Dynamic correction of servo following errors in a computer-numerically controlled system and fixed cycle utilizing same
First Claim
1. A method of correcting path radius errors in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement to be effected between a workpiece and a tool by motion of machine members along at least two orthogonal linear axes at a feedrate, (F) under control of a servo which receives position commands based on said instructions, said servo having at least one of, a position loop gain, (Kv) and a velocity loop integral time, (Ti), said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said method comprising the steps of:
- (a) receiving an instruction defining a desired radius, (R) of said curved portion;
(b) generating corrected radius data, (R2) to compensate for servo following errors appearing as path radius errors along said curved portion of said path such that the difference between the desired radius, (R) and said corrected radius data, (R2) compensates for at least a portion of the path radius error that would otherwise be induced in the movement by the servo, and(c) generating the position commands in response to said corrected radius data whereby the actual relative movement between the workpiece and the tool more closely follows said curved portion of said desired path.
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Accused Products
Abstract
The invention relates to servo-driven computer-numerically-controlled systems of the type adapted to receive part program instructions defining a desired path of relative movement between a tool and a workpiece, wherein the path may include an interior or exterior curved portion to be effected by coordinated linear movement of machine members along at least two orthogonal linear axes. The invention provides apparati and methods for correcting path radius errors to facilitate rapid and accurate movement along the curve. In a preferred embodiment, such path radius correction is applied to a fixed cycle for machining inside circles preferably incorporating such path radius correction and providing substantially tangential engagement between the tool and a machining locus orbited by the tool to avoid abrupt accelerations or decelerations while the tool is in contact with the workpiece. In addition to avoiding surface blemishes, this facilitates machining a broader range of hole sizes with a given sized tool thereby reducing the need for frequent tool changes. The invention carries out path radius correction by generating position commands received by the servo using corrected radius data, the difference between which and the desired radius to be machined compensates for at least a portion of the path radius error that would otherwise be generated by the servo. Apparatus and methods for threading holes using a non-helical threading tools with or without path radius correction are also disclosed.
81 Citations
57 Claims
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1. A method of correcting path radius errors in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement to be effected between a workpiece and a tool by motion of machine members along at least two orthogonal linear axes at a feedrate, (F) under control of a servo which receives position commands based on said instructions, said servo having at least one of, a position loop gain, (Kv) and a velocity loop integral time, (Ti), said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said method comprising the steps of:
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(a) receiving an instruction defining a desired radius, (R) of said curved portion; (b) generating corrected radius data, (R2) to compensate for servo following errors appearing as path radius errors along said curved portion of said path such that the difference between the desired radius, (R) and said corrected radius data, (R2) compensates for at least a portion of the path radius error that would otherwise be induced in the movement by the servo, and (c) generating the position commands in response to said corrected radius data whereby the actual relative movement between the workpiece and the tool more closely follows said curved portion of said desired path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of determining the integral time factor, (Ti) of a servo in a computer numerically controlled system of the type adapted to receive program instructions specifying a desired curved path of relative movement to be effected between a workpiece and a tool by coordinated linear motion of machine members along at least two orthogonal axes at a feedrate, (F) under control of the servo in response to position commands based on said instructions, said servo having in addition to said integral time factor, (Ti), a position loop gain, (Kv), said method comprising the steps of:
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(a) setting he values of Kv for each of said axes to equal, known values; (b) adjusting the value of Ti for at least one of said axes such that said servo will execute said relative movement along a substantially true circular arc concentric with said desired curved path; (c) determining a path radius error, (E) due to said integral term, (Ti), and (d) determining the value of Ti substantially in accordance with the expression;
space="preserve" listing-type="equation">T.sub.i =K.sub.v /2-(E*K.sub.v *R/VF.sup.1/2)where; R represents the radius of said desired curved path.
