Ring Laser Gyroscopes (RLGs) can experience performance errors and power loss due to mechanical bending of the laser block. Mechanical bending of the block can occur during exposures to temperature extremes if components are rigidly mounted to the laser block and possess different coefficients of thermal expansion from the laser block material. Laser block bending changes the internal alignment of the mirrors and causes changes in gyro power and performance.
An apparatus includes a sheet of circuit board material, at least one electrically conductive trace positioned on the sheet of circuit board material, and at least one electrically conductive contact pad positioned on the sheet of circuit board material and coupled to the at least one electrically conductive trace. The apparatus further includes at least one deformation point configured to absorb stresses developed in the sheet of circuit board material when the sheet of circuit board material experiences resistance to expansion or compression caused by connection to an object resisting expansion or compression.
Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which:
In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the method presented in the drawing figures and the specification is not to be construed as limiting the order in which the individual steps may be performed. The following detailed description is, therefore, not to be taken in a limiting sense.
The embodiments described below provide systems and methods for mitigating block bending in laser blocks (and other objects) caused by attachment of circuit board assemblies. More specifically, a circuit board assembly can be created with deformation points to absorb stresses developed in the circuit board assembly when the circuit board assembly experiences resistance to expansion or compression caused by connection to a laser block (or other object) resisting expansion or compression. In exemplary embodiments, these deformation points are created by removing portions of the circuit board assembly using cutouts. In other exemplary embodiments, these deformation points are created in other ways, such as by forming the circuit board material into specific geometries including forming folds, zig-zag shapes, accordion configurations, or other shapes to absorb the stresses by deforming. In other exemplary embodiments, a complete disconnect between two portions of the circuit board becomes a deformation point 103 (such as the disconnects formed by cutouts 146 and 148 shown in
In exemplary embodiments, the circuit board 100A is a flexible circuit board, such as a flex circuit designed using flexible printed circuit board (PCB). In other exemplary embodiments, the circuit board 100A is a rigid-flex circuit with portions of rigid PCB and portions of flexible PCB. In either flexible circuits or rigid-flex circuits, the flexible portions of the circuit board 100A allow the flexible circuit board material to bend and turn. In other exemplary embodiments, the circuit board 100A is a rigid circuit board, such as a rigid circuit designed using rigid PCB. In other embodiments, other suitable circuit board materials are used.
The cutouts 102A are configured to minimize the cross-sectional area of the circuit board 100A in locations to create deformation points 103 that absorb stresses developed in the circuit board 100A when the circuit board 100A experiences resistance to expansion or compression caused by connection to an object resisting expansion or compression. Thus, the deformation points 103 help minimize block bending in a laser block to which the circuit board 100A is attached. In exemplary embodiments, the cross-sectional area of the circuit board 100A can be further minimized by making the circuit board 100A thinner. In exemplary embodiments, deformation points are not created by reducing the cross-sectional area of the circuit board material. For example, the deformation points may be created by forming the circuit board material into specific geometries including forming folds, zig-zag shapes, accordion configuration, or other shapes to absorb the stresses by deforming. In other exemplary embodiments, a complete disconnect between two portions of the circuit board 100A becomes a deformation point 103 (such as the disconnects formed by cutouts 146 and 148 shown in
The deformation points 103 absorb thermal stresses generated by the thermal expansion and contraction of the circuit board 100A that can be passed to the laser block. This is true of all deformation points 103, regardless of how they are created. Lower thermal stresses transferred to the laser block result in less block bending. Even in exemplary embodiments where the circuit board 100A is a flexible PCB, thermal expansion and compression of the flexible PCB generates stresses that can be transferred to the laser block (or other component, substrate, or object) and cause block bending. In exemplary embodiments this occurs even though the laser block is substantially more rigid than the flexible PCB. In exemplary embodiments, block bending affects the position of the lasing plane within a laser block, which can degrade the performance of a ring laser gyroscope and reduce the power of the lasers.
