Virtual Spring Damper Research Articles

Flexible Control Strategy for Upper-Limb Rehabilitation Exoskeleton Based on Virtual Spring Damper Hypothesis

The focus of this work is to design a control strategy with the dynamic characteristics of spring damping to realize the virtual flexibility and softness of a rigid-joint exoskeleton without installing real, physical elastic devices. The basic idea of a “virtual softening control strategy” for a single rigid joint is that a virtual spring damper (VSD) is installed between the motor and the output shaft. By designing the control signal of the motor, the torque output of the joint actuator is softened so that the output has the characteristics of elasticity and variable stiffness. The transfer velocity profile of human limbs reaching from one posture to another always presents as bell-shaped. According to this characteristic, we constructed a trajectory planning method for a point-to-point position-tracking controller based on a normal distribution function, and it was successfully applied to the control of 5-DoF upper-limb rehabilitation exoskeleton. A multi-joint cooperative flexible controller based on the virtual spring damper hypothesis (VSDH) was successfully applied to solve the constrained control problem of the exoskeletons and the self-motion problem caused by redundant degrees of freedom (DoFs). The stability of the closed-loop controlled system is theoretically proven by use of the scalar energy function gradient method and the Riemann metric convergence analysis method.

Proxy-Based Control of Intelligent Assistive Walker for Intentional Sit-to-Stand Transfer

Sit-to-stand (STS) transfer is an easy everyday activity for healthy people, but it is a challenging task for the elderly, and patients with lower-limb weaknesses. This article presents an intelligent assistive walker, which assists the user to accomplish safe STS transfers. An STS intention recognition method is proposed based on an optimized adaptive network-based fuzzy inference system (ANFIS), where the walker is able to accurately detect a voluntary STS and to apply an appropriate control accordingly. The walker is controlled by using a proxy-based controller with respect to the detected human intention, that is measured using thin-film force sensing resistors. During the STS transfer, the assistance force is generated on-line using a virtual spring-damper between the proxy and the linear actuator of the assistive walker. The stability of the proposed controller is theoretically analyzed, and verified by simulations. Experiments with five young healthy subjects and one elderly subject demonstrated that the proposed assistive walker is able to efficiently follow the user’s intention to complete stable and compliant STS transfers.

Brake by wire control with pedal feedback and brake boost

"By wire" technology merged into multiple vehicular subsystems, including gear changing, drive, and braking systems. The brake by wire system is developed to overcome the problems associated with the integration of mechanical and hydraulic systems in novel vehicular systems. Even though brake by wire systems has potential advantages, the conventional brake systems' tactile sensation will be removed if migrated to the electrical by wire control scheme. This paper proposes a novel control mechanism that provides amplification of force, scaling of position replication, and a virtual spring-damper based pedal retraction which provides bilateral brake force feedback to the driver's pedal similar to the hydraulic brake system. The proposed system performance was simulated and tested using a bilateral teleoperation system with disturbance observers (DOB) and reaction force observers (RFOB). The proposed system provides pedal force amplification and brake force feedback to the driver's pedal using RFOBs. The virtual spring retracts the brake pedal, similar to a mechanical pedal retraction system. The system simulation and experimental results provide evidence of the proposed system's force amplification, position scaling, and pedal reaction capabilities.

Observer based dynamic control model for bilaterally controlled MU-lapa robot: Surgical tool force limiting

During laparoscopic surgeries, primary surgical tool insertion is the demanding and strenuous task. As the surgeon is unaware of the type of the tissue and associated parameters to conduct the insertion, therefore, to ease the procedure, the movement of the surgical tool needs to be controlled. It’s the operational capabilities that are to be manipulated to perform a smooth surgery even from a distant location. In this study, a robot system is being introduced for laparoscopic primary surgical tool insertion. It will incorporate a novel observer based dynamic control along with robot assisted bilateral control. Moreover, a virtual spring damper force lock system is introduced through which the slave system will notify the master regarding the target achieved and excessive force. The validation of the proposed control system is experimented with bilaterally controlled MU-LapaRobot. The experiment is comprising 3 cases of bilateral control criteria which are non-contact motion, contact motion, and limit force locking. The results defined the same value for contact and non-contact motion by 0.3N. The results depicted a force error of 3.6% and a position error of 5.8% which validated the proposed algorithm.

