Power supply circuit, related actuator and method for supplying power to a load

Abstract

The power supply circuit for powering the load (which may be an SMA component or a piezoelectric component) may use short high voltage pulses to achieve rapid heating of the load, and in order to comply with functional requirements, the SMA component or the piezoelectric component should not be powered by directly connecting it to a wire at a relatively high voltage. Also disclosed is: an actuator comprising the power supply circuit of the present disclosure and at least one load, the at least one load comprising at least one smart material selected between a piezoelectric device and a shape memory alloy (SMA) component; and a method for powering the load, the method comprising the steps of: connecting an AC to DC voltage converter of the power supply circuit to an AC power source by closing an input switch to charge an energy storage capacitor of the converter, and simultaneously opening an output switch to disconnect the load from the energy storage capacitor; disconnecting the AC to DC voltage converter of the power supply circuit from the AC power source by opening the input switch, and simultaneously closing the output switch to power the load by discharging the energy storage capacitor.

Description

Technical Field

[0001] The present disclosure relates generally to electric actuators, and more particularly to a power supply circuit suitable for powering a shape memory alloy (SMA) component, to an associated actuator including the power supply circuit and a load (the load including at least one smart material selected between a piezoelectric device and a shape memory alloy (SMA) component), and a method of powering the load. Background Art

[0002] Shape memory alloys (also known as SMAs) are materials that "remember" their original shape and return to the original shape when heated. Thermal activation of a component made of an SMA (e.g., a wire made of an SMA) can be driven by an electric current via Joule heating using a power supply circuit configured to force the current through the wire. Shape memory alloys that have the unique property of returning to shape when heated (e.g., those produced by SAES Getters SpA under the trade name SMA) SMA wire and springs) can be effectively packaged into compact, lightweight, powerful and silent actuators to replace alternative technologies based on wax, DC motors and electric motors. Unparalleled energy density, integration and design simplicity make shape memory alloys the new industry standard for linear and rotary actuators.

[0003] In order to have a fast response of the SMA actuator, it is important to quickly heat the SMA member of the SMA actuator by using a suitable power supply circuit configured to force an electric current through the SMA member.

[0004] Examples of fast SMA actuators are disclosed in document US 2016 / 0186730 and in Figure 1 Schematically shown in FIG. 3 . When the output MOSFET is closed by the drive unit 31, the SMA component is powered and the current flowing through it is provided by the tank capacitor C1 which is charged by the power supply unit 2. This existing SMA actuator has a simple structure, although it is specifically designed to work with a low voltage power supply unit 2 that injects a controlled DC current (typically 5 amps). The supply voltage is in turn adjusted according to the resistance of the SMA actuator.

[0005] Document US Pat. No. 3,710,062 discloses a full-wave rectifier comprising a storage capacitor and a large-value discharge resistor connected across the capacitor, which ensures rapid and complete discharge of the capacitor. Summary of the invention

[0006] Utilizing this existing actuator to control an SMA component or a piezoelectric component results in a slow actuation response due to the long time required to heat the SMA component or the piezoelectric component, and a large amount of heat is lost to the environment, which results in low efficiency.

[0007] According to the present disclosure, a power supply circuit for powering a load (which may be an SMA component or a piezoelectric component) may use short high voltage pulses to achieve rapid heating of the load, and in order to meet functional requirements and avoid component damage associated with overheating and / or burning, the SMA component or piezoelectric component should not be powered by connecting it directly to wires at relatively high voltages. In this regard, solutions such as those described in the paper "Cumulative Current Magnetizing Method for a Capacitor-Discharged Impulse Magnetizer" by Pai et al., published in the International Journal of Circuit Theory and Applications in 2017, are different because they will increase the output voltage relative to the power input, thereby causing damage to the voltage-responsive actuator component, and they do not provide any safety components that can discharge the capacitor in the event of damage to the load or electrical connections.

[0008] The power supply circuit defined in claim 1 meets the above requirements.

