The Basics Of Positioning Control - Mitsubishi Electric MELSEC iQ-F Series User Manual

FX Series Programmable Controllers
Introduction to FX Positioning Control Systems
1.

The Basics of Positioning Control

1.1 What is positioning control?
The positioning controller, together with the programmable logic controller, personal computer and operator
interface, is one of the four main units of FA (factory automation).
Among these units, the positioning controller plays an important role and is regarded as the center of the
mechatronics field in which many senior engineers have been playing active roles.
Positioning is all about motion, and motion often involves speed and precision. And since speed can be
directly related to productivity, positioning is an area of much development. When the speed of a machine
increases, a problem with the stop precision is often generated. In order to solve this problem, diversified
grades of positioning controllers have been required and developed.
Improving machine efficiency generates immeasurable added value, including reduced labor costs and
improved conservation of machine floor space for the same quantity of production. If there are no problems
related to the positioning aspect of a machine, it may mean that the machine is not running as efficiently as it
could be. This is where the science of developing and retrofitting an optimum positioning control system
comes in.
1.2 Actuators for positioning
The options available for positioning control depend on the type of actuator driving the system. An actuator is
a mechanical device that moves or controls a specific element or a series of elements within a system.
In a mechanical system, an actuator is often used with a sensor to detect the motion or position of a
workpiece. The following illustrations provide examples of diversified actuators, their features and their weak
points.
Actuator(s)
Pneumatic
Brake motor
Features and Drawbacks
• Air source and high grade piping
are required.
• High torque is not available.
• Multi-point positioning is complex
and very difficult to achieve.
• Change in positioning is difficult.
• Positioning mechanism is simple.
• Repeatability is poor.
• Change in positioning is difficult.
(When optical sensors or limit
switches are used for stop)
1 The Basics of Positioning Control
1.1 What is positioning control?
Schematic drawing
Piping
Motor with brake
Air cylinder
Workpiece
Compressor
Limit switch
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