Micro-force Sensor Research Articles

Three-dimensional indentation test system for observing the distribution of internal mechanical properties in materials

This paper describes the development of a three-dimensional (3D) indentation test system capable of observing the distribution of mechanical properties in structural materials. Serial sectioning with destructive treatment has traditionally been used as a method for observing microstructure within materials in three dimensions. The serial sectioning methods using precision cutting has attracted particular attention as it enables the observation of large sample volumes. However, those methods can only observe the microstructure as image, not the mechanical properties such as hardness and elastic modulus. To measure the 3D distribution of the mechanical properties of the material, it is effective to combine repeated cutting and indentation tests on each cutting surface. Morever, combining the image observation and mechanical property tests could allow a more sophisticated analysis of the interior of material. To implement this method, we have constructed an indentation test system on a precision machine using a Berkovich indenter, micro-force sensor, and micro-movement stage.In order to achieve a 3D indentation test, it is considered necessary to unify the measurement positions in the depth direction. Furthermore, the unloading rate needs to be controlled in order to carry out stable indentation tests. Therefore, we propose a method of 3D indentation test that can precisely control the maximum depth of indentation and unloading speed.In this paper, we devise a method for driving the constructed system and a method for obtaining data and confirm the accuracy of these methods by experiment. In addition, we determine indentation depth and unloading speed which are suitable for our method by performing indentation tests on a block for ultra-microhardness. Finally, we practice 3D indentation test in which the cutting and indentation tests are repeated on specimens with different mechanical properties in the depth direction. Experimental results show that our indentation test system is appropriate to measure three-dimensional mechanical properties inside the material.

Design, Prototyping, and Characterization of a Micro-Force Sensor Intended for Tissue Assessment in Confined Spaces

Design, Prototyping, and Characterization of a Micro-Force Sensor Intended for Tissue Assessment in Confined Spaces

Grooving and Absorption on Substrates to Reduce the Bulk Acoustic Wave for Surface Acoustic Wave Micro-Force Sensors.

Improving measurement accuracy is the core issue with surface acoustic wave (SAW) micro-force sensors. An electrode transducer can stimulate not only the SAW but also the bulk acoustic wave (BAW). A portion of the BAW can be picked up by the receiving transducer, leading to an unwanted or spurious signal. This can harm the device's frequency response characteristics, thereby potentially reducing the precision of the micro-force sensor's measurements. This paper examines the influence of anisotropy on wave propagation, and it also performs a phase-matching analysis between interdigital transducers (IDTs) and bulk waves. Two solutions are shown to reduce the influence of BAW for SAW micro sensors, which are arranged with acoustic absorbers at the ends of the substrate and in grooving in the piezoelectric substrate. Three different types of sensors were manufactured, and the test results showed that the sidelobes of the SAW micro-force sensor could be effectively inhibited (3.32 dB), thereby enhancing the sensitivity and performance of sensor detection. The SAW micro-force sensor manufactured using the new process was tested and the following results were obtained: the center frequency was 59.83 MHz, the fractional bandwidth was 1.33%, the range was 0-1000 mN, the linearity was 1.02%, the hysteresis was 0.59%, the repeatability was 1.11%, and the accuracy was 1.34%.

Microstructured Cantilever Probe on Optical Fiber Tip for Microforce Sensor

Benefiting from the great advances of the femtosecond laser two-photon polymerization (TPP) technology, customized microcantilever probes can be accurately 3-dimensional (3D) manufactured at the nanoscale size and thus have exhibited considerable potentials in the fields of microforce, micro-vibration, and microforce sensors. In this work, a controllable microstructured cantilever probe on an optical fiber tip for microforce detection is demonstrated both theoretically and experimentally. The static performances of the probe are firstly investigated based on the finite element method (FEM), which provides the basis for the structural design. The proposed cantilever probe is then 3D printed by means of the TPP technology. The experimental results show that the elastic constant k of the proposed cantilever probe can be actively tuned from 2.46 N/m to 62.35 N/m. The force sensitivity is 2.5 nm/µN, the Q-factor is 368.93, and the detection limit is 57.43 nN. Moreover, the mechanical properties of the cantilever probe can be flexibly adjusted by the geometric configuration of the cantilever. Thus, it has an enormous potential for matching the mechanical properties of biological samples in the direct contact mode.

