FIELD OF THE INVENTION
The present invention relates to a temperature compensating apparatus and method for a mechanically leveraged smart material actuator.
BACKGROUND OF THE INVENTION
Various smart material actuator technologies have been developed for a wide range of applications in different industries. One component used in this type of actuator is an electrically stimulated smart material actuator. These smart material actuators when electrically stimulated change shape. This shape change can be designed such that one axis predominantly changes. Such a smart material actuator can be incorporated within a main support structure. As the axis of the smart material actuator changes dimension its motion is magnified by a lever integral to the main support structure. As a result of the magnification factor developed by the main support structure, extremely small differences of thermal coefficients of expansion between the smart material and main support structure can create relatively large movements of output in the main support structure over normal operating temperature ranges. This movement can be as much as fifty percent of the usable output of the actuator system.
Previous designs place the compensating element in line with the smart material. This method suffers from several problems. One such problem is the length of the compensating element inserted between the main body and the smart material increases the overall length of the actuator. Further smart materials are capable of delivering large amounts of force, so the compensating element must be sufficiently stiff to prevent a reduction of the force and movement performance of the actuator while acting as the inline compensating element. This is a difficult combination to achieve with inexpensive materials.
Another common design is to place sleeves with different coefficients of thermal expansion around the smart material causing the cavity that captures the smart material to expand and contract with temperature. This system uses several parts, all of which are complex, and costly to machine and increases the overall size making it less desirable.
Electro-mechanical actuators are a well-known means to convert electrical energy into mechanical force and motion. Historically this has been accomplished via electromagnetic devices such as solenoids. A method receiving increasing application recently involves the use of various smart materials such as magnetostrictive or piezoelectric devices. In the case of piezoelectric devices, Ceramic Multilayer Actuators (CMA) are particularly attractive due to their ability to generate extremely high forces, potentially thousands of Newtons. On the other hand, such CMAs will generate such force over a very limited range of motion, on the order of 0.15% of the length of the CMA. In the case of a CMA 40 mm in length, free deflection, expansion of the CMA without a counteracting force applied to the stack, would be approximately 0.06 mm. The combination of such a high force with such a limited movement has been one of the impediments to broad use of CMAs in typical industrial and commercial applications. For example, a valve may require a total stroke of approximately 1 mm and a force of approximately 10N. To achieve the force and stroke for such a valve and a variety of alternate applications, various mechanisms have been designed to convert the excess force into increased motion. Examples of such mechanisms are described in U.S. Pat. No. 4,736,131 to Fujimoto, U.S. Pat. No. 4,570,095 to Utchikawa, and U.S. Pat. No. 6,759,790 to Bugel et al.
Each mechanism converts a portion of the force of the CMA to additional stroke at the working end of the stroke amplification mechanism. The actual structural magnitude of this amplification is dependent on the specific configuration. A key objective of this type of approach to amplifying the stroke of a CMA is to maximize the efficiency of the transfer of force into stroke. As an example, the mechanism described by Utchikawa in U.S. Pat. No. 4,570,095 teaches converting only 60% of the available deflection. A critical element in achieving higher transfer efficiency is the rigidity or stiffness of the support structure surrounding the CMA. The invention described by Bugel et al in U.S. Pat. No. 6,759,790, illustrates a design that can achieve such a high rigidity. It is therefore important to carry this support structure stiffness into designs incorporating other features such as a thermal compensation mechanism.
In general, stroke amplifying mechanisms are constructed of metallic materials, for example steel. Each such material has an identifiable and generally well known Coefficient of Thermal Expansion (CTE). This CTE is a measure of the rate and direction of expansion of a material with a change in temperature of that material. The CMA used to drive the amplifying mechanism also has a CTE. In general, the CTE of the CMAs differ from those of the materials typically used in such amplifying mechanisms. For example, a 17/4 grade of stainless steel that might be used in the support structure and amplifying mechanism of the current invention, as illustrated in FIG. 1, has a typical CTE of around 11×10−6 per degree Celsius. Similarly, it is generally recognized that the CMA has a slightly negative CTE of around approximately −1×10−6 to approximately −3×10−6 per degree Celsius. This difference in CTE between the steel mechanical structure and the CMA will result in a change in the force applied on the amplifying mechanism during a change in ambient temperature conditions. This force will effectively be added to the force applied by the CMA to the amplifying mechanism and will, in turn, contribute to the stroke and force output of the amplifying mechanism. Such a thermal effect can result in an improper operation of a device, such as the previously mentioned valve, using such an actuating mechanism. If, for example, the difference in CTE is such that it results in a reduction in the force applied to the stroke amplifying mechanism, the amount of stroke and associated force will be less than the expected amount. This reduction in stroke or force could cause an associated valve to demonstrate a flow rate that is less than nominal or inadequate sealing force resulting in leaking.
Various methods have been attempted to compensate for, or eliminate, this difference in CTE. For example, Salim in “Kleinste Objecte im Griff” (F&M 09/1996) describes a stroke amplifying mechanism that is constructed of silicon. This approach does minimize the difference in CTE of the CMA and the stroke amplifying mechanism. However, it does so with a severe impact to multiple characteristics, for example structural reliability, production complexity and cost. These will, in turn, limit the potential physical size and work capability. Therefore, also limiting the applicability of such an approach.
Wada et al. in U.S. Pat. No. 5,205,147 describe a method of minimizing the difference in CTE between a CMA and an associated housing. The invention described does not include amplification of the free deflection of the CMA. In contrast, the reference teaches “stacking” the CMAs to obtain sufficient stroke and then having an equivalent opposing mechanism to effectively double the working stroke of the assembly. Further, the construction of the housing enclosing the piezo is composed of multiple pieces that are bolted or welded together.
Others teach thermal compensation using various electronic control methods, for example U.S. Pat. No. 6,400,062. In general, this approach adds substantial complexity and cost to the actuation system.
Generally it is accepted that when a piezoelectric CMA is used for electro mechanical actuation a compressive preload will be applied. This preload force is typically applied as a means of ensuring that the CMA is maintained mostly in compression during operation. This, in turn, usually increases the dynamic lifetime of the piezoelectric CMA.
SUMMARY OF THE INVENTION
An apparatus according to the present invention includes a support structure with first and second arms spaced apart from one another. A smart material actuator, such as a piezoelectric actuator, moves the first and second arms with respect to one another in response to expansion and contraction of the actuator. Means for compensating for the effects of different thermal coefficients of expansion of the materials used in the support structure and actuator is provided to reduce or eliminate movement of the arms resulting from variations in working temperature and/or ambient temperature.
The present invention provides a simple, cost effective solution for compensating a mechanically leveraged actuator for temperature variations. The present invention provides means for compensating for the effects of different thermal coefficients of expansion while not increasing the envelope of the actuator system, and can correct the overall zero voltage error to no greater than ± seven percent of the maximum movement of the actuator system. As a result of the scalability of the actuator system, a process for the development of all parameters has been developed that reduces the time to design a particular physical configuration of an actuator/support structure combination for use in a specific application. The present invention uses a design system, a smart material actuator, a support structure with integral mechanically leveraged arm portions, and a temperature compensating insert element. The temperature compensating insert element is placed at a predetermined position on the support structure spaced from the actuator, such as along an arm portion. This insert element can be inserted into a cutout in the arm portion. By using two different materials for the insert and the arm portion, a bi-material or bi-metal type of movement cantilevering the arm portion can be created. Therefore, with the use of the design system, the placement, and material type of the temperature compensating insert element become readily apparent using a minimum number of components while maintaining an error band of less then 5 percent of travel.
