1. Field of the Invention
The present invention generally relates to a low-profile, fully-integrated active control device. Specifically, the invention is a flexible, thin-film actuator wherein the active material layer also functions as the substrate for control circuitry and sensors. The layered arrangement of thin-film actuator, control circuitry, and sensors retains the flexibility of the actuator substrate.
2. Description of the Related Art
Vibration and noise remain a substantial problem to airplanes, helicopters, tilt-rotor craft, automobiles and other vehicles. Aircraft applications are particularly challenging because the source of vibration and noise is disturbances produced by continuous pressure fluctuations.
While vibration and noise remission systems are known, practical applications of these externally controlled and powered technologies are not possible. In general, active damping devices are too large because of the size of the switching power electronics required to drive the actuators within the damping device. Furthermore, active damping requires large linear amplifiers and them management devices which are likewise difficult to accommodate within the volume constraints of most air and ground vehicles. A consequence of large control circuitry is that it precludes its direct integration onto an actuator, since to do so would inhibit the flexibility required of the actuator to properly damp targeted vibrations and noises.
Therefore, what is required is an active damping/control device comprising a flexible, thin-film actuator and drive electronics, wherein the drive electronics is dimensionally compatible with and integral to the form-factor of the actuator mechanism.
What is also required is a fully-integrated, actuator-controller-power-sensor package having a thin, flexible format, so as to be easily applied to a structure wherein access and volume are limited.
An object of the present invention is to provide an active damping/control device comprising a flexible, thin-film actuator and drive electronics, wherein the drive electronics is dimensionally compatible to and integral with the actuator mechanism.
Another object of the present invention is to provide a fully-integrated, actuator-control-power-sensor package having a flexible format which avoids compromising the performance of the active material layer and sensors therein.
The present invention includes an active material substrate that forms an actuator mechanism which is electrically coupled to a contiguous driver circuit, controller circuit, power converter circuit, and including at least one sensor. The multilayer flexible circuitry integrates interconnected power electronics to include miniaturized digital architecture. DC-to-DC converter, inverter, and controller are components with a total footprint contiguous with the active material substrate. These components are mounted onto the active material substrate which may be rigid, semi-rigid or flexible. The modular nature of the present invention enables a fully-integrated active device that is either semi-flexible or flexible so as to easily conform to and allow attachment to planar and non-planar structures.
The flexibility and modular design of the present invention is achieved in a low-profile integrated active device package. In preferred embodiments, the low-profile active substrate includes a flexible or semi-rigid piezoelectric composite.
Drive and control circuitry, namely, Isolation Device Technology or IDT and digital signal processor or DSP circuits, enable a low-noise, power amplifier solution wherein actuator control elements are directly integrated onto a low-profile actuator mechanism. The IDT drive employs a segmented load decoupling output filter within its low-profile packaging. The digital core within the power amplifiers facilitates distributed systems wherein two or more actuators may be controlled by a single master controller. A master/slave control architecture eliminates a wiring harness and ensures scalability.
The flexibility of the thin-film actuator substrate in the layered arrangement of actuator, control circuitry, and sensors is achieved via flex power electronics, flex electrical interconnections, and flex mounted power conversion block. An interdigitated electrode pattern communicates an electric field into the piezoelectric wafer or fibers, comprising the flexible actuator, thus enabling the primary piezoelectric effect within the wafers and fibers. The conformability and flexibility of flexible fiber piezo-composite actuators are typically achieved via an ordered arrangement of piezoelectric wafers or fibers, preferably extruded piezoceramics, within a pliable protective matrix communicating with interdigitated electrodes applied directly onto the matrix, preferably epoxy, or via a polyimide, oppositely disposed about the matrix. Strain energy density is enhanced via interdigitated electrodes which induce in-plane electrical fields along the actuator, thus producing nearly twice the strain actuation and four times the strain energy density of through-plane poled piezoceramic devices.
