Abstract:
A mechanical flexure with two legs in a symmetrical structure that provides straight line motion when a force is applied to one leg end, along an axis through both leg ends. Such a force translates leg ends solely along said axis in a straight line, without deviation in an orthogonal axis. Components attached to flexure leg ends will thus travel in a straight line in a single axis over a useful range. The flexure could also provide rotational translation over small angular ranges when used with appropriate hardware configurations. The flexure is capable of integral manufacture with other components and simultaneously provides alignment and translation functions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention concerns an alignment mechanism that uses flexures to both guide a single-axis translation of, and structurally support, a translation stage. 
     2. The Prior Art 
     Mechanisms providing gross movement in a single axis are known. These known mechanisms commonly employ guide shafts, bearings and other structures, and require several parts that must be carefully aligned. Such mechanisms are usually satisfactory for movements in the range of millimeters to meters. If, however, an accurate linear movement in a range of microns to millimeters is desired, such mechanisms become very expensive, and are difficult to install and maintain. 
     Piezo electric transducers (PZTs) have been used to provide linear motion over small distances. However, PZTs have limited mechanical ranges, are costly to purchase or manufacture, require extensive alignment and assembly procedures, and consume significant amounts of electricity. Complex electronic controllers and power supplies are also required to operate PZTs. 
     Moreover, linear movement from PZTs is limited to ranges of microns per device. Thus, to achieve a linear translation on the order of millimeters, many PZTs would have to be stacked such that their linear motion would be summed. Another disadvantage of PZTs is that they do not inherently provide an alignment function, but rather, provide only translation functions. 
     In view of the problems associated with the above mentioned mechanisms, a highly accurate mechanism for providing linear movement in a range of microns to millimeters, that do not cause location variations in a direction perpendicular to the direction of movement, that uses a minimum number of components, that is easy to fabricate and install, and that is low cost is desired. The mechanism should be capable of manufacture as an integral part of the body it is to translate and should simultaneously provide alignment and translation functions. The size of the mechanism should be scaleable such that it is able to impart linear motion to translation stages of various types and sizes. 
     SUMMARY OF THE INVENTION 
     The instant invention solves the above mentioned problems of known linear movement and alignment mechanisms by providing a mechanical flexure having two legs in a symmetrical structure that provides straight line motion along an axis defined by ends of the two legs when a force is applied to one of the two legs. Such a force translates the leg end solely along the axis in a straight line, without deviation in an orthogonal axis. Components attached to the flexure leg end will thus travel in a straight line along a single axis over a useful range. 
     The flexure could also be used to provide rotational translation over small angular ranges when appropriately configured. 
     The flexure is preferably capable of integral manufacture with other components and preferably provides both alignment and translation functions. 
     The instant invention advantageously has a simple design in which flexures can be manufactured as an integral part of other components, thereby eliminating the need for assembly and tighter tolerances. Alternatively, the flexures could be manufactured independently of, and assembled with, other components. In the instant invention, flexure stiffness compensates for variations in applied forces to provide linear operation. Furthermore, in the instant invention, flexure performance can be optimized by adjusting or trimming the legs of the flexure to provide exactly the response desired (analogous to the way a resistor is trimmed to provide exactly the performance needed). The instant invention does not require slides and bearings for a linear translation mechanism. The instant invention is also energy efficient relative to piezo electric transducers (PZTs). 
     The instant invention also does not require complex control electronics. In a refined embodiment of the present invention, a flexure of the present invention could provide rotational translation over small angular ranges. 
     Lastly, the size of the instant invention is scaleable such that translation stages of different types and sizes can be linearly translated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A shows a schematic of a flexure having two legs. 
     FIG. 1B shows the flexure of FIG. 1A when the free end of a first leg is stationary and the free end of a second leg is subject to a deflecting force. 
     FIG. 2 is a schematic of one implementation of the instant invention, where a flexure has one end attached to a stationary object and the other end attached to a movable object. 
     FIG. 3 shows the flexure of FIG. 2 when the movable object has translated away from the stationary object. 
     FIG. 4 shows the flexure of FIG. 2 when the movable object has translated towards the stationary object. 
     FIG. 5 illustrates a translation stage using two flexures to provide linear travel in a single axis. 
     FIG. 6 illustrates another embodiment of a single axis translation stage, using flexures on one side of the stage and dual linear actuators. 
     FIG. 7 illustrates a two-axis translation stage embodiment with two flexures and a single linear actuator for each axis. 
     FIG. 8 illustrates one embodiment of a rotational translation stage using a flexure and linear actuator to move the stage about a pivot. 
     FIG. 9 illustrates a translation stage using two paired flexures to provide linear travel in two axes. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1A, 1B and 2 through 4 illustrate a mechanical flexure of the instant invention. 
     As shown in FIG. 1A, the flexure 100 consists of a first leg 110 and a second leg 120 that are joined at one end. Each leg has a length (L1, L2), a Young&#39;s modulus (E1, E2) and a moment of inertia (I1, I2). The legs may have the same characteristics or they may be different. 
