| 摘要 |
<p>The tensioning device comprises at least two wheels (3, 4) with a peripheral race, rotatably installed, with substantial parallel axes, on a support (5), at a certain distance from each other. The support (5) can be orientated by being revolved around an axis substantially parallel to the axis of the wheels (3, 4), in order to move the wheels from a position in which they are not into contact with the thread (2) and are on opposite sides relatively to it, to a position of peripheral engagement with the thread (2). According to the angle of orientation of the support (5), the thread (2) engages a longer, or shorter, portion of the peripheral race of the wheels (3, 4), running according to an "S"-shaped, or "Z"-shaped trajectory. The larger or smaller extent of engagement determines a larger or smaller value of rolling friction, and therefore a higher or lower thread tension. By means of a programmed movement of the support (5), the thread tension value during processing can be varied according to a programmed schedule.</p> |
