CN109847952B - Dynamic balance method of double-shaft precision centrifuge turntable based on driving current - Google Patents
Dynamic balance method of double-shaft precision centrifuge turntable based on driving current Download PDFInfo
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Abstract
A dynamic balance method of a double-shaft precision centrifuge turntable based on driving current belongs to the technical field of mechanical rotor dynamic balance. Aiming at solving the problems of lower identification precision of dynamic unbalance, complex operation and calculation process and the like existing in the conventional dynamic balance method of a precision centrifuge turntableThe time consumption is large, and the like. Setting a main shaft of a double-shaft precision centrifuge at a low rotating speed omega0Operating with the rotary table at a speed of-omega0Operating, collecting reference data of the driving current of the rotary table; setting a main shaft of a double-shaft precision centrifuge to operate at a working rotating speed omega, operating a rotary table at a rotating speed-omega, collecting the driving current data of the rotary table, and extracting a frequency doubling component of current; and (3) setting a double-shaft precision centrifuge to operate at a rotating speed omega, and accurately identifying and balancing the dynamic unbalance of the rotary table in a way of adding trial weights according to the obtained current-frequency multiplication. The method does not depend on any external precise sensor, has higher identification precision on the dynamic unbalance of the rotary table shaft system, is simple and easy to implement, does not need multiple experiments, and is more practical from the aspect of engineering application.
Description
Technical Field
The invention relates to a dynamic balance method of a precision centrifuge, in particular to a dynamic balance method of a rotary table of a double-shaft precision centrifuge based on driving current, belonging to the technical field of dynamic balance of rotors of large-scale machinery.
Background
The double-shaft precision centrifuge is mainly used for providing a large overload environment for navigation precision world consistency test verification, and can be used for carrying out a control system large overload navigation precision test, an inertia system world consistency test, error model verification and related calibration tests. In actual work, the main shaft and the rotary table of the double-shaft precision centrifuge inevitably have dynamic unbalance and are main factors causing mechanical vibration of the shaft system and influencing the precision and safe operation of the system due to the current process levels of mechanical manufacturing, processing, assembly and the like and the self mass distribution and installation positioning errors of loads.
For the dynamic balance problem of a main shaft system of a double-shaft precision centrifuge, different types of external sensors can be selected, the physical quantity can be measured through reasonable configuration and layout, and the effective identification of the dynamic unbalance of a rotor is realized by combining a mechanical rotor dynamics method and a dynamic balance method. However, the dynamic balance problem of the two-shaft precision centrifuge rotary table shaft system is limited by the following problems: on one hand, due to the limitation of structural space, a precise sensor or even a probe is difficult to be installed in a rotary table shaft system on the premise of ensuring the supporting rigidity; on the other hand, even if the sensor is installed and the detection of the required physical quantity is realized, due to the continuous rotation requirement of the main shaft and the rotary table, the effective signal of the sensor needs to be transmitted to the acquisition equipment through a slip ring and a long distance, so that the signal is inevitably influenced by system noise, the signal quality is difficult to guarantee, and the difficulty is increased for the identification of the dynamic unbalance of the rotor. The prior art with the reference number of CN105478245A provides a method for identifying the dynamic unbalance of a secondary shaft of a two-degree-of-freedom precision centrifuge based on main shaft vibration detection, solves the problem of identifying the dynamic unbalance of the secondary shaft of the existing two-degree-of-freedom precision centrifuge, and provides reference and basis for the dynamic balance correction of the shaft. However, the method proposed in this document has the following disadvantages: firstly, a precision sensor is required to be configured to measure the vibration of a main shaft of the centrifuge, so that the dynamic unbalance of a secondary shaft is indirectly identified, and the accuracy of the sensor directly influences the identification accuracy of the dynamic unbalance; secondly, because the shaft system of the main shaft of the centrifuge has very high rigidity, the method has lower sensitivity to the dynamic unbalance of the rotary shaft system, and the dynamic unbalance identification precision is low; finally, the identification process needs to be performed for multiple experiments, and the operation and calculation processes are complex and time-consuming.