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FLEXO Magazine : July 2007
hot technologies w w w . f l e x o g r a p h y . o r g J U LY 2 0 0 7 F L E X o 2 5 We are just at the beginning with linear motor technology. For sure, the more we use linear motors, the more advantages we will discover. The next generation of presses is going to allow the control of the pressure between the print cylinder and the sub- strate, and the anilox roller. This will give the printer the ability to determine, generate and maintain a required dot gain through- out the print job. It is widely accepted that if flexo presses were to be able to control dot gain better then ball screw technology allows, they would be able to compete in markets that are typically controlled by rotogravure and offset. Linear vs. rotary Motors Both rotary and linear motors move cylinders to a working position, therefore, in that sense, they are absolutely identical. The first major difference between them is the way the motor is connected to the moving load. The rotary motor requires a trans- mission chain to be connected to the cylinder, which means cou- plings, joints, screws and housings that go from the motor, which is mounted to the print section frames, and to the cylinder. Unlike rotary motors, the linear motor is part of the load. The linear motor is an integral part of the cylinder support structure, and doesn’t require additional connections to the cylinder. The immediate advantage of linear technology is that backlash is completely removed, thus the achievable precision of the print and anilox mandrel’s positioning is much higher then allowed by rotary motors. Additionally, both the linear motor and the absolute encoder (position read out) move together because they are both part of the mandrel support. The first, immediate result of this comes from the total absence of relative position errors, which instead is unavoidable with rotary motors. The end result is that the linear motor, encoder, and mandrel form one single component with no joints and no connections to allow backlash or deflection. Linear technology can also move the cylinders at a much higher speed, which can reach six meters per second, allowing a further reduction in the changeover time. It is a maintenance free part, since the stator and the rotor don’t touch each other. In general, the linear motor is smooth and silent and doesn’t gener- ate any vibration. speed and efficiency The linear motor is not used to rotate the cylinders. For this reason, it doesn’t affect the press running speed at all. However, the first machines manufactured with this technology indicate the motor adjusts to the speed ramp-ups and does not require continued adjustment until the press reaches its final production speed. In addition, the linear motor is not more energy efficient, when compared to the rotary motor. There is no substantial ef- ficiency difference between the two motors. The advantage of using the linear motor in terms of energy efficiency comes from the fact that this motor forms an integral part with the load to move, with no sliding or dynamic frictions and for this reason
Golden Anniversary Commemorative Journal