The present invention is of a design and stiffness that allows significantly higher levels of preload to be applied to the CMA than is typically in the art. In applying high levels of preload it was found with the present invention that the level of compressive preload changes the extent or degree of the thermal expansion mismatch between the piezoelectric CMA and the substantially metal amplification mechanism. This effect has the added benefit of making it possible to adjust the amount of thermal compensation required as a function of preload applied. Furthermore this effect can be used as part of the overall process for designing the mechanism of the present invention for tuning the thermal compensation required in relation to the mechanism performance.
The present invention can provide a mechanism capable of amplifying the stroke of a CMA while simultaneously providing sufficient output force to be useful in a variety of typical, “real world” applications; and/or provide a stroke amplifying mechanism that transforms “excess” force to usable stroke with a high level of efficiency through the use of an extremely stiff support structure; and/or provide mechanical thermal compensation for the different values of CTE of a CMA and the support structure of an electro mechanical actuator so that such compensation; is mechanically simple and reliable, effectively integral to the mechanical support structure such that the structure maintains a high level of mechanical rigidity and, therefore, enables highly efficient work transfer; is effective across a broad range of temperatures typically experienced in industrial type applications, for example −20° C. to 60° C.; does not significantly affect the output of the amplifier, such as by causing increased curvilinear motion; can be adapted to operate at a range of preload forces from 0 psi to 10000 psi; does not substantially affect the size, weight or other physical characteristics of the actuator; can be easily integrated into the actuator during production; is based on and accounts for the effect of preload on the CMA CTE and/or is capable of being used as an element of the components providing preload, not merely sustaining it; and/or present a method for designing a thermal compensation element such that the length of the thermal compensating element is calculated as a function of the actuator design, the respective CTE values of the CMA and the materials to be used for thermal compensation and the amount of compressive preload applied to the CMA.
The basic approach of the present invention is contrary to the wide held industry and academic belief that there is a single CTE for the piezoelectric actuator stack in a short circuited condition. According to the present invention, the CTE of the CMA changes as a function of the amount of preload applied to the stack. The actuator according to the present invention operates at relatively high preloads when compared to other mechanically amplified actuators. If the present invention used the relatively high level of preload combined with the “known” stack CTE, the thermal compensation provided would be inaccurate.
The concept of changing CTE as a function of preload can tie several related features of the present invention with respect to one another. First, the present invention operates at high preload to maximize work performance. As a general statement, the preload typically used is higher, in certain cases many times much higher, than used in prior art. Second, the present invention ensures that the “central portion” of the actuator is “rigid”. As is known, the actual motion of the stack itself is on the order of “a few” ten thousandths of an inch (depending on a variety of factors). Since this motion is so small, any “stretch” in this area can be wasted motion that is not transferred to the “anvil” and, in turn, amplified at the arms. Therefore, the present invention maintains a high level of structural rigidity while incorporating the mechanical thermal compensating element, or, as presently embodied, an Invar material element forming at least one of an actuator seat and/or a portion of the rigid support structure. Any decrease in rigidity in the central support structure portion of the actuator results in diminished movement at the arms.
The present invention provides the ability to compensate for difference in values of the material CTE of the metal of the central portion of the amplifier versus the ceramic multilayer actuator. As temperature changes, the length of the “central metal support structure portion” and the ceramic multilayer actuator stack change at differing rates. Other dimensions change also, but the relevant dimension is oriented along the longitudinal length of the actuator stack. The different rates of CTE can result in reduced preload and, therefore, reduced stroke. The thermal compensation according to the present invention brings the CTE of the metal and the stack into balance. If this compensation is not designed based on the “correct” CTE, the amount of compensation provided will not be optimal. The CTE of the stack according to the present invention can change as a function of preload. With minimal levels of preload force applied to the multilayer ceramic actuator stack, this may not have a significant impact. However, since the present invention envisions a relatively high level of preload force applied to the ceramic multilayer actuator stack and the efficient conversion of stack movement to actuator movement is desired in the present invention, the thermal compensation can be significant in the present invention to ensure proper operation of the mechanism across the desired range of operating temperatures typically required for industrial applications. Therefore, it is desirable for the present invention to determine a design of the compensation structure and composition based on the CTE at the “nominal” (unactuated) preload.
A method is disclosed for determining the necessary CTE compensation for a mechanism including a piezoelectric or ceramic multilayer actuator stack and a mechanism for transforming the work output of the stack, typically made from steel, for amplifying or otherwise transferring or transforming the work output by the stack. The method according to the present invention provides appropriate thermal compensation based on the amount of preload on the stack.
Note that the phenomenon/method according to the present invention appears to be very general in nature. It can apply to any use where a piezoelectric or ceramic multilayer actuator stack is preloaded within a mechanism having a CTE different from the CTE of the stack in a wide variety of embodiments including those which are geometrically or operationally different from that illustrated in the accompanying drawings of an exemplary mechanism according to the present invention. It is desirable in the method according to the present invention to minimize, or result in negligible change to, structural rigidity of the assembly according to the present invention, thus ensuring maximal work transfer efficiency. It is desirable in the method according to the present invention to provide a simple, easily assembled, reliable, cost effective mechanism.
The present invention provides an apparatus and method for amplifying movement of an electrically activated ceramic based actuator with a structural assembly capable of providing consistent performance characteristics while operating across a desired range of temperature conditions including a support having a first rigid non-flexing portion with a first coefficient of thermal expansion value and a second rigid non-flexing portion with a second coefficient of thermal expansion value different from the first coefficient of thermal expansion value, the support including at least one pivotable arm portion extending from one of the rigid portions, and a force transfer member operably positionable for driving the at least one pivotable arm portion in rotational movement, and an electrically activated actuator having a third coefficient of thermal expansion value different than the first and second coefficients of thermal expansion values, the actuator operably engagable between one of the rigid portions and the force transfer member to drive the force transfer member relative to the rigid portions causing the at least one pivotable arm portion to pivot in response to an electrical activation of the actuator, wherein the different coefficient of thermal expansion values of the rigid portions in combination with a structural configuration of the support substantially compensate for the third coefficient of thermal expansion value of the actuator over a desired operating range of temperature conditions. In general, the desirable material characteristics for a compensating material are high mechanical stiffness, Young's Modulus, high mechanical yield stress and a CTE value different to the first rigid non-flexing portion and different to that of the CMA such that it can compensate for thermal excursions over the desired range. The present invention can use a number of commercially available materials for the second rigid non-flexing compensating portion of the mechanism, for example INVAR, KOVAR, NILVAR etc. Further, it may be possible to use other suitable materials, for example a metal matrix composite material, or similar, that has an appropriate value of CTE. By way of example and not limitation, a typical electrically activated ceramic based actuator or ceramic multilayer actuator has a CTE of approximately −1×10−6 to approximately −3×10−6 per degree Celsius. When such a grade of stainless steel is used to enclose the actuator in the rigid support structure then any temperature fluctuations can result in a differential change in length of this support structure section in relation to the actuator. In turn, this can produce a movement in the force transfer and amplifying mechanism such that the active arms can change position purely due to a thermal excursion. To compensate for this change a third material, for example and INVAR grade 36, can be added according to the present invention as part of the rigid support structure such that its CTE is different than the other materials already described. Finite Element Analysis (FEA) can be used along with a basic linear calculation to decide on the amount of stainless steel material to be replaced with this third material so as to match the motion of the support structure to that of the ceramic based actuator such that there is no change in position observed at the active arms due to thermal excursions within a temperature range.
