Position Feedback Research Articles

Suppress the vibration of a nonlinear dynamical system subjected to external force using a positive position feedback control.

Suppress the vibration of a nonlinear dynamical system subjected to external force using a positive position feedback control.

Influence of Augmented Visual Feedback on Balance Control in Unilateral Transfemoral Amputees.

Patients with a lower limb amputation rely more on visual feedback to maintain balance than able-bodied individuals. Altering this sensory modality in amputees thus results in a disrupted postural control. However, little is known about how lower limb amputees cope with augmented visual information during balance tasks. In this study, we investigated how unilateral transfemoral amputees incorporate visual feedback of their center of pressure (CoP) position during quiet standing. Ten transfemoral amputees and ten age-matched able-bodied participants were provided with real-time visual feedback of the position of their CoP while standing on a pressure platform. Their task was to keep their CoP within a small circle in the center of a computer screen placed at eye level, which could be achieved by minimizing their postural sway. The visual feedback was then delayed by 250 and 500 ms and was combined with a two- and five-fold amplification of the CoP displacements. Trials with eyes open without augmented visual feedback as well as with eyes closed were further performed. The overall performance was measured by computing the sway area. We further quantified the dynamics of the CoP adjustments using the entropic half-life (EnHL) to study possible physiological mechanisms behind postural control. Amputees showed an increased sway area compared to the control group. The EnHL values of the amputated leg were significantly higher than those of the intact leg and the dominant and non-dominant leg of controls. This indicates lower dynamics in the CoP adjustments of the amputated leg, which was compensated by increasing the dynamics of the CoP adjustments of the intact leg. Receiving real-time visual feedback of the CoP position did not significantly reduce the sway area neither in amputees nor in controls when comparing with the eyes open condition without visual feedback of the CoP position. Further, with increasing delay and amplification, both groups were able to compensate for small visual perturbations, yet their dynamics were significantly lower when additional information was not received in a physiologically relevant time frame. These findings may be used for future design of neurorehabilitation programs to restore sensory feedback in lower limb amputees.

Neural Decoding for Target Detection Using Multi-View Methods

Tendon–sheath mechanism (TSM) has inherent advantages in the development of flexible robotic systems because of its simplicity, safety, flexibility, and ease of transmission. However, the control of TSM is challenging due to the presence of nonlinearities, namely friction, backlash-like hysteresis and the time-varying configuration of the TSM during its operations. Existing studies of TSM found in the literature only address tendon transmission under the assumption of fixed configuration and a complex inverse model of backlash is required. In order to flexibly use the system in a wider range of applications, the aforementioned nonlinear effects have to be characterized for the purpose of compensation. In this paper, we endeavor to address these issues by presenting a series of controller strategies, namely a feedforward control scheme under the assumption of known backlash-like hysteresis profile, and an adaptive control scheme to characterize the nonlinearities with unknown backlash hysteresis and uncertainties. The proposed control schemes do not require information of the tendon–sheath configurations, which is challenging to obtain in practice, in the compensation structures. In the absence of output position feedback, a simple direct inverse model-based feedforward has been used that efficiently reduce the tracking errors. The feedforward compensation does not require any complex algorithm for the inverse model. In the presence of output position feedback, a nonlinear adaptive controller has been developed to enhance the tracking performances of the TSM regardless of the random change in the tendon–sheath configurations during compensation. In addition, exact values of the model parameters are not required. They are estimated online during the operations. A dedicated experimental setup is introduced to validate the proposed control approaches. The results show that the proposed control schemes significantly improve the tracking performances for the TSM in the presence of uncertainties and time-varying configurations during the operations. There is a significant decrease of 0.0158 rad2 (before compensation) to smaller value of 0.0012 rad2 (use feedforward control) and 8.2815 × 10−5 rad2 (use nonlinear controller) after compensation.

