Patent Application
20080084258
For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings which show at least one exemplary embodiment, and in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
It will be appreciated that for simplicity and clarity of illustration, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Furthermore, this description is not to be considered as limiting the scope of the embodiments described herein, but rather as merely describing the implementation of the various embodiments described herein.
The lever element 12 is a substantially flat section with three pivot openings formed therein located at pivot points A, B and C. Accordingly, the lever element 12 is designed to be coupled to the membrane section 14, the anchoring element 18 and the thermal expansion element 16 at the three pivot points A, B and C, respectively as shown in
The lever element 12 is preferably manufactured out of a material with high tensile strength and stiffness (e.g. steel). The lever element 12 is sized sufficiently large to have negligible elastic deformation under the reaction loads from the cavity end wall. In this way, the compensation rate is a function only of the geometry and the CTE of constituent parts and therefore is predictable and controllable to a high precision. Any structural material of suitable stiffness may be employed with ANSI 440-C stainless steel being preferred because of its superior bearing qualities at the pivot points A, B and C.
The lever element 12 is slotted at the end at which it pivotally connects to membrane section 14 (
The thermal expansion element 16 is coupled at pivot point C to the lever element 12 through the pivoting connector 24 (
Generally speaking, the top section 17 and bottom section 19 of the thermal expansion element 16 are both manufactured from material or materials that have a relatively low coefficient of thermal expansion (CTE) in relation to the cavity filter assembly 30 as will be discussed. Specifically, the top section 17 of thermal expansion element 16 is preferably manufactured from a material such as Invar having a coefficient of thermal expansion preferably in the range of 0.7 to 1.5 ppm/C.°. The bottom section 19 is preferably manufactured of the same material (e.g., Invar).
The bottom section 19 has a locating feature such as a shoulder (not shown) formed at the end of the bottom section 19 and which is adapted along with an mounting element 26 to securely couple the filter compensation assembly 10 to the bottom portion of the housing of a cavity filter assembly 30.
This is achieved by means of contact between the shoulder 26 and a land surface within the anchoring boss of cavity filter assembly 30 (
The two-piece design of the thermal expansion element 16 allows for the necessary assembly adjustments to mitigate the effect of a combination of manufacturing tolerances and permits the identical thermal expansion element to be applied to a range of different cavity lengths. While the thermal expansion element 16 could be of unitary design, the two-piece construction is highly advantageous because of the adjustments permitted.
While the top section 17 and the bottom section 19 are described above as both being manufactured out of a common material such as Invar, the inventors have observed that it is difficult to thread Invar material into Invar material because of the softness of the material. An alternative is to make one of the top section 17 and the bottom section 19 out of a material such as Invar and design it as long as possible dimensionally and make the companion part out of a harder material (e.g. steel) and as short dimensionally as possible. The underlying concept of this strategy would be that the short part would be optimized for strength but contributes little absolute expansion because of the minimum length. Another alternative for the thermal compensation element 16 to be manufactured as a single piece with an external thread positioned at the end that corresponds to the housing restraining element 32. A threaded nut fattener is then used to secure the thermal compensation element 16 to the restraining element 32 with adjustment provided by inserting shims under the fastener.
Also, it should be noted the thermal expansion element 16 is provided outside the cavity filter assembly 30 and is not strongly bound to the cavity in terms of heat flow. Therefore the thermal expansion element 16 can deviate in temperature from the cavity filter assembly 30 depending on application specific thermal boundary conditions. For this reason, the preferred material for the thermal expansion element 16 is Invar that is sufficiently near zero CTE that the temperature deviation is not of significant consequence. Thermal expansion element 16 can be manufactured out of higher CTE but this requires custom design.
Finally, the relatively long dimension of the thermal expansion element 16 in relation to the other elements of the filter compensation assembly 10 reduces the sensitivity of the filter compensation assembly 10 to manufacturing tolerances. This is because the compensation rate is proportional to the length of the length of thermal expansion element 16. The only other critical elements to maintaining controlled compensation rate are the locations of the pivot points A, B, and C on lever 12, which are can be readily controlled.
