Compact wedge prism beam steering

A beam steering device includes a housing and a transceiver that emits and receives light beams through at least one opening in the housing. A rotator includes a cylindrical body rotatably mounted within the housing axially between the transceiver and the at least one opening. A wedge-shaped prism is secured within the body and includes a first surface extending perpendicular to the axis and a second surface extending transverse to the axis. An encoder member and a drive member are provided on an outer surface of the body. Sensors are mounted to the housing to sense the encoder member and provide an encoder signal indicative of a rotational position of the prism about the axis. At least one drive element is mounted to the housing and applies force to the drive member to rotate the body and prism about the axis for steering light beams propagating through the prism.

TECHNICAL FIELD

This disclosure relates generally to a LIDAR device and, in particular, relates to a compact beam steering system.

BACKGROUND

Laser technology can be used where it is desirable to determine the distance between two points. For example, LIDAR is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light returning from the target. This technology is useful in certain automotive and gaming applications, among others. In some LIDAR systems, one or more laser sources are positioned in a housing that rotates over a prescribed angle to obtain measurements within a desired field of view. A prism is associated with each laser source and multiple lasers are stacked atop one another, as are the accompanying prisms. Multiple photodetectors receive and process the incoming light reflected from the target. This configuration requires a lot of parts and is therefore bulky, costly, and prone to breakdown.

SUMMARY

This disclosure relates generally to beam steering, and specifically to a compact wedge prism beam steering device and method for optical beam steering.

One example provides a beam steering device that includes a housing having at least one opening at an end. A transceiver emits and receives light beams through the at least one opening. A rotator includes a cylindrical body rotatably mounted within the housing axially between the transceiver and the at least one opening. The body extends along an axis and defines a central passage therethrough. A wedge-shaped prism is secured to the body within the central passage and includes a first surface extending perpendicular to the axis and a second surface extending transverse to the axis. An encoder member and a drive member are provided on an outer surface of the body. An encoder sensor is mounted to the housing to sense the encoder member and provide an encoder signal indicative of a rotational position of the prism about the axis and an index signal as an absolute position reference. A drive element is mounted to the housing and arranged to apply motive force to the drive member to rotate the body and prism about the axis for steering a beam of light propagating through the prism.

Another example provides a beam steering device having a housing with at least one opening at an end. A transceiver emits and receives light beams through the at least one opening. A pair of wedge elements each includes a cylindrical body rotatably mounted within the housing. The body extends along an axis and defines a central passage therethrough. A wedge-shaped prism is secured to the body within the central passage. The prism has a first surface extending perpendicular to the axis and a second surface extending transverse to the axis. An encoder member and drive member are provided on an outer surface of the body. An encoder sensor is mounted to the housing to sense the encoder member and provide an encoder signal indicative of a rotational position of the prism about the axis and an index signal as an absolute position reference. A drive element are mounted to the housing and arranged to apply motive force to the drive member to rotate the body and prism about the axis for steering a beam of light propagating through the prism. The prisms are individually rotatable to steer beams through the housing and are free from radial overlap with each other relative to the centerline of the housing.

Yet another example provides a method for steering a beam that includes rotatably mounting a pair of wedge elements inside a housing. Each wedge element includes a cylindrical body extending along an axis and defining a central passage. A wedge-shaped prism is secured to the body within the central passage. The prism has a first surface extending perpendicular to the axis and a second surface extending transverse to the axis. A drive member and an encoder member are provided on an outer surface of the body. Drive elements are secured to the housing for rotating the prisms about the axis. Sensors are secured to the housing for sensing the rotational position of the prism about the axes. Light beams are emitted from a transceiver through both prisms. The prisms are rotated relative to the housing with the drive elements while simultaneously monitoring the position of the prisms with the sensors to steer the beam from the light source through the prisms. Reflected light is received at the transceiver from an object external to the housing.

