Metal working – Plural diverse manufacturing apparatus including means for... – Binding or covering and cutting
Reexamination Certificate
1998-10-30
2001-04-17
Hughes, S. Thomas (Department: 3726)
Metal working
Plural diverse manufacturing apparatus including means for...
Binding or covering and cutting
C198S345100, C409S163000, C483S014000, C483S015000, C082S124000, C414S225010
Reexamination Certificate
active
06216325
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a machining center having a number of machine tools which each have a working space for machining workpieces, a clamping station in which workpieces to be machined are clamped into workpiece holders, and a loading device which transports the workpiece holders between the clamping station and the working space of at least one machine tool, and in order to transport the workpiece holder has a pivot arm which pivots in as the loading device moves, and which for workpiece changing is pivoted about a pivot axis into the working space or to the clamping station.
2. Related Prior Art
A machining center of this kind is known from DE 195 16 849 A1.
In the known machining center, a certain number of machine tools are arranged next to one another, a loading/unloading station in which a clamping station is located being provided next to that row of machine tools. In the clamping station, workpieces are inserted into workpiece holders which are held by a pivot arm of a loading device.
After the workpiece holder has been loaded with a new workpiece, the pivot arm is pivoted in and the loading device travels to one of the machine tools, where the pivot arm pivots back out and the workpiece holder is clamped in a fixture holder which is provided in the working space of that machine tool. After machining of the workpiece, the workpiece holder is transported either to another machine tool for a further machining operation or back to the loading/unloading station where the machine workpiece is replaced with a workpiece that is yet to be machined.
The pivot arm of the loading device grasps the workpiece holder on one side, the latter in turn grasping the workpiece to be machined on one side. The fixture holder in the working spaces also grasps the workpiece holder on one side; a buttress can selectably be provided so that clamped workpieces can be better centered.
It has been found that with the known machining center, the handling of the workpieces and workpiece holders is disadvantageous particularly when bulky and/or heavy workpieces are to be machined. On the one hand, surprisingly, the machining accuracy and the reproducibility of the machining operation decrease when heavier and/or more bulky workpieces are used. These disadvantages can be partially eliminated or at least diminished by performing workpiece handling in general at lower velocities. This means, however, that in order to achieve high machining accuracy and reproducibility in the machining of heavy and/or bulky workpieces, the workpiece-to-workpiece time is reduced with the known machining center, which of course is disadvantageous.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to improve the machining center mentioned at the outset in such a way that enhanced machining speed and machining accuracy are achieved by means of a simple design, in particular with heavy and/or bulky workpieces.
In the case of the machining center mentioned at the outset, this object is achieved in that the workpiece holder comprises a fixture for positionally accurate receiving of a workpiece, which has at its two end faces holding parts via which it is held in the clamping station and in the working space; that the loading device has a further pivot arm arranged parallel to the pivot arm; and that the pivot arms grasp the fixture at the end faces and receive it between them for transport.
The object underlying the invention is completely achieved thereby.
Specifically, the inventors of the present application have recognized that the accuracy gained by slowing down workpiece handling with heavy workpieces results from the fact that the workpiece holders no longer tilt or tend to vibrate, and because of the slower handling, any vibrations can decay before the workpiece holder is clamped in. According to the present invention provision is now made by way of the two-armed pivot arm, which in a manner of speaking grasps the fixture at both end faces between itself, for tilting of the mechanism to be impossible either during rapid transport or during rapid pivoting out or in at the clamping station and working space; the fixture moreover does not vibrate, so that more rapid movement becomes possible. The workpiece-to-workpiece time can in this fashion be greatly enhanced by way of physically simple actions, without reducing machining accuracy, when heavy workpieces are being machined.
It is preferred in this context if a double gripper which grips the fixture at each holding part is rotatably mounted on each pivot arm, the holding parts preferably comprising hollow shaft tapers and the double grippers grasping the hollow shaft tapers at gripper grooves; also preferably, one fixed and one movable buttress being provided in the clamping station and in each working space, each having a hollow shaft taper receptacle in order to clamp the fixture between them.
This feature is advantageous in terms of design: hollow shaft tapers are commonly known, for example, from tool changing mechanisms, where their tapers are inserted into tool receptacles on spindles, while gripper hands of tool changers grasp onto their gripper grooves in order to transport the hollow shaft tapers back and forth between their working position in the receptacle in the spindle and a magazine position. The hollow shaft tapers (hereinafter “HSKs”) are also used in similar fashion here: the fixture is braced between the buttresses via the HSK and HSK receptacle, and gripper hands of the pivot arm can grasp onto the gripper grooves in order to transport the fixture. This simple design ensures that the fixtures can be transported without tilting or jamming, so that they can be moved quickly without causing vibrations which must be allowed to decay before the fixtures are clamped in. These features thus enhance the machining speed and machining accuracy.
It is preferred, in this context, if the fixture has, at least at one end face, a positioner part oriented parallel to the hollow-shaft taper which, when the fixture is clamped in between the buttresses, is in engagement with a further positioner part on one of the buttresses.
The advantage here is that even more accurate positioning of the fixture results, since changes in the position of the fixture during transport by the pivot arm no longer have any effects, and the fixture is, so to speak, reoriented when clamped in the working space. This also enhances the machining accuracy.
It is preferred in general if the two double grippers are joined to one another via a rigid shaft, and if one of the double grippers is joined to a rotation motor, the two pivot arms preferably being driven via a shared pivot motor and, also preferably, a rotatably mounted coupling rod which extends parallel to the rigid shaft being arranged between the pivot motor and one of the pivot arms.
These features are advantageous in terms of design and also enhance both the machining accuracy and the machining speed. Because the pivot arm and the double gripper are now, so to speak, designed in double fashion and are doubly driven, tilting is now prevented even when a fixture is loaded with a heavy workpiece, so that it is unnecessary to wait for transient dissipation after pivoting in before the buttresses can clamp the fixture between them. Because of the double-sided drive, pivoting and rotation occur much more quickly than when the workpiece holder is held on one side, as is known from the prior art.
It is preferred in this context if the pivot motor is drivingly connected via a first toothed belt to a first gear joined to the one pivot arm, and via a second toothed belt to a second gear joined to the coupling rod, and if the coupling rod has a third gear which is drivingly joined, via a third toothed belt, to a fourth gear which is joined to the other pivot arm.
This feature is also advantageous in terms of design: the reason is that because of the even greater distances to be spanned by the toothed belts, the pivot motor and coupling rod can
Haninger Rudolf
Winkler Hans-Henning
Chiron - Werke GmbH & Co. KG
Cummings & Lockwood
Hong John C.
Hughes S. Thomas
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