A Two-Axis Piezoresistive Force Sensing Tool for Microgripping.

Force sensing has always been an important necessity in making decisions for manipulation. It becomes more appealing in the micro-scale context, especially where the surface forces become predominant. In addition, the deformations happening at the very local level are often coupled, and therefore providing multi-axis force sensing capabilities to microgripper becomes an important necessity. The manufacturing of a multi-axis instrumented microgripper comprises several levels of complexity, especially when it comes to the single wafer fabrication of a sensing and actuation mechanism. To address these requirements, in this work, an instrumented two-axis force sensing tool is proposed, which can then be integrated with the appropriate actuators for microgripping. Indeed, based on the task, the gripper design and shape requirements may differ. To cover wide needs, a versatile manufacturing strategy comprising of the separate fabrication of the passive and sensing parts was especially investigated. At the microscale, signal processing brings additional challenges, especially when we are dealing with multi-axis sensing. Therefore, a proper device, with efficient and appropriate systems and signal processing integration, is highly important. To keep these requirements in consideration, a dedicated clean-room based micro-fabrication of the devices and corresponding electronics to effectively process the signals are presented in this work. The fabricated sensing part can be assembled with wide varieties of passive parts to have different sensing tools as well as grippers. This force sensing tool is based upon the piezoresistive principle, and is experimentally demonstrated with a sensing capability up to 9 mN along the two axes with a resolution of 20 µN. The experimental results validate the measurement error within 1%. This work explains the system design, its working principle, FEM analysis, its fabrication and assembly, followed by the experimental validation of its performance. Moreover, the use of the proposed sensing tool for an instrumented gripper was also discussed and demonstrated with a micrograsping and release task.

Real-time Lissajous imaging with a low-voltage 2-axis MEMS scanner based on electrothermal actuation.

Laser scanning based on Micro-Electro-Mechanical Systems (MEMS) scanners has become very attractive for biomedical endoscopic imaging, such as confocal microscopy or Optical Coherence Tomography (OCT). These scanners are required to be fast to achieve real-time image reconstruction while working at low actuation voltage to comply with medical standards. In this context, we report a 2-axis Micro-Electro-Mechanical Systems (MEMS) electrothermal micro-scannercapable of imaging large fields of view at high frame rates, e.g. from 10 to 80 frames per second. For this purpose, Lissajous scan parameters are chosen to provide the optimal image quality within the scanner capabilities and the sampling rate limit, resulting from the limited A-scan rate of typical swept-sources used for OCT. Images of 233 px × 203 px and 53 px × 53 px at 10 fps and 61 fps, respectively, are experimentally obtained and demonstrate the potential of this micro-scannerfor high definition and high frame rate endoscopic Lissajous imaging.

Optimal Design of Piezoelectric Cantilevered Actuators for Charge-Based Self-Sensing Applications.

Charge-based Self-Sensing Actuation (SSA) is a cost and space-saving method for accurate piezoelectric based-actuator positioning. However, the performance of its implementation resides in the choice of its geometry and the properties of the constituent materials. This paper intends to analyze the charge-based SSA's performances dependence on the aforementioned parameters and properties for a piezoelectric cantilever. A model is established for this type of Piezoelectric Actuator (PEA), and a multi-objective function is defined. The multi-objective function consists of the weighted actuator and sensor objective functions of the PEA. The analytical optimization approach introduced herein aims to assess the evolution of the defined multi-objective function across a defined set of geometrical parameters and material properties and highlights the existence of a subset of solutions for an optimal charge-based SSA's implementation. The commercially-available finite element analysis software, COMSOL Multiphysics, is used on the parametric model of the given structure to validate the analytical model. Then, experiments are conducted to corroborate the numerical and analytical modeling and analysis.

Influence of mechanical noise inside a scanning electron microscope.

The scanning electron microscope is becoming a popular tool to perform tasks that require positioning, manipulation, characterization, and assembly of micro-components. However, some of these applications require a higher level of performance with respect to dynamics and precision of positioning. One limiting factor is the presence of unidentified noises and disturbances. This work aims to study the influence of mechanical disturbances generated by the environment and by the microscope, identifying how these can affect elements in the vacuum chamber. To achieve this objective, a dedicated setup, including a high-resolution vibrometer, was built inside the microscope. This work led to the identification and quantification of main disturbances and noise sources acting on a scanning electron microscope. Furthermore, the effects of external acoustic excitations were analysed. Potential applications of these results include noise compensation and real-time control for high accuracy tasks.

Study of thermal and acoustic noise interferences in low stiffness atomic force microscope cantilevers and characterization of their dynamic properties.

The atomic force microscope (AFM) is a powerful tool for the measurement of forces at the micro/nano scale when calibrated cantilevers are used. Besides many existing calibration techniques, the thermal calibration is one of the simplest and fastest methods for the dynamic characterization of an AFM cantilever. This method is efficient provided that the Brownian motion (thermal noise) is the most important source of excitation during the calibration process. Otherwise, the value of spring constant is underestimated. This paper investigates noise interference ranges in low stiffness AFM cantilevers taking into account thermal fluctuations and acoustic pressures as two main sources of noise. As a result, a preliminary knowledge about the conditions in which thermal fluctuations and acoustic pressures have closely the same effect on the AFM cantilever (noise interference) is provided with both theoretical and experimental arguments. Consequently, beyond the noise interference range, commercial low stiffness AFM cantilevers are calibrated in two ways: using the thermal noise (in a wide temperature range) and acoustic pressures generated by a loudspeaker. We then demonstrate that acoustic noises can also be used for an efficient characterization and calibration of low stiffness AFM cantilevers. The accuracy of the acoustic characterization is evaluated by comparison with results from the thermal calibration.

Quasistatic displacement self-sensing method for cantilevered piezoelectric actuators.

Piezoelectric meso- and microactuator systems required for manipulation or assembly of microscale objects demand reliable force and/or displacement information. Available sensors are prone to dimension restrictions or precision limitation. Self-sensing method, based on the electric charge measurement, may represent a solution in terms of cost-effectiveness and integration, the actuator performing simultaneously as its own sensor. This paper presents a self-sensing method dedicated to free uni- and bimorph piezocantilevers but can also be adapted to other piezoactuator types. The integrated electric current, used to convert the charge, can be compensated against piezoelectric material nonlinearities to provide accurate displacement information. The advantages relative to existing self-sensing methods consist in the ability to keep this displacement information for long-term periods (more than a thousand seconds) and in the reduction in signal noise. After introductive issues related to the method the base principle allowing the estimation of tip displacement is presented. Then, the identification procedure of the estimator parameters is depicted and representative experimental results are shown. Finally, a series of aspects related to electronic circuits are discussed, useful for successful system implementation.

Current integration force and displacement self-sensing method for cantilevered piezoelectric actuators.

This paper presents a new method of self-sensing both of the displacement and the external applied force at the tip of piezoelectric cantilevers. Integrated electric current across piezoelectric actuators is compensated against material nonlinearities (creep, hysteresis) to provide reliable information. We propose to compensate the hysteresis by using the Prandtl-Ishlinskii static approach while an auto regressive and moving average exogenous (ARMAX) model is used to minimize the creep influence. The quasistatic estimation, electronic circuit, and aspects related to long-term charge preservations are described or referenced. As an experiment, we tested the actuator entering in contact with a fixed force sensor. An input signal of 20 V peak-to-peak (10% of maximum range) led to force self-sensing errors inferior to +/-8%. A final discussion about method accuracy and its limitations is made.