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the invention aims to provide a dynamic balancing method of a rotary table of a double-shaft precision centrifuge based on a driving current, and aims to solve the problems of low identification precision of dynamic unbalance, complex operation and calculation processes and high time consumption of the conventional dynamic balancing method of the rotary table of the double-shaft precision centrifuge.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a dynamic balance method of a rotary table of a double-shaft precision centrifuge based on driving current is characterized in that the axis O of the rotary table of the double-shaft precision centrifuge (a double-freedom-degree arm type precision centrifuge) is defined as a coordinate origin, the direction of a main shaft center which is positioned on the same water surface with the axis of the rotary table and points to the axis of the rotary table is the positive direction of an x axis, the upward direction of the axis of the rotary table is the positive direction of a z axis, and the direction of a y axis is determined according to the right-hand rule; setting the initial position of the static unbalance mass point on the positive half shaft of the x axis, and rotating the rotary table at the rotating speed-omega when the main shaft rotates at the rotating speed-omega; under the condition of only considering the action of static unbalance (because the static unbalance is more than ten times of even unbalance, the influence of the even unbalance on the torque provided by the motor of the rotary table can be ignored, and only the influence of the static unbalance is considered), when the rotary table rotates around the main shaft by an angle theta, the angular acceleration of a static unbalance mass point relative to the axis of the rotary table is omega2Lsin theta/r, wherein L is the distance between the center of the main shaft and the axle center of the rotary table, r is the distance between the static unbalance and the axle center of the rotary table, and the torque T provided by the motor of the rotary table is
T＝T1+T2+mω2Lrsinθ (1)
Wherein m is the equivalent mass of static unbalance of the rotary table, T2The friction torque generated by the gravity of the rotary table system is a constant value; t is1The friction torque, T, generated for positive pressure between the turntable and the turntable bearing1＝k1FR，k1For equivalent friction coefficient, R is the radius of the bearing of the rotary table, and the obtained positive pressure F on the rotary table is
Wherein M is the total mass of the rotary table except the static unbalance mass, the expressions are carried into the formula (1), Fourier series expansion is carried out, high-order small quantity is omitted, and the expression of the rotary table motor torque T shown in the formula (3) is obtained
T＝T2+Acos(ωt+90°) (3)
Wherein, A ═ m ω2Lr, according to the formula (3), the magnitude of the frequency doubling amplitude of the driving current of the rotary table can reflect the magnitude of the dynamic unbalance of the rotary table, and the dynamic unbalance phase phiuPhase phi of driving current with respect to the turntableiThere is a relationship ofu＝φi+90 ° for the leveling of the turntable requires a mechanical angular position phi of the turntablei-mass compensation at 90 °;
the method comprises the following implementation processes:
step one, setting a main shaft of a double-shaft precision centrifugal machine at a low rotating speed omega0Operating with the rotary table at a speed of-omega0In operation, reference data of the driving current of the rotary table is collected (when the rotating speed is small, the centrifugal force generated by the rotary table due to dynamic unbalance can be ignored, but due to existence of undesirable factors such as friction, a frequency doubling component still exists in the driving current of the rotary table, so that the reference data of the driving current of the rotary table needs to be identified before identification of the dynamic unbalance) and is recorded as the reference data
Wherein A is0，φ0Amplitude and phase, respectively;
step two, setting a main shaft of the double-shaft precision centrifuge to operate at a working rotating speed omega, operating the rotary table at the rotating speed-omega, collecting the driving current data of the rotary table, extracting a frequency doubling component of the current, and recording the frequency doubling component as
Wherein A is10，φ10Respectively, an amplitude and a phase corresponding to a frequency doubling component, so that the frequency of the current due to the dynamic unbalance is doubled
A1,φ1Is the amplitude and phase of the first frequency multiplication of the current before trimming;
and step three, setting a double-shaft precision centrifuge to operate at the rotating speed in the step two, and accurately identifying and balancing the dynamic unbalance of the rotary table in a trial weight adding mode according to the obtained current first frequency multiplication.
