Inspection of precision and micro components improved by machine vision

(Pictured right: The measurement results are seamlessly exported to the quality control software, where they are available for the rest of the process chain. Image courtesy of Petitpierre)

Measuring and inspecting super-small parts repetitively, precisely, and at high speeds are key requirements for the watchmaking industry as well as all industries dealing with micro components, as they help to avoid production rejects and to produce precise pieces.

Petitpierre, headquartered in Cortaillod, Switzerland, specialises in sophisticated microtechnology committed to making this ideal a reality - with the help of machine vision. Founded in 1973, the family-owned company's portfolio includes complex measuring applications for the watchmaking, jewelry, medical and aerospace industries. The company also develops and produces high-precision systems for the automated assembly of high-end microtechnical components as well as sophisticated watchmaking tools.

One of Petitpierre's customers is KIF Parechoc, a flagship company in the Swiss watchmaking industry based in Valle-de-Joux. To comprehensively improve and automate their processes, Petitpierre developed a contactless inspection and cleaning system. This is suitable for a wide range of components for mechanical watch movements, such as shock absorbers, index assemblies, wheels, screws, trains, and complete barrels.

To elevate the quality of the processes to a new level, the objective was to optimize the measurement of these precision mechanical parts. "Our goal was to carry out the entire measurement process with just one click. We also wanted a wide variety of precision mechanical parts to be detected automatically and the data to be transferred directly to our quality control software," recalls Yoann Canon, COO at KIF Parechoc.

"The major challenge in implementing the project was to perform a highly precise and very fast series of measurements under harsh production conditions - a challenge, that could only be overcome by using machine vision technologies, ie MVTec HALCON."

From the clean room to the production facility

In the past, several systems carried out this process, including contact measurement, in a clean environment. "From there, we wanted to move the measurements directly to the production plant to reduce the effort and ensure continuous process chains.

"A further objective was to reduce the inspection time compared to conventional means and thus increase productivity substantially. And finally, the required measurement accuracy also needed to be brought into a harsh mechanical production environment. Here, it was important to reduce employee intervention in the process to a minimum," adds Yoann Canon.

Advanced measurement technology was needed to meet the diverse requirements. "It quickly became clear to us that there was no way around machine vision in this particular application. Machine vision makes it possible to automate the entire process seamlessly and with minimal effort. In addition, we benefit from a speed and precision in measurement that hardly any other technology can offer," explains Thomas Majoulet, Head of Metrology at Petitpierre.

Efficient combination of cleaning and measuring

The solution implemented by Petitpierre is a dual system, combining its products drop and lumen and empowering them with machine vision software. drop is a device for the automatic cleaning and drying of precision parts that ensures the optimum repeatability of cleaning quality. lumen is a telecentric optical device for the intelligent, automatic, and highly accurate measurement of precision micromechanical parts. It was developed specifically for use in demanding production environments and is compact, lightweight, and easy to operate.

The application, in which the micromechanical parts are cleaned and measured one by one, works as follows: The operator first places the components in a drop system container and starts the cleaning processes. The system then cleans both, the first part and a vacuum gripper, which is then used to transfer this part into the lumen system once it is clean and dry. Cleaning and drying cycles are configurable: solvent volume, cleaning/drying time, and the number of cycles can be adjusted by the operator.

Once the part has been transferred to lumen, the integrated machine vision software detects it automatically and starts the actual measuring process. The measuring is performed with just one 'start' click by the operator who does not need to make any manual adjustments. The measurement is then repeated with the other components. Once all parts have been inspected, the measurement results are seamlessly exported into the KIF Parechoc quality control software, where they are available for the rest of the process chain. The process can now be repeated with additional parts.

The optical measuring line in the lumen system consists of a telecentric lens including lighting, a V-shaped device for correct placement of the parts, and two prisms for reflecting the image onto a telecentric optical sensor. The setup also includes a motorised drawer to protect the measuring area from dust and oil as well as an LED to indicate proper system functionality. All components are controlled by an electronic circuit board.

High-precision measurement

MVTec HALCON is used as the machine vision software within the system. "We opted for HALCON, as it offers the manifold of functions needed within this application. Besides, its features are utmost robust and, in many cases, ahead of other providers", comments Thomas Majoulet.

For example, its shape-based 2D matching technologies can identify and locate the tiny parts precisely so that they can be picked up with the vacuum gripper and measured with sub-micrometre precision. The software detects even the smallest contours and inspects them reliably. In detail, diameters, lengths, concentricity, radiuses, and angles are measured and inspected with subpixel accuracy, using the technology 'subpixel threshold'. In addition, MVTec HALCON facilitates the precise camera calibration of the lumen system.

Another advantage is that MVTec HALCON is able to meet the special requirements of telecentric optics - as used in Petitpierre's lumen system - with precision right out of the box. The 360-degree measurement of the object means that there is no perspective distortion that would involve time-consuming corrections afterwards. This paves the way for a particularly high level of measurement accuracy.

Fully automated, much faster and more accurate

"MVTec HALCON is the ideal machine vision software to overcome the challenges we were facing. It not only offers the required accuracy and speed of detection, but also makes it possible to perform inspections that are completely contactless," concludes Thomas Majoulet. "This provides extra protection for the delicate and highly fragile watch components and prevents micro-contamination.

"We can now fully automate the entire measuring process, including cleaning, drying, and transferring the parts to the lumen system. This ensures reproducible processes and minimises manual intervention by personnel. We also reached the goal to make inspection processes much faster, as they are conducted with just one click. As a result, KIF Parechoc is able to cut costs and raise productivity to a new level."