They are used in medical technology and laboratories worldwide to dispense liquids in precise doses and then examine them: Pipettes. Their tips must meet very strict quality requirements in order to perform their task as desired, as Markus Urban, one of the Managing Directors of Ziemann & Urban from Moosinning in Bavaria, knows: "Even slight burrs in the injection mold or other defects on a pipette tip can lead to liquids not ending up where they should in the laboratory or to incorrect liquid quantities. This can lead to incorrect measurement results, which must be avoided at all costs in medical technology."

The production of such pipette tips, which are usually made of plastic, often takes place in fully automated injection molding processes that run around the clock without a break. The production speeds are so high that a 100% inspection of all manufactured parts would be technically feasible, but not economically justifiable. "As a compromise, we have therefore designed our systems to be so flexible that they can carry out isolated measurements cyclically and, depending on customer requirements, can check a complete tray with high precision once an hour, for example."

The test objects vary considerably depending on the manufacturer and application: The length is usually between 20 and 120 mm, the diameter can vary in the range of 0.5 to 2.5 mm, and transparent or black are most commonly used for the colors. "The effort required to cover this range with automated systems is considerable for a disposable product. However, due to the field of application in the medical sector, we believe it is absolutely necessary in order to realize the inspection of these essential components economically," emphasizes Urban.

Modular solution

The solution that Ziemann & Urban has developed for this challenging task is modular in order to meet the different requirements of pipette tip manufacturers from all over the world. When measuring diameters, burrs and wobble circles, some of their requirements are for accuracies of less than 1 μm, which is why the company relies on high-quality image processing: customers can choose between different versions with two to nine cameras to check the quality features, depending on their requirements. According to Urban, the most common version works with six cameras: "In this configuration, one camera inspects the pipette tips from above, one from below and four from the side, with the lower camera being movable in height to cover different pipette lengths." Optionally, additional cameras can also be used to measure the absolute length of the pipette tips and their wobble circle, including a 3D calculation as a stereo system.