Vibration isolation mount and method

The present invention provides an apparatus and method for vibration isolation. The invention may be conceptualized as a vibration isolation mount. The vibration isolation mount mounts a first member to a second member for reducing the transmission of vibrations from the first member to the second member. The vibration isolation mount comprises a first mounting means for mounting to the first member, and a second mounting means for mounting to the second member. A spring means is arranged between the first and second mounting means, wherein said spring means is coupled to the first mounting means and provides a spring force between said first and second mounting means. The invention may also be conceptualized as a vibration isolation method. The method controls vibrations transmitted from a first member to a second member when the second member is mounted on the first member using a spring arrangement. The spring arrangement provides a delay in transmission of an impulse between the first and second members. The method comprising the steps of (1) sensing vibrations in a first member; (2) applying a force on a second member in response to the sensed vibrations to reduce vibrations in the second member; and (3) wherein the spring arrangement provides a delay equal to or greater than a delay in the provision of said force in response to the vibrations in said first member.

TECHNICAL FIELD

The present invention generally relates to a vibration isolation mount and a vibration isolation method.

BACKGROUND OF THE INVENTION

Often there is a need to reduce the transmission of vibration between two elements of an engineering structure while still maintaining mechanical support. The ultimate aim can be associated with reducing the effects of vibration and/or noise on both people and equipment.

One such problem is the reduction of broadband cabin noise within civil aircraft. This is conventionally achieved by improving the soundproofing within the cabin (which normally entails a consequent increase in weight), together with the use of simple passive isolators to reduce vibration transmission between the main air frame and the interior trim panels. The latter is important because the vibration path through the trim panel mounts is the dominant one in many cases e.g. for excitation by the external turbulent boundary layer pressure field. The reason for this is that the boundary layer pressure field generally produces subsonic vibrations and thus transmission between the air frame and the trim panel through the air insulation gap is normally small compared to the transmission through the mechanical couplings.

Current practice is to use small blocks of elastomeric material for the isolation. Such isolators reduce vibration transmission above the resonant frequency associated with the isolators' stiffness reacting against the receiving mass: the so-called isolation frequency. The use of an elastomer provides sufficient internal damping so that the classical increase in transmission at the isolation frequency is small.

However, an elastomer does not behave as a classical stiffness isolator because its stiffness increases with increasing frequency. This can produce a much higher transmission than the classical spring at frequencies well above the isolation frequency. Also, elastomers are notoriously temperature sensitive which can compromise the performance.

The problem with replacing the elastomeric material with a member that has a classical spring stiffness behaviour is that high vibration transmission will occur at and around the resonance frequency associated with the isolator's stiffness against the receiving mass. Unfortunately, introducing large amounts of damping into such a spring arrangement such as a metal spring in order to reduce the vibration transmission at or around the resonance frequency is difficult when a long service life is required. Additionally, the use of heavy damping produces unwanted increases in transmission either side of the isolation frequency.

It is therefore an object of the present invention to provide an improved vibration isolation mount and method.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide an apparatus and method for vibration isolation.

Briefly described, in architecture, one embodiment of the system, among others, can be implemented as follows. The vibration isolation mount mounts a first member to a second member for reducing the transmission of vibrations from the first member to the second member. The vibration isolation mount comprises a first mounting means for mounting to the first member, and a second mounting means for mounting to the second member. A spring means is arranged between the first and second mounting means, wherein said spring means is coupled to the first mounting means and provides a spring force between said first and second mounting means.

The invention may also be conceptualized as a vibration isolation method. The method controls vibrations transmitted from a first member to a second member when the second member is mounted on the first member using a spring arrangement. The spring arrangement provides a delay in transmission of an impulse between the first and second members. The method comprising the steps of (1) sensing vibrations in a first member; (2) applying a force on a second member in response to the sensed vibrations to reduce vibrations in the second member; and (3) wherein the spring arrangement provides a delay equal to or greater than a delay in the provision of said force in response to the vibrations in said first member.

These and other embodiments and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional apparatuses, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.

Reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with a first aspect of the present invention, an active vibration isolation mount is provided for mounting a first member to a second member and for reducing the transmission of vibrations from the first member to the second member. Spring means are arranged to lie between the first and second member when the mount is inserted between the first and second members. Sensing means sense vibration in the first member and force means are provided for applying a controlling force to the second member in dependence upon vibrations sensed by the sensing means in order to reduce vibrations in the second member. The spring means provides a delay between the first and second members which gives advanced warning of the vibration transmitted to the second member. This delay is equal to or greater than a delay incurred in the application of the controlling force by the force means in response to the vibrations in the first member.

Thus in accordance with this aspect of the present invention, the vibrations transmitted from the first member to the second member through the spring means are delayed by an amount which is sufficient to provide for a control signal to be actively generated for the active control of the force means to apply a controlling force in order to reduce vibrations in the second member. The provision of the delay in the impulse response of the spring means provides for the feedforward control of the application of the controlling force to the second member. Thus this aspect of the present invention enables the utilization of the low passive transmission properties at high frequencies provided by the spring means whilst ameliorating the effect of resonance at the lower isolation frequency by using active control.

