This article proposes an original approach for robotic calibration that is based on measurements along a single direction (1-D). Among all applications, the field of microrobotics and nanorobotics has been chosen as case study because of the strong needs for high positioning accuracy (10–100 nm typically) while measuring with sufficient resolution along multi-degrees of freedom (DoF) is still a fully open question. The 1-D measurements relying on Fabry–Perot (FP) interferences is used, and the proposed modeling of a 6-DoF nanopositioning robot enables to derive the measurement strategy as well as the identification procedure for both extrinsic and intrinsic parameters. Experimental investigations demonstrate that the approach is easy to implement, low cost, and enables to understand what are the main influential parameters onto positioning accuracy. They also conduct to very high accuracy in 6-DoF positioning; a positioning accuracy estimate of 50 nm and 0.004° has notably been obtained for the full pose (position and orientation, respectively) and can be held during several hours after the measurements.Note to Practitioners—The motivation of this work is to give an answer to the growing needs for micro nanopositioning robots having a very high precision for applications in microassembly, in the characterization of micro and nano components or biological elements, or for minimally invasive surgery. The key contribution of the proposed work relies on the method proposed that enables to efficiently calibrate a serial 6-degree-of-freedom (DoF) robot using only 1-D interferometric measurements, which overcomes the need for multi-DoF, small size, and high-resolution sensors missing in commercial offers. Moreover, the behavior of such novel robotic solutions is not well known, difficult to model, and there is a clear lack of knowledge about the main influential parameters. The method proposed in this article notably enables to achieve the full calibration of the robot (all intrinsic and extrinsic parameters identified) to reach the best positioning accuracy. This first part takes times, and this article shows that it is then possible to adopt a less time taking procedure by only reidentifying extrinsic parameters and thus to hold these performances over long periods, typically a week.

The digital microrobot, called DiMiBot, opened a new paradigm in the design of microrobots by using mechanical stability instead of complex control strategies. Current DiMiBot robots are based on the use of bistable modules to reach discrete stable positions. However, the number of stable positions depends on the number of bistable modules. As a consequence, the mechanism size increases rapidly and its miniaturization becomes complex and non-intuitive. To tackle this issue, a new multistable module has been developed to reach several stable positions within a miniaturized structure. In this paper, we focus on the reapitability and the reproducibility analysis of the developed multistable module in terms of displacement. This study is mandatory to demonstrate the effectiveness of the module as it is expected to be an elementary component of the next generation of DiMiBot. To this end, a series of experimental measurements are conducted on individual and multiple modules. The results analysis show a good agreement between the theoretical and the experimental displacements. In other words, the multistable prototype is able to reach 13 stable positions linearly in one dimensional direction with a step of about 10 μm. These capabilities open a promising perspectives and applications of this module to achieve microrobotics tasks. For example, it can be integrated in complex systems devoted to advanced tasks or accurate positioning in MEMS devices.

Microassembly represents a very promising solution to microproducts and complex Micro-Electro-Mechanical Systems (MEMS) fabrication. Since, in the case of teleoperated assembly, an operator is the main source of errors, there is a great interest in microassembly automation. Its main issue consists in precise estimation of object position. Previous studies demonstrate the possibility of application of modelbased visual tracking algorithms from ViSP (Visual Servoing Platform) library. However, the methods of macroassembly cannot be directly applied when working with microobjects. The characterization of single-view visual tracking notably revealed the complexity of depth estimation in microscale, which is due to small depth variation in the seen images compared with the distance from camera. So, an algorithm of Z coordinate reconstruction using a second camera was developed and analyzed for visual servoing task. It was then used to automate microassembly. Experiments demonstrate the possibility of complex microcomponent automatic microassembly with precision better than 10 micrometers.

A new method to estimate the environment parameters is proposed in order to perform force tracking in impedance control despite the presence of an unknown environment. In impedance force tracking, the location of the environment relative to the robot and the stiffness of the environment should be known. The proposed method estimates the environment location and stiffness using only force and position measurements. The study is done for microscale taking into consideration microscale specificities, especially pull-off force. The impedance control formulation is tested experimentally in a contact transition scenario consisting of a compliant microforce sensor mounted on a microrobotic positioner, and three compliant microstructures with different stiffness. A traditional double mass-spring-damper model of the overall robot is employed to develop the closed-loop impedance control.