[0009] Also disclosed are: an actuator comprising the power supply circuit of the present disclosure and at least one load, the at least one load comprising at least one smart material selected between a piezoelectric component and a shape memory alloy (SMA) component; and a method for powering the load, comprising the following steps:

[0010] connecting an AC to DC voltage converter of the power supply circuit to an AC power source by closing an input switch to charge a storage capacitor of the converter, and simultaneously opening an output switch to disconnect the load from the storage capacitor;

[0011] • Disconnecting the AC to DC voltage converter of the power supply circuit from the AC power source by opening the input switch, and simultaneously closing the output switch to power the load by discharging the energy storage capacitor.

[0012] Preferred embodiments are defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A prior art SMA actuator operating at a DC low voltage is depicted.

[0014] Figure 2a An embodiment of an SMA actuator having a single input switch according to the present disclosure is depicted.

[0015] Figure 2b Another embodiment of an SMA actuator having two input switches according to the present disclosure is depicted.

[0016] Figure 3 is an exemplary time diagram of the voltage on the energy storage capacitor during the charging phase.

[0017] Figure 4 is an exemplary time diagram of the voltage on the energy storage capacitor during the discharge phase and the corresponding voltage pulse delivered to the powered load. DETAILED DESCRIPTION

[0018] Figure 2a and Figure 2b An exemplary embodiment of a power supply circuit suitable for powering a load using short high voltage pulses and without directly connecting the load to electrical wires at a relatively high voltage when powered is shown in FIG.

[0019] The power supply circuit comprises a main current path (marked with letters A and B) starting from the AC input terminals of the power supply circuit and leading to the DC output terminals connected to the powered load 1 and the output switch 2. In the electrical path B, there is an AC to DC voltage converter 3, 5, 6, 8 connected between the AC input terminals and the DC output terminals, wherein the AC to DC voltage converter 3, 5, 6, 8 is configured to receive an AC supply voltage at the AC input terminals to generate a corresponding rectified DC voltage at the DC output terminals, wherein the AC to DC voltage converter 3, 5, 6, 8 comprises a storage capacitor 3 functionally connected between the DC output terminals to maintain the rectified DC voltage.

[0020] As a general rule, the AC to DC voltage converter can be of any type. Figure 2a and Figure 2b In an optional aspect depicted in , the AC to DC voltage converter may include a full-wave diode bridge rectifier 6 functionally connected between the AC input terminals and the DC output terminals to produce a rectified DC voltage (provided to the powered load 1) as a rectified copy of the AC supply voltage. According to one aspect, the energy storage capacitor 3 has a capacitance value comprised between 10 μF and 470 μF.

[0021] according to Figure 2a and Figure 2b In an optional aspect depicted in , the AC to DC voltage converter may even include an input capacitor 8 functionally connected between the full-wave diode bridge rectifier 6 and the AC input terminal to limit the AC current absorbed by the full-wave diode bridge rectifier 6. According to one aspect, the input capacitor 8 may have a capacitance value comprised between 0.1 μF and 47 μF.

[0022] The auxiliary resistor 5 is electrically connected in parallel with the energy storage capacitor 3 to discharge the energy storage capacitor 3 when the load cannot be powered due to a fault in the load or damage to its electrical connection. The auxiliary resistor 4 may have a suitable resistance value so as not to significantly discharge the energy storage capacitor 3 when the electrical connection to the load 1 and the load 1 itself are working, but to safely discharge the energy storage capacitor 3 in the event of a fault in the load 1. According to one aspect, the auxiliary resistor 5 has a resistance value comprised between 150KΩ and 500KΩ.

[0023] In another current path A, there is a switching relay 7, which has: an excitation coil connected between the AC input terminals and configured to be energized whenever an AC voltage is applied to the AC input terminals from which the electrical paths A and B depart; and at least one internal switch controlled by the excitation coil and configured to connect the intermediate terminal T of the power supply circuit to one of the two DC output terminals when the excitation coil is not energized.

[0024] Both current paths A and B are powered at the same time, or are disconnected by the input switch 9, which is configured to connect / disconnect at least one of the AC input terminals to / from the AC power supply. When the input switch 9 is closed, the AC to DC converter is energized, and thus the energy storage capacitor 3 is charged by the rectified DC voltage, and at the same time, the excitation coil of the switching relay 7 attracts the switch of the relay 7 to keep the intermediate terminal T open. When the input switch 9 is open, the AC to DC converter is not energized, and thus the energy storage capacitor 3 is disconnected from the power supply terminal 10 and the switch of the relay 7 is released.

