Elettronica e Controllo degli Attuatori SMA

Elettronica e Controllo degli

Attuatori SMA

Adriano Basile

STMicroelectronics, System LAB

Content 2

STMicroelectronics: Who we are

Shape Memory Alloy

Brief Mechanical Considerations

SMA Driving Topology

Experimental Results

• A global semiconductor leader

• The largest European semiconductor company

• 2012 revenues of $8.49B(1)

• Approx. 48,000 employees worldwide(1)

• Approx. 11,500(1) people working in R&D

• 12 manufacturing sites

• Listed on New York Stock Exchange, Euronext Paris

and Borsa Italiana, Milano

Who we are 3

(1) Including ST-Ericsson

Partners with our Customers worldwide 4

79 sales offices

in 35 countries

An unwavering Commitment to R&D 5

(1) Including ST-Ericsson

Advanced research and development centers around the globe

16,000 patents; ~9,000 patent families; 515 new filings (in 2012)

~ 11,500(1) people working in R&D and product design

Digital

Convergence

Group

(DCG)

Imaging,

BiCMOS,

ASIC & Silicon

Photonics

(IBP)

Automotive

Product

Group

(APG)

Analog, MEMS

& Sensors

(AMS)

Microcontrollers,

Memory &

Secure MCU

(MMS)

Embedded Processing Solutions

(EPS)

Industrial &

Power Discrete

Group (IPD)

Product Segments 6

Sense & Power and Automotive

Products (SP&A)

Wireless

(WPS)*

* former ST-Ericsson legacy products

Where you find us 7

Our automotive products

are making driving safer,

greener and more

entertaining

Our smart power products

are making more of our energy resources

Our MEMS & Sensors

are augmenting

the consumer experience

Our Microcontrollers

are everywhere

making everything smarter

and more secure

Our digital consumer products

are powering the augmented

digital lifestyle

Content 8


Shape Memory Alloy




Shape Memory Alloy (1/2)

• Shape memory alloys (SMA) form group of

metals that recovers particular shape when

heated above their transformation temperatures.

• SMA deforms easily under stress, if such alloys

are plastically deformed at one temperature, they

will completely recover their original shape on

being raised to a higher temperature.

• The shape memory alloys have two stable

phases

• the high–temperature phase, called austenite

• the low–temperature phase, called martensite

• Shape memory alloys are also used in a wide

range of medical and dental applications (healing

broken bones, misaligned teeth . . . )

9

Solid-to-solid state transformation

9

Shape Memory Alloy (2/2) 10

Diametro

[μm]

Forza

massima [N]

Contrazione

Massima

Forza

suggerita

[N]

Contrazione

suggerita

25 0,3 5% 0,1 3,5%

50 1,2 5% 0,3 3,5%

76 2,7 5% 0,8 3,5%

100 4,7 5% 1,3 3,5%

150 6,2 5% 2,7 3,5%

200 19 5% 5 3,5%

300 42 5% 12 3,5%

400 75 5% 21 3,5%

500 118 5% 33 3,5%

10

Content 11


Shape Memory Alloy




Advantages for Linear Actuators 12

Traditional Approach SMA Approach

Pro:

• The movement is really linear

• The system is silent

• The SMA wire does not occupy space

Con:

• One direction with one wire (a counter force is needed)

Further Mechanical Considerations 13

Spring

as counterforce (no control)

Second Wire

as counterforce (fully controlled)

The Electronic has to satisfy both the approaches and…

Content 14


Shape Memory Alloy




SMA Control Drv Topology 15

Diametro

[μm]

Forza

massima [N]

Contrazione

Massima

Forza

suggerita

[N]

Contrazione

suggerita

25 0,3 5% 0,1 3,5%

50 1,2 5% 0,3 3,5%

76 2,7 5% 0,8 3,5%

100 4,7 5% 1,3 3,5%

150 6,2 5% 2,7 3,5%

200 19 5% 5 3,5%

300 42 5% 12 3,5%

400 75 5% 21 3,5%

500 118 5% 33 3,5%

High Side Driving

Low Side Driving

Current

Generator

VDD

Shape Memory Alloy

wire

Current

Sink

VDD

Shape Memory Alloy

wire

SMA Control Drv High Side Topology 16

• MCU schedules and controls the main process routines:

• External Commands and Communication;

• SMA Actuators Current generators control;

• SMA data acquisition and elaboration;

• Offset management.

P-MOS Driver

Vdd

S/H Offset MCU

+

– PGA

V_SMA

Shape

Memory

Alloy

wire

EXT

INPUT

DAC

ADC

Driver

R_sense

SMA Control Drv Low Side Topology 17

• MCU schedules and controls the main process routines:

• External Commands and Communication;

• SMA Actuators Current Sink control;

• SMA data acquisition and elaboration;

• Offset management.

