Cutting tool form compensaton system and method

• US 5,255,199 A
• Filed: 12/14/1990
• Issued: 10/19/1993
• Est. Priority Date: 12/14/1990
• Status: Expired due to Fees

• Current Assignee: Martin Marietta Energy Systems, Inc.
• Original Assignee: Martin Marietta Energy Systems, Inc.
• Inventors: Babelay, Edwin F. Jr., Barkman, William E., Klages, Edward J.
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): BROWN, THOMAS
• Application Number:
  US07/628,525
• Time in Patent Office: 1,040 Days
• Field of Search: 364/474.17, 364/474.16, 364/474.18, 364/474.35, 358/101, 358/106, 358/107, 382/1, 382/8, 382/394
• US Class Current: 700/175
• CPC Class Codes: B23Q 17/09 for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool arrangements preventing overload of tools B23Q11/04; devices for indicating failure of drills during boring B23B49/00
• CPC Class Codes: B23Q 17/24 using optics or electromagnetic waves
• 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 2219/34321 Database for control of a single machine
• CPC Class Codes: G05B 2219/36504 Adapt program to real coordinates, shape, dimension of tool, offset path
• CPC Class Codes: G05B 2219/37133 Linear, rotary variable differential transformer, lvdt, rvdt
• CPC Class Codes: G05B 2219/37272 Capacitive
• CPC Class Codes: G05B 2219/37559 Camera, vision of tool, compute tool center, detect tool wear
• CPC Class Codes: G05B 2219/49204 Control of heat to compensate for dilatation, thermal displacement
• CPC Class Codes: G05B 2219/49215 Regulate temperature of coolant
• CPC Class Codes: G05B 2219/50136 With sensor, potentiometer to measure relative displacement
• CPC Class Codes: G05B 2219/50137 Contact in probe, touch probe to detect contact, touch trigger
• CPC Class Codes: G05B 2219/50252 Replace, change tool with tracer head, probe, feeler

Abstract

A compensation system for a computer-controlled machining apparatus having a controller and including a cutting tool and a workpiece holder which are movable relative to one another along a preprogrammed path during a machining operation utilizes a camera and a vision computer for gathering information at a preselected stage of a machining operation relating to the actual shape and size of the cutting edge of the cutting tool and for altering the preprogrammed path in accordance with detected variations between the actual size and shape of the cutting edge and an assumed size and shape of the cutting edge. The camera obtains an image of the cutting tool against a background so that the cutting tool and background possess contrasting light intensities, and the vision computer utilizes the contrasting light intensities of the image to locate points therein which correspond to points along the actual cutting edge. Following a series of computations involving the determining of a tool center from the points identified along the tool edge, the results of the computations are fed to the controller where the preprogrammed path is altered as aforedescribed.

Claims

1. In a computer-controlled machining apparatus having a controller and including a cutting tool and a workpiece holder which are movable relative to one another along a preprogrammed path during a machining operation for effecting a cut in a workpiece held by the workpiece holder wherein the preprogrammed path of relative movement between the cutting tool and workpiece holder is based upon an assumed size and shape of the cutting edge of the cutting tool and the controller includes a database including criteria relating to the assumed size and shape of the cutting edge, the improvement comprising:

means for obtaining an image of the cutting edge of the cutting tool at a preselected stage of a marching operation;

means for generating information relating to the actual size and shape of the cutting edge at the preselected stage from the obtained image including means for obtaining an image of the cutting tool against a background so that the cutting tool and the background within the image possess contrasting light intensities, and wherein the image-obtaining means includes a light source and a camera having a lens so that by positioning the cutting tool between the lens of the camera and the light source, the cutting tool image received by the camera is a shadow of the cutting tool edge; and

means for comparing the generated information relating to the actual size and shape of the cutting edge with the criteria relating to the assumed size and shape of the cutting edge and for altering the preprogrammed path of relative movement in accordance with variations detected between the actual size and shape of the cutting edge and the assumed size and shape of the cutting edge;

the means for generating information includes means for scanning the obtained image along predetermined paths and identifying and collecting as data points along the cutting edge those points along each path at which sharp light intensity transitions occur;

the means for scanning includes means for scanning the image in one direction thereacross along a set of parallel paths and in another direction thereacross along another set of parallel paths wherein said one direction and another direction are orthogonal to one another; and

the means for generating information includes means for determining a center of the tool with the collected data points and means for removing from the collected data points those points which were collected from the image along paths oriented generally tangentially along the image of the cutting edge and includes means for redetermining a center of the cutting tool with the point data remaining after the removal of the tangentially-collected points.

2. The improvement of claim 1 wherein said means for generating information includes means for averaging, out of the remaining data points, the data points collected along a predetermined angular sector of the image wherein said angular sector is measured from the redetermined tool center.

3. The improvement of claim 2 wherein said means for generating includes means for determining an effective tool form from the averaged data points by identifying as edge points of the effective tool form those points contained within an angular increment of the image as measured about the redetermined tool center and which are located form the redetermined tool center at a radius equal to the largest distance that any point of the averaged data points contained within the angular increment is located from the redetermined tool center so that said comparing means compares the edge point locations of the effective tool form with the edge point locations of the assumed tool form.

4. In a machining operation including the steps of moving a cutting tool and a workpiece holder relative to one another along a predetermined path to effect a cut in a workpiece held by the holder and wherein the predetermined path is based upon criteria relating to an assumed size and shape of the cutting tool, the improvement comprising:

obtaining an image of the cutting edge of the cutting tool at a preselected stage of the machining operation wherein the image of the cutting tool is obtained against a background so that the cutting tool and the background within the image possess contrasting light intensities, and wherein said step of obtaining an image includes the steps of providing a light source and a camera having a lens and positioning the cutting tool between the lens of the camera and the light source so that the cutting tool image received by the camera is a shadow of the cutting tool edge;

generating information relating to the actual size and shape of the cutting edge from the obtained information;

comparing the generated information relating to the actual size and shape of the cutting edge with the criteria relating to the assumed size and shape of the cutting edge; and

altering the predetermined path of relative movement between the cutting tool and workpiece holder in accordance with variations detected between the actual size and shape of the cutting edge and the assumed size and shape of the cutting edge;

said step of generating information includes a step of scanning the obtained image along predetermined paths and identifying and collecting as data points along the cutting ege those points along each path at which sharp light intensity transitions occur;

said step of scanning includes the steps of scanning the image in one direction thereacross along a set of parallel paths and in another direction thereacross along another set of parallel paths wherein said one direction and said another direction are orthogonal to one another; and

said step of generating information includes the steps of determining a center of the tool with the data points collected and removing from the collected point data those points which were collected form the image along paths oriented generally tangentially along the image of the cutting edge and a step of redetermining a center of the cutting tool with the point data remaining after the removal of the tangentially-collected points.

5. The improvement of claim 4 wherein said step of generating information includes a step of averaging, out of the remaining data points, the data points collected along a predetermined angular sector of the image wherein said angular sector is measured from the redetermined tool center.

6. The improvement of claim 5 wherein said step of generating includes a step of determining an effective tool form from the averaged data points by identifying as edge points of the effective tool form those points contained within an angular increment of the image as measured about the redetermined tool center and which are located from the redetermined tool center at a radius equal to the largest distance that any point of the averaged data points contained within the angular increment is located from the redetermined tool center so that said step of comparing compares the edge point locations of the effective tool form with the edge point locations of the assumed tool form.