An Overview of Microrobotic Systems for Microforce Sensing

Considering microbotics, microforce sensing, their working environment, and their control architecture together, microrobotic force-sensing systems provide the potential to outperform traditional stand-alone approaches. Microrobotics is a unique way for humans to control interactions between a robot and micrometer-size samples by enabling the control of speeds, dynamics, approach angles, and localization of the contact in a highly versatile manner. Many highly integrated microforce sensors attempt to measure forces occurring during these interactions, which are highly difficult to predict because the forces strongly depend on many environmental and system parameters. This article discusses state-of-the-art microrobotic systems for microforce sensing, considering all of these factors. It starts by presenting the basic principles of microrobotic microforce sensing, robotics, and control. It then discusses the importance of microforce sensor calibration and active microforce-sensing techniques. Finally, it provides an overview of microrobotic microforce-sensing systems and applications, including both tethered and untethered microrobotic approaches.

Contractile and Tensile Measurement of Molecular Artificial Muscles for Biohybrid Robotics.

A printable artificial muscle assembled from biomolecular motors, which we have recently developed, showed great potential in overcoming the design limitations of conventional biohybrid robots as a new bio-actuator. Characterizing its contractility for extending its applicability is important. However, conventional measurement methods are composed of complex operations with poor reproducibility, flexibility, and real-time responsiveness. This study presents a new method for measuring the contractile force generated by artificial muscles. A measurement system was constructed, wherein artificial muscles were patterned by UV laser scanning in an oil-sealed microchamber, and the contractile force was measured in real time using a microforce sensor extended by a 3D-printed microcantilever. The measurement accuracy of the sensor was ensured through calibration and correction. For demonstration purposes, a series of contractile measurements were carried out using the proposed system. The relationship between contractile force and the dimensions of the activation space of the artificial muscles, as well as the tensile properties of the contracted muscle chain were evaluated. The results will help characterize the contractile properties of the artificial muscle and lay the foundations for its further application in biohybrid robotics.

Investigation on the oil bridge between air bubble and glass surface in water: Formation, deformation, mechanical force and implications for froth flotation

In froth flotation, the insoluble oil as a liquid bridge between an air bubble and a solid surface in water is a common and important interface phenomenon. This paper investigated the impact of the oil bridge between an air bubble and a glass plane from aspects of mechanical forces acting on complex interfaces. An air bubble was pulling towards an oil droplet anchored on a flat glass slide under water compulsively. In this process, the high-speed camera was applied to observe the deformation of the interfaces and the mechanical forces were measured using a micro-force sensor. It was found that the air-water-oil (A-W-O) three-phase contact line (TPL) can form, expand and become stable rapidly within 85.0 ms when the bubble is attached to the oil droplet. The expansion of the A-W-O TPL provides an extra adhesion force to the air bubble. The oil formed an oil bridge connecting the bubble and the solid surface which shortened the attachment distance and extended the detachment distance. The mechanical force resulting from the oil bridge acting on the air bubble is equivalent to an air bubble directly adhering to a hydrophobically modified surface. The capillary force and pressure force were calculated and were found to be the major components of the mechanical force in the detaching process. This mechanical force was directly influenced by the interfacial tension vectors, the interface curvatures, and the TPL radius. The deformation on the interface, especially the A-W interface, is significant to the detachment process and related mechanical forces.

FBG-based three-dimensional micro-force sensor with axial force sensitivity-enhancing and temperature compensation for micro-forceps.

During retinal microsurgery, excessive interaction force between surgical instruments and intraocular tissue can cause serious accidents such as tissue injury, irreversible retinal damage, and even vision loss. It is essential to accurately sense the micro tool-tissue interaction force, especially for the Ophthalmic Microsurgery Robot. In this study, a fiber Bragg grating (FBG) three-dimensional (3-D) micro-force sensor for micro-forceps is proposed, which is integrated with the drive module as an end-effector and can be conveniently mounted onto the ophthalmic surgical robot. An innovative axial force sensitivity-enhancing structure is proposed based on the principles of flexure-hinge and flexible levers to overcome the low sensitivity of axial force measurement. A dual-grating temperature compensation method is adopted for axial force measurement, which considers the differential temperature sensitivity of the two FBGs. Three FBGs are arranged along the circumference of the guide tube in this study to measure transverse forces and compensate for effects caused by changes in temperature. The experimental results demonstrate that the micro-forceps designed in this study achieved a resolution of 0.13 mN for transverse force and 0.30 mN for axial force. The temperature compensation experiments show that the 3-D micro-force sensor can simultaneously compensate for temperature effects in axial and transverse force measurement.

Instrumented Flexible Glass Structure: A Bragg Grating Inscribed with Femtosecond Laser Used as a Bending Sensor.

