Abstract:
The invention relates to a machining center comprising a pallet changing station in combination with a machining station. The pallet changing station includes a rotating column assembly supporting a platform on which multiple fixtures are supported and moved. A portion of the column assembly defines part of a hydraulic conduit for supplying hydraulic fluid from a fluid source to the fixture for use in clamping parts to the fixture. The integration of a portion of the hydraulic conduit with the rotating column reduces the tendency for the hydraulic conduit to become twisted during rotation of the column or for the various threaded connections of the hydraulic conduit from loosening.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims prioirty on U.S. Provisional Patent Application No. 60/180,320 filed Feb. 4, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a machining center for the machining (drilling, milling, etc.) of one or more parts clamped to a fixture; and, more particularly, to an integral continuous pressure hydraulic pressure clamping system for use with the machining center to supply hydraulic fluid to the fixtures to provide a controllable clamping force. 
     2. Related Art 
     Machining centers, such as CNC machining centers, are widely used in the production of precision parts. Generally, most machining centers employ a pallet changing station. The unmachined parts are clamped to a fixture that is moved into and out of the machining area by the pallet changing station. 
     The pallet changing station typically comprises an external housing in which is mounted a vertically-oriented rotating column that carries a dividing wall and a platform on which the fixtures are positioned. The dividing wall effectively encloses a portion of the column and divides the interior of the pallet changing station into a load area and a machining area. Each of the load area and the machining area support a fixture. In that manner, the parts of the fixture in the machining area can be machined while the fixture in the load area can be loaded with new parts or the fixture replaced entirely. The fixture in the load area can be rotated for better access in the load area. 
     To exchange one fixture for another the machining area fixture is retracted onto the rotating platform of the pallet changing station. The column is moved upward and rotated to move the one fixture currently in the machining area to the loading area, which simultaneously moves the fixture that was in the loading area into the machining area. Typically, the rotational movement of the column is coupled with a vertical upward movement, which unseals the dividing wall carried by the column with respect to the external housing. The rotation is typically limited to approximately 180° in a clockwise/counterclockwise operation. 
     The supplying of hydraulic fluid to the fixtures is a continuous source of problems because the fluid lines extending to the fixtures must be capable of rotating with the column of the pallet changing station while accommodating the extension and retraction and rotation of the fixture relative to the column without tangling or breaking the hydraulic connection or requiring their uncoupling and recoupling. 
     Applicants previous solution to addressing the problems of supplying hydraulic lines to the fixtures included directing the hydraulic lines into the pallet changing station along the rotating column and delivering the hydraulic lines from the rotating column to the fixture through a multi-segmented articulating arm. One end of each arm is mounted to an opposing portion of the rotating shaft and the other end of the arm mounts to a rotary coupling adapted to mount to the fixture. A disadvantage of this system is that the hydraulic lines required individual rotary couplings to permit them to run along the rotating column without twisting during rotation of the column and still be fed through the articulating arms. The repeated rotation of the pallet changing station loosened the individual rotary couplings requiring frequent maintenance and lost production time. 
     SUMMARY OF THE INVENTION 
     The invention relates to an improved machining center for machining parts carried by a fixture. The machining center comprises a housing that defines the fixture loading area for receiving the fixture and the machining area for receiving the fixture during the machining of the parts. A machining tool is located in the machining area for performing machining operations on a part that is carried by the fixture. The machining center further comprises a pallet changing station having a vertically-oriented rotating column assembly and a platform for supporting the fixture. The platform is mounted to the column and has a first portion that is located in the loading area and a second portion located in the machining area. The rotation of the column assembly moves the platform first portion from the loading area to the machining area and the platform second portion from the machining area to the loading area. In this manner, the fixture is moved on the loading area to the machining area for performing the machining operations on the parts and from the machining area to the loading area for removing the machined parts from the fixture. A clamping system comprising a hydraulic conduit extending into the pallet changing station is provided for supplying pressurized hydraulic fluid to the fixture from a source of pressurized hydraulic load to aid in the clamping of the parts to the fixture. The improvement in the machining center comprises the column assembly having a portion with an internal bore forming part of the hydraulic conduit for fluid connection of hydraulic fluid source with the clamping system. 
     Preferably, the internal bore has an inlet located on an exterior portion of the column assembly for fluidly connecting with the hydraulic fluid source and an outlet on an exterior portion of the column assembly for fluidly connecting with the clamping system. The outlet can be located interiorly of the housing and within the pallet changing station. The outlet can be located exteriorly of the housing. 
