Well, that about wraps it up for eDART Sequencing. For now, anyway. Let’s quickly review the important points.

• The eDART sequencer uses Seq. Module Inputs, stroke, injection pressure and others to create Machine Sequence signals.

• The sequencer creates Machine Sequence Signals, even with with very few inputs when necessary.

• The eDART uses its internal Machine Sequence signals to compute summary values such as Effective Viscosity etc.

• It also uses Machine Sequence signals to make decisions for control (V->P Transfer, Valve Gates, Alarms and Diverter Controls, Basic 3-Stage etc.)

• The more inputs the customer wires up the fewer manual steps required to get good sequencing information. With few inputs he must set and adjust things to get good sequencing.

• The names given to the various inputs are critical. The eDART is, after all, a computer and cannot guess at what you meant to say rather than what you did say. Incorrect names given on Sensor Locations will create incorrect data.

Operating Rules of Thumb – Memorize These

• Wire up all possible sequence signals as soon as you can (especially in a permanent installation) to avoid the chance of forgetting those manual steps that are required without them. Demos require fewer or no sequence signals unless you want to show full capability and how the user does not need to set things if they are all wired up.

• Carefully check the On/Off status in Sensor Locations before accepting. Operate the machine and watch at the little green lights.

• Name the sequence inputs correctly.

• If you don’t know what a signal is doing, call it Not Used (or Unknown for analysis purposes). If a signal does nothing, call it Not Used.

• Always set the fill volume once the process has stabilized (until we incorporate Auto-Set Fill Volume into the sequencer).

I hear after sending yesterday’s tip that I got a little carried away with too much information in one message. If so, you can just file it for later reference if you need it.

Today, in more abbreviated form, we discuss how controls depend on sequencing.

• Pack to Hold Transfer
  
  
  
  This is the control least sensitive to sequencing. It will turn its output on when the pressure setpoint is above a threshold and off when below 95% of it. Even if you wire sequence inputs incorrectly it will still work. Of course if the Injection Forward signal comes on part way into the cycle then the cavity pressures may auto-zero at the wrong point creating wrong thresholds. If you use volume to transfer then a good Screw Run signal will ensure proper zeroing.
  
  
  
  V->P transfer has an internal setting that you can use to force Control Output / V->P transfer off at the end of injection forward. If the setpoint is still above the threshold it will stay on anyway. But if you want it synchronous with the machine then you need a good injection forward signal.

• Valve Gate Control
  
  
  
  It is essential that you have good Injection Forward, Screw Run and Mold Clamped Seq. Module Inputs to run this control. Unlike V->P it depends heavily on knowing the stages of the cycle in order to arm / disarm valve controls so as to avoid chatter and provide for re-open control.

• Basic 3-Stage Control
  
  
  
  Must have good Injection Forward and Screw Run signals because it uses these to start the cycle and zero the screw. Unlike V->P Transfer it cannot run on just a threshold basis any time regardless of sequencing. It is intimately connected to the actual hydraulic valve on the machine and so it must be properly synchronized with the machine’s sequence.

• Shuttle Control
  
  
  
  The Shuttle Control only needs correct the Seq. Module Input / Shuttle Position(s) and Injection Forward to work. It checks the shuttle position at the start of each cycle (Injection Forward)

• Alarm Settings and Diverter Control
  
  
  
  Of course your set alarms depend on the proper computation of values. If sequencing is incorrect you will get incorrect values.
  
  
  
  Beyond that the Alarm Settings tool does its computations at the end of the cycle. So it needs a consistent end in order to do the work and fire the Diverter Control outputs at the same time on each cycle. As long as the process is set up the same every time then any end of cycle will work.

We have covered most of the ways that the eDART can get its Machine Sequence information. The reason for getting the sequence right is so that the eDART will calculate accurate summary values. One of the most important values calculated is Effective Viscosity during fill. This is generally a variable over which you have no control but is a huge factor in analyzing problems. Most of the other summary values record how the machine is working. A few in-cavity variables (e.g. cavity fill time) relate to the start of fill sequence.

I have tried to represent the more important summary values computed in the graph below.

