Slit Diaphragm Flexure

A gimbal is disclosed having a base with a bottom and a support structure extending up from the bottom. Two or more mounts connected to the base and a stiffener connects to two or more mounts. A slit diaphragm flexure connects to the stiffener around at least an outer circumference of the slit diaphragm flexure and one or more adjustors are provided to move the flexure. The stiffener may be two separate elements which releasably connect and secure the outer area of the flexure there between. The adjustors are configured to move upward or downward and contact the slit diaphragm flexure to thereby move the slit diaphragm flexure in response to movement of the adjustor. The flexure includes two or more slits that allow movement of a center area relative to an outer ring. The slit includes relieved areas that provide stress relief and increase orthogonal of movement.

DETAILED DESCRIPTION

FIG. 1illustrates an example environment of use which includes an optical environment4including a light source8which generates or presents a light signal to one or more optic paths12. The destination of the optic signal is an optic signal destination16which may comprise any element configured to receive a light signal. In addition, one or more intermediate optic devices20may be placed at any location within the optic paths112to monitor or modify the light signal.

To precisely control the path of the light signal, one or more mirrors24are provided as shown inFIG. 1. In this embodiment the mirrors are OAP (off axis parabolic) mirrors. Precise position control of these mirrors is essential to establish the desired optic signal path. To control the position of these mirrors, one or more mirror position controllers30are provided in connection to the mirror. Through adjustment of the position controllers, the position of the mirror24may be accurately adjusted and maintained.

Although shown in this example environment, it is contemplated that the innovation described below may be enabled in any environment which would benefit from precise position control and position maintenance of an element, including non-optic elements.

There are five main parts to the gimbal and associated elements as shown in the attached figures. These main parts include a gimbal base, one or more mounts, adjustors, which adjust the position of a flexure, a slit diaphragm flexure, and a stiffening structure which stiffens the flexure. Each of these elements is discussed below.

Although the discussion below is directed to use of a mirror, it is contemplated that any element may be mounted on or configured as part of the gimbal. In other embodiment the mirror106may be replaced with a light source, sensor, emitter, detector, or any other element for which precision adjustment is required.

FIG. 2illustrates an exemplary gimbal base104and mounts108that are part of a gimbal100. As shown, a base104is configured to support the mirror106. The base104also connects to support surface (not shown), such as a table or other solid structure. Also shown inFIG. 2are gimbal mounts108which connect to the base104and one or more of the mirror106, stiffener, or flexure. The stiffener and flexure are not shown inFIG. 2but are located behind the mirror106.

The base104may be made of any generally ridged material such as for example metal, plastic, resin or glass. The base104may be configured in any shape such as would be suitable to connect to a table or other solid structure and fit within the space allotted for the gimbal including the base. It is contemplated that the base104may be shaped to angle or direct the mirror at a predetermined angle as would depend on the particular use of the gimbal. For example, as shown inFIG. 2, the mirror106is angle at about a 45 degree angle in relation to the horizontal bottom surface of the base104. Mounting of the mirror may be achieved using any connection system known such as clamps, adhesive, glue, PTFE-impregnated glass tape on the mirror106may have a frame mounting surface to which such connections may be made. In addition, the mirror may be preload using any biasing system including use of spring plungers above the pads around the mirror's perimeter, which are generally discussed below.

FIG. 3illustrates an exemplary slit diaphragm flexure with stiffening element. In this exemplary embodiment the flexure116comprises a thin sheet of metal with sections cut and removed from the sheet to allow flexure of the metal sheet. The cut outs, which may be referred to as slits, may allow for flexing along one axes, two axes, or three axes. One or more bridges (not shown inFIG. 3) are between the slits and are area of the sheet which are not removed. As a result of the slits, the flexure116can accommodate a combination of angular and axial displacements. Because it is made from a thin sheet of metal, this type of flexure116is simple to machine with modern machining processes such as electro-discharge machining, water jet cutting, or laser cutting.