     The machining center can further comprise a rotary coupling for fluidly connecting the inlet of the internal bore with the hydraulic fluid source. A second rotary coupling can be provided for connecting the hydraulic conduit with the fixture. Preferably, the hydraulic conduit comprises a hydraulic line extending from the bore outlet to the fixture. 
     The machining center can include an articulating arm with a hollow interior. The arm includes a first end that is mounted to the column assembly and a second end that mounts to the second rotary coupling. The hydraulic line extends through the hollow interior of the arm from the column assembly to the second rotary coupling. The arm preferably comprises multiple segments, with each of the segments being hingedly connected to prevent their relative rotation. The hinged connections are oriented to permit the arm to rotate relative to both a horizontal aid a vertical axis. 
     The column assembly preferably comprises a shaft with an internal bore forming a portion of the column assembly that forms part of the hydraulic conduit and a column to which the platform is mounted. A lower end of the shaft is mounted to an upper end of the column to form the column assembly. The shaft comprises a base forming the shaft lower end, and the base has a peripheral wall on which the outlet is located. The shaft also has an upper on which the inlet is located. The bore comprises a first portion that extends from the inlet axially through the shaft toward the base and a second portion that extends radially from the first portion through the base to the outlet. 
     Preferably, there are multiple hydraulic conduits and multiple bores with corresponding inlets located on the shaft upper end and corresponding outlets located on the base peripheral wall. The bores are preferably formed by gun-drilling. 
     The machining center can further comprise a lift mechanism that is mounted to the housing and operably coupled to the shaft to thereby move the shaft between a lowered position and a raised position to effect the raising and lowering of the platform. The lift mechanism includes a lift cylinder having a hollow interior that slidably receives the shaft and a piston fixedly mounted to the shaft and located within the lift cylinder hollow interior. Pressurized fluid is introduced and exhausted from the lift cylinder to reciprocate the piston within the lift cylinder to move the shaft between the lowered and raised positions. 
     In another aspect, the invention relates to a column assembly for a machining center for machining parts carried by a fixture. The machining center comprises a housing defining a fixture loading area for receiving the fixture and a machining area for receiving the fixture during the machining of parts. A machining tool is located in the machining area for performing machining operations on a part carried by the fixture. The machining center further comprises a pallet changing station having a movable platform with a first portion located in the loading area and a second portion located in the machining area. The movement of the platform moves the platform first portion from the loading area to the machining area and the platform second portion from the machining area to the loading area to thereby move the fixture between the loading area and the machining area. A clamping system is provided and comprises a hydraulic conduit extending into the pallet changing station for supplying pressurized hydraulic fluid to the fixture from a source of pressurized hydraulic fluid to aid in the clamping of the parts to the fixture. The column assembly comprises a portion having an internal bore that forms part of the hydraulic conduit and is mounted for rotational movement relative to the housing. The column assembly carries the platform whereby the rotation of the column assembly moves the platform first portion from the loading area to the machining area in the platform second portion from the machining area to the loading area. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     In the drawings: 
     FIG. 1 is a perspective view of a machining center comprising a machining station in combination with a pallet changing station incorporating an integral continuous pressure clamping system according to the invention; 
     FIG. 2 is a schematic view of the machining station of FIG. 1 illustrating the pallet changing station, machining station and the integral continuous pressure clamping system of the invention; 
     FIG. 3 illustrates an articulated arm for coupling the fixtures to the column of the pallet changing station; 
     FIG. 4 illustrates a hydraulic lift assembly and a rotary coupling assembly, including a rotary coupling connected to a shaft through an adapter and an anti-rotation assembly for supporting a rotary coupling: 
     FIG. 5 illustrates a strap for the anti-rotation assembly of FIG. 4; 
     FIG. 6 is a top view of the adapter of FIG. 4; 
     FIG. 7 is a sectional view of the adapter taken along lines  7 — 7  of FIG.  4 : 
     FIG. 8 is a bottom view of the adapter of FIG. 4; 
     FIG. 9 is a side view of the shaft of FIG. 4; and 
     FIG. 10 is a top view of the shaft of FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a machining center  10  comprising a machining area  12  and a pallet changing station  14  incorporating an integral continuous pressure clamping system  16  according to the invention. There are many commercially available machining centers  10  that are suitable for use in the invention. Suitable machining centers are the A 77 , A 66  and the A 55  manufactured by Makino. The general components and functions of commercially available machining centers are commonly known. Therefore, the machining center  10  will only be described to the extent necessary to describe the invention. Components and functions of the machining center  10  not needed to understand the invention or which are commonly known to those skilled in the art, such as the programmable logic controller and the hydraulic plumbing, will not be described in detail. 
