Patent Application
20110208361
The invention relates generally to active vibration systems, which counteract ongoing vibrations, and active balancing systems, which counteract the onset of vibrations, particularly for applications in the aerospace and machine tool industries, and including power and communication links within the systems, such as links between sensors, controllers, and actuators.
Active vibration and balancing systems generally require a plurality of sensors for sensing vibrations, motions, and other environmental or performance variables to provide feedback to system controllers for controlling actuators. For example, accelerometers monitor vibrations, tachometers monitor the speed of rotating parts, such as propellers or machine spindles associated with the generation of the vibrations, and position sensors monitor operating performance of actuators.
Wiring to and from the sensors for delivering power to the sensors and for communicating data from the sensors particularly over large distances can add considerable weight and bulk to active vibration and balancing systems and subject the transmissions to environmental electromagnetic influences. Transmissions from sensors with low signal levels or over long runs of wires are particularly susceptible to such electromagnetic disturbances. Environments of machine tools and aircraft, requiring active vibration or balancing systems, often contain strong electromagnetic fields that can disrupt the transmission of sensor data over even short distances of travel. Similar problems can exist for data exchanges with actuators, particularly for actuators that are separated from their controllers or susceptible to intervening electromagnetic fields.
Preferred implementations of the invention provide secure data exchanges between groups of sensors and controllers of active vibration and balancing systems under a digital protocol that is largely impervious to local electromagnetic disturbances, electrical surges, and other environmental influences. Signals from multiple sensors combine at a transfer station under the digital protocol and transmit together over common wiring pairings to a base station associated with the controller. The wire pairings, which preferably include pairings for both transmitting and receiving data, also convey error-checking communications in accordance with the digital protocol and also provide for transmitting electrical power. Although signals from multiple sensors are collectively transmitted over the same wire pairings, transmission speeds can be increased while more evenly spreading the energy content of the transmissions to reduce the generation of electromagnetic interference that could otherwise affect other communications.
One implementation of the invention as a motion control system for regulating vibrations includes the usual features of a plurality of sensors for acquiring information about the vibrations, an actuator for counteracting the vibrations, and a controller for both processing the information acquired from the sensors and controlling the actuator to counteract the vibrations. In addition, the motion control system features a digital processing link between the plurality of sensors and the controller. The digital processing link includes a transfer station associated with the sensors and a base station associated with the controller. The transfer station includes a multiplexer/demultiplexer for combining signals from the sensors into a collective signal and a communication node for transmitting the collective signal under a communications protocol. The base station includes another communication node for receiving the collective signal under the communications protocol and a demultiplexer/multiplexer for dividing the collective signal into a plurality of separately processable digital signals. Data transmit and receive lines interconnect the transfer and base stations. The controller processes the digital signals from the base station and outputs a control signal for controlling the actuator to regulate vibrations.
The communication node of the base station and also be arranged to transmit the control signal for the actuator under the communications protocol. Where the actuator is located near the sensors, such as may be found in an active balancing system, the communication node of the base station transmits the control signal to the actuator over the data transmit and receive lines to the communication node of the transfer station. The actuator may be one of a plurality of actuators, and the controller can be arranged to output multiple control signals. The demultiplexer/multiplexer of the base station combines the multiple control signals into a collective control signal for transmission over the data transmit and receive lines, and the multiplexer/demultiplexer of the transfer station divides the collective control signal into a plurality of control signals that can be separately directed to the actuators.
The actuator can be one of a plurality of actuators and a second digital link can be provided between the same base station and a second transfer station for interconnecting the plurality of actuators with the base station. The demultiplexer/multiplexer of the base station combines output control signals for the actuators into a collective output control signal, and the communication node of the base station transmits the collective output control signal under the communications protocol to the second transfer station. A communication node of the second transfer station receives the collective output control signal and a multiplexer/demultiplexer of the second transfer station divides the collective output control signal into a plurality of control signals to the actuators.
The digital processing links can be used for transmitting power between the base and transfer stations. A power supply associated with the base station is coupled to the data transmit and receive lines for transmitting electrical power to the transfer station. A transformer at the transfer station receives the electrical power over the data transmit and receive lines and conditions the power for delivery to one or more of the sensors.
Preferably, the communication node of the transfer station converts the collective signal into a series of frames having a prescribed format for monitoring and resending errant transmissions. In addition, the communication node of the transfer station preferably spreads the energy content of the collective signal over the data transmit lines to reduce electrical interference. The communication node of the transfer station also preferably includes protection circuitry in the form of a disconnect to avoid transmitting lightning surges. The transfer station can include an analog to digital converter to convert analog signals from the sensors into digital signals.