Further, in the third step, the amount of dynamic unbalance of the rotary table is accurately identified and balanced by adding a trial weight, and the specific process is as follows:
step three, one, namely, in the mechanical angle position phi of the rotary table1Adding a trial weight with the mass of lambda kg at the position of 90 degrees, collecting the drive current data of the rotary table at the moment, extracting a frequency doubling component from the data, and
obtaining a current first frequency doubling amplitude A 'by difference'1Therefore, it can be known that the trial weight of unit mass causes the change of the frequency multiplication amplitude of the driving current of the rotary table at the same phase position to
k＝|A1-A′1|/λ
Step three and two, the mechanical angle position phi of the rotary table1At-90 ℃ with an addition mass A1A trial weight of/k kg; collecting the current data of the rotary table, extracting a frequency doubling component, and
make a difference to obtain
At this time, pair A1And A2Making a comparison, if A2/A1Less than or equal to 20 percent, considering that the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision at the moment, and ending the dynamic balance; otherwise, performing the third step;
step three, in the mechanical angular position phi of the rotary tablenAt 90 °, n 2,3, …, the mass added being anA test weight of/k kg, collecting the drive current data of the rotary table at the moment, extracting a frequency doubling component, increasing the value of n by 1, and
make a difference to obtain
Representing the frequency doubling of the driving current of the rotary table before the nth counterweightn/A1When the dynamic balance is less than or equal to 20 percent, the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision, and the dynamic balance is finished.
Further, in the third step, the amount of dynamic unbalance of the rotary table is accurately identified and balanced by adding a trial weight, and the specific process is as follows:
step three, one, namely, in the mechanical angle position phi of the rotary table1Adding xi kg of trial weight at 90 degrees, collecting the driving current data of the rotary table, extracting a frequency doubling component in the data, and
the difference is made to obtain the amplitude A of the current-frequency doubling caused by the dynamic unbalancem(m＝2,3,...)，
Representing the first frequency multiplication of the driving current of the rotary table before the mth counterweight;
step three, adding the trial weight each time and then driving the first frequency doubling amplitude A of the rotary table driving currentmAmplitude A of one frequency multiplication with that of the rotary table driving current caused by dynamic unbalance when no test weight is added initially1Making a comparison when Am/A1When the dynamic balance is less than or equal to 20 percent, the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision, and the dynamic balance is finished. In step III or II, when A ism/A1If the content is not more than 20 percent, performing the third step: if Am/A1>20%, judging again if Am>Am-1The test weight added last time is considered to have the best effect on identifying dynamic unbalance, and the test weight of ξ kg needs to be subtracted, so that the dynamic balance effect of the double-shaft precision centrifuge is the best.
Further, the method can be used for preparing a novel materialIn step one, the small rotation speed ω0Is not more than 6 DEG/s.
Further, in step two, for each obtained turntable driving current signal, the reference data of the turntable driving current needs to be subtracted to obtain a frequency doubling signal of the driving current caused by the dynamic unbalance of the turntable.
Further, in the first step, FFT analysis or correlation filtering is used to extract a frequency multiplication component of the turntable driving current.
Further, in step one, the dynamic unbalance is composed of a static unbalance and an even unbalance, wherein the static unbalance is represented by a small mass, and the even unbalance can be regarded as two masses with equal mass which are symmetrically distributed about the origin.
Further, in the first step, the positive pressure F applied to the rotary table is M omega applied to the rotary table along the L negative direction2The centripetal force and the static unbalance of L are subjected to the magnitude of m omega along the direction r2L cos θ centripetal force.
