System and method for aligning multiple sighting devices

A system of independently oriented sighting devices includes a first sighting device (120) and a second sighting device (110). Upon aligning a line of sight of the first sighting device (12) with a target object (130), the first sighting device transmits a reference signal over a communications link (140). The second sighting device (110) determines its orientation in space relative to the orientation of the first sighting device (120) from characteristics of the reference signal. Thus, absolute coordinates of the target object (130) need not be known by the second sighting device (110) nor is it required that they be transmitted by the first sighting device (120). The user (115) of the second sighting device is directed to rotate the second sighting device (110) towards the target object (130) via feedback through guidance indicators located in a viewing port (250) thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention most directly relates to alignment of two or more directional devices, and more particularly, to alignment of sighting devices. The invention further relates specifically to dynamically aligning sighting devices to allow two or more users to easily locate a common target object through independently translated viewing ports.

2. Description of the Prior Art

Sighting devices, particularly optical sighting devices, are used in many applications and are varied in configuration. Common optical sighting devices include, but are by no means limited to, binoculars, telescopes, rifle and other weapon sights, and surveying equipment. A user might sight through an optical device, generally, to (a) magnify or otherwise improve viewing of a target in the visual field and/or (b) to align an attached piece of equipment (e.g., rifle, survey tool, etc.) with a target.

In certain sighting applications, situations arise in which two or more users working together need to share information about target location so that both may view the same scene. For example, a bird watcher may wish to convey the location of a bird to a second bird watcher so that they both can focus quickly on the same bird. As a further example, one party equipped with a wide field optical device may wish to guide a second party equipped with a high power, narrow field optical sight towards a target object. Sighting applications in which it is desirable to share information between users also include tree and geologic identification, ship and terrain spotting at sea, aircraft spotting and identification, and military targeting, such as when a spotter with one optical device guides a second person equipped with an optically sighted weapon towards a specified target.

Communication between sighting device users is often in the form of haphazard directional descriptions, such as, “Two o'clock, a few degrees above the horizon,” or, “A little below the top branch of the tall forked tree.” Previous solutions to this shortcoming have included providing internal compass and declinometer readings in the displays of prior art sighting devices. Through such a display, users may communicate direction using precise numbers to co-ordinate their targeting. Other devices of the prior art have implemented detection of rotation via gyroscopically stabilized platforms, thereby subsequently conveying directional information to a remote user. This latter method, however, requires an initial coordinate alignment step to synchronize the two devices, which may preclude certain spontaneous operations.

An effort to overcome some of the shortcomings addressed above, while demonstrating other shortcomings, is disclosed in U.S. Pat. No. 5,764,344 issued to Taniguchi. The reference discloses an observing apparatus for simultaneous viewing of an object by two different users. A first operator locates a target through a first telescope and depresses a detection switch when the target is adequately framed in his field of view. An arithmetic control unit, upon notification that the detection switch has been activated, determines the distance from the first telescope to the target as well as a set of coordinates of the target. The coordinates are subsequently transmitted over a cable to a second telescope under the control of a second operator. At the second telescope, an arithmetic control unit activates indicators in the viewing field of the second operator, which specify to the second operator a direction of rotation through which the second telescope must be rotated in order for the target to be framed in the field of view of the second telescope.

While the visual feedback provided to the second operator directing her towards the location of the target ameliorates verbal direction commands such as those discussed above, several deficiencies of the Taniguchi system limit its range of applicability. First, the referenced system utilizes an absolute frame of reference, i.e., both telescopes are configured, via rotational encoders, to locate a point in a previously established coordinate system. Establishing the coordinate system is an involved process, as disclosed in the reference, involving calibrating both telescope platforms on a previously designated calibration target. Ironically, both operators must locate the same calibration target in their respective fields of view, which is the target location problem alleviated by the present invention. The Taniguchi system, though, first requires that the telescopes be collocated for a first calibration measurement prior to moving the second telescope to a remote location, where the second operator must once again locate the calibration target and make a second calibration measurement. The two telescopes then remain fixed in their respective locations for the duration of ordinary viewing operations, as the invention does not provide a means to dynamically recalibrate if one or the other user relocates.

A further shortcoming of the Taniguchi system lies in its means for determining the absolute bearing in the chosen coordinate system. The embodiments disclosed by the reference utilize rotational encoders on respective, fixed tripods of equal length. The tripod serves to fix the telescopes within the coordinate system and provides a non-rotating reference base for the rotational encoders. It should be apparent to the skilled observer that such a system severely restricts the movement of its users.

However, rotational encoders are not the only means by which absolute bearing may be determined. Other bearing sensors include magnetic compasses, which are known to be affected indeterminately by local magnetic disturbances, such as metal objects and electronic equipment. Rotational accelerometers are also capable of providing an absolute bearing, but are subject to drift. Neither of these devices can provide consistent reliable accuracy for aligning optical systems having magnification.

Certain military and camera devices utilize an instrument or weapon that is slaved to automatically move in response to adjustments in a remote optical sight. The mechanically slaved techniques of the prior art often rely on fixed spatial relationships and pre-alignment to solve the problem of common targeting. While duplicating, or even translating, the movement of one device through pointing movements of another device is both well-known and useful, the technique can be limiting in other sighting applications. For example, in certain applications, users should be allowed to aim their respective sighting equipment freely and independently of the aim of other sighting devices, until such time as one user wishes to direct another to view a common target object. At that time, communicating alignment information between users is warranted. Even then, a user may wish to ignore the sightings of other users and continue aiming his own equipment independently, a option that would not be possible in systems practicing the mechanical slaving techniques of the prior art.

In light of the shortcomings of the prior art, there is an apparent need for sighting devices that are operable to communicate alignment between two or more passively aimed devices.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a system is provided for aligning independently oriented sighting devices toward a common target object. The system includes a first sighting device having a first sighting axis and a transmitter for transmitting a reference signal once the first sighting axis is aligned on the common target object. A second sighting device having a second sighting axis is provided in the system, which includes a receiver for receiving the reference signal transmitted from the first sighting device. The second sighting device includes a processing unit coupled to the receiver for determining from a characteristic of the reference signal a relative orientation in space of the second sighting device with respect to an orientation in space of the first sighting device. The second sighting device also includes an indicator coupled to the processing unit for indicating a direction in which to direct the sighting axis of the second sighting device so as to be aligned on the common target object.

In another aspect of the invention, a system is provided for aligning independently oriented sighting devices toward a common target object, where a first sighting device having a first sighting axis includes a transmitter for transmitting a reference signal when the first sighting axis is aligned on the common target object. A second sighting device having a second sighting axis is provided, which includes a processing unit for determining an orientation in space of the second sighting device with respect to an orientation in space of the first sighting device. The second sighting device also includes at least one orientation sensor for determining its orientation within a corresponding single plane of space relative to a predetermined orientation in the same corresponding single plane. The at least one orientation sensor is coupled to the processing unit and provides a signal thereto responsive to its relative orientation in the corresponding plane. The second sighting device further includes a receiver for receiving the reference signal from the first sighting device, where the receiver is also coupled to the processing unit. The receiver provides a signal to the processing unit corresponding to an orientation of the second sighting device in at least one plane in space relative to the orientation in the at least one plane of the first sighting device. The receiver signal is responsive to a characteristic of the reference signal corresponding to the orientation of said second sighting device in the at least one plane in space relative to the orientation in the at least one plane of said first sighting device. The processing unit determines from the receiver signal and from the signal from the at least one orientation sensor a relative orientation in space of the second sighting device with respect to an orientation in space of said first sighting device. The second sighting device also includes an indicator coupled to the processing unit for indicating a direction in which to direct the second sighting axis so as to be aligned on the common target object.

