Fast stopping with Mitsubishi FRA520

Hi!

I have a motor without brake on an Mitsubishi FRA520 frequency inverter. When I stop this motor it still turns 1 1/2 revolution. This results in a 3 centimeter overshoot from the stop position. We tried DC injection braking without result. (Maybe we made some parameters errors?) Can anybody give me some hints/tips to solve this problem?

(Other solutions are using a mechanical brake or adjusting the sensor wich indicates the stop position. Unfortunatley both options take up a lot of time to achieve. Ofcourse this time is the problem, we don't have it. The parts must be shipped to Japan.)

Thanks!

Werner,

What control are you using to send the stop signal?

Rod

Rod,

We have a sensor connected to a digital input on an S7 300 PLC. The frequency inverter is controlled by digital outputs of the plc. So we have a start signal to the STF connection on the inverter. I know there is a delay caused by the plc cycle time. But the "overshoot" is to large to be caused by this delay.

Try a slow down limit switch to change the speed to a lower HZ before final stopping point. How fast is the motor moving when it is shut down?

The problem is that changing the sensor (or building a new sensor) is not an option. We will have to do with the sensor we have. At this point the motor is turning 60Hz. But with software we can change it to slower speeds (Time running then to slow speed)

I don't know if this will help or even if its valid on an A500 but here's the procedure to help the stopping accuracy on an E500 drive:

1). Read and record value of PR. 77
2). Change PR.77 to 801

3). Change PR. 248 to 1

4). Change PR. 77 back to original value.

Thanks! I'll give it a try

BTalbot said:

I don't know if this will help or even if its valid on an A500 but here's the procedure to help the stopping accuracy on an E500 drive:

1). Read and record value of PR. 77
2). Change PR.77 to 801

3). Change PR. 248 to 1

4). Change PR. 77 back to original value.

Click to expand...

Mr Talbot,

Are you sure that these are parameters for a E500?
Valid numbers for parameter 77 are 0, 1 or 2 only.
Parameter 248 doesn't exist.

If the load is not to big I would try putting the motor in reverse until 0 speed is achieved.
http://www.mitsubishi-automation.de/service/techcat/pdf_download/127217.pdf
A few parameters I would play with.
8 make it small
10,11,12,45
Play with them and see the results

Werner, your best bet is to set the drive to ramp to stop (not coast), then set the decel time to the short amount of time you need. This will almost certainly cause the drive to fault on High DC Bus Voltage.

To take care of that fault, buy a small snubber brake package for this drive from Mitsi. Usually, it attaches to the DC bus terminals and will waste the braking energy as heat in its resistors. You will need to mount this package somewhere where the occasional heat can be dissapated without damage.

With a properly sized snubber brake, you will be able to develop as much braking torque in the motor as you have motoring torque.

This is the maximum amount of electronic braking available without buying a bigger drive, motor, or both.