N12 grew carbon nanotubes on a continuous stainless steel ribbon under tension, and problems with web handling proved to be a large source of loss. Among the issues resulting from uneven loading of the web were:
- Differential plastic deformation of the web at high temperature, causing a bow upon cooling
- Inability to maintain constant vertical distance from heating elements
- Web walk (side to side)
After writing a work plan, the first step was to do background research into the issue. After doing some quick calculations, I determined that using a laser distance sensor to measure either the frequency or amplitude of vibrations in the web should yield a usable result. The data taken in background document was from a Keyence sensor that I requested a demo for.
Raw data collected from the distance sensor
After reviewing the background work with my boss, we decided to move forward with a full measurement system. Speccing the sensor came down to sample rate, which was based on the natural frequency calculations (around 1000Hz), the range, which was based on the amplitude observed during the initial testing with the Keyence sensor (a few millimeters), and the resolution, also determined empirically (10s-100s of microns). I also put a lot of weight on the sensor having a fast, reliable communication protocol (e.g. Modbus TCP). In the end, I chose the Wenglor PNBC002.
Finding a sensor that met these requirements meant shelling out a few thousand bucks, so we decided to switch from the initial plan of having two sensors looking at either edge of the web, to having a single sensor on a rastering stage. The stage I selected was from Newmark Systems, and communicated over RS232 (however, offline testing was done with a manual stage, for ease).
Once everything was assembled and scripted (I used python for collection/processing/control, and Remi for GUI), I went about validating it in an offline setting. This was done on test rigs for two widths (1" and 15", current and future) of stainless steel web. The test rigs allowed for the application of uneven loads to the web, and a manual tensiometer was used as a rough gauge of the global (1") and local (15") tension. The results of this was two reports showing the efficacy of the system.
1" web test rig 15" web test rig
After offline validation, I had a mount block machined for the automated stage and incorporated the measurement into our data acquisition system. Unfortunately, we stopped using this reactor (and abandoned roll-to-roll altogether) soon after finishing.
Display interface for integrated system
