METHOD THEREFOR

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates generally to navigational systems and arrangements for use in positioning applications, and in particular to an inertial navigation system and arrangement, and method for initializing and/or correcting an inertial navigation system and arrangement.

Description of the Related Art

[0002] The present invention relates generally to devices, systems and methods of determining the location of mobile personnel and, particularly, to devices, systems, and methods of determining the location of personnel working under hazardous conditions outdoors and/or within one or more structures.

[0003] Personal navigation and tracking systems are being developed for use in any number of applications. In one example, personal navigation and tracking systems may be useful in military applications for tracking and directing the movements of military personnel during military practice maneuvers and/or military battlefield environments. In another example, personal navigation and tracking systems may be useful in field service applications for tracking field service personnel and/or a fleet of vehicles that have been dispatched into the field. In yet another example, personal navigation and tracking systems may be useful in first responder applications for tracking and directing the positions of, for example, law enforcement personnel at the scene of a crime or accident, firefighters at the scene of an accident or fire, and/or emergency medical services (EMS) personnel at the scene of an accident.

[0004] Firefighters, first responders, and military personnel work in the world's most dangerous occupations in some of the world's most hazardous environments. Firefighters can easily become disoriented or separated in a burning building, since there is often zero visibility as a result of smoke. First responders constantly place themselves in danger, which sometimes results in becoming trapped or disabled. Military personnel face dangerous conditions on a daily basis, and knowing where each soldier is located, whether performing routine tasks or under hostile fire, would be extremely valuable to the commanding officer. In all cases, there are examples where fatalities might have been prevented or injuries lessened in severity with a location system that provides location information about a person in need of assistance to other personnel to relatively quickly find that person.

[0005] In cases in which personnel are outdoors, global positioning system (GPS) devices and solutions can, for example, be used to roughly locate such personnel. However, multipath propagation problems lead to poor signals and inaccurate results with GPS devices when used within a structure. Moreover, without significant processing, GPS devices are typically accurate to approximately ±3 meters. Although such inaccuracy can be acceptable for locating personnel and objects outdoors, an inaccuracy of 3 meters within a structure can, for example, result in sending a rescue team to a wrong floor within the structure and thus squandering precious time in a rescue mission. Like GPS devices, some localization devices which use, for example, radio frequency energy, ultrasound energy and/or infrared energy, can suffer from multipath propagation problems, leading to substantial inaccuracy when used within structures.

[0006] With respect to first responder applications, firefighters have lost their lives because of the lack of effective indoor navigation and tracking systems. As a result, there is particular interest in developing effective navigation and tracking systems for indoor use. Traditional systems for navigating indoors, such as within a building, are generally costly or ineffective. For example, the installation and operating costs associated with an installed base of radio frequency markers within a building are substantial barriers not readily overcome. In addition, poor reception of radio frequency navigation signals within a building, such as that used by satellite-based navigation systems, precludes widespread acceptance.

[0007] More specifically, indoor environments pose particular challenges with respect to implementing navigation and tracking systems. For example, signal transmission in indoor environments may be characterized by the presence of reflections, attenuation, low signal to noise ratio, and signal multipath effects; all of which may decrease tracking accuracy and may prevent signal acquisition altogether. Further, multiple story buildings pose additional obstacles for tracking, as they require three-dimensional positioning.

[0008] One type of navigating system is an inertial navigation system (INS), which is a navigation aid that uses a computer and motion sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references. Inertial navigation systems are used in many different moving objects, including vehicles, aircraft, submarines, spacecraft, and guided missiles. However, their components size, cost, and complexity places constraints on the environments in which INS is practical for use. [0009] An INS includes at least a computer and a platform or module containing accelerometers, gyroscopes, or other motion-sensing devices. A typical INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, etc.), and thereafter computes its own updated position and velocity by integrating information received from the motion sensors. The advantage of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized.

[0010] Further, and with respect to inertial navigation systems, some of the internal components of such systems require initialization. As is known, and upon power-up, an inertial navigation system has no knowledge of its attitude, velocity, position, or sensor biases. These quantities must be initialized to a best estimate of "truth." In certain known applications, this initial estimate is an average of the first few measurements or, alternatively, simply set to zero. However, in many applications, proper initialization of attitude is crucial.

