Abstract:
A high performance rotary axis. An upper and lower unit are coupled together by a pair of bearings to permit relative rotation between the units. The bearings are biased relative to others along a link to reduce play between the bearings. A processor and sensor provide for detection of relative positions between the units. A floating stop may be provided to permit rotation about the axis in greater than 360°.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a rotary axis. More specifically, the invention relates to a low-cost, high-performance motorized platform that minimizes play during rotation and recovers from clutching events. 
     2. Background 
     A high-performance rotary platform should typically address three kinds of problems. First, the rotational movement of the platform should be precise and minimize play. Second, the platform should be able to recover from clutching events, such as when a user attempts to forcibly rotate the platform or impede its rotation. Finally, the platform should be able to accommodate different kinds of equipment with different power, data, and signal cabling needs while being able to rotate freely. These factors have contributed to the unavailability of motorized platforms that have a low unit cost and, correspondingly, a low part count. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     FIG. 1 is an exploded view of the rotary axis of one embodiment of the invention. 
     FIG. 2 is a bottom view of the rotary axis of one embodiment of the invention. 
     FIG. 3 is a top view of the rotary axis of one embodiment of the invention. 
     FIG. 4 is a bottom view of the gear assembly of one embodiment of the invention. 
     FIG. 5 is another view of the gear assembly of one embodiment of the invention. 
     FIG. 6 is a cross-sectional view of the rotary axis of one embodiment of the invention. 
     FIG. 7 is a view of a floating stop of one embodiment of the invention. 
     FIG. 8 is another view of a floating stop of one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There are many contexts in which a high precision rotary axis may be desirable. Among these contexts is image capture of panoramic images. Precision control of the rotation of the capture device greatly facilitates assembly of the ultimate image and reduces the data processing required. While this is one context in which an embodiment of the invention may be used for other uses and embodiments. 
     FIG. 1 is an exploded view of the rotary axis of one embodiment of the invention. Upper unit  14  is rotatably coupled to lower unit  10  via bearings  22 ,  16 . Upper unit  14  is alternatively referred to as the “frame.” Lower unit  10  is alternatively referred to as the “base.” Lower unit  10  is coupled to lower bearing  16 , which is rotatably coupled to center shaft  12 . Upper unit  14  is rotatably coupled to upper bearing  22 , which is coupled to lower unit  10 . Upper unit  14  and lower unit  10  may provide areas for placement of an actuator  24 , a processor  26 , and other electronics (see FIG.  3 ). In one embodiment of the invention, lower unit  10  defines an internal drive gear  28  and a plurality of positioning blades  30 . In one embodiment, the internal drive gear  28  and positioning blades are formed as a single integral molded part. Internal drive gear  28  may be driven by actuator  24  under control of processor  26 . The plurality of positioning blades  30  are spaced around a circle defined on lower unit  10  to permit sensor  50  (see FIGS. 4 and 5) coupled to upper unit  14  to detect the passage of each blade during rotation of upper unit  14  relative to lower unit  10 . Processor  26  is also coupled to sensor  50  and can determine the location of the upper unit  14  relative to lower unit  10  based on signals received from sensor  50 . In one embodiment of the invention, rotation of upper unit  14  relative to lower unit  10  may be limited to less than 720° by floating stop  66 . Upper unit  14  and lower unit  10  may be molded out of glass filled Acrylonitrile Butadiene Styrene (ABS), a thermoplastic, or may be manufactured out of metal or some other suitably rigid material based on the expected load. 
     FIG. 2 is a bottom view of the rotary axis of one embodiment of the invention. Lower bearing  16  is coupled to lower unit  10  and mounted to permit the center shaft to rotate relative to the lower unit  10 . In one embodiment of the invention, a plurality of power, data and signal connections  20  such as cables, flexible circuits, or other similar devices may be fed around lower bearing  16  through one or more channels  18  to upper unit  14 . In another embodiment of the invention, lower bearing  16  could be made larger to accommodate the plurality of connections  20  through its center. However, this would require an additional structure (not shown) to couple lower bearing  16  to center shaft  12 . A fan (not shown) may also be coupled to lower unit  10  to drive air through one or more channels  18  to upper unit  14  to provide cooling for any heat producing components residing in the upper unit  14 . 