According to the present invention for the determination of the size of the compensating rigid portion, only the second rigid portion and the force transfer member are used in the calculations. The rest of the structure, i.e. hinges, arms, are not required to be used in the determination of an appropriate level of compensation but are optionally included. The present invention envisions the possibility of having more than two rigid portions, i.e. the “base” of the rigid area could be a material different from the other two rigid materials (or the same as “the first”). For example, if the first rigid portion is defined as integral to the force transfer member, hinges, etc., the second rigid portion can be composed of thermally compensating material and can be attached to the first rigid portion parallel to a longitudinal axis of the actuator. A third rigid portion can connect to the second at the end of the second rigid portion opposite from the end attached to the first rigid portion and perpendicular to the longitudinal axis of the actuator. According to the present invention, the coefficient of thermal expansion of one of the rigid nonflexing portions substantially compensates for the difference in the value of the coefficient of thermal expansion of the second rigid nonflexing portion and the coefficient of thermal expansion of the electrically activated ceramic based actuator over a desired operating range of temperatures.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:
FIG. 1 is a perspective view of an electromechanical actuator according to the present invention;
FIG. 2 is an exaggerated side view of FIG. 1 cut away to show the action of the compensating element according to the present invention;
FIG. 3 is a detailed view of an alternate construction of the present invention;
FIG. 4 is a detailed view of an alternate construction of the present invention;
FIG. 5 is a detailed view of an alternate construction of the present invention;
FIG. 6 is a stress analysis illustration of one possible construction of the present invention;
FIG. 7 is a detailed side view of an actuator preloading mechanism according to the present invention;
FIG. 8 is a detailed side elevated view of an alternate embodiment of the actuator of the present invention with an associated fluidic valve;
FIG. 9 is a perspective view of an alternate embodiment of the actuator of the present invention;
FIG. 10 is a simplified flowchart illustrating the steps of a method used in designing and placement of the temperature compensating element according to the present invention;
FIG. 11 is a graph showing arm deflection versus temperature;
FIG. 12 is a perspective view of an electromechanical actuator based on CMA actuation and mechanical motion amplification with temperature compensation for differences in the CTE of the materials;
FIG. 13 is a perspective view of an electromechanical actuator based on CMA actuation and mechanical motion amplification with temperature compensation for differences in the CTE of the materials;
FIG. 14 is a perspective view of the electromechanical actuator including a thermal compensation element incorporated into the rigid support structure of the amplification mechanism;
FIG. 15 is a perspective view of thermal compensation incorporated into the rigid support structure of the amplifying mechanism;
FIG. 16 is a perspective view of thermal compensation incorporated into the rigid support structure of the amplifying mechanism;
FIG. 17 is a perspective view of thermal compensation incorporated into the rigid support structure of the amplifying mechanism;
FIG. 18 illustrates compressive preload force, applied to the piezoelectric CMA in the amplifying mechanism, versus the amount of deflection due to thermal expansion mismatch between the CMA and the amplification mechanism; and
FIG. 19 is a perspective view of thermal compensation incorporated into the rigid support structure of the amplifying mechanism.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a perspective view of one embodiment of an apparatus 10 is illustrated having a support structure 12 including a non-flexing web portion 14 extending between an upper and a lower pair of rigid non-flexing side portions 16, 18 forming a C-shaped portion 20. At least one pivotable arm portion, such as a first arm portion, 22, or 24 is pivotably connected via a corresponding living integral hinge portion 26, or 28 to a corresponding side portion 16, or 18. Another pivotable arm, such as a second arm portion 24 can be optionally connected via a corresponding living integral hinge portion 28 to the other rigid side portion 18, if two opposing arms 22, 24 are desired. A force transfer member 30 includes a surface engagable with one end of a smart material actuator 32. The opposite end of the smart material actuator 32 engages with an adjustable seat 34. Adjustable seat 34 can be supported by an adjustable support screw 36, connected through the support structure 12. A compensating insert 38 is inserted in at least one pivotable arm portion 22, 24. The compensating insert 38 can be the same width as the corresponding pivotable arm portion 22, 24 and can be inserted to completely fill a cutout portion 40 of the support structure 12.
Referring now to FIG. 2, an exaggerated side view of the action of the compensating element 38 of the apparatus 10 shown in FIG. 1 is illustrated. By way of example and not limitation, the pivotable arm 22 can be made from a 416 stainless steel with a coefficient of thermal expansion of 5.7×10−6 in/in ° F., and the compensating insert 38 can be made from a 304 stainless steel alloy with a coefficient of thermal expansion of 9.6×10−6 in/in ° F. When two metal strips having different coefficients of expansion are joined together, a change in temperature will cause free deflection of the assembly. In this case the insert 38 expands with an in crease in temperature more than the pivotable arm 22 causing a free deflection in the direction shown. It should be noted that the insert 38 could be placed in a position located 180 degrees from the illustrated location, or in other words at the bottom of the pivotal arm 22 causing an upward deflection, also the insert 38 could be a material with a smaller coefficient of thermal expansion changing the direction of free deflection. This deflection is used to counter the difference in the thermal coefficients of expansion between the smart material actuator 32 and the support structure 12 as the temperature changes. Alternatively, other materials can be employed for the support structure 12 such as 17-4PH stainless steel having a coefficient of thermal expansion of 6×10−6 in/in ° F. and a high expansion metal alloy (nickel-chromium-iron) 22-3 having a coefficient of thermal expansion of 10.55×10−6 in/in ° F. In general, suitable materials for use in the support structure can be selected based on the materials ability to form a highly rigid structure. Such a rigid structure will help minimize undesirable motion and thereby enable maximum motion of the arms. Based on this criteria, the support structure could be formed using a range of materials such as steel or other metals, alloys, ceramics, composite materials, or any combination thereof. Composite materials by way of example and not limitation, can include a metal material blended with a nonmetallic material, or two different metal materials blended together, or two different nonmetallic materials blended together, or any combination thereof. In general, the thermal compensating element employed in conjunction with the support structure should not reduce arm stiffness compared to a thermally uncompensated arm. Loss of arm stiffness can reduce the output performance of the arms of the support structure. Based on this criteria, the support structure could be formed using a range of materials such as steel or other metals, alloys, ceramics, composite materials, or any combination thereof. Composite materials by way of example and not limitation, can include a metal material blended with a nonmetallic material, or two different metal materials blended together, or two different nonmetallic materials blended together, or any combination thereof. Any loss in output performance of the arms due to thermal compensation must be balanced against the full spectrum of application requirements such as size, weight, reliability, repeatability, etc.
Referring now to FIG. 3, the pivotable arm 22a can be composed of a bi-material strip 42a fastened to the support structure 12a with fasteners 44a. In this example, the bi-material strip 42a provides for a free deflection for temperature change in an approximately equal and opposite reaction to the net sum of the thermal expansions of the support structure 12a, and smart material actuator (not shown). It can be recognized by those skilled in the art that fasteners 44a are not the only method of attaching the pivotable arm 22a to the support structure. By way of example and not limitation, other means can include: welding, brazing, soldering, chemical bonding, etc, or any combination thereof.