In one embodiment of the present invention the active vibration mount is provided as a unit having first mounting means for mounting to the first member and second mounting means for mounting to the second member. The spring means is arranged between the first and second mounting means and the force means applies the controlling force to the second mounting means. Also in one embodiment, the sensing means is arranged to sense vibrations in the first mounting means.

The present invention enables the application of the force by the force means and the action of the spring means to be in parallel between the first and second mounting means. Conveniently, the force means and the spring means can be arranged substantially concentrically or axially symmetrically. For example, a single coaxial spring arrangement can be used or multiple spring arrangements arranged symmetrically with one or more force arrangements.

In one embodiment, the spring means preferably has a stiffness in a direction extending between the mounting means but does not vary substantially with the frequency of the vibrations.

In one embodiment, the spring means has a configuration which is selected to provide the required delay. For example, the mass per unit length and/or length of the spring or springs can be selected to provide the required delay.

In the feedforward active control system the required delay in the spring means is required because of the control system delay which is typically incurred by the response of the sensing means, force means and control means.

In one embodiment of the present invention the sensing means, spring means and force means are adapted to provide broadband vibration isolation, i.e. the control system is a broadband control system.

In one embodiment of the present invention, because the mount is required not only to provide vibration isolation, but also stiff mounting of the second member on the first member, the spring means has a high static stiffness. Stiff mounting comprises mounting with sufficient stiffness to support the static loads with an acceptable displacement.

At certain frequencies, the vibrations detected by the sensing means can reduce, for example, as a result of the tuned vibration absorber action of the mass on the spring means. In such conditions the vibrations detected by the sensing means reduce and thus potentially the active control of the application of the controlling force would cause a reduction in the application of such a controlling force. Thus in one embodiment of the present invention an error sensing means is provided for sensing vibrations in the second member. The error sensing means thus provides a feedback signal for control of the application of the controlling force. The force means is responsive to the sensed vibrations in the second member by virtue of a control signal from the control means which responds to the vibrations. Thus in accordance with this embodiment of the present invention, the control system comprises a combined feedforward and feedback control system which prevents loss of the reference signal caused by occurrences such as the tuned vibration absorber action of the mass on the spring.

In the present invention the spring means can comprise any suitable spring member or spring arrangement which can provide required impulse delay between the first and second members. Such a spring arrangement can comprise one or a number of springs such as helical springs or leaf springs. Conveniently, such springs are conventionally made of metal. The present invention is not, however, limited to any particular form of spring arrangement and any arrangement which provides a required delay is encompassed within the scope of the present invention.

In one embodiment of the present invention the force means is mechanically coupled between the first and second members (or the first and second mounting means) to apply the controlling force to the second member. In such an embodiment the force means can comprise an electromagnetic actuator comprising a coil member coupled to the first mounting means or first member and a magnetic member coupled to the second mounting means or second member. In one embodiment the magnetic member is substantially heavier than the coil member and provides a blocking mass connected to the second member or second mounting means. In one embodiment a coil member and magnetic member are coupled by coupling means providing low stiffness in a direction extending between the first and second mounting means and a high stiffness in a perpendicular direction.

In one embodiment of the present invention, a lumped blocking mass additional to or in place of the magnetic member can be provided coupled to the second mounting means or second member.

In another embodiment of the present invention a reactive inertial mass is provided and the force means is connected between the mass and the second mounting means or second member to apply the controlling force to the second mounting means or second member. Thus this embodiment of the present invention provides an inertial force on the second member. The force means can comprise an electromagnetic actuator comprising a coil member and a magnetic member, wherein the coil member or the magnetic member comprises the mass. Preferably the magnetic member comprises the mass and the coil member is coupled to the second mounting means or second member. The coil member and magnetic member can be coupled by coupling means providing low stiffness in a first direction extending between the first and second mounting means or first and second members and high stiffness in a perpendicular direction.

The present invention also provides an active vibration isolation mount arrangement comprising the active vibration mount and control means for generating the control signal in response to the vibrations sensed by the sensing means.

The present invention also provides an active vibration isolation mount arrangement comprising a plurality of the active vibration isolation mounts and control means for generating the control signals for the force means in response to the vibrations sensed by each respective sensing means. Thus, in this aspect of the present invention the active vibration isolation mount arrangement provides for a single central active control of a number of mounts.

One aspect of the present invention also provides a method of controlling vibrations transmitted from a first member to a second member when the second member is mounted on the first member using a spring arrangement providing a delay in transmission of an impulse between the first and second members. Vibrations in the first member are sensed and the force is applied on the second member in response to the sensed vibrations to reduce vibrations in the second member. The spring arrangement provides a delay equal to or greater than a delay in the provision of the force in response to the vibrations in the first member.

Another aspect of the present invention provides a method of isolating a trim panel mounted on an aircraft frame from vibrations in the aircraft frame caused by subsonic boundary layer noise using a trim mount having a spring arrangement providing a delay in transmission of an impulse between the trim panel and the aircraft frame. Vibrations in the aircraft frame are sensed and a force is applied to the trim panel in response to the sensed vibrations to reduce vibrations in the trim panel. The spring arrangement provides a delay equal to or greater than a delay in the provision of the force in response to the vibrations in the aircraft frame.

