Angular Transducer Research Articles

Effect of starting position of crankshaft on transient body vibrations of reciprocating compressor

The maximum reciprocating compressor vibrations occur during the startup and shutdown operations and understanding the factors that influence the transient vibrations can help in developing solutions to reduce the excessive displacements. In this study, the effect of crankshaft starting position on the vibration phenomenon is investigated and the optimal starting position to deliver a smooth start is proposed. The structural forces are analytically modeled to estimate the body displacements by considering the system resonance frequencies and modal vectors. An experimental setup is also constructed to validate the prediction model results, with the integration of an encoder to track the crankshaft angular position and transducers to measure the discharge and suction pressures. The transient responses of three different crankshaft start positions are then compared using the experimental setup and the analytical model. The results indicate that if the crankshaft starts to rotate from positions close to the bottom dead center, a higher amount of startup vibrations is observed, revealing the optimal starting position zone.The magnetization effect can potentially be addressed by the sensorless starting strategy developed by Lee et al. (2008) that implements a phase current controller for a smoother startup. While out of scope for this study, shutdown strategies can also be devised to have the piston consistently land at the favorable SAP range. By separately investigating the instances when the ‘stop’ command is provided to the steady-state operating compressor, solutions that attempt to replicate the conditions that lead to the favorable stop position can be developed; a limiting factor in mass production will be implementing the encoder for continuous position tracking and an accompanying undesirable cost increase in manufacturing. Nevertheless, the investigation of passive and active strategies is ripe for research in literature.

Measurement Method of Human Lower Limb Joint Range of Motion Through Human-Machine Interaction Based on Machine Vision.

To provide stroke patients with good rehabilitation training, the rehabilitation robot should ensure that each joint of the limb of the patient does not exceed its joint range of motion. Based on the machine vision combined with an RGB-Depth (RGB-D) camera, a convenient and quick human-machine interaction method to measure the lower limb joint range of motion of the stroke patient is proposed. By analyzing the principle of the RGB-D camera, the transformation relationship between the camera coordinate system and the pixel coordinate system in the image is established. Through the markers on the human body and chair on the rehabilitation robot, an RGB-D camera is used to obtain their image data with relative position. The threshold segmentation method is used to process the image. Through the analysis of the image data with the least square method and the vector product method, the range of motion of the hip joint, knee joint in the sagittal plane, and hip joint in the coronal plane could be obtained. Finally, to verify the effectiveness of the proposed method for measuring the lower limb joint range of motion of human, the mechanical leg joint range of motion from a lower limb rehabilitation robot, which will be measured by the angular transducers and the RGB-D camera, was used as the control group and experiment group for comparison. The angle difference in the sagittal plane measured by the proposed detection method and angle sensor is relatively conservative, and the maximum measurement error is not more than 2.2 degrees. The angle difference in the coronal plane between the angle at the peak obtained by the designed detection system and the angle sensor is not more than 2.65 degrees. This paper provides an important and valuable reference for the future rehabilitation robot to set each joint range of motion limited in the safe workspace of the patient.

Computational model and adjustment system of header height of soybean harvesters based on soil-machine system

With wide distribution and a large planting area, soybeans are an important cash crop in China. Due to the low position of soybean plants, improper control of the header height during harvesting is likely to cause poor harvesting and soil shoveling. To solve such problems, a soybean harvester header-height adjustment system is developed in this study. A profiling mechanism and hydraulic driving system were designed based on a current soybean harvester. The interaction between the soil and the harvester’s profiling mechanism was explored, the force and motion of the profiling mechanism were analyzed, and a relational model between the detection angle of the angular transducer and the rotational angle of the profiling mechanism was built. By analyzing the soil compactness of soybean growing plots, a linear fitting method was used to establish a mathematical model of soil compactness and compacting depth, a computational model of profiling the header height was determined, and an adaptive header-height adjustment system was designed. Evaluation indicators of the soybean harvester header-height adjustment system were constructed and a field harvesting experiment was conducted, whose results show that the absolute error between the average stubble height and the profiling height set by an industrial personal computer (IPC) before the tests was less than 2 mm. The variation coefficients of stubble height in the four groups of tests were 9.3%, 11.6%, 8.5%, and 6.5%, with respective profiling control accuracy of 88%, 86%, 90%, and 92%, ground flatness and soil compactness have little effect on the overall control effect of the control system.

