NZ722456B2 - Platform stabilization system - Google Patents

Abstract

platform stabilization system comprises a support frame, a platform and a plurality of isolators each extending directly between the support frame and the platform. Each isolator permits linear movement of the platform relative to the support frame with three degrees of freedom and permits rotational movement of the platform relative to the support frame with three degrees of freedom. The isolators cooperate to form an isolation array supporting the platform directly within, and spacing the platform from, the support frame. The isolation array permits limited linear movement of the platform within the support frame with three degrees of freedom and permits limited rotational movement of the platform relative to the support frame with three degrees of freedom. The isolation array is substantially more resistant to linear movement of the platform than to rotational movement of the platform and does not rotationally constrain the platform. nal movement of the platform relative to the support frame with three degrees of freedom. The isolators cooperate to form an isolation array supporting the platform directly within, and spacing the platform from, the support frame. The isolation array permits limited linear movement of the platform within the support frame with three degrees of freedom and permits limited rotational movement of the platform relative to the support frame with three degrees of freedom. The isolation array is substantially more resistant to linear movement of the platform than to rotational movement of the platform and does not rotationally constrain the platform.

Description

PLATFORM STABILIZATION SYSTEM TECHNICAL FIELD The present disclosure relates to platform stabilization systems, and more particularly to platform stabilization systems for isolating a payload from r motions and ational and angular Vibrations of a supporting structure.

BACKGROUND Stabilized platform systems have been around for many years, and are used to isolate a payload carried by the platform from the movement of the structure that carries the platform.

The structure may be a vehicle like an airplane, helicopter or automobile, or a relatively static structure which is still subject to some movement, such as a tall pole that may sway in the wind. There is virtually no limit to what may be carried as the payload of a stabilized platform system, and stabilized platform s may be used in a variety of applications for payloads including, but not limited to, still photographic and video (including cinema) cameras, electro-optical and infra-red imaging devices, spectrometers, antennae, lasers, and even weapon s. What distinguishes this category of stabilization technology from others is that the platform that s the payload is being stabilized and steered in inertial space. US. Patent No. 4,796,090 to Fraier provides a detailed description of the need for rm stabilization in long range, high tion, surveillance systems combined with the benefit of d integration times.

Various technologies for compensating for the movement of the structure ng a sensor payload are known, each with drawbacks and limitations.

One approach for image-capturing payloads such as camera systems is to try to lly stabilize the image captured by the payload, rather than stabilizing the payload itself.

US. Patent Application Publication No. 20120019660Al in the name of Golan describes the use of sequential image analysis, digital windowing and pixel shifting techniques as a means of digitally stabilizing the image and then further computing camera ering signals to steer a coarse pan/tilt gimbal system. US. Patent No. 7,876,359 to VonFlotow describes a r digital stabilization que, and US. Patent No. 6,720,994 to Grottodden et a1. 2014/000912 describes a technique for adjusting the sample time between individual lines of pixels on the detector array as the image is captured. The issue with these digital stabilization techniques is that nothing is done to sate for the motion of the payload’s line of sight during the integration time period of the pixels that make up the image. This may result in motion-based blur in the captured image.

Other approaches seek to ly stabilize the payload relative to the supporting structure by stabilizing the platform that carries the payload. Within this “platform stabilization system” category there are e and active systems. One example of a passive stabilization system is the STEADICAM® system described in U.S. Patents No. 4,017,168 and 4,156,512 to Brown and U.S. Patent No. 5,435,515 to DiGiulio et a1. Another passive system is described in U.S. Patent No. 5,243,370 to Slater. However, most platform stabilization systems make use of otors, inertial sensors, and a control system to augment the inherent inertia of the platform and are thus termed active systems.

Platform stabilization systems were initially developed to mount navigation instruments on moving vehicles such as ships and ft. Gyro compasses and vertical gyros, such as taught by U.S. Patent No. 2,551,069 to Strother et al., are early examples of platform ization systems. Eventually, photographic cameras were mounted on these stable platforms to remove the unwanted motion of the vehicles during the acquisition of the image, for example as taught by U.S. Patent No. 2,490,628 to Issertedt, U.S. Patent No. 2,523,267 to Aschenbrenner et al., U.S. Patent No. 2,883,863 to Karsten et al., U.S. Patent No. 3,060,824 to Brenner et al. and U.S. Patent No. 3,775,656 to Romans. Motion picture cameras, however, required more than just ity during the image acquisition; they also needed smooth steering control between the images.

New isolation , such as those taught by U.S. Patent No. 2,506,095 to Mantz, were developed to allow the camera to be manually steered while attenuating some of vehicle ion. Fixed gyros were added to the cameras to further improve stability and smoothness of steering. The camera or typically sat in the open doorway of a helicopter with the , attached to an isolation mount with fixed gyros adding stability, placed over one er. The camera operator would carefully coordinate with the pilot to steer the _ 2 _ camera. This obviously made it quite difficult to frame the subject of the movie shot and achieve Visually pleasing camera control.

In the late 19605, Westinghouse Canada developed the WESCAM® platform stabilization system to address these issues. This was the first commercially available gyro ized, remotely steered camera system and is the t of US. Patent No. 3,638,502 to t et al. This type of stabilization technology relies on the angular momentum generated in three orthogonal, large mechanical rate gyroscopes (gimbaled flywheels) to augment the natural inertia of the camera platform. This artificial mass or synthetic inertia is used passively to maintain a slightly pendulous stable platform, with the payload (a camera) being steered relative to that stabilized platform. An active servo system then uses the angular rates measured by the precession of the gyros to cancel any disturbances using servomotors. A dome enclosure keeps the wind and weather out and an internal passive vibration isolation system zes the vibration input to the system.

The prior art for active platform stabilization technology can be classified into four general types or “generations”: gyro ized systems (first generation), classical active gimbal systems (second generation), limited travel - active follow-up systems (third generation) and unconstrained actuator - active follow-up systems (fourth generation). Within each tion there may be subtle differences in the implementation methods and advantages, however, the basic techniques are the same. The original WESCAM® platform ization system technology described in US. Patent No. 3,638,502 is classified as first generation platform stabilization technology. It was further refined and a vertically slaved window was added, as bed in US. Patent No. 4,821,043 to Leavitt, to e the optical mance of the system. Other first generation rm stabilization systems are bed in US. Patent No. 466 to Goodman and US. Patents No. 5,184,521 and ,995,758 to Tyler. While the first generation platform stabilization systems achieved significant stability, they suffered from poor steering bandwidth, which made them incompatible with video-trackers and required a highly skilled operator to compensate for this poor steering performance.

A second generation of active platfor m stabilization technology was developed to address the poor steering performance of the early first generation rm stabilization systems. These second generation rm stabilization s, referred to as "classical active gimbal systems", interpose a plurality of gimbals between the structure and the platform and close rate loops ly about each gimbal axis. Inertial rate s, such as small ical sensing gyros, are used to sense angular rates of the platform ve to inertial space. These rates are summed with the steering commands to stabilize and steer each axis. U.S. Patent No. 3,986,092 to Tijsma et al., U.S. Patent No. 5,868,031 to Kokush et al., U.S. Patent No. 6,396,235 to Ellington et al., U.S. Patent No. 7,000,883 to Mercadal et al., U.S. Patent No. 591 to Chapman et al. and U.S. Patent No. 8,564,499 to Bateman et al. are all examples of classical active gimbal systems. While each patent document describes subtly different methods and ages, they all use a system of gimbals to support a platform, while closing rate loops directly about each gimbal axis using inertial rate sensors.

The actuator can be either a direct-drive or a geared motor. The use of a geared actuator will increase coupling forces substantially, introduce backlash, and limit the steering bandwidth of the system. The structure between each sive gimbal axis is subjected to the high frequency torques of the actuators. Compliance in this constraint structure will limit the bandwidth of the control system. For this , classical active gimbal systems are generally incapable of high bandwidth perform ance with large payloads. U.S. Patent No. 6,198,452 to Beheler presents an alternate, non-orthogonal, gimbal geometry for a cal active gimbal system, and U.S. Patent No. 6,609,037 to Bless et al. describes a control system for a classical gimbal system that uses rate feedback and feed-forward control loops combined with position ck and feed-forward control loops fo r each axis to further improve the steering perfo rmance. The classical active gimbal system was improved by the addition of an independent outer gimbal in the form of a dome enclosure with a vertically slaved window as described in U.S Patent No. 4,821,043 noted above and a passive isolator interposed between the dome and the inner platform stabilization system. The frictionfrom the large gimbal bearings and motor brushes, combined with the ural resonances of the gimbal constraint system, limited the achievable stabilization performance of this system.

In order to further improve platform stability over that achieved by classical active gimbal systems, a third generation of active platform stabilization system was developed. It uses a higher bandwidth, limited travel inner gimbal mounted on a passive isolator, which in turn is mounted on the final stage of a low bandwidth, large travel outer follow-up gimbal system. As such, this type of platform stabilization system is referred to as a “limited travel - active follow-up” system. The inner gimbal provides the high dth stabilization and fine steering performance, while the outer gimbal es the coarse steering over a large field of regard. The inner gimbal uses high performance, direct drive actuators and the outer gimbal uses geared actuators. The high frequency torques are, however, still d through the inner gimbals’ constraining ure, but the inner gimbals’ bearings are much smaller and the motors are typically ess. While with smaller ds, and with the use of fibre- optic gyros, the stabilization performance of this type of inner/outer gimbal system is actory, with large payloads the compliance of the large gimbal ring structure limits the bandwidth of the stabilization system. US. Patent Application Publication No. 2010/0171377A1 in the name of Aicher et al. and US. Patent No. 8,385,065 to Weaver et al. are recent examples of “limited travel - active follow-up” platform stabilization systems.

To address the bandwidth limitations caused by the structural resonances of the constraint system in the “limited travel - active follow-up” platform stabilization system, a fourth tion of active platform stabilization system was developed. This type of system, referred to herein as an “unconstrained actuator - active follow-up” system, avoids the bandwidth limitation of the “limited travel - active follow-up” system by using a process of torquing across the constraining structure instead of through it. The high frequency torques are applied directly from the outer gimbal to the platform. Combined with a high performance fibre-optic-gyro-based inertial measurement unit, this system raised the steering bandwidth significantly while maintaining stability. es of “limited travel - active follow-up” platform stabilization s are described in US. Patents No. 4,033,541 and 4,498,038 to Malueg, US. Patent No. 4,828,376 to Padera, US. Patent No. 271 to Kiunke et al., US. Patent No. 5,897,223 to Tritchew et al., US. Patent No. 6,196,514 to Kienholz, US. Patent No. 160 to Lewis, US. Patents No. 6,454,229 and 6,484,978 to Voigt et al. and U.S. Patent No. 6,849,980 to Voigt et al. While each patent describes subtly different methods and advantages, they all: 0 use a system of ening gimbals to support a platform on a support frame, while the gimbals constrain the platform’s motion to limited rotation in three axes; 0 use an array of voice coil actuators which are configured to apply torques across, rather than through, the gimbal constraint system (sometimes across the gimbal and the isolator array in series); and 0 use an array of r, inertial sensors to drive the voice coil motors to stabilize and steer the platform and thereby control the payload’s line of sight.

