Abstract:
A drive mechanism is described. One of the objectives, advantages and benefits of the drive mechanism is that is has high precision in rotation, great reliability and durability life, no backlash, and no particle contamination. It is very useful in high precision rotation driving processes for opto-mechanical inspection systems that require high movement precision and no-contamination. In one embodiment, two pulleys are used with their axes to be parallel from each other, two bands are used to rotate the pulleys in opposite directions. An eccentric disk mechanism is used to fine-tune the distance between the two pulleys so that tensions on the two bands can be optimized.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to the area of opto-mechanical inspection system, and more particularly related to a band drive mechanism for opto-mechanical system that has high precision in rotation, great reliability and durability, no backlash, and no particle contamination. 
         [0003]    2. Description of the Related Art 
         [0004]    In opto-mechanical inspection system designs, there is always a requirement or movement to rotate an optical part or component, for example, for measurement or inspection. An exemplary optical component is an optical polarizer, an optical aperture wheel, an optical filter assembly, and an optical compensator. To get an ideal optical inspection resolution, it is very critical to perform the rotation with very high precision (minimum backlash or no backlash at all). Further, the drive mechanism shall be of great reliability and durability. For the optical components under laser beams, if a rotation driving mechanism creates some particles in its movement process, the particles would fill in the gaps of the movement driving pair, such as gear pair or cam pair, causing dimension errors onto the rotation components. As a result, the transmission accuracy is affected. If the driving mechanism needs lubricant to be applied onto the driving parts, it would create contamination on the surface of the optical component, then causing defects to the optical component being moved. Currently, most typical optical component rotation driving mechanisms are using gear-pair, chain drive, cable drive, or cam-pair. These types of driving methods have the typical dis-advantages or issues mentioned above when used in the OPTO-mechanical inspection system. Hence there is a need for an optical component driving mechanism to be free of any contamination, both particles and lubricant. 
         [0005]    In a traditional rotation driving mechanism, gear-pair driving is widely used. Due to its mechanical nature of the driving principle, there is tooth-tooth meshing error due to the dimension tolerance of the gears. The backlash between the gear-pair shall happen even using anti-backlash gears, which could affect the rotation accuracy commonly required in an opto-mechanical inspection system. Further, due to the friction between the meshing surfaces of the gear-pair, particles are often generated when rotation happens. The particles become another source of the dimension errors of the gear surface. To decrease the friction between the surfaces of gears, oil or other lubricant are often applied in the gear-pair. The applied lubricant is a contamination source to damage the cleanness of the optical component surface. Besides these issues, the friction on the gear surface causes wears to the gears, which affects the life of the gear-pair. On considering the above-mentioned issues or drawbacks, the gear-pair is not an idea rotation driving mechanism for the opto-mechanical inspection system. Similarly, the worm driving mechanism is a special gear driving one and has the similar issues as the gear-pair does. 
         [0006]    Timing-belt/pulley, chain /sprocket are other methods often used to drive rotation movements. The timing-belt and pulley drive, although having a relatively low backlash, generate particles in its driving process. These particles will contaminate the environment of the rotation mechanism. These particles can also be dropped onto the surface of an optical component in an opto-mechanical inspection system. Most of the traditional timing belt material is also not suitable for the opto-mechanical inspection system which is always under the exposure of laser beam, and even Ultra-Violet (UV) light or deep Ultra-Violet (DUV) light. On the other hand, due to the structure of the chain/sprocket drive, the sprocket and the chain are not so tightly controlled with their dimensions, the tension of the chain will change after running for a certain period. These characteristics make it very easy to have a big backlash, and the particle issue is another big concern. Accordingly, the chain/sprocket driving mechanism is not suitable for the opto-mechanical inspection system. 