In yet another aspect of the invention, a method is provided for directing respective sighting axes of independent sighting devices towards a common target object. A first sighting device is operable by a first user to be oriented in space. The first sighting device has a first sighting axis and a transmitter for transmitting a reference signal. A second sighting device is operable by a second user to be oriented in space independently of said orientation in space of said first sighting device. The second sighting device has a second sighting axis and includes a receiver for receiving the reference signal. The second sighting device also includes an indicator for indicating to the second user an adjustment direction to apply to the orientation of the second sighting device. Once the first sighting axis is aligned on the target object, the reference signal is transmitted, whereupon it is subsequently received at the receiver. At the second sighting device, a characteristic of the reference signal is acquired, which is used to determine a relative orientation in space of the second sighting device with respect to the first sighting device. An orientation correction is determined from the relative orientation of the second sighting device and the user of thereof is provided with an indication of the orientation correction via the indicator so as to direct the second sighting axis towards the target object.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For purposes of explanation of the inventive concept, a basic configuration of fundamental components of the present invention is broadly illustrated inFIG. 1. As is shown in the Figure, two sighting devices,110and120are in use by two separate users115and125, respectively. Whereas, the sighting devices are illustrated schematically in the Figure as optical sighting devices, particularly binoculars, any sighting device may be substituted for either or both of110or120with no material change in the operation of the invention. Moreover, the sighting devices need not be configured for operation at optical wavelengths; the term “sighting device” as used herein will refer to a directive device in which a primary receiving aperture, such as is generally shown at114and124ofFIG. 1, is to be pointed or aimed at a target object. The exemplary embodiments, for purposes of description, will be optical sighting devices such as binoculars, telescopes, spotting scopes, rifle scopes, and weapons sights, but it should be apparent to the skilled artisan that other directive devices such as microphones and antennas may be used in accordance with the present invention. Moreover, it should be noted that sighting devices used in a particular application need not be of the same type. For example, in certain applications, one sighting device may be binoculars and another sighting device may be a directional microphone. A user may, for example, align the binoculars on a bird in a bird watching application and then subsequently wish to record the bird's song via the directional microphone. Through the present invention, the user of the binoculars may direct a user of the microphone to aim the microphone towards the target bird so as to be co-aligned therewith. The implementation of such useful embodiments will become clear through the various descriptions given below.

As shown inFIG. 1, the first user125has oriented sighting device120in space so that the sighting axis122thereof is aligned on a selected target object130. As will be discussed further below, sighting device120is furnished with means for alignment on the target130, such as a viewing port for establishing visual contact therewith. Additionally, sighting device120has installed thereon means for transmitting a reference signal, which is transmitted via one or more transmission channels140to the second sighting device110. In certain embodiments of the present invention, the reference signal may be continuously or periodically transmitted while in other embodiments, one or the other of users115or125will establish the transmission channel140using some appropriate means, such as a switch or button, on their respective sighting devices1110,120.

Typically, one of optical sighting devices110,120will act as a master or transmitter while the other will act as a slave or receiver. It is to be noted that the terms “master” and “slave” are used to distinguish a transmitting sighting device from a receiving device, respectively, and are not used to imply that the orientation of one sighting device is responsive to the orientation or movement of the other. Indeed, it is a principle objective of the present invention to allow co-alignment of sighting devices that are independently oriented in space, such as hand-held binoculars, respectively operated by independent users. As such, the roles of master and slave may be respectively fixed in certain embodiments and in other embodiments, the roles may be reversible. In certain other embodiments, each unit may simultaneously transmit and receive reference information by means of non-interfering transmissions.

For purposes of the present invention, the transmitted reference signal need only possess a characteristic sufficient for the receiving sighting device to determine its orientation in space relative to that of the transmitting sighting device. Such characteristics include, but are not limited to, time-of-flight of a pulse of a pulse modulated carrier wave, a phase relationship over several reference signal receiving apertures distributed on the receiving device and a polarization state of a carrier wave. However, certain portions of the reference signal may be designated to carry information-bearing data, such as through binary data encoded on a radio transmission, and may include absolute references, such as compass heading and declination, or relative information, such as rotational accelerometer outputs. In certain other embodiments, the reference signal carries no encoded data and the relative orientation between devices is determined by the characteristic of the reference signal waveform. Examples of both configurations are discussed further in paragraphs that follow.

The reference signal transmission may be transmitted directly from one sighting device to another or may be reflected from the target130. Exemplary embodiments of each of these orientation methods are discussed in further detail below. It is further contemplated within the scope of the invention that additional data, for purposes unrelated to relative orientation determination, may also be transmitted between devices.

Whereas, only two users115and125respectively operating two sighting devices110and120are shown inFIG. 1, any number of devices may participate as receivers in such a system and remain within the scope of the invention. Typically, only one master or transmitting user will send a reference signal at any given time, while any number of receiving units may receive the reference signal so as to align with the target object selected by the user of the master device. However, by utilizing any of the non-interfering transmission techniques known well in the communication art, e.g., duplex communications, time-division multiple access (TDMA), or code-division multiple access (CDMA), certain embodiments of the invention may allow multiple users to simultaneously exchange reference data. In some general applications, a receiving sighting device will be oriented in accordance with only one transmitted reference signal at any give time. However, it is within the scope of the invention that a receiving sighting device could integrate signals from two or more simultaneously transmitting source devices by parallel processing of reference signals, each reference signal being processed in accordance with the present invention as demonstrated through the exemplary embodiments.

In certain embodiments of the invention, the transmission channel140may be over a mechanically constrained or guided media, such as an electrical cable or optical fiber. Such a link, although possibly limiting the relative mobility of users, may be advantageous certain applications, such as in noisy environments and in applications where stealth requirements dictate carefully restricted energy transmission. However, since a large number of sighting device users generally value un-tethered freedom of movement, many useful embodiments of the present invention utilize one or more well-known wireless methods, such as radio frequency transmissions, ultrasonic or audio transmissions, and infra red or optical transmissions. Details of the implementation of wireless reference signal transmission methods are described below in certain exemplary embodiments and other similar implementations will be obvious to those skilled in the art.

Referring once again toFIG. 1, a generalized description of the operation of the illustrated embodiment of the present invention is now given. User120aligns the sighting axis122of sighting device125so that the primary receiving aperture124is directed towards, and preferably centered on the target130. User120establishes one or more transmission channels140, such as by depressing an indicator switch (not shown), and transmits the reference signal. Sighting device110receives the reference signal and processes it accordingly so as to obtain a relative orientation between devices110and120. User115is directed via feedback means (not shown inFIG. 1) to direct the primary receiving aperture114of sighting device110towards the target object130. The respective fields of view of sighting device120and sighting device110converge on the same target object130when the respective sighting axes122and112are aligned thereon.

Certain embodiments of the invention may include means by which to adjust the relative orientations of sighting devices110and120to compensate for parallax so that the target130is better centered in the respective fields of view thereof. However, since many optical sighting devices are typically employed to view distant objects, and users wishing to share viewing information will often be relatively close to each other in comparison to the distance to the target, parallax correction may be optionally omitted as a measure of reducing costs for a basic model of the invention in the marketplace. A description of an exemplary parallax correction method is given below.

Referring toFIGS. 2A–2D, there is shown exemplary displays for conveying orientation correction via visual feedback methods in accordance with certain embodiments of the present invention. In the illustrated exemplary embodiments, the visual feedback is provided via the viewing port of an optical sighting device, such as binocular110ofFIG. 1, to direct the aim of the second user115. The term “viewing port” is used herein as the aperture through which a user sights a target object. In certain embodiments of the present invention, such as when implemented on many optical sighting devices, the viewing port coincides with the primary receiving aperture, i.e., the aperture for which alignment with the target object is primarily desired. However, in certain other embodiments, such as when the primary receiving aperture is not an optical port, the viewing port may be removed therefrom. For example, a directive listening microphone, such as is known in the art to include a microphone positioned at the focus of a parabolic dish, may be a primary receiving aperture on which a separate target viewing mechanism, such as a CCD camera, is installed for purposes of aiming at a target. A separate viewing port, such as a video display device, may be coupled to, but removed from, the viewing mechanism, to provide visual feedback to a user for purposes of aligning his microphone on a target common to a remote user of a similarly adapted microphone. It will be apparent to those skilled in the art how such configuration is consistent with the present invention in light of the detailed descriptions of the exemplary embodiments provided herein.

In the examples ofFIGS. 2A–2D, a bird210provides a target object, which is already partially visible in the visual field250of the viewing port of a slave sighting device. The crosshairs260indicate the center of the visual field for purposes of reference in this discussion. Actual crosshairs are optional and are not necessary to implement the invention, but may be included in certain embodiments to assist the user in centering the visual field250on the target object210. Crosshairs260may take any of a numerous of forms known to those skilled in the art.

There are many analog and digital means for displaying information in the visual field of a viewing port of an optical device that are suitable for use with the present invention. Indicators may be installed in the viewing port so as to be observed directly, such as is disclosed in U.S. Pat. No. 4,274,149, issued to Flanagan. The use of prisms and other optical elements to project information into a viewing port is also well known, such as disclosed by U.S. Pat. No. 4,021,830, issued to Kanno, and may be used in implementing the present invention. The actual means for providing the visual feedback described with reference toFIGS. 2A–2Dmay be carried out by various electronic, optical or digital imaging methodologies without deviating from the intended scope of the present invention.

Referring toFIG. 2A, directional indicators220a–220dare selectively illuminated in accordance with the present invention to indicate to the user in which of four directions the user should adjust her aim. In the illustrated example of the Figure, upper indicator220aand left indicator220bare illuminated, thus advising the user to adjust her aim up and to the left. It should be clear to the skilled artisan that other indicator styles may easily be employed without departing from the scope of the present invention. For example the four indicators220a–220dmay be supplemented by any number of additional indicators; darkening of the indicators may replace illumination thereof; the arrows illustrated may be replaced by bars or other shapes; and so on. Additionally, some indication of being “on-target” may be required in certain applications. Hence, many embodiments of the present invention may include a display in the visual field250that changes in a recognizable way upon reaching an on-target state, such as by flashing or illuminating all four indicators220a–220dor illuminating the crosshairs260.

