Limitations and advanced development

The purpose of this section is to address the limitations of the framework and to introduce a list of advanced features that should be implemented as improvements to the system.

As discussed in chapter 3, a hybrid control architecture was adopted for the control of the mobile robots. The centralised part of the scheme is attributed to the OPC Server and this

makes it a single point of failure in the network. In order to reduce this risk, a redundant OPC Server can be implemented to ensure the availability and robustness of the system. This can be achieved in one of three ways; either cold, warm, or hot standby modes, depending on the time requirement of having the secondary system online. A hot standby would require the simultaneous operation of both primary and secondary OPC Servers, each using separate hardware so that there is no single point of failure. In the event of a primary failure, the switchover is instantaneous with no data loss, contrasted to the cold or warm cases where the recovery process is slower. The two OPC Servers would typically connect to a redundancy management system that is responsible for the switch over, data integrity, and maintenance of the single point of connections between OPC Clients.

In an Industry 4.0 factory, where the ease of access to data is essential, the establishment of security measures is critical to ensure that valuable data is protected against theft or loss. The OPC component of the framework does contain security protocols that ensure: 1) the authentication of clients and servers, 2) the authorisation of users, and 3) the integrity and auditing of communication between clients and servers [112]. In addition to this, OPC security is based on industry standard security algorithms and can be scalable to meet the environment and application requirements [112].

The ROS component of the framework is however, insecure in its communication protocol. The developers of ROS are currently implementing SROS, a set of security enhancements to ROS [113]. The motivation behind this development is the increase trend in cyber threats which poses great risks in industrial and home environments where robots are beginning to be integrated in Industry 4.0 and IIoT systems respectively.

The advanced development features of the framework include the following:

 Organisation of the framework code in a Python package, making it easier for the end-user to utilise, since it would require a simple installation process in a Windows or Linux OS.

 The creation of user access levels in the GUI that permits some users to read or write parameters and others to read only.

 The use of dynamic IP addresses (as opposed to the current system of static addresses) or MAC addresses of the robots in the network. The implementation of this feature will make the framework more easy to use, especially in fast paced FMS environments.

 Support for the development of end-user algorithms in other programming languages, since the present limitation is Python. The design factors to consider are: 1) the ability of integration with the OPC protocol, and 2) the support for machine learning algorithm development through other programming languages. The inclusion of this advanced feature will increase the scope of the framework to a wider audience who may not be familiar with Python.

 Functionality for the application of robotic swarm systems. This will require the performance test of the framework in these scenarios, where design factors to consider are communication bandwidth limitations and the local robot control methodology with regard to localisation and navigation in the large network of robots.

6.5 Chapter summary

The discussion in this chapter began by describing the benefits of the framework, which included the use of popular software platforms of Python and ROS, and features that enable the control and cooperation of heterogeneous mobile robots in smart factory environments. A further scope of the framework was also discussed, pertaining to areas such as business management systems, multi-robot resource sharing, and applications that involve fixed robotic manipulators.

Section 6.3 surveyed research related to the functionality of the framework. Some of the related aspects that were discussed included systems that support remote robot programming in single and multi-robot systems, networked robots, control of heterogeneous robots, and robot cooperation. The main conclusion from the survey was the industrial interoperability advantage that the framework in this study has over the related research.

The final section in this chapter discussed the two design sources of the framework that contribute to its limitations. The first one is the centralised OPC Server which creates a single

point of failure in the system. The solution to this drawback was discussed as an implementation of a redundant OPC Server that would use separate hardware to eliminate the single point of failure and increase the robustness of the system. The second limitation that was addressed is the issue of security, particularly in smart factory environments where data integrity and data protection are key requirements. The insecure communication protocol in the ROS component of the framework was identified, and it was also mentioned that the developers of ROS are currently implementing SROS, a set of security enhancements to ROS, which should provide a better, secure form of communication. Also discussed in the final section was a list of advanced features that should be implemented as improvements to the system.