High-accuracy Force Research Articles

Realization of Martens hardness method in macro range with high accuracy force and indentation depth

TÜBİTAK UME Hardness Laboratory has been working on instrumentation in the field of hardness metrology since 2005 and three generations of hardness standardizing machines were developed since then to be used as reference (calibration/standardizing) machines in Türkiye. In former designs conventional hardness methods such as Rockwell, Brinell and Vickers scales were the main scope of the projects. In the final Project that was supported and funded by TÜBİTAK UME to develop three hardness standard machines to be used as national standards for the conventional hardness scales mentioned, the Instrumented Indentation Test (IIT) was also aimed at and some parameters like Martens hardness, creep, indentation hardness, (elastic and plastic) indentation work, etc. were also implemented onto the machines developed. It was a good occasion that the measurands in Rockwell hardness and IIT were the same, force and indentation depth besides time and this made it easier to realize the IIT on the same machine with a more suitable design to achieve the highest accuracy in terms of the measurands mentioned. In this paper the new design of the Rockwell-Brinell-Vickers hardness standard machine developed also for Martens hardness in macro range (3 kgf – 150 kgf) and preliminary Martens hardness measurements are explained.

Large-scale atomistic simulation of quantum effects in SrTiO3 from first principles

Quantum effects of lattice vibration play a major role in many physical properties of condensed-matter systems, including thermal properties, such as specific heat, structural phase transition, as well as phenomena, such as quantum crystal and quantum paraelectricity that are closely related to zero-point fluctuations. However, realizing atomistic simulations for realistic materials with a fully quantum-mechanical description remains a great challenge. Here, we propose a first-principles strategy for large-scale molecular dynamics simulation, where a high-accuracy force field obtained by deep-potential (DP) is combined with quantum thermal bath (QTB) method to account for quantum effects. We demonstrate the power of this $\text{DP}+\text{QTB}$ method using the archetypal example $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$, which exhibits several phenomena induced by quantum fluctuations, such as the suppressed structure phase-transition temperature, the quantum paraelectric ground state at low temperatures and the quantum critical behavior $1/{T}^{2}$ law of dielectric constant. Our $\text{DP}+\text{QTB}$ strategy is efficient in simulating large-scale system and is first principles. More importantly, quantum effects of other systems could also be investigated as long as the corresponding DP model is trained. This strategy would greatly enrich our vision and means to study quantum behavior of condensed-matter physics.

Experimental Study to Quantify the Rotor-to-Rotor Interaction Characteristics of a Small Unmanned-Aerial-Vehicle

The flow interactions between laterally aligned rotors were investigated experimentally to study the rotor-to-rotor interactions on the aerodynamic and aeroacoustic performance of small unmanned aerial vehicles (UAVs). Two identical rotors, similar to the dimensions of Phantom 3 (DJI), were mounted separately on different stages in a wide-open space. High-accuracy force and sound measurements were conducted to document the thrust and noise at various separation distances. The detailed flow structures and corresponding vortex evolutions behind the rotors were resolved clearly by using high-resolution PIV measurements. As the rotor separation distance decreased, intensified flow interactions were noted within the rotors. More specifically, the twinrotor with separation distance of L= 0.05D exhibited a significantly enhanced thrust fluctuation (i.e., ~ 240% higher) and augmented noise level (i.e., ~ 3dB) in comparison with that of baseline case. Measured PIV results indicated that a strong recirculation region existed near the top-right of the twin-rotor case, which is believed to be the reason for the increased thrust fluctuations and aeroacoustic noise level.

An experimental study on the dynamic ice accretion processes on bridge cables with different surface modifications

An experimental study was conducted to investigate the dynamic ice accretion processes on bridge cables with different surface modifications (i.e., 1. Standard plain, 2. Pattern-indented surface, and 3. Helical fillets). An Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT) was used to generate two typical icing conditions (i.e., dry rime icing vs. wet glaze icing). During the experiments, while a high-speed imaging system was used to capture the transient behaviors of surface water transport and dynamic ice accretion processes over the surfaces of the cable models, a high-accuracy force measurement system was utilized to quantify the dynamic aerodynamic loadings acting on the cable models under different icing conditions. It was found that the addition of surface features (i.e., pattern-indented surface and helical fillets) could dramatically influence the dynamic ice accretion process and the final topology of the ice structures accreted on the cable surfaces. While the ice accretion on the standard plain cable and the cable with helical fillets was found to reduce the drag forces by about 25%, the ice accretion on the pattern-indented cable model would induce about 30% greater aerodynamic drag force acting on the cable model.

