Machine tool and pallet standby station

A machine tool and pallet standby station using a crane for changing a pallet between a table or pallet mounting table (27) of the machine tool and the pallet standby station are provided. The table (27) includes a plurality of guide pins (31) having tapered front ends, a plurality of elevatable lift pins (35) having spherical front ends, and a plurality of taper cones (37) having tapered outer peripheral surfaces. On the other hand, the pallet (P) includes at least two brackets (39) attached so as to project in the side directions from the two side surfaces of the pallet, and each bracket is formed with a guide hole (41) into which a guide pin (31) is inserted for rough positioning of the pallet. Further, the bottom of the pallet (P) is formed with a plurality of locate holes (45) having tapered inner peripheral surfaces and engaging with the spherical front ends of the lift pins for precision positioning of the pallet and a plurality of taper holes (47) having shapes complementary with the taper cones (37) and engaging with the taper cones for final positioning of the pallet.

TECHNICAL FIELD

The present invention relates to a machine tool and pallet standby station using a crane to change pallets between a pallet mounting table of a machine tool and a pallet standby station.

BACKGROUND ART

In a machine tool, when a workpiece finishes machining, the pallet having the machined workpiece mounted thereon is dismounted from a table or pallet mounting table of the machine tool and conveyed to a setup position or other pallet standby station, while another pallet having a setup workpiece mounted thereon is mounted on the table of the machine tool, thereby changing pallets between the table of the machine tool and the pallet standby station. Pallets are changed using an automatic pallet change system or manually by a worker using a crane etc. In each case, for good precision machining, the pallet has to be accurately arranged at a predetermined position on the table or pallet standby station.

For such positioning, various methods may be used. For example, Japanese Patent Publication (B2) No. 8-18216 discloses a method of positioning a pallet and a pallet support table in a pallet transfer system using a stacker crane by making knock pins provided on the pallet support table engage with holes provided in the bottom of the pallet. Further, Japanese Patent No. 3307477 discloses a method of making taper outer peripheral surfaces of front ends of a plurality of piston members provided on a table engage with a plurality of taper holes provided in the bottom of a pallet for rough positioning and then making a plurality of taper cones provided on the table and a plurality of taper holes provided in the bottom of the pallet engage for main positioning.

On the other hand, installation of an automatic pallet change system requires a large space for at least the conveyance of pallets and transfer of pallets. Therefore, when sufficient space cannot be secured, it is not possible to install an automatic pallet change system. Further, an automatic pallet change system requires a complicated mechanism and is high in price, and therefore this is not suited to cases where costs have to be kept down. In this case, a worker manually operates a crane etc. to hoist a pallet from the pallet standby station and move it to above the table and to lower the pallet while arranging the pallet at a predetermined position on the table to thereby change pallets.

In this regard, the positioning method disclosed in Japanese Patent Publication (B2) No. 8-181216 and Japanese Patent No. 3307477 utilizes holes provided in the bottom of the pallets. Therefore, when a worker manually operates a crane to position a pallet, visual recognition of holes is difficult and guiding the holes provided in the bottom of the pallet to the positions of pins on the table requires skill and takes time.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a machine tool and pallet standby station enabling use of a manually operated crane to easily arrange a pallet at a predetermined position on a machine tool or pallet standby station.

According to the present invention, there is provided a machine tool having a pallet mounting table for placing a pallet thereon, wherein the pallet mounting table includes a plurality of guide pins having tapered front ends, an elevatable lift pin having a spherical front end, and a taper cone having a tapered outer peripheral surface; the pallet includes at least two brackets provided on side surfaces of the pallet so as to project in the side directions from two side surfaces of the pallet; each bracket is formed with a guide hole into which a guide pin is inserted for rough positioning of the pallet; and a bottom surface of the pallet is formed with a locate hole having a tapered inner peripheral surface and engaging with the spherical front end of the lift pin for precision positioning of the pallet and a taper hole having a complementary shape with the taper cone and engaging with the taper cone for final positioning of the pallet.

In the machine tool according to the present invention, since the rough positioning guide holes of the pallet are provided in the brackets attached so as to project from the two side surfaces of the pallet, a worker can easily visually recognize the guide holes. Therefore, even when using a manually operated crane to move a pallet, a worker can easily guide the guide holes of the pallet to the guide pins on the pallet mounting table, so rough positioning of the pallet by a worker becomes easy. Further, even if the position of a pallet is somewhat off from a horizontal position of the target position on the table, it is easy to engage the spherical front end of the lift pin with the tapered inner peripheral surface of the corresponding locate hole of the pallets. If making these engage with each other, it is possible to precisely arrange the pallet at the target position on the table. Further, since the taper cone on the table and the corresponding taper hole of the pallet are complementary in shape, the pallet is accurately arranged at the target position on the table if making these engage with each other.

