Patent Publication Number: US-2021164545-A1

Title: Relative Translation System

Description:
RELATED APPLICATIONS 
     This is a divisional application of U.S. application Ser. No. 15/666,285, filed on Aug. 1, 2017, entitled, “Relative Translation System,” which is a divisional of, and which claims priority to, U.S. patent application Ser. No. 14/446,079 filed Jul. 29, 2014, entitled “Relative Translation System,” each of which are incorporated by reference in their entirety herein. 
    
    
     BACKGROUND 
     Relative translation mechanisms are used in a wide variety of applications. For example, in an aircraft optical assembly, a focus cell may be configured to support and translate an optical element, such as a lens, to facilitate focusing electromagnetic radiation for an optical sensor. In this application, a linear slide table with a ball screw drive shaft is typically used to move the optical element relative to the optical sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein: 
         FIGS. 1A and 1B  are example illustrations of a relative translation system in accordance with an example of the present disclosure. 
         FIGS. 2A and 2B  are example illustrations of the relative translation system of  FIGS. 1A and 1B , with a fixed support member omitted for clarity. 
         FIG. 3  is an end view of the relative translation system of  FIGS. 2A  and  2 B. 
         FIG. 4  is an example illustration of a drive mechanism in accordance with an example of the present disclosure. 
     
    
    
     Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. 
     DETAILED DESCRIPTION 
     As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result. 
     As used herein, “adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being “adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context. 
     An initial overview of technology embodiments is provided below and then specific technology embodiments are described in further detail later. This initial summary is intended to aid readers in understanding the technology more quickly but is not intended to identify key features or essential features of the technology nor is it intended to limit the scope of the claimed subject matter. 
     Although linear slide tables have been successfully utilized in focus cells for some time, increased performance demands on optical systems is revealing the limits and weaknesses of the design. For example, existing linear slide table/ball screw focus cell designs are over-constrained by the slide table and ball screw. As a result, designers must accept the risk of increased friction and potential binding of the mechanism over runout tolerances and thermal expansion mismatches of the slide table and ball screw over an operating temperature range, incorporate extra clearance, or incorporate extremely tight tolerances in the design. Runout tolerances between the linear slide table and the drive axis can create runout binding, which can vary in severity across an operating temperature range due to thermal expansion, thereby affecting responsiveness and repeatability due to the changing friction. To account for runout binding, designs may either include oversized gaps, which results in less accurate alignment and “jitter” of the optical element, or very expensive, tight, machining tolerances. Thermal expansion can also cause “boresight drift” over a temperature range, which can negatively impact performance of the optical system. In addition, linear slide tables rely on a drive shaft to provide at least some structural support and may exhibit non-symmetric stiffness about the optical element, which can cause jitter of the optical element. Thus, focus cell performance can be enhanced by maintaining responsiveness and repeatability while minimizing boresight drift and jitter. 
     Accordingly, a relative translation system is disclosed that can compensate for runout tolerances, minimize negative thermal expansion effects, and symmetrical support an optical element. In one aspect, drive mechanism structures are decoupled from structurally supporting the optical element. The relative translation system can include a relative translation assembly and a drive mechanism. The relative translation assembly can have a fixed support member, a translatable member supported by the fixed support member, and a translation guide portion to facilitate translation of the translatable member relative to the fixed support member. The translation guide portion can have a fixed translation member and a movable translation member. The movable translation member can be configured to maintain preload on the fixed and movable translation members and accommodate thermal expansion. The drive mechanism can be configured to cause translation of the translatable member relative to the fixed support member. 
     A relative translation assembly is also disclosed. The relative translation assembly can include a fixed support member, a translatable member supported by the fixed support member, and a translation guide portion to facilitate translation of the translatable member relative to the fixed support member. The translation guide portion can have a fixed translation member and a movable translation member. The movable translation member can be configured to maintain preload on the fixed and movable translation members and accommodate thermal expansion. 