An alternate, non-orthogonal, inner gimbal configuration is presented in U.S. Patent No. 4,733,839 to Gehris. The limited space available between the shells around the pivots suggests its ed use as either a “free gimbal”, missile seeker head, or unconstrained actuator - active follow-up platform stabilization system.

The primary problems with the t state of the art in active platform stabilization technology are cost, xity, and ility. The complex mechanical gimbal systems of the existing technologies are dominated by recurring costs. These include tight machining tolerances for bearing aces, the need for complex inspection and testing, precise alignment and preload of gimbal bearings during ly, and ongoing inspection and maintenance.

The present disclosure describes platform isolation systems in which an isolation array supports the platform directly within the support frame, without the use of intervening gimbals, rings or other rotational constraints, to provide linear isolation while permitting the platform to rotate relative to the support frame.

A platform stabilization system for ing a payload from motion of a supporting structure ses a support frame, a platform for carrying a payload, and a plurality of isolators each extending directly between the t frame and the platform absent any intervening s, rings or other motion-constraining structures between the platform and the support frame.Each isolator permits linear movement of the platform relative to the t frame with three degrees of freedom and each isolator permits rotational movement ofthe platform relative to the support frame with three degrees of fre edom. The isolators ate to form an isolation array supporting the platform ly within the support frame and the isolation array spaces the platform from the support frame. The isolation array permits limited linear movement of the platform relative to the t frame with three degrees of fr eedom along three orthogonal platform axes and the isolation array permits limited rotational movement of the platform relative to the support frame with three degrees of fr eedom about the three platform axes. The isolation array is substantially more resistant to linear movement of the platform relative to the support frame than to rotational movement of the platform relative to the support frame, and the rm is not rotationally constrained by the isolation array.

Preferably, the isolation array has an undamped l frequency for linear movement of the platform along the platform axes that is at least two times the undamped natural frequency for onal movement of the platform about the platform axes. More preferably, the undamped natural frequency for linear movement of the platform along the platform axes is at least three times the undamped l frequency for rotational movement of the platform about the platform axes. Still more preferably the undamped natural frequency for linear movement of the rm along the platform axes is at least five times the undamped natural frequency for rotational nt of the rm about the platform axes, and even more preferably the undamped natural frequency for linear nt of the platform along the platform axes is at least ten times the undamped natural frequency for rotational nt of the platform about the platform axes.

In one embodiment, each isolator comprises at least one compression spring having a respective spring axis, and to form the isolation array, the compression s are arranged with their respective spring axes radiating outward substantially fro m a common point within the platform, with the common point being the centroid of mass of the platform, and the compression springs are axially preloaded to produce a low lateral spring rate. In one particular embodiment, the isolation array comprises eight compression springs arranged ntially at corners of a notional cube and the common point is a id of the al cube. In r particular embodiment, the ion array comprises at least one array of four compression springs arranged substantially at comers of a notional regular tetrahedron and the common point is a centroid of the notional regular tetrahedron. In yet r particular embodiment, the isolation array comprises six compression springs radiating outward from a centroid of a notional cube substantially through centroids of the six faces of the notional cube.

In certain embodiments, the isolation array comprises a symmetrical array of compression s.

Where compression springs are used for isolators, the compression springs are preferably machined, multi-start, helical compression springs.

In another embodiment, each isolator comprises a flexural pivot element. Each flexural pivot element may comprise three single-axis flexural pivots arranged in series with each l pivot having a pivot axis. For each flexural pivot element, the pivot axes of each flexural pivot substantially meet at a centroid of mass of the platform and the flexural pivot elements are arranged in a substantially symmetrical array to form the isolation array.

Preferably, each flexural pivot element is of monolithic construction.

In a further embodiment, each isolator is a agm-based isolator. Each agm-based isolator may comprise two opposed diaphragms, a first housing carried by the support frame, a second housing carried by the platform, with each housing having a diaphragm receptacle defined therein and the diaphragm receptacles being opposed to one another. Each agm is supported at its periphery by one of the gs and extends across the diaphragm receptacle of that housing so that for each isolator, one of the diaphragms is coupled to the t frame and the other diaphragm is coupled to the platform. The diaphragms are coupled to one another by a torsional flexure element extending between radial centers of the diaphragms. The torsional flexure element is preferably axially resilient, and may be a helical spring. The diaphragms may be, for example, molded elastomeric structures or metal bellophragm structures. Each diaphragm- based isolator may further comprise a stop carried by the torsional flexure element to limit lateral travel of the torsional flexure element.

In one particular embodiment, each agm is fluid-impermeable and each housing cooperates with its respective diaphragm to form a damping reservoir, with each damping reservoir being in fluid communication with a respective sink reservoir for damping axial movement of the respective diaphragm by displacing damping fluid from the tive damping reservoir to the respective sink reservoir. In a particular implementation of this embodiment, each housing cooperates with its tive diaphragm to form an enclosure and a divider extends across each enclosure to divide the respective ure into the damping reservoir and the sink reservoir, with each damping reservoir being in fluid ication with the respective sink reservoir through at least one orifice in the respective divider.

The platform stabilization system preferably further comprises an active drive system acting directly between the support frame and the platform and a control system coupled to the active drive system for receiving sensor input and controlling the active drive system in response to the sensor input. The control system may use the sensor input to control the active drive system for stable motion of the platform and/or to l the active drive system for active damping of the platform.

In one embodiment, the active drive system comprises an array of at least three magnetic voice coil actuators. Each magnetic voice coil actuator comprises a first portion d by the support frame and a second n carried by the platform. Each magnetic voice coil actuator acts directly between the support frame and the platform to apply a first platform positioning force to the platform along a first motor axis and apply a second platform positioning force to the rm along a second motor axis while permitting free linear movement of the platform along a third motor axis and permitting free rotation of the platform about the three motor axes, with the first, second and third motor axes being substantially orthogonal to one another. The magnetic voice coil actuators are arranged relative to the rm for selectively driving linear movement of the platform relative to the support frame along the platform axes and for selectively driving rotation of the rm relative to the t frame about the platform axes, and the control system controls energization of the - 9 _ 2014/000912 voice coil actuators to apply controlled moments and linear forces to the platform. In one particular embodiment, the active drive system comprises four magnetic voice coil actuators arranged approximately 90 degrees apart on the circumference of a notional circle.

In r embodiment, the active drive system comprises an array of at least six magnetic voice coil actuators. Each magnetic voice coil actuator comprises a first portion carried by the support frame and a second portion carried by the platform. Each magnetic voice coil actuator acts directly between the t frame and the rm to apply a first platform positioning force to the platform along a first motor axis while permitting free linear movement of the second n along each of a second motor axis and a third motor axis and permitting free rotation of the second portion about each of the second motor axis and the third motor axis, with the first, second and third axes being substantially orthogonal to one another. The magnetic voice coil actuators are arranged relative to the platform for ively driving linear movement of the platform relative to the support frame along the platform axes and for selectively g rotation of the platform ve to the support frame about the platform axes, and the control system controls energization of the voice coil actuators to apply controlled moments and linear forces to the platform.

The platform ization system may further comprise an angle sensor system for sensing and providing a signal indicative of an angular position of the platform relative to the support frame about the platform axes, with the angle sensor system being coupled to the control .

The platform stabilization system may further se a linear position sensor system for sensing and providing a signal indicative of a linear position of the platform relative to the support frame on the platform axes, with the linear position sensor system being coupled to the control system.

In an embodiment, the platform carries at least three inertial rate sensors for sensing and providing a signal indicative of angular movement of the platform about the platform axes, with the inertial rate sensors being coupled to the control system. The inertial rate sensors may be fibre—optic gyros.

In an embodiment, the platfo rm carries at least three inertial acceleration sensors for sensing and providing a signal indicative of linear movement of the platform along the platform axes, with the inertial acceleration s being coupled to the control system.

The platfo rm stabilization system may further comprise an inertial measurement unit fo r sensing and providing signals indicative of linear and angular movement of the platform about the rm axes, with the inertial measurement unit being d to the control system.

The platform stabilization system may furt her comprise a GPS receiver coupled to the control system, and the control system may contain instructions for an al tion system for computing the phic position where a rm line of sight intersects the s surface. The control system may contain instructions for closing phic based steering control loops to maintain the platform line of sight pointing at a geographic position.

The control system may contain instructions fo r computing parameters to step and stare a payload line of sight of a payload carried by the platform, within its limited range ofmotion, to limit, during an image integration period of the payload, relative rotational motion of the payload line of sight with respect to the earth caused by rotational motion ofan orbiting aircraft carrying the platform stabilization system.

The t fr ame of the platform stabilization system may be carried by an outer gimbal assembly.

A method fo r isolating a payload from motion of a supporting structure comprises permitting limited linear movement of the platform relative to a support fr ame with three degrees offr eedom along three orthogonal platform axes, permitting limited rotational movement ofthe platfo rm ve to the support frame with three degrees of fr eedom about the three platform axes, and providing substantially greater resistance to linear movement of the platform relative to the support frame than to rotational movement ofthe platform relative to the support fr ame without rotationally constraining the platfo rm, wherein a ity of isolators each extend directly between the support frame and the platform absent any intervening gimbals, rings or other motion-constraining structures between the platform and the support frame.

