Profile sensor cuts the grind

| Information and Communication Technology

scanCONTROL 2910-100_BL laser profile sensor can be mounted directly onto a robot

Light weight, high resolution laser profile sensors are being used in the nuclear industry for smart robotic grinding on welded structures.

A 2D laser profile sensor from Micro-Epsilon is being used by the Nuclear Advanced Manufacturing and Research Centre (Nuclear AMRC) in a project to develop a smart robotic grinding and deburring system for the kind of welded components and structures used in the nuclear power industry. The sensor is mounted to a robot end effector and measures the profile of welded joints and planar surfaces.

Coroma is a robotic system development and integration project to automate a variety of manufacturing tasks. Most of these tasks are secondary finishing operations (e.g. grinding, sanding, deburring, etc.) which are typically carried out manually on welded components such as nuclear fuel racks and tube structures.

According to Ozan Gurdal, a research engineer at Nuclear AMRC, manual finishing can take dozens of hours of cycle time, as well as being a health and safety issue.

“The idea of the Coroma Project was to use robots to automate these processes with sensor and software assistance and to demonstrate the work on full-scale demonstrators provided by the companies that plan to operate them,” says Gurdal.

Smart robotic intervention

Nuclear AMRC’s involvement in the project was to develop a smart robotic grinding and deburring system for welded components. The owner of the application project was Equipos Nucleares SA, a nuclear fabrication organisation in Spain.

“We developed an integrated end effector for the robot with a Micro-Epsilon 2910-100 BL laser profile sensor on one end and a pneumatic spindle on the other. This would eliminate the need to use a tool changing system, which would stand out as an expensive item,” continues Gurdal.

He went on to explain that it is not possible to use the part’s design CAD model when it comes to programming robots for weld grinding or conditioning as there is a significant difference between the design and actual as-welded part because distortion and warpage is inevitable after welding.

“This difference is sufficient to affect robot paths and so exact weld sizes are unknown. Therefore, the 3D CAD model of the as-welded part is required to program paths accurately,” explains Gurdal.

Profile evaluation

The scanCONTROL 2910-100_BL laser sensor held by the end effector is used to scan the areas of interest on the part. These include welded joints and planar surfaces used for reference. The sensor provides the axial and lateral distance (2D) measurements between the scanned object and sensor frame. This in itself is not sufficient for reconstruction of part as a 3D CAD model for evaluation.

Therefore, the 2D data obtained from the laser sensor is combined with the position of the robot flange, which is read in real-time from the robot controller using a LabVIEW-based central controller. Combining these two pieces of information, the central controller can generate the 3D reconstruction of the as-welded part as a point-cloud and converts it into the desired CAD format.

According to Gurdal, the 3D CAD model of the as-welded part is then used to generate grinding and deburring paths either offline using CAM or robot path programming software or online using in-house developed path generation algorithms.

“Once path generation has been completed, the grinding or deburring operation begins. In this case, the robot used for this work was a 6-axis Staubli TX200 machine. This is because Staubli was one of the partners on the project,” he says.

Laser sensing

Nuclear AMRC found that tThe scanCONTROL 2910-100_BL was ideally suited to being mounted on a robot arm as it is a compact, high performance laser profile sensor or laser line scanner with integrated electronics that provide it with a degree of autonomy.

It operates using blue (violet) laser technology rather than red, making it especially useful for measuring against shiny metallic structures or difficult-to-measure surfaces. The sensor projects a wide laser line from 58mm to 143mm over the object with a profile resolution of 1280 measuring points. The measuring range in the z-axis is from 100mm to 290mm, which gives useful flexibility for the robot positioning.

Easy integration and connection to PCs & PLCs

The sensor is equipped with a Gigabit Ethernet interface for transferring profile data, as well as a multi-purpose connector for RS422, encoder input triggering, Digital In (HTL/TTL), power supply and synchronisation. The sensors support Power-over-Ethernet (PoE), which means they can be operated with only one cable, thus simplifying installation even further.

A simple and intuitive configuration interface is provided with all sensors to allow sensor configuration, as well as full SDK for more detailed machine integration. The sensors are configured with a unique IP address (user changeable), which enables future remote configuration and diagnostics. A Modbus protocol (supported via Ethernet and the RS422 interface) also enables direct connection between the sensor and a PLC.

“The scanCONTROL laser sensor is a good piece of equipment. We’ve successfully used the sensor in multiple projects, for example, weld monitoring and weld grinding. The integration was straightforward too. There are a variety of APIs/software tools provided by Micro-Epsilon for integration with different software platforms and programming languages such as LabVIEW and C++, so it was really a plug-and-play set up without much hassle which saved precious time for us,” concludes Gurdal.

The sensor is part of a range of laser scanners, which share similarly easy set up and a wide range of mounting options. Differences within the range lie mainly in the profile resolution depending on the degree of precision required in the application. Profile resolution varies between 600 point and 2048 points per profile with the resolution of the sensor used in the Nuclear AMRC application being 1280 points per profile.

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