Apparatus and method for detecting surface defects on a workpiece such as a rolled/drawn metal bar
The present invention is directed to solving the problems associated with the detection of surface defects on metal bars as well as the problems associated with applying metal flat inspection systems to metal bars for non-destructive surface defects detection. A specially designed imaging system, which is comprised of a computing unit, line lights and high data rate line scan cameras, is developed for the aforementioned purpose. The target application is the metal bars (1) that have a circumference/cross-section-area ratio equal to or smaller than 4.25 when the cross section area is unity for the given shape, (2) whose cross-sections are round, oval, or in the shape of a polygon, and (3) are manufactured by mechanically cross-section reduction processes. The said metal can be steel, stainless steel, aluminum, copper, bronze, titanium, nickel, and so forth, and/or their alloys. The said metal bars can be at the temperature when they are being manufactured. A removable cassette includes various mirrors. A protection tube isolates the moving metal bar from the line light assembly and image acquisition camera. A contaminant reduction mechanism applies a vacuum to remove airborne contaminants.
1. A system for imaging an elongated bar extending and moving along a longitudinal axis in a manufacturing process, said system comprising:
an image acquisition assembly having a field of view configured to image a first predetermined width over a circumference of a surface of said bar while said bar is moving to define an image belt and produce image data corresponding thereto, said image acquisition assembly including n digital cameras, where n is an integer 3 or greater, arranged so that a combined field of view thereof corresponds to said image belt, said cameras comprising line scan cameras;
a light line assembly configured to project a light line belt having a second predetermined width onto the surface of said bar, said light line assembly being disposed relative to said image acquisition assembly such that said image belt is within said light line belt, said light line assembly being further configured such that a light intensity is substantially uniform along said image belt;
a protection device comprising a tube having a first part and a second part spaced apart and offset from said first part along said longitudinal axis to define an access space, said tube being disposed intermediate the elongated bar and said image acquisition means and said light line assembly, said access space being configured in size and shape to allow (i) entry of said light line belt and (ii) exit of said image belt;
a contaminant reduction mechanism configured to reduce the presence of contaminants in the space proximate said access space of said protection tube; and
a computing unit coupled to said image acquisition assembly configured to receive image data for a plurality of image belts acquired by said image acquisition assembly as said bar moves along said longitudinal axis, said computing unit being further configured to process said image data to detect predetermined surface features of said bar.
2. The system of claim 1 wherein said contaminants comprise one of mill scale powder and water mist.
3. The system of claim 1 wherein said contaminant reduction mechanism comprises a vacuum end effector having an outer wall defining an interior vacuum chamber, said end effector further including a suction inlet located proximate said access space of said protection device, said vacuum end effector being configured to be connected to a vacuum source.
4. The system of claim 3 wherein said vacuum end effector is a ring shape having a ring axis that is substantially coincident with said longitudinal axis, said suction inlet being configured in size and shape to circumscribe the perimeter of said access space.
5. The system of claim 4 wherein said vacuum end effector is substantially rectangular in radial cross-section, said suction inlet being formed by removal of a radially-inward corner of said vacuum end effector.
6. The system of claim 3 wherein said vacuum end effector comprises a pair of half-ring shape body portions.
7. The system of claim 3 wherein said vacuum end effector comprises a plurality of straight bars.
8. The system of claim 3 wherein said contaminant reduction mechanism further includes a conduit for connecting said source of vacuum to said vacuum end effector, said source of vacuum comprising a vacuum pump.
9. The system of claim 8 wherein said vacuum pump is a venturi type.