[0011] In a strap-down navigation system (such as a portable navigation system attached to a portion of the user, e.g., the user's ankle, boot, leg, and the like), where the inertial sensors are fixed to the system's reference axes (i.e., body frame), it is necessary to understand the mathematical relationship between the navigation frame and the body frame. This relationship may be defined as a 3x3 rotation matrix, or direction cosine matrix. Alternate representations include quaternion, Euler angles, and the Euler axis/angle.

[0012] One goal, which is addressed by the present invention, is the desire to mitigate error in the computation of the system attitude using the accelerometer specific force vector. To start and for the sake of simplification, it is assumed that the navigation frame, or coordinate system, is tangent to the Earth's surface, where the vertical axis aligns with the local gravity vector. Further, the present invention is useful in connection with any inertial navigation system that utilizes the accelerometer specific force vector to align to the local gravity vector as the primary means of alignment. Certain common techniques and methods that are used in a variety of applications are described in Alignment of strapdown inertial navigation system: a literature survey spanned over the last 14 years, by Jamshaid Ali and Fang Jiancheng, Technical report, School of Instrumentation Science and Optoelectronics Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China.

[0013] Attitude initialization is crucial in applications with limited or no aiding measurements. While certain aiding measurements can mitigate alignment error, mathematical constraints may prevent total convergence. Further, error in attitude degrades inertial navigation performance by introducing error in the integration of total acceleration, which requires knowledge of the system attitude, local gravity vector, and Coriolis force. These errors compound into the velocity estimate, and further into ..the position estimate. EiTor growth in position is parabolic in nature.

[0014] Due to the coupling between accelerometer biases, noise, and tilt error, it is difficult or impossible to initialize the attitude precisely. Specifically, these measurements provide limited observability to estimate the tilt error in our attitude estimate. No physical measurements of velocity, position, or attitude are available to aid the navigation algorithm and improve performance. Therefore, and in order to obtain optimal performance, it is necessary to understand the true system attitude upon initialization.

[0015] In view of the shortcomings of the aforementioned navigation and tracking systems, a need exists for new approaches to personal navigation and tracking. It is further desirable to develop improved devices, systems, and methods of determining the location of mobile personnel that reduce the severity of or eliminate the above-described and other problems with current location devices, systems and methods.

SUMMARY OF THE INVENTION

[0016] Accordingly, the present invention provides an inertial navigation system and arrangement, and initialization/correction method that addresses or overcomes certain drawbacks and deficiencies in the prior art systems. Generally, the present invention provides an inertial navigation system and arrangement, and initialization/correction method that lead to quick system initialization. Preferably, the present invention provides an inertial navigation system and arrangement, and initialization/correction method that are useful in connection with existing and available inertial sensor systems, such as a consumer-grade inertial sensor. Preferably, the present invention provides an inertial navigation system and arrangement, and initialization/correction method that utilize virtual measurement for aiding the inertial navigation system. Preferably, the present invention provides an inertial navigation system and arrangement, and initialization/correction method that improve the initial estimate of attitude using an additional accelerometer or inertial navigation unit. Preferably, the present invention provides an inertial navigation system and arrangement, and initialization/correction method that uses a reference accelerometer and/or a plurality of accelerometers to initialize, correct, and/or validate the measurements of one or more components in the system.

[0017] Accordingly, and in one preferred and non-limiting embodiment, provided is an inertial navigation arrangement, including a first inertial navigation unit including at least one sensor configured to generate navigation data and at least one subsequent inertial navigation unit including at least one sensor configured to generate navigation data. The arrangement further includes at least one controller configured to determine at least one of the following: navigation data, attitude data, velocity data, force data, position data, direction data, bias data, error data, or any combination thereof, based at least partially upon at least one of the following: at least a portion of the navigation data of the first inertial navigation unit, at least a portion of the navigation data of the at least one subsequent navigation unit, or any combination thereof.