[0025] The power supply circuit also includes at least one drive unit 4, which is directly connected between one of the DC output terminals of the power supply circuit and the corresponding intermediate terminal T. The drive unit 4 is configured to generate a control signal that is logically valid when at least one corresponding intermediate terminal T is not disconnected, and the control signal is provided to the control terminal of the corresponding at least one output switch 2 that is configured to be turned on when the control signal is logically valid. In fact, when the input switch 9 is disconnected, the AC to DC converter is disconnected from the AC power supply terminal 10, and at the same time, the switch of the relay 7 connects the intermediate terminal T in the current path between the two DC output terminals of the power supply circuit. In this configuration, the drive unit 4 generates a logically valid control signal, and the output switch 2 connects the corresponding load 1 to be powered through the DC output terminal, thereby allowing the charge stored in the energy storage capacitor 3 to flow through the load 1.

[0026] When the input switch 9 is closed, the energy storage capacitor 3 is charged by the AC supply voltage, for example, with Figure 3During this charging phase, the load 1 is disconnected from the energy storage capacitor 3 and thus from the AC supply terminal 10. Figure 4 As shown in the timing diagram of , when the input switch 9 is turned off, the energy storage capacitor 3 is disconnected from the AC power supply terminal 10, and the output switch 2 connects the load 1 to the DC output terminal, so the load 1 is powered by the voltage pulse. Therefore, using the power supply circuit defined in claim 1, the load 1 is powered by the discharge pulse starting from a relatively high voltage, but the load 1 is never directly connected to the AC power supply terminal 10, so it is easy to meet the safety requirements for the electric load 1 that cannot be powered by a direct connection to a relatively high voltage line.

[0027] According to an aspect, the terminals 10 of the AC power supply are at a voltage comprised between 220 V and 240 V AC.

[0028] Generally, the driving unit 4 can be any circuit block that can generate a logically valid control signal when the corresponding intermediate terminal T is not disconnected. Figure 2a and Figure 2b In the optional aspect depicted in , at least one driving unit 4 is a resistor divider directly connected between the DC output terminal and the corresponding intermediate terminal T, wherein the control signal is a voltage provided at the intermediate terminal of the resistor divider. By way of example only, the resistor divider 4 includes a first resistor 4a that shares a connection node with the output switch 2 and a second resistor 4b that is directly connected to the intermediate node T, the first resistor 4a having a value included between 5KΩ and 10KΩ, and the second resistor 4b having a value included between 400KΩ and 450KΩ.

[0029] Depending on the optional aspects, Figure 2a and Figure 2b The drive unit 4 depicted in FIG. 4 and the resistor divider 4 as an example are connected to the negative DC output terminal of the energy storage capacitor 3 from one side and to the intermediate terminal T from the other side.

[0030] The output switch 2 may be any controlled switch that is closed when the control signal is valid and is open when the control signal is logically invalid. By way of example only, at least one output switch 2 may be a thyristor functionally connected to be turned on when the control signal is logically valid.

[0031] The power supply circuit of the present disclosure can be configured to supply power to multiple loads 1 by: providing multiple drive units 4 directly connected between a DC output terminal and a corresponding multiple intermediate terminal T, wherein all of the multiple drive units 4 are configured to generate a corresponding multiple control signal, and the corresponding multiple control signals are all logically valid when the corresponding intermediate terminal T is not disconnected; providing multiple output switches 2, which are configured to be turned on when the corresponding multiple control signals are logically valid, and are configured to connect the corresponding multiple loads 1 to be powered by the DC output terminal; and providing a switching relay 7 including multiple internal switches, which are all controlled by the same excitation coil and are configured to connect the multiple intermediate terminals T to the DC output terminal when the excitation coil is not energized.

[0032] The power supply circuit of the present disclosure may be used to implement an actuator for powering one or more loads 1 , wherein the load 1 includes at least one smart material selected between a piezoelectric device and a shape memory alloy (SMA) component.

