Strain Gauge Bridge Research Articles

A condition monitoring approach for the detection of defects in the primary suspension of railway vehicles

This work presents the main problems in the primary suspension of metro vehicles and a methodology to detect those using wayside systems. The primary suspension is usually based on rubber elements, which are space saving and have damping properties. However, rubber characteristics change with time, often in a different way in each element. Differences between elements can cause irregular transmission of loads to the wheels, and thus, a reduction or loss of guidance forces. The ageing of rubber can also lead to a general stiffening of the primary suspension, which increases the risk of derailment. This paper presents a wayside system that uses a few strain gauge bridges to detect those problems independently of the vehicle load and speed. Firstly, the system is developed by means of a multibody model. Secondly, a demonstrator is installed in an operating metro exploitation. Finally, the accuracy of the predictions is proven by testing some of the elements in the laboratory.

Torsion and bending loads on a ski-touring boot shell during uphill and downhill skiing

Ski touring is an established winter activity that has experienced a recent increase in popularity. Differently to alpine skiing, skier gains altitude without lifts, thus equipment weight must be minimized. Nevertheless, structural properties of the equipment, such as ski boots, must be adequate to withstand skiing loads. Several studies provided data on flexural stiffness of alpine ski boots in bench and field tests. The present study focused on the torsional properties of ski-touring boots. Indeed, touring bindings design implies a higher torque transmission to the front piece which induces a torsional load throughout the shell. To conduct the study, we prepared a ski-touring boot with strain gage bridges, and we performed bench tests to determine the stiffness of the boot and the bridge sensitivity. We also positioned and calibrated strain gage bridges to measure bending load in the shell and axial load in the ski/walk lever placed between shell and cuff of the boot. Then, we conducted a field test measuring the loads during a ski-touring trip including ascent and descent. Bench tests evidenced linearity of the torsion sensor, and a variation of stiffness depending on dummy leg absence/presence and boot buckle setting. Field tests showed torque ranges of 17 Nm in climbing and of 27 Nm in skiing. Bending moment range on the boot shell was of 150 and 228 Nm, respectively. Maximum force on the ski/walk mechanism reached 570 N. Results could be useful to test ski-touring boot performances and to optimize their design.

An Improved Approach for Grasp Force Sensing and Control of Upper Limb Soft Robotic Prosthetics.

The following research proposes a closed loop force control system, which is implemented on a soft robotic prosthetic hand. The proposed system uses a force sensing approach that does not require any sensing elements to be embedded in the prosthetic's fingers, therefore maintaining their monolithic structural integrity, and subsequently decreasing the cost and manufacturing complexity. This is achieved by embedding an aluminum test specimen with a full bridge strain gauge circuit directly inside the actuator's housing rather than in the finger. The location of the test specimen is precisely at the location of the critical section of the bending moment on the actuator housing due to the tension in the driving tendon. Therefore, the resulting loadcell can acquire a signal proportional to the prosthetic's grasping force. A PI controller is implemented and tested using this force sensing approach. The experiment design includes a flexible test object, which serves to visually demonstrate the force controller's performance through the deformation that the test object experiences. Setpoints corresponding to "light", "medium", and "hard" grasps were tested with pinch, tripod, and full grasps and the results of these tests are documented in this manuscript. The developed controller was found to have an accuracy of ±2%. Additionally, the deformation of the test object increased proportionally with the given grasp force setpoint, with almost no deformation during the light grasp test, slight deformation during the medium grasp test, and relatively large deformation of the test object during the hard grasp test.

Topology optimization for the design of a 3D-printed rotating shaft balance

Rotating shaft balances (RSBs) are devices that are used to measure rotor blade forces and moments of wind tunnel models during wind tunnel tests. The design of an RSB can be challenging, because it has to comply with many and sometimes contradicting requirements such as high stiffness and high strain gauge bridge outputs. The manufacturing of a conventional RSB consists of different subsequent steps, which can be time consuming, expensive and associated with many risks. Therefore, in this work, the authors investigate if a RSB can be designed by topology optimization and manufactured by 3D printing. A topology optimization method was developed with as design objective the minimization of strain energy with constraints for the volume of the RSB’s midsection, defined stresses at strain gauge locations used for the measurement of axial force and torque and an overhang constraint for additive manufacturing. The optimal preliminary design found by topology optimization was translated into a final printable design with the highest bridge sensitivity for axial force and torque, sufficient output for in-plane forces and moments and an acceptable safety factor on strength for combined loads. After adding extra supports required for printing, the RSB was successfully printed in metal by the laser powder bed fusion process, resulting in a product without external defects. The same topology optimization and manufacturing method can potentially be used for other balance types, leading to a reduction in total lead time and manufacturing costs while increasing the design freedom.

