Urban Simu

Fabrication of monolithic piezoelectric drive units for a miniature robot

In this paper, we present the design and assembly of a miniature robot, with a size of a few cm3, which should be able to move freely over distances in the centimetre range performing high precision manipulating operations on micrometre-sized objects with a precision in the nanometre range. The final robot will carry an application specific integrated circuit containing power drivers and a digital control system with a fast serial interface protocol. Two six-legged monolithic piezoelectric drive units generate the motion. Each leg is a three-axial multilayer piezoceramic enabling a five-axial manipulation operation. The fabrication of the drive units is described in detail. The multilayer structures are fabricated with wet building and screen printing. The green material is machined to single components using a high precision CNC micromilling machine. The motion capacity of the legs has been evaluated and major limitations restraining the motion capacity and further miniaturization have been identified. Firstly, the patterning of the internal electrodes should be improved, but also the milling operation has to be considered.

Evaluation of a monolithic piezoelectric drive unit for a miniature robot

In this paper, the evaluation of two different piezoelectric drive units developed for motion generation in a miniature robot is presented. The miniature robot is intended for high precision manipulation of microscale objects. The drive units have six drive elements integrated monolithically and each drive element is a three-axial multilayer piezoceramic actuator. This enables the robot to perform five-axial manipulation operations. Two inertial and two quasistatic walking mechanisms are evaluated. Due to the high level of miniaturisation the motion capacity of the drive elements is restrained. A fair step control is obtained for the inertial mechanisms while the quasistatic waveforms give a somewhat larger scatter. Walking mechanisms are expected to be advantageous at miniature scale, but the need for more complex motion patterns increases demands on design and fabrication. The height errors of the drive elements are believed to be the main reason for the larger variation in step length of the walking mechanisms. The inertial mechanisms appear to be affected by uncontrolled collisions between the drive elements and the moving body. With proper waveforms and optimised design all these undesired effects could be minimised and the second drive unit, which has an advantageous shape of the drive elements, demonstrates an improved behaviour.

From decimeter- to centimeter-sized mobile microrobots: the development of the MINIMAN system

Based on small mobile robots the presented MINIMAN system provides a platform for micro-manipulation tasks in very different kinds of applications. Three exemplary applications demonstrate the capabilities of the system. Both the high precision assembly of an optical system consisting of three millimeter-sized parts and the positioning of single 20-μm-cells under the light microscope as well as the handling of tiny samples inside the scanning electron microscope are done by the same kind of robot. For the different tasks, the robot is equipped with appropriate tools such as micro-pipettes or grippers with force and tactile sensors. For the extension to a multi-robot system, it is necessary to further reduce the size of robots. For the above mentioned robot prototypes a slip-stick driving principle is employed. While this design proves to work very well for the described decimeter-sized robots, it is not suitable for further miniaturized robots because of their reduced inertia. Therefore, the developed centimeter-sized robot is driven by multilayered piezoactuators performing defined steps without a slipping phase. To reduce the number of connecting wires the microrobot has integrated circuits on board. They include high voltage drivers and a serial communication interface for a minimized number of wires.

A metallic micropump for high-pressure microfluidics

This paper presents one of the strongest mechanical sub-cm3 sized micropumps for microfluidics. It consists of two active valves and one pumping chamber, each operated by a paraffin actuator that is driven by a low-voltage square pulse waveform. The pump is fabricated in a simple process using parylene-coated stainless steel stencils, paraffin and copper clad polyimide. When driving the pump at 0.07 Hz and 2.0 V (0.8 W) per actuator, it pumped water without leakage at a flow rate of 0.75 µL min−1 up to above 50 bar (5 MPa) back-pressure. The frequency dependence was evaluated and a maximum flow rate of 1 µL min−1 at 0.21 Hz and 1.8 V was observed. A thermomechanical FEM analysis, which was in good agreement with experiments at low frequencies, predicts the behaviour at higher frequencies.