The present invention also provides a method of designing an active mount arrangement for mounting a first member to a second member comprising selecting a sensor for sensing vibrations in the first member, designing an actuator arrangement for providing a force on the second member, selecting an active force controller for controlling the actuator in response to the sensed vibrations to reduce vibrations in the second member, and designing a spring member for provision between the first and second members to provide a delay in transmission of an impulse between the first and second members equal to or greater than a delay incurred by the sensor, the actuator and the active force controller in the provision of the force in response to the vibrations in the first member.

The present invention further provides a method of controlling vibrations transmitted from the first member to a second member when the second member is mounted on the first member. A sensor is provided sensing vibrations in the first member. An actuator arrangement is provided applying a force on the second member. An active force controller is provided to control the actuator in response to the sensed vibrations to reduce vibrations in the second member. The second member is mounted on the first member using a spring member providing a delay in transmission of an impulse between the first and second members equal to or greater than a delay in the provision of the force by the active force controller in response to the vibrations in the first member.

The present invention also provides an active mount arrangement for mounting a first member to a second member and for reducing the transmissions of vibrations from the first member to the second member. The mount comprises a spring arrangement between the first and second members having a stiffness in a first direction extending between the first and second members that does not vary substantially with frequency of the vibrations, a sensor arrangement for sensing vibrations in the first member, a force actuator for applying a controlling force to the second member, and a controller connected to the sensor for controlling the application of the force by the force actuator in response to the vibrations sensed by the sensor. A spring arrangement provides a delay equal to or greater than a delay in the application of the controlling force by the force actuator in response to the sensed vibrations.

A further aspect of the present invention provides an active vibration isolation mount for mounting a first member to a second member and for reducing the transmission of vibrations from the first member to the second member. The mount arrangement comprises a first mounting point for mounting to the first member, a second mounting point for mounting to the second member, a spring arrangement connected between the first and second mounting points, a sensor arrangement for sensing vibrations in the first member, and a force actuator arrangement for applying a controlling force to the second member and for the setting of parameters in a controller in response to the vibrations sensed by the sensor arrangement. The spring arrangement is adapted to provide a delay in the first direction equal to or greater than a delay in the application of the controlling force in response to the vibrations in the first member.

Another aspect of the present invention provides an active vibration isolation mount for mounting a first member to a second member and for reducing the transmission of vibrations from said first member to said second member, the active vibration isolation mount comprising a first mounting arrangement for mounting to said first member; a second mounting arrangement for mounting to said second member; a spring arrangement coupled between said first and second mounting arrangements; a substantially cylindrical coil frame extending axially between said first and second mounting arrangements and couple at one end thereof to said first or second mounting arrangements; a coil arrangement mounted coaxially on the coil frame; a magnetic circuit body for providing a magnetic flux path circuit from a radially inner position adjacent to said coil to a radially outer position adjacent to said coil such that said coil lies in the flux path, and forming an annular cavity between said magnetic circuit body and said coil frame; and a radial suspension arrangement extending radially between said coil frame and said magnetic circuit body in said cavity for providing radially stiff support and axial compliance.

Thus this aspect of the present invention provides a mount arrangement which provides for the efficient lateral support of the coil within the magnetic flux air gap while allowing for relative axial movement. The design is space efficient because of the provision of the lateral support close to the coil within the magnetic circuit in a region formed by the magnetic circuit.

In one embodiment the coil frame is coupled at one end thereof to the first or second mounting arrangements and the magnetic circuit body is coupled to the second or first mounting arrangements respectively. Thus in this arrangement the electromagnetic force can be applied directly between the first and second mounting arrangements substantially coaxially with the spring force.

In another embodiment the coil frame is coupled at one end thereof to the second mounting arrangements and the magnetic circuit body is free to move axially. Thus in this embodiment the mass of the magnetic circuit body acts as an inertial mass and the electromagnetic actuator provides a force between the inertial mass and the second mounting arrangement.

Another aspect of the present invention provides a vibration isolation mount for mounting a first member to a second member and for reducing the transmission of vibrations from said first member to said second member, the vibration isolation mount comprising first mounting means for mounting to said first member; second mounting means for mounting to said second member; spring means arranged between said first and second mounting means; and a mass coupled to said spring means so as to lie in or adjacent to a region between said spring means and said second mounting means; wherein said spring means is coupled to said first mounting means and provides a spring force between said first and second mounting means.

In this aspect of the present invention, the provision of the blocking mass as a lumped mass at the end of the spring arrangement at the point of coupling the vibration isolation mount to the second member provides an optimised passive mount. It is particularly suited for use with second members that have a distributed mass e.g. a trim panel, that is thin at the point that vibration isolation mounting is required.

Another aspect of the present invention provides a vibration absorber for reducing the vibrations in a member, the vibration absorber comprising mounting means for mounting to said member; an inertial mass; spring means coupled to said inertial mass and for providing a spring force between said inertial mass and said mounting means; and a blocking mass coupled to said spring means so as to lie in or adjacent to a region between said spring means and said mounting means.

