Active Vibration Control Of The Journal Of Flexure Pivot-Tilting Pad Bearing

Spindle vibrations are very common in high-speed rotary machines,such as unbalance response caused by rotor imbalance,or the vibration caused by transient load,acting directly on rotor,from outside bearing.When the vibration is too severe without control,it will have an adverse effect on spindle rotary accuracy;product's machining precision and even the safe operation of equipment.Especially for today's high-speed,high-precision development of rotating machinery,the problem of vibration control becomes more prominent.Although the vibration of the journal cannot be completely eliminated,suppressing the vibration amplitude to the minimum is of great significance to improve the safety of equipment operation,spindle rotary accuracy and product's machining precision.In this paper,a flexure pivot-tilting pads bearing with an oil chamber in the pad is taken as the research object.It can not only use the static pressure effect to reduce the spindle wear under low-speed operating conditions,but also use the stability mechanism of bearing itself to improve the stability of equipment operation.Even so,the rotor still inevitably produces unbalance vibration at high speeds or at ultra-high speeds.Although the nature of the bearing(structure)itself determines that it has a certain unbalance suppression capability,it is limited and requires external active control.In order to further suppress unbalance vibration,this paper conducts research work focus on this bearing.The main contents and conclusions are as follow.(1)Firstly,the purpose and significance of the research are pointed out.Secondly,the status of related research at home and abroad is introduced,including the active control of rotor vibration,the main types of active controllers,and the main control strategies in this field.Finally,the main research contents and corresponding research methods of the paper are clarified.(2)Introduction of bearing structure,establishment of mathematical model,and bearing response calculation.(3)Starting from the main structural parameters of the bearing,the relationship between structural parameters and journal vibration under step loads is studied,and a method for reducing journal vibration is sought.The simulation results show that appropriately increasing the preload coefficient or reducing the radius clearance can reduce journal vibration,and should be carefully selected during the bearing design.(4)An active control method is proposed by changing the centripetal force of the rotor and makes the rotor center trajectory converge to suppress unbalance response.First,a simplified system vibration model is established.Then,the applying scheme of control force and its calculation method are taken into account.Considering the difference of the oil film stiffness when the rotor's positions are different,we take the stiffness at the static equilibrium position as the value of the control area to simplify the calculation of the control force.The simulation results show that,the effect of proposed method is remarkable.When the amount of unbalance is 0.3 or 0.5,the unilateral control method can suppress the vibration amplitude of rotor in both x and y direction by about 70%.While the control results that by use of bilateral control method turn out to be about 90%.Another active control method is proposed by appropriately increasing the distance from the center of unbalance trajectory to the origin of coordinates to increase the oil film stiffness and thus suppress the unbalance response.The method still based on the simplified bearing-rotor vibration system as the mathematical model,and derives the standard transfer function according to the obtained motion differential equations of the simplified system.The rotor center positioning strategy is studied,and the rotor center positioning equation is obtained by least-squares fitting.The simulation results show that,the proposed rotor center positioning strategy can achieve high positioning accuracy and the unbalance response is significantly suppressed.The vibration amplitude in the x and y directions are both suppressed by about 90%.(5)Analyze the realization of the two control methods and draw the conclusion that the way to obtain the target control force through the control of the tilt angle of the bearing may have limited control capability,and the use of electromagnetic actuators can output relatively timely and accurate control force,but consider its installation and the impact on the bearing system.The two control methods are analyzed in terms of control effects and feasibility.The inhibitory effects of the two methods on unbalance response are all significant and can all reach about 90%;in terms of feasibility,the former has higher requirements for rapid response and reliability of the system devices,while the later has a longer preparation time,in which the exact calculation of the oil film stiffness has a certain degree of difficulty.Analyzing the deficiencies of the two methods,it is concluded that because two of them are to simplify the problem analysis,there will be differences between the established model and the actual one,so,the obtained equations will also lack of some key parameters,this will inevitably lead to a certain difference between the accuracy and effect of the control and the actual situation.