Link Angles Research Articles

Reducible compositions of spherical four-bar linkages with a spherical coupler component

We use the output angle of a spherical four-bar linkage C as the input angle of a second four-bar linkage D where the two frame links are assumed in aligned position as well as the follower of C and the input link of D. We determine all cases where the relation between the input angle of the input link of C and the output angle of the follower of D is reducible and where additionally at least one of these components produces a transmission which equals that of a single spherical coupler. The problem under consideration is of importance for the classification of flexible 3 × 3 complexes and for the determination of all flexible octahedra in the projective extension of the Euclidean 3-space.

Guidance and Control of a Planar Robot Manipulator Used in a Mounting Line

AbstractIn this study, the guidance and control of a two-link planar robot manipulator which is utilized to put the considered parts or components into the relevant slots on a moving belt of a mounting line is dealt with. In this extent, first the kinematic analysis of the robot manipulator is completed and its dynamic model is derived. Then, an indirect control scheme is built regarding the link angles of the manipulator as the control variables based on the mentioned dynamic model. Afterwards, the part carried by the end effector of the robot manipulator from the considered container is tried to be inserted to the relevant slot on the moving belt in accordance with the commands generated by the linear homing guidance law and the performance of the designed guidance and control algorithm is investigated through the computer simulations using the constructed models under different initial conditions.

Modeling of large-deflection links for compliant mechanisms

The traditional pseudo-rigid-body model (PRBM) has one degree of freedom (DOF) and performs a good simulation to the tip locus of flexible links for compliant mechanisms on the basis of a parametric approximation method. In this study, a new approach of a two-DOF PRBM is proposed to simulate both the tip locus and tip deflection angle of large-deflection links for compliant mechanisms on the basis of the angular deflection approximation technique. A linear regression for the spring stiffness coefficient of the 2R PRBM using the optimization technique is presented. The advantage of the new model is well illustrated through a numerical comparison between the 1R and the 2R PRBM.

On the Control of Two-link Flexible Robot Arm with Nonuniform Cross Section

We consider the motion of a two-link flexible arm with nonuniform cross section. We obtain the equations of motion by using the extended Hamilton’s principle. These equations consist of coupled partial differential equations and (nonlinear) ordinary differential equations with appropriate boundary conditions. Our control problem is to achieve the given desired link angles and suppress the link vibrations. To solve this problem, we propose a novel control scheme which consists of a dominant control law together with a parallel controller. We show that with the proposed controller, the control objectives are satisfied. Our stability analysis is based on the Lyapunov approach and LaSalle’s invariance principle extended to infinite-dimensional systems. We also present some simulation results, which indicate that large parameter uncertainties such as tip and hub mass changes are also handled effectively by the proposed controller.

Performance of a Vertical Axis Wind Turbine with Variable-Pitch Straight Blades utilizing a Linkage Mechanism

This paper describes the performance of a micro vertical-axis wind turbine with variable-pitch straight blades. The proposed variable-pitch angle mechanism has an eccentric point that is different from the main rotational point. One feature of the mechanism is its ability to vary the pitch angle of the blades according to the azimuth angle of the main links, without actuators. The performance of the wind turbine was measured in an open-circuit wind tunnel. The performance of the vertical-axis wind turbine with variable-pitch straight blades was better than one with fixed-pitch blades. A wind turbine with variable-pitch straight blades has wind directivity. It was found that the performance of a wind turbine is dependent upon the blade offset pitch angle, the blade pitch angle amplitude, the size of the turbine, the number of blades, and the airfoil profile.

マニピュレータの受動制御を利用した車輪型ロボットによる車椅子の段差移動

This paper proposes a method of wheelchair's step climbing using a wheeled robot which has two manipulators. The robot, TATEYAMA, has been developed to assist wheelchair users. In step climbing, the wheelchair and the robot are connected by the manipulators, and the shoulder and elbow joints of the manipulators are passively controlled. As it is important to control the link angle for the safe step climbing, we perform a numerical calculation to clarify its requirements. The system uses the robot's body to pin the passive rotary motions of the shoulder links during the pushing motion of the wheelchair. We ascertain the effectiveness of this method by the experiments.

Input-Shaped Link Motion for Attitude Control of Underactuated Planar Space Robot Equipped with Flexible Appendages

AbstractControl of a space robot without actuators on the main body is an underactuated control problem. As stabilization methods, various methods such as time-varying feedback controllers, discontinuous feedback controllers, center manifold-based methods, zero-dynamics methods, and sliding mode controllers have been proposed. However, the past studies have not considered an underactuated space robot equipped with flexible appendage, such as solar panels. If the manipulators were simply controlled to achieve the main body attitude using the past controllers with out taking the flexible appendage into consideration, residual vibration would be remained even after the link motion has finished. In order to suppress the residual vibration on the flexible appendage, we apply the input-shaping technique to the link motion of the underactuated plane space robot. Numerical simulations are carried out to validate the proposed method for a planar two-link space robot with flexible appendage. The results show that the proposed method was capable of not only changing the link angles and the main body attitude, but also suppressing the residual vibration on the flexible appendage.

