Absolute Coordinate Frame Research Articles

A new 3-D multi-physics coupling model for lubricated piston-liner systems

In this paper, a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems. The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are established and fully coupled on a unified absolute coordinate frame. The coupling model is discretized and solved using the unified spatial and temporal discrete methods. Then, an application example of a four-cylinder engine is employed to comprehensively investigate the coupling characteristics in the piston-liner system. The new coupling model reveals the presence of two distinct locations with the lowest local film thickness on either side of the piston's central axis, consequently yielding elevated local oil film pressures. This observation provides a reasonable explanation for the occurrence of wear and failure in the piston skirt on both sides.

Kinematics and Statics of a 3-UPURobot in Screw Coordinates

AbstractThis paper investigates the kinematics and statics of a 3-UPU robot in screw coordinates. According to the definition of a twist, both the angular velocity of a rigid body and the linear velocity of a point on it are expressed in screw components. The twist equation is established to calculate the position and posture of each joint. This equation can be applied directly to analyze the statics. According to the definition of a wrench, both the force and torque of the planar linkages are expressed in wrench components. As a result, the wrench equations are established to express the resultant action of a force system in one coordinate frame. Compared with the traditional Cartesian coordinate method, the wrench equation is free from complex algebraic manipulation and convenient to obtain wrench matrix by Plücker coordinates of each wrench. Numerical calculation is applied to solve the kinematics which can conveniently depict the position and posture of each joint in the absolute coordinate frame. Six unknown variables can be solved with each equation of wrench that contains three forces and three torques. The kinematics and static analysis of the 3−UPU robot validate this method.

ACCURATE VISUAL LOCALIZATION IN OUTDOOR AND INDOOR ENVIRONMENTS EXPLOITING 3D IMAGE SPACES AS SPATIAL REFERENCE

Abstract. In this paper, we present a method for visual localization and pose estimation based on 3D image spaces. The method works in indoor and outdoor environments and does not require the presence of control points or markers. The method is evaluated with different sensors in an outdoor and an indoor test field. The results of our research show the viability of single image localization with absolute position accuracies at the decimetre level for outdoor environments and 5 cm or better for indoor environments. However, the evaluation also revealed a number of limitations of single image visual localization in real-world environments. Some of them could be addressed by an alternative AR-based localization approach, which we also present and compare in this paper. We then discuss the strengths and weaknesses of the two approaches and show possibilities for combining them to obtain accurate and robust visual localization in an absolute coordinate frame.

Algorithms of motion planning for a six-legged walking machine

This paper investigates algorithms of motion planning for a six-legged walking machine over complex terrain. Application of the Rodrigues-Hamilton parameters for describing the orientation of the body enables one to develop algorithms of motion planning for the body and legs in an absolute coordinate frame with automatic adaptation to the surface. Experiments with a laboratory scale walking machine have demonstrated the efficiency of proposed algorithms.