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Constant Tension Drag Clutch

IP.com Disclosure Number: IPCOM000124036D
Publication Date: 2005-Apr-06
Document File: 4 page(s) / 135K

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A ribbon supply and clutch assembly that includes a ribbon supply roll, a spindle, and a clutch assembly. The ribbon supply roll is supported by the spindle, which is rotatably coupled to the clutch assembly. As a layer of ribbon is removed from the ribbon supply roll, the clutch assembly applies a predetermined opposing torque to the spindle. The opposing torque advantageously maintains a constant tension on the ribbon despite reduction in supply roll diameter. If ribbon is instead being wound onto the spool, the clutch will decrease torque as the diameter increases.

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1) Field of the Invention

            The present invention relates to a device and method for varying the torque applied to a spool of media.  More particularly, the present invention relates to a mechanical device for tailoring the torque output of a clutch associated with a spindle on which the spool is mounted to the amount of media on the spool.

2) Description of Related Art

            There are many operations which utilize media wound on a spool wherein the material is either gradually drawn from the spool or wound about the spool.  In many such operations, it is important to maintain a uniform tension on the media as it is either wound on or from the spool.  Tension can be maintained by controlling the torque of the spool.  The torque varies with the outer diameter of the rolled material.  In general, as the outer diameter of the rolled material decreases, the torque required to ensure proper tensioning increases.  Similarly, as the diameter of the roll of material increases, the amount of torque decreases.

            The varying torque requirements of the varying diameter rolls may cause inconsistencies with equipment having feed mechanisms that draw or wind wound material with a constant force.  Using a thermal printer as an example, the ribbon used in these printers is typically flimsy and subject to wrinkle when slack.  Wrinkling of the ribbon can seriously affect print quality.  Similar problems could pervade a variety of industries, such as papermaking, textiles, or any other application using rolled materials.

            The inconsistencies could be addressed by a clutch connected to a spindle on which the spool is maintained that would serve to reduce resistance on a spindle as the amount of material on the spool was reduced, i.e. as the outer diameter of the roll decreased.  Conventionally, only relatively complex computer controlled devices have been available to correlate the amount of ribbon remaining on a supply spool to the torque output of the ribbon supply clutch.  Previously, if such complex devices were not used, there was no mechanism to compensate for the gradual reduction of ribbon roll diameter that occurs during printing, thus, producing an increased ribbon tension, which has a detrimental affect.  There are some conventional mechanical clutch systems that us spring biasing to create torque.  However, these systems only use crude adjustments for altering torque.  It is therefore desired to provide a simple and inexpensive ribbon supply clutch that may be used to control the torque required in the use of rolled media. 


            The present invention automatically increases the torque provided by the clutch assembly as the diameter of a rolled material is reduced and may also decrease the torque as the diameter of the roll increases.  The invented clutch is desc...