The actuator preferably amplifies force at one or more tuned frequencies. For example, the actuator can include one or more eccentric masses that are rotatable about a rotation axis or a translatable mass that is reciprocable along a linear axis. The plurality of sensors can include accelerometers used for sensing vibration. The transfer station is preferably positioned for reducing an average distance between the transfer station and the plurality of sensors.
Another implementation of the invention as an active balancer for a rotatable shaft includes one or more eccentric masses that are positionable with respect to a rotational axis of the rotatable shaft. A driver repositions the one or more eccentric masses with respect to the rotational axis of the rotatable shaft. A plurality of sensors including one or more rotation sensors together with one or more vibration sensors monitor performance characteristics of the rotatable shaft. A controller processes the information acquired from the sensors and controls the operation of the driver to reduce vibrations in the rotatable shaft. A transfer station collects information from the sensors, and a base station is connected to the controller. Data is sent and received between the transfer and base stations under a communications protocol that also provides for monitoring and resending errant transmissions.
The driver can be formed as a part of a coil block within which one or more of the plurality of sensors is embedded. The plurality of sensors preferably includes one or more sensors within the coil block for monitoring the position of the one or more eccentric masses.
The transfer station preferably includes a multiplexer/demultiplexer for combining signals from the sensors into a collective signal and a communication node for transmitting the collective signal under the communications protocol. The base station preferably includes another communication node for receiving the collective signal under the communications protocol and a demultiplexer/multiplexer for dividing the collective signal into a plurality of separately processable digital signals. Data transmit and receive lines preferably interconnect the transfer and base stations for exchanging information under the communications protocol, and a power supply associated with the base station preferably provides electrical power for transmission over the data transmit and receive lines to the transfer station.
Yet another implementation of the invention as an active vibration control system minimizes vibrations in a structure that supports a member for rotation. A plurality of sensors mounted with the structure monitor vibrations. One or more actuators drive respective movable masses at tuned frequencies. A controller receives information from the plurality of sensors and controls operation of the one or more actuators for cancelling sensed vibrations within the structure. A transfer station, which collects information from the sensors, and a base station, which is connected to the controller, exchange information under a communications protocol in a prescribed format for monitoring and resending errant transmissions.
The invention can also be implemented as a method of counteracting vibration. Vibrations are monitored using a plurality of sensors. Signals output from the plurality of sensors convey information about the vibrations. The signals from the sensors are combined at a transfer station into a collective signal, and the collective signal is transmitted over data transmit and receive lines under a communications protocol in a prescribed format for monitoring and resending errant transmissions. The collective signal is received under the communications protocol at a base station associated with a controller. Power from a power source associated with the base station is also transmitted over the data transmit and receive lines to the transfer station. The power received at the transfer station is distributed to one or more of the sensors. The collective signal received at the base station is divided into a plurality of processable digital signals. The digital signals are processed within the controller, and a signal is output from the controller to an actuator for counteracting the monitored vibrations.
Preferably, the sensors are distributed according to results from an optimization study. The transfer station is preferably located among the sensors for reducing an average distance between the sensors and the transfer station.
Other implementations of the invention include a method of making a motion control system, a method of controlling machine vibrations, and a method of controlling vibrations in an aircraft structure.
It is to be understood that both the foregoing general description and the following detailed description are exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principals and operation of the invention.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
An exemplary digital processing link 10 depicted in
The communication node 22, which can be implemented with an LVDS (low voltage differential signaling) or RS422 chip together with an Ethernet interface, transmits the collective sensor signal under a communications protocol that converts the collective sensor signal into a series of frames having a prescribed format for monitoring and resending errant transmissions to the base station 14. Twisted wire pairings 24 and 26, which include data transmit and receive lines interconnecting the transfer and base stations 12 and 14, convey the collective sensor signal under the prescribed protocol. The protocol temporally spreads energy content of the collective sensor signal over the twisted wire pairings 24 and 26 to reduce the generation of electrical interference. Protection circuitry 28, including an automatic disconnect, can be incorporated into the transfer station 12 to provide surge protection against lightning strikes or other spurious high voltage disturbances. Similar protection circuitry 30 can be provided at the base station 14.
A similar communication node 32 within the base station 14 receives the collective sensor signal under the communications protocol and a similar demultiplexer/multiplexer 34 divides the collective sensor signal into a plurality of separately processable digital signals. A controller 36, which includes a digital signal processor operating under control software, receives the individual sensor signals and generates a plurality of output control signals for controlling the actuators 18. U.S. Pat. Nos. 5,757,662 and 6,236,934, which are hereby incorporated by reference, describe active balancers, also referred to as unbalance compensators, having control structures and algorithms for converting sensor signals relating to the unbalance to control signals for eccentrically driven mass actuators.