Referring now to FIG. 4, a portion of the pivotable arm 22b can be composed of a bi-material strip 42b fastened to the pivotable arm 22b and support structure 12b with fasteners 44b. In this example the bi-metallic and/or bi-material strip 42b can be positioned along the pivotable arm such that the bimetallic and/or bi-material strip 42b provides for a free deflection for temperature change in an approximately equal and opposite reaction to the sum of the thermal expansions of the support structure 12b, pivotable arm portion 22b, and smart material actuator (not shown). It should be recognized by those skilled in the art that fasteners 44a are not the only method of attaching the pivotable arm 22b to the support structure. By way of example and not limitation, other means can include: welding, brazing, soldering, chemical bonding, etc, or any combination thereof.
Referring now to FIG. 5, a portion of the pivotable arm 22c can be composed of a bi-material and/or bi-metallic strip 42c fastened to the pivotable arm 22c with a suitable attachment layer of material 23. The attachment layer of material can be any suitable adhesive, solder, welding/brazing rod residue or the like, or any combination thereof. The strip 42c is fixedly connected to the arm 22c within the notch or slot formed therein to provide for a free deflection in response to temperature changes in an approximately equal and opposite reaction to the sum of the thermal expansions of the support structure 12c, pivotable arm 22c, and smart material actuator (not shown).
Referring now to FIG. 10, a simplified flowchart illustrates the optimization of the material, orientation and dimensions of the compensation insert according to the present invention. Beginning at step 100, the requirements of the application are defined. The requirements can be a selection of parameters, by way example and not limitation, including the parameters of force, size, positioning, vibration, stress, impact resistance, cycle life, operating frequency, temperature, environmental resistance, corrosion resistance, production cost, hysteresis, linearity, galvanic reaction, and/or repeatability. After the requirements are defined in step 102, the process continues to step 104 where a three dimensional (3D) computer aided design (CAD) model is developed initially. An insert material is then chosen in step 106 and inserted in the 3D CAD model. Finite element stress analysis (FEA) is then conducted in step 108 to predict the performance of the compensating insert. As a result of the finite element stress analysis, the deflection of the arm is determined in step 110. The requirement is then checked in step 112 against the calculated deflection identified in step 110. If it is determined not to meet the requirements previously defined in step 102, the process branches back to step 104, where the model is further optimized and continues the loop until the requirements are satisfied. If the requirement in step 112 meets the requirements in step 102, the process continues to step 114, where the configuration is evaluated for, by way of example and not limitation, various characteristics including cost, manufacturability, component count, material type, and/or performance repeatability. If it is determined that the particular 3D CAD model under consideration does not meet the requirements, the process branches back to step 104, where the model is further optimized and continues the loop until the requirements are satisfied. If the requirement in step 114 meets the requirements in step 102, the process continues to step 116, where the configuration is evaluated by building and testing a prototype to verify the requirements of step 102 are met. If it is determined that the requirements are not met, the process branches back to step 104, where the model is further optimized and continues to loop until the prototype satisfies the requirements. If it is determined that the requirements are met, the process terminates with step 118, and the design is complete.
In the embodiment illustrated in FIG. 1, these components can be machined from two different types of material. By way of example and not limitation, the support structure 12 can be made from stainless steel and the compensating insert 38 can be made from brass.
The apparatus 10 shown in FIG. 1 has a support structure 12 with a first pivotable arm portion 22 and a second pivotable arm portion 24 spaced apart from one another. Each arm portion 22, 24 is connected to a corresponding rigid, non-flexing side portions 16, 18 via integrally formed living hinge portions 26, 28 respectively. Each hinge portion 26, 28 includes a corresponding primary hinge web 46, 48 connected to the corresponding side portions 16, 18, and corresponding secondary hinge webs 50, 52 are connected to the force transfer member portion 30. By way of example and not limitation, slots 54 and 56 can be formed between each arm portion 22, 24 and the side portions 16, 18 to allow the arm portions 22, 24 to move without contacting the side portions 16, 18 of the support structure 12. Slots 58 and 60 can be formed between the primary hinge portions 46, 48 and the force transfer portion member 30 for facilitating mechanical leverage from the force transfer member 30 to the arm portions 22, 24.
A smart material actuator 32, such as a piezoelectric actuator, operates by changing shape proportionally in response to electric power being applied to the material. The actuator 32 pivots the first and second arm portions 22, 24 with respect to one another in response to expansion and contraction of the material. The actuator 32 can be located between an adjustment seat 34 and the force transfer member portion 30. It should be recognized that a piezoelectric actuator is one possible type of smart material actuator, and other devices such as magnetostrictive or electrostrictive material actuators are also contemplated to be within the scope of the present invention.
The force transfer member portion 30 and the pivotable arm portions 22, 24 are designed to be substantially rigid component portions. Any flexure of these elements, even microscopic, results in inefficient work transfer due to undesirable motion. In general, the motion of a piezoelectric actuator stack is microscopic, generally approximately 0.1% of the length of the stack. Based on the length of stacks contemplated for the present invention, such motion would be on the order of 1500 micro inches to 100 micro inches maximum displacement depending on the actual embodiment. Therefore, all of the components of the support structure 12 are typically designed to minimize undesirable motion. In extreme, motion greater than 4 micro inches would be considered non-rigid and undesirable with respect to the disclosure of the present invention under expected design loads with infinite life for the support structure 12. In actual practice, rigidity is more effectively defined as a ratio of the displacement distance or motion of the side portions, for example 16, 18, toward and away from one another to the displacement distance during free deflection of the force transfer member 30 (i.e. where free deflection is being defined as operating against no load and performing no work). In this context, a displacement distance or motion of the side portions, 16, 18, in excess of 10% of the displacement distance or free deflection of the force transfer member 30 would be considered non-rigid according to the present invention. In practice, this percent is typically much lower. For example, in an embodiment wherein the piezo stack is approximately 0.394 inches long, the percentage of undesirable side portion motion to free deflection is on the order of 2%. Another indication of structural rigidity and resulting performance efficiency is the ratio of the measured free deflection of the arm portions, for example 22, 24, versus the theoretical or calculated values for such motion (i.e. assuming zero loss of motion through a theoretically rigid structure). The minimum efficiency achieved by the present invention using this definition is approximately 80%. Additionally, efficiency as high as approximately 90% has been achieved according to the present invention. It is expected that efficiencies greater than 90% can be achieved with configurations according to the present invention. For example, the hinge portion geometry is specifically designed for maximum performance without stress fatigue failure. According to the present invention, all portions of the support structure 12 are considered to be “rigid” except for the hinge portions. The hinge portions are the only components or portions of the support structure where flexure, deflection and movement are desirable. The hinge portions are locations of maximum stress in the support structure 12. The flex points of the hinge portion geometry are precisely selected to optimize performance for a particular use. The design process is supportive of this approach, by adapting the amplifier effect of the hinge portions to meet particular specifications. By way of example and not limitation, Finite Element Analysis has demonstrated hinge life should be “infinite” within the context of industrial applications. Lab testing of devices using a piezo stack as the primary actuation method combined with the motion amplifier as taught by the present invention have exceeded 500 million on/off cycle operations. The apparatus 10 can be formed of a homogenous material throughout, such as steel, or any suitable material or composite material known to those skilled in the art, as long as the material selected meets the design criteria discussed above for the particular application.