[0033] According to one aspect, the load 1 comprises at least one SMA wire, which may be made of a Ni—Ti alloy, for example a type comprising one or more elements selected from Hf, Pt, Cu, Nb.

[0034] According to an aspect, the SMA wire has a diameter comprised between 76 μm and 350 μm.

[0035] Using the power supply circuit of the present disclosure, an actuator may be realized which is suitable for activating a piezoelectric component or a SMA component within a time interval comprised between 1 ms and 100 ms, preferably between 5 ms and 25 ms.

Claims

1. A power supply circuit, comprising: an AC to DC voltage converter having an AC input terminal and a DC output terminal, wherein the AC to DC voltage converter is configured to receive an AC supply voltage at the AC input terminal to generate a corresponding rectified DC voltage at the DC output terminal, wherein the AC to DC voltage converter includes: a storage capacitor functionally connected between the DC output terminals to maintain the rectified DC voltage; and an input capacitor functionally connected between a full-wave diode bridge rectifier and the AC input terminal of the AC input terminals to limit the AC current absorbed by the full-wave diode bridge rectifier; and a resistor electrically connected in parallel with the storage capacitor to discharge the storage capacitor when the load cannot be powered due to a load fault or a damaged electrical connection of the load; at least one input switch configured to connect / disconnect at least one of the AC input terminals to / from an AC power source; at least one drive unit, the at least one drive unit being directly connected between a first one of the DC output terminals of the power supply circuit and at least one corresponding intermediate terminal, the at least one drive unit being configured to generate a control signal, the control signal being logically valid when the at least one corresponding intermediate terminal is not disconnected; at least one output switch configured to be turned on when the control signal is logically valid and configured to connect a corresponding at least one load to be powered by the DC output terminal, thereby allowing the charge stored in the energy storage capacitor to flow through the load; a switching relay having: an excitation coil connected between the AC input terminals and configured to be energized whenever an AC voltage is applied to the AC input terminals; and at least one internal switch controlled by the excitation coil and configured to connect the at least one corresponding intermediate terminal to a second DC output terminal of the DC output terminals when the excitation coil is not energized; Therein, the at least one driving unit is a resistor divider directly connected between the first DC output terminal and the at least one corresponding intermediate terminal, wherein the control signal is provided at the intermediate terminal of the resistor divider.

2. The power supply circuit according to claim 1, wherein: The full-wave diode bridge rectifier is functionally connected between the AC input terminals and the DC output terminals to generate the rectified DC voltage as a rectified replica of the AC supply voltage.

3. The power supply circuit according to claim 1, wherein: The at least one output switch is a thyristor functionally connected to be turned on when the control signal is logically valid.

4. The power supply circuit according to claim 1, comprising: a plurality of drive units, the plurality of drive units being directly connected between the first DC output terminal and the corresponding plurality of intermediate terminals, the plurality of drive units being configured to generate corresponding plurality of control signals, the corresponding plurality of control signals being all logically valid when the corresponding plurality of intermediate terminals are not disconnected, a plurality of output switches configured to be turned on when the corresponding plurality of control signals are logically valid and configured to connect a corresponding plurality of loads to be powered by the DC output terminals; The switching relay includes a plurality of internal switches, all of which are controlled by the excitation coil and are configured to connect the corresponding plurality of intermediate terminals to the second DC output terminal when the excitation coil is not energized.

5. An actuator comprising: The power supply circuit according to claim 1, and At least one load includes at least one smart material selected between a piezoelectric device and a shape memory alloy component.

6. A method for supplying power to a load from an AC power source, comprising: Installing the power supply circuit according to claim 1; an output switch connecting the load to the power supply circuit; connecting an AC to DC voltage converter of the power supply circuit to the AC power source by closing the input switch to charge a storage capacitor functionally connected between DC output terminals of the power supply circuit, and simultaneously opening the output switch to disconnect the load from the storage capacitor; The AC to DC voltage converter of the power supply circuit is disconnected from the AC power source by opening the input switch, and simultaneously the output switch is closed to power the load by discharging the energy storage capacitor.

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