In the above machine tool, preferably, the pallet mounting table is provided with an elevatable support pin having a flat front end surface and the bottom surface of the pallet is provided with a flat support pin abutting surface abutting against the flat front end surface of the support pin. By making this support pin and the corresponding support pin abutting surface abut against each other, the pallet is held horizontal with respect to the top surface of the table and the effect is exhibited that engagement of the spherical front end of the lift pin and the tapered inner peripheral surface of the locate hole and engagement of the taper cone and the taper hole are facilitated. Further, when lowering the pallet, the support pin has a cushioning action and a function to prevent damage to the lift pin and taper cone.

Further, preferably, the machine tool further includes a stopper abutting against the side surface of the pallet to stop the pallet at a predetermined position on the pallet mounting table. By making the side surface of the pallet abut against this stopper, it is possible to determine the coordinates of the pallet along one axis in the horizontal direction. By just making the pallet move in the other axial direction in the horizontal plane, it becomes possible to guide the guide holes over the guide pins.

There is provided a pallet standby station of a machine tool for placing a pallet thereon, which includes a plurality of guide pins having tapered front ends at positions corresponding to guide holes of the pallet, an elevatable lift pin having a spherical front end at a position corresponding to a locate pin of the pallet, and a taper cone haying a tapered outer peripheral surface at a position corresponding to a taper hole of the pallet. In this case, it similarly becomes possible to accurately position a pallet on the pallet standby station.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring toFIG. 1, a machining system11using a machine tool and a standby station according to the present invention is comprised of a machine tool13, a pallet standby station15, and a pallet conveyance system for conveying a pallet P having a workpiece W mounted thereon between machine tool13and pallet standby station15. Pallet standby station15is the place for keeping a pallet P on standby for conveyance to a pallet mounting table, that is, a table27, of machine tool13and includes a setup station for setup work including mounting workpiece W on pallet P and a table of a machine tool performing a previous machining process.

The pallet conveyance system is comprised of a suspension type crane17which is movable between machine tool13and pallet standby station15and manually operated by a worker. However, the pallet conveyance system need only convey pallet P between machine tool13and pallet standby station15, and an automatically operated crane, automatic pallet change system, or other type of pallet conveyance system can be used as the pallet conveyance system.

As machine tool13, for example, it is possible to use a machining center. Referring toFIG. 2, machine tool13includes a bed19installed on a floor, a column21provided on bed19, a spindle head23supported by column21, a spindle25supported rotatably on spindle head23and having a tool T mounted thereon, and a table27provided on bed19. In the illustrated embodiment, column21can move on bed19in a Z-axis direction (left-right direction inFIG. 1), spindle head23can move on column21in a Y-axis direction (vertical direction inFIG. 1), and table27can move on bed19in an X-axis direction perpendicular to the Y-axis and Z-axis (direction vertical to paper surface inFIG. 1). However, machine tool13may also have another configuration and is not limited to the illustrated embodiment.

On bed19of machine tool13, a stopper29is provided, so that the Z-axis position of pallet P on bed19or table27is restricted by making the back surface (side surface) of pallet P moved by crane17abut against stopper29.

Next, referring toFIG. 3, the positioning structure for positioning pallet P on table27will be described in detail.

There are provided on table27a plurality of guide pins31extending in the vertical direction and having tapered front ends, a plurality of elevatable support pins33having flat front end faces, a plurality of lift pins35having spherical front ends and able to be elevated independent from support pins33, and a plurality of fixed taper cones37having tapered outer peripheral surfaces. Support pins33and lift pins35are elevated by for example cylinder devices and can be locked in predetermined positions by lock devices. On the other hand, pallet P has a plurality of L-shaped brackets39attached to two side surfaces of pallet P in the longitudinal direction. The parts of L-shaped brackets39projecting in the side directions from the two side surfaces or pallet P are formed with guide holes41into which guide pins31are inserted. Further, a bottom surface of pallet P is formed with flat support pin abutting faces43against which the flat front end faces of support pins33abut, locate holes45having tapered inner peripheral surfaces and engaging with spherical front ends of lift pins35, and taper holes47having complementary shapes with taper cones37and engaging with taper cones37, corresponding to support pins33, lift pins35, and taper cones37.

