Athermalized Mounting of Inertial Measurement Unit
20170314922 · 2017-11-02
Inventors
Cpc classification
H05K7/1422
ELECTRICITY
H05K1/0271
ELECTRICITY
H05K7/12
ELECTRICITY
H05K2201/2036
ELECTRICITY
G01C19/00
PHYSICS
G01P15/02
PHYSICS
G01P3/00
PHYSICS
H05K2201/10295
ELECTRICITY
H05K2201/10393
ELECTRICITY
H05K2201/068
ELECTRICITY
H05K5/0078
ELECTRICITY
International classification
G01C19/00
PHYSICS
H05K7/14
ELECTRICITY
H05K1/18
ELECTRICITY
Abstract
Printed circuit boards (PCBs) are configured with an athermalized mounting suitable for securing and positioning and the PCBs within an inertial measurement unit (IMU). The PCBs include integrated circuit (IC) components, such as accelerometers and/or gyroscopes, which require relative positional stability within the IMU environment in order to provide accurate results. The athermalized mounting configuration of the PCB enables the PCBs to experience thermal expansion within the IMU without causing significant displacement of the IC relative to the IMU environment.
Claims
1. A printed circuit board configured with an athermalized mount, comprising: a substrate having a top substrate surface and an opposing bottom substrate surface; one or more sensors electrically and physically mounted to the substrate; and three mechanical mounting pins independently coupled to the substrate and extending away from the substrate to separate and corresponding pin ends configured in size and shape for physically engaging a mating surface of an object onto which the printed circuit board is to be mounted, and the three mechanical mounting pins being angularly equidistant from one another.
2. The printed circuit board of claim 1, wherein the three mechanical mounting pins are further equidistant from the center point.
3. The printed circuit board of claim 1, wherein the one or more sensors include an accelerometer.
4. The printed circuit board of claim 1, wherein the one or more sensors include at least one gyroscope.
5. The printed circuit board of claim 1, wherein the one or more sensors include an accelerometer and a gyroscope, wherein the gyroscope and accelerometer are each separately mounted to the substrate.
6. The printed circuit board of claim 1, wherein each of the mechanical mounting pins extends away from the bottom substrate surface to the corresponding pin ends, and the one or more sensors are mounted to the top substrate surface.
7. The printed circuit board of claim 1, wherein the coupling of the mechanical mounting pins to the substrate includes an adhesive coupling.
8. The printed circuit board of claim 1, wherein the mechanical mounting pins are physically interconnected with the substrate by having a mounting portion of each of the three mechanical mounting pins being physically inserted into a corresponding separate recess or aperture formed into at least the bottom substrate surface.
9. The printed circuit board of claim 1, wherein each of the pin ends terminates in a hemispherical-shaped head.
10. An inertial movement unit with an athermalized mount, comprising: a printed circuit board with one or more movement sensors; and three mechanical mounting pins independently coupled to the printed circuit board and extending away from the printed circuit board to separate and corresponding pin ends configured in size and shape for physically engaging a mating surface of a mounting substrate onto which the printed circuit board is to be mounted, and the three mechanical mounting pins being angularly equidistant from one another; and three recesses formed into the mating surface of the mounting substrate, the three recesses being configured in size and shape to physically receive the pin ends.
11. The inertial movement unit of claim 10, wherein the inertial movement unit further includes at least a cover plate and one or more biasing members disposed between the cover plate and the printed circuit board, the one or more biasing members applying a force to the printed circuit board that securely biases the printed circuit board towards the mounting substrate and to thereby securely maintain a position of the mechanical mounting pins correspondingly within the three recesses.
12. The inertial movement unit of claim 11, wherein the cover plate is secured to the mounting substrate with a plurality of screws.
13. The inertial movement unit of claim 11, wherein the one or more biasing members is integrally formed into an interference plate.
14. The inertial movement unit of claim 11, wherein the one or more biasing members includes a plurality of separate springs.
15. The inertial movement unit of claim 10, wherein the three recesses form grooved slots, each of the grooved slots having a longitudinally axis that axially aligns with and intersects the center point.
16. The inertial movement unit of claim 15, wherein the mounting pins terminate in separate free ends that are slidably and correspondingly received within the grooved slots.
17. The inertial movement unit of claim 16, wherein each of the separate free ends comprises a hemispherical head.
18. The inertial movement unit of claim 10, wherein the inertial movement unit further includes a shock buffer member disposed between the printed circuit board and the mounting substrate.
