TCP/IP Protocol Utilisation in Process of Dynamic Control of Robotic Cell According Industry 4.0 Concept

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1 TCP/IP Protocol Utilisation in Process of Dynamic Control of Robotic Cell According Industry 4.0 Concept Juhasova Bohuslava, Juhas Martin, Halenar Igor Institute of Applied Informatics, Automation and Mechatronics Faculty of Materials Science and Technology in Trnava Slovak University of Technology in Bratislava Trnava, Slovakia Abstract Communication and possibilities of flexible manufacturing systems control through a variety of communication protocols are described in this article. The main core of the article is to design robotic cells control by using the standard Ethernet (non-rt) while maintaining safety and quality of production, and the system is able to dynamically respond to changes in the production process. The core of the practical part is to design communication via the TCP/IP and socket technology, robot software design and the result of trials performed under real conditions in a heterogeneous environment of the production line with multiple types of robots and conveyor belt. Keywords robots; communication; dynamic control; socket; Industry 4.0 I. INTRODUCTION The communication and control of automation systems can be done through multiple homogeneous or heterogeneous network interfaces such as EtherNet/IP [7], Profinet [11], Profibus [12] and as well as by using Fast Ethernet and Gigabit Ethernet via metallic, fiber-optic or wireless network. Using classical ethernet networks there are mainly two popular RTE networks defined by IEC 61158, namely Ethernet POWERLINK (EPL) [15] and EtherCAT [16]. These protocols are just extension to existing TCP/IP communication and it is a software solution. Also in automation systems exists a number of other protocols that are used for communication and device control. All of the communication is realized through one or more network components like switches and routers. Utilization of these multiple interconnections among multiple devices while ensuring safety and reliability is very complex, especially in dynamic and heterogeneous environments. Our work is to try to use the classic non-rt ethernet network to control of a flexible manufacturing cell. Flexibility and production variability is in present days very important for new production standards based on Industry 4.0 [13]. II. CURRENT STATE OVERVIEW Numerous scientific papers are dedicated to communication in industrial networks and the area itself is very well researched and verified by real-life usage. The Fieldbus probably is the most widespread protocol. There are several standard and widespread fieldbus protocols available in the market, such as Control Area Network (CAN), WorldFIP, DeviceNet, Modbus, Profibus and Foundation Fieldbus (FF) [9]. Another group of protocols used for controlling in automation are protocols based on the Ethernet protocol. This is particularly the Profinet, which should replace the PROFIBUS with an Ethernet-based network. All of the interfaces offered for PROFIBUS are also offered for PROFINET. The obvious advantage is Ethernet s higher data rate and extension with both fiber-optic cabling and, lately, with Wi-Fi wireless transmission. The work of Caro, D. [6] provides a very good overview of the protocols used in automation. Every leading manufacturer of industrial automation systems would prefer to create a family of industry standards under their own control. Some choose to work closely with recognized standards-making organizations such as ISA, while others choose to work together with industry supporting organizations where they have more direct control such as ODVA (Open Device Vendors Association) or the HART Communications Foundation. CIP [6] is a common data-formatting applications layer published by ODVA for use with the set of communications networks originally created by Rockwell Automation: DeviceNet, ControlNet, CompoNet, and EtherNet/IP. All of these are now included in CPF 2 of the IEC fieldbus standard. The most recent reports include the previously mentioned Powerlink [15] and EtherCAT [16]. Their advantage is that they use the standardized IEEE protocol and conventional Ethernet devices. Vitturi et al. [4] in their work describe the use of these protocols for control. They evaluate the quality of control engine and sensors through these protocols. Also the work of authors Joonkyo Kim Bum Yong Lee, and Jaehyun Park [5] nicely describes the possibility of using RTE in control of the motion elements in real time. A very interesting solution of connecting communication networks based on Ethernet fieldbus is described in the thesis of Geng Liang [9]. It primarily focuses on describing the development of a distributed control system. Here, also fieldbus communication protocol is used for direct control of processes and network type 100M Industrial Ethernet is a connected control and predictive system that is not directly used to control the actuator. The thesis, however, shows an interesting way of control with predictive models based on BPNN created by Matlab. The available

2 literature in this area essentially indicates that classical, traditional switched Ethernet and traditional applications do not meet the requirements for implementation in RT environment. In practice, hybrid communication systems are the most commonly used. There are four types of applications, that are non-rt applications (diagnosis, maintenance, commissioning, slow mobile applications), soft RT applications (processes in manufacturing and process automation, data acquisition), hard RT applications (control applications, fast mobile applications, machine tools) and isochronous hard RT applications that are used in motion control. This is also consistent with the transport protocols used, which are designed primarily for direct control of motors and sensors and data transmission in the network is carried out preferably in real time. This control method requires the use of specialized components and transmission technologies. There are solutions, where the lack of non-rt network is designed so that the communication is routed through some other kind of transmission bus, such as the one referred to in by Bok-Jin Youm and Jaehyun Park [2], or artificial extension of Ethernet networks throughput by using additional devices - M. Nader, Al-Jaroodi, J. [1]. The work of authors Nazmin Arif Mohd Noh et al. [8] is another example from the field of robotics of using additional hardware to secure RT communication in non-rt environment of Ethernet network. In our work we describe the possibility of using standard Ethernet (IEEE 802.3) protocol in production control in a special case where the manufacturing process control uses conventional communication via TCP/IP protocol, which does not satisfy the requirements of RT (non-realtime) transmissions. In addition, it is not necessary to use any additional devices or other subprotocols. The condition is that the devices used be sufficiently autonomous and not dependent on precise timing of control information. III. DESCRIPTION OF THE PROPOSED SOLUTIONS The basic communication protocol used in our model of the production robot cell is TCP/IP. TCP/IP is equivalent to four layers of the OSI model and for communication it is possible to use two variants of the service. Connection service is represented by TCP protocol, while protocol UDP represents connectionless service. IP protocol is responsible for packets delivery within the network. Both protocols (TCP, UDP) are used for delivering messages to objects on the application layer using lower service model IP protocol. They also use ports for communication with the applications. Port is an application interface that is used for data exchange between programs on remote computers. The TCP/IP protocol has 16-bits defined for port numbers for TCP and UDP protocol. TCP protocol is able to recover lost packets, solve duplicate packets and produce reliable connection. In contrast, the UDP protocol does not provide control over transmitted packets. Within a design of a robotic cell with dynamic control design a communication client is used - server through the TCP protocol with a socket communication extension within the applications. Control application is divided into several parts. It consists of a server, running on the control computer and client subprograms positioned and executed at the individual robots. Fig. 1. Socket client-server communication in network application In network environments the application address within the communication network consists of a combination of known communication parameters. Namely the combination of IP address and TCP communications port of a particular application. TCP port number is a 16-bit value which means the number of addressable application is limited. Our solution uses this method of addressing application s input buffer on both sides. Similarly on the client side and server side, with the role of each device during the operating cycle not being fixed and held in a robotic cells in both directions, while the combination of IP address and TCP port represents an instance in a networked environment to the control program.

All requirements of all participating executive cells elements (slave) as well as all instructions from the control center of the cell towards the end devices will be processed as a TCP/IP sockets.

Creating an instance through combination of TCP and IP protocols in network environment - socket A particular example of the communication socket form containing an address and also the information

3 All requirements of all participating executive cells elements (slave) as well as all instructions from the control center of the cell towards the end devices will be processed as a TCP/IP sockets. Fig. 3. TCP/IP Socket example Fig. 2. Creating an instance through combination of TCP and IP protocols in network environment - socket A particular example of the communication socket form containing an address and also the information part is shown in Fig. 3. A. The Principle of Using TCP/IP Sockets for the Robotic Cell Control Robot cell model consists of three heterogeneous robotic arms, each with its own control system. Each of the two manipulators IRB 120 and IRB 140 manufactured by ABB has its own IRC5 compact controller with the possibility of using network communications via the Ethernet interface. Control of the manipulator Mitsubishi Melfa RV-2FB-D provides the controller CR750-D, which also allows network communication by means of Ethernet interface. Concept for the entire robot cell system can be realized in several ways. One option is to use the central control computer that will serve as a major superior communication node (master). The cell communication will take place exclusively via the control node. Communication via TCP sockets in this case is implemented using software Matlab based on the use of functions created in the Java language [14, 19]. An alternative could be any software tool enabling TCP/IP sockets software processing. In this case, the software Matlab was chosen because it is widely used for various scientific and technical applications and computing, including computer image processing to identify a static object, or tracking the trajectory of moving objects. These features are possibly useful in the next stage of development of the robotic cell, where the plan is to use a computer vision to guide the robotic arms to randomly distributed objects or moving object on a conveyor belt. Another way of controlling cells is to use control concept of master-slave type without central control computer. In this case, the control element is directly chosen from participating executive objects - robotic manipulators, or rather their control systems. Complete communication by means of TCP/IP sockets then takes place only through this element and it is this element that is responsible for the co-operation of activities of all cell elements. In both cases, the coordination of activities of robotic cells is carried out based on the messages exchanged in the form of TCP/IP sockets in two possible variants: Confirmed coordination - the completion of each operation or set of continuous operations by subordinated (slave) object is correctly notified to the control (master) object. The next operation, or the operations sequence

4 can be initiated only after receiving confirmation message from the control object. Without receiving this confirmation message subordinate object is not allowed proceed with in any activity. Unconfirmed coordination - Subordinated objects operate with simultaneous sending of interim reports to the control object. Continuation of the activity is not conditional on receiving a confirmation message from the superior object. Communication requires the opening of communication channel by the master object and its confirmation by the both slave devices: Mitsubishi robot Open "COM3:" As#1 Open "COM4:" As#2 ABB robot SocketCreate client_socket; SocketConnect client_socket," ",9999 \Time:=5; Confirmed coordination involves sending a terminating message on the side of the slave and waiting for a confirmation message: Fig. 4. The model robotic cell B. The Implementation of TCP/IP Communication in Robot Cell In the model case the concept of operation control of the robotic cell without central control computer is used. As master object (master) is chosen control system Mitsubishi CR750-D of Mitsubishi Melfa RV-2FB-D robot. Robots ABB IRB 120 and IRB 140 with the IRC5 Compact control systems are in this case the child objects (slave). TABLE I. ABB IRC5 COMPACT CONFIGURATION [17] SocketSend client_socket\str:="irb120 - done"; SocketReceive client_socket\str:=s_receive_string \Time:=120;!waiting Sending of confirmation message from the master that allows slave object activities is provided by using commands: Print #1,"IRB120 - continue" {MELFA BASIC operation commands} Print #2,"IRB140 - continue" Unconfirmed Coordination involves sending of continuing messages by slave objects without waiting for a confirmation message: Robot IRB IRB IP Address data:={technical data}; SocketSend client_socket\rawdata:=data; TABLE II. MITSUBISHI CR750-D CONFIGURATION [18] Parameter Value NETIP COMDEV 2 (OPT13) NETMODE 1 (SERVER) NETPORT 9999 CRPCE 2 (DATALINK) Evaluation of continuing messages of the slave objects is provided by master object. When an intervention by the control system to the process of coordination of the cell activity is necessary, the master element sends a control message to the particular slave object: Def Char message message from IRB 140 Input #2,message$ If {condition based on message} Then Print #1,"IRB120 do operation number X" EndIf

5 IV. CONCLUSION The article deals with the problem of communication in the environment of production systems created based on Industry 4.0 standard. It provides an overview of the most commonly used types of communication protocols, which are used in process control. Further are described possibilities of using classical non-rt Ethernet setup in control of technological processes. These findings are applied in the process of control of model robotic cell. Selected protocol provides an exchange of control information between control elements and other executive elements in this cell. There are described two possible scenarios designed cell control and there are also specified two options of communication forms between control system and the controlled objects. ACKNOWLEDGMENT This publication is the result of implementation of the project: UNIVERSITY SCIENTIFIC PARK: CAMPUS MTF STU CAMBO (ITMS: ) supported by the Research & Development Operational Program funded by the EFRR. This publication was written with financial support of the KEGA agency in the frame of the project 040STU-4/2016 Modernization of the Automatic Control Hardware course by applying the concept Industry 4.0 This publication is the result of implementation of the project VEGA 1/0673/15: Knowledge discovery for hierarchical control of technological and production processes supported by the VEGA. This publication is partial result of the project: Modelovanie a simulacia robotickeho dynamickeho systemu (MTF2016/008) REFERENCES [1] Nader M., Al-Jaroodi, J, Self-configured multiple-network-interface socket in Journal of Network and Computer Applications, Volume 33, 2010, pp [2] Bok-Jin Youm, Jaehyun Park, Tcp/ip protocol over ieee-1394 network for real-time control applications in. IFAC Proceedings Volumes Volume 38, Issue 1, 2005, pp [3] Michael J., Donahoo and Kenneth L. Calvert, TCP_IP_Sockets_in_C Practical_Guide_for_Programmers, Elsevier USA, ISBN-13: , 2001, 130 p. [4] S. Vitturi, L. Peretti, L. Seno, M. Zigliotto, C. Zunino, Real-time Ethernet networks for motion control in Computer Standards & Interfaces Vol. 33, 2011, p [5] Joonkyo Kim, Bum Yong Lee, Jaehyun Park, Preemptive Switched Ethernet for Real-time Process Control System in 11th IEEE International Conference on Industrial Informatics (INDIN) 2013,pp [6] D. Caro, Industrial data communications protocols and application layers in Industrial Wireless Sensor Networks Monitoring, Control and Automation A volume in Woodhead Publishing Series in Electronic and Optical Materials 2016, pp [7] John Rinaldi, An Overview of EtherNet/IP. An Application Layer Protocol for Industrial Automat, online, available at /07/EIP_Overview1.pdf [8] ion. Young, The Technical Writer s Handbook. Mill Valley, CA: University Science, 1989 [9] Nazmin Arif Mohd Noh, Azilah Saparon, Habibah Hashim, Real Time FPGA Communication System Using Ethernet for Robotics in Procedia Computer Science Volume 76, 2015, Pages [10] Geng Liang, Control and communication co-design: Analysis and practice on performance improvement in distributed measurement and control system based on fieldbus and Ethernet in ISA Transactions Volume 54, 2015, pp [11] PROFINET System Description, Siemens, 2008, online, available at tekniikka/teollinen_tiedonsiirto/profinet/man_pnsystem_description.pdf [12] PROFIBUS Technical Description. PROFIBUS Brochure - Order-No Online, available at TTK4175/Lab/Profibus/Profibus-Technical%20Description.pdf [13] I. Veza, M. Mladineo, N. Gjeldum, Managing Innovative Production Network of Smart Factories in International Federation of Automatic Control,2015, pp [14] MathWorks Matlab - Instrument Control Toolbox, online, available at [15] Ethernet POWERLINK Standardization Group, Ethernet POWERLINK communication profile specification V. 2.0, online, available at [16] EtherCAT Technology Group, EtherCAT: Ethernet for control automation technology, online, available at [17] ABB robotics: Technical reference manual - RAPID Instructions, Functions and Data types. ABB ABRobotics Products SE Västerås, Sweden, 2010 [18] Mitsubishi Electric Corporation: CR750/CR751 Series Controller INSTRUCTION MANUAL. MITSUBISHI ELECTRIC EUROPE B.V. GERMANY [19] MathWorks Matlab - Call Java Libraries, online, available at

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