DIRECTIONS

BACKGROUND OF THE INVENTION

Determining geographic direction, also known as "north finding" has long being a necessary knowledge of mankind in past, present and future traveling. Modern "north finding" solutions includes: gyrocompass (either mechanical, fiber optics or hemispherical resonate gyroscope), global positioning system (GPS) based north finding, magnetic compass, astronomic north finding (measuring vector between the position of the watcher and the astronomic body) and the like. All the above methods are either: accurate, and reliable though expensive, heavy and cumbrous equipment or low price, simple, light weight but inconsistent and less accurate.

Embodiments of the current invention are directed to north finding solution that is both accurate and reliable without being heavy, complicated or need for predefined data.

SUMMARY OF THE INVENTION

Aspects of the invention are related to a method of determining geographic directions. The method may include: vibrating a vibrating base, measuring first and second accelerations of the vibrating base, in a vertical direction, at known first and second positions on the vibrating base, determining linear velocities at the known first and second positions, processing the first and second acceleration measurements using the determined linear velocities and calculating the azimuth based on the processed first and second acceleration measurements.

Embodiments of the invention may be related to a method of determining geographic directions. The method may include: controlling a vibrating base to vibrate at a frequency, receiving first and second measurements of accelerations of the vibrating base, in a central vertical axis, measured at known first and second positions on the vibrating base, determining linear velocities at the known first and second positions, processing the first and second acceleration measurements using the determined linear velocities and calculating the azimuth based on the processed first and second acceleration measurements.

Other embodiments of the invention may be directed to an apparatus for determining geographic directions. The apparatus may include: a vibrating base, a first accelerometer located at a first known position on the vibrating base, a second accelerometer located at a second known position on the vibrating base, a vibrating actuator for vibrating the vibrating base and a synchronous detector.

Embodiments of the invention may be related to an apparatus for determining geographic directions. The apparatus may include: a vibrating base, at least one movable accelerometer connected to the vibrating base. In some embodiments, the at least one movable accelerometer is to measure a first acceleration in a first known position on the vibrating base and to measure a second acceleration in a second known position on the vibrating base. In some embodiments, the first and second accelerations may be in a vertical axis. The apparatus may further include a vibrating actuator for vibrating the vibrating base and a synchronous detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

Fig. 1 A is an illustration of an apparatus for determining geographic directions according to some embodiments of the invention; Fig. IB is a high-level block diagram of the apparatus for determining geographic directions according to some embodiments of the invention;

Fig. 2 is a flowchart of a method of determining geographic directions according to some embodiments of the invention;

Fig. 3 is a flowchart of a method of determining geographic directions according to some embodiments of the invention;

Fig. 4 is a graph of 3 Coriolis accelerations at various azimuths according to some embodiments of the invention; and

Fig. 5 is an output of a synchronous detector as function of the azimuth according to some embodiments of the invention.

It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

Some aspects of the invention are related to an apparatus and method of determining geographic directions, for example, by calculating an azimuth from the geographic north (the real north). Methods according to embodiments of the invention calculate the Coriolis acceleration acting on a linear moving body relative to a rotating body (e.g., rotating Earth) and use these Coriolis accelerations for finding the azimuth.

As used herein a central vertical axis is an axis perpendicular to a plane tangent to the Earth's surface at a particular location.

Reference is now made to Figs. 1 A and IB which are an illustration and high-level block diagram (respectively) of an apparatus for determining geographic directions according to some embodiments of the invention. An apparatus 100 may include, a vibrating base 110, a first accelerometer 122 located at a first known position on vibrating base 110 and a second accelerometer 124 located at a second known position on vibrating base 110. In some embodiments, apparatus 100 includes a single movable accelerometer 122 that is configured to move from a first position to a second position on vibrating base 100. Apparatus 100 may further include at least one vibrating actuator 130 for vibrating base 110 and a synchronous detector 140 (illustrated in Fig. IB). In some embodiments, apparatus 100 further include one or more sensors 160 for measuring the position or velocity of vibrating base 110.

In some embodiments, apparatus 100 further includes a third accelerometer 126 located at a third known position on vibrating base 110, a fourth accelerometer 128 located at a fourth known position on vibrating base 110 and a controller 150 (illustrated in Fig. IB). In some embodiments, apparatus 100 further includes housing 105 for holding at least vibrating base 110 and actuator 130. In some embodiments, apparatus 100 further includes one or more torsion springs 170. Vibrating base 110 may be any platform having any shape and size that is configured to vibrate. For example, vibrating base 110 may be a disc configured to vibrate, for example, in a known frequency. However, as will be appreciated by one skilled in the art, the invention is not limited to a single shape of the vibrating base.