DETAILED DESCRIPTION

This disclosure relates generally to a LIDAR device and, in particular, relates to a compact beam system.FIGS. 1-2illustrate an example of a beam steering device16that emits and receives laser light to determine distances to objects spaced from the device. The beam steering device16includes a housing20extending along a centerline (central longitudinal axis)22from a first end24to a second end26. The housing20could be a cast or extruded part. A sidewall28of the housing20defines a passage or cavity30extending along the centerline22from an opening40in the second end26towards the first end24. A lens42is secured to the second end24within the opening40. In one example (seeFIG. 5), the lens42includes a planar surface44facing the passage30and a non-planar surface46facing outward. Other lens configurations could be utilized depending on the application requirements for the directing light with respect to the housing20.

The passage30terminates at an end wall32at the first end24of the housing20. An interior wall50extends parallel to the end wall32and through the passage30. An opening52extends through the interior wall50along the centerline22. The opening52receives a monolithic LIDAR transceiver60adjacent the first end24. The transceiver60is configured to both emit and receive laser light (e.g., including a laser light source and a photodetector) along the centerline22. The transceiver60is electrically connected to one or more interface boards (e.g., printed circuit boards)70provided in the passage30between the interior wall50and the end wall32. The interface boards70are electrically connected to a data port/power connection80extending through the end wall32. The interface boards70can include control electronics to operate the transceiver60according to application requirements.

In the example ofFIGS. 1 and 2, a collimating lens64is also provided in the opening52along the centerline22between the transceiver60and the lens42. The lens64includes a planar first surface65(seeFIG. 5) extending perpendicular to the centerline22and facing the transceiver60. A second surface66is curved outward towards the wedge elements100. Each of the first and second surfaces65,66can alternatively be planar, arcuate, conical, hemispherical or any other known lens shape.

A plurality of rotators or wedge elements100are positioned in the passage30between the lens42and the transceiver60for steering laser beams emitted by the transceiver. As shown in the example ofFIG. 2, a pair of wedge elements100are rotatably mounted in the passage30coaxially along the centerline22.

One example wedge element100is illustrated inFIGS. 3-4. The wedge element100includes a cylindrical body110that extends along an axis112from a first end114to a second end116. The body110includes an inner sidewall surface118that defines a passage120extending along the axis112entirely through the body110. The body110also includes a radially outer surface122extending about the axis112to define the circumference of the body.

The wedge element100includes a drive member130and an encoder member140provided on the outer surface112and extending around the entire circumference of the body110. The drive member130is positioned near the longitudinal center of the wedge element100and is used to help rotate the wedge element about the axis112. To this end, the drive member130can constitute a series of radially extending teeth132formed into the outer surface122of the body110. Alternatively, the drive member130can constitute a magnetic strip with alternating north and south poles secured to or embedded in the outer surface122. Additionally, one of the poles is extended longitudinally to form an index track which serves as an absolute position indicator.

An encoder member140is positioned at the second end116of the body110and helps determine and track the rotational position of the wedge element100about the axis112. To this end, the encoder member140can constitute a magnetic strip secured to or embedded in the outer surface122. In this construction, the encoder member140includes two tracks: an index track with either a north or south pole on the outer radius of the magnetic strip and a incremental track constituting a series of alternating magnets142a,142bphased 180° from one another. The index track is needed to provide an absolute reference position and generates one pulse per revolution (PPR) whereas the incremental track generates NpPPR, where Npis the number of poles along the strip circumference. Alternatively, the encoder member140can constitute a series of radially extending teeth formed into the outer surface122of the body110(not shown). To form two tracks in this case, one of the teeth would be extended longitudinally to create an index track.

While the example ofFIGS. 3-4depicts separate encoder and drive members140and130, in other examples, the encoder member and the driver member can be implemented on the body110as a common structure (e.g., an annular array of alternating magnetic poles or teeth). Corresponding sensing and driving elements would thus be mounted in the associated housing20for sensing rotation and position thereof and for driving the wedge element about its axis.