In this aspect of the present invention, the provision of the blocking mass as a lumped mass at the end of the spring arrangement at the point of coupling the vibration absorber to the member provides an optimised passive absorber. It is particularly suited for use with members that have a distributed mass e.g. are thin at the point that vibration absorption is required.

Having summarized the invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims.

Referring now in detail to the drawings in which the reference numerals indicate like parts throughout several views.

FIG. 1illustrates the principles of a first embodiment of the present invention. Vibrations in a transmitter1are transmitted to a receiver2via a spring coupling3. The spring coupling3provides for the mounting of the receiver2on the transmitter1and provides for a stiff static mount. A force actuation arrangement4is provided coupled between the transmitter1and the receiver2in parallel with the spring arrangement3. Thus in accordance with the principles of this embodiment of the present invention, the vibrations transmitted from the transmitter1to the receiver2via the spring arrangement3are actively controlled by the application of a force to the receiver2by the force actuation arrangement4.

FIG. 2illustrates the principles of a second embodiment of the present invention. Vibrations in a transmitter5are transmitted to a receiver6via a spring arrangement7. The receiver6is statically mounted on the transmitter5via the spring arrangement7. A force actuation arrangement8is provided coupled to the receiver6. A mass9is provided coupled to the force actuation arrangement8. Thus in this way a controlling force is applied to the receiver6by the force actuation arrangement8. In this embodiment the force applied is an inertial force. This embodiment of the present invention has the benefit of avoiding a direct connection between the receiver6and transmitter5through the force actuation arrangement. This, unlike the embodiment ofFIG. 1, does not provide a secondary vibration path. However, this embodiment relies on an inertial force.

FIG. 3is a graph illustrating the transmission response with frequency of a conventional elastomeric mount, a spring mount, and an active mount, all three with the same static stiffness in accordance with an embodiment of the present invention. The elastomeric mount however suffers from a frequency dependant stiffness which causes high transmission in the mid and high frequency regions.

The requirement of a vibration isolation mount is to provide high stiffness to static loads and at frequencies above a few Hertz to reduce the transmission capabilities of the mount to provide for vibration isolation. As can be seen inFIG. 3, a conventional elastomeric mount provides for some vibration isolation at high frequencies. The elastomeric mount however suffers from resonance at low frequencies and at these frequencies the transmission is high. A spring mount provides for an improved isolation at high frequencies. However, a spring mount suffers from strong resonance at low frequencies which, in the example shown inFIG. 3, peaks at 200 Hz. Resonance occurs when the isolators' stiffness reacts against the receiving mass. The resonant frequency FRis given by:

FR=12⁢π⁢Km
where K is the spring constant and m is the mass on the spring.

Thus, the resonant frequency can be shifted to lower frequencies and an improved high frequency isolation can be achieved by increasing the mass, i.e. the blocking mass. However, for certain applications, such as in aircraft, there is a limited ability to increase the mass in the mount. Further, even by increasing the mass, the resonant frequency merely moves to lower frequencies but is still present.

Embodiments of the present invention aim to actively control the vibrations at the low frequency region in order to provide or improve isolation at low frequencies and to ameliorate the effects of resonance in a spring-type mount. The effect of the removal of the resonance effect in an active mount in accordance with an embodiment of the present invention is illustrated inFIG. 3. In order to achieve this, as illustrated inFIGS. 1 and 2, the active force controller operates in parallel with the spring arrangement.

The present invention encompasses any convenient manner of providing for the parallel operation of the force actuator and the spring arrangement. For example,FIG. 4illustrates an embodiment of the present invention in accordance with the principles of the embodiment ofFIG. 1in which a transmitting member10is mounted to a receiving member20by a mount arrangement comprising a spring arrangement30illustrated as a helical spring in this embodiment, arranged concentrically around a force actuator40connected between the transmitting10and the receiving member20.

FIG. 5illustrates another embodiment of the present invention in accordance with the principles of the embodiment ofFIG. 2in which a transmitting member50is mounted to a receiving member60by a mount arrangement comprising a spring arrangement70arranged concentrically around a force actuator80which is coupled between the receiving member60and a mass90which is also arranged concentrically within the spring arrangement70.

FIG. 6illustrates an alternative embodiment of the present invention in accordance with the principles of the embodiment ofFIG. 1in which a transmitting member11is mounted to a receiving member21by a mount arrangement comprising a spring arrangement31arranged concentrically within a force actuator41connected between the transmitting member11and the receiving member21.

FIG. 7illustrates an alternative embodiment to the present invention in accordance with the principles of the embodiment ofFIG. 2in which a transmitting member51is coupled to a receiving member61via a spring arrangement71. The spring arrangement71is arranged concentrically within a force actuator81and a mass91. The force actuator81is coupled between the mass91and the receiving member61to apply a controlling force to the receiving member61.

In the embodiments ofFIGS. 2,5and7, although the mass is shown separately to the force actuator, the force actuator will generally require a mass against which to react. For example, in an electromagnetic actuator there are two mutually moving components comprising a coil member and a magnet member. Either one of these can act as the mass. Typically, the magnet member comprises a magnetic circuit surrounding the coil member to provide the electromotive force. It is thus convenient for the magnet member to form the mass for providing the inertial force.

