Rotational Accelerometer Research Articles

Frequency assignment of an assembled structure through links of its substructures

Structural modifications for assigning desirable natural frequencies and modes are an effective passive vibration control strategy. In many assembled structures, the substructures, which may come from different manufacturers/suppliers or have intended individual functions, do not allow modifications or are difficult to modify. In such common situations, designing proper links or joints used for assembling the substructures will be an effective solution to ensure that the assembled structure possesses the right modal properties.In this paper, a receptance-based frequency assignment approach is presented, which consists of a theoretical method of frequency assignment suitable for assembled structures, an indirect method for estimating rotational recpetances and a substructuring method. It is implemented on an assembled structure, which is a simplified model of a floating raft platform installed on a ship hull. The model comprises two substructures and six links. A number of experiments are carried out to measure the required receptances systematically, including rotational receptances which are measured with the help of an auxiliary structure and two rotational accelerometers. One and two frequencies are successfully assigned by using the links with the right cross-sections determined by solving an optimisation problem. Key challenges are also discussed. This work should be practically very useful in passive vibration control of assembled structures.

IoT Integrated Accelerometer Design and Simulation for Smart Helmets

This article delves into the transformative potential of micro-electromechanical systems (MEMS) accelerometers, particularly their role in revolutionizing helmet safety. Accelerometers, ubiquitous in vehicle manufacturing, computer technology, and audio-video systems, play a crucial role in measuring acceleration. This work focuses on the design and simulation of a rotating accelerometer integrated into football helmets. The introduction of rotational acceleration addresses specific challenges in detecting and mitigating brain injuries that linear accelerometers may encounter. Additionally, the article explores the concept of piezoresistive football helmets, designed to resist force and reduce the impact of concussions. Piezoresistive helmets, designed to resist force and minimize the impact of concussions, when augmented with Internet of Things (IoT) capabilities can create a comprehensive smart safety solution. The incorporation of IoT sensors and connectivity into piezoresistive helmets enables real-time monitoring and data analysis of impact forces. This integration not only enhances player safety by providing immediate insights into potential risks but also opens avenues for injury prevention strategies. Leveraging COMSOL simulation software, this research not only conceives but also realizes the innovative integration of rotational accelerometers and piezoresistive materials in football helmet design, advancing safety standards in sports technology.

Field Measurement on Translational and Torsional Wind-Induced Response of a High-Rise Building during Typhoon Khanun

Full measurements for the wind field atop a 32-storey building (supported by four huge columns) and for the dynamic responses of different floors were conducted on 15 October 2017 to obtain the translational and torsional responses of the high-rise building during the Typhoon Khanun. The time histories of the torsional angular acceleration responses on the 24th and 32nd floors of the high-rise building were obtained using RA013 rotational accelerometer, and those of the translational acceleration responses on the 6th, 12th, 18th, 24th, 30th and 32nd floors along axial direction were recorded by the translational accelerometer. The variation rules of the translational and torsional acceleration responses with floor height and mean wind speed were disclosed, and the response ratios between the torsional and translational acceleration were analyzed when basic time intervals were 10 min. Based on the target probability method, the value range of the acceleration peak factor with different target reliability under Typhoon Khanun was proposed. The results show that the translational and torsional acceleration peak values and root mean squares are the power functions of mean wind speed. The values of acceleration peak factors are recommended to be 3.0 and 5.0 if target reliabilities are determined as 99.38% and 100%, respectively. Research on torsional response measurements can accumulate valuable scientific data and lay solid foundations for the subsequent studies on the torsional wind-resistant design of high-rise buildings.

Application of rotational accelerometers on the measurement of automotive headlamp cut-off deviation

Automotive lighting products, such as Head Lamps (HL), Fog Lamps (FL), Daytime Running Lamps (DRL), face with mechanical vibrations during service life which may coincide with the resonance frequencies of the light source. When excited at resonance frequencies, especially in the case of HL’s, light beam cut-offline may deteriorate and vibration of light beam occurs. This situation is also called light flickering. This state has disturbing effect on the driver’s visibility, which is valid for both the driver and the counter drivers. Most of the automotive manufacturers have developed test specifications for evaluation of flickering state under sinusoidal frequency sweep acceleration loading and they have introduced limits for flickering angle range or displacement range of the light beam with respect to frequency measured on a screen which is put on a prescribed distance from the light source. In this study a traditional way of light beam flickering angle deviation measurement method of HL is presented. Furthermore, application of precise & efficient way of measurement method by the use of quartz rotational accelerometer is inspected.

