Numerically controlled machine tool system with programmable tool offset

A machine tool system comprising a workpiece positioning table and a rotating cutting element, said cutting element having a cutting surface substantially symmetrically disposed about the cutting element rotational axis, and further comprising a control means for controlling translational motion of said cutting element with respect to said workpiece table in a plane perpendicular to said rotational axis, said control means including:

• selectively operable means to move said cutting element with respect to an ordered succession of spatial points in said plane, whereby said cutting surface has a point in common with a contact point path approximating a desired path defined by a succession of line segments connecting adjacent ones of said succession of spatial points, said contact point path being substantially coincident with said desired path for locally convex portions of said desired path, said selectively operable means including:
• means responsive to a succession of four data sequences associated with three successive points (A.sub.1, A.sub.2 and A.sub.3, respectively) of said succession of ordered spatial points which define a locally convex portion of said desired path to successively:
• i. in response to the first of said four data sequences, position said cutting element to have its axis at a point I.sub.1, point I.sub.1 lying in a first offset path, said first offset path being parallel to, and offset in a predetermined direction by the radius R of said cutting surface, from a first predetermined path connecting points A.sub.1 and A.sub.2, said first predetermined path being defined by the spatial points associated with the first and second of said four data sequences,
• ii. in response to the second of said four data sequences, move said cutting element so that its axis moves from I.sub.1 along said first offset path to a point I.sub.2, point I.sub.2 being offset from point A.sub.2 by R in said predetermined direction and lying along a second straight line extending from point A.sub.2, said second straight line being perpendicular to said first predetermined path at point A.sub.2,
• iii. in response to the third of said four data sequences, move said cutting element so that its axis moves along a circular path having radius R and extending from point I.sub.2 to point I.sub.3, point I.sub.3 being offset from point A.sub.2 by R in said predetermined direction and lying along a third straight line extending from point A.sub.2, said third straight line being perpendicular to a second predetermined path connecting points A.sub.2 and A.sub.3 at point A.sub.2, said second predetermined path being defined by the spatial points associated with the second and fourth of said four data sequences,
• iv. in response to the fourth of said four data sequences, move said cutting element so that its axis moves from point I.sub.3 along an offset path parallel to and offset by R in said predetermined direction from said second predetermined path,
• wherein said control means further comprises:
• selectively operable means to move said cutting element with respect to an ordered succession of spatial points in said plane, whereby said cutting surface has a point in common with a contact point path approximating a desired path defined by a succession of line segments connecting adjacent ones of said succession of spatial points, said contact point path being substantially coincident with said desired path for locally convex portions of said desired path, said selectively operable means including:
• means responsive to a succession of three data sequences associated with three successive points (A.sub.11, A.sub.22 and A.sub.33, respectively) of said succession of ordered spatial points which define a locally convex portion of said desired path to successively:
• i. in response to the first of said three data sequences, position said cutting element to have its axis at a point I.sub.11, point I.sub.11 lying in a first offset path, said first offset path being parallel to, and offset in a predetermined direction by the radius R of said cutting surface, from a first predetermined path connecting points A.sub.11 and A.sub.22, said first predetermined path being defined by the spatial points associated with the first and second of said three data sequences,
• ii. in response to the second of said three data sequences, move said cutting element so that its axis moves from I.sub.11 along said first offset path to a point I'.sub.22, point I'.sub.22 being defined by the intersection of said first offset path and a second offset path, said second offset path being parallel to and offset by R in said predetermined direction from a second predetermined path connecting points A.sub.22 and A.sub.33, said second predetermined path being defined by the spatial points associated with the second and third of said three data sequences,
• iii. in response to the third of said three data sequences, move said cutting element so that its axis moves from point I'.sub.22 along said second offset path parallel to and offset by R in said predetermined direction from said second predetermined path.

A machine tool system comprising a cutting element and workpiece positioning table, and control means for controlling the position of said cutting element with respect to said positioning table, said control means comprising:

• A. means for storing an ordered succession of data sequences, each sequence being associated with a spatial point, and said succession including at least one contiguous group of sequences having data representative of a path offset from a reference path connecting adjacent ones of a succession of said spatial points, each of said spatial points being associated with a sequence in said group, said reference path defining a closed shape when the first and last spatial points in said succession are identical, and defining an open shape otherwise,
• B. means for selecting one of said succession of sequences as a current sequence,
• C. path determining means responsive to said selected sequence, said path determining means including means for determining a tool path to be followed by said cutting element for a current sequence
• said tool path extending from the current coordinates of said cutting element to the point of intersection of the offset paths associated with the reference paths connecting the spatial point associated with said current sequence,
• when the spatial point of said current sequence corresponds to the first and last spatial points associated with one of said groups representing a closed shape, or
• when the spatial point of said current sequence corresponds to one of the intermediate spatial points associated with one of said groups,
• said tool path extending from the current coordinates of said cutting element to the point of intersection of the offset path associated with the reference path connecting the spatial point associated with said current sequence and a line segment perpendicular to said reference path and passing through said spatial point,
• when the spatial point of said current sequence corresponds to the first or last spatial point associated with one of said groups representing an open shape,
• D. drive means responsive to said path determining means for a current sequence to control the relative motion of said cutting element along said determined tool path.