Digital microrobotics

The nanorobotics team investigates a new paradigm in the design of microrobots by using mechanical stability instead of complex control strategies. Called digital microrobotic, this concept is based on discrete actuators (bistable and multistable modules). Switching between two or several states, these actuators guarantee a mechanical stability of the states in open loop without energy consumption unlike stick-slip, inertial or inchworms actuators.  This bottom-up approach takes advantage of MEMS technology and open-loop digital control to offer a flexible way to experiment various kinematics adapted to the microworld. This concept has several advantages:

- Open loop control (no sensor)

- No noises sensibility

- Low energy consumption

- Adapted to precise micro manipulation in confined environment (SEM, TEM)

- Robust and easy to fabricate (monolithic microfabrication)

First generation of digital microrobots:

The first generation of digital microrobots is based on the use of bistable modules combined with a flexible structure. The bistable module is composed of three elements: a mechanical bistable structure, two pairs of electro-thermal actuators and two stop-blocks. The electrothermal actuators push forth and back the bistable structure, one pair of actuators pushing in one direction, to reach each stable position. When several modules are combined, the displacement generated by each module is transmitted through the flexible structure to the tip of the microrobot. The resulted robot is able to generate a two dimensional workspace  and can perform binary actions in displacement and force. For instance, the combination of 4 bistable modules gives rise to a 2D microrobot able to reach 16 stable positions (likewise digital electronics circuits, the number of reached positions is equal to 2 of power the number of used modules, 16=2^4, 2 is the numbers of stables position and 4 is the number of modules).

Second generation of digital microrobots: 

Although the first generation of microrobots shows a great potential, it is subjected to a trade-off between the stable positions (directely related to the number of bistables) and the dimensions of the mechnism. Due to the combination of bistables, the size of the mechanism increases rapidily. As a consequence, the minuaturization and the control of the mechnism become complex and non-intuitive. To tackle this limitation, a second generation of digital microrobots is investigated. Instead of combining several bistables, a new mechanism architecture with multi stable positions is used.

This new architecture allows switching linearly its moving part between several stable positions in one dimensional direction. It combines the accuracy and robustness advantages of multi-elementary stable microsystems with the stepping principle which allows the actuator to have more positions by simply extending the range of motion as the case of stepping microactuators. Compared to the bistable, the multistable is  a promising solution that adds discrete positions to the workspace with a smaller footprint while adding many advantages. The main characteristics of the multistable are summarized in the following:

- Compact design with more discrete positions.

- Positioning robustness due to the digital concept and the use of stable structures.

- The number of internal actuators are reduced and the control is simplified.

- Increased accuracy due to the use of a mechanism to compensate microfabrication tolerances.

- No energy is needed to hold the moving part at rest.

Contact:

Abdenbi MOHAND-OUSAID (contact info) and Philippe LUTZ (contact info)

Involved people

Ismail Bouhadda (former postdoc), Hussein Hussein (former PhD),  Abdenbi Mohand-Ousaid, Gilles Bourbon (DMA dept.), Patrice Le Moal (DMA Dept.), Yassine Haddab (LIRMM) and Philippe Lutz.

Selection of publications:

H. Hussein, I. Bouhadda, A. Mohand-Ousaid , G. Bourbon, P. Le Moal, Y. Haddab, P. Lutz, Design and fabrication of novel discrete actuators for microrobotic tasks, Sensors and Actuators, A: Physical, Volume 271, Pages 373-382, 2018.

Q. Chen, Y. Haddab and P. Lutz, Microfabricated bistable module for digital microrobotics, Journal of Micro-Nano Mechatronics, Volume 6, Issue (1-2), Jan 2011, Pages :1-12.

V. Chalvet, Y. Haddab and P. Lutz, Microfabricated Planar Digital Microrobot for Precise Positioning Based on Bistable Modules,
IEEE Transactions on Robotics, Volume 3, Issue (29), jun 2013, Pages: 641 - 649.

H. Hussein, V. Chalvet, P. Le Moal, G. Bourbon, Y. Haddab and P. Lutz, Design optimization of bistable modules electrothermally actuated for digital microrobotics, IEEE/ASME International Conference on Advanced Intelligent Mechatronics, pages 1273 - 1278, 2014.