Method and apparatus for joining together portions of a geometric assembly

A housing comprises at least first and second portions. The first and second portions mate with each other at respective joining regions. The first and second portions each comprise a respective tapered flange along the joining region. The first and second portions of the housing are connected to each other by placing a plurality of collars over the tapered flanges of the first and second portions of the housing. Each of the collars has a respective groove formed therein. The grooves of the plurality of collars are placed over the tapered flanges of the first and second portions of the housing. A plurality of fasteners causes the plurality of collars to press the first and second portions of the housing together. In one embodiment, the housing is used in a sensor block assembly that is part of an inertial measurement unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to the following United States patents and patent applications, all of which are hereby incorporated herein by reference:

BACKGROUND

One type of inertial navigation system (INS) employs an inertial measurement unit (IMU) that is floated in gas. Floating the IMU in gas creates a near frictionless environment to enable the IMU to move in all directions. By enabling motion in all directions, complete calibration utilizing earth gravity and earth rate is possible. By floating the IMU in gas, the need for gimbals and ball bearings is eliminated, thereby reducing the complexity, size, and cost of the inertial navigation system. Also, by eliminating gimbals, ball bearings, and other moving physical structures, there is typically no wear on the physical structures from contact between rotating surfaces, which improves the accuracy and durability of such an INS. Examples of such an INS are described in the '184 application.

In one exemplary implementation of an INS that uses a gas-supported IMU, the IMU is housed within a spherical sensor block. Typically, such a spherical sensor block is formed as two hemispheres. The two hemispheres are attached to one another using a main shaft that extends from one hemisphere and is connected to the other hemisphere. In order to balance the two hemispheres, the main shaft includes a three dimensional balance assembly comprising a center shaft with two or more eccentric weighted shafts encompassing the center shaft. These weighted shafts can be used to balance the overall assembly. One example of such a spherical sensor block is described in the '902 patent.

When joining the two hemispheres of such a spherical sensor block together, it is important that distortion of the sphere be kept below a minimum threshold limit. It is also important to keep slippage between the hemispheres during high G level environments below a minimum threshold limit. One example of where this may be a concern is during the launch of a vehicle in which the sensor block is deployed. For example, the relative angular position of internal instruments housed within the sensor block must be held to very small tolerances during G loading. This dictates very precise alignment to be maintained between the two hemispheres. Distortion or slippage of the hemispheres would cause the sensor block to be less spherical, which could result in instrument axis alignment error. Minimizing tolerance conflicts between the two portions of the sphere helps to reduce shifting during loads or thermal excursion of the assembly.

The joining together of two portions of a sphere with an axle, as described in the '902 patent, typically puts a load on the sphere, which may distort the sphere. In some applications, such distortion may be beyond acceptable limits. The axle passes through the center of the spherical assembly and may interfere with internal components in some applications.

Another possible approach to joining the two hemispheres is using a tongue-in-groove mechanical joint. However, such mechanical joints often have tolerance conflicts or require match machining of two parts, which does not allow for interchangeability with other parts. Generally, it is desirable to manufacture the two hemispheres independent of one another so one can be interchangeable with another having a different design, manufacturing date, or source.

Also, as noted above, the sensor block must be balanced properly to enable free rotation. Typically, the sensor block must be disassembled to balance the sensor block. Adjustment of final fine balance from the outside of the assembled sphere is desirable in order to obtain consistent results with minimal assembly/disassembly time.

SUMMARY

In one embodiment, an apparatus comprises a housing, which comprises at least first and second portions. The first and second portions mate with each other at respective joining regions. The first and second portions each comprise a respective tapered flange along the joining region. The first and second portions of the housing are connected to each other by placing a plurality of collars over the tapered flanges of the first and second portions of the housing. Each of the collars has a respective groove formed therein. The grooves of the plurality of collars are placed over the tapered flanges of the first and second portions of the housing. A plurality of fasteners causes the plurality of collars to press the first and second portions of the housing together.

