Automatic detection system for broken tools in CNC machining centers using advanced machine vision techniques

• US 20050222705A1
• Filed: 04/02/2005
• Published: 10/06/2005
• Est. Priority Date: 04/03/2004
• Status: Active Grant

• Current Assignee: Gerald Walter Budd
• Original Assignee: Gerald Walter Budd
• Inventors: Budd, Gerald Walter
• Granted Patent: US 7,266,420 B2
• Time in Patent Office: Days
• US Class Current: 700/175
• CPC Class Codes: B23Q 17/0909 Detection of broken tools
• CPC Class Codes: B23Q 17/2457 of tools
• CPC Class Codes: G01B 11/2433 for measuring outlines by shadow casting

Abstract

The invention describes a method for the inspection of machining tools used in computational numerical control (CNC) machining centers. The invention will observe a machining tool immediately after use to determine if it has been damaged. The invention is based on a machine vision technology that uses one or more image sensors to acquire, locate and compare the tool to a good model. The inspection equipment is designed for implementation in the CNC automatic tool changing system and will alert the operator that tool has been damaged before the next operation. This immediate response of the invention will contain defect components and prevent damage to subsequent components. With the addition of an infrared image sensor the invention is capable of detecting worn or dull tools that may damage a component due to excessive heating.

Claims

1. A method and apparatus for substantially complete measurement and determination of key characteristics of machine cutting tools used in a CNC machining center therefor, said method comprising the steps of:

a) pre-positioning the tool holder with machining tools mounted in the cutting position in an inspection position in the machining center whereby the positioning of the machining tool exposes substantially all of the features that are to be evaluated by the inspection;

b) the CNC machining center provides a signal(s) to the present invention, referred to hereafter as the Broken Tool Detection System (or BTDS), indicating a unique code for the tool that is to be inspected;

c) the cell controller or programmable logic controller (PLC) of the BTDS distributes the inspection request to the primary devices that present invention is comprised of and awaits acknowledgement signal(s);

d) the BTDS opens equipment chamber pneumatically operated lift door;

e) the image sensor and illumination system are mounted on a bracket that holds their orientation and position to each other in a fixed position (Optical Sensor), with the bracket in turn mounted to a translation stage;

f) the translation stage moves the optical sensor to the proper inspection position as determined by the product code so that substantially all of the features to be inspected are visible and unobstructed to the optical sensor;

g) the illumination system is energized and the optical sensor acquires the necessary image(s), the illumination is extinguished and then the translation stage returns to the interior of the equipment chamber and the pneumatically operated lift door is closed;

h) one or more image processing systems and application specific software is used to determine the condition of the machining tools;

i) the BTDS distributes the inspection results to the CNC machining center;

characterized in that the sensor(s) are position relative to the tool, whereby a focal point of detection coincides with the center of the cross sectional diameter, so to view substantially all of the feature to be measured, whereby the tool is held in a consistent location for each inspection;

wherein said lighting means provides a contrasting geometric size and shape of substantially all of features on the tool.

4. The method of claim 1, wherein the detection of broken or defective tools is based primarily on light extinction and produces well defined geometric shapes.

5. The method of claim 4, wherein the measurement of particles is confined to the center two-thirds of the detector FOV, eliminating the extreme zones toward the edges of the sensor.

6. The method of claim 5, wherein the measurement of tool features are further confined to those with high contrast and well defined edges.

7. The method of claim 1, wherein a tool shape will determine the quality as compared to that of a stored “

acceptable”

tool shape.

8. The method of claim 7, wherein may be used to determine the equivalent diameter in micrometers (or inches) of tool when said invention determines diameter in pixels.

2. A method and apparatus for complete measurement of the shape and position, within a predetermined size range, of all machine tools as viewing by the sensor/lighting systems to determine tool wear therefor, said method comprising the steps of:

a) pre-positioning the tool holder with machining tools mounted in the cutting position in an inspection position in the machining center whereby the positioning of the machining tool exposes substantially all of the features that are to be evaluated by the inspection;

b) the CNC machining center provides a signal(s) to the present invention, referred to hereafter as the Broken Tool Detection System (or BTDS), indicating a unique code for the tool that is to be inspected;

c) the cell controller or programmable logic controller (PLC) of the BTDS distributes the inspection request to the primary devices that present invention is comprised of and awaits acknowledgement signal(s);

d) the BTDS opens equipment chamber pneumatically operated lift door;

e) the image sensor and illumination system are mounted on a bracket that holds their orientation and position to each other in a fixed position (Optical Sensor), with the bracket in turn mounted to a translation stage;

