Tip of the Day 139: V to P Transfer: “Active” vs. “On/Off” Lights

I had someone question the meaning of the lights on the V to P Transfer tool on the eDART™. He thought the “Active” light indicated that the output was active or On and wondered why it stayed on until the end of the cycle.


The “Active” light (  ) tells you which of the methods caused the transfer to take place. Each one is to the right of the specific setpoint control. It “latches” or stays on until the beginning of the next cycle. At that time all “Active” lights clear and the transfer method on the next cycle will light a new one, if it changes.


The “On / Off” light (  ) is the current state of the output at any instant in time. It changes in syncrhonization with the OR2-D (or voltage) output that goes to the machine.


You may watch a 30 second video that demostrates the difference between the two lights.

[youtube=3M9N3DvOE0c]


You may also see the following appear if you are using Valve Gate control:




This means that the V->P transfer output fired because all of the valve gates had closed. The valve gate control tool has a setting on its own menu that lets you turn this function off if the process does not require it.

 

Tip of the Day 116: Pack to Hold Transfer Ignores Sequence

Some recent questions made me realize that not everyone understands how the eDART™’s Pack to Hold Transfer tool works.

A customer wanted to do cavity pressure control with an eDART™. He could not get the sequence signals from the machine (I think Injection Forward). He and our support person were concerned that they could not do cavity pressure control without the sequence signals. So, the point is…

You can do reliable cavity pressure control on an eDART without having “hard” sequence signals from the machine.

Of course without the signals you will be missing some analytical information, will need to set the volume zero manually and may need to adjust Sequence Setting thresholds to get good data. But the V->P transfer will work with or without wired sequence signals.

The title of this tip says most of it. Since mistakes in sequence wiring are not uncommon we decided long ago that the signal to transfer the machine on cavity pressure should operate regardless of the sequence inputs. This way the signal to transfer at a certain cavity pressure always goes out to the machine even if the eDART sequence signals are wired or named wrong.

 

Key Point: This ignorance of sequence signals applies only to the cavity pressure setpoint in the V->P transfer tool. The backup values and temperature transfer values DO require proper sequence signals in order to work correctly.

 

Here is an example in which someone named the screw run signal from the machine “Injection Forward” by mistake.

Of course the eDART needs to know when to turn the Control Output / V->P Xfer. off. It can use 95 % of the setpoint or the end of Machine Sequence / Injection Forward. This is set in the “Settings” menu on the V to P Transfer tool. This graph shows the proper injection forward signal with the V->P off point set to end of injection.

As you may notice from the above V->P tool actually does examine at least one sequence signal if you choose to set it up that way. But, if you tell it to turn the V->P output off at the end of injection it will leave it on if it finds that the cavity pressure is still above the setpoint.

Here is an example with a high pressure at the end of injection.

The “point” comes from a problem. A customer wanted to do cavity pressure control with an eDART™. He could not get the sequence signals from the machine (I think Injection Forward). He and our support person were concerned that they could not do cavity pressure control without the sequence signals. So, the point is…

 

You can do reliable cavity pressure control on an eDART without having “hard” sequence signals from the machine.

 

Of course without the signals you will be missing some analytical information, will need to set the volume zero manually and may need to adjust Sequence Setting thresholds to get good data. But the V->P transfer will work with or without wired sequence signals.

Tip of the Day 110: Reaction Time to Analog Cavity Pressure Signals

To reduce the press and eDART™’s reaction time (details defined below) to the minimum for high-speed molding on some presses it may be best to use an analog output from the eDART wired to the press’ cavity pressure signal input.

Some machines have both an external transfer input (from an OR2-D contact closure) and an analog input into which you can put a cavity pressure signal voltage (0 – 10V). The eDART can drive either type of output to transfer the press: contact closure or analog output.

We have found that some machines “scan” (i.e. “pay attention to” or “react to”) the analog cavity pressure sensor signal faster or more often than they do the contact closure signal from the OR2-D. In one case we noticed that when we used Control Output / V->P Transfer on an OR2-D to transfer the press the press reaction time was about 20 mS. When we used an AO1-D analog output signal set up as Plastic Pressure Output / V->P Transfer† the reaction time of the press was less than 10 mS. Some presses may even react with with no measurable reaction time delay, if they have a fast controller.

A little of this can be attributed to the actual time that the OR2-D takes to move his contacts from open to close (about 3 mS). The analog output is electronic and does not included this time. But we think the remainder is due to scan time on the press. Some presses seem to scan the contact closures less often than the analog signals.

 

Defining Reaction and Response Times

From tip# 109 remember that there is a delay in the press’ ability to react to a signal from the eDART. The eDART also has a slight delay in getting the physical value of the cavity pressure in, making a decision and sending the signal back to the press to transfer. I have used “reaction time” for these delays. In electromechanical systems like an injection molding press the time to do something after the actuators actually actuate is sometimes called “response” time. While trying not to confuse the issue too much let’s define the following:

• • “Reaction Time”: Time for a controller to react to a signal and pass a command to an actuator. The eDART has a reaction time (from cavity pressure to OR2 contact closure) and the press has its own reaction time (OR2 closure to beginning physical action).

