A CAN Bus Based Control System for Joint Modular Robot

Transcription

1 A CAN Bus Based Control System for Joint Modular Robot Qingkai Han* a, Li Wang a, Yunpeng Ren b, Tianxia Zhang a, Bangchun Wen a a School of Mechanical Engineering, Northeastern Univeristy, Shenyang, China ; b R&D Institute, NHI Shenyang Heavy Machinery Group Co. Ltd, Shenyang, China ABSTRACT This paper is mainly about a new robot control system, which has open structures, and whose architecture is based on CAN bus for a joint modular robot. The hardware system of the joint control module is designed for signal sampling and processing, storage and communication. ATmega64 SCM is selected as the core processor. A CAN card is used for communication. FM256 RAM is used for storage and condensation. The monitoring software and lower level control processing software are developed with ZLGVCI interface functions of CAN bus, and in the ICC AVR IDE and AVR Studio online debug tool with C language. Some experiments are carried out to validate the basic functions of the control system. Keywords: Joint modular robot, control system, CAN bus 1. INTRODUCTION The CAN Bus (Controller Area Network BUS) is a kind of Serial Communication Protocol; it was firstly developed to solve the controlling and exchanging problems in vehicles by Bosch Company in the early 1980s. Nowadays, it can possess excellent network security, communication reliability and real-time ability and has been widely used in automobile industry and many other control areas too [1-3]. People now put forward higher requests to the robot capability, correspondingly, higher requests to robot control system. It is the development trend of currently robot control system that to have open structure, modularization and standardization. In robotics, the research on architectonic structures of robot control system is important, especially for its software and hardware. There are many investments on open control systems. The main research in open control system is to establish information exchange standardizations for function divisions and function elements in its architecture structure [4]. An open architecture modular control system was developed by OMAC in US [5]. Another system, OSACA (Open system architecture for control within automation system) is also popular in Europe [6]. Many Japanese companies are promoting the OSEC project (Open system environment for controller) and trying to make it as standardization in this field [7]. In the ASIMO robot (Advanced step innovative mobility, Honda, Japan), the distributed control system is chosen based on PCI bus [8]. In the THBIP-I humanoid robot developed by Tsinghua University, the control system is based as on CAN bus [9]. In the RPRS (Reconfigurable planetary robot system) developed by Shenyang Institute of Automation, China Academy of Sciences, the robot control system is composed with main planning module and performing module, and the transfers between two modules are based on CAN bus [10]. Here a new robot control system with an open structure is developed following the ideas of modularization and standardization, especially with an architecture based on CAN bus for the joint modular robot. The main achievement resolves correlated technique problems of joint control module, including hardware design technique and control system software design technique, which includes: the hardware system of joint control module with ATmega64 SCM, a suitable CAN card and some control processing programs with ZLGVCI interface functions of CAN bus, etc. In addition, some experiments are carried out to validate the basic functions of the control system. 2. COMPONENTS OF CAN BUS CONTROL SYSTEM The joint modular robot here is composed of many modules, and each module possesses one degree of freedom of translation or rotation, to move in a coordinate way to achieve any expected tasks. The total DOF of the robot system can be changed easily with more or less modules. The links are mostly regarded as rigid. Figure 1 shows a typical joint modular robot with 3 DOFs. *qhan@mail.neu.edu.cn; phone ; fax

2 Each joint module of the robot is an independent entity; its control system is one of field bus control strategy. The whole control system is surely open due to the design of independent joint module control unit based on CAN bus. The schematic diagram of the whole robot control system is shown in Fig. 2 as below. The main functions of a modular control unit are joint driving control, signal measurement and management, storage and communication between lower and upper computers. These functions are separately achieved in each joint module. upper computer CAN interface card CAN-bus joint module 1 joint module2 joint module n sensor sensor sensor Fig. 1. Three DOFs joint modular robot Fig. 2. Control system framework of joint modular robot based on CAN bus The forefront of the control system is all the sensors on the joint modular robot, signals include displacement, velocity, acceleration, force/torque, temperature and pressure are converted into analog voltage signals by the front sensors. The sensor signals are converted into digital signals by A/D converter after operational amplifiers and processed in the SCM. The SCM analyzes different input signals as required and uploads the in accordance to the upper master computer s instructions. Users can switch different options in the upper master computer control interface to realize real-time monitoring for the robot, including corresponding configuration parameters such as sampling frequencies and sampling length, transfer orders, through sending consequential orders to control bus. The control orders is sent to the CAN bus through the CAN intelligent interface card with the form of packet. The control software of upper computer is developed based on interface functions corresponding to the CAN interface card. 3. CONTROL SYSTEM HARDWARE The control hardware of CAN-bus-based joint module is designed as shown in Fig. 3. The hardware system takes an ATMEGA 64 SCM as its MCU. Through a stand-alone CAN controller chip SJA1000, a CAN bus driver PCA82C250 links to the CAN bus. The first two basic functions of signal acquisition and communications are firstly realized with the SCM system.