Humanoid Lower Limb: Design, Analysis, Observer-Based Fuzzy Adaptive Control and Experiment

With flexibility similar to human muscles, pneumatic artificial muscles (PAMs) are widely used in bionic robots. They have a high power-mass ratio and are only affected by single-acting pneumatic pressure. Some robots are actuated by a pair of PAMs in the form of antagonistic muscles or joints through a parallel mechanism. The pneumatic pressure and length of PAMs should be measured simultaneously for feedback using a pressure transducer and draw-wire displacement sensor. The PAM designed by the FESTO (10 mm diameter) is too small to install a draw-wire displacement sensor coaxially and cannot measure muscle length change directly. To solve this problem, an angular transducer is adopted to measure joint angles as a whole. Then, the inertia of the lower limb is identified, and observer-based fuzzy adaptive control is introduced to combine with integrated control of the angular transducer. The parameters of the fuzzy control are optimized by the Gaussian basis neural network function, and an observer is developed to estimate the unmeasured angular accelerations. Finally, two experiments are conducted to confirm the effectiveness of the method. It is demonstrated that piriformis and musculi obturator internus act as agonistic muscle and antagonistic muscles alternatively, and iliopsoas is mainly responsible for strengthening because of the constant output force. Piriformis has a greater influence on yaw and roll angles, while musculi obturator internus is the one that influences the pitch angle the most. Due to joint friction, the dead zone of the high-speed on-off valve, lag of compressed air in the trachea, and coupling among angles are very difficult to realize precise trajectory tracking of the pitch, yaw, and roll angles simultaneously.

Development of a sEMG-Based Joint Torque Estimation Strategy Using Hill-Type Muscle Model and Neural Network

Exoskeleton control based on motion intention recognition has received increasing attention due to its promising prospect, and estimating joint torque is an effective approach to conduct intention recognition. In this paper, a surface electromyography (sEMG) signals-based joint torque estimation strategy is proposed to quantify the motion intention. Different from the majority of existing torque estimation strategies, two major improvements have been achieved. System identification is presented to estimate elbow angle which can be used in the Hill-type muscle model, and hence, the use of angular transducer is replaced. Besides, neural network is used to train the optimal factor of muscle activation to make the estimated torque more accurate. Finally, static and dynamic experiments are conducted respectively to verify the effectiveness and improvements of this strategy in terms of torque estimation accuracy. Compared to the other two existing torque estimation strategies, results show that this method is proved to make some progress in respect of torque estimation accuracy under different experimental conditions. The correlation coefficient increases by 2–9%; root-mean-square error (RMSE) reduces by 0.2–2.5 Nm; normalized root-mean-square error (NRMSE) reduces by 0.5–9.5%. The proposed torque estimation strategy could accurately identify the motion intention and reduce the use of angle sensor. Besides, it lays a foundation for rehabilitation exoskeleton robot control.

Research on Rotational Angle Measurement for the Smart Wheel Force Sensor.

The measurement of the rotational angle of the wheel is critical for the smart wheel force sensor (SWFS) to obtain the wheel forces defined in the vehicle coordinates. To simplify the structure of the SWFS and overcome the shortcomings of the traditional angular transducer, a new method to evaluate the rotational speed of the wheel and then calculate the rotational angle is proposed in this paper. In this method, the centripetal acceleration caused by the rotation is recorded by three accelerometers and used carefully. What’s more, the possible sources of error are classified and analyzed. Simulations and stand experiment are carried out to demonstrate the effectiveness of the proposed method.

Study on the electromagnetic fields of a novel small-angle transducer used in high-precision inertial sensors

PurposeMicrosyn signal generators have been used in high-precision inertial sensors for their good structural stiffness and high sensitivity. However, as the stator and the rotor of the microsyn are both constructed of silicon-steel laminations with high permeability, an extremely small non-concentricity between the stator and rotor of microsyn will cause two random reaction torques acting on the output axis. As a result, difficulty arises in compensating for these random reaction torques. This study aims to investigate the electromagnetic fields of a novel angular transducer characterized by high sensitivity.Design/methodology/approachBased on the operation principles of the new transducer, the output voltage is decided by the time rate of change of the net magnetic flux of each output pole. The transient analysis of the electromagnetic field of the transducer is carried out by ANSYS Maxwell-3D.FindingsThe distributions of the magnetic flux of the transducer’s interior and eddy current on the rotor are consistent with the results of theory analysis. Moreover, the leakage flux mainly distributes nearby the excitation poles. The novel small-angle transducer also possesses a remarkably low reaction torque and power loss.Practical implicationsStudy on the electromagnetic fields of the new transducer not only provides a powerful basis to further improve the precision of the new transducer but also expands the scope of applications of the new transducer.Originality/valueThis new transducer is not only characterized by a high sensitivity, high linearity and fast response but also extremely low reaction torque and power losses. Thus, the new transducer is suitable for high-precision inertial sensors.