Using Updated and Expanded Data to Estimate the Unmeasured Rotational Data of a Bolted Structure

For frequency-based substructuring (FBS) to be accurate, translational and rotational data must be available at the connection points between substructures. However, obtaining rotational FRFs from experimental modal analyses is very difficult in practice. In this paper, an alternative method for estimating rotational FRFs is proposed using an approximated simplified finite element model (ASFE), modal updating, and mode expansion. The proposed approach was demonstrated on an assembled structure consisting of an irregular plate (test model) and a simple beam (FE model). The SEREP method was used to augment the translational and rotational FRFs to the updated ASFE mode shapes. The expanded rotational FRF of the test model was validated with the measured rotational FRF obtained from a piezoelectric direct rotational accelerometer. The results showed that the proposed approach for FBS correctly predicted the experimental FRF of the assembled structure with 90% accuracy. The FBS method is no longer dependent on the experimental rotational FRF, which is very difficult to measure with the methodology presented here.

A multi-orientation low-frequency rotational accelerometer.

We present a low frequency rotational accelerometer coined ALFRA with a few nrad/Hz readout sensitivity above 20 mHz and 0.1 nrad/Hz above 50 mHz. The ALFRA is a beam-balance style rotation sensor, which pivots about a cross flexure designed to allow mounting with any orientation, the axis of the pivot determining which rotational component is measured. The high sensitivity is achieved through the use of a walk-off sensor readout used in a feedback loop with an electromagnetic coil to keep the beam dynamically locked. The ALFRA is relatively compact for a ground rotation sensor, measuring at 780 × 240 × 55mm3.

Assessment of Rotational Accelerometer Mountings for Rotational Frequency Response Function Measurement

Kistler Kshear 8840 piezoelectric rotational accelerometer is designed with an M5 bolt type of mounting and a 5mm diameter of through or pre-tapped hole is required in a structure under test. However, the mounting is not applicable for some cases, and other types of mounting need to be used. This work investigates the applicability and accuracy of five different configurations of mounting for Kistler Ksher 8840 piezoelectric rotational accelerometer for the measurement of the rotational FRFs of a steel plate. The mounting configurations consist of 3D printed PLA and ABS mounting, bee’s wax, steel, and bolt mounting. The rotational FRF of the steel plate was measured by using impact testing method. The applicability and accuracy of the mountings were evaluated by comparing the measured FRFs with the finite element (FE) FRFs counterparts. The comparisons of the results revealed that using the bee’s wax mounting had produced the most accurate and least noisy FRF. It was also found that using the 3D printed PLA mounting had contributed to the highest contamination of noise and several spurious peaks in the measured FRFs. These findings provide useful information for selecting the appropriate types and designs of mounting for the Kistler 8840 rotational accelerometer.

Performance of the Expanded Virtual Point Transformation on a Complex Test Structure

The Virtual Point Transformation (VPT) makes it possible to experimentally identify the full DoF FRF matrix by projecting the measured displacements onto the Interface Deformation Modes (IDMs). The VP FRFs were already successfully used in Frequency-Based Substructuring (FBS); however, the VPT is susceptible to deviations in the impact location and orientation, as well as to deviations in the sensor’s sensitivity and positioning. Uncertainties associated with the sensors can be decreased by using the expanded VPT. This expanded VPT allows the projection of a directly measured rotational response onto the Interface Deformation Modes (IDMs). The consistency of the transformation is achieved by using a rotational weighting matrix, which is formulated to minimize the norm of the overall displacements due to the rotational residual at the VP for each rotational sensor. The rotational response is measured using a direct piezoelectric rotational accelerometer. In this paper the application of the expanded virtual point transformation and the possible advantages are explored on a complex and engineering-like test structure. Both transformations, standard and expanded, are performed for each VP to enable a side-by-side comparison.

Symmetric Triaxial Rotational Piezoelectric Seismometers

The possibilities of constructive implementation of rotational seismometers using fundamentally new two-and four-element piezoelectric rotation sensors are considered. Based on a detailed review of existing piezoelectric accelerometers for strong earthquakes, a design for triaxial rotational piezoelectric accelerometers symmetric with respect to the vertical location component is proposed. Calculation for an instrument suitable for downhole observations is presented. The prospects of using the new modern piezoelectric materials are noted.

Introduction of line contact in frequency-based substructuring process using measured rotational degrees of freedom

The theory of frequency-based substructuring enables us to combine the dynamical behavior of multiple subsystems into the common response of the whole system. Subsystem’s properties can be numerically or experimentally obtained in the form of frequency response functions. Response models are then coupled together taking into account a connectivity conditions. However, when one is dealing with a statically indeterminate multi-point connections such as flanges connected over several bolts, it is difficult to properly define a model in the numerical environment. In order to obtain real contact conditions a few methods like virtual point transformation and multi-point connection were proposed in recent years. Since an indirect approach of obtaining rotational motion struggle to accurately define local dynamic characteristics i.e. antiresonances, it also rely on assumption of rigid interface. In this paper we are introducing an alternative approach, where all six degrees of freedom are experimentally obtained with aim to directly address local joint flexibility in the substructuring process. This procedure represent an alternative to the method that removes the effects of a flexible fixture, however here it is done directly by measuring contact dynamic without the need of additional fixture block. Rotational responses are directly obtained using rotational accelerometer that enable us to gather all six degrees of freedom in each experimental point. Consequently, contact can be fully defined with less measurement points where several of them with only translational responses are required in other methods for reconstruction of rotational motion.