So far in the embodiments described hereinabove, no consideration has been given as to how the force actuation arrangement is controlled to perform the force actuation. In all of the embodiments, the force actuation arrangement is primarily controlled in accordance with vibrations detected by a reference sensor associated with the transmitting member to provide signals indicative of vibrations to be transmitted through the spring arrangement. Thus the control of the force actuation comprises a feedforward control system. Feedforward control systems are well known in the art and require advanced notice of a vibration upstream for control downstream. The spring arrangement provides for the delay to enable the reference sensor to detect an upstream vibration component for cancellation downstream, i.e. at the receiving member.

In the embodiments of the present invention described hereinabove, the spring arrangement can comprise any suitable spring arrangement to provide the delay. For example, the spring arrangement can comprise a helical spring or a leaf spring. Any arrangement which preferably provides a stiffness that does not substantially vary with frequency can be used. The present invention is not limited to the use of metal springs. In helical springs one of the properties of the spring which provides the delay is the mass per unit length. The length of the spring will also effect the delay. These properties can be independent of the stiffness. For example, a light spring can provide the same stiffness as a heavy spring. However, a heavy or long spring provides for a longer delay than a light or short spring. Thus in order to provide the required properties for an active vibration isolation mount, a stiff spring is required to provide for a strong static coupling, and the mass per unit length or length is required to be large enough to provide the required delay for feedforward vibration control. Other factors that affect the delay in a spring arrangement are other shape and configuration parameters.

FIG. 8is a schematic diagram of an embodiment of the present invention in accordance with the principles of the embodiment ofFIG. 1. An active mount100is arranged between a transmitting member12and a receiving member22to mount the receiving member22to the transmitting member12. The mount100includes couplings105and106for coupling the mount100to the receiving member22and the transmitting member12respectively. A blocking mass104is mounted on the coupling105. A spring arrangement32is provided between the coupling106and the blocking means104to stiffly statically mount the receiving member22to the transmitting member12. A force actuator arrangement42is provided coupled between the blocking mass104and the coupling106in order to provide the controlling force on the receiving member22. A reference sensor102is mounted on the coupling106in order to detect vibrations in the transmitting member which are transmitted through the spring arrangement32to the receiving member22. A controller101is provided for receiving the output of the reference sensor102in order for generating a controlling signal to control the force actuator arrangement42. An error sensor103is mounted on the coupling105for detecting vibrations in the receiving member22. The output of the error sensor103is input to the controller101to provide a feedback signal for control of the force actuator arrangement42. Thus in this embodiment of the present invention, the force actuator arrangement is controlled by a controller101which carries out a feedforward and feedback control.

FIG. 9illustrates an embodiment of the present invention in accordance with the principles of the embodiment ofFIG. 2. In this embodiment a mount110mounts a receiving member62to a transmitting member52. The mount includes couplings114and115for coupling the mount110to the receiving member62and the transmitting member52respectively. A blocking mass116is mounted on the coupling114. A spring arrangement72is coupled between the coupling115and the blocking mass116. A force actuator82is provided coupled to the blocking mass116to provide a force to the receiving member62. An inertial mass92is provided coupled to the force actuator82to enable the force actuator82to apply an inertial force to the receiving member62. A controller111is provided for generating control signals to control the force actuator82. A reference sensor112is mounted on the coupling115to detect vibrations in the transmitting member. The controller111receives signals from the reference sensor112and controls the force actuator82accordingly. An error sensor113is mounted on the coupling114to detect vibrations in the receiving member62. The controller111receives the signals from the error sensor113in order to control the force actuator82accordingly. Thus the controller111performs a combined feedforward and feedback control.

Although in the embodiments ofFIGS. 8 and 9single error and reference sensors are illustrated, any suitable error sensing arrangement can be used. The error sensors can comprise a number of sensors arranged in any suitable position to detect vibrations in the receiving member62and the transmitting member52respectively. Conveniently, the sensors are arranged within the mount100and110. However, the sensors can be provided for direct mounting on the receiving member62and/or the transmitting member52.

The embodiments ofFIGS. 8 and 9are schematic and although the spring and force actuator are illustrated as being side-by-side, they can be positioned in any suitable arrangement for providing for parallel actuation. Conveniently, in order to avoid shear forces between the force applied by the force actuation and the force applied by vibrations through the spring arrangement, the force actuator and the spring arrangement are arranged concentrically as for example illustrated inFIGS. 4 to 7.

In the embodiments ofFIGS. 8 and 9the controllers101and111perform a combined feedforward and feedback control, i.e. an adaptive feedforward control system. The controller thus conveniently comprises a programmable device for performing a control algorithm. Such control algorithms are well-known in the art (see for example “Adaptive Signal Processing” by B. Widrow and S. D. Stearns, Prentice Hall Signal Processing Series, 1985, the content of which is hereby incorporated by reference). Conventionally, adaptive feedforward control systems rely on the reference signal not being corrupted by the controlling force. However, this is often not the case due to leakage back of corrupting control signals. This is particularly the case in the example of the embodiment ofFIG. 1. The controllers101and111can thus carry out a control algorithm such as that described in UK patent application no. GB 0311085.5, the content of which is hereby incorporated by reference.

