Machine vision inspections using visual cameras can occasionally cause recognition problems if the product and background have too little colour contrast. In such cases, thermal imaging cameras can be a practical solution - especially if the product has a different temperature than the transport medium. In many cases such temperature differences are caused by the production process. Injection moulding applications are ideal candidates as manufactured parts come out of the machine at a relatively high temperature.
The injection moulding machine manufacturer, MAPLAN, provides a good example of how thermal imaging can be applied. The company decided to make customisable, rubber luggage tags as giveaways on an extrusion line at a trade fair; they would then be re-positioned by a robot and labelled using an inkjet printer. However, the weak colour contrast between the conveyor belt and product proved to be a challenge.
The conventional approach would have been for a visual camera to guide the robot to remove the luggage tags from the conveyor belt and position them for personalising with inkjet printing. However, the light grey luggage tags on a light grey conveyor belt provided insufficient colour contrast for the vision system to work effectively so the visual camera was replaced by a Flir A615, fixed mounted thermal imaging camera. This way heat radiation from the extrusion process could be used for reliable product detection.
The Flir A615 is widely used for thermal monitoring and quality assurance of production processes. The compact thermal imaging camera can be fully controlled from a PC and, thanks to its compliance with a wide range of standards, is suitable as a plug-and-play device with software for machine vision applications from third party manufacturers such as National Instruments, Cognex, and Halcon. It is also compatible with the GigE Vision standard and supports the GenICam protocol.
The thermal camera’s high-resolution detector with 640 x 480 pixels enables high-speed IR windowing. With its high thermal sensitivity of 50mK, it captures and visualises the smallest image details and the slightest temperature differences. Its Gigabit Ethernet port allows 16-bit image streaming to the computer in real time.
"The solution was very simple and worked right from the start," explained MAPLAN's technical manager Rudolf Eisenhuber. "The high thermal imaging resolution of the Flir A615 also enables quality analysis, which we would like to demonstrate with more complex injection moulded parts in the future."
MAPLAN is also considering the possibility of additional evaluation of thermal information for rubber injection moulding machines. The use of a thermal imaging camera could also provide additional information about the quality of a product. This method is particularly interesting for complex shaped components and in this regard, Flir thermal imaging technology has the potential to significantly optimise the injection moulding process.