FIG. 2Billustrates a further embodiment of the visual feedback display. The user is directed to change aim up and to the left by the presence of a radial arrowhead230. The arrowhead230may be a member of an array of discrete indicators, such as implemented by liquid crystal displays, or may be placed on a continuum, such as by any number of analog means including well-known cathode ray tube based visual displays.

FIG. 2Cillustrates another exemplary embodiment for which absolute reference information has been transmitted from one or more sighting devices. The information is processed in accordance with certain aspects of the present invention, as will be described below, and is displayed in the visual field250. As shown in the Figure, the compass heading242and elevation244defining the bearing of user's sighting device is indicated in the visual field250using digital numbers. The user is directed to change aim up and to the left by the illumination of arrows248aand246a, respectively, while arrows248band246bremain deactivated. Many similar, functionally equivalent display variations will be obvious to those skilled in the art.

FIG. 2Dillustrates yet another embodiment of an exemplary visual feedback display. To exemplify aspects of the variability of the display, the embodiment omits the crosshairs260shown inFIGS. 2A–2C. The user may locate the center point of the visual field250by referencing the center of the tick ranges262and266on the bottom and right of the visual field250, respectively. The illustrated embodiment implements a so-called “digital analog” display to provide the user information regarding both direction and a measure of degree as to how far the bearing of the sighting device must be adjusted to locate the target object selected by the transmitting sighting device. Ticks264and268are illuminated, or alternatively darkened, in proportion to the aim correction required, from none to the maximum span of the visual scales262and266. In the example shown, the user is directed to change aim up and to the left by relatively small amounts to achieve centering the target210in the visual field250.

Numerous other variations of feedback visualization methods will be obvious to those skilled in the art. Those shown in the Figures are intended to serve as exemplary embodiments demonstrating various aspects of the invention. The illustrated embodiments are neither exhaustive in representing the broad variability of display configurations useable with the present invention nor are they limiting to the scope thereof. Indeed, even non-visual methods of feedback for purposes of directing a user's aim to a target, such as through audible tones, may be implemented.

It should be noted that in certain embodiments of the invention, users need not have any visual means of sighting the target. For example, the master device may be aligned on the target by non-visual means and the slave device may be directed toward the target by following directional indicators without actual visual contact with the target. Indeed, many useful embodiments of the invention are intended for use in aligning systems of high magnification or high directivity where the target is not in the field of view of the sighting device until it is essentially aligned thereon. The user will typically attend to directional indicators during the alignment operation of such embodiments of the invention without visual contact with target. Thus, the overlay of the visual indicators in the viewing port of a sighting device is not a requirement of the invention. The indicators may be located elsewhere, while still providing the directional feedback to the user. To extend this idea to an exemplary embodiment, the directional microphone discussed above may be considered. In exemplary embodiments, the indicators thereof may be implemented by a plurality of, for example, light emitting diodes located on a portion of the parabolic dish far removed from the sighting axis of the device. Still, the indicators may be configured to direct the user towards the target object selected by the master device in accordance with the present invention.

Referring now toFIG. 3, there is shown a functional block diagram of fundamental components of an exemplary system implementing the present invention. Separate sighting devices are shown at310and350. In certain embodiments, both sighting devices310and350include the same functional elements and can each operate in both master and slave modes. For purposes of explanation, the following discussion assumes sighting device310to be a slave device to sighting device350, which is designated as the master device. In this configuration, information would flow in the direction of the arrows illustrated in the Figure.

Orientation sensors312and352provide reference data to their respective processing and control circuits316and356. Since device350is assumed to be the master device, it is thereby also assumed to be oriented on target. Thus, the reference signal of sighting device350, as determined by processes executed in processing and control circuit356, is designated as the reference for both systems350and310. Once processed for transmission by processing and control circuit356, the reference signal is conveyed via communication subsystem354to the counterpart subsystem314of sighting device310. Transmission channel370is shown as bi-directional since information may, in certain embodiments, be permitted to flow in both directions. However, the purpose of the link370is to provide processing and control circuit316with sufficient information so as to determine relative physical orientation of sighting device310to sighting device350. Processing and control circuit316may combine information from orientation sensor312with information communicated over the transmission channel370. Based upon a comparative analysis of the data from orientation sensor312and the reference data provided over the transmission channel370, processing and control circuit316updates a feedback display319in a manner consistent with the discussion above. As previously stated, any mechanism that conveys to the user the direction of aim correction required may be substituted for a visual display. It is also to be noted that the counterpart display359in the master device350is illustrated as being inactive, but it may include active indicators to supply useful information, such as system status. For example, in certain embodiments of the invention, the master device may include an indicator to signal the user thereof when the slave device is aligned with the target object. Obviously, such embodiment would require bidirectional communication capability over transmission channel370, as contemplated above.

As indicated above, certain embodiments of the invention may assume functionally identical components in both the sending and receiving systems so that they may exchange roles easily. However, such implementation is not necessary; certain embodiments of the invention will be implemented through unilateral sighting devices. Additionally, as discussed above, sighting devices need not be necessarily identically constructed to be compatible. In addition to the examples above, it is further contemplated that one sighting device may utilize a different orientation sensor than the sighting device to which it is to be linked. In any system constructed in accordance with the present invention, both master and slave sighting devices need only communicate and recognize, respectively, the reference signal to the extent that a characteristic thereof or information carried thereby can be processed by orientation determining processes executed by processing and control unit of the sighting device designated as the slave device so as to provide alignment feedback to the user thereof at any given time.

Process and control circuits316,356may be implemented in hardware, software or firmware, or a combination of such in accordance with known technologies. For example, process and control circuits316,356may be a general purpose microprocessor known in the art, which may be coupled to a storage system, such as random access memory (RAM) or read-only memory (ROM). In certain dynamic embodiments, a control program implementing aspects of the present invention and executable on the general purpose processor may be stored in ROM and variable data and computational memory may be provided by RAM, where the ROM and RAM are coupled to the general purpose processor by an appropriate bus. Alternatively, process and control circuits316,356may be implemented as an application specific integrated circuit (ASIC) or as a circuit formed from discrete components.

Communication subsystems314,354will vary considerably based on the specifics of transmission channel370. In certain embodiments, either of communication subsystems314,354will include a transmitter and the other subsystem314,354will include a receiver, or both subsystems314,354will include both a transmitter and a receiver. Additionally, communications subsystem may include circuitry to encode and decode data transmitted over the transmission channel370. Exemplary communication modes are demonstrated in the embodiments that follow, but it is to be made clear that any method for communicating the reference information between sighting devices may be used in carrying out the present invention.

In certain embodiments of the invention, the reference signal is divided into various component signals for purposes of conveying sufficient reference information to the slave sighting device. For example, in embodiments described in more detail below, the time-of-flight of a pulse of a modulated waveform requires timing data to be transferred to the slave device. To provide the timing information, the reference signal may be divided into a pulse modulated component, from which the characteristic time-of-flight can be determined, and a data carrying component, which may be used to convey the timing information. The components of the reference signal may be combined and transmitted over a single transmission channel or, alternatively, may be transmitted in separate transmission channels. Such embodiments are useful in implementing the invention when the pulse modulated component is in one form of energy, for example acoustic energy, and the data carrying component is in another form of energy, such as electromagnetic energy. When so embodied, the separate transmission channels may be established in different transmission media, such as air for transmitting the acoustic pulse waveform, and coaxial electrical cable, for transmitting the electromagnetic data carrying component. In any of these and other embodiments, the communication subsystem will include the appropriate means for carrying out the correct transmission of the reference signal over the appropriate number of transmission channels and in the associated transmission media.

Sensors312and352may utilize any number of widely recognized means to establish the orientation of their respective sighting devices. Exemplary means include encoding compasses and levels and micro-electromechanical systems (MEMS). A dual axis inclinometer for measuring pitch and roll, such as is included in an exemplary embodiment described below, can be constructed by placing two linear MEMS accelerometers at right angles in a plane and so that the relative direction of gravity is measured. These devices establish an absolute reference frame with respect to the surface of the earth. Using such sensors, the heading and elevation angle of device350, as measured by sensor352, is decoded by356and may be sent via a transmission channel370to processing and control unit316in the slave device310. Sensor312measures the heading and elevation angle of sighting device310and relays these data to processor316as well. Processing and control unit316then compares the data from each source and determines therefrom the relative correction in bearing required so as to direct sighting device310towards the target object. The aim correction feedback is then passed to the user via display319.