The invention has the beneficial effects that:
the invention provides a method for dynamically balancing a rotary table by detecting the driving current of the rotary table of a double-shaft arm type precision centrifugal machine based on the relation between a control signal of a closed-loop control system and external interference and by utilizing the characteristic that the driving current of the rotary table is sensitive to dynamic unbalance. Compared with the prior art of the document No. CN105478245A, the method does not depend on any external precise sensor, has higher sensitivity and identification precision to the dynamic unbalance of the rotary table shaft system, has the advantages of simplicity and feasibility, and no need of multiple experiments, not only improves the dynamic balance precision, but also greatly shortens the dynamic balance time, is more practical from the engineering application perspective, and solves the problem of the dynamic balance of the rotary table of the double-shaft arm type precise centrifuge.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is a flow chart of the present invention, wherein fig. 1(a) and fig. 1(b) are flow charts corresponding to the first embodiment and the second embodiment, respectively;
FIG. 2 is a schematic structural diagram of a two-degree-of-freedom precision centrifuge (wherein, 1-counterweight bin, 2-big arm, 3-turntable, 4-turntable motor, 5-spindle, 6-bearing, 7-spindle motor, 8-foundation);
FIG. 3 is a top view of a motion analysis of a dual-axis precision centrifuge;
FIG. 4 is a three-dimensional diagram of the position distribution of mass blocks used in the simulation of dynamic unbalance of a turntable of a two-axis precision centrifuge, wherein a large sphere is an added unbalance mass block and has coordinates of (x)10,0), two small spheres are added into the even unbalance mass block, and the coordinates are (x) respectively2,y2,z2) And (-x)2,-y2,-z2) The phase difference between the even balance mass block and the static unbalance mass block is
FIG. 5 is a comparison graph of a frequency doubling amplitude of a turntable driving current before dynamic balancing when the turntable of the dual-shaft precision centrifuge has or does not have even imbalance;
FIG. 6 is a comparison graph of driving current-frequency multiplication amplitude of the rotary table before and after balancing when the rotary table of the double-shaft precision centrifuge has only static unbalance;
FIG. 7 is a comparison graph of the driving current-frequency multiplication amplitude of the rotary table before and after balancing when the rotary table of the double-shaft precision centrifuge has static unbalance and even unbalance.
Detailed Description
The first embodiment is as follows: referring to fig. 1(a), fig. 2 and fig. 3, the implementation process of the dynamic balancing method for a two-axis precision centrifuge turret based on a driving current according to the present embodiment is as follows:
the schematic structural diagram of the dual-shaft arm type precision centrifuge is shown in fig. 2, the axis O of the rotary table of the dual-shaft arm type precision centrifuge is defined as the origin of coordinates, the direction from the center of the main shaft on the same water surface with the axis of the rotary table to the axis of the rotary table is the positive direction of the x-axis,the upward direction of the axis of the rotary table is the positive direction of the z axis, and the direction of the y axis is determined according to the right-hand rule; setting the initial position of the static unbalance mass point on the positive half shaft of the x axis, and rotating the rotary table at the rotating speed-omega when the main shaft rotates at the rotating speed-omega; under the condition of only considering the action of static unbalance (because the static unbalance is far greater than the even unbalance, the influence of the even unbalance on the torque provided by the motor of the rotary table can be ignored, and only the influence of the static unbalance is considered), when the rotary table rotates around the main shaft by an angle theta, the angular acceleration of a static unbalance mass point relative to the axis of the rotary table is omega2Lsin theta/r, wherein L is the distance between the center of the main shaft and the axle center of the rotary table, r is the distance between the static unbalance and the axle center of the rotary table, and the torque T provided by the motor of the rotary table is
T＝T1+T2+mω2Lrsinθ (4)
Wherein m is the equivalent mass of static unbalance of the rotary table, T2The friction torque generated by the gravity of the rotary table system is T because the mass distribution of the rotary table system is very small in change during the operation process2Can be approximated as a constant value. T is1The friction torque, T, generated for positive pressure between the turntable system and the turntable bearing1＝k1FR，k1For equivalent friction coefficient, R is the radius of the bearing of the rotary table, and the obtained positive pressure F on the rotary table is
Wherein M is the total mass of the rotary table except the static unbalance mass, the expressions are carried into the formula (4), Fourier series expansion is carried out, high-order small quantity is omitted, and the expression of the rotary table motor torque T shown in the formula (6) is obtained
T＝T2+Acos(ωt+90°)(6)
Wherein, A ═ m ω2Lr, according to the formula (6), the magnitude of the frequency doubling amplitude of the driving current of the rotary table can reflect the magnitude of the dynamic unbalance of the rotary table, and the dynamic unbalance phase phiuPhase phi of driving current with respect to the turntableiThere is a relationship ofu＝φi+90 ° for the leveling of the turntable requires a mechanical angular position phi of the turntablei-mass compensation at 90 °.
