Patent Publication Number: US-6220939-B1

Title: Method and apparatus for grinding round parts

Description:
This application claims the benefit of U.S. Provisional No. 60/087,704 filed Jun. 2, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to methods and apparatus for machining round parts. More particularly, the invention relates to methods and apparatus for grinding outside-diameter surfaces onto parts with an OD grinder, and which is especially useful in an automated or semi-automated grinding operation for continuously feeding parts to the grinder. 
     2. Description of Prior Art 
     Conventional methods for grinding an outer diameter surface onto a part are generally manual in nature, such as typically having a machine operator manually position a part on a guide or in a fixture associated with an OD or centerless grinder, and then grind the desired surface onto that part. The part is then removed from the grinder, and another part is inserted for grinding. This manual operation is carried out one piece at a time and is a relatively slow process. 
     For economic reasons, there is an ever-present need to increase productivity rate for grinding outside-diameter round surfaces onto parts. Thus, there is an ever-present need for improved methods for and apparatus to assist in grinding such round surfaces onto parts at a faster rate. 
     SUMMARY OF THE INVENTION 
     The general aim of the present invention is to provide new and improved methods and apparatus for grinding round, outside-diameter surfaces onto parts in a manner which increases productivity rates over conventional grinding methods, and thus reduce the associated cost of machining the parts. 
     A detailed objective is to achieve the foregoing by providing a fixture having a plurality of work piece holders in closely spaced relation, each holder being adapted to slidably receive and rotatably carry a work piece, the fixture being further adapted to parade the holders in continuous succession past a grinding wheel to carry the work pieces into rotating grinding engagement therewith for grinding the desired outside-diameter surfaces. 
     Another detailed objective of the invention is to automatically secure the work pieces in the fixture during engagement with the grinding wheel and to automatically release the finished part thereafter for ease of removal from the fixture. 
     These and other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     Briefly, a machine includes a rotating circular fixture that is adapted to releasably carry work pieces, one at a time, into rotating machining engagement with an OD grinding wheel for machining the desired OD surface onto the part. In this instance, the fixture includes a generally round base that is mounted for continuous rotation about a first horizontal axis by, for example, an electric motor, the base being equipped with work piece holding mechanisms in relatively closely spaced relation on an outer diameter thereof. As the base rotates, work pieces are slidably inserted into each holding mechanism as they pass through a loading station area near the front of the machine proximate the machine operator. The work pieces are then carried in the holders in a circular path, as the base rotates, into rotating grinding engagement with the grinding wheel for grinding the desired surface. The fixture also includes a drive roller that is mounted for continuous rotation about a second horizontal axis, and is positioned to engage the work piece as it approaches and passes by the grinding wheel, for controlled rotation of the work piece about its center in the holder during and to maintain grinding engagement with the grinding wheel. Thereafter, the base rotates the part back toward the front of the machine where the finish ground part is removed and another part is installed into the vacated holder. Thus, work pieces are paraded in continuous succession through the grinding operation to achieve relatively high productivity rate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a grinding machine incorporating the unique aspects of the present invention. 
     FIGS.  2 (A &amp; B) and  3 (A &amp; B) are perspective views of sample work pieces for grinding in a machine according to the invention. 
     FIG. 4 is a side view of a fixture and certain other parts of the machine of FIG.  1 . 
     FIG. 5 is a view taken substantially along the line  5 — 5  of FIG.  4 . 
     FIG. 6 is a is a view taken substantially along the line  6 — 6  of FIG.  5 . 
     FIG. 7 is an enlarged view of certain parts of FIG.  6 . 
     FIG. 8 is a is a view taken substantially along the line  8 — 8  of FIG.  5 . 
     FIG. 9 is a view similar to FIG. 4 of an alternate embodiment of the invention. 
     FIG. 10 is a is a view taken substantially along the line  10 — 10  of FIG.  9 . 
     FIG. 11 is a is a view taken substantially along the line  11 — 11  of FIG.  10 . 
     FIG. 12 is a view similar to FIG. 9 of a second alternate embodiment of the invention. 
     FIG. 13 is a view similar to FIG. 6 of a third alternate embodiment of the invention. 
     FIG. 14 is a veiw taken substantially along the line  14 — 14  of FIG.  13 . 
     While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiments have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of illustration, the present invention is shown in the drawings in connection with a machine  10  (FIG. 1) adapted to grind outside-diameter surfaces  12  onto generally round work pieces  14 . For illustrative purposes only, sample unfinished work pieces are shown in FIGS. 2A and 3A, and associated finished work pieces shown in FIGS. 2B and 3B. 
     In general, the machine  10  includes a supporting frame structure or base  16  resting on the floor (not shown), a power rotated fixture  20  adapted to releasably hold the work pieces  14 , and a conventional grinding wheel  18  that (i) is mounted for rotation in the direction indicated by arrow “B” about a vertical axis extending through the center thereof as indicated at “A”, (ii) is power rotated, by for example an electric motor (not shown), for grinding the work pieces, (iii) is substantially enclosed for safety, and (iv) is adapted for forward and backward translation toward and away from the base as indicated by arrow “C”, and optionally for lateral translation as indicated by arrow “E”, to permit selective positioning of the grinding wheel relative to the fixture. Control switches indicated generally at  33  control the operation of the machine, including the grinding wheel and the other components described herein. 
