Analysis of Dynamic Characteristics for Machine Tools Based on Dynamic Stiffness Sensitivity

Dynamic parameters are the intermediate information of the entirety of machine dynamics. The differences between components have not been combined with the structural vibration in the cutting process, so it is difficult to directly represent the dynamic characteristics of the whole machine related to spatial position. This paper presents a method to identify sensitive parts according to the dynamic stiffness-sensitivity algorithm, which represents the dynamic characteristics of the whole machine tool. In this study, two experiments were carried out, the simulation verification experiment (dynamic experiment with variable stiffness) and modal analysis experiment (vibration test of five-axis gantry milling machine). The key modes of sensitive parts obtained by this method can represent the position-related dynamic characteristics of the whole machine. The characteristic obtained is that the inherent properties of machine-tool structure are independent of excitation. The method proposed in this paper can accurately represent the dynamic characteristics of the whole machine tool.

3D printing technologies for creating models and nozzles in an aerodynamic shock tunnel experiment

The features of 3D printing method for rapid prototyping and manufacturing of models for a pulsed high-speed gas-dynamic experiment are considered. Modern additive technologies allow the production of models. The basic properties of the materials and the advantages of 3D printing methods are described. The structure and properties of the obtained models can be unattainable using traditional manufacturing techniques. The design of the wind tunnel nozzle block is considered, which provides for the production of profiled contours using 3D printing. The advantages and disadvantages of use of such units on the shock tube are considered.

Experimental Research on the Characteristics of Thermal Bow in an Aeroengine HP Spool

During the cooling process after shut down for aeroengines, internal hot air rises and cold air drops due to natural convection, which makes uneven temperature distribution in the casing and creates temperature difference in radial and axial directions, causing uneven deformation of rotor. Once aeroengine starts after a little time of cooling, thermal bow forms more easily, causing excessive vibration. In some cases, the thermal bow can be so severe that the engine will be unable to start. Based on the rotor for one certain type of aeroengine, the paper describes an experiment of thermal bow failure, which is divided into a static one and a dynamic one, both having simulated the uneven temperature field. Firstly, the static experiment measures temperature difference and deformation of rotor in different temperature environments and dissimilar cold blowing conditions. Results show temperature difference of each cross section increases with the growth of casing temperature. And cold blowing can quickly and effectively eliminate uneven temperature distribution and structural deformation. Secondly, the dynamic experiment produces the results that the vibration amplitude increases obviously when rotating frequency approaches critical speeds (2365r/min and 2892r/min). As the cooling time increases, the amplitude decreases until normal, which is the most important feature different from that in failure of initial mass imbalance. Thermal bow mainly influences the fundamental frequency vibration. Cold blowing can quickly and effectively reduce vibration amplitude. The conclusions obtained from the dynamic experiments are consistent with the known regulations from engineering experience.

CONSTRUCTION AND TEST OF BIO-INSPIRED IMAGING POLARIZATION NAVIGATION PROTOTYPE

Bio-inspired polarization navigation is a promising navigation method inspired by insects’ autonomous foraging and homing behaviour. Many insects acquire their spatial orientation by sensing the polarization pattern of the skylight. We propose utilization of solar meridian in the polarized skylight as an orientation cue because of its significant features. Using its features, we then design and construct an imaging polarization navigation prototype. The prototype consists of a field-division polarization imaging sensor, the corresponding software, an interface, and the solar-meridian recognizing and measurement algorithm. The field-division polarization imaging sensor is the core component of the prototype and acquires polarized intensity images. To adapt to the demand of real-time on navigation system, we then propose an optimized real-time polarization image processing and pattern recognition algorithm based on Hough transform. The azimuth measurement accuracy of the sensor is then calibrated using a facility that is able to get higher azimuth accuracy by measurement of the star light. To verify the navigation capability of the developed system, we use a dynamic experiment, where the prototype is installed on the top of a vehicle and its navigation performance is compared with GNSS.