Towards robot modularity — A review of international modularity standardization for service robots

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Yibo Zou a, Donghan Kim b, Philip Norman c, Jose Espinosa c, Jen-Chieh Wang d, Gurvinder S. Virk e

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Highlights

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First ISO modularity standardization for service robots.

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Line and circle diagrams for modular representation.

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Real commercial modular robots as user case examples are demonstrated.

Abstract

The paper presents ISO standardization work carried out to formulate guidelines for service robot modularity for assisting the development of open plug-n-play modules that can be easily assembled to create application specific robots and robot systems. Although robot modularity has been an active research field for many years, the developments have had little impact on advancing robot markets due to their individualist nature and the results not having sufficiently wide relevance or appeal. The paper initially provides an overview of the new ISO 22166-1 service robot modularity standard and aims to illustrate how to implement it with several use cases. Specific innovations produced in realizing robot modules under the guidance of ISO are introduced and two simple approaches based on block diagram approaches (the line and circle diagrams) are proposed for implementing and designing modular robots. Finally, the paper presents several use cases as examples where the new ISO robot modular approach can be used to good effect.

Introduction

Robotics is a relatively young sector with the main focus being on industrial robots introduced into a variety of automation and manufacturing applications in the 1960s. This industrial robot sector has become firmly established and stabilized over the years with the (mainly) manipulator industrial robots, typically large and potentially dangerous machines, being kept separate from humans to prevent harm while in operation suitable safety requirements based on maintaining separation distance, speed or power control have been developed and are presented in ISO 10218–1, -2 [1], [2]. Attempts to expand robotics to new sectors have failed due to extremely severe regulatory limitations on human–collaboration interactions. The community has as a result been trying to find suitable solutions. ISO began the exploration of new safety standardization projects for such new “service” applications in 2005 and a new safety standard for personal care robots ISO 13482 [3] was published in 2014. This new standard applied to service robots performing “useful tasks” involving “close human–robot interaction”. In parallel, the industrial robotics sector has seen the need to also evolve to allow human intervention in manufacturing applications. As a result, ISO TS 15066 [4] for collaborative (industrial) robots was published in 2016.

The recently published safety standards are intended to open the way for new service robots but barriers still remain due to lack of widespread knowledge of regulatory developments, how they should be implemented and availability of commercially viable solutions. At present, service robots are designed to meet the requirements in a multitude of small niche sectors. With a shortage of quality components available at affordable prices, the manufacturers of these service robot are obliged to adopt traditional approaches where they must develop their own closed supply chains to realize a commercially viable solution. This is a classic “chicken and egg” problem — what comes first, the robot or the supply chain that provides the parts?

While the expectation is that the market size and the number of applications will grow significantly. The current markets remain small, and this discourages component manufacturers from investing. To enable wide-spread and interoperable development of service robots and their constituent parts, and concomitantly, to foster the development of robust supply chains, a common approach for designing and building service robots is required.

On one side, the manufacturer-dependent architectural approaches currently adopted for designing service robots make design and development extremely difficult: substitution and reuse of modules in upgrading other robot products remain virtually impossible. There are however nascent indications of change with the recent emergence of companies specializing in modular robotics. These companies have successfully developed robust modular systems that are gaining traction in the marketplace. On the other side, the research community has forged ahead and has developed a vast knowledge-base in robot modular design. New approaches to modularity have resulted, however none to date has the widespread appeal needed to make a significant impact. In this polarized context, international standardization is felt to be urgently required, as it can assist the emerging service robotics manufacturing community by producing wide-ranging international guidelines under the ISO umbrella. The ISO guidelines can focus on how robot modules with sound interoperability features can be realized and commercialized at affordable cost, as demanded by the markets. In this more formalized context, new approaches are likely to emerge, helping markets evolve to meet the global challenges.

The ISO work on robot modularity was highlighted in 2006, but detailed standardization work commenced in 2012 in the form of a study group on Modularity within the service robots working group. A formal working group on Modularity for service robots was created after international balloting in 2014 with Prof Virk (UK) as the Convenor and Shuping Yang (China) and Professor Park (South Korea) as Co-conveners. The robot modularity work was supported by 11 countries initially, namely China, Denmark, France, India, Italy, Korea, Netherlands, Spain, Sweden, Switzerland and UK. Three countries opposed the work in the balloting, namely, Canada, Germany and Japan. Eight countries offered experts to start the standardization work in 2014, namely China, France, India, Korea, Netherlands, Spain, Switzerland and UK. However, when the work started, experts from other countries also registered to join the standardization work and currently experts from 17 countries are involved, namely, China, Denmark, Finland, France, Germany, India, Italy, Japan, Korea, Netherlands, Russia, Singapore, Spain, Sweden, Switzerland, UK and USA.