N-MOS Driver

Vdd

S/H Offset MCU

+

– PGA

V_SMA

Shape

Memory

Alloy

wire

EXT

INPUT

DAC

ADC R_sense

Driver

Spec Example 18

Diametro

[μm]

Forza

massima [N]

Contrazione

Massima

Forza

suggerita

[N]

Contrazione

suggerita

76 2,7 5% 0,8 3,5%

P-MOS Driver

Vdd

S/H Offset MCU

+

– PGA

V_SMA

Shape

Memory

Alloy

wire

EXT

INPUT

DAC

ADC

Driver

R_sense

SMA Driving Waveform

• Current generator supplies measuring pulses @40mA

• Measurement required (typical) is Δ1Ω

• Voltage read with 12bit ADC (ref @2.5V)

• Measurement has to be amplified by gain factor = 31

• 40mA * Δ1Ω = Δ40mV

• Δ40mV*31= Δ1.240V

• 2.5V / 4096 = 0.6mV

Bill of Material from Spec 19

Application Specific Integrated

Circuit (ASIC)

Channel #1

Drive +

Conditioning

Stage

Channel #2

Drive +

Conditioning

Stage

Channel #4

Drive +

Conditioning

Stage

Channel #3

Drive +

Conditioning

Stage

USB

conn

Analog

Conn.

Reset

PB

Dig

ital

Co

nn

.

Analog Power

Supply 6.5V

Sens

Digital

Power

Supply 5V

MCU

Control Waveforms • Each of the SMA wires is driven with a

control waveforms consisting of two

phases:

• Ph1: measuring phase 40mA

• Ph2: driving phase, PWM mode 90mA

• During Ph2 driving signal is modulated

by varying the duty cycle of timers

• The target is to have a maximum of 2mW

when doing the measurement to keep the

power delivered to the wire as low as

possible

• The total resistance variation depend on

the wire length (i.e. 14mm may reach 6Ω)

• Generally the requested measurement

accuracy is 1mΩ / 1Ω.

mWs

smAiRP 2

40

84033

2

2

Measuring

Phase

Driving Phase

Measuring

Amplitude

Measuring Phase (8μs) Driving Phase (32μs)

Ton

Driving

Amplitude= 90mA

40mA

Ph1 Ph2

f=25 kHz

20

Content 21


Shape Memory Alloy




Experimental Results 22

First step has been emulate SMA wires and SMA

based actuator with Matlab / Simulink

This has been obtained thanks to tri-lateral collaboration between

ST, SAES Getter and Scuola Superiore S. Anna of Pisa

Experiments: Parameter Determination 23

• Only a single wire is powered thus

allowing the resistance to leave the

associated martensite (R0) value

and progress along the SMA

resistance curve. This test intends

only to follow only a part of the

resistance curve and not enter the

austenite region.

• Procedure description

• Channel 2 is brought to R0 position, i.e.

Channel 1 is powered with a fixed duty cycle

(≈17.3%) in order to straighten Channel 2 wire

• DAC for Channel 2 is set in order to output

~2V on the ADC.

• A 0.5Hz Saw tooth duty cycle (0% ÷ 10%)

waveform is fed on channel 2; measurement

pulse only on the other channels

RMAX

Time

R

es

ista

nc

e

Experiments: Hysteresis Curves (1/3) 24

• Hysteresis curve Duty Cycle vs. Voltage is obtained

• The range of acquired voltage is [0:4095] ≡Δ2.5V

• With given amplification, considering Δ1Ω variation, the

range of output voltage is about 1.240V

• By performing consecutive acquisition with different DAC

values, the hysteresis curved is determined

• One wire is supplied with ramp waveform whose frequency

and max/min values are modified is several acquisitions

DC= DC_MIN

DC= DC_MAX Ch1

time

DC =DC_MAX DC =DC_MIN

T=1/25KHz

time

Temperature


• By increasing the frequency, the hysteresis curves results wider, time

is not enough for the wire to cool down

• opposite channel is power with opposite waveform in order to pull the hot wire

DC є [2:15]%, 1Hz

DC є [2:20]%, 1Hz

DC є [2:20]%, 2Hz

DC є [2:20]%, 4Hz

DC є [2:20]%, 8Hz

Duty Cycle

V R


• By modifying DAC value the whole hysteresis is exploited

Duty Cycle

V R

DC= DC_MIN

DC= DC_MAX Ch1

time

Ch2

time

V R

DAC DAC variation

Experiments: Signal Follower 27

• A sophisticated controller has been implemented in firmware, allowing

following results:

4 wires driven with ramp waveforms @20Hz, range [2000:3000]

Op

po

site

ch

an

ne

ls

Op

po

site

ch

an

ne

ls

Experimental Results: live video 28

Thank you!

Elettronica e Controllo degli Attuatori SMA

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