Method of dynamic balancing for magnetic levitation molecular pump (5)

A method of rotor dynamic balancing for magnetic levitation molecular pump, wherein comprising steps of:

• step 1:
• activating a force free control module of a controller of said magnetic levitation molecular pump after activating a motor of said magnetic levitation molecular pump for acceleration;
• controlling a displacement detector through said controller of said magnetic levitation molecular pump so as to collect radial displacement signals of a rotor of said magnetic levitation molecular pump and to detect radial vibration amplitude of said rotor;
• and
• sequentially executing step 2, if the maximum radial vibration amplitude does not exceed ½ of a protective clearance during the acceleration of said rotor under the force free control module control, indicating that the force free control module is able to inhibit the co-frequency vibration of said rotor, so as to allow the rotational speed of said rotor to exceed its rigid critical rotational speed;
• or
• applying a typical rotor dynamic balancing method to achieve a low-speed balancing, so as to ensure the radial vibration amplitude of said rotor not to exceed ½ of said protective clearance before the rotational speed of said rotor exceeds the rigid critical rotational speed thereof, if the maximum radial vibration amplitude of said rotor exceeds ½ of said protective clearance, and then sequentially executing step 2, after the rotational speed of said rotor exceeds the rigid critical rotational speed thereof;
• step 2:
• detecting the radial vibration amplitude of said rotor through said displacement detector during the further acceleration of said motor;
• and stopping accelerating said motor, so as to stabilize said rotor at rotational speed ωi(i=0, 1, 2 . . . ), when the radial vibration amplitude of said rotor exceeds a preset vibration threshold of said rotor with respect to the nonrated rotational speed
• detecting the current rotational speed ωi through a rotational speed detector controlled by said controller of said magnetic levitation molecular pump;
• and
• determining if the rotational speed ωi is below the rated rotational speed of said rotor ωE;
• if ωi is below ωE, then sequentially executing step 3, otherwise jumping to step 5;
• step 3:
• performing rotor dynamic balancing operation with respect to said rotor at the nonrated rotational speed, by means of influence coefficient method, under the force free control module, with the operation of rotor dynamic balancing for said rotor at ωi comprising steps of:
• 3a) calling a rotor dynamic balancing module through said controller of said magnetic levitation molecular pump according to the current radial vibration amplitude and the rotational speed of said rotor, after said rotor with two balance planes preset thereon is accelerated to ωi, and recording the current initial imbalance vector V0 measured by a first radial displacement sensor and a second radial displacement sensor;
• wherein, the two balance planes are preset respectively away from the barycenter of the rotor, but located close to both ends of the rotor;
• 3b) turning off said motor of said magnetic levitation molecular pump, so as to decelerate said rotor to zero, and adding a trial mass m1 on a first balance plane;
• then restarting said magnetic levitation molecular pump so as to accelerate to the rotational speed ωi, and recording the current imbalance vector V1 measured by said first radial displacement sensor and said second radial displacement sensor;
• 3c) decelerating said rotor again to zero, and removing said trial mass m1 while adding a trial mass m2 on a second balance plane;
• and then restarting said magnetic levitation molecular pump so as to accelerate it to rotational speed ωi to the aforesaid steps, and recording a current imbalance vector V2 measured by said first radial displacement sensor and said second radial displacement sensor;
• 3d) with M1 and M2 in correspondence to the initial imbalance masses of the two imbalance planes respectively. calculating influence coefficient matrix T by means of influence coefficient method, which is:
• V0=T[M1 M2]T
• V1=T[M1+m1 M2]T
• V2=T[M1 M2+m2]T
• obtaining the influence coefficient matrix T according to the aforesaid matrix equations, and obtaining the initial imbalance mass matrix [M1 M2]T=T−1V0 through substitution in the first matrix equation;
• 3e) decelerating said rotor to zero, performing the rotor dynamic balancing operation through adding or removing weight to or from said two imbalance planes respectively based on the initial imbalance masses measured by means of step 3d);
• 3f) restarting said magnetic levitation molecular pump, while accelerating said rotor to ωi, and detecting the vibration amplitude of said rotor if it is below the preset vibration threshold with respect to the nonrated rotational speed;
• if the detected radial vibration amplitude is below said preset vibration threshold regarding the nonrated rotational speed, completing the rotor dynamic balancing operation at the current rotational speed and jumping to the next step;
• otherwise, repeating with step 3a) to 3f) till said rotor rotating at speed ωi, and the detected radial vibration amplitude of said rotor is below the preset vibration threshold with respect to the nonrated rotational speed when the rotor rotates at speed ωi, and sequentially executing step 4;
• step 4:
• letting i=i+1, and repeating step 2;
• step 5:
• under the force free control module control, performing rotor dynamic balancing operation with respect to said rotor at a rated rotational speed;
• the radial vibration amplitude of said rotor is below the preset vibration threshold regarding the nonrated rotational speed during the acceleration of said rotor from zero to ωE;
• and when the rotational speed of said rotor reaches ωE, the radial vibration amplitude of said rotor is below the preset vibration threshold with respect to the rated rotational speed as well as the residual imbalance mass of said rotor is less than the preset imbalance mass, completing the rotor dynamic balancing operation.