Metal working – Plural diverse manufacturing apparatus including means for... – With turret mechanism
Reexamination Certificate
1997-03-26
2002-05-14
Briggs, William (Department: 3722)
Metal working
Plural diverse manufacturing apparatus including means for...
With turret mechanism
C029S03800E, C029S042000, C029S046000, C074S814000, C074S816000, C082S159000
Reexamination Certificate
active
06385831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a workpiece table, provided for a machine tool, that is movable back and forth between two end positions and has a rotational drive which has a gear part joined to the workpiece table for rotation thereof, a toothed rack in engagement therewith, as well as a medium-actuated shift drive for displacement of the toothed rack, which thereby performs a linear stroke motion, delimited by stops, between two end locations corresponding to the end positions of the workpiece table.
2. Related Prior Art
A workpiece table of this kind, often also called a turntable, is known from practical use.
In many machine tools, the workpiece table is divided into a machining side and a loading side, such that a first workpiece can be machined on the machining side while a second workpiece, yet to be machined, is at the same time being clamped on the loading side. In this context, the machining side and loading side are often separated from one another by a spray shielding panel in order to protect the operator from flying chips and sprays of cutting fluid.
For tool changing, the workpiece table and the spindle head of the machine tool perform a movement relative to one another in which the machining side and loading side are interchanged.
One possibility for performing said workpiece change consists in using the turntable cited initially. Turntables of this kind are often used when the machine tool constructed therewith is intended to occupy as little space as possible.
For a workpiece change, the workpiece table is rotated alternately by the rotational drive through +/−180 degrees, the workpiece table being positioned in its end positions by means of, for example, serration splining. When the workpiece table is to be rotated, it is first lifted out of the serration splining before a toothed rack is then shifted from its one end location into the other, whereby it rotates a gear part and, by means thereof, the workpiece table into the respective other end position. After completion of this rotary movement, the workpiece table is lowered back down onto the serration splining.
The shift drive for displacing the toothed rack generally operates with compressed air, the two end surfaces of the toothed rack acting as thrust faces of a bidirectionally medium-actuated thrust piston. At the end of its respective linear stroke, the toothed rack arrives, with its end face upon which compressed air is not acting, against a stop, so that the linear stroke is delimited in both directions by stops.
The general desire in the mechanical engineering industry is to perform not only tool changes but also workpiece changes at shorter and shorter intervals, so that rotation of the workpiece table should occur as quickly as possible. A very rapid rotation of the workpiece table means, however, that the toothed rack arrives against the stops at a high velocity, resulting in hard impacts and shocks. Impacts and shocks of this kind are disadvantageous, however, in terms of workpiece clamping, since such shocks can result in loss of alignment in workpiece clamping fixtures, impairing the reproducibility of the machining operation. Another concern is that the workpiece table with the fixtures clamped thereon has a very large mass, so that with a corresponding rotational velocity, a relatively high rotational energy must be nullified in the end locations of the toothed rack. In the case of the known machine tool, shock absorbers, which extend outward away from the toothed rack at the stops and face the end faces of the toothed rack with their pistons, are provided for this purpose. Because of the high rotational energy that must be nullified, these shock absorbers protrude a great deal, so that overall they contribute to a large physical width for the known machine tool.
The general desire in the case of such machine tools is to make available machine tools with the minimum possible overall size, which allow the quickest possible workpiece change with no repercussions on the working accuracy of the machine tool. In order to meet this need, it is an object of the present invention to improve the workpiece table mentioned at the outset in such a way that while having a physically simple design, it allows rapid rotation with as little impact and jerking as possible; the external dimensions of the machine tool containing the new workpiece table are intended to be as small as possible.
SUMMARY OF THE INVENTION
In the case of the workpiece table mentioned at the outset, this object is achieved by the fact that a mechanism is provided which acts upon the toothed rack with a higher feed force at the beginning of the linear stroke movement than during the remainder of the linear stroke.
The object underlying the invention is thereby completely achieved. Specifically, the inventors of this application have recognized that by means of a “starting acceleration” with a higher feed force, the inert mass of the workpiece table must first be overcome before the remaining rotary movement is performed with the usual feed force. This initially higher feed force thus ensures much faster rotation of the workpiece table between its two end positions, so that the workpiece change is thereby greatly accelerated. It is now entirely possible, by means of the new mechanism, to select the action upon the toothed rack in such a way that a high feed force is exerted initially, a usual feed force during the middle rotational range, and a lower feed force toward the end of the rotary movement, so that overall, the usual damping is sufficient to decelerate the rotating workpiece table in its end locations.
In an embodiment, it is preferred if the mechanism comprises an auxiliary shift drive which temporarily acts upon the toothed rack with an additional feed force at the beginning of the linear stroke movement.
This feature has the design-related advantage that the temporary additional feed force can be applied, for example, electrically or magnetically. A further advantage here is that said auxiliary shift drive can also be retrofitted, so that even existing machine tools can be subsequently refitted for more rapid rotation of the workpiece table.
The object underlying the invention is thus also achieved by means of an optionally retrofittable auxiliary shift drive for a rotational drive for a workpiece table of a machine tool which can be moved back and forth between two end positions, the rotational drive having a gear part joined to the workpiece table for rotation thereof, a toothed rack in engagement therewith, as well as a medium-actuated shift drive for displacement of the toothed rack, which thereby performs a linear stroke motion, delimited by stops, between two end locations corresponding to the end positions of the workpiece table, the auxiliary shift drive acting temporarily on the toothed rack with an additional feed force at the beginning of the linear stroke movement.
This auxiliary shift drive has the aforementioned advantage that it is retrofittable.
It is further preferred here if the auxiliary shift drive is medium-actuated, an auxiliary shift drive preferably being provided for each linear stroke direction of the toothed rack.
The advantage of this feature is that the same functional principle and actuation medium can be used for the auxiliary shift drive as for the original shift drive. This makes possible a generally simple physical design, since no additional energy sources need to be provided.
It is further preferred if the shift drive comprises thrust pistons at both end faces of the toothed rack acting respectively thereon, and if the auxiliary shift drive contains, at the two end faces, auxiliary thrust pistons acting respectively thereon, which preferably have a greater piston surface area than the thrust pistons and perform a shorter linear stroke than the latter.
The advantage here is that, so to speak, two thrust pistons one behind the other can be used, the auxiliary thrust piston, because of its greater piston surface area, exert
Briggs William
Cummings & Lockwood
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