f) the translation stage moves the optical sensor to the proper inspection position as determined by the product code so that substantially all of the features to be inspected are visible and unobstructed to the optical sensor;

g) the illumination system is energized and the optical sensor acquires the necessary image(s), the illumination is extinguished and then the translation stage returns to the interior of the equipment chamber and the pneumatically operated lift door is closed;

h) one or more image processing systems and application specific software is used to determine the condition of the machining tools;

i) the BTDS will determine the position of the tool tip relative the previously reported position;

j) The BTDS will determine the shape of the tool tip relative to the stored “

acceptable”

quality tool tip and provide a percentage match;

k) the BTDS distributes the inspection results to the CNC machining center,

characterized in that the sensor(s) are position in an absolute location as defined by the tool, whereby a focal point of detection coincides with the center of the cross sectional diameter, so to view substantially all of the feature to be measured, whereby the tool is held in a consistent location for each inspection;

wherein said lighting means provides a contrasting geometric size and shape of substantially all of features on the tool and relative position relative to the trained position of an “

acceptable”

tool.

9. The method of claim 2, wherein the position of the tool end is useful in the determination of tool wear.

10. The method of claim 9, wherein the quality of the tool may be measured by the shape and position of tool features relative to a known reference position of features.

11. The method of claim 10, wherein the lighting source means comprises a Standardized Illumination Module utilizing surface mount LED panels that produce very consistent luminous output, capable of operating for extremely long periods of time while tools are being tested.

12. The method of claim 11, wherein the lighting source means is provided with an intensity control to allow LED panels to be selectively energized or operated at a different voltage to increase or reduce luminous output to enhance the imaging of low contrast features.

13. The method of claim 12, wherein the optical path of the sensor allows substantially all the tool'"'"'s features to be viewed.

14. The method of claim 2, wherein infrared sensor technology may be used to examine the tool temperature.

15. The method of claim 14, wherein the temperature may be used to determine tool wear.

16. The method of claim 2, wherein the apparatus may be applied at multiple station in parallel to increase the rate of inspection with no reduction in capability.

3. A method and apparatus for complete measurement of the shape and position, within a predetermined size range, of all machine tools as viewing by the sensor/lighting systems to determine tool wear and broken edges on multiple tool milling heads therefor, said method comprising the steps of:

l) pre-positioning the tool holder with machining tools mounted in the cutting position in an inspection position in the machining center whereby the positioning of the machining tool exposes substantially all of the features that are to be evaluated by the inspection;

m) the CNC machining center provides a signal(s) to the present invention, referred to hereafter as the Broken Tool Detection System (or BTDS), indicating a unique code for the tool that is to be inspected;

n) the cell controller or programmable logic controller (PLC) of the BTDS distributes the inspection request to the primary devices that present invention is comprised of and awaits acknowledgement signal(s);

o) the BTDS opens equipment chamber pneumatically operated lift door;

p) the image sensor and illumination system are mounted on a bracket that holds their orientation and position to each other in a fixed position (Optical Sensor), with the bracket in turn mounted to a translation stage;

q) the translation stage moves the optical sensor to the proper inspection position as determined by the product code so that the sensor module has the proper working distance from the face of the cutting tool;

r) the orthogonal translation system then moves the on-axis sensor module to the center of first each cutting tool to acquire the necessary image(s);

s) substantially all of the features to be inspected are visible and unobstructed to the optical sensor;

t) the orthogonal translation system then moves the on-axis sensor module to the center of the next cutting tool to acquire the necessary image(s);

u) substantially all of the features to be inspected are visible and unobstructed to the optical sensor;

v) step t &

u) are repeated for as many cutting tools that are present on the mill

w) the illumination system is energized and the optical sensor acquires the necessary image(s), the illumination is extinguished and then the translation stage returns to the interior of the equipment chamber and the pneumatically operated lift door is closed;

x) one or more image processing systems and application specific software is used to determine the condition of the machining tools;

characterized in that the sensor(s) are position in an absolute location as defined by the tool, whereby a focal point of detection coincides with the working distance between the tool and the sensor module, so to view substantially all of the feature to be measured, whereby the tool is held in a consistent location for each inspection;

wherein said lighting means provides a contrasting geometric size and shape of substantially all of features on the tool and relative position relative to the trained position of an “

acceptable”

tool.

17. The method of claim 3, wherein the system may be used to determine the quality of cutting inserts on multiple head mills.

18. The method of claim 17, wherein the system may be used to determine the position of the cutting tools on multiple head mills.