Pressure Feedback Research Articles

Robust force tracking control via backstepping sliding mode control and virtual damping control for hydraulic quadruped robots

In order to improve the force tracking performance of hydraulic quadruped robots in uncertain and unstructured environments, an impedance-based adaptive reference trajectory generation scheme is used. Secondly, in order to improve the robustness to environmental changes and reduce the contact force errors caused by trajectory tracking errors, the backstepping sliding mode controller is combined with the adaptive reference trajectory generator. Finally, a virtual damping control based on velocity and pressure feedback is proposed to solve the problem of contact force disappearance and stall caused by sudden environmental change. The simulation results show that the proposed scheme has higher contact force tracking accuracy when the environment is unchanged; the contact force error can always be guaranteed within an acceptable range when the environment is reasonably changed; when the environment suddenly changes, the drive unit can move slowly until the robot re-contacts the environment.

The potential of heat release rate and cylinder pressure feedback control for conventional and premixed charge compression ignition combustion

Cylinder pressure or heat release rate tracking algorithms for direct-injected compression ignition engines allow to account for various disturbances, such as changes in the fuel characteristics or the effects of engine wear. They are suited for flex-fuel engines and allow the use of multi-injection strategies; hence, they show potential for mobile applications. However, they are based on the assumption that the heat release rate or cylinder pressure correlates well with engine efficiency and emissions and therefore allows a clean and efficient engine operation. With the objective to evaluate the potential of such tracking algorithms, this assumption is investigated for conventional as well as for low-temperature combustion strategies with diesel as fuel of choice. Based on experimental data, exploratory data analysis methods are applied to evaluate how sensitive engine efficiency and emissions are to changes of the heat release rate or cylinder pressure. Furthermore, an extended tracking algorithm is proposed, which can be applied for premixed charge compression ignition combustion concepts.

A programmable and self-adaptive dynamic pressure delivery and feedback system for efficient intermittent pneumatic compression therapy

Controlled dynamic pressure delivery is essential for efficiently promoting hemodynamics of the lower extremities in pneumatic compression therapy. Pressure dosage control is challenging because of diverse influencing factors, such as irregular interface contact geometries, different stiffnesses of body tissues and pressure materials, and customized pressure recipes and individual patient demands. To address these challenges, a programmable and self-adaptive dynamic pressure delivery and feedback system for enhanced compression therapy were developed in this study. This system comprised a soft pneumatic actuator (SPA) unit in a stocking laminated with multi-bladder, a programmable pressure control unit for pneumatic and interface pressure control, matrix soft sensors for real-time interface pressure detection, and differential pressure sensors for pneumatic pressure monitoring as well as connective accessories (air tubes and valves). A fluid–structure interaction model was developed to analyse the interaction between the bladder and lower limb by considering essential factors (bladder and soft tissue stiffness, contact area, and bladder-lower limb interface characteristics). An improved proportional–integral–derivative controller was designed to regulate dynamic interface pressure and personalized pneumatic compression treatment. Dedicated software was developed to monitor, process, and display the tested pressure data. In vitro and in vivo experiments were performed to validate the developed system. This study integrated theoretical and experimental approaches to a novel solution for customized dynamic pressure therapy. The findings enhanced our understanding of the working mechanisms and characteristics of the SPA–lower limb system. Moreover, the results serve as a foundation for the design and innovation of advanced programmable units for efficient compression treatment in various applications in healthcare, medicine, and rehabilitation.