     In accordance with the present invention, the fixture  20  is uniquely adapted to carry the work pieces  14  in continuous procession for controlled rotating engagement with the grinding wheel  18  for machining the desired outside-diameter surfaces  12  onto the work pieces. 
     In generally carrying out the invention, and as generally illustrated in FIG. 4, the fixture  20  includes a generally circular, power rotated base  22  driven by, for example, an electric motor through shaft  22 A and adapted to releasably carry (as discussed further below) a number of parts  14  in a circular path into rotating machining engagement with the grinding wheel  18 . As the fixture rotates as designated as “D”, each part approaches and then engages the grinding wheel to grind the desired surface  12  onto the work piece, after which that work piece rotates past the grinding wheel. The finished part is then carried to an unloading station near the front of the machine  10  and proximate the operator where the finished part is removed, and another part is installed into the fixture. Thus, as the fixture rotates, one-by-one each part on the fixture rotates from the loading station, into machining engagement with the grinding wheel and then to the unloading station. 
     As also indicated in FIG. 4, the parts  14  are rotatably carried on the fixture  20  in a manner that provides for controlled spinning of the parts in the fixture in the direction indicated as “F” generally between the loading and unloading stations, and in particular at least during machining engagement with the grinding wheel  18 , and such that the parts stop spinning for unloading of finished parts. In this instance, each part begins to rotate or spin about its center and on the fixture prior to reaching the grinding wheel such as indicated at “G”, the part continues to spin as it is carried through machining engagement with the grinding wheel and until the part is carried past the grinding wheel such as at “H” whereupon spinning of the part ceases. 
     In further carrying out the invention, the fixture includes a plurality of holding mechanisms or holders  24  for the work pieces  14 , each holder being connected to an outer diameter of the base  22  and being adapted to slidably receive a work piece for carrying the work pieces in a circular path on the rotating fixture, and to rotatably carry the work pieces for spinning of each part about its center as the part is carried into engagement with the grinding wheel. 
     In one embodiment shown in FIGS. 4-7, each holding mechanism  24  includes a pair of jaws or braces  26  connected to the OD of the base  22  and extending laterally therefrom. The braces are formed with facing surfaces  28  that define a slot for slidably receiving and rotatably supporting the work piece  14  therebetween. In the embodiment shown, the mating surfaces are generally in the form of facing V-shapes to create a laterally extending space for slidably receiving the part through the free, open end thereof. At the opposite end of the slot is shown a spacer  30  (FIG. 5) that may be connected to the base via an end cap  32  connected with threaded fasteners  34  for establishing the lateral positioning of the part in the braces and relative to the grinding wheel. In this instance, the work piece is slipped into between the braces to a depth allowed by the free end of the spacer. The work piece is then trapped between the braces, between the radially inner facing edges  26 A and the radially outer facing edges  26 B, but with clearance for some radial (with respect to the center D′ of the base  22 ) movement or translation therebetween. Although only one pair of braces  26  is shown in FIG. 4, it will be understood that multiple holders or multiple pairs of braces are preferably spaced along the entire OD of the base, as generally indicated by the dashed lines in FIG. 4., for carrying the multiple work pieces on the fixture. As will also be evident to the skilled artisan, other methods and arrangements may also be used to achieve a desired lateral positioning of the work pieces in the holders such as positioning the braces radially inwardly and utilizing the adjacent surface of the base  22  to limit lateral movement of the work piece. 
     In carrying out yet another aspect of the invention, the fixture includes drive means for engaging and spinning the work pieces  14  as they approach and travel through machining engagement with the grinding wheel  18 . Such drive means causes the parts to spin at a controlled speed to effect the machining of the desired outside-diameter surface  12 . The controlled lower-speed spinning of the part prevents the parts from simply spinning at a high speed that would otherwise result from surface contact with the grinding wheel, in which case, the part would simply spin and machining of the desired surfaces  12  would not occur. 
     The drive means in FIG. 4 includes a drive wheel  36  that is located within the circular path of the work pieces  14  on the base  22 . The drive wheel is continuously rotated by, for example, an electric motor, by shaft  36 A in the direction designated as “K” about its center K′, independently of the fixture base  22  and work pieces, and is positioned to engage each part as the part approaches the grinding wheel such as at “G”, to continue to engage the part as it travels through machining engagement with the grinding wheel, and until the part is carried past the grinding wheel such as at “H”. Thus, drive wheel engagement and controlled driving or spinning of work pieces occurs for each part as it approaches and travels through engagement with the grinding wheel. In other words, the drive wheel stays in driving contact with each part throughout the grinding operation on that part. For certain sized drive wheel, base and work piece diameter combinations, and possibly including other holding mechanisms such as described below, the drive wheel may be optionally spring-loaded (see FIG. 9) generally in the direction of the grinding wheel to assist in providing tracking of the drive wheel with the work pieces as they approach and travel through grinding engagement with the grinding wheel. 
