Motion Overview 405
Motion Overview
General Motion Theory – Servo Loop Control
The following is intended to assist customers / control system users in better
understanding motion theory. Note: It is highly recommended that any system
tuning be performed by qualified service technician as incorrect tuning may cause
damage to the system or personal injury.
Outline of Information
1) What is closed loop servo control?
a) What is an Encoder?
b) What is Following Error?
c) What is a Position / Servo Error?
2) Determining Edge per Inch Parameter
3) Gain Term Definitions
4) Recommended Tuning Procedures
1) What is Closed Loop Servo control?
A Servo System is the means of accurately controlling electrical motors to create force. The motor
output is generally connected to a gearing system to translate the rotational force of the motor into
linear motion. Additionally this gearing system is used to modify the strength and speed of the
motion.
Closed Loop Servo control is the continuous process of monitoring position and/or velocity
commands compared to actual position and velocity and adjusting the output accordingly. A servo
system without feedback devices and automatic adjustment capabilities would be referred to as Open
Loop Servo control.
The drawing below outlines a typical Velocity and Position Loop System. The most important aspect
of this for our motion control is the Position Loop. The process starts with the motion control
providing a motion command (voltage) to the motor to move at a specific speed to a desired position.
Position is tracked during the motion by means of a feedback device (Encoder) that provides both
directional and distance information. Based on that feedback, the control adjusts it‟s motion
command (voltage) to the motor to ensure that the motor is accurately positioning on the designated
motion path at the correct speed.
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