Multi-axis Force Research Articles

Multi-axis MEMS force sensor for measuring friction components involved in dexterous micromanipulation: design and optimisation

At the nanoscale and for particular applications such as dexterous micro-manipulation, two degrees of freedom nanotribometers are no longer adequate for studying and characterising the contacts. This paper deals with the specifications and working principle of a new multi-axis friction sensor designed for nanotribological testing applied to this purpose in order to extract each contribution independently (i.e., sliding, rolling and spin motion). It is composed of a central platform with a fixed ball and surrounded by a compliant table. Its sensing ability is based on piezoresistivity: four sets of piezoresistors are symmetrically distributed at the root of four central beams. Finite elements method simulations are performed to find the optimal dimensions of the sensor. As results, this sensor could measure independently normal and friction forces in the range of 1 mN and 100 µN, respectively and the three rotation components. Estimated crosstalk is lower than 1% with a good sensitivity.

Measurement of Multi-axis Contact Force by Vision-based Tactile Sensor Using Elastic Membrane

Measurement of Multi-axis Contact Force by Vision-based Tactile Sensor Using Elastic Membrane

J0260103 MEMS多軸力センサを用いたハエの飛翔力計測

J0260103 MEMS多軸力センサを用いたハエの飛翔力計測

A Laparoscopic Grasping Tool with Force Sensing Capability

This paper presents a laparoscopic grasping tool for minimally invasive surgery with the capability of multiaxis force sensing. The tool is able to sense three-axis Cartesian manipulation force and a single-axis grasping force. The forces are measured by a wrist force sensor located at the distal end of the tool, and two torque sensors at the tool base, respectively. We propose an innovative design of a miniature force sensor achieving structural simplicity and potential cost effectiveness. A prototype is manufactured and experiments are conducted in a simulated surgical environment by using an open platform for surgical robot research, called Raven-II.

First Results of Tilted Capacitive Sensors to Detect Shear Force

This paper proposes a new soft capacitive-type 3-axis force sensor. The prototype version which can detect a multi-axis force vector is embedded inside 7mm-thick silicone skin, and provides digital output via an I2C bus. Tilted capacitive force transducers were used to measure the force vector; the transducers faced different directions to differentiate the tangential forces. Preliminary experiments were performed and the concept of the tilted force transducers has been proven to have the capability of differentiating the force vector acting on the sensor surface.

Numerical Derivation-Based Serial Iterative Dynamic Decoupling-Compensation Method for Multiaxis Force Sensors

A novel serial iterative dynamic decouplingcompensation (SIDDC) method is proposed for multiaxis force sensors to solve their problems of cross-axis dynamic coupling interference and the main channel dynamic error. Specifically, based on the output coupling model of the sensor, the Jacobi, Gauss-Seidel (G-S), and successive over-relaxation (SOR) iterative methods are introduced into the sensor dynamic decoupling to solve the most critical problem of dynamic coupling interference. The frequency-domain analysis method of the iterative decoupling convergence characteristic is proposed, and the convergence characteristics of the three iterative methods are compared. Then, the frequency-dependent relaxation factorbased SOR M iterative dynamic decoupling method, which may be more effective is put forward, and the construction method of the frequency-dependent relaxation factor with its amplitudefrequency characteristic meeting the specific demand is given in detail. Subsequently, the compensator of the sensor main channel is adopted to directly compensate the decoupling result for reducing the main channel dynamic error. In addition, according to the static coefficient matrix of the sensor output coupling model, the dynamic compensation result is reconstructed so as to ensure the static characteristic of the sensor before and after dynamic decoupling-compensation remain unchanged. Finally, the experimental data verifications of the proposed SIDDC method are performed for a three-component bar-shaped wind tunnel strain gauge balance. The verification results indicate that the proposed SIDDC method, especially the SOR M iteration based method, is much effective for improving the dynamic performances of the multiaxis force sensors.

General Anisotropy Identification of Paperboard with Virtual Fields Method

This work extends previous efforts in plate bending of Virtual Fields Method (VFM) parameter identification to include a general 2-D anisotropic material. Such an extension was needed for instances in which material principal directions are unknown or when specimen orientation is not aligned with material principal directions. A new fixture with a multi-axial force configuration is introduced to provide full-field strain data for identification of the six anisotropic stiffnesses. Two paper materials were tested and their Q ij compared favorably with those determined by ultrasonic and tensile tests. Accuracy of VFM identification was also quantified by variance of stiffnesses. The load fixture and VFM provide an alternative stiffness identification tool for a wide variety of thin materials to more accurately determine Q 12 and Q 66.