Feedback controller for restoring the basal hemodynamic condition with a rotary blood pump used as left ventricular assist device

This work deals with the use of pulsatility indices in designing a ventricular assist device (VAD) control system. The control objective is to restore the patient's basal hemodynamic energy. The proposed control system structure comprises a hierarchy of cascaded control loops. At the highest level, there is the pressure feedback control loop, and at the lowest level, there are feedback control loops for both the rotational speed and the armature current. The reference signal for the high-level controller has a pulsatile profile. The generation of this pulsatile profile employs a procedure that takes into account the fulfillment of physiological specifications. Among the considered physiological requirements, there is the mean arterial pressure (MAP), the energy equivalent pressure (EEP), or the surplus hemodynamic energy (SHE). The gains of the low-level controllers are calculated based on the time-domain specification and the VAD mathematical model parameters. On the other hand, high-level controller gains are determined by using integral performance error criteria as tuning rule. The results obtained in silico indicate the feasibility of the proposed control system as well as its related design procedure. With the generated reference pump profile, it is possible to restore the basal hemodynamic condition for a heart failure patient. Besides, the restored basal hemodynamic condition is quite robust since it is maintained even under variations of the systemic resistance and heartbeat rate.

Trunk muscle activity during pressure feedback monitoring among individuals with and without chronic low Back pain

BackgroundPressure biofeedback unit (PBU) is a widely used non-invasive device to assist core muscle training by providing pressure feedback. The aim this study was to compare the muscle activities of transverse abdominis (TA) and multifidus (MF) at different target pressures (50, 60 and 70 mmHg) of PBU between individuals with and without cLBP.MethodsTwenty-two patients with chronic LBP (cLBP) and 24 age matched healthy individuals were recruited. Electromyography (EMG) signals were recorded from the TA and MF muscles while the TA and MF were contracted to achieve PBU pressure value of 50, 60 and 70 mmHg in random order. The average EMG amplitude (AEMG) of 3 replicate trials was used in the analysis after normalization to %MVIC. %MVIC is defined as the mean of the three AEMG divided by the AEMG of MVIC. Two-way ANOVA was performed to assess the effects of groups (healthy and cLBP) and the three different target pressures of PBU. Independent sample t-test was conducted to compare between the two groups. Spearman’s correlation analysis was performed in the cLBP group to determine potential correlations between EMG activity, NPRS and ODI.ResultsThe %MVIC of the TA and MF in the cLBP group were higher than the control group at each pressure value (P<0.05). During maximal voluntary isometric contraction (MVIC) of TA and MF, compared with healthy groups, cLBP subjects showed a decrease (TA mean = 47.61 μV; MF mean = 42.40 μV) in EMG amplitudes (P ≤ 0.001). The MVIC of MF was negatively correlated with Numerical Pain Rating Scale (r = − 0.48, P = 0.024) and Oswestry Disability Index (r = − 0.59, P = 0.004).ConclusionsWe measured the trunk muscles activities at different PBU pressure values, which allows the individual to estimate trunk muscle contraction via PBU. Clinicians may be able to confer the data obtained through EMG recordings to adjust the exercise intensity of PBU training accordingly.

Dynamic impact of hydraulic systems using pressure feedback for active damping

Pressure feedback has been an effective method for active damping and oscillation reduction in hydraulic systems. However, this study reveals a dynamic impact problem of a larger velocity overshoot and slower convergence excited by an external force/torque disturbance once pressure feedback is introduced for active damping. This problem is introduced through a theoretical analysis, and then illustrated by a numerical simulation. The solutions to this problem are analysed for a hydraulic system with a symmetric cylinder. For a trade-off between the active damping effect and reduction in dynamic impact, a multi-objective optimization method is proposed to determine the control parameters (gain and time constant) of the high-pass pressure filter. The multi-objective optimization method is validated by a simulation model with the symmetric cylinder under different disturbances. Moreover, an analysis is carried out for the system with an asymmetric cylinder or hydraulic motor. The theoretical analysis shows that the mathematical forms of the two systems are similar to that of the symmetric cylinder system. Therefore, the dynamic impact problem also exists in the two systems. The proposed method is also effective for the damping improvement and mitigation of the dynamic impact.

