Fiber-tip polymer clamped-beam probe for high-sensitivity nanoforce measurements

Micromanipulation and biological, material science, and medical applications often require to control or measure the forces asserted on small objects. Here, we demonstrate for the first time the microprinting of a novel fiber-tip-polymer clamped-beam probe micro-force sensor for the examination of biological samples. The proposed sensor consists of two bases, a clamped beam, and a force-sensing probe, which were developed using a femtosecond-laser-induced two-photon polymerization (TPP) technique. Based on the finite element method (FEM), the static performance of the structure was simulated to provide the basis for the structural design. A miniature all-fiber micro-force sensor of this type exhibited an ultrahigh force sensitivity of 1.51 nm μN−1, a detection limit of 54.9 nN, and an unambiguous sensor measurement range of ~2.9 mN. The Young’s modulus of polydimethylsiloxane, a butterfly feeler, and human hair were successfully measured with the proposed sensor. To the best of our knowledge, this fiber sensor has the smallest force-detection limit in direct contact mode reported to date, comparable to that of an atomic force microscope (AFM). This approach opens new avenues towards the realization of small-footprint AFMs that could be easily adapted for use in outside specialized laboratories. As such, we believe that this device will be beneficial for high-precision biomedical and material science examination, and the proposed fabrication method provides a new route for the next generation of research on complex fiber-integrated polymer devices.

Hydraulic Micro Device with Force Sensing for Measurement of Mechanical Characteristics

The medical and bio-engineering fields have been increasingly using information and communication technology. To introduce robots into surgical procedures, data on surgical operations are required. Several studies have tried the creation of data on living tissues for mechanical actions, which makes determining the mechanical characteristics of living tissues vital, but few have been commonly used. Therefore, we previously developed a sensing system that uses a hydraulic-driven micro mechanism to measure the force applied to an object when it is touched. Micro force sensors are necessary for various manipulations requiring careful operation. Unfortunately, the measurement accuracy of sensors tends to reduce with the reduction in sensor size. The proportional output in conventional force sensors, such as piezoelectric sensors, also decreases when the size of the sensor is reduced. However, a micro force sensor using a hydraulic-driven micro mechanism can obtain a large output even when it is small. Our system uses Pascal’s principle to measure small forces acting on the end effector. We propose methods for identifying the mechanical characteristics of certain viscoelastic materials similar to those used in a living organ. A hydraulic-driven micro device pushes an object and measures the reaction force and its displacement. We have used two types of micro devices, micro cylinder and micro bellows. Its stiffness and viscosity coefficient are obtained through calculations using Kelvin-Voigt and Zenner models. Discrete displacement and load data are applied to the estimated model, and the mechanical characteristics of the materials are identified as a minimized value between the estimated value and experimental one. We conducted experiments using the proposed identification methods on viscoelastic materials, and the results indicate that the value provided from the Kelvin-Voigt model was near the truth value.

Micro-force measurement with pre-curvature long-period fiber grating-based sensor

In this work, a long-period fiber grating (LPG) based sensor was evaluated as a sensing device for micro-force measurement, in the order of micro Newtons. It was used an LPG fabricated by arc-inducted technique in a SMF-28 standard optical fiber. The optical fiber was fixed between two clamps with a separation of 150 mm with the middle of the LPG located at the center. Characterizations were performed in terms of temperature, curvature and strain. The grating was then used as a micro-force sensor by means of both curvature and strain, induced by a hung mass in a stretched fiber. Furthermore, the evaluation of a precurvature LPG was performed to assess if an increase of sensitivity is achieved. Micro-force sensitivity achieved with the stretched LPG was 1.41 nm/mN and it was demonstrated that its sensitivity can be enhanced to 5.14 nm/mN with a pre-curvature of 2.2 m–1 applied to the LPG, achieving a spectral resolution of at least 15.6 μN.

Automatic precision robot assembly system with microscopic vision and force sensor

An automatic precision robot assembly system is established. The robot assembly system mainly consists of an industrial robot, three cameras, a micro force sensor, and a specific gripper. The industrial robot is a six-axis serial manipulator, which is used to conduct grasping and assembly subtasks. Two microscopic cameras are fixed on two high accuracy translational platforms to provide visual information in aligning stage for assembly. While one conventional camera is installed on the robotic end effector to guide the gripper to grasp component. The micro force sensor is installed on the robotic end effector to perceive the contacted forces in inserting stage. According to the characteristics of components, an adsorptive gripper is designed to pick up components. In addition, a three-stage “aligning–approaching–grasping” control strategy for grasping subtask and a two-stage “aligning–inserting” control strategy for assembly subtask are proposed. Position offset compensation is computed and introduced into aligning stage for assembly to make the grasped component in the microscopic cameras’ small field of view. Finally, based on the established robot assembly system and the proposed control strategies, the assembly tasks including grasping and assembly are carried out automatically. With 30 grasping experiments, the success rate is 100%. Besides, the position and orientation alignment errors of pose alignment for assembly are less than 20 μm and 0.1°.