Method and appartus for machining a screw thread with little dispersion

• US 4,761,891 A
• Filed: 11/10/1987
• Issued: 08/09/1988
• Est. Priority Date: 07/26/1984
• Status: Expired due to Fees

• Current Assignee: Wheelabrator Clean Water Systems Inc.
• Original Assignee: Nobuyuki Sugimura
• Inventors: Sugimura, Nobuyuki
• Primary Examiner(s): Schmidt, Frederick R.
• Assistant Examiner(s): Cruz, Lawrence
• Application Number:
  US07/120,736
• Time in Patent Office: 273 Days
• Field of Search: 82/2 B, 82/5, 82/14 D, 408/13, 33/199 R, 33/199 B, 33/504, 33/556, 33/557, 33/558, 33/559, 33/560, 33/561, 33/505, 33/532
• US Class Current: 33/503
• CPC Class Codes: G05B 19/186 Generation of screw- or gearlike surfaces
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/37345 Dimension of workpiece, diameter
• CPC Class Codes: G05B 2219/50296 Tool offset by verifying piece and registrating errors
• CPC Class Codes: Y10T 82/141 having transverse tool and templet guide
• CPC Class Codes: Y10T 82/20 Lathe for screw cutting
• CPC Class Codes: Y10T 82/2502 with program control

Abstract

In an NC-lathe comprising a thread touch sensor provided with a touch portion to be brought into contact with an effective radius/diameter portion of a screw thread, an automatic measuring device electrically connected to the thread touch sensor, and an automatic correction device connected to the automatic measuring device; an effective radius or diameter of a screw thread is measured by bringing the touch portion of the thread touch sensor into contact with an effective radius/diameter portion of the screw thread, the measured dimension is compared with a desired dimension, and when a difference is produced between the respective dimensions, the NC-lathe is controlled by correcting an amount of machining by means of the automatic correction device.

Claims

1. For an NC-lathe for machining a thread groove in a screw, a method of determining the effective radius of the machined thread groove comprising the steps of:

providing a set of coordinates wherein an X-coordinate direction extends along an axis parallel the longitudinal axis of said screw and a y-coordinate direction extends along an axis perpendicular to said x-coordinate direction;

providing a thread touch sensor;

providing means for indexing the thread touch sensor to a plurality of positions;

indexing said thread touch sensor into contact with an arbitrary point on said screw;

determining the coordinate values (Xa, Ya) of said arbitrary point;

indexing said thread touch sensor 1/2 pitch length in the X-coordinate direction away from said arbitrary point, while indexing said thread touch sensor in the Y-coordinate direction away from said screw to insure said screw does not interfere with said indexing of the thread touch sensor in the X-coordinate direction;

indexing said thread touch sensor in the Y-coordinate direction towards the screw until the thread touch sensor contacts the screw thread at an intermemiate point (Xi, Yi);

determining the coordinate values of the intermediate point (Xi, Yi);

determining which of the arbitrary point or the intermediate point is a start point, said start point being whichever of the arbitrary point or the intermediate point has a smaller Y-coordinate value indicating which of said points is located in the thread groove;

indexing said thread touch sensor to said start point;

incrementally indexing said thread touch sensor in the positive and negative X-coordinate direction from said start point and subsequently moving said thread touch sensor into contact with said screw following each of said incremental indexes, determining which of said alternate incremental points has the smaller Y-coordinate value and moving the thread touch sensor to the incremental point having the smaller Y-coordinate value, and repeating the step until the opposite points yield the same Y-coordinate value, thus indicating the thread touch sensor is centered in the thread groove, said point being a center point; and

determining the Y-coordinate value of the center point, said Y-coordinate value representing the radius of the screw thread.

2. The method of claim 1 wherein said second to last step is repeated at progressively smaller increments.

4. The method of claim 1 wherein said first position is determined by the steps of:

providing a set of coordinates wherein an X-coordinate direction extends along an axis parallel the longitudinal axis of said screw and a y-coordinate direction extends along an axis perpendicular to said x-coordinate direction;

indexing said thread touch sensor into contact with an arbitrary point on said screw;

determining the coordinate values (Xa, Ya) of said arbitrary point;

indexing said thread touch sensor 1/2 pitch in the X-coordinate direction away from said abritrary point, while indexing said thread touch sensor in the Y-coordinate direction away from said screw to insure said screw does not interfere with said movement of the thread touch sensor in the X-coordinate direction;

indexing said thread touch sensor in the Y-coordinate direction until the thread touch sensor contacts the screw thread at an intermediate point (Xi, Yi);

determining the coordinate values of the intermediate point (Xi, Yi);

determining which of the arbitrary point or the intermediate point is a start point, said start point being the arbitrary point or the intermediate point having a smaller Y-coordinate value indicating which of said points is located in the thread groove;

indexing said thread touch sensor to said determined start point; and

incrementally indexing said thread touch sensor in the positive and negative X-ccordinate direction from said start point, determining which of said incremental points has the smaller Y-coordinate value and moving the thread touch sensor to the incremental point having the smaller Y-coordinate value, and repeating this step umtil the the alternate points yield the same Y-coordinate value, thus indicating the thread touch sensor is centered in the thread groove, said point being the first point.

