Abstract:
A cradle device for large pinion gears or blanks wherein a pinion may be supported and rotated for machining. The cradle device comprises one or more adjustable prismatic units each including a plurality of angular plates that are movable toward and/or away from one another along the width of the cradle device in order to raise and lower, and/or laterally shift, a pinion placed thereon so as to position the pinion for machining.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 61/331,549 filed May 5, 2010 the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the machining of gears and in particular is directed to a cradle for the machining of large pinions. 
     BACKGROUND OF THE INVENTION 
     Gear sets with ring gear diameter of 1000 mm to 2500 mm or even above 2500 mm commonly have pinion shanks which are longer than 1000 mm, e.g., even above 2000 mm. Today, such pinions are held in a vertical position. Upside down clamping is in most cases not possible. Long pinions are clamped on the end, opposite to the pinion head to a rotary table in vertical orientation. This positions the machining zone to the upper area of the vertical travel of a multi-axis machining center, which will deliver reduced stiffness and reduced accuracy. However, in most cases it is impossible to machine pinions with shanks larger than 1500 mm because of the vertical travel limitations of those machines. 
     It is known to horizontally clamp objects with curved outer surfaces, such a round elongated work pieces, utilizing a V-block (known also as “vee block”) as disclosed, for example, in U.S. Pat. No. 4,340,211 to Chiappetti or a pair of V-blocks as disclosed by U.S. Pat. No. 4,445,678 to George. While such devices may be capable of clamping lengths of circular bar stock, the size of the head of a pinion may still be of a magnitude that the capability of axes travel of a multi-axis machining center will still be challenged and reduced stiffness and accuracy will continue to be of concern. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a cradle device for generally cylindrically-shaped workpieces such as large pinion gears or blanks (i.e. pinion workpieces) wherein the pinion workpiece may be supported and rotated for machining. The pinion cradle comprises one or more adjustable prismatic positioning units each including a plurality of angular plates that are movable toward and away from one another along the width of the pinion cradle in order to raise and lower, and/or laterally shift, a pinion placed thereon so as to position the pinion for machining. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  represents a top view of the pinion cradle of the present invention. 
         FIG. 2  illustrates a cut-away side view of the inventive pinion cradle. 
         FIG. 3  illustrates a rear view of the inventive pinion cradle 
         FIG. 4  is an exemplary illustration of two machining zones and the pinion cradle rotational motion for accessing the two machining zones in order to machine all slots of a pinion. 
         FIG. 5  shows the same view as  FIG. 3  with the inclusion of an additional rail segment thereby enabling 360 degree cradle rotation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before any features and at least one construction of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other constructions and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purposes of description and should not be regarded as limiting. 
       FIGS. 1-3  show the inventive pinion cradle  2  (clamping yokes omitted for viewing clarity in  FIG. 1 ) with a pinion  4  positioned thereon. The pinion cradle has a centerline, C, extending along the lengthwise (axial) direction of the cradle. The pinion  4  comprises a head  6 , a first shank portion  8  and a second shank portion  10  with shank portion  8  having a larger diameter than second shank portion  10 . It should be understood that the diameter of the pinion shank may be uniform along its entire length or the pinion shank may comprise two or more different diameter portions along its length. 
     Pinion cradle  2  comprises a base  12 , a first support stand  14  and a second support stand  16 . First support stand  14  is attached to base  12  via suitable removable attachment means such as a plurality of bolts  15  or by brackets. Second support stand  16  is attached to base  12  via suitable removable attachment means such as bolts  17  or by brackets. Alternatively, support stands  14 ,  16  may be attached to base  12  via welding or may be formed integral with the base  12  such as by casting as a single unit. Base  12 , first support stand  14  and second support stand  16  may be made of cast iron, steel or mineral cast aggregate for example. Pinion cradle  2  can be placed and/or removed by crane or fork truck and may be clamped down with brackets or bolts to the factory floor or to the frame, table or rotary table of a machining center or a gear manufacturing machine. 