     In addition, a drive mechanism is disclosed. The drive mechanism can include a drive shaft having a threaded portion. The drive mechanism can also include a bearing to facilitate rotation of the drive shaft. The bearing can be configured to support the drive shaft and interface with a first structure. Additionally, the drive mechanism can include a drive member engaged with the threaded portion of the drive shaft and configured to be fixed to a second structure to facilitate translation relative to the threaded portion upon rotation of the drive shaft. An angle of misalignment of the bearing can compensate for drive shaft rotational misalignment. A position of the drive member can be adjustable upon assembly to compensate for drive axis translational misalignment. 
     One example of a relative translation system  100  is illustrated in  FIGS. 1A and 1B . The relative translation system  100  is shown configured as a focus cell, where an optical element  103 , such as a lens, is supported and translatable in direction  104  to facilitate focusing electromagnetic radiation for an optical sensor (not shown), such as may be used in an aircraft optical assembly. Although a focus cell is shown and described throughout the present disclosure, it should be recognized that a focus cell is only one exemplary embodiment of a relative translation system. Accordingly, a relative translation system as disclosed herein may be of any suitable configuration and adapted for use in any suitable application, such as where precision translation is needed over a significant temperature variation and/or in a vibration environment. For example, a relative translation system may be used in high powered medical equipment, robotics, and applications for vehicles or equipment used in harsh environments. 
     The relative translation system  100  can comprise a relative translation assembly  101 . The relative translation assembly can include a fixed support member  110 , a translatable member  120  supported by the fixed support member  110 , and a translation guide portion  130  to facilitate translation of the translatable member  120  relative to the fixed support member  110 . The relative translation system  100  can also comprise a drive mechanism  102  configured to cause translation of the translatable member  120  relative to the fixed support member  110 . 
     With continued reference to  FIGS. 1A and 1B ,  FIGS. 2A and 2B  illustrate aspects of the translation guide portion  130 , with the fixed support member  110  omitted in  FIGS. 2A and 2B  for clarity. The translation guide portion  130  can have a fixed translation member  131   a ,  131   b ,  132   a ,  132   b ,  133   a  and a movable translation member  133   b . The fixed translation member  131   a ,  131   b ,  132   a ,  132   b ,  133   a  can be coupled to, and supported by, the fixed support member  110 . The movable translation member  133   b  can be movably supported by the fixed support member  110 . In one aspect, the movable translation member  133   b  can be configured to rotate and/or translate relative to the fixed support member  110 . For example, the movable translation member  133   b  can be coupled to a swing arm  134 , which can be rotatably coupled to the fixed support member  110  to provide rotation about an axis  105 . 
     The translation guide portion  130  can also include a translation member support  121 ,  123  with interface surfaces  121   a ,  121   b ,  122   a ,  122   b ,  123   a ,  123   b  configured to interface with the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b , respectively. The translation member support  121 ,  123  can be of any suitable configuration, such as a rail, track, guide, etc., and may be coupled to the translatable member  120  via a permanent coupling (i.e., integrally formed, or non-removably coupled with the translatable member  120 ) or a removable coupling. Alternatively, it should be recognized that a translation member support may be coupled to a fixed support member and that a translation member may be coupled to, and supported by, a translatable member. The fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b  and the interface surfaces  121   a ,  121   b ,  122   a ,  122   b ,  123   a ,  123   b  can be configured for a rolling and/or sliding interface. 
     In one aspect, the translation guide portion  130  can provide adequate support and/or constraint of the translatable member  120  sufficient to facilitate translation of the translatable member  120  without utilizing the drive mechanism  102  for structural support and/or constraint of the translatable member  120 . As a result, the drive mechanism  102  can serve purely as a means to exert a drive force to cause translation of the translatable member  120 . The drive mechanism  102  can therefore be of any suitable type or configuration to cause translation of the translatable member  120 , and can include an electric motor, a hydraulic ram, a pneumatic ram, a lead screw, a drive train, or any other linear drive mechanism or device that can cause translation of the translatable member  120 . As described further hereinafter, separation of the drive mechanism  102  from structural support and/or constraint of the translatable member  120  can provide benefits to reliability, switching speed, motion precision over a long range of travel, and others. 
