Mill Calibration
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Mill Calibration
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FOR IMMEDIATE RELEASE Vision System reduces Mill Setup time from tens of minutes to seconds!The Problem: Best Cutting Die, a 46 year old manufacturer and acknowledged technological leader in the production of high quality rotary cutting dies, needed to improve the quality and throughput of their precision manufacturing process. A bottleneck in their existing process was the alignment of the “raw” cutting die to the X and Y axis of the Numerically Controlled (NC ) Mill which is used to “sharpen” the die’s cutting ridges. A rotary cutting die is a thin metal plate approximately .062” thick with a pattern of razor sharp ridges standing vertically from the plate’s surface forming a shape. These dies are used on machines which cut out intricate patterns from paper or other materials. These die cut patterns are then used for window envelopes, decals, and other paper and film products. The height of the unsharpened ridges on a raw die vary, but are typically in the .008” to .012” and the initial width of these ridges are as small as .010” making conventional touch probe usage unrealistic. The specification for this job is to have a reasonably unskilled operator quickly place the raw cutting die onto the NC mill and have the mill automatically sharpen the ridges like a razor blade, typically .0002” wide. Obviously any misalignment of the part to the preprogrammed NC mill path will cause improper sharpening. If its too wide the result is a dull edge or if too thin there could be no material there at all making it a scrap die.
THE CONVENTIONAL METHOD: The conventional method for aligning these parts was to place the part on a vacuum plate and optically sight the part into proper orientation, jogging it’s location over and over again until it appeared to be aligned to a cross-hair type sight. This procedure required a highly trained operator and was an intense, time consuming task. Parts were often damaged in the setup process, and it was not uncommon to take 45 minutes to over an hour to set up the system for a single part run. Ed Parento Sr., founder and technological innovator of Best Cutting Die, sent his staff out to locate an alternative method of setup. He instructed his people to look at any concept that might work, not limiting them to previously used technologies.
THE SOLUTION: Their hunt led to InoSys, Inc., a Machine Vision systems integrator in the Chicago, IL area. InoSys offered Best Cutting Die their free solution evaluation service to help determine an effective technique that was both accurate and affordable. The answer determined, use a Vision System as a smart, non-contact optical locating probe to define the raw die’s actual location, no matter how poorly the part is mechanically aligned to the mill, and send corrected rotational and offset information for this setup to the mill, dynamically altering the mill’s cutting program for each and every part. In practice setup time was reduced from almost an hour to less than 30 seconds and eliminated the need for the highly trained operator. The process became automatic with simply a touch of a button.
THE IMPLIMENTATION: An industrial video camera was mounted to the NC mill as if it were just another cutting tool that the mill could use. The precise distance from the center of the mill’s normal cutting tools to the center of the camera was then defined. The camera, lenses and lighting were connected to an industrially hardened Pentium II computer housed in a NEMA-12 enclosure. Imaging Technology’s Sherlock32 Machine Vision software and their PCVision Frame grabber board were installed in the PC. Sherlock32 has extensive I/O and communication capabilities imbedded within its comprehensive library of easy to use vision tools making it an ideal candidate to control the NC mill. The NC mill selected for this task had the ability to accept variable control data via an RS-232 interface. Shelock32 and the software in the mill were programmed so that they could “talk “ to each other exchanging information concerning when location data was needed by the mill to establish a new parts datum.
HOW IT WORKS: The operator places a “raw” part on a vacuum plate on the mill’s stage. The operator then starts the mill which moves the raw part so that its “home” position, identified by an accurately placed detent should be exactly in the center of the camera. Of course the mark will not be in the correct location since the operator only placed the part somewhat close to the correct position; however, the Vision System views the area around the expected starting point and accurately locates the “actual” position of the starting datum. The precise X And Y locations of the actual position of the starting point are sent from the vision system to the mill. The mill then moves to a second mark signifying the opposite corner of the part. The vision system repeats the inspection process sending this second piece of information to the mill. Once the mill has these two actual locations, the offset and rotation angle of this particular piece is calculated. The mill then sends the cutting tools to the calculated locations and the actual cutting process begins. The elapsed time from the start of this Dynamic Fixturing process until the actual cutting begins, is less than 30 seconds. The .010” to .020” ridge is “sharpened to better than .0002” without loss of material from misaligned part placement.
ADDITIONAL FEATURE: An second, high resolution, microscope quality camera and lens were mounted similarly to the alignment camera system. This camera’s location was again precisely identified. Upon completion of the cutting process, an inspection process begins. The mill moves the part so that the newly sharpened edge traverses directly under the inspection camera. The magnified view of the razor sharp edge is visible on the computer’s monitor. The vision system accurately measures the width of the cutting surface, inspecting for any possible mechanical damage or faulty processing. This process can be automatic or manual depending upon the requirements of the part being manufactured.
EPILOG: The first of these vision systems was installed at Best Cutting Die in 1996 and has been operating well within specification. A second system was installed in May of 1998, with a third system currently on owrder.
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