Applied Mechanics and Materials Vols. 284-287

Abstract: Virtual machine tool has been used in the toolpath simulation of a real machine tool with very promising achievement in teaching assistance. However, a five-axis milling machine is generally very expensive in comparison with traditional three-axis milling machine in its configuration. This is mostly resulted from the addition of two more rotational axes in five-axis machine. This paper focuses on the development of a Web-based five-axis milling machining toolpath simulation system so as to facilitate the comprehensive understanding of students and to ease the explanation of operations. A user can access the developed system through the web browsers such as the Microsoft Internet Explorer and Google Chrome as long as the Java Runtime Environment and OpenGL are installed. Three general configurations of five-axis milling machine tool have been implemented including Head-Head, Head-Table, and Table-Table. Furthermore, five-axis post-processing is generally a bottleneck in the popularization of toolpath simulation. An intelligent distributed agent-based post-processor has been integrated in this system. For example, an APT file created by the usage of Catia CAD/CAM software according to a five-axis toolpath could be post-processed by the developed system for the generation of a five-axis NC program. This NC program could then be simulated in the proposed system. The developed system has been successfully implemented and shown very promising application in the understanding of five-axis milling operation.

Abstract: Over worn tires in a vehicle endanger vehicle operation and driving safety. Vehicles with worn tires frequently have flat tires in highway, and then result in fatal traffic accidents. This research developed a RFID-based automatic tire-wear detection system. A tire-wear detection RFID cell, which contains RFID tag, isolation layer and noninterference layer, was buried in specified depth of a tire. The RFID cell can provide a signal to controller to issue a tire-wear warning if the tire is over worn. The wear detection system has benefits of small size, no battery, no maintenance, low cost and low false alarm. Bench test results confirm that this system can achieve real-time and effective detection for worn tires to enhance driving safety.

Abstract: The article programs the shortest path searching problems of the mobile robot in the complexity unknown environment, and uses the mobile robot to present the movement scenario from the start point to the target point in a collision-free space. The complexity environment contains variety obstacles, such as road, tree, river, gravel, grass, highway and unknown obstacle. We set the relative dangerous grade for variety obstacles. The mobile robot searches the target point to locate the positions of unknown obstacles, and avoids these obstacles moving in the motion platform. We develop the user interface to help users filling out the positions of the mobile robot and the obstacles on the supervised computer, such the initial point of the mobile robot, the start point and the target point. The supervised computer programs the motion paths of the mobile robot according to A* searching algorithm, flood-fill algorithm and 2-op exchange algorithm The simulation results present the proposed algorithms that program the shortest motion paths from the initial point approach to the target point for the mobile robot. The supervised computer controls the mobile robot that follows the programmed motion path moving to the target point in the complexity environment via wireless radio frequency (RF) interface.

Abstract: In this paper, two experimental techniques, Electronic Speckle Pattern Interferometry and Stroboscopic Interferometry, and two different finite element analysis packages are used to measure or to analyze the frequencies and mode shapes of a micromachined, cross-shaped torsion structure. Four sets of modal data are compared and shown having a significant discrepancy in their frequency values, although their mode shapes are quite consistent. Inconsistency in the frequency results due to erroneous inputs of geometrical and material parameters to the finite element analysis can be salvaged by applying the finite element model updating procedure. Two updating cases show that the optimization sequences converge quickly and significant improvements in frequency prediction are achieved. With the inclusion of the thickness parameter, the second case yields a maximum of under 0.4% in frequency difference, and all parameters attain more reliable updated values.

Abstract: Some researchers have recently investigated the effects of joint stiffness on both robot safety and performance in human-friendly robots using pneumatic artificial muscles (PAMs). However, due to the limited control bandwidth of pneumatic muscles, dynamic stiffness characteristics and their effects on safety as well as performance should be taken into account in the frequency domain. This paper introduces the concept of instantaneous stiffness and validates its model with the Stanford Safety Robot (S2ρ). The potential effects of dynamic stiffness on safety and performance are explored through experimental comparison of peak impact accelerations and sinusoidal position tracking, respectively. Simulation and experimental results with the Stanford Safety Robot show that the stiffness demonstrates limited effects on the impact acceleration given the same impact velocity and controller gain, whereas it significantly affects control performance due to pressure-induced non-linearities. A strategy for stiffness optimization for robot safety and performance is discussed as a design guideline of human-friendly robot design.