Referring toFIG. 4, a wedge-shaped prism180is provided in the passage120of the body110and is secured to the inner surface118. The prism180includes a first surface182and a second surface184. Each of the first and second surfaces182,184can be planar, arcuate, conical, hemispherical or any other known prism180shape. As shown, both of the surfaces182,184are planar. The first and second surfaces182,184extend at an angle1relative to one another.

The prism180can be secured to the inner surface118in a variety of ways. For example, as illustrated inFIG. 4, the prism180can be threaded to the inner surface118, indicated at111. Alternatively of additionally, the prism180can be retained in a recess formed in the inner surface by a retaining ring, set screw or adhesive (not shown). Regardless, the prism180is secured to the body110so as to be rotatable therewith. In any case, the prism180is oriented within the passage120such that the first surface182extends perpendicular to the axis112and the second surface184extends transverse to the axis. The first surface182can be positioned either at the first end114of the body110(as shown) or at the second end116(not shown). The second surface184is oriented at an angle φ with respect to the first surface182. While demonstrated as a planar surfaces, in other examples, one or both such surfaces182or184could be curved (e.g., concave or convex).

As shown in the example ofFIG. 5, a drive element104cooperates with the drive member130to rotate the wedge element100about the axis112in the direction indicated generally by the arrow R. In this example, the drive element104constitutes a motor that includes a gear106that engages the teeth132on the drive member130for rotating the wedge element100about the axis112. The drive element104can be designed to rotate the wedge element100in only one direction R about the axis112or in both directions about the axis. In an alternative example construction when the drive member130is a magnetic strip with alternating poles (in place of teeth132), the drive elements104constitute a plurality of drive coils arranged about the circumference of the wedge element100secured to the sidewall28radially outward of the drive member (not shown). Typically, the drive coils would be wound around a bonded ferromagnetic lamination stack which would have poles and a backiron to efficiency “conduct” the stator flux. In some examples, two or more drive coils can be used to start reliable rotation in a given direction. In other examples, three or more drive coils can be used to enable starting reliable rotation in both the clockwise and counterclockwise directions.

While the examples disclosed herein describe the drive elements104and drive members130as constituting motors that include permanent magnets or teeth on their rotors, other types of motors could be utilized. For example, motors could be implemented as switched reluctance motors or brushless DC motors. In such alternative examples, the encoder sensor and controls would be appropriately modified to operate the motors accordingly.

FIGS. 6A and 6Bdepict examples configurations of encoder sensors that can be utilized. In the example ofFIGS. 6A-6B, at least three sensors170are secured to the sidewall28within the cavity30and cooperate with the encoder member (e.g., teeth or poles)140to sense the rotational position of the wedge element100about the axis112. In one example, the encoder member140acts as an encoder track to carry a code that is detected by sensors170for providing incremental and/or absolute position encoding of the wedge element100.

When the encoder member140is a magnetic strip, for example, the sensors170are configured to detect magnetic poles arranged about the circumference of the wedge element100. The magnetic sensors170can be, for example, a magneto-resistive or Hall Effect sensor. As shown inFIG. 6A, three sensors170(Sa, Sb, and Siconfigured ½ a pole pitch apart from one another, with Sicoinciding with Sa) are provided that are symmetrically spaced about the circumference of the wedge element100. Alternatively, the sensors170can be asymmetrically spaced (FIG. 6B) about the circumference of the wedge element100. As another example, when the encoder member140is formed from teeth, the sensors170are inductive sensors (not shown) that track tooth movement to determine the rotational position of the wedge element100about the axis112. In any case, although three sensors170are illustrated in this example, in other examples, more or fewer sensors can be implemented to sense the rotational position of the wedge element100.

It will be appreciated that although separate members130,140are shown the members130,140could alternatively be formed as a single element secured to or formed integrally with the body110. In this construction, the single element could have a collective width equal to the width of the drive and encoder members130,140along the length of the body110. The single element need only be wide enough in the direction of the axis112to allow both the drive element104and sensors170to simultaneously interact with the encoder member.