This reluctance in some countries to support the development of open robot modularity approaches is likely to be due to the established industrial robot manufacturers fearing that the open modularity guidelines could impact on their already created supply chains which they have set up and wish to keep operational in a commercially competitive manner. This traditional supply chain-based industrial robot market is dominated by the “four robot giants”, namely ABB, KUKA, FUNUC and YASKAWA. It was because of such resistance that the initial plan to develop “robot modularity” was amended to “service robot modularity” in 2014 within the ISO Robotics Technical Committee. Hence the current focus is on service robot modularity but the approach is of course equally valid and important for the entire robotics sector and could even be expanded to other types of machines and systems. The ISO concept of modularity is aimed at defining common and independent parts of a system which make it possible to build specific bespoke products and applications using common, defined parts which are referred to as “modules”.

Companies developing modular robotic systems for everyday have been obliged to test theory against practice. In so doing they have garnered a number of points-of-learning making it possible to formulate statements about the specification of suitable use-case systems. Modular robotic systems designed for use in real-world conditions are unlikely to be composed of a set of identical modules as proposed by many researchers, such as cubes or spheres in the case of a number of laboratory/ research style robots. The modules are more likely to be members of a family of modules with a wide range of characteristics. It follows that a module of a robotic system should perform one function or a combination of functions in order to contribute to the overall performance of that system. These functions may include sensing, computing, communicating, power management and power delivery. They may also include mechanical functions: structural actuation or the provision of attachment points. A modular robotic system comes into existence when two or more modules interact with each other; this may involve physical connection but is not mandatory. The ISO concepts presented in the recently published ISO 22166-1 standard provides guidelines for the conception of modules as they are defined and constrained by their role in the system or by their potential roles. “Potential roles” is a term relating to the plasticity of functionality required by modules: a module’s role in one system may not be identical to its role in another. The line and circle diagrams developed in Virk [5] and Norman [6] respectively have been adopted by ISO 22166-1 to provide a way of ensuring that these characteristics are included in defining the interfacing specifications.

Considering some fundamental characteristics of a modular robotic system, a module’s power design should incorporate the notion that some modules may be required to supply power (in the case of electrical systems), provided by the battery, fuel cell or by AC/mains power, or may require power for its own use, or both. Depending on the composition of the robot system the module may therefore need to let power pass to other modules. To maximize the compatibility between modules, it is desirable that each module has the capacity to receive a wide range of power inputs: if the module is designed to supply the power to other modules, it will require appropriate high current-carrying capability. Depending on the system this may range from 10 to 100 A or significantly more. Ideally, a module should have a power pass-through from the power input to an output or to multiple outputs while in parallel having the capacity to use power for its own requirements. The power system should be effectively protected for inverse polarity power surges, also for noise induced by other connected modules. Modular systems using other forms of power, for example pneumatic, should be similarly designed.

There is no single appropriate solution when selecting communication protocols and architectures. Some robotic systems use I2C, SPI and even serial/USB to manage sensors and actuators at close distance to the processing unit. Over larger distances the preference will be for Controller Area Network (CAN) busses, wireless communication or Ethernet for Control Automation Technology (EtherCAT) and Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) protocols. I2C, SPI and serial communications may be preferred for internal use only within a module. A module should communicate with other modules using robust protocols that are able to cope with user set topologies and configurations, such as CAN, EtherCAT and TCP/UDP. Each of the external communication protocols has advantages, disadvantages and may suit some intended use cases and not others; therefore, standardization may be both difficult and inappropriate for widespread use and some differences in implementation specializations may need to be determined in practice.

As an alternative to standardization, a solution would be for modules to specify the type of communication system that they use, and for “middlemen” to translate if inter-protocol communication is required. As an example, using TCP or UDP based on ROS as the entry point of the robotic system, then translating it to CAN, EtherCAT or to another communication protocol as needed; for example:

High Level Computing Unit  ROS converter to CAN  Motor1  CAN  Motor2  CAN  Motor3.

In terms of evolutions in the industry, open source communication systems such as ROS1 (Robot Operating System) have been widely adopted for research and, in some cases, commercial platforms. However, the uptake of ROS1 in industrial and service robotics has not followed due to the lack of real-time process control and safety certifications. ROS2’s primary purpose is to resolve these issues by addressing the challenge of real-time process management, and secondarily at the organizational/ resourcing level by forming a consortium of industries to help shape the software standards. Therefore, as ROS2 is developed it is likely to be used as the base system for the communications of robotic modules without compromising the real-time scheduling of processes and ensuring mandatory safety requirements will be met.

