March 29, 2012 IFAC Conference on Advances in PID Control1

PID APPROACH & ISSUESIN SERIES CONTROL SYSTEMSFOR MACHINE AUTOMATION

Ing. Adriano Chinello

Technical Director Automation DivisionGefran S.p.A.

General Targets for Series Control Systems

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Standard PLC application development (IEC 61131-3, PLCopen) High-value PLC software libraries: easy, complete, time-saving, … Cost – optimized hardware architecture Respect of target control specifications among many different

machines and over a wide range of operating conditions

Reference applications: full-electric injection moulding machine (FE IMM) Hydraulic injection moulding machine (HY IMM)

Specific Targets for IMM Control Systems

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Precise, repeatable and smooth changes between different control loops on single motion axes (position – speed – torque – mould pressure)

Electronic Noise Filtering / Tolerance (high power and inductive loads, poor cabling and shielding, …)

Compresence of very different processes:

- Electric Motion control (cyclic + events) 0.1 ÷ 1 ms- Hydraulic Motion control (cyclic + events) 1 ÷ 5 ms- I/O (cyclic) 5 ÷ 20 ms- Thermoregulation (cyclic) 50 ÷ 100 ms- HMI (events) > 100 ms- Supervisoring, Statistics, etc… (cyclic + events) low priority

PID Distribution in a FE IMM Architecture

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Modbus / CANopen

I/O real-time control loops

Motion high-level control

HMItask

PLC / SPC / aux

tasks

Monitoring / data

collection

Analog Input

Current Torque Speed Loop

Position / AI Loop

Speed / Torque Ref

Optical internal link

Power high-level control

GDnet / CANopen

Power / Thermo Loop

Remote I/O

Servo rack

Panel PC

Power Controller

Pressure Sensor

Panel PC - Fieldbus Performance and Cost

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cost

www.cpubenchmark.net

PID decentralisation allows Panel PC and fieldbus downsizing

PLC Motion Application Library

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Standard PLCopen

Only one software application for the whole machine

High-level programming, fieldbus and hardware independent

Standard Function Blocks with add-on (more flexibility)

Special Function Blocks with interfaces in line with the standard

Example: Injection Axis Control

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1 - MC_MoveAbsolute P1 V1 Aborting2 - MC_MoveAbsolute P2 V2 Blending Previous3 - MC_MoveAbsolute P3 V3 Blending Previous4 - MC_MoveAbsolute P4 V4 Blending Previous5 - MC_AnalogControl PR5 Blending6 - MC_AnalogControl PR6 Aborting7 - MC_AnalogControl PR7 Aborting8 - MC_Stop Aborting

EXE1ABORT.

EXE2BL. PREV.

P2

P1

P3

t

V1

V2

V, PR

DONE1

V3

V4

EXE3BL. PREV.

EXE4BL. PREV.

DONE2 INCONTROL5

SWITCHOVER

PR5

EXE6ABORT.

EXE7ABORT.

EXE8ABORT.

PR6

PR7

INCONTROL6 INCONTROL7 DONE8

ANALOGINPUTTHRESHOLD

P4EXE5BLENDING

Easy to develop, with a series of Function Blocks in blending

Switchover on position, pressure, … Control phases preloaded into the drive

PID Open Issues

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Smooth control switch vs time reactivity

Noise rejection vs time reactivity

Robust tuning procedures for reliability in series production: possibly one single tuning (or tuning procedure) for many machines and many different moulds for each machine

PID modularization and packaging into PLC software libraries, with both “simple entry level” and “complex advanced” user interface