In another embodiment, an inertial navigation system comprises a navigation unit and an inertial measurement unit communicatively coupled to the navigation unit. The inertial measurement unit comprises a sensor block and a plurality of gas pads. The gas pads are configured to suspend the sensor block in gas. The sensor block comprises a housing comprising at least first and second portions. The first and second portions mate with each other at respective joining regions. The first and second portions each comprise a respective tapered flange along the joining region. The first and second portions of the housing are connected to each other by placing a plurality of collars over the tapered flanges of the first and second portions of the housing. Each of the collars has a respective groove formed therein. The grooves of the plurality of collars are placed over the tapered flanges of the first and second portions of the housing. A plurality of fasteners causes the plurality of collars to press the first and second portions of the housing together.

Another embodiment is directed to a method for clamping at least a first portion and a second portion of a housing for an apparatus. The first and second portions mate with each other at respective joining regions. The first and second portions each comprise a respective tapered flange along the joining region. The method comprises positioning a plurality of collars over the tapered flange of the first portion of the housing. The method further comprises joining at least the second portion to at least the first portion. The plurality of collars is positioned over the tapered flanges the first and second portions. The method further comprises fastening at least the first portion to at least the second portion using a plurality of fasteners that engage the plurality of collars.

The details of various embodiments of the claimed invention are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims.

DETAILED DESCRIPTION

FIG. 1is a block diagram of one embodiment of an inertial navigation system (INS)100. The INS100includes an inertial measurement unit (IMU)101that is floated in gas. In particular, the IMU101comprises a sensor block102(also referred to as sensor block assembly102) that houses one or more instruments or sensors104(shown inFIG. 2) for monitoring (or otherwise generating signals or information indicative of) angular position, acceleration, calibration and the like.

The system100further includes one or more gas pads106and one or more gas jet assemblies108that are positioned around the sensor block102. In such an embodiment, pressurized gas is supplied to, and flows out from, the gas pads106and the gas jet assemblies108. The gas flowing from the gas pads106is used to pressurize the gap between the gas pads106(and an enclosure for the sensor block102(not shown)) and the sensor block102, which causes the sensor block102to float in the gas. This creates a near frictionless environment free of any physical contact. The sensor block102is shown supported (or floated) within the gas bearing107generated by the gas pads106. In the particular embodiment shown inFIG. 1, the gas flowing from the gas jet assemblies108is used to rotate the sensor block102(for example, by releasing gas from the gas jet assemblies108in short pulses or bursts). The gas jet assemblies108are used to move the sensor block102in various directions and into various positions, and are typically used in the calibration of the sensors104housed within the sensor block102. Reference number109generally illustrates an example of a rotational motion of the sensor block102.

The system100further includes a navigation unit110to control the operation of the various components of the system100and to process the information output by the sensors104housed within the sensor block102(for example, to generate a navigation solution using the information output from the sensors104housed within the sensor block102). The sensors104are in wireless communication with the navigation unit110.

Additional information about such an embodiment is set forth in the '344 patent, the '399 patent, the '184 application, and the '452 application.

FIGS. 2A and 2Bshow one embodiment of a sensor block102suitable for use in the system ofFIG. 1. The sensor block102comprises a housing112that is formed out of two or more portions114that are connected to one another (using techniques described herein) when the sensor block102is assembled.FIG. 2Ashows the sensor block102in an unassembled or open state, andFIG. 2Bshows the sensor block102in an assembled state. In the particular embodiment shown inFIGS. 2A-2B, the housing112of the sensor block102comprises two substantially equal hemispherical portions114(referred to individually as first and second portions114-1and114-2). In such an embodiment, the portions114are formed from aluminum or any other suitable material. In one implementation of such an embodiment, the housing112(and the portions114thereof) is formed with a quarter-inch thick aluminum wall.

The circumference124of the housing112where the first and second portions114-1and114-2mate when the housing112is assembled is referred to here as the “joining circumference”124.

Sensor block102further includes a divider116connected to both the hemispherical portions114of the housing112. In the particular embodiment shown inFIGS. 2A-2B, the divider116comprises a circuit board having a disk shape and includes one or more electronic components mounted thereon. In alternate embodiments, divider disk116has no electronic components mounted thereon or the sensor block102does not include a divider116and any electronics are mounted at other locations within housing112.