The support structure 12 includes a first rigid, non-flexing side portion 16, a second rigid, non-flexing side portion 18, and a rigid non-flexing web portion 14. Each side portion 16, 18 is integrally connected with the rigid, non-flexing web 14. The side portions 16, 18 are integrally formed with the hinge portions 26, 28 of the first and second pivotable arm portions 22, 24. The first and second arm portions 22, 24 are rigid, non-flexing structures.
The flex points and hinge geometry are precisely selected to optimize performance for a particular application. The design process is supportive of the approach to adapt the “amplifier” effect of arm portions 22, 24 in combination with the hinge portions 26, 28 to meet the specifications required for a particular application for maximizing performance without inducing material fatigue. The life expectancy verified in lab tests show no measurable change in performance of the apparatus 10 according to the present invention after five hundred million on/off cycles.
Referring now to FIGS. 1 and 7 the apparatus 10 includes means 62 for preloading a compressive force on the actuator 32. Preloading means 62 can include a screw 36 for threadably engaging with a threaded aperture 64 located in the web portion 14 of the support structure 12. The screw 36 can be capable of imparting a compressive force with respect to the actuator 32 through an adjustment seat 34. The adjustment seat 34 transmits the compressive force from the screw 36 into the actuator 32. The adjustment seat 34 can include a force focusing shim having a substantially curved surface for transmitting the preload force evenly into the actuator as purely compressive load without any shear load.
Means 66 is used for compensating for the effects of different thermal coefficients of expansion of the materials used in the support structure 12 and actuator 32 to reduce or eliminate movement caused by variations in working temperature and/or ambient temperature. Every material has a coefficient of thermal expansion. Materials expand or contract in size as the working temperature and/or ambient temperature surrounding the material changes. The magnitude of the expansion and contraction is proportional to the coefficient of thermal expansion. Temperature compensation according to the present invention can reduce or eliminate the effect of temperature variation on the apparatus 10. The temperature compensating means 66 according to the present invention can include a compensating insert 38 operably engagable with the support structure 12, such as being connectible with at least one arm portion 22 as shown in FIG. 2. A cutout portion 40 of the arm portion 22 can be removed and a compensating insert 38 can be inserted in the cutout portion 40. The insert 38 can be operably connectible to the arm portions 22 in any suitable fashion such as by suitable adhesive bonding, brazing, welding, fastening, etc. or any combination thereof. The compensating insert 38 has a different coefficient of thermal expansion (i.e. either lower or higher) relative to the arm portion 22 so that the arm 22 is deflected in an amount substantially equal to and in an opposite direction with respect to any deflection caused by changes in working temperature and/or ambient temperature. The cutout portion 40 can be in an outer surface 68 of arm portion 22 or can be in an inner surface 70 of the arm portion 22. Although temperature compensation according to the present invention involves use of an insert to deflect the arm portions 22, 24 as a result of expansion and/or contraction of the material proportional with the ambient temperature variation, the arm portions 22, 24 are still rigid in the sense that the support structure substantially limits flexing motion under design load conditions. While the present invention has been illustrated and described in detail with respect to a physically separate “insert” with respect to the arm portions 22, 24, the present invention also discloses and encompasses an integral “insert” configuration. It should be recognized by those skilled in the art that the present invention can be formed with the insert integrally embedded internally within a corresponding arm portion 22, 24 and/or can be formed with the arm portion 22, 24 itself being a suitable blending of materials in order to provide the desired characteristics. By way of example and not limitation, the present invention can be made by forming the support structure 12 using composite sintered material molding techniques. Therefore, the use of the generic term “insert” herein is defined to encompass a physically separate “insert” configuration, or an integrally formed “insert” configuration, or any combination of the separate and integral formed configurations.
Referring now to FIG. 3, at least one arm portion 22a can be made from a bimaterial layer 42a forming an entire length of at least one of the arm portions 22a. The arm portion 22a can be fastened to the support structure 12a with a fastener 44a. Alternatively, arm portion 22a may be fastened to the support structure 12a using other suitable means such as brazing, soldering, welding, chemically bonding, or any combination thereof.
Referring now to FIG. 4, a bimaterial layer 42b forms a partial length of the arm portion 22b. A fastener 44b is used to fasten the arm portion 22b having a bimaterial layer 42b to the support structure 12b. Alternatively, arm portion 22b may be fastened to the support structure 12b using other suitable means such as brazing, soldering, welding, chemically bonding, or any combination thereof.
Now referring to FIG. 10, a method is disclosed for designing an apparatus 10 according to the present invention. The steps include the step of defining the design requirements 102, modeling the support structure 12, insert 38 in arm 22 and actuator 32 of the apparatus 10 with 3D CAD 104, selecting a temperature compensating insert material 106, running finite element analysis on the finite element model 108, comparing the results with the design requirements 110, modifying the model and repeating the process until the computed results meet the design requirements 112, determining whether the design can be manufactured at a specified cost 114, verifying the design in step 116 with prototype testing until the design meets the requirements of step 102, and repeating the design process until the design meets all requirements 102 of step.
Referring now to FIG. 6, an example of finite element analysis results on the apparatus 10 is illustrated. The actuator transmits force through the force transfer member 30 causing peak stress of the apparatus 10 to be localized in the hinge portion 26. The arm portion 22 is deflected from an initial position to a deflected position as a result of the force transfer member 30 imparting force through hinge portions 26 of the apparatus 10. As a result of the illustrated stress distribution using a finite element method, a desired design life of the actuator can be achieved. The stress localized in the hinge areas portions 26, 28 increases as the force of the actuator 32 increases. The apparatus 10 is substantially rigid, and the only bending movement allowed as a result of the force from the actuator is in the hinge portions 26, 28. The hinge portions 26, 28 are designed for infinite life of the apparatus 10 under design load conditions. In other words, the hinge portions 26, 28 have sufficient strength and cross-sections to not yield or fracture during the life of the apparatus 10 as a result of the design and manufacturing methods employed in producing the apparatus 10. An additional finite element analysis is used to examine the motion of the arm portion 22 extending from the hinge portion 26 to the end of the arm portion 22. In this aspect of the analysis, motion of the uncompensated arm is compared to motion of the thermally compensated arm. The motion and forces of both arm types are modeled through the range of normal operating temperatures to ensure effectiveness of the thermal compensation employed and to minimize loss of performance due to undesirable flexing caused by insufficient rigidity. The illustration of FIG. 6 shows the arm portion 22 with greatly exaggerated curvature to graphically signify the thermal compensation analysis.
Referring now to FIG. 7, the actuator 32 is shown preloaded with a compressive force by screw 36. The screw 36 is threadingly engagable with the web 14 of the support structure 12. The screw 36 contacts an adjustment seat 34, such as a rigid force focusing shim, operably engaging the actuator 32. The seat 34 can include a generally curved surface or domed shape for transferring force as a purely compressive force without any shear force component. Actuators made from piezoelectric stacks are not amenable to being placed under tension or side loading. By creating a preload greater than the total displacement of the piezoelectric stack, the stack will always be under compression even while the apparatus is returning to an initial position after discharge of the piezoelectric stack.
