Brazilian Tunable Filter Imager (BTFI) Preliminary Design Review (PDR)‏ USP-IAG Universidade de São Paulo 18-19th June 2008 Etalon Controller (Luiz Cavalcanti/Jean-Luc Gach)‏ Version 2.2

2 Low Level Objectives Test and implement of the following modules Test and implement of the following modules Lattice FPGA – a device which allows you to build logical and arithmetic modules freely using its internal logic (e.g. Micro-processors, input/output, communication modules, filters, arithmetic operators) ‏ Lattice FPGA – a device which allows you to build logical and arithmetic modules freely using its internal logic (e.g. Micro-processors, input/output, communication modules, filters, arithmetic operators) ‏ DSP Mico32 created using the FPGA logic – DSP is a very powerful microprocessor, within which runs the control loop routine DSP Mico32 created using the FPGA logic – DSP is a very powerful microprocessor, within which runs the control loop routine Communication ports of the FPGA – interface with CDC or ADC, DAC, Ethernet port Communication ports of the FPGA – interface with CDC or ADC, DAC, Ethernet port 2 Jun 19, 2008

3 Low Level Objectives Test and implement the following modules Test and implement the following modules Capacitive micrometer Capacitive micrometer Piezo Actuator and the amplifier for driving it Piezo Actuator and the amplifier for driving it Capacitance-to-Digital Converter (CDC) – 21-bit, up to 30aF RMS conversion time Capacitance-to-Digital Converter (CDC) – 21-bit, up to 30aF RMS conversion time Digital-to-Analog Converter (DAC) – 20-bit – 1μV RMS noise Digital-to-Analog Converter (DAC) – 20-bit – 1μV RMS noise Lantronix Ethernet Adapter – achieve communication with the computer and other modules of the BTFI Lantronix Ethernet Adapter – achieve communication with the computer and other modules of the BTFI 3 Jun 19, 2008

4 High Level Objectives Development of a control loop strategy using one channel with a capacitance micrometer and one actuator – already done and working, but can be improved Development of a control loop strategy using one channel with a capacitance micrometer and one actuator – already done and working, but can be improved Achieve control for three channels mounted on the etalon with dummy plates – not done yet Achieve control for three channels mounted on the etalon with dummy plates – not done yet Development of a GUI to command the system and acquire data – not done yet; data is being transferred through Ethernet port but stored using HyperTerminal (Windows) ‏ Development of a GUI to command the system and acquire data – not done yet; data is being transferred through Ethernet port but stored using HyperTerminal (Windows) ‏ 4 Jun 19, 2008

5 New Etalon Controller 5 LAMCS100 Control measurement Absolute (gives the FP gap)‏ Relative (bridge)‏ Control loopDigitalAnalog Dynamics20 bits(120dB)‏12 bits (72dB)‏ Measurement range  m0-5  m Resolution<1nm Bandwidth1-100Hz1-1000Hz Weight~1kg (max)‏30kg Jun 19, 2008

6 New SESO Etalon Optical clear diameter: 100 mm Optical clear diameter: 100 mm Gap range: 0 to 200μm or 200μm to 400μm Gap range: 0 to 200μm or 200μm to 400μm 6 Sensors here Plate rotation with 1V applied on one piezo. Gain is ~1.2  m/V Jun 19, 2008

7 Controller Design Controller architecture Controller architecture 7 Jun 19, 2008

8 Controller Design Programming environment : ispLever 7.0 & LatticeMico32 System (DSP programmed in C language) ‏ Programming environment : ispLever 7.0 & LatticeMico32 System (DSP programmed in C language) ‏ 8 Jun 19, 2008

9 Capacitance Micrometer Distance measurement is made by capacitors. Distance measurement is made by capacitors. The actual absolute capacitance is measured giving a direct relationship with the distance. The actual absolute capacitance is measured giving a direct relationship with the distance. 9 Capacitance sensor Fogale readout electronics – MC900 Outputs a voltage proportional to the distance by measuring the capacitance – back-up solution Jun 19, 2008