In this embodiment the flexure is a slit diaphragm flexure. Slit diaphragm flexures is utilized in this application because stiffness in radial directions is preferred but axial and angular position is constrained by other components. When used directly in a two-axis gimbal application where angular displacements about specific axes are preferred and axial displacements are to be avoided. As a result, special attention must be given to adjustment mechanism placement and flexure stiffening to reduce coupling of the X and Y adjustments and provide orthogonal axes of rotation. This is discussed below in greater detail in connection withFIGS. 7 and 8.

In this example embodiment the flexure is electro-discharge-machined out of a 0.032″ thick sheet of titanium 6A1-4V. In other embodiments the flexure may be made out of other materials or elements, or a combination of materials or alloys. Likewise, the flexure may be established at other thicknesses and such thicknesses may be uniform across the flexure or variable. In this embodiment the high-strength titanium alloy 6A1-4V has a high tensile yield strength and low modulus of elasticity, allowing for large deformation in the linear elastic region of the flexure.

The flexures disclosed herein have the additional feature of one or more stiffening elements120in order to provide specific preferred regions of deformation while reducing or eliminating deformation in other areas. These stiffeners120provide enhanced performance by providing nearly perpendicular adjustment axes and a center of rotation near the center of the gimbal. As an advantage over prior art designs both of these features achieve a lower profile and simpler design than conventional gimbals.

As shown inFIG. 3, the flexure116is thus supported on its outer edge by a stiffener120. In this embodiment, the stiffener120comprises two stiffeners matched to the outer edge of the flexure116. The stiffeners120clamp together on both sides of the flexure116with twelve screws124securing the outer edge. In other embodiment other shapes and connection means for the stiffeners120may be enabled, such as glue, adhesive, or any other connection means.

FIG. 4illustrates exemplary adjustors associated with a flexure. In this embodiment one or more adjustors112are in contact with the back side of the inner part of the flexure. In this configuration the adjustors112are shown below and behind the flexure116and are configured to apply pressure to the flexure which in turn moves the flexure.

The adjustors112translate input from a user or machine to movement of the flexure116(which in turn moves the mirror). The adjustors112may comprise any type adjustment mechanism. The adjustors112accept movement input from the user, such as through turning of a screw or from a stepper motor, which in turn physically pushes on the flexure116upward or downward, which in turn moves the flexure and the associated mirror attached thereto.

In one example embodiment, the angular adjustment about the X axis and Y axis is achieved with two spherical-tip pushers112, as shown. The depth of the pushers112may be is set with setscrews, and each adjustment may include a non-influencing locking mechanism. Preload may be is maintained on each of the pushers with a pair of extension springs or other biasing device. In one embodiment, the X adjustment is located 1.125″ from the center of the flexure, and the Y adjustment is located 1.325″ from the center of the flexure. Estimating that a skilled technician using a hex wrench has at least 1° of sensitivity in adjustment, this equates to a sensitivity of 3.5 μm using a ¼-28 setscrew. With this adjustment sensitivity, the gimbal thus achieves an angular sensitivity of 0.12 mrad about the X axis, and 0.11 mrad about the Y axis. In other embodiment, using other locations for the adjustors in relation to the flexure and other adjustment configurations, different resolutions may be achieved.

In other embodiment any type of device or system may be utilized as the adjustors112. In addition, any number of adjustors112may be utilized to provide the adjustment. For example, if motion along a single axis is desired then a single adjustor112may be included while a greater number of axis of adjustment may be achieved with two or more adjustors. In one embodiment, the adjustors are linked, either mechanically or via electrical or magnetic controllers to operate in unison or individually to achieve motion control over the mirror. Although shown as threaded114or screw type adjustor, it is contemplated that any type mechanism may be utilized to effect upward and downward movement of the adjustors112. In addition, it is contemplated that the adjustors112may be placed at different angles relative to the flexure116.

FIGS. 5A,5B,5C illustrate an exemplary slit diaphragm flexure including performance capability in for axial displacement and angular displacement. This type of flexure is valuable for its design and ability to provide radial support while providing a wide range of motion. As shown inFIG. 5A, the flexure may have any arrangement of slits408and bridges416within a generally planer solid sections412. In this embodiment one or more radial concenter slits408cut into the sections412but in other embodiment patterns other than radial arcs may be established.

