Changing periodically the speed of an electric AC motor using an inverter - pros and cons

Thread Starter

onlyonce18

Joined May 8, 2016
48
Hello everyone

I have a machine that moves a 40 pound piston up and down, the piston acts as a press at about 1 cycle (up and down) per second at its maximun speed, and half of it at its minimun, very simple machine.
The AC motor has a reduction of 1/10. so it runs between 300-600 RPMs and is oversized (2 HP)
I need to change the speed of the piston, so it will be faster when it reaches the bottom, and slower when it is on its up-down movement.

I thought of changing the frequency on the inverter, which is controlled by a PLC, so it would go faster for about 3-4 revolutions and slower for the 6-7 revolutions to complete a cycle, and the frequency change would happen twice on every second.
My other option would be to use a stepper motor, but I would have to change the transmission and mechanisms.

I´m leaning towards the stepper motor, but I ´m also curious about what are the pros/cons of using an inverter to control speed changes repeatedly. This method must also consider acceleration/deceleration times/inertia etc. so the cycle time remains stable and under control.

As a background, I have little knowledge on how an inverter works, my expertise is mostly on the programming area (the plc) so I would appreciate any comment, guide or reading reference so I can choose the best alternative.

Thanks!
 

MaxHeadRoom

Joined Jul 18, 2013
25,977
What is the make of the VFD?
I would look into see if it has the pre-set speeds option, this would entail the PLC outputting to the required speed input terminal.
Many VFD's offer this option with four preset inputs available.
 

Thread Starter

onlyonce18

Joined May 8, 2016
48
What is the make of the VFD?
I would look into see if it has the pre-set speeds option, this would entail the PLC outputting to the required speed input terminal.
Many VFD's offer this option with four preset inputs available.
Thank you, will be faster to change on the plc and test if the changes on speed are as needed.
 
Top