The demultiplexer/multiplexer 34 combines the plurality of output control signals into a single collective control signal, which is converted by the communication node 32 for transmission under the communications protocol through the wire pairings 24 and 26 to the communication node 22 transfer station 12. The multiplexer/demultiplexer 20 of the transfer station 12 divides the collective control signal into a plurality of individual control signals that are separately directed to the plurality of actuators 18.
Although the digital processing link 10 is capable of communicating both a plurality of sensor signals and a plurality of control signals under a preferred communications protocol, such as an Ethernet protocol, the digital processing link 10 could be arranged to communicate only the sensor signals or only the control signals or the base station could be combined with more than one transfer station to separately convey the sensor and control signals.
In addition to supporting digital communications, the digital processing link 10 also supports the transmission of electrical power from the base station 14 to the transfer station 12. A power supply 40 is mounted within the base station 14 and separately connected to the twisted wire pairs 24 and 26 through the electrical couplings 42 and 44 according to a standard implementation such as a Power over Ethernet (PoE) system. Within the transfer station 12, a transformer 46 receives the electrical power through electrical couplings 48 and 50 for powering one or more of the sensors 16 or other devices within or otherwise associated with the transfer station 12.
An implementation of the digital processing link 10 is as a part of an active balancing system 60, such as depicted in
Continuous balancing processes, also referred to as active balancing processes, adapt to changing balancing requirements. As such, reliable communications are required during machine operation for conveying sensor signals about the changing conditions and for conveying control signals for making ongoing balancing corrections. Electromagnetic environments of electronically controlled machine tools, rotary powered aircraft, or other rotating machinery, such as industrial fans, can produce electrical interference that and disrupt the transmission of sensor and control signals, especially such signals that are inherently weak or required to travel considerable distances.
As shown in
Correction is provided by anterior and posterior balancers 80 and 82, which provide corrections in two traverse planes adjacent the anterior and posterior bearings 66 and 68. The two balancers 80 and 82 include adjustable rotor assemblies 84 and 88 that rotate together with the spindle or shaft 62 and coil assemblies 86 and 90 that provide for angularly adjusting rotors within the assemblies 84 and 88 for effecting the balance corrections. Status sensors 92, 94, 96 and 98 are embedded within the coil assemblies 88 and 90 for reporting on the performance of the spindle or shaft 62 and the balancers 80 and 82. The status sensors 92, 94, 96 and 98 can include Hall Effect sensors for monitoring the speed and relative location of the rotors, temperature sensors, and digital accelerometers, all preferably integrated in the coil assemblies 88 and 90.
Both the vibration information acquired by the vibration sensors 72 and 74 and the status information acquired by the performance sensors 92, 94, 96, and 98 are routed as shown to the transfer station 12. Especially if just one of the balancers 80 and 82 is used for performing the balancing operation, the transfer station 12 itself can be integrated into one of the coil assemblies 86 and 90 (e.g., located within one or more boards that reside within the coil assembly).
As described with respect to the digital processing link of
The base station 14, which includes the system controller 36 with embedded software, can be located remote from the transfer station 12 or even incorporated into the controller of the machine tool, aircraft, or other rotary machine requiring balancing. The communications between the base station and the transfer station are protected against environmental electrical disturbances and themselves produce little electrical interference to other communications.
The active balancing system 60 of
As shown in
The balancers 80 and 82 sense vibration and make imbalance adjustments to reduce the vibration. The controller 36 continuously monitors accelerometer vibration levels and when the vibration exceeds a maximum allowable level set in the software, the controller 36 determines the magnitude and phase angle of the required imbalance correction. Control signals output from the controller 36 can be in the form of precisely shaped current pulses to the balancer coil assemblies 86 and 90 to move the rotors to new angular positions. When the vibration level is below the maximum allowable level, the rotors remain in their set angular positions without further input from the controller 36.
Status information from the balancer coil assemblies 86 and 90 along with the accelerometer vibration signals provide inputs to an adaptive algorithm within the controller 36. The preferred algorithm calculates system dynamic coefficients and generates amplifier output control signals to the coil assemblies 86 and 90. The output control signals angularly shift the weighted rotor assemblies to desired angular positions. The coil assemblies are fixed to a stationary frame or housing, and actuating power is passed across an air gap in the form of magnetic fields. The use of permanent magnets allows the counterweight rotors to be fixed in place passively without external power.