Instrumented platform for assessment of isometric hand muscles contractions

Measurement of forces exerted by a human hand while performing common gestures is a highly valuable task for assessment of neurorehabilitation and neurological disorders, but also, for control of movement that could be directly transferred to assistive devices. Even though accurate and selective multi-joint measurement of hand forces is desirable in both clinical and research applications there is no commercially available device able to perform such measurements. Moreover, the custom-made systems used in research commonly impose limitations, such as availability of only single, predefined hand aperture. Furthermore, there is no consensus on design requirements for custom made measurement systems that would enable comparison of results obtained during research or clinical hand function studies. In an attempt to provide a possible solution for a device capable of multi-joint hand forces measurement and disseminate it to the research community, this paper presents the mechanical and electronic design of an instrumented platform for assessment of isometric hand muscles contractions. Some of the key features related to the developed system are: flexibility in placing the hand/fingers, fast and easy hand fitting, adjustability to different lengths, circumferences and postures of the digits, and the possibility to register individual bidirectional forces from the digits and the wrist. The accuracy of isometric force measurements was evaluated in a controlled test with the reference high accuracy force gauge device during which the developed system showed high linearity (R2 = 0.9999). As the more realistic test, the device was evaluated when force was applied to individual sensors but also during the intramuscular electromyography (iEMG) study. The data gathered during the iEMG measurements was thoroughly assessed to obtain three appropriate metrics; the first estimating crosstalk between individual force sensors; the second evaluating agreement between measured forces and forces estimated through iEMG; and the third providing qualitative evaluation of hand force in respect to activations of individual muscle units. The results of these analyses performed on multiple joint forces show agreement with previously published results, but with the difference that in that case, the measurement was performed with a single degree of freedom device.

High-Accuracy Force Control With Nonlinear Feedforward Compensation for a Hydraulic Drive Unit

The hydraulic drive unit (HDU) applied in a hydraulic drive legged robot joints adopts an outer loop impedance control method based on the hydraulic control's inner loop during motion so that the entire system obtains certain compliance characteristics. There are two types of inner loops, namely, the position closed loop control and the force closed loop control; this paper studies a system in which the inner loop is a force closed loop control system and improves its accuracy in order to provide references for the outer loop impedance control. Therefore, designing a compensation method that improves the inner loop force control's accuracy has important research significance. In view of the above research significance, this paper first deduces a mathematical model for the force closed loop control and simplifies the sixth-order mathematical model to find the transfer function of each part. Second, combined with influence factors, such as pressure-flow nonlinearity, friction nonlinearity, and complex and variable loads on the system, the feedforward compensation controller of the force control input is derived. Considering the practical application in engineering, the controller order is reduced, and a partial compensation is achieved. Finally, on the HDU performance test platform, the force control performance is quantitatively analyzed by inputting typical signals and random signals. The experimental results show that the feedforward compensation controller can greatly improve the system force control performance with different input signals. The above research results can be combined with a corresponding disturbance rejection strategy for the force control system to provide an important reference and experimental basis for the hydraulic inner loop control strategy of force-based impedance.

Design and Application of MVIC for Hydraulic Drive Unit of Legged Robot

A hydraulic drive unit (HDU), applied in each joint of a hydraulic driven legged robot, usually adopts the impedance control outer loop based on the hydraulic position or the force control inner loop during the motion process. When the hydraulic control adopts closed-loop force control, its control performance can directly determine the control performance of the impedance control outer loop. Therefore, it is significant to design a high-accuracy force control method aimed at HDUs. In this paper, aiming at the above research concept, the force control system of the HDU is introduced first, and the lack of the force control performance is studied under different working conditions on the HDU performance test platform. Second, a model-based variable input controller (MVIC) is designed to improve the force control performance. Finally, the control performance of the MVIC is verified on the HDU performance test platform. The experimental results show that the MVIC can greatly improve the force control accuracy under different working conditions and that the controller has good robustness. The above research results can provide important reference and lay the experimental foundation for force-based impedance control.

A Novel and Safe Approach to Simulate Cutting Movements Using Ground Reaction Forces.

Control of shear ground reaction forces (sGRF) is important in performing running and cutting tasks as poor sGRF control has implications for those with knee injuries, such as anterior cruciate ligament (ACL) ruptures. The goal of this study was to develop a novel and safe task to evaluate control or accurate modulation of shear ground reaction forces related to those generated during cutting. Our approach utilized a force control task using real-time visual feedback of a subject’s force production and evaluated control capabilities through accuracy and divergence measurements. Ten healthy recreational athletes completed the force control task while force control via accuracy measures and divergence calculations was investigated. Participants were able to accurately control sGRF in multiple directions based on error measurements. Forces generated during the task were equal to or greater than those measured during a number of functional activities. We found no significant difference in the divergence of the force profiles using the Lyapunov Exponent of the sGRF trajectories. Participants using our approach produced high accuracy and low divergence force profiles and functional force magnitudes. Moving forward, we will utilize this task in at-risk populations who are unable to complete a cutting maneuver in early stages of rehabilitation, such as ACL deficient and newly reconstructed individuals, allowing insight into force control not obtainable otherwise.

