ArmorStart Controller can release brake with no voltage on motor

[factoryrat]

We have an ArmorStart Distributed Motor Controller (284G-FVD7P6D-25-RRG-CBG-DB1-EMI). It is used to run an Over Head Lift motor on a Hoist. One day someone disconnected the Motor Power Cord Connector at the Motor (which is on a platform about 15 feet off the ground). I did not know the power feed to motor was disconnected. The Hoist was in the UP position and holding a Car. When I went to the HMI screen and retracted the “Locking Pins” and then selected “Manual Lower Hoist” the ArmorStart Controller released the Brake and with no torque / voltage on the Motor (motor power feed disconnected @ motor) gravity brought the Car speedily down (about a five foot drop). The Lift’s wire cable unspooled from the Lifter’s Drum and did some other minor damage to Car and tooling.

I do not, ever, want this to happen again.

My thought is I do not want to release the brake when there is zero voltage applied to the Motor. I was thinking of adding a relay at the pecker head of the Motor and interlock the brake through this relay. In other words if the Motor is not energized the contacts on the relay will be open and the 120v brake cannot energize and release. My problem is I do not know if this is possible with this VFD driven Motor. The motor is a 480V AC Motor. Would a 480 volt relay work on what I think is PW modulated VFD voltage to motor?

Any suggestions or thoughts? Is this a proper application for this type of AmorStart Controller? I feel something is wrong here because this should be engineered so the above mentioned cannot happen.

See page 42 & page 43 of the "ArmorStart Distributed Motor Controller Application Guide" for a simple diagram.
https://rockwellautomation.custhelp.com/ci/fattach/get/114920/‎

 

[jraef]

If you have applied an Armorstart drive to a hoist and want it to control the brake release, you got bad advice. Hoist applications require a specialized drive application called "Torque Proving" in which the drive becomes capable of providing full torque at zero speed. That can ONLY be done with Flux Vector Control (or better) in which you use a shaft encoder on the motor. The Armorstart is not capable of that. PowerFlex 70, 700 and 750 drives are, but they are not of the "Distributed Control" architecture where you have that nice pre-packaged unit.

 

[Eddie Willers]

I absolutely agree with jraef; the risk of dropping a hoist when you release the brake are the whole reason that torque proving was invented.

Is this a proper application for this type of AmorStart Controller? I feel something is wrong here because this should be engineered so the above mentioned cannot happen.

And you're right. Somebody took a shortcut and used the wrong product, then put a cord disconnect where it could cause a dangerous failure.

A relay at the motor might work, but you'd have to do some experimenting with it. I wouldn't want to rely on it because you're correct that the voltage and frequency might not always run that relay, or worse, it would "chatter".

The right thing to do is put in a drive that features torque-proving. The ArmorStart doesn't, and that's one of the reasons it's not advertised or demonstrated on vertically held loads.

 

[factoryrat]

Wow! Thank you for your answers. What a great place to share knowledge and information. I had no idea there were drives specifically designed for Over Head Hoist. I knew there was a serious flaw with the setup we have but did not know where to get help and information. Thank you! Thank you!

I am going to search Torque Proving on Internet but can someone explain briefly what it is and how it works?

Would the proper Drive have prevented the scenario I mentioned above - having no power on the Lift's Motor and being able to release the Lift's brake?

 

[Ken Roach]

The PowerFlex 755 drive is the modern platform that Rockwell uses for hoist applications. The User Manual for that drive has a chapter on torque proving.

Direct Link to User Manual :
http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/750-pm001_-en-p.pdf

There's also a good RA Knowledgebase document summarizing several aspects of torque proving:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/508482

 

[Plastic]

Torque Proving

The VFD has an imbedded application where when commanded to move, it will apply static magnetic flux to the motor, then measure and prove that the drive is in control, THEN release the brake and drive the load.

It is the de facto-standard for vertical applications.

But, don't drink the cool-aid. You said you "Never want this to happen again".

Although Torque Proving is a good thing, your vertical load is held up by a single device. A single failure will cause the vertical load to fall to destruction.

Research vendors that do material handling vertical elevator with REDUNDANT secondary systems.

 

[Eddie Willers]

I don't know exactly how the internal brake contactor on the ArmorStart works, but there is a setting that allows you to cause the single Output Relay contact (not the same as the internal EM Brake contactor) to be set when the output current goes above a programmed threshold.