     In one aspect, the movable translation member  133   b  can be configured to maintain preload on the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b . For example, a spring  135  supported by the fixed support member  110  can provide a force to preload the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b , such as by acting on a pin or plunger  136  in contact with the swing arm  134 . The movement of the movable translation member  133   b  can accommodate thermal expansion over a temperature range, such as thermal expansion of the translatable member  120 , while maintaining preload on the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b  without substantially increasing friction, load, or stress on the fixed and movable translation members. 
     The fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b  can be located or positioned in any suitable manner with respect to one another, the fixed support member  110 , and/or the translatable member  120 . For example, as illustrated, the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b  can be arranged in pairs, with two pairs of fixed translation members  131   a - b ,  132   a - b  configured to interface with the translation member support  121 , and a mixed pair of the fixed translation member and the movable translation member  133   a - b  configured to interface with the translation member support  123 . This is one example of a translation member configuration that can provide adequate support and/or constraint of the translatable member  120 . Such an arrangement or configuration can therefore provide a kinematic or semi-kinematic mounting scheme. In one aspect, one of the fixed translation members  131   a ,  131   b ,  132   a ,  132   b  can be omitted from the configuration illustrated to provide three points of contact with the translation member support  121  and preserve the same degree of constraint for the translatable member  120 . In one example (not shown), a single fixed translation member can be configured to support and constrain a translatable member at a bottom end of the translatable member and a single movable translation member can be configured to support and constrain the translatable member at a top end of the translatable member. 
     As illustrated in  FIG. 3 , the translation member supports  121 ,  123 , and associated fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b , can be located diametrically opposite one another about a center of mass  106  of the translatable member  120  and attached structures (i.e., optical element  103 ). In other words, a plane  107  defined by the locations of the translation member supports  121 ,  123 , and associated fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b , can pass through the center of mass  106 . In one aspect, the plane  107  can include an optical axis of the lens  103 , in this case extending perpendicular to the view in  FIG. 3  through the center of mass  106 . In another aspect, the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b  can interface with the translation member supports  121 ,  123  at a minimal distance from the center of mass  106 . Such an arrangement or configuration can symmetrically support the translatable member  120  and attached structures about the center of mass  106  to minimize or reduce the moments created due to dynamic loading (i.e., vibrations), which can minimize or reduce jitter of the lens thereby improving performance. It should be recognized that an optical axis can be offset from the plane  107  or in any suitable orientation relative to the plane, such as to improve packaging efficiency and/or meet space constraints. 
     In one aspect, the fixed and movable translation members  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b  can comprise one or more rollers, as illustrated in  FIGS. 1A-3 . A roller is any structure, feature, or device that rotates to facilitate relative translation of the translatable member  120  and the fixed member  110 , typically of a cylindrical and/or spherical configuration, such as a wheel. Accordingly, the interface surfaces  121   a ,  121   b ,  122   a ,  122   b ,  123   a ,  123   b  can be configured to interface with rollers. In a particular aspect, an interface between a roller and an interface surface can be “line” contact, which can prevent or minimize yielding of the interface surface due to shock that can create localized depressions in the interface surface, thereby maintaining smooth motion and motion precision capabilities. 
     A roller can include a bearing, such as a ball bearing and/or a roller bearing, which can be configured as a radial and/or a thrust bearing. A bearing can have an angle of misalignment that is the maximum amount an inner bearing race can go off-axis relative to an outer bearing race. In one aspect, a bearing can have an angle of misalignment between inner and outer races that can serve to maintain line contact between a roller and an interface surface. For example, manufacturing tolerances can be selected such that the angle of misalignment can be sufficient to facilitate line contact between a roller and an interface surface upon assembly and maintained during operation. The bearings can therefore “self-align” to maintain line contact, which can preserve smooth motion and motion precision capabilities even after high loading events, such as shock. 
