*Article* **Communication and Control of an Assembly, Disassembly and Repair Flexible Manufacturing Technology on a Mechatronics Line Assisted by an Autonomous Robotic System**

**Dan Ionescu 1,2,\*, Adrian Filipescu 1,2, Georgian Simion 1,2, Eugenia Mincă 2,3, Daniela Cernega 1, Răzvan S, olea <sup>1</sup> and Adriana Filipescu <sup>1</sup>**


**Abstract:** This paper aims to describe modeling and control in what concerns advanced manufacturing technology running on a flexible assembly, disassembly and repair on a mechatronic line (A/D/RML) assisted by an Autonomous Robotic System (ARS), two robotic manipulators (RM) and visual servoing system (VSS). The A/D/RML consists of a six workstations (WS) mechatronics line (ML) connected to a flexible cell (FC) equipped with a 6-DOF ABB industrial robotic manipulator (IRM) and an ARS used for manipulation and transport. A hybrid communication and control based on programmable logic controller (PLC) architecture is used, which consists of two interconnected systems that feature both distributed and centralized topology, with specific tasks for all the manufacturing stages. Profinet communication link is used to interconnect and control FC and A/D/RML. The paper also discusses how to synchronize data between different field equipment used in the industry and the control systems. Synchronization signals between the master PLC and ARS is performed by means of Modbus TCP protocol and OPC UA. The structure of the ARS consists of a wheeled mobile robot (WMR) with two driving wheels and one free wheel (2DW/1FW) equipped with a 7-DOF RM. Trajectory tracking sliding-mode control (TTSMC) is used to control WMR. The end effector of the ARS RM is equipped with a mobile eye-in-hand VSS technology for the precise positioning of RM to pick and place the workparts in the desired location. Technology operates synchronously with signals from sensors and from the VSS HD camera. If the workpiece does not pass the quality test, the process handles it by transporting back from the end storage unit to the flexible cell where it will be considered for reprocessing, repair or disassembling with the recovery of the dismantled parts. The recovered or replaced components are taken over by the ARS from disassembling location and transported back to the dedicated storage warehouses to be reused in the further assembly processes.

**Keywords:** programmable logic controller; modbus TCP; open platform communications; visual servoing system; wheeled mobile robot; industrial robotic manipulator

### **1. Introduction**

The continuous development of software and automation in industrial environments brings new concepts for communication, design and control for manufacturing technology. There is a growing need for high-speed robotic assembly and transport of small parts, which often means higher throughput and greater precision than can be achieved using human labor [1].

**Citation:** Ionescu, D.; Filipescu, A.; Simion, G.; Minc ˘a, E.; Cernega, D.; S, olea, R.; Filipescu, A. Communication and Control of an Assembly, Disassembly and Repair Flexible Manufacturing Technology on a Mechatronics Line Assisted by an Autonomous Robotic System. *Inventions* **2022**, *7*, 43. https://

doi.org/10.3390/inventions7020043 Academic Editor: Luigi Fortuna

Received: 15 May 2022 Accepted: 10 June 2022 Published: 15 June 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

This study focused on the implementation, simulation and system design of the hybrid communication and control for the advanced flexible manufacturing technology presented on a laboratory system that integrates several subsystems and different field equipment and autonomous robotic systems (ARSs) [2]. A fully automated assembly line assisted by mobile robots is still in its early stages and is not yet widely used. ARSs are extremely flexible because once the facility map is built, they can travel from one destination to the next, autonomously avoiding obstacles along the way, unlike conveyor systems that have limited flexibility, and are quite expensive and time-consuming to reconfigure [3].

The objective of this research is to introduce a new perspective upon the framework of manufacturing technology design where implementation and setup was based more on engineering experience and less on simulations, investigation and validation methods to increase efficiency and to evaluate the performance of the manufacturing lines assisted by ARS [4].

The main elements of originality and contributions are concentrated in the following areas: task scheduling and assigning; planning and synchronization of A/D/RML assisted by ARS, RMs and VSS; Petri Nets modeling; hardware architecture design of the entire system to allow flexible manufacturing, communication concepts, supervisory control and data acquisition (SCADA) [5]; implementation and network topology, synchronization of signals from sensors and between subsystems, distributed control and image processing for precise positioning; VSS and real-time control for implementation of a fully automated manufacturing technology; improving the automation level; security; and increasing the efficiency by using the ARS IRM with VSS technology [6,7]. The presented flexible manufacturing concept allows the assembly of two different products and complete disassembly or repair of the products depending on the quality test. Disassembled components from the rejected products are recovered by ARS and placed back in the designated storage compartments. The recovery process implementation allows the reuse of the products subcomponents through reprocessing, technology that works automatically, completely independent without the operator intervention, increasing efficiency, productivity and safety [8].

