Does your library work with PLC?
Yes, it supports all the slave devices that able to manage modbus RTU requests through rs485. It works also with Arduino as well.

What kind of experience is supposed to have in order to interface with my actuators?
You basically need to know how to create an Android application. Many tutorials are available in the net. Google it. Take a look at our wiki section about Android.

Is it possible to query more than one device on the rs485 bus?
Yes, you can connect up to 128 devices. You have to carefully evaluate the distances between them though. However, this characteristic does not depends on the library itself but on the 485 transceiver used.

Sometimes the communication with the devices is erroneous.
Check whether you have connected the GND of the Ltouch board with those of the slave device.

What are the functions that you plan to implement in the future releases of the library?
We are working on the function 6.

Is the library royalty free?