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13. A method of correcting path radius errors in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement between a workpiece and a tool to be effected by motion of machine members along at least two orthogonal linear axes at a desired feedrate, (F) under control of a servo which receives position commands based on said instruction, said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said servo having at least one of, a position loop gain, (Kv) and a velocity loop integral time, (Ti), said method comprising the steps of:
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(a) receiving an instruction defining a desired radius, (R) of said curved portion; (b) determining a feedrate limit, (FL); (c) generating corrected radius data, (R2) to compensate for servo following error along said curved portion, said corrected radius data (R2) being generated based on a limited feedrate, (Factive), whose magnitude does not significantly exceed said feedrate limit, (FL), and (d) generating the position commands in responses to said corrected radius data whereby the actual relative movement between the workpiece and the tool more closely follows said curved portion of said desired path. - View Dependent Claims (14, 15, 16, 17)
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18. A method of machining holes in a workpiece using a tool, said method comprising the steps of:
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(a) positioning the tool interiorly of a bore previously formed in the workpiece; (b) moving the tool to substantially tangentially engage a closed locus of points defining a desired path to be machined; (c) orbiting the tool at least 360 degrees around said locus to machine a hole of a desired size from said bore, and (d) moving the tool to substantially tangentially disengage said tool from substantial coincidence with said locus. - View Dependent Claims (19, 20, 21, 22, 23)
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24. A method of machining holes in a workpiece with correction of path radius errors for use in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement to be effected by motion of machine members along at least two orthogonal linear axes between a workpiece and a tool at a feedrate, (F) under control of a servo which receives position commands based on said instructions, said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said servo having at least one of, a position loop said method comprising the steps of:
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(a) receiving data defining at least X and Y coordinates of an interior location of a hole to be machined, a desired feedrate, (F), and the radius, (R) of a desired path to be traversed by the tool in order to machine a hole of a given size; (b) generating corrected radius data (R2) to compensate for servo following errors appearing as path radius errors along said curved portion of said path so that the difference between the desired radius, (R) and the corrected radius data, (R2) compensates for at least a portion of the path radius error that would otherwise be induced in the movement by the servo; (c) generating tangential engagement data for defining a second path for moving said tool to substantially tangentially engage said desired path; (d) generating tangential disengagement data for defining a third path for moving said tool to substantially tangentially disengage said desired path; (e) moving said tool to a particular location interiorly of a bore in accordance with at least said coordinates; (f) moving said tool in accordance with . said tangential engagement data along said second path into substantially tangential coincidence with said desired path; (g) orbiting said tool at least about 360 degrees around said desired path in accordance with said corrected radius data to machine said hole to said given size, and (h) moving said tool in accordance with said tangential disengagement data along said third path to substantially tangentially disengage said tool from the surface of the workpiece. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A method of machining holes in a workpiece using a non-helical threading tool, said method comprising the steps of:
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(a) positioning the tool interiorly of a bore previously formed in the workpiece; (b) moving the tool into substantially tangential coincidence with a locus of points defining a desired circular path to be machined; (c) orbiting the tool around said locus while simultaneously moving the tool in a direction parallel to the longitudinal axis of said bore at a rate appropriate to form threads of a desired pitch int he hole, and (d) moving the tool to substantially tangentially disengage said tool from the surface of the workpiece.
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36. A method of forming threaded holes in a workpiece with correction of path radius errors for use in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement between a workpiece and a rotating non-helical threading tool to be effected by motion of machine members along at least three orthogonal axes at a feedrate, (F) under control of a servo which receives position commands based on said instructions, said path including a curved portion to be executed by carrying out coordinated linear movement along at least two of said axes, said servo having at least one of, a position loop gain, (Kv) and an integral time, (Ti), said method comprising the steps of:
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(a) receiving data defining at least X and Y interior coordinates of a hole to be threaded, a desired feedrate, (F), and the radius, (R) of a desired path to be traversed by the tool in order to thread the hole; (b) generating corrected radius data (R2) for driving said servo to compensate for servo following errors appearing as path radius errors along said curved portion of said path so that the difference between the desired radius, (R) and the corrected radius data, (R2) compensates for at least a portion of the path radius error that would otherwise be induced in the movement by the servo; (c) generating tangential engagement data for defining a second path for moving said tool to substantially tangentially engage with said desired path; (d) generating tangential disengagement data for defining a third path for moving said tool to substantially tangentially disengage said desired path; (e) moving said tool to a location interiorly of the hole in accordance with at least said X and Y coordinates; (f) moving said tool in accordance with said tangential engagement along said second path into substantially tangential coincidence with said desired path; (g) orbiting the tool around said desired path in accordance with said corrected radius data while simultaneously moving the tool in a direction parallel to the longitudinal axis of the hole at a rate appropriate to form threads of a desired pitch in the hole, and (h) moving said tool in accordance with said tangential disengagement data along said third path to substantially tangentially disengage said tool from the surface of the workpiece. - View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44)