This paper studies automated tasks based on hybrid force/position control of a flexible object at the microscale. A guiding task of a flexible micropart is the case of the study and is achieved by a two-sensing-finger microgripper. An experimental model of the behavior of the microgripper is given and the interaction forces are studied. Based on grasp stability, a guiding strategy taking into account the pull off forces is proposed. A specific control strategy using an external hybrid force/position control and taking into account microscale specificities is proposed. The experimental results of automated guiding task are presented.

This Special Section presents recent and original advances in microassembly methods and technologies. An overview of the technical articles and features is provided.

Size reduction is a constant objective in new technologies for which very accurate devices are needed when manipulating submillimetric objects. A new kind of microfabricated microrobot based on the use of bistable modules is designed to perform open-loop controlled micropositioning tasks. The DiMiBot (a specific digital microrobot) opens a new paradigm in the design of microrobots by using mechanical stability instead of complex control strategies. We propose a new architecture of digital microrobot for which forward and inverse kinematics models are easy to use. These kinematic models are validated with finite-element-analysis simulations before the fabrication of a real DiMiBot prototype. Tests and characterization of the prototype are made and compared with the desired behavior. Thanks to its submicrometric resolution and to its small dimensions (~ 400-μm thickness), it is able to manipulate microobjects in confined environments, where no other robot can be used.

This paper presents a study about the effects of environmental noise on millimeter sized grippers in cantilever configuration. The study is motivated and conducted aiming at assessing the level of accuracy loss when performing micromanipulation/microassembly tasks in noisy environments as well in typical microrobotics laboratories as in industrial locations or operating rooms. Ground motion and acoustic noises within a typical microrobotic laboratory are characterized in the frequency domain and their effects on cantilevers of different lengths are inspected. The relevance of a typical vibration isolation table is evaluated and the effects of low and high acoustic noises are assessed. A modeling of a cantilever with base excitation is thereafter conducted in the state space using finite difference formulation and a stabilization of a disturbed cantilever is obtained at the nanometer level in noisy environments allowing perspectives to high precision micromanipulation tasks in hostile locations.

High precision manipulation becomes a recurrent need in micro or nanoscale. Microrobots based on active material were designed to perform micromanipulation tasks in various environments such as microrobotic stations or electronic microscopes (SEM, TEM). These active materials are used to generate proportional actuation, but show some drawbacks we want to avoid (non linearity, integration of sensors, ...). In this paper we propose a new type of microrobot, called digital microrobot. It is based on the use of bistable modules (Fig. 1), and generates a discrete workspace. This microrobot can be used in open-loop mode and gets rid of bulky and expensive instruments and sensor integration. Moreover, no external energy is required to maintain the microrobot in a given position. The study presented in this paper is dedicated to the design of the robotic structure in order to generate a desired workspace.

This paper presents an analytical model and experimental results from a study of guiding tasks in micro-assembly. This work is focused on the use of two fingers for gripping microparts. The stability of the grasp when the contact appears is investigated and strategies during the guiding task are discussed. The contact side detection and the contact force estimation are studied. The incremental control in static mode is then investigated for controlling the guiding task. Experimental setups are proposed and some experimental results are presented.

Microrobots are widely used for microassembly and micromanipulation. However achieving performances compatible with the work in the microworld requires the use of bulky and expensive systems for measurement, signal processing and real time control. In this paper, we present the characterization and the control of a bistable module that can be used to build microrobots. This bistable module is fabricated monolithically using microfabrication technology. It offers two stable and blocked positions. High resolutions can be reached using this approach. Static and dynamic characteristics of the bistable module are studied and an open-loop control strategy is proposed in order to switch smoothly from one position to the other. The presented bistable module is the basic module for building digital microrobots.

Force feedback control constitutes a promising solution for achieving fully automated micro-assembly. In this paper, we report the study of force feedback control used during guiding task. An experimental setup with two sensorized fingers is proposed. It enables to grasp a micropart of 2 mm × 50 μm × 50 μm in size and to estimate the lateral contact force. A simulator is developed to take into account the gripping forces evolution during a lateral perturbation. External hybrid force/position control is chosen for performing automated guiding tasks. Experimental results demonstrate the ability of the implemented controller and suitable design of microsystems.

The feedforward compensation of nonlinearities, i.e., hysteresis and creep, and unwanted vibrations in micromanipulators is presented in this paper. The aim is to improve the general performances of piezocantilevers dedicated to micromanipulation/microassembly tasks. While hysteresis is attenuated using the Prandtl-Ishlinskii inverse model, a new method is proposed to decrease the creep phenomenon. As no model inversion is used, the proposed method is simple and easy to implement. Finally, we employ an input shaping technique to reduce the vibration of the piezocantilevers. The experimental results show the efficiency of the feedforward techniques and their convenience to the micromanipulation/microassembly requirements.