A Polymeric Paraffin Microactuator

Paraffin wax is a promising material in microactuators not only because of its ability of producing large displacements and high forces at the same time but also because of the variety of manufacturing techniques available. In this paper, a simple actuator based on paraffin wax as the active material is fabricated and tested. Ultraviolet-curable epoxy is used in a technique combining simultaneous moulding and liquid-phase photopolymerization in a single-process step to build the stiff part of the actuator body. A heater is integrated in the paraffin reservoir, and a polyimide tape is used as the deflecting membrane. Thermomechanical analysis of the paraffin wax shows that it exhibits a volume expansion of 10%, including phase transitions and linear expansion. As for the actuator, a stroke of 90 mum is obtained for the unloaded device, whereas 37 mum is recorded with a 0.5-N contact load at a driving voltage of 0.71 V and a frequency of 1/32 Hz. The actuator can be used in microsystems, where both large strokes and forces are needed. The low-cost materials and low driving voltage also makes it suitable for disposable systems.

Smart Power Integrated Circuit for a Piezoelectric Miniature Robot

A BCD technology (Bipolar, CMOS, DMOS) is used to implement a high voltage smart power integrated circuit in order to obtain a fully integrated Smart Powered Piezoactuator Unit (SPU) for a new generation of miniature robots with sizes around 1 cm3. The integrated circuit is based on a mixed-mode circuit with power analogue output circuitry and digital input control circuitry. A specific driving system strategy is defined based on ICs assembled on-board with a serial communication interface. This minimizes the number of wires connecting the miniature robot to improve the robot motion performances and is a first step towards fully autonomy. Six samples of the ICs have been assembled onto a driving platform and tested with good results.

Multilayer telescopic piezoactuator fabricated by a prototyping process based on milling

Abstract A miniature piezoceramic actuator with telescoping multilayer d33 tubes is presented. The monolithic structure was realized using a rapid prototyping process, which is evaluated and discussed. The process based on wet building, green machining and lamination has proven to be flexible, fast and suitable for small-scale prototyping of multilayer piezoceramic actuators. Green machining in a milling machine is not only used to shape the actual device, but also to pattern the internal electrodes in the multilayer structure. Patterning of internal electrodes using milling demonstrated as good pattern definition as an ordinary screen-printing process would give, but with a superior flexibility due to the lack of mask changes. A comparison of the fabricated actuator has been made with state of the art piezoelectric actuators utilizing magnifying mechanisms. The d33-actuated multilayer telescopic actuator has proved to be a promising component with a displacement amplification of about 5 and an energy density comparable to other levered actuator designs. Several routes to improve the performance of the first design are identified.

A polymeric paraffin micropump with active valves for high-pressure microfluidics

We present the potentially strongest micropump in sub-cm/sup 3/ size yet for microfluidics, using simple processes and materials such as epoxy, paraffin, and polyimide. Utilizing the large volume expansion associated with the melting of paraffin for actuation, a pump consisting of two active valves and one pumping chamber operated by three identical paraffin actuators has been realized. UV-curable epoxy, which encloses the paraffin, forms the channel structure and joins the glass cover, actuator membrane and resistive heaters for melting the paraffin, is the main construction material. With water as a pumping fluid and a 2 V drive voltage, the valves were subjected to pressures up to about 1 MPa without showing any leakage. A flow rate of 74 nl/min was obtained in normal operation.

Design and fabrication of PZT-actuated tools for micromanipulation

In this paper novel tools for micromanipulation are presented. The devices have been purposely designed for integration in small mobile micro-robots, aimed at performing co-operative precision manipulation and assembly tasks. Concerning the actuation, multilayer piezoceramic components were developed and employed. The selected fabrication techniques for the grippers are shape deposition manufacturing of polymer and electro-discharge machining of stainless steel, and different alternatives have been investigated in order to select the optimal design. Several prototypes have been fabricated and preliminary experimental tests have been performed, both regarding the characterization and the grasping capabilities.

A piezoelectric disc-shaped motor using a quasi-static walking mechanism

A compact piezoelectric motor that comprises good positioning capabilities has been developed. The stator is manufactured with a multilayer structure that lowers the driving voltage to levels that can be provided by the onboard electronics of a future robot application. The motor exploits a walking mechanism by using three bimorphs to move the rotor in a stepwise manner. Height errors between bimorph tips and stator body stemming from the manufacturing process are recognized and their effects on the motion performance is documented and described. With increasing normal force on the rotor several artifacts in the motion pattern are suppressed enabling a motion performance with high resolution. The maximum torque of the motor is 80 µN m at a drive voltage of 50 V and a normal force of 1.15 N.