Another exemplary method for determining the orientation of sighting device310,350utilizes known rotational accelerometers as the orientation sensors312,352. Numerous electronically readable means to measure rotational acceleration are well known to those skilled in the art. When the invention is so embodied, sensors312,352convey information at an output thereof regarding the orientation of the respective sighting device310,350on two or more axes of rotation. The rotational information is relayed to respective processing and control units316,356. An initial known alignment of the two devices is required, after which relative changes in the relative bearing of sighting device310,350may be ascertained and integrated in their respective processing and control unit316,356. Changes from the known baseline in device350may be transmitted via a transmission channel370to processing and control unit316of sighting device310. The comparison analysis is conducted and correction information is again passed to the user via display319. Variations of this method include the use of an encoding gyroscope as a reference sensor so as to maintain a fixed frame of reference in one or more of the devices310,350.

As previously stated, a primary object of the present invention is to provide a system by which the lines of sight of independent sighting devices may be mutually aligned toward a common target object. Certain aspects of the methods of alignment discussed above are reliant on the availability of a global frame of reference. The static reference frame system may be useful in certain applications, but may be excessively resource intensive in other applications. Thus, certain embodiments of the present invention avoid the complications of what essentially amounts to maintaining a coordinate system at each sighting device to navigate in the fixed frame of reference by determining orientation of a sighting device via relative reference frames, i.e., one sighting device determines its orientation with respect to another sighting device without first evaluating its orientation in a static, global frame of reference.

To more easily implement certain relative orientation determining methods, an assumption may be made that the users have some mutual knowledge of or have otherwise conveyed an approximate target direction—at least so far as a visual field hemisphere. Thus, embodiments of the invention may be simplified in construction, but remain useful even if they cannot distinguish alignments that are 180 degrees apart. Because gross aim can be achieved by many complimentary means, many embodiments of the present invention are adapted to distinguish fine differences in alignment rather than to distinguish large differences therein. However, many sophisticated embodiments may include means to ensure that all users are aiming their respective sighting devices in the same direction.

Referring toFIG. 4, there is shown fundamental components of an exemplary system for determining relative orientation between sighting devices using electromagnetic radiation of, for example radio frequency (RF). Considering first two sighting devices410and430each having installed thereon an RF antenna412and432, respectively. Each antenna412,430is respectively affixed to a substrate414and434such that the orientation of the antenna with respect to the sighting device is known. With prudently selected antennas, the RF energy490emanates from antenna412linearly polarized relative thereto. By judicious antenna design and choice of reference signal characteristics, the signal strength at receiving antenna432can be made to be proportional to its alignment with transmitting antenna412. Of course, the effectiveness of this technique will depend on the distance between antenna412and antenna432, antenna geometry, and wavelength of the transmitted reference signal in accordance with well-known electromagnetic field theory. The two antennas412,432are substantially aligned when a peak in received signal strength is detected at the receiving sighting device430.

In an alternative embodiment, a plurality of antennas may be arranged on a receiving sighting device, such as is illustrated at device450. As is shown in the Figure, receiving device450includes multiple non-parallel antennas452a–452don a fixed substrate454. The receiving device450determines the relative signal strength impinging on antennas452a–452dto derive a directional adjustment indication. Each antenna in the array will respond according to its relative orientation with the reference antenna412. Those antennas closer to parallel with the reference axis respond slightly stronger than those less well aligned. For example, if the signal were determined to be strongest at antenna352dwhen compared with signal strength at the other antennas, then a rotation of the sighting device450in that direction would be indicated. In the exemplary array shown, directional feedback is derived from two dimensions of rotation by comparing the signal strength at opposing pairs of antennas. Antenna352dis opposed by352b, and hence, in this example, a subtraction of the signal amplitude at one antenna from that of the other will yield a positive or negative result that would dictate rotation in the plane passing through these antennas, either toward352dor toward352b. When signal strength from all four antennas is balanced, the device450is aligned with device410.

It should be noted that where four antennas are shown inFIG. 4, other numbers may be utilized. Additionally, it is to be noted that while the antennas shown in the Figure are illustrated schematically as dark lines showing their primary orientations, it is done so only to be illustrative of the operation of an exemplary embodiment of the invention. Similar schema based on properties of electromagnetic radiation may be applied via mechanisms other than polarity to form the frame of reference. In other operational modes of alignment, phase differences, Doppler shifts and other directionally dependent measures known in the art may replace the simple single strength model described. Automatic direction finding techniques may also be employed and exemplary embodiments of such are discussed below.

In certain embodiments, an antenna472mounted on substrate474may be mounted on moveable gimbals476and controlled by a feedback circuit478as to be operable to seek and align the antenna472with antenna412. The direction required to bring the sighting devices410,470into common orientation toward the target object would be translated from the gimbals feedback circuit478by, for example, processing and control unit316, and displayed on display319.

Certain limitations may be encountered when implementing the RF alignment technique described above. The exemplary systems previously described are reliant on the maintenance of a polarization state of the transmitted signal across the transmission medium. However, the polarity arriving at a receiving device is highly dependent on the path traversed. Intervening obstructions introduced into the path may cause refraction or reflection of the transmitted radiation, thereby destroying the reference information. Weather, trees, buildings, and even the users' body parts may introduce not only shifts in polarity, but other errors in the electromagnetic reference signal. Thus, many embodiments may put into practice techniques known in the art, such as prudent selection of frequency ranges and well-known phase and error correction procedures, to mitigate the effects of such disturbances.

FIG. 5illustrates yet another method for aligning sighting devices. Two optical sighting devices510and550are respectively equipped with a plurality of transmitters512and514and receivers552and554at previously established locations on their physical framework. Each transmitter512,514emits a beam of energy serving as the reference signal transmitted over respective transmission channels. Each reference beam is received by one or more of the receivers552,554. The energy beams560a,560bmay consist of acoustic, ultrasonic, radio frequency, light or any other form of energy that may be transmitted and received in a point-to-point fashion. In the exemplary embodiment illustrated, transmitter512emits a component signal560athat is received by receiver552, while transmitter514emits a component signal560bthat is received by receiver554. Alignment between sighting devices510and550is determined by a distance measurement between each transmitter/receiver pair as either an absolute or relative value. Distance may be determined by a characteristic of the reference signal appropriate to the type of energy beam utilized, including time-of-flight pulse timing and or distributed phase alignment or any by other means known in the art.

For purposes of demonstration, assume transmitters512and514emit energy pulses synchronously and phase-coherently, i.e., zero phase difference, and are received at their respective receivers552and554. The sighting devices510,550are known to be in alignment only when the pulses are received simultaneously and are in phase. If, for example, a pulse arrives at receiver552before it arrives at receiver554, then it is known that the primary receiving aperture of slave sighting device550should be rotated away from that of master sighting device510to align on the selected target.

According to aspects of the invention, the reference signal transmissions need not be simultaneous, and may be multi-directional, and may include encoded data that is not necessary for the distance determination function. It is sufficient for aiming in a spatial plane that path lengths between at least two independent points on each of the master and on the slave sighting devices be determined in the geometry defining the alignment of master and slave devices, such is illustrated in the Figure. These measurements are compared to the expected relative path lengths of the aligned state, for example through coincident arrival at multiple receivers of synchronously transmitted energy pulses. These principles are discussed further below with respect to other embodiments involving alignment in three dimensions and rotation in two axes. It should be emphasized that relative rather than absolute path lengths are utilized because the distance between devices, elevation differences, inclination of a sighting axis and any offset of one user in front or behind the otherare unimportant in establishing parallel alignment of sighting axes, such as when mutually sighting a distant target object. However, the geometric factors in multiple orthogonal spatial planes, such as distance between devices, elevation differences, and offset of one user in front or behind the other, may be determined by similar sensor configurations, but are really only necessary for parallax correction, i.e., when the sighting axes of the sighting devices are not expected to be nearly parallel because the target object is close to one or both sighting devices.

FIG. 6depicts a means of determining relative orientation of a remote slave sighting device by angle of incidence of the reference signal based on observing fixed points on its frame. Transmitters612and614are emissive energy sources mounted on a master sighting device610. Receiving sighting device630includes an entrance aperture appropriate to the energy source, e.g., lens632, and an array of detectors634. The array634may be linear for two-dimensional alignment or planar for alignment in three dimensions. The detector array634may be realized by a charge-coupled device (CCD) known in the art, which are available in both linear and planar configurations. Other simpler arrays may be utilized also, including an array of discrete detectors. Furthermore, whereas the receiver entrance aperture is shown as a single lens632, a lens system having predetermined optical characteristics may be substituted therefor. The receiver entrance aperture may also be void of any refractive element and may simply be implemented by a pinhole. The entrance aperture may also be replaced by a discrete series of waveguides, such as an optical fiber bundle.

