WO2015077830A1

WO2015077830A1 - Systems and methods for driving piezoelectric benders

Info

Publication number: WO2015077830A1
Application number: PCT/AU2014/001088
Authority: WO
Inventors: Andrew Fleming; Shannon RIOS
Original assignee: Newcastle Innovation Limited
Priority date: 2013-11-29
Filing date: 2014-11-28
Publication date: 2015-06-04

Abstract

Described herein are systems and methods for driving piezoelectric bender devices being operable within a specified voltage tolerance range extending between predetermined upper and lower operable voltages. The bender devices include one or more piezoelectric layers, at least one reference electrode and at least one drive electrode. One embodiment provides a system (1) for driving a piezoelectric bender device (3). The system (1) includes an input (23) for receiving a variable signal (V _in), a drive circuit (25) that is responsive to the variable signal (V _in) at the input for providing a drive voltage (V _d) to a drive electrode (11) and a controller (27) for maintaining the drive voltage within the voltage tolerance range of the bender device.

Description

SYSTEMS AND METHODS FOR DRIVING

PIEZOELECTRIC BENDERS

FIELD OF THE INVENTION

[0001] The present invention relates to piezoelectric actuators and in particular to systems and methods of driving piezoelectric bender type actuators. While some embodiments will be described herein with particular reference to that application, it will be appreciated that the invention is not limited to such a field of use, and is applicable in broader contexts.

BACKGROUND

[0002] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0003] Piezoelectric benders are a common type of piezoelectric actuator and are used in applications such as textile machines, fluid control devices and beam steering. Benders can be of the unimorph, bimorph or multimorph type. Unimorph actuators have a single piezoelectric layer bonded to a non-piezoelectric elastic plate. Conventional bimorph piezoelectric benders consist of two piezoelectric layers joined together to form a beam, usually with a centre shim sandwiched between the layers to increase the mechanical reliability. The beam is usually attached to a mount at one end in a cantilever arrangement. However it can also be simply supported or fixed on both ends.

[0004] By controlling the voltage across the piezoelectric layers with respect to the poling direction, the beam can be made to bend up or down and extend or contract. Bimorph actuators develop deflection and force when one piezoelectric layer contracts while the other layer expands. Unimorph benders deflect when the single piezoelectric layer contracts or expands. Multimorph benders work in a similar fashion to bimorph benders except that each piezoelectric layer is comprised of many thinner piezoelectric layers co-fired together and will alternately contract and expand about the neutral axis.

[0005] A number of techniques for driving piezoelectric benders are known. US Patent 5,382,864 discloses a technique for switching the centre electrode between the bias voltage and ground. Similarly, US Patent 6,888,291 to Arbogast & Calkins describes a method for driving an electrostrictive bimorph actuator by controlling the centre voltage between the top and bottom electrode voltages. [0006] US Patent Application Publication 201 1/0223044 to Nakayama et al. relates to a piezoelectric element driving circuit that uses a transformer with a centre tap, diodes and a capacitor to control a piezoelectric pump by sending a series of voltage pulses to the device.

[0007] US Patent 8,508,104 to Kamitani et al. describes a method for driving a piezoelectric actuator in a way to suppress higher-order resonant modes. This method uses a feedback circuit to drive the piezoelectric actuator.

[0008] The various known methods of driving piezoelectric benders can be broadly classified into several main categories, including: series driven benders which use two wires and the poling direction of the two piezo layers are opposite; parallel driven benders, which use two wires for control and the poling direction of the two layers are aligned, one wire is connected to the centre electrode and the other wire is connected to the two outer electrodes; biased uni-polar driven benders, which require three wires and three electrodes to operate and two power supplies; and bridge driven benders.

[0009] All of the known systems for driving piezoelectric bender actuator devices only drive the devices across a subset of the full device tolerance range and/or require restriction of the input control signal so as to avoid exceeding the specified tolerances.

SUMMARY OF THE INVENTION

[0010] It is an object of the invention, in its preferred form to provide improved or alternative systems and methods for driving piezoelectric benders.

[001 1] In accordance with a first aspect of the present invention there is provided A system for driving a piezoelectric bender device being operable within a specified voltage tolerance range extending between predetermined upper and lower operable voltages, the bender device including one or more piezoelectric layers, at least a first electrode and a second electrode, the system including:

an input for receiving a variable signal;

a drive circuit that is responsive to the variable signal at the input for providing a drive voltage to the second electrode; and

a controller for maintaining the drive voltage within the range.

[0012] The controller preferably maintains the drive voltage in a range that extends substantially the full tolerance range between the upper and lower operable voltages. [0013] The controller preferably includes the power supply for the drive circuit. The controller preferably also includes a bias circuit providing a DC bias voltage.

[0014] The drive circuit preferably includes at least one amplifier configured for receiving the variable signal and outputting the drive voltage between upper and lower cut-off voltages.

[0015] The controller preferably controls the upper and lower cut-off voltages of the at least one amplifier. Preferably one or both of the upper and lower cut-off voltages are derived from one or both of the upper and lower operable voltages.

