Local Force Feedback Research Articles

Active lateral support system for a thin 1-meter meniscus mirror with virtual fixed points

This publication presents an active lateral support system for the thin 1-m meniscus mirror of a Ritchey-Chrétien telescope system. The goal is to keep the mirror at its position under varying external influences, such as gravity and temperature, therefore maintaining the alignment and optical image quality. To achieve this, the lateral support consists of eight actuators, based on stepper motors with gearboxes, with local force measurement and three laser triangulation sensors to measure the mirror’s lateral position. A cascaded control structure with local force feedback in the inner loop and position feedback in the outer loop is proposed. In the outer loop, three single-input single-output PI-controllers are implemented to maintain mirror position in the three lateral degrees of freedom. The developed system is able to position the mirror with root mean square errors of 0.27 and 0.18 μm in translational directions and 5.1 μrad in the rotational direction over the operational altitude range with a slewing speed of 0.2 deg / s.

Density ratio effects on the topology of coherent turbulent structures in two-way coupled particle-laden channel flows

This investigation considers the effect of density ratio on the modification of coherent turbulent structures in particle-laden channel flows at a shear Reynolds number of Reτ = 180. Direct numerical simulation and Lagrangian particle tracking are used to accurately predict the motion of particles dispersed within the flow at three Stokes numbers, St+ = 0.1, 50, and 92. Particle–fluid coupling is achieved through a local element-based force feedback field in the Navier–Stokes equations, which are solved using a seventh-order accurate spectral element method. After an initial transitory period wherein the effects of particle–fluid interaction are emphasized, the low density ratio particles are found to enhance the turbulence field, increasing the frequency of Q-criterion satisfying regions, while the inertial particles suppress the turbulence, reducing the number of quasistreamwise vortices. Results indicate that the topology of the quasistreamwise vortices is altered by the presence of the particles in the viscous sublayer, the buffer layer, and the log-law region such that the distribution of the third invariant of the deviatoric tensor, R, is widened by the presence of tracer-like particles and made thinner by the inertial particles. This effect reduces the amount of unstable focus/compressing regions and stable focus/stretching regions, which account for the streamwise vortical structures observed in these types of flow. Investigating the instantaneous coupling force field surrounding turbulent structures and low speed streaks shows that particles exert their greatest influence on the fluid in the regions noted, and mechanisms by which the particulate phase interacts with turbulent vortices are analyzed.

An Improved Wave-Variable Based Four-Channel Control Design in Bilateral Teleoperation System for Time-Delay Compensation

Good transparency performance (including position tracking and force feedback) is a significant issue for teleoperation control design. The four-channel control approach, which is based on the impedance matching between the master and slave, is an effective method to achieve the perfect transparency performance of teleoperation system. However, the obvious drawback of this design is that the time delay existing in the communication channel is neglected and thus the stability of this design under time delay cannot be guaranteed. Some passivity based control approaches such as wave-variable are developed to handle the stability problem of teleoperation system under time delay, and have been tried to add into four-channel control design. Though the stability under time delay is achieved for this kind of design, the transparency performance may largely decrease since the traditional wave-variable may essentially suffer some performance limitations (e.g., wave reflection). Thus, simultaneously realizing the stability and good transparency performance for four channel teleoperation system is still a challenging issue. In this paper, an improved wave-variable based four-channel control design is developed for bilateral teleoperation system to guarantee stability and further improve transparency performance. Under four channel control architecture, the passivity based time-delay compensator by the modified wave transform and the local force feedback are provided to compensate the distortion by reducing wave reflection and further enhance the stability and transparency of teleoperation system. The experiment is carried out, and the results show the great improvement of the proposed method to achieve the good transparency performance compared to the previous four-channel control designs.

Non-Linear Local Force Feedback Control for Haptic Interfaces

Abstract In this paper, a time-continuous, non-linear local force feedback control is proposed which produces low inertia of the haptic interface during free slave motion as well as higher transparency during slave-environment interactions, by modifying the local force gain as a function of the measured forces of the slave-environment interaction. Stability of the system is proven using damping injection based on a model-based passivation approach and a model-free time domain passivity approach. Teleoperation experiments with time-delay on a KUKA light weight robot-based master device show improvements in performance while using the proposed method.

Simplified Triped Robot for Analysis of Three-Dimensional Gait Generation

[abstFig src='/00290003/08.jpg' width='230' text='The tripedal robot “Martian petit”' ] Significant efforts to simplify the body structure of multi-legged walking robots have been made over the years. Of these, the Spring-Loaded-Inverted-Pendulum (SLIP) model has been very popular, therefore widely employed in the design of walking robots. In this paper, we develop a SLIP-based tripedal walking robot with a focus on the geometric symmetry of the body structure. The proposed robot possesses a compact, light-weight, and compliant leg modules. These modules are controlled by a distributed control law that consists of decoupled oscillators with only local force feedback. As demonstrated through experiments, the simplified design of the robot makes possible the generation of high-speed dynamic locomotion. Despite the structural simplicity of the proposed model, the generation of several gait-patterns is demonstrated. The proposed minimalistic design approach with radial symmetry simplifies the function of each limb in the three-dimensional gait generation of the robot.