Research on a Multi-Axis Wrist Force Sensor with Double Bending Beams

First of all, a new multi-axis wrist force sensor with double bending beams was designed to meet the requirements of the intelligent manipulator. The new structure was easy to process and install. The impact of deformation, error and asymmetry caused by machining and aging treatment was avoided, and the performance of sensor was improved. Secondly, mechanical model of the sensor was established, and the force analyses from different directions were made. Thirdly, after strain gauges were pasted and the bridge was designed, loading tests to single beam and whole sensor were carried out, theoretical calculation and finite element analysis were completed, and the relative error was analyzed. Finally, the causes of relative error in different loading test were studied, and a solution of sensor calibration was put forward.

English

The wheel force transducer (WFT), which measures the force or torque applied to the wheel, is an important instrument in vehicle testing field and has been extremely promoted by researchers. Since the high cost and technical secret of the commercial products may slow down the development of WFT to some extent, Southeast University has devoted to the WFT research with some prototypes. Essentially, the WFT is a multi-axis force sensor (MFS) in which an elastic-body will deform under the applied forces. However, when applying a MFS into vehicle wheel and making it to be a WFT, it may be subjected to forces/moments which exceed the measuring range under the over rated load, especially on a heavy truck WFT under loads of X or Z direction. Plastic deformation and damage may occur on the elastic-body of WFT. This paper presents a mechanical approach of the overload protection mechanism which can prevent the overload damage and guarantee the sensor performance. An intermediate flange, which is elaborately designed using Computer Aided Engineering (CAE) tools, is installed between wheel hub and the elastic body to meet the overload protection. Experiment and prototyping test are conducted on the hydraulic platform. Results show that the proposed overload protection mechanism performs well. In particular, the applied loads over ±120 kN and ±30 kNm are prevented from damage for the heavy truck WFT.   Key words: Wheel force transducer, overload protection mechanism, vehicle wheels/typres, heavy duty trucks.

Design and implementation of multiaxial force sensing gripper fingers

This paper focuses on the integration of elementary force sensors into the fingers of parallel grippers. The theory of the approach of integrating three sensor elements into a gripper finger is described and the results of the practical evaluations are given. Strain gauges are used as elementary sensor elements. Two different design approaches are evaluated. The first one uses H-shaped cut-outs to weaken the structure at designated areas. The measurement accuracy of this system is compared with a second approach without cut-outs, which is easier to manufacture. Finite element analysis is used in both approaches to simulate the behaviour and to determine the best locations for strain gauge application. The performances of both design concepts are experimentally evaluated. It can be seen that the results of the finite-element analysis are correct and that a satisfactory decoupling of the basic sensors can be achieved using a physical or mathematical approach. Both prototypes are able to measure the gripping force with sufficient accuracy.

Enabling Force Sensing During Ground Locomotion: A Bio-Inspired, Multi-Axis, Composite Force Sensor Using Discrete Pressure Mapping

This paper presents a new force sensor design approach that maps the local sampling of pressure inside a composite polymeric footpad to forces in three axes, designed for running robots. Conventional multiaxis force sensors made of heavy metallic materials tend to be too bulky and heavy to be fitted in the feet of legged robots, and vulnerable to inertial noise upon high acceleration. To satisfy the requirements for high speed running, which include mitigating high impact forces, protecting the sensors from ground collision, and enhancing traction, these stiff sensors should be paired with additional layers of durable, soft materials; but this also degrades the integrity of the foot structure. The proposed foot sensor is manufactured as a monolithic, composite structure composed of an array of barometric pressure sensors completely embedded in a protective polyurethane rubber layer. This composite architecture allows the layers to provide compliance and traction for foot collision while the deformation and the sampled pressure distribution of the structure can be mapped into three axis force measurement. Normal and shear forces can be measured upon contact with the ground, which causes the footpad to deform and change the readings of the individual pressure sensors in the array. A one-time training process using an artificial neural network is all that is necessary to relate the normal and shear forces with the multiaxis foot sensor output. The results show that the sensor can predict normal forces in the Z-axis up to 300 N with a root mean squared error of 0.66% and up to 80 N in the X- and Y-axis. The experiment results demonstrates a proof-of-concept for a lightweight, low cost, yet robust footpad sensor suitable for use in legged robots undergoing ground locomotion.

