Laser based seam tracking system for robotic welding machines

15 December 2010

Meta Vision Systems has introduced Smart Laser Pilot, a new seam tracking system for robots incorporating the company's Smart Laser Sensor (SLS) technology. This integrates a high-resolution megapixel camera, a laser stripe projector and advanced image processing hardware and software within a compact and rugged sensor head design. Integral cooling, front window blow-off and an integrated weld spatter shield ensure the sensor will survive the most hostile of welding environments.

The SLS central to each Smart Laser Pilot system is mounted just ahead of the welding torch on the robot end effector and acquires data at 30 full frame images per second. Much higher frame rates are possible using a windowing function that concentrates image analysis on a defined region of interest. All image processing is done in the sensor head itself and a tracking accuracy of ±0.1 mm is possible in both the horizontal and vertical planes with a field of view of 50 mm.

SLS features several advancements that simplify setup and operation of the system and that greatly improve performance on shiny and other difficult surfaces. This includes an automatic laser intensity control function, exclusive to Meta, which solves laser reflection problems that are common in applications involving variable material surface conditions.

For example, when welding two different materials together whose surfaces have been prepared differently or when fillet welding shiny aluminium components, the laser line from a conventional sensor may appear too bright in certain areas and dull in others. This may also cause the laser light to reflect brightly, causing the vision analysis software to make poor and inaccurate measurements.

Automatic laser intensity control in the SLS rapidly varies the intensity of the laser stripe so that darker areas become brighter and brighter areas become darker. The result is an image of more uniform intensity along the entire length, contributing to more reliable and accurate measurements. This also simplifies the setup process, as varying surface conditions no longer need to be considered while setting up a system.

The Smart Laser Pilot communicates with the robot controller using an Ethernet connection. Provided with each system is a break out board incorporating an Ethernet switch, laser safety circuitry and a 24V DC power supply for the SLS. The break out board allows the use of a single cable for Ethernet and power between the robot controller and the sensor.

The Ethernet switch can route the SLS signal to the robot controller or to the user's own Windows XP/Vista/Win7 computer running Meta Smart Laser Pilot Tools software supplied for setting up and changing system operating configurations. The laser safety circuit is incorporated as required by international regulations to manage and control how and when the SLS laser is activated.

Ease of use is leveraged further using a dedicated graphical user interface touch screen device (GIO). Housed in its own protective enclosure, the GIO displays the analysed weld joint profile and other data as processed by the SLS, providing an important tool for production monitoring and problem rectification.

The GIO is implemented as an independent yet convenient means to display data of interest to the user coming from the SLS head via the Ethernet interface. The use of an Ethernet interface also makes it easy for the sensor to be used more generally when information on the position of a feature or its surface profile is required by another application to achieve greater levels of integration.

The Smart Laser Pilot is able to control virtually any robot that has a real-time Ethernet interface. If a robot is not equipped with an Ethernet interface, an optional Ethernet I/O board (EIO) is available to convert the Ethernet signals and send them to the robot controller via a serial or analogue/digital interface.

In many critical applications, robots that are performing automated arc welding without some form of external guidance will produce defects if the parts to be welded are not in the proper position. While costly, high quality joint preparation or complex fixtures may be employed to ensure the robot does what it is programmed to do, a more precise and less costly alternative is to use a non-contact laser sensor to track the weld joint and to adjust the robot’s path while welding. This allows the welding torch to follow the actual joint position and to correct for changes in part positioning in real time.