The digital hydraulic challenge, to switch or not to switch

Dr. Magnus Sethson Assistant Professor, Senior Lecturer

Division of Fluid and Mechatronic Systems, Linköping UniversitySweden

Digital Hydraulics

Switched Controlled Force

Project Update

Cooperative Work with Linköping University

Norrhydro Oy, Finland

Volvo Construction Equipment AB, Sweden

HYDAC GmbH, Germany

Project Mission:!To evaluate the Norrhydro multi chamber cylinder technology in a digital hydraulic configuration with focus on applications of Volvo Construction Equipments products using valves from HYDAC. The digital hydraulic technology is originally invented by prof. Matti Linjama at Tampere University in Finland.

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Switched Circuits

The Electronic Analogy

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Switched Circuits

The supply does not need to be the same!

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Multi Chamber Cylinder

Discrete force actuator

Several cylinders can be put in parallel.

The Norrhydro 4 chamber cylinder

qA

qB

qC

qD

The test setup

Valve package 27 valves

4 A chamber 2 B chamber 2 C chamber 1 D chamber

Valve inline orifice configuration

Lift main cylinder & WS10 valvesOrifice diameter configuration

A B C D

1 - 1,5 3 1,2

2 3,5 1 2

3 2,5

4 1,5

Chamber

Valv

e nu

mbe

r

Photo of test rigg

qBqC

qA

qD

27:9:3:1

Force steps

3 pressure lines and 4 chambers gives 81 force steps

Overall system layout

ControlStrategies for force and

position control

Control structure

pH :

pM :

pL :

PI-Controller ui Valve selector

Actuator

x

iABCD�x

xref

u = ui such as min

⇣|Fref � ˆF (ui)|

⌘for i 2 [1..81]

u : Controller signal

ui : Valve combination index

Fref : Estimated force reference

ˆF (ui) : Calculated force response

i : index in the 81 combination set

Strategy: min�F

Strategy: min�F + Fpenalty

u = ui

such as min

⇣|F

ref

� ˆF (ui

)|+ Fp

⌘for i 2 [1..81]

u : Controller signal

ui

: Valve combination index

Fref

: Estimated force reference

ˆF (ui

) : Calculated force response

i : index in the 81 combination set

Fp

= 2000N if ui

6= uprevious

otherwise 0N

Strategy: min�F + Fpenalty + Score

u = ui such as min

⇣|Fref � ˆF (ui)|+ Fp

⌘for i 2 [1..81]

u : Controller signal

ui : Valve combination index

Fref : Estimated force reference

ˆF (ui) : Calculated force response

i : index in the 81 combination set

Fp = f(ui, uprevious, pH , pM , pL)

ComparisonStrategy: min�F + Fpenalty + ScoreStrategy: min�F + Fpenalty + ScoreStrategy: min�F + Fpenalty + Score

Extensive switching Smoother switchingLarger errors

Some switchingSome errors

Phase 2Reevaluating the switching

trigger functions and energy harvesting

Human in-the-loop

pH :

pM :

pL :

PI � Controller

ui Valve selector

Actuator

Brain

fprex�x

xref iABCD

ObservationExperience

Handling

Example: Velocity matching

tt1 t2

xref (t)x(t)

x(2,N2)x(1,N1)

x(1,i)

x(2,i)

Path following

tt1 t2

xref (t)

x(t)

xmeasure(t)

AH BG

DE CF BG AH

33

22

44

11

DESIGNED BYXXX

DATE

XXX

CHECKED BYXXX

DATE

XXX

DRAWN BYulfbe60

DATE

4/8/2013

This drawing is our property.It can't be reproducedor communicated withoutour written agreement.

SCALE 1:25 WEIGHT(kg) SHEET 1/1

SIZE

A3DRAWING NUMBER

12 15 300 Bl.1REV

X

DRAWING TITLE

Tower

12 15 060

2/ Slutlig CE-märkning och momentdragning av bultförband utförs av beställaren. Se e-mail 2012-10-24 och 2014-04-11. SkruvM16 12.9 Mv: 333 Nm.1/ Lagenliga skyddsanordningar ombesörjes av beställaren.

12 15 070

Conclusions• Digital hydraulics have

potential in multi-axis systems.

• The switching strategy is paramount to its energy efficiency and controllability.

• Research is still needed to understand the non pre-filtered applications.