The cutouts 102A include both cutouts on the periphery of the circuit board 100A and cutouts surrounded by the circuit board 100A. The cutouts 102A on the periphery of the circuit board 100A include cutouts 108, 110, 112, 114, 116, 118, 120, and 122. The cutouts 102A surrounded by the circuit board 100A include cutouts 124, 126, 128, 130, 132, 134, and 136. The cutouts 102A in the circuit board 100A can be created in various ways, including but not limited etching, cutting, dicing, or stamping. While the cutouts 102A are shown as various shapes in
In exemplary embodiments, placement of the cutouts is restricted based on the location of the conductive traces 104, conductive contact pads 106, and other components and/or elements of the circuit board 100A. In exemplary embodiments, placement of the cutouts is selected to reduce/minimize the cross-sectional area of the circuit board 100A in at least one location. In exemplary embodiments, placement of the cutouts is selected to minimize the cross-sectional area of the circuit board 100A connecting at least two corners of the triangular shape created by the circuit board 100A. This area of minimized cross-sectional area is a deformation point 103.
For example, the size and placement of cutout 128 in addition to the size and placement of cutouts 116 and cutouts 118 minimizes the cross-sectional area of the circuit board 100A at the bottom of
In addition, the size and placement of cutout 126, cutout 128, and each of cutouts 132 and 134 minimize the cross-sectional area of the circuit board 100A on the right side of
Similarly, the size and placement of cutout 128, cutout 124, and each of cutouts 136 and 130 minimize the cross-sectional area of the circuit board 100A on the left side of
As will be shown below with reference to
In exemplary embodiments, at least some of the cutouts are symmetrically positioned on the circuit board 100A, such as cutouts 130 and 132, cutouts 136 and 134, cutouts 118 and 116, etc. The symmetric positioning of the cutouts causes symmetric positioning of the deformation points 103 because they deform to absorb stresses before other parts of the circuit board 100A. In other exemplary embodiments, the cutouts are not symmetrically positioned. In exemplary embodiments, symmetrically positioned cutouts are approximately the same shape and size as each other, such as cutouts 130 and 132, cutouts 136 and 134, cutouts 118 and 116, etc.
In exemplary embodiments, a first service loop 138 is positioned on the left side of the circuit board 100A and a second service loop 140 is positioned on the right side of the circuit board 100A. In exemplary embodiments, these service loops include connectors used to communicatively couple the conductive traces 104, conductive contact pads 106, and the circuit board 100A generally to an external system. In exemplary embodiments, service loops 138 and 140 are flexible and minimize the transfer of stresses between the circuit board 100A and the external systems. In exemplary embodiments, the flexible service loops 138 and 140 are bent upward above the rest of the circuit board 100A where they are attached to the external systems. In exemplary embodiments, the service loops 138 and 140 include connectors for communicatively coupling to external systems.
Instead of circular cutouts 130, 132, 134, and 136, circuit board 100B includes rectangular shaped cutouts 142, 144, 146, and 148. Both rectangular shaped cutout 142 and rectangular shaped cutout 144 are surrounded by circuit board 100B. In contrast, rectangular shaped cutout 146 and rectangular shaped cutout 148 are only partially surrounded by circuit board 100B. Specifically, rectangular shaped cutout 146 couples cutout 126 with cutout 128 and rectangular shaped cutout 148 couples cutout 124 with cutout 128. While rectangular shaped cutouts 146 and 148 effectively and advantageously reduces the cross-sectional area of the circuit board 100B to zero in two portions of the circuit board 100B, the exemplary embodiment of circuit board 100B shown in
The cutouts 102B are configured to minimize the cross-sectional area of the circuit board 100B in locations to create deformation points 103 that absorb stresses developed in the circuit board 100B when the circuit board 100B experiences resistance to expansion or compression caused by connection to a substrate (or other object) resisting expansion or compression. The deformation points 103 help minimize block bending in a laser block (or other object) to which the circuit board 100B is attached. In exemplary embodiments, the cross-sectional area of the circuit board 100B can be further minimized by making the circuit board 100B thinner.
The deformation points 103 absorb the thermal stresses generated by the thermal expansion and contraction of the circuit board 100B that can be passed to the laser block (or other object). Lower thermal stresses transferred to the laser block result in less block bending. Even in exemplary embodiments where the circuit board 100B is a flexible PCB, thermal expansion and compression of the flexible PCB generates stresses that can be transferred to the laser block (or other component, substrate, or object) and cause block bending. In exemplary embodiments this occurs even though the laser block is substantially more rigid than the flexible PCB. In exemplary embodiments, block bending affects the position of the lasing plane within a laser block, which can degrade the performance of a ring laser gyroscope and reduce the power of the lasers.