Each of the instruments or sensors104is mounted to the inside of the housing112in a particular position. The housing112also protects the instruments104from vibrations, thermal variations, radiation and other environments that could degrade the sensors104. In one implementation of the embodiment shown inFIGS. 2A-2B, the sensors104housed within the sensor block102include an arrangement of three accelerometers and three gyroscopes that are used to generate a position and attitude estimate for a vehicle (or other device) in which the system100is deployed. Accelerometers are inertial sensors that sense a linear change in rate (that is, acceleration) along a given axis. Gyroscopes are inertial sensors that sense angular rate (that is used to determine, rotational velocity or angular position). In such an implementation, the three accelerometers are typically oriented around three mutually orthogonal axes (for example, the x, y, and z axes) and the three gyroscopes are typically oriented around three mutually orthogonal axes (for example, pitch, yaw, and roll axes). The outputs of the sensors104are processed by, for example, the navigation unit110.

Although a particular embodiment of the system100and sensor block102are shown in FIGS.1and2A-2B, it is to be understood that other embodiments are implemented in other ways. For example, sensor blocks can have other numbers of portions, or portions having unequal sizes or volumes.

In some applications, the embodiment of the sensor block102shown in FIGS.1and2A-2B needs to keep within a minimum threshold limit to its intended shape over many environmental factors. Environmental changes that the sensor block102may experience include a temperature range from about 60 degrees Fahrenheit to about 130 degrees Fahrenheit. The sensor block102may be exposed to high G level forces, such as 20 Gs. Exposure to radiation may cause the sensor block102to heat unevenly. Also, the pressure load in the initial assembly of the sensor block102could cause uneven loading, such as up to 100 lbs. Despite these environmental conditions, the sensor block102should maintain stability within a threshold limit for a period of time, such as 20 years. Rotation and translation of the first portion114-1relative to the second portion114-2should be kept below a minimum threshold limit. Embodiments of the sensor block102described here keep the portions114from shifting beyond small fractions of an inch. Such embodiments provide ways and apparatuses for keeping these environmental effects to a minimum threshold limit.

FIGS. 3A-3Dare various views illustrating one embodiment for joining together the first and second portions114-1and114-2of the housing112of the sensor block102shown inFIGS. 2A and 2B.

As used herein, the region of each portion114of the housing112that mates with the other portion114of the housing112is referred to here as the “joining region”118, where joining region118-1refers to the joining region of the first portion114-1and joining region118-2refers to the joining region of the second portion114-2.

As shown inFIG. 3B, each of the joining regions118-1and118-2has a respective tapered flange120that extends into the interior of the housing112. The tapered flange of the joining region118-1of the first portion114-1is referred to as the first tapered flange120-1, and the tapered flange of the joining region118-2of the second portion114-2is referred to as the second tapered flange120-2. When the joining regions118-1and118-2of the first and second portions114of the housing112are brought together, the combined tapered flanges120-1and120-2join together to form a v-shaped ridge122along an interior surface of the joining circumference124.

A plurality of collars126, each having a v-shaped groove128formed therein (which is shown inFIGS. 3B and 3C), is used to press the first and second portions114-1and114-2of the housing112together. InFIG. 3D, only the joining region118-1of the first portion114-1of the housing112is depicted in order to show the plurality of collars126. Each of the collars126is positioned over a respective portion of the v-shaped ridge122formed along the interior circumference124of the housing112. The v-shaped groove128formed in each of the plurality of collars126is sized to be slightly smaller than the v-shaped ridge122formed by the tapered flanges120-1and120-2of the first and second portions114-1and114-2of the housing112so that, when the plurality of collars126is positioned over the v-shaped ridge122and pressed toward the interior surface of the housing112, the v-shaped groove128formed in each of the plurality of collars126presses along the outer surfaces130-1and130-2of the tapered flanges120-1and120-2and clamps the first and second portions114-1and114-2together. The radial load placed on the collars126is transferred to a clamping load by the ramps of the v-shaped groove128and the v-shaped ridge122.

A plurality of holes132is formed in the joining regions118-1and118-2along the joining circumference124. In the particular embodiment shown inFIGS. 3A-3D, a respective half of each of the holes132is formed in each of the joining regions118-1and118-2of the first and second portions114-1and114-2of the housing112. Each of the plurality of collars126includes a threaded hole134formed therein. Each of the plurality of collars126is positioned so that a respective bolt136(or similar fastener) can be inserted through a respective hole132of the housing112and screwed into the respective threaded hole134of the collar126. When the fastener136is tightened, the fastener136presses the collar126toward the interior surface of the housing112.