Analytical Harmonic Method for Modeling High-Frequency Oscillation With Applications to Aircraft Piston Pump Vibration Analysis

Undesired oscillations are often encountered in controlled systems at steady state due to high-frequency (HF) periodic disturbance and/or feedback noises. This article presents a computationally efficient alternative to derive an analytical harmonic model (AHM) that expresses the oscillatory variable as a series of harmonic kernel vectors and a position-independent harmonic amplitude vector for identifying the dominant harmonic components of the undesired effects on the manipulated variables. Illustrated in the context of an aircraft pressure-controlled piston pump (PC-PP) where the pressure feedback pulsations and the torque disturbances from the piston/slipper assemblies lead to HF swash-plate (SP) oscillation at steady state, the AHM and its significance were investigated experimentally on a PC-PP test-rig capable of simultaneously measuring the HF feedback pressure and SP-angle. Good agreements between the experimental and numerical results validate the AHM, and reveal that the HF SP-oscillation is dominated by its fundamental harmonic component, and primarily contributed by the disturbance torque.

Shape analysis of H ii regions – II. Synthetic observations

ABSTRACT The statistical shape analysis method developed for probing the link between physical parameters and morphologies of Galactic H ii regions is applied here to a set of synthetic observations (SOs) of a numerically modelled H ii region. The systematic extraction of H ii region shape, presented in the first paper of this series, allows for a quantifiable confirmation of the accuracy of the numerical simulation, with respect to the real observational counterparts of the resulting SOs. A further aim of this investigation is to determine whether such SOs can be used for direct interpretation of the observational data, in a future supervised classification scheme based upon H ii region shape. The numerical H ii region data were the result of photoionization and radiation pressure feedback of a 34 M⊙ star, in a 1000 M⊙ cloud. The SOs analysed herein comprised four evolutionary snapshots (0.1, 0.2, 0.4, and 0.6 Myr), and multiple viewing projection angles. The shape analysis results provided conclusive evidence of the efficacy of the numerical simulations. When comparing the shapes of the synthetic regions to their observational counterparts, the SOs were grouped in amongst the Galactic H ii regions by the hierarchical clustering procedure. There was also an association between the evolutionary distribution of regions and the respective groups. This suggested that the shape analysis method could be further developed for morphological classification of H ii regions by using a synthetic data training set, with differing initial conditions of well-defined parameters.

Active Fault-Tolerant Control for Electro-Hydraulic Systems With an Independent Metering Valve Against Valve Faults

Aiming at the tough requirements for safety and maintainability in mobile hydraulic systems, in this article, an active fault-tolerant control (FTC) system is proposed against the valve faults of an independent metering valve. Not only moderate faults of activated valves, but also significant faults and unactivated valve faults are considered. Without additional hardware redundancy, analytical redundancy is derived by the coordinate control of other fault-free valves. Accordingly, an FTC system in parallel with a normal controller is designed based on the pressure feedback. It consists of a set of reconfigurable controllers and a decision mechanism. The control signals, control loops, and operating modes can all be precisely reconfigured to adaptively match unmodeled fault dynamics. A bumpless transfer controller based on a latent tracking loop is designed to smooth the switching between the normal controller and FTC. Consequently, random valve faults can be tolerated with minor degradations in motion tracking and energy-saving performance. The feasibility of the FTC system is evaluated by a 2-ton excavator.

Four-dimensional surface motions of the Slumgullion landslide and quantification of hydrometeorological forcing

Landslides modify the natural landscape and cause fatalities and property damage worldwide. Quantifying landslide dynamics is challenging due to the stochastic nature of the environment. With its large area of ~1 km2 and perennial motions at ~10–20 mm per day, the Slumgullion landslide in Colorado, USA, represents an ideal natural laboratory to better understand landslide behavior. Here, we use hybrid remote sensing data and methods to recover the four-dimensional surface motions during 2011–2018. We refine the boundaries of an area of ~0.35 km2 below the crest of the prehistoric landslide. We construct a mechanical framework to quantify the rheology, subsurface channel geometry, mass flow rate, and spatiotemporally dependent pore-water pressure feedback through a joint analysis of displacement and hydrometeorological measurements from ground, air and space. Our study demonstrates the importance of remotely characterizing often inaccessible, dangerous slopes to better understand landslides and other quasi-static mass fluxes in natural and industrial environments, which will ultimately help reduce associated hazards.