Contact Region Estimation Based on a Vision-Based Tactile Sensor Using a Deformable Touchpad

A new method is proposed to estimate the contact region between a sensor and an object using a deformable tactile sensor. The sensor consists of a charge-coupled device (CCD) camera, light-emitting diode (LED) lights and a deformable touchpad. The sensor can obtain a variety of tactile information, such as the contact region, multi-axis contact force, slippage, shape, position and orientation of an object in contact with the touchpad. The proposed method is based on the movements of dots printed on the surface of the touchpad and classifies the contact state of dots into three types—A non-contacting dot, a sticking dot and a slipping dot. Considering the movements of the dots with noise and errors, equations are formulated to discriminate between the contacting dots and the non-contacting dots. A set of the contacting dots discriminated by the formulated equations can construct the contact region. Next, a method is developed to detect the dots in images of the surface of the touchpad captured by the CCD camera. A method to assign numbers to dots for calculating the displacements of the dots is also proposed. Finally, the proposed methods are validated by experimental results.

Real-Time Knee Adduction Moment Feedback Training Using an Elliptical Trainer

The external knee adduction moment (EKAM) is associated with knee osteoarthritis (OA) in many aspects including presence, progression, and severity of knee OA. Despite of its importance, there is a lack of EKAM estimation methods that can provide patients with knee OA real-time EKAM biofeedback for training and clinical evaluations without using a motion analysis laboratory. A practical real-time EKAM estimation method, which utilizes kinematics measured by a simple six degree-of-freedom goniometer and kinetics measured by a multi-axis force sensor underneath the foot, was developed to provide real-time feedback of the EKAM to the patients during stepping on an elliptical trainer, which can potentially be used to control and alter the EKAM. High reliability (ICC(2,1): 0.9580) of the real-time EKAM estimation method was verified through stepping trials of seven subjects without musculoskeletal disorders. Combined with advantages of elliptical trainers including functional weight-bearing stepping and mitigation of impulsive forces, the real-time EKAM estimation method is expected to help patients with knee OA better control frontal plane knee loading and reduce knee OA development and progression.

Active Design Method for the Static Characteristics of a Piezoelectric Six-Axis Force/Torque Sensor

To address the bottleneck issues of an elastic-style six-axis force/torque sensor (six-axis force sensor), this work proposes a no-elastic piezoelectric six-axis force sensor. The operating principle of the piezoelectric six-axis force sensor is analyzed, and a structural model is constructed. The static-active design theory of the piezoelectric six-axis force sensor is established, including a static analytical/mathematical model and numerical simulation model (finite element model). A piezoelectric six-axis force sensor experimental prototype is developed according to the analytical mathematical model and numerical simulation model, and selected static characteristic parameters (including sensitivity, isotropic degree and cross-coupling) are tested using this model with three approaches. The measured results are in agreement with the analytical results from the static-active design method. Therefore, this study has successfully established a foundation for further research into the piezoelectric multi-axis force sensor and an overall design approach based on static characteristics.

Active Touch Sensing by Multi-axial Force Measurement Using High-Resolution Tactile Sensor with Microcantilevers

Active Touch Sensing by Multi-axial Force Measurement Using High-Resolution Tactile Sensor with Microcantilevers

Does an instrumented treadmill correctly measure the ground reaction forces?

SummarySince the 1990s, treadmills have been equipped with multi-axis force transducers to measure the three components of the ground reaction forces during walking and running. These measurements are correctly performed if the whole treadmill (including the motor) is mounted on the transducers. In this case, the acceleration of the treadmill centre of mass relative to the reference frame of the laboratory is nil. The external forces exerted on one side of the treadmill are thus equal in magnitude and opposite in direction to the external forces exerted on the other side. However, uncertainty exists about the accuracy of these measures: due to friction between the belt and the tread-surface, due to the motor pulling the belt, some believe that it is not possible to correctly measure the horizontal components of the forces exerted by the feet on the belt. Here, we propose a simple model of an instrumented treadmill and we demonstrate (1) that the forces exerted by the subject moving on the upper part of the treadmill are accurately transmitted to the transducers placed under it and (2) that all internal forces – including friction – between the parts of the treadmill are cancelling each other.

Design and Characterization of a Soft Multi-Axis Force Sensor Using Embedded Microfluidic Channels

Thin, highly compliant sensing skins could provide valuable information for a host of grasping and locomotion tasks with minimal impact on the host system. We describe the design, fabrication, and characterization of a novel soft multi-axis force sensor made of highly deformable materials. The sensor is capable of measuring normal and in-plane shear forces. This soft sensor is composed of an elastomer (modulus: 69 kPa) with embedded microchannels filled with a conductive liquid. Depending on the magnitude and the direction of an applied force, all or part of the microchannels will be compressed, changing their electrical resistance. The two designs presented in this paper differ in their flexibility and channel configurations. The channel dimensions are approximately 200 × 200 μm and 300 × 700 μm for the two prototypes, respectively. The overall size of each sensor is 50 × 60 × 7 mm. The first prototype demonstrated force sensitivities along the two principal in-plane axes of 37.0 and -28.6 mV/N. The second prototype demonstrated the capability to detecting and differentiating normal and in-plane forces. In addition, this paper presents the results of a parameter study for different design configurations.