19. The inertial movement unit of claim 16, wherein the shock buffer member comprises an adhesive.
20. A method for manufacturing an inertial movement unit with an athermalized mount, comprising: securing a printed circuit board with one or more movement sensors between a cover plate and mounting substrate, wherein the printed circuit board is configured with three mechanical mounting pins independently coupled to the printed circuit board and extending away from the printed circuit board to separate and corresponding pin ends configured in size and shape for physically engaging a mating surface of a mounting substrate onto which the printed circuit board is to be mounted, and the three mechanical mounting pins being angularly equidistant from one another, and wherein said securing further includes positioning the three separate corresponding pin ends into three corresponding grooved recesses formed into the mating surface of the mounting substrate and biasing the three mechanical mounting pins towards the mounting substrate with one or more biasing members that are positioned between the printed circuit board and the cover plate and in such a manner that the three separate corresponding pin ends are enabled to slide within the grooved recesses during thermal expansion and thermal contraction of the printed circuit board.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to describe the manner in which the above-recited and other advantages and features can be obtained, a more particular description of the subject matter briefly described above will be rendered by reference to specific embodiments which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments and are not therefore to be considered to be limiting in scope, embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
[0018]
[0019]
[0020]
[0021]
[0022]
[0023]
[0024]
[0025]
[0026]
[0027]
[0028]
[0029]
DETAILED DESCRIPTION
[0030] The disclosed embodiments include printed circuit boards (PCBs) and corresponding inertial measurement units (IMUs) that are configured with athermal mounting structures, as well as methods of assembly.
[0031] The athermal mounting structures of the PCBs are operable to position and contain the PCBs within the IMU in such a manner that the integrated circuit (IC) components (e.g., accelerometers and/or gyroscopes) of the PCB are not displaced within the IMU relative to the IMU environment and/or other components that are required to calculate overall position and/or movement of the IMU.
[0032] In some embodiments, the PCB is configured to experience thermal expansion at a different rate than other IMU components that the PCB is mounted to and thereby reduce bowing, warping and/or other distortions to the PCB, particularly distortions that would otherwise occur during use without the disclosed athermal mounting structures and configurations.
[0033]
[0034] In some embodiments, a structure such as pedestal 152 is used to further secure the PCB 100 in place. The pedestal 152 is formed out of a pressure sensitive adhesive (PSA) or another structure that is configured to absorb shock forces. This is beneficial to provide relative stability to the PCB 100 during use and to help prevent the PCB 100 from becoming dislodged during use.
[0035] In some embodiments, the ambient temperatures experienced within an IMU environment will cause the PCB 100 to expand or shrink at different rates than the substrate 160 or other structures the PCB 100 is mounted to. This can cause the PCB 100 to become dislodged from the adhesives applied to the pedestal 152 and/or the pin(s) due to shear forces experienced during the thermal expansion/contraction of the PCB 100. Once the PCB 100 is dislodged, the IMU position and movement calculations will be inaccurately calculated, based on the relative movement of the PCB components themselves (including movements and relative change in positioning within the IMU environment), rather than based on the movement and positioning of the IMU.
[0036] Even if the mounting locations 130, 140 and/or 150 do not fail/break during thermal expansion of the PCB 100, the PCB 100 may bow and/or warp in such a way as to cause angular displacement of the sensor 110. Even a miliradian offset to the sensor 110 in any axis of rotation, relative to the IMU structures that the PCB 100 is mounted to (e.g., substrate 160), can cause inaccuracies in the calculated positioning and/or movement of the IMU.
[0037] Various IMU and PCB embodiments incorporating athermal mounting structures will now be described, which can help to mitigate against one or more of the problems addressed above.
[0038]
[0039] The PCB 210 includes holes (214, 216, 218) for receiving the stems of mechanical mounting pins (234, 236, 238), respectively. The holes (214, 216, 218) are angularly offset or equidistant from each other by 120°, as described in more detail below. While the holes (214, 216, 218) are implicitly shown as passing all the way through the PCB (inasmuch as they extend to the top surface of the PCB 210), in other embodiments, the holes are only partially formed into the opposing bottom surface of the PCB 210, similar to the hole configuration shown in
[0040] Each of the mounting pins (234, 236, 238) is configured with a pin end which is configured in size and shape to be received within and to slidably engage corresponding grooves or slots (234, 236, 238) of the IMU mounting substrate 220. This will be described in more detail below with regard to
[0041] The axial orientations of the grooves (224, 226, 228) are also offset by 120° to correspond with the angular offset of the mounting pins (234, 236, 238) and PCB mounting holes (214, 216, 218). During thermal expansion of the PCB, the pins (234, 236, 238) are enabled to freely slide/float within the slotted grooves (224, 226, 228) as the PCB 210 contracts or expands relative to the mounting substrate 220, and without causing angular distortion to the sensor(s) 212 relative to the mounting structure substrate 220 and IMU environment.
