Abstract:Parallel kinematic machines (PKMs) are commonly used for tasks that require high precision and stiffness. In this sense, the rigidity of the drive system of the robot, which is composed of actuators and transmissions, plays a fundamental role. In this paper, ball-screw drive actuators are considered and a 6-degree of freedom (DoF) parallel robot with prismatic actuated joints is used as application case. A mathematical model of the ball-screw drive is proposed considering the most influencing sources of nonlin… Show more
“…The equivalent dynamic model of a single-nut double-cycle ball screw feed system is established by ignoring the effect of motor stiffness, in which the screw, screw-nut joint, and bearings are modeled as springs, and the worktable is modeled as a lumped mass element. 12,14,15 To analyze the dynamic characteristics of the ball screw feed system, the system can be simplified as a single-degree-of-freedom mechanical system with variable stiffness shown in Figure 2. Figure 2.Single-degree-of-freedom dynamic model with variable stiffness.…”
Section: Dynamic Modeling Of the Ball Screw Feed Systemmentioning
confidence: 99%
“…14 and Negahbani et al. 15 established a lumped mass-spring model of the ball screw feed system to calculate the elastic deformations. However, in their works, they all treated the ball screw feed system as a linear system to analyze the natural vibration characteristics, but the nonlinearities of the kinematic joints and screw were not considered.…”
In this study, a single-degree-of-freedom model is established to investigate the dynamic characteristics of a single-nut double-cycle ball screw feed system by considering the contact states of the nonlinear kinematic joints. Based on fully considering the parameters of the ball screw feed system, the axial deformations and forces of the key components are calculated to construct a set of piecewise-nonlinear restoring force functions of the system displacement and worktable position. The variations of the contact stiffnesses of the kinematic joints and transmission stiffness of the system with different boundary conditions are analyzed and the results indicate that they all have abrupt changes when the system displacement reaches a critical value. The changing law of the system transmission stiffness in the whole stoke is discussed. Additionally, the effects of excitation force, worktable position and system mass on the dynamic characteristics of the system and its correlative components are analyzed.
“…The equivalent dynamic model of a single-nut double-cycle ball screw feed system is established by ignoring the effect of motor stiffness, in which the screw, screw-nut joint, and bearings are modeled as springs, and the worktable is modeled as a lumped mass element. 12,14,15 To analyze the dynamic characteristics of the ball screw feed system, the system can be simplified as a single-degree-of-freedom mechanical system with variable stiffness shown in Figure 2. Figure 2.Single-degree-of-freedom dynamic model with variable stiffness.…”
Section: Dynamic Modeling Of the Ball Screw Feed Systemmentioning
confidence: 99%
“…14 and Negahbani et al. 15 established a lumped mass-spring model of the ball screw feed system to calculate the elastic deformations. However, in their works, they all treated the ball screw feed system as a linear system to analyze the natural vibration characteristics, but the nonlinearities of the kinematic joints and screw were not considered.…”
In this study, a single-degree-of-freedom model is established to investigate the dynamic characteristics of a single-nut double-cycle ball screw feed system by considering the contact states of the nonlinear kinematic joints. Based on fully considering the parameters of the ball screw feed system, the axial deformations and forces of the key components are calculated to construct a set of piecewise-nonlinear restoring force functions of the system displacement and worktable position. The variations of the contact stiffnesses of the kinematic joints and transmission stiffness of the system with different boundary conditions are analyzed and the results indicate that they all have abrupt changes when the system displacement reaches a critical value. The changing law of the system transmission stiffness in the whole stoke is discussed. Additionally, the effects of excitation force, worktable position and system mass on the dynamic characteristics of the system and its correlative components are analyzed.
“…In the literature, papers focusing on both the robotic system and on the transmission can be found. However, they generally concern the definition of control algorithms for the suppression of vibrations [26,27], the estimation of the system's parameters [28], or the definition of the positioning error in the workspace [29,30].…”
Several industrial robotic applications that require high speed or high stiffness-to-inertia ratios use parallel kinematic robots. In the cases where the critical point of the application is the speed, the compliance of the main mechanical transmissions placed between the actuators and the parallel kinematic structure can be significantly higher than that of the parallel kinematic structure itself. This paper deals with this kind of system, where the overall performance depends on the maximum speed and on the dynamic behavior. Our research proposes a new approach for the investigation of the modes of vibration of the end-effector placed on the robot structure for a system where the transmission’s compliance is not negligible in relation to the flexibility of the parallel kinematic structure. The approach considers the kinematic and dynamic coupling due to the parallel kinematic structure, the system’s mass distribution and the transmission’s stiffness. In the literature, several papers deal with the dynamic vibration analysis of parallel robots. Some of these also consider the transmissions between the motors and the actuated joints. However, these works mainly deal with the modal analysis of the robot’s mechanical structure or the displacement analysis of the transmission’s effects on the positioning error of the end-effector. The discussion of the proposed approach takes into consideration a linear delta robot. The results show that the system’s natural frequencies and the directions of the end-effector’s modal displacements strongly depend on its position in the working space.
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