In this paper, a new numerical method for inverse kinematics with prioritized multiple targets is proposed. The proposed method is constructed based on the virtual spring model and joint-based damping control. The targets are prioritized by adjusting the effect of the virtual springs. The proposed method has the following three features. First, it does not require complex calculations such as a Jacobian matrix projection into the null space. Second, it can solve prioritized inverse kinematics problems in the position level without integrating the joint velocity. Third, it is robust to parameter variations and singular configurations. The second feature is motivated by the background that most industrial robots in factories are used as position-controlled robots. Simulation experiments using a 9-DOF redundant robot show that the proposed method is faster and more robust than the conventional method. The proposed method is expected to be useful for helping to avoid collisions between links and obstacles using the redundancy. GRAPHICAL ABSTRACT

Most robots involved in vertical movement against gravitation require actuators large enough to support their own weight. To improve the inherent safety of such robots against the large actuators and reduce their energy consumption, numerous gravity compensation mechanisms (GCMs) have been proposed. Our previous study proposed a variable GCM (VGCM) that uses two types of springs and can adjust the compensation force. In this paper, a VGCM-based scissor lift (pantograph lift) that uses three springs and a smaller actuator is proposed. A prototype is designed and fabricated, and the performance of the prototype is evaluated experimentally. The results demonstrate that the developed scissor lift meets the design specifications. In addition, a load estimator is established based on the dynamic model of the scissor lift. A real-time self-adjustment method that automatically changes the compensation force is proposed, and its effectiveness is verified. Graphical Abstract

In this paper, a new inverse kinematics strategy is proposed for avoiding deadlock caused by joint limits. The proposed method is a combination of the conventional numerical method for inverse kinematics and an extended angle-axis vector. The extended angle-axis vector, instead of Euler angles, represents the orientation error. In the proposed method, the rotation direction of the end effector is changed by using the extended angle-axis vector to avoid deadlock. This paper describes the specific parameters included in the extended angle-axis vector that are necessary to change the rotation direction. The effectiveness of the proposed method was verified through simulations using a 9-degree-of-freedom robot. The proposed method is expected to be useful for solving inverse kinematics problems, which remain analytically unresolved. GRAPHICAL ABSTRACT