Trajectory planning for residual vibration suppression of a two-link rigid-flexible manipulator considering large deformation

In this paper an optimal trajectory planning technique for suppressing residual vibrations in two-link rigid-flexible manipulators is proposed. In order to obtain an accurate mathematical model, the flexible link is modeled by taking the axial displacement and nonlinear curvature arising from large bending deformation into consideration. The equations of motion of the manipulator are derived using the Lagrangian approach and the assumed modes method. For the trajectory planning, the joint angle of the flexible link is expressed as a cubic spline function, and then the particle swarm optimization algorithm is used to determine the optimal trajectory. The optimal trajectory thus obtained satisfies the minimum vibration condition. By performing numerical simulations, the effectiveness of the proposed trajectory planning technique is verified.

平面2リンク宇宙ロボットに対する適応不変マニフォールドベースト切替制御

Controlling of a space robot without actuators on the main body is an underactuated control problem. As stabilization methods, time-varying feedback controllers, discontinuous feedback controllers, center manifold based methods, zero-dynamics methods, and sliding mode controllers have been proposed. However, these methods sometime suffer from slow rate of convergence. In addition, modeling errors and delay time have not been sufficiently considered in the past studies. In order to obtain faster convergence time and compensate modeling errors and delay time, the adaptive invariant manifold based switching control method is proposed. Firstly the link angles are controlled to reach the invariant manifold by constant periodic motion and the modeling error is estimated by a discrete adaptive method. In the first stage, the delay time is also detected by measuring the difference between the predicted response and the actual one. Secondly the angular velocity rate of the two links is controlled to constant so that the state slides on the invariant manifold and reaches the goal state. In order to evaluate performance of the proposed control method, numerical simulations are conducted for not only the case with modeling error, but also with delay time.

Swing-up controller for the Acrobot using skill of human movements

In this paper, a control method to swing up the Acrobot, which is a model of horizontal bar gymnast, is proposed. In order to materialise the movement of the Acrobot as same as movement of human, the swing-up controller of the Acrobot with considering limitation of joint which is model of human hip is proposed. And from an analysis of the gymnastic technique called tap swing forward (TSF), the proposed swing-up controller can make the two links of the Acrobot do a human-like movement. That is, the desired value of angle of the second link is decided based on the movement of TSF technique, where the controller is based on the partial linearisation method. Numerical simulation and experimental result to swing up of the Acrobot are given to show the effectiveness of the proposed method.

2A2-A22 高速ビジョンを用いた多指ハンドによる紙のハンドリング

The purpose of the study is to achieve various types of paper handling such as turning over, bending, and folding, and the final goal is to achieve Origami task by multifingered hand. As a first step, in this paper, a position control of a paper by visual servoing is achieved. A paper is moved by using two fingertips. Each fingertip is controlled independently, and the paper can be controlled to a desired position and orientation by controlling the rotation speed of each fingertip and the angle of each finger link at the contact point. Experimental Results are shown

Fibre Bragg grating (FBG) sensor system for highly flexible single-link robots

This paper presents a sensor system based on optical fibre sensors (FBG) with which to measure the deflexion of a highly flexible lightweight beam. Epoxy glue is used to attach these optical sensors to specific locations on the surface of the beam in order to measure local strain measurements. These strain measurements, provided by FBG sensors, are used in a method proposed in this paper to estimate the deflection of the beam (the tip position and the tip rotation angle) in both static and dynamic cases. The correct number and the optimum distribution of the sensors on the beam are chosen by using the Chebyshev criterion which minimizes the error in estimating the position and the rotation angle of the tip link. Static and dynamic experiments are presented to verify the effectiveness of the estimation method and the sensor system proposed.

Kinematic Analysis and Optimization of a Novel Robot for Surgical Tool Manipulation

The size and limited dexterity of current surgical robotic systems are factors that limit their usefulness. To improve the level of assimilation of surgical robots in minimally invasive surgery (MIS), a compact, lightweight surgical robotic positioning mechanism with four degrees of freedom (DOFs) (three rotational DOFs and one translation DOF) is proposed in this paper. This spatial mechanism based on a bevel-gear wrist is remotely driven with three rotation axes intersecting at a remote rotation center (the MIS entry port). Forward and inverse kinematics are derived, and these are used for optimizing the mechanism structure given workspace requirements. By evaluating different spherical geared configurations with various link angles and pitch angles, an optimal design is achieved, which performs surgical tool positioning throughout the desired kinematic workspace while occupying a small space bounded by a hemisphere of radius 13.7cm. This optimized workspace conservatively accounts for collision avoidance between the patient and robot or internally between the robot links. This resultant mechanism is highly compact and yet has the dexterity to cover the extended workspace typically required in telesurgery. It can also be used for tool tracking and skills assessment. Due to the linear nature of the gearing relationships, it may also be well suited for implementing force feedback for telesurgery.

Disturbance Observer-Based Robust Control of Free-Floating Space Manipulators

A disturbance observer-based control scheme is proposed for free-floating space manipulator with nonlinear dynamics derived using the virtual manipulator approach. The derived dynamic equation uses only link angles as generalized coordinates, which is suitable for the controller design in joint space. Since joint coupling, model uncertainties in robot dynamics are treated as lumped disturbances, a disturbance observer is developed at each joint of degree-of-freedom space manipulator to decouple and simplify the controller design. Simulation results of a six-link space manipulator show that the proposed scheme achieves superior performance, especially when large external disturbances are present.