     A line intersecting the free ends 111, 121 of the flexure legs 110, 120 defines an axis of movement. Generally, as shown in FIG. 1B, when one leg end (e.g., 111) is assumed stationary and a force F 0  is applied to other leg end leg (e.g., 121) along the axis of movement, the free leg end (e.g., 121) can translate vertically (ΔV) and horizontally (ΔH). The free leg end (e.g., 121) also experiences a moment M 0 . ##EQU1## where: L 1  =length of first leg of flexure 
     L 2  =length of second leg of flexure 
     E 1  =Young&#39;s modulus of first leg of flexure 
     E 2  =Young&#39;s modulus of second leg of flexure 
     I 1  =moment of inertia of first leg of flexure 
     I 2  =moment of inertia of second leg of flexure 
     ΔV=vertical deflection 
     ΔH =horizontal deflection 
     F 0  =load applied to flexure 
     M c  =moment at GE=zero slope 
     Equations 1-4 describe the motion of the free leg end (e.g., 121) under these conditions. The ratio of-the leg lengths (or beam lengths) is N, as given in Equation 1. The stiffness ratio, i, is defined by Equation 2. Equation 3 describes the horizontal deflection (ΔH) of the free leg end (e.g., 121) in terms of leg lengths and values for Young&#39;s modulus and moments of inertia. To design a flexure that only translates in a single axis, for example the vertical axis (ΔV), the deflection in the other axis (ΔH) must be set to zero, as shown in Equation 4. 
     Equation 4 is quadratic in i (the stiffness ratio) and contains the beam length ratio N as a coefficient of i. There are five roots to Equation 4; one pair of complex conjugate roots, a pair of real roots (positive and negative) and another root. Only the positive real root is of interest, and it can be found using standard mathematical techniques such as Newton-Raphson numerical methods. 
     FIG. 2 illustrates a flexure 200 at rest that satisfies Equation 4. In this example, the flexure&#39;s first leg end 211 is attached to a stationary component 230, and the second leg end 221 is attached to a movable component 240. In FIG. 3, force F 0  is applied along the axis through the leg ends 211, 221 thereby causing the movable component 240 to translate away from the stationary component 230. Although the flexure 200 moves in response to F 0 , the movement of the component 240 is linear, along the axis defined by the leg ends 211, 221. Similarly, in FIG. 4, an oppositely directed force -F 0  is applied along the axis through the leg ends 211, 221 thereby causing the movable component 240 to translate toward the stationary component 230 in a straight line. 
     The flexure of the present invention can be formed of almost any material, as long as Equation 4 is satisfied. Accordingly, a metal (such as aluminum, steel, titanium, or an alloy, for example), a plastic, or a composite material may be used to form the flexure. If, for example, an aluminum flexure is needed to align 5&#34; by 5&#34; glass plates for an LCD device, the flexure may be fabricated by wire electric discharge machining (or &#34;EDM&#34;) a piece of solid aluminum. Alternatively, other fabrication methods may be used, depending mainly on the material of which the flexure is formed. 
     FIG. 5 illustrates an implementation of the instant invention, where two flexures 510, 520 that satisfy Equation 4, are integrally located on opposite sides of a translation stage 500. A linear translator 530 is installed between the legs 511, 515 of the first flexure 510, and a spring 540 is installed between the legs 521, 525 of the second flexure 520. The linear translator 530 may be an electromechanical device (such as a piezo-electric device or a stepper motor, for example), a mechanical device (such as micrometer screws with a readout for example), or an electromagnetic device (such as a speaker coil for example). In this configuration, when the linear translator 530 urges the ends of legs 511, 515 of the first flexure 510 apart, the stage 500 is pushed in a straight line along the axis through the first flexure&#39;s leg ends. The stage movement causes the ends of legs 521, 525 of the second flexure 520 to move towards one another, thereby compressing the spring 540. If the linear translator 530 is moved in the opposite direction thereby urging the legs 511, 515 of the first flexure 510 towards each other, the ends of legs 521, 525 of the second flexure 520 would be urged apart thereby stretching the spring 540. As a result, the stage 500 would move toward the first flexure 510. 
     The implementation illustrated in FIG. 5 can be easily manufactured from a single piece of material (e.g., aluminum) using conventional processes such as electric discharge machining (EDM) or lithographic processes common to circuit board manufacturing. As described above, other manufacturing methods are equally feasible. This design advantageously requires no assembly beyond the installation of the linear translator 530 and the spring 540, thereby significantly increasing manufacturing accuracy, reducing assembly alignment errors, simplifying assembly and reducing cost. 
     FIG. 9 illustrates a refinement of the embodiment of FIG. 5 in which a pair of flexures 910 and 920 is added to permit movement of the translation stage 900 in a second direction. 
     FIG. 6 shows another implementation of the instant invention. In this case, two flexures 610, 620 are located on the same side of a translation stage 600. Linear translators 615, 625 are is provided across the leg ends 611, 612, 621, 622 of each flexure 610, 620. This configuration provides some benefits over that shown in FIG. 5; namely it can provide small angular adjustments as well as linear movements. For example, if each linear translator 615, 625 is driven a different distance, the translation stage 600 will effectively rotate through a small angle. Thus, this configuration can provide both linear and angular motion of the translation stage 600. 
     FIG. 7 shows a variation of the single axis translation stage detailed in FIG. 6. In this example, a second pair of flexures 710, 720 have been attached to the previously stationary rail 750 that anchored the first flexure pair 610, 620. A single linear translator 730 is shown in this example for simplicity (eliminating the angular movement feature). With this configuration, precise linear movement in two axes is available. As shown in phantom, an embodiment having two linear translators per axis is equally feasible, thus providing linear and angular motion of the translation stage 700 in two axes. 
     FIG. 8 presents a variation of the instant invention, in which small angular rotations can be achieved using the linear movement of the flexure. In this example, a single flexure 810 and linear translator 820 can move a translation stage 800 that is fixed at one point by a pivot 830. When the linear translator 820 pushes the flexure legs 811, 812 apart, the translation stage 800 moves in an arc about the pivot point 830, providing angular rotation. Proper design of this configuration could provide nearly linear correspondence between movement of the linear translator and rotation of the translation stage over small angular ranges.