The electrical traces and components, comprising the control circuitry of the present invention, are deposited and patterned onto the exterior of the actuator via known techniques, including solution-based, direct-write printing and photolithography. For example, solution-based, direct-write printing is a method in which materials are deposited additively only where passive electrical components and interconnections (conductive traces) are required. This method of printing is performed at low-temperatures, thus avoiding temperature and mechanical stability problems inherent with writing circuitry onto a flexible polymer substrate. Furthermore, this method is compatible with continuous roll-to-roll processing and more scalable than lithographic methods.
Several advantages are noteworthy for the present invention. The invention provides complete functionality within a single, yet flexible, package, including integrated power source, drive electronics, sensing, control and actuation that can achieve dynamic flexing requirements. The package can move, bend and even slightly twist without damage to its functional integrity. The invention provides a low-cost, flexible activation mechanism that can be directly coupled to a DC power source. The invention provides structural actuation and sensing that enables directional, conformable actuation in a simple, cost-effective and fully-integrated device. The direct coupling of drive circuitry to interdigitated electrodes in the present invention enhances electrical performance and efficiency. The invention provides an autonomously responsive active mechanism that is conducive to being integrated to conformal (non-flat) surfaces in ships, aircraft and spacecraft. The flex interconnected power/control architecture simplifies connection of the actuator to external instrumentation. The form factor of the present invention is determined solely by the footprint of the active material layer, rather than the footprint of the drive/control circuitry.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:
Referring now to
In certain applications, it may be advantageous to partially or completely embed a flexible actuator 1 within a laminate composite or molded polymer of arbitrary shape via laminating and molding methods of manufacture understood within the art. The composite or molded structure should minimize stiffening of the flexible actuator 1 so as to avoid impeding both sensing and shape changing performance characteristics.
The flexible actuator 1 may be mechanically attached, laminated or embedded within a structure 45 or adhesively bonded thereto via a variety of commercially available glues, adhesives or other similar bonding materials. Adhesive material may be pre-applied to the flexible actuator 1 during its manufacture or applied immediately prior to its application onto a structure 45. It is preferred for the adhesive layer to be located along the active substrate 2 opposite of the drive, power, control, and sensing devices, as represented in
The flexible actuator 1 comprises an active substrate 2 having thereon a drive circuit 3, a power converter circuit 5, an optional controller circuit 4, one or more optional flexible sensors 7a-7d, and a power buss supply 6. Circuits 3-5 and flexible sensors 7a-7d are mounted to the exterior of the active substrate 2, preferably along a common surface, as represented in
The active substrate 2 is a piezoelectric device capable of changing shape when exposed to an electric field, as described in U.S. Pat. Nos. 5,869,189 and 6,048,622 to Hagood, IV et al., and U.S. Pat. No. 6,629,341 to Wilkie et al.
Referring now to
In some embodiments, it is advantageous to also provide a pair of optional thin films 46, 47 that are either adhesively or otherwise bonded to the matrix 53 in a parallel arranged fashion with respect to the piezoelectric elements 9a-9e. Thin films 46, 47 are likewise compliant so as to change shape in response to dimensional expansion and contraction of the piezoelectric elements 9a-9e. Thin films 46, 47 may be composed of a polyester, one example being Mylar®, a registered trademark of the E.I. DuPont De Nemours and Company located in Wilmington, Del., a polyimide, one example being Kapton®, a registered trademark of the E.I. DuPont De Nemours and Company located in Wilmington, Del., and other flexible polymer material.
A plurality of first electrodes 48a-48e and second electrodes 49a-49e are required to electrically activate the piezoelectric elements 9a-9e. One first electrode 48a-48e and one second electrode 49a-49e are coupled at opposite ends of each piezoelectric element 9a-9e. Electrodes 48a-48e, 49a-49e may be directly integrated into the matrix 53 via flat wires or the like, or printed, etched or deposited, via methods understood in the art, onto each of the thin films 46, 47 so as to provide an interdigitated arrangement.