[0018] In another preferred and non-limiting embodiment, provided is a method of initializing an inertial navigation arrangement including a first inertial navigation unit including at least one sensor configured to generate navigation data and at least one subsequent inertial navigation unit including at least one sensor configured to generate navigation data. The method includes: receiving at least a portion of the navigation data from the at least one subsequent inertial navigation unit; deteraiining data associated with at least one of the following: navigation data, attitude data, velocity data, force data, position data, direction data, bias data, error data, or any combination thereof, based at least partially upon at least a portion of the navigation data received from the at least one subsequent navigation unit; receiving at least a portion of the navigation data from the first inertial navigation unit; and applying at least a portion of the determined data to the navigation data received from the first inertial navigation unit, thereby initializing the first inertial navigation unit.

[0019] In a further preferred and non-limiting embodiment, provided is a method of analyzing navigation data in an inertial navigation arrangement having a first inertial navigation unit including at least one sensor configured to generate navigation data and at least one subsequent inertial navigation unit including at least one sensor configured to generate navigation data. The method includes: receiving at least a portion of the navigation data from the at least one subsequent inertial navigation unit; receiving at least a portion of the navigation data from the first inertial navigation unit; and analyzing at least a portion of the navigation data received from the at least one subsequent inertial navigation unit and at least a portion of the navigation data received from the first inertial navigation unit.

[0020] In a still further preferred and non-limiting embodiment, provided is a method of navigating using an inertial navigation arrangement including a first inertial navigation unit including at least one sensor configured to generate navigation data and at least one subsequent inertial navigation unit including at least one sensor configured to generate navigation data. The method includes: deteraiining at least one navigational condition; based upon the at least one navigational condition, selecting one of the first inertial navigation units and the at least one subsequent inertial navigation unit; and receiving navigation data from the selected inertial navigation unit for a specified period of time.

[0021] These and other features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structures and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. As used in the specification and the claims, the singular form of "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 is an alignment vector diagram for an inertial navigation system;

[0023] Fig. 2 is a schematic view of one embodiment of an inertial navigation system according to the principles of the present invention;

[0024] Fig. 3 is a schematic view of one embodiment of an inertial navigation arrangement according to the principles of the present invention;

[0025] Fig. 4 is a schematic view of one embodiment of an accelerometer in an inertial navigation arrangement according to the principles of the present invention;

[0026] Fig. 5 is a schematic view of another embodiment of an inertial navigation arrangement according to the principles of the present invention; and

[0027] Fig. 6 is a front view of one embodiment of an inertial navigation arrangement according to the principles of the present invention and worn by a user.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTfS

[0028] For purposes of the description hereinafter, the terns "end", "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "lateral", "longitudinal" and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting. Further, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary.

[0029] As discussed hereinafter, an initial consideration in the field of navigation is the reference frames, or coordinate systems, and their relationships between each other. These reference frames include the inertial frame i, the Earth-centered, Earth- fixed frame e, a northeast-down tangent frame t, and the body frame b. The inertial frame i is Earth-centered with the z axis parallel to the Earth's spin axis and passing through the North Pole. This reference frame is non-rotating, non-accelerating, and is not subject to gravity. Newton's laws apply in this frame. The Earth-centered, Earth- fixed (ECEF) frame e has an x axis extending through the intersection of the prime meridian and equator, and the z axis parallel to the Earth's spin axis and passing through the North Pole. This frame rotates about the z axis of the inertial frame with an angular rate:

Tangent and fixed to the Earth's surface is the tangent frame t. This tangent frame has a geographic origin of latitude longitude λ, and height with x axis pointing north,

y axis pointing east, and z axis pointing down. The rotation between the ECEF frame and the tangent frame is:

[0030] The Earth's rotation expressed in the tangent frame is:

Finally, the body frame b navigates relative to the tangent frame, and it is assumed that the sensor frame and body frame are identical. [0031] To understand the kinematic relationships between the body and inertial frames, let vector describe the position of the body b relative to the inertial frame. Vector describes the position of the tangent frame origin relative to the inertial frame origin. Vector describes the position of the body relative to the tangent frame origin. The position of the body is as follows:

Differentiating (3) with respect to time yields the velocity of the body relative to the inertial frame as follows:

where matrix is the skew symmetric form of vector Differentiating (4) with respect to time yields the acceleration of the body relative to the inertial frame is as follows:

Solving (5) for the acceleration of the body relative to the tangent frame (i.e., yields:

where inertial acceleration has been substituted with the accelerometer specific

plus position dependent gravitational

Vector the local gravity vector, represented in the tangent frame. It is assumed that the tangent frame origin is fixed, such that = 0, and the Earth rotational rate is constant, i.e.,

[0032] Fig. 1 is an alignment vector diagram for an inertial navigation system, where the system is stationary. The accelerometer triad A measures the vector sum of the specific force vector, accelerometer turn-on biases, and accelerometer measurement noise. The direction of the specific force vector may not align with the true local gravity vector as a result of bias and noise. If the accelerometer measurement does not align with the local gravity vector, a tilt error Θ will result in the initial attitude estimate. True azimuth is unknown without an additional reference.

[0033] Expression (6) relates the total acceleration of the body with respect to the tangent frame to the specific force vector gravity vector the Coriolis

acceleration . When stationary, the total acceleration and Coriolis acceleration

are zero, thus or (7).

[0034]

measured via accelerometer measurement: which contains

sensor bias and noise . The local gravity vector, is approximated using an Earth model and ] Given this information, the

next step is to solve for [0035] Next, expression (7) is solved for using knowledge of the local gravity vector and the accelerometer specific force measurement (8). Expression (7) is manipulated such that:

However, it also holds that _W n always be rank 1 (i.e., not full rank), and thus a

unique solution does not exist. With respect to the vector diagram in Fig. 1, the specific force is known within the body frame, while the local gravity vector is known in the navigation frame. This information allows one to resolve provides no information concerning

azimuth. Additional information is necessary to solve for . It is necessary to have knowledge of at least two linearly independent vectors described in both the body and frames to solve for uniquely.

[0036] Because true azimuth is unknown, and no additional information is available in our system, it is necessary to assume an arbitrary second vector. This case implies that the accelerometer specific force measurement aligns exactly with the local gravity vector. Due to accelerometer measurement bias and noise, it is recognized that this assumption will not yield perfect results. Regardless, without additional information, this technique is the best option.

[0037] Next, the sub-optimal quaternion estimation method is used to solve

where it is assumed that the accelerometer specific force vector aligns exactly with the local gravity vector. Vector b _\ describes the accelerometer specific force vector. Vector r _\ describes the local gravity vector. Vector r is chosen to be perpendicular to r _\ , where:

It is then assumed that vector b ₂ is equivalent to r ₂ . The result of this calculation is a coupling between tilt error and accelerometer bias and noise, which creates a tilt error in the initial attitude estimate. Hence, a reduction in the accelerometer bias and noise will reduce the initial tilt error.

[0038] For example, a horizontal bias of 10 mg equates to a tilt error of 0.57°. A tilt error of 0.57° could create a vertical error of 1% distance traveled. Additional error will result from the horizontal bias. A horizontal bias of 50 mg equates to a tilt error of 2.86°. A horizontal bias of 100 mg equates to a tilt error of 5.71°. If the algorithm is unable to estimate the accelerometer bias error and tilt error, the resulting position estimate will degrade.

[0039] In general, and in one preferred and non-limiting embodiment illustrated in Fig. 2, the present invention is directed to an inertial navigation system 1, which includes at least one inertial navigation arrangement 10, a personal communication device 12, and an onsite computer 14. The inertial navigation arrangement 10 is typically portable and removably attached to a user U, e.g., a firefighter, such as on a boot B of the user U (see Fig. 6).

[0040] Further, and with reference to Fig. 3, the inertial navigation arrangement 10 includes a housing 16 surrounding at least one inertial navigation unit 18 comprising at least one sensor 20. The inertial navigation unit 18 may have one or more sensors 20, such as at least one gyroscope 22, at least one accelerometer 24, or the like. It should be noted that, as used hereinafter, an accelerometer may comprise a unit that is configured or arranged to measure accurate acceleration along one or more axes, e.g., the x-, y-, and z-axis (often referred to as an accelerometer triad, i.e., an x-accelerometer 25, a y-accelerometer 27, and a z-accelerometer 29 (see Fig. 4)). Accordingly, such an accelerometer senses and produces data associated with magnitude, velocity, and direction, such that it can be used to sense orientation, vibration, shock, and the like. As used herein, the accelerometer may be used alone or in connection with a gyroscope 22 (or other sensors) in the context of the inertial navigation arrangement 10.

