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electrical engineering

Getting the paper right

Electronic sensor eliminates loses in the drying process of cellulose paste

EDUARDO CESARLaser emitter (in blue) and the reflector (below): information going to a microcontroller (at the back)EDUARDO CESAR

Electronic sensors developed with national technology, after some five years of research, show their efficiency in improving the process of paper manufacturing and reducing the lose coming from the mechanical wear and tear of equipment during the pre-drying phase. At this stage, prior to the transformation of the cellulose paste into paper, excess water needs to be eliminated. For this to occur, the paste is placed over a plastic fiber screen, sustained and transported by giant cylinders.

Monitoring is done by a system made up of a mechanical sensor, also called a feeler gauge, which works with a rectangular haste placed against the border of the screen, which perceives the positioning and any lateral deviations. Control is carried out through the pneumatic working of the cylinders, displaced forwards or backwards, in such a way as to maintain the screen centered on the equipment to the maximum possible. The task is extremely complex because of the dimensions of the screen, which can measure up to 60 meters in length by 5 meters in width.

It so happens that the permanent contact of the mechanical sensor with the moving screen provokes friction, and, as a consequence, both the screen and the gauge get worn out. In some cases, even the working of all of the equipment can be damaged, causing serious losses to the paper industry during the production process not only because of the high cost of the screen but principally because of the time lost for maintenance.

The solution developed by Akros Tecnologia, a small company from Sao José dos Campos (SP), is based on a system that automatically controls the positioning of the screen by way of an optical system. “In this manner, the screen is placed in the desired position without having any contact with the feeling gauge, thus avoiding wear on the screen and the equipment”, says the electronic engineer Benedito Carlos da Silva, one of the Akros partners and the coordinator of the project financed by FAPESP through the Small Business Innovation Research (PIPE) program.

The system, installed together with the screen, is made up of a sensor, which emits a laser beam, and a reflector. The intensity of the reflected beam shows the position of the screen. The information is passed on, via an optical fiber cable, to a microcontroller that perceives the variations and sends commands to a module of pneumatic working, responsible for the positioning of the screen, for the ideal condition for working.

Silva says that the idea to develop the Optical System for Automatic Screen Positioning (Sopat) came about during a professional visit to a paper factory in 1998, when he istened to reports on the limitations of the mechanical system. At that time Akros had been mainly working on the development of new products and on the building of machines for various industrial niches, after having felt the reduction of projects in the aeronautical and aerospace sectors, areas which had been the focus since the founding of the company in 1993. Thus, the paper industry had been of interest to Akros and Silva explained to his partners, a naval engineer and the other a graduate in mechanical and aeronautical engineering, the proposal to develop the electronic control system.

The engineers quickly perceived that they could not use the sensors existing on the market because during the drying phase of the paste the average temperatures go higher than 100 ºC and the environment is full of chemical fumes. For this reason the choice made was to develop sensors using optical fibers, immune to electromagnetic interference and resistant to aggressive environments. The electronic units (transmitter, receptor and microcontroller) were located outside of the machine, whilst the sensors and the optical fibers operate within the equipment because they are resistant to the adverse conditions.

Real tests
During the era of the presentation of the PIPE project, in 1998, Akros returned to providing services for Embraer, having been contracted to work on calculations and projects for the new family of regional jets. But this did not stop the company dedicating itself to the Sopat. The system interested some paper manufacturers, but the major obstacle encountered up until then for the installation of sensors in the factories was the operating condition of the paper production machines that worked up to fifty days without interruption, and had only one stoppage day during which all the adjustments, part changes and repairs had to be completed. For this reason only parts of the system were tested under real conditions of use, by making use of these stoppages.

Nevertheless, the difficulties did not discourage Akros’s partners. They contacted one of the main manufacturers of industrial equipment, the German company Voith. “A presentation on the system was made to the company’s technical personnel who became very interested”, related Silva. “Even at the world level, there is no equipment similar to that of the Sopat, which incorporates a microcontroller. The software used in the equipment allows for the calibration of the system to the most diverse types of machinery.”

The market for the Sopat, according to data from the Brazilian Association of Cellulose and Paper (Bracelpa), is extremely promising. There are 220 paper and cellulose manufacturing companies distributed throughout sixteen Brazilian states. As each factory has between two and six pre-drying sectors, and in each one various sensors are necessary (between two and eight) the potential demand estimate is in the order of 5,000 devices.

The adoption of the electronic system would not definitely signify the end of the mechanical system, which would be switched off but still attached to the machine. In emergency situations, such as the lack of electrical energy or breakdown of the Sopat’s component parts, the feeling gage would be liberated automatically and the working of the old system re-established.

The Project
Optical System for the Automatic Positioning of Screens (Sopat) (nº 98/14929-0); Modality Small Business Innovation Research (PIPE); Coordinator Benedito Carlos da Silva – Akros Tecnologia; Investment R$ 206,400.00