One or more bridges416interconnect the solid sections412and interrupt the slits408. The location of the bridges416and slits408are selected based on the angular displacement that is desired and the location of the adjustors in relation to the location of the bridges and slits. As can be appreciated, the flexure will flex along the slits418and resist flexure or movement where solid bridges416remain connected.

In this embodiment, the center is void of any material but in other embodiments one or more sections of sheet or other matter may remain in the center. As can be appreciated by one of ordinary skill in the art, this is but one possible configuration and other configuration may also be enabled. When compared to other solutions such as blade flexures or bearings, a slit diaphragm flexure has advantages such as large displacement, simplified assembly, reduced design complexity, and excellent sensitivity.

FIG. 5Billustrates the axial deflection of the flexure extending from the plane of the outermost ring. This provides the benefit of being able to adjust the location of the mirror, or other element, along an axis that is non radial or which is aligned with an axis that perpendicularly intersects the plane of the generally flat flexure surface.FIG. 5Cillustrates angular deflections of the flexure. As can be appreciated fromFIGS. 5B and 5C, the flexure enjoys a range of motion enabled by the slits408and constrained by the bridges416. By adjusting the location and width of the bridges416and slits408, in connection with the adjustors, the degree of deflection is controlled while maintaining support for the mirror or other element.

FIG. 6illustrates an alternative configuration of a slit diaphragm flexure with stiffening element. This configuration is generally similar to the flexure and stiffener shown inFIG. 3but is arranged in a generally rectangular configuration. As shown a generally planar and ridged sections604is configured from a sheet of metal or other generally planer and ridged material. Cut from the section of planar material are one or more slits610which provide an opening between the solid sections604. Linking an inner and outer solid section is a bridge608. In this embodiment the bridge608is formed by not removing a portion of the solid section604.

In this configuration the flexure is formed as a rectangle having an opposing top and bottom and two opposing sides which together connect at the ends to form a rectangle. A slit610runs the length of each side forming two parallel solid sections which are separate by the slit. A bridge608is located at the center of slit and the bridge interrupts the linear slit to connect the solid sections as shown. The center area620is generally open as shown but in other embodiments may be solid.

A stiffener612is provide around the outer edge of the solid sections604t provide support as described herein. The stiffener612may be established as having a front section and a back section between which the solid section604is secured. Multiple connectors624, such as screws or bolts, may secure the front section to the back section. In one embodiment the stiffener612comprises a single element and the flexure mounts directly to the stiffener.

Using adjustors (not shown inFIG. 6), which contact the solid surface604, the position and angle, relative to the plane of the stiffener624, of the solid surface may be adjusted. The adjustors may comprise any type adjustor as discussed herein capable of moving the solid surface, regardless of whether the solid surface is as shown or a solid inner section.

The flexure shown inFIG. 6allows the overall gimbal profile to be kept low while still maintaining the necessary degrees of sensitivity and adjustment range. In one configuration, the gimbal design has an overall thickness of 1.75″ not including the micrometer adjusters and further achieves orthogonal X and Y adjustment axes. Moreover, it also provides a center of rotation centered about the gimbal.

In one configuration angular adjustment about the X and Y axes is achieved with a pair of Newport DM-L series differential micrometers, which have a sensitivity of 0.1 μm and a non-influencing lock. Preload is maintained on each micrometer with a pair of extension springs around each adjuster for both positive and negative adjustment. The X adjustment micrometer is located 5.38″ from the center of the mirror and the Y adjustment micrometer is located 4.63″ from the center of the mirror. With the 0.1 μm sensitivity of the micrometers, the gimbal achieves an angular sensitivity of 0.73 μrad in X adjustment and 0.85 μrad in Y adjustment.