An experimental study regarding the effect of streamwise vorticity on trailing edge vortex induced vibrations of a hydrofoil

A set of experiments testing the effect on vortex induced vibrations from three different trailing edge designs on a generic hydrofoil has been carried out at the Waterpower Laboratory of NTNU. One of the designs, a Donaldson type semi-blunt trailing edge not a-typical for use in hydraulic machinery serves as a reference. The other two, a trailing edge with boundary layer vortex generators and a trailing edge with rounded serrations cut into the blade, both introduce streamwise vorticity in the wake of the hydrofoil, as shown by particle image velocimetry measurements. The trailing edge of the hydrofoil is made exchangeable, so that a direct comparison of the strain intensity levels measured with a structurally embedded strain gauge bridge located close to the trailing edge can be made. The results indicate that the vortex generators are effective at mitigating the lock-in state of resonance and significantly reduces the maximum strain intensity measured, compared to the more conventional reference design. Velocity measurements both at lock-off conditions as well as close to resonance reveal a de-correlation of the streamwise velocity fluctuations in the wake for this design, suggesting that the von Kármán type vortex shedding is weakened even at resonance conditions. A de-correlation of the streamwise velocity fluctuations in the wake of the serrated trailing edge is also observed at lock-off conditions, but the vortex shedding appear to become gradually more coherent, as well as strengthened, for this design as the foil vibrations increase closer to resonance.

Dynamic characteristics of a switch and crossing on the West Coast main line in the UK

Railway switches and crossings constitute a small fraction of linear track length but consume a large proportion of the railway track system maintenance budget. While switch and crossing (S&C) faults rarely prevent trains from running, switches and crossings are the source of many faults and need continual attention. On the rare occasions when trains are prevented from running the cost of the disruption is very high. Condition monitoring of the point operating equipment that moves the switchblades has been in use for many years but condition monitoring of the state of the switch in terms of the support and mechanical damage as trains pass over has only recently started to become possible. To this end, it is important to understand the correlation between S&C faults and sensor data that can detect those faults. This paper assesses some of the data collected from multiple sensors variously positioned on and around a switch and crossing on the UK mainline for a few days of normal train operation. Accelerometers, geophones, and strain gauges were installed at the locations where they were anticipated to be most useful. Forces at the load transfer point on the crossing nose were estimated from two separate strain gauge bridges and possible use of acceleration on the crossing is discussed. Correlations between different data are analysed and assessed and correlation between peak estimated load transfer forces and accelerations is presented. Based on the analysis, conclusions are drawn about the different types of dynamic information around S&Cs that can be obtained from a variety of sensor types.

Development of methods to measure the forces at the rear suspension of a race car during racetrack driving

The forces generated by the tyres of a vehicle are responsible for the maximum achievable performance for a race car. In this work, a geometric matrix method combined with a sensitivity matrix method has been applied to a rear multi-link suspension of a rear-wheel-drive race car to estimate the tyre forces from the measurement of the loads acting on the suspension arms. The geometric matrix method calculates the wheel forces from the equilibrium of the wheel assembly, thus involving all reaction forces exchanged with the suspension arms. The reaction forces have been measured through the application of axial strain gauge bridges on the link arms; however, the lower arm has a complex geometry and exchanges multi-axial forces with the upright, therefore a sensitivity matrix method has been implemented. The strain gauges positions have been identified with FE analyses and after installing the sensors, the calibration of the entire suspension assembly has been performed in a dedicated test rig where known forces at the ideal contact point between the wheel and the ground can be applied. After the calibration and validation in the laboratory, the instrumented suspension has been installed in a race vehicle and multiple racetrack acquisitions have been successfully performed.