     FIG. 3 is a top view of the rotary axis of one embodiment of the invention. Upper bearing  22  is coupled to lower unit  10  and mounted to rotate relative to center shaft  12 . In one embodiment of the invention, the plurality of connections  20  passing around lower bearing  16  may be fed through one or more channels  18  and then through upper bearing  22 . This allows upper unit  14  to rotate without entangling the plurality of connections  20 . Upper unit  14  may have an actuator  24  to drive internal drive gear  28  in lower unit  10 . As used herein, an actuator may include a galvo, a servo, a solenoid, a piezoelectric motor, an electric motor, or other similar devices. In one embodiment of the invention, actuator  24  may be a bi-directional motor that may cause relative rotation in either of two directions between upper unit  14  and to lower unit  10 . The actuator may drive one or more gears that form a gear assembly which in turn engage internal drive gear  28 . In one embodiment of the invention, internal drive gear  28  is part of upper unit  14  with actuator  24  coupled to lower unit  10 . 
     FIG. 4 is a bottom view of the gear assembly of one embodiment of the invention. Gear box  32  on which actuator  24  and a gear assembly is mounted, is pivotally coupled to upper unit  14  at pivot point  34 . An opposing end of the gear box  32  is coupled to biasing spring  38 , which is also coupled to an inner portion of upper unit  14 . Biasing spring  38  causes compound gear  40  to engage internal drive gear  28  in lower unit  10 . Compound gear  40  is driven by compound gear  44 , which in turn is driven by compound gear  48 , which is driven by actuator  24 . In one embodiment of the invention, the gear ratio from the actuator  24  to the internal drive gear  28  is 506. In another embodiment of the invention, the compound gears  40 ,  44 , and  48  may be anti-backlash gears. 
     The biasing spring  38  in conjunction with the pivotal connection at pivot point  34  creates a clutching function between compound gear  40  and internal drive gear  28  of lower unit  10 . Additionally, the spring bias takes out inconsistencies related to manufacturing imprecision or wear on the teeth of internal drive gear  28 . The clutching function further permits less expensive gears to be used as it reduces the risk of teeth breakage. The clutching function occurs when a force is applied in either the forward or reverse direction greater than the resultant spring force (e.g., clutching). When this occurs, compound gear  40  will disengage from internal drive gear  28  of lower unit  10  as gear box  32  pivots away from such engagement. By appropriately selecting the spring and the angle of pivot of the gear box, risk of gear damage by clutching the upper unit  14  is minimized and the force required to clutch may be approximately the same in both directions. 
     Also mounted on upper unit  14  is sensor  50  which is disposed so as to be along the positioning blade ( 30  in FIG. 1) travel path. Accordingly, the plurality of positioning blades  30  defined by lower unit  10  trigger sensor  50  and make possible the detection of clutching events. Detection of clutching events is discussed below with reference to FIG.  5 . It is also within the scope and contemplation of the invention for the positioning blades to be part of the upper unit and have the sensor mounted on the lower unit. 
     FIG. 5 is another view of the gear assembly of one embodiment of the invention. Positioning blades  30  are arranged around a circle defined on lower unit  10 . The circle is divided into segments of equal size each segment having a blade. In one embodiment, each blade, however, has a unique cross dimension relative to the other blades. In one embodiment of the invention, the blades are rectangular in shape. Generally, any shape that can have a unique cross dimension may be used. Thus, other shapes are within the scope and contemplation of the invention. In one embodiment, the positioning blades  30  and the internal drive gear  28  are formed as part of lower unit  10  during the molding process. This reduces the part count and, hence, the cost of manufacture. 
     Sensor  50  is coupled to upper unit  14  and detects changes in the ratio between blade cross dimension and segment size as upper unit  14  rotates relative to lower unit  10 . It is the relative motion that permits detection. Thus, various embodiments may rotate the sensor while the blades remain fixed in a global coordinate system, while other embodiments may fix the sensor in the global coordinate system and rotate the blades. As used herein, detecting a change in ratio is deemed to include detecting the cross dimension of a blade even if no explicit ratio is actually calculated. In one embodiment of the invention, positioning blades  30  may be defined by upper unit  14  and sensor  50  may be coupled to the lower unit  10 . In another embodiment of the invention, sensor  50  may be an optical sensor (e.g., a photo interrupter) or other such similar devices, such that positioning blade edges are detected as the upper unit  14  rotates sensor  50  across the blades. 
     By determining the location of sensor  50 , processor  26  can ascertain the position of upper unit  14  relative to lower unit  10 . In one embodiment of the invention, processor  26  determines sensor location based on the time elapsed between detection of positioning blade edges and a known relative speed between lower unit  10  and sensor  50 . In another embodiment of the invention, the relative motion between lower unit  10  and sensor  50  is in discrete steps (e.g., via a stepping motor) and processor  26  may determine sensor location based on the number of steps between detection of blade edges. In one embodiment, combination of logic or an ASIC may be employed instead of processor  26 . 
