*2.3. Communication, Synchronization and Control Architecture of Multifunctional Flexible Manufacturing Technology*

2.3.1. A/D/RML Control Architecture and Network Topology

SCADA (Supervisory Control And Data Acquisition) systems are used in industrial settings to monitor and control field devices from a distance remotely.

The complete structure of the A/DML real-time control served by ARS is shown in Figure 19. The presented control strategy is a hybrid structure, which consists of two interconnected systems, that features both distributed and centralized topology, with specific tasks for all the manufacturing stages. Moreover, for sequence control and synchronizing of all the routines of the manufacturing line, the control algorithm architecture is agent-based type, managed strictly through Siemens S7-1200 PLC from the FC, which acts as a Central System communicating with all subsystems' PLCs to control the complete manufacturing process by means of signal interface for sending and acknowledging commands or actions. In this control setup, every subsystem or slave from the presented technology of A/D/RML

assisted by ARS is considered to be an agent, which includes a separate control, managed by a local agent software synchronized with the master PLC [11].

**Figure 17.** ARS task scheduling for repair/replace Cylinder 1.

**Figure 18.** ARS task scheduling for repair/replace Cylinder 2.

**Figure 19.** Control structure of A/DML Hera&Horstmann and Flexible Cell ABB served by ARS.

Using SCADA system (Figure 20) along with both HMI's functionality (Figure 21) for controlling, real-time monitoring and visualizing the A/D/RML complete process, it integrates the following major functions:


### 2.3.2. ARS Control Input Design

In this approach, the mobile part of the A/D/RML, referred to as ARS with PeopleBot WMR from Mobile Robots, will be used and has an odometric system, two driving wheels and one rear freewheel. Additionally, an onboard embedded microcontroller is able to read the position information and send it, via WI–FI link, to a Remote PC according to a specific protocol. The SCADA application from the Remote PC computes the control input and sends it to WMR. Additionally, the Remote PC sends the data to the A/D/RML PLCs [21,22]. For controlling the ARS and WMR movements between the parking/grabbing and placing positions, dedicated functions from the ARIA (Advanced Robotic Interface for Applications) programming package are used and the TTSMC algorithm is implemented [23–26].

**Figure 20.** SCADA with Siemens TIA implementation for A/D/RML.


**Figure 21.** Control and visualization of A/D/RML via Siemens HMI (KTP700).

The ARS is equipped with 7-DOF Cyton 1500 RM and eye-in-hand VSS for picking up the dismantled workpieces from the FC trays in the case of a repair/disassembly process and transporting them to their proper storage warehouses. The control of the ARS is based on 3 control loops:

• Control loop for the synchronization commands between Main PLC and ARS Cyton RM using Modbus TCP signals (Figure 22). As designed, the communication link between the Cyton RM and the Remote PC is performed wirelessly using a USB over Ethernet adapter and a specific TCP/IP protocol;



All three control loops communicate through Remote PC, which also acts as a SCADA server and controls the ARS, eye-in-hand VSS and Cyton 1500 RM and manages the synchronization with the FC, ML and the coordination between them.

#### 2.3.3. Communication and Synchronization between A/D/RML and ARS

As mentioned before, centralized architecture is used, where the Main PLC (Siemens S7 1200) acts as the master PLC and synchronizes the operation with the ARS, which handles the recovering process. The communication between master PLC (Flexible Cell S7-1200 PLC) and ARS is conducted via a Modbus TCP link (Figure 22).

The Modbus protocol was developed in 1979 by Modicon, Incorporated, for industrial automation systems, and it became an industry standard method for the transfer of discrete and analog I/O information and register data between industrial control and monitoring devices. Modbus TCP/IP shares the same physical and data link layers as the traditional IEEE 802.3 Ethernet and uses the same TCP/IP suite of protocols. Therefore, it remains fully compatible with the already installed Ethernet infrastructure of cables, connectors and network-related devices. Unlike traditional Ethernet, which was not considered a viable fieldbus for industrial control, Modbus itself is an a deterministic industrial application protocol, as it defines rules for organizing and interpreting data, but remains simply a messaging structure, independent of the underlying physical layer, and every message is sent or received in a finite and predictable amount of time. Modbus devices communicate using a master–slave (client–server) technique in which only one device (the master/client) can initiate transactions (called queries). The other devices (slaves/servers) respond by supplying the requested data to the master or by taking the action requested in the query. A master's query will consist of a slave address (or broadcast address), a function code defining the requested action, any required data and an error checking field. A slave's response consists of fields confirming the action taken, any data to be returned and an error checking field. Note that the query and response both include a device address, a function code, plus applicable data and an error checking field. A Modbus map is required to know how to interpret the data that is returned. Because TCP is a connection-oriented protocol, a TCP connection must first be established before a message can be sent via Modbus TCP/IP. Following the client–server principle, this connection is established by the client (master). This connection can be handled explicitly by the client user-application

software or automatically by the client TCP connection manager. More commonly, this is handled automatically by the client protocol software via the TCP socket interface, and this operation remains transparent to the application. All Modbus TCP/IP message connections are point-to-point communication paths between two devices, which require a source address, a destination address and a connection ID in each direction. Thus, Modbus TCP/IP communication is restricted to unicast messages only. The well-known port 502 has been specifically reserved for Modbus applications. A Modbus server will listen for communication on port 502. When a Modbus client wants to send a message to a remote Modbus server, it opens a connection with remote port 502. As soon as a connection is established, the same connection can be used to transfer user data in either direction between a client and server and may also establish several TCP/IP connections simultaneously [8].

Depending on the task performed by the A/D/RML, Repair process (one cylinder released) (Figure 11) or Disassembly process (all workparts released) (Figure 10), distinct command signals , as shown in Figure 23, will be needed for interfacing between master PLC S7 1200 and ARS:



**Figure 23.** Modbus message interface (Modbus Map).

In the same way, ARS must acknowledge that the received command/action from A/D/RML is handled (Figure 24); therefore, 3 synchronization signals will be used between ARS and master PLC S7 1200:


Network topology as shown in Figures 1 and 19 is implemented in the A/D/RML assisted by ARS. OPC UA is the communication data structure between SCADA and main PLC, integrated into an industrial system to provide a standard way for setting a secure and reliable data exchange between industrial devices of multiple vendors and software systems [29], but the other main reason for using this technology for the proposed assisted manufacturing line is that it operates and communicates with other industrial protocols. The flexible manufacturing line also runs with a multitude of protocols such as Profibus, Profinet, Modbus and Ethernet/IP.

**Figure 24.** Handshake sequence interfacing master PLC S7 1200 and ARS.