Identification of torsional receptances

Identification of torsional receptances of shaft structures has been a challenge. This paper presents a method for measuring or estimating high-quality torsional receptances using two different methods based on the Receptance Decoupling Technique. In both methods, a T-block needs to be attached to facilitate the generation of torsion, and only the numerical receptance data of the T-block cast in a simple theoretical model and a few measured receptance data of the assembled system are required. Both methods are studied and assessed in numerical simulation, and the more robust method is further validated in experiments. The usage of rotational accelerometer is shown to significantly improve the quality of the estimation when the noise level is high. It is demonstrated that high-quality torsional receptances can be indirectly measured with high repeatability using the proposed method and thus can be used subsequently to identify torsional modal parameters, update finite element models, make structural modifications, or implement active torsional vibration control. Due to ubiquitous use of rotating machines, this novel method has significant applications.

On the performance of direct piezoelectric rotational accelerometers in experimental structural dynamics

Rotational responses are comparing to the translational responses less frequently used in the experimental structural dynamics. Even though they represent half of all the existing degrees of freedom they are often omitted, since they are difficult to measure. Nevertheless, they have an important contribution in structural dynamic modifications, model validation, substructuring, etc. Therefore in this paper a performance evaluation of two direct piezoelectric rotational accelerometers is made in order to show the possibilities of their usage in the structural dynamic applications. Additionally, the results are compared to a commonly used method of approximated rotational responses obtained from two offset translational accelerometers. Sensors were tested with impact and sine-sweep excitations. Data is analyzed in the form of frequency response functions and compared to a numerical reference with a coherence criterion. The quality of directly obtained rotations are expected to have great potential in structural dynamics.

Piezoelectric Rotational Accelerometers

A rotational accelerometer using piezoelectric material, preferably quartz, in a shear orientation. Piezoplates and conducting seismic masses, each having bores therethrough, are bolted to posts that are symmetrically mounted to a body in such a manner that the bolt passes through the piezoplates but does not make contact. The accelerometer can be assembled as a single-axis accelerometer by mounting a pair of posts symmetrically about the body along the measured axis; additionally, the accelerometer may be assembled as a double or triple axis accelerometer by symmetrically mounting additional pairs of posts to the body. The total weight of the seismic masses and the crystals of the shear-type accelerometer halves should be equal. The invention sets forth a novel rotational accelerometer that reduces or eliminates the need for signal-processing electronics.

Full-degrees-of-freedom frequency based substructuring

Abstract Dividing the whole system into multiple subsystems and a separate dynamic analysis is common practice in the field of structural dynamics. The substructuring process improves the computational efficiency and enables an effective realization of the local optimization, modal updating and sensitivity analyses. This paper focuses on frequency-based substructuring methods using experimentally obtained data. An efficient substructuring process has already been demonstrated using numerically obtained frequency-response functions (FRFs). However, the experimental process suffers from several difficulties, among which, many of them are related to the rotational degrees of freedom. Thus, several attempts have been made to measure, expand or combine numerical correction methods in order to obtain a complete response model. The proposed methods have numerous limitations and are not yet generally applicable. Therefore, in this paper an alternative approach based on experimentally obtained data only, is proposed. The force-excited part of the FRF matrix is measured with piezoelectric translational and rotational direct accelerometers. The incomplete moment-excited part of the FRF matrix is expanded, based on the modal model. The proposed procedure is integrated in a Lagrange Multiplier Frequency Based Substructuring method and demonstrated on a simple beam structure, where the connection coordinates are mainly associated with the rotational degrees of freedom.

Study on High Accuracy Constant Tension Controller of Winding Machine

Fiber winding tension control is a key technique in the winding machine which influences the quality of winding product directly. The change of diameter results in the winding tension becoming more complicated, time varying and non-linear and has a severe influence on steady and transient performance of winding system. This paper proposes a novel control scheme, which integrates the feedforward observation algorithm with PID control algorithm. One of the most merits is that it can compensate disturbance value based on the measuring data of rotational inertia and rotational accelerometer in real time. Simulation results show that control system has well qualified with high control precision and high response speed.