Fused silica glass is a material with outstanding mechanical, thermal and optical properties. Being a brittle material, it is challenging to shape. In the last decade, the manufacturing of monolithic flexible mechanisms in fused silica has evolved with the femtosecond-laser-assisted etching process. However, instrumenting those structures is demanding. To address this obstacle, this article proposes to inscribe a Bragg Grating sensor inside a flexure and interface it with an optical fibre to record the strain using a spectrum analyser. The strain sensitivity of this Bragg Grating sensor is characterized at 1.2 pm/μϵ (1 μϵ = 1 microstrain). Among other applications, deformation sensing can be used to record a force. Its use as a micro-force sensor is estimated. The sensor resolution is limited by our recording equipment to 30 μN over a measurement range above 10 mN. This technology can offer opportunities for surgery applications or others where precision and stability in harsh environments are required.

A 3D-Printed Microforce Sensor for Microscopic Objects

A cantilever probe microstructure is designed using mechanical metamaterials for an optical fiber microforce sensor tip.

Three-dimensional printed microcantilever with mechanical metamaterial for fiber-optic microforce sensing

Mechanical metamaterials can adjust mechanical properties of structures flexibly through a mechanical structural design based on the premise that the materials remain unchanged. Here, a cantilever probe microstructure is designed using mechanical metamaterials for an optical fiber microforce sensor tip that can be prepared by femtosecond laser-induced two-photon polymerization. The elastic constant k of the fabricated fiber-optic microforce sensor has been adjusted by two orders of magnitude from 0.165 to 46 N/m, and the geometric configuration of the cantilever beam can be tailored to match the mechanical properties of biological specimens. This fiber microforce sensor shows an ultra-high force sensitivity of 154 nm/µN and a force resolution of up to 130 pN. The optical fiber microforce sensor that shows the lowest force resolution in a direct-contact mode has high potential for biosensing applications, and the results reveal a potential design strategy for special scanning tunneling microscope probes with unique physical properties.

A Mechanical Evaluation of a Robot-Assisted Cutting Cornea Based on Force Response.

The aim of this paper is to propose laws of trephine operation based on a robot-assisted cutting cornea in order to obtain better microsurgical effects for keratoplasty. Using a trephine robot integrated with a microforce sensor and a handheld trephine manipulator, robotic and manual experiments were performed, with porcine corneas as the test subjects. The effect of trephine operational parameters on the results reflected by the biomechanical response is discussed, and the parameters include linear velocity, rotating angle, and angular velocity. Using probability density functions, the distributions of the manual operational parameters show some randomness, and there is a large fluctuation in the trephine force during the experiments. The biomechanical response shows regular trends in the robotic experiments even under different parameters, and compared to manual trephination, the robot may perform the operation of trephine cornea cutting more stably. Under different operational parameters, the cutting force shows different trends, and the optimal initial parameters that result in better trephine effects can be obtained based on the trends. Based on this derived law, the operational parameters can be set in robotic trephination, and surgeons can also be specially trained to achieve a better microsurgical result.

Micro ECDM scanning process with feedback control of flexible contact force

Quartz glass has been widely used in frontier fields of MEMS (micro electro-mechanical systems) and sensors due to its excellent chemical and mechanical properties. Although ECDM (electrochemical discharge machining) is a non-traditional material removal process suitable for machining electrically non-conductive materials of high temperature resistance and hard brittleness, the adopted feeding strategy of tool electrode directly affects the machining results, especially in a micro ECDM scanning process. The existing feed methods still cannot maintain a suitable machining gap with a minimum given contact force during the micro ECDM scanning process, causing inconsistent gap state and the damage to machining stability and geometric accuracy of micro structures. In this research, a novel spindle combining a flexure hinge and a high-resolution micro-force sensor is designed, achieving the function of real-time servo control of a given micro contact force. Using the micro tool electrodes (<Φ200 μm) fabricated by the combined process of reverse-copying micro EDM and TF-WEDG (tangential feed-wire electrode discharge grinding), the circular structures are successfully machined on quartz glass with the optimized parameters of open-circuit voltage, scanning speed, and number of scanning. To guarantee the consistent depth along a scanning layer, a feed strategy of quantified depth with servo control of flexible micro force (SCFMF-QDFS) is proposed, and micro 3D structures of S-shape and square are machined with controllable accuracy of ±2 μm and ±4 μm in depth and width.

