Sergej Fatikow

A Novel Direct Inverse Modeling Approach for Hysteresis Compensation of Piezoelectric Actuator in Feedforward Applications

The Prandtl-Ishlinskii (PI) model is widely utilized in hysteresis modeling and compensation of piezoelectric actuators. For systems with rate-independent hysteresis, the inverse PI model is analytically feasible and it can be adopted as a feedforward compensator for the hysteretic nonlinearity of piezoelectric actuators. However, for the rate-dependent PI model, the applicable valid inversion methodology is not yet available. Although simply replacing all the rate-independent terms in the conventional inversion law with the rate-dependent terms can achieve acceptable results at very slow trajectories. However, a large theoretical modeling error is inevitable at fast trajectories, which is investigated through simulations. This paper proposes a new direct approach to derive the inverse PI model directly from experimental data. As no inversion calculation is involved, the proposed direct approach is efficient and the theoretical modeling error can be avoided. In order to validate the accuracy of the direct approach, a number of experiments have been implemented on a piezo-driven compliant mechanism by utilizing the inverse PI model as a feedforward controller. The tracking performance of the mechanism is significantly improved by the direct approach.

Modeling and Control of Piezo-Actuated Nanopositioning Stages: A Survey

Piezo-actuated stages have become more and more promising in nanopositioning applications due to the excellent advantages of the fast response time, large mechanical force, and extremely fine resolution. Modeling and control are critical to achieve objectives for high-precision motion. However, piezo-actuated stages themselves suffer from the inherent drawbacks produced by the inherent creep and hysteresis nonlinearities and vibration caused by the lightly damped resonant dynamics, which make modeling and control of such systems challenging. To address these challenges, various techniques have been reported in the literature. This paper surveys and discusses the progresses of different modeling and control approaches for piezo-actuated nanopositioning stages and highlights new opportunities for the extended studies.

Microrobot System for Automatic Nanohandling Inside a Scanning Electron Microscope

In this paper, current research work on the development of an automated nano handling station in a scanning electron microscope (SEM) is presented. An experimental setup is described, in which two mobile microrobots cooperate in the vacuum chamber of an SEM. The robots are positioned by a closed-loop controller with sensor data, which is provided by three charge-coupled device cameras and the SEM. Continuous pose estimation is carried out by processing noisy SEM images in real time. To enable the automation of complex tasks, a client-server control system that can integrate various microrobots and sensors is introduced. Finally, the overall system is evaluated by automatic handling of transmission electron microscope lamellae.

Real-time object tracking for the robot-based nanohandling in a scanning electron microscope

In this paper, current research work on an automated nanohandling station using mobile microrobots is presented. For the automated positioning of mobile microrobots a closed-loop control system is necessary, usually using data from pose sensors for the degrees of freedom (DOF) of the microrobot are needed. Mobile microrobots with piezo slip-stick actuation mostly do not have internal pose sensors to determine a global pose. This paper focuses on the continuous pose estimation (tracking) of mobile microrobots by external visual sensors. One possibility for fast pose estimation is the application of video cameras in combination with image processing algorithms as global sensors. However, for pose estimation with accuracy in the nanometer range high-resolution sensors are necessary. In consideration of resolution, image acquisition time and depth of focus a scanning electron microscope (SEM) is a powerful sensor for high-resolution pose estimation of a microrobot. On the other hand, the use of a SEM requires high demands on the image processing. High update rates of the pose data for the robot control require a short image acquisition time of the SEM images. As a result, the image noise increases as frame averaging or averaging of the detector signal is time consuming. This paper presents two approaches to tracking a micro-object in a SEM image stream. First, a cross-correlation algorithm is described, which enables pose estimation (x, y, ϕ) in extremely noised images in real-time. Afterwards object tracking with active contours is presented. This approach allows real-time tracking with more than 3 DOF by using shape spaces, instead of defining large model sets as it is necessary for correlation-based pattern matching.

