CN113420255B - Method for calculating reliability of ultrasonic motor - Google Patents
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Abstract
The invention relates to a method for calculating the reliability of an ultrasonic motor, and belongs to the technical field of motors. Firstly, systematically analyzing and determining the fault type of the ultrasonic motor, secondly, comprehensively considering the influence of the working environment of the ultrasonic motor on the failure rate of each part, calculating the failure rate of the parts of the ultrasonic motor, analyzing the distribution type of each fault to determine the reliability model of each part, and finally obtaining the integral reliability of the motor according to the reliability model of the ultrasonic motor. The types of failures that easily occur in the ultrasonic motor are: piezoelectric ceramic failure, friction material failure, bearing failure. The invention comprehensively considers the relation among piezoelectric ceramics, friction materials and bearing in the ultrasonic motor and the reliability of the motor, realizes the accurate calculation of the reliability of the motor, shortens the working time of the service life test of the ultrasonic motor, and can avoid economic loss caused by motor faults by actively calculating the reliability.
Description
Technical Field
The invention belongs to the technical field of motors, and particularly relates to a method for calculating the reliability of an ultrasonic motor.
Background
As a novel direct drive motor, the ultrasonic motor receives more and more attention at home and abroad due to the advantages of high power density, high response speed, no noise in operation, simple structure, high control precision and the like. The method is widely applied to the fields of robots, computers, aerospace and the like. However, the development of the ultrasonic motor is limited by the service life of the ultrasonic motor, and elements such as piezoelectric ceramics, friction materials, bearings and the like are very easy to break down in the operation process of the ultrasonic motor, and the driving system is affected by the faults, so that serious economic loss is caused. Therefore, the calculation of the operation reliability of the ultrasonic motor is particularly important.
The existing evaluation mode for the reliability of the ultrasonic motor is a motor service life test experiment, namely, the motor is operated to a fault, so that the service life of the motor is obtained. The method needs a large amount of test time and cost, cannot evaluate the reliability of the motor in a certain specified time in real time, and cannot meet the requirement of rapidity of reliability measurement of the ultrasonic motor.
Disclosure of Invention
Technical problem to be solved
In order to solve the problems of long time, high cost and the like of the reliability test of the ultrasonic motor in the prior art, the invention provides a reliability calculation method of the ultrasonic motor, the reliability of the motor can be obtained through formula calculation, and the complicated and long-time reliability measurement experiment is avoided.
Technical scheme
A reliability calculation method for an ultrasonic motor is characterized in that main faults of the ultrasonic motor are divided into piezoelectric ceramic faults, friction material faults and bearing faults, the reliability of the piezoelectric ceramic, the reliability of the friction material and the reliability of a bearing in the motor are calculated in sequence, and then the three reliabilities are multiplied.
The invention further adopts the technical scheme that: the reliability R of the piezoelectric ceramic 1 The calculation formula of (a) is as follows:
λ P1 ＝λ b1 π E1 π Q1 π f1
wherein λ is p1 Is failure rate of piezoelectric ceramics, lambda b1 Is the fundamental failure rate of piezoelectric ceramics, pi E1 Is an environmental coefficient, pi Q1 Is a mass coefficient of π f1 Is a frequency coefficient.
The invention further adopts the technical scheme that: the reliability R of the friction material 2 The calculation formula of (c) is as follows:
wherein, t p Rated life for friction material:
W a k is unit wear loss, W, for allowable wear loss e The abrasion power; m is a shape parameter, t is a run time, t p Is the rated life of the friction material.
The invention further adopts the technical scheme that: the bearing reliability R Z The calculation formula of (a) is as follows:
wherein P is the equivalent dynamic load borne by the rolling bearing, and n is the rotating speed of the bearing; f. of Q Temperature coefficient introduced to characterize basic dynamic load rating, f p To characterize the load factor induced by vibration or shock in operation; m and epsilon are shape parameters; c is the rated dynamic load of the rolling bearing, and the value of the rated dynamic load is related to the temperature and parameters of the bearing.
The invention further adopts the technical scheme that: the values of m of different bearings are as follows: and m =10/9 for a ball bearing, m =3/2 for a cylindrical roller bearing, and m =4/3 for a tapered roller bearing.
The invention further adopts the technical scheme that: the values of epsilon of different bearings are as follows: ball bearing epsilon =3 and roller bearing epsilon =10/3.