In terms of the physical conception of a modular robotic system, modules must be able to be linked and unlinked either manually or by the robot system itself and this method should be straightforward, ideally self-explanatory and rapid. The assembled modules must, once connected, be robustly linked, both mechanically and also in terms of power and data transfer (functionally). In normal operation, vibration and mechanical shock should not destabilize the assembly, functionality or communications. The assembly relations between the modules should be selectable by the user or by the robot itself, for example a range of relative rotational relations in order to allow for many variant configurations. In terms of power transmission, the connector should be capable of transmitting the total power requirement of the robot system as in some configurations this requirement may arise. The connector must also guarantee uninterrupted data transmission and be capable of transmitting enough data channels to satisfy the requirements of the communication protocol selected.

A robotic module should be able to describe itself to other modules of the system (version, technical data, limits, specifications, etc.), to make it possible for the robotic system to automatically detect it, integrate with it and inter-operate with it. The user should not be required to configure the system as a whole, but be limited to having to present the specific requirements to perform intended tasks.

A module must be able to provide data and power output to the rest of the system to allow modules to be daisy-chained if desired, e.g. a TCP/UDP communication based module should have a network switch with a minimum of 3 ports, an input, one to connect to the module’s processor/computer, and one as an output, for connecting to the rest of the system.

Modules that require high instant spikes of current to operate (such as motors) should have a power reservoir that is able to provide the instant energy required as the distance from the main power supply cannot be known and in some robot configurations this distance may be considerable.

A module should have a standard software safety stop that can be addressed to the module itself or be broadcast across the robotic system. Hardware safety stop switches should be considered if the module is to be used in safety-related applications where harm can occur.

An actuator module should have inputs for limit switches (soft and hard) and safety stop switches that allow the user to safely operate the module without the need for additional hardware.

A power supply module should be fully protected for reverse polarity, over-currenting, overheating, inrush protection (soft start), etc. The module should also be capable of reacting to a short circuit with a hardware safety stop to shut off all current flowing from the main power supply.

In light of the real-world requirements for developing robot modularity guidelines, interest in having an ISO standard has grown and has gathered pace. The original aim of the ISO work on modularity in the international balloting document was agreed to be as follows: To explore the standardization modularity needs for service robots covering software modularity, hardware modularity, with safety aspects, integrated design approach and interoperability. ISO 22166-1 is the first international standard on service robot modularity and interoperability; it focuses on the main issues of safety, security, connectivity (from both hardware and software perspectives) and functionality; these issues are pivotal in the approach adopted and are expected to change the service robotics landscape and speed up the development of the new service robot market sectors and adoption must be strongly supported and encouraged. The robot modularity issues in the published document are classified into basic modules with hardware and/or software aspects and composite modules. Requirements and guidelines are formulated so that module-based design approaches are realized allowing application specific service robots and service robot systems, meeting customer’s requirements, to be easily configured. The issues are classified into (a) safety and security, and (b) interoperability guidelines. In addition, an open modular approach has been adopted to enable modules to be easily substituted by other modules having the same interface specifications but perhaps with enhanced functionalities as needed. These are presented as guidelines and not requirements to encourage rather than force component manufacturers to adopt the open interfacing suggestions voluntarily.

In ISO 22166-1, it is assumed that safety requirements specified in already existing safety standards (e.g. ISO 13482, ISO 10218-1, ISO 10218-2, ISO TS 15066) which are applicable on the system level as well as on the level of single modules. Security issues are also important when adopting open modularity approaches and hence have been included in ISO 22166-1 (e.g. to align with emerging IEC TC44 [7] and IEC TC65 [8] security related work projects). Future parts of the ISO 22166 series are intended to include more specific requirements relating to particular types of robot modules, e.g., basic and composite modules with hardware and/or software aspects, and for particular types of service robots, e.g., mobile servant robots, physical assistant robots, person carrier robots, and service robots in professional environments such as medical applications. Moreover, ISO 22166-1 presents key definitions on robot modularity to ensure a common understanding of key terms, general guidelines on modularity, safety and security guidelines, hardware and software guidelines on robot module design and information for use. A robot template has been developed to present module details in a standardized format to facilitate common understanding of interoperability and how some important robot modules examples can be realized.

