Rotation Accuracy Analysis of Spindle Under Variable Preload

Variable preload technology is used to achieve appropriate preload applied on spindle bearing based on machining conditions. However, the bearing temperature rise will be directly affected by bearing preload as well as bearing rotation accuracy. So, the main objective of this paper is to propose a method to determine the rotation accuracy of the spindle affected by the thermal expensive due to heat generation under variable preloads. Five degrees of freedom (5-DOF) quasi-static model of angular contact ball bearing was established to investigate the internal load distribution of the contact areas between the race way and balls. Then local contact heat generation of the bearing is calculated based on hertz contact theory. Finally, an experimental platform equipped with hydraulic system is designed and fabricated, which is preloaded by a hydraulic chamber. Studies have shown that the rotation accuracy presents drastically with the spindle rotational speed. Moreover, the influence of the bearing preload has a secondary importance. Comparative analysis about the rotation accuracy between starting running state and stable running state after a few hours under the same preload has been investigated. Results show that the accuracy of rotation spindle present no obviously difference when the uneven thermal deformation of parts occurs in the spindle system.

A Novel Digital Speed Control Design for Brushless DC Motor Drives

This paper presents a novel robust digital speed control design for brushless DC motors (BLDCs). The speed control can be achieved by regulating the DC link voltage of a six-step inverter. The discrete-time brushless DC motor dynamics is derived through bilinear transform. A robust digital control algorithm is designed to guarantee the closed loop system stability by satisfying the desired phase and gain margin. Computer numerical simulation studies and hardware implementation have demonstrated the effectiveness and robustness of the proposed scheme.

Mixed Sensitivity Design of PID Controller-Applied to a Ball and Beam System

This paper presents a set of algorithm for all achievable coefficients of Proportional Integral Derivative (PID) controllers that stabilize the system and satisfy a mixed sensitivity constraint with an uncertain time delay. Additive uncertainty modeling is used to describe the uncertainty of perturbed system. Additive uncertainty modeling performs much faster response with the time running of computer programming in MATLAB. This technique is applied to a ball and beam system transfer function with the assumption of uncertain communication time delays in the system process. The goal of this application is to regulate a ball position on a beam and also satisfy the mixed sensitivity constraint.

Modeling and Experimentation of a Ribbed Caudal Fin for Aquatic Robots

Presented in this study is a mathematical model and preliminary experimental results of a ribbed caudal fin to be used in an aquatic robot. The ribbed caudal fin is comprised of two thin beams separated by ribbed sectionals as it tapers towards the fin. By oscillating the ribbed caudal fin, the aquatic robot can achieve forward propulsion and maneuver around its environment. The fully enclosed system allows for the aquatic robot to have very little effect on marine life and fully blend into its respective environment. Because of these advantages, there are many applications including surveillance, sensing, and detection. Because the caudal fin actuator has very thin side walls, Kirchhoff-Love’s large deformation beam theory is applicable for the large deformation of the fish-fin actuator. In the model, it is critical to accurately model the curvature of beams. To this end, C1 beam elements for thin beams are developed by specializing the shear-deformable beam elements, developed by the authors, based upon Reissner’s shear-deformable nonlinear beam model. Furthermore, preliminary experiments on the ribbed fin are presented to supplement the FE model.

Non-Linear Dynamic Analysis of a Cam With Flat-Faced Follower Linkage Mechanism

A mechanism with a cam and a flat-faced follower is considered for distinct angular velocities. The dynamic analysis presents follower linkage displacement driven by a cam rotating at a uniform angular velocity. The system has clearances between the flat-faced follower and the guides and the effect of clearance is analyzed. The cam-follower linkage mechanism is simulated using Solidworks program taking into account the impact and the friction between the cam, flat-faced follower, and the guides. The non-linear analysis tools are employed for the movement of the flat-faced follower. An experimental set up is established to capture the motion of the follower. High-resolution optical marker is mounted on the follower stem to capture the follower motion in the y-direction. The simulation and experimental results are compared and verified for largest Lyapunov exponent.