[0016] In some embodiments the system preferably includes a single amplifier configured for outputting the drive voltage to at least the second electrode between the upper and lower cut-off voltages.

[0017] In some embodiments the drive voltage is preferably output to only a single electrode. In other embodiments the drive voltage is preferably output to the first and second electrodes. In some embodiments the system preferably includes a third electrode.

[0018] The bias circuit is preferably connected to at least one of the first and third electrodes. The bias circuit is preferably connected to the first electrode for providing a first DC bias voltage to the first electrode. The bias circuit is preferably also connected to the third electrode for providing a second DC bias voltage to the third electrode.

[0019] The upper cut-off voltage is preferably higher than or equal to the first DC bias voltage and the lower cut-off voltage is preferably lower than or equal to the second DC bias voltage. In some embodiments the upper cut-off voltage is preferably equal to the upper operable voltage. In some embodiments the lower cut-off voltage is preferably equal to the lower operable voltage. In other embodiments the lower cut-off voltage is preferably zero volts.

[0020] In some embodiments the first DC bias voltage is preferably equal to the sum of the upper and lower operable voltages and the second DC bias voltage is preferably zero.

[0021] In some embodiments the upper cut-off voltage is preferably equal to one half of the upper operable voltage. In these embodiments the lower cut-off voltage is preferably equal to minus one half of the upper operable voltage.

[0022] In some embodiments the upper cut-off voltage is preferably equal to one half of the difference between the upper operable voltage and the lower operable voltage. In these embodiments the lower cut-off voltage is equal to minus one half of the difference between the upper operable voltage and the lower operable voltage.

[0023] In some embodiments the first DC bias voltage is preferably equal to one half of the sum of the upper and lower operable voltages and the second DC bias voltage is preferably equal to minus one half of the sum of the upper and lower operable voltages.

[0024] In some embodiments the upper cut-off voltage is preferably equal to the absolute value of the minimum operable voltage and the lower cut-off voltage is preferably equal to the negative absolute value of the minimum operable voltage.

[0025] In some embodiments at least one of the electrodes is preferably electrically grounded. In other embodiments both the first and third electrodes are preferably electrically grounded.

[0026] In some embodiments the upper cut-off voltage is preferably equal to twice the absolute value of the minimum operable voltage and the lower cut-off voltage is preferably equal to zero.

[0027] In some embodiments both the first and second DC bias voltages are preferably equal to the absolute value of the minimum operable voltage.

[0028] In some embodiments the upper cut-off voltage is preferably equal to twice the absolute value of the minimum operable voltage and the lower cut-off voltage is preferably equal to negative twice the absolute value of the minimum operable voltage.

[0029] In some embodiments the first electrode is preferably held at zero volts. In some embodiments the upper cut-off voltage is preferably equal to four times the absolute value of the minimum operable voltage and the lower cut-off voltage is preferably held at zero volts.

[0030] In some embodiments the bias circuit is preferably connected to the reference electrode. In some embodiments the bias circuit preferably provides a DC bias voltage of twice the absolute value of the minimum operable voltage to the reference electrode.

[0031] In some embodiments the bias circuit is preferably connected to the input for providing a third DC bias voltage to the variable signal.

[0032] In some embodiments the drive circuit preferably includes first and second amplifiers, the first amplifier configured for outputting the drive voltage to a first drive electrode between first upper and lower cut-off voltages and the second amplifier configured for outputting the drive voltage to a second drive electrode between second upper and lower cut-off voltages. [0033] In some embodiments the first and second upper cut-off voltages are preferably the same and the first and second lower cut-off voltages are preferably the same.

[0034] The first and second upper cut-off voltages are preferably defined relative to the upper operable voltage. In some embodiments the first and second upper cut-off voltages are preferably equal to the upper operable voltage.

[0035] In some embodiments the first and second upper cut-off voltages are preferably equal to the absolute value of the upper operable voltage.

[0036] The first and second lower cut-off voltages are preferably defined relative to the lower operable voltage. In some embodiments the first and second lower cut-off voltages are preferably equal to the lower operable voltage. In some embodiments the first and second lower cut-off voltages are preferably equal to the negative of the absolute value of the lower operable voltage.

[0037] In some embodiments the first upper cut-off voltage is preferably equal to the upper operable voltage, the first lower cut-off voltage is preferably equal to the lower operable voltage, the second upper cut-off voltage is preferably equal to the negative of the minimum operable voltage, and the second lower cut-off voltage is preferably equal to the negative of the upper operable voltage.

[0038] In some embodiments the first and second upper cut-off voltages are preferably equal to one half of the difference between the upper operable voltage and the lower operable voltage, the first lower cut-off voltage is preferably equal to zero volts, and the second lower cut-off voltage is preferably equal to negative one half of the difference between the upper operable voltage and the lower operable voltage.

[0039] In some embodiments the first electrode is preferably electrically grounded.

