Industrial robots have advantages of large workspace, compact structure, and good flexibility, but the stiffness of the robot is relatively weak due to the compliance of reducers and its series structure. In this article, a five-degree-of-freedom robot with non-backlash driving is presented. A parallelogram structure with diagonal driven is used for robotic arms which is useful to improve the overall stiffness of the robot. First, the detailed structure of the robot is introduced, and the kinematic characteristics of the robot are analyzed. Second, a stiffness approximation method is proposed to evaluate the stiffness of the robot in the global workspace. The overall deformations under certain external loads which are composed of deflection deformations and stretching deformations are calculated based on the strain energy method and the properties of the components. The effectiveness of the approximation method used for evaluating the stiffness of the robot which has hybrid open-and closed-loop kinematic chains is verified through the finite element analysis results and the experimental results. Finally, the stiffness evaluation results show that the stiffness of the proposed robot is better than that of the industrial robot, which makes it more suitable for most of the industrial applications, such as handling, palletizing, and drilling.

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Stiffness control of an actuator is important to ensure stable contact motion and collision safety for human-robot integration tasks. The variable stiffness mechanism (VSM) is an important part of the variable stiffness actuator. We propose a novel reconfigurable rotational VSM that uses magnet springs and swing guide mechanisms in this paper. Magnet springs are used as elastic elements that are driven by the cable, and the initial stiffness of the mechanism can be regulated by adjusting the air gap distance between the magnets. The mathematical stiffness model of the VSM is developed, and the numerical calculation simulation and experiments are conducted to verify the feasibility of the proposed VSM.

The joint deformation has great influence on machining accuracy for a robotic arm. In this paper, the deformation characteristics of the robotic arm with hybrid kinematic chains is investigated in order to improve its machining accuracy. Firstly, the deformation model of the joints has been established based on the Strain energy method and Castigliano theorem according to the robot structure. Secondly, the deformation influence coefficient (DIC) is defined to investigate the deformation influence of main components on the end-effector, and the deformation characteristics are evaluated by the simulation. Finally, a small size robotic arm prototype is established and robotic drilling comparative experiments are conducted. The theoretical and experiment results show that the machining method can be selected according to the DIC, which the force can be applied to the components with better stiffness. On the other hand, the deformation of driving components can also be reduced when the DIC cannot be adjusted to meet the accuracy requirement.