     

• • “Response Time”: Time from when the actuator fires until the press physically completes its response (stops moving or reaches hold pressure).

     

• • “Total Transfer Time”: Time from cavity pressure level reached until hold =

     

    eDART reaction time + press reaction time + press response time

Click here for the next tip on Splitting the eDART Port Load for Speed

Tip of the Day 109: Anatomy of Press Transfer Time

In high speed molding of tiny or very thin parts it is critical that the machine transfer as quickly as possible in response to cavity pressure or temperature transfer inputs from the eDART™ When the fill time is only 0.2 seconds every 1/000th of a second (“millisecond” or mS) is critical. The eDART takes about 5 mS (for modest numbers of sensors) from the time the pressure or volume threshold is reached until the OR2 relay contact closes. The relays are specified to actuate in an additional 3 mS. Then the controller needs to recognize the signal and transfer to hold. Some of the machines time to transfer is electronic; i.e. controller computer reaction time. The remainder is mechanical: physically stopping the screw and reaching hold pressure. This tip relates to the controller reaction time .

Anatomy of Press Transfer

This is a particularly slow responding press (an old hydraulic)

The controller here takes 55 mS to notice the signal from the eDART and react by shifting its valves. It then takes another 150 mS to actually drop hydraulic pressure down to holding pressure. This makes the total time from reaching cavity pressure to reaching hold pressure equal to almost 0.2 seconds.

Anatomy of a Fast Acting Press

(the Arburg in the RJG lab)

Here you can see that the press reaction time from the estimated relay contact closure point is only 20 mS. It then takes the press about 30 mS to drop the pressure to the hold pressure. Total time from cavity pressure setpoint to reach hold = 58 mS. Presses with these controller reaction and physical response times are critical in high speed molding.

Next tip: Using an analog signal from the eDART to reduce reaction time.

Tip of the Day 108: Will the eDART’s V-P Actually Control Transfer?

When setting up the eDART™ system to supply an external transfer signal there is some danger to the mold if the transfer output fires but the machine does not recognize it. Here is a tip for ensuring that it is working before you turn control over to the eDART.

Test of Signal

First, the “V to P Transfer” tool on the eDART has a “Test” button on the “Settings” menu.

You can select this item, press the on and off buttons and check the press controller’s diagnostic page for changes in the input. The eDART does not allow you to manipulate the test button when the press is cycling.

Test of Function

However this only tells you if the input is going into the machine. It does not tell you whether the machine software will listen to it or when. To be absolutely sure that it the V->P will transfer here is a suggestion.

1. 1. Set up a process (D2 or D3) with transfer to hold on the machine’s screw position.

       

1. 1. Make sure the process ends with almost no cushion, probably bottoming out shortly after transfer. This will avoid mold damage if the transfer does not work.

       

1. 1.  

      Make a template.

      Place the cursor on the eDART‘s Cycle Graph slightly before the place where you see the machine dropping into hold.

       

1. 1. Read the volume number from the cursor and put it in the V->P transfer tool’s volume control, enabling the control.

       

      

       

1. 1. Enable the machine’s external transfer. Some machines allow both external and internal and some force you to use one or the other.

1. 1. The V->P volume switchover should show “Active” and the machine should transfer earlier as shown below.

      You should be able to move the transfer point around at will by changing the volume number in the eDART‘s V->P tool. If the curve does not change from the template (as shown below) then the machine is not accepting the transfer signal from the eDART.

      

      Here is an example in which the machine did change its transfer on the signal from the eDART. Therefore the external transfer is working.

      

1. 1. Once you are sure that the eDART‘s V->P will transfer the machine (early, as above) then you can turn on cavity pressure control, add shot size as needed for cushion and increase the V->P transfer volume number as a backup.

• • The machine may have the input but not the proper software installed.

• • It may have an “enable” position, injection pressure or time where it will not look for the external V->P until the enable position is reached.

• • The V->P may be wired incorrectly. For example one machine wiring guy thought the OR2-D would supply a 24V signal to the machine. He did not know he needed to “power” it.

• • The machine doesn’t like you.

 

You can put the Control Output / V->P Transfer on the Sequence traces on the cycle graph to see when the eDART is actually sending the V->P signal. For machines that transfer on a 0-10V analog signal you can put this signal (Plastic Pressure Output / V->P Transfer) on the cycle graph’s main pane (with the other curves).