Numerical and Experimental Investigation of a Semi-Active Vibration Control System by Means of Vibration Energy Conversion

A vibration control concept based on vibration energy conversion and storage with respect to a serial-stiffness-switch system (4S) has previously been proposed. Here, we first present a rotational electromagnetic serial-stiffness-switch system as a novel practical vibration control system for experimental validation of the concept and, furthermore, an improved control strategy for higher vibration suppression performance is also proposed. The system consists of two spring-switch elements in series, where a parallel switch can block a spring. As an alternating mechanical switch, the experimental system uses two electromagnets with a shared armature. By connecting the armature to the rotating load or the base, the electromagnets decide which of the two spiral springs is blocked, while the other is active. A switching law based on the rotation velocity of the payload is used. Modelling and building of the experimental system were carried out. The corresponding experiment and simulation were executed and they matched well. These results prove that our serial-stiffness-switch system is capable of converting vibration energy and realizing vibration reduction under a forced harmonic disturbance. The effects of disturbance frequency, disturbance amplitude and sampling frequency on the system performance are shown as well. A position feedback control-based switching law is further put forward and experimentally verified to improve the repositioning accuracy of the disturbed system.

Modified PID like fuzzy servo control applied to smart actuator based miniature Parallel Robot

Miniature flexible parallel robots, popularly used for micro positioning application demands the use of non conventional actuators. Shape memory alloys (SMA) are popular smart actuators because of its light weight, integration compatibility, ease of actuation and high power density. Inclusion of shape memory alloy actuators to the parallel robot brings in control challenges due to its nonlinearity, coupling effects and cocontraction of antagonistic pair of actuators in the mechanism in order to achieve bi directional motion. In this paper, a PID like fuzzy controller is designed and applied to a nonlinear SMA spring actuator connected to a symmetric 2 DOF miniature parallel robot. The fuzzy rules are designed from the general response plot and modified to be applied to a parallel mechanism which involves cocontraction of antagonistic actuators. The paper has also presented the control and electrical circuit design used in the experimental set up. The fuzzy control is implemented in the hardware controller with model based position feedback and tested for the trajectory tracking characteristics of the end effector with disturbances. Experimental results are presented with quantitative analysis to show the effectiveness of the proposed controller in handling nonlinearities and disturbances compared to the conventional PID control and nonlinear Sliding mode control (NSMC). The test results has demonstrated the superior nature of proposed control over other controllers in the trajectory tracking with disturbances and also linearizing the hysteresis of controlled system.

Symplectic discrete-time energy-based control for nonlinear mechanical systems

We present a novel approach for discrete-time state feedback control implementation which reduces the deteriorating effects of sampling on stability and performance in digitally controlled nonlinear mechanical systems. We translate the argument of energy shaping to discrete time by using the symplectic implicit midpoint rule. The method is motivated by recent results for linear systems, where feedback imposes closed-loop behavior that exactly represents the symplectic discretization of a desired target system. For the nonlinear case, the sampled system and the target dynamics are approximated with second order accuracy using the implicit midpoint rule. The implicit nature of the resulting state feedback requires the numerical solution of an in general nonlinear system of algebraic equations in every sampling interval. For an implementation with pure position feedback, the velocities/momenta have to be approximated in the sampling instants, which gives a clear interpretation of our approach in terms of the Störmer–Verlet integration scheme on a staggered grid. Both the Hamiltonian and the Lagrangian perspective are adopted. We present discrete-time versions of impedance or energy shaping plus damping injection control as well as computed torque tracking control in the simulation examples to illustrate the performance and stability gain compared to the quasi-continuous implementation. We discuss computational aspects and show the structural advantages of the implicit midpoint rule compared to other integration schemes in the appendix.