     Positioning blades  30  make possible the discovery of clutching events. A clutching event occurs when a user forcibly rotates or impedes the rotation of upper unit  14 , thus putting upper unit  14  out of synchronization with lower unit  10 . Processor  26  can predict, based on the last positioning blade detected by sensor  50  and the direction of rotation, when a blade edge should next be detected by sensor  50 . If upper unit  14  is clutched, the detection of the next blade edge will not coincide with the predicted value. If the expected number of edges are not detected within the expected number of steps, a clutching event is presumed to have occurred. In that case, processor  26  can cause actuator  24  to return upper unit  10  to its proper position, for example, by signaling actuator  24  to move upper unit  14  relative to lower unit  10  until sensor  50  detects the last blade edge encountered before the clutching event occurred. In one embodiment, processor  26  correlates the blade edges with the commands to the actuator to reduce error between expected and actual angular displacement on a substantially continuous basis. 
     FIG. 6 is a cross-sectional view of the rotary axis of one embodiment of the invention. Lower bearing  16  is rotatably coupled to center shaft  12 . In one embodiment of the invention, center shaft  12  may be a screw, a cylinder with attachment points, or other such similar apparatuses. Center shaft  12  may have a head  52 . Inner race  56  of lower bearing  16  may be supported by head  52 . A washer may also be used. Lower unit  10  rides on outer race  54  of lower bearing  16 . Lower unit  10  supports outer race  58  of upper bearing  22 . Upper unit  14  rides on inner race  60  of upper bearing  22  and rotates relative to lower unit  10 . Lower bearing  16  is biased by head  52  towards upper bearing  22  and conversely, upper bearing  22  is biased by upper unit  14  towards lower bearing  16 , such that vertical play between upper bearing  22  and lower bearing  16  is reduced along center shaft  12  during rotation of upper unit  10 . This permits the pair of low cost bearings to emulate the precision of much more expensive multiple row bearings. 
     In some embodiments, rotation of greater than 360° is desirable. In such embodiments, a fixed stop is impractical. FIG. 7 is a view of a floating stop of one embodiment of the invention. Floating stop  66  is interposed between upper unit  14  and lower unit  10  to permit rotational travel of upper unit  14  relative to lower unit  10  in greater than 360° but less than 720°. The range of rotation is limited by the sizes of the arc of the lips. For example, assuming the upper lip  62  and lower lip  64  each cover a 60° arc and the stop tab  68  covers a 30° arc and the push tab  70  covers a 30°, maximum rotation would be 540°. Without a floating stop, clutching events and/or over rotation could cause undue stress on the plurality of connections  20  running through lower unit  10  to upper unit  14 . Floating stop  66  has an upper lip  62 , a lower lip  64 , and a hollow center through which center shaft  12  and the plurality of connections  20  pass. The upper and lower lips are aligned with each other along the circumference of floating stop  66 . In one embodiment of the invention, the lips may not be so aligned. In another embodiment of the invention, upper lip  62  and lower lip  64  may each be comprised of two posts rather than solid tabs. 
     The range of motion of the floating stop results from the engagement of one lip by a portion of e.g., the upper unit and engagement of the other lip by e.g., a portion of the lower unit. Referring now to FIG. 8, it is another view of a floating stop of one embodiment of the invention. The upper and lower lips on floating stop  66  both terminate at points  72  and  74 . Push tab  70  is coupled to upper unit  14 . Stop tab  68  is coupled to lower unit  10 . Rotation of upper unit  14  causes rotation of side tab  70 . Push tab  70 , in turn, causes floating stop  66  to rotate by engaging upper lip  62  at endpoint  72  or  74 . Floating stop  66  will rotate freely until lower lip  64  engages stop tab  68  at endpoint  72  or  74 . 
     Thus, rotating the upper unit, and therefore the push tab clockwise causes floating stop to rotate until lower lip abuts right end  69  of stop tab  68 . The upper unit is free to rotate counter clockwise for 360° less the dimension of upper lip  74  before it will begin pushing the floating stop counter clockwise for an additional 360° less the dimension of the lower lip  64  and the dimension of stop tab  68  until lower lip  64  at endpoint  74  abuts the left side of stop tab  68  at endpoint  67 . While push tab  70  and stop tab  68  are shown with a particular shape, nearly any shape or dimension is within the scope and contemplation of the invention. 
     While one floating stop has been described in detail, other floating stops are also within the scope and contemplation of the invention. For example, an arcuatate track could be defined in the lower unit having an arc dimension of e.g., 60° a rigid member extending from and engaging the track could be engaged by a push tab to push the rigid member to one end of the track. This permits maximum rotation in the opposite direction of 360° plus the track dimension. Other examples exist. The important characteristics of a floating stop include the ability to permit rotation of greater than 360° and to effect a hard stop at some range beyond 360°. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.