 

Tip of the Day 102: Securing Individual Alarms

Per the previous tip it may have occurred to you that you may need to make machine setup changes in order to adjust the process for viscosity changes.Using training your technician should have re-centered the process for the new material using systematic techniques (e.g. checking fill-only parts etc) The new process may be producing good parts with the different material but the viscosity warnings could still be active as noted from the graphic of the previous tip:

The re-centered process should now match the templates and alarms inside the cavity, even if the machine settings had to change to accommodate the new viscosity. Any in-cavity part alarms should not be changed because they should have been correlated to good and bad parts. Remember it is the in-cavity or “intermediate” variables that best detect changes in part quality (see page 4 of “Finding Correlations to Part Quality“, tip # 55).

So you decide to allow the technician to re-set the viscosity warning for the new material. But you do not want him to adjust the in-cavity part alarms. We sell an optional tool for the eDART‘s that lets the engineer/administrator select which alarms are secure (part quality specific) and which the technician can change (process specific). This tool adds an additional column to the Alarm Settings window that the engineer can use to select which alarms are secure and which are not.

Of course the “Security” column itself is secured so that the technician cannot change it.

Note: Even though viscosity alarm changes are allowed technicians require training so that they do not simply make random adjustments. They must also know how to pick a reasonable new set of warnings for Effective Viscosity/Fill or any other selected process alarms.

Tip of the Day 101: Preemptive (human) Control using Warnings

The previous tip is a reminder that there other uses for the “Warnings” on the Alarm Settings tool. The “Warnings” that you add to the eDART’s™ Alarm Settings tool originally came from our plans to encourage 3-way sorting: Good, Bad & Ugly (see tip # 5). Few customers, however, have implemented this strategy of sorting parts into 3 bins. Herewith a description of using warnings without 3-way sorting.

The essence is this: Set “Alarms” (rejects) with the “Sort” switch On to automatically sort bad parts. Set “Warnings” (suspects) with the “Sort” switch “Off” to detect changes before bad parts are made. You can then read the status on the system overviews. If the status is “Warning” you can preemptively solve a problem before any rejects are made or parts stick or the press shuts down. Here is an example with cavity pressure sensors sorting and warning:

When observing the System Overview the supervisor notices a press with a “Warning” indicator on it

When he checks the summary graph on that press he can see that the parts are not yet being discarded but that they will be soon if he does not take action. In this case the action required was to clean the hot runner tips.

Warnings on Material Changes – Example without Cavity Sensors

Effective Viscosity / Fill is a key variable to monitor because the material itself is one of the most uncontrolled variables in the molding process (tip # 45). Variations in viscosity affect different parts to different degrees. But it is wise to always know that variation is occurring so that you can check your product for quality. In this example we have set a warning on Effective Viscosity / Fill.

Next tip: Securing Individual Alarms

Tip of the Day 100: Who is Controlling the Process?

For those running cavity pressure control using the eDART the question arises: Is the eDART controlling transfer or is the machine doing so? We have discussed adding various features to select a “master” control on the eDART and other ideas. Here is a simple one that you can use to discover whether the eDART is actually performing the control as required or not.

Typically what happens is that you have set up a very nice cavity pressure setpoint but someone has set a machine timer or position that does not allow the eDART to reach the setpoint. Or they have turned off external transfer on the machine. In any case the eDART tries to transfer the press but the press does not transfer at the right time. All you need to do to detect this is to set a warning or alarm around Value at V->P Xfer for the sensor you are using for control.

Warning Set, Process Transferring Correctly on Post Gate

In the following example the eDART IS doing the transfer. We have a cavity pressure transfer value set to 2600 psi on the Post Gate sensor. The warning window is set +/- 50 psi around the 2500 psi. The eDART uses the machine’s first stage signal to determine when the switchover occurs. The value it sees on the Post Gate sensor at the time first stage goes off is Value at V->P Xfer / Post Gate.

Warning Set, Process Not Transferring on Post Gate

Now consider the case below when the eDART was supposed to be transferring the press at 3000 psi. The value measured at transfer is closer to 2600. Again the warnings are set +/- 50 psi around the setpoint. In this case the eDART catches the fact that the transfer did not occur at the correct setpoint and sets a warning visible on the system overview, turns on an indicator light or sends a message through the Alert software.

Note that the “Sort” switches are turned off. In this example we have decided to alert someone using the System Overview, light tree or Alert but not to actually sort parts. We probably have cavity pressure integral or other alarms for actual part sorting using in-cavity measurements. If the transfer control is not operating from the eDART but the parts are still good (per the other alarms) then those parts do not need to be rejected. Yet the technician would be alerted to look at the problem and discover why the process is not using eDART control.

Note also that we have used a warning for this non-sorting purpose (“Add Warnings” with sort switch off). We suggest you create a policy of using warnings for things that require preemptive action but are not critical to the parts. If you are not doing 3-way sorting then the sorting switch should be off for those cases. When the supervisor sees a “Warning” on the system overview he knows that someone should look at the process to check the reason (under the count column) and adjust as necessary. When he sees “Alarm” he knows that the parts are being thrown away and immediate action is required.