The basic dispensing is fine, but with high viscosity liquids, puddling and trailing can occur when the dispense head turns on and off. In order to battle this problem, we arm you with the "back-to- back" PATH method of turning on outputs in mid-path. For this to work, the best thing to do is to have one output for dispense on and one for dispense off. Going this route, we use the POST field in the software to turn on these outputs since there is no way to turn them off in the post field. By keeping them separate, we can turn on the head and turn off the head without breaking the PATH statements.
So how does this work?
Since the PATH command (and ARC, CIR) use b-spline approximation, we can turn on outputs before the path is completed. B-spline approximation looks three points ahead in order to determine the route and speed the actuators will take to best fit the curve.
Normally, with the POST field, and using one PATH command, the output will only turn on once the PATH is finished. But if you place the PATH commands back to back, splitting up the path, you can turn on outputs before the PATH is complete. B-spline approximation sees back-to-back commands as one continuous math calculation allowing the user to post outputs in the POST column.
For example, if you want the dispense head to be fully off by position 24, with no trailing or puddling, you would turn on the output to toggle off that dispense head three points before, at 20.
The code would look like this:
Where "303" is the output used to turn off the dispense head. This could then be applied to turning the dispense head back on so that the liquid is running before reaching the start position. By combining both the start and stop with back-to-back PATHs yields a much cleaner, smoother dispensing system. The following I/O has been chosen by the user:
- Output 303 : "On" = dispense off
- Output 304 : "On" = dispense on
- Output 305 : "On" = purge on, "Off" = purge off
- Input 12 : "On" = go to purge location