The plurality of fasteners136may be bolts, screws, clasps, or the like. The fasteners136may be comprised of aluminum, steel, tungsten, or any other suitable material. In one implementation of such an embodiment, the fasteners136are made of the same material as the housing112of the sensor block102in order to decrease the difference in thermal expansion between the fasteners136and the sensor block102. In other implementations, the fasteners136may be made out of a material that differs from the housing112. Also, in some implementations, in order to balance the sensor block102, the fasteners136may vary in density, mass, length, type of material, or any other parameter that could aid in balancing the sensor block102. Varying the properties of the fasteners136allows for fine adjustments to the balance of the sensor block102in two axes with minimal opening and closing of the assembly. The third axis of balance is achieved by additional fasteners136that are positioned toward or away from the center of the sensor block102and are placed on axes away from the joining circumference124.

In the particular embodiment shown inFIGS. 3A-3D, each of the collars126also has a second groove138into which a flexible band140is inserted. The flexible band140is used to assist in positioning collars126. The flexible band140is shaped to match the joining circumference124of the housing112. In the particular embodiment shown inFIGS. 3A-3Dwhere the sensor block102has spherical shape, flexible band140comprises an o-ring. Flexible band140may be composed of rubber, or of any other suitable material. Flexible band140fits into the groove138in the plurality of collars126and is used to hold collars126in place during the process of assembling the housing112. Since tightening the fasteners136may cause the collars126to move closer to each other, it is desirable for the collars126to be positioned so that there are gaps between each of them and for flexible band140to be able to bend or compress as the fasteners136are tightened.

In the particular embodiments shown inFIGS. 3A-3D, a tooling shelf142is included on an inner surface of the housing112. The tooling shelf142supports the plurality of collars126while they are being positioned during assembly. Tooling shelf142supports the plurality of collars126prior to and during the tightening of the fasteners136. Either, or both, portions114-1or114-2of the housing112may have a tooling shelf.

The fasteners136and the collars126may be placed every few inches along the joining circumference124. In one implementation of such an embodiment, the heads of the fasteners136are flush with the outer surface of the housing112. In other implementations, the fasteners136sink approximately 2 millimeters to 3 millimeters below the outer surface of the housing112. In yet other implementations, the shape of the heads of the fasteners136are matched to the outer surface of the sensor block102. For example, in one example of such an implementation, if the sensor block102is spherical, the fasteners136have rounded heads to match the shape of the outer surface of the housing112. In other implementations, the fasteners136have other shapes. Examples of suitable materials that the collars126can be formed of include aluminum, steel, tungsten, or any other suitable material. In some implementations of such an embodiment, each of the collars126may have an insert in which the threaded hole134is formed. For example, in one such implementation, the insert made of steel. In another implementation, the collars126are made of the same material as the sensor block102in order to decrease the difference in thermal expansion between the collars126and the sensor block102. In order to balance the sensor block102, the collars126may vary in density, mass, length, type of material, or any other parameter which could aid in proper balancing of the sensor block102.

The clamping system described here can achieve a high rate of interchangeability of parts. In one embodiment, the portions114-1and114-2are independent so one can be interchanged with another design, manufacture date, or source. For example, a hemisphere could be replaced with another hemisphere since the portions can be nearly identical. The overall sensor block102is easy to disassemble and reassemble (requiring removal and replacement of the fasteners136and repositioning of the collars126). Also, balancing requires less disassembly than typical solutions. In one embodiment, only some of the fasteners136have to be replaced to achieve a balanced sensor block102.

Moreover, the joint between the first portion114-1and the second portion114-2of the housing112allows for disassembly and reassembly with very good repeatability of the alignment of the portions114-1and114-2. Balance of the sensor block102can be finely adjusted by varying properties of the plurality of collars126and the fasteners136while minimizing disassembly of the sensor block102and while maintaining the shape of the sensor block102within threshold limits.

FIG. 4shows an alternative embodiment of a sensor block102suitable for use in the system ofFIG. 1. In this embodiment, the sensor block102(and the fastening system thereof) is the same as the sensor block102described above except as described here in connection withFIG. 4. Those parts of the sensor block102that are the same as the sensor block102described above are referenced in the following description using similar reference numerals.

