# Development of a Conveyor Cart with Magnetic Levitation Mechanism Based on Multi Control Strategies
## 3 Magnetic Levitation Unit Support Force Analysis  
_Magnetic Levitation Transfer Equipment Position Measurement Circuit_  
The magnet levitation support force measurement is the basic condition to analyze the magnetic levitation conveyor cart system. Figure 4 shows the structure of the designed suspension force measurement device. The magnetic force measurement apparatus consists of a core unit, a plate spring to which a strain gauge is attached, a side panel, an eddy-current displacement sensor, and a laser displacement transducer. The side panel is fixed to the plate spring. When a rail is placed on the side panel, a suspension force is generated between the rail and the core. Since the rail is supported by the side panel, the core unit is pulled toward the rail which generates displacement and strain on the plate spring. This strain is detected by strain gauges attached to the bottom of the plate spring to determine the support force. The position of the rails can be adjusted by inserting spacers between the side panels and the rails. Thus, this allows the gap dependence of the support force by the core unit to be measured. The detailed position of the rail was measured by an eddy-current displacement sensor which is attached to the side panel. The displacement of the core unit during suction was measured with a laser displacement meter attached separately. The magnetic force is determined by analyzing the output of strain gauges when the rail is placed on the attachment force measuring device. For data acquisition and processing, we utilized the dSPACE DS1104 Digital Signal Processor in this experiment. Additionally, to measure the displacement of the core unit during suction, a laser displacement meter was employed. During the measurement process, we inserted spacers between the rail and the side panel, as illustrated in Figure 4, to deliberately adjust the gap between the core and the rail. This adjustment allowed us to precisely measure the suction force. The exact position of the rail was confirmed using eddy current displacement sensors that were securely attached to the side panels. In our assessment of adsorption force, we also recorded variations in the adsorption force resulting from the application of control current to the coil. Figure 3: Overall and detailed photograph of the Maglev system. (**a**) Maglev unit. (**b**) Overall Maglev unit photograph. (**c**) Transport equipment photograph. In the suspension force measurement experiment, we systematically varied the gap between the rail and the magnetic levitation unit to the following values: 0.7 mm, 2.4 mm, 3.9 mm, 5.2 mm, and 6.8 mm. Concurrently, we applied a range of input currents, including \(-\)3 A, \(-\)2 A, \(-\)1 A, 0 A, 1 A, 2 A, and 3 A. This enabled us to investigate the influence of both current and air gap on the magnetic force. Of particular interest is the scenario when the current is set to 0 A. In this condition, the magnetic levitation force is primarily generated by the permanent magnet (PM). Figure 5 displayed the results of attaching the core unit to the rail and measuring the bearing force. When comparing these measurement results with the magnetic field analysis results shown in Figure 2b, it was observed that the measured values were approximately 30% lower than the analytical values. The supporting force provided by the permanent magnets alone per unit, at an air gap of 4.0 mm, amounted to 560 N. By combining the forces generated by all four magnetic levitation units, we were able to achieve a total levitation force of approximately 2240 N. Moreover, the levitation force has a movable range ranged from 1520 N to 2800 N in the air gap and control current adjustable range. Although the sum magnetic force of four units was lower than the result of the magnetic field analysis, it still could levitate the weight of the carrier cart and baggage. The initial design specifications for each magnetic levitation unit called for a support force of 750 N when no current input (0 A) was applied.