3 CAN-bus CAN communication interface storage CAN communication interface storage microprocessor microprocessor acquisition driver acquisition driver joint module 1 joint module n Fig. 3. Hardware structure frame of a joint module control unit Fig. 4. Control board of joint module control unit 3.1 Chips and assistant circuits of the main controller To achieve the needed functions, working accuracy and environment of the robot, the ATmega64, a higher-speed AVR series chip is chosen as the main controller of the control unit. It is an 8-bit RISC SCM and made by ATMEL Ltd. The assistant peripheral circuits around the SCM are fundamental and normally external circuits, including system reset circuit, JTAG interface circuit, and clock circuit and so on. 3.2 CAN communication interface design The CAN communication interface makes up of a stand-alone CAN controller SJA1000 and a CAN driver PCA82C250. They are connected with the MCU ATmega64 directly. (1) CAN controller SJA1000. A CAN controller is needed, as an external expansion due to the MCU doesn t have any CAN controller in it. Some producers like Philips, Intel, Motorola have a number of integrated chips such as 82526, SJA1000, 68C05X4/X16/X32 to support CAN bus Protocol. Here the Philips stand-alone CAN controller SJA1000 is selected, and it is used to response for the main functions of the CAN protocol physical layer and layer. It also can support the two typical models of BASIC CAN and pelican. Here the BASIC CAN (CAN 2.0A standardization) mode is chosen. The microprocessor accesses SJA1000 in an easy way as accessing its extended memories. (2) The CAN bus driver PCA82C250 is the important interface device connecting the CAN controller SJA1000 with the physical bus and affects network performance severely. It provides differential transmit and receives functions to the CAN bus. The 82C250 driver circuit has current limiting circuits internally and can prevent circuit shortages from power supply, grand or load caused by the transmit output pole. It can achieve three control modes, high-speed, slope control or wait, by different connections of pins R and S. When RS pin is connected to the ground, 82C250 works on the mode of high-speed way. When connected to a resistance R before grand, 82C250 can control the slopes of up and down to reduce RF interferences. The resistance is greatly performed when the resistance value is change from 15 to 200 kω in experiments. When RS pin is connected with higher voltage level, 82C250 works as the waiting mode. At that time, the transmitter to CAN bus turns off, the receiver works in the state of low current, and so it can respond to the dominant bit on CAN bus. (3) The CAN bus communication interface circuit. The microprocessor ATmega64 links to CAN bus through the standalone CAN controller SJA1000 and CAN bus driver PCA82C250. For the microprocessor ATmega64, SJA1000 is a bus interface, and its memory cells can be regarded as the out-of-chip memories. ATmega64 can access SJA1000 s register addresses in the way of expanded out-of-chip memories. When SJA1000 s AD0-AD7 connect to PA of ATmega64, CS (chip-selection) connect to PC7 of ATmega64, the out-of-chip memory addresses of CPU are referred to the SJA1000 in the case of PC7 of low voltage, and read and write operations can be applied. When ALE, WR, RD of

4 SJA1000 are connecting with the responding pins of ATmega64, and its INT connecting to INT7 of ATmega64, ATmega64 can access SJA1000 in the interruption mode. 3.3 Motor driving design Considering the rated loads of the robot links are not too much, step s, type BS57HB76-03, are selected as the driving s for all joint modules. The driver card, type Q2HB44, is a special step driving card with one/half step accuracy. The two-phase input electrical current is DC12V-40V in voltage and below 4A. When the driver is in its single pulse and one step mode, the MCU of the control system gives release signal MF, step signal PU and rotating direction signal DR through its ports PD2, PD3, PD4. Motor release signal MF decides s startup or shutdown. When MF is at low voltage, current is cut down and the is free. The higher or lower voltages of DR decide the rotating directions of. The PU frequency is parallel to the s rotating speed. The pulse number is parallel to the rotating angle. 4.1 Establishment of the communication protocols 4. CONTROL SYSTEM SOFTWARE The message delivery of CAN bus has two frames: standard and expanded, where the standard has 11 bites identifiers and the expanded one has 29. The message delivery of CAN has four different kinds of frames for denotation and control, i.e. -frame, remote-frame, error-frame and over-loading frame. When the system is turned on, the default frame of CAN controller SJA1000 is the standard. 4.2 Programs in lower computer The main tasks of the lower computer are acquisition and CAN communication. The programs in lower computer are designed in modular structures with several task modules being relatively independent. When the system turns on and its working modes are settled down, the main task program calls the corresponding modules to achieve needed functions following the order coming from the upper computer. The program flowchart of the lower computer is shown as in Fig. 5. Fig. 5. Program flowchart of the lower computer Fig. 6. The initialization flowchart of SJA1000 The tasks of CAN communication mainly include three subroutines: initialization of the SJA1000, transmitter and reception. Those three subroutines are the basic parts of a CAN communication.