128 大変形を考慮した2リンク剛体-フレキシブルマニピュレータのモデリングと残留振動抑制

This paper proposes a new method for the trajectory planning of a two-link rigid-flexible manipulator in a point-to-point motion. In order to obtain a mathematical model properly, the flexible link is modeled by considering the axial displacement and the nonlinear curvature due to large bending deformation. The Lagrangian approach in conjunction with the assumed modes method is applied to derive the equations of motion of the manipulator. In the trajectory planning, we express the desired joint angle of the flexible link by a cubic spline function, and then use a particle swarm optimization to minimize the joint driving torque. We show that the residual vibrations of the flexible link can be suppressed as a result of the minimum driving torque requirement. In the numerical calculation, we verify the effectiveness of the proposed trajectory planning.

1827 可変ピッチ式直線翼垂直軸風車性能の流管モデルによる予測と風洞実験(S17-2 風力発電(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The paper describes the predicting of power performance for a micro vertical axis wind turbine(VAWT) with variable-pitch straight blades. A main feature of the variable-pith angle mechanism is to be able to vary the pitch angles of blades according to the azimuth angle of the main links, without actuators. The performance of the wind turbine is measured by using an open circuit type wind tunnel while the single stream tube model. Performance measurements of the rotor are carried out to understand the effects of variable-pitch with different airfoils (NACA0018, 0021, 63_4-221) and to assess the capability of the dynamic-stall models in predicting flows with relatively low tip speed ratios. It was found that VAWT with variable-pitch straight blades has the optimum swing angle and the optimum airfoil.

A Switching Controller System for a Wheeled Mobile Robot

A wheeled mobile mechanism with a passive and/or active linkage mechanism for rough terrain environment is developed and evaluated. The wheeled mobile mechanism which has high mobility in rough terrain needs sophisticated system to adapt various environments. We focus on the development of a switching controller system for wheeled mobile robots in rough terrain. This system consists of two sub-systems: an environment recognition system using link angles and an adaptive control system. In the environment recognition system, we introduce a Self-Organizing Map (SOM) for clustering link angles. In the adaptive controllers, we introduce neural networks to calculate the inverse model of the wheeled mobile robot. The environment recognition system can recognize the environment in which the robot travels, and the adjustable controllers are tuned by experimental results for each environment. The dual sub-system switching controller system is experimentally evaluated. The system recognizes its environment and adapts by switching the adjustable controllers. This system demonstrates superior performance to a well-tuned single PID controller.

A Unified Passivity-based Control Framework for Position, Torque and Impedance Control of Flexible Joint Robots

This paper describes a general passivity-based framework for the control of flexible joint robots. Recent results on torque, position, as well as impedance control of flexible joint robots are summarized, and the relations between the individual contributions are highlighted. It is shown that an inner torque feedback loop can be incorporated into a passivity-based analysis by interpreting torque feedback in terms of shaping of the motor inertia. This result, which implicitly was already included in earlier work on torque and position control, can also be used for the design of impedance controllers. For impedance control, furthermore, potential energy shaping is of special interest. It is shown how, based only on the motor angles, a potential function can be designed which simultaneously incorporates gravity compensation and a desired Cartesian stiffness relation for the link angles. All the presented controllers were experimentally evaluated on DLR lightweight robots and their performance and robustness shown with respect to uncertain model parameters. Experimental results with position controllers as well as an impact experiment are presented briefly, and an overview of several applications is given in which the controllers have been applied.

Adaptive robust control design and experimental demonstration for flexible joint manipulators

A control design for flexible joint manipulator in the presence of nonlinearity and mismatched uncertainty is introduced. The control does not need the possible bound of uncertainty a priori. Only the existence of the bound is assumed. A state transformation is introduced via implanted control to tackle a mismatched system. The scheme utilizes the bounding function by combining states and parameters, which is to be estimated. Then an appropriate parameters update laws are designed to guarantee an asymptotic convergency by adopting Lyapunov approach. The control version shows that states converge to zero for the transformed system, and guarantees the uniform stability and boundness. This is also true for the original system in case either the gravitational force is absent or the system is coordinated such that the gravitational force converges to zero as link angles approach zero. The control performance is verified through experiments and shows an enhanced tracking performance for given references.

2P1-A11 アクチュエータ束により駆動されるLoosely Coupled Mechanismの角度制御(フレキシブル・メカニズム)

We present a link mechanism with a loosely coupled mechanism (LCM), modeled on a human joint. A viscoelastic object functions as a cartilaginous area and soft actuators as muscles. The link of an LCM has high compliance with soft materials, additionally bends smoothly as a human joint. We made an LCM using shape memory alloy (SMA) actuator bundles to regulate the link angle. Due to large generative force of actuator bundles, we have better response in angle control. Although it is impossible to set a high gain for each SMA, the whole system using actuator bundles can realize high gain feedback in angle control.