Peg-in-a-hole by haptic teleoperation

This paper presents the experimental study on the application of the peg-in-a-hole task in the proposed haptic teleoperation system. Motion references from the user towards the remote manipulator and force feedback signals from the remote environment towards the user are transmitted through a virtual reality layer where the remote operation is simulated in real-tme. Various physical interactions occuring in the bilatral loop are modelled and controlled through the introduction of virtual spring-damper elements. Modeling and controller design of the teleoperation system is made modular and straightforward with the use of identical virtual dynamics. The design approach combines the introduction of the middle layer of virtual reality and modeling of all interactons by identical virtual spring-dampers. The haptic teleoperation system is experimentally evaluated with experienced and unexperienced users in the bilateral loop. Experimental results show that stable peg-in-a-hole operation is achieved in presence of bounded time-delays in all communication channels between the user, virtual reality layer and remote environment. Improvements of the teleoperation performances in terms of position tracking and total operation time are also observed in experiments.

Virtual spring damper method for nonholonomic robotic swarm self-organization and leader following

In this paper, we demonstrate a method for self-organization and leader following of nonholonomic robotic swarm based on spring damper mesh. By self-organization of swarm robots we mean the emergence of order in a swarm as the result of interactions among the single robots. In other words the self-organization of swarm robots mimics some natural behavior of social animals like ants among others. The dynamics of two-wheel robot is derived, and a relation between virtual forces and robot control inputs is defined in order to establish stable swarm formation. Two cases of swarm control are analyzed. In the first case the swarm cohesion is achieved by virtual spring damper mesh connecting nearest neighboring robots without designated leader. In the second case we introduce a swarm leader interacting with nearest and second neighbors allowing the swarm to follow the leader. The paper ends with numeric simulation for performance evaluation of the proposed control method.

Interactive Flow-Induced Vibrations of Two Staggered, Low Mass-Ratio Cylinders in the TrSL3 Flow Regime (2.5 × 104 < Re < 1.2 × 105): Smooth Cylinders

Flow-induced vibrations (FIVs) of two elastically mounted circular cylinders in staggered arrangement were experimentally investigated. The Reynolds number range for all experiments (2.5 × 104 < Re < 1.2 × 105) was in the transition in shear layer 3 (TrSL3) flow regime. The oscillator parameters selected were: mass ratio m* = 1.343 (ratio of oscillating mass to displaced fluid mass), spring stiffness K = 250 N/m, and damping ratio ζ = 0.02. The experiments were conducted in the low turbulence free surface water (LTFSW) channel in the MRELab of the University of Michigan. A closed-loop, virtual spring–damper system (Vck) was used to facilitate quick and accurate parameter setting. Based on the characteristics of the displacement response, five vibration patterns were identified and their corresponding regions in the parametric plane of the in-flow spacing (1.57 < L/D < 4.57) and transverse cylinder spacing (0 < T/D < 2) were defined. The hydrodynamic forces and frequency characteristics of the vibration response are also discussed.