5. The method of claim 1 wherein the last step of incrementally indexing the thread touch sensor is repeated at progressively smaller increments.

9. The control circuit of claim 1 wherein said means for determining said first position comprises:

means for indexing said thread touch sensor into contact with an arbitrary point on said screw;

means for determining the coordinate values (Xa, Ya) of said arbitrary point;

means for indexing said thread touch sensor 1/2 pitch in an X-coordinate direction away from said arbitrary point, while indexing said thread touch sensor in a Y-coordinate direction away from said screw to insure said screw does not interfere with said movement of the thread touch sensor in the X-corrdinate direction wherein said x-coordinate direction extends along an axis parallel to the longitudinal axis of said screw and said y-coordinate direction extends along an axis perpendicular to said x-coordinate direction;

means for indexing said thread touch sensor in the Y-coordinate direction until the thread touch sensor contacts the screw thread at an intermediate point (Xi, Yi);

means for determining the coordinate values of the intermediate point (Xi, Yi);

means for determining which of the arbitrary point or the intermediate point is a start point, said start point being the arbitrary point or the intermediate point having a smaller Y-coordinate value indicating which of said points is located in the thread groove;

means for indexing said thread touch sensor to said start point; and

means for incrementally indexing said thread touch sensor in the positive and negative X-coordinate directions from said start point, determining which of said incremental points has the smaller Y-coordinate value and moving the thread touch sensor to the incremental point having the smaller Y-coordinate value, and repeating this step until the the alternate points yield the same Y-coordinate value, thus indicating the thread touch sensor is center in the thread groove, said point being the first point.

3. For an NC-lathe for machining a thread groove at a constant pitch length (P) on a tapered screw at a predetermined taper angle (θ

), said NC-lathe having a thread touch sensor and means for indexing the thread touch sensor to a plurality of positions, a method of determining the actual taper angle threaded in the tapered screw comprising the steps of;

determining the coordinate values of a first position in centered contact with the thread groove;

determining the radius of said thread groove at said first position;

determining the coordinate values of a second position in centered contact with the thread groove, said second position located an integral number (n) of thread pitches from said first position;

determining the radius of said thread groove at said second position;

determining the difference (R) between said first radius and said second radius; and

calculating said taper angle (? ) pursuant to the determined values of the radius difference (R), the pitch length (P) and the number of thread pitches (n) between said first position and said second position.

6. For an NC-lathe for machining a thread groove in a screw, a method of determining the effective diameter of the machined thread groove comprising the steps of:

providing a set of coordinates wherein an X-coordinates direction extends along an axis parallel to the longitudinal axis of said screw and a y-coordinate direction extends along an axis perpendicular to said x-coordinate direction;

providing a thread touch sensor;

providing means for indexing the thread touch sensor to a plurality of predetermined positions;

indexing said thread touch sensor into contact with an arbitrary point on said screw;

determining the coordinate values (Xa,Ya) of said arbitrary point;

indexing said thread touch sensor 1/2 pitch in the X-coordinate direction away from said arbitrary point, while indexing said thread touch sensor in the Y-coordinate direction away from said screw to insure said screw does not interfere with said movement of the thread touch sensor in the X-coordinate direction;

indexing said thread touch sensor in the Y-coordinate direction until the thread touch sensor contacts the screw thread at an intermediate point (Xi, Yi);

determining the coordinate values of the intermediate points (Xi, Yi);

determining which of the arbitrary point or the intermediate point is a start point, said start point being the arbitrary point or the intermediate point having a smaller Y-coordinate valaue indicating which of said points is located in the thread groove;

indexing said thread touch sensor to said determined start point;

incrementally indexing said thread touch sensor in the positive and negative X-coordinate direction from said start points, determining which of said incremental points has the smaller Y-coordinate value and moving the thread touch sensor to the incremental point having the smaller Y-coordinate value, and repeating this step until the alternate points yield the same Y-coordinate value, thus indicating the thread touch sensor is centered in the thread groove, said point being a center point;

determining the Y-coordinate value of the center point;

rotating said thread touch sensor 180 degrees about said screw while indexing said thread touch sensor in the X-direction by an amount equal to 1/2 of the pitch length;

advancing the thread touch sensor in the Y-coordinate direction toward the screw until said thread touch sensor contact said screw thread at a rotated point, said rotated point being in centered contact with said screw thread;

determining the Y-coordinate value of said rotated point; and

summing said Y-coordinate value of said first point with said Y-coordinate value of said rotated point, said sum representing the effective diameter of the screw.