Advantageous effects
The invention provides a method for calculating the reliability of an ultrasonic motor, which comprehensively considers the relationship between piezoelectric ceramics, friction materials, bearings and the reliability of the motor in the ultrasonic motor, firstly independently calculates the failure rate and the reliability of each element in a specific environment and in a specific working time, and finally obtains the total reliability of the motor according to an ultrasonic motor reliability model. The reliability of the ultrasonic motor is obtained by adopting a formula calculation mode, and compared with the existing reliability test, the reliability test method avoids long-time test work and saves certain reliability test cost.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a fault tree for an ultrasonic motor
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Different from other types of motor structures, the ultrasonic motor mainly comprises a stator, a rotor, piezoelectric ceramics, friction materials and the like. Fig. 1 is an ultrasonic motor fault tree. As is known from past experience, the most likely components to fail during operation of an ultrasonic motor are piezoelectric ceramics, friction materials, and bearings. The existing ultrasonic motor service life calculation is mainly verified through experiments, so that the requirement of rapidity is not met, and a large amount of time and cost are also needed. Different from the existing method, the reliability calculation method for the ultrasonic motor provided by the invention comprehensively considers the reliability of each component, and can calculate the reliability of the ultrasonic motor in real time.
The invention provides a method for calculating the reliability of an ultrasonic motor, which comprises the following steps:
step 1: the main faults of the ultrasonic motor are divided into piezoelectric ceramic faults, friction material faults and bearing faults.
Step 2: and calculating the failure rate and reliability of the piezoelectric ceramic of the ultrasonic motor.
The failure rate of the piezoelectric ceramic is as follows: lambda [ alpha ] P1 ＝λ b1 π E1 π Q1 π f1
For an electronic element, the service life of the electronic element is related to the impact, and the electronic element accords with the memorability of exponential distribution, so that the service life of the piezoelectric ceramic in the ultrasonic motor is considered to be subjected to the exponential distribution with lambda as a parameter, and the total reliability of the piezoelectric ceramic after the piezoelectric ceramic works for t hours under a specific working environment is as follows:
wherein λ is b1 Is the basic failure rate of piezoelectric ceramics, pi E1 Is an environmental coefficient, pi Q1 Is a mass coefficient of π f1 Is a frequency coefficient.
And step 3: and calculating the failure rate and reliability of the friction material of the ultrasonic motor.
The friction material in the ultrasonic motor has a main failure mode of wear failure, and the failure distribution of the friction material can be considered to approximately follow Shan Canshu Weibull distribution, and the reliability of the friction material is as follows:
wherein the rated life of the friction material is as follows:
the abrasion power is as follows:
where eta is the characteristic lifetime of the material, W a T is the vibration period, P, for allowable wear C For impact load, K is unit abrasion loss, | V | is relative sliding velocity, U is horizontal moving velocity of vibration body, V m Is the rotational speed of the ultrasonic motor, W e To wear out power. m is a shape parameter, t is a run time, t p Is the rated life of the friction material.
And 4, step 4: and calculating the failure rate and reliability of the bearing of the ultrasonic motor.
The bearing failure rate is as follows:
the ultrasonic motor adopts a single bearing. The total bearing reliability after t hours of operation is:
wherein P is the equivalent dynamic load borne by the rolling bearing, and n is the rotating speed of the bearing; f. of Q Temperature coefficient introduced to characterize basic dynamic load rating, f p To characterize the load factor induced by vibration or shock in operation; m is a shape parameter, and m =10/9 for a ball bearing, m =3/2 for a cylindrical roller bearing, and m =4/3 for a tapered roller bearing; the ball bearing epsilon =3, and the roller bearing epsilon =10/3; c is the rated dynamic load of the rolling bearing, and the value of the rated dynamic load is related to the temperature and parameters of the bearing.
And 5: the reliability model of the ultrasonic motor is formed by connecting piezoelectric ceramics, friction materials and a rotating shaft in series, so that the total reliability of the motor is as follows:
R(t)＝R 1 ×R 2 ×R Z
example 1:
the USR60-B3 ultrasonic motor has the power of 5W and the rated rotating speed of 100r/min, the adopted friction material is a resin-based friction material, and the wear coefficient is K =0.82 multiplied by 10 -7 The wavelength of the traveling wave is 19mm, and the preload is P C =100N, acoustic vibration frequency 40kHz, allowable wear loss W a ＝20mm 3 Let m =2. The reliability of this type of motor after 2000 hours of operation was calculated.
Step 1: according to the fault tree of the ultrasonic motor shown in fig. 1, the main faults of the ultrasonic motor are determined to be piezoelectric ceramic faults, friction material faults and bearing faults.
Step 2: and calculating the failure rate and reliability of the piezoelectric ceramic of the ultrasonic motor.
Taking the basic failure rate lambda of piezoelectric ceramics b1 ＝0.0713×10 -6 Coefficient of environment pi E1 =1.2, mass coefficient pi Q1 =0.4, frequency coefficient pi f1 ＝1.3f 0.23 =0.63706, the failure rate of the piezoelectric ceramic is:
λ P1 ＝λ b1 π E1 π Q1 π f1 ＝0.021803×10 -6
the total reliability of the piezoelectric ceramic after t hours of operation is as follows:
and step 3: and calculating the reliability of the friction material of the ultrasonic motor.