The positions of guide pins31are set so that pallet P is placed at generally the desired position on table27when guide pins31of table27are inserted into guide holes41of pallet P. Guide pins31are preferably different in lengths. Further, guide holes41preferably have diameters one size larger than guide pins31. Note that, in the embodiment shown inFIG. 3, table27is provided with two guide pins31, but three or more guide pins31may also be provided of course.

Further, the positions of support pin abutting faces43, locate holes45, and taper holes47are determined so that support pin abutting surfaces43, locate holes45, and taper holes47of pallet P are opposed to corresponding support pins33, lift pins35, and taper cones37provided on table27when guide pins31are inserted into corresponding guide holes41of pallet P. Furthermore, the front end faces of all of support pins33are positioned in the same plane when support pins33are at the highest elevated positions, while the front ends of all of lift pins35are positioned in the same plane when lift pins35are at the highest elevated positions.

Table27is further provided with a pallet position confirmation system49for confirming a relative position of the bottom surface of pallet P with respect to the top surface of table27and clamp devices51for clamping pallet P to table27. In the embodiment shown inFIG. 3, pallet position confirmation system49includes a position detection rod49awhich is biased so as to project upward from the surface of table27. By detecting the position of position detection rod49awhen the front end of position detection rod49acontacts the bottom of pallet P and is pushed downward, it is detected that the top surface of table27and the bottom surface of pallet P are in a predetermined positional relationship. However, pallet position confirmation system49need only recognize the relative position between the bottom surface of pallet P and the top surface of table27, and other types of contact type position detection systems, noncontact type position detectors using lasers or magnetism, etc. may also be used as pallet position confirmation system49. Further, in the embodiment shown inFIG. 3, each clamp device51is comprised of a stud51aextending from the bottom center of taper hole47and having an enlarged front end and a hole51cformed at the center portion of taper cone37and having lock balls51binside it. When studs51aare inserted into holes51c, the enlarged front ends of studs51aare locked by biased balls51bto thereby clamp pallet P on table27. However, clamp devices51need only clamp pallet P on table27, and another structure may also be used. Further, in the embodiment shown inFIG. 3, clamp devices51are integrated with taper cones37and taper holes47, but they may also be provided separately.

Next, referring toFIGS. 4A to 4E, the procedure for positioning pallet P with respect to table27shown inFIG. 2will be described.

At pallet standby station15, a worker attaches a conveyor wire53to a pallet P having a setup workpiece W mounted thereon, in order to enable pallet P to be suspended by crane17. Next, the worker manually operates crane17to hoist pallet P from pallet standby station15and move it to above table27of machine tool13. At this time, support pins33on table27are elevated. Next, the worker manually operates crane17to lower pallet P and finely adjusting the horizontal position of crane17while visually recognizing guide holes41, thereby making guide pins31of table27be inserted into guide holes41of pallet P. In this way, readily visible guide holes41are utilized for the rough positioning of pallet P on table27, and therefore pallet can be arranged so that support pin abutting surfaces43, locate holes45, and taper holes47are opposed to corresponding support pins33, lift pins35, and taper cones37without having to recognize the hard to see positions of support pin abutting surfaces43, locate holes45, and taper holes47at the bottom of pallet P.

In the pallet change system according to the present invention, guide holes41are formed on the parts, projecting in the side directions, of brackets39attached to the side surfaces of pallet P, and therefore the worker can easily recognize the positions of guide holes41and positioning of guide holes41and guide pins31becomes easy. Further, since guide pins31have tapered front ends and guide holes41have diameters one size larger than guide pins31, guide pins31can be easily inserted into guide holes41. Furthermore, in the case where guide pins31are different in length, the front ends of guide pins31differ in height. Therefore, it is possible to lower pallet P while inserting guide pins31into corresponding guide holes41one by one, whereby insertion of guide pins31in guide holes41becomes further easier. In addition, before guide pins31are inserted into guide holes41, if the back surface of pallet P (rear side surface) is made to abut against stopper29provided on bed19of machine tool13, the Z-axis direction position of pallet P (that is, the position in the left-right direction inFIG. 2) is restricted, so that guide holes41can be positioned above guide pins31by just making crane17move in the X-axial direction. Therefore, the crane operation becomes easier.

