Closed-loop Measurement Research Articles

A noninvasive method for monitoring respiratory rate of rats based on a microcantilever resonant humidity sensor

Respiratory rate is a vital physiological signal in laboratory rodents research. This paper presents a noninvasive method based on resonant humidity sensor for monitoring respiratory rate of rats. The sensor is composed of an aluminum nitride (AlN) resonant microcantilever coated with graphene oxide (GO) film. The sensor shows high sensitivity and good repeatability. By combining the sensor with a control circuit, a closed-loop respiration measurement system is realized for fast response. The system can monitor respiratory rate of rats in real time by detecting relative humidity difference between exhaled and inhaled breath. The method has advantages of fast response, small size and low cost. Furthermore, the respiratory rate of rats can be noninvasively monitored by integrating the sensor with a face mask.

A Fully Differential SOI-MEMS Thermal Piezoresistive Ring Oscillator in Liquid Environment Intended for Mass Sensing

In this paper, we present a silicon on insulator (SOI)-based MEMS oscillator that comprises a ring-shaped rotational mode resonator incorporating fully differential design for operation in aquatic environment using the thermal drive piezoresistive sense transduction. The differential scheme used in the resonator design enables high feedthrough cancellation, thus leading to floor value close to −62 dB with sufficient signal to feedthrough ratio (SFR) and allowing a later oscillator implementation. The proposed differential ring-shaped thermal piezoresistive resonator (DR-TPR) when made to operate in the rotational mode exhibits the special feature of minimizing the effect of viscous damping in liquid environment, attaining a quality factor value as high as 537 with a stopband rejection of 8.5 dB. The closed-loop measurement using the HF2LI lock-in amplifier with PLL from Zurich Instruments helps us to realize the differential ring-shaped thermal piezoresistive oscillator (DR-TPO) showing phase noise of −77.6 dBc/Hz at 1-kHz offset and −89.54 dBc/Hz at 10-kHz offset. The proposed DR-TPO in liquid environment can provide a frequency resolution of 6.95 Hz extracted from the measured Allan deviation, which corresponds to a minimum detectable mass of 4.11 pg, thus paving a way to both physical and biomedical detection in liquid.

Nonsmooth Optimization Method for H∞ Output Feedback Control

This paper proposes a nonsmooth optimization method for [Formula: see text] output feedback control problem of linear time-invariant(LTI) systems based on bundle technique. We formulate this problem as a nonconvex and nonsmooth semi-infinite constrained optimization problem by quantifying both internal stability of closed-loop system and measurement of system performance, where [Formula: see text] norm of closed-loop transfer function and a stabilization channel is used. Our method uses progress function and bundle technique to solve the resulting problem which has a composite structure. We prove the convergence to a critical point from a feasible initial point and test some benchmarks to demonstrate the effectiveness of this method.

Development of a 3-PRR Precision Tracking System with Full Closed-Loop Measurement and Control.

A 3-PRR (three links with each link consisting of a prismatic pair and two rotating pairs) parallel platform was designed for application in a vacuum environment. To meet the requirement of high tracking accuracy of the 3-PRR parallel platform, a full closed-loop control precision tracking system with laser displacement sensors and linear grating encoders was analysed and implemented. Equally-spaced laser displacement sensors and linear grating encoders were adopted not only for measurement but also for feedback control. A feed-forward control method was applied for comparison before conducting the closed-loop feedback control experiments. The closed-loop control experiments were conducted by adopting the PI (proportion and integration) feedback control and RBF (radial basis function) neural network control algorithms. The experimental results demonstrate that the feed-forward control, PI feedback control, and RBF neural-network control algorithms all have a better control effect than that of semi-closed-loop control, which proves the validity of the designed full closed-loop control system based on the combination of laser displacement sensors and linear grating encoders.

