Project Description (see also attached file):

My project has an inverter that actuates a set of 4 motors (parallel connection) and they turn drive traction wheels with polyurethane cover that drags/pushes a platform with one degree of freedom, thus moving it. However, since the transmission of the wheels to the platform is done by friction (not mechanically coupled with gear) there is a small transmition loss due slippage of the wheels.

For this purpose, it was planned to install an encoder for measuring the actual plataform speed (speed which is, in fact, necessary to control).

Therefore, this is an application with speed feedback via encoder coupled to the platform and not the motor.

In summary:

The inverter actuates 4 motors in parallel;

There is an encoder connecteddirectly on the inverter (X06 - encoder HTL for speed measurement);

The encoder is not coupled in the motor axis;

The encoder measures the platform real speed;

The angular speed of the encoder is always smaller than the angular speed of the traction wheel (considering they have the same diameter);

Tecnology in this project:

- CPU 319F (PN/DP) + CP343-1 lean

- Encoder 6FX2001-4HB00 (https://mall.industry.siemens.com/mall/en/us/Catalog/Product/6FX20014HB00)

- Drivebox: PM250 + CU240D-2 (6SL3544-0FA20-1FA0)

- Profinet Network

I foresee three possible scenarios to implement the system:

Scenario 1:

1.  Speed closed loop control done by the inverter and encoder signal processed by the inverter:

The speed feedback received by the encoder is treated before being used as feedback in the speed loop. Since the encoder is not coupled to the motor, but to the platform, there is a relation between its speed and the encoder that can be reached by multiplying it by a real number.

Considering this scenario:

Is it possible to take the encoder data and multiply it (internally, in the inverter itself) before playing as speed feedback in the control loop?

Scenario 2:

2. Speed closed loop control done by the inverter and encoder signal processed by the PLC:

Similar to scenario 1, but in case of not being possible to treat the inverter signal internally in the inverter. In this case the encoder data would be sent to the CPU via the profinet telegram, internally processed in the PLC. Then the encoder data is sent back to the inverter (also via telegram profinet) and then written in the feedback parameter of the speed control loop.

Considering this scenario:

2.1. Is it possible to send the encoder speed signal to the PLC via profinet?

2.2. Is it possible to send the processed speed signal from the PLC to the encoder via profinet?

2.3. Is the response time sufficient for the speed control loop to remain stable?

Scenario 3:

3. CLP control and encoder signal processed by the PLC:

Send the encoder signal to the PLC and treat it internally. Implement a PID (internally PLC) to make speed control and send speed setpoints via profinet to the inverter.

Considering this scenario:

3.1. Is it possible to send the encoder speed signal to the PLC via profinet?

3.2. Would not the difference / delay between PID processing and motor drive by the inverter generate instability?

3.3. Is this application usual?