Robust Control and Optimization for Autonomous and Connected Vehicle Platoons with Vehicle-to-Vehicle Communication Delay

Recent advances in vehicle-to-vehicle (V2V) communication technologies enable autonomous vehicle platoons to better utilize the information of other members in the platoon to achieve the desired longitudinal intervehicular spacing specifications. However, most existing studies adopt a fixed time headway hw, and do not take into account the effects of V2V communication delay on the desired design specifications for the platoons. Moreover, for stability analysis, the commonly adopted Routh-Hurwitz approach usually needs a lot of computation time, which will significantly reduce the efficiency and flexibility of the platoons in real-time applications. In order to overcome the aforementioned issues with the existing results on autonomous vehicle platoons, this paper investigates the robust control and optimization problem for a platoon of autonomous and connected vehicles subject to V2V communication delay and uncertain parasitic actuation lag under a constant time headway policy (CTHP). First, by employing the Padé approximation approach, the spacing error propagation transfer function, from the preceding vehicle to the following vehicle, under immediate predecessor’s acceleration, velocity, and position feedback control mechanism is derived. In addition, in order to improve the computation efficiency, a signature method is utilized for the Hurwitz stability analysis. Then the string stability analysis for attenuating the spacing propagation error along the platoon is performed. Both lower and upper bounds for the time headway hw as well as the admissible sets for controller gains are achieved for Hurwitz stability and string stability. Comparative simulation results are finally provided to demonstrate the effectiveness of the proposed design scheme.

Differential Games for Fractional-Order Systems: Hamilton–Jacobi–Bellman–Isaacs Equation and Optimal Feedback Strategies

The paper deals with a two-person zero-sum differential game for a dynamical system described by differential equations with the Caputo fractional derivatives of an order α∈(0,1) and a Bolza-type cost functional. A relationship between the differential game and the Cauchy problem for the corresponding Hamilton–Jacobi–Bellman–Isaacs equation with fractional coinvariant derivatives of the order α and the natural boundary condition is established. An emphasis is given to construction of optimal positional (feedback) strategies of the players. First, a smooth case is studied when the considered Cauchy problem is assumed to have a sufficiently smooth solution. After that, to cope with a general non-smooth case, a generalized minimax solution of this problem is involved.

Comparison of control strategies for HCPV sun tracking

This paper presents a comparison between five control strategies for HCPV sun tracking that comprise open-loop by means of Solar Equations, closed-loop by Sun position feedback (using an electro-optical sensor and a DC power sensor), and pointing ahead of the Sun. The performance of the control strategies is tested under a fully calibrated sun-tracker conditions and not-calibrated conditions to expose the problematic of the high accuracy sun pointing. When the sun-tracker is calibrated, all control strategies perform in a very similar way in terms of efficiency of use of available light energy, with the exception that one of the control strategies does not need prior calibration. The measured loss in efficiency when the sun-tracker is not calibrated precisely is approximately equal to 6%.

Compact Pneumatic Clutch With Integrated Stiffness Variation and Position Feedback

Stiffness variation and real-time position feedback are critical for any robotic system but most importantly for active and wearable devices to interact with the user and environment. Currently, for compact sizes, there is a lack of solutions bringing high-fidelity feedback and maintaining design and functional integrity. In this work, we propose a novel minimal clutch with integrated stiffness variation and real-time position feedback whose performance surpasses conventional jamming solutions. We introduce integrated design, modeling, and verification of the clutch in detail. Preliminary experimental results show the change in impedance force of the clutch is close to 24-fold at the maximum force density of 15.64 N/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . We validated the clutch experimentally in (1) enhancing the bending stiffness of a soft actuator to increase a soft manipulator's gripping force by 73%; (2) enabling a soft cylindrical actuator to execute omnidirectional movement; (3) providing real-time position feedback for hand posture detection and impedance force for kinesthetic haptic feedback. This manuscript presents the functional components with a focus on the integrated design methodology, which will have an impact on the development of soft robots and wearable devices.

