HK1202143B - Driving an active vibration balancer to minimize vibrations at the fundamental and harmonic frequencies - Google Patents

Abstract

Vibrations of a principal machine are reduced at the fundamental and harmonic frequencies by driving the drive motor of an active balancer with balancing signals at the fundamental and selected harmonics. Vibrations are sensed to provide a signal representing the mechanical vibrations. A balancing signal generator for the fundamental and for each selected harmonic processes the sensed vibration signal with adaptive filter algorithms of adaptive filters for each frequency to generate a balancing signal for each frequency. Reference inputs for each frequency are applied to the adaptive filter algorithms of each balancing signal generator at the frequency assigned to the generator. The harmonic balancing signals for all of the frequencies are summed and applied to drive the drive motor. The harmonic balancing signals drive the drive motor with a drive voltage component in opposition to the vibration at each frequency.

Description

Driving an active vibration balancer to minimize vibration at fundamental and harmonic frequencies

Technical Field

The present invention relates generally to reducing or eliminating mechanical vibration of a main machine by: driving an active balancer coupled to the main machine causes the active balancer to generate a balancing force against a force generated by the main machine. More particularly, the present invention relates to reducing or eliminating mechanical vibrations not only at the fundamental operating frequency of the main machine, but also at harmonics of that fundamental frequency (harmonic).

Background

Many machines vibrate due to the repeated acceleration and deceleration of one or more periodically moving masses (masses) that are part of the machine. In certain circumstances, the vibrations may be uncomfortable, distracting or annoying to a person, and in some cases they may interfere with the operation of other equipment and may even cause damage. One way to reduce vibration is to mount the vibrating machine to another mass through an intermediate damper (which may be a device or material that absorbs some of the vibration energy). However, because this approach only partially reduces the vibrations, a more efficient way to eliminate or at least minimize the amplitude of the vibrations is to rigidly mount the vibration balancer to the vibrating machine. The vibration balancer generates a force opposite to the vibration; i.e. it generates forces of equal or almost equal magnitude but opposite phase and thereby counteracts or almost counteracts the forces generated by the vibrations.

Vibration balancers are generally of two types, passive vibration balancers and active vibration balancers, some of which are also known as tuned mass dampers, active mass dampers or shock absorbers. A passive vibration balancer is essentially a resonant spring and mass system tuned to the operating frequency of the vibrating machine, but arranged to apply forces to the vibrating machine from its accelerating and decelerating mass in a phase 180 ° out of phase with the forces generated by the vibrations. An active vibration balancer is essentially a mass and may also be linked to springs, but the motion of the mass is controlled by a control system that senses the vibration and drives the mass relative to the vibration.

Although a passive balancer is less expensive, it has the following disadvantages: it can only respond to vibration at one resonant frequency to which it is tuned. Active balancers can respond to small changes in vibration frequency and can apply a compensating force with an amplitude that better cancels the vibration, but active balancers are more expensive and require a controller to drive the active balancer with the required amplitude and phase. It is known to the person that either a passive balancer or an active balancer does not have balanced vibrations at harmonics of the fundamental operating frequency of the vibrating machine.

It is therefore an object and feature of the present invention to provide a method for reducing or eliminating vibration of a machine at both the fundamental operating frequency of the machine and harmonics of the fundamental frequency.

Disclosure of Invention

The present invention is for balancing the vibration of a primary vibration machine at a fundamental operating frequency of the primary vibration machine and at a selected harmonic of the operating frequency. Vibrations of the main vibrating machine are sensed to provide a sensed vibration signal representative of sensed mechanical vibrations of the main vibrating machine. A balancing signal is generated for the fundamental and selected harmonics of the operating frequency and preferably a harmonic balancing signal is generated for each of several selected harmonics. Each balance signal is generated by processing the sensed vibration signal by an adaptive filtering algorithm of the adaptive filter. The adaptive filtering algorithm for each selected frequency has a reference input that varies sinusoidally in quadrature at its assigned selected frequency. The harmonic balancing signals of all selected frequencies are summed and applied to drive the drive motor of the active balancer. Each harmonic balancing signal at each selected frequency thus drives the drive motor with a drive voltage component for each selected frequency relative to the vibration at each selected frequency.