[0040] In some embodiments the bias circuit is preferably connected to the reference electrode to provide a DC bias voltage to the first electrode. In some embodiments the bias circuit preferably provides a first DC bias voltage to the first electrode that is derived from one or both of the upper and lower operable voltages.

[0041] In some embodiments the first DC bias voltage is preferably equal to half of the sum of the upper and lower operable voltages. In some embodiments the bias circuit is preferably connected to the input to provide a second DC bias voltage to the variable signal prior to the amplifiers.

[0042] In some embodiments the drive circuit preferably includes a first circuit branch for providing the variable signal to the first amplifier and a second circuit branch for providing the variable signal to the second amplifier. In some embodiments the bias circuit is preferably connected to each of the first and second circuit branches to apply a DC bias voltage to the variable signal along each circuit branch. In some embodiments the DC bias voltage is preferably a positive DC offset. In other embodiments the DC bias voltage applied to the variable signal in the first circuit branch is preferably positive and the DC bias voltage applied to the variable signal in the second circuit branch is preferably negative.

[0043] In some embodiments the bender device preferably includes a pair of planar piezoelectric bender layers disposed substantially parallel each other and poled in the parallel or anti-parallel with respect to each other. In some embodiments the first electrode is preferably connected to a first side of a first bender layer, the second electrode is preferably connected to both a second side of the first bender layer and a first side of a second bender layer, and the third electrode is preferably connected to a second side of the second bender layer.

[0044] In some embodiments the first electrode is preferably connected to a first side of a first bender layer, the second electrode is preferably connected to both a second side of the first bender layer and a first side of a second bender layer, and the third electrode is preferably connected to a second side of the second bender layer.

[0045] The controller is preferably adapted to maintain the drive voltage within the tolerance range independent of the variable signal.

[0046] In some embodiments the bender device preferably includes two adjacent central layers and two or more outer layers disposed about the central layers. In these embodiments the adjacent outer layers are preferably oppositely poled with respect to one another.

[0047] The controller is preferably adapted to maintain the drive voltage in substantially any range of voltages between the upper and lower operable voltages.

[0048] In accordance with a second aspect of the present invention there is provided a method for driving a piezoelectric bender device being operable within a specified voltage tolerance range extending between predetermined upper and lower operable voltages, the bender device including one or more piezoelectric layers, at least a first electrode and a second electrode, the method including:

receiving a variable signal; providing a drive voltage to the second electrode based on the variable signal; and

maintaining the drive voltage within the range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 illustrates circuit diagrams of prior art configurations for driving a piezoelectric bimorph bender, panel a) showing a series configuration, panel b) showing a parallel configuration and panel c) showing a biased uni-polar configuration;

Figure 2 is a schematic diagram illustrating a system for driving a piezoelectric bender device according to the present invention;

Figure 3 is a circuit diagram of a first bridged bipolar parallel poled configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 4 is a circuit diagram of a second bridged bipolar parallel poled

configuration for driving a piezoelectric bimorph bender according to an

embodiment of the invention;

Figure 5 is a circuit diagram of a first bridged bipolar series poled configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 6 is a circuit diagram of a second bridged bipolar series poled configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 7 is a circuit diagram of a bridged series configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 8 is a circuit diagram of a first biased bi-polar configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention; Figure 9 is a circuit diagram of a second biased bi-polar configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention, the configuration having symmetric power supply rails;

Figure 10 is a circuit diagram of a first biased uni-polar configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 1 1 is a circuit diagram of a second biased uni-polar configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention, the configuration having a shifted ground voltage;

Figure 12 is a circuit diagram of a first parallel configuration for driving a

piezoelectric bimorph bender according to an embodiment of the invention;

Figure 13 is a circuit diagram of a second parallel configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention, the configuration having a uni-polar drive voltage;

Figure 14 is a circuit diagram of a series configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 15 is a circuit diagram of a uni-polar series configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention;

Figure 16 is a circuit diagram of a third parallel configuration for driving a piezoelectric bimorph bender according to an embodiment of the invention, the configuration having the middle electrode grounded and the upper and lower electrodes actively driven; and

Figure 17 is a schematic illustration of a multimorph piezoelectric bender system.

DETAILED DESCRIPTION

GENERAL OVERVIEW

[0050] Referring to Figure 2 there is provided a system 1 for driving a piezoelectric bender device 3 being operable within a specified voltage tolerance range extending between predetermined upper and lower operable voltages {V_max and V_min). This tolerance range is determined by the material properties and dimensions of the piezoelectric material forming device 3 and the manner in which it is electrically driven. The tolerance is typically provided by the material or system manufacturer in the product specification. However, for the purpose of this invention, the operable voltage tolerance may constitute only a subset of the specified range or, alternatively, a range extending beyond that specified.

[0051] For a given piezoelectric material, the upper and lower limits of this operable tolerance range are derived respectively from the poling and coercive electric fields. The poling electric field is defined as the point at which an increase in electric field has little or no effect to the stress in the layer, and is usually around 1 to 2 kV/mm. The coercive electric field is the point at which the piezoelectric layer will start to depolarise, and is typically between -200 to -500 V/mm. For example, a bender with layer thicknesses of 0.1 mm can tolerate a voltage of -50 V to +200 V across each layer.

