chain breaking causes

im finding out the cause of a chain link breakage and I would like to ask for advice in this good forum. The chain is with a servo(kinetix 6000+17, rslogix v17) controlling which controls a filling hose. attached below is the profile used in MAPC instrcution .

EDIT: The servo follows the curve under numerous cycles.
position gains:
proportional 151.99413
integral:5.775554

velocity gains
proportional: 389.105
integral: 0

feed forward gains both 0

integrator hold enabled

max speed: 637.50006
max accel:13088.422
max decel: 14390.466
max accel jerk 268716.5
max decel jerk: 324839.97

I am thinking that the cause is the reverse motion after reaching the maximum point without any rest so in order to have address that, the speed is really sacrificed and the profile will be changed to this or something similar
.

Thank you for any advice.

the MAPC looks ok but what is the servo really doing? Is it following the curve?


Please post a trend of the axis while moving showing
1) servo velocity
2) servo acceleration (either command or actual)
3) Servo Position error
4) servo position feedback
5) Master Axis Speed

How was the axis tuned?
Please post the axis "Gains" and dynamics tab

ASSuming that you are using RSLogix V17

thank you michaelG, yes im using rs5000 v17

The servo follows the curve under numerous cycles. next time i have a test I will save you a trend. I also editted first post to contain these

position gains:
proportional 151.99413
integral:5.775554

velocity gains
proportional: 389.105
integral: 0

feed forward gains both 0

integrator hold enabled

max speed: 637.50006
max accel:13088.422
max decel: 14390.466
max accel jerk 268716.5
max decel jerk: 324839.97

I am most interested in the position error but to be able to help need the other trend pens on the same chart

OOPS please add servo Torque to the trend scaled +/-120%

It looks like an auto tune was performed with integrator turned on for position and no feedforward for velocity and acceleration.
- Not recommended which you will see when monitoring the position error.

now waiting for the trend.

a chain breaks when it gets slack when changing direction.
the tension must be higher as the torque on the sprocketwheel.

I remember that the position error maintained a 1 all through out but now I need to repeat the trend again.

shooter said:

a chain breaks when it gets slack when changing direction.
the tension must be higher as the torque on the sprocketwheel.

Click to expand...

so maintenance/adjustment would be needed? since originally the servo only ran in one direction but now it changes direction with 60. sorry shooter I dont have much to say since I wasnt there when it happened.

Is this an existing installation?
if so how long has it been working?

Some chain questions
Is this a simplex chain
What is the chain sprocket ratio
What type of load is the servo driving
I think shooter is referring to the chain going slack as the servo reverses
Momentary only. This can cause a high torque
Personally I would suggest duplex chain without knowing the details

@michaelG, yes.this is the same thing i was working on earlier months.

@iant,yes,i suppose i will have to look for the sudden "jerk" when the thing reverses. thank you for clarifying it.

what is the application
What type of chain are you using
What is the Sprocket ratio

I have found that usually the problem is not taking up the slack at slow speeds before accelerating hard. Think about it.

I think there might be a 100% chance you are right Peter

iant said:

I think there might be a 100% chance you are right Peter

Click to expand...

More machinery vehicles and rigging gear have been torn up by letting slack in and then getting a good running start on it.

This is true for chain drive also.

For both V belt and chain drive and for only one direction it is better to have the "bottom do the driving" and leave slack on top. In the case of V belt the slack will naturally want to lay on the sheaves thus increasing surface area contact thus "traction"

Now when reversing the slack is in the bottom and this is where a lot of problems start. First for a V belt the surface area decreases because the belt hangs away from the sheave. In the chase of chain drive there may be so much slack the chain can skip a tooth (or try) - this causes a quick unload of the chain and a quick reload and HIGH tension - this is quite likely the cause of your snapping chain drives.

To fix your problem - if you can switch to v belt drive - more forgiving at the cost of slip.

Put a tensioner device on the bottom run of chain drive - an idle sprocket may suffice.

The first and worst tendancy is to tighten the belt or chain. This may cure the problem but now you are increasing the side load on both motor and driven load bearings. You should keep spare bearings on hand if you go this route.

Once you get the mechanical problems fixed THEN you can go and play with the PLC. I would make start and stop ramps as flat as you can and ease the torque demand.

Dan Bentler