Sistemas De Control Automatico

1. Introduction

Classification of controllers by type of information representation

Controllers can be divided into different categories according to the type of information representation, into analogue, digital and binary controllers.

Controllers

Binary controllers

Analogue controllers

Digital controllers

Classification of controllers by type of information representationLogic controller

A logic controller generates output signals through logical association of input signals.

Application example

The assembly device for sub-bases is extended so that it can be operated from two positions. The two output signals are linked. The piston rod advances if either pushbutton 1 or 2 is pressed or if both are pressed.

Sequence controller

A sequence controlleris characterized by its step by step operation. The next step can only be carried out when certain criteria are met.

Application example

Drilling station. The first step is clamping of the workpiece. As soon as the piston rod of the clamping cylinder has reached the forward end position, this step has been completed. The second step is to advance the drill. When this motion has beencompleted (piston rod of drill feed cylinder in forward end position), the third step is carried out, etc.

© Festo Didactic GmbH & Co. KG • TP 601

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1. Introduction

Signal flow in a control system

A control system can be divided into the functions signal input, signal control, signal output and command execution. The mutual influence of these functions is shown by the signal flowdiagram. • Signals from the signal input are logically associated (signal control). Signals for signal input and signal process are low power signals. Both functions are part of the signal control section. • At the signal output stage, signals are amplified from low power to higher power. Signal output forms the link between the signal control section and the power section. • Command execution takesplace at a high power level – that is, in order to move heavy loads (e.g. a lock gate) or to exert a high force (such as for a press). Command execution belongs to the power section of a control system.

Signal output

Signal processing

Signal input

Signal flow in a control system

The components in the circuit diagram of a purely hydraulic control system are arranged so that the signalflow is clear. Bottom up: input elements (such as manually operated valves), logical association elements (such as shuttle valves), signal output elements (power valves, such as 4/2-way valves) and finally command execution (such as cylinders).

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Signal control section

Power section

Command execution

© Festo Didactic GmbH & Co. KG • TP 601

1. Introduction

1.3 Hydraulic andelectrohydraulic control systems

Hydraulic and electrohydraulic control systems both exhibit a hydraulic power section. However, the signal control section is constructed differently. • In the case of hydraulic control systems, this section is mainly carried out manually. It is rare for the signal control to be effected by means of a hydraulic circuit, which then comprises for example shuttlevalves. • In the case of an electrohydraulic control system, the signal control section is constructed using electrical components, which include for example electrical input keys, proximity sensors, pressure switches, relays or a programmable logic controller. In the case of both types of control, the directional control valves form the inteface between the signal control section and the hydraulicpower section.

Command execution

Signal output

Final control elements Directional control valves

Signal processing

Processing elements Directional control valves Shuttle valves Pressure control valves

Signal input

Input elements Directional control valves (mechanically operated) Directional control valves (manually operated)

Signal flow

Hydraulic components

Signal...