kinetix 6000 controlled decel from gravity

I have a pick and place that is controlled by a Kinetix 6000 and Control Logix 5000. It consists of two motors that drive a pick and place by means of a cogged belt.

It has brakes that are employed only when the PnP is not under servo control... just to hold it,

When the brakes are released, the PnP will fall due to gravity. So when the PnP is moving down to do a place, the motors must hold it back so that it does a controlled descent.

Sometimes this results in a "shuddering" of the PnP. I am convinced it is not mechanical, but something in the properties/ programming of the Kinetix axes. The pick head has been modified so that it does not weigh as much as it used to.

What could I look into check or set that could cause / relieve this?

I have the stuff online in front of me.

thank you

check brake wiring
the brake should be controlled directly from the Kinetix's axis

in the axis properties settings there are two times that must be set
Brake engage time and brake disengage time
they are on an additional popup I think in the stopping methods

The Brake engage time causes the servo to maintain control of the load until the brake has engaged (part of MSF)
The brake disengage time causes the servo to engage to control the load and does not permit any command reference until the timer has completed (MSO command)

OOPs I may have gone off on a tangent


Shuddering while moving - It may be that an auto tune is required or the belts are loose or sticking

For a Hoist ONLY perform an auto tune in the lifting (raising) direction
(do not do a bidirectional autotune ) and ignore the Decel rate calculated (gravity is assisting) and use the Accel rate value in the Decel rate



A method of verifying that your tuning is to test the position overshoot on a lower at close to maximum acceleration and velocity rates. NOTE: this test is dependent on your mechanics and travel etc

Thank you

I think you are in the area that I want to know about. the belts are good and mechanically I am convinced that this thing is good. I don't think it's the brakes either because it only does it on one move... the place. There are no errors.

Suppose the desired move is from 0 to 3000 in 3 seconds. If it falls due to gravity it will do it in a second.

If one second elapsed and things went correctly, the "counter in the drive" would be at 1000. It would have to be incremented in some manner by the encoders on the motors.

How often does the drive check to see that the "counter" is where it should be, and what does the drive do about it, and can any settings affect that?

For a Hoist ONLY perform an auto tune in the lifting (raising) direction
(do not do a bidirectional autotune ) and ignore the Decel rate calculated (gravity is assisting) and use the Accel rate value in the Decel rate

A method of verifying that your tuning is to test the position overshoot on a lower at close to maximum acceleration and velocity rates. NOTE: this test is dependent on your mechanics and travel etc

Click to expand...

Would you explain that a little... I don't think I quite understand... and it there a way to see the position in the RSLogix 5000?

again... thank you I think you are in the area that I want to learn about

gear box ?

osmanmom said:

gear box ?

Click to expand...

thank you for your response osmanmom.

.... the way the thing is set up, if only one motor or gearbox would have a problem, the pick head would move at a 45 degree angle instead of straight up and down. It actually does that when the servos are disabled and the brakes are employed, because the brakes do not engage at exactly the same time. so the pick head falls a bit, and moves off to the side a bit.

So unless both gearboxes have exactly the same problem, I don't see how it could be that.

but I certainly appreciate you considering my problem


thank you

what version of kinetix and rslogix 5000 are you using?

do you use trends?
monitor the axis tag members eg axis1

depending on your RS5K version you may have
axis1.actualposition
axis1.actualvelocity


the values that you want to trend are
Position
velocity
acceleration
torque

I also like to trend position error

to get theses values to be updated every coarse update period depends on your version

thank you Michael ...I have done that yesterday...you can see a marked difference between when the PnP moves as it's supposed to and when it does weird things ( which is getting worse) so the program and the drive know where it's at, but none seem to care.... it is a mystery to me

It is actually pausing at different places randomly for up to several seconds while the rest of the machine continues to run

version 12 ControlLogix I don't know about the Kinetix

If the issue is "getting worse", then I would strongly suspect mechanical issues. However...

1. Have you tried to old technician's trick? (Did you completley power down the servo?). My servos often keep the 24Vdc power on with only 480V being locked out. I recently struggled with a servo that was acting quite odd until I removed the 24Vdc and completley powered down the servo.

2. Shuddering often means that the servo is not tuned properly for the given mechanics. If this worked before and doesn't now, I would suspect the mechanics have changed. Maybe the tuning was marginally acceptable before and now the mechanics have worn a little. Of course, you state that the pick head has been lightened? Was that before or after problems started (becuase that is definitley a change in the mechanical system).

I would try doing an new autotune. Depending on the system, an autotune may not provide the best results and will require manual tuning. That is all done through the axis properties (Tune and Gains tabs).

realolman said:

It is actually pausing at different places randomly for up to several seconds while the rest of the machine continues to run

Click to expand...

During these pauses you need to monitor the actual torque and position error
IF the position error is going up (control is still occurring and the servo is unable to follow the reference) then it is more likely the mechanics are jamming - check for twisting in the axis guide rails and the torque flatlining at maximum (anywhere from 110% to 250%)
IF the position error is not increasing (+ or -) then usually it is under program control

realolman said:

version 12 ControlLogix I don't know about the Kinetix

Click to expand...

Ohh that is an old version ( installed about 10 years ago?)

use the gsv command to read the axis values into variables for trending
eg GSV "axisName" "PositionError" myREALPositionErrorTAG
and TorqueCommand

you may need to set up the real time axis information as shown

Hind sight is 20-20. After consulting the machine manufacturer ( for the third time) he suggested that it was probably a prox switch for a component that needs to be out of the way for the PnP to work.

When he said that I thought, "that sure sounds reasonable". Sure enough the plug for the switch in a block of 16 was just sitting in the connector and was not screwed in.

I guess it could seem like I should have found that sooner, but the way things presented themselves and the steps I took, unless you were very familiar with the structure of the program, I don't know how anyone could have done it much better.

A random bad connection ... drive a person nuts.
Anyway.... thanks to everyone who tried to help ...you are the best.

Thank you MichaelG I actually know a bit about what you are talking about now.... I wouldn't have when this started.


thank you

thank you for telling us you worked it all out

glad to help