CN-121978961-A - Four-point angular contact ball bearing for robot and pretightening force self-adaptive adjusting method thereof

CN121978961ACN 121978961 ACN121978961 ACN 121978961ACN-121978961-A

Abstract

The invention relates to the technical field of precise bearing pretightening force control, and discloses a four-point angular contact ball bearing for a robot and a pretightening force self-adaptive adjusting method thereof. The method adopts a Preisach hysteresis model to describe the temperature-displacement nonlinear relation of the shape memory alloy, determines a hysteresis path through phase identification, corrects model parameters according to the ambient temperature and the cycle times, reversely solves a temperature control instruction, continuously optimizes model precision through an online updating mechanism, and solves the problem of unstable pretightening force adjusting precision caused by hysteresis characteristics of the shape memory alloy and drifting thereof.

Inventors

LI JINGYANG
XIONG JUWU
LI TIEZHU

Assignees

宁波实隆轴承有限公司

Dates

Publication Date: 20260505
Application Date: 20260320

Claims (10)

1. The four-point angular contact ball bearing for the robot and the self-adaptive pretightening force adjusting method thereof are characterized by comprising the following steps: collecting current temperature data, temperature change rate data, environment temperature data and accumulated working cycle times of the shape memory alloy element to generate a working condition parameter set; Judging that the shape memory alloy element is currently in a heating phase or a cooling phase based on the temperature change rate data, and acquiring the starting point temperature and the starting point displacement of the phase switching moment when the phase switching moment is detected to generate a hysteresis loop path identifier; Inputting the hysteresis loop path identifier and the working condition parameter set into a Preisach hysteresis model, and outputting a dynamic mapping relation between a temperature increment and a displacement increment in a current state; Acquiring a target displacement corresponding to the target pretightening force, acquiring current actual displacement, calculating a required displacement increment, carrying out inverse solution based on the dynamic mapping relation, calculating a temperature increment corresponding to the required displacement increment, and generating a temperature control instruction; executing the temperature control instruction to perform heating or cooling control on the shape memory alloy element, collecting actual displacement data, calculating residual error between the actual displacement and target displacement, and updating parameters of a Preisach hysteresis model on line based on the residual error; The Preisach hysteresis model represents hysteresis characteristics of the shape memory alloy as weighted superposition of a plurality of basic hysteresis operators, each basic hysteresis operator has an ascending threshold and a descending threshold, displacement output of the shape memory alloy element is obtained by performing weighted integration on the output of all the basic hysteresis operators, and the weighted integration adopts a Preisach weight distribution function as weight.
2. The four-point angular contact ball bearing for the robot and the self-adaptive pretightening force adjusting method thereof according to claim 1, wherein the calculation of the temperature change rate data is obtained by dividing the temperature data at two adjacent sampling moments by a sampling period after differential operation, and the accumulated work cycle number is the number of complete heating-cooling cycles completed by the shape memory alloy element.
3. The four-point angular contact ball bearing for a robot and the adaptive pretightening force adjusting method thereof according to claim 1, wherein the step of judging whether the shape memory alloy element is currently in a heating phase or a cooling phase comprises judging that the shape memory alloy element is in the heating phase when the temperature change rate is larger than zero, judging that the shape memory alloy element is in the cooling phase when the temperature change rate is smaller than zero, judging that the shape memory alloy element is in the steady-state maintaining phase when the temperature change rate is equal to zero and the duration exceeds a preset time threshold, and the phase switching time is a time when the temperature change rate sign of the current sampling time is opposite to the temperature change rate sign of the last sampling time in the continuous sampling process.
4. The four-point angular contact ball bearing for a robot and the pretightening force self-adaptive adjustment method thereof according to claim 1, wherein the pretreat weight distribution function adopts first-order inversion curve experiment data to perform offline identification to obtain an initial value, the first-order inversion curve experiment heats the shape memory alloy element from low temperature to different inversion temperature points and then cools the shape memory alloy element, a displacement response curve corresponding to each inversion point is recorded, and numerical expression of the weight distribution function is obtained by performing numerical processing on the displacement response curve data.
5. The four-point angular contact ball bearing for a robot and the pretightening force self-adaptive adjustment method thereof according to claim 1, wherein the rising threshold and the falling threshold of a basic hysteresis operator in the pretach hysteresis model are corrected according to environmental temperature data, and the corrected rising threshold and the corrected falling threshold are obtained by calculating according to the deviation of the environmental temperature and the reference environmental temperature and a threshold temperature drift coefficient.
6. The four-point angular contact ball bearing for a robot and the pretightening force self-adaptive adjustment method thereof according to claim 1, wherein the weight distribution function in the pretach hysteresis model is corrected according to the accumulated work cycle times, and the corrected weight distribution function is obtained by calculation based on an initial weight distribution function, a cycle degradation coefficient and a reference cycle times base.
7. The four-point angular contact ball bearing for the robot and the pretightening force self-adaptive adjusting method thereof according to claim 1, wherein the step of carrying out inverse solving and calculating the temperature increment based on the dynamic mapping relation comprises the steps of gradually increasing or decreasing the temperature value according to a fixed step length from the current temperature, calculating the corresponding displacement increment at each temperature step until the accumulated displacement increment reaches the required displacement increment, recording the accumulated temperature increment as the required temperature increment, and adding the required temperature increment and the current temperature to generate a temperature control instruction.
8. The four-point angular contact ball bearing for a robot and the pretightening force adaptive adjustment method thereof according to claim 7, wherein the temperature control command superimposes an ambient temperature drift compensation amount and a cyclic degradation compensation amount on the basis of a basic temperature control amount, the ambient temperature drift compensation amount being calculated from a deviation of an ambient temperature from a reference ambient temperature and an ambient temperature compensation coefficient, the cyclic degradation compensation amount being calculated from an accumulated number of cycles and a cyclic degradation compensation coefficient.
9. The four-point angular contact ball bearing for the robot and the pretightening force self-adaptive adjustment method thereof according to claim 1, wherein the parameters based on the residual error online updating pretach hysteresis model adopt a recursive least square algorithm to carry out incremental updating on the discretization parameters of the pretach weight distribution function, the online updating is triggered only when the absolute value of the residual error exceeds a preset residual error threshold, and the parameter value after updating is limited at a boundary value when the updated parameters exceed a preset effective range.
10. A four-point angular ball bearing for a robot and a pretightening force adaptive adjustment system thereof for executing the four-point angular ball bearing for a robot and a pretightening force adaptive adjustment method thereof according to any one of claims 1 to 9, characterized by comprising: The working condition parameter acquisition module is used for acquiring current temperature data, temperature change rate data, environment temperature data and accumulated working cycle times of the shape memory alloy element to generate a working condition parameter set; The phase judgment module is used for judging that the shape memory alloy element is currently in a heating phase or a cooling phase based on the temperature change rate data, acquiring the starting point temperature and the starting point displacement of the phase switching moment when the phase switching moment is detected, and generating a hysteresis loop path identifier; The dynamic mapping calculation module is used for inputting the hysteresis loop path identifier and the working condition parameter set into a Preisach hysteresis model and outputting a dynamic mapping relation between the temperature increment and the displacement increment in the current state; the temperature control instruction generation module is used for acquiring a target displacement corresponding to the target pretightening force, acquiring current actual displacement, calculating a required displacement increment, carrying out inverse solution based on the dynamic mapping relation, calculating a temperature increment corresponding to the required displacement increment, and generating a temperature control instruction; The control execution and model updating module is used for executing the temperature control instruction to perform heating or cooling control on the shape memory alloy element, collecting actual displacement data, calculating residual errors between the actual displacement and the target displacement, and updating parameters of the Preisach hysteresis model on line based on the residual errors.