Iterative Learning Procedure With Reinforcement for High-Accuracy Force Tracking in Robotized Tasks

The paper focuses on industrial interaction robotics tasks, investigating a control approach involving multiples learning levels for training the manipulator to execute a repetitive (partially) changeable task, accurately controlling the interaction. Based on compliance control, the proposed approach consists of two main control levels: 1) iterative friction learning compensation controller with reinforcement and 2) iterative force-tracking learning controller with reinforcement. The learning algorithms rely on the iterative learning and reinforcement learning procedures to automatize the controllers parameters tuning. The proposed procedure has been applied to an automotive industrial assembly task. A standard industrial UR 10 Universal Robot has been used, equipped by a compliant pneumatic gripper and a force/torque sensor at the robot end-effector.

Modelling and Numerical Simulation of Cutting Stress in End Milling of Titanium Alloy using Carbide Coated Tool

Based on the cutting force theory, the cutting stress in end milling operation was predicted satisfactorily through simulation of using finite element method. The mechanistic force models were introduced in high accuracy force predictions for most applications. The material properties in the simulations were defined based on the cutting force theory, as a function of strain and strain rate whereas in the theoretical relationships, these properties were simply kept constant. According to the analysis, the maximum deformation and effective stress showed an increasing trend for the machining with end-milling cutting tool. A reasonable set of milling parameters for the machining of titanium alloy by coated cemented carbide cutting tool were obtained by analyzing the cutting efficiency in relation to cutting force of the tools. It is expected that this study would provide a fundamental basis for the optimization of the cutting parameters for titanium alloy.

高精度力覚検出による包装リーク検査装置の開発

高精度力覚検出による包装リーク検査装置の開発

Bioinspired non-invasive radial pulse sensor: from biomimetic design, system calibration, to clinic application

Abstract The research work aims at developing a real-time non-invasive metabolism and blood circulation surveillance system for monitoring human’s health condition by sensing the various bio-signals on the human body. Our goal is to use the developed system to study the functions and characters of organs and tissues that highly relate with the metabolism and blood circulation system, and also, it is expected to help modeling the entire circulation system. At phase I of the research, in this paper we focus on developing a new low-cost, portable, high-accuracy, non-invasive radial pulse sensor. Inspired by touch capability and related biomechanical advantage of human fingertip, the mechanical design of the sensor mimics the physiological structure of human fingertip. The biomimetic sensor is then well calibrated using a high-accuracy force sensor, and the model is accurately identified by the system identification method. Further the calibrated sensor is applied to diagnose the arterial stiffness by measuring the augmentation index (AI) which is the important biomarker of vascular aging. Preliminary results demonstrate the sensor performance that it is capable of non-invasively, accurately, and reliably measuring radial pulse signals at real time, as well as to quantitatively determine the vessel aging.

Impact Force Identification by Using Modal Transformation Method for Automobile Test Rig

In the automobile industry, impact force is the main cause for material fatigue in lightweight vehicles. Bump-excited impact force is the most common case, which causes damage to vehicles and reduces the quality of the ride. Force identification is important to reflect the structure's health so that action such as structure modification can be taken before material fatigue. However, direct measurement by using force transducer is not practical due to difficulty in force sensor configuration. A methodology utilizing Operating Deflection Shape (ODS) analysis, Frequency Response Function (FRF) measurement and Modal Transformation Method (MTM) to evaluate the dynamic force is proposed here. This method is called indirect force measurement by using inverse technique. The performance of this approach was demonstrated via experiment. From the measured responses and measured dynamic characteristics of an automobile test rig, a real time mathematical manipulation can generate the systems input force. The force location is known in priori for impact excitation and therefore the inverse problem is well-posed. This method was tested using different force location with unique input force. It shows that high quality of curve fitting to extract the modal parameters such as damped natural frequency, modal damping and residue mode shape is essential to obtain a high accuracy force determination result.

State Space System Identification of 3-Degree-of-Freedom (DOF) Piezo-Actuator-Driven Stages with Unknown Configuration

Due to their fast response, high accuracy and non-friction force, piezo-actuators have been widely employed in multiple degree-of-freedom (DOF) stages for various nano-positioning applications. The use of flexible hinges in these piezo-actuator-driven stages allows the elimination of the influence of friction and backlash clearance, as observed in other configurations; meanwhile it also causes more complicated stage performance in terms of dynamics and the cross-coupling effect between different axes. Based on the system identification technique, this paper presents the development of a model for the 3-DOF piezo-actuator-driven stages with unknown configuration, with its parameters estimated from the Hankel matrix by means of the maximum a posteriori (MAP) online estimation. Experiments were carried out on a commercially-available piezo-actuator-driven stage to verify the effectiveness of the developed model, as compared to other methods. The results show that the developed model is able to predict the stage performance with improved accuracy, while the model parameters can be well updated online by using the MAP estimation. These capabilities allow investigation of the complicated stage performance and also provide a starting point from which the mode-based control scheme can be established for improved performance.