[0041] Further, and in this preferred and non-limiting embodiment, the inertial navigation arrangement includes a controller 26 that is programmed or configured to interface with the sensors 20 and obtain the necessary data to perform certain automated calculations and determinations. This resulting data can be used to adjust or configure the sensors 20, the inertial navigation units 18, the inertial navigation arrangement 10, or the like. In addition, this data can be transmitted or delivered for use in further processes or in comiection with additional calculations and determinations, such as navigational calculations, initiation calculations, validation calculations, and/or any of the calculations and algorithms set forth and discussed above. The navigation data and/or the determinations and resultant data can be used within the inertial navigation system 1 in order to facilitate the effective tracking of multiple users U or objects in a given environment. It should further be noted that the controller 26 may be remote from the inertial navigation arrangement 10, and will receive the raw data through wireless or hardwired communication. Preferably, however, the controller 26 is positioned locally and within the housing 16 of the inertial navigation arrangement 10. [0042] The inertial navigation arrangement 10 may be in wireless communication, via a local communication device 28, with the personal communication device 12, which is also worn by the user U, typically on the user's jacket. The personal communication device 12 is programmed or configured to wirelessly transmit data to the onsite computer 14, which is normally operated by a site coordinator C, e.g., the commander. It is further envisioned that the raw data or the resulting (determined) data can be transmitted directly from the inertial navigation arrangement 10 to the onsite computer 14, or some other desired destination.

[0043] With specific respect to an inertial navigation arrangement 10 of the present invention, it is recognized that accelerometers with low dynamic range normally have greater stability characteristics than those with high dynamic range. These stability characteristics include the magnitude of turn-on biases, long-term bias stability, thermal stability, and noise density. Accordingly, and in one preferred and non-limiting embodiment as illustrated in Fig. 3, the present invention is directed to an inertial navigation arrangement 10 that utilizes a first inertial navigation unit 30 having at least one sensor 20 (preferably at least one gyroscope 22 and at least one accelerometer 24) configured to generate navigational data, and at least one subsequent inertial navigation unit 32, also having at least one sensor 20 (preferably at least one accelerometer 24) configured to generate navigational data. In one preferred and non- limiting embodiment, the first inertial navigation unit 30 and the at least one subsequent inertial navigation unit 32 are co-located and rigidly coupled to each other.

[0044] Further, at least one controller 26 is provided and programmed or configured to determine certain desired data points 34, including, but not limited to, navigation data, attitude data, velocity data, force data, position data, direction data, bias data, and/or error data. Still further, these data points 34 are determined based at least partially upon at least a portion of the navigation data of the first inertial navigation unit 30 and/or at least a portion of the navigation data of the at least one subsequent navigation unit 32. In one preferred and non-limiting embodiment, the data points 34 include attitude initialization data, which is then utilized and/or applied during an initialization process of either or both of the first inertial navigation unit 30 or the subsequent inertial navigation unit 32. Further, it should be noted that one or both of the inertial navigation units 30, 32 may generate navigational data that is used for purpose of navigation in the inertial navigation system 1. Alternatively, the navigational data may be data and information that is used in an initialization, validation, and/or correction process (as discussed hereinafter).

[0045] In order to improve attitude initialization performance, it is recognized that a more stable sensor will improve the characteristics of these critical parameters. Reduction in the accelerometer bias and noise, for example, will reduce the initial tilt error upon initialization. Therefore, and according to one preferred and non-limiting embodiment of the present invention, and as illustrated in Fig. 3, the at least one subsequent inertial navigation unit 32 is in the form of a reference accelerometer 36. In one embodiment, this reference accelerometer 36 is not capable of accurately providing measurements at the navigation rate. Instead, reference accelerometer 36 functions as a stable reference to the accelerometer 24 (i.e., the "navigation" accelerometer) of the first inertial navigation unit 30, and provides a low dynamic range to improve attitude initialization and performance.

