# Investigation on Sensorless Estimating Method and Characteristics of Friction for Ball Screw System
## 2 Experimental Setup and Data Collection  
This experimental study was conducted using a lathe with a Fanuc 0i Mate-TD, as illustrated in Figure 1, which consists of two worktables that are referenced to the x-axis and the z-axis. The z-axis worktable was installed on a 45\({}^{\circ}\)-slant bed by a pair of linear ball guides. The x-axis worktable was installed on the z-axis worktable using another pair of linear ball guides. The servo data read is facilitated by the remote functions of the CNC Fanuc 0i Mate-TD via the FOCAS1/Ethernet protocol. This API and the FOCAS1/Ethernet driver installed in the CNC, which is accessed through a TCP/IP socket (192.168.1.1, 8193) using an Ethernet communication network, enables an application on a personal computer to execute the function, cnc_r_daxisdata, to read various data related to the servo axis or the spindle axis. Figure 2 shows the current communication ability of the CNC Fanuc 0i Mate-TD, which contains the Ethernet card and the FOCAS1 communication protocol [13]. Here, a PC104 bus computer is used to execute an application program on a Microsoft Windows XP system to read the positions of the servo axes and the servo motor torque current (SMTC). The program was written in the C language. The data for the servo axes that are retrieved from the CNCFanuc 0i Mate-TD do not have time stamps. Thus, the motion parameters of the worktable cannot be calculated. However, Microsoft Windows XP provides APIs that can be used to acquire high-resolution time stamps or measure time intervals. The program uses the functions Query Performance Frequency and Query Performance Counter to mark the time stamps after the retrieval of a piece of data related to the servo axes. These operations for performance measurement include the computation of the response time of the CNC system and latency, as well as the execution of the profiling code, and the time interval between the ends of the events for executing the function, cnc_r_daxisdata, twice and can be independent of any external time of day [14]. Hence, these intervals can be defined as the intervals between two data points that are related to the servo axes. Figure 3 provides a block diagram of the application program. In Figure 3, the interval of one loop is approximately 70 to 73 ms. Prior to conducting the experiment, the runtime of the NC program was evaluated to determine the number of acquisition data, thereby ensuring that the runtime of the NC program would be less that of the acquisition data application program on the PC104 computer. Here, only the z-axis worktable is investigated, and its specifications are listed in Table 1. The experimental procedure is given below. Figure 1: Experimental setup. Figure 2: The API FOCAS1 protocol. * [1]Manually adjust the z-axis worktable using the control panel to locate the starting position for the experiment. * [2]Run the application program on the PC104 computer and ensure that the PC104 computer connects successfully to the CNC Fanuc 0i Mate-TD. * [3]Input the number of acquisition data, N, and begin data sampling. * [4]Run the NC program on the CNC Fanuc 0i Mate-TD to perform an idling test. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Parameters** & **Value** & **Unit** \\ \hline \hline \multirow{2}{*}{Lathe} & Worktable mass & 425 & kg \\  & Screw lead & 10 & mm \\  & Ball diameter of lead screw & 5.56 & mm \\  & Ball diameter of linear guideway & 5.56 & mm \\  & Number of balls for the guideway in a raceway & 19 & \\  & Return position Z0 & 410 & mm \\  & Return position Z1 & 0 & mm \\ Servomotor & Type & \(\delta\)12/3000 is & \\  & Torque coefficient & 1.82 & Nm/A \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications for the ball screw drive system. Figure 3: Block diagram of the data collection application program. The application program on the PC104 computer ends after the lathe stops. Then, the time stamps relating the WP and the SMTC are redefined.