## 2 The Principle of Printing and Key Parameters  
Hot barcode printing is a method for generating barcodes by heating. When the print head is heated, the thermal coating reacts chemically to display the barcode information. Thermal printing primarily involves controlling the thermal print head to generate heat, thereby heating the thermally sensitive medium to enable information printing. The core of the thermal printer is the thermal print head, which is an electronic component that uses Joule heating effects to print information. As shown in Figure 1, it is mainly composed of resistors, ceramic substrates, driver chips, circuit boards, socket interfaces, radiators, and other components. The quality of barcode printing is influenced by several key parameters, including print head temperature, print speed, print density, and print quality.  
The printer firmware manages the printing speed by adjusting the rotational speed of the stepping motor, thereby allowing for various speed settings. Additionally, the firmware controls the printing concentration by regulating the heating duration of the printer head to achieve different levels of concentration. Temperature is modeled to reflect the ambient temperature of the natural environment.  
The temperature of the print head plays a vital role in determining the quality of the thermal barcode printing, as shown in Figure 2. If the temperature is too high or too low, unsatisfactory printing results can be obtained, including unclear or damaged barcodes. Different countries and regions experience diverse climate conditions, which can notably affect printing quality, particularly in colder environments. In this study, the  
Figure 1: The principle of thermal printing.  
temperature examined variable pertains to the ambient temperature, which was simulated in a temperature-controlled chamber to mimic the actual conditions. Print density affects the darkness of barcodes; if the density is too high, the barcode may become overly dark and difficult to scan, whereas if it is too low, the barcode might be too light and prone to blurring. Furthermore, the type of thermal paper used and the conditions under which it is stored can affect the print density of thermal barcodes. This density is mainly adjusted through software that offers 15 different settings.  
Printing at excessively high speeds can lead to inadequate contact time between the print head and thermal paper, which can negatively impact the print quality. However, printing too slowly may cause the print head to overheat, damaging the thermal coating. The speed variable discussed in this study was categorized into nine levels. The primary equipment used for testing barcodes is the WebScan Barcode Verifier (Barcode Detection Scanning Sensor, Model USB-DC71), and its accompanying barcode detection software is the Barcode Recognition Prediction System V1.0 (1D and 2D Barcode Recognition and Detection). The specific evaluation metrics of the scan reflectance profile offer important insights into quality control in the barcode printing process. Consequently, when assessing the quality grades of the barcode symbols, such as grades A, B, C, D, and E, we can compute the average values of the individual evaluation metrics from each scan reflectance profile and determine the arithmetic mean of the grades for each parameter across the profiles. To enhance information regarding the quality of the barcode symbol, the average values of these evaluation metrics or their grade averages can be included in the test report data, as illustrated in Table 1 and Figure 3.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Level of Numeric Symbol** & **Grade of Letter** \\ \hline
[3.5–4.0) & A \\
[2.5–3.5) & B \\
[1.5–2.5) & C \\
[0.5–1.5) & D \\ Less than 0.5 & E \\ \hline \hline \end{tabular}
\end{table}
Table 1: The grades of letters (ANSI) corresponding to the level of the numeric symbol.  
Figure 2: Temperature-controlled chamber.