Robust control of a hydraulically driven flexible arm

A new robust controller is proposed to regulate both flexural vibrations and rigid body motion of a hydraulically driven flexible arm. The controller combines backstepping control and sliding mode to arrive at a controller capable of dealing with a nonlinear system with uncertainties. The sliding mode technique is used to achieve an asymptotic joint angle and vibration regulation in the presence of payload uncertainty by providing a virtual torque input at the joint while the backstepping technique is used to regulate the spool position of a hydraulic valve to provide the required torque. It is shown that there is no chatter in the hydraulic valve, which results in smoother operation of the system.

STUDY ON RESTRAINING THE RESIDUAL VIBRATION OF FLEXIBLE ARM BY PLANNING ACCELERATION

The method of planning acceleration is discussed to restrain the residual vibration of flexible arm. Based on the built mathematical model of the flexible arm, the equations of vibration with acceleration,vibration frequency,damping and time are obtained theoretically.According to the vibration frequency and damping, the suitable acceleration is executed experimentally to the flexible arm at the corresponding time. The result shows that this way can give rise to good effect to restrain the residual vibration.

BFEEDBACK CONTROL OF SINGLE-LINK FLEXIBLE ARMS

It is well known that it is rather difficult to control the tip position of a flexible arm by applying a suitable torque at the base of the link. In this paper, a linearized model of single-link flexible arm is considered. The spectral properties of the system are analyzed. With the rotational angle and angular velocity measurements available, a PID feedback control scheme for the control torque applied to the motor at the base of the link is presented. The asymptotic stability of the closed loop system is shown. Finally, the numerical simulation results are given.

Recursive Lagrangian dynamic modeling and simulation of multi-link spatial flexible manipulator arms

The dynamics for multi-link spatial flexible manipulator arms consisting of n links and n rotary joints is investigated. Kinematics of both rotary-joint motion and link deformation is described by 4 - 4 homogenous transformation matrices, and the Lagrangian equations are used to derive the governing equations of motion of the system. In the modeling the recursive strategy for kinematics is adopted to improve the computational efficiency. Both the bending and torsional flexibility of the link are taken into account. Based on the present method a general-purpose software package for dynamic simulation is developed. Dynamic simulation of a spatial flexible manipulator arm is given as an example to validate the algorithm.

Dynamic analysis of multi-link spatial flexible manipulator arms with dynamic stiffening effects

The dynamics for multi-link spatial flexible manipulator arms is investigated. The system considered here is an N-flexible-link manipulator driven by N DC-motors through N revolute flexiblejoints. The flexibility of each flexible joint is modeled as a linearly elastic torsional spring, and the mass of the joint is also considered. For the flexibility of the link, all of the stretching deformation, bending deformation and the torsional deformation are included. The complete governing equations of motion of the system are derived via the Lagrange equations. The nonlinear description of the deformation field of the flexible link is adopted in the dynamic modeling, and thus the dynamic stiffening effects are captured. Based on this model, a general-purpose software package for dynamic simulation of multi-link spatial flexible manipulator arms is developed. Several illustrative examples are given to validate the algorithm presented in this paper and to indicate that not only dynamic stiffening effects but also the flexibility of the structure has significant influence on the dynamic performance of the manipulator.

Bio-inspired design of alternate rigid-flexible segments to improve the stiffness of a continuum manipulator

Intrinsic flexible structures enable a continuum manipulator to exhibit attractive dexterity and intrinsic compliance over traditional hyper-redundant robots.However,its insufficient stiffness makes the performance of continuum manipulators unsatisfactory and thus limits the applications in many fields.A significant challenge is how to make a trade-off among dexterity,compliance and stiffness.From an evolutionary perspective,this paper compares several biological structures that enable the continuum manipulator function,and intends to reveal the mechanism on how the biological structures can improve the stiffness.The notochord and the vertebral column with acoelous centra are abstracted and physically implemented.A fundamental roddriven continuum manipulator is also introduced as a comparison.The stiffness models of these three continuum manipulators are proposed,and comparative experiments are conducted to verify their stiffness properties.Our results demonstrate that the rigid-flexible segmental structure can improve the stiffness properties of a continuum manipulator.