Multi-sensor systems are a crucial basis for the success of Industry 4.0 applications: They record, process and transmit several measured variables such as pressure, acceleration and temperature in the smallest of spaces. Not only machines, but also workpieces are increasingly being equipped with intelligent sensor systems so that every product can report its construction plan and production status. Production largely organizes and monitors itself on the basis of this status data.

The development of such multi-sensor systems for I4.0 applications is technically challenging: two technologies need to be combined in a very small space - on the one hand, microelectromechanical sensors (MEMS), which measure mechanical variables such as pressure or acceleration, and on the other, microelectronic sensor components, which determine temperature, light intensity or chemical concentrations, for example. The finished systems must also process large amounts of data as energy-efficiently as possible and be robust enough to function reliably in an industrial environment.

Other demands on the development and production processes for sensor technology arise from the fact that applications in Industry 4.0 require particularly diverse sensor systems. The process of developing such sensor systems, from the idea to the specification and implementation in a circuit diagram to the finished circuit, must therefore be flexible and standardized in order to be able to manufacture sensors economically even in small quantities without direct access to semiconductor technology development.

Sensor technology characterized by SMEs

The aim of the 'Romulus' project is to simplify and accelerate the development of multi-sensor systems in order to ultimately standardize and refine the steps to the finished product in such a way that even small quantities can be produced cost-effectively. The German sensor industry is predominantly characterized by small and medium-sized companies that are generally unable to cover all the services required for the development and production of multi-sensor systems themselves. They are therefore dependent on close cooperation with semiconductor manufacturers and service providers for research and development. This is also where the 'Romulus' project comes in and stimulates this cooperation in order to unbundle and standardize the design and production process. In future, SMEs will be able to select and assemble both development services and electronic components from a large modular system - depending on which solution a customer requires for their specific industrial application.

Qualified standard processes as a goal

One aim of Romulus is therefore to develop and test new processes that can be used to efficiently implement and cost-effectively manufacture robust, energy-efficient multi-sensor systems, even in limited numbers. The processes include industrial, technological possibilities and new computer-aided design methods. Robustness and energy efficiency of the systems are the focus of the development when converting them into a circuit diagram. Qualified standard processes are the goal for the subsequent production of the sensor systems.

A further aim is to develop elementary component models for sensors and actuators whose accuracy and speed enable the creation of realistic system models of different integration levels. Suitable system models are an essential prerequisite for the successful integration of controlled sensor-actuator systems in a complex manufacturing machine. They enable flexible, real-time production control with a large number of networked sensors and actuators. In addition, the research project aims to identify new Industry 4.0 applications and evaluate and exemplarily test their improvement potential for manufacturing machines, their components or associated processes in order to create a basis for decision-making for implementation.

Sensors for Industry 4.0 applications are characterized in particular by the fact that they can be networked into complex, dynamically scalable and reconfigurable, multifunctional sensor networks using integrated digital communication interfaces. Particular importance is attached to the spatial integration density and energy efficiency of the sensor units as well as wireless networking using RFID and radio technologies. This is what makes it possible to integrate sensory intelligence into tools, workpieces and mobile production units.

The research objectives

Two overarching research objectives of Romulus directly address these specific technical requirements on the one hand, and on the other, aspects of design and production economy for industrial multi-sensor systems are at the forefront of the planned work:

• Development of energy-efficient electronic components (ultra-low power) and wireless communication solutions for integrated multi-sensors.
• Research into PDK- and IP-oriented design processes for intelligent multisensor microsystems with micromechanical and microelectronic sensor components. Explanation: The Foundry-Process Design Kit (PDK) forms the interface between the foundry process used for production and the design tools used by the customer for design. The quality and completeness of this interface have a significant influence on the possible design automation and thus on the quality of the customer designs and their time-to-market.

The technical project objectives include in detail

• A stronger abstraction of the MEMS device design from the technology development by means of new, PDK-supported structural design methods,
• Increasing the design reliability and robustness of MEMS-based integrated electronic systems with the help of new computer-aided design methods (EDA),
• the development of a standardized mixed-signal IP platform for the design, self-calibration, self-monitoring and testing of networked multi-sensors, in particular RFID-based sensors,
• the development of special CMOS circuit components and PDK logic libraries for the implementation of ultra-low-power mixed-signal circuits for smart sensor and energy harvesting front-ends,
• the optimization of wireless solutions in terms of latency and usability in metal-shielded environments,
• validation of the new technologies and processes based on the exemplary design of multi-sensor microsystems for selected Industry 4.0 demonstrator applications
• the creation of adapted MEMS models that are suitable for modeling system behaviour at different integration levels, and
• the identification, evaluation and testing of further Industry 4.0 applications, taking into account integration into an overall socio-technical system.

Integration from the 'Romulus' perspective

Figure 1: Perspectives on the term 'integration' in the context of electronic sensor systems for Industry 4.0 applications and (in red or blue) exemplary areas of work in the 'Romulus' project.

© Reutlingen University

In the public discussion of the significance of 'Industrie 4.0', there is a broad consensus that it is primarily about the integration and networking of existing and evolutionarily developed approaches to information technology-integrated, intelligent production systems and service processes.

In the context of electronic sensor systems for Industry 4.0, the Romulus consortium deals with the term 'integration' and its implementation in technical and organizational solutions for I4.0 applications from different perspectives and at several levels of the system hierarchy. The perspectives under consideration can be seen in Figure 1 as coordinate axes: The graphic shows selected examples of the associated specific areas of work and objectives in the project, which are presented individually below. Progress in the degree of integration is being sought in all the dimensions mentioned.

The technological perspective

Figure 2: Multi-frequency and multi-sensor-capable RFID networks integrate various communication standards in wireless sensor technology.

© Institute for Microelectronics and Mechatronics Systems

For the Romulus consortium, 'functional integration' means researching technologies and design methods for structurally or logically linking heterogeneous sensor, actuator, electronic and communication functions (such as MEMS, CMOS and RFID) to form a sensor system or production system that functions as a unit. An exemplary objective of the project (work area 1 in Fig. 1) is the development of a multi-frequency and multi-sensor-capable RFID network: using various sensors and communication technologies, a standardized interface for the integration of sensors in RFID networks for industrial applications is to be developed. A number of aspects need to be considered here, such as different carrier frequencies, a mix of passive and semi-active sensors and the use of analog and digital sensors. The intention is to technically implement such a heterogeneous sensor network with a data interface to backend systems.

For Romulus, 'spatial integration' means the miniaturization of multi-sensors with the help of microelectronics and microsystem technologies. An exemplary objective in the project (work area 2 in Fig. 1) concerns the development of a monolithically integrated RFID multisensor. The aim of the work here is to develop a CMOS ASIC with an area of just a few square millimeters, on which sensors for various physical variables, low-power sensor evaluation circuits and an RFID communication interface are integrated(Fig. 2).