     In one aspect, the relative translation system  100  disclosed herein can be minimally affected by thermal expansion. For example, temperature variations can cause misalignment due to coefficient of thermal expansion (CTE) mismatch. With regard to a relative translation system in accordance with the present disclosure, the only CTE mismatch may be due to the thickness of the bearing inner and outer races, which are small thicknesses compared to other designs. In the case of a focus cell, this can minimize boresight drift or lens misalignment over a temperature range, which can substantially maintain lens position over the temperature range. The relative translation system  100  can thus provide consistent, reliable, and repeatable performance over a range of temperatures and when subjected to high (i.e., shock) loads. 
       FIG. 4  is a schematic illustration of a drive mechanism  202 . The drive mechanism  202  can include a drive shaft  240  having a threaded portion  241 . The drive mechanism  202  can also include a drive shaft support bearing  250  to facilitate rotation of the drive shaft  240  about a drive axis  208 . The drive shaft support bearing  250  can be configured to support the drive shaft  240  and interface with a first structure  210 , such as a fixed support structure of a relative translation system as disclosed above. For example, an outer race  251  of the drive shaft support bearing  250  can be configured to interface with the first structure  210  and an inner race  252  of the drive shaft support bearing  250  can be configured to interface with a locating portion  242  of the drive shaft  240 . The locating portion  242  and the inner race  252  can interface with one another in an interference, clearance, or slip fit. In addition, the drive mechanism  202  can include a drive member  260  engaged with the threaded portion  241  of the drive shaft  240 . The drive member  260  can be configured to be fixed to a second structure  220 , such as a translatable member of a relative translation system as disclosed above, to facilitate translation relative to the threaded portion  241  upon rotation of the drive shaft  240 . In other words, the interface of the drive member  260  and the threaded portion  241  can convert rotational motion of the drive shaft  240  about the drive axis  208  to linear motion of the drive member  260  in direction  204 . Although the drive shaft support bearing  250  is illustrated as interfacing with a fixed structure and the drive member  260  is illustrated as being fixed to a movable structure, it should be recognized that the drive shaft support bearing  250  can interface with a movable structure and the drive member  260  can be fixed to a fixed structure. 
     In one aspect, a position of the drive member  260  can be adjustable upon assembly relative to the second structure  220  to compensate for drive axis translation tolerance or misalignment, which occurs when a drive axis does not “line up” with a translating member and may result due to manufacturing tolerances. To accommodate this, the second structure  220  can have an opening  224  to receive the drive shaft  240  that is sufficiently oversized to allow the drive member  260  to “float” for lateral adjustment and “centering” without interference between the drive shaft  240  and the second structure  220 . After being centered, the drive member  260  can then be fixed to the second structure  220  via any suitable means, such as a fastener  261 , pin, rivet, weld, etc. In this manner, compensation for “as-built” tolerances leading to misalignment of the drive axis  208  can occur at assembly. In another aspect, an angle of misalignment of the drive shaft support bearing  250  can compensate for angular misalignment or rotational tolerances of the drive shaft, which may result due to manufacturing tolerances, such as the roundness and/or non-concentricity of drive shaft  240  features and/or a perpendicularity tolerance of the first structure  210  to bearing  250  interface. The drive shaft  240  can therefore be prevented from binding or increased resistance with the drive member  260  due to misalignment and/or runout tolerances of the drive shaft  240 , such as rotational and/or translational tolerances, by a one-time adjustment of the drive member  260  and taking advantage of the angular misalignment of the drive shaft support bearing  250 . This can facilitate manufacture of the drive mechanism  202  with more relaxed tolerances than would otherwise be possible, which can reduce costs. 
