Disclosure of Invention
1. A dynamic performance analysis method for a parallel mechanism is characterized by comprising the following steps:
1) establishing a dynamic model of the parallel mechanism in a joint space:
in the formula, τ
mIs the driving moment of the parallel mechanism, M is an inertia matrix, C is a centrifugal force/Coriolis force matrix, G is a gravity matrix,
and
the angular acceleration and the angular velocity of the drive shaft servo motor are respectively;
singular value decomposition is carried out on the inertia matrix M to obtain the maximum singular value JL,JLThe maximum load inertia of the driving shaft;
2) establishing a double-inertia control system of the driving shaft of the parallel mechanism to obtain an angular velocity transfer relation:
in the formula, ωaActual angular velocity, ω, of load inertiarAt a desired angular velocity, KpvAnd TivProportional gain of speed loop controllerWith integral time coefficient, JmFor driving the inertia of the servo motor, KtIs the moment coefficient, s is the Laplace operator, ωnAnd omegacRespectively an antiresonance frequency and a resonance frequency, omeganAnd omegacThe calculation method comprises the following steps:
in the formula, k
sIn order to control the connection rigidity of the system by double inertia,
is the inertia ratio;
based on the angular velocity transfer relationship, further obtaining an angular position transfer relationship:
in the formula, thetaaIs the actual angle of inertia of the load, θrAt a desired angle, KppIs the proportional gain of the position loop controller;
3) and when the rotation angle α of the parallel mechanism is equal to β and equal to 0, the original pose of the parallel mechanism is taken, α and β are euler angles, and further, the total damping ratio zeta is selected for the double-inertia control system, wherein the zeta meets the constraint relation:
determining a proportional gain K of the speed loop controller after the overall damping ratio ζ is determinedpvIntegral time coefficient TivAnd proportional gain K of position loop controllerpp:
Kpv=Jm(2ζ1ω1+2ζ2ω2)
In the formula, ζ1、ζ2First damping ratio and second damping ratio, omega, for a dual inertia control system1、ω2The first natural frequency and the second natural frequency of the double-inertia control system;
5) calculating a new first damping ratio, a new second damping ratio, a new first natural frequency and a new second natural frequency of the parallel mechanism driving shaft double-inertia control system at different poses:
in the formula, ζn1For a new first damping ratio, ζn2Is the new second damping ratio, ωn1Is a new first natural frequency, ωn2Is a new second natural frequency, t1、t2、t3And t4Is the root of the characteristic equation Δ, and Δ is:
using ζn1、ζn2、ωn1、ωn2Relative ζ1、ζ2、ω1、ω2The change of the parallel mechanism explains the change of the dynamic performance of the parallel mechanism, and finally the analysis of the dynamic performance of the parallel mechanism is completed.
Hair brushIn step 3) of the above process, ζ1、ζ2、ω1、ω2And KppIs determined according to the following steps:
1) determining Zeta according to the determined overall damping ratio Zeta of the dual inertia control system1、ζ2Comprises the following steps:
ζ1=ζ2=ζ
2) further calculate ω1And omega2Comprises the following steps:
3) writing out an open-loop transfer function G of a dual-inertia control systempComprises the following steps:
according to GpDetermining proportional gain K of position loop controller by using root track methodpp。
The invention provides a dynamic performance analysis method for a parallel mechanism, which has the following advantages and prominent technical effects: the invention provides a widely effective dynamic performance analysis method aiming at the problem that the dynamic performance time-varying characteristic of the parallel mechanism cannot be fully reflected by using the traditional dynamic performance analysis method of the series mechanism and combining the characteristics of the parallel mechanism, which is lack of an effective method for analyzing the dynamic performance of the parallel mechanism at present, has important significance for deeply understanding and explaining the change of the dynamic performance of the parallel mechanism in the motion process, is an important basis for further improving the dynamic performance of the parallel mechanism, and provides an effective tool for analyzing the dynamic performance of the parallel mechanism, namely a complex electromechanical integrated device.
