A Low-Code Development Platform (LCDP) empowers domain experts without software engineering training to address their software requirements themselves. Techniques such as visual programming and programming by natural language allow them to create software in a way that is more natural to how they think about their problems, thereby leveraging the low-code paradigm rather than traditional textual code. In this paper, we present an LCDP based on the visual programming paradigm and the considerations that guided its design. The LCDP allows assembly workers to generate Programmable Logic Controller (PLC) code for the assembly devices they operate. Feedback from this industry-academia collaboration suggests that the platform can help to reduce the need for professional PLC programmers and allow them to focus on other important issues.
By raising the level of abstraction beyond code, a Low-Code Development Platform (LCDP) empowers
domain experts without software engineering training to address their software requirements
themselves, bridging the gap between the high demand for software and the low supply of professional
developers [
This paper reports on an industry-academia collaboration centered on PLC-Flow, an LCDP designed and
intended for assembly workers. The industry partner is a manufacturer of engines for the recreational
vehicle industry with a turnover of 1 billion euros and 1,700 employees. Some assembly line stations
require custom-built devices that are controlled by Programmable Logic Controllers (PLCs). However,
the shortage of PLC software developers poses a challenge. One possible solution, which served as the
starting point for the industry-academia collaboration, was to empower assembly workers to program
these devices directly using a low-code approach. This issue was first identified and described in [
This chapter presents the history of PLC-Flow, from early design considerations to an initial digital prototype to the platform in its current state.
The overall idea was to design the platform to reflect the mental model of its users. A mental model is a
person’s internal representation of reality [
The first versions of the digital prototype were built using Next.js 1 and React2 to discuss the main building blocks of the platform and how to interact with them. Figure 1 (left) shows a list of components (sensors and actuators), including their addresses, process steps defined as components and their respective state.
PLC-FLow was built using Angular v173 with Angular Material4. To generate Structured Control Language (SCL) code, a visitor was implemented based on ANTLR45. A grammar was defined for ANTLR4 to generate the lexer, parser, and the visitor base class. This visitor is included in PLC-Flow as a service.
The User Interface (UI) has a column-based layout, guiding the user to work from left to right to complete a process. The first main column lists all available components. As shown in Figure 1 (right), columns can be expanded and collapsed. When the column is expanded, the user can add, edit, or remove components. The second column enables the user to define the program, which is divided into four parts: (i) the initial position of the assembly device, (ii) the reset action, (iii) the steps of the assembly process, and (iv) the actions to be executed when a process completes successfully or unsuccessfully. On the left side of PLC-Flow, there are two additional columns to import a CAD drawing of the assembly device, to load other projects, and to define whether the assembly device is part of an an assembly line. On the right, the provided export functionality enables the user to save the program as an archive. The archive contains the generated SCL code and a flow file, which represents the project in the defined grammar. This column also contains a preview of the generated SCL code.
This section demonstrates how a user can create a program using PLC-Flow6, a process that is divided into eight steps.
First, the user can import the flow file of an existing project, which extracts all the components and process steps. The user can also import a CAD drawing of the assembly device, as shown in Figure 2 (left).
In the second step, the user can define if the assembly device is used in an assembly line or before. If it is used in an assembly line, the user can define the inputs and outputs of this line. For the assembly 3https://angular.dev/ 4https://material.angular.io/ 5https://www.antlr.org/ 6A public version of PLC-Flow is available online at https://plcflow.scch.at. line case, an input signaling when to start a process and two outputs signaling when the process is completed successfully or not must be configured, as illustrated in Figure 2 (right).
Next, the components need to be assigned a name and multiple inputs and outputs, each with its own name and logical address, as shown in Figure 3 (left). The logical address refers to the physical address used on the PLC.
The next step is to define the initial position of the assembly device by selecting the initial states of the required inputs from drop-down menus. In the first drop-down menu, the component can be selected by its name. The second drop-down menu defines the state that corresponds to the initial position. Examples of these drop-down menus can be seen in Figure 3 (right). Each of these conditions is connected by a logical conjunction in the generated SCL code. 4.5. Reset
The user can then define how to reset the assembly device by adding a reset gate and an action. A gate defines the conditions that must be met for the device to be reset. An action defines the state of a PLC output upon reset. These definitions are again made using drop-down menus (see Figure 3, right). Then, the steps to be executed for each production cycle can be defined. Each step is indexed, starting with 1, and consists of an action that defines what happens in that step, a description of the step, and a gate. The gate defines the conditions that must be fulfilled for the step to be successfully completed and for the next step to begin. Steps can be rearranged using drag and drop, and expanded and collapsed. When collapsed, only the index and the description of a step are displayed, as shown in Figure 1 (right). Otherwise, the action, description and gate can be edited (see Figure 3, right).
The final step in defining a complete process in PLC-Flow is to define what happens at the end of each cycle by setting the actions to be executed after a successful or unsuccessful production cycle.
The user can preview the generated SCL code in the export area of PLC-Flow. In addition, the user can name and download an archive containing the SCL code and a flow file, as shown in Figure 4 (right). This paper reports on an industry-academia collaboration centered on PLC-Flow, an LCDP designed and intended for assembly workers to generate Programmable Logic Controller (PLC) code.
Throughout the design process, reviews with assembly workers–who will be the future users–have confirmed that the implementation aligns with the original goals. This includes the level of abstraction (see Section 3.1) and PLC-Flow’s overall usability.
The research reported in this paper has been funded by the Federal Ministry for Innovation, Mobility and Infrastructure (BMIMI), the Federal Ministry for Economy, Energy and Tourism (BMWET), and the State of Upper Austria in the frame of the SCCH competence center INTEGRATE (FFG grant no. 892418) in the COMET - Competence Centers for Excellent Technologies Programme managed by Austrian Research Promotion Agency FFG.
During the preparation of this work, the author used DeepL Write and DeepL Translate in order to: Text Translation, Improve writing style, and Grammar and spelling check. After using these tools/services, the author reviewed and edited the content as needed and takes full responsibility for the publication’s content.