Drawings

Fig. 1 is a block diagram illustrating the basic operation of the present invention.

Fig. 2 is a block diagram illustrating the operation of an adaptive balancing signal generator, which is a component of the present invention.

Figure 3 shows a diagram of one embodiment of the present invention.

Fig. 4 shows a diagram of another embodiment of the present invention.

Fig. 5 shows a diagram of yet another embodiment of the present invention.

In describing the preferred embodiments of the present invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Detailed Description

U.S. patent 7,511,459 is incorporated by reference herein. This prior art patent shows an example of a control system for controlling a linear motor/alternator drivingly linked to a stirling machine and usable with embodiments of the present invention. More specifically, this patent discloses examples of what is referred to herein as the primary control system for applying a primary electric drive voltage and current to its motor/alternator armature windings for controlling its operation at its operating frequency.

Although the originally envisaged application of the present invention was to balance the vibration of a stirling machine drivingly linked to a linear motor/alternator, the present invention is also applicable to reduce the vibration of other primary vibrating machines. The present invention may operate independently of the control system of the main vibrating machine and therefore does not necessarily rely on this control system. However, the interaction between the present invention and the control system of the main vibrating machine may be added to the present invention and one illustrated embodiment of the present invention (fig. 3) utilizes signals from the control system of the main vibrating machine.

Terminology and the basic principles of the prior art

Stirling machines are typically drivingly linked to a linear electric motor or linear alternator. The stirling machine may be a prime mover connected to a linear alternator to generate electrical power. A stirling machine operating in heat pump mode may be connected to and driven by a linear electric motor and pump thermal energy from one of its heat exchangers to the other of its heat exchangers. Stirling machines that pump heat for the purpose of cooling the mass are sometimes referred to as coolers, and heat pumps for the purpose of heating the mass. The stirling heat pump and the stirling cooler are basically the same machine with different terminology being applied. Both transfer thermal energy from one mass to the other. Thus, the terms chiller/heat pump, chiller and heat pump are used equivalently when applied to the basic machine. Since the stirling machine may be an engine (prime mover), or a cooler/heat pump, the term stirling "machine" is used generically to include both stirling engines and stirling coolers/heat pumps. Which is basically the same transducer that can arbitrarily convert energy between two types of energy (mechanical and thermal).

Similarly, an electric linear motor (motor) and an electric linear generator (alternator) are the same basic devices. They have a stator, which generally has armature windings; and a reciprocating member comprising one or more magnets, typically permanent magnets. The linear motor/alternator may be mechanically driven back and forth by the prime mover to operate as a generator to produce electricity or may be driven by an alternating current power source to operate as a motor providing a mechanically reciprocating output. Thus, the term linear motor/alternator may be used to refer to such basic electromechanical devices.

Due to the above-described duality of operation (duty), the stirling machine operating as an engine may be used to drive a linear alternator and the linear electric machine may be used to drive a stirling machine operating in a heat pump mode. In both cases, the power piston of a stirling machine is typically directly connected to the reciprocating member of a linear motor or alternator so that they reciprocate as a unit. Furthermore, linear motors and stirling engines may be used to drive other loads, such as pistons for compressors for compressing gas or for pumping fluids, for example in refrigerators.

This description of the invention relates to drive motors for active balancers. Active balancers driven by drive motors are well known in the art. Linear motors are particularly well suited for use with an active balancer for use with the present invention, but the present invention is applicable to other motors that drive an active balancer.

In connection with the practice of the inventionPrior art of use of embodiments together

All embodiments of the present invention are used with the main vibrating machine of the present invention which is intended to minimize vibrations. The primary vibrating machine typically has a control system that controls the motion of the primary vibrating machine. Embodiments of the present invention are described and illustrated in association with a master control system of a master vibratory machine. However, the present invention is not limited to the illustrated vibratory machines or their control systems. The only necessary connection between the present invention and the main vibrating machine and its control system is that the active balancer must be mechanically connected to the main vibrating machine in order to apply a counterbalancing force to the main vibrating machine, and the present invention uses a vibration sensor that is also mechanically connected to the main vibrating machine in order to sense its vibration. Because the active balancer is mechanically connected to the main vibrating machine, sensors may be connected to the active balancer to sense vibrations.