     Referring to FIGS. 1 and 2, the pallet changing station  14  comprises an external housing  20  in which is mounted a vertical-oriented, rotating column  24  which is positioned within the housing and supports a platform  26  on which the fixtures  28  are located during a pallet change. A partition wall  30  extends laterally from the rotatable column  24  and effectively divides the interior of the pallet changing station  14  into a load area  32  and a machining area  34 , which is adjacent to a machining tool  35  of the machining spindle  36 . The fixtures  28  include a chuck assembly  40  and a clamp assembly  42 . The clamp assembly  42  and the chuck assembly  40  are operated by hydraulic pressure. 
     A brief generic description of the operation of the machining center  10  will be helpful to a complete understanding of the invention. The pallet changing station  14  permits a fixture  28  loaded with parts for machining to be moved from the load area  32  into the machining area  34  adjacent the machining tool  36 , where the desired machining operations (drilling, milling, etc.) are performed on the parts clamped onto fixture  28 . While the various machine operations are being performed on the fixture  28  within the machining area  34 , a technician loads new parts on to the fixture  28  in the load station or replaces the fixture  28  with another fixture  28  already containing parts for machining. Once the machining operations are completed on the parts in the fixture  28  in the machining area  34 , the fixture  28  in the machining area is retracted onto the platform  26  of the pallet changing station  14 . The pallet changing station  14  is then hydraulically moved up and rotated to swap the positions of the fixtures  28  and continue the production cycle of the parts on the fixtures. In this manner, parts in one fixture  28  can be machined as desired while parts in the other fixture  28  are replaced with unmachined parts to permit the continuous manufacturing of the parts. 
     Referring to FIG. 2, the hydraulic fluid is supplied to the fixtures  28  in the pallet changing station  14  from a traditional hydraulic fluid supply (not shown) through a rotary coupling assembly  50 . The rotary coupling is reciprocally mounted to the housing by a lift cylinder assembly  52 , which is fixed to the housing  20 . The rotary coupling assembly  50  couples the source of hydraulic fluid to the column  24  of the pallet changing station  14 . An articulating arm  54  carries hydraulic lines  56  from the rotary coupling assembly  50  to the fixtures  28 . 
     FIGS. 2 and 3 better illustrate the articulating arm  54  which comprises multiple vertically oriented hinges  57  and multiple horizontal hinges  59  coupled together by tubular portions  58 . Preferably, the tubular portions are threaded onto an end of the adjacent vertical or horizontal hinges  57 ,  59  to complete the articulating arm  54 . The interior of the articulating arm is essentially hollow and can receive multiple hydraulic lines  56  emanating from the rotary coupling assembly  50 , carried within the interior of the articulating arm  54 , and terminating in and connected to a rotary coupling  60  mounted to the end of the arm and connected to the fixture  28 . The articulating arm  54  is capable of movement toward and away from the column  24  and vertically relative to column  24 . 
     FIGS. 2 and 4 illustrate the lift cylinder assembly  52  which comprises a lift cylinder  90  defining an interior bore  92  in which is slidably received a piston  94 , which is threaded onto the exterior of the shaft  66 . The shaft and the piston  94  extend through the bore  92 . A bottom plate  96  comprises a bore  97  with an O-ring seal  99  for sealing the bottom of the lift cylinder  90  with respect to the shaft  66 . A fluid port  98  extends from the exterior of the bottom plate  96 , into the bore  92  below the piston  94 , permitting the introduction or exhaustion of hydraulic fluid beneath the piston  94  through the port  98 . Similarly, a top plate  100  has a bore  101  that contains an O-ring seal  103  for sealing the top of the lift cylinder  90  with respect to the shaft  66 . A port  102  extends from the exterior of the top plate  100  to the bore  92  of the lift cylinder above the piston  94  to permit the introduction or exhaustion of hydraulic fluid above the piston  94 . By introducing or exhausting hydraulic fluid through the ports  98  and  102 , it is possible to raise and lower the shaft  66  and, thus, raise and lower the column  24  with the lift cylinder assembly  52 . 
