At small scales, automating robotic tasks such as assembly, force/displacement characterization, positioning, etc., appear to be particularly limited. This is due to the lack of sufficiently performing and easy-to-implement multi-degrees-of-freedom measurement systems able to measure the relative pose between micro-parts. In order to address this issue, a measurement method based on High-Precision fiducial markers (named HP code) is proposed. This measurement method combines a periodic pattern (providing high resolution by phase-based computation) with more regular QR codes (bringing versatile implementations and a quick detection). The design and method to efficiently locate these HP codes are presented in this paper. Experimental investigations demonstrate ultra-high resolution: 2 nm and$5 ~\mu $rad along$X,Y$and$\Theta $respectively (i.e. one thousandth of a pixel typically). The method is designed to be scalable as well as self-calibrated and to provide high robustness and high versatility. Two typical challenging applications in the field of microrobotics are automated to demonstrate these disruptive performances and the easy-to-implement capability of the method: (1) the automated assembly of two micro-fluidic chips through visual servoing with an achieved positioning accuracy below 50 nm, and (2) the automated micromechanical characterization of single fibers achieved by the integration of HP codes into a compliant structure enabling simultaneous micro-force and displacement sensing capabilities. These achievements highlight the versatility of the method and open the door to the rapid automation of high-quality robotic tasks at the micro scale. Note to Practitioners—The motivation for this work/study is based on the fact that many application areas are extensively orienting towards microrobotic systems to perform precise tasks with versatility. However, at the micro scale, many disturbances such as the effects of climate change strongly affect this precision. This problem is amplified by the fact that sensors cannot be easily integrated, either by lack of space or by the lack of measurement systems available. Vision-based approaches are widespread at this scale and appear very promising to measure the relative pose between micro-parts. Nevertheless, existing vision-based approaches like digital image correlation are both scale and texture dependent. Due to the lack of space, they are also difficult to use in practice at small scales for high resolution measurement. The main contribution of this paper lies in the capability to achieve ultra-high resolution measurements. For that, a structure based on High-Precision fiducial markers (named HP codes) is proposed and requires few and simple settings while achieving very high resolution both in position and orientation, typically down to one thousandth of a pixel and a few micro radians, respectively. It provides an off-the-shelf solution, versatile, easy to implement and achieves high resolution measurements in the plane (XY$\Theta $). HP codes are applicable to a wide range of applications such as tracking of a component/part of a mobile or deformable system, visual servoing of microrobots, positioning of samples, assembly of components or even mechanical characterization. A free distribution of the library is available online athttps://projects.femto-st.fr/vernier/.

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.

Collaborative robotics allows merging the best capabilities of humans and robots to perform complex tasks. This allows the user to interact with remote and directly inaccessible environments such as the micro-scale world. This interaction is made possible by the bidirectional exchange of information (displacement - force) between the user and the environment through a haptic interface. The effectiveness of the human/robot interaction is highly dependent on how the human feels the forces. This is a key point to enable humans to make the right decisions in a collaborative task. This paper discusses the design of a dynamic observer to estimate the forces applied by a human operator on a class of parallel pantograph-type haptic interfaces used to control small-scale robotic systems. The objective is to reject disturbances in order to improve the human force perception capability over a wide frequency range. A dynamic pantograph model is proposed and experimentally validated. The observer is designed on the basis of the proposed dynamic model and its efficiency in estimating the applied human force is demonstrated for the first time with pantograph-type interfaces. Experimental validation first shows the effectiveness of the perturbation observer for external human force estimation with a response time of less than 0.2 s and a mean error of less than 7 mN and then the effectiveness of the controller in improving the quality of human sensation of forces down to 10 mN.

Recently, high resolution visual methods based on direct-phase measurement of periodic patterns has been proposed with successful applications to microrobotics. This paper proposes a new implementation of direct-phase measurement methods to achieve 3-DoF (degrees of freedom) visual servoing. The proposed algorithm relies on a single frequency tracking rather than a complete 2D discrete Fourier transform that was required in previous works. The method does not require any calibration step and has many advantages such as high subpixelic resolution, high robustness and short computation time. Several experimental validations (in favorable and unfavorable conditions of use) were performed using a XYθ microrobotic platform. The obtained results demonstrate the efficiency of the frequency-based controller, this in term of accuracy (micrometric error), convergence rate (30 iterations in nominal conditions) and robustness.