Fig. 1, 3, 4 and 5 all include the primary control system of the prior art. Fig. 1 illustrates the basic principle of the present invention. Modern prior art control systems utilize a digital processor, such as a microprocessor, microcontroller, or Digital Signal Processor (DSP). As is known to those skilled in the art, digital control circuit operation is generally described in terms of mathematical operations on signals by control algorithms executed by a digital processor. "Signal" includes a representation of an analog signal in a digital data format. Operations are often described in terms of historically prior analog devices (such as filters and signal generators) performing such operations, even though those operations in modern circuits are instead performed by digital processors programmed to perform algorithms.

Referring to fig. 1, the main control system of the prior art is shown along a path across the top of a digital processor 10. As in the prior art, a master control signal is generated by a master control system at the operating frequency of reciprocation and applied to a power stage that controls the main vibratory machine by applying an alternating main electrical drive voltage to the armature winding of a prime mover or motor or alternator coupled to the stirling engine. As is common in most control systems, presence is applied to control algorithmsCommand input 12 of the method. Command input 12A_cmdA desired value of a parameter characterizing operation of the primary vibrating machine at the fundamental drive frequency. Command input A_cmdAmplitudes are often characterized, such as travel distance (e.g., millimeters) or armature coil voltage used to drive the motor/alternator. The output of the main control system controls the reciprocating motion of the main vibrating machine at its fundamental operating frequency, such as a coupled pair (coupliedpair).

In fig. 1, a prior art control algorithm is shown as control algorithm 13. The result of the operation of the control algorithm 13 is applied by a digital to analog converter 16 to a power stage 18 which converts the control signal to the high power required to drive a main vibrating machine 20. The power stage may include additional control circuitry.

As one example, the output of the power stage 18 may be applied to the armature windings of a motor/alternator in the main machine. The motor/alternator is drivingly connected to the stirling machine through a mechanical link to form a coupled pair, the two components of which are mounted to a common mechanical support. In practice, the housing of the alternator and the housing of the stirling machine are integrally formed or directly connected together.

The invention

The method of the present invention minimizes vibration of the main vibratory machine at the fundamental operating frequency of the machine and at selected harmonics of the operating frequency. The basic concept is to sense and feed back the currently sensed amplitude and phase of the vibrations at these frequencies. The sensing of vibrations is essentially error detection, as any vibration is an error that is sought to be eliminated or at least minimized. A sinusoidally varying signal is generated at the fundamental operating frequency and at each selected harmonic frequency. The amplitude and phase of each generated sinusoidally varying signal varies periodically, is updated and is adapted to generate and maintain a balanced signal at each frequency. The balance signals of each frequency are summed and fed back together continuously to drive the drive motor that drives the active balancer. Each balance signal at each frequency adapts the balance signal to the presently sensed vibration through a periodically updated variation such that a sinusoidal balance signal at each frequency is continuously applied to the drive motor to generate a compensating force at the appropriate phase, amplitude and frequency to minimize the sensed vibration at each frequency. This is slightly different from a standard closed loop, negative feedback control system that requires an error in the drive output. In this context, the error (vibration) is driven to zero, but once it is driven to zero, the adaptive algorithm keeps the same compensation output unless it detects an increase or decrease in vibration, in which case it modifies the compensation output to again bring the vibration (error) to zero or a minimum.

Referring again to fig. 1, the vibration sensor 30 is mounted in mechanical connection with the coupling main vibrating machine 20 and the active balancer 22, for example, by mounting to a housing or bracket on which the coupling pair is mounted. The vibration sensor 30 may be an accelerometer and senses vibrations of the coupled pair to provide a sensed vibration signal representative of the sensed vibrations.