[0046] In a further embodiment, at least a portion of the navigation data obtained from the first inertial navigation unit 30 and/or the at least one subsequent inertial navigation unit 32 can be effectively used to: (1) dynamically correct navigation data, dynamically validate navigation data, initialize at least one component of the inertial navigation arrangement 10, determine specific force data, determine initial attitude data, determine initial bias data, determine error data, determine navigation data, or any combination thereof.

[0047] In another preferred and non-limiting embodiment, the accelerometer 24 of the first inertial navigation unit 30 exhibits a dynamic range of from about +1,000 g to about -1,000 g, and in one preferred and non-limiting embodiment, a dynamic range of from about -50 g to about +50 g. Further, the reference accelerometer 36 of the at least one subsequent inertial navigation unit 32 exhibits a dynamic range of from about -5 g to about +5 g, and in one preferred and non-limiting embodiment, a dynamic range of from about -1.7 g to about +1.7 g. Normally, and in this embodiment, the low dynamic range of the reference accelerometer 36 is not available at the full navigation rate. However, the stability characteristics of the reference accelerometer 36 exceed those of the navigation accelerometer 24 of the first inertial navigation unit 30, which exhibits a higher dynamic range. When the accelerometer specific force measurement of the navigation accelerometer 24 is below the dynamic range of the reference accelerometer 36, the reference accelerometer 36 provides an alternate measurement of specific force. In such a case, it is assumed that this measurement is more accurate than that of the navigation accelerometer 24.

[0048] During initialization of the inertial navigation arrangement 10, where the arrangement is stationary, the reference accelerometer 36 can be used as a more accurate measurement of the specific force vector. The result is an initial attitude with less tilt error. Furthermore, the reference accelerometer 36 can specify initial bias estimates of the navigation accelerometer 24 to be utilized in the inertial navigation arrangement 10 and inertial navigation system 1. [0049] Yet another capability of the present invention is the use of the reference accelerometer 36 to aid the inertial navigation system 1 in the navigational process. When the accelerometer specific force measurement of the navigation accelerometer 24 is below the dynamic range of the reference accelerometer 36, the residual between the navigation algorithm's s ecific force estimate and the reference accelerometer 36 output is:

where subscript N indicates the navigation accelerometer and subscript R indicates the reference accelerometer. represent the bias and noise of

the navigation accelerometer 24 and the reference accelerometer 36, respectively. The hat (^) notation refers to an estimated quantity of the navigation algorithm, where the delta is the error between truth and the estimate. Expression (9) can then be utilized in a navigation algoritltm to estimate the navigation accelerometer's 24 bias error within the magnitude of the reference accelerometer's 36 bias and noise.

[0050] Another capability is to provide a check of the navigation accelerometer estimates. It is expected that the result of expression (9) be within the magnitude of the reference accelerometer's 36 bias and noise. A navigation algorithm may then be used to validate measurement corrections utilizing these criteria. If a measurement attempts to move the navigation accelerometer's 24 bias estimate, such that (9) exceeds some magnitude, then that measurement could be ignored.

[0051] According to one preferred and non-limiting embodiment, two accelerometers 24, 36 (preferably, accelerometer triads) are used and exhibit a different dynamic range. The reference accelerometer 36 can be used in the initialization process, as well as an aid to the inertial navigation system 1. Further, the use of the reference accelerometer 36 provides a validation or check of the navigation process. Still further, and as discussed in greater detail hereinafter, the controller 26 may be programmed or configured to determine when to use the data provided by either of the accelerometers 24, 36 of the respective first inertial navigation unit 30 and the at least one subsequent inertial navigation unit 32. It is further envisioned that a number of subsequent inertial navigation units 32 could be used in the context and environment of the present invention, and the accelerometers 36 of these units 32 could exhibit a variety of specified dynamic ranges to function in different environments and applications.

