4 replies to this topic

[ajeet]

I have gone to the article-variable speed drive theory.
I have a sheet cutting machine. I am using a 20 hp induction motor, encoder, gear boxes and counter to cut the specified lengths from rim of metal sheet. you know it can not be possible to get fix length of sheet each time .
Now i have some option, to use hydraulic motor drive with flow control mechanism or to use AC drive directly on motor as variable speed drive so that the inertia could remain in limit in end as .I want to know is it possible and which will be more echonomical?

[AB2005]

Hello

What is the problem which you are facing in your existing system? What is the existing control system of your induction motor?

[Mike]

I have used both systems on purlin mills
The VSD solution was better IMHO
VSD gave me repeatable +/- 0.5 mm accuracy, No inertia problems once the decel rate on the VSD was set
correctly

Hydraulics gave me extra problems with the viscocity of the fluid changing causing different stopping rates between cold and hot.

I found that the major reason for length errors was the contact pressure of the encoder rolling on the sheet (never tried an encoder directly on the motor but would expect some slipping)

[marke]

Hello Mike

I would expect that the VSD would be more accurate, particularly if you have some form of regen braking fitted. You could use a braking resistor of an active front end drive. The braking resistor is the more economic method, but less efficient.

Alternative technologies are four quadrant DC drive systems, servo systems and stepper systems depending on the size, feed through rate and accuracy required.

Best regards,

[KBrown]

Your optimum solution will obviously depend on your accuracy requirements - This is a relatively simple application using an ACVector drive with a built in motion controller and dynamic braking resistor. You should have no problem achieving +/- 0.050 inches with relatively aggressive acc/decs and fast cycle times.