[0052] Bender device 3 includes a mount 4, two piezoelectric layers 5 and 7 forming a bimorph bender pair and three electrodes 9, 1 1 and 13. As will be described below, in various embodiments, electrodes 9, 1 1 and 13 are driven by either a variable voltage or a constant voltage (including 0 V). As illustrated, electrode 9 is disposed adjacent an upper surface 15 of layer 5. Electrode 1 1 is disposed between layers 5 and 7 adjacent a lower surface 17 of layer 5 and an upper surface 19 of layer 7. Electrode 13 is disposed adjacent a lower surface 21 of layer 7. Electrodes 9, 1 1 and 13 are formed of a flexible conductive material and extend along substantially the whole width and length of layers 5 and 7. However, in other embodiments, electrodes 9, 1 1 and 13 extend only partially along the length of layers 5 and 7 and/or are rigid in structure. In some embodiments, a central shim is sandwiched between layers 5 and 7 adjacent electrode 1 1 to enhance the mechanical reliability of system 1 . In some embodiments, electrode 1 1 is split into a pair of electrodes about the central shim and driven at the same voltage so as to be electrically equivalent to a single electrode.

[0053] Each piezoelectric layer has a defined poling direction which specifies the preferred axis of alignment of the atoms within the piezoelectric material. The orientation of the poling direction determines the orientation of the mechanical and electrical axes. Therefore, the relative orientation of piezoelectric layers in a bender device will determine the type of mechanical actuation that occurs under an applied electric field.

[0054] It will be appreciated by those skilled in the art that the illustrated bender pair is exemplary only and that benders may be arranged in other configurations with fewer or more piezoelectric layers and electrodes such as a single piezoelectric layer with two opposing electrodes or a stack or piezoelectric layers with electrodes disposed between each layer. [0055] System 1 includes an input 23 for receiving a control signal in the form of a variable signal V_in, which is typically an AC signal with a known frequency and amplitude. By way of example, typical amplitude and frequency values for V_in may be in the range 0 to 360 mV and 1 to 2 kHz. A drive circuit 25 is responsive to the variable signal at input 23 for providing a drive voltage V_d to the one or more drive electrodes. Circuit 25 includes the various electrical connections required for driving bender device 3 in different configurations as described below, including series, parallel and bridged type electrical configurations.

[0056] System 1 includes a controller 27 for maintaining the drive voltage within the specified voltage tolerance range. Controller 27 includes one or more controllable power supplies for drive circuit 25 and/or a bias circuit for providing a DC bias voltage or voltages to one or more of the variable signal and/or constant voltage electrodes in system 1. In some embodiments, controller 27 includes a processor for selectively specifying, monitoring and/or modifying the bias voltages applied to the variable input signal and electrodes. Use of controller 27 allows system 1 to drive bender device 3 across substantially the full tolerance range between the upper and lower operable voltages using a non-specific variable signal V_in. This results in improved bender deflection during operation.

[0057] Drive circuit 25 includes at least one amplifier 29 configured for receiving variable signal V_in and outputting the drive voltage V_d between upper and lower cut-off voltages which are specified by controller 27. The upper and lower cut-off drive voltages are each derived from one or both of the upper and lower operable voltages {V_max and V_min).

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0058] Using a controller as described above, a number of different electrical configurations can be realised. Some exemplary configurations are described below. In the following figures 3 to 16, central electrode 1 1 is separated into two electrodes 1 1 a and 1 1 b disposed around a central shim 37 and driven at the same voltage. Electrically, electrodes 1 1 a and 1 1 b are equivalent to a single electrode.

Double amplifier systems

[0059] Referring to Figures 3 to 7 there is illustrated three variations of a bridged-type electrical configuration for driving piezoelectric bender device 3 including two amplifiers. Figures 3 and 4 illustrate bridged bi-polar parallel poled bender systems 31 and 33 respectively. Figures 5 and 6 illustrate bridged bi-polar series poled bender systems 34 and 35 respectively. Figure 5 illustrates a bridged series driven bender system 36. Bender device 3 extends a length L beyond mount 4 and is able to deflect an amount δ from a blocking force F. A central shim 37 is disposed between layers 5 and 7.

[0060] In each of these embodiments, drive circuit 25 includes first and second amplifiers 39 and 41 . Amplifier 39 is configured for outputting a first drive voltage V_dl to electrode 9, which is in this case a drive electrode. Amplifier 41 is configured for outputting a second drive voltage V_d2 to electrode 13, which is also a drive electrode. In the configurations of Figures 3 and 4, electrode 1 1 is electrically grounded and maintained at 0 volts.

