Micro-electro-discharge machining as microsensor fabrication technology

This paper presents the design and fabrication of three miniaturized mechanical sensors to demonstrate the three-dimensional machining capabilities of micro-electro-discharge machining (EDM). The first sensor is an inertial bi-axial inclination sensor. The displacement of an inertial mass is measured optically by means of a two-dimensional position sensitive device (PSD). The machining freedom of micro-EDM makes it possible to produce both sensor and housing in one monolithic structure. The second sensor is an inertial uni-axial inclination sensor, which demonstrates the compatibility of the micro-EDM technology with the conventional photolithographic micromachining technologies. The mechanical structure of the sensor is machined by micro-EDM and the capacitive sensing part is produced by lithography. The aim of the integration is to set up a hybrid technology, which inherits the benefits of both micro-EDM and photolithography. The third miniaturized sensor is a three-component force sensor. The mechanical structure of the force sensor converts forces into displacements, which are measured optically. The mechanical structure of the force sensor is produced by wire-EDM and micro-EDM.     

Minimising heat dissipation in ultrasonic piezomotors by working in a resonant mode

Heat dissipation in ultrasonic motors should be limited, especially in precision applications since it causes thermal deformations. Therefore, an easy-to-understand mechanical model was developed to simulate heat dissipation in an ultrasonic motor. This model involves the dielectric, piezoelectric and mechanical hysteretic losses of the piezoelectric material. Both the model and the experiments lead to the same recommendations to minimise the heat dissipation for ultrasonic motors. Large piezoactuators, exciting passive structures at high resonance frequencies result in a minimum heat dissipation. Furthermore, it was shown that the optimal frequency regarding minimal heat dissipation lies between the resonance and the antiresonance frequency of the system, close to the resonance frequency.     

A mechatronic approach to microsystem design

This paper discusses the implementation of a concurrent-engineering view of microsystem design. The proposed concurrent-engineering or mechatronic approach to the design of hybrid microsystems is illustrated by three case studies. First, the design of an advanced computer writing tool is discussed. The design of this consumer product requires a mechatronic approach at different functional levels and at different levels of miniaturization. Another illustration of this approach is the design of an implantable drug delivery device. A device for solid drug delivery, as well as a device for liquid drug delivery, are presented. It is demonstrated that miniaturization can be obtained by a combination of functions in a single component. The multiplication of functions in a single component automatically leads to a concurrent-engineering approach far the design. Finally, the micromanufacturing of silicon parts by electrodischarge machining is described. It is demonstrated that electrodischarge machining of silicon is not only feasible, but forms an interesting and complementary technology to traditional silicon micromachining. Therefore, this powerful manufacturing technique opens the way for concurrent engineering of real three-dimensional micromechanical sensors and actuators with integrated processing electronics on the same wafer     

Artificial Soft Cilia with Asymmetric Beating Patterns for Biomimetic Low‐Reynolds‐Number Fluid Propulsion

In nature, liquid propulsion in low‐Reynolds‐number regimes is often achieved by arrays of beating cilia with various forms of motion asymmetry. In particular, spatial asymmetry, where the cilia follow a different trajectory in their effective and recovery strokes, is an efficient way of generating flow in low Reynolds regimes. However, this type of asymmetry is difficult to mimic and control artificially. In this paper, an artificial soft cilium that comprises two pneumatic actuators that can be controlled individually is developed. These two independent degrees of freedom allow for the first time adjustment and study of spatial asymmetry in the cilium's beating pattern. Using low‐Reynolds‐number flow measurements, it is confirmed that spatial asymmetry allows for the generation of fluid propulsion. These two‐degree‐of‐freedom soft cilia provide a platform to study ciliary fluid transport mechanisms and to mimic biologic viscous propulsion.     

Hardware Sequencing of Inflatable Nonlinear Actuators for Autonomous Soft Robots

Soft robots are an interesting alternative for classic rigid robots in applications requiring interaction with organisms or delicate objects. Elastic in?atable actuators are one of the preferred actuation mechanisms for soft robots since they are intrinsically safe and soft. However, these pneumatic actuators each require a dedicated pressure supply and valve to drive and control their actuation sequence. Because of the relatively large size of pressure supplies and valves compared to electrical leads and electronic controllers, tethering pneumatic soft robots with multiple degrees of freedom is bulky and unpractical. Here, a new approach is described to embed hardware intelligence in soft robots where multiple actuators are attached to the same pressure supply, and their actuation sequence is programmed by the interaction between nonlinear actuators and passive ?ow restrictions. How to model this hardware sequencing is discussed, and it is demonstrated on an 8‐degree‐of‐freedom walking robot where each limb comprises two actuators with a sequence embedded in their hardware. The robot is able to carry pay loads of 800 g in addition to its own weight and is able to walk at travel speeds of 3 body lengths per minute, without the need for complex on‐board valves or bulky tethers.     

Pathogenesis of Helicobacter pullorum infections in broilers

Four groups of 23 one-day-old broiler chickens were each inoculated by gavage with a different Helicobacter pullorum strain isolated from humans or poultry. As a control, a fifth group of eight animals was inoculated with phosphate-buffered saline. Faecal samples were collected weekly and tested for the presence of H. pullorum DNA using PCR. At 1, 8, 15, 22 and 42 days postinoculation, birds were euthanized and samples from the liver and intestinal tract were histologically, immunohistochemically and bacteriologically examined. The samples were also tested for the presence of H. pullorum DNA by PCR. All animals remained clinically healthy throughout the experiment although mild lesions in the caeca were present in animals inoculated with H. pullorum. In all H. pullorum-inoculated groups, DNA of this bacterium was detected in faecal samples until 42 days postinoculation. The main site of colonization was the caecum. Immunohistochemical examination revealed that the bacterium was closely associated with the caecal epithelial cells. It was concluded that H. pullorum may colonize the caecum of broilers and is excreted in their faeces until slaughter age. This implies that chicken meat might constitute a source of infection for human beings.     

High-damping carbon nanotube hinged micromirrors

New developments in digital mirror devices (DMDs) require suspension hinges with a good damping and high temperature stability. Carbon nanotubes (CNTs) offer these unique properties. Herein it is shown how CNT hinges can be integrated in micromirrors. The image illustrates a micromirror with a CNT suspension, and a typical overdamped stepresponse (Q-factor < 0.5).     

Reducing the Radial Error Motion of an Aerostatic Journal Bearing to a Nanometre Level: Theoretical Modelling

Ultra-precision air bearings could enable novel and more accurate precision applications. In this paper we report on the design of an ultra-precision air-bearing system, intended to reduce the radial error motion, i.e. the deviation from perfectly centric motion, to a nanometre level (i.e.<10 nm). To this end, the influence of several manufacturing errors, bearing parameters and feeding geometries is analysed on the radial error motion of an aerostatic journal bearing. This finally leads to the formulation of several design guidelines. On this basis, a numerical gas film model is developed and validated. Increasing the number of feedholes proves to be a promising solution as it results in an evenly distributed air film. The latter is confirmed by the fact that the radial error motion of an aerostatic journal bearing with a porous ring feeding geometry, which can be seen as a limiting case of infinite number of feedholes, is only 1 nm.