The sensed vibration signal from the vibration sensor 30 is applied through an analog-to-digital converter 32 for processing by the digital processor 10. The sensed vibration signal in digital format is applied to one of a plurality of adaptive balancing signal generators, shown schematically as 34, 36 and 38, each of which is an algorithm that generates a balancing signal for a different frequency. Therefore, there is an adaptive balanced signal generator for both the fundamental frequency and each selected harmonic. Each adaptive balancing signal generator is assigned to and responsive to a frequency. While the invention may be practiced to balance vibrations at a single frequency or fundamental and single harmonic, it is preferred to have a plurality of such balanced signal generators for balancing a plurality of different harmonics. Although three balanced signal generators are shown for the fundamental frequency ω and the two harmonics 2 ω and h ω, where ω is the fundamental operating frequency and h is the h-th harmonic, there may be as many balanced signal generators as there are harmonics and any harmonics chosen by the designer.

As described in more detail below, the harmonic balancing signal for each selected frequency is generated by processing the sensed vibration signal by an adaptive filtering algorithm of the adaptive filter. The reference input at each selected frequency is applied to an adaptive filtering algorithm. Thus, each of the balance signal generators 34, 36 and 38 has an output 34B, 36B and 38B that is a balance signal of the balance vibrations at its assigned frequency.

All of the balance signals at outputs 34B, 36B and 38B are summed and the sum is used to control drive motor 24. The sum is the resultant of having the fourier components at the fundamental frequency of operation and the selected harmonic frequency. The resulting sum thus drives the drive motor 24 so that its motion has those fourier components. The amplitude and phase of each component at each frequency opposes the force generated by the vibration of the main vibratory machine 20 at that frequency of that component. In fig. 1, the balanced signals for each selected frequency summed at summing junction 40 are shown and the sum is applied to the power stage 28 and then to the active balancer drive motor 24 through the digital to analog converter 26. Thus, the sum of the balance signals is a feed-forward signal that controls the motoring drive voltage of the drive motor 24, so that the motor 24 is driven by a drive voltage component of each selected frequency that opposes the vibration of each selected frequency. Each balanced signal generator therefore provides an output signal having a frequency, amplitude and phase to the summing node 40 which drives the drive motor 24 at a frequency, amplitude and phase to cancel vibration at its assigned frequency to a practical level.

Adaptive filter

The harmonic balancing signals at outputs 34B, 36B and 38B are generated in part by using adaptive filters. Adaptive filter techniques have been known in the prior art for decades. That is, the adaptive filtering algorithm that is preferably used with the present invention is the Least Mean Square (LMS) filtering algorithm that was invented half a century ago. Various modified LMS algorithms have been developed in the art, as well as other adaptive filtering algorithms that may be used with the present invention. These algorithms include SLMS (a slight modification of the LMS algorithm), NLMS (normalized least mean square filter) and RLS (recursive least squares algorithm). The LMS algorithm is preferred because of the relative simplicity and applicability of use with the present invention. The LMS algorithm models the desired filter by finding the filter coefficients related to the least mean square that produced the error signal. The error signal is the difference between the desired signal and the actual signal. In the present invention, the error signal is the sensed vibration because the desired signal is vibration-free.

The adaptive filter is basically a variable filter that is changed by its adaptive algorithm in response to the sensing error. The adaptive filter is adjusted based on the current sensing error. The error signal is processed by an algorithm that then modifies or updates the variable filter. In the present invention, the variable filter is a simple gain; i.e. a multiplier (amplifier), whose value is controllably varied by an algorithm in response to the sensing error. The value of the variable filter is modified in response to the sensing error by incrementing or decrementing an amount selected and controlled by the designer and at a periodic rate selected by the designer and controlled by the algorithm. In this way, the algorithm increments and decrements the variable filter in a manner such that the error tends to approach zero in practice, and continues incrementing and decrementing the variable filter as needed for subsequent error signals, to keep the error close to zero in practice. An adaptive filtering algorithm, such as the LMS algorithm, is a standard algorithm that operates to drive the error signal to zero as described in the literature.

