Abstract: This paper mainly introduces the hardware communication platform and software architecture of a robot control system based on an SMP control kernel, and describes the robot operation interface and trajectory reproducible teaching function developed using Visual Basic.
Keywords: SMP system; software motion control; trajectory reproducibility; teach-in operation
1 Introduction
With the rapid development of modern industry, ordinary manual labor is no longer suitable for high-intensity and harsh working conditions. As the level of robot manufacturing improves, robots with high efficiency, stable quality, and strong versatility have become increasingly popular and are widely used in flexible manufacturing production lines. At present, heavy work such as handling, welding, and spraying in industrial production has been gradually replaced by robots. In addition, special robots have also been applied in deep-sea exploration, fire rescue and other fields [1]. As early as the 1970s, robots in some industrialized countries abroad had entered the stage of practical application. After more than 30 years of research, application and improvement, at present, a few industrialized countries, represented by Japan and Germany, have an absolute advantage in terms of both technical level and equipment quantity [1]. Such as ABB of Sweden, Kawasaki Heavy Industries of Japan, and KUKA of Germany. my country's "863" program has included robot research, and the development of robots with good stability and practicality has also received widespread attention from enterprises. This article mainly introduces a robot control system based on SMP pure software motion control kernel and its practical application in welding.
2 System Overall Structure
The SMP system is a PC-based pure software motion control kernel developed by Soft ServoSystems in the United States. The SMP software runs on a Windows system with Ardence's RTX installed, and uses the host computer's CPU to run a real-time motion engine. It features closed-loop feedback, multi-axis interpolation, motion program processing, and PLC logic operation functions. It can be used with various servo communication networks such as VersioBus fiber optic, Panasonic RTEX, Yaskawa MECHATROLINK, Mitsubishi SSCNET, and FXI-40 [2]. This robot control system uses the FPA-200 adapter card and Panasonic A4N series servo system to build the system's communication platform.
2.1 System Overall Structure
The SMP system operates on Windows 2000/XP. Hardware options include a standard PC or a more stable IPC. A high-speed CPU core handles motion interpolation and PLC calculations in pure software, establishing bus communication with the FPA-200 via a standard PCI slot. The FPA-200 adapter card connects directly to the A4N servo drive and I/O via its network and fiber optic interfaces. Utilizing the CPU for pure software calculations eliminates the need for separate motion control cards and PLCs, effectively reducing hardware costs. The FPA-200's fiber optic interface allows for further expansion of I/O modules and the addition of peripheral auxiliary functions. The overall structure is shown in Figure 1.
2.2 SMP Software Architecture
The underlying module of the SMP software contains three upgradeable real-time engines: a PLC engine, an SMP engine, and an SMP motion parser. The three engines work together in a loop to complete motion control calculations. The CPU gives the underlying module the highest priority. The upper-level SMP module is used to execute the SMP controller, such as loading the program, setting parameters, managing files, and running the user interface. By using Ardence RTX to extend the real-time performance of Windows, the SMP Real-Time DLL intermediate link layer allows the application of the upper-level module to call and read the motion engine data and system status information of the underlying module in real time [2].
3. Robot Hardware Components
The robot's hardware structure consists of four parts: an industrial computer and a touch screen display teach pendant, an FPA-200 RTEX network adapter card, Panasonic A4N motors and servo drives, and the robot body. The industrial computer is the hardware foundation for system operation, and the application software interface of the teach pendant is directly object-oriented. The FPA-200 establishes bus communication with the host through the standard PCI slot on the IPC, and the power supply of the adapter card is also provided by the PCI bus. The FPA-200 has two network structure interfaces, RX and TX, which use a 100Mbit/s Ethernet network to connect the joint servo drives in series, and implement high-speed cyclic control and programmable acceleration and deceleration control for the six joint servo drives at a cycle speed of 0.5~1ms [3]. The system communication has extremely high responsiveness and stability. The servo motors are directly mounted on the robot joints and run through the internal mechanical wiring. They are connected to the servo drives at the bottom of the robot using standard aviation plugs. The X5 interface on the A4N servo drive provides abundant I/O contacts. Through PLC programming, the control of the welding torch equipment can be completed through the I/O points on the X5 interface, as shown in Figure 3.
The SMP-850 used in this system can achieve 8-axis interpolation linkage control. By expanding the IM-300 I/O module through the VersioBus fiber optic interface of the FPA-200, the number of input/output points can be increased to a maximum of 416.
4. Application Software Development
The SMP system provides application software library interfaces for Visual C++, Visual Basic, and Java, MAPI source code, and real-time DLL files for calling the engine kernel. The powerful MDK secondary development software package allows users to easily develop their own application software according to their operating habits and actual needs. The robot control system described in this article uses Visual Basic software as the development environment.
4.1 Software Development Process
The application software must first initialize the SMP system and start the RTX engine to run. SMP system initialization includes opening the SMP devices and loading system parameters. After successful system initialization and RTX engine startup, the system operation mode is set, the interrupt loop is enabled, and communication with remote devices is established. When the interrupt status of the main program loop is normal, the PLC engine is started and the servo motors are activated. In different operation modes, interface operation programs are written according to actual needs. During software development, the engine status and system information required for interface operation can be read in real time using the MAPI call statements and dynamic link files (DLLs) provided by the MDK secondary development package.
4.2 Teaching Operation Interface
The function of the manual teaching mode is to allow the operator to record the robot's position and posture and generate a welding trajectory. In the actual application of the robot, the operator needs to move the robot joints in manual operation mode so that the end of the welding torch always moves along the specified welding trajectory. Then, in teaching mode, the operator records the key position points during the movement process and inserts function commands such as opening the welding torch, closing the welding torch, inputting the welding speed, and pausing according to the welding requirements. Finally, the trajectory is saved to generate a reproducible teaching program [4]. The control of the welding torch in the program is to decode the M instruction and hand it over to the PLC engine for calculation, and control the start and end points of the welding torch through the PLC output points. The teaching function interface is shown in Figure 5. In the automatic operation interface, the operator can repeatedly call the saved teaching trajectory program to control the robot movement and complete the welding.
5. Conclusion
This paper introduces a robot control system based on a PC and Windows system, which boasts advantages such as stable operation, convenient system kernel upgrades, short application software development cycle, and a user-friendly interface. This system achieves coordinated control of a 6-DOF robot, completing the programming of functional modules including teach programming, parameter setting, and automatic operation. Paired with a Panasonic A4N series servo motor and a Guangdong Servo NBC-350 CO2 gas shielded welding machine, it has achieved excellent results in practical welding applications. By adjusting parameters such as welding speed, welding current, and voltage, the welding quality meets technical requirements, with accurate trajectory and smooth weld seams. Further research on the robot system will focus on the following two aspects:
(1) Conduct in-depth research on the velocity feedforward and acceleration/deceleration algorithms of robot motion to improve the positioning accuracy of the robot under high-speed motion, reduce vibration, and ensure the smoothness of robot motion;
(2) Establish a three-dimensional model of the robot, study the robot's inverse kinematics algorithm, plan the robot's spatial motion trajectory, and write an offline programming processing program.
References:
[1] Xie Cunxi, Zhang Tie. Robotics Technology and Its Applications [M]. Beijing: China Machine Press, 2005.
[2] RTEX_SMP_SetupGuide [Z]. Soft Servo System． U. S. A. 2006.
[3] MINAS＿A4N_Manual [Z]． Panasonic. Japan, 2005.
[4] Chen Shanben, Lin Tao, et al. Intelligent Welding Robot Technology [M]. Beijing: China Machine Press, 2006.
