R.H. Munnig Schmidt

Fiber-coupled displacement interferometry without periodic nonlinearity

Displacement interferometry is widely used for accurately characterizing nanometer and subnanometer displacements in many applications. In many modern systems, fiber delivery is desired to limit optical alignment and remove heat sources from the system, but fiber delivery can exacerbate common interferometric measurement problems, such as periodic nonlinearity, and account for fiber-induced drift. In this Letter, we describe a novel, general Joo-type interferometer that inherently has an optical reference after any fiber delivery that eliminates fiber-induced drift. This interferometer demonstrated no detectable periodic nonlinearity in both free-space and fiber-delivered variants.

Micromilling of thin ribs with high aspect ratios

Micro features with high aspect ratios are one of the commonly encountered geometries found in micro products. In the literature, these structures are often used in demonstrator products machined by a micromilling process. In this paper, the challenges in micromilling thin ribs ith high aspect ratios have been studied. Due to the scaling effect, micro-ribs have relatively low stiffness but high natural frequency. Therefore, on the one hand, average forces have to be controlled well to avoid structural bending or even damage, while on the other hand, micro features are unlikely to be excited by the dynamic forces. The characteristics of micromilling forces and their relationships to the machining parameters, namely, feed per tooth, depth of cut and width of cut, were studied theoretically by force models. In addition, the effects of different milling strategies (up-/down-milling) and tool paths on the quality of thin features have been investigated using FEM. The results allow measures to be taken to minimize the force effects and support the micro features during machining. The experimental results verify the theoretical studies. Thin ribs about 15 ?m wide and with an aspect ratio of more than 50 were machined with good form and surface quality.

A Haptic Tele-operated System for Microassembly

A tele-haptic system for microassembly applications is currently being developed at the Delft University of Technology, with the goal of achieving superior performance by providing enhanced feedback to the human operator. Assembly of a micro-harmonic drive is used as a benchmark to fully evaluate the proposed tele-haptic system by investigating the control strategies and the individual subsystems: master device, microgrippers and slave system. The master device will be comprised of a parallel robot with a built-in gripper. The slave system and end effector are focused on providing efficient and effective force feedback of the interactions on the microenvironment to the human operator, in addition to detecting position and orientation of the object being grasped. Novel control strategies are also investigated to allow the transmission of high frequency transients to the operator, carrying information from hard contact interactions between the microgripper and the part to be assembled.

Toward interferometry for dimensional drift measurements with nanometer uncertainty

High-end industrial equipment evolves toward ever higher accuracies, and dimensional drift phenomena appear as a limitation for the required uncertainty level of precision metrology instrumentation. Detailed knowledge of the drift stability on timescales from minutes to weeks is needed for materials and constructional elements such as glued or bolted connections. We investigate a balanced, double-sided heterodyne interferometer for dimensional stability measurements. The complete interferometer includes an integrated refractometer and aims for a measurement uncertainty better than 100 pm. Measurements with a preliminary test setup of the instrument performance show an intrinsic stability of ±0.6 nm peak-to-peak over 23 h and 30 pm noise level at a timescale of a minute and shorter, limited by thermal and air refractive index fluctuations. Considerable improvement is expected for more stable ambient conditions and with dedicated, custom-made components.

Dynamic model for design optimization of a high bandwidth thermal linear motor

This paper presents the model for the design optimization of an aluminum Thermal Linear Motor (TLM) for high bandwidth positioning systems. The aluminum TLM is the crucial driving element for our Hard Disk Drive thermal micro actuator. It occupies less area than an electrostatic actuator with the same driving force while still reaching 3–5 kHz bandwidth for positioning accuracy better than 5 nm. Optimized thermal actuators, as found in literature, improve the stroke versus power consumption by reducing the heat loss to the frame. However, for fast cooling, i.e. fast thermal response, good heat transport to the frame is necessary. This means that a thermal actuator design which is optimal for quasi-static operation is different from a design that is optimal for high bandwidth applications.

Interferometry for picometer-level dimensional stability measurements

The accuracy of high-end industrial equipment and the reliability of produced goods can be limited by dimensional drift phenomena. Examples are the life cycle stability of instrumentation for space missions and the tight requirements for measurement uncertainty in the integrated circuit semiconductor industry. Re-calibration intervals of metrology instrumentation are a relevant cost factor in production. Detailed knowledge of drift stability on various timescales from minutes to weeks is needed for materials and constructional elements, such as glued or bolted joints. We report on the development of an optical heterodyne interferometer concept for the investigation of dimensional stability. The contactless, double-sided optical scheme directly probes dimensional length changes of prismatic samples, whilst the balanced configuration provides common mode rejection of perturbations that act similarly on the measurement and the reference beam. For a detailed description of the optical scheme, see Ref. [1]. In a twin configuration, a second interferometer with similar beam paths is located in close proximity to the sample measurement interferometer. With a vacuum tube included, this second interferometer is considered to act as a refractometer for efficient in-situ correction of air refractive index fluctuations. Alternatively, angular degrees of freedom, such as sample flexure, may be accessed through the twin-configuration. Given a sampling rate larger than approximately 10 Hz, i.e. larger than the thermal expansion rate of typical sample materials (e.g. Zerodur, SiC), sudden intrinsic sample instability events should be observable and discriminated from the slower thermal drift behaviour of both sample and interferometer.