While this isn't nearly as reliable as a proper torque-proving drive with an encoder, it's something you could do to prevent the same issue (a disconnected motor) from occurring again.

Since you have an accident with an accident review, you're going to want to propose a solution that uses "industry best practices" to cover your butt. Relying on a programmed parameter in a drive that shouldn't have been used probably isn't a "industry best practice".

 

[factoryrat]

This is GREAT information!

there is a setting that allows you to cause the single Output Relay contact (not the same as the internal EM Brake contactor) to be set when the output current goes above a programmed threshold.

I am going to look through the parameters to see if I can I.D. the parameter you mention. If you know which one(s) it is please let me know? As you say this may be a temporary band aide for now.

I have shared this post with my bosses and I am pretty sure we are going to take your advice and change the ArmorStart Drive with one of the one's (i.e. PowerFlex 755 drive) you guys have recommended.

Thanks again, this information is invaluable.

 

[factoryrat]

Parameter 103

Looking at the many parameters - parameter 103 which is in the Display Group is labeled "Output Current". I am wondering if I can see this in my RSLogix 5000 Program. I will have to look when I get to work Monday. If I can see it, then perhaps, I can use it as mentioned in a post from above.

 

[Lancie1]

Looking at the many parameters - parameter 103 which is in the Display Group is labeled "Output Current". I am wondering if I can see this in my RSLogix 5000 Program.

From experience with other drives, you cannot use any of the specific Display parameters (display only), but there will be another parameter NOT in Display for the drive output Current that you can use. It appears to write a DeviceLogix program for this drive, you first turn off the Display parameters and turn on the DeviceLogix parameters.

1. Change the parameter group from Starter Display to DeviceLogix.

Another temporary band aid would be to put the factory plug-in cord in a rigid conduit that will require a little more effort to disconnect.

 

[factoryrat]

Don't know if I can use parameter 103. I was just thinking parameter 103 may be only viewable using RSNetWorks and looking at the Lifter's Drive Node parameters as Motor Runs. I'll check on Monday.

Any thoughts appreciated.

 

[factoryrat]

From experiece, you cannot use any of the specific Display parameters (display only), but there will be another parameter NOT in Display for the drive output Current that you can use.

Thanks Lancie. Funny (if you look) we posted at the same time. I did not see your post until I made my post. We are thinking the same.

I would like to know which paramater(s) I could utilize. As of now I don"t know.

 

[Lancie1]

The manual indicates that you have to switch from Display Parameters to DeviceLogix in order to see which parameters are available for programming use, including 4 digital inputs from the terminal blocks.

 

[factoryrat]

This drive is not running DeviceLogix at present time. We have several ArmorStart Drives (that do utilize DeviceLogix) controlling what we call Power Roller Beds which make up a Conveyor System that move the Car bodies through various Cells for different processes.

As of now, with a somewhat limited knowledge of the ArmorStart Drives, I just don't see how I could monitor the Drive Motor current and use that to make a decision on whether to release the ArmorStart controlled motor brake. I am thinking it may not be possible. If someone knows different please let me know.

I am pretty sure we will replace what we have, but you know how that is, it takes money, planning, and time if it ever gets done.

 

[Eddie Willers]

I was thinking of Parameter 155 and 156, described on page 5-39 of the Publication Number 280-UM002 User Manual.

Parameter 155 is "Relay Output Select"
Paramteer 156 is "Relay Out Level".

If you selected Parameter 155 = 7, that means the Relay Output turns on when the drive is "Above Current". It's described as: "Drive exceeds the current (% Amps) value set in Parameter 156 (Relay Out Level)".

You could then use the Relay Output circuit to run the motor brake once current is detected flowing through the motor.

The ArmorStart has an option where there is an internal contactor that connects the motor brake connector to 2 phases of the incoming line. That doesn't involve the Relay Output. If your system is using that feature, you would have to wire the motor brake differently to use the Relay Output.

Measuring the output current is not the same as "Torque Proving". I am by no means an expert, but the basic idea is that some of the output current goes into magnetizing the motor and some goes into creating torque. Real torque-proving drives have the sophistication to tell the difference.

The ArmorStart would only be able to (probably) tell if the motor is completely disconnected, because the current flow would be close to zero.

This method would be better than nothing, with regard to determining if somebody had disconnected the motor. But it will probably not pass the scrutiny of your safety engineers or your OSHA inspector.