The control algorithm is preferably based on the use of so-called “influence coefficients”, which are complex-valued transfer function coefficients that relate unbalance input from a certain balance plane to steady-state output of the associated vibration sensors 72 or 74 at a given rotational speed. These influence coefficients can be obtained experimentally or through adaptive control methods. For example, vibration data can be sampled during each of a plurality of vibration control iterations and demodulated to obtain a complex-valued tonal vibration. Based on the measured vibration data and stored influence coefficients, the controller computes the angular positions or the rotors required to minimize the sensed vibration. Preferably, the control re-computes influence coefficients after each correction for adapting to changing conditions. A preferred control algorithm, as schematically depicted in
The active balancing system 60 can be applied to In-Flight Propeller Balancing Systems (IPBS) for aircraft such as the C-130 and E2C aircraft propellers. This system can be designed to reduce once-per-revolution (1P) vibration levels at the propeller and gearbox such as may be caused by static or dynamic imbalances of the propeller. A schematic of the balance system is shown in
The balance system preferably operates autonomously to monitor the propeller imbalance during both ground idle and in-flight operations and counteracts the monitored imbalances to reduce vibrations. During in-flight operations, aircraft propellers can be damaged by impacts from foreign objects that imbalance the propellers and produce cabin noise and vibration. The required balance corrections can also vary for different engine power settings or aerodynamic propeller loading. On variable pitch propellers, minor variations in the pitches and contours of the blades can produce once-per-revolution vibrations. Thus, active balancing, involving critical in-flight communications between the balancer and the balancer controller, is required to compensate for the dynamic balance changes in different flight conditions. The active balancing system 60 can reduce the once-per-revolution (1P) vibration caused by both the static and the aerodynamic imbalance and thus improve the life of the propeller assembly and other engine components.
An active vibration control system 150, as shown in
A plurality of vibration sensors 154, such as in the form of accelerometers, together with a speed sensor 156, such as in the form of a tachometer, collects information concerning ongoing vibrations and routes this information to a transfer station 158. Within the transfer station 158, as described particularly with respect to the transfer station 12 of
The collective sensor signal is divided into its separate sensor signals within the base station 162, as also described particularly with respect to the base station 14 of
The numbers of sensors and actuators are adapted to particular applications. The actuators 170, 172, and 174 can be electromagnetic force generators fixed to the vibrating structure 184, such as the fuselage, and including electromagnetically driven masses via linear oscillation or rotation. Preferably, the electromechanical actuators exploit mechanical resonance to amplify the force at the N/rev frequency. Typical tuning frequencies for helicopter applications range from 17.2 Hertz to 28 Hertz at a force of 300 pounds to 1200 pounds.
The control algorithm is preferably based on a time domain Filtered-X least mean square (LMS) such as the LORD NVXTM systems for fixed wing aircraft including the DC-9 and Citation X available from Lord Corporation of Cary, N.C. A block diagram showing Filtered-X LMS Algorithm used in LORD® AVCS is presented in
The system design process for adapting the active vibration control system to a helicopter or other aircraft is preferably carried out in three stages. In the first stage, transfer functions are obtained and fuselage vibrations at various flight conditions are measured. In the second stage, the measured data is used to optimize a system by defining the location and force capacity of each actuator and the location of each of the accelerometers. In the third stage, the active vibration control system is installed on the aircraft and performance is demonstrated through flight testing.
Measurements of in-flight vibration as well as the transfer functions are compared between potential actuator locations and control accelerometer locations. This data is preferably collected for three of more weight and center of gravity configurations of the aircraft including the minimum takeoff weight and the maximum takeoff weight. For each of these configurations, a flight tests is also performed to measure the in-flight vibration. Typically, each flight consists of 20 stable (steady state) and transient flight conditions.
An optimization analysis is performed using the collected data for determining the appropriate number of locations of sensors and actuators and for predicting the associated vibration reduction performance and its associated weight penalty. A few different configurations of active vibration control system are preferably installed for demonstrating in-flight performance. Vibration measurements are recorded with the system activated and de-activated for purposes of comparison. The system performance is tested under transient conditions like turns and flare. The system stability and tracking is evaluated and final software tuning is performed.
The digital processing link 152, similar to the digital processing links 10, is expected to reduce weight, cost, and complexity by eliminating long runs of wires between sensors or other appliances and the controller and to improve reliability by exploiting a digital communication protocol and incorporating protective circuitry at both ends of the transmissions.
It will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the spirit and scope of the invention. Thus, it is intended that the invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. It is intended that the scope of differing terms or phrases in the claims may be fulfilled by the same or different structure(s) or step(s).
The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/094,895 filed Sep. 6, 2008, and which is incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2009/056092 | 9/4/2009 | WO | 00 | 5/11/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61094895 | Sep 2008 | US |
