chain conveyor speed control opinion

I hate to be different but I stand by my statement that torque control for the slave is the only way to do it. Do not consider a flux vector drive for any slave drive in that configuration.
Here is a link to Yaskawa elearning video explaining it. I would encourage everybody to heck out there videos. I know they are from Yaskawa and most of you don’t use them but they are free and the principles apply to all drives.

https://www.yaskawa.com/support-tra...let_selectprodsubgrp=&_yastabstemplate_WAR_ya
I have been doing drives for over 30 years, doing factory service for a numberof those years. And have seen many try to do a common load system with all the drives in speed control. Just looking at the lines run it does look like they achieve that. But if you look deeper and watch what the drives and motors are doing you will see they are actually fighting each other. One will pull high current and drop the output frequency back a little while the other will deliver less current while the frequency go up a little. And them the condition reverses. If you try to set up both drives as flux vector drive the y will both try to be speed masters on the system with no motor slip so one or both drives will over current and shut down.
As we all know there can be only one master in any system at a time.

Think about the

Chain conveyor and how it’s made I this case it is over 1300 feet long the average ling of this type of chain is about 6 inc long with a pin at each end. Each pin has fitting tolerance of maybe 1/32 of an inc each but you have over 2600 pins the slop on each will add up and increase over time ( they never get better) We all know you can’t push a chain it can only be pulled so each drive will have to pull its share of the chain. But the load on the chain is never going to be loaded equally over the length of the chain. And that load will be constantly changing as it runs. You couple that with the accumulated ware of the pins and other parts of the system it becomes increasingly impossible to have both drive run at the same exact speed and actually share the load. You have to decide either to match speed or share the load you can’t do both .
I has a system a few years ago the chain conveyor was a loop of about 2000 feet with 3 identical drive systems same VFD same gearbox everything was identical on each system. The original designer set it up as a speed follower. In the PLC they had over 10 rungs of very complex math code to try and get them to share the load. When I observer the PLC code it was commanding a constantly changing speed command to each VFD of between 5 and 10 HZ none were getting the same speed command. The calculations were using the VFD current to calculate the necessary VFD speed command not working very well. To the human eye it looked like the line was running very well. So they were happy with it. All 3 of the VFD’s were just V/F control allowing the motor speed to slip back from the VFD output speed depending on load. Using flux vector VFDs on those would be a disaster.

I actually installed and set up the first Flux Vector drive brought in to the US. That was about 1993 I think
They were for a pair of 30 ton bridge cranes, for the bridge drives the bridge was 80 wide, motor and gearbox on each end of the bridge. A Flux Vector VFD for each motor, new matched gearboxes on each and new precision machined wheels on each drive as well. We had 2 cranes that had to run together with a common load shared on the hooks of both cranes so it was 4 drives in total all set up identical in every way the crane bay was about 800 feet long. But when we ran the cranes they would not run more than about 50 ft before the bridge would rack so far that it would try to jump off the rails. We ended up having the VFD design engineers come in from Japan to do a set and discovered the only way to make it work was to detune one of the VFDs to allow it to have less precise speed control over one motor on the bridge ( More slip in the motor) It ran great for over 5 years they normally replace their VFDs about every 5 years or so these were replace with a newer models.
A thought to keep in mind, no 2 VFDs no matter who’s they are will ever produce exactly the same output frequency you may not be able to see the difference but over a long time it will show up.

As for the comment that you need to replace the existing VFD because it can’t do torque control to add a second one is just not true. I can add the second VFD in Torque mode and leave the original in place. The original would be master speed control. One has to run as master speed control. Also no encoder is necessary on this conveyor system at all. You would be better off using a limit switch or photo eye for positioning you eliminate the problem with slack in the chain due to load and wear.



I have see other examples of this to many to go into here.
 
I have worked with 300m (near 1000ft), this used equally spaced motor driven sprockets, all motor connects to the same VFD, this relies purely on motor slip though, not the best method IMO

As said already, master to drive your speed, and extra drives to pick up the load (based on torque)
 
Today I monitored PF525 (3P 460V 3.0HP) Drive Parameters:
P1-Output Freq: 33.75Hz
P3-Output Current: 2.13A-2.22A
P4-Output Voltage: 257.1V-258.8V
P15-Output RPM; 1012RPM
P17-Output Power: 0.34KW-0.46KW
P31-Motor NP Volts: 460V
P32-Motor NP Herz: 60Hz
P33-Motor OL Current: 6.0A
P34-Motor NP FLA: 4.0A
P35-Motor NP Poles: 4
P36-Motor NP RPM: 1750RPM
P37-Motor NP Power: 2.2KW
P382-Torque current: 0.80A-1.04A

the output current is only half of the full load,so the drive has enough power to drive the chain motor.
I apologize about my misleading the topic, I thought that we added so many heavy racks, those might cause too much load, but I never checked it before.
I just knew today: the output current is still in the limit range
Now I probably only can play a little bit with PID parameters to make the conveyor velocity smoother.
I appreciated everyone inputs .
Thanks a lot.
 
