US 4,382,215 A · System and method of precision machining

Abstract

A system and method are disclosed for automatically machining a work piece to precise selectively determined dimensions under computer numerical control. A movable probe is calibrated against position reference surfaces and is then used to calibrate the position of a fixed probe. The latter serves as a position reference for calibrating the cutting edge of one or more cutting tools. All calibrations are performed under closed loop control. Appropriate tool position offsets are automatically determined from deviations between the programmed and the actual probe and tool positions and are entered into numerical control means to modify the programmed machining operation. After machining has been initiated, probing of the work piece occurs at least once before the final cut is taken and the appropriate tool position offsets are determined and entered to assure that the dimensions of the finished surface will conform to the desired selectively determined dimensions. Any dimensional deviations which are shown to exist upon probing of the finished surface, are indicated together with the allowable machining tolerances for each dimension.

A method for automatically machining at least one surface of a work piece to precise, selectively determined dimensions by the use of a closed loop numerically controlled machining system;

said system comprising programmable computer numerical control means adapted to operate under the direction of a machining program which includes said selectively determined dimensions, machining apparatus including a stationary bed, work piece holding means, and tool holding means adapted to carry one or more tools and to place selected ones of said tools into operating position, means for providing relative motion between the selected tool and said work piece when each is mounted in its respective holding means, said tool being adapted to effect the removal of material from said work piece during said relative motion when a cutting edge of said tool bears against said work piece, means controlled by said numerical control means for positioning said holding means relative to each other at least in first and second axes of motion of said machining apparatus, position feedback means adapted to indicate to said numerical control means the relative position of said respective holding means at least in said first and second axis respectively, position reference means associated with said machining apparatus and including at least a pair of reference surfaces each corresponding to a separate one of said axes, each of said reference surfaces providing a calibrated position reference with respect to the origin position of said program, a first contact probe adapted to be mounted in a tool holding location of said tool holding means, and a second contact probe mounted with its probe tip accessible for contact by the tip of said first probe and by said cutting edge respectively, each of said contact probes being adapted to provide an indication to said numerical control means when the tip of said probe makes contact with a surface;
said method comprising the steps of:
(1) placing said first probe into operating position in said tool holding means;
(2) probing said at least first and second reference surfaces with said first probe to calibrate the position of its probe tip at least in said first and second axes, said reference surface probing operation including the steps of positioning said respective holding means relative to each other in each of said axes until said first probe tip individually establishes contact with the reference surface corresponding to each axis;
(3) storing a first set of deviations in said numerical control means each determined by the difference along one of said axes between the programmed position of said first probe tip for contact with a reference surface in said axis and its actual contact position derived from the concurrently indicated position feedback;
(4) probing the tip of said second contact probe with said first probe to calibrate the position of said second probe tip at least in said first and second axes, the last-recited probing operation including the steps of positioning said respective holding means relative to each other in each of said axes until said first probe tip establishes contact with said second probe tip individually along each axis;
(5) storing a second set of deviations in said numerical control means each determined by the difference along one of said axes between the programmed position of said first probe tip for contact with said second probe tip in said axis and the corresponding actual contact position of said first probe tip derived from the concurrently indicated position feedback;
(6) placing a selected tool into operating position in said tool holding means;
(7) probing said second probe tip with said cutting edge of said selected tool to calibrate the position of said cutting edge at least in said first and second axes, said edge probing operation including the steps of positioning said respective holding means relative to each other in each of said axes until said cutting edge establishes contact with said second probe tip individually along each axis;
(8) storing a third set of deviations in said numerical control means each determined by the difference along one of said axes between the programmed position of said cutting edge for contact with said second probe tip in said axis and its actual contact position derived from the concurrently indicated position feedback;
(9) storing a first set of compensating offsets for said selected tool in said numerical control means determined by one of each said first, second and third sets of deviations for each axis;
(10) machining said work piece in accordance with said program modified by said first set of offsets to provide a semi-finished surface on said work piece;
(11) placing said first probe into operating position in said tool holding means;
(12) probing said semi-finished surface with said first probe at least in one of said axes, said last-recited probing operation including at least the step of positioning said respective holding means relative to each other in said axis until said first probe tip establishes contact with said semi-finished surface;
(13) storing a fourth set of deviations in said numerical control means each determined by the difference along one of said axes between the originally programmed position of said first probe tip for contact with said semi-finished surface in said axis and its actual contact position derived from the concurrently indicated position feedback;
(14) storing a set of offset ocrrections for said selected tool in said numerical control means determined at least in part by one of said fourth set of deviations for each axis;
(15) storing a final set of compensating offsets for said selected tool in said numerical control means determined by one of each of said first set of offsets and said set of offset corrections for each axis;
(16) placing a selected tool into operating position in said tool holding means;
and
(17) machining said work piece in accordance with said program modified by said final set of offsets to provide said finished surface.

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System and method of precision machining

Life of this patent

System and method of precision machining

Life of this patent

Abstract

Claims12