X-ray observations of luminous dusty quasars at z &amp;gt; 2

ABSTRACT We present new X-ray observations of luminous heavily dust-reddened quasars (HRQs) selected from infrared (IR) sky surveys. HRQs appear to be a dominant population at high redshifts and the highest luminosities, and may be associated with a transitional ‘blowout’ phase of black hole and galaxy co-evolution models. Despite this, their high-energy properties have been poorly known. We use the overall sample of 10 objects with XMM–Newton coverage to study the high-energy properties of HRQs at $\langle$Lbol$\rangle$ =1047.5 erg s−1 and $\langle$z$\rangle$ =2.5. For seven sources with strong X-ray detections, we perform spectral analyses. These find a median X-ray luminosity of $\left\langle L_{\rm 2\!-\!10\, keV} \right\rangle = 10^{45.1}$ erg s−1, comparable to the most powerful X-ray quasars known. The gas column densities are NH = (1–8) × 1022 cm−2, in agreement with the amount of dust extinction observed. The dust-to-gas ratios are sub-Galactic, but are higher than found in local AGN. The intrinsic X-ray luminosities of HRQs are weak compared to the mid-IR ($L_{\rm 6\, \mu m}$) and bolometric luminosities (Lbol), in agreement with findings for other luminous quasar samples. For instance, the X-ray to bolometric corrections range from κbol ≈ 50 to 3000. The moderate absorption levels and accretion rates close to the Eddington limit ($\langle$λEdd$\rangle$ =1.06) are in agreement with a quasar blowout phase. Indeed, we find that the HRQs lie in the forbidden region of the NH–λEdd plane, and therefore that radiation pressure feedback on the dusty interstellar medium may be driving a phase of blowout that has been ongoing for a few 105 yr. The wider properties, including [O iii] narrow-line region kinematics, broadly agree with this interpretation.

Effect of inlet and outlet boundary conditions on rotating detonation combustion

In this work, the effect of different injector geometries and different outlet restrictions on the operating modes of a hydrogen-air Rotating Detonation Combustor (RDC) is investigated. The different operating modes are identified based on pressure measurements in the combustor annulus and the reactant supply, combined with high-speed video from the aft end of the combustor. The pressure frequency spectra are analyzed to determine the global operating mode in terms of number, direction, and speed of waves. The results explore the ability of the RDC to establish rotating, counter-rotating, and longitudinal waves, as well as their superpositions. A good agreement between longitudinal modes and the acoustic resonance frequencies of the RDC annulus was found. Overall, operation was found to be highly injector and outlet restriction dependent. Adding an outlet restriction helped to suppress counter-rotating waves, which is a prerequisite to stabilize single detonation waves. However, it was also shown to prompt high frequency pulsed operation. Apart from the total reactant supply pressure, the relative strength of the injectors was identified as a key factor for stable RDC operation. Pressure feedback into the reactant supply was observed to be dependent on the reactant supply pressure and the RDC operating mode. The study further revealed the presence of transverse resonance modes in the fuel plenum, however these oscillations were weak relative to the injector pressures and do not appear to influence the combustion.

Development of Backdrivable Servovalve With Feedback Spring for Enhanced Electro-Hydraulic Torque Actuator

This letter proposes a novel backdrivable servovalve to implement a torque-controlled electro-hydraulic actuator. The proposed backdrivable servovalve simultaneously contains the characteristics of a flow-control servo valve (=feedback spring) and a pressure-control servovalve (=pressure feedback port). Consequently, the torque control performance of electro-hydraulic torque actuators (EHTAs), which consist of the backdrivable servovalve and rotary vane-type hydraulic actuators, can be enhanced. First, the effective torque bandwidth, which represents the region where the torque output remains constant within a 90 $^{\circ }$ phase lag, is improved. Second, torque-based control algorithms developed for electric motors are realized in a wide frequency region. Finally, although the effect of viscous friction increases, the effect of static friction is reduced. With these advantages, we achieved an enhanced EHTA with calculated torque output of −372 $\sim$ 355 Nm; this could facilitate in the development of a high-performance interactive robot system. The proposed backdrivable servovalve and enhanced EHTA were evaluated through experiments.