Accelerometers 122, 124, 126 and 128 may be any devices that are configured to measure accelerations along the sensitive axis. For example, accelerometers 122, 124, 126 and 128 may be Micro Electro Mechanical System (MEMS) devices that are both accurate and inexpensive. In some embodiments, accelerometer 122 is placed in a first known position on vibrating base 110 (as illustrated in Fig. 1 A). In some embodiments, accelerometer 124 is placed in a second known position on vibrating base 110 (illustrated in Fig. 1 A), different from the first position such that a first known angle is formed between the first and second positions around a central vertical axis 180 (illustrated in Fig. 1A) with the known distance (radius) from central vertical axis 180 of vibrating base 110. In some embodiments, the first known angle is, approximately 90° or 80°, 60° or less, and the radius is approximately 5cm, 6cm, 10 cm or more. In some embodiments, accelerometers 126 and 128 may be placed in third and fourth positions on vibrating base 110 (respectively) different from the first and second positions, such that a second known angle is formed between the third and fourth positions around central vertical axis 180. In some embodiments, the second known angle is, approximately 90° or 80°, 60° or less, and the radius is approximately 5cm, 6cm, 10cm or more. All accelerometers may be mounted on rotating base 110 in the way that provides the vertical direction to the sensitive axis of the accelerometers. Vibrating actuator 130 may be any device configured to vibrate vibrating base 110 around central vertical axis 180. For example, vibrating actuator 130 may be a motor, a vibrator and the like. In some embodiments, vibrating actuator 130 may vibrate vibrating base 110 in a frequency, for example, the resonance frequency of the moving part.

One or more sensors 160 may be velocity sensors or positioning sensors. Sensors 160 may be linear velocity sensors for measuring the linear velocities at the first, second, third and/or fourth locations or may be single angular velocity sensor for measuring the angular velocity of vibrating base and calculating the linear velocities according to, for example, equation (4) disclosed below. In some embodiments, the linear velocities at the first, second, third and/or fourth locations may be determined by calculating the angular velocity from an angular position of vibrating base 110 measured by an angular positioning sensor 160 and calculating the linear velocities as disclosed below. Synchronous detector 140 may include any processing unit that is configured to processes accelerations measured by accelerometers 122-128 using the determined velocity, as will be explained and discussed with respect to the methods of Figs. 2 and 3.

Controller 150 may be or may include any sensitive device, intended to measure the outputs of synchronous detector 140 (for example, Analog to Digital Converter - ADC) and any processing unit (for example, CPU) configured to execute methods according to embodiments of the invention, Controller 150 may include a memory for storing codes or instructions of the methods according to embodiments of the invention, for example, the method of Figs. 2 and 3. The memory may further store measurement results.

Reference is now made to Fig. 2 which is a flowchart of a method of determining geographic directions according to some embodiments of the invention. The method of Fig. 2 may be performed by an apparatus such as apparatus 100. In operation 210, embodiments include vibrating a vibrating base (e.g., vibrating base 110), for example, at a known frequency. In some embodiments, the known frequency is the resonance frequency of all the moving elements in apparatus 100. In some embodiment, a controller such as controller 150 controls actuator 130 to vibrate vibration base 110, for example, at the known frequency. In some embodiments, controller 150 controls the timing (stop -start), the amplitude and/or the frequency in which actuator 130 vibrate vibration base 110. For example, actuator 130 may rotationally vibrate the vibrating base about angular amplitude of 5°, and a distance between the sensitive axes of accelerometers and central vertical axes 180 of 5 cm. and a vibration frequency of 100 Hz.

In operation 220, embodiments include measuring first and second accelerations of the vibrating base, in a vertical direction, at known first and second positions on the vibrating base. The first and second accelerations may be measured by first accelerometer 122 and second accelerometer 124 positioned in the known first and second positions on vibrating base 110. In some embodiments, the method further includes measuring third and fourth accelerations of the vibrating base, in a vertical direction, at known third and fourth positions on the vibrating base. The third and fourth accelerations may be measured by third and fourth accelerometers 126 and 128 located in the third and fourth positions on vibrating base 110.

Alternatively, the first and second accelerations may be measured by a single movable accelerometer 122, configured to measure first the first acceleration in the first position on vibration base 110 and then to move to the second position and measure the acceleration in the second position. In some embodiments, movable accelerometer 122 further moves to a third position of vibration base 110 and measures the third acceleration and then moves to the fourth position and measures the fourth acceleration.

Some embodiments of the invention are directed to extract the Coriolis accelerations from the measured accelerations.

The general form of the Coriolis acceleration is given in equation 1.

(1) cl = -2 - c x V _t

Where:

Ωχ- Vector of Earth rotation rate in local coordinates (depends on latitude λ)

V _t - Linear velocity of sensor, vibrating in a horizontal plane:

→ dR _t ,

V _t = = 2π ^■ A p f ^■ COS(2TT ft)

^■ [sm(xp + A ^■ sin(27r t)) ∞s(i > + A ^■ cos(2n ft)) 0] ^T

p - Radius of vibrations (for example, 5cm)

A - Amplitude of angular vibration (for example, 5°)

f - Vibration frequency (for example, 100 Hz)

ψ - Unknown azimuth which is defined as an angle between a direction to the North and the direction from central vertical axis 180 to the position of first accelerometer 124.

