Cutting by use of rotating axially moving tool – Processes – Bit detachable
Reexamination Certificate
2000-05-26
2001-09-04
Bishop, Steven C. (Department: 3722)
Cutting by use of rotating axially moving tool
Processes
Bit detachable
C408S003000, C409S131000, C700S192000
Reexamination Certificate
active
06283681
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and relative device for automatically aligning a workpiece, in particular a pack of printed circuit boards, on a machine tool table.
As is known, a workpiece must be positioned accurately on the worktable of a machine tool, which is achieved by means of locating elements normally provided on the workpiece itself. In the case of packs of printed circuit boards, each pack features a pair of pins projecting from one face of the pack, and which are fitted inside seats on a clamping fixture fitted to the table. The fixture comprises a locating member for clamping one of the pins, and a pair of bars for gripping the other pin.
Machining printed circuits calls for a high degree of precision. For example, each hole drilled on a drilling machine is about 0.5 mm in diameter and must be centered exactly on the respective circuit pad, which may be about 0.6 mm in diameter. As such, the circuit must be positioned up to one micron, and the same degree of precision must be guaranteed over the entire surface of the circuit, which is normally rectangular with sides measuring many centimeters in length.
The positioning precision of the pack clamping fixture depends on how accurately the fixture and the fixture connection to the table are machined, and on how accurately the two pins are fitted to the pack. And, since the drilling position is determined by the machine on the basis of two coordinate axes referred to the table, the coordinate axes of the drilling positions must coincide with those of the table for the pack to be positioned accurately.
Even minor mechanical inaccuracies on the fixture, the fixture connection and/or the pins, may result in linear or angular deviation of the coordinate axes of the pack with respect to those of the table, thus resulting in unacceptably inaccurate drilling. Known fixtures therefore have the drawback, on the one hand, of having to be machined and assembled extremely accurately, and, on the other, of being incapable of correcting inevitable inaccuracies in machining and/or assembly.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a highly straightforward, reliable method and device for automatically aligning a workpiece on a machine tool, and which provide for eliminating the aforementioned drawbacks typically associated with the known state of the art.
According to the present invention, there is provided a method of automatically aligning a workpiece on a table of a machine tool, wherein the workpiece is fitted to a clamping fixture carried by said table and is machined by a machining head; said head and said table being movable with respect to each other along two coordinate axes; and the method being characterized by comprising the steps of:
providing said workpiece with two locating elements;
fitting said workpiece to said fixture;
determining the distances between the real positions of said locating elements and two corresponding reference positions; and
moving said workpiece on said fixture to eliminate said distances.
According to the present invention, there is also provided a device for automatically aligning the workpiece on the table of the machine tool, wherein the workpiece is fitted to said fixture by means of clamping means movable on said fixture by means of electric motors; control means being provided to so control said motors as to align said workpiece in a predetermined position.
More specifically, the workpiece is defined by a pack of printed circuit boards, and comprises two locating pins which are fitted to said fixture by means of a locating member for one of said pins, and by two bars movable towards each other to grip the other of said pins; said electric motors driving two actuators for moving said locating member along two coordinate X, Y axes, and a third actuator for moving one of said bars along one of said X, Y axes.
The locating member is advantageously carried by a slide traveling along one of said X, Y axes; said slide being guided by a shift member moved along a first surface inclined with respect to said X, Y axes; a first of said bars being moved along a second surface inclined with respect to said X, Y axes; said inclined surfaces producing a component of movement of said locating member and of said first bar along the other of said X, Y axes.
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Bishop Steven C.
Sheridan & Ross P.C.
LandOfFree
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