Although in the embodiments ofFIGS. 8 and 9the controllers101and111are illustrated as residing within the mounts100and110, the controllers can be provided separately, i.e. one per mount, or centrally, i.e. one per plurality of mounts.

In the embodiments of the present invention the actuator can comprise any suitable actuator such as an electromagnetic actuator, a piezo electric actuator, a hydraulic actuator, a magnetostrictive actuator, an electrostatic actuator, a pneumatic actuator or a thermal expansive actuator.

A mount is illustrated inFIGS. 10,11and12, which comprises a specific detailed embodiment of the schematic embodiment illustrated inFIG. 1. The mount200comprises a cap201for mounting to a receiving member and a coil frame202for mounting to a transmitting member. The coil frame is cup-shaped and carries an annular coil203within an annular channel204on an external circumference of the coil frame202. The coil frame202is mounted coaxially with the cap201and is provided with an aperture205for receiving a spring seat206. The spring seat206has an inner threaded portion207and an annular recess208for receiving a helical spring209. The helical spring209sits in the annular recess208, the spring seat206and extends axially towards the cap201. The cap201is provided with an annular recess210for receiving the other end of the helical spring. The cap201is also provided with an inner threaded portion211. The inner threaded portions207and211provide for the coupling of the mount200to a transmitting member and a receiving member respectively.

The cap201lies within a spring seat sleeve212which extends coaxially with the spring209towards the spring seat206. A magnet213is provided around a circumferential position of a spring seat sleeve adjacent to the magnet213there is provided an annular iron member214arranged to lie at an inner circumferential position to the coil203. The annular iron member204lies to one side of the magnet213. To the other side of the magnet213lies a second annular iron member215which extends away from the spring seat sleeve212and curves around to extend over an end of the coil frame at a distant radial position. A third iron member216is provided and comprises an annular member lying adjacent to the coil203and extending away from the coil203. The second and third iron member215and216meet each other and are connected at their outer radial positions to form an annular cavity217at four quadrant positions around the circumference of the second and third iron members215and216, resilient members218are provided for supporting support arm219. The four support arms219extend radially from the coil frame202and are held in place by a locking ring220.

A seal221is provided between the coil frame202and the third iron member216to seal the gap between the coil203and the third iron member216to thus provide a seal on the unit.

The helical spring209provides for the strong static coupling between the two sides of the mount200to thus enable the strong passive coupling of first member to the second member.

In this embodiment the coil203is mechanically coupled to the coil frame202which in turn is coupled to the first member, i.e. a transmitting member. For application of the mount to mounting of trim panels to an aircraft air frame, provision of the coil on the coil frame enables heat to be dissipated to the air frame.

The spring209provides for a reduction of the transmission vibrations along the axis. The application of current to the coil203will generate a force which is applied between the coil frame and cap. Relative movement between the coil203carried on the coil frame202and the iron members214,215,216, magnet, spring seat sleeve and cap201causes the bending of the support arms219. The support arms219have a low stiffness in the axial direction and a strong stiffness in the perpendicular direction. Thus they provide for strong support of the magnetic components in the magnetic circuit formed by the iron members213,214and215relative to the coil frame202. They also provide the stiffness in a shear direction. The support arms219are mounted in the resilient members218to allow for the change in radial length of the support arms219caused by the relative axial displacement of the coil frame202and the magnetic circuit comprised of the iron members214,215and216.

As illustrated inFIG. 12, sensor rings222and223of piezo electric material is provided within the mount for sensing vibrations. A first piezo electric sensor223is provided in the coil frame222for sensing vibrations coming from the first member i.e. the feedforward or reference signal and a second piezo electric sensor222is provided in the second iron member215for sensing vibrations in the second member i.e. the feedback or error signal. In this embodiment the piezo electric sensors222and223are annular and substantially concentric with the axis of the mount. This enables the sensors to detect the axial vibrations in the first and second members. Any axially symmetric sensing arrangement can be used in place of the ring sensors222and223.

It can thus be seen that this embodiment of the present invention provides for a coaxial spring mount and electromagnetic actuator acting between the two sides of the mount. The electromagnetic actuator is formed by the coil203lying within a magnetic circuit comprised of the iron members214,215and216and the magnet213. It can be seen inFIG. 12that the coil213has an axial length which is greater than the axial length of the third iron member216. The reason for this is to ensure that the coil203always lies within the magnetic field provided between the third iron member216and the first iron member214, i.e. to ensure no edge effects caused by an edge of the coil203entering into the field region between the third iron member216and the first iron member214. Although in this embodiment the coil203is shown as being sufficiently long in the axial direction so as to ensure no edge ever enters the region between the third iron member and the first iron member, in an alternative embodiment the coil203can be shorter in axial length than the third iron member so that an edge of the coil never leaves the field region between the third iron member and the first iron member.