Identification of the noise structure of micromechanical inertial transducers of motion parameters

The article presents the results of the analysis of the noise structure of micromechanical transducers of motion parameters – micromechanical gyroscopes (MMG) and micromechanical accelerometers (MMA) of an experimental measuring unit of strapdown inertial position navigation systems. The unit is manufactured and developed at JSC «GYROOPTICS» (St. Petersburg). It consists of a LL–MMG triad with measuring ranges of ±400°/s and an axial-type MMA triad with measuring ranges of ± 50 g. Micromechanical gyroscopes and accelerometers manufactured using modern microelectronics technologies are among the most promising microsystem technology devices that are widely used as sensors of the primary information of strapdown inertial orientation and navigation systems. The accuracy of the functioning of the inertial orientation and navigation inertial systems is significantly affected by the noise structure of the output signals of the inertial motion parameters sensors. For this reason, the urgent task of identifying the noise of micromechanical gyroscopes and accelerometers. The noise structure of the angular rate and linear acceleration transducers of the tested SINS block was identified by the Allan variance method. The output signals of the transducers were recorded in normal climatic conditions, the sampling interval was 1.0 ms, and the recording duration was 90 minutes. The processing of the output signals of the transducers was carried out on the basis of special software using the AlaVar 5.2 program. It has been established that the predominant noise components of the transducers are the random walk of the output signal – white noise and the instability of the zero signal – flicker noise. No quantization noise was detected in the output signals of the transducers. The values of the noise characteristics in Allan variance of the output signals of the angular rate transducers and the linear acceleration of the test block are compared with the noise characteristics of the most advanced modules produced by foreign companies.

Measuring transducer of angular displacements using phase raids of the surface acoustic waves electric field

The phase method for angular displacement unambiguous measurement based on the use of surface acoustic waves (SAW) devices is proposed and theoretically grounded.To eliminate any ambiguity of phase measurements, the construction of acousto-electronic angular displacement transducer using phase incursion of several SAW on the surface of the piezoelectric circular waveguide at different frequencies is proposed. The information parameters that determine the position of SAW receiver are measured at these frequencies.The rating of potential metrological parameters of the 3-frequency angular displacement transducer in the range 0…..360 degrees with the formation of precise, intermediate and rough measurement scales is carried out. The use of phase incursion on the surface of the piezoelectric waveguide electric field of three SAW at different frequencies taking by moving SAW receiver allows to form precise, intermediate and rough measurement scales in accordance with 11, 6 and 5 binary digits representing the measurement results.The experimental test results of models of a 3-frequency generator block, an amplifying-selective block and a 3-frequencies angular displacement transducer containing circular piezoelectric waveguide with a radius of 15 mm based on zinc oxide-fused quartz structure over which displaces a circular sectional SAW receiver are presented. The amplitude of the SAW receiver output signal varies exponentially depending on a gap between the piezoelectric waveguide surface and SAW receiver. It requires high precision of transducer manufacturing to ensure parallel to the acoustic line surface movement of receiver thus eliminating the influence of the phase velocity dispersion of the surface acoustic wave as a result of the SAW receiver electric field perturbation on the accuracy of measurements. Grading characteristics of angular displacement transducer are linear. The coefficients of angular displacement transformation on the precise scales are 0.54, 0.55 and 0.56 electric degrees/arcsec in the central frequencies of 69.52, 70.62 and 71.69 MHz. At the same time, the resolution and angular displacements measurement error on the precise scale are respectively less than 0.5 arcsec and 1.5 arcsec.The test results of model based on piezoelectric waveguide of zinc oxide-fused quartz structure confirm the possibility of creating highly sensitive angular displacements transducers with a resolution and accuracy properties that are close to the parameters of inductosyns, photoelectric transducers and laser interferometers. However, it may have considerably less weight and dimensions, cost and complexity of construction.Ref. 20, fig.6.

