Snepping ~pmparature 10~
~F
STATEMENT OF INVENTION
The present invention in one aspect provides a snap thermal switch comprising a first electrical contact element a second electrical contact element and a snap element for providing temperature dependent electrical contact between said first and second electrical contact elements said snap element comprising a primary contact component and a shape memory alloy component, said primary contact component being in electrical contact with said second electrical contact element, said shape memory alloy component being configured and disposed such that said shape memory alloy component has a first (e. g. working) configuration wherein said shape memory alloy component is in electrical contact with said first electrical contact element and a second (e. g. non-working) configuration wherein said shape memory alloy component is electrically disconnected from said first electrical contact element, said shape memory alloy component being configured and disposed such that when said shape memory alloy component is subjected to a predetermined snap temperature, said shape memory alloy component is able to pass with snap action from said first configuration to said second configuration.
In accordance with the present invention a snap thermal switch as dedescribed herein may have a said snap element which has a disk shape and comprises a peripheral portion and a centrally disposed semi-spherical er partially-spherical protrusion or portion wherein the peripheral portion thereof defines said primary contact component and wherein said a central portion defines said shape memory alloy component.
DESCRIPTION OF THE INVENTION
The present invention includes three major types of devices, which can be used in three different kinds of applications. V~hen electrical circuits must be protected thermally without having to reset afterwards the electrical connection, a One lVa~~ Shape Memory Interrupter can be proposed. When the electrical connection should be restored after a fault, a Reset Shape ~Iemor~y~ Interr~rpter can be used. Finally, in order to perform alternate switching and resetting actions, a Two iVay Slrape Memory Interrrrpter can be devised. All these devices make use of one or two layers of shape memory material, that can be provided in various shapes.
One Way Shane Memory Interrupter The one-way SMA switch consists of the following main parts (Figure 4): the casing (1) that contains the isolated contact flat element (2) and the shape memory flexible element, called the snap (3). The shape memory element has two stable symmetric shapes: a low temperature shape (upward position) and a high temperature shape (downward position).
No power is required for it to stay in either position and it will remain so until activated to change position. Upon heating, the switch will move from the low temperature position to the high temperature one. However, in order to go from the high temperature position to the low temperature one, an external mechanical action is needed.
., i Figure 4 Schematics of the Shape Memory Active Single Layer Interrupter: (1) casing, (2) flat contact element and (3) flexible shape memory element (snap).
The proposed invention can be realized in the followin~way:
~ Plastic deformation of a shape memory film using conventional drawing procedure in order to obtain a semi-spherical (domed) shape (Figure 5, left).
Annealing of the deformed element in a clamping tool that retains its shape during the thermal treatment in order to memorize the high temperature shape (Figure 5, right).
~ Deformation of the shape memory element at ambient temperature in the direction opposite to that of stage 1 in order to obtain the low temperature shape.
~ Instal lation of the shape memory element in the casing.
~ The device presented in Figure 4 is normally closed. It means that in normal working conditions, an electrical connection is established between the shape memory element (3) and the contact element (2). When the temperature of the system and of the shape memory element (3) exceeds the phase transformation temperature of the shape memory material, the device tends to regain its initial downward shape. (This temperature elevation can be provoked by direct heating due to Joule effect as well as by convection, conductive or radiation heating.) However, the shape memory element (3) is maintained in its upward position as long as the energy of shape recovery accumulating in the material does not exceed tl~e energy that ensures the mechanical stability of the shape memory element (3).
When the energy of shape recovery becomes higher than the stability limit of the device, it will rock abruptly from the low temperature upward stable position to the high temperature downward position, thus interrupting the electrical connection.
Figure 5 Typical drawing process (left): (1) punch, (2) holding ring, (3) snap element, (4) die. ~1'hcrmal treatment crimping tool (right).
