understanding circuit logic of PID blocks in ltspice circuit

[yefj]

Hello, There Is this great working PID system I am trying to understand its logic.I am trying to compare this circuit to the classic diagram of PID feedback system.
Two questions:
1. what is the analog logic of block I designates as 1,how can I analize its tranfer function?
2. Why are they inverting the output signal before going into PID?
https://github.com/HemakanthNatkuna...t/blob/main/EC5030_DesignProject_2020e050.pdf
Ltspice and photos are attached.

 

[yefj]

UPDATE:
Hello , what is the logic of all these inverters stages 1 and 3?
how does it make our systems feedback functioning?
Thanks.