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45. An apparatus for correcting path radius errors in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement to be effected by motion of machine members along at least two orthogonal linear axes between a workpiece and a tool at a feedrate, (F) under control of a servo which receives position commands based on said instructions, said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said servo having at least one of, a position loop gain, (Kv) and a velocity loop integral time, (Ti), said apparatus comprising:
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(a) input means for receiving program instructions including an instruction defining a desired radius, (R) of said curved portion, and (b) compensation means connected to said input means for generating corrected radius data, (R2) to compensate for servo following errors appearing as path radius errors along said curved portion of said path such that the difference between the desired radius, (R) and said corrected radius data, (R2) compensates for at least a portion of the path radius error that would otherwise be induced in the movement by the servo, said compensation means also being connected to said servo so that said servo receives position commands correlated to said corrected radius data whereby the actual relative movement between the workpiece and the tool more closely follows said curved portion of said desired path. - View Dependent Claims (46, 47, 48)
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49. An apparatus for correcting path radius errors in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement to be effected between a workpiece and a tool by motion of machine members along at least two orthogonal linear axes at a desired feedrate, (F) under control of a servo which receives position commands based on said instructions, said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said servo having at least one of, a position loop gain, (Kv) and a velocity loop integral time, (Ti), said apparatus comprising:
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(a) input means for receiving an instruction defining a desired radius, (R) of said curved portion; (b) feedrate limiting means for determining a feedrate limit, (FL), and (c) compensation means connected to said input means and said feedrate limiting means for generating corrected radius data, (R2) using a limited feedrate, (Factive), whose magnitude does not significantly exceed said feedrate limit, (FL), said compensation means also being connected to said servo so that said servo receives position commands correlated to said corrected radius data whereby the actual relative movement between the workpiece and the tool more closely follows said curved portion of said desired path. - View Dependent Claims (50, 51)
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52. An apparatus for machining holes in a workpiece using a tool, said apparatus comprising:
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(a) means for positioning the tool interiorly of a bore previously formed int he workpiece; (b) means for moving the tool to substantially tangentially engage a closed locus of points surrounding said bore, said locus defining a desired path to be machined; (c) means for orbiting the tool at least 360 degrees around said locus to machine a hole of a desired size from said bore, and (d) means for moving the tool to substantially tangentially disengage said tool from said locus. - View Dependent Claims (53, 54)
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55. An apparatus for machining holes in a workpiece with correction of path radius errors for use in a computer numerically controlled system of the type adapted to receive program instructions defining a desired path of relative movement between a workpiece and a tool to be effected by motion of machine members along at least two orthogonal linear axes at a feedrate, (F) under control of a servo which receives position commands based on said instructions, said path including a curved portion to be executed by effecting coordinated linear movement along said axes, said servo having at least one of, a position loop gain, (Kv) and a velocity loop integral time, (Ti), said apparatus comprising:
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(a) input means for receiving data defining an interior location of a bore, a desired feedrate, (F), and the radius, (R) of a desired path to be traversed by the tool in order to machine said bore to a hole of a given size; (b) processor means means for; (i) generating corrected radius data (R2) to compensate for servo following errors appearing as path radius errors along said curved portion of said path so that the difference between the desired radius, (R) and the corrected radius data, (R2) compensates for at least a portion of the path radius error that would otherwise be induced in the movement by the servo; (ii) generating tangential engagement data for defining a second path for moving said tool to substantially tangentially engage with said desired path; (iii) generating tangential disengagement data for defining a third path for moving said tool to substantially tangentially disengage said desired path, and (c) means connected to said processor means for sequentially; (i) moving said tool interiorly of said bore in accordance with said coordinates; (ii) moving said tool in accordance with said tangential engagement data along said second path into substantially tangential coincidence with said desired path; (iii) orbiting said tool at least about 360 degrees around said desired path in accordance with said corrected radius data to machine said hole to said given size, and (iv) moving said tool in accordance with said tangential disengagement data along said third path to substantially tangentially disengage said tool from the surface of the workpiece. - View Dependent Claims (56, 57)
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Specification