A Microrobot With an Attached Microforce Sensor for Transurethral Access to the Bladder Interior Wall

AbstractWe present the conceptual design and limited functionality prototype and characterization of a system for application in transurethral palpation of any targeted area of the bladder interior wall tissue consisting of a robotic manipulator and a microforce sensor attached at its tip all less than 3.5 mm in diameter. A hyper-redundant ten-joint six degrees-of-freedom (6DOF) manipulator (5DOF rigid and five-joint continuum segments) is presented along with the forward and inverse kinematics analyses based on a Jacobian formulation to prevent configuration singularities. Simulated motion studies demonstrate the ability of the proposed manipulator to attain a desired pose (normal to the tissue) with any area in the bladder including the difficult to reach trigone area. A strain gauge-based microforce sensor is designed using finite element analysis (safety factor &amp;gt; 3), prototyped using additive manufacturing, and characterized. The characterized sensor was used to acquire in vivo measurements to evaluate human palm tissue viscoelastic properties. A single module of the continuum segment is designed and prototyped using additive manufacturing, and used to characterize its tension-bend angle behavior. Finite element analysis is used to improve structurally weak regions of the vertebra. A three-joint four-vertebrae prototype was successfully actuated to reach a bend state using tendons. The developed robot and sensor prototypes demonstrate capabilities of the proposed concept which could be a possible solution to quantitatively evaluate localized biomechanical properties of the bladder tissue to improve treatment and provide better patient care.

Design and Development of a Highly Performant 3-D Flexible Microforce Sensor for Miniature Biomedical Applications

Microforce sensors capable of measuring multiple degrees of freedom are in wide demand in miniature medical applications, but they are currently not available on a large scale due to high cost, fragility, and limited resolution. Therefore, this article presents a low-cost 3-D microforce sensor based on hybrid carbon/polymer-based soft piezoresistive (HCP) films with high sensitivity and robustness, as well as low thermal drift and hysteresis. Besides, due to the difficulty of constructing an accurate model to calibrate the flexible material-based sensor, this article employs data-based calibration methods to achieve fast calibration. In addition, the developed prototype is continuously and dynamically tested from hundreds of micronewtons to dozens of millinewtons. The developed sensor is experimentally proven to be highly sensitive, durable, low cost, self-decoupling, and impact-resistant for potential miniature biomedical applications.

An SMA Transducer for Sensing Tactile Sensation Focusing on Stroking Motion.

The authors have developed a micro-vibration actuator using filiform SMA wire electrically driven by periodic electric current. While applying the SMA actuators to tactile displays, we discovered a phenomenon that the deformation caused by a given stress to an SMA wire generated a change in the electrical resistance. With this characteristic, the SMA wire works as a micro-force sensor with high sensitivity, while generating micro-vibration. In this paper, the micro-force sensing ability of an SMA transducer is described and discussed. Experiments are conducted by sliding the SMA sensor on the surface of different objects with different speeds, and the sensing ability is evaluated to be related with human tactile sensation.

Development of a Microforce Sensor Based on a Fiber Bragg Grating Used for Micro-/Nanomanipulation

In the micro/nano manipulation process, the detection of micro-forces is essential not only for sample protection but also for mechanical property tests. In general, optical fiber sensors have excellent sensitivities so they can be used as a kind of new sensing element for microforce sensor design. This paper proposes a cantilever-type fiber Bragg grating (FBG)-based microforce sensor with micro-Newton resolution. A complete theoretical model is proposed to establish the mapping between the optical wavelength and the external force, and simulations are also carried out. A series of experiments are performed to evaluate the sensor, which agrees well with the calculation results, showing the sensor has the resolution of 7 μN force in the range of 10 mN. Finally, the calibrated sensor is applied in a micro/nano manipulation system to achieve the mechanical property test of the zebrafish embryo. The result fits well with the reference results, proving the microforce sensor has the capability of measuring the mechanical property of the biological sample.

Evaluation of Friction Force on the Nanostructures Mimicking Invertebrate Body Surface by Two-Axis Microforce Sensor

Evaluation of Friction Force on the Nanostructures Mimicking Invertebrate Body Surface by Two-Axis Microforce Sensor

Microforce Sensing and Flexible Assembly Method for Key Parts of ICF Microtargets

Microassembly is one of the key techniques in various advanced industrial applications. Meanwhile, high success rates for axial hole assembly of thin-walled deep-cavity-type items remain a challenging issue. Hence, the flexible assembly approach of thin-walled deep-cavity parts is investigated in this study using the assembly of the key components, the microtarget component TMP (thermomechanical package) and the hohlraum in ICF (inertial confinement fusion) research, as examples. A clamping force-assembly force mapping model based on multisource microforce sensors was developed to overcome the incapacity of microscopic vision to properly identify the condition of components after contact. The ICF microtarget flexible assembly system, which integrates multisource microforce sensing and a six degrees of freedom micromotion sliding table, is presented to address the constraint that the standard microassembly approach is difficult to operate once the parts contact. This method can detect contact force down to the mN level, modify deviation of the component posture efficiently, and achieve nondestructive ICF microtarget assembly at the end.

3D printed vision-based micro-force sensors for microrobotic applications

3D printed vision-based micro-force sensors for microrobotic applications