In an alternative embodiment, emitters612and614may be replaced by separately distinctive passive elements, such as reflectors, which can be imaged onto the detector array634. In that the elements612and614may interchanged as either active emitters or passive image objects, they will be referred to in the following discussion as master targets, which is not to be confused with the common target object being observed by both users.

The receiving device630determines angles of relative orientation by tracking the master targets612,614across the cells of array detector634. In embodiments where the master targets are passive images, image detection and recognition techniques known in the art may be utilized to track their movements. In embodiments where the master targets are active emitters, each may be identified by their brightness in certain frequency bands or by modulating their respective emissions so that may be identified and decoded by the detector. An exemplary embodiment of the present invention is implemented by infrared diodes as the master targets612and614and phototransistors or a CCD sensor array as detector array634. Each diode612,614may be modulated by respectively unique signatures to that they are distinguishable at the detector634. The sighting devices610and630are aligned on the common target object upon detection of a predetermined condition, such as when the signatures of the diodes612,614are measured as equal in optical intensity at the detector634or in predetermined relative locations on the detector array634.

The number of master targets need not be limited to two. However, at least two physically separated master target points are required to determine relative orientation about an axis. Additional master targets can provide additional geometric information about other dimensions of orientation of the slave device630. If a single master target is used, the device630functions as an incident angle detector and can be utilized as described with reference toFIG. 8B. A linear or planar array detector634will be most accurate when used to determine orientation in axes perpendicular to its imaging plane. Thus, combining optical information with information derived from a model of the physical geometry of the master device610as maintained at the slave device630, allows the slave sighting device630to determine its relative orientation more accurately. Moreover, the depicted mechanism can be combined with time-of-flight or relative phase detection to determine the relative distance of each target point from the sensor. Range may also be triangulated stereoscopically by using multiple sensors on a single frame, or by placing such a sensor on each of the master and slave units and coordinating the data.

Referring toFIG. 7there is shown yet another alignment method for directing a slave sighting device towards a target being viewed by the user of a master sighting device. The master sighting device710is shown approximately focused on target730. It has an energy-radiating device712that emits a tight beam720of energy that impinges the target730. The energy radiated by energy-radiating device712may be optical, such as via a laser or an LED, radio frequency, such as by a radio or microwave transmitter, ultra-sonic, or any other energy that can be directed in a tight beam and be at least partially reflected by the target730. Energy reflected by the target730returns in a scattered fashion, some of which will be directed towards an energy-receiving device752on the slave sighting device750.

Receiver752is configured to determine the relative direction of incidence of the scattered radiation740. This may be accomplished through any one of a variety of techniques known in the art, for example by scanning the area in front of sighting device750with a highly directional receiver. The scanning operation searches for the direction in which a maximum in signal strength is acquired. The determined angle(s) of incidence provides sufficient information to instruct the user of sighting device750to correct his or her aim appropriately. Optionally, the sighting devices710and750can communicate target location information directly over a communication link760. It should be noted that illuminating a target with certain forms of energy may not be desirable in certain applications, thus illustrating the beneficial features of the invention, i.e., that the invention may be implemented utilizing a wide variety of energy forms for the reference signal. Other modes of the invention disclosed herein will be preferable in applications such as stealth observation wherein illuminating a target with energy becomes undesirable.

FIGS. 8A–8Billustrate yet another alignment method, based upon automatic direction finding with respect to a common reference beam. Two sighting devices810and830each contain a means for determining their angle of alignment relative to a common reference beam840. The reference beam840may be conceptualized, and even embodied, as a physical rod or cord stretched tight. In certain useful embodiments, the reference beam840will be implemented by energy radiated from one or both of sighting devices810and830via transmitters812and832, respectively. As in previously described embodiments, the energy beam840may consist of acoustic, ultrasonic, radio frequency, light or any other form of energy that may be transmitted and received in such fashion that its radial direction can be determined.

FIG. 8Billustrates components of a system embodied as that ofFIG. 8A, further abstracted for purposes of description. Angle determining units850and870are respectively located on sighting devices810and830such that angles0and q) can be determined between reference beam840and each of the alignment vectors852and872, respectively. As in previous schematics, the method is only illustrated for a single axis aiming system. To adjust aim on two axes, a second set of angles linearly independent of the first set must be obtained at each end of the beam840. This may be accomplished, for example, by reference to polarization of the energy, by reference to more than one beam, or by other means for multiple axis direction finding known in the art. It may also be accomplished by combining the determination of orientation relative to the reference beam in one plane, such as the plane shown in the Figure, with a determination of relative orientation with an absolute reference, such as an inclinometer, such as to detect sighting axis inclination and/or to compensate for roll, i.e., rotation about the sighting axis.

Angle determining units850and870may be configured to measure change in angle (or rotation) as referenced to the framework of the sighting device810and830, respectively. The angle data is conveyed to whichever sighting device is the slave device for purposes of indicating adjustments in aim to the user via the feedback display discussed above. When the slave device is aligned on the selected target, the sum of angles θ and φ will be π radians (or 180 degrees), less any parallax compensation as discussed below. The total angle may be smaller, in which case parallax compensation is indicated, as discussed below.

Certain embodiments of the present invention may employ omni-directional radio transmissions at either angle determining unit850,870or both, which may be coupled to an automatic direction finding (ADF) device at angle determining unit850or870or both. Such equipment may utilize multi-antenna phase differences, Doppler rotations, narrow beam directional search patterns, or any of a host of other methods well known to those skilled in the art. Similarly omni-directional light, acoustic or other energy may be broadcast and its direction interpreted in similar fashion as that used in the radio frequency energy transmission method.

Other exemplary embodiments may utilize directional beams for reference signal840. For example, a laser coupled with a target feedback system may track angle determining unit850from angle determining unit870, or vice versa. Or a narrow beam radio or optical transmission may also be used, which allows one or both systems850,870to determine angles θ and φ from the transmitting direction rather than receiving direction. Reciprocal systems may also be used, such as electronically steerable antennas, which can serve as both transmit and receive apertures.

Referring toFIG. 9A, there is shown an exemplary configuration for a rotating angle determining unit900. By principles of reciprocity, the unit may be implemented as either a receiver or an emitter, but will be described in an emitting mode. The mechanism900comprises a first omni-directional energy source910, a second energy source920, a mask930or other means for directing the second energy source920through swept angles, and a means for moving the directional mask such as an electric motor935. The mask930may be omitted if the energy source920is collimated, such as in a laser diode. However, omni-directional sources such as light emitting diodes have advantages of low cost and broad availability. Energy sources910,920may be optical, radio frequency, acoustic, or any other detectable energy that may be masked and/or collimated. The device900operates by rotating the mask930about the source920so that it is swept through angles of up to 360 degrees. Energy source910emits an omni-directional energy pulse synchronized with a fixed rotation point of the mask, e.g., zero degrees. A remote detector need only compare the timing of the two apparent pulses in order to determine the angle of emission from the source device900. However, it should be noted that when the unit is operating in the reciprocal mode, i.e., the mask rotates around a detector, the mask may be coupled to a rotational encoder to determine the angle of the arriving signal.

FIG. 9Billustrates the operation of device900more schematically. A receiving device940includes a remote detector945appropriate for the energy emitted by920and910. Transmitter905includes source910, which is shown in the same plane as the930mask arrangement, but only for clear illustration. In certain useful embodiments, the planar configuration would prevent operation in directions that are blocked by the rotating mask930. Hence, the physical configuration of9A is more practical.

In operation, emitter910emits an energy pulse each time the rotating mask passes a fixed radial point. Detector945receives a pulse from source910at regular intervals corresponding to the rotation rate of the detector. Detector945also receives a second pulse from source920every time the mask is oriented with the opening in the mask being in the line of sight with detector945. In certain embodiments, the source910is strobed at a known rate, such as once per interval of time for the mask to complete a single rotation about its axis. For example, the source910may be strobed every time the mask is at a certain point in its rotation, such as zero degrees. The arrival time of the second pulse from source920will then indicate the mask rotational position relative to the predetermined zero-point thereof, which would be known to both receiving device940and transmitting device905.

Other physical configurations of the rotational angle finding device described above will be obvious to those skilled in the art.FIG. 9Cillustrates the use of a rotating reflector970rather than a rotating mask. The emissive energy source is illustrated at950, a reflector or mirror appropriate to the energy type is illustrated at970, and a means for rotation is illustrated at975. Fixed mask960prevents energy from being emitted except onto the reflector970. In certain embodiments,960may also include an internal focusing reflector to increase the efficiency of energy utilization from the emitter950.