New controller (NPDCVF) outcome of FG cylindrical shell structure

This paper presents a new active controller technique effect of functionally graded (FG) cylindrical shell structure model within joint harmonic and parametric excitations. The new active controller involves Nonlinear Proportional-Derivative (NPD) plus Negative Cubic Velocity Feedback (NCVF) as a new nonlinear control method (NPDCVF). The motivation of this study is the well-known observation that NPDCVF control method can offer a means to improve the performance of plant systems. The coupled nonlinear differential equations with two modes have been derived applying the von Kármán nonlinear theory, Galerkin’s process, and the static condensation technique. Static condensation is the process of decreasing the number of free displacements or degrees of freedom. We have added other three different controller methods over the structure to select the best controller. The three applied controller methods to the considered structure are: Integral Resonant Control (IRC), Positive Position Feedback (PPF), and Nonlinear Integral Positive Position Feedback (NIPPF) which are applied to the considered structure. We establish that the best one for dipping the high vibration amplitudes is the NPDCVF as a new controller. The perturbation technique is useful to solve the present model including quadratic and cubic nonlinearities subjected to mixed harmonic and parametric forces within the simultaneous primary resonance case (Ω=ω1,Ω=ω2) as the worst resonance case of the system. All numerical outcomes have been completed with the help of MATLAB Ra 18.0 program software over the investigated model. The obtained results have proved that this new controller is excellent for improving the structure by reducing the risky vibrations caused during primary resonances. Frequency response equations have helped in observing the stability examination of the obtained numerical solutions. The actions of several factors performed on the controlled model have been examined and described. Some comparisons have also been prepared with the available recent published papers of a similar model.

Time-delayed positive position feedback control of nonlinear vibrations of continuous rotating shafts

The objective of the present study is to suppress the large amplitudes of a continuous spinning shaft under an active vibration control. For this purpose, the Positive Position Feedback (PPF) control with time-delays are applied to the system via Macro-Fiber-Composite (MFC) sensors and actuators. The nonlinear dynamics of the system is explored analytically utilizing the perturbation method in the primary and one-to-one internal resonances. The steady state solutions of the system and controller in the Cartesian and polar forms are obtained. The effects of the controller gains and time delays on the stability and loci of bifurcations of the system are investigated. The controller shows its feasibility in controlling the system vibrations. Also, it is demonstrated that by increasing the controller gain coefficients the minimum amplitude regions of the system are increased. Furthermore, the safe boundary of the loop delays is studied. The results of the analytical approach are in good agreement with the numerical results of the original system of equations.

Hybrid rayleigh–van der pol–duffing oscillator: Stability analysis and controller

The current study examines the hybrid Rayleigh–Van der Pol–Duffing oscillator (HRVD) with a cubic–quintic nonlinear term and an external excited force. The Poincaré–Lindstedt technique is adapted to attain an approximate bounded solution. A comparison between the approximate solution with the fourth-order Runge–Kutta method (RK4) shows a good matching. In case of the autonomous system, the linearized stability approach is employed to realize the stability performance near fixed points. The phase portraits are plotted to visualize the behavior of HRVD around their fixed points. The multiple scales method, along with a nonlinear integrated positive position feedback (NIPPF) controller, is employed to minimize the vibrations of the excited force. Optimal conditions of the operation system and frequency response curves (FRCs) are discussed at different values of the controller and the system parameters. The system is scrutinized numerically and graphically before and after providing the controller at the primary resonance case. The MATLAB program is employed to simulate the effectiveness of different parameters and the controller on the system. The calculations showed that NIPPF is the best controller. The validations of time history and FRC of the analysis as well as the numerical results are satisfied by making a comparison among them.

