Automated inspection systems ensure that everything runs smoothly without human intervention. But who checks the quality inspection systems? With increasing automation, the machine can and must monitor itself more and more. This requires a sophisticated strategy for inspection process reliability. It ensures that every inspection step runs smoothly, even in very short cycle times and in complex processes.

Just a few years ago, employees were largely responsible for quality control. However, due to fatigue during long and late shifts, differences in the level of experience of individual employees or other circumstances, they often represented a source of error themselves. By integrating in-line inspection systems for 100 percent inspection, manufacturers are now increasingly freeing up employee capacity for more demanding tasks while maintaining product and inspection quality at a consistent level. But who checks whether the machine itself is becoming a source of error?

Inspection Process Reliability: the Machine Monitors Itself

To ensure that the individual inspection systems and sensors fulfill their tasks as required and that no produced part leaves the line untested, manufacturing companies need a strategy for both the testing and the safety of the process. To achieve this, the interaction between the individual components and inspection steps must be precisely defined, as well as the consequences if one of the process steps fails.

Use case: Every Process Step is Fully Monitored

An example from the inline inspection of series-produced components using the Kistler KVC 621 SE optical quality inspection system illustrates what such a concept might look like. This compact testing system for punched metal components can perform an optical inspection of up to 4,000 parts per minute to check for dimensional accuracy and surface defects such as scratches or dents. Up to three integrated camera stations take pictures of the test part, the image processing software Kivision does the evaluation. Thanks to the tightly knit design for inspection process reliability, it ensures that every part is inspected even at high cycle rates. The built-in camera stations and the software for image processing are connected by the programmable logic controller (PLC). This initiates the individual steps such as the recording of the test piece, the data transfer and the evaluation by the image processing software. It also checks the communication between the individual components. The camera, for example, sends the signal to the PLC when an image has been taken and transmits the image to the software.

At this point, a problem can arise that computer users know only too well: parallel processes slow down data processing. If the camera delivers a new inspection image before the inspection of the last one has been completed, it can put additional strain on the software. In such cases, the PLC detects that the expected feedback is not being provided, stops the system and issues an error message to the operators, including the cause of the error. This ensures that the inspection system checks each part and defines its status as OK or NOK.

Another typical source of error when testing punched parts in endless strips is the removal of NOK parts from the strip using a stamp. Here, it is not sufficient to identify a part as defective if it is not subsequently removed. Therefore, sensors monitor the up and down movement of the stamp to check its end position. An additional laser light barrier is also used to ensure that the NOK part has actually been separated – after all, a stamp stroke does not necessarily mean that a part has been completely separated.

Careful design of the inspection processes avoids stumbling blocks

When designing systems and the associated inspection processes, a wide range of potential sources of error that could affect smooth operation come to light. Individual requirements are almost always hidden in production processes which become increasingly complex with a higher level of automation. To ensure a smooth process, it is therefore important to analyze, implement and secure all crucial process and quality assurance steps accordingly.

Author
Edgar Wuchrer, Business Development Manager at Kistler