Referring back toFIG. 5, the pair of wedge elements100are rotatably mounted in the passage30with the axes112of the bodies110being coaxial with the centerline22, i.e., the wedge elements are axially aligned along the centerline. The wedge elements100are also spaced entirely from one another in both the axial and radial directions along the centerline22. No portion of one wedge element100radially overlaps a portion of the other wedge element100. In other words, both ends24,26of the rightmost wedge element100(as shown inFIG. 5) are positioned closer to the opening40than both ends24,26of the leftmost wedge element100. The wedge elements100therefore do not rotate within one another in use.

An idler gear216is provided radially between the sidewall28of the housing20and the teeth232diametrically opposed to the gear106. This ensures that the wedge elements100are adequately centered and supported for rotation in the housing20. The drive element104and gear106positioned radially outward of each wedge element100are secured to the sidewall28for rotating the wedge elements100about the axes112. The wedge elements100can be rotated separately, simultaneously, in the same direction and/or in opposite directions. It will be appreciated that one or more additional idler gears216can be provided anywhere along the circumference of each body110and radially aligned with the teeth232on that body to help support the wedge element100.

In operation, beam light from the transceiver60passes through the lens64, through the prisms180, and out of the opening40through the lens42. After the light beams strike the target object(s), the light is collimated through the lens42, passes through the prisms180, through the lens64, and ultimately reaches a photodector of the transceiver60, where it is collected and processed.

The drive elements104positioned about each wedge element100can be actuated/energized by a computer (not shown) in order to rotate one or both wedge elements about the axes112and centerline22in the direction R. This results in rotation of the prisms180in the direction R, which changes the orientation of one or both second surfaces184on the prisms180relative to the beam path through the housing20. The first surfaces182remain perpendicular to the centerline22regardless of the rotational position of the prisms180. The prisms180can be rotated to a number of different positions relative to each other sufficient to generate a field of view for the beam steering device16, illustrated by the cone190inFIG. 5. In one instance, the cone190extends over an angle α1of about 20°. The beam steering device16can therefore capture and measure objects within the viewing cone190.

Rotating each wedge element100about the axis can vary the relative angle of the second surfaces184to adjust the angle at which the laser light exits the respective wedge element. The wedge elements100can be rotated in any desired manner, e.g., individually, simultaneously, in the same direction, in opposite directions, etc., to achieve the desired light trajectory. Rotating one wedge element100in relation to the other will change the direction of the beam. When the prisms180angle in the same direction, the angle of the refracted beam becomes greater. When the prisms180are rotated in the direction R to angle in opposite directions, they cancel each other out, and the beam is allowed to pass straight through the prisms in a direction extending along/parallel to the centerline22. During rotation, the axially aligned orientation of the wedge elements100results in the first or leftmost prism180directing the light from the transceiver60along one axis and the second or rightmost prism180directing the light from the transceiver along another axis. Consequently, the multiple wedge elements100produce a two-dimensional scanning pattern.

The gear106,216between the housing20and each wedge element100can help stabilize and center the wedge element during rotation in the direction R to prevent inaccurate positioning thereof. When the drive elements104start and stop rotation of the wedge elements100, there is a tendency for the wedge element to jerk, oscillate or wiggle. This negatively affects beam steering accuracy and, thus, it is desirable to ensure the wedge element100rotates with minimal oscillation. Consequently, gears106,216and/or bearings (see, e.g.,FIG. 8) can cooperate to maintain beam steering accuracy from the wedge element100.

While the prisms180are rotated, the sensors170track rotational movement of the encoder members140. The position can be absolute or relative but, in any case, the precise location of each prism180about the centerline22is known. The sensors170and drive elements104are in constant communication with one another via the computer (not shown) or the like. Consequently, the rotational position of each prism180can be precisely controlled and maintained during operation of the beam steering device16.