Design of Low-cost Automated Ventilator Using AMBU-bag

본 연구는 COVID-19의 ëŒ€ìœ í–‰ìœ¼ë¡œ 인해 자동 인공 호흡기의 공급이 ì„¸ê³„ì ì¸ 긴급 수요에 비해 원활하지 않은 상황에 도움이 ë ìˆ˜ìžˆëŠ” ì €ê°€í˜• 응급 인공 호흡기의 설계 및 구현을 ì œì•ˆí•œë‹¤. AMBU-bagê³¼ 기성용 ìž„ë² ë””ë“œ 마이크로 컨트롤러 보드를 사용하여 구현이 ìš©ì´í•˜ê³ ë¹„ìš©ì„ 최소화했다. 또한, 3D í”„ë¦°íŒ ì€ ì „ 세계 ê¸°ì— ê³¼ ì „ë¬¸ê°€ë“¤ì´ í”„ë¡œí† íƒ€ìž í•˜ë“œì›¨ì–´ë¥¼ 구축하는 데 사용하는 반면, 주변 환경에서 쉽게 êµ¬í• ìˆ˜ 있는 재료는 많은 첨단 ê¸°ìˆ ì— ì ‘ê·¼í•˜ê¸° ì–´ë ¤ìš´ 국가의 사람들이 ì‹œìŠ¤í œì„ ì œì¡°í• ìˆ˜ 있도록 한다. 설계한 간이 인공호흡기 모형의 특징은 암부 백을 자동화 했다는 ì , 3d í”„ë¦°íŒ ì„ 사용하지 않는다는 ì , ì†ë„ì¡°ì ˆì´ 가능하다는 ì ì´ë‹¤. 속도 ì¡°ì ˆì´ 가능하게 함으로써 사용하는 환자의 상황에 맞게 환기가 가능하다. 연구 시 ë³´ì™„í• ì ìœ¼ë¡œëŠ” 첫 번째, 사용한 와이퍼 모터의 구동 ì‹œìž‘ì ì„ ê³ ì •í•˜ê¸° ì–´ë µë‹¤ëŠ” 것이다. 이를 보완하기 위한 방법으로 위치 피드백기능이 있는 브러시 DC모터로 교체하는 방법이 있다. 두 번째로 팔부분과 ê³ ì • 틀이 나무 재질이라 암부 백을 ìž¥ê¸°ì ìœ¼ë¡œ 압축하는 ê³¼ì •ì—ì„œ 암부백이 ë§ˆëª¨ë ê°€ëŠ¥ì„± 있다는 것이다. 이를 보완하기 위해 암부백이 닿는 틀과 팔 부분을 실리콘과 같은 재료로 감싸 마찰을 최소화해야 í• í•„ìš”ê°€ 있다. This study proposes the design and implementation of a low-cost emergency ventilator which can be helpful during the COVID-19 pandemic where the supply of automatic ventilators is not smooth compared with the urgent demand worldwide. Easy implementation and lower price were made possible by using AMBU-bag and off-the-shelf embedded microcontroller board. Moreover, while 3D printing is used by companies and experts around the world to build prototype hardware, materials which are readily available from surrounding environments so that people in countries where it is difficult to access many advanced technologies could manufacture the system. The design features AMBU-bag automation, not use 3D printing, and it can contrl speed. By allowing speed control, ventilation can be performed according to the conditions of the patient being used. A complementary point in the study is that it is difficult to fix the start point of the wiper motor used first. A method for complementing this is a method for replacing the brush DC motor with a position feedback function. Secondly, the AMBU-bag may wear out in the long-term process of compressing the AMBU-bag because the arm and the fixing frame are made of wood. To complement this, the part of fixing frame and arm parts that the AMBU-bag touches need to be wrapped in a material such as silicon to minimize friction. Keywords: BVM, COVID-19, Emergency, Respiration

Vibration reduction of a non-linear ship model using positive position feedback controllers

Vibration reduction of a non-linear ship model using positive position feedback controllers

Minimizing OCT quantification error via a surface-tracking imaging probe.