The dynamic balance method of the rotary table of the double-shaft precision centrifuge based on the driving current is realized by the following steps:
step one, setting a main shaft of a double-shaft precision centrifugal machine at a low rotating speed omega0Operating with the rotary table at a speed of-omega0In operation, reference data of the driving current of the rotary table is collected (when the rotating speed is small, the centrifugal force generated by the rotary table due to dynamic unbalance can be ignored, but due to the existence of undesirable factors such as friction, a frequency doubling component still exists in the driving current of the rotary table, so the reference data of the driving current of the rotary table needs to be measured before the dynamic unbalance identification is carried out), and is recorded as the reference data
Step two, setting a main shaft of the double-shaft precise centrifuge to operate at a rotating speed omega, operating the rotary table at the rotating speed-omega, collecting the drive current data of the rotary table, extracting a frequency doubling component of the drive current, and recording the frequency doubling component as
So that the frequency of the current due to the dynamic unbalance is doubled
A1Phi and phi1Is the amplitude and phase of the first frequency multiplication of the current before trimming;
step three, setting a double-shaft precision centrifuge to operate at the rotating speed in the step two, and accurately identifying and balancing the dynamic unbalance of the rotary table in a way of adding trial weights according to the obtained current first frequency multiplication, wherein the step can be realized in the following way, as shown in fig. 1 (a):
step three, one, namely, in the mechanical angle position phi of the rotary table1Adding a trial weight with the mass of lambda kg at the position of 90 degrees, collecting the drive current data of the rotary table at the moment, extracting a frequency doubling component from the data, and
obtaining a current first frequency doubling amplitude A 'by difference'1Therefore, it can be known that the trial weight of unit mass causes the change of the frequency multiplication amplitude of the driving current of the rotary table at the same phase position to
k＝|A1-A′1|/λ
Step three and two, the mechanical angle position phi of the rotary table1At-90 ℃ with an addition mass A1Test weight of/k kg. Collecting the current data of the rotary table, extracting a frequency doubling component, and
make a difference to obtain
At this time, pair A1And A2Making a comparison, if A2/A1Less than or equal to 20 percent, considering that the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision at the moment, and ending the dynamic balance; otherwise, performing the third step;
step three, in the mechanical angular position phi of the rotary tablenAt 90 ° (n ═ 2, 3. -), the mass added is anA test weight of/k kg, collecting the driving current data of the rotary table at the moment, extracting a frequency doubling component, wherein n is n +1, and
make a difference to obtain
Representing the frequency doubling of the driving current of the rotary table before the nth counterweightn/A1When the dynamic balance is less than or equal to 20 percent, the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision, and the dynamic balance is finished.
The second embodiment is as follows: the first difference between this embodiment and the specific embodiment is that step three can also be implemented in the following manner, as shown in fig. 1 (b):
step three, one, namely, in the mechanical angle position phi of the rotary table1Adding xi kg of trial weight at 90 degrees, collecting the driving current data of the rotary table, extracting a frequency doubling component in the data, and
the difference is made to obtain the amplitude A of the current-frequency doubling caused by the dynamic unbalancem，m＝2,3,…；
Representing the first frequency multiplication of the driving current of the rotary table before the mth counterweight;
step three, adding the trial weight each time and then driving the first frequency doubling amplitude A of the rotary table driving currentmAmplitude A of one frequency multiplication with that of the rotary table driving current caused by dynamic unbalance when no test weight is added initially1Making a comparison when Am/A1When the dynamic balance is less than or equal to 20 percent, the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision, and the dynamic balance is finished; otherwise, performing the third step;
step three, if Am/A1>20%, judging again if Am>Am-1The test weight added last time is considered to have the best effect on identifying dynamic unbalance, and the test weight of ξ kg needs to be subtracted, so that the dynamic balance effect of the double-shaft precision centrifuge is the best. Otherwise, repeating the third step until the requirement is met.
Example (b): the invention is further described in detail with reference to fig. 1-7, and the dynamic balance method of the dual-shaft precision centrifuge turntable based on the driving current is used for identifying and balancing the dynamic unbalance in an ideal simulation environment without adding undesirable factors such as friction and the like, so that reference data does not need to be measured.