This paper presents the estimation of the force applied by a piezocantilever dedicated to micro-manipulation/microassembly. Relative to previous works, the presented method avoids the reliance on the force dynamics on the characteristics of the micro-objects. Furthermore, the estimation is a closed-loop kind technique so that convergency can be ensured efficiently. To perform these, we consider the force at the tip of a piezocantilever as an unknown input and we use an unknown input observation technique. We especially use the inverse-dynamics-based UIO technique because it is well suited for a piezo-cantilever model. The experiments show that the performances of the observer are convenient for micromanipulation/microassembly tasks.

This paper deals with the description of a method for the measurement of friction force between a very small object (80 to 300 mum) and a support. The goal is to design a feeder based on controlled mechanical vibrations in order to drive microcomponents by breaking the friction force. The contact model is based on the Hertz theory and the Greenwood-Williamson multi-asperity model. The amplitude of the static friction force is measured in a clean environment with an AFM (atomic force microscope) whose cantilever is placed in the vertical position. Using this setup and the modeling, we have estimated the interfacial shear stress between the microcomponent and the support.

Due to their rapidity and their high resolution, piezoelectric materials are very prized in microactuators and microrobotics. The classical example is the piezocantilevers. Notwithstanding, piezoecantilevers present nonlinearities (hysteresis and creep) when the applied electric field becomes large. On the other hand, they present lightly damped vibration. Feedback control is a classical issue to eliminate this unwanted behavior but it involves the use of sensors. In micromanipulation and in microassembly, sensors still remain one of the problematic because of their sizes and difficulty of packaging. This paper presents the feedforward compensation of the hysteresis and the vibrations in piezocantilevers. While the Prandtl-Ishlinskii (PI) static hysteresis model is used to compute the hysteresis compensator, we employ the Input-Shaping method to reject the unwanted vibration. The experiments show that the accuracy can be highly increased while the setling time ameliorated and the vibration largely decreased.

A new control type for stick-slip microsystems is proposed in this paper: the voltage/frequency (U/f) proportional control. It gives a best resolution relatively to the classical control algorithm. It is also an englobalization of three classical controllers: the sign controller, the classical proportional controller and the frequency proportional controller. A high stroke model of a stick-slip microsystem is first given. Then, we theoretically analyze the performances of the closed loop process with the U/f controller. Finally, we give some experimental results obtained with different values of the proportional gains.

The effect of the temperature variation on a unimorph piezoelectric cantilever is studied. Its influences on the thermal expansion, the piezoelectric constant, the transient part and the creep are experimentally analyzed. Afterwards, a Hinfincontroller is synthesized in order to reject the thermal disturbance and to reach performances required in micromanipulation. Finally, the closed-loop experiments end the paper.

During a micromanipulation, it is important to have the same performances whatever the manipulated object is. We present in this paper the control of the force applied to flexible and rigid micro-objects by a piezoelectric cantilever. First, the voltage-force transfer function is modeled. The hysteresis and creep phenomena are taken into account. The reliance of the model on the characteristics of the micro-objects is clearly detailed. Then, in order to reject disturbances and maintain tracking performances required in micromanipulation, a Hinfincontroller is designed. Finally, the experimental results end the paper.

First, we present a survey on modeling and control of bending piezoelectric microactuators. Second, a simple model for nonlinear piezoelectric actuators (hysteresis and creep) is presented. It is based on the multilinear approximation. This model requires low computing power and is well adapted for embedded systems. Finally, a μ-synthesis controller is implemented. Experiments show that the obtained performances are compatible with the requirements of micromanipulation tasks

This paper presents the design, the development and the experiments on a two degrees of freedom (2DoF) microsystem. The originality of the microsystem is its ability to do angular and linear motions independently with a very high stroke and a submicrometric precision. The target performances are first presented. Afterwards the stick-slip piezoelectric microactuators that are used are presented. Then, their integration inside the microsystem is detailed. Finally, results of experiments are given

In this paper, a new type of microsystem is presented : a system able to perform linear and angular motion. First, the microactuator used is studied. An approximation of the working equations is proposed in accordance with Finite-Element simulation. The microactuator used is inserted in the microsystem and a separated modelling of the whole system in linear and in angular motion is given. Stick and skid phases of each motion are independently studied.