# Indoor Positioning Systems Can Revolutionise Digital Lean
## 4 Application to the Monitoring of a Flexible Manufacturing Process
### Description of the Applied IPS  
The hardware architecture of the IPS is illustrated in Figure 3. The applied ultra-wide band (UWB)-based real-time locating system (RTLS) uses active tags and anchors for localization. There are 15 anchors installed on the shop floor, which is nearly 2000 m\({}^{2}\)  
Figure 2: IPS data is the key element of the proposed PDCA-cycle-based methodology.  
The anchors are connected to two central units. The raw sensory data are transferred into the position calculation server. The calculation of the position is based on the TDoA (Time Difference Of Arrival) method and applies a Kalman filter to obtain more accurate information. The IPS is installed to track carts with the shop floor's semi-finished products. These carts are moving (manually) between the workstation and the IPS sends information to the MES if the actual cart with the defined (paired) product has arrived at the actual station. There are 40 carts, every cart has a dedicated IPS tag. Each time a semi-finished product was put on a cart, the operator paired the order number with the tag ID with a timestamp. The positional data accuracy is around 0.5 m, which is sufficient to obtain an accurate spaghetti diagram (Figure 4a) from each produced order. The shop floor with a tracked motion of one product is shown in Figure 4a. As this figure illustrates, the analysis of the positional data allows the identification of the temporary stations and motion paths.  
The proposed lean analysis was performed on the production data from MES and positional data (where the sample time is three seconds) from IPS. The process-flow was discovered with a process mining algorithm based on the MES data. We used the Disco software for process mining, and in the following subsection, the results are shown. The positional data are used to calculate the loss of process. We analyzed the transportation path, where we calculate the transportation periods for orders and the hidden temporary storage and queuing times are identified.  
The collected positional data contain the tag IDs with the x-y position \([m]\) according to the predefined coordinate system (fitted for the shop floor layout). These data are updated every three seconds (the sample time can be set--maximum 1 kHz) to ensure most of the carts' motion is covered in this production scenario. The factory layout with the zone (workstation) definitions is provided by the rectangles (Figure 4a) to match the activity order. This layout is elaborated based on the facility's overall layout, and with the designated area represented where the production activities are performed. These areas are determined with the hardware's capability, and the system can detect the corresponding processes that are occurring. The entering and exiting times define the time that a product spends on one process step. The information (resources, produced pieces, quality issues) for every _Task_ ID, which includes the _Start_ time when the tag entered the zone (_Workplace_), is stored in the MES.  
Figure 3: The hardware architecture of the applied IPS (based on Sunstone-RTLS Ltd.—Hungary).