Patent Publication Number: US-2020284300-A1

Title: Low-drift optical mount

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The subject application claims priority on Chinese patent application no. 201910159078.0 filed on Mar. 4, 2019 in China. The contents and subject matter of the Chinese priority application is incorporated herein by reference. 
     FIELD OF TECHNOLOGY 
     The present invention relates to optical mount, particularly, an optical mount with relieved position drift due to introduced grease in thread fit clearance, which is useful for fine micro tuning of the angle and position change of optical elements. 
     BACKGROUND OF INVENTION 
     A common optical mount as shown in  FIG. 1  is mainly used for precisely adjusting the angular position of the optical device  7  (such as lenses and mirrors) mounted on the first plate  1 . The mount includes a first plate  1 , a second plate  2 , at least one drive rods  3 , at least one spring  4 , at least two pins  5 , and at least one collet  6 . A drive rod  3  threads through a collet  6  which is attached to the second plate  2 . A spring  4  is opened by two pins  5  respectively inserted into the first plate  1  and the second plate  2 , resulting in the first plate  1  being pulled toward the second plate  2  and pressing against the spherical end of the drive rod  3 . By rotating the drive rod  3 , one can precisely adjust angular position of the mount and the optical device  7 . In order to ensure the smoothness of thread adjustment, grease is usually added to the thread pair. On the one hand, the grease may produce hysteresis after each adjustment, and on the other hand, it may produce slow creep under the tension of one-way springs, which is disadvantage to the angular position of the first plate and optical device relative to the second plate. 
       FIG. 2  shows a thread engagement diagram of the common optical mount when the spring  4  is not tensioned. The external thread surface of a drive rod  3  is fully applied with grease and then screwed into a collet  6 . Before the spherical end touching the first plate  1 , the drive rod  3  is not subjected to force, so the thread engagement is loose fit and the grease  10  is not pressed at this moment.  FIG. 3  shows the thread engagement diagram of the common optical mount when the spring  4  has been one-way tensioned. The spherical end of the drive rod  3  is pulled against the first plate  1 . The screw teeth of the drive rod  3  and the collet  6  are one-way fitted, that is, the inner thread  8  of the collet  6  is attached to the external thread  9  of the drive rod  3 . Due to the axial and radial local contact of the thread fit, it is easy to form a plurality of partially enclosed small spaces. In the situation, the grease  11  on the pressure side under one-way tension force may be local blocking which produces non-rigid contact similar to piton effect. The contact makes the relative position of the drive rod  3  and the collet  6  susceptible to change in environment (such as temperature change and vibration shock), that is, drift phenomenon. It will also continually produce small position change as the grease  11  on the pressure side creeps over time which will react directly to the optical device and may have great influence in high power laser optical system. 
     Some manufacturers have done some measures to achieve rigid contact to improve such drift of the optical mount, such as not adding grease but selecting wear-resistant materials for precision machining, controlling gap of the thread fit and roughness of the thread surface. However these materials will also wear out for a certain period of time for lacking of grease and requirements for materials and manufacture are relatively strict and the price is relatively expensive. In view of the issues, it is necessary to improve the common optical mount to solve above problems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a low-drift optical mount that can relieve the drift performance induced by grease which fills in the thread fit clearance and further improves the position stability of the optical mount. 
     The low-drift optical mount of the present invention may include a first plate, a second plate, at least one drive rod, and at least one collet. 
     In the present invention, a drive rod has an external thread surface with an inner hexagonal slot on one side and a spherical end on the other side which engage the first plate. 
     In the present invention, a collet that is attached to the second plate has an external cylinder surface with a shoulder on one end. An inner screw surface of the collet is machined to match the external screw surface of the drive rod. At least one slot is uniformly distributed in the circumferential direction of the inner screw surface and extends through the entire internal thread length. 
     In the present invention, grease is applied to the external thread surface of the drive rod. 
     The drive rod is screwed into the collet after the external thread surface of the drive rod is applied enough grease. The first plate and the second plate are respectively mounted with pins on which two ends of a spring are respectively mounted pulling the first plate toward the second plate. The drive rod may have a contact end with the first plate under one-way tension of the spring. 
     Compared with the common optical mount, the low-drift optical mount of the present invention has beneficial effects. Because of the inner thread surface of the collet having at least one slot, a plurality of partially enclosed small spaces mentioned above will be connected with each other to form a pressure relief groove of the grease. Each time when the drive rod is turned, the grease on the pressure side under one-way tension force will be pressed into the slot to achieve close fit of the thread surface. It can improve the non-rigid contact caused by grease and improve the position stability of the optical mount. At the same time, a small amount of grease is carried into the thread surface to achieve lubrication of the screw surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the common optical mount in the prior art. 
         FIG. 2  shows the thread engagement diagram of the common optical mount when the spring is not tensioned. 
         FIG. 3  shows the thread engagement diagram of the common optical mount when the spring has been one-way tensioned. 
         FIG. 4  shows an exploded view of an embodiment of the low-drift mount of the present invention. 
         FIG. 5  shows the specific fit structure of a drive rod and a collet of the present invention. 
         FIG. 6  shows the thread engagement diagram of the low-drift optical mount of the present invention when the spring has been one-way tensioned. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In connection with the attached figures, the present invention is further explained in details. 
     As shown in  FIG. 4 , a low-drift optical mount may include a first plate  1 , a second plate  2 , at least one drive rod  12 , at least one collet  13 , at least one spring  4 , at least two pins  5  and pivot ball  14 . 
       FIG. 5  shows the specific fit structure of a drive rod and a collet of the present invention. A drive rod  12  has an external thread surface  15  around the cylinder surface, an inner hexagonal slot  16  on one end surface and a spherical end  17  on the other end surface. The thread surface  15  is used to match the inner thread surface  20  of the collet  13 . The hexagonal slot is used to adjust the position of the drive rod  12  and the spherical end  17  has a contact end with the first plate  1 . 
     As shown in  FIG. 5 , the left side of the collet  13  is a cylindrical surface  18  forming a stationary fit with the corresponding hole surface of the second plate  2  and the right side is a short shoulder  19  which can achieve axial positioning of the collet  13  relative to the second plate  2 . The thread surface  20  is machined to match the thread surface  15  of the drive rod  12 . At least one slot  21  is evenly distributed in the circumferential direction of the inner screw thread  20  and extends through the entire internal thread length of the collet  13 . 
     The collet  13  is first fixed to the second plate  2  by a cylindrical surface  18 , and the drive rod  12  is screwed into the collet  13  until the spherical end touches the first plate  1 . Before screwing into the collet  13 , the external thread surface  15  of the drive rod  12  is applied enough grease. The first plate  1  and the second plate  2  are respectively mounted with pins  5  on which two ends of a spring  4  are respectively mounted pulling the first plate  1  toward the second plate  2 .  FIG. 6  shows the thread engagement diagram of a low-drift optical mount of the present invention when the spring  4  has been one-way tensioned. When the drive rod  12  is pulled against the first plate  1 , the inner thread  23  of the collet  13  will press close to the external thread  22  of the drive rod  12  under the pre-tensioned force of the spring  4 . Each time when the drive rod  12  is turned, the excess grease on the pressure side which hinders the one-way contact of the inner thread  23  and the external thread  22  is squeezed into the slot, achieving close fit of the thread surface. This can improve the non-rigid contact caused by grease, improving the position stability of the optical mount. At the same time a small amount of grease is carried into the thread surface to achieve lubrication of the screw. 
     The scope of the present invention is not limited by the detailed descriptions, and one of ordinary skill in the art could modify and change of the low-drift optical mount without departing from the scope of the present invention.