The presented technology for flexible assembly, disassembly and repair with components recovery, consists of an assembly/disassembly mechatronics line (A/D/ML), a flexible cell (FC), which is an assembly/disassembly station with an integrated 6-DOF industrial robotic manipulator (IRM), and an ARS which is a WMR equipped with a 7-DOF RM and an eye-in-hand visual servoing system (VSS) [1,2]. Along with the communication concept and real-time implementation, several aspects will be discussed regarding the design of the flexible manufacturing technology, such as: task planning, hybrid modeling, simulation, sensors and actuators, interoperability between field level devices, synchronization, data acquisition, remote monitoring and control [9].

An assembly/disassembly and repair flexible manufacturing line (A/D/R/ML), consists of the following subsystems: IRMs, WMRs, workstations and manufacturing cells, component storage units, transporting system (conveyor belts) and monitoring, control and data acquisition systems, able to perform specific tasks for manufacturing technology such as product assembly, quality check and repair or disassembly operations with components recovery, including a reconfigurable manner that confers reversibility, repeatability, and last but not least, flexibility [3]. The main idea of flexibility added to a manufacturing line, a FML (Flexible Manufacturing Line), means a technology capable to automatically manufacture different products, in small or medium batches, without adding hardware changes or the complete redesign of the system.

The automatic control of all system components and automatic supervision, controls and diagnosis is performed with the help of two PLCs in a hybrid hardware architecture for controlling all the subsystems of the complete A/D/RML and managing the process and operation facilities, thereby coordinating control tasks as well as synchronizing the operations of the ARS with process timings [10]. On top of that, for controlling assembly/disassembly and repair for the flexible manufacturing line, the algorithm architecture is agent-based

control, in which the PLC from the FC station acts as a main control unit, or "master PLC", for centrally managing both subsystems of the complete A/D/RML by means of synchronization and confirmation signals [11]. Therefore, master PLC synchronizes with subsystems PLCs to automate their respective areas and for operating and controlling locally their components, after confirmation from the main control unit is applied.

The presented hardware structure includes two Human-Machine Interfaces (HMI) as operator control panels for both major subsystems (A/D/ML and FC) and a SCADA application running on the Remote PC as the main visualization, control and data acquisition system. The information to perform the flexible manufacturing process tasks is obtained from the system using IO Field Devices such as sensors, cameras, measuring devices and transducers and is processed by the PLCs and interfaced via a communication link with Remote PC or SCADA [5].

Industrial development has been evolving rapidly, bringing new smart technologies to automation systems and becoming more dynamic and adaptable production systems. Visual servoing is a commonly used technology in combination with RM and works by processing and implementing the results obtained from several research fields such as real-time image analysis and processing, robotics, control theory and systems and real-time application design. Therefore, a visual sensor—an HD camera—is connected on the end effector, "the eye" of the RM, which allows the visual inspection and investigation of the working environment without contact with its elements. VSS behavior is mainly influenced by the type of visual features used to generate control law [12]. There are several VSS control architectures corresponding to the servoing systems; in this approach, the Hybrid Visual Servoing (HVS) architecture is used for driving the mobile VSS mounted on the ARS robot manipulator [13,14].

The rest of the paper is organized as follows: the proposed hardware technology of the A/D/RML assisted by ARS is presented in Section 2.1 describing FC, ARS and eye-in-hand VSS control architectures; in Section 2.2, Petri Nets modeling is presented and also task planning and scheduling for each of the flexible manufacturing operation; in Section 2.3, the communication concept of the A/D/RML assisted by ARS is described; real-time control results for assembly, disassembly and repair operations are shown in Section 3; Section 4 provides a vision of the experimental laboratory level A/D/RML assisted by ARS, discusses the real-time control results and highlights the laboratory tests limitations of the study and Section 5 is reserved for final conclusions of the approach from this research paper, draws the main research findings and gives an insight to future directions for research/recommendations.