5 The initialization of SJA1000 is to give initial values to the SJA1000 s interior registers only working under its reset mode. Initialization consists of the work routine setting, acquisition mask register (AMR) setting, acquisition code register (ACR) setting, timing register setting of bus, outputting mode register setting and interrupting register setting. The initialization flowchart is shown as Fig. 6. After the initialization, SJA1000 can go into its operation status for normal communications. Transmitting subroutine takes charge of the massage s transmitting. Based on the CAN technology specifications, the transmitting of massages is auto-accomplished by SJA1000. After combining the transmitted into a set of in specific patterns, the are sent into SJA1000 send buffers, the flag of send beg is then set in the order buffer and SJA1000 starts to transmit. The transmit course is controlled by interrupt-requester or control field status query symbol of CAN. Reception subroutine takes charge of the massage acceptance, which is also auto-accomplished by the CAN controller. When incepting the, CAN controller transmits to the incept buffer from bus. When the is valid, RBS register states set bit. The incepting program only reads from the incept buffers, then releases the incept buffer. There are two modes for reception, i.e. interrupting mode and query mode. Here both transmit and incept subroutines use the query mode. In addition, another important program is the acquisition. It mostly aims at the analog signals transmitted from the sensors. Data acquisition program is used to carry out the A/D converts based on the settled acquisition channels and acquisition frequencies, and save the converted digital signal into buffer, waiting processing and transmitting. 4.3 Programs in upper computer In a CAN-bus based network, the lower computer carries through all the control processes, including acquisition, processing and uploading, etc. Considering the limitations of lower computer resources, it is difficult for complex tasks like control arithmetic, analyses. A personal computer (PC) can be used as a general developing platform to achieve necessary tasks due to its friendly man-machine interface, complete software-developing environment and plenty soft-hardware resources. Here a PC is chosen as the upper computer for robot control system to make fulfill the following functions: (1) The initialization of control system; (2) Offering friendly man-machine interface such as browse and control interface; (3) Data storage, process and analysis; (4) Communication with the lower computer; (5) System diagnoses, error alarm and solving. The upper computer control interface is not only the system s operator but also a monitoring screen, which is convenient for users any interference. In the running of the system, the basic work flow is: (1) set the CAN interface parameters and connecting to startup the CAN card; (2) set the acquisition parameters and sending transmitting control orders; (3) convert the control orders to the CAN packet and sending to the corresponding module in lower computer; (4) receive signals from the lower computer and displaying them on the upper PC. The upper computer programs are developed in Borland C++ Builder 6.0, together with the interface functions of ZLGVCI for the CAN interface card which is also provided by the Borland company. 5.1 Data communication tests 5. EXPERIMENTS In order to test the communication speed, reliability and stability of the CAN bus net between the joint modules and the upper computer, some communication test are achieved. Basically, 8 bit are sent from main node at the upper computer to a joint module. The joint module receives and sends back them. If a byte is sent failed or the received byte is not correct, 1 time of error is taken in count. As some test results showing, only 1 error could take place after transmissions. The averaged time is only milliseconds for each communication circle. 5.2 Step control tests In order to check whether the step could rotate correctly and stably following the orders from upper computer, the output rotating speeds are measured.

