Performance evaluation of a special 6-PUS type parallel manipulator

In this paper, a special 6-PUS parallel manipulator (PM) is utilized as a shaking table. Unlike the existing results about 6-PUS PMs, we make the actuator direction collinear with the linkage direction at neutral position. With respect to the application background, a further analysis of the special PM is carried out from the perspective of motion/force transmissibility, natural frequency and acceleration capability. Specially, the complete dynamics model is established based on the Kane method. Then, generalized transmission indices based on the screw theory are utilized to reflect its motion ability, and a model of natural frequency is proposed with the axial stiffness of linkages considered. Finally, the effect of the angle between the actuator direction and the linkage direction α on various performances is analyzed, and other results are included to illustrate its feasibility and usability.

PD CONTROL WITH DESIRED GRAVITY COMPENSATION FOR A NOVEL DYNAMIC BRACE

A novel dynamic brace for the treatment of idiopathic scoliosis based on parallel-actuated robotic system is proposed in this paper. The new brace can apply corrective forces on patients’ spine actively to correct the abnormal spine. However, the gravity of the dynamic system results in some adverse impacts, such as reducing comfort degree of patients, accuracy loss of rehabilitation force control, big error in direction and value of force. To overcome this problem, a new active force control strategy, proportional-derivative (PD) control with desired-gravity-compensation (DGC), is proposed to improve the effectiveness of scoliosis rehabilitation. Considering the electrically driven system and the environment contacting with the brace, the dynamic model of the active brace system is derived using Kane method. Based on the above mentioned, the force controller with DGC is designed for the brace system to compensate the impact of system gravity. The brace experiment system is built and various experiment tests are performed to verify the proposed control strategy. Experiment results demonstrate that the proposed control strategy, PD control with DGC, can distinctly reduce the influence of the brace system gravity and has more efficient control effectiveness compared with the classical PID controller.

Modeling and control for ultra-low altitude cargo airdrop

Purpose The purpose of this paper is to model the aircraft-cargo’s coupling dynamics during ultra-low altitude heavy cargo airdrop and to design the aircraft’s robust flight control law counteracting its aerodynamic coefficients perturbation induced by ground effect and the disturbance from the sliding cargo inside. Design/methodology/approach Aircraft-cargo system coupling dynamics model in vertical plane is derived using the Kane method. Trimmed point is calculated when the cargo fixed in the cabin and then the approximate linearized motion equation of the aircraft upon it is derived. The robust stability and robust H∞ optimal disturbance restraint flight control law are designed countering the aircraft’s aerodynamic coefficients perturbation and the disturbance moment, respectively. Findings Numerical simulation shows the effectiveness of the proposed control law with elevator deflection as a unique control input. Practical implications The model derived and control law designed in the paper can be applied to heavy cargo airdrop integrated design and relevant parameters choice. Originality/value The dynamics model derived is closed, namely, the model can be called in numerical simulation free of assuming the values of parachute’s extraction force or cargo’s relative sliding acceleration or velocity as seen in many literatures. The modeling is simplified using Kane method rather than Newton’s laws. The robust control law proposed is effective in guaranteeing the aircraft’s flight stability and disturbance restraint performance in the presence of aerodynamic coefficients perturbation.

Prototype design, modeling, and experimental research of a novel lower limb powered exoskeleton

In this paper, a new type of lower limb powered exoskeleton is presented, which is based on a screw-nut actuated mechanism to help paraplegics to stand, walk and accomplish activities of daily living. The Denavit–Hartenberg method and the Kane method are adopted to establish a kinematic and dynamic model of novel lower limb powered exoskeleton to analyze the workspace and the control strategy simulation. A double-closed loop control strategy is proposed to ensure precision, and its effectiveness is validated. The results of prototype gait control and patient experiments show that the new type of lower limb powered exoskeleton can enable patients to realize stable and smooth walking.

Kane Method Based Dynamics Modeling and Control Study for Space Manipulator Capturing a Space Target

Dynamics modeling and control problem of a two-link manipulator mounted on a spacecraft (so-called carrier) freely flying around a space target on earth’s circular orbit is studied in the paper. The influence of the carrier’s relative movement on its manipulator is considered in dynamics modeling; nevertheless, that of the manipulator on its carrier is neglected with the assumption that the mass and inertia moment of the manipulator is far less than that of the carrier. Meanwhile, we suppose that the attitude control system of the carrier guarantees its side on which the manipulator is mounted points accurately always the space target during approaching operation. The ideal constraint forces can be out of consideration in dynamics modeling as Kane method is used. The path functions of the manipulator’s end-effector approaching the space target as well as the manipulator’s joints control torque functions are programmed to meet the soft touch requirement that the end-effector’s relative velocity to the space target is zero at touch moment. Numerical simulation validation is conducted finally.