Circuits 3-5 may be fabricated and mounted to the active substrate 2 via a variety of methods. For example in
In yet another method, circuits 3-5 may be deposited or patterned directly onto either the matrix 53 or the thin films 46, 47 disposed about the matrix 53. As such, electrical interconnects or traces within and between circuits 3-5 and passive electrical components comprising the circuit 3-5, namely, resistors, capacitors and the like, are printed, etched or deposited via known techniques, examples including solution-based, direct-write printing and photolithography. Other components comprising the circuits 3-5 are bonded onto the matrix 53 and thin films 46, 47 via techniques understood in the art.
Flexible sensors 7a-7d include a variety of commercial devices capable of measuring strain, stress, shear stress, pressure, velocity, and acceleration. Flexible sensors 7a-7d and electrode patterns (interdigitated and wheatstone bridge) are either bonded to or printed, etched or deposited on, via methods understood in the art or referred to herein, onto the active substrate 2. For example, flexible sensors 7a-7d may be attached to the active substrate 2 via potting materials 8 understood in the art, as represented in
Referring now to
In the present invention, the driver circuit 51 is required to drive capacitance loads in the range of 0.01 to 20.0 μF at efficiencies greater than 95% over a broad range of bandwidths from low (sub-hertz to kilohertz and tonal) to high (megahertz). In order to ensure that the driver circuit 51 fits within the planar form factor of most typical active substrates 2, it is generally required to deliver voltages from near-DC to ±100 Vac; however, larger field effect transistor (FET) components may be used to allow for the efficient delivery of ±500 Vac.
Isolation Device Technology (IDT) architecture, described in Non-Provisional patent application Ser. No. 11/201,567 entitled “High Frequency Switch Control” and hereby incorporated in its entirety by reference thereto, ensures the signal-to-noise ratio required to meet the operational performance of the power stage 11. The IDT circuit is a commercial device, one example being circuit model no. IDT-50 sold by QorTek, Inc. located in Williamsport, Pa. The present invention includes a full-bridge output with IDT architecture to significantly improve switching performance by isolating the high and low side devices. As such, inner-bridge coupling of noise and transients are eliminated so as to allow each device to function in a decoupled fashion.
Switching waveforms are likewise tailored to the specific application based upon loads, device type and performance, and noise level. Tailored waveforms ensure the driver circuit 51 functions within a safe operating area (SOA) and exhibits less device dissipation because of the reduced presence of extraneous losses from poor switching practices. The ability to drive devices within their appropriate SOA affords several primary benefits, namely, less output noise, reduced output filtering, higher switching frequencies, and higher overall efficiencies.
Referring now to
A converter may be coupled to the IDT circuit described above to facilitate the step-up conversion of a 28 Vdc buss to a 150 Vdc drive voltage for the active substrate 2. While a three-stage control system is preferred, single and other multi-stage systems are possible. The switching DC power supply converts the 28 Vdc to the input voltage required by control system and signal conditioner.
Referring again to
Referring now to
Each sensor controller 31a-31c has a communications pathway to receive control commands and transmit drive information to and from the master communication controller 30. An exemplary sensor controller 31a-31c is a C2000 model DSP sold by the Texas Instruments Company. Preferred devices included a 16-bit, 40 MHz DSP with embedded PWM, analog-to-digital converters, serial communications interface, internal RAM, and internal program FLASH ROM. A small DSP allowed more sensor controllers 31a-31c for greater sensing fidelity.
The primary responsibility of each sensor controller 31a-31c is to digitally stabilize the power driver based upon commands it receives from the master communication controller 30 and feedback from an output driver card. Commands are transmitted from the digital-to-analog converter within the master communication controller 30. Voltage and current feedback signals are routed back to an analog-to-digital convert within each DSP.
