Abstract: To design a simulation system for a laser range finder, this paper first analyzes the design requirements and presents the system design scheme; then, it proposes some hardware selections for the system design; and finally, it suggests some methods to suppress interference. Keywords: slip orbit; motion controller; servo motor 1 Introduction The flight and landing of a UAV are controlled by the control center based on comprehensive analysis of detection information. During the approach and landing process, altitude information is indispensable, and accurate altitude measurement is crucial for the precise landing of the UAV. The UAV laser altimeter simulation device is part of the development of the UAV navigation and landing autonomous guidance system. It provides highly accurate real-time altitude information for aircraft approaching the ground (below 30m), enabling precise navigation and landing guidance and all-weather autonomous precision landing. When the aircraft approaches the ground, it receives control signals from the main control system, activates the rangefinder, compares and calculates the measured real-time distance information with data from the main control system, and then sends the relevant distance information to the main control system via an RS422 interface, simulating real-time laser distance measurement and aircraft altitude measurement. 2. System Design Requirements 2.1 System Functionality The sliding guide rail is a comprehensive, high-precision, mechatronic simulation device that provides a real-time changing distance environment to test the ranging accuracy, real-time performance, and other technical indicators of the UAV laser altimeter simulation device. It can also be connected to the UAV landing and navigation hardware-in-the-loop simulation system to receive and execute altitude data from the flight control simulator in real time, forming a simulation closed loop and further improving the confidence level of the simulation. 2.2 Main Technical Indicators The sliding simulation system simulates the motion of an aircraft approaching the ground. The aircraft is initially 30m above the ground with a vertical initial velocity v (~5m/s), and decelerates uniformly with acceleration a until it reaches zero vertical velocity upon landing. Based on this, considering feasibility, the length of the simulation system's sliding rail is chosen to be 6m. If the simulated aircraft landing time is required to remain constant (~t=12s), the maximum velocity v/5 (~1m/s) and acceleration a/5 can be correspondingly required. [align=center]Figure 1 Aircraft landing process[/align] Based on this, the main performance indicators of the simulation system are as follows: 1. Target plate movement range: 6m; 2. Maximum movement speed: 3m/s; 3. Positioning accuracy: ±5cm; 4. Control cycle: 5ms; 5. The diffuse reflection target plate is fixed on the slider of the linear guide rail, and its pitch angle is adjustable within a range of ±5°. 2.3 System Composition The system consists of a support frame, linear guide rail, slider mechanism, synchronous belt drive mechanism, servo system, base, laser rangefinder, control box, and computer. The linear guide rail is at least 6 meters long. The slider mechanism and linear guide rail are in rolling contact, ensuring smooth movement. The slider mechanism is connected to the diffuse reflection target plate, and the target plate angle is adjustable (±5°). The synchronous belt drive mechanism is connected to the slider mechanism, enabling it to complete linear motion, which is controlled by a servo motor control system. The servo system consists of a servo motor, motor driver, photoelectric encoder, tachometer, and microcontroller, controlling the position and speed of the slider. 3 System Implementation 3.1 Overall Design and Control Principle Based on the requirements of the sliding guide rail for the control system, real-time control, monitoring, and adjustment of the target plate's speed and position are necessary. The entire control system combines inner-loop speed control and outer-loop position control to control the target plate's movement in real time, ensuring high precision, stability, and high confidence in the closed-loop simulation system. To achieve overall system stability, reliability, and control precision, a servo control system was chosen as the core of this control system. As shown below: [align=center] Figure 2 Block Diagram of the Control System[/align] This control system uses a servo motor control unit based on the PCI bus. It forms a master-slave control structure with the PC. This control unit completes all the details of motion control, including the output of pulse and direction signals, the processing of automatic acceleration and deceleration, and the feedback signals from the servo motor encoder. In this control system, the motion control card sends pulse and direction control signals to the servo driver. The servo driver amplifies and drives the servo motor. The motor's speed and position are obtained through the motor's internal system and fed back to the control card through the