     Pinion cradle  2  further includes an inner rotatable member  18  comprising front arcuate member  20 , rear arcuate member  22  and floor member  24 . Preferably, arcuate members  20 ,  22  have the form of a circular arc, most preferably a semi-circle. Arcuate members  20 ,  22  are positioned for rotation on the inner surface of respective support stands  14 ,  16 . A reversible motor  26  and worm wheel  28  ( FIG. 3 ) may engage with corresponding teeth (e.g. worm gear teeth, not shown) formed in the outer periphery of arcuate member  22  in order to rotate and position the inner rotatable member  18  about centerline, C, for machining and loading/unloading of a pinion  4 . Thus, centerline, C, represents the rotational axis of the inner rotatable member  18 . Alternatively, motor  26  and worm wheel  28  may engage arcuate member  20  or each arcuate member  20 ,  22  may be associated with a motor  26  and worm wheel  28 . Other means to rotate and position inner rotatable member  18  may be utilized as can be appreciated by the skilled artisan. 
     Located on floor  24  is at least one, preferably two, adjustable prismatic positioning units  30 ,  32  arranged along the length of the pinion cradle  2  with each prismatic unit comprising a plurality of alternating and opposing angular plates. Prismatic unit  30  comprises angular plates  34 ,  36  and prismatic unit  32  comprises angular plates  38 ,  40 . The angular plates  34 ,  36  and  38 ,  40  are movable toward and away from one another along the width of the pinion cradle  2  (i.e. generally perpendicular to centerline, C) in order to raise and lower a pinion positioned thereon. 
     Prismatic unit  30  includes a pair of axially positioned rails  42 ,  44  between which the angular plates  34 ,  36  are alternately arranged. Angular plates  34  are moved via motor  46  acting through appropriate means (e.g. worm gears, ball sleeves) at  48  and  50  to move bar  52  in either direction along rails  42 ,  44 . Bar  52  is attached to angular plates  34  thereby moving the angular plates along with the moving bar  52 . The drive shaft from motor  46  extending to means  48 ,  50  may be located within bar  52 . Similarly, angular plates  36  are moved via motor  54  in either direction along rails  42 ,  44 . Bar  56  is attached to angular plates  36  thereby moving the angular plates  36  along with the moving bar  56 . The drive shaft from motor  54  extending to means  58 ,  60  may be located within bar  56 . It can be seen that movement of angular plates  34 ,  36  toward one another results in an upward movement of a work piece while movement of angular plates  34 ,  36  away from one another results in a downward movement of a work piece. 
     In a similar manner, prismatic unit  32  includes a pair of axially positioned rails  62 ,  64  between which the angular plates  38 ,  40  are alternately arranged. Angular plates  38  are moved via motor  66  acting through appropriate means (e.g. worm gears, ball sleeves) at  68  and  70  to move bar  72  in either direction along rails  62 ,  64 . Bar  72  is attached to angular plates  38  thereby moving the angular plates along with the moving bar  72 . The drive shaft  74  from motor  66  extending to means  68  (e.g. worm gear  76  and ball sleeve  78  as seen in  FIG. 3) and 70  may be located within bar  72 . Similarly, angular plates  40  are moved via motor  80  in either direction along rails  42 ,  44 . Bar  82  is attached to angular plates  40  thereby moving the angular plates  40  along with the moving bar  82 . The drive shaft  84  from motor  80  extending to means  86  (e.g. worm gear  90  and ball sleeve  92  as seen in  FIG. 3) and 88  may be located within bar  82 . It can be seen that movement of angular plates  38 ,  40  toward one another results in an upward movement of a work piece while movement of angular plates  38 ,  40  away from one another results in a downward movement of a work piece. 
