Speed synchronization in vertical filling machine

[Hossamhegab]

Dear all
Iam working on a project for continuous vertical filling machine and this a video for my application
https://youtu.be/coQyr06dDK8
My question is
How can I syncronise the speed of drawing belts(driven by VFD) and horizontal jaws (driven by servo) during sealing and cutting
Any tips will be helpful
Thanks in advance

 

[drbitboy]

Dear all
Iam working on a project for continuous vertical filling machine and this a video for my application
https://youtu.be/coQyr06dDK8
My question is
How can I syncronise the speed of drawing belts(driven by VFD) and horizontal jaws (driven by servo) during sealing and cutting
Any tips will be helpful
Thanks in advance

From the video, it looks to me that there are registration marks on the packaging material, detected by an optical sensor.

Could it be as simple as using the optical sensor detecting that registration mark as a trigger for seal-and-cut? And the return of the jaws after the seal-and-cut is a passive device (springs, or weights and air-shocks)?

When the registration mark is past the sensor, that would release the jaws, then a spring or summat similar would open them, and another spring/whatever would return them to the top position, quickly enough that they get to that top position in time to wait for the next registration mark event.

That next registration mark would trigger closing the jaws, sealing and cutting, and the package motion, plus friction, would draw the jaws down (again, against some kind of spring or other malleable resistance device).

Rinse, repeat.

Obviously there might be some empirical work to put the registration marks at the right place on the packaging, and tuning the passive return mechanism. But other than that the process looks repeatable.

[Update: d'Oh; the registration marks' positions could probably be estimated with a tape measure to the nearest inch or so, and then the tuning process adjusts the position of the optical sensor; this requires designing the optical sensor mount to have enough room and to be adjustable]

There are a ton of motion control people here, so you should wait for answers from them.

 

[BlueAltezza]

Which axis is the one you want to treat as the master?

If the VFD, then see if the drive has a pulse or analog output. Use that output to set the speed of the servo. Servos typically react quicker, so an analog output could be feasible.

If the Servo is the master, then you'll have to see if the VFD has an encoder input as a command/master signal. If the servo drive can't output it's own encoder signal, then an encoder may have to be installed on the servo axis.

I've tried to do somewhat precise following with AC drives and found the best performance when a drive can use a pulse input signal, not an analog signal. Some drives like a Fuji Ace can be wired in closed loop and performance is really good for an AC drive.

 

[Hossamhegab]

That's great
But I still have a question , if I need to cut the web to get a bag of 16cm length how can I determine the speed of jaws servo during moving up automatically, and so for various bag's length

 

[drbitboy]

That's great
But I still have a question , if I need to cut the web to get a bag of 16cm length how can I determine the speed of jaws servo during moving up automatically, and so for various bag's length

If the jaws' closing is triggered by the registration mark, then it does not matter if the jaws return to the top position early, so I would send them up as quickly as possible, or at least quickly enough to be ready for the shortest bag's length (time, or distance if the rate of the packaging movement is constant and independent of the bag length).


That said, the calculation of the up rate should be straightforward.

Assume

1. Sp is the speed of the packaging, cm/s
2. Lb is the bag length, cm
3. Tjact is the time it takes the jaws to perform all actions except return, i.e. time to [close] + [seal] + [cut] + [open], s
4. The jaws are moving down, at rate Sp, with the packaging for the entire time Tjact

Assumption 4 should be conservative (i.e. model the jaws at a lower position), because the jaws will be in contact with the packaging neither for the start of [close], nor for the end of the [open], operations

From there we can to calculate the time available, and distance required, for the jaws' [return]. Try the following steps

• Ttot is the total time available for one complete cycle
  • Ttot = Lb / Sp
• Tjpad is pad time, a user-specified parameter, an amount of time between the end of the jaws' [return] and the start of the jaws [close]; zero may be a suitable value for Tjpad
• Tjrtn is the time available for the jaws to return i.e. the time from the end of the [open] to the start of the [Tpad]
  • Tjrtn = Ttot - (Tjact + Tjpad)
• Ljact is the distance the jaws travel down during their action
  • Ljact = Tjact * Sp
    • Cf. Assumption 4, above
• Ljrtn is the distance the jaws travel up during their [return]; this is the same as the distance traveled down, Ljact
  • Ljrtn = Ljact
• Sjrtn is the required speed of the jaws' [return]
  • Sjrtn = Ljrtn / Tjrtn

This is a very simple model of your process, so you may need to modify it. E.g. it assumes the transition from the jaws going down at Sp to up at Sjrtn is instantaneous; you may want to modify that to add in startup and stop ramps for the servo control algorithm, which would add some parameters for the ramps and change the form of the final Sjrtn equation.