Reset Shane Memor-y Interrupter The electrical connection can be restored by moving the shape memory element back to its initial upward low temperature position. This resetting action can be performed using for example a two layer structure combining a shape memory layer and a superelastic layer bonded together instead a single shape memory element (Figure 6, left). These layers, because of their different phase states with respect to the service temperature range, will demonstrate different behaviors during heating or cooling.
Upon heating, the shape memory layer becomes more rigid than the superelastic one, thus forcing the whole system to rock into the opposite stable position (Figure 6, right). Upon cooling, the superelastic layer becomes more rigid and will reverse the shape of the device.
Therefore, alternate heating and cooling of the two layer SMA structure will provoke its motion from one stable position to another (Figure 6, right and left).
The proposed technolo~.y can be realized in the following way:
~ Plastic deformation of a shape memory and superelastic layers using conventional drawing procedure in order to obtain a dome shaped zone (Figure 5, left).
~ Annealing of the deformed layers in a clamping tool so that the shape memory and superelastic layers will retain and memorize their respective shapes during thermal treatment (Figure 5, right).
~ Assembly of the two layers with an adhesive film between their back (opposite to the protruded zones) surfaces (Figure 7a).
~ Bonding of the two layers by fixing them between two rigid plates (Figure 7b).
~ Unce the contact forces are released, the superelastic layer being more rigid at low temperature than the shape memory layer will force the last one to follow the former in the high temperature position (Figure 7c).
~ If a two layer system is heated, the shape memory layer becomes more rigid than the superelastic one and will inverse the device position (Figure 7d). When heating is interrupted, the system wilt cool down and the contact element returns to its low-temperature position (Figure 7c).
Figure 6 Schematics of the Reset Shape Memory Interrupter: (1) casing, (2) flat contact element and (3) flexible shape memory element (snap); (1) casing, (2) and (S) flat contact elements, (3) aIld (4) bistable shape memory and superelastic elements bonded together.
Adhesive film Shape memory layer / / / l / /~l (b) Bonding (a) Assembling St~perelastic layer (c) Low temperature shape (d) High temperature shape ~~3 Figure 7 Assembly, bonding and testing of the Two Layer Shape Memory Interrupter.
Two Way Shape Memory Interrupter No power is required for the Reset Shnpe Memory Ir:terrr~pter presented above to reset the electrical connection (in case of a closed switch) or break this connection (in case of an open switch). however, to activate the system, i.e., io bring it into the high temperature position and maintain it in this position, a permanent heating of the shape memory layer is needed. In certain cases, especially for energy saving considerations, it can be important to ensure that external power is necessary only to activate the switching action so that any position of the switch can be retained without external power input.
O
i 'This principle can be realized using for example a three layer structure combining two shape memory layers separated by a polymer film. Upon heating the first shape memory layer, this layer becomes more rigid than the second one, thus forcing the whole system to rock into the opposite stable position. Upon heating the second layer, then in turn this layer becomes more rigid and hence the device will reverse its shape. Therefore, alternatively heating the first or the second shape memory layers will move the interrupter from one stable position to another.
The proposed technology can be realized in the followi~way:
~ Plastic deformation of shape memory layers using conventional drawing procedure in order to obtain a dome shaped zone (Figure 5, left).
~ Annealing of the deformed layers in a clamping tool so that the shape memory layers will retain and memorize their respective shapes during thermal treatment (Figure S, right).
~ Assembly of the two layers with a polymer film between their back (opposite to the protruded zones) surfaces (Figure 8a).
~ Bonding of the two layers by fixing them between two rigid plates (Figure 8b).
~ Once the contact forces are released, the whole system will not move because both layers have equal rigidity. However, if one of the shape memory layers is heated, it becomes more rigid at high temperature than another one and will force the last to move in the high temperature position of tire former (Figure 8c).
Pohm~er film 1" .Shane menrorv layer (b) Bonding (a) Assembly 2"" Shape memory layer (c) fiieating of the 2"d shape memory layer (d) Heating of the 1" shape memory layer Figure 8 Assembly, bonding and testing of the Two Way Shape Memory Interrupter.