The anchoring element 18 is utilized to secure the filter compensation assembly 10 to the housing of the cavity filter assembly 30 as will be discussed. The anchoring element 18 is preferably a relatively short rod, however, it should be understood that anchoring element 18 could be of any suitable shape and/or cross-section. The anchoring element 18 includes a restraining element 28 which is positioned near the end of the anchoring element 18 and which is adapted to securely couple the filter compensation assembly 10 to the top portion of a filter housing at pivot point B. The anchoring element 18 is preferably manufactured from a material with substantial tensile strength (e.g. steel) to ensure stability. The restraining element 28 is sufficiently small that the CTE of the material does not significantly affect the compensation mechanism.
Now referring to
As shown, the filter cavities are arranged such that the longitudinal dimension of the filter cavities are arranged in a parallel orientation and there is internal coupling through the side walls (not shown). The cavity filter assembly 30 is typically manufactured from aluminum with a relatively high CTE. As previously discussed, each filter compensation assembly 10 provides a driving mechanism that consists of the thermal expansion element 16 having a low CTE which in the presence of temperature increase, causes the lever element 12 to bear down onto the membrane section 14 (i.e. the cavity end wall) of the filter cavity assembly 30. Conversely, in the presence of a temperature decrease, the mechanism causes the lever element 12 to pull up on the membrane section 14.
These actions of the compensating mechanism of the filter compensation assembly 10 are described relative to a quiescent flat condition of the membrane section 14. Possible alternative embodiments of the mechanism include cases where the filter compensation assembly 10 is initially installed in a pre-stressed condition where the membrane section 14 is initially deformed so that the mechanism action is to either pull or push only during operation in order to negate the effects on mechanism slop (or backlash).
As can be seen in
As previously discussed, the mounting element 26 on the bottom section 19 of the thermal expansion element 16 is used to secure the filter compensation assembly 10 to the bottom housing of cavity filter assembly 30 and is specifically secured within a restraining element 32 as shown in
Also, as previously discussed, the anchoring element 18 is used to pivotally secure the filter compensation assembly 10 to the top portion of the housing of cavity filter assembly 30 through a pivoting connector 22 at pivot point B. Specifically, and as shown in
Finally, the lever element 12 is pivotally coupled to the membrane section 14 of the cavity filter assembly 30 through pivoting connector 20 at pivoting point A.
As shown in
As previously discussed, since the lever element 12 is slotted at the end where it meets the membrane section 14 (
As shown in
Specifically, in the presence of an increase in operational temperature the thermal expansion element 16 will expand less relative to the aluminum cavity filter assembly 30 (
Since the anchoring element 18 anchors one end of the lever element 12 at pivot point B, and since the thermal expansion element 16 does not expand as readily as the cavity filter assembly 30, the lever element 12 will exert downwards pressure on the membrane section 14 at pivot point A (as illustrated by arrow A in
The filter compensation assembly 10 has freely moving pivot points that permit the mechanism to be arbitrarily stiff relative to the membrane section 14 and therefore highly deterministic in performance. In contrast, the prior art compensation assemblies employ bi-metal material or flexure structures to deform cavity end walls. In these designs, the cavity wall position is determined by an equilibrium of opposing elastic forces and specifically the restoring force of the cavity wall and the deforming forces of the thermally induced stresses. The precision of these kinds of compensation assemblies is dependent on the stiffness of the elements that are difficult to control in manufacture.
It should be noted that the design of the anchoring element 18 determines the degree of mechanical amplification at issue according to conventional principles of lever mechanical operation. Specifically, the difference between the lengthwise thermal expansion (or contraction) of the cavity filter assembly 30 and the expansion (or contraction) of the thermal expansion element 16 imparts a countervailing and larger displacement towards (or away from) the center of membrane section 14 of a magnitude equal to the expansion of the cavity filter assembly 14 times the ratio of the between pivot-point lengths B-A to B-C. This lever mechanism of the filter compensation assembly 10 amplifies the differential expansion (or contraction) of the various assembly elements, allowing for larger displacements than permitted in prior art devices, thereby accommodating greater temperature excursions that are inherent in high power applications.