OCT-based quantitative tissue optical properties imaging is a promising technique for intraoperative brain cancer assessment. The attenuation coefficient analysis relies on the depth-dependent OCT intensity profile, thus sensitive to tissue surface positions relative to the imaging beam focus. However, it is almost impossible to maintain a steady tissue surface during intraoperative imaging due to the patient's arterial pulsation and breathing, the operator's motion, and the complex tissue surface geometry of the surgical cavity. In this work, we developed an intraoperative OCT imaging probe with a surface-tracking function to minimize the quantification errors in optical attenuation due to the tissue surface position variations. A compact OCT imaging probe was designed and engineered to have a long working distance of ∼ 41 mm and a large field of view of 4 × 4 mm2 while keeping the probe diameter small (9 mm) to maximize clinical versatility. A piezo-based linear motor was integrated with the imaging probe and controlled based upon real-time feedback of tissue surface position inferred from OCT images. A GPU-assisted parallel processing algorithm was implemented, enabling detection and tracking of tissue surface in real-time and successfully suppressing more than 90% of the typical physiologically induced motion range. The surface-tracking intraoperative OCT imaging probe could maintain a steady beam focus inside the target tissue regardless of the surface geometry or physiological motions and enabled to obtain tissue optical attenuation reliably for assessing brain cancer margins in challenging intraoperative settings.

Feedback attitude control of spacecraft using two single gimbal control moment gyros

In this paper, feedback attitude control of an underactuated spacecraft with two single gimbal control moment gyros (SGCMGs) is considered. For a two-SGCMG system in an arbitrary configuration, a feedback control method based on a real-time optimization approach is proposed. Here, the gimbal angle trajectories as the solution to the minimum-time control are parameterized by the time polynomials, and their coefficients are modified at each sampling period. Numerical simulations are performed to demonstrate the validity of the proposed method as well as a certain robustness against unmodeled dynamics. Furthermore, the experimental verification is also conducted to demonstrate the actual effectiveness.

Waypoint following dynamics of a quaternion error feedback attitude control system

Closed-loop attitude steering is a concept for implementing an attitude trajectory by using a conventional quaternion error feedback controller to track the time-varying attitude reference, rather than to simply regulate to a desired orientation. This is done by sampling the reference input and executing the maneuver as a sequence of closely spaced regulating commands that are read out from the spacecraft’s command buffer. The idea has been employed in practice to perform zero-propellant maneuvers on the International Space Station and minimum-time maneuvers on NASA’s TRACE space telescope as well as NASA’s Lunar Reconnaissance Orbiter (LRO). A challenge for operational implementation of the idea is the limited capacity of a space vehicle’s command storage buffer, which is normally not designed with attitude tracking in mind. One approach to mitigate the problem is to downsample-and-hold the attitude commands so that the attitude control system (ACS) regulates to a series of waypoints. This article explores the waypoint following dynamics of a quaternion error feedback control law for such an approach. It is shown that downsample-and-hold induces a ripple between downsamples that causes the satellite angular rate to significantly overshoot the desired limit. Analysis in the z-domain is carried out in order to understand the phenomenon. An interpolating Chebyshev-type filter is proposed that allows the desired attitude trajectory to alternatively be encoded in terms of a small set of filter coefficients. Using the interpolating filter, the continuous-time reference trajectory can be reconstructed and issued at the ACS rate but with significantly reduced memory requirements. The ACS of the LRO is used as an example to illustrate the behavior of a practical ACS.

Trajectory tracking of a bouncing ball in a triangular billiard by unfolding and folding the billiard table

In this paper, a feedback control law is proposed to solve the asymptotic tracking problem for a ball bouncing in a triangular billiard. This controller is designed by firstly transforming the billiard table into a surface on which the ball moves without experiencing any impact, i.e. by reflecting the billiard table rather than the ball trajectory and designing a position feedback controller based on such an unfolded billiard table. Furthermore, it is shown how such an infinite-billiard table can be mapped to the surface of a torus, thus leading to bounded trajectories of the ball.

GazeWheels: Recommendations for using wheel widgets for feedback during dwell-time gaze input

Abstract We present GazeWheels: a series of visual feedback methods for dwell-based gaze input in the form of a wheel that is filled gradually until target selection. We evaluate three variations: Resetting, Pause &amp; Resume and Infinite GazeWheel, and study how dwell duration and visual feedback position (co-located vs remote) impact performance. Findings from a user study (N = 19) show that Infinite and Pause &amp; Resume GazeWheels are error prone but significantly faster than Resetting GazeWheel even when including error correction time. We conclude with five design recommendations.