[0052] In another preferred and non-limiting embodiment, and as illustrated in Fig. 5, the first inertial navigation unit 30 includes a low dynamic range accelerometer 38, while the at least one subsequent inertial navigation unit 32 includes a high dynamic range accelerometer 40. Again, and preferably, each of these accelerometers 38, 40 are in the form of an accelerometer triad for use in measuring in the x-, y-, and z-direction. In this embodiment, both of these accelerometers 38, 40 are configured and capable of providing or outputting data at a navigation rate. Further, it is envisioned that the low dynamic range accelerometer 38 can be used as the reference accelerometer 36 (as discussed above) to improve initialization and performance. In general, and according to this preferred and non-limiting embodiment, the low dynamic range accelerometer 38 is utilized as the primary navigation accelerometer, while the high dynamic range accelerometer 40 is utilized to capture data during certain conditions, e.g., momentary events of high acceleration.

[0053] In this embodiment, it is recognized that shoe-mounted pedestrian navigation systems are unique in that the majority of the inertial data lies within a low dynamic range. In particular, typical inertial data lies within the range of about -5 g to about +5 g. However, during impact and other momentary events, the accelerometer signals easily exceed this dynamic range. Therefore, rather than choose a single accelerometer to cover the entire dynamic range of the inertial navigation system 1 , the present embodiment provides the low dynamic range accelerometer 38 and the high dynamic range accelerometer 40. The low dynamic range accelerometer 38 (± 50 g, and in one preferred and non-limiting embodiment, ±5 g) is the primary navigation sensor during normal navigational conditions 42, and the high dynamic range accelerometer 40 (± 1,000 g, and in one preferred and non-limiting embodiment, ±50 g) is used during other specified navigational conditions 42.

[0054] The controller 26 is programmed or configured to detemiine the presence of at least one navigational condition 42, and based upon this condition 42, determines or derives navigation data (and/or data points 34) from the accelerometer that provides the most accurate data during such a condition 42. While this determination may be made based upon data derived from the first inertial navigation unit 30 or the at least one subsequent inertial navigation unit 32, it may also be made based upon data derived from or obtained by a condition sensor 44. This condition sensor 44 would be in communication with and controlled by the controller 26, and be further configured or capable of sensing the presence or absence of some predetermined navigational condition 42. [0055] Accordingly, this embodiment optimizes the sensor noise characteristics for the majority of the data, yet provides capability to measure high dynamic range motions. The navigation algorithm estimates the biases of the primary accelerometer 38, and then deterministically sets those of the high-range accelerometer 40. The navigational condition 42 may be a rest condition, an impact condition, an initiation condition, a movement condition, an environmental condition, or the like.

[0056] One consideration in this embodiment is the handling of the inertial measurement noise statistics in relationship to measurement correction timing. As the system propagates, it is necessary to communicate to the navigation algorithm (e.g., as programmed on the controller 26) the noise characterization parameters of the inertial sensors 20. If the inertial navigation system 1 contains two accelerometers 38, 40, the algorithm will need to adjust these parameters depending on the active accelerometer 38, 40. These parameters include the accelerometer' s velocity random walk and rate random walk. Velocity random walk describes how the uncertainty in the velocity estimate error grows with time, and rate random walk describes how the uncertainty in the accelerometer bias estimate error grows with time. If only the primary accelerometer 38 biases are estimated, then the implications of applying corrections when the high-range accelerometer 40 is active should be considered. This is less of a consideration when the present invention is used in connection with shoe-mounted pedestrian navigation systems, as the majority of the aiding measurements occur when the shoe is at rest.

[0057] In addition, the inertial navigation unit 18 according to this embodiment mitigates the initial attitude en-or via the utilization of a ±5 g accelerometer for initialization rather than a ±50 g accelerometer. Like the ±1.7 g accelerometer discussed above, the ±5 g accelerometer should preferably have improved noise statistics with respect to the ±50 g accelerometer. Accordingly, this embodiment provides the dual use of two accelerometers 38, 40 (preferably, accelerometer triads), where each accelerometer 38, 40 exhibits a different dynamic range. The low dynamic range accelerometer 38 could also be used in the initialization process. This embodiment provides for the optimization of the sensor noise parameters in connection with pedestrian navigation systems, as well as effectively determines which inertial navigation unit 30, 32 should be used in specific situations. As discussed above, any number of units 30, 32 (or accelerometers) could be used with a variety of optimal ranges for addressing specific navigational conditions 42.