BRIEF DESCRIPTION OF THE GS These and other features will become more apparent from the following description in which reference is made to the appended drawings wherein: FIGURE 1 is an exploded perspective view of an exemplary rm stabilization system; FIGURE 2a is a front cross sectional View of the platform stabilization system of Figure 1 with the sensor package removed; FIGURE 2b is an angled side cross sectional View of the platform stabilization system of Figure 1 with the sensor package removed; FIGURE 3a shows a simplified mathematical model of a spring; FIGURE 3b is a graph showing the columnar instability phenomenon of a compression spring suitable for use in the isolation array of the platform stabilization system of Figure 1; FIGURE 3c is a graph g the onal characteristics of an exemplary embodiment of the isolation array of the platform stabilization system of Figure 1; FIGURE 3d shows a simplified mathematical model for a diaphragm-based isolator; FIGURE 4a is a schematic representation of a first cubic isolation array; FIGURE 4b is a schematic representation of a tetrahedral isolation array; FIGURE 4c shows two perspective views of an exemplary flexural pivot element isolator; FIGURE 4d is a cross-sectional view of a agm-based isolator; FIGURE 4e is a schematic entation of an exemplary tetrahedral isolation array comprising a ity of the flexural pivot element isolator of Figure 4c; FIGURE 4f is a schematic representation of an exemplary tetrahedral isolation array comprising a plurality of the diaphragm-based isolators of Figure 4d; FIGURE 4g is a schematic representation showing how the cubic ion array shown in Figure 4a can be considered as being made up of two equally sized tetrahedral isolation arrays in Figure 4b, superimposed on one another with one of the tetrahedral isolation arrays rotated 180 degrees relative to the other; FIGURE 4h is a schematic representation of a second cubic isolation array; FIGURE 5a shows the relative positions and orientations of the voice coil actuators in an exemplary active drive system comprising four two-axis voice coil actuators; FIGURE 5b shows the relative positions and orientations of the voice coil actuators in an ary active drive system comprising six single-axis voice coil actuators; FIGURE 5c shows the relative positions and ations of the voice coil actuators in an exemplary active drive system comprising three two-axis voice coil actuators; FIGURE 6a is a detailed perspective view of an exemplary two-axis voice coil actuator; FIGURE 6b is a detailed ctive view of the voice coil or of Figure 6a integrated into an exemplary mounting structure that is positioned in registration with mounting projections of the support structure of the platform stabilization system of Figure 1; FIGURE 7 is a graph comparing ary undamped and passively damped isolation systems with an exemplary actively damped isolation system as described herein; FIGURE 8 is a schematic diagram of the platform stabilization system of Figure 1 including the active drive system and the control ; FIGURE 9a shows the platform stabilization system of Figure 1 installed in a first exemplary two-axis outer gimbal assembly; FIGURE 9b shows the platform stabilization system of Figure 1 installed in an ary three-axis outer gimbal assembly; FIGURE 9c shows the platform stabilization system of Figure 1 led in a second exemplary two-axis outer gimbal assembly; and FIGURE 10 is a block m showing an ary computer system which may be used in implementing aspects of the present technology.

DETAILED DESCRIPTION The t disclosure describes l exemplary embodiments of a platform stabilization system for isolating a payload from the motion of a supporting structure, such as an aircraft or other vehicle or a fixed emplacement subject to movement, for example caused by wind. The platform ization system generally comprises a support frame, a rm adapted to carry a payload and a plurality of isolators each extending directly between the support frame and the platform, and also preferably comprises an active drive system acting directly between the support frame and the platform. As used herein, the term “isolator” means a device connecting two masses and whose structure acts to decouple the vibratory motions of each mass. As such, a single isolator may se one isolation element or a plurality of isolation elements coupled to one another to operate in concert. The isolators cooperate to form an isolation array, preferably an attitude-independent isolation array, supporting the platform directly within the support frame and in which the platform is not rotationally ained by the ion array. The term “isolation array”, as used herein, refers to an array of spatially ted isolators configured to support a mass mounted to another mass such that the vibratory motions of the masses are decoupled from one other.

The term “directly between the support frame and the platform” and similar terms, as used herein in reference to the isolators and the active drive system and its components, means that aside from the isolators and active drive system components, there are no intervening gimbals, rings or other motion-constraining structures between the platform and the support structure.

Similarly, the term “supporting the platform directly within the support frame”, as used in reference to the isolation array, means that it is the isolation array alone that supports the platform within the support frame, without the use of intervening gimbals, rings or other rotational constraints; that is, only the isolators support the rm within the support frame and the platform is otherwise unsupported within the support frame. For example, while ical wiring may extend between the platform and the support frame, such wiring does not t the platform in the support frame. While the platform and the support frame will e features for mounting the isolators and active drive system components, when the platform stabilization system is assembled such features are generally fixed relative to the platform and support frame, respectively. As such, when construing the terms “directly between the support frame and the platform” and “supporting the platform directly within the support frame”, these ng features may therefore be considered part of the platform and support frame, respectively. Moreover, the terms “platform” and “support , as used herein, do not encompass structures that include gimbals, rings or other onal constraints as part of a mechanical coupling between the support frame and the platform. Furthermore, the term “rotationally constrained”, as used herein, refers to a condition in which motion of one body relative to r is limited to rotation about one or more axes without significant linear motion; the mechanical arrangement which causes one body to be rotationally constrained relative to another is referred to herein as a ional constraint”. In this context, the term “significant linear motion” means linear motion beyond that ted by the inherent tolerances of the rotational constraint. The gimbals and rings used in conventional platform stabilization systems are examples of rotational constraints. When one body is not rotationally constrained ve to r body, it can be said to be “rotationally trained”. The term “rotationally constraining” refers to the act of imposing rotational constraint. Thus, the platform support systems as described herein avoid the conventional arrangement in which a rotational constraint is arranged in series with a linear isolation structure; instead the isolation arrays bed herein support the platform directly within the support frame and do not rotationally constrain the rm. [003 7] Reference is now made to Figure l, in which a first exemplary platform stabilization system is indicated generally by reference 100. The exemplary platform stabilization system 100 comprises a support frame 102 and a platform 104 carrying a payload in the form of a sensor package 106, four mounting structures 108 secured to the sensor package 106 at 90 degree intervals thereabout, and an inertial measurement unit 110 disposed in the platform 104. Thus, while d to the sensor package 106, the mounting structures 108 and the inertial measurement unit 110 are part of the rm 104. One or more sensors within the sensor package 106 may be independently ble relative to the sensor package 106 and hence may be independently steerable relative to the platform 104. While the ng ism within the sensor package 106, or other elements of the payload, may include rotational constraints as part of their mechanisms, these rotational constraints would not form part of a mechanical coupling between the support frame and the platform. [003 8] In the aerospace and navigation fields the “NED” coordinate system is typically used, in which the X, Y and Z axes are mapped to North, East and Down. This is extended to an aircraft as X, Y and Z, where the positive direction of the X axis is along the fuselage towards the nose, the Y axis is perpendicular to the X axis and positive in the direction of the right wing and the Z axis is perpendicular to the X and Y axes and ve in the down ion during level flight. This coordinate reference frame is extended to a platform stabilization system with the X axis generally being the line of sight of the payload, the Y axis being toward the right side of the payload relative to the line of sight, and the Z axis toward the bottom of the payload relative to the line of sight. This means that the X axis is the roll axis, the Y axis is the pitch axis and the Z is the yaw axis. The terms “platform axis” and “platform axes”, as used herein, refer to these roll (X), pitch (Y) and yaw (Z) axes, held fixed relative to the support frame to provide a coordinate frame of reference for movement of the platform ve to the support frame, and the designations Xp, Yp and Zp are used to denote the roll (X), pitch (Y) and yaw (Z) axes, respectively. One skilled in the art will appreciate that when implementing a control system 142, a different frame of reference may be used; for example the roll (X), pitch (Y) and yaw (Z) axes may be held fixed relative to the platform. [003 9] The supporting structure to which the support frame 102 is secured may be d by a vehicle such as an aircraft or sufficiently tall fixed structure, and the sensor package 106 Front and rear fittings 112, may be, for example, an imaging system or other sensor array. 114, respectively, may be fitted to the t frame 102 to provide a sealed environmental enclosure. In the rated embodiment, electronic components for a control system 142, described further below, are disposed inside of the upper and lower platform ization electronics assemblies 116A and 116B on the support frame 102. In alternate embodiments the control system may be disposed outside of the enclosure, or partly inside and partly WO 95951 outside the enclosure. The entire platform stabilization system 100 is securable to a supporting structure such as an outer gimbal assembly, as is known in the art, configured to permit the support frame 102 a large amount of r movement relative thereto about at least one, but preferably two or three orthogonal axes. Figure 9a shows the exemplary platform stabilization system 100 installed in a first exemplary two-axis yaw/pitch (or azimuth/elevation) outer gimbal assembly 118a, Figure 9b shows the exemplary platform stabilization system 100 installed in an exemplary three-axis ll/pitch outer gimbal assembly 118b, and Figure 9c shows the exemplary platform stabilization system 100 installed in a second exemplary two-axis outer gimbal assembly 118e, which is a two-axis roll/pitch, “look down” outer gimbal configuration. Thus, in certain preferred embodiments, the t frame 102 is carried by an outer gimbal ly 118a, 118b, 1180. y, outer gimbal assemblies are used for gross steering of the platform stabilization system 100, and hence the stabilized platform 104, and need not provide any stabilization function.

The platform 104 is carried by the support frame 102 via a plurality of isolators 120.

In the exemplary embodiment shown in Figure 1, the ors 120 are compression springs arranged with their tive spring axes 120A radiating outward substantially from a common point A within the platform 104 and extending directly between the support frame 102 and the platform 104. The common point A is the id of mass of the platform 104, including the mass of the sensor package 106. The spring axes 120A are shown more clearly in Figures 2a and 2b, which show, tively, front and angled side cross sectional views of the platform stabilization system 100 with the sensor package 106 removed.

Each isolator 120 permits linear movement of the platform 104 relative to the t frame 102 with three degrees of freedom and also permits rotational movement of the platform 104 relative to the support frame 102 with three degrees of freedom. The ors 120 cooperate to form a substantially symmetrical isolation array 124 supporting the platform 104 directly within the support frame 102 and ing six degrees of freedom to the platform 104, relative to the support frame 102. The isolation array 124 is preferably attitudeindependent.

As used herein, the term “attitude—independent” refers to an arrangement in which the travel limits in all ions substantially exceed 1G for the ion array as a whole.

The isolation array 124 spaces the platform 104 from the support frame 102 so that the platform 104 can move within the support frame, and provides passive isolation of motion of the platform 104 relative to the support frame 102. The platform 104 is not onally constrained by the exemplary isolators 120 or by the exemplary isolation array 124 formed by the isolators 120.

As shown schematically in Figure 4a, in the particular exemplary platform ization system 100 shown in Figure 1, the isolation array 124 is a cubic isolation array which comprises eight substantially identical compression springs 120 arranged at comers of a notional cube C, radiating outward substantially from the centroid A of the notional cube C, In other embodiments, the isolation array may comprise a different arrangement of compression springs as isolators, with suitable ation to the associated hardware. For example, Figure 4b shows a schematic representation of a tetrahedral isolation array 424 comprising an array of four compression springs 120 arranged at corners of a notional regular tetrahedron T, with the compression springs 120 radiating outward substantially from the centroid M of the notional regular tetrahedron T. The cubic ion array shown in Figure 4a can be considered as being made up of two equally sized tetrahedral isolation arrays 424 as shown in Figure 4b, mposed on one another with one of tetrahedral isolation arrays 424 rotated 180 s relative to the other, as shown in Figure 4g, and any suitable combination of tetrahedral isolation arrays may be used. Other symmetrical isolator configurations will be apparent to one skilled in the art, now informed by the present disclosure. For example, as shown in Figure 4h, an isolation array 424h may comprise six isolators 420h radiating outward from the centroid A of the al cube C through the ids AF of the six faces F of the notional cube C. Thus, where compression springs are used as isolators, the spring axes preferably radiate out ntially from a common point within the platform to produce a substantially ed array of springs arranged in opposition to one another so that the isolation array 424h is attitude ndent and has substantially the same spring rate for linear movement along the platform axes X, Y and Z (see Figure 1). Accordingly, an isolation array may comprise any symmetrical array of compression springs arranged so that their spring axes radiate outwardly substantially from a common point within the periphery of the platform. The common point will generally be, or be very close to, the centroid of mass for the platform with the payload installed.