In operation, the apparatus 10 will compensate for thermal variations to maintain proportional control of the deflection of the arm portions 22, 24. When the working temperature and/or ambient temperature varies from the design temperature the arm portions are deflected due to variations in the coefficient of thermal expansion between the material of the actuator and the material of the support structure. An experimental example is illustrated in FIG. 11. FIG. 11 illustrates a graph of one possible arm configuration and the arm deflection in inches versus temperature in degrees Celsius for a temperature compensated arm and for an uncompensated arm. The graph shows that the uncompensated arm can deflect over 0.006 of an inch at 80 degrees Celsius, while the temperature compensated arm limits deflection to less than 0.001 of an inch. This is significant since in the tested configuration of the arm, the temperature induced deflection of the uncompensated arm corresponded to approximately 50% of the effective arm displacement of the support structure at a constant temperature in response to electrical actuation of the smart material actuator. In other words, depending on the direction of temperature induced deflection, the illustrated uncompensated arm configuration could be subject to an increase in deflection of approximately 50%, or a loss of deflection of approximately 50%, solely as a result of temperature variation.
Referring now to FIG. 8, a perspective view of the apparatus 10 combined with a fluid valve section 76 having a support structure 12 including a non-flexing web 14 extending between first and second rigid non-flexing side portions 16, 18 forming a C-shaped portion 20. At least one rigid pivotable arm portion 22 can be pivotably connected via a living integral hinge 26. A second rigid pivotable arm portion 24 can be connected via a living integral hinge 28, if two opposing arms are desired. The force transfer member 30 operably engages the smart material actuator 32 in cooperation with the adjustable seat 34. Adjustable seat 34 can be supported by the screw 36 threadably engaged through the support structure 12. Temperature compensating insert 38 is inserted in at least one pivotable arm portion 22. A valve seat 72 can be attached to pivotable arm portion 24. A valve stem 74 can be attached to pivotable arm portion 24. Valve components 72, 74 can form a general purpose proportionally controllable 2-way valve. The valve can be exposed to temperature variations such as within the ambient environment or of the controlled fluid, and the smart material actuator 32 expands and contracts differently from the support structure 12. Pivotable arms 22, 24 can move as a result of the temperature variations causing valve stem 74 to move in relation to valve seat 72. Temperature compensating insert 38 expands or contracts in relation to pivotable arm portion 22, 24 providing compensation for the mismatch in the coefficients of thermal expansion of the smart material actuator 32 and support structure 12. The compensating means 66 according to the present invention prevent the valve stem 74 and valve seat 72 from significant movement in relation to each other as the temperature changes allowing proportional control over a wider range of ambient and operating temperature ranges.
Referring now to FIG. 9, an actuator 10 is shown with a double acting arm portions 22d, 24d. The arm portions 22d, 24d pivot about hinge portions 26d, 28d as the actuator 32 is actuated. The arm portions 22d, 24d can provide work at opposite ends as the actuator 32 is energized and de-energized. The compensating insert 38d, 38e can be positioned on opposite sides of the arm portions 22d, 28d to counteract the thermal expansion effects resulting from variation in ambient temperature.
The present invention can include a force amplifying mechanism having one or more elements. These elements can be based on materials chosen to provide an effective combined value of CTE that substantially minimizes the difference of individual values of CTE between the materials used for the piezoelectric CMA and the amplifying mechanism. Further, the thermal compensating elements can be integral to the operation of the amplifying mechanism. These elements provide a very rigid structure so as to allow applying the necessary compression preload force to the piezoelectric CMA and so as not to lose any of the extension provided by the CMA. As already stated, the amount of deflection provided by a CMA is very small, typically 0.10% to 0.15% of its total length, during operation. Any flexure in the support structure would be a direct reduction in this output from the CMA and result in a significant lowering of the efficiency of operation of the invention. In the case of a multiple element configuration, the elements can be designed so as to quickly and easily interconnect with each other as part of the overall mechanism assembly process and do not require additional assembly components such as bolts nor do the multiple elements require additional assembly procedures such as welding for example, although such components or procedures can be used. Further, the present method retains the simplicity of a mechanical solution versus an electronic circuit.
In the various drawings, similar and/or identical basic elements are identified with similar base numerals and with base numerals having different alphabetic notations annotated thereto. The description of the basic elements throughout the various drawings and views are applicable to all figures, configurations, and combinations of elements, unless otherwise specifically noted.
Referring now to FIG. 12, a perspective view of a single piece support and actuator apparatus 110 according to the present invention with thermal compensation applied at the actuator seat 122, or applied homogeneously or non-homogeneously as a combination of materials mixed within the feed stream or within the molds used to form the monolithic support. By way of example and not limitation, the support can be formed by any suitable method known to those skilled in the art, such as by sintering or liquid metal injection molding. A piezoelectric CMA 112 can be contained or supported within a rigid, non-flexing, support structure 114. In the present invention, the support structure 114 of the apparatus 110 can be made from one homogeneous or non-homogeneous material, by way of example and not limitation a type of steel, except for the piezoelectric CMA element 112. The output from the piezoelectric CMA 112 can be transferred to the operating arms 115 and 116 through the force transfer structure 118. A compressive preload force can be applied to the piezoelectric CMA 112 by means of an adjustable loading device 120 associated with either the support 114a and/or the force transfer member 118, and a support plate 122 associated with the actuator 112. The support plate 122 can have a higher value for the CTE than the value for the CTE of the CMA 112 in order to compensate for the lower value of CTE of the actuator 112 compared with the value of the CTE of the support 114. Nominal free deflection at the end of the operating arms 115 and 116, as indicated between arrows A, for an embodiment of this type with a width of 7.5 mm can be on the order of 2 mm, for example. Movement in a non-temperature compensated apparatus of similar configuration and structure to apparatus 110 due to thermal excursions from approximately −20° C. to approximately 60° C. can be in the order of 15% of the full nominal deflection which is undesirable for many applications.
Referring now to FIG. 13, a perspective view of a thermally compensated actuator apparatus 110a according to the present invention is illustrated. A piezoelectric CMA 112a can be contained or supported within a rigid, non-flexing, support structure 114a, 128a. In the present invention, the support structure of the apparatus 110a can be made from one or more elements, by way of example and not limitation, such as a type of steel. The output from the piezoelectric CMA 112a can be transferred to the operating arms 115a and 116a through the force transfer structure 118a. A compressive preload force can be applied to the piezoelectric CMA 112a by means of an adjustable loading device 120a associated with either the rigid support portion 128a and/or the force transfer structure 118a, and a support plate 122a associated with the actuator 112a. The support plate 122a can also optionally have a higher value for the CTE than the value for the CTE of the CMA 112a in order to compensate for the lower value of CTE of the actuator 112a compared with the value of the CTE of the support 114a. In FIG. 13, part of the material of the rigid, non-flexing, support structure 114 (from the structure shown in FIG. 12) has been replaced with an element 128a made from a material with a coefficient of thermal expansion capable of compensating for the movement at the operating arms 115a and 116a caused by the thermal expansion mismatch between the materials of the support structure 114a and the piezoelectric CMA 112a. In this way the deflection at the arms can be controlled very accurately over a broad operating temperature range that, for instance, is typical of industrial type applications. Further, the means of calculating the length of the element 128a to ensure the correct amount of thermal compensation can be controlled in relation to the overall design operation requirement of the actuator apparatus according to the present invention. Further the design of the profile of the joint configuration used for the means of achieving the interconnection between the two elements 114a and 128a can minimize any of the stresses arising in the interconnection zone when the compressive preload is applied to the CMA and during operation of the invention. Additionally, the interconnection between the two mechanical elements, the support structure 114a and the compensation structure 128a, can be simple and yet can maintain the secure and rigid relationship between the two or more elements fundamental for the efficient operation of the invention without requiring additional fastening means or methods. By means of illustration, an actuator 112a using the thermal compensation method shown in FIG. 13 and of similar overall dimensions to the previously described, uncompensated, actuator can now have a thermally induced movement controlled to a level of less than 1% of the nominal actuator stroke.