The micrometers have a total travel range of 13.0 mm, which results in a total angular adjustment range of ±2.7° in X adjustment, and ±3.2° in Y adjustment. Hardened carbide pads may be provided under each micrometer head to ensured that the contact surfaces would not dimple under compression which would compromise the angular sensitivity of the gimbal. A thin layer of damping grease may be applied to the carbide pad to prevent frictional jumping or sticking at the micrometer/pad interface during adjustment. The flexure-based design provided excellent sensitivity for back-reflection alignments over a long lever arm. In this embodiment, the angular sensitivity of the gimbal provides a beam positioning sensitivity of 24 μm at a distance of 30 m. The flexure shown inFIG. 6may utilize the same basic components as the gimbal shown inFIGS. 3 and 4including the slit diaphragm flexure and two stiffeners that clamp both sides of the flexure. The flexure may be electro-discharge-machined out of a 0.032″ thick sheet of titanium 6A1-4V, providing large adjustment range and low required force on the micrometers.

FIG. 7illustrates an exemplary flexure without a stiffening element including center of rotation based on finite element analysis. The flexure700is shown as a basic design having two or more bridges740spanning the circular slits744. In this figure, the Y axis adjustor is at position704while the X axis adjustor is at position708. The X axis adjustor712is partially visible. The X axis720defines the axis along which the flexure moves in response to adjustment of the X axis adjustor712. The Y axis724defines the axis along which the flexure moves in response to adjustment of the Y axis adjustor.

In operation movement of the adjustors presents pressure on the inner section of the flexure700at the adjustor location704,708, which in turn flexes the flexure along the slits. The bridges740resist movement. Movement of the X axis adjustor712causes the flexure700to move along the X axis. Movement of the X axis adjustor712causes the flexure700to move along the X axis. However, as discussed below, movement of one adjustor individually, may generate movement along both axis, which is typically unwanted.

For example, one of the design challenges presented when building the gimbal with slit flexure is non-orthogonality, which may also be referred to as coupling, of alignment axes when only a single pusher for each axis is used. One of the more basic slit diaphragm flexure that was designed, as seen inFIG. 7, is essentially a set of four curved beams supporting an inner plate. It can be shown that the stiffness and stress in such a flexure can be calculated in these individual beams for certain load cases, but these loading conditions make the assumption that moments and forces are evenly distributed between the beams. In the case of a slit diaphragm flexure, which is loaded irregularly, more advanced modeling was performed.

Modeling the slit diaphragm flexure in ANSYS was used to accurately predict adjustment capabilities of the gimbal for various designs. ANSYS is a mathematical modeling software available from ANSYS Inc. located in Canonsburg, Pa. For the ANSYS model the outer ring of the diaphragm flexure was constrained with a fixed condition, and the spherical-tipped adjusters were modeled with a frictionless contact condition on the back side of the flexure. The inner ring of the flexure was stiffened by the mirror mounting plate, and spring forces were applied to the mirror plate corresponding to preload springs in the design. By moving each adjustment individually, deflection and stress results were calculated for the purpose of finding the gimbal's axes and center of rotation.

As shown inFIG. 7, when a single pusher is provided for an axis and the outer stiffener is not utilized, the resulting axes of rotation are not orthogonal, and the center of rotation is not centered on the flexure. These conditions are caused by the position of the adjustments on the back side of the flexure and their relative location to each of the four beams that make up the flexure. By pushing at a point near the flexure's side, a combination of moments and bending forces are produced in each flexure beam. This action results in a coupled deflection pattern, such that the portion closest to the adjustor (also referred to as beam elements) closest to the adjusters deflect more than the one farthest from the adjuster. Ideally, orthogonal adjustment axes are desired to provide simpler adjustment by the user or system, and in many cases a center of rotation that is centered about the optic is preferred.

As a result of this analysis, the embodiment ofFIG. 8is provided. After the ANSYS modeling results and prototype testing in the laboratory, it was determined that for some applications the slit diaphragm flexure's degree of adjustment coupling was too high to satisfy the requirements of the unit. In order to improve this parameter a flexure stiffener was designed to regulate the bending of the flexure in only in specific regions near where a conventional pivot point would be located. Stiffening the flexure provided fixed areas where bending could occur and, therefore, better-defined rotational axes.