Experiment one: when only static unbalance exists in the rotary table of the double-shaft precise centrifuge, a static unbalance mass block (blue) as shown in fig. 4 is added, the mass of the mass block is 2.091kg, the coordinates are (0.35,0,0), the main shaft of the double-shaft precise centrifuge is set to operate at the rotating speed omega which is 360 degrees/s, the rotary table operates at the rotating speed omega which is 360 degrees/s, and the driving current of the rotary table of the double-shaft precise centrifuge is collectedExtracting a frequency doubling component from the signal to obtain
At this moment phi1-90.2 °. At the mechanical angular position phi of the turntable1At-90 ° -180.2 °, i.e., (-0.400,0.001), a trial weight of λ ═ 1kg was added to obtain the first harmonic amplitude a 'of the drive current signal at that time'143.348A, it can be seen that the trial weight of unit mass causes a change in the amplitude of the frequency doubled of the turntable drive current at the same phase to
k＝|A1-A′1|/λ＝58.44A/kg
At the mechanical angular position phi of the turntable1Adding 1.742kg of test weight at the position of-180.2 degrees when the angle is 90 degrees to-180 degrees, and obtaining that the frequency doubling amplitude of the driving current is A at the moment2＝0.488A。
Due to A2/A1＝0.48％<20%, as shown in fig. 6, when the rotary table of the dual-shaft precision centrifuge only has static unbalance, the comparison graph of the first frequency multiplication amplitude of the driving current of the rotary table before and after balancing is shown, at this time, the dynamic balance of the dual-shaft precision centrifuge reaches the specified precision, and the dynamic balance is finished.
Experiment two: when static unbalance and even unbalance exist in the rotary table, a static unbalance mass block (blue) and an even unbalance mass block (red) shown in figure 4 are added, and the phase difference between the static unbalance and the even unbalance is realized
Wherein the mass of the static unbalance mass block is 2.091kg, the coordinates are (0.35,0,0), the mass of each even unbalance mass block is 0.207kg, and the coordinates are (0.1,0.23,0.08) and (-0.1, -0.23, -0.08), respectively. Setting a main shaft of a double-shaft precise centrifuge to operate at a rotating speed omega of 360 DEG/s, operating a rotary table at the rotating speed omega of 360 DEG/s, collecting a signal of a driving current of the rotary table of the double-shaft precise centrifuge, extracting a frequency doubling component in the signal, and obtaining the frequency doubling component
At this moment phi1-90.2 °. As shown in FIG. 5, the dynamic balance is achieved with or without even unbalanceThe comparison graph of the frequency doubling amplitude of the driving current of the rotary table of the double-shaft precision centrifugal machine before balancing can be seen from the graph 5, before dynamic balancing, even unbalance exists, the frequency doubling amplitude of the driving current of the rotary table is very large, and when the even unbalance exists, the frequency doubling amplitude of the driving current is slightly larger.
At the mechanical angular position phi of the turntable1Adding a test weight of lambda 1kg at a position of-90 DEG to-180.2 DEG to obtain a first doubling amplitude A 'of the driving current signal at the moment'145.675A, it can be seen that the trial weight of unit mass causes a change in the amplitude of the frequency doubled of the turntable drive current at the same phase to
k＝|A1-A′1|/λ＝56.117A/kg
At the mechanical angular position phi of the turntable1Adding 1.814kg of test weight at the position of-90 degrees to-180.2 degrees to obtain the driving current-frequency doubling amplitude A at the moment2＝0.586A。
Due to A2/A1＝0.58％<20%, as shown in fig. 7, when static imbalance and even imbalance simultaneously exist in the revolving platform of the dual-shaft precision centrifuge, a comparison graph of a frequency doubling amplitude of the driving current of the revolving platform before and after balancing is shown, at this time, dynamic balance of the dual-shaft precision centrifuge reaches specified precision, and dynamic balance is finished.
