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Optical measurement of position and size of wood panels for intelligent automation of sanding machines

Final Report Summary - MEPOS (Optical measurement of position and size of wood panels for intelligent automation of sanding machines)

The MEPOS project tackled problems for automation of wood-sanding machine, in 24 months through the development of a robotic agency based on 3 interacting agents:
a) an optical sensing system to detect wood panel shape and position;
b) an intelligent control system;
c) driving an improved array of pneumatic actuators.

In order to control the sanding process and to optimise panel surface finish it is necessary that panel dimensions, shape and position are measured on line, while the panel is moving on the transport belt and entering the machine and that actuators are controlled in force in order to apply the required force distribution on the panel surface, so that each part of the panel is machined at the desired pressure level.

The project objectives have been to introduce an intelligent automation strategy and advanced optical sensing to control and optimise the sanding process. In particular the project has developed three independent agents, interacting with each other so to realise an automatic sanding process:
a) a measurement system based on imaging acquisition and processing under off-axis structured illumination, so that real time information on the panel position and size / shape can be measured by triangulation and made available to the control system which supervises machine operation;
b) a two-pressure pneumatic actuator be able to vary and optimise the pressure applied on the moving wood panels during the sanding process, based on information on panel shape and dimension, available from the optical measurement system which inspects each panel entering the machine;
c) an intelligent control strategy based on fuzzy logic in order to use information on panel position and size/shape to control the actuator valves that press the sanding belt on the wood panel.

The following technical Work packages (WPs) were active during year 2.

WP1 - Optical sensor for panel position and shape
The first three months of year 2 were devoted to optimise each sensor based on metrological performance evaluation. Some important modifications and improvements were made on all sensors, in particular for the structured illumination, which strongly affects signal-to-noise ratio and sensor uncertainty. The final testing of the sensor installed on the machine performed in WP6 has provided a large amount of information which will allow selecting the best technical solutions, for a possible future industrialisation.

WP2 - Development of improved pneumatic actuator
VIET spent a long time testing the pneumatic bloc unit. During life tests, the pneumatic performances were satisfying. The valves and the bloc performed in a reproducible way and the system proved to be very sensitive. A few valves did not perform appropriately during the endurance tests. These were replaced by FAS. During these tests, VIET found that electronic noise interfered with the communication between the master unit and the bus system. UNIVPM within has developed an instrumented panel which is aimed to observe the applied forces during sanding; this is a tool to characterise performance of the pneumatic actuators. This panel has been used during machine testing in WP6 and results have been fully positive.

WP3 - Development of intelligent control
The specifications for the Intelligent control system (ICS) were defined by POLIMI together with the other partners. Knowledge to be embedded in the ICS was in part acquired from experts of the machine, available at VIET, and encoded in a conceptual model. The fuzzy rules implementing each of the modules of the architecture have been defined and implemented from the knowledge acquired. Rules can be modified by the user of the ICS. Parameters, variables and input data to be taken into account in the implementation of the ICS have been identified, together with their relationship with the desired shape of sanding paper that should be obtained by imposing the correct pressure to the pistons.

WP4 - Development of machine architecture
The classic architecture of the sanding machine of VIET has been modified so to host the new agents. Both mechanical and electric/electronic modifications had to be implemented. An improved software interface with the new necessary functions has been implemented, making use of the machine PLC, which will communicate on an Ethernet link.

WP5 - Integration of all elements
Integration has been the crucial issue in this project; due to the delays in WP1, WP3 and WP4, it was decided to extend by one month the duration of WP5 and to maximise man-power efforts aimed to integrate the optical sensor, the pneumatic actuator and the ICS in the new machine architecture. WP5 has produced a prototype machine which hosts a PC based network of independent agents, namely a vision system, realised in four different versions, a pneumatic actuator with two pressure levels and the intelligent control system, all interacting together and with the machine PLC.

WP6 - Testing of the automatic sanding machine
The objectives of WP6 were the testing of performance achieved by the sanding-machine equipped with optical sensing unit, two-pressure actuator and intelligent control. Tests should have aimed to a comparative validation of quality and flexibility of the innovative sanding process, with respect to a conventional mode of operation. To this purpose VIET, SIBOIS and COSMOB have defined the procedure for testing, according to the experience in panel testing. State of art shows that finishing is evaluated by visual observation of the light scattering over the sanded panel and by observing the surface aesthetics and the dust distribution on the panel surface at the exit of the sanding machine. To this purpose SIBOIS and VIET have selected a set of panels which were considered as test cases; they were different in colour and surface finish and size, so to test the system in various typical working conditions. Being available different optical sensors, part of these tests have been made with each of the sensors.

Two industrial sectors are directly affected from the results of MEPOS project. They are:
1. wood-working machinery;
2. optical sensor manufacturing.

The first, wood-working machinery, may exploit directly the results achieved and mainly the automatic sanding machine. One relevant result has been the transfer of know-how and technologies about optical systems and intelligent control to an industrial sector which does not make a large use of high-technologies. VIET and SIBOIS as representatives of machinery producers, and FAS as producer of pneumatic devices may take advantage from these results. Their mutual cooperation is also an indirect result of this project, with potential future follow-ups.

The second industrial sector, optical sensor manufacturers, represented by MEL, has been exposed to a number of new ideas and technical solutions to be adopted in sensor design, that will highly probably be implemented in the future production of large size optical scanners. Its interaction with the wood-working industry has also opened opportunities for new market areas, that now MEL is exploring together with VIET.

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