FIG. 8illustrates an exemplary flexure performance improved by a stiffening element including a center of rotation calculation based on finite element analysis. The embodiment ofFIG. 8is generally similar to the embodiment shown inFIG. 7, with the addition of the stiffener (not shown). Elements which are the same as the elements identified inFIG. 7are labeled with identical reference numbers. The stiffener is not shown because the purpose ofFIGS. 7 and 8is to discuss the improvement of the center of rotation gained by the stiffener in relation to The stiffener as described above in connection withFIGS. 3 and 4is one example embodiment of a stiffener although other configurations of stiffeners may be utilized.

In the stiffened version of the flexure, the adjustment axes are closer to perpendicular, and the gimbal's center of rotation is closer to the center of the gimbal. Consequently, by limiting the area in which the flexure can deform, a deformation pattern approximating a conventionally supported gimbal can be achieved. Stated another way, by limiting the area in which the flexure can deform movement of the X axis adjustor moves the flexure along only the X axis, with some degree of variance. By limiting the area in which the flexure can deform movement of the Y axis adjustor moves the flexure along only the Y axis, with some degree of variance.

Ideally, a flexure that is only able to deform in an infinitely small area around the four quadrants of the flexure's perimeter will provide two perfectly perpendicular axes with a perfectly centered center of rotation. In reality the beams in the flexure require some length to provide deflection, and this length prevents a perfect result. Although not perfect, the stiffened version of the flexure as shown herein is able to provide a relatively large amount of deflection in a tight space and simple alignment in an area with limited access, which is an improvement over the non-stiffened version.

FIG. 9illustrates an exemplary embodiment of the flexure showing relieved sections934near a flexure bridge930.FIG. 9shows but one possible embodiment and it is contemplated that the relieved section934may be located at different locations and configured with a different shape. As shown, the flexure system includes adjustors112, as describe above, which provides a force on the flexure116against a bias provided by the one or more springs904. A stiffener916is connected to the flexure116with mounting bolts908as shown. Although shown with bolts it is contemplated that any other connector may be used including screws rivets, welds, glue or other adhesive, clamps, or any other connector. The stiffener916may also be integral with the flexure116, such as if the stiffener is constructed of the same piece of material as the flexure. In this embodiment, the stiffener916limits motion to two orthogonal rotational axes.

Also shown in greater detail inFIG. 9is a bridge930(shown as element740inFIG. 7) between the inner and outer portions of the flexure116. The bridge930is between the circular slits944(shown as element744inFIG. 7). At the end of one or more slits944is a relieved portion934which is generally wider than the slit944. As shown, the stiffener916is also relieved, in the area of the relieve portion934, or at or near the bridge so that rotation of the flexure is a combination of twisting and bending. The relieved portion934provides additional flexibility to the flexure to maintain orthogonal movement and reduce stresses and strain on the flexure.

In the example embodiment ofFIG. 9, the relieved portions934are shown as circular in shape and located at the end of the slits944on each end of the bridge930. In other embodiments, the relieved portions934the may be any shape such as but not limited to oval, triangular, square, or rectangular. In addition, the relieved portion934may be located at other locations on the flexure or on only one side of the bridge.

FIG. 10illustrates an exemplary flexure under flexing rotational force with an enlarged view of the bridge showing numeric flex values. The numeric values shown inFIG. 10are associated with the example embodiment ofFIG. 10. As shown, the stiffeners916provide additional support. In enlarged section, the relieved portion934located at the end of the slit944is provide for reference. Based on the relative motion key940shown at the upper left-hand corner ofFIG. 10, the movement and strain at the bridge is shown resulting from the rational movement of the flexure.

An analysis of directional deformation confirms that the axis of rotation is highly orthogonal. In this example embodiment the direction of rotation is in and out of the plane defined by the page ofFIG. 10. In this configuration, the total deflection is about +/−0.25 inches but between the two inner most bands on each side of the center point the deflection is only about +/−0.005 includes. Upon close inspection of the relative movement at the bridge, the deformation pattern indicates both twisting near the bridge and bending in the relieved portion.