The compression springs 120 used as isolators in the first exemplary platform stabilization system 100 are preferably machined, multi—start, helical compression s, which are monolithic structures machined to form two or more spring elements running in parallel. As such, a start, helical ssion spring may be considered as a plurality of individual spring elements acting in concert. The compression springs 120 are y preloaded to produce a low, positive lateral spring rate, so that the isolation array 124 has a low rotational stiffness ed to its te linear stiffness. This is achieved by exploiting a columnar instability phenomenon in compression springs.

Figure 3a shows a simplified mathematical model 300 of a spring, in which: Ka is the axial spring rate; K. is the lateral spring rate; Kb is the bending spring rate; Kt (not shown in Figure 3a) is the nal spring rate; x is lateral displacement; z is operating height; L is free length (not shown — free length is a standard specification for springs); l is length; 9 is centerline cant; and B is end cant.

In the simplified atical model 300 in Figure 3a, the ing ons apply: Preload Fa = Ka (L — 1) Lateral F] = Fa sin 0 +K1 x + Kb (0/2) + Kb (13/2) As the ratio of a spring’s length over its diameter increases, when the spring preload is increased the lateral spring rate will decrease as shown in Figure 3b, based on the mathematical model of the spring shown in Figure 3a. Preload curves that cross the X axis and hence have negative Y values are laterally unstable while preload curves that do not cross the X axis and hence have positive Y values are considered stable. Regions of operation where the lateral spring rate is negative are typically avoided in conventional applications.

When the springs 120 are arranged as shown in or 4b with the s 120 having a negative spring rate, the lateral instability of each individual spring results in rotational instability for the isolation array as a whole. By selecting a preload that results in a low, positive lateral spring rate for each spring 120, i.e. a preload that is close to but does not cross the X axis, the isolation array 124, 424 can be configured to achieve the desired low rotational and moderate linear characteristics, permitting the platform 104 a limited amount of angular movement about and linear movement along the three orthogonal X, Y and Z platform axes shown in Figure 1, without the use of gimbals or gimbal rings and their associated mechanical rements. Thus, the isolation array 124, 424 will permit limited linear movement of the platform 104 relative to the support frame 102 with three degrees of freedom along the platform axes Xp, Yp and Zp and will permit limited rotational movement of the rm 104 relative to the support frame 102 with three degrees of freedom about the platform axes Xp, Y1) and Zp, and is substantially more resistant to linear movement of the platform 104 relative to the support frame 102 than to rotational movement of the platform 104 relative to the t frame 102.

Preferably, an isolation array for use in a platform stabilization system, such as the isolation arrays 124, 424 described above and the isolation arrays 424C, 424D described below, configured for a given linear stiffness, has an undamped l ncy for linear movement of the rm along the platform axes Xp, Yp and Zp that is at least two times an undamped natural ncy for onal movement of the platform about the platform axes Xp, Yp and Zp. More preferably, the undamped natural frequency for linear movement of the platform along the platform axes Xp, Yp and Zp is at least three times the ed natural frequency for rotational movement of the platform about the platform axes Xp, Yp and Zp.

Even more preferably the undamped natural frequency for linear movement of the platform along the platform axes Xp, Yp and 2}) is at least five times the undamped natural frequency for rotational movement of the platform about the rm axes Xp, Yp and Zp, and still more preferably the undamped l frequency for linear movement of the platform along the platform axes Xp, Y1) and Zp is at least ten times the undamped natural frequency for rotational movement of the platform about the platform axes Xp, Yp and Zp. While the undamped natural frequency for linear movement of the platform along the platform axes Xp, Yp and Zp may need to be adjusted to suit a particular application, the undamped natural frequency for rotational movement of the platform about the platform axes Xp, Yp and Zp should be as low as practically possible. However, it is not necessary to increase the undamped natural frequency for linear movement of the platform along the platform axes Xp, Yp and Zp beyond the demands of the application solely to obtain a ratio of linear to rotational stiffness.

Figure 3c shows the rotational characteristics of an exemplary embodiment of the isolation array depicted in Figures 1 and 4a. In this exemplary embodiment, the individual isolators 120 were each dual start ed s with an axial spring rate of about 180 lb/in, a lateral spring rate of about 30 lb/in unloaded and about 10 lb/in when ded, a bending spring rate of about 0.35 inlb/deg, a torsional spring rate of about 0.25 inlb/deg, and a free length to diameter ratio of about 3.7. The test payload weight was about 20 pounds. This resulted in a system with an undamped natural frequency of about 15 Hz for linear movement along the platform axes Xp, Yp and Zp and about 1.5 Hz for onal movement of the rm about the platform axes Xp, Yp and Zp; thus, the undamped natural ncy for linear movement along the rm axes Xp, Yp and Zp is at least ten times the undamped natural frequency for rotational movement of the platform about the platform axes Xp, Yp and Zp. These are suitable characteristics for an airborne platform stabilization system.

As can be seen in Figure 1, the isolators 120 each extend ly between the support frame 102 and the platform 104, which includes the four mounting structures 108. As noted above, while the platform and the support structure may include features for mounting the isolators, such as the mounting structures 108 and the mounting projections 128, these components form part of the platform and support ure, and moreover do not constrain the motion of the platform.

As best seen in Figure 6b although also shown in Figure 1, in the ary illustrated embodiment the mounting structures 108 each have d outwardly extending fingers 126 and the support frame 102 includes four sets of opposed outwardly extending mounting tions 128 each spaced 90 degrees apart. When the platform stabilization system 100 is assembled, the fingers 126 on the mounting ures 108 and the mounting tions 128 are in registration with one another so that there are opposed pairs of fingers 126 and mounting projections 128 arranged at 90 degree intervals on either side of the support frame 102. The fingers 126 and the mounting projections 128 each have a respective recess for receiving an end of one of the isolators 120, with the recesses opposed to one another, and each isolator 120 extends between a tive finger 126 and mounting tion 128 and thus ly between the support frame 102 and the platform 104.

The exemplary isolation array 124, as well as the other exemplary isolation arrays described further below, serve a dual role in providing passive linear ion with three degrees of freedom while also functioning as a three degree of freedom flexural pivot in the platform stabilization system.

The role of passive isolation in platform stabilization systems is to attenuate the vibration input to the system, thus reducing the workload on the control . The purpose of damping in the passive isolator is to limit the dynamic amplification at resonance (see Figure 7, discussed below). Mechanical damping techniques work across all frequencies and create coupling forces that can disturb the payload’s line of sight. Active damping can make use of the control system to apply damping using the “sky hook” technique, which is well known in the art. US. Patent No. 3,606,233 to Scharton et al., US. Patent No. 4,531,699 to Pinson and US. Patent Application Publication No. 2008/0158371A1 in the name of Trescott are examples of active damping of a passive isolator.

Traditional mechanical damping is unsuitable for the isolation arrays described herein because damping across the rotational pivot should be avoided and the isolation arrays described herein extend directly between the platform and the support structure; there is no gimbal system in series to decouple the platform rotationally from the damping. As a result, it would be difficult to apply mechanical damping to the linear motion of the platform without also applying it to the rotational motion, and rotational damping would couple disturbing forces to the rm. US. Patent No. 223 to Tritchew et a1. and US. Patent No. 7,320,389 to Meyers et al. be the use of an array of mechanical t dampers mounted on ball joint pivots to apply damping predominantly to the linear motion of the isolator, however, this would be unsuitable for use in the presently disclosed rm stabilization system because the friction in the ball joint pivots would couple disturbing rotational forces through to the payload. Accordingly, when active damping is applied to isolation arrays as taught by the present disclosure, an active drive system comprising a six degree of freedom voice coil actuator array is used to apply damping forces to the linear axes only while it stabilizes the platform’s line of sight in the three rotational degrees of freedom.

Isolators of the type shown in Figure 4d (described below) are capable of providing some or all of the required damping passively.

Thus, the exemplary platform ization system 100 further comprises an active drive system 140 (see Figures 1, 5a and 8) acting directly between the t frame 102 and the platform 104, and a l system 142 (see Figure 8) coupled to the active drive system 140 for receiving sensor input and controlling the active drive system in response to the sensor input. The term “active drive system”, as used herein, refers to a system for causing lled movement of the rm 104 relative to the support frame 102. As will be explained in r detail below, the control system 142 uses the sensor input to control the active drive system 140 for active damping and stable motion of the rm 104 relative to the support frame 102. In the exemplary platform stabilization system 100, the active drive system 140 is a six degree of freedom active drive system that can selectively drive linear movement of the platform 104 relative to the support frame 102 along the orthogonal platform axes Xp, Yp and Zp and can selectively drive rotation of the platform 104 relative to the support frame 102 about the platform axes Xp, Yp and Zp. The use of a six degree of freedom active drive system in parallel with a six degree of freedom isolation array such as the isolation array 124 enables the use of passive, and even undamped, isolators, since the drive system can also provide damping .

In the illustrated embodiment of the exemplary platform stabilization system 100, the active drive system 140 comprises four two—axis ic voice coil actuators 144 (see Figure 5a) ed approximately 90 degrees apart on a circumference of a notional circle S. As best seen in Figures 1, 6a and 6b, each magnetic voice coil actuator 144 comprises a first portion 144A carried by the support frame 102 and a second portion 144B carried by the platform 104. In the illustrated embodiment, each magnetic voice coil actuator 144 comprises a coil portion 144A carried by the support frame 102 and a magnetic structure portion 144B carried by the platform 104; in other embodiments the relative positions of the coil portions and magnetic structure portions could be reversed Each coil portion 144A comprises two electrically energizable coils 144Al, 144A2 (Figures 6a and 6b), in the form of loops arranged orthogonally to one another and secured to the interior surface of the support frame 102 by coil ing members 146. Each ic structure portion 144B ses a pair of spaced-apart ed plates 148 d by the platform 104, with each plate 148 having one or more magnets to create a magnetic flux field within a gap between the plates 148.