In some embodiments, it may be preferred to have a DSP with a faster clock speed and capable of generating a pulse width modulated (PWM) signal upwards of 150 kHz so as to reduce the power supply output filter requirements. It is likewise preferred for the DSP to be signal processing capable and, if applicable, to allow multiple flexible actuators 32a-32c to be controlled by one DSP. For example, the DSP sub-system in
Preferred embodiments of the present invention include selectable feedback allowing a function generator or accelerometer as the feedback source. Signal conditioning may be required prior to analog-to-digital conversion so that high-frequency or out-of-band noise is removed. Filtering prevents aliasing and extraneous noise from occurring. After the command signal is digitized, it is used as the command for the proportional-integral (PI) control algorithm. The PI control algorithm either recreates the command at the power supply output, when the feedback source is a function generator, or nulls any motion, when the feedback source is an accelerometer. Two additional feedback channels for voltage and current may be used for feedback from the power supply so as to allow the command signal from a function generator to be accurately recreated at the flexible actuators 32a-32c. Protection also is incorporated into the control so that power supply and flexible actuators 32a-32c are not overdriven.
Identified DSPs maximize flexibility, robustness, and re-configurability in the control algorithm. A further advantage of the identified DSPs is quick and easy software modifications and improvements to adjust algorithm parameters or to alter the control approach. Although analog PWM controllers may provide acceptable performance, their adaptability and re-configurability are limited thereby preventing additional functionality after a design is implemented. Another limitation of analog controllers is that non-linear functions, such as adaptive least-mean-square (LMS) filters, are difficult to achieve with analog components and often approximated thereby. Software implementations of non-linear features are simpler and more precise with software in digital DSPs. While preferred embodiments of the present invention include a control algorithm current that is primarily linear, non-linear control functions are preferred for scalability and upgradeability purposes.
Referring now to
Feedback signals to the DSP control laws 38 are analyzed to stabilize drive signals to loads, as well as, to maintain circuit protection and health monitoring. The DSP control laws 38 employ multi-staged proportional integral control loops for each half bridge to recreate input command signals. Loops are coupled with non-linear functions, such as signal limiting and command shut-down, for system protection. Algorithms are coded and assembled to maximize efficiency and execution speed and enable multi-channel capability. The described methodology allows for an adaptive LMS noise cancellation algorithm within the DSP driver for the power stage 11. As such, functionality is directly implemented into the controller without requiring a bulky external PC or embedded computer.
In some embodiments, a converter having an operational frequency above 100 kHz may be required to eliminate noise generated by the step-down DC-to-DC converter. In yet other embodiments, it may be required to damp interactions between the active substrate 2 and output filter to eliminate extraneous noise and bring the single-to-noise ratio into an acceptable range. It is likewise possible to reduce DC-to-DC converter noise by having the drive operate at a nominal 28 Vdc. As such, the duty cycle is in a range typically associated with efficient power conversion. The power stage DC buss voltage is also stepped up, which is generally an easier, low-noise task.
In some embodiments, a voltage of 150 Vdc is used to directly supply the power stage 11 with some filtering and control system voltages are stepped down. In yet other embodiments, it may be required to step up the power stage buss voltage. The step-up conversion of the 150 Vdc buss may be performed via a commercially available converter, one example being Converter Model No. SRC-50, sold by QorTek, Inc.
Exemplary signal-to-noise ratios (SNR) are shown in
The description above indicates that a great degree of flexibility is offered in terms of the present invention. Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
This application is based upon and claims priority under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60/649,202 filed Feb. 2, 2005, entitled “Low-Profile, Power-Integrated Actuator for Structural Vibration and Noise Abatement”, the contents of which are hereby incorporated in its entirety by reference thereto.
One or more of the inventions disclosed herein were supported, at least in part, by a grant from the National Aeronautics and Space Administration (NASA), Contract No. NNL04AB14P awarded by NASA, Langley Research Center. The Government has certain limited rights to at least one form of the invention(s).
Number | Date | Country | |
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60649202 | Feb 2005 | US |