| In order to obtain high-quality imaging data when the space optical remote sensor is scanning and imaging the detection target,the internal scanning mirror motion control system should have high dynamic control accuracy,and can scan the target stably and accurately.It is necessary to continuously improve the control accuracy of the scanning mirror motion control system to meet the ever-increasing requirements of remote sensing accuracy indicators.In general optical-mechanical scanning systems,due to the optical aperture design of the optical remote sensor,the scanning mirror is designed to be large and has a large inertia.At the same time,in order to ensure that the scanning mirror has a good surface accuracy,the coupling stiffness between the drive motor rotor,the transmission shaft and the scanning mirror cannot be set too high.These two factors make the transmission shaft cause large elastic deformation due to insufficient stiffness during system operation,which may cause mechanical resonance.If the control parameter gain of the system controller is simply increased to obtain higher control accuracy,the mechanical resonance can make scanning mirror motion control system unstable.The improvement of the control performance of the entire system will be limited.The requirements for high-control performance scanning mirror systems of the remote sensors are constantly increasing.It is difficult to overcome the limitations of mechanical resonance on the system performance by using classic control theory to design such large-inertia scanning mirror control systems with low coupling stiffness.Therefore,this subject uses the observer and state feedback design methods of modern control theory to optimize the system that designed by the original classical control theory method,suppress the mechanical resonance in the system,and improve the control performance of the system.This article analyzes and discusses step by step through the aspects:system control object analysis,improvement control method design,control system design and simulation,system software and hardware design and control method experimental verification.First,the control object with low coupling stiffness and large inertia scanning mirror is analyzed and establish a corresponding control model.The causes of mechanical resonance and mechanical resonance limitation on system control performance during mechanism operation are analyzed through simulation.The influence of large inertia load on the mechanical resonance in the control system is analyzed.According to the investigation and the design of the actual system,a modern control theory method of designing an acceleration observer with the current and position feedback signals is proposed.The observed acceleration is feed back to the front of the current loop to form an acceleration loop.It can increase the cut-off frequency of the system while reducing the peak value of mechanical resonance.So,this method can achieve the purpose of suppressing resonance and improving the control performance of the system.Then,the control system is theoretically designed,based on the current-speed-position three closed-loop system control structure,an acceleration observer is added between the current loop and the speed loop.Establish discrete control models for each loop of the control system and simulate.The simulation obtain the command response,open loop bode diagram,close loop bode diagram and disturbance response bode diagram of each loop in the system.As for the current loop,the close loop control bandwidth can reach 1k Hz,has a good anti-interference ability.Comparing the control performance before and after adding the acceleration observer of the speed loop and position loop under the condition that the stability margin remain equally.As for the speed loop,the bandwidth is 28.85 Hz before the acceleration observer is added,and the bandwidth is increased to 65.23 Hz after the optimization.As for the position loop,the bandwidth is 25.41 Hz before the acceleration observer is added,and the bandwidth is increased to 60.75 Hz after the optimization.The system simulation shows that the proposed optimized method can improve the control performance of the system.And,design and build the software and hardware system of the scanning mirror system.The DSP+FPGA is used as the main control architecture of the system.The DSP acts as the main controller for the calculation of control algorithms and the output the control signals.The FPGA acts as a coprocessor for data signal transmission and processing.The entire control system includes feedback data acquisition and transmission module,motor drive module,control algorithm operation module and host computer control terminal module.Finally,the constructed scanning controller is matched with a one-dimensional low coupling stiffness large inertia scanning mechanism.The low speed scanning experiment was performed to test the control performance of the system.In the experiment,the current loop command response and error of the control system were tested.And also test and compare the command response and error of the speed loop and position loop before and after adding the acceleration observer.The current loop of the system can quickly respond to current commands,and the actual bandwidth can reach about 900 Hz.The speed loop of the system can quickly track the speed command.The root mean square of the tracking error in the uniform speed section decreases from1.37×10-3 rad/s to 0.55×10-3 rad/s,the speed dynamic control accuracy is improved by about 60%.The position loop of the system can also track position commands quickly and with high precision.The root mean square of the tracking error in the uniform speed section decreases from 1.062×10-5 rad to 0.407×10-5 rad,the position dynamic control accuracy in the uniform speed section is improved by about 62%.The frequency test of the system shows that the amplitude of the system at the mechanical resonance frequency declines after optimization,the resonance is suppressed.The simulation results of the system are consistent with the measured results.Based on the above research,both theoretical simulations and practical experiments have shown that the method of adding an acceleration observer to the speed loop can significantly suppress the mechanical resonance effect in the system,improve the control bandwidth and control accuracy of the system.It is easy to implement in engineering and parameter adjustment is very convenient. |
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