Tip of the Day 85: False Cycle Start on Press Power Up

We have observed some sequence behavior on some machines that some of you will need to know.







Key Point: Always start the job on the eDART after powering up the machine (and before purging).

Note: This is especially important on valve gate control systems because the valves are told to operate on the eDART‘s interpretation of Machine Sequence or its reading of stroke and volume.



Why?



First, this is particularly true of electric machines or machines that use analog signals wired to Analog Input modules to provide position and pressure to the eDART. These analog signals tend to do strange things on startup. Sometimes they have a spike or a sudden “lurch” from zero to a specific position voltage. Often this jump forward on a stroke signal will cause the eDART to think the cycle has started. But then everything stops.



As mentioned in earlier tips the eDART is designed to recognize changes in position as action (e.g. injection start) on the machine. The RJG stroke encoder only provides position changes when the screw physically moves. So it is not likely to pick up false motion. Unless, of course, the screw jerks on machine start.



The Sumitomo machines are particularly prone to this false trigger problem because they go through a calibration cycle at power-up. The screen capture below documents what happens. Note that the eDART has already been run once on this machine so it knows that the stroke signal is inverted: 0V in from the machine is full scale positive stroke on the eDART and 10V is full negative stroke.




  1. Here is the sequence on the Sumitomo at power-up:

  2. The stroke signal moves forward slightly (small voltage drop)

  3. The eDART picks this up as forward motion and assumes start of Machine Sequence / Injection Forward

  4. The injection pressure voltage goes to full scale (+ 10V)

  5. The screw turns slightly (not sure if it goes backwards as well as forwards).The eDART sees this as screw RPM and assumes screw run forward and back.

  6. The eDART ends injection forward at start of screw run, having nothing else to use first.



Note that on fully digital Sumitomo machines where Screw RPM is not wired in (using Seq. Module input instead) there may be no cycle end. So the eDART‘s Machine Sequence / Injection Forward simply stays on waiting for the end of the cycle. This can cause valve gates to open and stay open if the valve gate control is set to open during manual (or manual is not on).



The fully digital Sumitomo machines are models SEDU and SEHS/HD. Some earlier models had digital sequence signals as optional outputs. Contact RJG customer support for details.

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