         [0007]    Cam driving is a typical friction driving mechanism, it can transform a linear movement into rotation. It relies on the friction between the cam and the cam follower to pass a driving movement. This process generates particles easily. There is often a need to lubricate the cam follower, which can be a source to contaminate the surface of the optical component. Some band driving mechanism such as Timothy David Puckett&#39;s band driving mechanism used in telescope rotation system relies on the friction between the band and the pulley, which has the particles issue as well. The rotation driving mechanisms are not suitable in an opto-mechanical inspection system. 
         [0008]    Cable rotation drive has been found in many applications. In general, it has low or no contamination, and is relatively low or of no backlash if the cable material is of high quality. The cost of the special required cable material is of a concern in some driving applications. 
         [0009]    In this disclosure, a novel band drive rotation mechanism is described. One of the advantages, objectives and benefits of the band drive rotation mechanism is of high precision in rotation, great reliability and durability, and has no backlash and no particle contamination. 
       SUMMARY OF THE INVENTION 
       [0010]    This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention. 
         [0011]    In general, the present invention is related to a moving mechanism particularly suitable for an opto-mechanical inspection system. According to one aspect of the present invention, a band drive rotation mechanism includes two pulleys, a driving one and a driven one, of the same size or similar size. The driving pulley is motorized by a motor and drives the driving one via one or more bands. It provides rotations from 0° to 360°. Due to its special driving mechanism, there is no relative movement between a band and a pulley so to minimize possible friction between the band and pulley. With a proper material selected for the bands and the pulleys, there are no contamination particles produced in the rotation process, the surface of optical components being moved can be free of contamination all the time. 
         [0012]    According to another aspect of the present invention, the wear and tear is minimized on either the band or the pulley. As a result, this driving mechanism enjoys an advantage of substantial operating life. It is an ideal driving mechanism for an opto-mechanical inspection system that requires only less than 1 full rotation. 
         [0013]    Other objects, features, benefits and advantages, together with the foregoing, are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0015]      FIG. 1  shows an exemplary rotation driving mechanism  100  according to one embodiment of the present invention; 
           [0016]      FIG. 2  shows an exemplary band structure according to one embodiment of the present invention; 
           [0017]      FIG. 3A  shows a front view of two pulleys; 
           [0018]      FIG. 3B  shows an enlarged view of an eccentric disk with a specified off-center parameter according to one embodiment of the present invention; 
           [0019]      FIG. 4A  shows a perspective view of a driving disk with a notch made to accommodate a spring and a holding block; 
           [0020]      FIG. 4B  shows a spring loaded pushing force generating mechanism in operation; 
           [0021]      FIG. 5A  and  FIG. 5B , both show a top view and a front view of two pulleys in two different sizes; 
           [0022]      FIG. 5E  and  FIG. 5F  show together the up-side band and the down-side bands are positioned symmetrically about a vertical center of each of the disks in the pulleys; 
           [0023]      FIG. 5G  and  FIG. 5H  show that the lengths of the top-side band and the down-side band may not be necessarily identical; 
           [0024]      FIG. 5I  and  FIG. 5J  show that one example of mounting a band when the lengths of the top-side band and the down-side band are identical; 
           [0025]      FIG. 5K  shows a different configuration of mounting the top-side band and the down-side bands, which as a result changes the rotational direction of the driven pulley; 
           [0026]      FIG. 5N - FIG. 5Q  shows additional possible mountings of the top-side band and the down-side bands on a disk in each of the pulleys, and 
           [0027]      FIG. 6A - FIG. 6C , each showing an example of how to attach an end of a band to the disk. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of mechanical devices. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the present invention. 
         [0029]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. 
         [0030]    Embodiments of the present invention are discussed herein with reference to  FIGS. 1-6C . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. 
