Experimental Research On A Pneumatic Support System Of The Primary Mirror For A Ring Solar Telescope

Aiming at the primary mirror support system of the 2 meter ring solar telescope,we proposed a semi-active pneumatic primary mirror supporting scheme to ensure the surface shape quality of the primary mirror in observation and to accomplish the positioning and aligning of the primary mirror simultaneously.According to the primary mirror’s design specifications,profound research and comprehensive experimental tests of the axial support prototype system of the primary mirror were conducted,including the testing of a unit pneumatic force actuator,a unit displacement actuator and the prototype of the support system.The research covers the following aspects:i.Working principle and overall design of the pneumatic forceactuator were introduced with elastic,high-strength and high-elastic metal bellow as the core pneumatic unit.A force sensor/load cell was integrated to build the closed-loop control by feedback of force.A test setup was constructed for the actuator to carry out the tests of the range of output force,the linearity of whole force range and force resolution.Also,the static system stiffness of the pneumatic actuator was assessed.The experimental results show that the actuator can achieve high precision output force to meet design requirements in the closed-loop control mode.ii.Working principle and overall design of the high-precision displacement actuator were introduced with planetary reducer stepper motor as the key driving element.The real-time feedback based ondisplacement sensingand adaptive control strategy based on deviation were adopted,where theoutput forcewas acquiredby aload cell.Also,specific test setup was designed to verify the performance in terms of its design specificationof the displacement actuator system and the accuracy of the closed-loop control loop.The experimental results show that the accuracy of the displacement closed-loop control is up to 1μm,which meets the technical design requirements of high-precision displacement aligning and positioning.iii.Overall structural design of the axial support prototype system of the primary mirror was introduced using pneumatic force actuator and displacement actuator.A closed-loop control plan of axial support was designed,and the system integration control software was developed on this basis.According to the primary mirror support system’s actual engineering demand of the 2 meter ring solar telescope,the closed-loop control tests of the experimental system was conducted by applying load.The experimental results show that the accuracy in the closed-loop control mode is good,but it cannot fully match the high precision control requirements of the actual engineering design specifications.The next step is to optimize the closed-loop control and to decouple control of each partition pneumatic force actuators of the primary mirror.Test results indicate that the pneumatic force actuator and displacement actuator applied in this paper have reliable performance,clear principle,simple structure and high precision closed-loop control.These all confirm that the axial support design would hopefully be applied for the primary mirror of the 2 meter ring solar telescope.