Referring now to FIG. 14, a perspective view of a thermally compensated actuator apparatus 110b according to the present invention is illustrated. In the present invention, the support structure of the apparatus 110b can be made from one or more elements, by way of example and not limitation, such as a type of steel. The output from the piezoelectric CMA 112b can be transferred to the operating arms 115b and 116b through the force transfer structure 118b. A compressive preload force can be applied to the piezoelectric CMA 112b by means of an adjustable loading device 120b associated with the either the rigid support portion 128b and/or the rigid force transfer structure 118b, and a support plate 122b associated with the actuator 112b. The support plate 122b can also optionally have a higher value for the CTE than the value for the CTE of the CMA 112b in order to compensate for the lower value of CTE of the actuator 112b compared with the value of the CTE of the support 114b. In FIG. 14, part of the material of the rigid, non-flexing, support structure 114 (from the structure shown in FIG. 12) has been replaced with an element 128b made from a material with a coefficient of thermal expansion capable of compensating for the movement at the operating arms 115b and 116b caused by the thermal expansion mismatch between the materials of the support structure 114b and the piezoelectric CMA 112b. In this way the deflection at the arms can be controlled very accurately over a broad operating temperature range that, for instance, is typical of industrial type applications. Further, the means of calculating the length of the element 128b to ensure the correct amount of thermal compensation can be controlled in relation to the overall design operation requirement of the actuator apparatus according to the present invention. Further the design of the profile of the joint configuration used for the means of achieving the interconnection between the two elements 114b and 128b can minimize any of the stresses arising in the interconnection zone when the compressive preload is applied to the CMA and during operation of the invention. Additionally, the interconnection between the two mechanical elements, the support structure 114b and the compensation structure 128b, can be simple and yet can maintain the secure and rigid relationship between the two or more elements fundamental for the efficient operation of the invention without requiring additional fastening means or methods. By means of illustration, an actuator using the thermal compensation method shown in FIG. 14 and of similar overall dimensions to the previously described, uncompensated, actuator can now have a thermally induced movement controlled to a level of less than 1% of the nominal actuator stroke.
Referring now to FIG. 15, a perspective view of a thermally compensated actuator apparatus 110c according to the present invention is illustrated. In the illustrated configuration the replacement element 128c performs the thermal compensation as described with respect to FIG. 14 and can be attached to the support structure 114c using a variation of the configuration shown in FIG. 14. The present invention envisions that the interconnection of the support structure element 114c and the thermal compensating element 128c can be achieved in a variety of ways. In the present invention, the support structure of the apparatus 110c can be made from one or more elements, by way of example and not limitation, such as a type of steel. The output from the piezoelectric CMA 112c can be transferred to the operating arms 115c and 116c through the force transfer structure 118c. A compressive preload force can be applied to the piezoelectric CMA 112c by means of an adjustable loading device 120c associated with the either the rigid support portion 128c and/or the rigid force transfer structure 118c, and a support plate 122c associated with the actuator 112c. The support plate 122c can also optionally have a higher value for the CTE than the value for the CTE of the CMA 112c in order to compensate for the lower value of CTE of the actuator 112c compared with the value of the CTE of the support 114c. In FIG. 15, part of the material of the rigid, non-flexing, support structure 114 (from the structure shown in FIG. 12) has been replaced with an element 128c made from a material with a coefficient of thermal expansion capable of compensating for the movement at the operating arms 115c and 116c caused by the thermal expansion mismatch between the materials of the support structure 114c and the piezoelectric CMA 112c. In this way the deflection at the arms can be controlled very accurately over a broad operating temperature range that, for instance, is typical of industrial type applications. Further, the means of calculating the length of the element 128c to ensure the correct amount of thermal compensation can be controlled in relation to the overall design operation requirement of the actuator apparatus according to the present invention. Further the design of the profile of the joint configuration used for the means of achieving the interconnection between the two elements 114c and 128c can minimize any of the stresses arising in the interconnection zone when the compressive preload is applied to the CMA and during operation of the invention. Additionally, the interconnection between the two mechanical elements, the support structure 114c and the compensation structure 128c, can be simple and yet can maintain the secure and rigid relationship between the two or more elements fundamental for the efficient operation of the invention without requiring additional fastening means or methods. By means of illustration, an actuator using the thermal compensation method shown in FIG. 15 and of similar overall dimensions to the previously described, uncompensated, actuator can now have a thermally induced movement controlled to a level of less than 1% of the nominal actuator stroke.
Referring now to FIG. 16, a perspective view of a thermally compensated actuator apparatus 110d is shown. An interconnection between the support structure 114d and the thermal compensating element 128d is illustrated as including two pins 133d and 134d extending through coaxially aligned apertures formed in the mating configuration surfaces. In the present invention, the support structure of the apparatus 110d can be made from one or more elements, by way of example and not limitation, such as a type of steel. The output from the piezoelectric CMA 112d can be transferred to the operating arms 115d and 116d through the force transfer structure 118d. A compressive preload force can be applied to the piezoelectric CMA 112d by means of an adjustable loading device 120d associated with the either the rigid support portion 128d and/or the rigid force transfer structure 118d, and a support plate 122d associated with the actuator 112d. The support plate 122d can also optionally have a higher value for the CTE than the value for the CTE of the CMA 112d in order to compensate for the lower value of CTE of the actuator 112d compared with the value of the CTE of the support 114d. In FIG. 16, part of the material of the rigid, non-flexing, support structure 114 (from the structure shown in FIG. 12) has been replaced with an element 128d made from a material with a coefficient of thermal expansion capable of compensating for the movement at the operating arms 115d and 116d caused by the thermal expansion mismatch between the materials of the support structure 114d and the piezoelectric CMA 112d. In this way the deflection at the arms can be controlled very accurately over a broad operating temperature range that, for instance, is typical of industrial type applications. Further, the means of calculating the length of the element 128d to ensure the correct amount of thermal compensation can be controlled in relation to the overall design operation requirement of the actuator apparatus according to the present invention. Further the design of the profile of the joint configuration used for the means of achieving the interconnection between the two elements 114d and 128d can minimize any of the stresses arising in the interconnection zone when the compressive preload is applied to the CMA and during operation of the invention. Additionally, the interconnection between the two mechanical elements, the support structure 114d and the compensation structure 128d, can be simple and yet can maintain the secure and rigid relationship between the two or more elements fundamental for the efficient operation of the invention with simple fastening means or methods. By means of illustration, an actuator using the thermal compensation method shown in FIG. 16 and of similar overall dimensions to the previously described, uncompensated, actuator can now have a thermally induced movement controlled to a level of less than 1% of the nominal actuator stroke.