Decentralized control mechanism underlying interlimb coordination of millipedes

Legged animals exhibit adaptive and resilient locomotion through interlimb coordination. The long-term goal of this study is to clarify the relationship between the number of legs and the inherent decentralized control mechanism for interlimb coordination. As a preliminary step, the study focuses on millipedes as they represent the species with the greatest number of legs among various animal species. A decentralized control mechanism involving local force feedback was proposed based on the qualitative findings of behavioural experiments in which responses to the removal of part of the terrain and leg amputation were observed. The proposed mechanism was implemented in a developed millipede-like robot to demonstrate that the robot can adapt to the removal of the part of the terrain and leg amputation in a manner similar to that in behavioural experiments.

環境からの力覚情報を活用した自律分散型多脚ロボットの開発

環境からの力覚情報を活用した自律分散型多脚ロボットの開発

足場を活用して推進するクモヒトデのロコモーションに内在する自律分散制御則

Robots are now required to adapt to changes in the environments and physical damages so that they can work under harsh environments. To meet the requirement, we focused on ophiuroid’ s highly adaptive and resilient locomotion. In our previous work, we proposed a decentralized control scheme for the well-balanced coupling between inter- and intra-limb coordination, using local force feedback. However, this scheme could not reproduce an avoidance behavior observed when arms detect reaction forces that impede propulsion. To tackle this problem, in this study, we redesigned a decentralized control scheme based on “ TEGOTAE ”, a Japanese concept describing how well a perceived reaction matches an expectation.

Development of Mechanostimulated Patch-Clamp System for Cellular Physiological Study

Mechanosensitive ion channels play important roles for sensing and responding to the mechanical stimuli signals in living life. Here we report the development of a mechanostimulated patch-clamp system for simultaneous recording of external stimuli and acquisition of cellular physiological responses. This system integrates a custom-designed planar patch-clamp system with a robot-assisted atomic force microscope (AFM) system. The former, with a microfluidic channel, can realize not only recording electrical signals but also exchanging intracellular solution; while the latter, enhanced by robotic techniques (local scan force feedback, augmented reality vision feedback), can generate force stimuli with controllable patterns and magnitudes under the operator's real-time monitoring. To verify the performance of the developed system, we first measured the whole-cell current of the voltage-gated potassium ion channel Kv1.1 expressed on Human Embryonic Kidney (HEK293) cells and then recorded the mechanosensitive ion channel current in a mouse neuroblastoma cell line (Neuro2 A) in the whole-cell configuration during the AFM indenting on the membrane surface; finally, confirmed the ability to exchange intracellular solution by delivering propidium iodide into the captured cell through intracellular solution. The results prove the effectiveness of the system.

Simple robot suggests physical interlimb communication is essential for quadruped walking

Quadrupeds have versatile gait patterns, depending on the locomotion speed, environmental conditions and animal species. These locomotor patterns are generated via the coordination between limbs and are partly controlled by an intraspinal neural network called the central pattern generator (CPG). Although this forms the basis for current control paradigms of interlimb coordination, the mechanism responsible for interlimb coordination remains elusive. By using a minimalistic approach, we have developed a simple-structured quadruped robot, with the help of which we propose an unconventional CPG model that consists of four decoupled oscillators with only local force feedback in each leg. Our robot exhibits good adaptability to changes in weight distribution and walking speed simply by responding to local feedback, and it can mimic the walking patterns of actual quadrupeds. Our proposed CPG-based control method suggests that physical interaction between legs during movements is essential for interlimb coordination in quadruped walking.

On Distributed Multirate Control of Direct User-to-User Touch in Networked Haptic Systems with Passive Wave-Domain Communications

This paper investigates the stability and performance of distributed multirate control of direct touch in networked haptic systems that provide users with a remote dynamic proxy of their peer and with passive wave domain communications. The paper considers communication networks with fixed delay and with packet update rate smaller than the update rate of the users' local force feedback loops. After developing a multirate state space model of the direct touch haptic system, the paper uses eigenvalue-based stability analysis to determine the maximum contact stiffness that can be applied to users, as well as the maximum coordination gain that can be used to synchronize the user sites. The analysis predicts that both remote dynamic proxies and passive wave-domain communications make the contact stiffness robust to delay, but only passive wave-domain communications mitigate the negative impact of delay on the coordination gain. In other words, the analysis suggests that passive wave-domain communications should be employed to make the distributed multirate control of direct touch in networked haptic systems stable regardless of the fixed communication delay. However, if power-domain communications are employed, remote dynamic proxies should be used to allow rendering of stiffer contact between users. Experiments in which two users probe each other using similar haptic interfaces validate the analytical results.