[0042] In some instances, the aforementioned athermal structures (e.g., pins and grooves) are operable to reduce or eliminate the angular distortion (e.g., warping or bowing) and/or linear displacement that would otherwise occur to the PCB 210 relative to the IMU environment if the PCB 210 was fixedly mounted to the substrate 220 in the manner described above with regard to
[0043] In some instances, a shock absorbing mount 230 is also provided, similar to the pedestal mount 152 of
[0044] The IMU 200 also includes one or more biasing springs 250, which are configured to apply a biasing force against the PCB 210, causing the PCB to be biased towards the mounting substrate 220, once it is completely assembled. A mounting plate 240 is also provided to secure the biasing springs 250 in a placement between the mounting plate 240 and the PCB 210. The PCB 210 is ultimately secured between the mounting plate 240 and the IMU mounting substrate 220 when the screws 242 are threaded into receiving holes 222 of the IMU mounting substrate 220. This will be explained in more detail, below, with regard to
[0045] With regard to the foregoing, it will be appreciated that the scope of this disclosure includes IMUs containing one or more combinations of the various components that are illustrated for IMU 200, as well as components that are not shown. For instance, the IMU 200 may include display engine components, imaging systems, laser systems, SoC systems, processors and/or other components that are integrated into and/or hidden from view. These hidden components are operable to receive and use the IMU position and movement information obtained from the PCB 210 sensor(s) 212 in order to perform a particular operation. In the present embodiment, a laser 260 is being generated and emitted from a housing 270 the IMU 200. However, the IMUs of this application are not limited to embodiments including lasers. They can include IMUs integrated into AR and VR devices, GPS devices, measurement devices, personal monitors and other devices.
[0046] Attention will now be directed to
[0047] The sensor 310 includes a combination of one or more accelerometer and one or more gyroscope. In some instances, the sensor 310 includes at least one accelerometer and at least one gyroscope. In some instances, the sensor 310 includes a plurality of separately mounted sensors that are mounted to the substrate 324.
[0048] The sensor 310 is also electrically coupled to other electronic sensors and components of the PCB 300 and IMU. However, electronic coupling for a PCB is not illustrated at this time, as it is well-understood to those of skill in the art.
[0049] The PCB 300 also includes three mechanical mounting pins 330, 340 and 350 that are each independently and physically coupled to the bottom surface 322 of the PCB 300. Each of these mechanical pins extend away from the PCB substrate to separate and corresponding pin ends that are configured in size and shape for physically engaging a receiving surface of an object (e.g., an IMU mounting substrate) onto which the PCB is to be mounted. In some embodiments, the three mechanical mounting pins are angularly equidistant from one another, being spaced apart 120° relative to each other and a centralized location encompassed by or otherwise bounded by the pin locations.
[0050] In some embodiments, the three mechanical mounting pins are also equidistant from the center point or central location 360 where the sensor 310 is located on the PCB 320, such that the distances (D1, D2 and D3) are substantially the same. However, this is not necessarily always the case, as reflected in
[0051]
[0052] The respective positioning (444, 454, 464) of the slotted grooves that are formed into the IMU mounting substrate and that configured to receive the mounting pins are also aligned with the 120° angular offset boundaries (452, 462 and 472). In this manner, each of the three recesses of the grooved slots has a longitudinal axis that intersects the center point 470 and that is co-axially aligned with one of the 120° angular offset boundaries (452, 462 and 472), respectively.
[0053]
[0054] In some embodiments, the one or more movement sensors on the PCB are positioned directly above at or at least substantially proximate a central point or location that exists and that is defined by the intersection between the 120° angular offsets between the mounting pin locations. In
[0055]
[0056] The mechanical pin 530 is physically secured to the PCB 520 by an adhesive between the pin surface and the PCB substrate, a friction fit, a tapered fit, a snap fit, soldering and/or another means for attaching the mechanical pin 530 to the PCB 520.
[0057] In some embodiments the mechanical pin does not include a stem, such as implied by the illustration of the mechanical pin 560 shown in
[0058] It is also possible for the mechanical pin to have a stem and no shoulder. For instance, the stem 572 of the mechanical pin 570, which is shown in
[0059] Notably, each of the pin ends (536, 566, 576) preferably, although not necessarily, terminates in a free and hemispherical-shaped head, such as head 580. This can help enable the pin(s) to slidably engage the corresponding slotted groove(s) 540 formed into the IMU mounting substrate(s) 550. In this manner, the mechanical mounting pins are enabled to move (slide/float) within the grooved recesses without causing linear and/or angular displacement of an IC component (which is substantially centrally positioned relative to the mounting pins), relative to one or more other IC components or IMU components, as described above.