Abstract: Here a low cost embedded robotic gripper with force control function is designed for frangible fruit manipulation. This embedded control gripper is integrated with a Mitsubishi robot based on FPGA control structure. The model-free intelligent fuzzy sliding mode control strategy is employed to design the position controller of each joint and gripper force controller, respectively. Experimental results of pick-and-place frangible small tomato and banana fruit are shown by pictures to evaluate this embedded position/force hybrid control system performance.

Abstract: As the portable electronics and wireless sensors continue to be minimized in size and power consumption, the energy harvesting from the surrounding environment has become a potential major or supplementary power source for those devices. As an energy harvesting option for converting the mechanical vibrations to the electrical energy, the structure-electricity field coupled piezoelectric materials have relatively high conversion efficiency, light weight and small size, making them preferable for wireless sensor networks and portable electronics. In this paper, the modeling work on coupled field dynamics of the piezoelectric cantilevered bimorph (PCB) energy harvester is presented, in terms of structure tip displacement and open-circuit electrical potential generated through harmonic excitation. First, a single degree of freedom (SDOF) analytical model is presented for predicting the tip displacement of the PCB structure, and then a finite element (FE) model is created to simulate the tip displacement and open-circuit voltage of the PCB structure. Then, both the analytical and finite element models are compared against the laboratory experimental results. The comparison shows that the FE model has a better agreement with the experimental result than the analytical model. Based on the evaluation, these two models could be adopted as design tools in different cases.

Abstract: In this paper, model based design was introduced for fast developing the flexible motor control system. Unification of synchronous and asynchronous motors was proposed as they have same control framework. Based on the combinatorial study of motor control system’s inputs, outputs and state variables, a flexible motor control system was established that for synchronous and asynchronous motors, variety of control algorithms can switch, expand to and combine with each other freely. Building the finite element model of the motor with Ansoft Maxwell, the parameters and the electromagnetic characteristics of the motor have been obtained by finite element analysis. With the PID parameter auto-tuning method, the result of the system simulation proves the correctness of the control algorithm. After continuous testing and validation, the simulation model was changed into fixed-point model according to the embedded processor. Combining underlying drive with automatic code generation, the software of the motor control system was achieved rapidly. A servo driver and a motor servo performance test-bed were designed to test the automatically generated code and control algorithm. The experimental results show that a flexible motor control system with good servo performance has been achieved rapidly with model based design.

Abstract: In this paper, the pneumatic driven manipulation system is driven by the pneumatic cylinders. The proposed system is built by the designed pneumatic force control system and the microscope, which is integrated with the control interface. Firstly, the characteristics of the pneumatic force control system are measured as the proportional pressure control valve. In accordance with these nonlinear characteristics, a self tuning fuzzy controller with a dead zone compensator is designed to improve precision of the pneumatic force control system. From experimental results, the force error can be controlled within ±1 mN. Next, the real-time image is captured by the microscope with a 1/2 type CCD camera. Through designed image processing, image tracking and image recognition, visual image is used to define the position a probe tip. The distance between the target position and a probe tip can be calculated. Finally, the force control of the pneumatic force control system, calculating the distance between the target position and a probe tip, the control processes are integrated with designed the control interface. Visual C++ code from MFC is used to finish the control interface. From experimental results, the position error can be controlled within ± 1 pixel.

Abstract: Binocular vision or stereo vision for extraction of three-dimensional information from stereo images has been widely used in many applications like robot navigation, recovering the three-dimensional structure of a scene, and optical inspection systems. More recently, the majority of research in binocular vision has focused on the establishment of stereo matching. However, to date, there has been relatively little research conducted on the effect of computational models of binocular vision with variable focal length of lens. In this paper, a modified computational model of binocular vision is presented to develop a new depth estimation algorithm with no effect of changes in focal length. This method provides an obvious advantage in accuracy of depth estimation by reducing the effect of changing the lens focal length. The experimental results show that the proposed depth estimation method in binocular vision provides better accuracy than conventional method. Finally, we apply the new depth estimation method to a stereo-vision-based automatic docking system for a mobile robot to verify its accuracy.