Here is the same information from the graph but shown in a list (plus a few more). These are the more important summary values that depend on Machine Sequence signals (the sequence signals computed by the sequencer, not those directly input from the machine).

Machine Sequence / Injection Forward

• All Injection Integrals


• Sequence Time / Injection Forward


• Gate Seal


• Mold Deflection Pressure


• 
  Peaks on cavity pressures are normally computed only during injection forward (unless selected otherwise in the Sequence Settings “Other” tab).

Machine Sequence / Fill

• 
  Effective Viscosity / Fill (both start and end of fill)


• Fill Shear Rate / Inverse Fill Time


• Sequence Time / Fill Time


• 
  Process Time / Cavity Fill depends on the start of fill being correct


• 
  Fill and Pack Time and Fill and Pack Integral depend upon the start of fill being correct


• 
  Average Values for Fill Flow Rate (volumetric) and Fill Speed (linear)


• 
  Process Metric / Match Error (depends on correct fill start; currently generated by Process Match Meter)


• 
  Dynamic Pressure Loss (needs end of fill to know when to compute pressure loss)


• 
  Values at V1->V2 Xfer (if a 3-stage process).
  


• 
  Value at V->P Xfer. if it is a 2-stage process (no pack)

Machine Sequence / Pack

• 
  Average Values for Pack Flow Rate (volumetric) and Pack Speed (linear)


• Sequence Time / Pack Time


• 
  Value at V->P Xfer. (also works in 2-stage process if there is no pack)

Machine Sequence / Hold

• Sequence Time / Hold Time


• Average Value / Hold Pressure


• Average Value / Stable Hold Pressure

Machine Sequence / Screw Run

• Correct zeroing and direction of the stroke sensor which in turn affect Machine Sequence / Fill and all that follow from it.


• 
  Sequence Time / Cycle Time if there are no other sequence signals after (such as Mold Clamped)


• Sequence Time / Screw Run


• All Cycle Integrals (unless the Sequence Settings “Other” tab is used to set a fixed integration limit)


• Average Value / Backpressure


• 
  Decompresssion / Shot Volume and Decompression / Shot Stroke
  

Machine Sequence / Mold Clamped

• Sequence Time / Cycle Time


• Sequence Time / Mold Clamped


• 
  Cycle Integrals if time before mold clamped is set up for the integration limit in the Sequence Settings “Other” tab

We have covered Machine Sequence / Injection Forward and Machine Sequence / Fill ad nauseum. Let’s complete the punishment by covering the rest.

Sequences Dependent on External Inputs

• Machine Sequence / Screw Run:
  
  Usually goes on and off with the Seq. Module Input / Screw Run, directly matching the sequence input.
  
  
  
  Can also use thresholds on Revolution Rate / Screw Motor (as in the Sumitomo Oscillograph Interface), Hydraulic Pressure / Screw Motor or Flow Switch / Screw Motor. The last one has not yet been built as a product.
  
  
  
  Remember: Each of these is designed to go ON when the motor starts turning and OFF when it stops (NOT after suck-back).

• Machine Sequence / Mold Clamped
  
  This signal directly follows Seq. Module Input / Mold Clamped.
  
  
  
  If you have no Seq. Module Input / Mold Clamped but do have both Seq. Module Input / Mold Opening and Seq. Module Input / Mold Closing then the sequencer will create Machine Sequence / Mold Clamped. It will use the end of Mold Closing for Mold Clamped ON and the start of Opening for Mold Clamped OFF.

• Machine Sequence / Machine in Manual
  
  This signal directly follows the Seq. Module Input / Machine in Manual.
  
  
  
  If you have Seq. Module Input / Semi-Auto or Auto then the sequencer inverts it and creates an internal Seq. Module Input / Machine in Manual.

• Machine Sequence / Mold Opening and Mold Closing
  
  These signals simply follow the action of their respective Seq. Module Inputs. The sequencer will also use them to create Machine Sequence / Mold Open like it does with Mold Clamped. Machine Sequence / Mold Open will go ON when Opening goes off and OFF when Closing goes ON.

Sequences Generated by the Sequencer

These Machine Sequence signals have no corresponding Seq. Module Input signal in the “real” world. Instead they are derived entirely from the other sequence signals. The eDART uses them to do internal computations (e.g. Average Value / Pack Speed) or for teaching people the stages of a process.