I agree everything with the drive looks good but I think the OL is set to high
I don't mean to pry but why are you using a PID loop control on a conveyor.
A PID control will not help you with anything on a conveyor application if you are going to a setpoint, use a preset setpoint and ramp from there to the stop point I think you will find you get better results.
 
I am sorry for the late reply.
Since we had many the racks crashes happened at ovens (we have three ovens in the path of the conveyor), those crashes made us lose a lot time to fix, we thought unstable conveyor velocity maybe one of the reason caused the rack crashes. we have one limit switch for conveyor motor, when the rack crash happens,that limit switch activates and stop the conveyor drive.
now we knew it is very hard to find conveyor velocity feedback to make PID velocity closed loop.
So we want to use the drive output current as trigger to stop the conveyor drive, that way we can make the rack crash happens not seriously to save some time for the production.
the question is how big the drive output current should be to set this trigger.
we will set up this trigger into PLC program to monitor it, if the rack crashes,see if the trigger works or not, maybe have to set up it many times to get the best trigger. if that works, put the trigger into PLC program to stop conveyor drive when the rack crashes.
thanks a lot!
 
Monitor, log, and trend the drive output current to see what your peaks are during normal operation. Then set your alarm/shutdown limit a little beyond that range. How long to trend to come up with these values might be easy for you to figure out (knowing the equipment) or might be more complicated. ALso, there might be other factors that need to be considered to validate this data (like when not running, performing any abnormal taks, ie. jog, reverse, etc). But start trending it right away to accumulate some data.
 
From what you just posted I don’t think you have an electrical / programming problem.
While I do see room for some improvements there.
You say that the racks crash more often at the ovens my guess would be at the entrance.
I have worked on many chain conveyor systems and they require a lot of maintaince to keep then operational the heaver the load the more ware on all the components
It would be very unusual for an electrical problem to cause a crash or jam.
What is the temperature of the ovens ?
Metal expands when it is heated and will cause the rails to shift, coupler can open up these should have been accounted for in the original design but sometimes things get missed or things come apart with repeated heating and cooling. You should have a regular inspections to insure the alignment of the rails.
Crashes or jams on chain conveyor are more likely caused by misaliment or ware on the rails.
Without seeing the conveyor it would be very difficult to guess where to look. Travel over the length of the chain would be even through it’s length even you had the pallets just sitting on the conveyor something would have to catch a pallet to prevent from moving with the chain.
 
the PLC program works fine, every time the racks crashing at a different place,
we can't stop the rack crashing, we just want to make the crashing not seriously by setting up threshold for the conveyor output current, if the output current is over the threshold then stop the conveyor drive.
one oven temp is about 320 C and other two temp are 400 C.
the the rack crashing at oven mostly is mechanic issue, many things will cause the rack crashing: bad bearing ( we use I-Beam as rail, each side has one bearing); the load on the rack getting loose then the load falls; and many more.
Thanks a lot !
 
it sounds like you figured out your problem it mechanical
I don't think you will be able to find a current setting that you can use to tell when the conveyor is jammed the level will have to so far above the normal range you would be crashed before you set the alarm, several motion sensor on the chain my work better for
motion stops set the alarm
 
Conveyor Motor Drive PF525 (3P 460V 3.0HP) Drive Parameters:
P1-Output Freq: 33.75Hz
P3-Output Current: 2.13A-2.22A
P4-Output Voltage: 257.1V-258.8V
P15-Output RPM; 1012RPM
P17-Output Power: 0.34KW-0.46KW
P31-Motor NP Volts: 460V
P32-Motor NP Herz: 60Hz
P33-Motor OL Current: 6.0A
P34-Motor NP FLA: 4.0A
P35-Motor NP Poles: 4
P36-Motor NP RPM: 1750RPM
P37-Motor NP Power: 2.2KW
P382-Torque current: 0.80A-1.04A

GayS said OL is set too high, can I set it to 4A or low than 4A? another question: If the OL is set to 4A, so after the drive output current is reaching to 4A then the drive will shut down with OL fault?
Thanks!
 
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6A OL for 4A FLA is typical. The value is entered based on motor capabilities (purely for the motor protection), however, there's nothing stopping you lowering the value for process protection so to speak.
If your application uses 2.22A fully loaded, then no harm in it being set to 2.5A.
If you get nuisance OL alarm then simply increase the OL value until you don't.
 

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