7. In an NC-lathe utilizing a cutting tool subject to wear, said NC-lathe for machining a screw thread and having a thread touch sensor and means for indexing said thread touch sensor to a plurality of positions, a control circuit for maintaining the machining of said screw thread at a desired radius as said tool wears, the control circuit comprising:

means for indexing said thread touch sensor into contact with an arbitrary point on said screw;

means for determining the coordinate values (Xa, Ya) of said arbitrary point;

means for indexing said thread touch sensor 1/2 pitch length in an X-coordinate direction away from said arbitrary point, while indexing said thread touch sensor in a Y-coordinate direction away from said screw to insure said screw does not interfere with said indexing of the thread touch sensor in the X-coordinate direction

wherein said x-coordinate direction extends along an axis parallel to the longitudinal axis of said screw and said y-coordinate direction extends along an axis perpendicular to said x-coordinate direction;

means for indexing said thread touch sensor in the Y-coordinate direction towards the screw until the thread touch sensor contact the screw thread at an intermediate point (Xi, Yi);

means for determining the coordinate values of the intermediate point (Xi, Yi);

means for determining which of the arbitrary point or the intermediate point is a start point, said start point being whichever of the arbitrary point or the intermediate point has a smaller Y-coordinate value indicating which of said points is located in the thread groove;

means for indexing said thread touch sensor to said determined start point;

means for incrementally indexing said thread touch sensor in the positive and negative X-coordinate direction from said start point and, subsequent to each incremental move, moving said thread touch sensor into contact with said screw following each of said incremental indexes, determining which of said incremental points has the smaller Y-coordinate value and moving the thread touch sensor to the incremental point having the smaller Y-coordinate value, and repeating this step until the incremental points yield the same Y-coordinate vaslue, thus indicating the thread touch sensor is centered in the thread groove, said point being a center point;

means for determining the Y-coordinate value of the center point, said Y-coordinate vaslue representing the radius of the screw thread;

means for comparing said desired radius to said actual radius; and

means for correcting said position of said tool in response to said comparison.

8. In an NC-lathe utilizing a cutting tool subject to wear, said NC-lathe for machining a tapered screw at a desired taper angle (θ

d) and having a thread touch sensor and means for indexing said thread touch sensor to a plurality of positions, a control circuit for maintaining the machine of said tapered screw at the desired taper angle (θ

a) as said cutting tool wears, the control circuit comprising;

means for determining the coordinate values of a f1rst position in centered contact with the thread groove;

means for determining the radius of said thread groove at said first position;

means for determining the coordinate values of a second position in centered contact with the thread groove, said second position located an integral (n) number of thread pitches from said first position;

means for determining the radius of said thread groove at said second position;

means for determining the difference (R) between said first radius and said second radius;

means for determining an actual taper angle (θ

a) pursuant to the determined value of the radius difference (R), the pitch length (P) and the number of thread pitches (n) between said first position and said second position (X);

means for comparing said actual taper angle (θ

a) to said desired taper angle (θ

d); and

means for correcting said position of said cutting tool in response to said comparison.

10. For an NC-lathe utilizing a cutting tool subject to wear, said NC-lathe for machining a thread groove in a screw and including a thread touch sensor, means for indexing the thread touch sensor to a plurality of positions, a control cirucit for determining the effective radius of the machined thread groove comprising:

means for indexing said thread touch sensor into contact with an arbitrary point on said screw;

means for determining the coordinate values (Xa, Ya) of said arbitrary point;

means for indexing said thread touch sensor 1/2 pitch length in an X-coordinate direction away from said arbitrary point, while indexing said thread touch sensor in a Y-coordinate direction away from said screw to insure said screw does not interfere with said indexing of the thread touch sensor in the X-coordinate direction wherein said x-coordinate direction extends along an axis parallel to the longitudinal axis of said screw and said y-coordinate direction extends along an axis perpendicular to said x-coordinate direction;

means for indexing said thead touch sensor in the Y-coordinate direction towards the screw until the thread touch sensor contacts the screw thread at an intermediate point (Xi, Yi);

means for determining the coordinate value of the intermediate point (Xi, Yi);

means for determining which of the arbitrary point or the intermediate point is a start point, said start point being whichever of the arbitrary point or the intermediate point has a smaller Y-coordinate value indicating which of said points is located in the thread groove;

means for indexing said theead touch sensor to said determined start point;

means for incrementally indexing said thread touch sensor in alternately opposite X-coordinate directions from said start point and subsequently moving said thread touch sensor into contact with said screw following each of said alternate incremental indexes, determining which of said incremental points has the smaller Y-coordinate value and moving the thread touch sensor to the incremental point having the smaller Y-coordinate value, and repeating this step until the alternate points yield the same Y-coordinate value, thus indicating the thread touch sensor is centered in the thread groove, said point being a center point; and

means for determining the Y-coordinate value of the center point, said Y-coordinate value representing the radius of the screw thread.