Each of these configurations may be implemented with the sources replaced by detectors in the same locations. This alternative embodiment would allow the system to determine angle of incidence. A third embodiment combines sources and detectors to measure both angle of emission and incidence. Additionally, either omni-directional or directional sources or both may be modulated by means known in the art to (a) identify the angle determining unit by a signature or (b) to transfer data between devices. Moreover, rotating masks may also be utilized to scan the angles on more than one axis to achieve multidimensional angle detection.

FIG. 10illustrates a variation on previous alignment methods that utilizes an external fixed reference device. An external reference device1010is located physically removed from both user sighting devices1030and1050. In certain embodiments, external reference device1010will have been previously aligned in a known fashion with a reference vector1012, which may, for example, point north and perpendicular to the surface of the earth. However, any known bearing will suffice for the reference vector1012.

The external reference device1010conveys the reference signal to sighting devices1030and1050via transmitters and/or receivers1032and1052, respectively, utilizing energy beams1060cand1060a, respectively. These beams may be transmitted and received by known means, examples of such are given in the exemplary embodiments described herein. The reference signal1060bbetween devices may also be transmitted according to exemplary embodiments above. As is shown in the figure, a complete triangle is defined and may be used to aid in calculating relative orientation of sighting devices1030,1050. External reference device1010may function as a secondary angle reference per the method described in reference toFIG. 8A–8B. When so embodied, external reference device1010provides not only a second beam to each of1030and1050, but may also provide a reference to a known alignment. Similarly, external reference device1010may be used with any of the previous alignment methods to provide a third, fixed reference point in the system. The external device may also be used to provide stronger and better-calibrated energy sources that may be difficult or impossible to include in handheld units due to size, weight, or power restrictions, or may be undesirable in the mobile units due to stealth requirements. Moreover, an array of two or more external devices may be incorporated in the network to provide more extensive triangulation reference points for the mobile sighting devices. A third device may also be used to provide a fixed time-code reference to aid in calculation of absolute times at two or more independent devices.

Referring toFIGS. 11A–11B, there is illustrated another method for aligning a sighting device. As shown inFIG. 11A, view field1130of the master sighting device is focused on target1120, while the slaved view field1110is misaligned. By utilizing any of a number of well-known image processing techniques, target images are filtered and transformed in such a way that similar reference points1120a–1120c, as shown inFIG. 11B, are consistently established. Exemplary image processing techniques include time-frequency transforms, such as wavelet analysis, and various computational edge and feature abstraction methods. A “feature” is commonly understood in the art to be an identifiable subcomponent of an image. For purposes of implementation in the present invention, features must be selected to be robust to image noise, lighting variations, and parallax related distortions of a particular scene. By facilitating rapid communications between the two units, feature extraction in one unit can be rapidly coupled to feature detection in the second unit. The processing may produce reference points by any means so long as the results are consistent for two reasonably offset views of the same target. Note that the features and reference points may not actually lie on the target per se, but may be extracted from the visual field around the target. In certain embodiments, such a system may also utilize points in a completely different region of space, such as by reference to a prominent fixed point such as the sun, or other bright light or reflection in the environment.

Once target reference points1120a–1120chave been established in both sighting devices by image processing techniques known in the art, certain embodiments compute vectors indicating a direction in which the reference points1120a–1120cmust be translated in the slave view1110from positions in the master view1130, which may be used to provide feedback to adjust the aim of slave sighting device.

The exemplary method just described requires only data communications between units, and the devices need not radiate direction finding or other specialized energy transmissions. However, it will be recognized by those skilled in the art that such image registration procedures are limited by parallax angle, lighting changes, camera variation and other factors. Hence, communication of distance between devices, offsets and relative orientations by means described herein can provide additional information to augment the image processing. The complexity of the signal processing involved with the method illustrated inFIG. 11A–11Bis much greater than that of previous methods and requires a more expensive, complex and power hungry device. Nonetheless, increased precision in identifying very specific target points may justify the tradeoffs.

FIG. 12illustrates schematically the fundamental elements of an exemplary parallax compensation system that may be used in conjunction with certain embodiments of the present invention. Sighting devices1210and1230are shown focused on the common target object1250, with vectors1212and1232respectively indicating the orientation of each device. In accordance with certain embodiments of the invention, each of the distances d1, d2and d3will be known, thus fully defining a triangle from which angles θ and φ may be derived by trigonometric methods. The sum of the angles θ and φ will be less than π radians, which may be used to compensate aiming of the slave unit.

In certain useful embodiments, master sighting device1210includes any of a host of well known range finding mechanisms to determine the distance d3to the target object1250. Similarly, the distance d, between sighting devices1210and1230is determined, such as by techniques previously described. It should be apparent that the distance d2will not be directly measurable until such time as the aim of slave sighting device1230is corrected. However, knowledge of angle (p, as determined by, for example, methods described above, completely defines the triangle and angle θ may be easily calculated using well-known trigonometric formulas. Once angle θ is known, processing and control circuits, such as those previously described, compensate the orientation of the slave sighting device1230and the user thereof will be directed via the feedback display towards the target object1250with greater accuracy.

As previously stated, in many applications, sighting devices will operate at a large distance from their target and distances d2and d3will be much larger than separation distance d1. If the ratio d3/d1(or d2/d1) is sufficiently large, very little need for parallax compensation will exist and the system can operate within certain design limits while safely omitting it. Some embodiments of the invention may also partially compensate for parallax by fixing an estimate of typical operating range d3and utilizing only the distance between sighting devices d1to adjust angles θ and φ. Some slightly more advanced embodiments will estimate distance d3by encoding focal distance as set by the user, by, for example, sensing the position of a focusing thumbwheel or knob, or by entering a best guess with some other input means. Higher magnification and/or narrower fields of view will require better and more accurate parallax compensation known in the art.

Referring toFIG. 13, there is shown two sighting devices1310and1330, electrically coupled through data line1350. Data line1350may be used, in certain embodiments of the invention, to implement a transmission channel to convey timing information so that the devices1310,1330can determine absolute distances between reference signal emitter/receiver pairs. Data line1450may be replaced with a radio frequency or optical link to compliment slower reference signal links used to calculate distance. For example, an ultrasonic pulse may be transmitted in one transmission channel to be used for providing the characteristic of the reference signal, i.e., time-of-flight of a pulse, with a radio or optical transmission channel used for convey reference timing information. Since the speed of light is much greater than the speed of sound, the difference in arrival times can be used to reliably measure the sonic time-of-fight with sufficient accuracy to measure the distances for the purposes of certain embodiments of the present invention. In the exemplary configuration shown in the Figure, the reference signal link, whether the transmission channel is by cable, or by an electromagnetic signal in air, ultrasonic pulses may also be simultaneously transmitted by both devices without interfering one with the other and respective arrival times thereof can be accurately timed by the opposing sighting device.

The sighting devices1310,1330are configured to be used in an approximately side-by-side arrangement. Each device has an emitter on one side of the primary sighting axis and a physically separated receiver on the opposite side of the primary sighting axis. They are arranged such that the distances d1and d2can be determined via energy propagation along the illustrated paths. The emitter/receiver pairs are so organized to resolve the relative (left/right) positions of the devices by determining which receiver detects the incoming reference signal.

Using the illustrated example of a cable transmission channel for transmitting a data carrying component of the reference signal and an air transmission channel for conveying the pulse modulated ultrasonic waveform for conveying a measurable reference characteristic, i.e., time-of-flight distance measurement, operation of the exemplary embodiment is now described. When the system is activated, pulses are emitted by sources1312and1334at regular intervals. The pulses may be emitted sequentially, simultaneously, or in any reasonable pattern since they will not interfere in flight. Coincident with each pulse emission, a timer is started. When the pulse wave front reaches the opposing sensor, the timer state information is communicated via the data carrying transmission channel and the timer is stopped. By timing the traversal time from transmitter1312to receiver1332(distance d1) as well as the transversal time from transmitter1334to receiver1314(distance d2), the distances d1and d2are determined and convergence or divergence in the illustrated spatial plane of the sighting axes of the devices can be determined. Timing and control circuits can be installed in either or both of devices1310and1330, or may be located in a separate control chassis of the system (not shown). Further details of exemplary filtering and display update are described below with reference toFIG. 14. As mentioned above, the implementation of the transmission channel in a wire cable can be replaced by a wireless electromagnetic transmission with no substantial change in operation other than the timing data communications modality.

Only one dimension of alignment is illustrated inFIG. 13. Additional planes of orientation may be added by utilizing other detection means on orthogonal axes, such as by inclinometers, or by placing additional sensors displaced in other axes, as will be discussed below.

