*Corresponding author. Keywords: Omni-directional wheel, Equipment assembly under the high speed train, Intelligent control.

Transcription

1 2017 International Conference on Mechanical and Mechatronics Engineering (ICMME 2017) ISBN: Development of Intelligent Omni-directional Mobile Platform for Assembly of High Speed Train Hui YANG 1, Yun-ping SUN 2, Long-liang PANG 2, Hai-feng WANG 1 and Guang LIU 3,* 1 Beijing Spacecrafts Manufacturing Factory, Beijing , China 2 Beijing Star Technology Development co. LTD, Beijing , China 3 School of Mechanical Engineering and Automation, Beihang University, Beijing , China *Corresponding author Keywords: Omni-directional wheel, Equipment assembly under the high speed train, Intelligent control. Abstract. Due to the reality of the equipment assembly under the high speed train, an intelligent omni-directional mobile platform is developed. The principle and structure of the platform are discussed.the intelligent omni-directional mobile platform is designed and applied. It has proved in practice that the intelligent omni-directional mobile platform based on above designs can move fluently and accurate in the limited assembly space. Assembly efficiency and quality of the equipment under the high speed train can be improved effectively. Introduction With the rapid development of high-speed railway, the assembly efficiency of high speed train becomes a vital factor to limit the production capacity[1,2,3,4]. Due to large size, heavy load, complex structure, complex assembly, limited assembly space and high accuracy requirements of high speed train, conventional auxiliary assembly equipment such as forklift[5], hovercraft[6], etc. cannot meet the rapid positioning requirement for lack of accuracy, flexibility and other causes. Herein, a kind of intelligent omni-directional mobile platform under the high speed train based on Mecanum wheel has been introduced to cope with the issues mentioned above[7,8,9,10]. This platform can move omni-directionally in two-dimensional planer without transforming its direction. It also has the ability to lift and reach the preset height accurately. Special control algorithm is used to realize the high accuracy locating, and the spliced-double platform can carry more load. Additionally, this intelligent omni-directional mobile platform has been applied to CRRC Qingdao Sifang Co., Ltd and achieved good application result. Principle of Intelligent Mobile Platform With the help of Mecanum wheel, the intelligent mobile platform can achieve omni-directional move in two-dimensional planer[11]. Hydraulic servo system is applied to obtain high locating accuracy in the altitude direction. Adopting high precision position transducer to gather displacement parameters makes the system a closed-loop control system, which maintains the rapid and exact orientation. Realization of Omi-directional Movement Mecanum wheel can realize omni-directional movement. As shown in Figure 1, the Mecanum wheel mainly composes of hub and roller. The uniformly distributed rollers can rotate respectively and with an angle of 45 degrees between the axis of roller and hub, making all rollers exterior lines formed a circle[12]. Each omni-directional wheel group has two degrees of freedom, the rotation of roller and the rotation of hub. There is a certain angle between two degrees of freedom. The function of omni-directional moving can be obtained by at least four Mecanum wheels via 270

2 collaborative control. Figure 2 shows the orientation, differential and decomposition or synthesis of the two-degrees of freedom between the two wheel groups, which can meet the requirement of omni-directional moving [13,14]. Figure 1. General structure of Mecanum wheel. Figure 2. Analysis of omni-directional moving and its driving force. On the basis of interpolation algorithm, the driving controller system controls the servo motor of each wheel group to realize joint movement, ultimately achieves the function of omni-directional movement in two-dimensional planer. Traveling controller converts the command received from remote control into signal which can be recognized by the four servo motor controllers respectively. Motors within the control of identifiable signal can rotate forward or reverse then makes the assembly platform move omni-directionally. In order to improve the control precision, the platform speed is hierarchically designed. In lower speed, the platform can realize the locating precision within 1mm via pointing control. The principle of the moving system controller is shown in Figure

3 Realization of Lifting Function Figure 3. Principle of moving system controller. The lifting system of platform adopts servo proportional valve as control element. Displacement of cylinder is feedback to a magnetostriction position transducer, which makes the hydraulic system a closed-loop control system that can ensure the platform accurate positioning, small micro distance and fast response speed. Due to this closed-loop control system, spliced-double platform can realize a high synchronous lifting accuracy of ±1mm. Figure 4. Schematic diagram of the hydraulic system. The lifting hydraulic system is mainly composed of a constant pressure oil source, servo proportional valve, balanced valve and oil cylinder with position transducer. The schematic diagram of the hydraulic system is shown in Figure 4. The hydraulic oil pumped out flows to the servo proportional valve after filtered. Servo proportional valve adopts the straight type sliding sleeve structure with LVDT position transducer and can control cylinder action according to the input 272