• Machine equence / Pack
  
  Goes ON at the end of Machine Sequence / Fill and OFF at the end of Seq. Module Input / 1^st Stage. If the eDART is doing V->P control then it will also go off at the V->P transfer point (when Control Output / V->P Transfer goes ON).

• Machine Sequence / Hold
  
  Goes ON when Machine Sequence / Pack goes off. If there is no Pack (i.e. no V->P control or 1^st stage) then Machine Sequence / Hold goes on when Machine Sequence / Fill goes off. The eDART assumes a 2-stage process in that case. Hold then goes off at the end of Injection Forward.
  
  
  
  If you provide the eDART with a Seq. Module Input / Second Stage then it the sequencer will make Machine Sequence / Hold match it.

• Machine Sequence / Plastic Cooling
  
  Goes ON when Machine Sequence / Fill goes off and OFF at the last point in the cycle when the part could be cooling. If you have Mold Clamped. then it uses the end of Machine Sequence / Mold Clamped. If not it will use the end of Screw Run. If you have a Mold Open signal then this will be the end of the cooing point.

In Tip #36 you saw how the eDART uses a fixed fill volume number to mark the end of fill, as the machine says it.

Typically the user forgets to set the fill volume when he starts up a mold¹ (see footnote at end). The sequencer starts with a default fill volume of 10000 cu. in. – a number that volume never reaches. So it uses the next best thing to denote the end of fill: peak injection pressure.

You can notice immediately that it is using peak injection pressure because it can’t figure out where fill ends until the end of the cycle. So the Machine Sequence / Fill trace (orange below) goes up at the start of fill and then just “sticks” there, drawing no horizontal line.

The Problem: What if Injection Pressure Peak is Not at End of Machine Fill Speed?

Many times there can be a cold slug in the nozzle or in hot runner tips that the injection unit needs to push out to get injection start. So the peak pressure may not be that at the end of fill. This will create a false end of fill and so not compute good viscosities, speeds and times. Here is an example.

What if the Peak Alternates

Sometimes the spike from the cold slug is very close to the actual peak when the machine slows down. In that case the end of fill may oscillate between the two times to peak as shown below. This causes the computations of viscosity and times to vary wildly and create useless data.

  ¹The footnote at the end

Since it has been a perennial problem that people forget to set the fill volume I have developed a tool that does it for you: “Auto-Set Fill Volume”.

This is a bit of an experimental tool. It watches the stroke / volume sensor and uses the first dramatic slow-down (change in slope) to decide where the machine fill ends. It waits for 10 stable cycles in which it gets the same end of fill volume. Then, if the sequencer does not have a fill volume set yet it puts in the average from those 10 stable cycles as the fill volume. If the sequencer already has a fill volume the Auto-Set Fill Volume function will not overwrite it.

This has worked when tested against most of the customer data we have collected here and is running at one customer. It has some limitations as follows.

• If you never run stable shots very long it will never set volume (i.e. as our students often do in the lab).


• If you intend to run rheology curves and your machine goes to a different end position as you change speeds then you will need to set the fill volume manually before running the rheology curve.


• If there is noise on the stroke signal it would get the wrong fill volume.

As the previous tip discussed the best measurement of “filling” from the machine’s point of view is to have fill start after the suck-back is “used up” and then end fill at a fixed volume. This provides a stable signal for such summary values as Effective Viscosity / Fill, Average Value / Fill Flow Rate (and Fill Speed), Process Time(s) / Cavity Fill and Fill and Pack computations. In valve gate control the start of fill is volume = 0. This provides a stable reference point for opening and closing valves on volume.

In the graphic below fill begins when the screw moves forward past the point where it was when the screw motor stopped on the previous shot (volume = 0). The “Defined fill volume” of 1.025 cu. in. was set by the user. This is commonly done on the cycle graph with the cursor but can also be done by making a short shot and pressing the button on the “Sequence Settings” Fill tab.

If the user does NOT set the fill volume (after the process has stabilized) then the eDART will use peak injection pressure as the end of fill. More detail to follow.