When the worker finishes inserting all of guide holes41of pallet P over guide pins31of table27, pallet P is further lowered and, as shown inFIG. 4B, flat support pin abutting surfaces43of pallet P is made to abut against the flat front end surfaces of support pins33at the elevated position. Due to this, pallet P is supported so that the bottom surface thereof extends parallel to the top surface of table27. At this time, locate holes45and taper holes47are respectively separated from lift pins35and taper cones37and not engaged with them. Further, by placing pallet P on support pins33, the impact at the time pallet P contacts is absorbed by support pins33to prevent damage to lift pins35and taper cones37. Note that, at this point of time, conveyor wire53is detached from pallet P, and crane17is moved from above machine tool13to a position not interfering with machining.

When pallet position confirmation system49confirms that pallet P is lowered to a position where support pin abutting surfaces43of pallet P abut against elevated support pins33, as shown inFIG. 4C, the plurality of lift pins35are simultaneously elevated, the spherical front ends of lift pins35is engaged with the tapered inner peripheral surfaces of locate holes45and pallet P is elevated to separate from support pins33. This being the case, the spherical faces of the front ends of lift pins35and the tapered inner peripheral surfaces of locate holes45cooperate with each other to accurately arrange pallet P at the desired horizontal position. In this way, the pallet P is precisely positioned.

When pallet position confirmation system49confirms that pallet P is elevated by lift pins35to a position where support pin abutting surfaces43of pallet P separate from support pins33, as shown inFIG. 4D, support pins33are lowered. Next, as shown inFIG. 4E, lift pins35are lowered to make taper cones37on table27engage with complementarily shaped taper holes47of pallet P and accurately arrange pallet P at a desired position on table27. At this time, pallet P is clamped at that position by clamp devices51. In this way, pallet P is finally positioned.

When pallet position confirmation system49confirms that pallet P is lowered to the lowest lowered position, it is judged that the final positioning of pallet P has been completed and workpiece W on pallet P is machined by machine tool13. After this, when workpiece W finishes being machined, pallet P is elevated from table27to obtain the state shown inFIG. 4Bby a procedure reverse to the above. Conveyor wire53is attached to pallet P to again enable pallet P to be hoisted by crane17, and then pallet P is moved to pallet standby station15or a downstream machining process. After workpiece W finishes being machined, it is also possible to use support pins33to lift pallet P from table27.

Next, referring toFIG. 5, the overall configuration or pallet standby station15according to the present invention will be described.

Pallet standby station15includes a base55installed on the floor and a pallet pivot system57provided pivotably on base55. Pallet pivot system57pivots 90 degrees about a pivot58between the position shown by the solid line inFIG. 5and the position shown by the dotted line, so that an L-shaped pallet P can be moved between a horizontally laid state (the state shown by the solid line inFIG. 5where the long part is at the bottom) and a standing state (the state shown by the dotted line inFIG. 5where the short part is at the bottom). Therefore, it is possible to mount workpiece W on pallet P in safe position shown by the solid line inFIG. 5where there is no danger of workpiece W falling off pallet P and then make the pallet stand up by pallet pivot system57so as to support pallet P in a state where workpiece W is easy to machine.

Further, base55is provided with a pallet position measuring device59for confirming that pallet P is arranged at a predetermined position on pallet pivot system57and a workpiece position measuring device61for confirming that workpiece W is mounted at a predetermined position on pallet P. In the embodiment shown inFIG. 5, as pallet position measuring device59and workpiece position measuring device61, contact type position detectors bringing pins into contact with the pallet or workpiece and detecting the positions of the pins so as to measure the position of the object are used, but noncontact type position detection systems using laser beams or magnetism may be used.

In pallet pivot system57of pallet standby station15as well, to accurately arrange pallet P at a desired position, guide pins63, lift pins, support pins, and taper cones similar to those of table27ofFIG. 3are provided at positions corresponding to guide holes41, support pin abutting surfaces43, locate holes45, and taper holes47of pallet P on the part becoming the bottom in the state shown by the dotted line inFIG. 5. Note that, inFIG. 5, only a guide pin63is shown.

When positioning pallet P on pallet pivot system57, pallet pivot system57is pivoted to the position shown by the dotted line inFIG. 5, and then the worker manually operates crane17so that guide pins63of pallet pivot system57are inserted into guide holes41of pallet P. Since the rest of the procedure is similar to the case of positioning pallet P on table27, the explanation thereof will be omitted. Further, since the action and effect of guide holes41, support pin abutting surfaces43, locate holes45, and taper holes47of pallet P and guide pins63, lift pins, support pins, and taper cones of pallet pivot system57are similar to the action and effect between table27and pallet P, the explanation will be omitted.