It can be seen in the embodiment ofFIGS. 10 to 12that the magnetic circuit comprised of the iron members214,215and216comprises a more massive component than the coil203and the coil frame202. Thus in this embodiment the iron members214,215and216and the magnet213comprise a mass which is coupled to the cap201and provides a blocking mass on the receiving end of the mount.

Although not shown in the embodiments ofFIGS. 10 to 12, when the mount200is coupled to first and second members to provide active vibration isolation therebetween, the mount200is attached by screws to the first and second members. The screws thread into the threaded portions207and211. The attachment of the mount to the second member is by way of a rotational decoupling device e.g. a pin or ball joint to allow for the shear rotational decoupling of the mounting of the second member to the first member while still supporting shear loads. A grommet can be used, which can for example be made out of rubber, for attachment to the second member, i.e. for attachment around the screw threaded into the threaded portion211. The rubber grommet between the thread fitted into the threaded portion211and the second member (i.e. the receiving member) allows for bending, i.e. rotation about any axis and effectively provides a pin joint at the receiving end. The mounting of the coil frame202via the threaded portion207to the first member is stiff.

A controller for controlling the actuation of the electromagnetic actuator in this embodiment of the present invention can be provided separately or attached to the mount200.

A second specific embodiment of the present invention in accordance with the principles of the embodiment ofFIG. 2will now be described with reference toFIGS. 13 to 15.

An annular casing plate is provided on an axis coaxially with a spring seat302, a cup-shaped casing body303is provided coupled to the casing plate301to provide a housing. Within the housing a helical spring304extends along the axis. The helical spring304sits at one end within an annular recess305within the spring seat302. The other end of the helical spring304lies in annular recess306in a second spring seat307. The second spring seat307is connected to a cup-shaped coil frame308. The coil frame308extends axially over the spring304. An annular coil309lies at an outer circumferential position at an axial position along the coil frame308. A magnetic circuit is suspended from the axial end of the coil frame308on support arms310. The support arms310radially extend from quadrant positions at the axial end of the coil frame308and are locked in place at an inner radial position thereof by a locking ring311. At outer radial positions the support arms310are mounted in resilient members312. The resilient members312lie within and support the magnetic circuit. Resilient members312are held between a first magnetic member313and a second magnetic member314. The first magnetic member313comprises a generally annular member extending radially inwards towards the coil309to lie adjacent the coil309. The second magnetic member314comprises an annular member extending radially inwardly from the resilient members312to a radial position inward of the coil frame308. An annular magnet315is provided adjacent to the radially inner portion of the second magnetic member314. A third magnetic member316comprises an annular member which lies adjacent to the magnet315in an axial position. The first magnet member313and the third magnet member316lie in radially opposed positions either side of the annular coil309. Thus the first magnet member313, the second magnet member314, the third magnet member316and the magnet315form the magnetic circuit in which the coil309lies. The magnetic circuit is relatively heavy compared to the coil frame and the coil and it thus provides the inertial mass suspended by the support arms. In this embodiment of the present invention, the electromagnetic actuator includes the inertial mass.

The resilient members312are provided to allow for the radial length variations of the support arms310as the electromagnetic actuator causes the relative movement of the magnetic circuit and the coil309. The support arms310are low in stiffness in the axial direction and strong in stiffness in the radial direction, thereby providing for support for the magnetic circuit and the inertial mass which in this embodiment comprise the same components.

A coil frame308is connected to a base317, support arms318radially extend from the base317and are held to the base317at inner radial positions thereof by a locking ring319. At their outer radial ends the support arms318are connected to a resilient support ring320which sits on the casing body303and is locked in place thereon by a locking ring321.

The base317is for coupling to the receiving member via a threaded portion322to provide for rotation along the axis, the bolt threaded into the threaded portion322is threaded through a grommet in the second member so that there is a resilient grommet connection between the second member and the base317to provide a pin joint. To connect the casing plate301to the transmitting member, a hole is provided in the casing to allow a bolt to be inserted into a threaded portion323in the spring seat302. The connection made to the transmitting member by the bolt is fixed to provide a solid connection between the casing plate301and the spring seat302and the transmitting member.

A reference sensor331in the form of a piezoelectric ring is provided mounted on the casing plate301. An error sensor330in the form of a piezoelectric ring is provided mounted on the coil frame308.

It can thus be seen in this embodiment, as illustrated schematically inFIG. 7, the electromagnetic actuator lies coaxially about the spring. Also the inertial mass lies concentrically around the spring and in this embodiment the inertial mass comprises the magnetic circuit of the electromagnetic actuator. The electromagnetic actual components are not physically connected to the transmitting member. There is no coupling with any axial stiffness between the base317and the casing plate301and the spring seat302. The support arms318provide for the axially stiff decoupling of the body317and the casing plate301(and the spring seat302). There is thus no axially stiff coupling between the two sides of the mount300.

It can be seen from the above embodiments that the present invention is primarily concerned with the reduction of transmission of vibrations in a direction perpendicular between two objects or members.

The present invention has application where it is necessary to mount two bodies and it is desirable to prevent the transfer of vibrations from one body to the other while firmly mounting the bodies together.

