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Figure 1 shows an application example of the vertical dancer in which Length A from the fulcrum to the axis core of the dancer roll coincides with Length B from the fulcrum to the supporting point of the non-friction cylinder (hereinafter to be referred as NFC). In this case, the thrust equivalent to the thrust of the NFC except for mechanical losses will be transferred to the dancer roll as changing its direction. For instance, when the thrust of the NFC is 50 N, -50 N will be transferred to the dancer roll. Since the winding angle of the base material of the dancer roll is 180 degrees, the thrust of the NFC will be divided into two, namely the upper and lower streams of the dancer roll, and be balanced with the thrust of the NFC at a tension of 25 N.
In this kind of application, the dancer arm will be moved in a direction of the upper or the lower side of the dancer roll if the film tension varies due to some factors. The amount of movement will be transferred to the NFC through setting the dancer arm fulcrum as the center, and then the cylinder will be pulled or pushed. Thereby, the internal pressure of the NFC will vary accordingly. Since the electric-air converter and the precise pressure adjustment valve are provided in the NFC air intake part, amount of air will be increased or decreased automatically according to the variation of internal pressure of the NFC. If a ratio for A and B of the dancer arm is large as shown in figure 4, the dancer performance will be deteriorated consequently due to the total distortion of the dancer arm, mechanical losses at the NFC, bearing friction at the fulcrum, and deviation of the moment of inertia when the dancer arm rotates as the dancer equipment with the dancer fulcrum as the center, even if the amount of movement of the dancer roll is large according to the ratio. In order to prevent this, avoiding the application shown in figure 4 is recommended.
In the case of NFC’s application for the dancer, only a single unit must be used. If you use two, they may generate defective conditions due to interference between the two of them. |
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