Optical sensing sheets, based on Fibre Bragg Grating (FBG) sensing elements embedded in
siloxane (PDMS), are produced and tested. The device shows promise in pressure mapping and tactile applications, in fields such as robotics and rehabilitation. FBGs inscribed in highly-birefringent photonic crystal fibres,
reflecting two Bragg peaks, are used, and the potential to discriminate pressure and temperature is explored.
The prototypes were produced by moulding technology and PDMS was cured at room temperature. One sample
with FBGs embedded in the middle layer of a 2 mm thick PDMS sheet exhibited a linear pressure sensitivity
of about 2:6 pm/kPa over the range of 0 - 250 kPa. Another sample was proposed and tested for temperature
insensitive measurements, by realising local stress concentration at FBG sections of the embedded fibre.
To realize a high density matrix of pressure sensors, mainly electrical approaches are reported. The proposed highdensity
optical pressure sensor is based on a matrix of 2 stacked layers of crossing multimode waveguides. When
pressure is applied on a crossing point, the distance between the waveguides from the upper and lower layer will
decrease and power is transmitted between these waveguides. The sensor consists of polymer waveguides embedded in
polydimethylsiloxane (PDMS) which is a very flexible material. Therefore, it is ideally suited to be applied on irregular
or moving surfaces especially for applications which require covering small areas with high density pressure sensors.
This paper describes the fabrication of a novel type of pressure sensor based on optical feedback in a Vertical Cavity
Surface Emitting Laser (VCSEL). The detection mechanism of the sensor is based on a displacement measurement
through self-mixing interferometry in the laser cavity. Using this technique a sensing resolution of half the laser
wavelength can be achieved. The use of unpackaged VCSELs allows the integration of the sensor in a flexible polymer
material, which enables thin and ultimately bendable optical sensing foils. Moreover, the use of unpackaged dies limits
the sensor dimensions and minimizes the distance between two sensing points. Consequently, dense matrices of highly
accurate sensing points can be fabricated. A proof of principle set-up for this new sensing mechanism has been developed and a first demonstrator has been fabricated and characterized.
An important technological barrier in the development of microrobotic systems is the lack of compact sensor-actuator
systems. This paper presents a piston-cylinder fluidic microactuator with an integrated inductive position sensor. Such
positioning systems offer great opportunities for all devices that need to control a large number of degrees of freedom in
a restricted volume. The main advantage of fluidic actuators is their high force and power density at microscale. The
outside diameter of the actuator developed in this research is 1.3 mm and the length is 15 mm. The stroke is 12 mm, and
the actuation force is more than 0.4 N at a supply pressure of 550 kPa. The position sensor consists of two coils wound
around the cylinder of the actuator. The measurement principle is based on the change in coupling factor between the
coils as the piston moves in the actuator. The sensor is extremely small since one layer of 25 μm copper wire is sufficient
to achieve an accuracy of 10 μm over the total stroke. Measurements showed that the actuator achieves a positioning
accuracy of 20 μm in closed loop control.
Recent research revealed that microactuators driven by pressurized fluids are able to generate high power and force
densities at microscale. Despite these promising properties, fluidic actuators are rare in microsystem technology. The
main technological barrier in the development of these actuators is the fabrication of powerful seals with low leakage.
This paper presents a seal technology for linear fluidic microactuators based on ferrofluids. An accurate design method
for these seals has been developed and validated by measurements on miniaturized actuator prototypes. Our current
actuator prototypes are able to seal pressures up to 16 bar without leakage. The actuator has an outside diameter of 2
mm, a length of 13 mm and the actuator is able to generate forces of 0.65 N and a stroke of 10 mm. Moreover, promising
properties such as the restoration of the seal after a pressure overload have been observed.
Optics offers great possibilities for the design of cheap force sensors. One of the applications where these sensors are needed, is a computer pen. There, the force sensor is used to measure the contact forces between the pen tip and the paper. The optical tri-axial force sensor presented in this paper is designed for this purpose. The sensor is based on a flexible structure, which converts the force into a displacement. This displacement is measured optically, with a LED, a photodiode and a moving plate between these two components. Tests show that this simple measuring principle reaches a resolution of 60nm and a linearity of 1% in the range of 500μm. Based on these experiments, a mechanical structure is designed. Special attention is spent to get an equal stiffness and, therefore, an equal sensitivity in all directions. In addition each axis is provided with an emergency stop, to protect the sensor against overloading. The design results in a sensor with the size of 8.4mm x 8.4mm x 44.2mm. After production and assembly, this sensor is tested. It has a resolution of 0.01N, a sensitivity of 40mV/N and a linearity of 2%. Moreover, the sensor is insensitive to temperature variations, due to an extra dummy pair of LED and photodiode.