4 signal. Displacement sensor is inserted in the oil cylinder and the position of hydraulic cylinder can be monitored online from the sensor. The displacement deviation value calculated from the actual and theoretical value is converted to voltage signal by the A/D converter and then transformed to corresponded current signal via proportional amplifier. The current signal controls the motion of servo proportional valve and regulates loop flow by the gathered accurate displacement to make the load an accurate closed-loop speed control. The principle of closed-loop control is shown in Figure 5. Implementation of Splicing Function Figure 5. Principle of closed-loop control. The splicing function of this intelligent platform means two platforms can be jointed to one spliced-double platform which improves the bearing capacity. However, the stitching process needs to ensure the synchronization of moving and lifting process. The spliced-double platform realizes the omni-directional moving function through 8 collaborated Mecanum wheels which principle is the same as shown in Figure 2. Unlike odd platform, in order to maintain the synchronization of each platform the spliced-double platform needs to detect the location of each platform via position transducer to make timely adjustment when moving deviation occurs. The lifting altitude of spliced-double platform is on-line measured by position transducer and the controller makes corresponding adjustment according to the actual value and theoretical value which realizes accurate control of flow proportional servo valve and ensures the consistent action of lifting. Development of Equipment and Control System Design of Overall Equipment According to the principle mentioned above, a kind of multifunctional intelligent omni-directional mobile platform is designed to meet the assembly requirements under the high speed train. The moving direction and speed of four omni-directional wheels are controlled by four moving motors respectively. The platform moving omni-directionally in two-dimensional planer, including straight, transverse, oblique and arbitrary curve movement, zero radius of gyration rotating can be achieved by decomposition or synthesis of the four wheels orientation, differential and two-degrees of freedom. Through the servo proportional valve, flow of the loop is adjusted to achieve the regulation of the altitude. The movement and lifting process are controlled with closed-loop with the application of high precision sensors[15]. The principle of control system for the spliced-double platform is shown in Figure 6. The technician selects odd platform or spliced-double platform through the handle controller and sends the operation information to the controller. After analyzed the operation information and combined the feedback from position transducer, the controller figured out the location and speed parameters of the platform. Then the speed and direction of motor can be specified through the kinematics equations. According to the specified signals, motor driver alters its moving conditions immediately. Meanwhile, the controller transfers relevant information such as the displacement and speed of the platform to the monitor that technician supervised. 273

5 Figure 6. Principle of control system for the spliced-double platform. Performance Testing of Overall Equipment Figure 7 shows the overall intelligent omni-directional mobile platform which is based on Mecanum wheel to realize omni-directionally move in two-dimensional planer. Hydraulic servo control is applied to ensure high precision altitude location. Wireless handle controller makes it easier to operate the platform moving or lifting. A spliced-double platform shown in Figure 8 can support more load than the odd platform. The laser tracker test shows the intelligent omni-directional mobile platform a better performance with high flexibility and reliability. It can move steadily in any direction at any attitude within the travel ranges. The minimum positioning accuracy of odd-platform is lower than 0.5mm in the jog operation better than that of spliced-double platform which is approximately 1mm (see table 1). Figure 7. Overall assembly of intelligent omni-directional mobile platform. Figure 8. Overall assembly of spliced-double platform. 274

6 Table 1. Performance tests of assembly of intelligent omni-directional mobile platform. Model Motion form X1 [mm] X2 [mm] Locating precision [mm] Odd-platform Straight move Longitudinal move spliced-double Straight move platform Longitudinal move Conclusion In order to solve the problems in the assembly of large parts under the high speed train, an intelligent omni-directional mobile platform is developed based on Mecanum wheel which is capable of omni-directionally move in space limited two-dimensional planer. Hydraulic servo control is applied to ensure high precision altitude location. The rapid and accuracy movement are controlled with closed-loop with the application of high precision sensors that enable a high working efficiency. Test results show that the intelligent omni-directional mobile platform an ideal performance with high locating precision and more flexible motion form. The spliced-double platform carries more load than the odd platform and can be well adapted to the complex assembly environment high speed train. Moreover, the equipment has already been applied to CRRC Qingdao Sifang Co., Ltd and greatly facilitates assembly operations under high speed train. Acknowledgement This research was financially supported by China Academy of Space Technology Incubation Project Foundation (2012FH06529). 275

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