Interaction imaging with amplitude-dependence force spectroscopy

Knowledge of surface forces is the key to understanding a large number of processes in fields ranging from physics to material science and biology. The most common method to study surfaces is dynamic atomic force microscopy (AFM). Dynamic AFM has been enormously successful in imaging surface topography, even to atomic resolution, but the force between the AFM tip and the surface remains unknown during imaging. Here we present a new approach that combines high-accuracy force measurements and high-resolution scanning. The method, called amplitude-dependence force spectroscopy (ADFS), is based on the amplitude dependence of the cantilever's response near resonance and allows for separate determination of both conservative and dissipative tip-surface interactions. We use ADFS to quantitatively study and map the nano-mechanical interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is compatible with commercial atomic force microscopes and we anticipate its widespread use in taking AFM toward quantitative microscopy.

Reliable, Built-in, High-Accuracy Force Sensing for Legged Robots

An approach for achieving reliable, built-in, high-accuracy force sensing for legged robots is presented, based on direct exploitation of the properties of a robot’s mechanical structure. The proposed methodology relies on taking account of force-sensing requirements at the robot design stage, with a view to embedding force-sensing capability within the mechanical structure of the robot itself. The test case is ROBOCLIMBER, a bulky, quadruped climbing and walking machine whose weighty legs enable it to carry out heavy-duty drilling operations. The paper shows that, with finite-element analysis of ROBOCLIMBER’s mechanical configuration during the design stage, candidate positions can be selected for the placement of force transducers to measure indirectly the contact forces between the feet and the ground. Force sensors are then installed at the theoretically best positions on the mechanical structure, and several experiments are carried out to calibrate all sensors within their operational range of interest. After calibration, the built-in sensors are subjected to experimental performance evaluation, and the final best sensor option is found. The built-in force-sensing capability thus implemented is subjected to its first test of usability when it is employed to compute the actual centre of gravity of ROBOCLIMBER. The method is shown to be useful for determining variation during a gait (due to the non-negligible weight of the legs). Afterwards the force sensors are shown to be useful for controlling foot-ground interaction, and several illustrative experiments confirm the high sensitivity, reliability and accuracy of the selected approach. Lastly, the built-in sensors are used to measure ground-reaction forces and to compute the zero-moment point for ROBOCLIMBER in real time, both while standing and while executing a dynamically balanced gait.

Piezoresistive cantilevers and measurement system for characterizing low force electrical contacts

Abstract The continued miniaturization of integrated circuits (ICs), interconnects, relays, and packaging critically depends on the electrical properties of low force electrical contacts. This paper presents the design, fabrication, and characterization a micro-mechanical force sensor integrated with a four-wire electrical contact characterization capability to evaluate low force and small area electrical contacts comprised of thin films. The sensor consists of a silicon cantilever beam with a piezoresistive force sensor suitable for high-accuracy force measurements in the nanoNewton to milliNewton range. The work presented expands the characterization capabilities for the electromechanical properties of such contacts over what is currently available, using instrumented micro-electromechanical system (MEMS) force sensors. The effects of varied contact tip dimensions and different gold films manufactured using standard semiconductor processing techniques are studied. The cantilevers are evaluated for force sensitivity, range, noise and sensitivity of four-wire contact resistance measurements. The piezoresistors have a gage factor of about 35 and noise of

Theory and Practice of Force Measurement

Abstract The senior author, A. Bray, has been with the Institute of Metrology “G. Colonetti” in Turin, Italy, for many years, having established the first nucleus of the institute, which is today the Force Measurement Section. His colleagues G. Barbato and R. Levi are associated also with Politecnico di Torino. Reflective of the authors' experience, the major focus of the book is on high accuracy force measurement and calibration in standards laboratories. This relatively narrow focus limits the range of readership to which the book is addressed, but allows a high technical level in the treatment of those topics which are covered. Of the eight chapters, only the fifth, “Force-Measuring Devices,” would be of prime interest to the more general force-measurement community. The entire book, however, is of uniformly high quality and fills an important gap in the measurement literature.

Large forces for industry

With the installation in 1943 of a 50 tonf (~ 500 kN) deadweight standard, the National Physical Laboratory was able to provide, for the first time, a high accuracy force calibration service. Originally this service was almost entirely directed towards the calibration of proving devices used in the verification of materials testing machines.