Detailed Description
Firstly, establishing a dynamic model of a parallel mechanism in a joint space, and calculating the maximum load inertia of a driving shaft; establishing a double-inertia control system of a driving shaft of the parallel mechanism to obtain an angular speed transfer relation and an angular position transfer relation; further selecting a proper total damping ratio for the double-inertia control system, and determining control parameters of a speed ring controller and a position ring controller; and finally, calculating the change of the first damping ratio and the second damping ratio of the double-inertia control system and the change of the first natural frequency and the second natural frequency, and explaining the change of the dynamic performance of the parallel mechanism.
The invention is described in further detail below with reference to the figures and the embodiments.
Fig. 1 shows a typical three-degree-of-freedom parallel mechanism, where the parallel mechanism drives a terminal moving platform 4 to move through the movement of a first slider 1, a second slider 2, and a third slider 3, the first slider 1, the second slider 2, and the third slider 3 are driven by corresponding servo motors, the moving platform 4 is connected with the first slider 1 through a first rod 5, the moving platform 4 is connected with the second slider 2 through a second rod 6, the moving platform 4 is connected with the third slider 3 through a third rod 7, a shaft of the slider 1 is a first driving shaft, a shaft of the slider 2 is a second driving shaft, and a shaft of the slider 3 is a third driving shaft.
FIG. 2 is a flow chart of a method for analyzing dynamic performance of a parallel mechanism according to the present invention. The proposed method for analyzing the dynamic performance of the parallel mechanism is applied to the parallel mechanism, and the method comprises the following specific steps:
1) firstly, a dynamic model of the parallel mechanism is established in a joint space as follows:
in the formula, τ
mRepresenting the driving moment of the parallel mechanism, M is an inertia matrix, C is a centrifugal force/Coriolis force matrix, G is a gravity matrix,
and
the angular acceleration and the angular velocity of the drive shaft servo motor are respectively;
2) the inertia matrix M is further represented as:
in the formula, PhIs ball screw lead, MsInertia matrix, M, for driving the sliders for parallel mechanismspIs an inertia matrix of a movable platform of a parallel mechanism terminal, MliIs an inertia matrix of the rods of the parallel mechanism, GaIs a transmission matrix between the speed of the driving shaft of the parallel mechanism and the speed of the terminal moving platform, JivωThe transmission matrix is the transmission matrix between the speed of the terminal moving platform of the parallel mechanism and the speed of the rod piece;
3) at the corner α e [ -2 π/92 π/9 of the parallel mechanism]rad,β∈[-2π/9 2π/9]In the rad range, α and β are Euler angles, singular value decomposition is carried out on the inertia matrix M to obtain the maximum load inertia J of the driving shaftLThe variation range of (A) is as follows:
0.0085kg·m2≤JL≤0.0432kg·m2(3)
4) establishing a double-inertia control system of the driving shaft of the parallel mechanism to obtain an angular velocity transfer relation:
in the formula, ωaActual angular velocity, ω, of load inertiarAt a desired angular velocity, KpvAnd TivProportional gain and integral time coefficient, J, respectively, of the speed loop controllermThe inertia of the servo motor of the driving shaft is 0.0103 kg.m2,KtThe moment coefficient is 1.4 N.m/A, s is Laplace operator, omeganAnd omegacRespectively an antiresonance frequency and a resonance frequency, omeganAnd omegacThe calculation method comprises the following steps:
in the formula, k
sThe connecting rigidity of the double-inertia control system is 1200 N.m/rad,
is the inertia ratio;
based on the angular velocity transfer relationship, further obtaining an angular position transfer relationship:
in the formula, thetaaIs the actual angle of inertia of the load, θrAt a desired angle, KppIs the proportional gain of the position loop controller;
5) when the rotating angle α is selected to be β is selected to be 0, the original pose of the parallel mechanism is selected, and the maximum load inertia at the moment is 0.0085 kg-m2The inertia ratio R is 0.8252, and the overall damping ratio ζ of the available dual inertia control system needs to satisfy the relationship:
combining the constraint condition, selecting an overall damping ratio zeta of 0.4 for the double-inertia control system;
6) let first damping ratio ζ of double inertia control system1Zeta second damping ratio2Comprises the following steps:
ζ1=ζ2=ζ=0.4 (7)
further obtaining the first natural frequency omega of the double inertia control system1And a second natural frequency omega2Comprises the following steps:
in the formula, ωnTaking the value of 375.7646 rad/s;
7) according to ζ1、ζ2、ω1And omega2Obtaining the proportional gain K of the speed ring controller of the parallel mechanism driving shaft double-inertia control systempvAnd integral time coefficient TivComprises the following steps:
Kpv=Jm(2ζ1ω1+2ζ2ω2)=7.3847 (10)
8) writing out an open-loop transfer function G of a dual-inertia control systempComprises the following steps:
obtaining proportional gain K of position loop controller by root track methodpp=60;
9) The parallel mechanism is respectively in an original pose, a middle pose and an edge pose, and the maximum load inertia and the corresponding inertia ratio of a driving shaft of the parallel mechanism at the moment are as follows:
in the formula, JL1、JL2And JL3The maximum load inertia R of the driving shaft when the parallel mechanism is in the original pose, the middle pose and the edge pose respectively1、R2And R3Respectively corresponding inertia ratios;
based on the established double-inertia control system and the obtained control parameters, under the condition that the speed input signal is sin (2 pi t) rad/s and the position input signal is sin (2 pi t) rad, speed and position response results of the parallel mechanism under three poses are obtained, response errors are shown in fig. 3 and fig. 4, the abscissa of fig. 3 and fig. 4 represents a time change range, the unit is s, and the ordinate represents the speed response error and the position response error respectively, and the unit is rad/s and rad; curve R in fig. 31、R2And R3Respectively representing the speed response errors of the parallel mechanism under the original pose, the middle pose and the edge pose, and a curve R in figure 41、R2And R3Respectively representing the position response errors of the parallel mechanism under the original pose, the middle pose and the edge pose. It is clear from the two figures that the speed and position response errors of the parallel mechanism appear in the obvious vibration situation at the initial stage of the movement, and the curve R3Is most obvious, curve R1The vibration of the parallel mechanism is the weakest, which shows that the dynamic performance of the parallel mechanism changes correspondingly along with the change of the pose of the parallel mechanism;
10) in order to explain the change of the dynamic performance of the parallel mechanism, after the pose of the parallel mechanism is changed from the original pose to the middle pose and the edge pose, calculating a new first damping ratio, a new second damping ratio, a new first natural frequency and a new second natural frequency of a parallel mechanism driving shaft double-inertia control system;
when the parallel mechanism changes from the original pose to the intermediate pose, the calculation result is as follows:
in the formula, ζn1(1)、ζn2(1)、ω1(1)、ω2(1)Respectively, a new first damping ratio, a new second damping ratio, a new first natural frequency and a new second natural frequency of the double-inertia control system when the parallel mechanism is in the middle pose;
when the parallel mechanism changes from the original pose to the edge pose, the calculation result is as follows:
in the formula, ζn1(2)、ζn2(2)、ω1(2)、ω2(2)Respectively, a new first damping ratio, a new second damping ratio, a new first natural frequency and a new second natural frequency of the double-inertia control system when the parallel mechanism is in the edge pose;
comparing the results of the equations (14), (15) and (7), (8) and (9), it can be clearly seen that when the parallel mechanism changes from the original pose to the middle pose and the edge pose, the first damping ratio, the second damping ratio, the first natural frequency and the second natural frequency of the driving shaft dual inertia control system change, and further cause the dynamic performance change shown in fig. 3 and 4, therefore, by using the proposed method, the reason for the change of the dynamic performance of the parallel mechanism can be better explained, and an effective tool is provided for the analysis of the dynamic performance of the parallel mechanism.