Importance

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Abstract

Hitherto, in the tension control for a reel, it is impossible to exceed the tension controlling range of about 1:10 which is determined by the tension controlling range of a single DC motor, so that for the reel which requires a tension controlling range over 1:10, a plurality of DC motors have been combined and used or a gear ratio between the reel and the DC motor has been changed for many years so far. In this invention an attention is paid to the fact such that the unpreferable phenomena such as a change in characteristic due to an armature reaction, and deterioration of rectification or the like which are caused by setting the field system to a low level can be fairly suppressed by limiting the setting and controlling range to a low region of an armature current. The field system is set to a low level so that a ratio of a field magnetic flux to a diameter of a coil becomes a value lower than the maximum value and also the upper limit of an operating armature current which is practically applied is set to be low, thereby making it possible to perform the stable tension control within a low tension range which could not be realized so far by a single DC motor.

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First Claim