     Angular plates  34 ,  36  and  38 ,  40  are preferably initially positioned relative to one another in accordance with the diameter of a pinion to be positioned in the cradle  2  such that the rotational axis of the pinion is aligned with the centerline, C, of the cradle  2 . With respect to the pinion  4  shown in the drawings, it can be seen that given the different diameters of the pinion shank portions  8 ,  10 , angular plates  38 ,  40  would be positioned closer to one another than would be angular plates  34 ,  36 . Once pinion  4  is placed into cradle  2 , adjustment of the position of angular plates  34 ,  36  and/or  38 ,  40  may be necessary to achieve the proper axis/centerline alignment. Once aligned, one or more top clamping yokes may be positioned at each prismatic unit  30 ,  32 . Rear top lamping yoke  94  is shown in  FIG. 3 . 
     It should also be understood that movement of angular plates  34 ,  36  (and/or  38 ,  40 ) each in the same direction may be utilized to shift the position of a workpiece along the width of the cradle  2 . 
     The rotational actuator (e.g. motor  26 ) is preferably linked to the control (e.g. CNC) of a machine tool such as a multi-axis machining center. It is also possible to use an individual control which receives a manual or electronic signal for indexing from one pinion tooth slot position to the next. While the cradle is primarily utilized to index between tooth slot positions (i.e. slot spacings), the cradle may also perform partial or complete roll motions. Motors  46 ,  54 ,  66  and  80  are also preferably linked to the control of the machine tool but may instead have a separate control at the cradle  2 . 
     A measuring probe can be used to locate the reference surfaces in order to establish the cradle axis in the machine control. The pinion axial position can also be determined with a measuring probe. The cradle can rotate +/−90° and as such will allow every point on a pinion blank to rotate 180° about its axis. 
     As seen in  FIG. 4 , if the slot milling area is first ( 1 ) for half the number of teeth and if the machining zone is changed from ( 1 ) to a zone ( 2 ), where ( 2 ) is about 180° apart from ( 1 ) in a direction around the pinion axis, then the entire circumference of 360° can be reached with a milling or grinding tool in order to machine all the slots of a pinion. The cradle rotation can cover some amount more than +/−90° in order to achieve an overlapping zone between the segments of machining. 
     As seen in  FIG. 5 , the present invention further contemplates one or more additional arcuate rail segments  96  (one shown), preferably circular arc-shaped rail segments, mounted above members  20  and/or  22  in order to achieve a 360 degree cradle rotation. The additional arcuate rail segment is connected to members  20  and/or  22  at end surfaces thereof via any suitable connection (e.g. dove-tail) such that a seam  98  formed between members  22  and  96  would pose no hindrance to rotation of a pinion mounted in the cradle  2 . Preferably, members  20  and/or  22  are preassembled with the additional arcuate (e.g. circular arc) rail member segment  96  to form a circular rail and then teeth (e.g. worm gear teeth) are formed in the outer periphery of the preassembled circular rail. The circular rail is then disassembled and members  20  and/or  22  are positioned in cradle  2 . When desired, additional member  96  is positioned on cradle  2  and an accurate level of transmission across seam  98 , suitable for tooth cutting or grinding operations, is realized due to the formation of all circular rail teeth in the preassembled condition. 
     An advantage of the cradle is the horizontal orientation which allows positioning of the toothed zone in the lower vertical travel range in machines with limited vertical travel. Another advantage of the inventive cradle is the fact that gravity is utilized to hold long pinions tight in the prismatic seating until the centerline adjustment is finished and the pinion is clamped with yokes to the cradle. 
     It is also possible not to adjust the center line height and orientation and use the results of a measurement of a local machine probe to locate the actual center line and axial pinion position and transform the flank surfaces of the tool paths to the actual location of the pinion, relative to the multi-axis machining center. 
     While the invention has been described with reference to preferred embodiments it is to be understood that the invention is not limited to the particulars thereof. The present invention is intended to include modifications which would be apparent to those skilled in the art to which the subject matter pertains without deviating from the spirit and scope of the appended claims.