Estimation of Soft Tissue Mechanical Parameters from Robotic Manipulation Data.

Robotic motion planning algorithms used for task automation in robotic surgical systems rely on availability of accurate models of target soft tissue's deformation. Relying on generic tissue parameters in constructing the tissue deformation models is problematic because, biological tissues are known to have very large (inter- and intra-subject) variability. A priori mechanical characterization (e.g., uniaxial bench test) of the target tissues before a surgical procedure is also not usually practical. In this paper, a method for estimating mechanical parameters of soft tissue from sensory data collected during robotic surgical manipulation is presented. The method uses force data collected from a multiaxial force sensor mounted on the robotic manipulator, and tissue deformation data collected from a stereo camera system. The tissue parameters are then estimated using an inverse finite element method. The effects of measurement and modeling uncertainties on the proposed method are analyzed in simulation. The results of experimental evaluation of the method are also presented.

Frequency-Domain Decoupling-Correction Method for Wind Tunnel Strain-Gauge Balance

A frequency-domain decoupling-correction (FDC) method based on frequency-domain parameter matrix inversion is proposed to solve the problems of cross-axis dynamic coupling interference and dynamic error existing in the main channel output for multiaxis force sensors, for example, wind tunnel strain-gauge balance. The frequency-domain decoupling-correction function is calculated by means of power spectrum estimation according to the sensor step response experimental data, and the windowing approach is adopted to overcome the calculation error caused by the cycle extension of the intercepting data when FFT or IFFT is conducted. The method of FDC based on high/low-frequency signal decomposition is put forward in the process of the dynamic decoupling correction for the sensor output. The low-frequency components are decoupled and corrected by the method of static linear decoupling and static linear correction, and the high-frequency components are decoupled and corrected by the method of frequency-domain parameter matrix inversion in order to overcome the boundary aliasing error and the Gibbs phenomenon caused by the cycle extension of the intercepting data when FFT or IFFT is conducted. According to the static relationship between the sensor input and output, the static characteristic between the sensor input and the sensor dynamic decoupling-correction result is reconstructed so as to ensure that the sensor static characteristic remains unchanged. The dynamic decoupling-correction method is applied to the bar-shaped strain-gauge balance to validate its effectiveness. The result shows that the cross-axis dynamic coupling error ratios are reduced from 98.09% to less than 2%, and the adjust time of the balance main channel step response is shortened from nearly 4 s to less than 6 ms with the overshoot being reduced from 111.24% to less than 5% at the same time. The proposed method can substantially reduce the cross-axis dynamic coupling interference and further improve the response speed of the balance.

Biomechanics of the heel-raise test performed on an incline in two knee flexion positions

BackgroundAlthough single-legged heel-raise cycles are often performed on an incline in different knee flexion positions to discriminate the relative contribution of the triceps surae muscles, detailed kinematic and kinetic analyses of this procedure are not available. Our study characterizes and compares the biomechanics and clinical outcomes of single-legged heel-raise cycles performed to volitional exhaustion on an incline with the knee straight (0°) and bent (45°), considering the effect of sex and age. MethodsFifty-six male and female volunteers, with equal numbers of younger (20 to 40years of age) and older (40 to 60years of age) individuals, completed a maximal number of heel-raise cycles on an incline at both nominal knee angles. Kinematic and kinetic data were acquired during testing using a 3D motion capturing system and multi-axial force plate. The impact of fatigue on performance was quantified using changes in maximal voluntary isometric contraction force and biomechanical performance of cycles. FindingsOverall, participants completed three more cycles and maintained better biomechanical performance with 45° than 0° of knee flexion. More precisely, the decreases in maximal heel-raise heights, plantar-flexion angles at maximal height and ranges of ankle motion per cycle were all smaller with the knee bent. However, several outcomes indicated similar plantar-flexion fatigue at both knee angles. Males demonstrated a more rapid decline in peak ground reaction forces during testing; but otherwise, neither sex nor age significantly impacted outcomes. InterpretationIt is concluded that the differences discerned here in the biomechanics of single-legged heel-raise cycles performed at 0° and 45° of knee flexion to volitional exhaustion on an incline may be too small to identify in clinical settings or reflect substantial alterations in the relative contribution of the triceps surae muscles.