Motor movement during transision between power/torque control and brake

Hi All

I have a problem with my cartesian robot Z axis. When the Power to the motor is turned on/off there is a slight drop. The motor has a brake and the drop occurs when the brake is turned off and the power to the motor is applied and vice versa when the power is removed and the brake is applied.

The motors are Allen Bradley Servos and the Drive is Kinetix 6000 Guard Motion

I have experimented with the BrakeEngageDelayTime parameter of the drive and this does not cure the problem. Aswell as the BrakeReleaseDelaTime.

The motors are Allen Bradley Servos and the Drive is Kinetix 6000 Guard Motion

Is this a new install or it has been previously functional?
Are you using a dry contact brake relay or directly one of the drive's on-board outputs?
What are the configured RBM (resistive brake module) turn-on or turn-off delays within the RSL5K/Axis Configuration (Brake Active Delay and Brake Inactive Delay)application file?
If you have tried "adjusting" the delays to no avail, it could be a defective drive RBM module, brake dedicated output or a brake malfunction.

Hi dmargineau

There is no RBM installed, from my understanding this is used to stop the motor under an e-stop situation.

The brake is controlled directly from the drive output.

In this case maybe the lack of an installed RBM module (or a dry contact/solid state relay) is this issue.
I have personally always used an interposing relay or a dedicated drive module to control the highly resistive loads induced by a brake winding.
The on-board output circuitry is not quite designed to withstand the "electrical abuse" caused by the energizing/de-energizing of a high power inductor.
It might be a brake malfunction after all, however, I would first try to install a dedicated brake relay on the brake's power wiring and control the relay's coil with an on-board drive output (preferably a different output than the seemingly failing one!).

dr_cronik said:

Hi All

I have a problem with my cartesian robot Z axis. When the Power to the motor is turned on/off there is a slight drop. The motor has a brake and the drop occurs when the brake is turned off and the power to the motor is applied and vice versa when the power is removed and the brake is applied.

The motors are Allen Bradley Servos and the Drive is Kinetix 6000 Guard Motion

I have experimented with the BrakeEngageDelayTime parameter of the drive and this does not cure the problem. Aswell as the BrakeReleaseDelaTime.

The motors are Allen Bradley Servos and the Drive is Kinetix 6000 Guard Motion

Click to expand...

Nice system -
Have you tried using MSO, and MSF combined with the Brake Delay times?
Ignore the Power off issue Get it to work using MSO MSF first (drive always has power and is in control).

On the Vertical Systems that I have got running
1) Safety Circuit had a short delay before removing power and the servo enable if used (on the Safety Servo just kept the safety cct up a short time)
2) Commissioned using MSO, MSF and BrakeReleaseDelayTime etc

Hi All

@dmargineau - I have replaced the motor and the condition still exists. I will be installing a new drive and placing a relay into the system to remove the load of the brake from the drive.

@MichaelG - I have used MCD Commands to test both MSO and MSF while adjusting the BrakeEngageDelay Attribute. I always get a drop. On the runnign system it is in the order of 1-2mm sometimes upto 17mm. On my offline test robot I am getting a drop of 0.014mm or so, tiny but still a drop non the less. The drop increased to 3mm when I set the delay to 0, just as expected

There is a drop after MSO and MSF. I am surprised to see a drop on MSO as in the manuals it states the motor will be energised before the brake is released. For an MSF the brake is engaged immediatly and the motor remains energised for the duration of the BrakeEngageDelay Attribute. Am I missing something?

What could be the cause of the bigger drop on the line robot?

After inclusion of the relay the drop is now down to 0.9mm

Is this acceptable?
If not, I can't think of anything else short of replacing the motor/brake with next available larger size...
It seems that the system was slightly "undersized" considering the mechanical load magnitude...
If this is a brand new system I'd seriously consider "up-sizing" though...Operating time will definitely increase the original 0.9 mm drift.

Hi

No this is not really acceptable as should the operator enable and disable multiple times the robot can drop by quite enough.

I have contained the problem by moving the Axis back to the orignal position after an MSO before operation can continue.

Should help.

We have also tried a new motor/brake.

I would concentrate on the MSO MSF as others are probably using the same motor in a hoist situation and it is working for them.
What times are you using on the Brake engage time eg 150ms?

What is the full motor part number - including the brake voltage etc
What is the ratio from the motor to the z axis

Do you have enough voltage on the brake at the motor ? I had one servo brake/motor that failed over time due to this. - sorry dmargineau seems to have this one covered.

As a trial - Can you use an external switch (output) to turn on /off the brake
with the MSO MSF (obviously do not move until the brake is lifted)
Get a trend of the servo Torque and Brake operation and Action Status

How did you tune the Servo?
Which version of RS5000?
Can you post the program? (Zip) If not then the just the Axis is better than nothing.



dmargineau Motion UM001 pdf - search "Brake Engage Delay Time"
command reference (Servo Action Status) versus Drive Enable is a bit confusing especially when added with a brake - if during the brake engage Time a load is on the servo the servo can move?

MichaelG said:

I would concentrate on the MSO MSF as others are probably using the same motor in a hoist situation and it is working for them.
What times are you using on the Brake engage time eg 150ms?

What is the full motor part number - including the brake voltage etc
What is the ratio from the motor to the z axis

Do you have enough voltage on the brake at the motor ? I had one servo brake/motor that failed over time due to this. - sorry dmargineau seems to have this one covered.

As a trial - Can you use an external switch (output) to turn on /off the brake
with the MSO MSF (obviously do not move until the brake is lifted)
Get a trend of the servo Torque and Brake operation and Action Status

How did you tune the Servo?
Which version of RS5000?
Can you post the program? (Zip) If not then the just the Axis is better than nothing.



dmargineau Motion UM001 pdf - search "Brake Engage Delay Time"
command reference (Servo Action Status) versus Drive Enable is a bit confusing especially when added with a brake - if during the brake engage Time a load is on the servo the servo can move?

Click to expand...

Michael, I have long ago given up on RA Literature Library contents as being user friendly and void of any personal interpretation inteventions requirements......They are getting better though...Maybe one of these days, they will contain only "black and white" statements...
It looks like the OP has done his homework and knows his way around motion applications.
We still have to learn about the history of the at hand system and, at least in my head, the original lack of a brake interposing relay, lit up a warning light bulb...
I am not sure if the application's functionality has been fully explored within the design stage; and I have a hunch that the x and y axii are identically "operated" even if, obviously, the z axis does a lot more "work" and its "reaction" needs to be as close to instantaneous as possible.
A brake will need an X amount of time to engage (Off command timing + internal springs tension/friction characteristics) and an Y amount of time to disengage (inductor magnetical characteristics + command/supply voltage application timing).
An electro-mechanical brake interposing relay has more On/Off timing lag than a solid state one and probably the latter will reduce the load drift some; as you have proposed, a "faster" relay command source could also help since the application is very "close" to be perfectly functional.
The increase in load drift might have been induced by the mechanical gearing "loosenes" acquired during normal functionality; a new gear reduction provides more internal friction than a "broken-in" one hence the comissioning tunning and drive sizing do not quite apply anymore, especially if the "financially efficient" path has been originally chosen...
As stated within my previous post, the application might be slightly "undersized" for a perfect, long term functionality; a larger brake, providing high quality controls and the most expedite commands timing have been implemented, will engage faster (and disengage slower!)thus the drift could be further reduced.