[0061] In each of the configurations of Figures 3 to 7, drive circuit 25 includes a first circuit branch 43 for providing the variable signal to amplifier 39 and a second circuit branch 45 for providing the variable signal to amplifier 41 . Controller 27 is adapted to provide, through a bias circuit, a voltage bias in the form of a DC offset voltage V₀ to the variable signal V_in along each circuit branch. In the configurations of Figures 3, 5 and 6, controller 27 applies a positive DC bias voltage to the variable signal along branch 43 and a negative DC bias voltage to the variable signal along branch 45. In the configuration of Figures 4 and 7, controller 27 applies a positive DC bias voltage to the variable signal along both branches 43 and 45.

[0062] In the parallel configurations of Figures 3 and 4, controller 27 drives amplifier 39 such that drive voltage V_dl is maintained between upper and lower cut-off voltages equal to V_max and V_min respectively. Controller 27 also drives amplifier 41 such that drive voltage V_d2 is maintained between upper and lower cut-off voltages equal to —V_min and—V_max respectively. In system 31 of Figure 3, both amplifiers 39 and 41 provide a positive gain of a and both layers 5 and 7 are poled in the same direction (given by the arrows on the respective layers). In system 33 of Figure 4, amplifier 39 provides a positive gain of a and amplifier 41 provides a negative gain of —a. In system 31 , piezoelectric layers 5 and 7 are poled in the same direction. However, a configuration with layers 5 and 7 both being poled in the opposite direction (but same relative orientation) is possible.

[0063] In the series configuration of Figure 5, controller 27 drives both amplifier 39 and amplifier 41 such that both drive voltages V_dl and V_d2 are maintained between upper and lower cut-off voltages equal to V_max and V_min respectively. In this configuration, amplifier 39 provides a positive gain of a and amplifier 41 provides a negative gain of -a. Layers 5 and 7 are poled in opposite direction. However, in another embodiment, layers 5 and 7 are poled in the opposite directions to those shown in Figure 5. [0064] In the series configuration of Figure 6, controller 27 drives both amplifier 39 and amplifier 41 such that both drive voltages V_dl and V_d2 are maintained between upper and lower cut-off voltages equal to {V_max - V_min) and - {V_max - V_min) respectively.

Amplifier 39 provides a positive gain of a and amplifier 41 provides a negative gain of -a. Layers 5 and 7 are poled in opposite directions. However, in another embodiment, layers 5 and 7 are poled in the opposite directions to those shown in Figure 6.

[0065] In the series configuration of Figure 7, controller 27 drives both amplifier 39 and amplifier 41 such that both drive voltages V_dl and V_dl are maintained between upper and lower cut-off voltages equal to \V_min\ and -l ^mm l respectively. In this configuration, amplifier 39 provides a positive gain of a and amplifier 41 provides a negative gain of -a. Layers 5 and 7 are poled in opposite directions but, in other embodiments, they may be poled in the same direction. In this configuration, the centre electrode is not driven or biased. This configuration has the advantage of only requiring two electrodes to be accessible and therefore reduces system complexity and cost.

[0066] The bridged systems described above are able to be used on both aligned and opposite poled benders. The advantage of using the bridged bipolar configurations of Figures 3 to 6 is the ability to use the full voltage range, and the ability to use the bender device 3 as an extender by changing the phase difference or voltage offset of the two drive signals V_dl and V_d2.

[0067] A system according to claim 8 wherein the first upper cut-off voltage is equal to the upper operable voltage, the first lower cut-off voltage is equal to the lower operable voltage, the second upper cut-off voltage is equal to the negative of the minimum operable voltage, and the second lower cut-off voltage is equal to the negative of the upper operable voltage.

[0068] The bridged systems described above can be used on both aligned and opposite poled bender devices.

Single amplifier systems

[0069] Referring now to Figures 8 to 16 there is illustrated various systems for driving piezoelectric bender device 3 using a single amplifier. Referring initially to Figures 8 and 9 there are illustrated biased bi-polar electrical configurations. System 47 of Figure 8 is an asymmetric system with electrode 13 electrically grounded at zero volts and controller 27 applying a bias voltage of V_max + V_min to electrode 9. System 49 of Figure 9 is a symmetric system with controller 27 respectively applying electrodes 9 and 13 with bias voltage of ^ {V_max + V_min) and - ^ {V_max + V_min). In both systems 47 and 49, electrodes 9 and 13 are held at a constant voltage and central electrode 1 1 is driven with a variable voltage. Systems 47 and 49 include a single amplifier 51 configured for outputting a drive voltage V_d to electrode 1 1 between upper and lower cut-off voltages specified by the upper and lower operable tolerance voltages for device 3.

[0070] Systems 47 and 49 are electrically equivalent but offset in bias so that the variable signal V_in and bias of the electrodes are equivalently offset. In system 47 of Figure 8, controller 27 applies, through the bias circuit, a bias offset V₀ to variable signal V_in. Amplifier 51 is driven between an upper cut-off voltage of V_max and a lower cutoff voltage oi V_min. In System 47, the bias offset V₀ and the bias to electrode 9 are provided by a bias circuit connected with controller 27. In system 49 of Figure 9, variable signal V_in is not biased and amplifier 51 is driven between the cut-off range of ± ^ {V_max +

Vmin) , which is symmetric about zero volts. Controller 27 is connected, through a bias circuit, to electrodes 9 and 1 1 for providing the respective biases.