The invention relates to an adaptive balance signal generator

For each frequency for which balance is sought, there is an adaptive balance signal generator assigned to that particular frequency. The purpose of each adaptive balancing signal generator is to derive and maintain from the sensed vibration input a signal in the drive motor of the active balancer that generates a force opposing and canceling the vibration at its assigned frequency. Fig. 2 shows the adaptive balancing signal generator 34, 36 or 38, which is shown as a block in fig. 1. These adaptive balancing signal generators are identical except that each is adapted to operate at a different frequency assigned thereto. Each adaptive balanced signal generator 50 (fig. 2) includes quadrature sinusoidally varying reference signal generators 52 and 54. The reference generator 52 generates cos (h ω t), where h is 1 (fundamental frequency) or the h harmonic of the assigned balanced signal generatorAnd ω is the fundamental operating frequency of the coupled pair. The reference voltage generator 54 generates sin (h ω t). As can be visualized from phasors (phasor) representing orthogonal cos and sin functions, orthogonal sinusoids are components that can be summed into a resultant. The result can have any phase and any amplitude simply by varying the amplitude of the two orthogonal components. As can be seen in FIG. 3, the amplitude of the reference generator can be determined by taking the amplitude of the reference generator as A_cmdAre controlled such that their amplitude is proportional to Acmd. Alternatively, as seen in fig. 4 and 5, the reference generator may have a constant unit amplitude. The purpose of the sine reference signal generators 52 and 54 is to generate a pair of quadrature sinusoidally varying cos and sin reference signals at their assigned frequencies.

The adaptive balanced signal generator 50 also has two adaptive filters 56 and 58. The adaptive filter 56 has an LMS algorithm adapted by it₀A controllably variable filter W0. The adaptive filter 58 has an LMS algorithm adapted by it₁A variable filter W1 variably controlled.

The sensed vibration signal is applied as an input to an adaptive filtering algorithm that controls each of a pair of variable filters. More specifically, the sensed vibration signal e (n) is applied to an adaptive filtering algorithm LMS₀And LMS₁. The outputs of the reference generators 52 and 54 are also applied to each of a pair of variable filters of a pair of adaptive filters controlled by an adaptive filtering algorithm. More specifically, the signal from the reference generator 52, which produces cos (h ω t), is applied to the variable filter W0 and the signal from the reference generator 54, which produces sin (h ω t), is applied to the variable filter W1. Thus, the output signals from the variable filters W0 and W1 are quadrature sinusoidal signals, each having an amplitude determined by the respective gains of the variable filters W0 and W1. The respective gains of the variable filters W0 and W1 are controlled by their respective adaptive algorithms LMS₀And LMS₁Determined and updated periodically. The quadrature sinusoidal signals from W0 and WL are phasor components that may be summed (vector/phasor summation) at summing junction 60 to provide from summing junction 60Having harmonic frequencies distributed to the balanced signal generator 50 and having a frequency of the harmonic frequencies distributed by the LMS₀And LMS₁The resulting output of the phase and amplitude determined by the adaptive filtering algorithm. These adaptive filtering algorithms produce a balanced signal of the assigned frequencies. The balancing signal has an amplitude and phase such that when fed forward to the armature winding of the drive motor of the active balancer, it will produce a motor force at the assigned frequency of the adaptive balancing signal generator 50 that opposes and substantially cancels the vibration.

The design parameters of the adaptive filter are relatively simple. The algorithm itself is readily available in the prior art. The algorithm controlling each variable filter updates the variable filter in incremental steps. Two parameters chosen by the designer are: (1) the update rate (how often the update is done), and (2) the update amount (how much the gain of the variable filter changes in each update). The update rate is the frequency with which the LMS algorithm is processed. The update rate is selected to be some multiple of the frequency assigned to the balanced signal generator. Typically the update should occur 5 to 10 times during the allocated frequency. The amount of change in the gain of the variable filter for each incremental update is preferably determined by repeated trial and error experiments. Several update amounts over a range are tried separately and then the stability, effect, and response speed of reducing the vibration are observed. The selected amount of change for each update typically varies with the feedback error, with smaller errors varying less and typically proportional to the error magnitude. The LMS or other control algorithm determines the direction of change based on the sign of the error.

