Robot drops as soon as the motor brake is disengaged

[GunT]

I have already submitted this post in another forum. I apologize for repeating it here.

We are an equipment manufacturer. We are using 2 axis Linear transfer for pick and place of the product. The vertical axis has brake motor and we are controlling using a PLC. Whenever we are disengaging the brake, to start the vertical motion, the robot is free falling for 1/4" before the controller kicks in.

We were thinking that gravity compensation should be able to solve this jerk in the motion. But we are unable to solve the problem. These are following components we are using:

Motor: Mitsubishi - HFKP43BK
Amplifier: Mistubishi - MR-J3-40B1
PLC: Mitsubishi - Q02CPU

Any help to resolve the problem would be greatly appreciated.

 

[cbarn24050]

Turn the controller on before releasing the brake.

 

[GunT]

We are turning the controller on before releasing the brake.

 

[cbarn24050]

You could try a time delay or monitor the motor current and not release the brake untill you have sufficient current.

 

[GunT]

Cbarn,
Thanks for replying to my post. But looks like thats also not helping much.

 

[cbarn24050]

Well in that case you need to have the controller on all the time and only use the brake when the power is off.

 

[tygerdawg]

Not sufficient to have the controller on. Should probably start to drive the motor in the direction you desire for a short period of time to develop motor torque. Then release the brake.

Are you certain this is not a *backlash* issue? I've seen a situation before where the coupling between motor & driven element was loose, allowed a few degrees of motion before engaging.

TygerDawg