In exemplary embodiments, placement of the cutouts is restricted based on the location of the conductive traces 104, conductive contact pads 106, and other components and/or elements of the circuit board 100B. In exemplary embodiments, placement of the cutouts is selected to reduce/minimize the cross-sectional area of the circuit board 100B in at least one location. In exemplary embodiments, placement of the cutouts is selected to minimize the cross-sectional area of the circuit board 100B connecting at least two corners of the triangular shape created by the circuit board 100B. This area of minimized cross-sectional area is a deformation point 103 that deforms before other parts of the circuit board 100B to absorb thermal and other stresses.
For example, the size and placement of cutout 128 in addition to the size and placement of cutouts 116 and cutouts 118 minimizes the cross-sectional area of the circuit board 100B at the bottom of
In addition, the size and placement of cutout 126, cutout 128, and each of cutouts 144 and 146 minimize the cross-sectional area of the circuit board 100B on the right side of
Similarly, the size and placement of cutout 128, cutout 124, and each of cutouts 142 and 148 minimize the cross-sectional area of the circuit board 100B on the left side of
As will be shown below with reference to
In exemplary embodiments, at least some of the cutouts are symmetrically positioned on the circuit board 100B, such as cutouts 142 and 144, cutouts 148 and 146, cutouts 118 and 116, etc. The symmetric positioning of the cutouts causes symmetric positioning of the deformation points 103. In other exemplary embodiments, the cutouts are not symmetrically positioned. In exemplary embodiments, symmetrically positioned cutouts are approximately the same shape and size as each other, such as cutouts 142 and 144, cutouts 148 and 146, cutouts 118 and 116, etc.
Cutout 150 replaces cutout 128 in the center of the circuit board 100C. Its shape is slightly different. In exemplary embodiments, the difference in shape is based on the position of the conductive traces 104, conductive contact pads 106, and other components. In other exemplary embodiments, differences in shape further reduce the cross-sectional area of the circuit board 100C in additional areas to further reduce thermal stresses generated by the expansion and contraction of the circuit board 100C in response to temperature changes in the environment surrounding the circuit board 100C.
The cutouts 102C are configured to minimize the cross-sectional area of the circuit board 100C in locations to create deformation points 103 that absorb stresses developed in the circuit board 100C when the circuit board 100C experiences resistance to expansion or compression caused by connection to an object resisting expansion or compression. The deformation points 103 help minimize block bending in a laser block to which the circuit board 100C is attached. In exemplary embodiments, the cross-sectional area of the circuit board 100C can be further minimized by making the circuit board 100C thinner. As described above with reference to
The deformation points 103 absorb the thermal stresses generated by the thermal expansion and contraction of the circuit board 100C that can be passed to the laser block. This is true of all deformation points 103, regardless of how they are created. In exemplary embodiments, other stresses are also absorbed by the deformation points 103. Lower thermal stresses transferred to the laser block result in less block bending. Even in exemplary embodiments where the circuit board 100C is a flexible PCB, thermal expansion and compression of the flexible PCB generates stresses that can be transferred to the laser block (or other component, substrate, or object) and cause block bending. In exemplary embodiments this occurs even though the laser block is much more rigid than the flexible PCB. In exemplary embodiments, block bending affects the position of the lasing plane within a laser block, which can degrade the performance of a ring laser gyroscope and reduce the power of the lasers.
In addition, the placement of cutouts 130 and 132 in circuit board 100C is slightly different than in circuit board 100A. In exemplary embodiments, the change in placement of cutouts 130 and 132 is at least partly due to the change in placement of the conductive traces 104 and/or the conductive contact pads 106. In exemplary embodiments, the change in placement of cutouts 130 and 132 is at least partly designed to further minimize the cross-sectional area of the circuit board 100C. In exemplary embodiments, placement of the cutouts is selected to minimize the cross-sectional area of the circuit board 100C connecting at least two corners of the triangular shape created by the circuit board 100C. This area of minimized cross-sectional area is a deformation point 103 that deforms before other parts of the circuit board 100B to absorb thermal and other stresses.
For example, the size and placement of cutout 150 in addition to the size and placement of cutouts 116 and cutouts 118 minimizes the cross-sectional area of the circuit board 100C at the bottom of
In addition, the size and placement of cutout 126, cutout 150, and each of cutouts 132 and 134 minimize the cross-sectional area of the circuit board 100C on the right side of
Similarly, the size and placement of cutout 126, cutout 150, and each of cutouts 136 and 130 minimize the cross-sectional area of the circuit board on the left side of
As will be shown below with reference to
In exemplary embodiments, at least some of the cutouts are symmetrically positioned on the circuit board 100C, such as cutouts 130 and 132, cutouts 136 and 134, cutouts 118 and 116, etc. The symmetric positioning of the cutouts causes symmetric positioning of the deformation points 103. In other exemplary embodiments, the cutouts are not symmetrically positioned. In exemplary embodiments, symmetrically positioned cutouts are approximately the same shape and size as each other, such as cutouts 130 and 132, cutouts 136 and 134, cutouts 118 and 116, etc.