The signals from each of the sine varying cos and sin reference generators 52 and 54 are also multiplied by a transfer functionAnd the resulting product is applied as input to the adaptive filtering algorithm LMS of the adaptive filters 56 and 58₀And LMS₁. Transfer functionTransmission from the output 50B of the balance signal generator 50 to the sensed vibration input 62A transfer function. The transfer function is a complex mathematical expression for balancing the entire external system of the signal generator 50. As is well known, the transfer function is the ratio of the output divided by the input, and in this case the sensed vibration signal input at input 62 divided by the output at output 50B of the balanced signal generator 50.

The transfer function is provided by an adaptive filtering algorithm LMS₀And LMS₁The estimated or predicted response used. The transfer function creates a model in the sense that it provides a transfer function that represents the system. The transfer function accounts for the fact that: the response of the external system includes a balancer component. It estimates the behavior of a system with a balancer that also produces a reaction force opposite the vibration at the fundamental operating frequency. The transfer function provides an estimate of the vibrations that would result if a certain vibration cancellation signal were applied by the balance signal generator 50. It is of course contemplated that the system will vary greatly during operation. The LMS algorithm uses the transfer function signal to determine the direction (increase or decrease) to change the gain of the variable filters W0 and W1 to try to reduce the vibration to zero.

The transfer function may be determined in a conventional manner by determining the transfer function of each component along the path from the input to the output it represents and multiplying them to obtain the resulting total transfer function from the input to the outputAlternatively, however, because this is a complex and difficult mathematical calculation, instead of a mathematical expression of the transfer function developed in this way, it is possible and preferred to obtain it by laboratory measurements. For each of each frequencyBy disconnecting each output 50B and input 62 (of each adaptive balanced signal generator) from the inactive circuitry and systems, the input unit sine wave is applied to summing point 40. The returned error signal output by the vibration sensor 30 (fig. 1) is observed and its amplitude and phase are measured. Removing deviceThe measured return output signal with the measured injected input signal is the transfer function. Both the input and output are simple with amplitude a, phase theta and frequency for each assigned frequency. The output of the functional block is therefore the expected output from the system outside the balanced signal generator at its assigned frequency and representing the expected error e (n). The transfer function represents a harmonic balancing signal for the assigned frequency divided by the sensed vibration signal corresponding to the vibration at the selected frequency.

As described above, by summing (phase or/vector sum) the quadrature outputs of the variable filters W0 and W1, a harmonic balance signal of a selected frequency assigned to the balance signal generator is obtained. This summing operation is represented by summing junction 60. Referring back to fig. 1, a composite balance signal of all frequencies is generated by summing the balance signals of all frequencies and applying the sum to the drive motor 24. This is illustrated by applying outputs 34B, 36B and 38B to summing junction 40 and the sum to digital-to-analog converter 26 (fig. 1).

Fig. 3 shows an embodiment of the invention. The adaptive balancing signal generators 334 and 336 are the same as those shown in fig. 1 and 2. However, in the embodiment of FIG. 3, command input A_cmdIs applied to all reference generators, such as cos reference generator 352 and sin reference generator 354. This compares the amplitude of the reference signal with A_cmdProportionally. With A_cmdVarying the amplitude of the reference generator provides the additional advantage of amplitude feed forward control.

Fig. 3, as well as fig. 4 and 5, also show the vibration sensor 330 in more detail. The vibration is preferably sensed by accelerometer 370 (which applies its output to amplifier 372). The amplified output is filtered by a low pass filter 374. The cut-off frequency of the low pass filter 374 is higher than the frequency of the highest selected harmonic at which the designer wishes to minimize vibration using the techniques of the present invention. The purpose of which is to filter out noise at frequencies above the highest selected harmonic frequency.

The sensed vibration signal e (n) applied to the digital processor 310 from the low pass filter 374 through the analog-to-digital converter 332 is a composite analog signal that is the sum of the fundamental operating frequency and the vibrations at all harmonics thereof below the filter cutoff frequency. The composite signal is applied to each adaptive balanced signal generator in a digital format and thus includes all fourier components of the composite vibration signal. However, it is an inherent characteristic of the adaptive filtering algorithm that it responds only to Fourier components at the frequencies of the reference generators 52 and 54 (FIG. 2). Each balanced signal generator has a reference generator at its assigned frequency, so each balanced signal generator is responsive only to the component of e (n) at its assigned frequency. Therefore, no further filtering of the composite vibration signal e (n) is required in order to extract the fourier components of each assigned frequency. A prior art control system that can be used to control the primary vibration machine 380 and for the present invention is shown and described in my patent 7,511,459.