During assembly of the platform stabilization system 100, the coils 144A1, 144A2 and magnetic structure portions 144B are arranged so that the outermost plate 148 is disposed within the loops formed by the coils 144A1, 144A2 and the innermost parts of the loops formed by the coils 144A], 144A2 are disposed between the plates 148. The magnetic voice coil actuators 144 shown and bed are merely exemplary, and other types of magnetic voice coil actuators may also be used.

The control system 142 is coupled to the magnetic voice coil actuators 144 via platform servo drives 180 e 8), which receive and amplify the control signals from the control system 142 and transmit electric current to the respective coils 144A1, 144A2 of the WO 95951 respective magnetic voice coil actuators 144. Thus, the control system 142 can control energization of the magnetic voice coil actuators 144 to apply controlled moments and linear forces to the platform 104.

As shown in Figure 6a, each magnetic voice coil actuator 144 has two ntially orthogonal motor axes M1 and M2 along which a platform positioning force can be applied but has freedom of movement along the third motor axis M3, which is substantially orthogonal to the other two motor axes M1 and M2. Thus, each magnetic voice coil actuator 144 acts between the support frame 102 and the platform 104 to apply a first platform positioning force to the platform along its first motor axis M1 and apply a second platform positioning force to the platform along its second motor axis M2 while permitting free linear movement of the platform along its third motor axis M3. At the same time, each magnetic voice coil actuator 144 permits free rotation of the platform 104 about its three motor axes M1, M2 and M3. The term “free”, as used in the context of linear motion along and rotational motion about the motor axes M1, M2 and M3 is to be understood as being free within the limited range of motion d by the physical structure of the magnetic voice coil or, including physical stops used to impose that limited range of motion. Moreover, it is to be understood that the isolation array 124 supports the platform 104 within the support frame 102 such that the coils 144Al, 144A2 of the magnetic voice coil actuators 144 are spaced from the plates 148 thereof and as such the magnetic voice coil actuators 144 provide no support function.

Thus, the magnetic voice coil actuators 144 do not support the platform 104 within the support frame 102; the platform 104 is supported only by the ion array 124.

As can be seen in Figures 1 and 5a, the magnetic voice coil actuators 144 are arranged relative to the platform 104 for selectively g linear movement of the rm 104 relative to the support frame 102 along the orthogonal platform axes Xp, Yp and Zp and for selectively driving rotation of the platform 104 relative to the t frame 102 about the platform axes Xp, Yp and Zp. More particularly, and referring now specifically to Figure 5a, when a current is passed through the coil 144A1 it creates an electromotive force along motor axis M1. Similarly, when a t is passed through coil 144A2 it creates an electromotive force along axis M2. Motor axis M3 represents the general ion of the magnetic flux field, in the gap between the plates 148 of the magnetic structure 144B, used to create these electromotive forces. It can be seen that if coil 144A1 on all of the magnetic voice coil actuators 144 were energized with the same polarity of current the combined force vector would be along the rm axis Xp, parallel to the motor axis M1 of each magnetic voice coil actuator 144. However, if the polarity of the current in the lower two magnetic voice coil actuators 144 were reversed their forces would be in the negative direction of each of their motor axes M1 axis. The linear forces cancel and create a moment about the platform axis Yp, which in the exemplary ment is the pitch axis. Thus, by changing the polarity of the current in the coils 144A1, 144A2, the active drive system 140 can produce linear forces and rotational moments. The linear forces are used for damping and the rotational moments are used to stabilize the line of sight, which has particular application when the platform 104 carries a sensor array as a payload. [005 9] As noted above, in the rated embodiment an inertial measurement unit 110 is ed in the platform 104. As shown schematically in Figure 8, the inertial measurement unit 110 comprises three inertial rate sensors 152, 154, 156, ably fibre-optic gyro based s, which e signals representing the angular movement of the platform 104 about the pre-determined platform axes Xp, Yp and Zp (see Figures 1 and 6a) which are defined relative to the support frame 102. ably, as shown in Figure 8, the inertial measurement unit 110 d by the platform 104 also includes three inertial acceleration sensors 158, 160, 162, which provide signals representing the linear movement of the platform 104 along the platform axes XP, Yp and Zp. The inertial rate s 152, 154, 156 and the inertial acceleration sensors 158, 160, 162 are coupled to the control system 142, and the signals generated by the inertial rate sensors 152, 154, 156 and the inertial acceleration sensors 158, 160, 162 are delivered to the control system 142. Thus, the inertial measurement unit 110 is coupled to the control system 142 and can sense and e signals indicative of linear and angular movement of the platform relative to the platform axes Xp, Yp and Zp. Although three al rate sensors and three inertial acceleration sensors are shown in Figure 8, other embodiments may include more than three inertial rate sensors and/or more than three inertial acceleration sensors.

Preferably, the platform stabilization system 100 also includes a position sensor system 164 carried by the platform 104 and sing an angle sensor system 165 and a linear position sensor system 171. The angle sensor system 165 senses and provides a signal indicative of the angular position of the platform 104 relative to the support frame and comprises three angular position sensors 166, 168 and 170 which provide respective signals representing the angular position of the platform 104 relative to the platform axes Xp, Yp and Zp. Analogously, the linear position sensor system 171 senses and provides a signal indicative of the linear position of the platform 104 ve to the support frame 102 and comprises three linear on sensors 172, 174 and 176 which e respective signals representing the linear position of the platform 104 along the platform axes Xp, Yp and Zp.

The position sensor system 164 is also coupled to the control system 142 to deliver sensor input thereto.

The l system 142 can use the inputs from the inertial measurement system 110 and/or the position sensor system 164 to drive the magnetic voice coil ors 144, Via the platform servo drives 180, to provide active damping of motion of the platform 104 relative to the support frame 102. The platform stabilization system 100 preferably r includes a global positioning system (GPS) receiver 184 coupled to the control system 142 in communication therewith. The GPS receiver 184 may be disposed on a fixed (non-yawing) portion of an outer gimbal (e.g. outer gimbal assembly 118a, 118b, 118C in Figure 9), or inside an aircraft carrying the rm stabilization system 100. The GPS receiver 184 may be fixed to the top of the aircraft to have a good field of view of the GPS satellites. Typically the GPS receiver 184 would not be positioned within the enclosure formed by the front and rear fittings 112, 114 and the support frame 102 because the ure is typically electromagnetically shielded, but the GPS receiver 184 may be placed inside such an enclosure if it is unshielded. The control system 142 can therefore ent an inertial navigation procedure using the signals from the inertial measurement unit 110 and the GPS er 184 to compute the geographic location of the intersection of the payload’s line of sight with the earth’s surface. In this t, the term “the earth’s surface” includes not only the earth’s a point on the actual surface of the earth but also a point at a ed height above surface; this point is often referred to as the “target”. The control system 142 can also use the WO 95951 signals from the inertial measurement unit 110 and the GPS receiver 184 to close ng loops on a geographic position or vector, without the use of image based auto-trackers. This geographic based steering enables platform stabilization systems according to the present disclosure to operate autonomously for many surveillance applications such as wide area persistent surveillance. The l system 142 also contains instructions for computing the ed steering parameters to drive the magnetic voice coil actuators 144 to “step” and “stare” the d’s line of sight, within its limited range of , to minimize the relative rotational motion of the line of sight with t to the earth, during the image integration period of a given payload, caused by the rotational motion of an orbiting aircraft carrying the platform stabilization system 100. This is particularly well suited to the very high pixel count s used in wide area persistent surveillance applications.

As noted above, the entire platform ization system 100 is ble to an outer gimbal assembly, denoted by reference 118 in Figure 8, and the control system 142 ably also controls the outer gimbal assembly 118. The outer gimbal assembly 118 includes at least an azimuth axis drive 186 and an elevation axis drive 188 and for a three-axis outer gimbal assembly will also e a roll axis drive (not shown in Figure 8). The outer gimbal assembly 118 also includes outer gimbal inertial rate sensors 192, 194, 196 coupled to the control system 142. The control system 142 is coupled to the azimuth axis drive 186 and the elevation axis drive 188, and to the roll axis drive when present, via one or more outer gimbal servo drives 198. The control system 142 receives gimbal control signals from a gimbal control input source 190, such as a controller on an aircraft carrying the platform stabilization system 100 and outer gimbal assembly 118, and also receives sensor signals from the outer gimbal inertial rate sensors 192, 194, 196, and uses this input to drive the azimuth axis drive 186 and the elevation axis drive 188, as well as the roll axis drive when present.

The control system 142 may be a general purpose computer, a special purpose computer, or other programmable data processing apparatus and functions as an instruction execution system which implements instructions for controlling the magnetic voice coil actuators 144 and for controlling the azimuth axis drive 186 and the elevation axis drive 188, as well as the roll axis drive in the case of a three-axis outer gimbal assembly. The control system 142 may be implemented as any suitable ation of hardware and software. In the exemplary platform stabilization system 100, the l system 142 executes ctions including a platform stabilization control algorithm 202, an inertial navigation algorithm 204, an inertial coordinates computation algorithm 206, a geographic steering algorithm 208, a power management algorithm 210 and an outer gimbal control algorithm 212.

In a typical implementation of the platform stabilization control thm 202, the l system 142 would accept data derived from external gimbal control input from the gimbal control input source 190 representing the desired yaw, pitch, and roll line of sight (LOS) rates and compare them to the measured LOS rates returned by the al acceleration sensors 158, 160, 162 in the inertial measurement unit 110 to e an error signal. The desired yaw, pitch, and roll line of sight (LOS) rates may be calculated from the external gimbal control input or by the phic steering algorithm 208 bed below. The control system 142 may implement a proportional-integral-derivative (PID) type controller to calculate the demanded yaw, pitch, and roll torques required to ize the LOS based on the computed error signal. A PID controller ates the difference between a measured value and a desired value as an error signal and then modifies the input variables in an attempt to reduce the error. Other types of controllers may also be used. The currents required, in each coil 144A], 144A2 of the magnetic voice coil actuators 144 forming the active drive system 140, to produce the demanded torques is then calculated based on the omagnetic characteristics of the magnetic voice coil actuators 144 and the geometry of the active drive of the system 140. The platform servo drives 180 then ensure that the coils 144Al, 144A2 magnetic voice coil actuators 144 are supplied the correct current to produce the correct electromotive forces to produce the required torques to stabilize the line of sight. This process is typically repeated thousands of times per second.

In a typical entation of the inertial navigation algorithm 204, the control receiver 184, system 142 would accept GPS data (time, location and velocity) from the GPS internal rate and acceleration data from the inertial measurement unit 110, angular position data from the position sensor system 164 and angular position data from the outer gimbal inertial rate sensors 192, 194, 196. The angular position data from the position sensor system 2014/000912 164 and outer gimbal al rate sensors 192, 194, 196 are used to resolve the GPS data into the nate frame of the inertial measurement unit 110. The inertial position, velocity and aCceleration for the inertial measurement unit 110 are then computed using standard inertial navigation system (INS) algorithms as are known in the art. The data from the position sensor system 164 and outer gimbal inertial rate sensors 192, 194, 196 are then used to back-compute the inertial position, attitude, heading and track for a e (e.g. an aircraft) carrying the platform stabilization system.

