| 摘要 |
An assist drive assembly for adjusting tension in a web generated when the web is moved over a roller in a contacting relationship therewith. A plurality of north and south pole elements are disposed about the roller. A controller is coupled to a magnetic pole sensor and an magnetic coil. The magnetic pole sensor and magnetic coil are disposed adjacent the north and south pole elements such that, when, during rotation of the roller in a direction of rotation, as a result of the web moving over the roller, the magnetic pole sensor observes a south pole element a first signal is generated that actuates the controller to energize the magnetic coil to generate a north pole field that attracts an immediately adjacent south pole element thereby imparting a torque to the roller in a direction of rotation of the roller.
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