Control Strategy for Modifiable Bipedal Walking on Unknown Uneven Terrain

Previous walking pattern generation methods could generate walking patterns that allow only straight walking on flat and uneven terrain. They were unable to generate modifiable walking patterns whereby the sagittal and lateral step lengths and walking direction can be changed at every footstep. This paper proposes a novel walking pattern generation method to realize modifiable walking of humanoid robots on unknown uneven terrain. The proposed method employs a walking pattern generator based on the 3-D linear inverted pendulum model (LIPM), which enables a humanoid robot to vary its walking patterns at every footstep. A control strategy for walking on unknown uneven terrain is proposed. Virtual spring-damper (VSD) models are used to compensate for the disturbances that occur between the robot and the terrain when the robot walks on uneven terrain with unknown height. In addition, methods for generating the foot and vertical center of mass (COM) of the 3-D LIPM trajectories are developed to realize stable walking on unknown uneven terrain. The proposed method is implemented on a small-sized humanoid robot platform, DARwIn-OP and its effectiveness is demonstrated experimentally.

Method for improving the position precision of a hydraulic robot arm: dual virtual spring–damper controller

Recently, control approaches for a hydraulic robot in the field of robotics have attracted considerable attention owing to their high power-to-weight ratio. Many studies on behavior and control exploiting the advantages of hydraulic robots have been pursued. Application to hydraulically actuated systems, however, is not straightforward due to the nonlinear internal dynamics of the actuators. This paper presents a relatively simple method to improve the position precision of a hydraulic robot arm. We propose a simple control method concept based on a virtual spring---damper (VSD) controller, which enables the robot to realize a desired position. The main advantage of the VSD control is its simple calculation method, which eliminates the need to solve the Jacobian pseudo-inverse or ill-posed inverse kinematics. In this study, experiments were conducted to identify the problems in previous study results and evaluated the applicability of VSD control to the hydraulic robot arm. A relatively simple method was proposed to solve these problems and to verify improvements in the position precision. The proposed method is the dual VSD controller in which an additional VSD model is applied to the elbow, in addition to the conventional VSD model connected to the wrist. The effectiveness of the proposed control scheme is demonstrated in experimentation with the hydraulic robot arm.

A distributed market-based boundary coverage algorithm for multiple microrobots with network connectivity maintenance

In this paper, the boundary coverage of known environments is investigated using multiple microrobots (MMR) involved in a distributed inspection case study. A strong need for an operator is able to control and receive feedback from microrobots. However, communication range is limited because of the size effect of microrobot, and obstacles may also prevent microrobots from communicating. To enable MMR to accomplish coverage task while maintaining the network connectivity with a base station, we propose a market-based boundary coverage algorithm. This algorithm can dynamically allocate the boundary coverage task to a microrobot, so as to adapt to the change of communication network topology. A motion control model based on virtual spring–damper system is established to prevent communication network splitting by monitoring infrared link quantity information among microrobot nodes. Simulations and experimental results, obtained using our MMR tested in a distributed inspection case study, demonstrate that the proposed solution fulfills the objective of maintaining network connectivity at all times while completing the allocated boundary coverage task.

"仮想バネ・ダンパー仮説"に基づいた筋内力と手先粘性の関係に関する考察

"仮想バネ・ダンパー仮説"に基づいた筋内力と手先粘性の関係に関する考察

Reactive multi-agent approach to local platoon control: stability analysis and experimentations

This paper presents a local control approach to linear platoons, systems of vehicles that displace together adopting a train configuration without any material coupling. Linear platoon technology is considered as a potential base for the definition of new urban transportation services. The main problems related to platoon systems is the geometry control: control of inter-vehicle distance and common trajectory matching. The geometry control problem is generally treated according to one of two approaches: global or local. This paper focuses on a local approach which does not require sophisticated sensors and/or costly road equipment. The objective of this local control approach allows satisfactory distance regulation and matching to any common trajectory, by using local perception capabilities of platoon's vehicles. The basic perception capability consists in measuring the vectorial distance between a given vehicle and its predecessor. The behaviour of each platoon vehicle is determined by a physics inspired interaction model based on a virtual spring-damper. Stability and other platoon safety properties are analysed on the base of the physics inspired interaction model. Both simulation and experimentation have been used to measure trajectory error and to evaluate inter-vehicle distance during platoon evolution.

