Omron SYSMAC CS Series Instruction & Reference Manual page 593

Block Diagram for Target Value PID with Two Degrees of Freedom
When overshooting is prevented with simple PID control, stabilization of disturbances is slowed (1). If
stabilization of disturbances is speeded up, on the other hand, overshooting occurs and response
toward the target value is slowed (2).
When target-value PID control with two degrees of freedom is used, on the other hand, there is no
overshooting, and response toward the target value and stabilization of disturbances can both be
speeded up (3).
Set value
(target value)
Measured
value (PV)
(1)
(2)
Overshoot
CS/CJ/NSJ Series Instructions Reference Manual (W474)
Target value filter Proportional + integral elements
1 + (1 – λ) Ti · s
+
1 + Ti · s
–
Simple PID Control
As the target response is slowed,
the disturbance response worsens.
As the disturbance response is
slowed, the target response worsens.
+
Kp
Kp +
Ti · s
–
Preceding
Kp: Proportional constant
derivative-type elements
Ti: Integral time
Td: Derivative time
Kp Td/s
s: Laplace operator
1 + λ Td · s .
α: 2-PID parameter
λ: Incomplete derivative coefficient
(3)
Target response
3. Instructions
Manipulated variable
Feed-forward PID Control
Disturbance response
3
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