It is understood that other embodiments may combine features of the exemplary embodiments shown in
A modulus of elasticity for an adhesive is a measurement of the adhesive's tendency to be deformed elastically when a force is applied to it. An adhesive with a low modulus of elasticity will not transmit the thermally compressive and expansive forces as easily as adhesives with a higher modulus of elasticity.
A glass transition temperature for an adhesive is the temperature at which the adhesive transitions from a hard and relatively brittle state into a molten or rubber-like state. An adhesive with a low glass transition temperature will be in the molten or rubber-like state for a larger temperature range. If an adhesive transitions from the molten or rubber-like state into the hard and relatively brittle state, it will begin to transmit the thermally compressive and expansive forces more.
In exemplary embodiments, the thickness of the adhesive 304 between the circuit board 102 and the laser block 302 is also selected to minimize transmission of thermally compressive and expansive forces. Specifically, in exemplary embodiments, thicker adhesive layers further minimize transmission of thermally compressive and expansive forces between the circuit board 102 and the laser block 302.
In exemplary embodiments, the adhesive 304 between the circuit board 102 and the laser block 302 is positioned between the entire bottom surface of the circuit board 102 and the top surface of the laser block 302. In other exemplary embodiments, the adhesive 304 between the circuit board 102 and the laser block 302 is only positioned between portions of the bottom surface of the circuit board 102 and the top surface of the laser block 302 to further decouple the circuit board 102 from the laser block 302.
Thus, in exemplary embodiments, the adhesive 304 is chosen based on its modulus of elasticity being low enough to minimize the transmission of thermally compressive and expansive forces between the circuit board 102 and the laser block 302. Similarly, in exemplary embodiments, the adhesive 304 is chosen based on its glass transition temperature being as low as possible within the temperature operating range of the RLG 202 so that the adhesive will not transition into the hard and relatively brittle state that would transmit thermally compressive and expansive forces more than when the adhesive 304 is in its molten or rubber-like state. In exemplary embodiments, it is desirable that the adhesive 304 have consistent stress transfer properties across an operating temperature range so that the adhesive 304 does not stop minimizing the transmission of thermally compressive and expansive forces at a temperature within the operating temperature range. In exemplary embodiments, the adhesive 304 is an acrylic foam pressure sensitive adhesive (PSA).
In exemplary embodiments, the adhesive 304 is also chosen based on its thermal and electrical conductivity. Specifically, in exemplary embodiments it is desirable to select an adhesive 304 with low thermal and electrical conductivity to avoid thermal or electrical transfer between the circuit board 102 and the laser block 302 through the adhesive 304.
While each of the methodologies for minimizing block bending described above, including (1) creating deformation points 103 by minimizing the cross-sectional area of portions of the circuit board 102 (and by creating deformation points in other ways); and (2) using an adhesive 304 that minimizes the transfer of forces between the circuit board 102 and the laser block 302 can be implemented individually, exemplary embodiments combine the methodologies into apparatuses, systems, and methods to produce the best results. Thus, exemplary embodiments of systems and methods include two prongs. First, by minimizing the cross-sectional area of the circuit board 102, fewer forces are developed based on thermal compression and expansion. Second, by using the adhesive material 304 with the low modulus of elasticity and the low glass transition temperature, the remaining thermal stresses that are generated from the expansion or contraction of the circuit board 102 of the circuit board assembly 300 are de-coupled from the laser block 302, further mitigating block bending.
At block 404, at least one electrically conductive trace is fabricated on the sheet of circuit board material. At block 406, at least one electrically conductive contact pad is positioned on the sheet of circuit board material and coupled to the at least one electrically conductive trace 406. At block 408, the deformation points absorb thermal stresses developed in the sheet of circuit board material when the sheet of circuit board material experiences resistance to expansion or compression caused by connection to an object resisting expansion or compression. In exemplary embodiments, the expansion or compression is caused by temperature changes in the circuit board material.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
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