Autorange Thermal Sigma–Delta Converter for Incident Radiation Measurement

Thermal sigma–delta modulator is a closed-loop measurement approach, where the sensing element performs part of the $\Sigma \Delta$ modulation in the thermal domain. A new architecture is proposed in this paper for measuring the thermal incident radiation using thermoresistive sensors, where the modulator input range is automatically adjusted to fit the complete thermal radiation. The proposed architecture is compared with a similar one, which uses the same transducer interface circuit but without range adjustment, and is validated experimentally with a reference pyranometer. The proposed architecture has the main advantage of presenting a signal-to-noise ratio and sensitivity that is independent of the ambient temperature range definition. Experimental results for an ambient temperature range of 45 °C show a gain of 13 dB over the similar one.

A Wideband Inductorless dB-Linear Automatic Gain Control Amplifier Using a Single-Branch Negative Exponential Generator for Wireline Applications

This paper reports a wideband inductorless automatic gain control (AGC) amplifier for wireline applications. To realize a dB-linear AGC range, a pseudo-folded Gilbert cell driven by a single-branch negative exponential generator (NEG) is proposed as the core variable-gain amplifier. The NEG features a composite of dual Taylor series to extend the AGC approximation range without sacrificing the precision. Fabricated in 65-nm CMOS, the AGC amplifier occupies a tiny die area of 0.045 mm2 and consumes 28 mW at 1.2 V. Measured over a dB-linear gain range of ~40 dB, < ± 1 dB gain error is achieved and the 3-dB bandwidth stays roughly constant at 7 GHz. For the closed-loop AGC measurement, the input dynamic range is ~40 dB (10 mVpp to 1 Vpp) for a BER <10−12 under a 27 − 1 PRBS data at 10 Gb/s. The achieved figure-of-merit (FOM) of 2.8 pJ/bit compares favorably with state-of-the-art.

An implementation of real-time feedback control of cured part height in Exposure Controlled Projection Lithography with in-situ interferometric measurement feedback

Exposure Controlled Projection Lithography (ECPL) is an in-house additive manufacturing process that can cure microscale photopolymer parts on a stationary transparent substrate with a time sequence of patterned ultraviolet beams delivered from underneath. An in-situ interferometric curing monitoring and measurement (ICM&M) system has been developed to measure the ECPL process output of cured height profile. This study develops a real-time feedback control system that utilizes an empirical process model and an online ICM&M feedback to automatically and accurately cure a part with targeted height. Due to the nature of photopolymerization, the total height of an ECPL cured part is divided into exposure cured height and dark cured height. The exposure cured height is controlled by a closed-loop feedback on-off controller. The dark cured height is compensated by an empirical process model obtained from the ICM&M measurements for a series of cured parts. A parallel computing software application is developed to implement the real-time measurement and control simultaneously. The experimental results directly validate the ICM&M system’s real-time capability in capturing the process dynamics and in sensing the process output. Meanwhile, it evidently demonstrates the feedback control system’s satisfactory performance in achieving the setpoint of total height, despite the presence of ECPL process uncertainties, ICM&M noises and computing interruptions. A comprehensive error analysis is reported, implying a promising submicron control with enhanced hardware. Generally, the study establishes a paradigm of improving additive manufacturing with a real-time closed-loop measurement and control system.

A Closed-Loop Accelerometer Based on Three Degree-of-Freedom Weakly Coupled Resonator With Self-Elimination of Feedthrough Signal

This paper, for the first time, reports a closed-loop accelerometer based on three degree-of-freedom weakly coupled resonator (WCR). Three resonators are weakly coupled by two bridge-type coupling beams. When acceleration acts on the proof masses, the stiffness perturbation between the two outer resonators will incur the mode localization and cause the shift of amplitude ratio. The accelerometer is tested under open-loop circuit and closed-loop circuit to obtain the frequency responses and transient responses, respectively. The experimental results show that the sensitivity based on the amplitude ratio readout is improved by 348% compared with the 2-DoF WCR accelerometer. The measured signal-to-ratio noise is 124.2 dB and resolution reaches $1.1~\mu \text {g} / \surd \text {Hz}$ , which are significantly improved compared with the previous works. The resolution and signal-to-ratio noise under closed-loop measurement are improved by 46181% and 123.2%, respectively, compared with those under open-loop measurement which demonstrate that the performance of the mode-localized accelerometer can be improved using the closed-loop measurement method.