'this three layer structure can be used in electro-mechanical matrix connection devices consisting of "n" inputs and "m" outputs giving the possibility of connecting each input to one or many outputs, and vice versa. This interconnection can be performed by means of an electrically driven mechanical actuator acting ars a micro-switch that connects interconnecting pads on a printed circuit board. This technology including micro-relays laid out in a matrix configuration is a natural extension of the single actuator tcchnologres presented beforehand.
In order to perform an actuation, the contact zone selected must be heated so that one shape memory layer becomes locally more rigid than the second one and hence the device will inverse its position. Once the second shape memory layer is heated, the system will switch back to the opposite position. Therefore, by alternatively heating or cooling each elementary micro-relay, it is possible to establish or interrupt electrical connections.
ADVANTAGES
The main advantages of Multi-Layer Shape Memory Interrupters are the following:
~ rapid action (contact separation time in the range of 0.1 millisecond);
~ stability of each contact position;
~ compactness (strokes of 0,6 - 0,8 mm);
~ high predictability and thermal accuracy (up to t2°C);
REFERENCES
1. P. Tautzenberger, Thermal actuators: a comparaison of shape memory alloys with tliern~ostatic bimetals and wax actuators, in Engineering Aspects of Shape Memory Alloys, Edit. T.W. Duerig, K.N. Melton and C.M. Wayman, Butterworth-Heinemann, 1990.
2. US Patent 5,747,187, Lithium Baitery having an over-loading preventing device May 1988.
3. US Patent 6,005,469, Thermal switch assembly, December 1999.
4. US Patent 5,670,930, Temperature-dependent switch, Sept. 1997.
5. US Patent 4,470,033, 'Thermal switch, Sept. I 984.
6. US Patent 5,574,421, Snap disc thermostat and self calibrating assembly method, Nov. 1996.
7. F.E. Schneider, Thermobimetalle (F.E. Schneider editor), expert verlag 93, 1982.
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Claims (3)
1. A snap thermal switch comprising a first electrical contact element a second electrical contact element and a snap element for providing temperature dependent electrical contact between said first and second electrical contact elements said snap element comprising a primary contact component and a shape memory alloy component, said primary contact component being in electrical contact with said second electrical contact element, said shape memory alloy component being configured and disposed such that said shape memory alloy component has a first (e. g. working) configuration wherein said shape memory alloy component is in electrical contact with said first electrical contact element and a second (e. g. non-working) configuration wherein said shape memory alloy component is electrically disconnected from said first electrical contact element, said shape memory alloy component being configured and disposed such that when said shape memory alloy component is subjected to a predetermined snap temperature, said shape memory alloy component is able to pass with snap action from said first configuration to said second configuration.
2. A snap thermal switch as defined in claim 1 wherein said snap element has a disk shape and comprises a peripheral portion and a centrally disposed semi-spherical or partially-spherical protrusion or portion wherein the peripheral portion thereof defines said primary contact component and wherein said a central portion defines said shape memory alloy component.
3. A snap thermal switch, system or device as described herein
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002314955A CA2314955A1 (en) | 2000-08-03 | 2000-08-03 | Thermal snap switch |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002314955A CA2314955A1 (en) | 2000-08-03 | 2000-08-03 | Thermal snap switch |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2314955A1 true CA2314955A1 (en) | 2002-02-03 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002314955A Abandoned CA2314955A1 (en) | 2000-08-03 | 2000-08-03 | Thermal snap switch |
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| CA (1) | CA2314955A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20130081389A1 (en) * | 2011-09-30 | 2013-04-04 | GM Global Technology Operations LLC | Composite Bi-Stable Device |
-
2000
- 2000-08-03 CA CA002314955A patent/CA2314955A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20130081389A1 (en) * | 2011-09-30 | 2013-04-04 | GM Global Technology Operations LLC | Composite Bi-Stable Device |
| US9236207B2 (en) * | 2011-09-30 | 2016-01-12 | GM Global Technology Operations LLC | Composite bi-stable device |
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