[0071] Referring now to Figures 10 and 1 1 , there is illustrated biased uni-polar systems 53 and 55 with central drive electrode 1 1. Systems 53 and 55 are similar but are offset in voltage with respect to electrical ground. In system 53, a bias voltage V₀ is applied to variable signal V_in, amplifier 51 is driven between zero volts and V_max, and electrodes 9 and 13 are set at V_max and zero volts respectively. In system 55, no bias is applied to the variable signal, amplifier 51 is driven between ± ^ V_max and electrodes 9 and 13 are biased ai ^ V_max and - ^ V_max respectively.

[0072] Referring to Figures 12 and 13, there is illustrated parallel driven bender systems 57 and 59. In system 57 of Figure 12, controller 27 applies a bias voltage offset V₀ to variable signal V_in. Amplifier 51 is driven between respective upper and lower cut-offs \ V_min \ and -|V_min| . Electrodes 9 and 13 are both electrically grounded at zero volts. In system 59 of Figure 13, controller 27 applies a bias voltage offset of 1 V to variable signal V_in. Amplifier 51 is driven between upper cut-off 2\ V_min \ and lower cut-off of zero volts. Electrodes 9 and 13 are both biased to a voltage of \ V_min \ .

[0073] In the single amplifier single central drive electrode systems described above (Figures 8 to 13), the upper cut-off voltage of amplifier 51 is always maintained higher than or equal to the voltage applied to electrode 9 and the lower cut-off voltage of amplifier 51 is always maintained lower than or equal to the voltage applied to electrode 13. [0074] Referring now to Figures 14 and 15, there is illustrated two series driven bender systems 61 and 63. In both systems 61 and 63, only two electrodes are required - electrode 9 is actively driven by drive signal V_d and electrode 13 is held at a constant voltage. No central electrode is required thereby reducing complexity and cost over the three electrode systems described above. In both systems 61 and 63, layers 5 and 7 are poled in opposite directions as illustrated by the arrows on the layers.

[0075] In system 61 of Figure 14, controller 27 applies a bias voltage offset V₀ to variable signal V_in. In some embodiments V_o=0 \/. Amplifier 51 is driven between upper and lower cut-off voltages ± 2\ V_min \ and electrode 13 is electrically grounded at zero volts.

[0076] In system 63 of Figure 15, controller 27 applies a bias voltage offset V₀ to variable signal V_in. In embodiments where V_in varies between -1 V and l V, 1 ₀=1 V In other embodiments the offset is set to other values depending on V_in. Amplifier 51 is driven between upper cut-off voltage 4| l _mi„| and lower cut-off voltage of 0 V. Controller 27 biases electrode 13 at 2\ V_min \ .

[0077] Referring now to Figure 16, there is illustrated a parallel driven bender system 65 wherein the drive signal V_d is applied to both electrodes 9 and 13. Central electrodes 1 1 a and 1 1 b are electrically grounded at zero volts. Controller 27 applies a bias voltage offset V₀ to variable signal V_in and amplifier 51 is driven between upper and lower cut-offs of ± | V_min | . In some embodiments using this configuration, V₀ = 0. As with the other parallel systems, layers 5 and 7 are poled in the same direction in system 65.

[0078] It will be appreciated that the various driving systems described above are able to be applied to different piezoelectric bender devices having different dimensions and piezoelectric materials. Provided the tolerance specifications are known or can be calculated, these can be input to controller 27, which determines the appropriate bias voltages and amplifier cut-off voltages. As these are independent of the variable input signal, there is no need to specify different input signals for different systems.

[0079] The techniques and systems described above can be applied to multi-layer benders. Multi-layer benders are benders that have more than two piezoelectric layers. Each of the control methods described above can be implemented on a three wire, multilayer bender, such as that shown in Figure 17. Regardless of the poling direction (see the arrows on the respective layers) of the centre two layers, each additional layer is poled in the opposite direction to the previous layer as per Figure 17. Additionally, the electrode voltages alternate between the centre electrode voltage and the outer electrode voltage. [0080] For two piezoelectric benders with the same overall thickness, a multi-layer bender will require a lower driving voltage than the equivalent bimorph bender. The deflection and force is generally comparable.

[0081] Through modelling of the above described systems for driving bender devices, significant improvements in actuator tip deflection over presently known devices are expected.

CONCLUSIONS

[0082] It will be appreciated that the embodiments described above provide improved or alternative systems and methods for driving piezoelectric benders.

[0083] Utilisation of controller 27 allows selection of the amplifier gain (a) and biasing of the variable signal and electrode voltages independent of the variable input signal. This allows substantially any input voltage to be used as long as the gain (a) and offset (V₀) are set accordingly. System can be tailored to suit any bender system having different tolerances by simply varying the control voltages. Moreover, the system can be tailored to operate over the full voltage tolerance range of the bender device.