Referring now to FIG. 17, a perspective view of a thermally compensated actuator apparatus 110e according to the present invention is illustrated. In the illustrated configuration the replacement element 128e performs the thermal compensation as described with respect to FIG. 15 and can be attached to the support structure 114e using a variation of the configuration shown in FIG. 15. The present invention envisions that the interconnection of the support structure element 114e and the thermal compensating element 128e can be achieved in a variety of ways. In the present invention, the support structure of the apparatus 110e can be made from one or more elements, by way of example and not limitation, such as a type of steel. The output from the piezoelectric CMA 112e can be transferred to the operating arms 115e and 116e through the force transfer structure 118e. A compressive preload force can be applied to the piezoelectric CMA 112e by means of an adjustable loading device 120e associated with the either the rigid support portion 140e and/or the rigid force transfer structure 118e, and a support plate 122e associated with the actuator 112e. The support plate 122e can also optionally have a higher value for the CTE than the value for the CTE of the CMA 112e in order to compensate for the lower value of CTE of the actuator 112e compared with the value of the CTE of the support 114e. In FIG. 17, part of the material of the rigid, non-flexing, support structure 114 (from the structure shown in FIG. 12) has been replaced with an element 128e made from a material with a coefficient of thermal expansion capable of compensating for the movement at the operating arms 115e and 116e caused by the thermal expansion mismatch between the materials of the support structure 114e, 140e and the piezoelectric CMA 112e. The rigid support portion 140e can be formed of a material similar to the rigid portion 114e or can be a higher CTE material than the rigid portion 114e, since the compensation for the thermal expansion mismatch can occur in rigid support portion 128e and/or actuator seat plate 122e. In this way the deflection at the arms can be controlled very accurately over a broad operating temperature range that, for instance, is typical of industrial type applications. Further, the means of calculating the length of the element 128e to ensure the correct amount of thermal compensation can be controlled in relation to the overall design operation requirement of the actuator apparatus according to the present invention. Further the design of the profile of the joint configuration used for the means of achieving the interconnection between the elements 114e, 140e, and 128e can minimize any of the stresses arising in the interconnection zone when the compressive preload is applied to the CMA and during operation of the invention. Additionally, the interconnection between the mechanical elements, the support structure 114e, 140e, and the compensation structure 128e, can be simple and yet can maintain the secure and rigid relationship between the two or more elements fundamental for the efficient operation of the invention without requiring additional fastening means or methods. By means of illustration, an actuator using the thermal compensation method shown in FIG. 17 and of similar overall dimensions to the previously described, uncompensated, actuator can now have a thermally induced movement controlled to a level of less than 1% of the nominal actuator stroke.
Referring now to FIG. 18, a curve can illustrate the influence of CMA preload on the deflection of the amplifying mechanism caused by thermal excursions alone. FIG. 18 shows a typical adjustment that can be accomplished, over the temperature excursion of between −20 Celsius and +60 Celsius, with one particular CMA product and one particular amplifying mechanism according to the current invention by adjusting the compressive preload force applied to the CMA. The data reported in FIG. 18 used an amplifying mechanism similar to that illustrated in FIG. 14. The support structure 114b, the force transfer mechanism 118b and the operating arms 115b and 116b were made from a 17-4 PH grade of stainless steel. The thermal compensating element 128b was made from an Invar 36 alloy. The degree of thermal compensation is reported as percentage of full deflection which is the amount of deflection of the amplifying mechanism due to the thermal excursion divided by the amount of deflection of the amplifying mechanism due to full operation of the piezoelectric CMA. The compressive preload force is expressed as a percentage of the actual blocking force of the stack used for the experiment. The range of compressive preload force applied is to illustrate the effect of using this approach as a means of adjusting the thermal compensation of the amplification mechanism and should not be take as the total range of preload force to be used in this invention. Further, FIG. 18 is not intended to demonstrate the full extent of adjustment that can be obtained using the preload force on the CMA. The concept of adjustment using preload force has been explored and demonstrated for other CMA products and design configurations according to the present invention. In the illustration depicted by FIG. 18 the amount of thermal compensating element 128b required to compensate for deflection in the amplifying mechanism due to thermal excursion would decrease with increasing preload force. In this way, the compressive preload applied to the piezoelectric CMA can be used as part of the overall process to design the amplifying mechanism with thermal compensation according to the present invention. Based on an amplifying mechanism according to the present invention then the level of preload can be selected that allows for the correct amount of thermal compensation to be applied in order to ensure that the amount of deflection in the amplifying mechanism due to a defined thermal excursion can be suitably compensated. In this way, a device that might be using the amplifying mechanism, a valve for example, can be controlled within required performance targets over the desired thermal excursion.
Referring now to FIG. 19, a perspective view of a thermally compensated actuator apparatus 110f according to the present invention is illustrated. In the illustrated configuration the replacement element 128f performs the thermal compensation as described with respect to FIG. 15 and can be attached to the support structure 114f using a variation of the configuration shown in FIG. 15. The present invention envisions that the interconnection of the support structure element 114f and the thermal compensating element 128f can be achieved in a variety of ways. In the present invention, the support structure of the apparatus 110f can be made from one or more elements, by way of example and not limitation, such as a type of steel. The output from the piezoelectric CMA 112f can be transferred to the operating arms 115f and 116f through the force transfer structure 118f. A compressive preload force can be applied to the piezoelectric CMA 112f by means of an adjustable loading device 120f associated with the either the rigid support portion 140f and/or the rigid force transfer structure 118f, and a support plate 122f associated with the actuator 112f. The support plate 122f can also optionally have a higher value for the CTE than the value for the CTE of the CMA 112f in order to compensate for the lower value of CTE of the actuator 112f compared with the value of the CTE of the support 114f. In FIG. 19, part of the material of the rigid, non-flexing, support structure 114 (from the structure shown in FIG. 12) has been replaced with an element 128f made from a material with a coefficient of thermal expansion capable of compensating for the movement at the operating arms 115f and 116f caused by the thermal expansion mismatch between the materials of the support structure 114f, 114f and the piezoelectric CMA 112f. The rigid support portion 140f can be formed of a material similar to the rigid portion 114f or can be a higher CTE material than the rigid portion 114f, since the compensation for the thermal expansion mismatch can occur in rigid support portion 128f and/or actuator seat plate 122f. In this way the deflection at the arms can be controlled very accurately over a broad operating temperature range that, for instance, is typical of industrial type applications. Further, the means of calculating the length of the element 128f to ensure the correct amount of thermal compensation can be controlled in relation to the overall design operation requirement of the actuator apparatus according to the present invention. Further the design of the profile of the joint configuration used for the means of achieving the interconnection between the elements 114f, 140f, and 128f can minimize any of the stresses arising in the interconnection zone when the compressive preload is applied to the CMA and during operation of the invention. Additionally, the interconnection between the mechanical elements, the support structure 114f, 140f, and the compensation structure 128f, can be simple and yet can maintain the secure and rigid relationship between the two or more elements fundamental for the efficient operation of the invention without requiring additional fastening means or methods. By means of illustration, an actuator using the thermal compensation method shown in FIG. 19 and of similar overall dimensions to the previously described, uncompensated, actuator can now have a thermally induced movement controlled to a level of less than 1% of the nominal actuator stroke.
The present invention has been shown with thermal compensation inserts in the arms of the apparatus in one embodiment and thermal compensation elements integrated into the structure of the apparatus in another embodiment. It should be recognized that the present invention can include both thermal compensation inserts in the arms and thermal compensation elements integrated into the structure of the apparatus. In other words, the various elements of the present invention can be combined in different combinations without departing from the teaching of the present invention.
While the invention has been described in conjunction with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under law.
Patent Application
20060017349