The drive elements104and magnets142a,142ballow the prisms180to be rotated in the direction R in a microstep fashion. The resolution of this rotation is tied directly to pole pitch (mechanical spacing between the north and south pole centers) of the magnets142a,142b, e.g., the smaller and closer together the magnets, the more precise the rotational positioning of the prism180.

FIG. 7illustrates another example beam steering device200. Features inFIG. 7that are identical to features areFIGS. 1-5are given the same reference number. The beam steering device200ofFIG. 7is configured to emit laser light in directions extending perpendicular to the centerline22, also known as side-emitting. In this construction, both ends24,26of the housing20are closed along the centerline22. To this end, an end wall202is provided at the second end26of the housing20. A non-planar mirror210is secured to the end wall202within the passage30and extends along the centerline22towards the wedge elements100. In one example, the mirror210has a conical shape but could alternatively be hemispherical or have a polygonal shape. In any case, the mirror210is symmetric about the centerline22.

A plurality of lateral openings204extends radially through the sidewall28. The openings204are radially aligned with the mirror210. A lens or window (not shown) can be provided in each opening204. Light beams striking the mirror210are reflected radially away from the centerline22towards the openings204. The prisms180can be rotated to a number of different positions relative to each other sufficient to generate a field of view for the beam steering device200, illustrated by the pair of cones220inFIG. 7. In one instance, each cone220extends over an angle α2of about 20°. The beam steering device200can therefore capture and measure objects within the viewing cones220.

The beam steering device200operates in the same manner as the beam scanning device16except that the field of view220of the beam steering device200extends radially from the centerline22whereas the field of view190of the beam steering device16extends axially along the centerline22. After the light beams strike the target object(s), the light passes through the openings204, is reflected by the mirror210towards and through the prisms180, through the lens64, and ultimately reaches the transceiver60, where it is collected and processed.

Similar to the beam steering device16, the wedge elements100in the beam steering device200are also spaced entirely in both the axial and radial direction from one another along the centerline22. No portion of one wedge element100radially overlaps a portion of the other wedge element100. In other words, both ends24,26of the rightmost wedge element100(as shown inFIG. 7) are positioned closer to the openings204than both ends24,26of the leftmost wedge element100. The wedge elements100therefore do not rotate within one another in use. Moreover, since the same bodies30are used for each wedge element100the inner diameters of the central passages40receiving the prisms180are the same.

FIGS. 8-10illustrate yet another example beam steering device250. Features inFIGS. 8-10that are identical to features areFIGS. 1-5are given the same reference number. In this configuration, the beam steering device250includes multiple wedge elements252that are each configured with the drive member or drive member260positioned on an outer surface262of the body110at one of the ends114,116. As shown inFIGS. 8-9, the outer surface262is the axial end surface of the second end116of the body110extending substantially perpendicular to the axis112. The drive member260constitutes a series of alternating magnets264a,264bphased 180° from one another. The magnets264a,264bare arranged in a circumferential pattern about the passage120. The magnets264a,264bcan be integrally formed on the outer surface262or attached to a strip or base member secured to the outer surface (not shown).

The drive member260cooperates with a PCB270secured to the housing20within the passage30. The PCB270has an annular shape with a central opening276aligned with the centerline22for allowing beam light to pass therethrough in an unobstructed manner. The PCB270includes a plurality of magnetic drive coils274a,274b. The drive coils274a,274bare arranged in a circumferential pattern about the opening276. The drive coils274a,274bcan be integrally formed on the PCB270, e.g., via printing, or attached to a strip or base member secured to the PCB (not shown). As shown, the drive coils274a,274bare integrally formed into a surface272of the PCB270.