Experimental Modal Analysis of a Fixed-Fixed Beam Under Axial Force

In this paper, an experimental procedure is proposed for determining the resonance frequencies and mode shapes of vibration of a fixed-fixed beam. Since it is fixed at both ends, the beam may sustain an axial force due to several factors including the fasteners and/or change of temperature. The analytical governing equations of motion, frequency equation, and mode shapes of vibration are presented. The analytical model is used to justify the experimental approach as well as interpretation of the experiment data. In this study, a hammer is used to excite the beam, and then the vibration of the beam is observed and recorded at two different points on the beam using two laser Doppler vibrometers. The data from the vibrometers are used to extract the resonance frequencies and mode shapes of vibrations. Using the analytical model, the axial force in the beam is estimated.

A Computer Vision Approach for Balancing of Rotating Machines

Unbalance is one of the most common mechanical faults in rotating machines. Different balancing methods to stabilize the unbalanced rotor are investigated in this paper. One approach of using solely the accelerometers data and intricate vibration theories is discussed. Although the method can eliminate the need of balancing equipment, and the amplitude and phase of the machine’s vibrations can be identified, it needs numerous measurements, and in some cases is impossible to be implemented. Therefore, a novel approach with reduced number of required measurements is proposed. Our method only requires two measurements, one from the original unbalanced condition, and the other from modified situation after adding an arbitrary trial mass to a marked location on the rotor. The rotating rotor is being video recorded during this process. The goal is to identify the position of the marked area whenever the amplitude of the sinusoidal vibration response reaches the maximum. To demonstrate the effectiveness of our method, an experiment is setup. Vibration of healthy and unbalanced flywheel attached on a three-phase induction motor is analyzed in both time and frequency domains. The rotation of the motor is video recorded under original unbalanced and modified situations. The correction mass and its adding location are calculated using proposed method. The vibration analysis of balancing result demonstrated that the system got dynamically balanced by adding right value and location of a mass. The method proposed and developed in this paper is more cost effective with the same accuracy as the other contested balancing techniques.

Investigation of Composite Hydrodynamic Thrust Bearing Operating Temperature Under Varying Axial Loads

The purpose of this experiment was to explore the operational behavior of hydrodynamic thrust bearings machined from various composite materials (PTFE-Filled Delrin Acetal Resin and MDS-Filled Nylon) and general Aluminum under a set of different axial loading conditions. Since thrust bearings allow mechanical components subjected to axial loads to rotate more freely, they must counter a great deal of friction which can cause bearing failure in order to maintain proper movement. In order to reduce friction and weight, this research posits that thrust bearings machined from composite materials of lower friction coefficients and densities to that of conventionally used materials such as aluminum may provide some advantages. This hypothesis was tested by machining three thrust bearings, all to the same geometric specifications (two composites and one Aluminum) and subjecting them to thrust loads of 25, 50, 75, and 100 pounds while rotating them at a constant rotational speed of 3050 RPM for 10 minutes at each load using a customized test rig. A thermocouple implanted into the bearings themselves recorded the operation temperatures at a sampling rate of 20 Hz. Based on the average temperatures recorded at the 100 pound axial/thrust load, the experiments suggest that the PTFE-Filled Delrin Acetal maintains the lowest average operating temperature of 29.5 °C, followed by the MDS-Filled Nylon at 41.6 °C and lastly the Aluminum at 54.4 °C — a trend that is observed at each axial load albeit less pronounced. These results suggest that composite materials such as PTFE-Filled Acetal and MDS-Filled Nylon to be used in lieu of conventional metals and operate at lower temperatures and lower friction.

ByeLab: An Agricultural Mobile Robot Prototype for Proximal Sensing and Precision Farming

At today, available mechatronics technology allows exploiting smart and precise sensors as well as embedded and effective mechatronic systems for developing (semi-)autonomous robotic platforms able to both navigate in different outdoor environments and implementing Precision Farming techniques. In this work, the experimental outdoor assessment of the performance of a mobile robotic lab, the ByeLab — Bionic eYe Laboratory — is presented and discussed. The ByeLab, developed at the Faculty of Science and Technology of the Free University of Bolzano (I), has been conceived with the aim of creating a (semi-)autonomous robotic system able to sense and monitor the health status of orchards and vineyards. For assessing and measuring the shape and the volume of the canopy, LIDAR technology coupled with ad-hoc developed algorithms have been exploited. To validate the ByeLab different experimental tests have been carried out. In addition to the in-lab and structured environments experimental tests that allowed to tune the algorithms, in this work the assessment of its capabilities — in particular the sensoric system — has been made outdoor controlled environment tests.