Elettronica e Controllo degli Attuatori SMA

Transcription

1 Elettronica e Controllo degli Attuatori SMA Adriano Basile STMicroelectronics, System LAB

2 Content 2 STMicroelectronics: Who we are Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

3 Who we are 3 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 (1) Including ST-Ericsson

4 Partners with our Customers worldwide 4 79 sales offices in 35 countries

5 An unwavering Commitment to R&D 5 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 (1) Including ST-Ericsson

6 Product Segments 6 Sense & Power and Automotive Products (SP&A) Embedded Processing Solutions (EPS) Analog, MEMS & Sensors (AMS) Automotive Product Group (APG) Industrial & Power Discrete Group (IPD) Digital Convergence Group (DCG) Imaging, BiCMOS, ASIC & Silicon Photonics (IBP) Microcontrollers, Memory & Secure MCU (MMS) Wireless (WPS)* * former ST-Ericsson legacy products

7 Where you find us 7 Our MEMS & Sensors are augmenting the consumer experience Our digital consumer products are powering the augmented digital lifestyle Our automotive products are making driving safer, greener and more entertaining Our Microcontrollers are everywhere making everything smarter and more secure Our smart power products are making more of our energy resources

8 Content 8 STMicroelectronics: Who we are Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

9 Shape Memory Alloy (1/2) 9 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... ) Solid-to-solid state transformation

10 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% % 5 3,5% % 12 3,5% % 21 3,5% % 33 3,5%

11 Content 11 STMicroelectronics: Who we are Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

12 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)

13 Further Mechanical Considerations 13 Spring as counterforce (no control) Second Wire as counterforce (fully controlled) The Electronic has to satisfy both the approaches and

14 Content 14 STMicroelectronics: Who we are Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

15 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% % 5 3,5% % 12 3,5% % 21 3,5% % 33 3,5% High Side Driving Low Side Driving VDD Current Generator VDD Shape Memory Alloy wire Shape Memory Alloy wire Current Sink

16 SMA Control Drv High Side Topology 16 Vdd EXT INPUT Driver P-MOS Driver MCU ADC S/H + PGA V_SMA Offset R_sense DAC Shape Memory Alloy wire MCU schedules and controls the main process routines: External Commands and Communication; SMA Actuators Current generators control; SMA data acquisition and elaboration; Offset management.

17 SMA Control Drv Low Side Topology 17 Vdd EXT INPUT MCU ADC S/H + PGA V_SMA Offset Shape Memory Alloy wire R_sense DAC Driver N-MOS Driver MCU schedules and controls the main process routines: External Commands and Communication; SMA Actuators Current Sink control; SMA data acquisition and elaboration; Offset management.

18 Spec Example 18 Diametro [μm] Forza massima [N] Contrazione Massima Forza suggerita [N] Contrazione suggerita 76 2,7 5% 0,8 3,5% Vdd EXT INPUT Driver P-MOS Driver MCU ADC S/H + PGA V_SMA Offset R_sense SMA Driving Waveform DAC Shape Memory Alloy wire Current generator supplies measuring Measurement required (typical) is Δ1Ω Voltage read with 12bit ADC Measurement has to be amplified by gain factor = 31 40mA * Δ1Ω = Δ40mV Δ40mV*31= Δ1.240V 2.5V / 4096 = 0.6mV

19 Analog Power Supply 6.5V USB conn Sens Analog Conn. Channel #3 Drive + Conditioning Stage Bill of Material from Spec 19 Channel #4 Drive + Conditioning Stage Digital Conn. MCU Digital Power Supply 5V Reset PB Channel #1 Drive + Conditioning Stage Channel #2 Drive + Conditioning Stage Application Specific Integrated Circuit (ASIC)

20 Control Waveforms 20 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 2 8 s P R i 33 40mA 2mW 40 s The total resistance variation depend on the wire length (i.e. 14mm may reach 6Ω) Generally the requested measurement accuracy is 1mΩ / 1Ω. 2 Driving Amplitude= 90mA Measuring Amplitude 40mA Measuring Phase (8μs) Measuring Phase Ph1 Ph2 Ton Driving Phase (32μs) Driving Phase f=25 khz

21 Content 21 STMicroelectronics: Who we are Shape Memory Alloy Brief Mechanical Considerations SMA Driving Topology Experimental Results

22 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

23 Resistance 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 R MAX Time

24 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 Temperature DC =DC_MIN DC =DC_MAX DC= DC_MAX Ch1 T=1/25KHz time DC= DC_MIN time

25 Experiments: Hysteresis Curves (2/3) 25 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 V R DC є [2:20]%, 1Hz DC є [2:20]%, 2Hz DC є [2:20]%, 4Hz DC є [2:20]%, 8Hz Duty Cycle

26 Experiments: Hysteresis Curves (3/3) 26 By modifying DAC value the whole hysteresis is exploited DC= DC_MAX Ch1 Ch2 DC= DC_MIN time DAC DAC variation V R V R Duty Cycle time

27 Experiments: Signal Follower 27 A sophisticated controller has been implemented in firmware, allowing following results: 4 wires driven with ramp range [2000:3000] Opposite channels Opposite channels

28 Experimental Results: live video 28

29 Thank you!