Many of the embodiments as yet described have been limited in their implementations, for purposes of illustration, to two-dimensional adjustment, i.e., the sighting devices operating in a single plane. For example, the exemplary embodiment illustrated inFIG. 5is shown with two transmitters and two receivers to illustrate a simple alignment system in one plane according to the present invention. In order to adjust aim along two axes, the system must contain at least three points on at least one of the optical sighting devices. Note that each physically separated point must be at a known location relative to the others on the same device. Details are now provided as to embodiments that are fully operational in three-dimensional space.

InFIG. 14, two optical sighting devices1410and1430, are abstracted to reveal their primary alignment characteristics. Each sighting device is situated with respect to its own set of X, Y, and Z-axes, with the Y-axis of each coordinate system aligned with its respective primary sighting axis. To resolve orientation differences, the required relative rotation about X, rotation about Y, and rotation about Z for each device is determined, as are the separation distance d1and elevation offset d3between the devices (or alternatively, the shortest path d2), and the target range R. Rotations about Z correspond to convergence/divergence of the Y-axis, i.e. sighting axes, on the target1450. Rotations about X correspond to declination (or pitch angle) and rotations about Y correspond to roll angle. Target range is used in conjunction with offset and separation to correct for parallax. Not shown is offset in the Y-axis, which also factors into parallax in case users are not at similar distances to the target.

Referring now toFIG. 15A, there is schematically shown two sighting devices1510and1530. Device1510has disposed thereon emitters1512and1514that transmits a reference signal in one reference plane to an opposing pair of receivers1532and1534. Receivers1532,1534are physically separated by a distance a along the primary optical axis of the sighting device1530, as are, for purposes of simplicity, the emitters1512,1534. Obviously, the emitters may be separated by a different distance. The distances d1and d3are the minimum distances along a path from emitter1512to receivers1532and1534, respectively, and distances d4and d2are the minimum distances from emitter1514to receivers1532and1534, respectively.

FIG. 105Billustrates the devices ofFIG. 15Aas viewed from the ends thereof, i.e., parallel to the primary sighting axes. The emitter1512is shown on the side of sighting device1510as an alternative arrangement to the top mounted position shown inFIG. 105A. It should be clear that a similar arrangement would be viewed from the other end of the sighting devices, with emitter1514shown where emitter1512is shown inFIG. 15B. The following description will be made with respect to emitter1512, while forgoing a parallel description of the view from the opposing end of the sighting devices.

As shown inFIG. 15B, two receivers1536and1538are physically separated by a distance b along an axis perpendicular to the primary sighting axis of the device. The distances d5and d6are the minimum paths from emitter1512to receivers1538and1536, respectively. The dashed image1510′ of sighting device1510refers to displacement of the primary optical axis of sighting device1510below that of sighting device1530, which will be referred to hereinafter as “elevation offset.”

FIGS. 15A and 15Billustrate a configuration in two planar views. As such, certain sensors enumerated in one view may be collocated with a sensor enumerated in the other view, e.g., element1534and1538may be embodied in a single receiving element. It should be apparent to those with skill in the art that alignment in three dimensions may be achieved via the configuration of sensors shown in the Figures. The distances a and b are peculiar to a particular sighting device and are known. The distances d1–d6are variable and may be acquired by means previously discussed. Alignment is achieved when a known relationship between distances d1–d6is obtained through relative orientations of the devices1510,1530.

The separation of sensors shown may be achieved with only three (rather than four) receivers are arranged in a triangle in the vertical plane. Conversely, additional receivers and emitters may be added to enhance information and field coverage around the device. One natural configuration would be to arrange emitters and receivers to cover left and right visual hemispheres around each device. Such implementation would allow the determination relative placement of the devices with respect to “handedness”, i.e., which device is to the left or right of the other. As will be shown, such knowledge is useful in updating the guidance display so as to properly correct the alignment. Additionally, the information from the detectors1532–1538may be combined with information acquired from other sources to provide further accuracy.

Among its beneficial features, the present invention can determine an offset in elevation between master and slave devices and correcting therewith the orientation of the slave device accordingly. An exemplary elevation offset correction is explained with reference toFIG. 15B, which shows the master device1510, on the right, and the slave device1530, on the left, in the direction of the sighting axes, i.e., the sighting axis of each device, which are assumed to be parallel for purposes of illustration, is perpendicular to the drawing page. It is now assumed that each device is equipped with means to detect rotation about its respective sighting axis, which is referred to herein as “roll”. In certain embodiments of the invention, roll detection may be accomplished by installing a gravity sensitive accelerometer, or inclinometer, in the appropriate orientation with respect to the sighting device. The output of the inclinometer may be processed in the orientation process executing on the processing and control unit of each device and the distances between devices can be calculate so as to account for sighting device roll.

An exemplary elevation offset determination is apparent fromFIG. 15B. When the slave sighting device1510is lowered in elevation to its location at1510′, the path lengths of d5and d6become longer. This path difference may be detected by any of the means previously described, such as by a phase differential or by time-of-flight timing. The elevation offset may be compensated for by, for example, transmitting the master device roll as indicated by the inclinometer over a transmission channel to the slave device. The slave device, in turn, determines its own roll, and the correct distances, d′5and d′6. Once the elevation offset has been determined, the user of the slave device, through the visual display previously described, may be directed to rotate the sighting device in the appropriate direction, which in the case ofFIG. 15B, would be by rotating the distal end of the slave device at1510′ upward.

Of course, there are other means for determining elevation offset. For example, if the sighting devices were equipped with an altimeter or provided with altitude information from some other source, such as through a Global Positioning Satellite (GPS) receiver, the aiming direction of the slave sighting device could be compensated in the Z-Axis ofFIG. 14when mutual viewing in a common plane is not possible. In certain applications, such as when the GPS data is already available for use in other systems, such configuration may be preferred over

In certain embodiments of the invention, operational modes may be combined so that absolute distances d1–d4are determined as illustrated inFIG. 13, while relative distances d5and d6are determined by phase or time-of-flight differences. Thus, one complete multi-plane embodiment will include emitter/receiver pairs as illustrated inFIG. 13on both upper and lower portions of the device. This configuration will permit operation of the system without an absolute reference such as a gravity-reference inclinometer, since the relative offset of front and rear of the primary optical axis can be determined. However, since the distance d5and d6also change with roll about the respective sighting axis of each device, an inclinometer adapted to track a fixed reference orientation, such as level with the horizon, may stabilize measurements of elevation offset.

InFIG. 16, there are shown fundamental method steps of certain embodiments of the present invention via a flow diagram. The exemplary method illustrated details operation of a multi-sensor embodiment of the present invention. The exemplary embodiment may utilize ultrasonic or other energy sources such as infrared emitters or radio frequency transmitters known in the art. It may utilize collimated energy such as generated by a laser, but such is not necessary since the exemplary embodiment relies on relative timing and phase information rather than angle of emission or incidence.

The exemplary embodiment demonstrated inFIG. 16includes two sighting devices, assumed in this example to be identical. Physical configuration of each device will include at least one emitter at a known location thereon, and at least one receiver at a known location thereon. The exemplary method conforms to the physical arrangement described with respect toFIG. 15, in which at least two receivers are physically separated along the primary sighting axis and two receivers are separately positioned along the axis perpendicular to the primary sighting axis. There is a minimum of three receivers on each device. The receivers may be physically combined with emitters in some embodiments, for example ultrasonic transducers and radio frequency antennas may be operated in either transmit of receive modes, by principle of reciprocity. The exemplary embodiment includes two emitters physically separated along the optical axis of the device1510. This facilitates determination of distances d1and d2directly and simplifies operations. Of course, other emitter configurations are clearly possible and are within the scope of the present invention as long as the relationship between d, and d2is calculable therefrom. Additional receivers and emitters will be located on the device frames to increase energy dispersion and reception fields as appropriate to the application. It is to be noted that the display update process described below requires knowledge as to which device is on the left and which is on the right relative to the direction of view. This can be determined by, for example, using the hemi-field configuration discussed with reference toFIG. 13.

The exemplary operation demonstrated inFIG. 16assumes the units are symmetrical with emitters collocated with the receivers. For example, inFIG. 15A, sighting device1510is shown as transmitting with emitters1512and1514and unit1530is shown as receiving with receivers1532and1530. It should be clear that the operation of the transducers would be reversed when sighting device1530is transmitting. Collocation is achieved by using bi-directional devices, or transceivers, such as ultrasonic transducers and radio frequency antennas. Alternatively, transmitters and receivers may be placed substantially at the same point on the frame, such as an LED adjacent to a photodiode.

Knowledge of distances d1and d2is sufficient to determine divergence or convergence of the sighting axes within the plane of the Figure. The present invention does not strictly require that distances d3and d4be determined. It should be apparent to those skilled in the art, however, that these additional distances provide both a means for determining front-to-back offset of the observers and a means of improving the estimates of divergence for parallax correction.

