Bumper OK?

As a machine vision specialist, attentra in Tübingen develops complete solutions for industrial image processing and industrial automation, such as for the inspection of automotive assemblies. This tailor-made, highly flexible, inline testing technology with 3D measurements is based on the so-called Robot Vision Center. Here, attentra combines optical detection systems with robotics. Also present on the robot hand: light section sensors from Leuze electronic.

Light section sensors are based on the principle of triangulation. They consist of a line projector as light source as well as an electronic camera. In the case of the LPS (Line Profile Sensor) light section sensors from Leuze electronic, the light source is a laser that projects a narrow and bright line on a measurement object while the camera observes the projection of the line. The shift of the line in the camera image is converted to 3D coordinates. Thus, the light section is a method of optical 3D measurement technology that facilitates the measurement of a height profile along a projected light line.

"We use the triangulation principle whenever, e.g., specific objects need to be detected three dimensionally within the scope of the inspection of automotive assemblies. In such cases, we use the LPS profile cameras from Leuze electronic," explained Christian Vollrath, one of the three managing directors of attentra in Tübingen. The core area of business of attentra is industrial image processing. On the basis of the Robot Vision Center software, the company realises customer-specific image processing systems for the various tasks in the areas of quality assurance and automation of a wide variety of large and complex components. As an example, Vollrath mentions the highly flexible inspection systems for bumper production lines at REHAU: "Here, it is necessary to inspect, among other things, whether a pressure hose sensor is laid correctly in the bumper. To do this, we scan the profile of the hose with an LPS light section sensor from Leuze electronic.“

Variety requires flexibility

Bumper production at REHAU is one example of many that demonstrates how automotive assemblies have developed into complex systems over recent decades. Their production requires a high level of flexibility. This also applies, in particular, for quality control, i.e., inline testing technology.

As a plastics specialist, REHAU, headquartered in Rehau in Germany's Upper Franconia region, offers integrated developments and technologies for polymer-based solutions in the areas of construction, automotive and industry. In the automotive sector, bumper systems are among the main products the company supplies to the automotive industry, including big names such as Mercedes-Benz, BMW and Audi.

In addition to playing a significant role in the design of the front and rear view of an automobile, these components today meet the highest safety standards. Through the use of highly complex technology, they contribute to a reduction in the risk of accidents on roadways. The variety of integrated sensor systems ranges, e.g., from lane change and blind spot assistants to short-range radars and parking assistance systems.

Another key factor is the protection of pedestrians. In this context, the so-called "active engine hood" is a modern and additional protective measure. By raising the motor hood, it ensures more deformation space, thereby reducing the risk of injury to a pedestrian. The sensor system for this is likewise built into the bumper and poses special challenges within the scope of the quality inspection.

Against the backdrop of just-in-time or just-in-sequence production, the variety of brands, models and equipment features demands highly flexible assembly lines and, at the same time, equally flexible testing devices. After all, Rehau now delivers bumpers in more than 500,000 variants. With static test systems, in which cameras and sensors are permanently mounted, it is not usually possible to meet such requirements. "And not at all if inspection tasks utilising image processing are arranged directly in the assembly line, as is increasingly the case in modern production lines," added Vollrath.

Offering an adequate solution here is the Robot Vision Center software from attentra. It combines the flexibility of industrial robots with the capability of image processing to very precisely detect objects. Here, the robot performs the exact positioning of the cameras and/or 2D/3D sensors and also handles the illumination systems.

Integrated in a production system, the sensor passes on the component variant that is to be inspected to the Robot Vision Center software. The software then performs the adapted test sequence, which may include a wide range of inspections. In this way, individual inspection tasks can be performed without modifications quickly and with minimal inspection work even if models are changed frequently.

Predestined for large assemblies, the Robot Vision Center installed at REHAU as bumper inspection system facilitates fast and reliable detection of the often numerous components in their intended positions. The software visualises and documents the inspection results and transmits them to the production interfaces. "Robot-controlled camera positioning allows the number of required cameras and sensors to be greatly reduced. And the system remains flexible, even if something changes on the component or at the inspection positions," added Vollrath.

In the bumper inspection systems, a robot from Universal Robots ensures maximum adaptability for the positioning of the cameras. It controls two 2D-cameras with different optics that enable different levels of magnification. The robot is also specially equipped with a 3D sensor for the installation inspection of the pressure hose sensor for the "active engine hood" – an LPS 36 light section sensor to be precise – that allows images to be created with depth information.

The pressure hose sensor is laid in the bumper over the entire width of the vehicle. It is positioned in a block of plastic foam, the so-called impact absorber, and must be fitted in a guide with extremely high precision. At no point may it protrude over the plastic foam. Here, the LPS 36 light section sensor performs the precise measurement of the depth of the hose in the plastic foam. For this purpose, the sensor is moved by the robot over the component. An additional encoder in the LPS 36 sensor supports the capture of three-dimensional images.

"To meet the high requirements on precision, we use the high resolution version of the LPS 36 light section sensor here, which allows us to detect with an accuracy of within a few tenths of a millimeter," explained Vollrath, who above all values the very compact construction and the unmatched, economical price/performance ratio of the sensors from Leuze electronic.

One very important criterion for using these sensors is, however, the HALCON interface. With the image acquisition interface, the sensors can be operated with the globally used HALCON image processing software from the Munich-based company MVTec. It permits simple detection of equidistant 3D data using the light-section sensors and direct reading of the calibrated 3D data with HALCON software.

Summary

The Robot Vision Center software from attentra is a control software that connects optical detection systems, robot controls and production systems. The performance of the robots as well as the camera systems and sensors is adapted according to requirements. This results in highly flexible solutions for automation and inspection tasks.

The LPS 36 sensors from Leuze electronic are a perfect fit for this concept, as they can measure the dimensions or the position of objects and are able to eliminate the need for complex sensor solutions, combinations of sensors or additional evaluation units. They are used above all in cases where the 2D cameras are pushed to their limits.

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