Tip of the Day 122: Set Screw Bottom to Get Cushion
Recently a customer asked if the eDART could compute the cushion. It can. But there is a manual procedure required that is sometimes forgotten. It looks like this:
- Start the job on the eDART before purging the machine.
- Sometime during the purge sequence pause while the screw is all the way to bottom (machine’s stroke indicator = 0).
Open « Set Screw Bottom » from the main menu and click the button that says « ».
- Continue starting up the process on the machine.
The eDART will now compute two summary values that you can put on the Summary Graph, set alarms on or view on the Cycle Values window. These are Cushion / Shot Stroke and Cushion / Shot Volume. Each is the amount of travel remaining from the point furthest forward of the screw to screw bottom. Variation and trends in these values indicate possible check-ring (or non-return-valve) problems.
Tech Stuff:
- The eDART remembers screw bottom between jobs. So technically you don’t have to re-set it on each job start. I suggested a re-set at each job start because the tech starting the job may not know that sensors were unplugged or the eDART restarted or powered down; all events that require a reset.
- Un-plugging the stroke sensor looses the location of screw bottom. Also, if the ports are not split (tip # 111 ) and the stroke sensor is on the same Lynx port as the mold sensors then plugging and unplugging mold sensors can confuse the stroke sensor as to where bottom is. Split the sensors so that mold sensors are on one port and machine (including stroke) are on the other.
- The reason that the eDART requires a screw bottom reset is that the stroke encoder is a « relative » device. It has no marker on the cable for an exact position of extension after power up. While this requires the extra step it makes the stroke sensor a very precise solution for a wide variety of machine sizes without the need to carry a whole line of absolute encoders of different lengths.