In the embodiment of the sensor block102shown inFIG. 4, each of the holes132in the joining regions118-1and118-2of the housing112are formed so as to include a respective circular ring flange144that extends radially outward from the outer surface of the housing112. In this embodiment, a respective half of each of the circular ring flanges144is formed in each the joining regions118-1and118-2of the first and second portions114-1and114-2of the housing112. A tapered washer146is placed over each of the circular ring flanges144. Each fastener136is inserted through a respective tapered washer146and a respective hole132of the housing112and screwed into the respective threaded hole134of the collar126. When the fastener136is tightened, the fastener136presses the tapered washer146down onto the circular ring flange144, which also presses first and second portions114-1and114-2of the housing112together.

FIG. 5is a flow chart depicting one embodiment of a method500for joining a sensor block102. Method500is described here as being implemented using the embodiment of the sensor block102described above in connection withFIGS. 1,2A-2B, and3A-3D (though other embodiments are implemented in other ways).

Method500begins at block510. At block510, the plurality of collars126is positioned on one of the portions114-1or114-2along the inside of the respective joining region118-1and118-2. In one implementation of such an embodiment, the second portion114-2includes a tooling shelf142. The plurality of collars126can be held in place on tooling shelf142. As noted above, a flexible band140can be used to position and hold in place the plurality of collars126while the sensor block102is being assembled.

After the plurality of collars is positioned, method500moves to block520. At block520, first and second portions114-1and114-2are mated together so that respective inner surfaces of the joining regions118-1and118-2touch. The v-shaped groove128formed in each of the plurality of collars126is fitted over the v-shaped ridge122that is formed by the tapered flanges120-1and120-2. In other embodiments, the ridge122is of a shape other than a v-shape, and groove128matches inversely the shape of ridge122.

In one implementation of this embodiment, the first and second portions114-1and114-2are mated together in the following manner. Fasteners136are set into place on first portion114-1and partially threaded into the collars126prior to adding the second portion114-2. The fasteners holes132being semicircular on each portion114allows the fasteners136to be laid in place prior to tightening. Laying fasteners136before tightening provides additional control over the positioning of the collars126once the second portion114-2is in place since limited access to the collars126is available once the portions114are joined. In other implementations, fasteners136are inserted at a later point in the joining process.

After the two portions114-1and114-2of the housing112are joined, method500proceeds to block530. At block530, first and second portions114-1and114-2are fastened together. In one implementation where fasteners136are partially threaded when portions114-1and114-2are mated in block520, the fasteners136are tightened in block530. In other implementations, the fasteners136are inserted into the holes132in the housing112and screwed into respective threaded holes134formed in the collars126.

Each of the plurality of collars126is positioned so that a respective bolt136(or similar fastener) can be inserted through a respective hole132of the housing112and screwed into the respective threaded hole134of the collar126. When the fastener136is tightened, the fastener136presses the collar126toward the interior surface of the housing112. In one implementation, the fasteners136are bolts which pull the plurality of collars136radially outward until they engage the tapered flanges120-1and120-2of the first and second portions114-1and114-2. In fastening first portion114-1to second portion114-2, it is important that distortion of sensor block102is kept to a minimum threshold limit. Therefore, tightening fasteners136may proceed by tightening them alternatively on opposing sides of sensor block102, in order to keep application of torque and loads evenly distributed during assembly.

Method500then proceeds to block540. At block540, sensor block102is balanced. The sensor block102may be balanced by changing the length or composition of some of the plurality of fasteners136. Balancing of the sensor block102is important because balancing aids to prevent unwanted rotation of the sensor block102due to G loading. The torque applied by the gas jet assemblies108must be able to overcome the off balance torque in a high G environment.

A number of embodiments of the invention defined by the following claims have been described. Nevertheless, it will be understood that various modifications to the described embodiments may be made without departing from the spirit and scope of the claimed invention. For example, although the technique for joining multiple portions of a housing is described above in connection with embodiments in which the housing has a substantially spherical shape, the joining technique described here can be used with housings having other shapes (including, without limitation, cubes, pyramids, and cylinders) and with housings used in other applications. Accordingly, other embodiments are within the scope of the following claims.