The invention provides a dynamic balance method of a double-shaft precision centrifuge turntable based on driving current, which can effectively identify the amplitude and phase of dynamic unbalance of the double-shaft precision centrifuge turntable and carry out balancing by collecting and processing data of the driving current of the turntable, wherein the first frequency multiplication amplitude of the driving current of the double-shaft precision centrifuge turntable before and after the first dynamic balance experiment and the second dynamic balance experiment is shown in table 1, the attenuation rate of the dynamic unbalance of the method can reach about 99 percent, and the effectiveness of the method is proved.
TABLE 1 frequency-doubled amplitude of driving current before and after dynamic balance
The present invention is suitable for dynamic balancing of a two-shaft precision centrifuge, and various changes and modifications can be made by those skilled in the art without departing from the spirit and essence of the present invention, and these changes and modifications should fall within the protection scope of the appended claims.
Claims (9)
1. A dynamic balance method of a rotary table of a double-shaft precision centrifuge based on driving current is characterized in that the axis O of the rotary table of the double-shaft precision centrifuge is defined as the origin of coordinates, the direction of the center of a main shaft which is positioned on the same water surface with the axis of the rotary table and points to the axis of the rotary table is the positive direction of an x axis, the upward direction of the axis of the rotary table is the positive direction of a z axis, and the direction of a y axis is determined according to the right-hand rule; setting the initial position of the static unbalance mass point on the positive half shaft of the x axis, and rotating the rotary table at the rotating speed-omega when the main shaft rotates at the rotating speed-omega; under the condition of only considering the static unbalance action, when the rotary table rotates around the main shaft by an angle theta, the angular acceleration of a static unbalance mass point relative to the axis of the rotary table is omega2Lsin theta/r, wherein L is the distance between the center of the main shaft and the axle center of the rotary table, r is the distance between the static unbalance and the axle center of the rotary table, and the torque T provided by the motor of the rotary table is
T＝T1+T2+mω2Lrsinθ (1)
Wherein m is the equivalent mass of static unbalance of the rotary table, T2The friction torque generated by the gravity of the rotary table system is a constant value; t is1The friction torque, T, generated for positive pressure between the turntable and the turntable bearing1＝k1FR，k1For equivalent friction coefficient, R is the radius of the bearing of the rotary table, and the obtained positive pressure F on the rotary table is
Wherein M is the total mass of the rotary table except the static unbalance mass, the expressions are carried into the formula (1), Fourier series expansion is carried out, high-order small quantity is omitted, and the expression of the rotary table motor torque T shown in the formula (3) is obtained
T＝T2+Acos(ωt+90°) (3)
Wherein, A ═ m ω2Lr, according to the formula (3), the magnitude of the frequency doubling amplitude of the driving current of the rotary table can reflect the magnitude of the dynamic unbalance of the rotary table, and the dynamic unbalance phase phiuPhase phi of driving current with respect to the turntableiThere is a relationship ofu＝φi+90 ° for the leveling of the turntable requires a mechanical angular position phi of the turntablei-mass compensation at 90 °;
the method is characterized by comprising the following implementation processes:
step one, setting a main shaft of a double-shaft precision centrifugal machine at a low rotating speed omega0Operating with the rotary table at a speed of-omega0Operating, collecting reference data of the driving current of the rotary table, and recording the reference data
Wherein A is0，φ0Amplitude and phase, respectively;
step two, setting a main shaft of the double-shaft precision centrifuge to operate at a working rotating speed omega, operating the rotary table at the rotating speed-omega, collecting the driving current data of the rotary table, extracting a frequency doubling component of the current, and recording the frequency doubling component as
Wherein A is10，φ10Respectively, an amplitude and a phase corresponding to a frequency doubling component, so that the frequency of the current due to the dynamic unbalance is doubled
A1,φ1Is the amplitude and phase of the first frequency multiplication of the current before trimming;
and step three, setting a double-shaft precision centrifuge to operate at the rotating speed in the step two, and accurately identifying and balancing the dynamic unbalance of the rotary table in a trial weight adding mode according to the obtained current first frequency multiplication.