In a typical implementation of the inertial coordinates computation algorithm 206, the control system 142 would use the output from the inertial navigation algorithm 204, combined with a digital elevation map (DEM) for the earth to compute the location and velocity of the point where the payload line of sight intersects the earth’s e. In this context, the term “the earth’s surface” includes not only a point on the actual surface of the earth but also a point at a specified height above the earth’s surface; this point is often referred to as the “target”. Thus, the control system 142 contains instructions for an inertial navigation system for computing the geographic position Where a payload line of sight intersects the earth’s In a typical implementation of the geographic steering thm 208, the l system 142 would accept gimbal control inputs from the gimbal control input source 190 for the geographic on and velocity of a desired target and compare this to the output of the inertial nates computation algorithm 206 to produce position and velocity error signals.

The control system 142 may use a PID controller to calculate the ed steering rates required to minimize the error, and the demanded steering rates may be transformed into the coordinate frame of the inertial measurement unit 110 either before or after the PID controller.

Other types of controllers may also be used. The output of the geographic steering algorithm 208 is provided to the platform stabilization control thm 202 as the desired yaw, pitch, and roll line of sight (LOS) rates. Thus, the geographic steering algorithm 208 comprises instructions for closing geographic based ng control loops to maintain the payload line of sight pointing at a geographic position.

In a typical implementation of the power management algorithm 210, the control system 142 may accept inputs from voltage, current, and temperature sensors (not shown) throughout the system together with other data regarding the current state of the system. By using the past, present and predicted values for power consumption in the various sub—systems the overall system power can be maintained within the specified limits while maximizing the overall system performance. For example, power for heaters or fans (not shown) could be temporarily d in order to provide more power to the active drive system 140 during instances of higher than normal demand. In this manner power can be managed between competing sub-systems thousands of times per second. The overall power limits for a system can be dynamic, allowing an external master controller to manage power across l systems, in real time, to ze overall performance while maintaining overall power consumption within the power available.

In a typical implementation of the outer gimbal control algorithm 212, the control system 142 may accept angular position, rate, and al rate inputs from the sensors on the outer gimbal assembly 118, angular position data from the position sensor system 164 and desired rate data from (or calculated by the phic steering algorithm 208 based on data from) the gimbal control input source 190. The control system 142 may use data from the position sensor system 164, resolved into the coordinate frame of the outer gimbal assembly 118, as an error signal in a PID controller to cause the outer gimbal assembly 118 to follow the line of sight. Additionally, the control system 142 may use the desired rates from the gimbal control input source 190 and/or the output of the phic steering thm 208 as a feed-forward term. The control system 142 may also use data from the outer gimbal inertial rate sensors 192, 194, 196 as compared to the d rates resolved into the coordinate frame of the outer gimbal assembly 118 to produce an error signal to be used in a PID type controller to compute demanded rates. The sum of the demanded rates from the position sensor system 164, feed-forward calculation, and outer gimbal inertial rate s 192, 194, 196 may be used as the final demand to the outer gimbal ly actuators.

Development of a suitable platform stabilization control algorithm 202, inertial navigation algorithm 204, inertial coordinates ation algorithm 206, geographic steering algorithm 208, power ment algorithm 210 and outer gimbal l algorithm 212 is within the lity of one skilled in the art, now informed by the present disclosure. For example, and without limitation, Figure 8 of US. Patent No. 6,263,160 to Lewis shows a platform stabilization loop, and Figures 7a and 7b ofUS Patent No. 5,897,223 to Tritchew et al. show a block diagram of inner and outer control loops for two- and three-axis outer gimbal systems. These patents are hereby incorporated by reference.

The transfer functions of exemplary undamped, actively damped and passively damped (elastomeric) isolation systems are compared in Figure 7. Figure 7 shows the improved isolator performance provided by active damping used in the platform stabilization systems described herein. At frequencies well above the undamped natural ncy, the transmissibility for the actively damped system rolls off proportional to the square of the frequency ratio (Wm/W) while for the passive system it rolls off proportional to twice the g ratio (C/Cc) multiplied by the frequency ratio (Wn/W). This means that higher g can be applied to reduce the dynamic amplification or Q at resonance without the corresponding transmissibility penalty at higher frequencies. Also, e of this steeper roll-off, the undamped natural frequency can be pushed up enough to reduce the static displacement of the isolation system. The active isolator shown in Figure 1, and whose performance is charted in the graph in Figure 7, only requires +/- 3/16” travel in the platform axes Xp, Yp and 21;) for a range of +/—3G to the stops while the typical passive elastomeric system requires +/—1/4” travel for a range of only +/-2G to the stops. This represents a cant reduction in sway space required with a ponding increase in payload volume efficiency. This reduction in sway space also reduces the required size and weight of the isolators and the voice coil actuators, increasing d volume efficiency.

In the exemplary rm stabilization system 100, the active drive system 140 comprises an array of four magnetic voice coil actuators 144. In other embodiments, an active drive system for a rm stabilization system may include more or fewer magnetic voice coil actuators.

Figure 5b shows the arrangement of an exemplary active drive system 540B comprising an array of six single-axis magnetic voice coil actuators 544B each comprising a first portion 544B2, in this case the magnetic structure portion, carried by the support frame and a second portion 544Bl, in this case the coil portion, carried by the platform. Each magnetic voice coil actuator 544B has a single active motor axis M2 along which a platform oning force can be applied and two inactive motor axes M1 and M3 for which there is freedom of movement, with the three axes M1, M2 and M3 being substantially orthogonal to one another. Thus, each magnetic voice coil or 544B acts between the support frame and the platform to apply a first platform oning force to the platform along a first motor axis M2 while permitting free linear movement of the second portion along each of a second motor axis M1 and a third motor axis M3 and permitting free rotation of the second portion 544B1 about each of the second motor axis M1 and the third motor axis M3. As can be seen in Figure 5b, the ic voice coil actuators 544B are arranged relative to the platform (not shown in Figure 5b) for selectively driving linear movement of the platform relative to the t frame (not shown in Figure 5b) along the orthogonal platform axes Xp, Yp and Zp and for selectively driving rotation of the platform relative to the support frame about the platform axes Xp, Yp and 2}). More particularly, when a current is passed through the coil 544B1 it creates an electromotive force along motor axis M2 for that ic voice coil actuator 544B. When the polarity of two opposed magnetic voice coil actuators 544B is the same, those magnetic voice coil actuators 544B will produce a linear force parallel to the motor axes M2 and when two opposed magnetic voice coil actuators 544B have the te polarity, those magnetic voice coil actuators 544B will produce a moment about an axis perpendicular to the motor axes M2. Thus, h selective energization, the desired linear movement along and rotational movement about the platform axes Xp, Yp and Zp can be obtained. The l system, shown schematically at 542B in Figure 5b, controls energization of the magnetic voice coil actuators 544B to apply the lled moments and linear forces to the platform.

Figure Sc shows the arrangement of an exemplary active drive system 540C comprising an array of three two—axis magnetic voice coil actuators 544C. Each magnetic voice coil actuator 544C acts between the t frame (not shown in Figure 5c) and the platform (not shown in Figure SC) to apply a first platform positioning force to the platform along a first motor axis M1 and apply a second platform positioning force to the platform along a second motor axis M2 while permitting free linear movement of the rm along a third motor axis M3 and permitting free rotation of the platform about the three motor axes M1, M2, M3, which are substantially orthogonal to one another. The ic voice coil actuators 544C are arranged relative to the platform for ively driving linear movement of the platform relative to the support frame along the platform axes Xp, Yp and Zp of the platform and for selectively driving rotation of the platform relative to the support frame about the platform axes Xp, Yp and Zp. In particular, it can be seen in Figure Sc that if the same coil 544CA1 on all of the magnetic voice coil actuators 544C were energized with the same polarity of current, the combined force vector would be along the platform axis Xp (parallel to the motor axis M1 of each ic voice coil actuator 544C). However, if the polarity of the current in the coil 544CA1 of the lower magnetic voice coil actuator 544C (lower left of Figure 5c) were reversed and the t in the coil 544CA1 on the right side of Figure 5c were zero, the combined forces would produce a moment about the platform axis Yp. If the upper and lower magnetic voice coil actuators 544C (left side of Figure Sc) were energized to produce a unit force along their motor axes M1 and the third magnetic voice coil actuator 544C (right side of Figure 5c) were to have the opposite polarity, and be energized to produce a force of two units, they would e a moment about platform axis Zp. Varying the ude and direction of the current in the coils 544CA1, 544CA2 allows control in six degrees of freedom. The control system 540C controls zation of the voice coil actuators to apply controlled moments and linear forces to the platform.

In the exemplary platform stabilization system 100 shown in Figures 1 to 30, 5a, 6b and 8, the isolators have taken the form of compression springs 120. This is merely one exemplary type of isolator, and other types of isolators can also be used to build a platform stabilization system ing to the teachings of the present disclosure.

Figure 4c shows exemplary isolators 420C which take the form of a three-axis flexural pivot elements 420C sing three -axis flexural pivots 422C arranged in series, with the flexural pivots 422C separated from one another by spacing members 430C. Each flexural pivot 422C has a respective pivot axis 432C, and these pivot axes 432C substantially intersect at a common point P within the platform (not shown in Figure 4c). The flexural pivot elements 420C are preferably of monolithic uction, and the spacing members 430C may be designed to produce the desired ratio of linear to rotational stiffness when used in an isolation array, for example as shown in Figure 4e.

Figure 4e shows an exemplary symmetrical isolation array 424C comprising a plurality of three-axis flexural pivot element isolators 420C each extending directly between a t frame 402C and a platform 404C. gh the flexural pivots 422C that make up the isolators 420C are not symmetrical, the isolation array 424C is rical.

The support frame 402C includes a plurality of mounting projections 428C and the platform 404C includes a plurality of outwardly extending fingers 426C, and each l pivot element or 420C extends between a respective finger 426C and ng projection 428C. In the rated embodiment, the flexural pivot element isolators 420C are arranged at the vertices of a notional tetrahedron T; other embodiments may use other arrangements, such as having the flexural pivot element isolators 420C ed at the vertices of a notional cube analogously to the arrangement shown in Figure 4A. The three pivot axes 432C of each of the flexural pivot elements 420C substantially intersect at the same common point P within the platform 404C; thus in Figure 4e there are four flexural pivot elements 420C each having three pivot axes 432C for a total of twelve pivot axes 432C, and all twelve pivot axes 432C substantially meet at the same common point P. The common point P is the centroid of mass of the platform 404C.