[0058] As illustrated in Fig. 6, the inertial navigation arrangement 10 includes multiple units (or sensors 20) positioned within a common housing 16. Accordingly, some attachment arrangement 46 can be used to attach the housing 16 to the user U. For example, a detachable strap arrangement 48 connected to the housing 16 could be used for connection to the boot B of the user U, which is one preferable arrangement used in the firefighting environment. However, any suitable attachment arrangement 46 is envisioned.

[0059] In a further preferred and non-limiting embodiment, the present invention is directed to a method of initializing an inertial navigation arrangement 10, which includes the first inertial navigation unit 30 including at least one sensor 20 for generating navigation data, and at least one subsequent inertial navigation unit 32 including at least one sensor 20 for generating navigation data. This method includes: (i) receiving at least a portion of the navigation data from the at least one subsequent inertial navigation unit 32; (ii) determining data associated with at least one of the following: navigation data, attitude data, velocity data, force data, position data, direction data, bias data, error data, or any combination thereof, based at least partially upon at least a portion of the navigation data received from the at least one subsequent navigation unit 32; (iii) receiving at least a portion of the navigation data from the first inertial navigation unit 30; and (iv) applying at least a portion of the determined data to the navigation data received from the first inertial navigation unit 30, thereby initializing the first inertial navigation unit 30. Any one or more of the receiving, determining, and applying steps is implemented by a specially-programmed controller 26.

[0060] In another preferred and non-limiting embodiment, the present invention provides a method of analyzing navigation data in an inertial navigation arrangement 10 having a first inertial navigation unit 30 including at least one sensor 20 for generating navigation data and at least one subsequent inertial navigation unit 32 including at least one sensor 20 for generating navigation data. This method includes: (i) receiving at least a portion of the navigation data from the at least one subsequent inertial navigation unit 32; (ii) receiving at least a portion of the navigation data from the first inertial navigation unit 30; and (iii) analyzing at least a portion of the navigation data received from the at least one subsequent inertial navigation unit 32 and at least a portion of the navigation data received from the first inertial navigation unit 30.

[0061] In the analytical method of this embodiment, the controller 26 (or some remote controller) could be utilized to determine data associated with at least one of the following: navigation data, attitude data, velocity data, force data, position data, direction data, bias data, error data, or any combination thereof, based at least partially upon at least a portion of the navigation data received from the at least one subsequent inertial navigation unit 32 and/or the first inertial navigation unit 30. Further, this analysis may include: comparing at least a portion of the navigation data of the first inertial navigation unit 30 to at least a portion of the navigation data of the at least one subsequent inertial navigation unit 32; and, based upon the comparison, either: (i) validate at least a portion of the navigation data of the first inertial navigation unit 30, thereby providing a validated navigation data set; or (ii) correct at least a portion of the navigation data of the first inertial navigation unit 30, thereby providing a corrected navigation data set.

[0062] In yet another preferred and non-limiting embodiment, the present invention provides a method of navigating using an inertial navigation arrangement 10 comprising a first inertial navigation unit 30 including at least one sensor 20 for generating navigation data and at least one subsequent inertial navigation unit 32 including at least one sensor 20 for generating navigation data. This method includes: (i) detennining at least one navigational condition 42; (ii) based upon the at least one navigational condition 42, selecting one of the first inertial navigation unit 30 and the at least one subsequent inertial navigation unit 32; and (iii) receiving navigation data from the selected inertial navigation unit 30, 32 for a specified period of time (or until a different navigational condition 42 is sensed).

[0063] In this manner, the present invention provides an inertial navigation system 1 and arrangement 10, and initialization/correction method that lead to quick system initialization and are useful in connection with existing and available inertial sensor systems. The inertial navigation system 1 and arrangement 10, and initialization/correction method according to the present invention improve the initial estimate of attitude using an additional accelerometer, and assist in the initialization, correction, and/or validation of the measurements of one or more components in the system.

[0064] Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.