[0060] The hemispherical-shaped head 580 is not presently shown as being in direct contact with the sidewall surfaces of the slotted grooves (540). However, during actual use (subsequent to full assembly), the pin 570 of
[0061] The mechanical pins are operable with different sizes in diameter and length. In some instances, the diameter of the pin ends is between about 0.5 mm and 1.0 mm. However, the pin diameters can also be smaller than 0.5 mm or larger than 1.0 mm.
[0062] The slotted groove is presently shown to include an inner angle that is be greater than about 90°. However, in some embodiments, the inner angle is about 90°, or even less than 90°. The angle and depth of the slotted grooves is based on the size of the pin ends and the biasing forces applied by the biasing springs, so as to enable the pin ends to freely slide/float with the slotted grooves during thermal expansion of the PCB. In some alternative embodiments (not shown), the pin ends terminate in substantially flat surfaces and the slotted grooves comprise substantially rectilinear channels.
[0063] Attention will now be directed to
[0064] As shown, a PCB 610 is configured with a measurement sensor 612, as well as mounting pins (634, 636, 638) that are aligned with corresponding slotted grooves (624, 626, 628), respectively.
[0065] The spring force(s) applied by the biasing spring(s) 650 is sufficient to press and hold the PCB 610 against the mounting substrate 620 in such a manner as to securely maintain positioning of the mechanical mounting pins (634, 636, 638) correspondingly within the recesses of the slotted grooves (624, 626, 628), while still enabling the mechanical mounting pins (634, 636, 638) to slide/float within the recesses of the slotted grooves (624, 626, 628) during thermal expansion of the PCB 610.
[0066] While screws/bolts 642 are shown as one means for affixing the cover plate 640 to the IMU mounting substrate 620, it will be appreciated that various other mechanisms can also be used as a means for affixing the cover plate 640 to the IMU mounting substrate 620, including one or more latch(es), rivet(s), snap or friction fit(s) and so forth.
[0067] The biasing spring(s) 650 described above represent only one example of a biasing means that is suitable for biasing the PCB towards the IMU mounting substrate. These biasing spring(s) 650 can be replaced with or supplemented with any other biasing means that is capable of biasing the PCB towards the IMU mounting substrate, including any type of spring, spacers, or other structures. In one embodiment, the biasing means includes mechanical structures that protrude away from the cover 640, towards the PCB 610. An example of such protrusions are shown in
[0068] The view shown in
[0069] Currently, the dimpled and recessed protrusions (794, 796, 798) are aligned with the positioning of the mechanical pins. For instance, protrusion 794 is aligned with pin 734 and protrusion 796 is aligned with pin 739. The last protrusion 798 is also aligned with another pin (not shown). In this manner, the protrusions act as biasing members that are integrally formed into the cover (interference plate), which are sufficient to bias/hold the PCB 710 against the mounting substrate 720.
[0070] The cover 790 also includes a recessed portion or an outward protrusion 792 that is sufficient to receive/house the sensor(s) 712 when the cover 790 is positioned and affixed into the desired location relative to the IMU mounting substrate 720. Means for affixing the cover to the IMU mounting substrate 720 are not shown. However any of the means for affixing described above can also be used to affix the cover 790 to the IMU mounting substrate 720 (e.g., latch(es), rivet(s), snap or friction fit(s)), as well as any adhesive or other suitable attachment mechanism.
[0071] The foregoing embodiments describe PCBs and IMUs having athermalized mounting structures. The scope of this disclosure also extends to methods of use and manufacture of any of the disclosed PCBs and IMUs having athermalized mounting structures.
[0072] In some embodiments, methods are provided for securing a PCB containing one or more movement sensors between a cover plate and mounting substrate, wherein the PCB is configured with three mechanical mounting pins independently coupled to the printed circuit board and extending away from the printed circuit board to corresponding separate pin ends that are each configured in size and shape to physically/slidably engage a receiving surface of a mounting substrate onto which the PCB board is to be mounted. The three mechanical mounting pins are angularly equidistant from one another relative to a location positioned along a plane between the mounting pins.
[0073] The securing also includes positioning the three separate corresponding pin ends into three corresponding grooved recesses formed into the mating surface of the mounting substrate and which are also angularly equidistant from one another. The securing includes using one or more biasing members that are positioned between the PCB and the cover plate to flexibly bias the three mechanical mounting pins towards the mounting substrate and in such a manner that the three separate corresponding pin ends are enabled to slide within the grooved recesses during thermal expansion and thermal contraction of the printed circuit board.
[0074] The present invention may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.