In this paper, we provide an overview of the new 22166-1 standard but our focus is on the use case examples so that the thinking of the ISO group on robot modularity can be explained to the wider community; in this way it is hoped that the advantages of adopting modular design approaches becomes more firmly established in reality. Moreover, this paper is more oriented to industrial applications, aiming to provide some useful references and approaches to the users for modular robots design. With the demonstration of the use case examples, the benefits of the modularity in terms of engineering productivity, time-to-market, cost savings etc. are presented [9], [10]. The paper is organized as follows: in Section 2, the state of the art of academic research and the challenges in industry in the field of service robot are presented firstly. Afterwards, the gap between them is illustrated in detail and the corresponding motivation of ISO is presented; in Section 3, a comprehensive overview of the ISO 22166-1document is provided; in Section 4, some innovative small-size companies from worldwide and their modular products under the guideline of ISO are introduced; in Section 5, detailed use case examples are presented in which the new ISO robot modular approach can be used to good effect.

Section snippets

R&D academic state of the art

The evolution of developing modularity concepts through R&D processes has been emerging as modular self-reconfigurable robots goes back to the “quick change” end effector and automatic tool changers that were used in computer numerical controlled machining centers in the 1970s. A common connection mechanism was introduced in the cellular CEBOT robot in 1990 [11]. Further development in the 1990s by Greg Chirikjian [12], Mark Yim, Joseph Michael [13], and Satoshi Murata [14] led to the creation

Overview of ISO 22166-1

In the robotics industry, the creation of an ISO standard on robot modularity enables open supply chains to be created where the robot parts (or “modules”) are easily interchangeable by those provided by different manufacturers. The advantages of modular robots are manifold, but in essence modularity allows robots to be easily configured, reconfigured and adapted to different situations and the resulting robot systems are likely to be more robust in comparison with conventional (non-modular)

International innovations under ISO

With the ISO’s guidance and help, international cooperation is taking place and there are already many innovations in the field of modularity. For example, Yun et al. [35] presented ModMan (see Fig. 3(a)), as a thoroughly synthesized formulation for a reconfigurable modular manipulator in terms of both hardware and software. A genderless connector with high capacity mechanical/electrical characteristics drives reconfigurable manipulators with up to 7 joint elements. An automatic kinematic

Use case examples of robot modularity

Robot modularity makes the design and development of the specific requirements easily achievable, ranging from simple robot applications to complex ones. In this section, examples of service robots from ISO TC299 WG6 are presented in order to demonstrate how modularity can be used to develop module-based solutions for various service robot domains. The essential issues of modular safety and modular security are described, also guidelines for modular connectivity and interoperability, as

Conclusions

In this paper, we have presented the importance of modularity in robot systems design and also reviewed the trends and development of modularity in recent years with perspectives given to R&D industrial communities. Innovations of modularity in service robot area have been introduced and the on-going international cooperation for promoting the development of modular robots is described by trying to encourage the development of open supply chains with openly defined inter-operability

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to thank ISO (International Standard Organization) and the open international community for supporting the standardization project ISO 22166-1 Modularity for service Robots. At the same time, we are grateful for the support and work from the experts in ISO/TC299/WG6 to contribute their expertise, and the manufacturers, Taiwan Intelligent Robotics Company, Ross Robotics Company, Endoenergy Systems and M-TECH Co Ltd, to share their industrial experiences. The authors also

Yibo Zou was born in Suzhou, China in 1987. He received the B.S. degree in power mechanical engineering from Jiangsu University, China in 2010. After that, he studied in Germany and received M.S. in 2013 and Ph.D. degrees in 2017 in mechanical engineering from Leibniz University Hannover, Germany. From 2013 to 2017, he was a research associate at the Institute of Measurement and Automatic control in Leibniz University of Hannover. From 2018 to 2019, he was the vice director of the R&D

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Yibo Zou was born in Suzhou, China in 1987. He received the B.S. degree in power mechanical engineering from Jiangsu University, China in 2010. After that, he studied in Germany and received M.S. in 2013 and Ph.D. degrees in 2017 in mechanical engineering from Leibniz University Hannover, Germany. From 2013 to 2017, he was a research associate at the Institute of Measurement and Automatic control in Leibniz University of Hannover. From 2018 to 2019, he was the vice director of the R&D department of Bozhong Robotics (China), leading the team to focus on developing service robots. Since 2020, he returned to research community and worked as research associate in Soochow University, China. Dr. Zou’s research interests include robot control system, image processing and non-contact precision measurement, laser cladding technology. Since 2018, he was elected as ISO/TC299/WG6 formal member and joined the ISO project of “Modularity for Service Robot”.