Mechanoreception for Soft Robots via Intuitive Body Cues.

Mechanoreception, the ability of robots to detect mechanical stimuli from the internal and external environments, contributes significantly to improving safety and task performance during the operation of robots in unstructured environments. Various approaches have been proposed to endow robot systems with mechanoreception. In the case of soft robots, the state-of-the-art mechanosensory solutions typically embedded dedicated deformable sensors into the soft body, giving rise to fabrication complexity and signal sophistication. In this study, we propose a novel mechanoreception scheme to enable pneumatic-driven soft robots to perceive proprioceptive movements as well as external contacts. Both internal and external mechanical parameters can be decoded from intuitive cues of body deformation and pneumatic pressure signals. In contrast to most existing solutions employing dedicated deformable sensors, the proposed approach only utilizes pressure feedback, which is typically available from the pneumatic pressure sensors incorporated in the control loop of most pneumatic soft robots. The concept was implemented and validated on a proprietary robotic gripper with a linear soft pneumatic actuator, demonstrating the capability in simultaneous detection of actuator position and external contact forceAfter the proposed approach, the gripper can achieve both active and passive mechanosensation, with demonstrated experiments in grasping force estimation, contact loss detection, object stiffness identification, and contour measurements. This approach offers an alternative route to achieving excellent internal/environmental awareness without requiring dedicated sensing modalities.

A Hybrid Haptic Feedback Stimulation Device to Recover the Missing Sensation of the Upper Limb Amputees

Providing sensory feedback for prostheses users increases the manipulation ability, as well as introduces a feeling of the embodiment. A novel hybrid haptic feedback stimulation system of the amputees of upper limb mutilation was designed, developed, and evaluated in this study. The haptic wearable device was built by mean of single servomotor as a pressure feedback display and a pair of vibration motors as a vibration feedback display. Accordingly, the pressure display is responsible for conveying the missing sensing of the contact pressure and its force level. While the vibration display has utilized to provide an indication about the continued contact pressure. Able-body participants are engaged to evaluate the performance of the proposed feedback stimulation system. The results show that the participants are able to distinguish the touch, the start of touch, the end of touch, and the range of force with 100 % accuracy. While 96 % and 88 % of the able-body participants are capable to identify the grasp and the slipping objects, respectively. Furthermore, the ability of the proposed haptic wearable device to convey the tactile sensory information to the user’s brain without confusing or pre-training was improved.

LPV robust servo control of aircraft active side-sticks

PurposeThis paper aims to focus on the variable stick force-displacement (SFD) gradience in the active side stick (ASS) servo system for the civil aircraft.Design/methodology/approachThe problem of variable SFD gradience was introduced first, followed by the analysis of its impact on the ASS servo system. To solve this problem, a linear-parameter-varying (LPV) control approach was suggested to process the variable gradience of the SFD. A H∞ robust control method was proposed to deal with the external disturbance.FindingsTo validate the algorithm performance, a linear time-variant system was calculated to be used to worst cases and the SFD gradience was set to linear and non-linear variation to test the algorithm, and some typical examples of pitch angle and side-slip angle tracking control for a large civil aircraft were also used to verify the algorithm. The results showed that the LPV control method had less settling time and less steady tracking errors than H∞ control, even in the variable SFD case.Practical implicationsThis paper presented an ASS servo system using the LPV control method to solve the problem caused by the variable SFD gradience. The motor torque command was calculated by pressure and position feedback without additional hardware support. It was more useful for the electronic hydraulic servo actuator.Originality/valueThis was the research paper that analyzed the impact of the variable SFD gradience in the ASS servo system and presented an LPV control method to solve it. It was applicable for the SFD gradience changing in the linear and non-linear cases.

