Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Cubic centimetre onboard electronic module

The main challenge of the microrobot implementation is the size minimization with powering and communication autonomy. The electronic module is designed to perform it and the following predefined robot capabilities: read/write from/to PC the desired microrobot movement and manipulation with the robot tool, drive 10 different piezoelectric actuators with capacitance values of 10nF to 35nF with trapezoidal and sawtooth voltages waveforms up to 2.5 kHz, provide a force control system to work with some tools (specifically the AFM tip and the syringe, which need closed loop control).

In order to accomplish these requirements, 4 different modules are designed and implemented: Power source generation module (PSG), Input sensing for control system (ISC), Mixed signal IC module (MXS) and Power addressing and amplification IC module (PAA). All these modules are full custom designed and placed in a 4 printed circuit boards of 12mmx12mm. The microrobot electronics needs three different constant voltages for work: 3,3V for the digital circuitry and the instrumentation system, 20V for the power circuitry actuation (driving power to the piezoelectric actuators) and 5V for the power circuitry control signals. Because of the powering microrobot system (battery or power floor), the input robot voltage could be in the range of 2V-4V. The full power source generation module is implemented in two printed circuit boards (one layer each one) with a size of 6mmx12mm (the first one) and 12mmx12mm (the second one). The PSG3.3 integrates a low power DC/DC Buck/Boost converter, which supplies 3,3V from an input voltage in the range 1.6V-5.5V. The nominal performances of the circuit are: output current 115mA; high efficiency (up to 80%); low quiescent current (50µA); low output voltage ripple (3.2% in the worst case). These nominal values comply with the microrobot requirements. It also complies with the dimensions requirements due to the capacity of the DC/DC for work without an external inductor.

The PSG20 is also a low power DC/DC converter (Boost). The converter output voltage is fixed to 20V and the nominal performances of the circuit are: high efficiency (up to 77%); low quiescent current (28 µA); low output voltage ripple (2.7%). This PCB also regulates 5V for driving the control signals in the analogic ICs. Due to the dimensions requirements and the low power consumption for this control signals (about 1mW), a zener diode solution is implemented.

The CPD module integrates a full custom mixed-signal IC (the robot ¿brain¿), two full custom power amplifiers ICs (for drive the piezoelectric actuators) and the system's clock. The ICs are soldered using wire-bonding interconnections. The full PCB is 12mmx12mm (one layer). The mixed-signal IC is designed using the AMS (Austria MicroSystem) 0.35µm microelectronic technology from Europractice service. This IC is the responsible of interfacing with the IR protocol, generating the appropriate signals (trapezoidal, sawtooth and triangular) for the microrobot movement and controlling the tool-closed loop by an externally programmable digital PID. The power addressing and amplification module is full custom designed using the IIT microelectronic technology from Europractice service. Using two ICs, the system is able to amplify the signals, which come from the mixed-signal IC, obtaining 10 independent power outputs, which are able to drive the microrobot piezoelectric actuators.

The ISC Module is implemented in the two layers of a 12mmx12mm printed circuit board. Due to the kind of tools, which the robot has to sense (an AFM head, a micro-syringe and a micro-gripper), the instrumentation is designed for work with resistive. A Wheatstone's bridge solution has been implemented for signal conditioning, and an instrumentation amplifier is used to obtain the desired signal range to work with the software system range. This measure is fully differential, allowing work in noisy environments. In the experimental results we see about 10% of noise error, but lower than 1.2% when filtered in the host PC with a first order low-pass filter. Taking into account the possibility of interchanging tools to the microrobot and resistance's tolerance value, two multi-turn variable resistances are used to adjust accurately the Wheatstone's bridge (it could be adjusted externally, allowing the tip exchange). The instrumentation amplifier used fits with the system low noise (35nV/√Hz), low offset (250µV in the worst case), high gain (100dB) and small dimensions requirements.

All this electronics modules have been interconnected using a 3D structure which is used also as a mechanical holding and make possible to minimize robot's dimension.

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Reported by

Instrumentation and Communications Systems SIC Lab
1,University of Barcelona Electronics Department 1, Marti i Franques
08028 Barcelona
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