Donghan Kim is a Professor in the Department of Electrical Engineering at Kyung Hee University (South Korea) since 2007. He founded the HRI Lab at Kyung Hee University, which performs research in Human–Robot interaction, service robotics, cooperative robotics, and multi-robot system. He serves on the Board on International Robot-soccer Committee, Intelligent Robot Standards Forum, Institute of Control, Robotics and Systems and International Standard Organization. Prior to his position at Kyung Hee University, Prof. Kim was in industrial and commercial hardware development as a senior engineer at Samsung Electronics for 3 years. In that experience, he developed and lead numerous mobile phone projects. Prof. Kim has a Ph.D., M.S.E. and B.S. in Electrical Engineering from the Korea Advanced Institute of Science and Technology. He was a postdoctoral fellow at University of Illinois at Urbana-Champaign in 2003. His current research interests are in the area of a multi-agent robot system.

Philip Ross Norman is a co-founder of Ross Robotics, a UK privately owned company specializing in modular robotics. He is the named inventor on over forty internationally granted patents. The technologies under these patents relate to reconfigurable modular systems, biomimetic mobility, power & data connectivity and to manufacturing processes which create three dimensional monolithic structures (multifunctional structures that integrate electronics and sensors). A published author and a graduate of Cambridge University, prior to robotics he ran his own architecture business in France. Philip is responsible for technology development and intellectual property at Ross and for seeking out early-stage business opportunities.

Jose Luis (Pepe) Espinosa is a Mechatronic Engineer (UNAM) and Ph.D. in Robotics (University of Manchester). His interests are electronic systems design, robotics software engineering and integration, collaborative systems, image based localization systems and sensor fusion techniques. He specializes in sensing, navigation and localization systems for modular robotic systems. His current focus is the development of modular robotics architectures with plug and play functionality.

Jen-Chieh Wang is the Manager of Industrial Strategy Execution Department, Planning and Promotion Division, Center for Measurement Standards, Industrial Technology Research Institute (ITRI). He joined ITRI as a Medical Device Evaluation Engineer in 2017, and founded the Industrial Strategy Execution Department in 2020. His team is in charge of developing industrial and international connections. He serves as the member of National Standards Technical Committee and is committed to the standardization of advanced technologies, such as robotics and usability engineering in the healthcare industry. His current work is to promote metrology in the commercial applications and facilitate the industrial growth through enhancing the quality and safety by standards. He received the Ph.D. from School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, the M.S. from Department of Physics, State University of New York at Buffalo, U.S.A., and the B.S. from Department of Physics, National Taiwan University, Taiwan. His research interests include cosmic microwave background, high-intensity focused ultrasound, shock wave lithotripsy, medical device regulations, human factors engineering, robot safety, modularity in supply chains, industry analysis, and marketing.

Professor Gurvinder Singh Virk (Ph.D., DIC, B.Sc., C.Eng., FIET, FCIBSE, CMath, FIMA, MIEEE) is Chairman and CEO of Endoenergy Systems focused on developing wearable assistive exoskeletons in service applications involving close human–robot interactions having bases in UK and in India. His current interests are in wearable exoskeleton robots for wellbeing, robot safety standardization, robot modularity and inter-operability, social robotics and robot ethics. In addition to his industrial position at Endoenergy, he is Visiting Professor at London South Bank University, and University of Lincoln, UK, and Adjunct Professor at IIT Ropar, India. He holds a Ph.D. in Control theory from Imperial College, University of London, UK and has held senior leadership roles in UK (Universities of Bradford, Portsmouth and Leeds), Sweden (University of Gävle and KTH Royal Institute of Technology) and New Zealand (Massey University) as well as visiting Professor positions in China (Zhejiang University), France (Université Pierre et Marie Curie, Paris), and Germany (Fachochschule Südwestfalen, Soest). In addition, he has had commercial experience as Technical Director at InnotecUK, UK where he led R&D activities for realizing commercially viable inspection robots for hazardous environments where mobility, climbing and manipulation capabilities were needed in the robot systems being developed. Professor Virk is Treasurer and Trustee of the UK registered charity CLAWAR having the mission to advance robotics globally for public benefit. For this he has been nominated as a UK robot expert since 2005 and has led several international ISO/IEC robot standardization activities on safety and inter-operability. Prof Virk was also Coordinator of the euRobotics’ Topic Group on Standardization in Europe as part the Horizon 2020 programme and beyond from 2011–2019. He has been actively networking and working with stakeholder organizations in Europe, China, South Korea, Japan, USA and India on linking international robot R&D with robot standardization to facilitate the creation of new robot markets.

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