What is a Cyber-Physical System and How Do I Know When I See One?

martint Wednesday July 26, 2017

The concept of Cyber-Physical Systems (CPS) was introduced 2006 in the US to represent the Integration of computation, networking and physical processes where CPS range from minuscule (pace makers) to large-scale (e.g. national power-grid), [Ref]. Several other definitions have been proposed including the following one by NIST: Cyber-Physical Systems or "smart" systems are co-engineered interacting networks of physical and computational components.

The mainstream interpretation of the term “cyber” refers to the use of computers or computer networks (see e.g. Merriam-Webster), with many related connotations and usages (see e.g. here for a review). The term however originates from Norbert Wiener who coined cybernetics based on the Greek term “kybernetike” which means "governance", essentially referring to broad classes of feedback systems.

As CPS is centered on interactions and integration among cyber- and physical elements, “cyber” as part of CPS therefore relates to the computer interpretation of the term cyber. However, the second interpretation in terms of “feedback" is also relevant for many types of CPS, since any CPS will involve some form of sensing and/or control as means for cyber-physical interactions. As for systems (e.g human vs. nature made), there will be different types of CPS, referring to for example the structuring of the system (level of decentralization/distribution), the scale, the level of criticality (referring to safety and security), the level of automation and whether the CPS directly includes humans, (see e.g. this CyPhERS project deliverable for an elaboration).

When does a system qualify as a CPS? Let us take the following examples:

The first example does not represent any significant interactions nor integration among the computer (cyber part) and the physical elements (the house), although the computer may make use of power from the house (if not run on a battery). The second example instead provides an example of an integrated functionality, representing both physical and informational integration. The third example, illustrates an even tighter interaction where the physical environment will be essential for the design of the cyber part, and where the cyber part is designed explicitly to monitor and control the engine, requiring detailed knowledge of the physical engine. The CPS engine is likely be integrated to form part of a larger system such as a car. The fourth example, the industrial robot (IRB), encompasses a mechanical structure, energy provisioning and a computer control system. Often, an IRB system emphasizes feed-forward but also includes feed-back control. The system clearly represents a co-engineered system, although the level of optimization of both cyber- and physical parts with respect to each-other may vary.

This emphasizes again that there will be different types of CPS with different types of integration and interactions. When these interactions are significant, co-engineering becomes crucial for cost-effective development, production, operation and maintenance.

A further key aspect of CPS is that they embody the potential integration among information technologies and embedded systems/control systems, representing very different traditions and expected properties (from very fast turn-around, open and security aware systems to safety-critical real-time closed systems). This poses particular opportunities as well as integration challenges!

CPS’s do not represent a new phenomenon per se; the novelty lies in the potential scale and capabilities of upcoming CPS, the potential to combine and incorporate new technologies, their widespread use in society, and the resulting impact on our lives and societies. Examples of future CPS can be found essentially in all kinds of domains (from individual devices and machines up to interacting systems of systems: consider autonomous vehicles to coordinated transportation systems), and also across existing domains. The cyber integration enables integration and coordination among previously not integrated systems. Mastering their design therefore becomes extremely important.

As projected by several investigations, (see e.g. CPSoS, Road2CPS, and CyPhERS) the opportunities and challenges with future CPS are enormous, and their full impact and potential have yet to be understood. In future posting on this blog, we will be discussing such impacts and concerns.

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