Triaxial variation of the modulus of elasticity in the thermo-elastic range of six tropical wood species

ABSTRACT This work highlights the effect of temperature on the modulus of elasticity following the orthotropic axis of six species of tropical woods: assamela, bibolo, doussié, iroko, movingui, and sapelli of scientific names Afzelia, Pericopsiselata, Distemonanthus benthamianus, Entandrophragma cylindricum, Miliciaexcelsa, and Lovoatrichilioides, respectively. The four-point bending and compression tests were conducted to determine the failure loads, which can help further tests performed in the elastic domain. In order to determine the Young's modulus in the thermoselastic field, the above tests were carried out at different levels of loads and temperature; the samples of 20 × 20 × 340 mm dimensions for bending tests and 20 × 20 × 60 mm dimensions for compression tests according to current standards. The strains were read by means of two strain gauges, connected to the strain gauge bridge. Test results under the different constant thermo-hydric conditions showed an increase in the longitudinal, radial and tangential MOE of all six species as the temperature increased from 22°C to 40°C, and a regression above 40°C. In terms of lost in elastic modulus, due to the temperature, the tests showed the following classification: . Those results may be crucial while selecting the wood species for a typical use in a range of temperature.

Design Optimization of Instrumented Strikers for Charpy V-Notch Pendulum Impact Testing

Abstract The Charpy impact test was originally devised to measure the amount of energy absorbed by a material during fracture. Instrumentation of the striker extended the scope of this inexpensive dynamic test significantly. By not only recording the absorbed energy but also the force applied to the specimen as a function of time, additional information about the material’s properties is obtainable. At the present day, however, no internationally accepted procedure to calibrate or verify the measured dynamic force exists. From an engineering viewpoint, an instrumented striker for which a static force calibration is sufficient to accurately measure the force applied to the specimen during a Charpy impact test would be ideal. To investigate if such an instrumented striker can be designed, the influence of the striker geometry, the location of the strain gauges, and the static force calibration procedure on the force measured by an instrumented International Organization for Standardization striker is assessed using finite element analysis. It is demonstrated that when the strain gauge bridge on the striker is sensitive to the load distribution at the striking edge, the voltage response for the Charpy impact test deviates from the static force calibration curve, and the conversion of the voltage readout to force values introduces an error in the force value and hence a discrepancy between computed and angle-based energies. A striker with a height of 12 mm and strain gauges positioned at 17 mm from the striking edge is nearly insensitive to the load distribution, and a static force calibration is sufficient to accurately measure the force during an impact test.

Influence of bolts bending on the strength of flanges joints of pressure vessels

This paper highlighted the shortcomings of the current international normative on the calculation of flanges joints with gasket situated inside the circle of bolts holes. The current codes do not take into account, when calculating the flanged joints of the vessels, the bending stress that occurs as a result of the movement of the plates of the joint subjected to internal pressure. The bending of the bolts influences the deformation of the sealing gasket and – namely – the sealing of the flange joint. The knowledge of the bolts bending stresses allows to increase the time between two revisions/repairs and – namely – the useful life of the sealing gasket. The experimental data, obtained with the help of a strain gage bridge and by the Digital Image Correlation method on the designed experimental installation, highlighted the bending of the flange bolts, both for pressurization and depressurization. The experiments were performed at an internal pressure of 0.5; 1.0; 1.5 and 2.0 MPa.

A Flight Load Test Method for Helicopter Rotor Blade

This paper studies a flight load test method for helicopter blade, including the structural force of helicopter blade, strain gauge bridge modification, load calibration method and the establishment of load calibration equation in the typical maneuvers. First, blade structure of the helicopter was analyzed and the strain gauges were pasted in the load profile which were considered to be important positions to analysis the flight safe of helicopter. Second, Load calibration equations were obtained by ground calibration test, which would be used to convert the strain time curve to the load time curve. The helicopter flighted in different maneuvers, such as hovering, horizontal flight and climbing. At the same time, flight parameters were recorded, such as helicopter altitude, pitch angle, roll angle and yaw Angle. The flight parameters can be used to analysis the flight conditions. Then the blade flight load in different flight maneuvers was analyzed. The result was that the time-domain waveform was neat, good periodicity, strong regularity, no hybrid interference and jump point. It was illustrated that the blade load test flight data were accurate and reliable, which met the accuracy requirements of Engineering. The blade load data obtained through different flight maneuvers can be used to structural modification, fatigue analysis and blade design.

