Servo Tuning Objectives - Renishaw SPA1 Installation Manual

2.4.1

Servo tuning objectives

The servo tuning objective is to find the controller parameters that meet the performance requirements for
a specific application.
Typical requirements are:
•
Stability
•
High disturbance rejection (reflected through a high proportional gain)
•
Steady state error required (precision achievable)
•
Very little or no overshoot
•
Small rise time and small settling time i.e. quick response
•
Small tunnelling error (specified by user) for trajectory following applications
The following table shows the effect of a change in the controller parameters. It is a guidance table for the
effect of change in proportional gain, lead or lag terms in the system.
NOTE: The following is valid only if all three parameters are used.
K (Higher)
P
K (Lower)
P
Ta (Higher)
2
Ta (Lower)
2
Ta (Higher)
1
Ta (Lower)
1
K is the proportional gain of the controller.
P
Ta is the time constant corresponding to the zero.
1
A higher value for Ta
Ta is the time constant corresponding to the pole.
2
A higher value for Ta
As the table shows, the parameters are inter-dependent making the tuning process far from trivial.
Speed of
Overshoot
response
(Higher) (Higher)
Better Worse
(Lower) (Lower)
Worse Better
(Lower) (Higher)
Worse Worse
(Higher) (Lower)
Better Better
(Higher) (Lower)
Better Better
(Lower) (Higher)
Worse Worse
means higher lead.
1
means higher lag.
2
SPA1 commissioning sequence
Stability
(Lower)
Worse
(Higher)
Better
(Higher)
Better
(Lower)
Worse
(Lower)
Worse
(Higher)
Better
21
Precision
steady state
(Higher)
Better
(Lower)
Worse
No Effect
No Effect
No Effect
No Effect