Fig. 4 shows another embodiment of the present invention and its adaptive balancing signal generators 434 and 436 are also the same as those shown in fig. 1 and 2. The embodiment of FIG. 4 is similar to the embodiment of FIG. 3, except that in the embodiment of FIG. 4, command input A_cmd(412) Is not applied to any reference signal generator such as cos reference generator 452 and sin reference generator 454. Therefore, the amplitude of the reference signals they generate always has unity value, so do not match a_cmdThe proportional amplitude is fed forward. Fig. 4 also shows a primary vibration machine, which is a refrigerator that can be driven by a linear motor.

Fig. 5 is an embodiment of the invention similar to that of fig. 4, except that it shows the invention in combination with a different prior art primary vibratory machine, such as a stirling engine driving an alternator, and having a feedback leg 580 providing a feed-forward control signal that is summed with the primary control signal at summing junction 581.

This detailed description, when taken in conjunction with the drawings, is intended primarily as a description of the presently preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. However, it is to be understood that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be resorted to without departing from the scope of the invention or the claims that follow.

Claims (7)

1. A method for balancing the vibration of a primary vibrating machine operating at a fundamental operating frequency, the primary vibrating machine mechanically coupled to an active vibration balancer driven by a drive motor, the method minimizing vibration of the coupled primary machine and balancer at the fundamental operating frequency and at any harmonic of the fundamental operating frequency, and comprising:

(a) sensing vibration of the coupled main machine and counterbalance to provide a sensed vibration signal representative of the sensed vibration;

(b) generating a balance signal for the fundamental operating frequency and for at least one selected harmonic frequency of the fundamental operating frequency by processing the sensed vibration signal with an adaptive filtering algorithm of an adaptive filter for the fundamental operating frequency and for the selected harmonic frequency, the adaptive filtering algorithm having a reference input at the fundamental operating frequency and each selected harmonic frequency; and

(c) summing the generated balancing signals and applying the summed signal to the active vibration balancer drive motor and thereby driving the drive motor with drive voltage components for the fundamental operating frequency and for each selected harmonic frequency that are opposite to the vibration at the fundamental operating frequency and each selected harmonic frequency.

2. The method of claim 1, wherein generating a harmonic balancing signal for the fundamental operating frequency and for each selected harmonic frequency further comprises:

generating a pair of quadrature sinusoidally varying cos and sin reference signals at the fundamental operating frequency and each selected harmonic frequency and applying those signals to each of a pair of variable filters of a pair of adaptive filters controlled by an adaptive filtering algorithm; each of the pair of adaptive filters includes one of the pair of variable filters, respectively;

(ii) inputting the sensed vibration signal to an adaptive filtering algorithm that controls each of the pair of variable filters;

(iii) multiplying each sinusoidally varying cos and sin reference signal by a transfer function characterizing the balance signal for each selected frequency divided by the sensed vibration signal corresponding to the vibration at that selected frequency and inputting the multiplied reference signals to the adaptive filtering algorithm of each adaptive filter; and

(iv) the outputs of the variable filters are summed to provide a balanced signal for the selected frequency.

3. The method of claim 2, wherein the method is performed for a plurality of selected harmonics.

4. A method according to claim 3, wherein the amplitude of each pair of orthogonal sinusoidally varying cos and sin reference signals is controllably varied in proportion to a command input for control of the primary vibrating machine.

5. The method of claim 4, wherein each variable filter is an amplitude multiplier having a gain controlled by its own adaptive filtering algorithm.

6. The method of claim 5, wherein the adaptive filtering algorithm is a least mean square algorithm.

7. The method of claim 6, wherein each adaptive filtering algorithm has a periodic update rate at which the adaptive filtering algorithm changes its variable filter in the range of 5 to 10 times the frequency at which the algorithm generates a balanced signal.