Ultrasound imaging transducer motion during standing postural tasks with and without using transducer fixator

BackgroundChanges in the orientation of ultrasound (US) transducer relative to the body surface during dynamic standing tests can affect US measurements. ObjectiveThe purpose of the study was to evaluate ultrasound imaging transducer motion while measuring the lateral abdominal muscle thickness during standing tasks with and without using transducer fixator (TF). DesignCross-sectional experimental study. MethodsA digital optical motion analysis system was used to assess the motions of US transducer during double-leg stance in different levels of platform stability of Biodex Balance System (BBS) (static, levels 6 and 3) with and without using TF in 45 healthy individuals. In addition, lateral abdominal muscle thickness was evaluated by US imaging. ResultsThe results indicated that the amount of angular and linear transducer motions during static and dynamic standing tasks significantly decreased by the use of TF as compared to the conditions without TF (P < 0.001, effect size> 0.84). ConclusionTF can significantly control US transducer motions within acceptable threshold limits during standing postural task. This may improve the clinical application of US imaging.

Optoacoustic characterization of broadband directivity patterns of capacitive micromachined ultrasonic transducers.

Frequency characteristics of ultrasound detectors used in optoacoustic tomography have a major impact on imaging performance. It is common practice to select transducers based on their sensitivity at the central frequency and under normal incidence. However, the bandwidth and angular sensitivity play an equally important role in establishing the quality and accuracy of the reconstructed images. Here, we developed a calibrated optoacoustic characterization method specifically tailored for broadband measurements of the angular transducer sensitivity (directivity). Ultrawideband omnidirectional optoacoustic responses were generated by uniformly illuminating thin absorbing sutures with nanosecond laser pulses and characterized with a needle hydrophone. This calibrated optoacoustic source was used to characterize the frequency dependence of the angular response by a conventional piezoelectric transducer (PZT) and a capacitive micromachined ultrasonic transducer (cMUT) with similar size and central frequency. Furthermore, both transducers had no preamplification electronics directly attached to the detection elements. While the PZT presented a 7.8 dB sensitivity advantage at normal incidence, it was able to provide detectable signal-to-noise levels only at incidence angles of up to 20 deg whereas the cMUT maintained reasonable sensitivity levels and broadband response at incidence angles of 40 deg and beyond. We further experimentally showcase a reduction in the limited-view image artifacts resulting from the broader acceptance angle of the cMUT.

An indirect torsional vibration receptance measurement method for shaft structures

In this paper, an indirect method for measuring torsional vibration of shaft structures is established. In conventional torsional vibration measurement, knowledge of two fundamental quantities is needed: a torque applied to the system and the angle of twist thus produced, which are both difficult to measure in experiment. In this indirect method, neither a deliberate torque excitation system nor an angular transducer is needed. Instead, a T-like beam structure is introduced and attached to one end of a shaft structure whereby the torques are produced by ordinary forces and only linear accelerometers at a few locations of the beam structure are used. Through the small finite element model of the T-like beam structure, the torsional receptance linking the torque to the angle of twist of the shafting systems is derived from the measured receptances of linear acceleration to the excitation force. This indirect theoretical-experimental combined method overcomes the difficulties and the associated poor accuracy in measuring receptances of torsional vibration of shaft structures, and hence is very useful. Numerical simulation of a test structure with noisy parameters and noisy simulated receptance data is made to validate the theoretical soundness of the method. Vibration tests are carried out on a laboratory shaft structure to demonstrate its accuracy and ease of use.

Molecular Electronic Angular Motion Transducer Broad Band Self-Noise

Modern molecular electronic transfer (MET) angular motion sensors combine high technical characteristics with low cost. Self-noise is one of the key characteristics which determine applications for MET sensors. However, until the present there has not been a model describing the sensor noise in the complete operating frequency range. The present work reports the results of an experimental study of the self-noise level of such sensors in the frequency range of 0.01–200 Hz. Based on the experimental data, a theoretical model is developed. According to the model, self-noise is conditioned by thermal hydrodynamic fluctuations of the operating fluid flow in the frequency range of 0.01–2 Hz. At the frequency range of 2–100 Hz, the noise power spectral density has a specific inversely proportional dependence of the power spectral density on the frequency that could be attributed to convective processes. In the high frequency range of 100–200 Hz, the noise is conditioned by the voltage noise of the electronics module input stage operational amplifiers and is heavily reliant to the sensor electrical impedance. The presented results allow a deeper understanding of the molecular electronic sensor noise nature to suggest the ways to reduce it.