Nonlinear Reference Shaping with Endpoint Position Feedback for Large Acceleration Avoidance in Reaching Movement

The nonlinear reference shaping for manipulators used in ordinary living environments is proposed. It generates an intermediate reference position, and it is combined with control based on the virtual springdamper hypothesis. Initial acceleration is moderated by the reference position inserted between the original target and current endpoint position and by a secondorder lag filter. The endpoint position is fed back to prevent from excessive trailing force and large acceleration, resulting in smooth reaching movement and flexible behavior against external force. The feasibility of the concept of the proposed controller is confirmed through computer simulation on a planar 4-DOF manipulator.

Enforcing Network Connectivity in Robot Team Missions

The growing interest in robot teams for surveillance or rescue missions entails new technological challenges. Robots have to move to complete their tasks while maintaining communication among themselves and with their human operators, in many cases without the aid of a communication infrastructure. Guaranteeing connectivity enables robots to explicitly exchange information needed in collaborative task execution, and allows operators to monitor or manually control any robot at all times. Network paths should be multi-hop, so as not to unnecessarily restrict the team’s range. In this work we contribute a complete system which integrates three research aspects, usually studied separately, to achieve these characteristics: a multi-robot cooperative motion control technique based on a virtual spring—damper model which prevents communication network splits, a task allocation algorithm that takes advantage of network link information in order to ensure autonomous mission completion, and a network layer which works over wireless 802.11 devices, capable of sustaining hard real-time traffic and changing topologies. Link quality among peers is the key metric used to cooperatively move the robots and maintain uninterrupted connectivity, and the basis for novel ideas presented in each subsystem. Simulations and experimental results with real robots are presented and discussed.

Reaching Movements of a Redundant Musculoskeletal Arm: Acquisition of an Adequate Internal Force by Iterative Learning and Its Evaluation through a Dynamic Damping Ellipsoid

This paper presents a proposal of an iterative learning control method for a musculoskeletal arm to acquire adequate internal force in order to realize human-like natural movements. Additionally, a dynamic damping ellipsoid at the end-point is introduced to evaluate internal forces obtained through the iterative learning scheme. Our previous works presented that a human-like smooth reaching movement using a musculoskeletal redundant arm model can be achieved by introducing a nonlinear muscle model and 'the virtual spring–damper hypothesis'. However, to date, the internal forces have been determined heuristically. As described in this paper, to determine internal forces more systematically, an iterative learning control method is used for acquisition of an adequate dynamic damping ellipsoid according to a given task. It is presented that the learning control method can perform effectively to realize given tasks, even though strong nonlinear characteristics of the muscles exist. After acquiring a given task, the dynamic damping ellipsoid is introduced to evaluate the relation between a damping effect generated by the acquired internal forces and a trajectory of the end-point. Some numerical simulations are performed and the usefulness of the learning control strategy, despite strong nonlinearity, is demonstrated through these results.

Adaptive Dynamic Walking of a Quadruped Robot on Natural Ground Based on Biological Concepts

The paper reports on a project to make a quadruped robot walk with medium forward speed on irregular terrain in an outdoor environment using a neural system model. The necessary conditions for stable dynamic walking on irregular terrain in general are proposed, and the neural system is designed by comparing biological concepts with those necessary conditions described in physical terms. A PD-controller is used at joints to construct a virtual spring—damper system as the visco-elasticity model of a muscle. The neural system model consists of a CPG (central pattern generator), responses and reflexes. A response directly and quickly modulates the CPG phase, and a reflex directly generates joint torque. The state of the virtual spring—damper system is switched, based on the CPG phase. In order to make a self-contained quadruped (called Tekken2) walk on natural ground, several new reflexes and responses are developed in addition to those developed in previous studies. A flexor reflex prevents a leg from stumbling on small bumps and pebbles. A sideways stepping reflex stabilizes rolling motion on a sideways inclined slope. A corrective stepping reflex/response prevents the robot from falling down in the case of loss of ground contact. A crossed flexor reflex helps a swinging leg keep enough clearance between the toe and the ground. The effectiveness of the proposed neural system model control and especially the newly developed reflexes and responses are validated by indoor and outdoor experiments using Tekken2. A CPG receives sensory feedback as a result of motions induced by reflexes, and changes the period of its own active phase. Since a CPG has the ability of mutual entrainment with pitching motion of legs and rolling motion of the body in addition, the consistency between motion of a leg temporally modified by a reflex and motions of the other legs is maintained autonomously. It is shown that CPGs can be the center of sensorimotor coordination, and that the neural system model simply defining the relationships between CPGs, sensory input, reflexes and mechanical system works very well even in complicated tasks such as adaptive dynamic walking on unstructured natural ground.