Accordingly, the vertical component of the Coriolis acceleration is given in equation 2.

(2) =— 4π ^■ A p f Ω ^■ cos λ ^■ cos(27T ft) · cos > + A ^■ cos(27r ft))

A graph of the vertical component of the Coriolis acceleration in various azimuths is given in Fig. 4. As one can see there are profound differences in the Coriolis accelerations of different azimuths (e.g., 0°, 45° and 90°). Therefore, extracting the vertical component of the Coriolis acceleration may lead to finding the azimuth.

In operation 230, embodiments include determining linear velocities at the known first and second positions. The linear velocity may be measured relative to a static body. The linear velocities may be determined by directly measuring the linear velocities using linear velocity sensors located in the first, second, third and fourth known positions, calculating the linear velocities using measurements from an angular velocity sensor, or by calculating (applying a time derivative to) the linear velocity from measurements of an angular position of vibrating base 110 from an angular positioning sensor. In some embodiments, the linear velocities may be calculated from measurements of the angular velocity as given in equation 3. The linear velocity given in equation 4 may be calculated by multiplying the angular velocity with horizontal distances (radius p (for example, 5cm)) of the known first, second, third and/or fourth positions (e.g., the positions of accelerometers 122, 124, 126 and 128) from the central vertical axis 180 of the vibrating base 110

(3) o) _t = -A ^■ cos(2 ^■ / ^■ t)

(4) Vi =0)f _Pi

Wherein V is the linear velocity for accelerometer i positioned at distance from the central vertical axis 180 of the vibrating base 110.

In operation 240, embodiments include processing the first and second acceleration measurements (and optionally the third and fourth accelerations) using the determined linear velocities. Synchronous detector 140 may process the first and second accelerations and optionally also the third and fourth accelerations, for example, by multiplying each of the measured accelerations with the respective V followed by an integration of the multiplication over the total time T, as illustrated in Fig. IB. The outcome of the processing is a signal that includes only the Coriolis acceleration component from each measured acceleration. In some embodiments, the processing of the measured accelerations causes all other components (e.g., noises) to be zeroed leaving only the Coriolis acceleration component. In some embodiments, the zeroed components may include components having different phase and/or different frequency than the measured angular velocity. The outcome of the processing of synchronous detector 140, the processed acceleration, is given in equation 5 and illustrated in the graph of Fig. 5, calculated for a single measured acceleration.

(5) ί/(ι = J ₀ ^T CvtW - a)f dt

In operation 250, embodiments include calculating the azimuth based on the processed first and second acceleration measurements. Controller 150 may calculate the azimuth using at least two processed accelerations, for example, the first and second processed accelerations. In some embodiments, controller 150 may calculated the azimuth using the first, second third and fourth accelerations. For example, when the first and second accelerations are measured at first and second positions having a known angle of 90° between them, the azimuth Az may be calculated using equation 6.

(6) Az = atan2(U(i];), u (i]; + ))

Wherein υ(ψ) is the first processed acceleration and U + is the second processed acceleration. In some embodiments, increasing at least one of the radius, the frequency and the vibration amplitude increases the Coriolis accelerations, thus making them easier to be extracted from the measured accelerations. In some embodiments, the radius between each sensor and the central vertical axis 180 may be different.

Reference is now made to Fig. 3 which is a flowchart of a method of determining geographic directions according to some embodiments of the invention. The method of Fig. 3 may be performed by a synchronous detector and a controller, for example, synchronous detector 140 and controller 150 of apparatus 100. In operation 310, embodiments include controlling a vibrating base to vibrate at a known frequency. Controller 150 may control actuator 130 to vibrate vibration base 110 at the known frequency, for example, the resonance frequency of vibrating base 110. In some embodiments, controller 150 may control the timing (stop -start), the amplitude and/or the frequency in which actuator 130 vibrate vibration base 110. For example, actuator 130 may rotationally vibrate at angular amplitude of 5°, radius of 5 cm. and vibration frequency of 100 Hz. In operation 320, embodiments may include receiving first and second measurements of accelerations of the vibrating base, in a vertical axis, measured at known first and second positions on the vibrating base. Synchronous detector 140 may receive from first accelerometer 122 and second accelerometer 124 positioned in the known first and second positions on vibrating base 110 measurements of the first and second accelerations. In some embodiments, synchronous detector 140 receives from third accelerometer 126 and fourth accelerometer 128 positioned in the known third and fourth positions on vibrating base 110 measurements of third and fourth accelerations.

Operations 330-350 are substantially the same as operations 230-250 of the method of Fig. 2. While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.