In contrast, in many prior art compensation assemblies, both the motion inducing element (e.g. the low CTE element) and the target element (e.g. membrane) are designed to bend together. The main appeal of the present approach is that the motion inducing element is highly rigid, with all rotations achieved through pivots, so that the amount of mechanical compensation results from simple geometry calculations, such as the lever ratio, instead of a balance between opposing spring forces, which can be notoriously inconsistent in respect of material properties and manufacturing dimensions. Since the cavity wall must be displaced by more than the lengthwise thermal expansion of the cavity filter assembly 30 because radial expansion of the cavity filter assembly 30 affects the resonant frequency in a similar sense and must be compensated, the ability to amplify the relative size changes of the relevant elements of the filter compensation assembly 10 significantly extends the operating range of the mechanism in comparison with the prior art.
Finally, the mechanical action of the filter compensation assembly 10 is substantially more linear in nature than is the case in prior art compensation assemblies. The resonant frequency of a cylindrical cavity is proportional to the scale, therefore, the proportional change in frequency with temperature is precisely the same as the CTE of the material from which it is made. The resonant frequency is not proportional to length alone, but over the range of operation of the present invention, very closely approximates a linear relationship. Therefore, a compensation method where the compensation is directly proportional to expansion represents a preferred solution. Accordingly, the filter compensation assembly 10 is more effective in controlling the linear effects of thermal expansion then other conventional non-linear solutions.
As shown in
Each of the first and second lever elements 52a and 52b are adapted to be coupled at pivot points D and D′, respectively to a spreader beam 86 mounted on a narrow wall 84 of a manifold 80 (
The first and second lever elements 52a and 52b are preferably manufactured out of a material with very high tensile strength and stiffness (e.g. steel). The lever elements 52a and 52b are sized sufficiently large to have negligible elastic deformation under the reaction loads from the manifold wall. In this way, the compensation rate is a function only of the geometry and the CTE of constituent parts and therefore is predictable and controllable to a high precision. The coefficient of thermal expansion (CTE) of the lever elements 52a and 52b is inconsequential because of the slotted pivot holes at the pivot points D and D′ which are designed to accommodate any in-plane expansion of the manifold narrow wall. Any structural material of suitable stiffness may be employed with ANSI 440-C stainless steel being preferred because of its superior bearing qualities at the various pivot points.
As shown in
It should be noted that
The thermal expansion element 56 is a substantially rectangular element and has openings formed therein at pivot points F and F′ (
Now referring to
As shown, in
Each manifold compensation assembly 50 is positioned transverse to the length of the manifold such that the first and second lever elements 52a and 52b are located on opposite sides of the manifold 80. The first and second anchoring elements 54a and 54b are fixed to the manifold using standard fasteners. The first and second lever elements 52a and 52b have amplification which results from the relative spacing of the pivot points E, F, and D and E′, F′, and D′, along the length of the first and second lever elements 52a.
Specifically, as the separation of E and E′ increases (or decreases) due to thermal expansion (or contraction) of the rigid broad wall of the manifold, the levers rotate about F and F′. The displacement seen at D or D′ exceeds the relative displacement between E and F in accordance with the ratio of lengths. That is, the difference between the thermal expansion (or contraction) of the manifold 80 and the expansion (or contraction) of the thermal expansion element 16 imparts a countervailing and larger displacement towards (or away from) the narrow wall 84 of manifold 80 that is directly proportional to the ratio of the between pivot-point lengths E-D to E-F (and E′-D′ to E′-F′). Again, this lever mechanism of the manifold compensation assembly 50 amplifies the differential expansion (or contraction) of the various assembly elements, allowing for larger displacements than permitted in prior art devices, thereby accommodating greater temperature excursions that are inherent in high power applications.
As shown in
Accordingly, the first and second lever elements 52a and 52b exert deforming pressure inwards at pivot points D and D′ onto the spreader beams 86 which then translates into inward pressure from the inside ridges 89 on the narrow walls 84 of the waveguide 80 as shown by the arrows D and D′ in
As with the filter compensation assembly 10, the manifold compensation assembly 50 has freely moving pivot points D, D′, E, E′, F, and F′ that permit the temperature dependent mechanism to be arbitrarily stiff relative to the membrane section 84 and therefore highly deterministic in performance.
Further, as with the filter compensation assembly 10, the lever mechanism of the manifold compensation assembly 50 amplifies the differential expansion of the various assembly elements, allowing for larger displacements than permitted in prior art devices, thereby accommodating greater temperature excursions that are inherent in high power applications.
Finally, the manifold compensation assembly 50 is substantially more compact or of lower mass than other prior art solutions.
While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