In the exemplary embodiment, no physical connection is assumed between devices. communication may be carried out by modulating the emissive energy source providing the reference signal. However, the use of a cable is not excluded. It is within the scope of the invention to utilize a cable for data transmission and to transmit the characteristic portions of the reference signal in a separate channel for alignment purposes.

In the exemplary physical configuration, inclinometers, such as gravity sensitive accelerometers, are utilized to determine rotations in pitch and roll relative to gravity according to the geometry described with reference toFIG. 14. A two-axis accelerometer oriented in the X-Y plane of each sighting device1510and1530are operable to indicate a value proportional to rotation about Y (roll) and about X (pitch, or declination.) It should be noted that these inclinometers do not require a fixed tripod reference.

Referring now toFIG. 16, operation of each sighting device begins in a wait loop, illustrated at1605. Previous activity of the device may have placed display data on the feedback display. After a predetermined timeout period, if no activity is detected, flow is transferred to1670to clear any existing information on the display. Depressing a switch on a sighting device activates that device in the Master Mode and is thereafter referred to as the “Master Device”. A conflict may arise when both devices attempt to become the Master, and is resolved by “time out” exits later in the process under the assumption that one of the users will eventually release the switch and yield.

The Master Device transmits a start/ID code as shown at1610. The receiving sighting device receives the start code and is placed into Slave Mode, where it becomes the “Slave Device”. Method steps executed by the Master Device are shown on the left side of the flow diagram and those executed by the Slave Device are shown on the right side of the diagram.

The Slave Device changes state, as illustrated at1613, to wait for a ranging pulse from the Master. The Master Device sends the ranging pulse at block1615and starts a timer at block1620. Upon receipt of the ranging pulse, the Slave Device sends a return ranging pulse at1618and starts its own timer at1623. Both devices wait for respective return pulses, at block1625for the Master and at block1628for the Slave, which may overlap in time since time-of-flight between the devices is finite and assumed to be on a longer time scale than is measured by the timer. If either the Master or the Slave device fails to detect a return pulse in predetermined period of time, that device times out and returns to wait mode at block1605.

When a return pulse is detected by the Master Device, the timer is stopped, as shown at block1630and a second ranging pulse is sent to the Slave Device. The second pulse is followed by at least two pieces of data, as shown at block1640: the round trip elapsed time T1and the inclination in the primary axis of the Master device IncX, as measured by the inclinometer.

The Slave Device receives the return pulse at block1628, stops its timer at block1633and stores the round trip time of its ranging pulse together as well as phase information of the return for each receiver element. The relative time-of-flight and phase information will be utilized to calculate relative orientation based on the physical geometry of the emitters and receivers. The Slave Device also receives the data transmitted from the Master, as shown at block1643. The Slave Device calculates mean round-trip time at block1648by averaging the respective timer values of each sighting device. Each timer value can be converted directly to an estimate of inter-device distance by multiplying with the speed of the energy transmission and dividing by two.

In certain embodiments of the invention, the incoming range data will generally be filtered to screen out false returns. Typically, the first pulse (minimum time) of a series is used since additional pulses may be environmental reflections. Moreover, reasonable distances may be used to window the range of times and screen out near-field back scattering of one device's emitter into its own detector. Pulse time windows may also be set dynamically based on prior knowledge of previously sampled positions. Minimum and windowed data will also be averaged in order to smooth random variations due to sampling error, vibration, and quantization. Inclinometer information will be similarly smoothed so that a relatively stable mean inclination is utilized in calculations. Additionally, human reaction time may be considered and the directional indicators should provide stable, averaged information to the user. For example, sampling on the order of 10 times per second and averaging over ten such samples (1 second) for each update of the indicator display provides a stable feedback display for a typical handheld consumer optical device. However, these figures will vary widely with application and magnification settings.

Referring once again toFIGS. 15A–15B, assume for purposes of illustration that sighting device1510is the Master Device. The transducers may operate in the following sequence. A first ranging pulse (block1615) is emitted by transducer1512. Transducer1532receives the pulse (block1613) and after a known delay, sighting device1530transmits a ranging pulse (block1618) back to the master using transducer1532as an emitter. When this ranging pulse is received at transducer1512, (block1625) the Master's timer has measured twice the time-of-flight for the distance d, plus a constant value taking into account the processing delay between receiving and recognizing a pulse and sending one out as a response thereto. The second ranging pulse is transmitted (block1635) using transducer1514as an emitter. This pulse is received (block1628) by transducer1534on sighting device1530causing the Slave's timer to stop (block1633). The Slave's timer now has measured the time-of-flight for d1+d2, again plus a known constant. The Master sends (block1640) and the Slave receives (block1643) time and inclination data. The mean distance along the leg d1is calculated by subtracting any known constant delays from the Master timer data and dividing by two. The distance along leg d2is calculated by subtracting the d1time value from the slave timer measurement along with any known constant delays. The distances may be converted to a physical length using the speed of the energy medium in some embodiments or the time value may be utilized directly for simple comparison operations.

The relative angle of orientation in the plane ofFIG. 15Ais determined by the values of d1and d2and the inter-sensor distances a. The distances d3and d4are calculated in some embodiments and may be utilized to cross check this primary orientation information, as well as to measure offset between the users front-to-back along the optical axis. The difference in lengths d5and d6combined with the fixed base of the triangle defined by inter-sensor distance b determine the vertical (z-axis) offset of the devices as depicted inFIG. 15B. Roll inclination IncY can be used to fix relative interior angles, and pitch incline IncX to correct for twist in the triangle frame. The distance calculations are performed at block1653.

In the exemplary embodiment, relative inclination can be determined simply by exchanging inclination information as measured by gravitationally sensitive accelerometers. The reference signal transmitted as the energy pulse adds the additional information necessary to determine divergence and convergence and optical axis horizontal separation and vertical offset. This is a specific improvement over prior art that offered no means for achieving these measures in an arbitrary setting.

The Slave Device further corrects its calculations for parallax in two dimensions, as shown at block1658. The sighting axis offset is used to adjust the relative inclination information. The inter-device distance is utilized to adjust the relative convergence/divergence information. The front-to-back offset along the optical axis may be determined from d3and d4(if available) may be used to further correct for parallax. As previously discussed, the range of the target enters into these calculations and may be determined in a host of well-known ways including by determining focal distance, or by direct ranging or in simpler embodiments, may be approximated with a preset typical value.

The Slave Device updates its display, as shown at block1663, according to a process similar to the exemplary process discussed in paragraphs that follow. Slave Device flow is transferred to block1605, where the device enters a wait state. Meanwhile, the Master Device enters a predetermined delay shown at block1645. The delay period is made long enough to allow all calculations and display updates in the Slave Device. The Master then enters the wait state at block1605. If the switch remains depressed, then the process repeats with the same Master and Slave devices until the switch is eventually released.

Variations of the exemplary method are within the scope of the invention. By introducing a fixed timing reference, such as might be provided by a time-locked external signal, such as GPS, or by an electrical coordination signal, such as via a physical cable), it is possible to determine one-way transit times rather than round-trip times. Hence, embodiments of the invention with a common time source may calculate distance from the transmitter of one device to the receiver of the other directly and compare absolute values rather than compare indirectly calculated information.

FIG. 17illustrates an exemplary method for handling the information for display update. Upon entry at block1710, it is assumed that relative angle in yaw and pitch of the primary sighting axis have been determined and correction for any offset or parallax has been applied as appropriate. In block1715, the relative angle is compared to determine the convergence or divergence of the optical axis in the horizontal plane (yaw). If divergence is detected, then the relative locations of the two devices are determined at block1720. If the Slave Device determines that the reference signal is arriving on its left, then a rotation to the right is indicated in the display, as shown at block1730. If the positions of the Master and Slave devices are reversed, then an indication to rotate left is provided in the display, as shown at1735. In similar fashion, if the units are converging then the relative locations of the devices, as determined at block1725, is used to indicate the rotation in alignment in an opposite manner, as shown at blocks1740and1745. If the sighting axes of both devices are aligned with the target, and the applicable data corrections have been applied, an indication of centered is displayed, as shown at block1750.

A similar process is used to compare the units in the vertical plane (pitch). First, it is assumed that the inclination of the Slave Device and the inclination of the Master Device have been determined. The relative angles are simply compared and indications are displayed to rotate up, at block1760, down, at block1765, or centered, at block1770. The process then ends at block1775and flow is transferred to the calling routine.

The descriptions above are intended to illustrate possible implementations of the present invention and are not intended to be restrictive. Many variations, modifications and alternatives will become apparent to the skilled artisan upon review of this disclosure. For example, components equivalent to those shown and described may be substituted therefor, elements and methods individually described may be combined, and elements described as discrete may be distributed across many components. The scope of the invention should therefore be determined with reference to the description above, but with reference to the appended claims, along with their full range of equivalents.