In the beam steering device250ofFIG. 8a pair of wedge elements252are provided therein. Similar to the beam steering devices16,200, the wedge elements252in the beam steering device250are also spaced entirely in both the axial and radial direction from one another along the centerline22. No portion of one wedge element252radially overlaps a portion of the other wedge element252. In other words, both ends24,26of the rightmost wedge element252(as shown inFIG. 8) are positioned closer to the openings204than both ends24,26of the leftmost wedge element252. The wedge elements252therefore do not rotate within one another in use. Moreover, since the same bodies30are used for each wedge element252the inner diameters of the central passages40receiving the prisms180are the same.

The wedge elements250are oriented in the passage30such that the outer surfaces262face opposite directions. A PCB270associated with the leftmost wedge element252is secured to the housing20between that wedge element and the mirror210, with the surface272facing the outer surface262. A PCB270associated with the rightmost wedge element252is secured to the housing20between that wedge element and the lens212, with the surface272facing the outer surface262. Both PCBs270are spaced axially from their respective wedge element252and the openings276are centered on the centerline22. During operation, the drive coils274a,274bon one or both PCBs270are energized to rotate the respective wedge element(s)252in the direction R to the desired positions about the centerline22.

The PCBs270can be configured to include a position sensing structure, such as the encoder sensors170, to sense rotation of the drive members260. This position sensing structure can sense rotation of the magnets264a,264bon the body110or other encoding structure provided on the outer surface262(not shown). Alternatively, the second encoding member84and sensors100previously described can be used on an outer surface of the body110(not shown).

Referring toFIG. 8, the wedge elements250are rotatably mounted in the housing20by bearings216positioned radially between the bodies110and the sidewall28of the housing. In one example, the bearings216are located within an annular groove146extending along the entire circumference of the body110and an annular groove217extending along the entire circumference of the inner wall of the housing20. The annular grooves146,217and bearings216cooperate to maintain beam steering accuracy from the wedge elements250.

Alternatively, the surfaces272of the PCBs270and the surfaces262of the bodies110can be modified to include bearing races to receive bearings such that the wedge elements250are axially supported for rotation in the housing20(not shown). In this construction, the axial end faces of the wedge elements250facing each other would also be provided with bearing tracks to allow bearings to extend between and connect the wedge elements to one another (also not shown). Such a configuration would allow the housing200to be reduced as a smaller radial clearance between the wedge elements250and inner housing wall would be needed for the axially mounted bearings.

The beam steering device disclosed herein is advantageous in that only a single optic unit—the monolithic transceiver—is needed to undertake the scan. Prior beam steering devices use multiple optic units, sometimes stacked linearly atop one another, to send and receive laser light. The prior constructions, however, are bulky, require many electrical connections, and are limited in the clarity of the scan performed. The transceiver, as disclosed herein, alleviates these concerns by implementing a laser, photodiode, and photodetector in a single, compact unit positioned along the centerline. The beam steering device further can be manufactured as to be advantageously small, compact, and can be readily scaled to meet nearly every automobile mounting configuration. In one example, the beam steering device can be scaled down to about a 1.5″ diameter and be about 2″ in length (front-emitting) or about 3″ in length (side-emitting).

The wedge element disclosed herein is advantageous in that it produces a two-dimensional scanning pattern, compared to line scans common in many other devices. Furthermore, by positioning both the drive and position sensing structure on the outer surface of the device, i.e., the outer circumferential surface or outer axial surface, the wedge elements disclosed herein can be made more compact and efficient than other devices, for example, providing a space reduction of about ⅔ to about ¾ over such devices. This advantage is further realized by the non-overlapping positioning of the wedge elements within the housing.

These configurations also reduce the number of moving components and can eliminate the use of gears to drive the wedge elements, thereby reducing the packing complexity and simplifying the design. In other words, building the drive system around the body that retains the wedge reduces the footprint and complexity of the wedge element, which allows it to be adapted/sized for a wide range of applications, e.g., automotive LIDAR, occupancy sensing, and gaming. The wedge elements disclosed herein are also advantageous in that the same component, namely the camera, e.g., photodetector, is used to both emit and detect the laser light.