| 摘要 |
A mechanism (C) for tensioning a web extending from a rotating roll (R) includes three fluid relays (200-202) and two amplifiers (204, 205). A variable pressure pilot signal (P) drives a piston (66) of a rotational control apparatus (A) to create a pilot torque to the rotating roll (R). In the event that the variable pressure pilot signal (P) exceeds the bias pressures (B1-B3) of the fluid relays (200-202), the pistons (64, 68, 70, 72 and 74) are driven by fluid relays (200-202) to create relay torques to the rotating roll (R) in addition to the pilot torque in direct proportion to differences between the variable pressure pilot signal (P) and the bias pressures (B1-B3). The relay torques created by the second and third relays (201, 202) are amplified by the amplifiers (204, 205). Thus, the rotational control apparatus (A) can be fully utilized for its full torque range while still providing enough resolution to control tension of the web (W) precisely.
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