Dear All,

I am new to motion control and your help will be greatly appreciated.

I want to build a machine that uses an AC drive to measure and cut specified lengths of wire. What I intend to do is use a VFD (Altivar 31) with a shaft encoder, a Twido PLC and a Magelis screen to input the required length (correct me if any of this is not right).

Could someone give guidelines on what is needed to realise the above? PID control, vector control?? Could someone highlight the steps required? Is it just a matter of simply counting pulses from the encoder that are equivalent to the specified length and getting the motor to stop the right moment?

Please advise.

Best regards,

Nik Avlogiaris

 

Nik,

Good thing you use the word intend, that generally means you haven't bought anything yet. This is not an application you want to do with a Twido PLC or an Altivar Drive. Find a VFD that is capable of Position Control of a Vector Motor. (Closed-Loop Position Control of an Inverter Duty motor with Encoder Feedback). The Uni-Drive SP from Emerson/Control Techniques would be a decent choice. Interface your HMI directly to drive via Modbus RTU... throw the Twido away... and do the simple logic in the drive. I know you would be much happier if you use a hardware scheme like this... not to mention some of the vector drives today can give very good position control depending on the application requirements!

 

It depends on the accuracy of the length and how fast that you want to payout the wire. High accuracy and or high response rate might require a true servo. Low speed, high accuracy/low inertia might be perfect for a stepper. Any idea of the spool diameter, payout speed and accuracy desired?
For relatively low power 90mm frame and smaller the prices for steppers can be very compelling.

There are now inverters with controllers inside like the Altivar 71 that can do simple positioning very inexpensively, often eliminating the need for a PLC.