# Evaluating the Effectiveness of Designs for Low-Cost Digital Manufacturing Systems
## 1 Introduction  
Design approaches describe the systematic creation of systems by analysing system requirements and using appropriate design techniques [1]. There are many well-know systematic design approaches to digital systems used in manufacturing [2, 3, 4, 5, 6]. They cover a wide range of industrial applications, from an individual machine monitoring system to a fully integrated factory. However, there are only a limited number of systematic design approaches that specifically deal with low-cost components. Most low-cost digital system deployments have been designed in an ad hoc manner and have only emphasised specific aspects of the development process. In particular, designers are mainly concerned with reducing the procurement costs of hardware and software components [7, 8, 9, 10]. Low-cost components may not offer the same level of completeness as more expensive industrial alternatives and may need to be combined with other components to become comparable. Hence, common design challenges for systems comprising such low-cost components revolve around extendability and interface standardisation. These design challenges are particularly relevant to small and medium-sized enterprises (SMEs). In contrast to larger companies, SMEs lack the necessary technical skills and resources that are required to adopt digital technologies and build these low-cost digital manufacturing systems [11, 12, 13]. There is a need for analysing the capability of current design approaches to effectively support the design of low-cost digital manufacturing systems. Digital manufacturing revolves around the application of digital information for the enhancement of manufacturing processes, supply chains, products and services [14]. Several concepts fall under the umbrella of 'digital manufacturing', such as cyber-physical systems (CPS) and Internet of Things (IoT). Above all, the design of digital manufacturing systems is particularly relevant for Industry 4.0. By combining CPS, IoT and other disruptive decentralising technologies, Industry 4.0 aims to achieve a horizontal integration of manufacturing and enterprise systems [15]. Effectively designing such decentralised digital systems to enhance production and the control of manufacturing resources is a key concern of Industry 4.0. In this study, we focus on the systematic design of particularly _low-cost_ digital systems used in manufacturing. _Low-cost digital manufacturing_ refers to _the development of digital systems to meet specific operational needs and for which the overall cost of deployment it keeps low_[16]. A _low-cost digital manufacturing system_ is a special type of digital system that consists of a combination of affordable hardware and software components and satisfies the entry-level digitalisation needs of a manufacturing SME [16]. Low-cost digital systems can be used to deliver a _solution_ to a particular problem. For example, these systems can be used to digitise a core production process or help integrate a legacy system into an IT environment [12]. The low-cost digital systems considered here characterise systems that are typically peripheral to core production processes, such as tracking and monitoring applications [13]. It is crucial to lay a foundation based on these elementary low-cost systems to help implement and adapt more complex integrated digital systems [17], such as a digital twin mirroring a factory that consists of various connected systems and applications [18; 19]. A key challenge when building low-cost digital systems is that the cost is not only governed by the component costs alone but also comprises the time spent during the design, development and deployment [20]. As part of these 'design costs', this study evaluates the effectiveness of designs for low-cost digital manufacturing systems in terms of the effort required to design these systems. We define _design effort_ as _the combination of physical, virtual and human resources required to develop, implement and deploy a digital system_.