         [0031]    The present invention pertains to a band drive mechanism that can be advantageously used in an opto-mechanical inspection system.  FIG. 1  shows an exemplary rotation driving mechanism  100  according to one embodiment of the present invention. From a perspective view of the drive system  100 , there are two pulleys a and b referenced, respectively, referenced by  102  and  104 . The pulleys  102  and  104  may be identical or different in diameters. In one embodiment, the pulley  102  is the driving pulley and includes a disk driven by a motor  30  to provide the driving torque to the moving mechanism  100 . It gives a transmission gear ratio of about 1:1. The pulley  104  includes a ring  20  and is driven by the pulley  102  via a band belt or an up-side band  40  as there is a down-side band  50 . Depending on implementation, more than one of the up-side or down-side band may be used in parallel. When employed in an opto-mechanical inspection system, an optical component (not shown) is mounted onto the driven pulley  104  and rotates the driven pulley  104  is driven by the driving pulley  102 . In operation, when the motor drives the driving pulley  102  to rotate anti-clockwise, through the top-band  40 , a pulling force is translated through the top band  40  and drives the driven pulley  104 , and causes the optical component to rotate to a predefined angle up to 360°. 
         [0032]    The down-side band  50  is a follower that balances the rotations of the pulleys  102  and  104 . When the driving pulley  102  rotates anti-clockwise, the up-side band  50  provides a pulling force to rotate the driven pulley  104  and the down-side band  50  acts as follower. When the driving pulley  102  rotates clockwise, the down-side band  50  provides a pulling force to rotate the driven pulley  104 , the top-side band  40  acts as a follower. 
         [0033]    Since the rotation movement is generated by the pulling force through the band  40  or  50 , there is no friction between the band  40  or  50  and the pulley  104 . With carefully selected material for the band  40  or  50 , there are no particles falling from the band in the rotation process, thus no contamination from the particles would occur. Again with carefully selected materials the pulleys  102  and  104  as well as for the band  40  or  50 , the wear and tear can be minimized on both the bands and the pulleys. In one embodiment, the material selected for the pulleys is aluminum, which is of low cost and in general easy to make. As described above, no contamination would happen from the bands, when used in the opto-mechanical system, the surface of the optical component can be kept clean. As a result of the invention, an optical system employing one embodiment of the present invention is guaranteed to provide a moving mechanism for a very long term. 
         [0034]      FIG. 2  shows an exemplary band structure according to one embodiment of the present invention. The band material is preferably a kind of high strength and produces no particles so as not to contaminate any parts that are being driven by the pulleys using the band. One exemplary band material is Elgiloy that is a cobalt chromium nickel with the composition of: CO 40%, CR20%, NI 15% Mo7%, MN2% etc. After its heat treatment process, this material processing produces thin bands with very high strength. There is no-contamination being generated by this material. It has an excellent fatigue resistance, thus a substantial operating life of the bands is achievable. Besides elgiloy, stainless steel is also a very good choice for this kind band drive applications. Depending on application, a selection of the bend radius, band thickness and band width may be made according to the stress calculation of the band mechanism. 
         [0035]    To get an optimized band tension for this rotation driving mechanism, the eccentric disk  10  on which the motor is mounted is uniquely designed.  FIG. 3A  shows a front view of the pulleys  102  and  104 . As shown in  FIG. 3A , the disk  302  has a round opening to accommodate a shaft of a motor. The center of the round opening is off the center of the disk  302 , hence the disk  302  is also referred to as an eccentric disk.  FIG. 3B  shows an enlarged view of an eccentric disk with a specified off-center parameter according to one embodiment of the present invention. 
         [0036]    In between the eccentric disk  10  and the driving pulley  20 , there is a ball bearing to make the adjustment of a certain orientation (i.e., a required angle for the eccentric disk) easier. At the beginning of assembling the eccentric disk  302 , an alignment line is in the horizontal direction, the smaller radius direction is facing to the driven pulley  104 . At this orientation, the distance between the two pulleys  102  and  104  is the smallest. When the eccentric disk is rotated to a certain angle, for example, one step can be 360°/24=15°, there are totally 24 hole locations, which means the eccentric disk can be rotated from 15° to 360°, so the distance between the two pulleys can be increased from 0 mm to 2 mm while the distance adjustment step is 0.083 mm. When the band tension is optimized, the eccentric disk  302  can be locked to that orientation by a fastening means (e.g., screws). 
