Camera controlled painting system Finnish Road Enterprise (Tieliikelaitos) has developed a camera controlled nozzle painting system (pat.pend.), which can be attached to the chassis of a truck to repaint road centre line markings. The system uses National Instruments machine vision hardware and software and it has been developed by Antero Angelva, from Angelva Engineering. The project was initiated by Pertti Ylitörmänen, from Finnish Road Enterprise. Traditionally, centre line painting require two people, the truck driver, and the operator, who inspects faded line marks and manually aligns the nozzle bench so that the new line marks will be painted on the old ones. The new painting system requires only one person, who starts the system, and thereafter only needs to concentrate on driving the vehicle (figure 1).
Figure 1: Camera controlled centre line painting system in use The equipment can be installed
in existing painting fixtures by adding a camera, computer and motion controller
equipment. An analogue CCD greyscale camera is used, connected to a standard
computer via PCI-1408, which is a greyscale camera interface board from
National Instruments (figure 2).
The software, written in National Instruments LabVIEW™ graphical programming language and Imaq Vision function libraries, analyses the grabbed picture to find old paintings on the road. Analysis functions are used not only to enhance images of the sometimes vague traces and to find the line edges positions, but also to differentiate between proper centre lines and smudges on the road. The program will send movement commands to an i/o board which controls the servo motor that positions the painting unit. The position can be set to sideways accuracy of less than ±1mm in relation to the old lines, and this requires that the driver follows the old track within accuracy of no less than ±100mm. An important requirement for successful vision systems is the computer’s ability to process live image data fast enough. Advances in computer technologies have made this possible. Instead of using dedicated image acquisition systems with DSA processors, industry-standard computers, with National Instruments modular hardware, can be programmed to handle image analysis tasks. Use of standard computers allows more cost-effective solutions, without degrading performance. Furthermore, the system can be easily upgraded and modified if necessary. In the current solution, a standard computer with a 400 MHz Celeron processor was used (figure 3). The camera and the nozzles are 2 m apart, so at 5 m/s velocity, the system has 400 ms to respond to any sideways changes. In practice, the unit can respond to sideways changes of 16 mm. As a matter of fact, the sideways movement should not even exceed this, since sharper changes in the lines can be disruptive to the eye.
Figure 3: The controlling unit, a pc with standard components. A damping unit has been attached to the front and all i/o points are connected via two connectors in the front due to strong vibration inside the vehicle. The new equipment reduces costs in centre line painting significantly. In addition to savings in salaries, painting can be carried out faster than with the manually operated system. Furthermore, the higher precision of the automatic system means that the user does not have to deal with penalties due to paint smudges. Use of standard computers with modular hardware and programmable software from National Instruments makes the device very economical to set up and upgrade. Contact information: Finnish Road enterprise
Angelva Engineering
National Instruments Finland
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