This work package deals with the development of a reconfigurable and low-cost microgripper, which will be integrated in the demonstrator. Currently the microgrippers available on the market are monolithic structures based only on MEMS processes. As all the functions are realized in the same process (actuator, end-effector), these grippers are not reconfigurable and each application requires the design, fabrication and test of new tweezers.

Microhandling achievements

New actuation principle was developed based on piezoelectric multilayered do-bimorphs actuators, allowing 2 degrees-of-freedom continuous motion of both gripper fingers on 100 µm stroke. Thanks to this new actuation principle, and the reduction of the analog input amplitude for piezoelectric drive from +/- 150 V to +/- 20V, electronics is far less expensive and much easier to integrate. Piezoelectric behavior as gripping principle is better, with less than 10 % coupling effect on both degrees-of-freedom and 150 % of increasing stroke comparing to the first high voltage piezoelectric gripper device.

Innovative tool exchanger was developed to interface the actuators and the manipulating end-effectors in order to achieve fast and easy replacement of this fragile parts. Thermal melting adhesive was used thanks to a compact thermal control inside the gripper to fix and unfix at will the end-effectors to the piezoelectric actuators. Fragile and high precision end-effector replacement takes less than one minute to change with bare hands, with more than 90% of success (without damaging the end-effectors). This result is much better than the previous device, where changing end-effectors required a dedicated robotic system or to dismount the actuators with a changing time about half-an-hour.

Low voltage gripper prototype was designed in two versions, a first one with high stroke (100 µm) which was characterized with 150% of increased stroke comparing to the previous version. The maximum force of gripping was characterized thanks to the CSEM load cell at 40 mN maximum. The second version is a high force gripper with low stroke (6 µm) but a high gripping force which was characterized as well at 1,7 N (more than 40 times greater). Pulling test on micro-assembled device showed that the maximum pulling force could reach 300 mN, and that is beyond numerous destructive test already done in microelectronic industry.

The objective of this WP is the development, manufacturing, integration, characterisation and procurement of force sensor modules (load cell) targeted for micro assembly and mechanical characterisation of small size (10 µm – 2 mm) components. In these fields, there is a need for 1D, 2D and 3D load cells able to measure in the 0.1 N to 10 N ranges with at least sub millinewton resolutions; however such force sensors are hard, if not impossible, to find on the market.

Objectives:

This work package deals with the development of a force-based closed-loop control and coupling between the end-user and the microrobotic system.


Force-based closed-loop control gives helpful information for performing tasks at the micro-scale. In fact, fully position based already shows very promising results but does not enable to take into account interaction forces and surface forces like pull-off forces that are greatly influent at the micro-scale. The force based control at these scales appears to be an appropriate solution for guidance of the tool toward the object.

Coupling between the end-user and the microrobotic system is a promising solution to use man in the loop for the control of microrobotic systems. In fact, force feedback teleoperation with a sufficient level of fidelity in the reproduction of micro-scale physics would assist end-user in carrying out manipulation and assembly tasks.

 

The objective is to integrate the components developed in WP1-WP3 into a microassembly device and a testing device. Both devices will additionally be combined into one reconfigurable system for microassembly and quality inspection. The capabilities of these devices will be demonstrated using a sample application.

Micro-assembly platform: Main Achievements

Modular design of the robotic platform was integrated at the beginning of the project. Specific mechanical and electrical interface were developed to enable cameras and robotics component exchange. A full software framework was designed to integrate these exchanges inside the robotic driving software and the computer vision software. Exchange of cameras, cameras objectives, high stroke/high force gripper and robotics components was achieved to validate this principle. As an example, the same software framework was used on a cartesian robotic device (4 DOF) and an hexapod (6 DOF) without any change noticed by the assembly device operator.

Some dummy manipulation and assembly task have been done to validate the robotic demonstrator. Glue dispenser and laser reticulation device were tested to increase the capabilities of the assembly. In the remaining months, parts of the benchmark should be available for assembly and primary quality test on the assembly.

Assembly of microspheres on the robotic platform

Test platform: Main Achievements

After having defined the specification of the test platform, Alemnis started the design and development for the demonstrator. In September 2014, the test platform was assembled and the 3 axis loadcell from CSEM was integrated. Preliminary tests show the good performances of the instrument. During the next period, the Percipio micro-gripper will be integrated. Alemnis is currently upgrading its software to integrate the loadcell. New metrology functionalities based on a newly developed embarked microscope are being implemented too. Alemnis is also working on the development and integration of an ad-hoc microgripper for the testing of various samples.

The test platform was presented at MICRONORA in Besançon (23 – 26 September 2014)

 

 

Preliminary specifications:

 

Force measurement:

  3-axis (x-y-z)

  range +/-500 mN

  resolution 25 mN

  stiffness 150 mN/mm

  error < 0.1% FS

  cross coupling < 2.5%

  eigen frequency 430 Hz

 

Positioning :

  3 axis (x-y-z)

  range 25 mm

  resolution 1nm

  high stability for creep and fatigue tests

  Vacuum compatible

 

Alemnis test platform equipped with the 3 axis force sensor developed in cooperation with CSEM. The platform will further be equipped with micro-grippers and a miniature microscope for additional metrology functionalities.