The friction material adopted in the ultrasonic motor is resin base, the main failure mode is abrasion failure, the failure distribution of the ultrasonic motor can be considered to approximately obey Shan Canshu Weibull distribution, and the reliability is as follows:
the abrasion power is as follows:
the rated life of the friction material is:
and 4, step 4: and calculating the failure rate and reliability of the bearing of the ultrasonic motor.
The bearing model adopts a 628/7 type deep groove ball bearing, and the rotating speed n =100r/min; temperature coefficient f introduced for characterizing basic rated dynamic load change Q =1.1, characteristic of the load factor f induced by vibration or shock in operation p =1.5; shape ofParameter m =10/9; ball bearing epsilon =3; the equivalent dynamic load P =10N borne by the rolling bearing, and the rated dynamic load C =500N of the rolling bearing.
The bearing failure rate is as follows:
the ultrasonic motor adopts a single-shaft type. The total bearing reliability after t hours of operation is:
and 5: the reliability model of the ultrasonic motor is formed by connecting piezoelectric ceramics, friction materials and bearings in series, so that the total reliability of the motor after 2000 hours of working is as follows:
R(t)＝R 1 ×R 2 ×R Z ＝0.956955≈95.7％
the method comprises the steps of firstly systematically analyzing and determining the fault type of the ultrasonic motor, secondly comprehensively considering the influence of the working environment of the ultrasonic motor on the failure rate of each part, calculating the failure rate of the parts of the ultrasonic motor, analyzing the distribution type of each fault to determine the reliability model of each part, and finally obtaining the integral reliability of the motor according to the reliability model of the ultrasonic motor. The types of failures that easily occur in the ultrasonic motor are: piezoelectric ceramic failure, friction material failure, bearing failure. The invention comprehensively considers the relation among piezoelectric ceramics, friction materials and bearing in the ultrasonic motor and the reliability of the motor, realizes the accurate calculation of the reliability of the motor, shortens the working time of the service life test of the ultrasonic motor, and can avoid economic loss caused by motor faults by actively calculating the reliability.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications or substitutions can be easily made by those skilled in the art within the technical scope of the present disclosure.
Claims (3)
1. A reliability calculation method of an ultrasonic motor is characterized in that main faults of the ultrasonic motor are divided into piezoelectric ceramic faults, friction material faults and bearing faults, the reliability of the piezoelectric ceramic, the reliability of the friction material and the reliability of a bearing in the motor are calculated in sequence, and then the three reliabilities are multiplied; the reliability R of the piezoelectric ceramic 1 The calculation formula of (c) is as follows:
λ P1 ＝λ b1 π E1 π Q1 π f1
wherein λ is P1 Is failure rate of piezoelectric ceramics, lambda b1 Is the fundamental failure rate of piezoelectric ceramics, pi E1 Is an environmental coefficient, pi Q1 Is a mass coefficient of pi f1 Is a frequency coefficient;
the reliability R of the friction material 2 The calculation formula of (a) is as follows:
wherein, t p Rated life for friction material:
W a k is unit wear loss, W, for allowable wear loss e The abrasion power; m is a shape parameter, t is a run time, t p Is the rated life of the friction material;
the bearing reliability R Z The calculation formula of (a) is as follows:
wherein P is the equivalent dynamic load born by the rolling bearing, and n is the rotating speed of the bearing; f. of Q Temperature coefficient introduced to characterize basic dynamic load rating, f p To characterize the load factor induced by vibration or shock in operation; m and epsilon are shape parameters; c is the rated dynamic load of the rolling bearing, and the value of the rated dynamic load is related to the temperature and parameters of the bearing.
2. The method for calculating the reliability of the ultrasonic motor according to claim 1, wherein the values of m of different bearings are as follows: and m =10/9 for a ball bearing, m =3/2 for a cylindrical roller bearing, and m =4/3 for a tapered roller bearing.
3. The method for calculating the reliability of the ultrasonic motor according to claim 1, wherein the values of epsilon of different bearings are as follows: ball bearing epsilon =3 and roller bearing epsilon =10/3.
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| CN111509957B (en) * | 2020-03-12 | 2023-04-07 | 安徽大学 | Motor inverter reliability calculation method |
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| CN201418043Y (en) * | 2009-06-19 | 2010-03-03 | 东南大学 | Ring-shaped traveling wave type ultrasonic wave motor |
| CN103219917A (en) * | 2013-04-09 | 2013-07-24 | 北京控制工程研究所 | High-reliability high-stability-degree hollow rotating traveling wave ultrasonic motor |
| CN106650275A (en) * | 2016-12-29 | 2017-05-10 | 西北工业大学 | Permanent magnet motor reliability calculation method |
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| RESEARCH ON THE OVERLOAD CHARACTERISTIC OF TRAVELING WAVE TYPE ROTARY ULTRASONIC MOTOR;Jin-hua REN,et al;《2013 Symposium on Piezoelectricity,Acoustic Waves,and Device Applications》;20131027;第1-4页 * |
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