Each flexural pivot element isolator 420C permits linear movement of the platform 404C ve to the support frame 402C with three degrees of freedom and also permits onal movement of the platform 404C relative to the support frame 402C with three degrees of freedom. The flexural pivot element isolators 420C cooperate to form an attitude- independent ion array 424C supporting the platform 404C directly within the support frame 402C and spacing the platform 404C from the support frame 402C. As with the ion array 124 using compression springs 120 as isolators, the isolation array 424C using flexural pivot element isolators 420C permits limited linear movement of the platform 404C relative to the support frame 402C with three degrees of freedom and permits limited rotational movement of the platform 404C relative to the support frame 402C with three degrees of freedom, and is substantially more resistant to linear movement of the platform 404C relative to the support frame 402C than to rotational movement of the platform 404C relative to the support frame 402C. gh the flexural pivots 422C may be considered to be rotational constraints, the platform 404C is not rotationally constrained by the exemplary flexural pivot element isolators 420C or by the exemplary isolation array 424C (see Figure 4e) formed by the flexural pivot element isolators 420C.

Figure 4d shows yet r exemplary ration for an isolator, in this case a agm-based isolator 420D. The exemplary diaphragm-based isolator 420D r comprises first and second hollow, open-ended generally cylindrical housings 430D, with each housing having a diaphragm receptacle 431D defined therein. The housings 430D are arranged so that the diaphragm acles 431D are opposed to one another. The diaphragm— based isolator 420D further comprises two opposed substantially cal generally circular diaphragms 432D, with each diaphragm 432D supported at its periphery 433D by one of the housings 430D and extending across the diaphragm receptacle 431D of that housing 43 0D.

The diaphragms 432D are coupled to one another by a torsional flexure element 434D extending between radial centers 435D of the diaphragms 432D. Thus, the diaphragm-based isolator 420D is an example of multiple isolation elements coupled to one another to act in concert. When used in an isolation array, for example the isolation array 424D shown in Figure 4f, one of the gs 430D is coupled to the support frame 402D and the other g 430D is coupled to the platform 404D, such that for each isolator 420D, one of the diaphragms 432D is coupled to the support frame 402D and the other agm 432D is coupled to the platform 404D. In the rated embodiment, the diaphragms 432D are metal structures in the form of concentrically ribbed bellophragms; in other embodiments a spoked structure, clock spring structure or molded elastomeric structure may be used. The torsional flexure t 434D is preferably axially resilient, and is long enough to cause the desired ratio of axial to lateral ess. In some embodiments, the torsional flexure element 434D may se a helical spring. Although certain types of flexure elements may be considered to be a rotational constraint acting between the diaphragms, the platform 404D is not rotationally constrained by the exemplary diaphragm-based isolators 420D or by the —36- 2014/000912 ary isolation array 424D (see Figure 4f) formed by the diaphragm-based isolators 420D.

In the illustrated embodiment, the torsional flexure element 434D carries a stop 436D to limit l travel of the diaphragm-based isolator 420D. The exemplary stop 436D shown in Figure 4d takes the form of a disk, and during lateral motion the disk-shaped stop 436D will tip until it contacts the edges 437D of the housings 430D, thereby ing further lateral travel of the diaphragm-based isolator 420D.

In the ary embodiment shown in Figure 4d, each diaphragm 432D is fluid- impermeable, and each housing 430D cooperates with its respective diaphragm 432D to form a damping reservoir 438D. Each damping reservoir 438D is in fluid communication with a respective sink reservoir 439D for damping axial nt of the respective diaphragm 432D by displacing damping fluid from the respective g reservoir 438D to the respective sink reservoir 439D. More particularly, in the illustrated embodiment each housing 430D cooperates with its respective diaphragm 432D to form an enclosure 441D. A flanged frusto-conical r 443D extends across each enclosure 441D to divide the respective enclosure 441D into the damping reservoir 438D and the sink reservoir 439D. Each damping reservoir 438D is in fluid communication with the respective sink reservoir 439D through an orifice 449D in the center of the respective divider 443D. The damping reservoirs 438D can be filled with a suitable fluid, such as oil, which will be forced h the orifice 449D in the center of the respective divider 443D into the sink reservoir 439D by axial movement at the center of the diaphragm 432D so as to produce a damping force that is proportional to the velocity of the axial movement only. Because the volume change in the cavity would be very small during lateral movement, the lateral damping in the element for lateral motion would be minimal. The flange 445D of each divider 443D and the periphery 433D of each agm 432D are received in a respective annular recess 447D on the inside surface of the tive housing 420D.

Although the exemplary diaphragm-based ors 420D provide passive damping by displacing fluid through the orifice 449D they may be modified to provide active damping by using an actuator to control the area of the orifice or by controlling the viscosity of the fluid in 2014/000912 the region of the orifice by using an electrical coil at the orifice and using a suitable ferrofluid as the damping fluid.

Figure 3d shows a simplified mathematical model 320 for a agm-based isolator such as the exemplary isolator 420D. The mathematical model is formed from two opposed open-ended housings 330 each having a diaphragm 332 extending across the open end, with the diaphragms being joined at their s by a torsional flexure element 334. In the simplified mathematical model 320 for a diaphragm-based isolator: K3.) is the axial spring rate of the diaphragm; K113 is the lateral spring rate of the diaphragm; KmD is the moment spring rate of the diaphragm; KtD is the torsional spring rate of the diaphragm; KaT is the axial spring rate of the torsional flexure element; KIT is the axial spring rate of the torsional flexure element; KbT is the g spring rate of the torsional flexure element; Kn is the torsional spring rate of the torsional flexure element; and L is the length of the torsional flexure t.

In the simplified mathematical model 320 in Figure 3d: Lateral stiffness is dominated by 2 Km L; Torsional stiffness is dominated by K5; and Axial stiffness Ka = 1 / ((2 / Kan) + (l / KaT)).

Reference is now made to Figure 4f, which shows an exemplary isolation array 424D comprising a ity of diaphragm-based isolators 420D each extending directly between a —38- support frame 402D and a platform 404D. Similarly to the embodiment shown in Figure 4e employing l pivot element isolators 420C, in the embodiment shown in Figure 4f, the diaphragm-based isolators 420D are arranged at the vertices of a notional tetrahedron T so as to radiate outward from the id of mass of the platform 404D; other ments may use other arrangements. For e, the agm—based isolators 420D may be arranged at the vertices of a notional cube analogously to the arrangement shown in Figure 4A.

Each of the diaphragm-based isolators 420D permits linear movement of the platform 404D relative to the support frame 402D with three degrees of m and also permits rotational movement of the platform 404D relative to the support frame 402D with three s of freedom. The diaphragm-based isolators 420D therefore cooperate to form an attitude-independent isolation array 424D supporting the platform 404D directly within the support frame 402D while spacing the platform 404D from the support frame 402C. The isolation array 424D permits limited linear movement of the platform 404D relative to the support frame 402D with three degrees of freedom and permits limited rotational movement of the platform 404D relative to the support frame 402D with three degrees of freedom. The construction and positioning of the agm-based isolators 420D makes the ion array 424D substantially more resistant to linear movement of the platform 404D relative to the support frame 402D than to rotational movement of the platform 404D relative to the support frame 402D.

An isolation array comprising flexural pivot element ors, such as the isolation isolators, such as array 424C in Figure 40, or an isolation array comprising diaphragm-based the isolation array 424D in Figure 4d, may be combined with an active drive system and control system, such as the active drive systems 140, 540B, 540C shown in Figures 5a, 5b and 5c, respectively and the control system 142 shown in Figure 8. method The exemplary systems described above are exemplary implementations of a for isolating a payload from motion of a supporting structure. This method comprises permitting limited linear movement of the platform relative to the support frame with three s of freedom along three orthogonal platform axes and permitting limited rotational movement of the rm relative to the support frame with three degrees of freedom about the three platform axes while providing substantially greater resistance to linear movement of the platform relative to the support frame than to rotational movement of the platform relative to the support frame, without rotationally constraining the platform.

Aspects of the present technology have been described above with reference to a block diagram (Figure 8) showing methods, apparatus ms) and computer program products according to various embodiments. In this regard, the block diagram in Figure 8 illustrates the architecture, functionality, and operation of possible implementations of s, methods and computer m products ing to various embodiments of the present technology.

For instance, each block in the block diagram may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It will also be noted that each block of the block diagram, and combinations of blocks in'the block m, can be implemented by special purpose re-based s that perform the specified functions or acts, or ations of special purpose hardware and computer instructions.

It also will be understood that each block of the block diagram, and combinations of blocks in the block diagram, can be ented by computer program instructions. These er program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagram.

These computer program instructions may also be stored in a er readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture ing ctions which implement the function/act specified in the block diagram block or blocks. The computer m instructions may also be loaded onto a er, other programmable data processing apparatus, or other s to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented s such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the block diagram block.

An illustrative computer system in t of which the methods herein described may be implemented is presented as a block diagram in Figure 10. The illustrative computer system is denoted generally by reference numeral 1000 and includes a display 1002, input devices in the form of keyboard 1004A and pointing device 1004B, computer 1006 and external devices 1008. While pointing device 1004B is depicted as a mouse, it will be appreciated that other types of pointing device, or a touch-screen display, may also be used.

The computer 1006 may contain one or more processors or microprocessors, such as a central processing unit (CPU) 1010. The CPU 1010 performs arithmetic calculations and control ons to e software stored in an internal memory 1012, preferably random access memory (RAM) and/or read only memory (ROM), and possibly additional memory 1014. The additional memory 1014 may include, for example, mass memory storage, hard disk drives, l disk drives (including CD and DVD drives), ic disk drives, magnetic tape drives (including LTO, DLT, DAT and DCC), flash , program dges and cartridge interfaces such as those found in video game devices, removable memory chips such as EPROM or PROM, emerging storage media, such as holographic storage, or similar storage media as known in the art. This additional memory 1014 may be ally internal to the computer 1006, or external as shown in Figure 10, or both.

The computer system 1000 may also include other similar means for allowing computer programs or other instructions to be loaded. Such means can include, for example, a ications interface 1016 which allows software and data to be erred between the communications computer system 1000 and external systems and networks. Examples of interface 1016 can include a modem, a network interface such as an Ethernet card, a wireless ication interface, or a serial or parallel communications port. Software and data transferred via communications interface 1016 are in the form of signals which can be electronic, acoustic, electromagnetic, optical or other signals capable of being received by WO 95951 2014/000912 communications interface 1016. le interfaces, of course, can be provided on a single er system 1000.