     Referring to FIGS. 2,  4  and  5 , the rotary coupling  50  comprises a rotary coupling  62  with an adapter  64  connecting the rotary coupling to a shaft  66 , which is fixedly connected to the top of the column  24 . The shaft effectively functions as an extension of the column  24  and is operably coupled to the lift cylinder assembly  52  whereby the lifting of the shaft  66  by the lift cylinder assembly  52  will correspondingly lift the column  24 . 
     The rotary coupling  62  is of a well-known configuration and comprises an inlet portion  72  and an outlet portion  74 , which rotate relative to each other. The inlet portion  72  comprises multiple inlet ports  76 , which through the internal structure of the rotary coupling  62 , are fluidly connected to discrete outlet ports (not shown) arranged on the bottom of the outlet portion  74 , adjacent the adapter  64 . A suitable rotary coupling  62  is manufactured by Carr Lane Mfg. in St. Louis, Mo. 
     Shoulder bolts  80  extend from the top of the inlet portion  72  of the rotary coupling  62  and operably connect the rotary coupling  62  to an anti-rotation device  82 . The anti-rotation device  82  comprises a strap  84  having openings  86  in which are pressed bushings  87  to slidably receive the shoulder bolts  80  of the rotary coupling  62 . The strap  84  is fixedly supported from the base plate  96  of the lift cylinder assembly  52  by anti-rotation standoffs  88 . 
     Referring to FIGS.  4  and  6 - 8 , the adapter  64  physically and fluidly couples the rotary coupling  62  to the upper end of the shaft  66 . The adapter  64  comprises a main body  112  from which extends an externally threaded collar  114 . A series of angled ports  116  having their inlet  118  on the upper surface of the main body  112  and their outlet  120  on the lower surface of the main body  112  within the interior of the threaded collar  114 . The inlets  118  to the ports  116  are spaced about the upper surface of the main body  112  so that they correspond to the outlet ports of the rotary coupling  62 . Essentially, the ports  116  collect the outlet ports of the rotary coupling  62  into a much closer radial spacing and one that which will fit within the outer diameter of the upper end of the shaft  66 . 
     A series of openings  122  are spaced around the periphery of the main body  112  and permit bolts or other fasteners to pass through the main body  112  to secure the adapter  64  to the outlet portion  74  of the rotary coupling  62 . Two dowel pin openings  124  are disposed radially interiorly of the ports  116  in the main body  112  and receive dowels for aligning the shaft and the adapter  64 . 
     Referring to FIGS. 4,  9  and  10 , the shaft  66  comprises a circular base  130  at one end of the shaft  66  and a generally flat end  132  at the opposing end of the shaft  66 . Dowel pin openings  152 , corresponding to dowel pin openings  124 , are formed in the upper end  132  of the shaft  66  and receive a portion of the dowels (not shown) to align the adapter  64  and the shaft  66 . 
     A portion of the shaft between the base  130  and the end  132  is threaded at  134  and threadably receives the piston  94  of the lift cylinder assembly  52 . A groove  136  for receiving a conventional snap ring (not shown) is positioned near the upper end  132  of the shaft  66 . A sleeve  140  is slidably received over the end of the shaft  132  prior to the mounting of the snap ring within the groove  136  and threads onto the threaded collar  14  of the adapter  64  to connect the upper end  132  of the shaft  66  to the adapter  64 . 
     Multiple fluid passages  144  extend from inlet ports  146  on the upper end  132  of the shaft axially therethrough to the base  130 , where the ports turn radially outward to emanate in outlet ports  148 . The base  130  comprises multiple openings  142  disposed about its periphery through which fasteners such as bolts or the like will pass to secure the base of the shaft to the rotatable support column  24  of the pallet changing station  14 . Preferably, the fluid passages  144  are gun drilled through the shaft  66 . 
     The passages  144  extending through the shaft  66  along with the rotary coupling  62  and the hydraulic lines  56  form part of a hydraulic conduit that permits the hydraulic fluid to be distributed from the hydraulic fluid source to the fixtures  28 . The fluid passages  144  eliminate the need for a set of hydraulic lines extending from the rotary coupling  62  to the lines  56 , along with their corresponding individual rotary couplings. The advantage of integrating the fluid passages  144  with the shaft  66  instead of using separate lines is that the passages  144  are always fluidly aligned with the column  24  and are not subject to twisting or wrapping about the column  24 . Additionally, since the articulating arm  54  has one end fixed to the column  24 , the lines  56 , which run from the base of the shaft  66  and through the arm  54 , are not subject to any relative movement between the column and the arm  54 , effectively eliminating the twisting of the prior art lines that led to the loosening of the individual rotary couplings. 
     While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.