Transparent Rate Mode Bilateral Teleoperation Control

Transparent teleoperation under rate mode has proven to be difficult in terms of stability, performance and implementation. This is mainly due to the need for an exchange of derivative and integral of measured positions and forces which make transparent rate mode controllers prone to noise and abrupt contact force changes. Moreover, the performance of controllers declines in the presence of communication delays. This paper proposes two control architectures based on the use of local force feedback (LFF) and environment impedance reflection (EIR). The LFF controllers eliminate a force channel while preserving transparency under ideal conditions. In the EIR controller, the identified impedance of the environment is employed in the master controller to predict the slave position and contact force derivatives. The stability robustness and performance of these controllers are evaluated and compared to those of a benchmark controller under different operational conditions, such as noise and delay, using analytical methods and experimental results.

Active vibration isolation using an inertial actuator with local force feedback control

The design of inertial actuators with local force feedback control and their use in active vibration isolation systems is considered. Unlike reactive actuators, inertial actuators do not need to react off a base structure and can therefore be directly installed on a vibrating structure. In order to guarantee good stability margins in the active isolation controller, however, the actuator resonance must have a low natural frequency and it must be well damped. The behaviour of an inertial actuator with different local force feedback control schemes is first analysed, and it is shown that a phase-lag controller has a good stability margin and can effectively damp the actuator resonance using relatively low gains, compared with a direct force feedback or integrated force feedback controller. A frequency-domain formulation is then used to analyse the stability and performance of an active isolation system using an inertial actuator with local force feedback control and an outer velocity feedback control loop. The plant response, from force actuator input to sensor output, is derived in terms of the mechanical mobilities of the equipment structure being isolated and the vibrating base structure, and the mechanical impedance of the intervening mount. An experimental study of active vibration isolation using an inertial actuator with local feedback control was then carried out. Theory and experiments agree well, demonstrating the effectiveness of the phase-lag controller. However, the need to have an inertial actuator with a low resonance frequency leads to problems with static deflections.

Transparency in time-delayed systems and the effect of local force feedback for transparent teleoperation

This paper first investigates the issue of transparency in time-delayed teleoperation. It then studies the advantages of employing local force feedback for enhanced stability and performance. In addition, two classes of three-channel control architectures, that are perfectly transparent under ideal conditions are introduced. The stability robustness of the proposed architectures to delays is rigorously analyzed, leading to certain bounds on force feedforward control parameters. Experimental results are included in support of the theoretical work.

An Intelligent Control System for Multiple Degree-of-Freedom Vibration Isolation

Multiple degree-of freedom (DOF) vibration isolation and suppression capabilities are essential for precision control of a wide range of space-borne structures as well as earth-based systems. This paper presents the system design and implementation, control algorithms, parallel computing architecture, and real-time experiments of a six DOF Hexapod Active Vibration Isolation (HAVI) system developed at Intelligent Automation, Inc. The system design of the HAVI is based on the hexapod (Stewart Platform) concept. A novel geometric arrangement of a hexapod, called the "Cubic Configuration" is used. Magnetostrictive material Terfenol-D actuators are employed. A two-layer control system architecture incorporating local force feedback control and a robust adaptive filter control for active vibration isolation are employed. A high performance parallel computation engine MDSP-100 with multiple DSP processors and maximum 566 MFLOPs throughput is also developed for the HAVI applications and was used to implement proposed control algorithms. The unique architecture and functionality of the MDSP-100 facilitate the data acquisition and control law computation operations in a parallel computing fashion. Mechanical hardware for the HAVI system has been fabricated and tested. The six channel simultaneous active vibration control experiments were performed to demonstrate HAVI system's 6 DOF vibration isolation and suppression capabilities. A wide band (below 250 Hz) active vibration attenuation for all six channels was obtained in the real-time experiments.

Active damping by a local force feedback with piezoelectric actuators

This paper summarizes a research in the field of active damping of space structures. The test facility consists of a truss structure provided with two active elements that can be placed in various locations. Each of the active elements consists of a linear piezoelectric actuator collocated with a force transducer. Each active element is controlled in a decentralized manner, with an integral feedback of the force on the voltage applied to the piezoactuator. This control law is always stable and has been found very effective; the damping ratio of the first mode has been increased from 0.003 (open loop) to 0.09 with one actuator.