The present invention has particular application in the aircraft industry for the mounting of trim panels to the aircraft air frame. When an aircraft is flying, around the skin of the aircraft there is generated boundary layer field pressure fluctuations. These pressure fluctuations are generally subsonic and thus they are not well coupled between the airframe and the cabin via the air/insulation gap therebetween. They are instead primarily transmitted through the trim panel mounts which in the prior art have comprised elastomeric members. The embodiments of the present invention have a broadband frequency capability and are thus ideally suited to the control of vibrations generated by the turbulent boundary layer pressure variations. In an aircraft the active vibration isolation mounts can replace some or all of the conventional passive mounts to provide a reduction of the transmission of vibrations from the airframe to the trim panels. Each mount can be controlled independently by a controller either provided with a mount in the unit, or provided separately. Alternatively, a plurality of mounts can be controlled from a single controller. A controller receives the reference (feedforward) and error (feedback) signals from the sensors and generates respective control signals. Each mount is controlled independently.

The present invention is applicable to any situation where broadband vibration isolation is required. It can, of course, also be applied to tonal noise. For example, the mounts can be used as engine mounts for an engine that operates over a wide range of frequencies. The use of the active vibration isolation mounts will reduce the transmission of vibrations from the engine to the framework in which the engine is mounted. The provision of the active control in the active vibration mount enables control of low frequencies. When an engine is started up, as it begins to start, if no active control is provided, then severe vibration can be transmitted to the framework holding the engine. The active vibration isolation mount reduces this vibration. Thus the active vibration mount is particularly useful for an engine which is repeatedly started and stopped and thus generates a broad range of vibration frequencies. It can also be used as a mount in an environment subject to broadband combustion flow noise.

The present invention encompasses not just the active vibration mount and its method of operation, but also the design and manufacture of such a mount. In the design of such a mount, sensors must be selected, the actuator must be designed to apply the force to the receiving member and the spring arrangement must be designed to lie between the transmitting member and the receiving member and to provide the necessary delay between the transmitting member and the receiving member to allow for the feedforward control of the generation of the controlling force on the receiving member. Thus the design of the mount requires the designing of the spring arrangement to provide such a delay. Some of the parameters that can affect delay are the mass per unit length, the length of the spring, the shape of the spring, and the type of spring configuration. In one embodiment where the spring arrangement comprises a helical spring, the spring is chosen to provide a mass per unit length and length which is sufficient to provide the required delay. A typical delay required for feedforward active control is 200 μsec. This can readily be achieved by selecting a spring having an appropriate mass per unit length. Further, the selection of the spring requires the selection of a spring having a force per unit displacement which remains substantially constant with frequency. Embodiments which use metal springs provide such a requisite response. However, the present invention encompasses any other form of spring means which can provide the required physical behaviour.

This embodiment of the invention also includes the selection of an appropriate blocking mass and an inertial mass, where used, to provide for efficient vibration isolation. The mass, shape and mass distribution or number of masses can be designed appropriately.

The present invention encompasses passive vibration isolation mounts. One such mount is illustrated schematically inFIG. 16. A first member1000is a member through or from which vibrations can be transmitted to a second member1001by a mount1005for mounting the second member1001to the first member in a spaced relationship. The mount comprises a spring arrangement1002which is coupled at one end thereof to the first member1000and a blocking mass1003which is positioned between the second member1001and the spring arrangement1003so as to lie at the other end of the spring arrangement1002. Thus the spring arrangement1002provides a spring force between the first member1000and second member1001via the blocking mass1003. Mounting arrangements1006and1007are provided for mounting the mount1005to the first member1000and the second member1001respectively.

The blocking mass1003comprises a mass provided in or adjacent to a region between the second member1001and the second mounting arrangement1007to increase the localised mass of the second member1001at the point of mounting of the mount to the second member1001. This increases the efficiency of the mount. The blocking mass can comprise a single mass or a distribution of masses arranged substantially coaxially with the spring arrangement.

Although a helical spring arrangement is illustrated inFIG. 16, any spring arrangement comprising a single spring or combination of springs can be used. A spring member can be a leaf spring, a coil spring or any other spring material or structure to provide a spring force.

The present invention also encompasses a vibration absorber as illustrated schematically inFIG. 17. A blocking mass2003is mounted to a member2001by a mounting arrangement2005. A spring arrangement2002is mounted at one end thereof on the blocking mass2003. On the other end of the spring member2002an inertial mass2004is mounted. The spring member thus provides a spring force between the blocking mass2003and the inertial mass2004.

The blocking mass2003comprises a mass provided in or adjacent to a region between the member2001and the vibration absorber to increase the localised mass of the member2001at the point of mounting of the absorber to the member2001. This increases the efficiency of the vibration absorber. The blocking mass can comprise a single mass or a distribution of masses arranged substantially coaxially with the spring arrangement.

This arrangement provides a tuned vibration absorber which more efficiently couples to the member2001to absorb vibrations in the member.

Although a helical spring arrangement is illustrated inFIG. 17, any spring arrangement comprising a single spring or combination of springs can be used. A spring member can be a leaf spring, a coil spring or any other spring material or structure to provide a spring force.