Improving the measurement sensitivity of angular deflection of a torsion pendulum by an electrostatic spring

The torsion pendulum is widely employed in gravitational experiments as a weak force sensitive instrument, and its resolution is limited by the thermal noise of the pendulum and detection noise of angular deflection. Different kinds of angular deflection transducers are proposed and realized to improve its resolution. A torsion pendulum combined with an electrostatic spring is proposed here in order to improve the measurement sensitivity of angular deflection. Noise analysis and demonstration experiments show that the electrostatic torsion pendulum can relax the requirement of angular deflection detection, which is useful for gravitational experiments with much higher precision requirements.

Development of a high-resolution micro-torsion tester for measuring the shear modulus of metallic glass fibers

A high-resolution micro-torsion tester is developed based on electromagnetism, and the shear modulus of metallic glass fiber (Pd40Cu30Ni10P20) is measured using this tester. The torque is measured by a coil-magnet component and the rotation angle is measured by an inductive angular transducer. The calibration results show that the torque capacity of this tester is 1.1 × 10−3 N m with resolution of 3 × 10−8 N m and the rotation angle capacity is 90° with a resolution of 0.01°. A set of metallic glass fibers, with diameter of about 90 µm, are tested using this tester. The average shear modulus is obtained as 20.2 GPa (±6%).

On-Line Monitoring Method of Drive Motor Operational for On-Load Tap Changers

Motor-driven on-load tap changers (OLTC) operational within power transformers are extensively used for voltage regulation in power systems, whose principal malfunctions or failures are of mechanical type. Hence, monitoring of the mechanical characteristics of OLTC is of utmost significance. Based on a rotating angular transducer as well as digital signal processing techniques, an on-line monitoring methodology is established to measure, analyze and evaluate the dynamic or transient changes of the rotating angle of the drive motor operational in an OLTC, which can effectively indicate the underlying deficiency or even potential fault of the mechanical drive system connected to the motor. Computer simulations and experiments are carried out respectively, both showing the proposed on-line monitoring scheme is feasible and applicable.

Mechatronic Elements for Measuring Systems

This presentation deals with a new application of mechatronic means for angle measuring system; it can be applied in precision instrumentation and measurement equipment. Precise angle measuring is based on usage of angle measurement standards such as polygons, precision indexing tables and circular scales. Ring lasers and precision rotary encoders can also be used for this purpose as well as test benches created for angle calibration. Many angular and linear measurement transducers or encoders are used in industry and machine engineering for the position and displacement measurement. The accuracy of angular position fixed by means of these devices reach approximately 0.3" 0.1" (arc second). Control of their accuracy parameters is complicated task consisting from some high requirements needed for rotation, positioning, signal processing, object adjustment and data processing.

Laboratory Station for Research on Angular Translocation in Human Lower Limbs

In the article a construction of a laboratory station for determination of angles in three kinematic pairs of human lower limbs exoskeleton is described. The constructed exoskeleton is supposed to support human lower limbs only on plane vertical to ground. In article the results of measurement of movement parameters of walking human lower limbs obtained using the measuring station. Measurement of angular displacement on the station is realized using six angular displacement absolute transducers. The station is also one of the components contained in lower limb exoskeleton being constructed. The measuring construction will be used to identify actuating systems during exoskeleton construction phase.

Measuring relative acceleration: a relative angular acceleration prototype transducer

The present paper describes a novel prototype transducer for the measurement of relative angular acceleration. This transducer, of contactless type, is based on eddy current induction within a conductor slab moving in the presence of permanent magnets, and its contactless working principle is readily applicable to the measurement of linear or angular relative acceleration. The precision mechanics and the sensing element design of a prototype for an angular version of the transducer are based on FEM studies. The experimental results of the prototype performance are also presented.

Time–frequency characterization of the unsteady phenomena in a centrifugal pump

The paper presents an experimental investigation of the flow field instability in a centrifugal pump. Pressure fluctuations were measured with transducers placed flush with the inlet duct, and at the impeller discharge. Two impeller rotation speeds were utilized in the study, as well as several angular and radial transducer positions at design, and at off-design flow rates. A spectral analysis was carried out on the pressure signals in frequency and in time–frequency domains. The results highlighted the existence of an asymmetrical rotating pressure structure at the impeller discharge, having a fluid-dynamical origin and propagating both in the radial and circumferential direction, inside and downstream of the impeller.