加速度計出力を用いた柔軟構造衛星のシステム同定

This paper presents an application of single-input multi-output (SIMO) system identification in the time domain using accelerometer outputs that are typical of satellite on-board sensors.The algorithm is suitable for the on-orbit system identification of six degrees-of-freedom spacecraft motions using the responses to thruster impulse inputs. Our new method identifies the input and output matrices of a SIMO collocated system by applying a recursive least-squares iteration scheme to refine the matrices obtained from conventional ERA. In a numerical simulation of an actual spacecraft to verify the algorithm, a mathematical model of the Engineering Test Satellite-VI (ETS-VI) is excited by a body-mounted thruster, and the translational and rotational accelerometers are measured simultaneously. Our method successfully identifies all of the natural frequencies, damping ratios, and mode shape vectors except for pitch rotational motion that has low sensitivity, confirming its validity.

Technology‐Driven Alternatives for Smart Sensor Interfaces

AbstractThe importance of integrated microsystems is continuously growing because of the combination of two trends: the progress of silicon sensor technology and the introduction of new techniques for interface circuits. In this chapter we show how different approaches to the implementation of smart sensor systems, basically driven by the available fabrication technologies, can lead to successful designs. Three examples are presented: a fully integrated current monitor, a biaxial accelerometer, and a rotational accelerometer. The current monitor is an example of single chip implementation. It supports two different operating ranges (20 A and 200 A full scale), provides digitally programmable gain and offset with an on‐chip PROM, and achieves 9 bits of resolution and ± 0.6 LSB of linearity. The biaxial accelerometer and the rotational accelerometer are examples of implementations based on two chips in the same package. They achieve 80 dB of dynamic range with ± 1 g full‐scale signal over a 30 Hz bandwidth and 38 dB of dynamic range with 200 rad/s2 full‐scale signal over an 800 Hz bandwidth.

Interface for MEMS-based rotational accelerometer for HDD applications with 2.5 rad/s/sup 2/ resolution and digital output

A 0.6 /spl mu/m BiCMOS interface for microelectromechanical systems (MEMS) based rotational accelerometers is presented. It is housed in an inexpensive standard SO-24 plastic package with a capacitive rotational accelerometer sensor produced using MEMS technology. This sensitive interface chip includes the analog-to-digital conversion, filtering, and interface functions. The analog-to-digital conversion is realized through a single-bit electromechanical /spl Sigma/-/spl Delta/ loop able to detect capacitive unbalancing as low as 50 aF (50/spl times/10/sup -18/ F). The produced bitstream is then processed by a digital chain and made available through a standard 3.3 V (5 V tolerant) three-wire serial bus. The signal bandwidth is about 800 Hz, the sensitivity is 2.5 rad/s/sup 2/, with a full-scale sinewave of 200 rad/s/sup 2/ and a signal-to-noise ratio peak of 38 dB over 30-800 Hz. Through the serial bus, it is also possible to program device characteristics including gain, offset, filter performance, and phase delay. The complete sensor is used in a feed-forward compensation scheme to cancel external disturbances acting on computer hard-disk drives so as to steadily keep the read-write heads on track: this allows greater track densities and better speed performance.

A 2.5-rad/s/sup 2/ resolution digital output MEMS-based rotational accelerometer for HDD applications

Mechanical vibration of a HDD can cause head mis-positioning. This effect can be compensated by using the device presented in the following. It is a capacitive rotational accelerometer sensor which uses MEMS. The vibrations of the disk drive cause tiny rotational displacements of the moving part of the MEMS structure, which are measured by sensing the small variations in capacitance that they cause. Capacitance changes as small as 0.05 fF can be measured by the device. The device operates as follows: the minute rotational vibrations are detected and measured in order to generate a feed-forward correction signal for the voice coil drive circuit to keep the head in the correct position. This allows the track spacing to be reduced significantly, increasing the storage density per unit area. The circuit has been realized in a 0.61 /spl mu/m BiCMOS technology with an area of 9.5 mm/sup 2/. The power consumption is 150 mW from a single 5V supply.

Expanding the bandwidth of rotational accelerometers by autonomous gain–phasetailoring

The concept of an autonomous gain–phase piezoelectric device is adapted to thedesign of a rotational accelerometer. It can be shown that a no-phase-delaylow-pass filter can be introduced into the transfer function of an accelerometer byweighting the structure vibration strain spatially. This can be achieved bymodifying either the shape or the effective surface electrode of a thin layerpiezoelectric film. With the introduction of this new class of filter, the usablebandwidth of the rotational accelerometer created can be shown to expandsignificantly. It can also be demonstrated that the concept is applicable tomechanical systems that can be represented using a second-order partialdifferential equation including a shaft, rod, etc. To verify the performance ofthe newly developed rotational accelerometer, which is difficult to testdue to its wide bandwidth, the design and implementation of a testingmethodology based on a wideband rotational shaker is also detailed.