10 Capacitance Micrometer Non linear behavior Non linear behavior Using the range beyond 100μm to minimize this effect (giving an offset spacing) ‏ Using the range beyond 100μm to minimize this effect (giving an offset spacing) ‏ On the other hand, only a small part (2pF) of the CDC (16pF) full range is used. Gives more noise when converting to distance On the other hand, only a small part (2pF) of the CDC (16pF) full range is used. Gives more noise when converting to distance 10 Jun 19, 2008

11 CDC converter Single chip providing 21-bits conversion Single chip providing 21-bits conversion Serial communication (I2C protocol) Serial communication (I2C protocol) Trade-off: Conversion Time vs. Noise Trade-off: Conversion Time vs. Noise Good noise suppression is achieved with a response with RMS noise <40aF; pk-to-pk noise ~100aF; 21 bits Good noise suppression is achieved with a response with RMS noise <40aF; pk-to-pk noise ~100aF; 21 bits Up to 20 bits noiseless (120 dB of noise free dynamic range) ‏. – the RMS noise is below 1 bit Up to 20 bits noiseless (120 dB of noise free dynamic range) ‏. – the RMS noise is below 1 bit 11 Jun 19, 2008

12 CDC converter Measurement of discrete fixed capacitor Measurement of discrete fixed capacitor - Top: 1000 samples at 124ms conversion time. Capacitance: 10pF - Top: 1000 samples at 124ms conversion time. Capacitance: 10pF - Bottom: RMS noise over a range of conversion times, calculated over 1000 samples for each conversion time interval. - Bottom: RMS noise over a range of conversion times, calculated over 1000 samples for each conversion time interval. 12 Jun 19, 2008

13 Piezo Actuator 13 RéférencesAPA 400MMLUnit Excursion over [-20, +150]V365µm blocked force189N Stiffness in mouvement axis0.59N/µm Mass56.5g Jun 19, 2008

14 Piezo Actuator It is well known that piezo actuators exhibit hysteresis It is well known that piezo actuators exhibit hysteresis This effect can be mitigated using a closed loop control system, i.e., a feedback system that compares its input with the set-point, compensating any error modifying the output value This effect can be mitigated using a closed loop control system, i.e., a feedback system that compares its input with the set-point, compensating any error modifying the output value The DAC + Amplifier ensures that the output signal is stable and without significant ripple The DAC + Amplifier ensures that the output signal is stable and without significant ripple 14 Jun 19, 2008

15 Piezo Actuator Step response. Voltage on the piezo goes from 60V to 100V. Left: capacitance; Right: distance Step response. Voltage on the piezo goes from 60V to 100V. Left: capacitance; Right: distance 15 Jun 19, 2008

16 Control System We do not use a classical PID controller We do not use a classical PID controller The output is incremented or decremented with a value according to the error computed by the difference between the set-point and the actual gap – which is effectively a closed loop control (feedback system) ‏ The output is incremented or decremented with a value according to the error computed by the difference between the set-point and the actual gap – which is effectively a closed loop control (feedback system) ‏ The system is stable (ie: error converges to zero for an certain frequency band and gain range), nevertheless we still could improve it in order to get a better dynamic response (less overshooting, faster settling) ‏ The system is stable (ie: error converges to zero for an certain frequency band and gain range), nevertheless we still could improve it in order to get a better dynamic response (less overshooting, faster settling) ‏ In the future it is planned to identify the system, obtaining the Transfer Function, for tuning a PID control system or even to implement some more sophisticated technique (e.g. Fuzzy, H∞) ‏ In the future it is planned to identify the system, obtaining the Transfer Function, for tuning a PID control system or even to implement some more sophisticated technique (e.g. Fuzzy, H∞) ‏ 16 Jun 19, 2008