Input and output to and from the computer 1006 is administered by the input/output (I/O) interface 1018. This I/O interface 1018 administers control of the display 1002, keyboard 1004A, external devices 1008 and other such components of the computer system 1000, as well as input from various sensors. The er 1006 also includes a graphical processing unit (GPU) 1020. The latter may also be used for computational purposes as an adjunct to, or instead of, the (CPU) 1010, for mathematical calculations.

The various components of the computer system 1000 are coupled to one another either ly or by coupling to suitable buses. It will be appreciated that a computer system used for a control system for a platform stabilization system as described herein may omit some of the above-described components.

The term “computer system”, as used herein, is not limited to any particular type of computer system and encompasses servers, desktop ers, laptop computers, networked mobile wireless telecommunication computing devices such as hones, tablet ers, as well as other types of computer systems.

As will be appreciated by one skilled in the art, aspects of the technology described herein may be embodied as a , method or computer program product. Accordingly, aspects of the technology described herein may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro- code, etc.) or an embodiment combining software and hardware aspects that may all lly be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the presently described technology may take the form of a computer program product embodied in one or more computer readable medium(s) carrying er readable program code.

Where aspects of the technology described herein are implemented as a computer le medium(s) may be program product, any combination of one or more computer utilized. The computer readable medium may be a computer readable signal medium or a computer readable e medium. A computer readable storage medium may be, example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or , or any suitable combination of the foregoing.

More specific examples (a non-exhaustive list) of the computer readable storage medium would e the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a nly memory (ROM), an erasable programmable nly memory (EPROM or Flash memory), an optical fiber, a le compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a er readable storage medium may be any tangible medium that can n, or store a program for use by or in connection with an instruction execution system, apparatus, or device. Thus, computer readable program code for implementing aspects of the technology described herein may be contained or stored in the memory 1012 of the computer 1006, or on a computer usable or computer readable medium external to the computer 1006, or on any combination thereof.

A computer readable signal medium may include a propagated data signal with computer le program code embodied therein, for example, in baseband or as part of a carrier wave. Such a ated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any le combination thereof. A computer readable signal medium may be any computer le medium that is not a computer readable storage medium and that can communicate, propagate, or transport a m for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, radiofrequency, and the like, or any suitable combination of the foregoing. er program code for ng out operations for aspects of the presently described logy may be written in any combination of one or more programming languages, including an object oriented programming language and conventional procedural programming languages.

The program code may execute entirely on the user's computer, partly on the user's er, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the et using an Internet Service Provider).

] Finally, the ology used herein is for the e of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be r understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, ts, and/or components, but do not preclude the presence or addition of one or more other es, integers, steps, operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description has been presented for purposes of illustration and description, but is not ed to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art t departing from the scope of the claims. The embodiments were chosen and described in order and to enable to best explain the principles of the technology and the practical application, with others of ordinary skill in the art to understand the technology for various ments various modifications as are suited to the particular use contemplated.

Several currently preferred embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of ions defined in the modifications can be made without departing from the scope of the invention as claims.

Where the terms ise”, “comprises”, “comprised” or “comprising” are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other features, integers, steps, components to be d therewith. -44a-

Claims (31)

CLAIMS :

1. A platform stabilization system fo r isolating a payload from motion of a supporting ure, the platform stabilization system sing: a t fr ame; a platform for carrying a payload; a plurality of isolators each extending ly between the support frame and the platfor m absent any intervening gimbals, rings or other motion-constraining structures between the platform and the support frame; each isolator permitting linear movement of the platform relative to the support fra me with three degrees of freedom; each isolator permitting rotational movement of the platform relative to the support frame with three degrees of fr eedom; the plurality of isolators cooperating to form an ion array supporting the platform directly within the support fr ame; the isolation array spacing the platform fr om the support fr ame; the isolation array permitting limited linear movement of the platform ve to the support frame with three degrees offreedom along three orthogonal platform axes; the isolation array permitting limited rotational movement of the platform relative to the t frame with three degrees of fre edom about the three platform axes; the isolation array being substantially more resistant to linear movement of the platform relative to the support fr ame than to rotational movement ofthe platform relative to the t frame; and wherein the platform is not onally constrained by the isolation array.

2. The platform stabilization system of claim 1, wherein the isolation array has an undamped natural frequency for linear movement of the platform along the platform axes that is at least two times an undamped natural frequency for rotational movement of the platform about the platform axes.

3. The platform ization system of claim 2, wherein the undamped natural frequency for linear movement of the platform along the platform axes is at least three times the ed natural frequency for rotational movement of the platform about the platform axes.

4. The platform stabilization system of claim 3, wherein the undamped l frequency for linear movement of the platform along the platform axes is at least five times the undamped natural frequency for rotational movement of the platform about the platform axes.

5. The platform stabilization system of claim 3, wherein the undamped natural frequency for linear movement of the platform along the platform axes is at least ten times the undamped l ncy for rotational movement of the platform about the platform axes.

6. The rm stabilization system of claim 1, wherein: each isolator ses at least one ssion spring having a respective spring axis; and to form the isolation array: the compression springs are arranged with their respective spring axes radiating outward substantially from a common point within the platform; the common point being the centroid of mass of the platform; and the compression springs are y preloaded to produce a low lateral spring rate.

7. The platform stabilization system of claim 6, wherein the isolation array comprises eight compression springs arranged substantially at comers of a notional cube and the common point is a centroid of the notional cube.

8. The platform stabilization system of claim 6, wherein the isolation array comprises at least one array of four compression springs arranged substantially at s of a notional regular tetrahedron and the common point is a centroid of the notional regular tetrahedron.

9. The rm stabilization system of claim 6, wherein the isolation array comprises six ssion s radiating outward from a id of a notional cube substantially through centroids of the six faces of the al cube.

10. The platform stabilization system of claim 6, wherein the isolation array comprises a symmetrical array of compression springs.

11. The platform stabilization system of claim 6, wherein the compression springs are machined, multi-start, helical compression springs.

12. The platform stabilization system of claim 1, wherein each isolator comprises a flexural pivot element.

13. The platform stabilization system of claim 12, wherein: each flexural pivot element comprises three single-axis flexural pivots ed in series with each flexural pivot having a pivot axis; for each l pivot element, the pivot axes of each flexural pivot substantially meet at a id of mass of the platform; and the flexural pivot elements are arranged in a substantially symmetrical array to form the isolation array.

14. The platform stabilization system of claim 13, wherein each flexural pivot element is of monolithic construction.

15. The platform stabilization system of claim 1 wherein each isolator is a diaphragm- based isolator.

16. The rm stabilization system of claim 15, wherein each diaphragm-based isolator comprises: a first housing carried by the support frame; a second housing carried by the platform; each housing having a agm receptacle defined n; the diaphragm receptacles being opposed to one another; two opposed diaphragms, each diaphragm being supported at its periphery by one of the housings and extending across the diaphragm receptacle of that housing so that for each isolator, one of the diaphragms is coupled to the t frame and the other of the opposed diaphragms is d to the platform; and the diaphragms are d to one another by a torsional flexure element extending between radial centers of the diaphragms.

17. The platform stabilization system of claim 16, wherein the torsional flexure element is axially resilient.

18. The platform stabilization system of claim 16, wherein the torsional flexure element is a helical spring.

19. The platform stabilization system of claim 16 wherein the diaphragms are molded elastomeric structures.

20. The platform stabilization system of claim 16 wherein the diaphragms are metal hragm structures.

21. The platform stabilization system of claim 16, wherein each diaphragm-based isolator of the r comprises a stop carried by the torsional flexure element to limit lateral travel torsional flexure element.

22. The rm stabilization system of claim 16, wherein: each diaphragm is fluid-impermeable; each housing ates with its respective diaphragm to form a damping reservoir; and each damping reservoir is in fluid communication with a respective sink reservoir for damping axial movement of the respective diaphragm by displacing damping fluid from the respective damping reservoir to the respective sink reservoir.

23. The platform stabilization system of claim 22, wherein: each housing cooperates with its respective diaphragm to form an enclosure; a divider s across each ure to divide the respective enclosure into the damping reservoir and the sink reservoir; and each damping reservoir is in fluid communication with the respective sink reservoir through at least one orifice in the tive divider.

24. The platform stabilization system of claim 1, further comprising: an active drive system acting directly between the support frame and the platform; and and controlling a control system coupled to the active drive system for receiving sensor input the active drive system in response to the sensor input.

25. The platform stabilization system of claim 24, wherein the control system uses the sensor input to l the active drive system for stable motion of the platform.

26. The platform ization system of claim 24, wherein the l system uses the sensor input to control the active drive system for active damping of the platform.

27. The platform stabilization system of claim 24, wherein the active drive system comprises an array of at least three magnetic voice coil actuators, wherein: each magnetic voice coil actuator ses a first n carried by the support frame and a second portion carried by the platform; each magnetic voice coil actuator acts directly between the t frame and the platform to apply a first platform positioning force to the platform along a first motor axis and apply a second rm positioning force to the platform along a second motor axis while permitting free linear nt of the platform along a third motor axis and permitting free rotation of the platform about the three motor axes, with the first, second and third motor axes being substantially orthogonal to one another; the magnetic voice coil actuators arranged relative to the platform for ively driving linear movement of the platform relative to the support frame along the platform axes and for selectively driving rotation of the platform relative to the support frame about the platform axes; and the control system controls energization of the voice coil actuators to apply controlled moments and linear forces to the platform.

28. The platform stabilization system of claim 27, wherein the at least three magnetic voice coil actuators are four magnetic voice coil actuators arranged approximately 90 degrees apart on a circumference of a notional circle.

29. The platform stabilization system of claim 24, wherein the active drive system comprises an array of at least six magnetic voice coil ors, wherein: each magnetic voice coil or comprises a first portion carried by the support frame and a second portion d by the platform; each magnetic voice coil actuator acts directly between the support frame and the platform to apply a first platform positioning force to the platform along a first motor axis while permitting free linear movement of the second n along each of a second motor axis and a third motor axis and permitting free rotation of the second portion about each of the second motor axis and the third motor axis, with the first, second and third axes being ntially orthogonal to one another; the magnetic voice coil actuators arranged ve to the platform for selectively driving linear movement of the platform relative to the support frame along the platform axes and for selectively driving rotation of the platform relative to the support frame about the platform axes; and the control system controls zation of the voice coil ors to apply controlled moments and linear forces to the platform.

30. The platform stabilization system of claim 24, r comprising an angle sensor of the platform system for sensing and providing a signal indicative of an angular position relative to the support frame about the platform axes, the angle sensor system being coupled to the control system.

31. The platform stabilization system of claim 24, further comprising a linear position linear position of the platform sensor system for sensing and providing a signal indicative of a relative to the support frame on the platform axes, the linear position sensor system being coupled to the control system.