Hybrid algorithm for accumulated error suppression in open‐loop Doppler receiver

A hybrid algorithm is proposed to decrease the integration phase measurement error accumulation in open-loop Doppler receiver which is designed for space orbit determination and positioning applications when cooperated closed-loop system is unavailable. Firstly, adaptive-neuro-fuzzy inference system (ANFIS) module α is implemented for the interrupted closed-loop measurement data prediction. Then to improve the prediction accuracy of the ANFIS module α, an adaptive Kalman filter is employed for data fusion with predicted data from ANFIS module α and open-loop measurement data for complementation and corrections. Meanwhile, ANFIS module β is embedded in the Kalman filter for adaptive error compensation to optimise the filter performance. Finally, the time costly ANFIS computations are accelerated by reconfigurable software–hardware co-design module implemented in the receiver system to improve the computing capability and efficiency of system. Experiment results are analysed to demonstrate the effectiveness of proposed hybrid algorithm. It suppresses error accumulation in open-loop receiver phase measurement by 85.89% compared to the directly integration results when closed-loop system is off-line and has 61.02% enhancement compared to the algorithm without adaptive error compensations. Thus, the whole combinatory system accuracy is improved.

High-Resolution Distributed Dispersion Characterization for Polarization Maintaining Fibers Based on a Closed-Loop Measurement Framework

A closed-loop dispersion measurement framework (CLDM) is proposed. Carrying out dispersion compensation with an arbitrary trial dispersion on the interferogram under test, and using a criterion function as feedback to adjust the trial dispersion until the optimum is reached the trial dispersion is the measured result. The CLDM framework is not only noise-robust but can also cope with the case of multiple peaks that provides high resolution. We use it to measure the distributed birefringence dispersion (BD) chromatic dispersion difference of the two polarized modes of polarization maintaining fibers (PMFs). In this regime, the optimum of dispersion compensation is that the signal energy of every peak in the interferogram is concentrated. Thus, we present a criterion function to evaluate the signal energy concentration. Theoretical and experimental demonstration of this method is implemented. In addition, the spatial resolution ( $ 10 cm) is discussed. Eventually, a $\approx$ 3 km-length PMF coil is tested. The measurement error for BD and its slope @1550 nm are $ ps/nm/km and $2\;\times\; 10^{-4}$ ps/nm $^2$ /km, respectively.

Magnetooptic Sensor Based on Electrogyration Compensation for Faraday Effect in Lead Molybdate Crystal

A novel magnetooptic sensor is proposed which is based on electrogyration compensation for the Faraday rotation angle in single lead molybdate (PbMoO4, PMO) crystal. The optical sensing unit is only composed of two polarizers and one single PMO crystal exhibiting both the Faraday and electrogyration effects. AC 50-Hz magnetic field in the range of 167 Gs has been measured by the method of electrogyration compensation, and the nonlinear error is $\sim 16$ V/Gs for a block of PMO crystal with 5 mm in length. Verdet constant of the PMO crystal sample has also been measured for light wavelength of 635 nm, and it is $\sim 51.6\pm 1.1$ rad. $\text{T}^{-1}$ . $\text{m}^{-1}\vphantom {\sum ^{R^{R}}}$ . The proposed magnetooptic sensor provides a promising closed-loop measurement method of current, magnetic field, and Verdet constant.

