Temporal Fidelity Assessment of a PLC-Mediated Digital Twin for Takt-Time Estimation in Manual Disassembly and Parts Sorting

Designing modern disassembly systems requires the integration of industrial automation equipment. Due to the support of various communication protocols, PLCs not only perform control tasks but also act as intelligent data centers in distributed production systems. PLC solutions increasingly combine traditional approaches to automation with modern digital technologies, enabling predictive maintenance, real-time data analysis, as well as remote process management and integration with digital twin simulation. The takt time of manual disassembly may vary due to human and technical factors; therefore, its estimation is a problem in many processes including, for example, Bluetooth speakers. This article discusses the issue of PLC-based control systems for a sorting process of dismantled parts, and the methodology of a digital twin framework in FlexSim software. A prototype of a sorting line based on a conveyor belt with an S7-1200 series PLC controller and a full digital twin development cycle were presented. The explicit assessment of takt-related temporal fidelity in PLC-mediated event streams remains less developed. Therefore, this article addresses this gap by using a Digital-Twin-in-the-Loop (DTiL) configuration as a digital twin validation setup in which a source process model generates PLC-mediated events and a separate resulting digital twin model is evaluated against this source. The article focuses on temporal fidelity, PLC-mediated event transfer, and takt-time estimation. Thus, the gathered empirical time data were then fed into the digital twin model and analyzed to obtain information about the time delay of the PLC signals. This article separates the general digital twin architecture from one specific validation scenario implemented in a digital twin in-the-loop configuration with FlexSim, Siemens TIA Portal, PLCSim Advanced, and a local network communication chain. Delay analysis is based on photocell event timestamps and inter-event time differences, which reduce the effect of initial clock mismatch. The results indicate that, under the tested local-network DTiL configuration, absolute event delays are visible, while inter-event timing and aggregated takt statistics remain highly consistent between the source and resulting models. These findings support the preliminary feasibility of PLC-mediated takt-oriented monitoring for long manual operations. Nevertheless, broader validation under different controller configurations, communication conditions, and operating scenarios is required before generalizing the proposed approach.