A Test Method for Helicopter Landing Gear Load

In this paper, a load test method of landing gear during take-off and landing of helicopter was proposed and the structure of helicopter landing gear, the modification of strain gauge bridge, the establishment of load calibration equation and the flight test of helicopter were studied. Firstly, according to the structure of helicopter landing gear, the stress analysis of landing gear was carried out, and the load position and force form of landing gear were determined during take-off and landing. Then, the measuring principle of the strain bridge was studied. According to the technical requirements, structural characteristics of the landing gear load test and the properties and principles of the strain bridge, the distribution and load measurement form of the strain bridge of the dangerous structure of the landing gear were designed. Then, studying load calibration test scheme of landing gear and carrying out load calibration test, the load calibration equation of landing gear was obtained, and the accuracy of load calibration equation was verified by comparing the expected load and actual load. Through the flight test, the landing gear load during the take-off and landing of the helicopter was obtained. Finally, the valid analysis of flight load data was carried out. The results show that the proposed method is feasible, and the flight test data of landing gear load are accurate and reliable, which can provide data support for the structure modification, fatigue analysis and the life evaluation of landing gear.

Modeling frequency integrating unfolding converter operation taking into account technological variation in parameters

The article considers issues for taking into account technological variation in parameters for a bridge circuit of a frequency integrating unfolding converter containing semiconductor strain gauges at high temperature, using the Mathcad software as simulation environment. An analysis of the influence of technological variation in parameters has revealed the emergence of the initial imbalance of the bridge circuit, which is equivalent to the presence of a non-zero input signal, i.e. the pulse repetition frequency error, which is present at the output of frequency integrating unfolding converter at high temperature. A mathematical model for taking into account technological variation in parameters of a frequency integrating unfolding converter based on a semiconductor strain gauge bridge is proposed, which allows calculating the corresponding error. As a result, the above mentioned can be used in the development of additional methods and means for temperature compensation, taking into account features of semiconductor strain gauges, and to increase objectivity in the analysis of calculation results applied to converters of mechanical values into frequency.

Modeling frequency integrating unfolding converter with a semiconductor strain gauge bridge taking into account temperature effect

The article considers development of an algorithm and construction of a simulation model of frequency integrating unfolding converter characteristics for a bridge circuit with semiconductor strain gauges, using the MathCAD software as simulation environment. Construction of a simulation model gives the possibility of joint application of bridge circuits with semiconductor strain gauges and frequency integrating unfolding converters in the development of sensitive elements of sensors for mechanical quantities that able to function at high temperatures. An algorithm for determining components of the output signal frequency error is proposed, taking into account variation in parameters of strain gauges and the effect of high temperature, which will allow revealing influence of the error components on the output signal frequency. As a result, the above mentioned can be used in the development of additional methods and means for temperature compensation, taking into account features of semiconductor strain gauges, and to increase objectivity in the analysis of calculation results applied to converters of mechanical values into frequency.

Development of Instrumented Running Prosthetic Feet for the Collection of Track Loads on Elite Athletes.

Knowledge of loads acting on running specific prostheses (RSP), and in particular on running prosthetic feet (RPF), is crucial for evaluating athletes’ technique, designing safe feet, and biomechanical modelling. The aim of this work was to develop a J-shaped and a C-shaped wearable instrumented running prosthetic foot (iRPF) starting from commercial RPF, suitable for load data collection on the track. The sensing elements are strain gauge bridges mounted on the foot in a configuration that allows decoupling loads parallel and normal to the socket-foot clamp during the stance phase. The system records data on lightweight athlete-worn loggers and transmits them via Wi-Fi to a base station for real-time monitoring. iRPF calibration procedure and static and dynamic validation of predicted ground-reaction forces against those measured by a force platform embedded in the track are reported. The potential application of this wearable system in estimating determinants of sprint performance is presented.

Adjusting Ankle Angle Measurement Based on a Strain Gauge Bridge for Powered Transtibial Prosthesis

Abstract Inaccurate ankle angle measurement may affect gait event detection accuracy, control parameter precision and assessment validity, and even finally result in gait asymmetry. This paper proposed an adjustment method based on a strain gauge bridge to obtain accurate ankle joint angle measurement for a powered transtibial prosthesis. The characteristics of relative creep, hysteresis, and temperature were studied. Then the curving fitting was used to study the relationship between the measured value of the strain gauge bridge and the compensation angle. Three male transtibial amputees participated in the experiments. Experimental results show that the strain gauge bridge can sense the deformation of carbon-fiber footplate, and be utilized to adjust the ankle angle. The effects of an inaccurate ankle angle were further discussed.