encoder output. The entire control system uses servo drivers and servo motors. Since the AC servo drive system is a closed-loop control, the driver can directly sample the motor encoder feedback signal, forming a position loop and a speed loop internally. Generally, the step loss or overshoot phenomenon of stepper motors will not occur, and the control performance is more reliable than the closed-loop system formed by stepper motors. Overall, it improves the accuracy and speed of the sliding guide rail operation and ensures the stability and confidence of the entire closed-loop simulation system. The power supply system provides power to each controlled object in the control system. These power supplies include single-phase 200V or three-phase 200V commercial power supplies for the servo amplifier, 12-24V switching power supplies for switching signals (origin, deceleration, limit, and I/O signals, etc.), and 5V DC switching power supplies for pulse signals (pulse, direction, etc.). The commercial power supplies are filtered before being connected to the driver to ensure the power system meets the requirements for interference immunity and stable output. Furthermore, the grounding of the system test equipment meets the requirements for equipment safety, electromagnetic interference immunity, and stable operation. The servo system obtains a clean 200-230V AC power supply through a power filter, effectively isolating the mains voltage spikes and protecting the servo amplifier from voltage fluctuations, providing a stable input power supply for the servo system. The 5V or 12-24V DC switching power supplies required for various switching and pulse signals are obtained by directly rectifying and filtering the 220V AC power supply, then isolating and transforming it through a high-frequency transformer, and finally rectifying it again to the required DC voltage output. Switching power supplies have the advantages of small size, high efficiency, and resistance to overvoltage or undervoltage when the mains voltage varies over a wide range. 3.2 Hardware Selection 3.2.1 Control Card Selection The controller section of this control system uses a currently popular and mature industrial control product—the motion control card—as the core of the control system. The motion control card is a digital electronic system designed specifically for industrial applications. It adopts a typical computer architecture, mainly composed of a CPU, RAM, ROM, and specially designed input/output interface circuits. Therefore, it can be used to internally store programs to execute logical operations, sequential control, timing, counting, and arithmetic operations, and control various types of machinery or production processes through digital and analog input/output. As a popular industrial control device, the motion control card has the following characteristics: high reliability and strong anti-interference capability, good flexibility, simple and easy-to-learn programming, simple system installation, and convenient maintenance. The control card used in the control system is the mature MPC08 professional motion control card, whose main technical specifications are: 1. 4-axis stepper or digital servo control, pulse output frequency up to 4.0MHz; 2. Multi-axis high-speed linear interpolation, each axis with origin, deceleration, and limit interfaces; 3. Trapezoidal acceleration and deceleration, variable speed during motion, outputting pulse/direction or dual-pulse signals; 4. External encoder position feedback, expandable to 16 general-purpose inputs and 16 general-purpose outputs; 5. WDM and DLL libraries under Windows environment, demonstration program. The MPC08 motion control card uses an FPGA as its control core. Its main function is to execute control commands from the upper-level computer, process the feedback information from the actuator, and feed the processing results back to the computer to display the current status of the actuator (real-time running speed, position reached, etc.). It sends pulse signals to drive the servo motor through the control card, and simultaneously feeds back the real-time information of the servo motor to the control card for processing. The motion control function of the MPC08 control card mainly depends on the motion function library. The motion function library provides many motion functions for single-axis and multi-axis stepper or servo control: single-axis motion, multi-axis independent motion, multi-axis interpolation motion, etc. To facilitate the development of motion control systems, backlash compensation is also provided. The functions of single-axis motion control are briefly introduced below. Single-axis motion has three basic types: point-to-point motion (pmove), continuous motion (vmove), and homing motion (hmove). These motions can operate in constant speed mode or trapezoidal speed mode, resulting in a total of six basic types, listed below: [align=center] Figure 3 Motion speed graph[/align] 3.2.2 Servo Motor Selection A servo motor, also known as an actuator motor, is used as an actuator in automatic control systems, converting received