INTERPRETATION

[0084] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing," "computing," "calculating," "determining", analysing" or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities into other data similarly represented as physical quantities.

[0085] In a similar manner, the term "processor" may refer to any device or portion of a device that processes electronic data, e.g., from registers and/or memory to transform that electronic data into other electronic data that, e.g., may be stored in registers and/or memory. A "computer" or a "computing machine" or a "computing platform" may include one or more processors.

[0086] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. [0087] In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

[0088] It should be appreciated that in the above description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, Fig., or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claims require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this disclosure.

[0089] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the disclosure, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0090] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the disclosure may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0091] Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical, electrical or optical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[0092] Thus, while there has been described what are believed to be the preferred embodiments of the disclosure, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the disclosure, and it is intended to claim all such changes and modifications as fall within the scope of the disclosure. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present disclosure.

Claims

We claim:

1. A system for driving a piezoelectric bender device being operable within a specified voltage tolerance range extending between predetermined upper and lower operable voltages, the bender device including one or more piezoelectric layers, at least a first electrode and a second electrode, the system including:

an input for receiving a variable signal;

a controller for maintaining the drive voltage within the range.

2. A system according to claim 1 wherein the controller maintains the drive voltage in a range that extends substantially the full tolerance range between the upper and lower operable voltages.

3. A system according to any one of the preceding claims wherein the controller

includes the power supply for the drive circuit.

4. A system according to claim 1 or claim 2 wherein the controller includes a bias

circuit providing a DC bias voltage.

5. A system according to claim 4 wherein the drive circuit includes at least one

amplifier configured for receiving the variable signal and outputting the drive voltage between upper and lower cut-off voltages.

6. A system according to claim 5 wherein the controller controls the upper and lower cut-off voltages of the at least one amplifier.

7. A system according to claim 6 wherein one or both of the upper and lower cut-off voltages are derived from one or both of the upper and lower operable voltages.

8. A system according to claim 7 including a single amplifier configured for outputting the drive voltage to at least the second electrode between the upper and lower cutoff voltages.

9. A system according to claim 8 wherein the drive voltage is output to only a single electrode.

10. A system according to claim 8 wherein the drive voltage is output to the first and second electrodes.

1 1 . A system according to claim 9 including a third electrode.

12. A system according to claim 1 1 wherein the bias circuit is connected to at least one of the first and third electrodes.

13. A system according to claim 12 wherein the bias circuit is connected to the first electrode for providing a first DC bias voltage to the first electrode.

14. A system according to claim 12 or claim 13 wherein the bias circuit is connected to the third electrode for providing a second DC bias voltage to the third electrode.

15. A system according to claim 14 wherein the upper cut-off voltage is higher than or equal to the first DC bias voltage and the lower cut-off voltage is lower than or equal to the second DC bias voltage.

16. A system according to claim 15 wherein the upper cut-off voltage is equal to the upper operable voltage.

17. A system according to claim 15 or claim 16 wherein the lower cut-off voltage is

equal to the lower operable voltage.

18. A system according to claim 15 or claim 16 wherein the lower cut-off voltage is zero volts.

19. A system according to claim 16 wherein the first DC bias voltage is equal to the sum of the upper and lower operable voltages and the second DC bias voltage is zero.

20. A system according to claim 15 wherein the upper cut-off voltage is equal to one half of the upper operable voltage.

21 . A system according to claim 20 wherein the lower cut-off voltage is equal to minus one half of the upper operable voltage.

22. A system according to claim 15 wherein the upper cut-off voltage is equal to one half of the difference between the upper operable voltage and the lower operable voltage.

23. A system according to claim 22 wherein the lower cut-off voltage is equal to minus one half of the difference between the upper operable voltage and the lower operable voltage.

24. A system according to claim 23 wherein the first DC bias voltage is equal to one half of the sum of the upper and lower operable voltages and the second DC bias voltage is equal to minus one half of the sum of the upper and lower operable voltages.

25. A system according to claim 10 or claim 15 wherein the upper cut-off voltage is equal to the absolute value of the minimum operable voltage and the lower cut-off voltage is equal to the negative absolute value of the minimum operable voltage.

26. A system according to claim 25 wherein at least one of the electrodes is electrically grounded.

27. A system according to claim 26 wherein both the first and third electrodes are

electrically grounded.

28. A system according to claim 15 wherein the upper cut-off voltage is equal to twice the absolute value of the minimum operable voltage and the lower cut-off voltage is equal to zero.

29. A system according to claim 28 wherein both the first and second DC bias voltages are equal to the absolute value of the minimum operable voltage.

30. A system according to claim 9 wherein the upper cut-off voltage is equal to twice the absolute value of the minimum operable voltage and the lower cut-off voltage is equal to negative twice the absolute value of the minimum operable voltage.

31 . A system according to claim 30 wherein the first electrode is held at zero volts.