2. The dynamic balancing method of the turntable of the biaxial precision centrifuge based on the driving current as claimed in claim 1, wherein in the third step, the dynamic unbalance amount of the turntable is accurately identified and balanced by adding a trial weight, and the specific process is as follows:
step three, one, namely, in the mechanical angle position phi of the rotary table1Adding a trial weight with the mass of lambda kg at the position of 90 degrees, collecting the drive current data of the rotary table at the moment, extracting a frequency doubling component from the data, and
obtaining a current first frequency doubling amplitude A 'by difference'1Therefore, it can be known that the trial weight of unit mass causes the change of the frequency multiplication amplitude of the driving current of the rotary table at the same phase position to
k＝|A1-A′1|/λ
Step three and two, the mechanical angle position phi of the rotary table1At-90 ℃ with an addition mass A1A trial weight of/k kg; collecting the current data of the rotary table, extracting a frequency doubling component, and
make a difference to obtain
At this time, pair A1And A2Making a comparison, if A2/A1Less than or equal to 20 percent, considering that the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision at the moment, and ending the dynamic balance; otherwise, performing the third step;
step three, in the mechanical angular position phi of the rotary tablenAt 90 °, n 2,3, …, the mass added being anA test weight of/k kg, collecting the drive current data of the rotary table at the moment, extracting a frequency doubling component, increasing the value of n by 1, and
make a difference to obtain
Representing the frequency doubling of the driving current of the rotary table before the nth counterweightn/A1When the dynamic balance is less than or equal to 20 percent, the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision, and the dynamic balance is finished.
3. The dynamic balancing method of the turntable of the biaxial precision centrifuge based on the driving current as claimed in claim 1, wherein in the third step, the dynamic unbalance amount of the turntable is accurately identified and balanced by adding a trial weight, and the specific process is as follows:
step three, one, namely, in the mechanical angle position phi of the rotary table1Adding xi kg of trial weight at 90 degrees, collecting the driving current data of the rotary table, extracting a frequency doubling component in the data, and
the difference is made to obtain the amplitude A of the current-frequency doubling caused by the dynamic unbalancem，m＝2,3,…；
Representing the first frequency multiplication of the driving current of the rotary table before the mth counterweight;
step three, adding the trial weight each time and then driving the first frequency doubling amplitude A of the rotary table driving currentmAmplitude A of one frequency multiplication with that of the rotary table driving current caused by dynamic unbalance when no test weight is added initially1Making a comparison when Am/A1When the dynamic balance is less than or equal to 20 percent, the dynamic balance of the double-shaft precise centrifugal machine reaches the required precision, and the dynamic balance is finished.
4. The dynamic balancing method of claim 3, wherein in step three, when A is in step two, the dynamic balancing method is performedm/A1If the content is not more than 20 percent, performing the third step: if Am/A1>20%, judging again if Am>Am-1The test weight added last time is considered to have the best effect on identifying dynamic unbalance, and the test weight of ξ kg needs to be subtracted.
5. A method for dynamic balancing of a two-axis precision centrifuge turret based on driving current according to claim 1, 2,3 or 4, wherein in step one, the small rotation speed ω is small0Is not more than 6 DEG/s.
6. The method of claim 5, wherein in step two, for each obtained turret drive current signal, the reference data of the turret drive current is subtracted to obtain a multiple frequency signal of the drive current caused by the turret dynamic imbalance.
7. The dynamic balancing method for the turntable of the biaxial precise centrifuge based on the driving current as claimed in claim 1, 2,3 or 4, wherein in the step one, the FFT analysis or the related filtering method is adopted for the extraction of a frequency doubling component of the driving current of the turntable.
8. A dynamic balancing method for a two-axis precision centrifuge turret based on driving currents according to claim 1, 2,3 or 4, characterized in that in step one, the dynamic imbalance is composed of static imbalance and even imbalance, wherein the static imbalance is represented by a small mass, and the even imbalance can be regarded as two masses with equal mass symmetrically distributed about the origin.
9. The dynamic balancing method of claim 8, wherein in the first step, the positive pressure F applied to the turntable is M ω in a magnitude that the turntable is applied to along the L negative direction2The centripetal force and the static unbalance of L are subjected to the magnitude of m omega along the direction r2L cos θ centripetal force.
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