Improving calibration accuracy of a vibration sensor through a closed loop measurement system

A sensor is a transducer whose purpose is to sense (that is, to detect) some characteristic of its environments. It detects events or changes in quantities and provides a corresponding output, generally as an electrical or optical signal. It has been widely used in mechanical engineering, aeronautics and astronautics engineering, industrial control, etc. Sensors play important roles in industries such as manufacturing, where all require the sensor to act as a reliable unit [1], [2]. In practical engineering applications, a sensor is often used for measuring vibrations, including acceleration, velocity, and displacement. It is the primary link in achieving conversion, processing, recording, and storage of information. Therefore, its performance directly influences the reliability and accuracy of the entire system. The calibration for vibration sensors, which need to ascertain sensitivity, frequency response characteristics, amplitude linearity, etc., are required before the measurement is made [3], [4]. Traditionally, an open loop device (in which the excitation signal is adjusted manually and the parameters are recorded manually) is used for sensor calibration. This type of manual calibration generates a large amount of work and active jamming, which results in errors. If a closed loop calibration system can be designed (i.e., the excitation signals are adjusted automatically by devices, and the real time data are sampled and analyzed), it will offer abundant measurement information and analysis methods which can help improve calibration accuracy and efficiency. In this article, we introduce such a closed loop calibration system for vibration sensors.

Mutual compensation property of electrooptic and magnetooptic effects and its application to sensor

Mutual compensation property between electrooptic and magnetooptic modulations in a crystal with electrooptic and magnetooptic effects and its application to magnetooptic sensor are investigated theoretically and experimentally. Under the condition of light intensity modulation, electrooptic and magnetooptic modulation effects can compensate for each other, so that the transmitted light intensity through the crystal can be kept at a certain fixed value. Based on this mutual compensation property, a novel optical current (or magnetic field) sensor is proposed and demonstrated experimentally by use of a single bismuth germanate (Bi4Ge3O12, BGO) crystal. The optical sensing unit is composed mainly of two polarizers and a block of BGO crystal with the shape of parallelogram. The BGO crystal itself can produce an optical phase bias of π/2, and it can be used as both a current sensing element and an electrooptic compensator. The change of magnetooptic rotation angle through the crystal can be compensated in real time by the change of electrooptic phase retardation caused by the applied voltage, thus the closed-loop optical measurement of current (or magnetic field) can be achieved. The 50 Hz ac current within 5 A is measured experimentally. The required compensating ac voltage is about 21.2 V/A in root-mean-square value. Experimental data show a good linear relationship between measured current and compensating voltage, and the nonlinear error is less than 1.7%.

A Dynamically Reconfigurable System for Closed-Loop Measurements of Network Traffic

Streaming network traffic measurement and analysis is critical for detecting and preventing any real-time anomalies in the network. The high speeds and complexity of today's networks, coupled with ever evolving threats, necessitate closing of the loop between measurements and their analysis in real time. The ensuing system demands high levels of programmability and processing where streaming measurements adapt to the changing network behavior in a goal-oriented manner. In this work, we exploit the features and requirements of the problem and develop an application-specific FPGA-based closed-loop measurement (CLM) system. We make novel use of fine-grained partial dynamic reconfiguration (PDR) as underlying reprogramming paradigm, performing low-latency just-in-time compiled logic changes in FPGA fabric corresponding to the dynamic measurement requirements. Our innovative dynamically reconfigurable socket offers 3× logic savings over conventional static solutions, while offering much reduced reconfiguration latencies over conventional PDR mechanisms. We integrate multiple sockets in a highly parallel CLM framework and demonstrate its effectiveness in identifying heavy flows in streaming network traffic. The results using an FPGA prototype offer 100 percent detection accuracy while sustaining increasing link speeds.