Pneumatic Resistance Control of an Upper Limb Active Rehabilitation System

Abstract This paper proposes a pneumatic upper limb rehabilitation robot (PULRR) which is designed for bilateral upper limb active rehabilitation of the patients after stroke. The PULRR provides an active resistance rehabilitation method based on the pneumatic control system. The air kinetics of the pneumatic cylinder model and the dynamics of the pneumatic system with load are established. An antisaturation proportional-integral-differential (PID) controller is presented for the constant resistance force control through directly adjusting the position of the throttle valve spool according to the patient's active moving speed and the feedback of the air pressure in both chambers. In addition, simulation and experimental results indicate that the controller is effective in constant resistance force control. The resistance mode proposed in this paper shows great potential in active resistance rehabilitation for the patients who suffer from the dyskinesia and insufficient muscle strength of the upper limb with enhanced safety and compliance.

PD Plus Dynamic Pressure Feedback Control for a Direct Drive Stewart Manipulator

In order to ensure good dynamic characteristics, servo valve is usually adopted as the drive part of Stewart manipulator which causes huge power consumption, while direct drive electro-hydraulic servo system has the advantages of energy saving, simple structure, convenient installation, and low failure rate. But its dynamic characteristics are so poor that it can only be applied to occasions where quick response is not needed. On the consideration above, following works are done in this paper. Since current coupling exists in the control system based on the speed of the servo motor as the control input, the control system of the direct drive Stewart manipulator is established based on the current of the servo motor as the control input in which the current coupling can be solved. In order to improve the dynamic characteristics of the direct drive Stewart manipulator, a Proportion Differentiation (PD) plus dynamic pressure feedback control strategy is also put forward in this paper, which is verified by using a simulated hydraulically driven Stewart manipulator. Simulation results show that both dynamic coupling and current coupling are solved and the control strategy proposed in this paper can significantly increase the bandwidths of all degrees of freedom.

The experiences of operating room teams working with real-time feedback of interface pressure to prevent pressure injuries—A feasibility study

BackgroundSurgical patients have an increased risk of sustaining a pressure induced injury. Novel technology has made it possible to objectively measure and visualize the interface pressure between the patient's tissue and the support surface in real time. The aim of this study was to describe operating room team members’ experiences of working with a pressure mapping system as a means to prevent intraoperative and postoperative recovery unit pressure injuries, and to describe the interface pressures and the incidence of observed pressure injuries. MethodsWe used a descriptive design with a qualitative approach to investigate the operating room team members’ experiences of working with real-time feedback of interface pressure, and a quantitative approach to investigate the interface pressures and the incidence of observed pressure injuries. The technology was used during 49 surgeries. ResultsThe system increased clinician awareness and was considered beneficial in pressure injury prevention activities. There were wide variations in the interface pressures that measured from < 50 to 255 mmHg. Eight patients developed blanchable erythema during surgery and five other patients developed category 1 pressure injuries two hours postoperatively. ConclusionsThis study shows that the new technology could play an important role in preventing pressure injuries during surgery in the future.

Smartphone-Based SpO 2 Measurement by Exploiting Wavelengths Separation and Chromophore Compensation

Patients with respiratory diseases require frequent and accurate blood oxygen level monitoring. Existing techniques, however, either need a dedicated hardware or fail to predict low saturation levels. To fill in this gap, we propose a phone-based oxygen level estimation system, called PhO 2 , using camera and flashlight functions that are readily available on today’s off-the-shelf smartphones. Since the phone’s camera and flashlight were not made for this purpose, utilizing them for oxygen level estimation poses many difficulties. We introduce a cost-effective add-on together with a set of algorithms for spatial and spectral optical signal modulation to amplify the optical signal of interest while minimizing noise. A near-field-based pressure detection and feedback mechanism are also proposed to mitigate the negative impacts of user’s behavior during the measurement. We also derive a non-linear referencing model with an outlier removal technique that allows PhO 2 to accurately estimate the oxygen level from color intensity ratios produced by the smartphone’s camera. An evaluation on COTS smartphone with six subjects shows that PhO 2 can estimate the oxygen saturation within 3.5% error rate comparing to FDA-approved gold standard pulse oximetry. In addition, our evaluation in hospitals presents high correlation with ground-truth qualified by the 0.83/1.0 Kendall τ coefficient.