6 The expected rotating angles and rotating speeds are set in the monitoring program of the upper computer. The robot joint module receives motion control orders and gives orders to drive its. The rotating speeds are measured and displayed in real time. The measured speeds show that the rotates smoothly as expected with only very slight differences. 5.3 Signal A/D tests In order to test the accuracy and stability of digital converting for analog signals in the robot control system based on CAN-bus, some different standard signals with different frequencies are sent to the robot joint modules. The measured link motions are transferred to the upper computer through CAN-bus in real time. All the input standard signals are compared with the received in the upper computer. Many test results confirm that the signal A/D speed and accuracy is enough for the control of the joint modular robot discussed here. 6. CONCLUSIONS The control system for a joint modular robot is designed here with a new structure based on CAN-bus. It is convenient for such a robot to add hardware and functions. The communication ability is also confirmed for the CAN-bus system. The finished control model for each joint can work independently with its own control processor, storage unit, sampling unit, and motion driver. All the hardware and software are accomplished for the joint modular robot control system. Some advanced control strategies are also achieved in the upper computer. Some basic experiment results confirm that the robot control system based CAN bus behaves with good performance in reliability, real-time. The new control system is open and can satisfy the requirements of a joint modular robot. Acknowledgments This work is financially aided by National Natural Science Foundation of China. (No: and ). REFERENCES 1. S. Chen, L. Liu, X. Yu, The design of CAN bus-based electronic control system for air-powered engine, Modern Machinery, (1), (2007). 2. J.Wang, Automotive electronics technology integrated control system based on CAN bus, Journal of Harbin Institute of Technology, 38(5), (2006). 3. K. Wu, CAN bus principles and apply system design, Beijing University of Aeronautics and Astronautics Press, Beijing, T. Wang, D. Qu, Open system architecture for control system for industrial robot, Robot, 24(3), (2002) 5. K. Nilsson, Integrated architecture for industrial robot programming and control, Robotics and Autonomous Systems, 29, (1999). 6. A. Gueorguiev, P. Allen, E. Gold, P. Blaer, Architecture and control of a mobile site-modeling robot, Proceedings of IEEE on ICRA, (2000). 7. H. Bruyninckx, Open robot control software: the OROCOS project, Proceedings of IEEE on ICRA, (2001). 8. Y. Sakagami, R. Watanabe, C. Aoyama, etc, The intelligent ASIMO: system overview and integration, IEEE/RSJ International Conference on Intelligent Robots and System, 3, (2002). 9. J. Zhao, L. Shao, Study on humanoid joint servo control system based on CAN bus, Robot, 24(5), (2002). 10. M. Wang, S. Ma, B. Li, etc, Design and implementation of a reconfigurable planetary robot control system, Robot, 27(3), (2005).

7 ISI Web of Knowledge [v.4.7] - 所有数据库全记录 页码,1/ 登录我的 EndNote Web 我的 ResearcherID 我的引文跟踪我已保存的检索注销帮助 体验新版本 : - 中国科学引文数据库 - Web of Science 检索检索历史标记结果列表 (0) 所有数据库 << 返回结果列表第 12 条记录 ( 共 39 条记录 ) Web of Science 中的记录 A CAN bus based control system for joint modular robot - art. no / 施引文献列表 : 0 本文已被引用 0 次 ( 来自 Web of Science) Shanghai Jiaotong University 更多选项 作者 : Han QK (Han, Qingkai) 1, Wang L (Wang, Li) 1, Ren YP (Ren, Yunpeng), Zhang TX (Zhang, Tianxia) 1, Wen BC (Wen, Bangchun) 1 编者 : Sasaki M; Sang GC; Li Z; Ikeura R; Kim H; Xue F 来源出版物 : ICMIT 2007: MECHATRONICS, MEMS, AND SMART MATERIALS, PTS 1 AND 2 丛书 : PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS (SPIE) 卷 : 6794 页 : 子辑 : Part 1-2 出版年 : 2008 被引频次 : 0 参考文献 : 10 引证关系图 会议信息 : 4th International Conference on Metronics and Information Technology (ICMIT 2007) Gifu, JAPAN, DEC 05-06, 2007 Gifu Univ, Fac Engn; Korea Japan Joint Adv Mechatron Res Assoc; Japan Soc Appl Electromagnet & Mech, Biomed & Welfare Div; Yamaguchi Univ, Inst BWE; Gifu Convent Ctr; GES Inc; KAHA Inc; Chongqing Inst Technol; Soc Instruments & Control Engineers; Chinese Assoc Artificial Intelligence; Inst Control, Automat & Syst Engineers; Robot Soc Japan; Nat Sci Fdn China; Korea Soc Precis Engn; Japan Soc Mech Engineers; Chongqing Artificial Intelligence Soc; Korea Inst Informat & Telecommun Facilities Engn; Fukushima Univ, Fac Symbiot Syst Sci; Intelligent Automat Comm Chinese Automat Assoc; Inst Elect Engineers Korea Related Records: 根据共同引用的参考文献查找相似记录 ( 来自 Web of Science) [ 查看 Related Records ] 参考文献 : 10 查看此记录的题录信息 ( 来自 Web of Science) 其他信息 在其他数据库中查看此记录 : 查看引文数据 ( 来自 Web of Science) 摘要 : This paper is mainly about a new robot control system, which has open structures, and whose architecture is based on CAN bus for a joint modular robot. The hardware system of the joint control module is designed for signal sampling and processing, storage and communication. ATmega64 SCM is selected as the core processor. A CAN card is used for communication. FM256 RAM is used for storage and condensation. The monitoring software and lower level control processing software are developed with ZLGVCI interface functions of CAN bus, and in the ICC AVR IDE and AVR Studio online debug tool with C language. Some experiments are carried out to validate the basic functions of the control system. 文献类型 : Proceedings Paper 语言 : English 作者关键词 : joint modular robot; control system; CAN bus 通讯作者地址 : Han, QK ( 通讯作者 ), Northeastern Univ, Sch Mech Engn, Shenyang , Peoples R China