Final Design

Overall System

• • Free spinning primary spool

  • Pinch-roller based feeder mechanism to provide decoupled peeling force on the Nafion to remove it from the primary spool, and let it out to the rest of the system

    • One roller motor driven, other free rotating, spring applied force to pull the rollers toward each other and maintain contact to provide normal force required for friction to overcome peel tension

  • Tension sensor based on load cell and idler pulleys

  • Servo driven guide to ensure Nafion is uniformly wrapped along the height/thickness of the secondary spool

  • Motor driven secondary spool with attachment points and removable cap

  • LCD screen + 2 buttons + light/buzzer + master on/off switch UI and internal control system

  • Enclosures for all electronics, wires, etc.

  • Base plate with handles for self-contained mounting and easy transportation

Primary Spool Mount

The supply spool of Nafion must be allowed to freely rotate as the pinch-rollers peel the tubing off the spool. The operator must also be able to to easily put on and take off the spool. Therefore, the mount for the primary spool was made as a smooth aluminum tube mounted horizontally by welding to a vertical plate on one side, with a smaller outer diameter than the inside of the primary spool’s hole. On the unsupported end of the tube, a pinhole was drilled to allow for a removable locking pin to be put in place by the operator to keep the primary spool from falling off the mount during operation.

Pinch-Roller

The pinch-rollers come in direct contact with the Nafion, and apply the tension force to the tubing which overcomes the self-adhesion force which causes the Nafion to stick to itself when it is being removed from the primary spool. The system features two spring loaded polypropylene rollers, one of which is driven by a DC gearmotor, which peel the Nafion off the supply spool when the tubing is fed between the rollers and the motor is turned on.

Tension Monitoring Idler Pulleys

To ensure the Nafion tubing doesn’t undergo damage during spool transfer, and doesn’t wrap too tightly on the take-up spool, the system features a tension monitoring subsystem consisting of a set of idler pulleys and load cells in tension zone two. After passing through the pinch-rollers, the tubing gets routed by the first idler up vertically to a second idler, which rotates on a static shaft which is mounted to a pair of load cells, and then goes back down to a third idler and continues on to the take-up spool. With this arrangement of the idler pulleys, the signal being output by the load cells can be directly correlated to the tubing tension.

Servo-Driven Tubing Guide

The tubing guide is to allow for uniform distribution of the tubing on the take-up spool. As the take-up spool turns and wraps the material onto it, the tubing guide moves back and forth at a speed proportional to the take-up spool speed to make the material wrap on uniformly along the length of the take-up spool. Similar to the pinch-rollers, the tubing guide comes in direct contact with the Nafion, so was made from non-contaminating polypropylene. It features a simple convex, smooth hole at the top for the Nafion to pass through, and connects the bottom to a servo motor which is programmed to sweep the polypropylene guide back and forth. This whole operation allows the tubing to pass through the guide at different points along the arc it sweeps and be wrapped on to the take-up spool uniformly along its length.

Take-up Spool

As a part that comes in direct contact with the Nafion, the take-up spool is made of polypropylene, with a large diameter cylindrical geometry. It comes apart into two separate pieces which can be easily connected and disconnected with the use of a locking pin. The take-up spool holds the Nafion during winding, and the removable cap gives the operator access to remove the tubing once winding is completed. The locking pin allows torque to transfer from the large motor driven piece to the smaller cap piece. The two pieces are both rigidly connected to shafts which are radially supported by sealed bearings, and the whole spool assembly is rigidly coupled to a DC motor which drives at a velocity proportional to the tubing tension in tension zone two, which nominally matches with the pinch-roller and servo speeds.