Back to Basics: Sensors rule in error proofing

By Michael Dean, technical marketing manager, Banner Engineering Corp. February 1, 2002
With cost-effective measurement algorithms in the latest photoelectric sensors, a part can be economically inspected on the production line in real time for many parameters.

Error proofing creates significant benefits for both automated and manual assembly procedures, including increased quality and productivity. With new sensor technologies, assemblies can be validated and error-proofed automatically in-process rather than post-process. High-precision photoelectric sensors, dimensional gauging sensors, light screens, and camera-based technologies, as well as manual techniques can be applied to ensure critical product attributes.

Part presence/position

Verifying that a critical part is in place and in the correct position before the next step in the process is a common requirement. Photoelectric sensors can easily achieve this objective. Two sensors can each form a convergent point a mere one-hundredth of an inch to accurately detect the edges of a product

Short-range measurement

Long-range measurement

pection applications.

Light screen part profiling

Many parts or assemblies cannot be inspected with traditional single-beam sensors. Often the user needs to determine if any one or more of several parts are in the proper position on an assembly. A light screen system can profile an entire assembly for missing or misplaced components.

Image recognition

Often, an entire product area must be inspected because the flaw could be anywhere in the defined area. Image sensors are designed to easily solve these applications with a camera that counts pixels and then compares the count to a predetermined reference count. An application example would be the sensor inspecting a plastic steering column component for irregularities in a flange area, and rejecting parts that register 80% or less white pixels, compared to a good part.

Manual bin pick verification

Accuracy of humans in sequential manual assembly is also a huge issue in error proofing. PLC-controlled “picking” systems use lights indicating which item to pick next, and a light screen in front of each bin to verify that the correct part has been taken. These systems increase quality percentages for assembly operations by reducing missed parts, and parts assembled in the wrong order. Along with error-proofing the assembly process, they also increase worker efficiency by verifying at all times where an assembler left off during the assembly process, even after a break or work-stoppage. This totally visual communication system is also a worldwide solution that eliminates training obstacles, such as language barriers, and technical ability.

In today’s marketplace, it is not good enough to simply make parts. Manufacturers and customers demand high quality that is measurable and verifiable, for every part or assembly. Error proofing reduces the time spent on quality inspections and rework, in addition to lowering the reject and scrap percentages. This adds up to reduced manufacturing costs and higher plant profitability. Manufacturers are now able to optimize their production speeds and produce quality products faster than ever before.