Method of metrological self-checking of a strain gauge pressure sensor

Existing methods of metrological self-monitoring of measuring sensors for temperature and pressure of technological industries are considered. The analysis of methods of metrological self-checking of strain gauge pressure sensors is carried out. Method is proposed based on measuring the supply voltage and voltage on the measuring diagonal of the bridge. The temperature of the strain gauge bridge is determined using a semiconductor thermistor installed near the bridge. This allows you to adjust the measured value of the total resistance of the bridge from the temperature of the bridge. With aging and exposure to external conditions, a change in the overall resistance of the bridge can be used to judge the error of the sensor. An experimental sample of the sensor was made. The failure of the strain gage bridge is simulated by parallel connection of an additional resistor to one of the shoulders of the bridge. Experimental studies have shown that modern technical means make it possible to assess the effect of changes in the total bridge resistance on the sensor error.

Способ метрологического самоконтроля тензорезистивного датчика давления

Existing methods of metrological self-monitoring of measuring sensors for temperature and pressure of technological industries are considered. The analysis of methods of metrological self-checking of strain gauge pressure sensors is carried out. Method is proposed based on measuring the supply voltage and voltage on the measuring diagonal of the bridge. The temperature of the strain gauge bridge is determined using a semiconductor thermistor installed near the bridge. This allows you to adjust the measured value of the total resistance of the bridge from the temperature of the bridge. With aging and exposure to external conditions, a change in the overall resistance of the bridge can be used to judge the error of the sensor. An experimental sample of the sensor was made. The failure of the strain gage bridge is simulated by parallel connection of an additional resistor to one of the shoulders of the bridge. Experimental studies have shown that modern technical means make it possible to assess the effect of changes in the total bridge resistance on the sensor error.

A Vascular Interventional Surgical Robotic System Based on Force-Visual Feedback

In this paper, based on the previous research of our research team. We proposed a Vascular Interventional Surgical Robotic System based on Force-Visual feedback. In the process of vascular interventional surgery, it is very important to accurately detect the resistance force of surgical catheter, which can improve the safety of operation. Therefore, we developed a force sensor for the vascular interventional surgery robotic system based on the principle of resistance strain gauge bridge circuit. In addition, a complete robotic system with only force feedback is not enough. Therefore, it is necessary to combine the visual feedback interface to complete the operation. Finally, some verification experiments have been completed, including the evaluation experiment of the internal fixture of the force sensor, the calibration experiment of the force sensor, the evaluation experiment of the force sensor, the evaluation experiment of the force feedback, The axial and radial synchronous motion experiment between the master and slave side. Experimental results showed that the feasibility of the force sensor. Vascular Interventional Surgical Robotic System based on Force-Visual feedback has good performance of the force feedback and the synchronous motion between the master and slave side. There is a certain error in the synchronous motion between the master and slave side and the force feedback of the vascular interventional surgery robotic system based on Force-Visual feedback, the error is within the allowable range.

Real-Time Monitoring of Wind Turbine Blade Alignment Using Laser Displacement and Strain Measurement

Wind turbine (WT) blade structural health monitoring (SHM) is important as it allows damage or misalignment to be detected before it causes catastrophic damage such as that caused by the blade striking the tower. Both of these can be very costly and justify the expense of monitoring. This paper aims to deduce whether a SICK DT-50 laser displacement sensor (LDS) installed inside the tower and a half-bridge type II strain gauge bridge installed at the blade root are capable of detecting ice loading, misalignment, and bolt loosening while the WT is running. Blade faults were detected by the virtual instrument, which conducted a z-test at 99% and 98% significance levels for the LDS and at 99.5% and 99% significance levels for the strain gauge. The significance levels chosen correspond to typical Z-values for statistical tests. A higher significance was used for the strain gauge as it used a one-tail test as opposed to a two-tail test for the LDS. The two different tests were used to test for different sensitivities of the tests. The results show that the strain gauge was capable of detecting all the mass loading cases to 99.5% significance, and the LDS was capable of detecting misalignment, bolt loosening, and 3 out of 4 mass loading cases to 99% significance. It was able to detect the least severe mass loading case of 11 g at the root to only a 98% significance.