     The drive mechanism  202  can also include a bearing  270  configured to interface with the first structure  210  proximate the drive shaft support bearing  250 . For example, an outer race  271  of the bearing  270  can be configured to interface with the first structure  210 . The bearing  270  can have a clearance or loose slip fit for the drive shaft  240  extending through an inner race  272  of the bearing  270 . In one aspect, the drive shaft  240  can have a reduced diameter portion  243  to provide the clearance or loose slip fit with the bearing  270 . Thus, the bearing  270  may have no contact with the drive shaft  240 . The bearings  250 ,  270  can each have a rolling element  253 ,  273 , respectively, which can comprise a ball, roller, or other suitable bearing rolling element. The bearings  250 ,  270  can also be configured as radial and/or thrust bearings. 
     In addition, the drive mechanism  202  can include a spring  280 , such as a spring washer, configured to act on the inner race  272  of the bearing  270  to facilitate preload of the bearings  250 ,  270 . For example, the drive shaft  240  can include a spring interface feature  244  to interface with the spring  280 . The spring interface feature  244  can comprise a locally increased diameter portion of the drive shaft  240 . A fastener  281 , such as a nut, can be threaded onto a threaded feature  245  of the drive shaft  240  to preload the spring  280  and the bearings  250 ,  270 . A tool interface feature  245 , such as a hole, can be used to interface with a tool to resist rotation of the drive shaft while the fastener  281  is rotated to apply preload. The drive shaft support bearing  250  can therefore serve to locate and support the drive shaft  240  and the bearing  270  can serve to reduce rotating friction of the spring  280 . The low friction provided by the bearing  270  for the spring  280  can provide performance benefits, such as repeatability of lens adjustment when the drive mechanism  202  is incorporated in a focus cell. 
     In one aspect, the drive shaft  240  can have a mid portion  246  configured to provide flexibility sufficient to accommodate a misalignment and/or runout tolerances of the drive shaft  240 . For example, the mid portion  246  can have a length  247  and a diameter  248  configured to flex in response to forces tending to bind and/or increase friction of the threaded portion  241  and the drive member  260  while transferring torque sufficient to cause relative translation of the first and second structures  210 ,  220 . The flexibility of the mid portion  246  can therefore compensate for any remaining problems due to part and/or assembly tolerances. 
     By preventing or minimizing any binding or increased friction between the drive shaft  240  and the drive member  260  due to misalignment or runout tolerances, the drive mechanism  202  can be configured to simply exert a drive force to cause translation of the second member  220  without providing any structural support for the second member  220 . Thus, the second member  220  can be structurally supported and constrained for linear motion in direction  204  independent of the drive mechanism  202 . This separation of the drive mechanism  202  from structural support and/or constraint of the second member  220  can provide benefits to reliability, switching speed, and motion precision over a long range of travel. 
     In one aspect, the drive mechanism  202  can include a backlash compensation mechanism  263 . The backlash compensation mechanism  263  can comprise a nut  264  threaded onto the threaded portion  241  and coupled to the drive member  260  via a pin  265  or other suitable fastener. A spring  266  between the drive member  260  and the nut  264  can preload the nut  264 . Threads of the nut  264  can cooperate with threads of the drive member  260  to remove backlash with the threads of the threaded portion  241 . 
     In an alternate example (not shown), the backlash compensation mechanism  263 , the bearing  270 , and the spring interface feature  244  can be omitted. In this case, the spring  280  could contact and extend between the inner race  252  of the drive shaft support bearing  250  and the drive member  260 , which could preload the drive member  260 , as well as the drive shaft support bearing  250 , to prevent or eliminate backlash between the threads of the drive member  260  and the threaded portion  241  of the drive shaft  240 . 
     The drive mechanism  202  can also include a motor  290  coupled to the drive shaft  240 . For example, the motor  290  can be coupled to the drive shaft  240  via a drive train comprising one or more gears  291 ,  292 , a chain, a belt, and/or a pulley. The drive shaft  240  can include a drive interface portion  249  to facilitate coupling with the motor  290 , such as by interfacing with the gear  292 . The motor  290  can be an electric motor or any other suitable motor for imparting torque to the drive shaft  240 . In one aspect, the motor  290  can be coupled to and supported by the first structure  210 . 
     It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. 
     As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention. 
     Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.