17 Control System Response for a set point of 100µm. CDC conversion time 124ms. Without filtering. Response for a set point of 100µm. CDC conversion time 124ms. Without filtering. Noise: ~30nm pk-pk, 6.3nm RMS Noise: ~30nm pk-pk, 6.3nm RMS 17 Jun 19, 2008

18 Control System Response for a set point of 100µm. CDC conversion time 124ms. With moving average filter (4 averages) Response for a set point of 100µm. CDC conversion time 124ms. With moving average filter (4 averages) Noise: 12 nm pk-pk, 3.3 nm RMS Noise: 12 nm pk-pk, 3.3 nm RMS 18 Jun 19, 2008

19 Problems with acquisition The capacitance range provided by the sensor is too small in comparison to the full range of the Capacitance-to- Digital converter – this is a problem because of the non linearity (inverse function); the error, in nm, is bigger as the capacitance is small The capacitance range provided by the sensor is too small in comparison to the full range of the Capacitance-to- Digital converter – this is a problem because of the non linearity (inverse function); the error, in nm, is bigger as the capacitance is small Some extra noise appears when acquiring signals from the capacitive micrometer. – this is additional to the noise of the measurement of a capacitor directly soldered onto the board Some extra noise appears when acquiring signals from the capacitive micrometer. – this is additional to the noise of the measurement of a capacitor directly soldered onto the board The noise doesn't comes from the electronic board but perhaps coupled along the cable – almost 10 times bigger than expected The noise doesn't comes from the electronic board but perhaps coupled along the cable – almost 10 times bigger than expected 19 Jun 19, 2008

20 Solution For a while we have been considering changing the acquisition method For a while we have been considering changing the acquisition method Instead using CDC, we'll use the MC 900 module from FOGALE (it gives the analog values corresponding to the position) + ADC (24 bits) ‏ Instead using CDC, we'll use the MC 900 module from FOGALE (it gives the analog values corresponding to the position) + ADC (24 bits) ‏ At the beginning this technique was planned only for use as a comparison At the beginning this technique was planned only for use as a comparison Disadvantage: Extra cost and large size of the MC900 electronic conditioning module Disadvantage: Extra cost and large size of the MC900 electronic conditioning module So we are returning to a solution using only the CDC for conversion of capacitance again – ie: managing the problem of the capacitance range – once we have a improved control system So we are returning to a solution using only the CDC for conversion of capacitance again – ie: managing the problem of the capacitance range – once we have a improved control system 20 Jun 19, 2008

21 Remaining Activities LAM Finish the implementation of the MC900 + ADC for acquire signals, in order to get the best acquisition possible for now Finish the implementation of the MC900 + ADC for acquire signals, in order to get the best acquisition possible for now Improve the control loop technique Improve the control loop technique Create one simple GUI to command the system and access data more easily through the Ethernet port – with help of Philippe Balard – possibility of reusing existing code. Create one simple GUI to command the system and access data more easily through the Ethernet port – with help of Philippe Balard – possibility of reusing existing code. 21 Jun 19, 2008

22 Next Goals – With collaboration of BTFI team USP Identify the system and implement a more sophisticated control system approach Identify the system and implement a more sophisticated control system approach Implement the control with three channels – ability to set an arbitrary gap while keeping the system parallel and stable Implement the control with three channels – ability to set an arbitrary gap while keeping the system parallel and stable Study and implement a calibration method Study and implement a calibration method Create one definitive GUI Create one definitive GUI Establish communication of the Etalon Controller with the other BTFI modules Establish communication of the Etalon Controller with the other BTFI modules Realize full command of the Etalon Controller from the 'central computer' of the BTFI – z-scanning and automatic calibration Realize full command of the Etalon Controller from the 'central computer' of the BTFI – z-scanning and automatic calibration 22 Jun 19, 2008

23 Next Goals: timescale 23 Jun 19, 2008