Pete Kepf, Certified Vision Professional -
Advanced
Problem
A manufacturer of rubber seals needed to inspect a variety of its
products. Increased sales volumes exceeded the capacity of the
inspectors, resulting in more defective parts being shipped to
customers. This was beginning to adversely affect costs and
long-standing customer relationships.
Products were manufactured using a proprietary continual stamping
process which produced large volumes. The wear and batch inconsistencies
resulted in a repeatable percentage of parts with the primary defects:
flash and voids. Because the process was mature and repeatable,
management was reluctant to change it. Because the percentage of defects
was fairly fixed and detected defective parts were recycled into the
process, management explored an automated inspection option to support
the increased sales volume.
The challenge was to introduce a 100%-part inspection methodology for
the product. After evaluating several inspection concepts, management
selected a non-contact visual inspection method. Major technical issues
were:
- A part handling system for inspection needed to be developed
- All sides of the parts were to be inspected
- Flash and voids were to be detected simultaneously
- Rubber by its nature is pliable and non-reflective
- Required inspection rates were up to 600 parts per minute
(10/second)
Solution
The picture at the right shows a simplified layout. The actual
installation consisted of successive multiple identical
stations for a total of eight cameras: four back lit to detect flash
and four front lit to detect voids.
A sensor detects the part at the 3 o'clock position. A sensor pulse
and an encoder pulse are sent to the controller; the controller
stores the relative position of the "current" part. When that part
reaches the 6 o'clock location, the controller sends a pulse to the
backlit camera and light; followed by a pulse to the front lit
camera and light. The ability of the controller to coordinate the
part detection, multiple camera/ lighting pulses and a single reject
station was indispensable to the operation of this work cell.