electrical signals into angular displacement or angular velocity output on the motor shaft. Servo motors are broadly classified into DC and AC servo motors. Their main characteristic is that they exhibit no self-rotation when the signal voltage is zero, and their speed decreases uniformly as torque increases. The rotor inside the servo motor is a permanent magnet. The three-phase (U/V/W) electricity controlled by the driver creates an electromagnetic field, causing the rotor to rotate under the influence of this magnetic field. Simultaneously, the motor's built-in encoder feeds back signals to the driver, which compares the feedback value with the target value and adjusts the rotor's rotation angle accordingly. The accuracy of the servo motor depends on the accuracy (line count) of the encoder. Based on a comparison of the performance of products from multiple manufacturers, the GYG501BC2-T2 medium-inertia servo motor and driver were selected. Its main parameters are as follows: [Motor parameter table]. The servo driver selected is a matching driver, model RYC501B3-VVT2. This driver has position, speed, and torque control functions, as well as corresponding input and output signals, and also exhibits good stability. The main technical data of the driver are as follows: 1. DSP all-digital motor control mode, which can realize a variety of motor control algorithms and software updates. 2. It can provide three control modes: position, speed and torque. 3. It has an incremental 17-bit encoder. 4. It can switch between any two of the three modes: position, speed and torque at any time. 5. The 7-segment 4-digit display touch panel can easily set various parameters of the servo system. Its torque characteristic diagram is shown below: [align=center] Figure 4 Torque characteristic diagram of RYC501B3-VVT2[/align] Its main performance indicators are shown in the table below: 3.3 Anti-interference technology The power supply is the energy supply part of the entire system. Since overvoltage and undervoltage often occur in the mains power grid, when the voltage exceeds the power supply's operating range, it will cause the power supply to malfunction or be damaged, directly threatening the safety of the control system. Instantaneous overvoltage or undervoltage forms inrush current, which will also cause strong interference and damage. In order to effectively suppress power supply interference, the following methods can be adopted: 1. Use AC purified power supply. It has over/under voltage protection and filtering functions to ensure the stability of the system power supply; 2. Use a high-quality anti-interference switching power supply as the power supply for motor control, etc.; 3. Connect a large capacitor in parallel at the power output terminal to eliminate the influence of power fluctuations during high-power operation. In this control system, the servo amplifier, like a general frequency converter, performs high-frequency switching operations in the PWM control circuit. Therefore, radiated interference and conducted interference often affect external machines of peripheral equipment. The following countermeasures can be taken to address the above situation: 1. Install the servo amplifier in a grounded control container (control panel), and do not place it too close to the computer and measuring instruments. 2. Install a filter (power filter) at the primary end of the servo amplifier. 3. The wiring connecting the servo amplifier to the servo motor should be installed in a metal conduit and grounded. 4. Use short and thick wires for grounding as much as possible. 5. Grounding terminals, command control sequence input/output, and encoder power supply 0V signals should not be connected to each other. 6. The wiring of the main circuit and control circuit must not be bundled together or wired in parallel. In addition to the aforementioned hardware measures, software measures such as redundancy design and self-recovery functions can also be adopted to improve the anti-interference performance of the equipment through a combination of hardware and software approaches. 4. Conclusion The mechanical slide rail system designed for the laser altimeter simulation system in this paper utilizes the mature MPC08 professional motion control card and the GYG501BC2-T2 medium-inertia servo motor. Furthermore, the design method of this system proposes some hardware anti-interference techniques, providing a reference for the system's hardware and software implementation. The actual verification results of the specific system will be reported in a separate article. References : (1) MPC08 Motion Control Card Operation Manual. (2) Gao Zhongyu. Electromechanical Control Engineering [M]. Beijing: Tsinghua University Press, 2006. (3) Liu Weiguo. MATLAB Programming Tutorial [M]. Beijing: China Water Resources and Hydropower Press, 2005. (4) Xu Ruihua and He Junhua. "Stepper Motor Group Control System Based on NextMoveES Motion Control Card". "Microcomputer Information". (5) Wang Xiaocheng and Pan Xiao. "PLC Parameter Setting and Display Design". "Microcomputer Information". Vol. 16, No. 6, 2000.