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.

High positioning accuracy with micropositioning robots (MPRs) is required to successfully perform many complex tasks, such as microassembly, manipulation, and characterization of biological tissues and minimally invasive inspection and surgery. Despite the widespread use of high-resolution micro- and nanopositioning robots, there is very little knowledge about the real positioning accuracy that can be obtained and what the main influential factors are. Indeed, very few notable methods are available to measure multi-degree-of-freedom motions with adapted range, resolution, and dynamic capabilities. The main objective of this paper is to quantify the positioning accuracy of serial MPRs and to identify the main influential factors (a typical XY Θ serial robot is chosen as a case study). To reach this goal, a measuring system that combines vision and pseudoperiodic patterns with an extremely large range-to-resolution ratio is introduced as a new way to quantify the positioning accuracy of MPRs for in-plane motions. Then, an open-loop control approach based on MPR calibration is chosen for several reasons: the use of different models to identify influential factors, the quantification of the positioning accuracy, and the necessity of the method when sensor integration is too complex. Experiments using five different calibration models were conducted to classify factors influencing the positioning accuracy of MPRs. The results show that positioning accuracy can be improved by more than 35 times from 96 μ with no imperfection compensation to 2.5 μ by compensating for geometric, position-dependent, and angle-dependent errors through the MPR calibration approach.

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.

Accuracy is an important issue for microrobotic applications. High accuracy is usually a necessary condition for reliable system performance. However there are many sources of inaccuracy acting on the microrobotic systems. Characterization and compensation enable reduction of the systematic errors of the micropositioning stages and improve the positioning accuracy. In this paper, we propose a novel method based on vision and pseudo-periodic encoded patterns to characterize the position-dependent errors along XY stages. This method is particularly suitable for microscale motion characterization thanks to its high range-to-resolution ratio and avoidance of camera calibration. Based on look-up tables and interpolation techniques, we perform compensation and get improved accuracy. The experimental results show an accuracy improved by 84% for square tracking and by 68% for random points reaching (respectively from 22 μm to 3.5 μm and from 22 μm to 7 μm).

In micromanipulation, especially microassembly, accuracy is a criterion useful for characterizing the performance of microrobots. The increase of positioning accuracy is a very important issue before making automatic assembly or other micro-tasks such as characterization. Thermal drift is one of the major sources of inaccuracy for automatic micromanipulation in ambient conditions and even in clean room. This paper addresses the calibration of a 1-DOF (Degree Of Freedom) nanopositioning cell including thermal drift compensation. The nanopositioning cell consists of a single-axis PZT stage and a XYZ manual stage which is usually used for fine positioning in microassembly platform. Subsequently, validations are implemented to test the performance by integrating the calibrated model. The experimental results show an effective improvement of the accuracy by a factor of 7 when temperature changes in the range of temperature for training, and 2.4 times improvement is achieved when temperature goes out of the training range.

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.

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.

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.

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.

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.

The purpose of this paper is to present a temporary fixing system based on a thermal glue that is well-adapted to micro-robotics. In the paper, this system is used to design a tool changer but can be generalized to other micro-robotic applications. A thermal modeling and an identification procedure are presented to propose a strategy to control the system. This system takes place into a micromanipulation station to gain flexibility, space and complexity. Indeed, to perform sequences of micromanipulation tasks (i.e. micro-assembly sequences), only one manipulator, able to use sequentially several end-effectors, has to be used instead of several dedicated to one specific task

This paper deals with the design, fabrication and characterization of a new micro-tools changer for a micromanipulation station including three translation stages (X-Y-Z manipulator) and a new piezoelectric microgripper. This system can be implemented in confined workspaces such as a scanning electron microscope (SEM) or more generally in a micro-factory station by the reduction of the manipulator's size and the flexibility gain. The principle of this micro-tools changer is based on the use of a thermal glue whose state (liquid or solid) is controlled by surface mounted device (SMD) electrical resistances. Such system allows hundreds of automatic micro-tools exchanges with a maximum position error between two consecutive tools exchanges of respectively 4.2, 2.8 and 5.4 /spl mu/m on the X, Y and Z axis. To validate the use of the micromanipulation station in a SEM, an experimental comparison of the working principle in low (vacuum) and high (air) pressure has also been established through thermal and degassing studies.