Concept for a Self-correcting Sheet Metal Bending Operation

Abstract Geometrical deviations can appear in the production of plug contacts used in electrical connection technology and in fittings for the furniture industry. The reasons for this can be a variation in the properties of the semi-finished product, or wear phenomena on the forming machine itself or on the bending tools. When geometrical deviations appear, the process parameters normally have to be adjusted manually. Finding the most appropriate process parameters is currently done manually and is thus very time consuming. In order to reduce the scrap rate and the setup time for production scenarios, a concept for self-correcting bending operations is being developed using the V-model of the VDI guideline 2206. In this case, the V-model will make it possible to set up a self-correcting control strategy consisting of a closed-loop control approach, measurement devices and actuators. Having implemented these components in the forming machines, it will be possible to recognize geometrical deviations automatically and to take corrective action during production, aiming at a reduction of the scrap rate and setup-time.

A Micro Dynamically Tuned Gyroscope with Adjustable Static Capacitance

This paper presents a novel micro dynamically tuned gyroscope (MDTG) with adjustable static capacitance. First, the principle of MDTG is theoretically analyzed. Next, some simulations under the optimized structure parameters are given as a reference for the mask design of the rotor wafer and electrode plates. As two key components, the process flows of the rotor wafer and electrode plates are described in detail. All the scanning electron microscopy (SEM) photos show that the fabrication process is effective and optimized. Then, an assembly model is designed for the static capacitance adjustable MDTG, whose static capacitance can be changed by rotating the lower electrode plate support and substituting gasket rings of different thicknesses. Thus, the scale factor is easily changeable. Afterwards, the digitalized closed-loop measurement circuit is simulated. The discrete correction and decoupling modules are designed to make the closed-loop stable and cross-coupling effect small. The dual axis closed-loop system bandwidths can reach more than 60 Hz and the dual axis scale factors are completely symmetrical. All the simulation results demonstrate the proposed fabrication of the MDTG can meet the application requirements. Finally, the paper presents the test results of static and dynamic capacitance values which are consistent with the simulation values.

Study on the sensitivity of laser-pumped cesium atomic magnetometer

A cesium atomic magnetometer based on laser-pumped rf resonance has been investigated and demonstrated experimentally. Atoms are polarized and pumped to dark states by circularly polarized light. When there exists a magnetic field, the corresponding magnetization will be precessing around the magnetic field at Larmor frequency. By means of adding a resonant rf magnetic field, the atoms will be depolarized and absorb photons again. By detecting the spectrum of the transmitted light, one can obtain the information about the external magnetic field. We build an 894nm external cavity diode laser with a frequency stabilization device, and a low noise magnetic field measurement environment. After the optimization of the magnetometer parameter and closed-loop measurement, an ultimate sensitivity of 19 fT/Hz1/2 and an intrinsic sensitivity of 1.8 pT/Hz1/2 have been achieved with the spatial resolution smaller than 2 cm.

Differential Roll-Scanning Technology for Accuracy Measurement of Fine-Pitch Gears

The accuracy measurement of fine-pitch gears within module 0.02-0.2mm in batch production is one of the puzzle problems in industry because of its small amout of dimension and rigidity. Based on the gear integrated error measurement technology developed by CTRI in China and Frenco in Germany, a kind of differential roll-scanning measuring technology and a differential fine-pitch gear integrated error measuring machine first developed by the authors are introduced briefly in the paper, including the working principle and calculation formulas of ‘two synchronized rotate-driving systems, one differential-compensation closed-loop measurement’ , the stucture of ‘spindle on spindle’ and ‘differential composite driving spindle system’ of the master gear, and the unique master gear with ‘every other tooth thinned’ followed the principle of overlap coefficient not bigger than 1 for a few certain gear pairs，and also the special made hob for making the thinned master gear. The measuring results of four items of deviations, including pitch, profile, tangential composite and integrated deviations of product fine-pitch gears show the feasibility and prospect of the new developed measuring technology and machine in future industry application.

Novel method for closed-loop electroretinogram measurement of sensitivity in Drosophila

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Optical stress sensor based on electro-optic compensation for photoelastic birefringence in a single crystal

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3 m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement.