2.1.1. Hardware Structure of A/D/RML

An experimental A/D/RML assisted by ARS is developed at the laboratory level that works in real-time, for testing purposes and for the implementation of different methods and techniques for analyzing, optimizing and manufacturing line balancing, to study the actual technology and improve efficiency, reliability and precision. Figure 1 shows the basic design concept of the A/D/RML, consisting of 3 major subsystems, which operate, communicate and synchronize together by means of PLCs and SCADA and act as a single flexible manufacturing line that performs several tasks such as assembly, the disassembly of 2 different products with reprocessing, repair and components recovery functionality.

The main A/D/RML hardware components are:


• ARS—WMR PeopleBot equipped with an RM Cyton 7-DOF used for recovery, transport and return operations for the dismantled components.

**Figure 1.** Structure of A/DML Hera&Horstmann and Flexible Cell ABB served by ARS.

The A/D/RML, as described above, is characterized by a modular structure. The hardware structure consists of 2 Siemens PLC controlled subsystems/modules with specific tasks for all the manufacturing operations. FC is a RM pick-and-place station, Siemens S7-1200 PLC controlled assembly/disassembly station, positioned next to mechatronics line, which handles the supply of workparts, assembly and transport for workpiece product type 1 (WP1) on the manufacturing line, acting as a feeding unit and handles the disassembly and repair operation for workpiece product type 2(WP2) upon request. The Hera&Horstmann mechatronics laboratory line is a Siemens S7-300 PLC controlled subsystem that has a predefined role as a logistics unit that assemblies individual workparts into workpiece product type 2(WP2), transports between workstations and stores the assembled workpieces on the final storage place—Storage Rack Tower.

The PLC-based hardware and software design architecture, as seen in Figure 2, is a hybrid structure that features both distributed and centralized topology:


Each PLC hosts several routines for automatic control but the manual, initial task for choosing and starting the manufacturing process operation is made remotely from SCADA or locally from HMIs. The assembly/disassembly and processing/reprocessing routines are managed strictly through Siemens S7-1200 PLC from the FC, which acts as a Central

System that handles visualization and manages the overall operation of the complete A/D/RML [15].

**Figure 2.** A/D/RML PLC Network hardware structure.

In the mechatronics line, Siemens S7-300 PLC communicates with the I/O field via Profibus (magenta line Figure 2). The Profibus link is used for communicating and the control of the transporting conveyor belts drives, workpiece positioning and PLC to PLC synchronization methods as well as for handshake and signal exchange interface with the FC by means of a Profibus adapter. An additional HMI (Siemens TP 177) is connected for process visualization purposes only. FC communication is based on the industrial Ethernet network Profinet technology (green line Figure 2) for communicating with the main HMI (Siemens KTP 700), ABB IRB120 Robot controller and Intelligent Siemens Servomotor Drives Sinamics V90 with accurate positioning control functionality. The compatibility between the FC and mechatronics line, by means of communication, is performed as mentioned before, via a Profibus adapter to bridge/interconnect the 2 different communication technologies: Profinet (protocol based on the Industrial Ethernet) and Profibus (protocol based on serial communication).

For disassembly or repairing tasks, pick-and-place and transport actions are performed by the ARS with the help of the Cyton RM, which is equipped. First, the FC station with the ABB robot dismantles or repairs the workpiece by replacing the bad components and sliding them on a specific tray. Then, the ARS system will grab the recovered workparts for transporting and place them into the designated storage ML locations. Several synchronization signals will be needed between the master PLC and ARS by means of the Modbus TCP protocol, a standard communications protocol widely used in industrial automation. These signals will be sent when the FC station has ended the repair/disassembly action and the dismantled component (workpart) is released and ready for recovery by the ARS. Synchronization acknowledgment signals will be returned when ARS is busy handling a task such as reprocessing/transport or when placing operation job is completed and ARS becomes available again.

For the developed technology, at the PLC level, several algorithms have been developed by using Siemens programming packages such as TIA Portal, Step7 Manager, as

well as WinCC Flexible for the HMIs. SCADA is developed on the Remote PC and also in TIA Portal. In both PLCs, modular programming is used; functions or function blocks are created as an entity, providing a particular functionality or controlling a particular type of device in the system (ABB Robot, conveyors motors, storage, electrical and pneumatic actuators). During each scan, the PLC reads all local and remote inputs, executes every function in a predefined order (using IRQ) and updates all outputs at the end of each scan. PLC programs and algorithms are mainly programmed with Structured Text (ST) or Structured Control Language (SCL) which, according Siemens, corresponds to the IEC 1131-3 language "ST". SCL opens up several new constructs that are unavailable while programming in conventional ladder logic, including the FOR and WHILE loops as well as the CASE statement. These are particularly useful when dealing with large amounts of data in an array form. Using SCL also increases the readability of any sort of arithmetic calculation. The instances of Function Blocks are executed in the cyclical order in every PLC scan (10–12 msec time range). An additional part of the PLC program is the Modbus TCP link between master PLC from the FC station (S7-1200 PLC) and ARS. For that a Modbus TCP Server is configured and programmed, as shown in Section 2.3.3, in the Main Routine of the Siemens master PLC at the beginning of the scan, prior to the program execution, to establish and maintain a stable connection and a quick data exchange/synchronization signals with the ARS.

As shown in Figure 2, a separate Profibus communication link is used to interface data between both PLCs. This data must be sent and received between the master PLC and Siemens S7-300 PLC via the Profibus communication adapter.