32. A system according to claim 30 wherein the upper cut-off voltage is equal to four times the absolute value of the minimum operable voltage and the lower cut-off is held at zero volts.

33. A system according to claim 32 wherein the bias circuit is connected to the first electrode.

34. A system according to claim 33 wherein the bias circuit provides a DC bias voltage of twice the absolute value of the minimum operable voltage to the reference electrode.

35. A system according to any one of claims 8 to 34 wherein the bias circuit is

connected to the input for providing a third DC bias voltage to the variable signal.

36. A system according to claim 7 wherein the drive circuit includes first and second amplifiers, the first amplifier configured for outputting the drive voltage to a first drive electrode between first upper and lower cut-off voltages and the second amplifier configured for outputting the drive voltage to a second drive electrode between second upper and lower cut-off voltages.

37. A system according to claim 36 wherein the first and second upper cut-off voltages are the same and the first and second lower cut-off voltages are the same.

38. A system according to claim 36 wherein the first and second upper cut-off voltages are defined relative to the upper operable voltage.

39. A system according to claim 38 wherein the first and second upper cut-off voltages are equal to the upper operable voltage.

40. A system according to claim 38 wherein the first and second upper cut-off voltages are equal to the absolute value of the upper operable voltage.

41 . A system according to any one of claims 36 or 38 to 40 wherein the first and second lower cut-off voltages are defined relative to the lower operable voltage.

42. A system according to claim 41 wherein the first and second lower cut-off voltages are equal to the lower operable voltage.

43. A system according to claim 1 wherein the first and second lower cut-off voltages are equal to the negative of the absolute value of the lower operable voltage.

44. A system according to claim 36 wherein the first upper cut-off voltage is equal to the upper operable voltage, the first lower cut-off voltage is equal to the lower operable voltage, the second upper cut-off voltage is equal to the negative of the minimum operable voltage, and the second lower cut-off voltage is equal to the negative of the upper operable voltage.

45. A system according to claim 36 wherein the first and second upper cut-off voltages are equal to one half of the difference between the upper operable voltage and the lower operable voltage, the first lower cut-off voltage is equal to zero volts, and the second lower cut-off voltage is equal to negative one half of the difference between the upper operable voltage and the lower operable voltage.

46. A system according to any one of claims 36 to 45 wherein the first electrode is electrically grounded.

47. A system according to claim 46 wherein the bias circuit is connected to the first electrode to provide a DC bias voltage to the first electrode.

48. A system according to claim 47 wherein the bias circuit provides a first DC bias voltage to the first electrode that is derived from one or both of the upper and lower operable voltages.

49. A system according to claim 48 wherein the first DC bias voltage is equal to half of the sum of the upper and lower operable voltages.

50. A system according to any one of claims 36 to 45 wherein the bias circuit is

connected to the input to provide a second DC bias voltage to the variable signal prior to the amplifiers.

51 . A system according to claim 50 wherein the drive circuit includes a first circuit

branch for providing the variable signal to the first amplifier and a second circuit branch for providing the variable signal to the second amplifier.

52. A system according to claim 51 wherein the bias circuit is connected to each of the first and second circuit branches to apply a DC bias voltage to the variable signal along each circuit branch.

53. A system according to claim 52 wherein the DC bias voltage is a positive DC offset.

54. A system according to claim 52 wherein the DC bias voltage applied to the variable signal in the first circuit branch is positive and the DC bias voltage applied to the variable signal in the second circuit branch is negative.

55. A system according to any one of the preceding claims wherein the bender device includes a pair of planar piezoelectric bender layers disposed substantially parallel each other and poled in the parallel or anti-parallel with respect to each other.

56. A system according to any one of claims 8 to 35 wherein the reference electrode is connected to a first side of a first bender layer, the drive electrode is connected to both a second side of the first bender layer and a first side of a second bender layer, and the second reference electrode is connected to a second side of the second bender layer.

57. A system according to any one of claims 45 to 54 wherein the first electrode is

connected to a first side of a first bender layer, the second electrode is connected to both a second side of the first bender layer and a first side of a second bender layer, and the third electrode is connected to a second side of the second bender layer.

58. A system according to any one of the preceding claims wherein the controller is adapted to maintain the drive voltage within the tolerance range independent of the variable signal.

59. A system according to any one of claims 1 to 54 wherein the bender device includes two adjacent central layers and two or more outer layers disposed about the central layers.

60. A system according to claim 59 wherein adjacent outer layers are oppositely poled with respect to one another.

61 . A system according to any one of the preceding claims wherein the controller is adapted to maintain the drive voltage in substantially any range of voltages between the upper and lower operable voltages.

62. A method for driving a piezoelectric bender device being operable within a specified voltage tolerance range extending between predetermined upper and lower operable voltages, the bender device including one or more piezoelectric layers, at least a first electrode and a second electrode, the method including:

receiving a variable signal;

providing a drive voltage to the second electrode based on the variable signal; and

maintaining the drive voltage within the range.