## 4 Experimental Results  
### Experimental Setup and Data Acquisition  
Planetary gearboxes play an important role in the transmission train of a satellite communication antenna or a telemetry, tracking, and command (TT&C) antenna for the aerospace industry. The aerospace measurement ship is mainly responsible for the maritime measurement and control, communication, salvage and recovery of spacecrafts. Satellite communication antennas (SCA) are critical devices of a measurement ship to support voice, data, fax and video integration services. An SCA comprises three axes, which are the azimuth axis, the pitching axis and the crossing axis. Searching satellite is that makes an SCA circumrotate the azimuth axis, the pitching axis and the crossing axis with controllers to change these axis angles, so the antenna can point itself to different satellite in the light of demands. If the SCA direction departs from a satellite or the satellite makes an excursion, it can adjust the SCA to track the satellite signal automatically. Figure 8 shows the transmission mechanism of the azimuth axis in an SCA. The azimuth axis is fixed, a two-stage gearbox rotates around the azimuth axis. A double-motor dispelling clearance transmission train is designed to raise the transmission accuracy. Each transmission train consists of a tachometer generator, a brake, a motor, a planetary gearbox and a two-stage fixed-shaft gearbox. Planetary gearboxes inevitably generate various faults because of chronically running under such  
Figure 7: The flow chart of the customized multiwavelets. complex and severe conditions as heavy load, ocean wave and tide, fatigue and corrosion. As the core components in the transmission train of an SCA, the performance of planetary gearboxes directly influences the success or failure of these tasks for an SCA. The testing framework is shown in Figure 9 when a measurement ship was sailing at sea. The left transmission train of the azimuth axis had a slightly abnormal sound when the measurement ship was sailing. The operators replace the defective planetary gearbox with a normal one. Vibration signals are measured before and after the replacement of the planetary gearboxes. Equipment operators controlled the SCA to search and track satellite by using the manual mode. We collected the vibration signals of the transmission trains of the azimuth axis, the pitching axis and the crossing axis using internal electronics piezoelectric (ICP) acceleration sensors. The parameters of these sensors are shown in Table 1. X and Y represented the horizontal and vertical measurement points of the planetary gearbox in the left transmission train of the azimuth axis, respectively. The vibration signals were measured using Sony EX data acquisition system when the SCA was running. A four-order elliptic filter with an anti-aliasing filtering up to 5,500 Hz was adopted. The drive motor was a permanent magnet synchronous AC motor, which was running at two different motor speeds, 150 r/m and 255 r/m. The motor speeds were measured by the tachometer generator at the end of the AC motors. Figure 8: The transmission mechanism of the azimuth axis. The planetary gearbox of the azimuth axis transmission train is a two-stage gearbox. The carrier of the first stage works as the input shaft of the second stage. The parameters of the planetary gearbox are shown in Table 2. The number of planet gears in each stage is three. With the special gear transmission structure, the transmission ratio is calculated using the primary principle of the conversion mechanism method. The first stage in the planetary gearbox has a transmission ratio 8. The meshing frequency of the first stage is calculated by using Equation (24):  
\[f_{mesh}=(N_{in}-N_{out})*Z_{sim}/60 \tag{24}\]  
where \(f_{mesh}\) represents the meshing frequency of the first stage, \(N_{in}\) represents the input speed of the sun gear, \(N_{out}\) represents the output speed of the carrier, \(Z_{sun}\) is the teeth number of the sun gear.