It is known the micro-EDM is a proper and flexible technology to machine freeform three-dimensional microstructures. Unfortunately, its capabilities are underestimated by the ruling microsystem designers due to the lack of widespread modeling and simulation tools. In this paper the strength of micro-EDM is reflected onto a solid modeling design environment, in which all designs are parametric and feature based. On top of standard features, user defined features can be created, which are automatically assessed on their producibility. The producibility of user defined features is verified by generating a tool electrode, that is able to machine the proposed user defined features. When the tool electrode is producible by WEDG and when it passes the strength check, the user defined feature is added to the feature library of the design environment. To compensate electrode wear the required number of tool electrodes for the multiple electrode strategy is calculated using an analytical expression, which is introduced in this paper. Finally, a number of microstructures are designed and machined to illustrate the implemented micro-EDM design environment.
The micro-EDM silicon machining performances have been stud on a highly doped P-type silicon wafer. To demonstrate and to emphasize the silicon micro-EDM, one kind of stainless steel is machine das a reference material. Both materials are sparked with specific sparking energy in micro-Joule energy range and machining characteristics such as material removal mechanism, cutting rate, relative electrode wear ratio and surface quality are examined and analyzed. The thermally induced microcracks are also examined and analyzed using a an optical and a SEM. It is found that for silicon, the micro-EDM material removal mechanism is not completely similar to conventional metal micro-EDM; besides melting and evaporation there is a significant contribution from thermal spallation, which is a kind of direct mechanical material damage without melting. This paper also present that microcrack generation is not only relate to the sparking energy but also has a close relationship with the silicon crystal lattice. In order to get microcrack free silicon surfaces, the sparking energy should be controlled to low levels, which are much lower than the voltage levels used in metal micro-EDM. All in all, thermal spalling should be reduced as much as possible, to obtain smooth and crack free machined surfaces.
Currently, most silicon microstructures used in microstructures are produced by photolithographic methods. The reason for this is the well-developed etching technology, used in microelectronics, that has been transferred to the microsystem domain. But since the making of an arbitrary shape or angle on silicon mainly depends on the crystal orientation, some severe limits exist in the production of 3D structures. Electro-discharge machining (EDM) is basically a thermal process. During the EDM process material is removed by electric sparking. It is therefore completely different from etching. In this work, micro-EDM is introduce as a potential approach for solving the above mentioned drawbacks. First, this work presents several testing experiments with different process parameters to investigate the influence of the micro-EDM process on the silicon structure. Main emphasis is put on the surface roughness and on avoiding microcracks generated by the sparking process. It is found that microstructures with a sufficiently low surface roughness and with small microcracks can be produced. The remainder of the work concentrates on making small beam structures, which is a common structure in many microsensor designs. It is found that for a wafer thickness of 650 micrometers , the thinnest beam that can be produced is about 30 micrometers wide. This means that micro-EDM can offer an aspect ratio of 20 in combination with a god dimensional control.
Currently, nearly all microcomponents are fabricated by microelectronic production technologies like etching, deposition and other (photo)lithographic techniques. In this way, main emphasis has been put on surface micromechanics. The major challenges for the future will be the development of real 3D microstructures. Electro-discharge machining (EDM) is a so-called non-conventional machining technique, whereby material is removed through the erosive action of electrical discharges provided by a generator. As shown in this paper, electro-discharge machining proves to be a versatile technique which is very well suited for machining complex microstructures. First, an overview of the applicability of micro electro-discharge machining for manufacturing silicon micromechanical parts is given. Also the machine on which these structures were made is introduced. The main advantages of micro-EDM are its low installation cost, high accuracy and large design freedom. Micro-EDM can indeed easily machine complex 3D shapes that prove difficult for etching techniques. Next, the appropriate setting of the machining parameters in order to keep the material removal on the tool electrode at least an order of magnitude smaller than the material removal on the workpiece electrode are discussed. Micro-EDM requires electrodes as a tool A reliable method for producing these electrodes, with custom shape and small sizes is also presented. The primary applications of micro-EDM are in rapid prototyping and products with small batchsizes. However, the technique is versatile enough to be adapted to large series. Several examples are given of the possibilities of micro-EDM: an electric force motor, micromirrors at any angle with respect to the wafer plane, an acceleration sensor, and micro bevel and spur gears.