     As can be seen in FIG. 6, in this embodiment, the fixture base  22  is off-set laterally from the grinding wheel  18 , and the power rotated drive wheel  36  is generally aligned with the grinding wheel. With this arrangement, the drive wheel engages the part for controlled speed spinning just prior to and as it rotates through engagement with the grinding wheel, and the part stops spinning as it rotates past the drive wheel. As will be evident, the diameter of the finished surface of the work piece is established by the distance between the OD of the drive wheel and the OD of the grinding wheel. Advantageously, rotatably carrying the part between the braces or an equivalent holding arrangement, and then driving or at least limiting the spinning of the parts about their axis, eliminates the potential spinning surface contact between the work piece and the grinding wheel. 
     Alternate work piece holding mechanisms may also be utilized with the fixture  20 , such mechanisms permitting controlled spinning of the work pieces  14 , and preferably being adapted to slidably receive the work pieces for ease of installation and removal from the fixture. 
     One alternate holding mechanism embodiment is shown in FIGS. 9-12. In this instance, each holder  50  includes an arm or pair of arms  52  and an idler roller or rollers  54 . The arm is connected to the fixture base with a pin  56  such that the arm is pivotable on the fixture as indicated at “M”, and is spring  60  biased with, for example a coil spring  58  connected and acting between the base  22  and the arm  52  to loosely clamp the part  14  against the OD of the fixture base  22 . The idle roller  54  is connected to the base for free spinning. Thus, each holder arrangement  50  comprising the arm  52 , spring  58  and idler  54 , as well as the part therein, rotates on the circular path with the fixture base. The drive wheel  36 A is positioned to engage the work pieces  14  for controlled spinning as they each approach grinding engagement with the grinding wheel  18 , and is in this instance preferably spring loaded with spring  58  generally toward the grinding wheel to assist in providing tracking of the drive wheel with the work pieces as they approach and travel through grinding engagement with the grinding wheel. With this arrangement, the work piece may be positioned into the holder, between the arms  52  and the idle rollers  54  by pressing the work piece in a generally tangential to the circumference of the base  22 , causing the arm to pivot against the spring bias to allow entry of the part, after which the spring-biased arms retain the part in position on the fixture. 
     In the instance of the work piece  14  resting on the OD of the base  22 , and as shown in FIG. 11, the OD of the base may optionally include wear support surfaces  61  that are raised above a relief cut  62  in the fixture to support the spinning part on relatively short surface lengths to reduce the spinning friction between the spinning part and the fixture. The embodiment shown is also equipped with a stop plate  64  to establish a lateral position or limit on side-to-side movement of the work piece in the fixture in at least one of the two lateral directions such as designated at “T”, and particularly during the time the part is spinning and through the grinding operation. It is noted that in certain instances, such as indicated in FIG. 9, it may be desirable to rotate the drive wheel in a direction opposite the direction of rotation of the base  22 . The embodiment shown in FIG. 12 illustrates the use of the larger drive wheel  36  with the holding arrangement of FIG.  9 . 
     In yet another alternate embodiment, the work pieces  14  may be rotatably carried in a pair of collars  70  (FIGS. 13-14) connected to the OD of the fixture base  22  as indicated at  72 . One such suitable-type collar is equipped with radially inwardly spring  76  biased balls  74  for centering the part therein and for quick installation and removal from the fixture. In this instance, the collars are positioned to provide for work piece engagement with the grinding wheel, and the drive wheel as previously described for controlled work piece spinning through the grinding operation. Such an arrangement is likely especially suitable for use with relatively small work pieces. 
     Provision may also be included for imparting a lateral-biasing force such as indicated at “T” on the work piece as it proceeds through the grinding operation for insuring that the part is biased against the spacer  30 , the stop plate  64 , or the inside surface of the base  22  as the case may be, and thus insure desired lateral positioning of the part in the holder during the grinding operation. Such lateral-biasing means may be provided by, for example, providing an appropriately angled surface toward the stop or spacer such as the support surfaces  61 , the radial outer edges  26 B of the braces, or forming the desired biasing angle onto the drive wheel  36 . Such provision will tend to drive the work piece toward and maintain it against the spacer during the grinding operation. 
     The skilled artisan will recognize that the methods and apparatus disclosed herein may be further modified for machining round surfaces  12  onto work pieces  14  through other alternate embodiments that remain within the scope of the present invention. Such artisans will also recognize that a machine equipped with a fixture in accordance herewith may also be provided with automatic unloading of finished work pieces, such as discussed in U.S. patent application Ser. No. 09/078,855, and other known timed discharge methods, as well as providing for automatic loading of work pieces such as with conventional parts feeders and associated timing mechanisms. 
     From the foregoing, it will be apparent that the present invention brings to the art new and improved methods and apparatus for grinding round, outside-diameter surfaces onto work pieces. By continuously parading work pieces through engagement with a grinding wheel, the work pieces being rotatably carried in a fixture adapted to provide for controlled spinning of the parts during the grinding operation, the productivity of grinding round surfaces onto the work pieces is substantially enhanced over prior methods and apparatus for grinding such surfaces.