Biologically inspired adaptive walking of a quadruped robot

We describe here the efforts to induce a quadruped robot to walk with medium-walking speed on irregular terrain based on biological concepts. We propose the necessary conditions for stable dynamic walking on irregular terrain in general, and we design the mechanical and the neural systems by comparing biological concepts with those necessary conditions described in physical terms. PD-controller at joints constructs the virtual spring-damper system as the viscoelasticity model of a muscle. The neural system model consists of a central pattern generator (CPG), reflexes and responses. We validate the effectiveness of the proposed neural system model control using the quadruped robots called 'Tekken1&2'. MPEG footage of experiments can be seen at http://www.kimura.is.uec.ac.jp.

A Spring Model for Whole-Hand Virtual Grasping

We present a physically-based approach to grasping and manipulation of virtual objects that produces visually realistic results, addresses the problem of visual inter-penetration of hand and object models, and performs force rendering for force-feedback gloves, in a single framework. Our approach couples a simulation-controlled articulated hand model to tracked hand configuration using a system of linear and torsional virtual spring-dampers. We discuss an implementation of our approach that uses a widely available simulation tool for collision detection and response. We pictorially illustrate the resulting behavior of the virtual hand model and of grasped objects, discuss user behavior and difficulties encountered, and show that the simulation rate is sufficient for control of current force-feedback glove designs. We also present a prototype system for natural whole-hand interactions in a desktop-sized workspace.

A Spring Model for Whole-Hand Virtual Grasping

We present a physically-based approach to grasping and manipulation of virtual objects that produces visually realistic results, addresses the problem of visual inter-penetration of hand and object models, and performs force rendering for force-feedback gloves, in a single framework. Our approach couples a simulation-controlled articulated hand model to tracked hand configuration using a system of linear and torsional virtual spring-dampers. We discuss an implementation of our approach that uses a widely available simulation tool for collision detection and response. We pictorially illustrate the resulting behavior of the virtual hand model and of grasped objects, discuss user behavior and difficulties encountered, and show that the simulation rate is sufficient for control of current force-feedback glove designs. We also present a prototype system for natural whole-hand interactions in a desktop-sized workspace.

Numerical Linearisation Method to Efficiently Optimise the Oscillation Damping of an Interdisciplinary System Model

This paper presents a method to numerically linearise a complex mechanicalsystem. The method is applied to the parameter optimisation of a controlled elastic hydro-mechanical system. The virtual spring damper control concept is used to damp the oscillating system. The system dynamics of the full system are modelled as an interdisciplinary model. From this a mechanical substitution model is derived and linearised at a given operating point. The system matrix of the linearised system is used to efficiently calculate an optimisation criterion that leads to optimal control parameters for rapid oscillation damping. To verify the results a classical, but very time consuming, optimisation is performed. The quality of the optimal parameter sets found is evaluated by comparing simulation results of the complex interdisciplinary model. The system response is almost the same in both cases. The parameters found using the linear model are only slightly different to the parameters found using the non-linear and interdisciplinary model. The performance of the linear model based optimisation is good – it reduces the computational cost by a factor of more than one hundred.