A carbon nanofibre scanning probe assembled using an electrothermal microgripper

Functional devices can be directly assembled using microgrippers with an in situ electron microscope. Two simple and compact silicon microgripper designs are investigated here. These are operated by electrothermal actuation, and are used to transfer a catalytically grown multi-walled carbon nanofibre from a fixed position on a substrate to the tip of an atomic force microscope cantilever, inside a scanning electron microscope. Scanning of high aspect ratio trenches using the nanofibre supertip shows a significantly better performance than that with standard pyramidal silicon tips. Based on manipulation experiments as well as a simple analysis, we show that shear pulling (lateral movement of the gripper) is far more effective than tensile pulling (vertical movement of gripper) for the mechanical removal of carbon nanotubes from a substrate.

Rapid prototyping of nanotube-based devices using topology-optimized microgrippers

Nanorobotic handling of carbon nanotubes (CNTs) using microgrippers is one of the most promising approaches for the rapid characterization of the CNTs and also for the assembly of prototypic nanotube-based devices. In this paper, we present pick-and-place nanomanipulation of multi-walled CNTs in a rapid and a reproducible manner. We placed CNTs on copper TEM grids for structural analysis and on AFM probes for the assembly of AFM super-tips. We used electrothermally actuated polysilicon microgrippers designed using topology optimization in the experiments. The microgrippers are able to open as well as close. Topology optimization leads to a 10-100 times improvement of the gripping force compared to conventional designs of similar size. Furthermore, we improved our nanorobotic system to offer more degrees of freedom. TEM investigation of the CNTs shows that the multi-walled tubes are coated with an amorphous carbon layer, which is locally removed at the contact points with the microgripper. The assembled AFM super-tips are used for AFM measurements of microstructures with high aspect ratios.

Force sensing in microrobotic systems-an overview

This paper describes methods of force sensing and gives a brief overview about applications of micro force sensors. Realisation of reliable force sensing during manipulation of microobjects is one of the important objectives of the current research activities. At present, the most common technique used for force sensing in micromanipulation is that of strain gauges; some of the proposed force sensors make use of-the piezoelectric effect. Other promising methods for strain measurement are also explored, but in general, only a few provide a basic and analytical description of force sensors for micromanipulation. However, these data are of fundamental importance for a proper functionality of microrobots capable of grasping with force feedback.

An automated microrobot-based desktop station for micro assembly and handling of micro-objects

One of the main problems of present-day microsystem technology (MST) is the assembly of a whole microsystem from different micro-components. This paper presents an automated micromanipulation desktop station the main feature of which are piezoelectrically driven microrobots placed on a highly precise x-y table of a microscope. The microrobots can perform high-precise manipulations (with an accuracy of up to 10 nm) and the transport of very small objects (at a speed of several mm/sec). To control the desktop station automatically, a sensor system is provided for fine and for gross positioning of the robots, respectively. Apart from assembly tasks this automated station can be used, for examples, for handling biological cells or testing silicon chips.

NanoLab: A nanorobotic system for automated pick-and-place handling and characterization of CNTs

Carbon nanotubes (CNTs) are one of the most promising materials for nanoelectronic applications. Before bringing CNTs into large-scale production, a reliable nanorobotic system for automated handling and characterization as well as prototyping of CNT-based components is essential. This paper presents the NanoLab setup, a nanorobotic system that combines specially developed key components such as electrothermal microgrippers and mobile microrobots inside a scanning electron microscope. The working principle and fabrication of mobile microrobots and electrothermal microgripper as well as their interaction and integration is described. Furthermore, the NanoLab is used to explore novel key strategies such as automated locating of CNTs for pick-and-place handling and methods for electrical characterization of CNTs. The results have been achieved within the framework of a European research project where the scientific knowledge will be transfered into an industrial system that will be commercially available for potential customers.

Multimodal Electrothermal Silicon Microgrippers for Nanotube Manipulation

Microgrippers that are able to manipulate nanoobjects reproducibly are key components in 3-D nanomanipulation systems. We present here a monolithic electrothermal microgripper prepared by silicon microfabrication, and demonstrate pick-and-place of an as-grown carbon nanotube from a 2-D array onto a transmission electron microscopy grid, as a first step toward a reliable and precise pick-and-place process for carbon nanotubes.