         [0037]    To have an even fine band tension adjustment, a fine band tension adjustment mechanism is built on the driving pulley. In one embodiment, a spring loaded pushing force generating mechanism is provided.  FIG. 4A  shows a perspective view of a disk  400 . A notch is made on the disk  400  to accommodate a spring  402  and a holding block  404 . The spring  402  is stiff enough but compressed and held up by the spring holding block  404 . A shoulder screw  406  is used to hold the block  404  and the spring  402  on the right position, in the notch of the driving pulley. In operation, the holding block  404  is pushed by the compressed spring  402  to move outwards in the direction of the radius of the pulley. The direction of this movement is guided by the shoulder screw  406 . When two bands (not shown in  FIG. 4A ) are used, both are lying outside of this spring holding block  404 , so the movement of the block  404  is pushing inwards, resulting in both bands to be tighter as shown in  FIG. 4B . By selecting different spring with different stiffness, the pushing force provided by the spring  402  can be fine-tuned. The final band tension is optimized to an even finer degree when this fine-tune mechanism is employed. 
         [0038]    It is very critical to have no backlash in such high precision movement process, such as the opto-mechanical inspection system. Using the above mentioned two band tension adjustment methods, the band tensions can be optimized, so there is no-backlash in this driving mechanism. 
         [0039]    According to one embodiment of using two bands on one side, as shown in  FIG. 4A , two groves (e.g., flat) are machined on the outer surfaces of the two pulleys. According, three ridges are formed on the outer surface of each pulley to confine the two bands respectively. In operation, these two groves work as tracks to keep the bands in track, preventing them from running off the outer surfaces of the pulleys. 
         [0040]    Referring now to  FIG. 5A  and  FIG. 5B , both show a top view and a front view of two pulleys in two different sizes, where both ends of the up-side band and down-side band are separately fastened on the outside of the disk. In an alternative embodiment,  FIG. 5C  or  FIG. 5D  shows both ends of the up-side band and down-side band are fastened together on the outside of the disk. 
         [0041]      FIG. 5E  and  FIG. 5F  show together the up-side band and the down-side bands are positioned symmetrically about the vertical center of each by the disks in the pulleys. Two respective groves (for the up-side band and the other for the down-side band) are made on the outer surfaces of the two pulleys. Geometrically, these two groves are not on the same plane, but are on two parallel planes with a distance therebetween. 
         [0042]      FIG. 5G  and  FIG. 5H  show that the lengths of the top-side band and the down-side band may not be necessarily identical. The two ends of a band may be fixed in a notch made on a disk wherever it is deemed appropriate, resulting in asymmetric locations of the notches for the ends of the top-side band and the down-side band on a disk. 
         [0043]      FIG. 5I  and  FIG. 5J  show that one example of mounting a band when the lengths of the top-side band and the down-side band are identical. In the example, one band is to encircle one disk and another band is to encircle another disk. 
         [0044]      FIG. 5K  shows a different configuration of mounting the top-side band and the down-side bands, which as a result changes the rotational direction of the driven pulley. As an option,  FIG. 5K  further shows that the top-side band and the down-side bands are driving the driven pulley on two separate planes.  FIG. 5L  and  FIG. 5M  show the corresponding front views. 
         [0045]      FIG. 5N - FIG. 5Q  shows additional possible mountings of the top-side band and the down-side bands on a disk in each of the pulleys. 
         [0046]    Referring now to  FIG. 6A - FIG. 6C , each showing an example of how to attach the ends of the bands to the disk. Essentially, a notch is made on the disk to bend the end of a band and insert the end of the band into the notch, where a fastening means is provided to secure the end of the band to the disk. 
         [0047]    The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.