Description

Four-point angular contact ball bearing for robot and pretightening force self-adaptive adjusting method thereof Technical Field The invention relates to the technical field of precise bearing pretightening force control, in particular to a four-point angular contact ball bearing for a robot and a pretightening force self-adaptive adjusting method thereof. Background In precision spindle systems and robotic joints, precise control of bearing preload has important implications for system stiffness, slewing accuracy, and service life. Shape memory alloy is gradually applied to the field of active adjustment of bearing pretightening force due to the advantages of small volume, large output force, no electromagnetic interference and the like, and the pretightening force is adjusted by generating recoverable macroscopic displacement through temperature-induced phase transformation between martensite and austenite. Existing control schemes typically employ a linear or piecewise linear relationship between temperature and displacement for control quantity calculation. However, shape memory alloys exhibit significant hysteresis characteristics during phase transformation, i.e., there is a difference in displacement amounts corresponding to the same temperature during heating and cooling, forming a closed hysteresis loop. In addition, the hysteresis characteristics of the shape memory alloy generate degradation drift with the increase of the accumulated working cycle times and are offset under the influence of environmental temperature fluctuation. The prior art ignores the influence of hysteresis characteristics and drift thereof, so that a control strategy based on a simplified temperature-displacement relationship generates a remarkable pretightening force adjusting error in practical application, and the technical problem that pretightening force adjusting precision is unstable because the requirement of a precision system on pretightening force adjusting precision is difficult to meet is solved. Disclosure of Invention The invention provides a four-point angular contact ball bearing for a robot and a self-adaptive pretightening force adjusting method thereof, which solve the technical problems that a pretightening force control precision is low and environmental temperature drift and cyclic degradation influence cannot be effectively compensated due to hysteresis characteristics of a shape memory alloy driving system in the related art. The invention discloses a four-point angular contact ball bearing for a robot and a pre-tightening force self-adaptive adjustment method thereof, which comprises the following steps of collecting current temperature data, temperature change rate data, environment temperature data and accumulated working cycle times of a shape memory alloy element, generating a working condition parameter set, judging that the shape memory alloy element is currently in a heating phase or a cooling phase based on the temperature change rate data, obtaining a starting point temperature and a starting point displacement at a phase switching moment when the phase switching moment is detected, generating a hysteresis loop path identifier, inputting the hysteresis loop identifier and the working condition parameter set into a hysteresis model, outputting a dynamic mapping relation between a temperature increment and a displacement increment in a current state, acquiring a target displacement amount corresponding to a target pre-tightening force, collecting current actual displacement, calculating a required displacement increment, carrying out inverse solution based on the dynamic mapping relation, calculating to generate a temperature increment corresponding to the required displacement increment, generating a temperature control instruction, executing heating or cooling control on the shape memory alloy element, calculating actual displacement data, and a residual error between the actual displacement and the target displacement, and the hysteresis model based on the phase switching moment, outputting a hysteresis weighting factor, and a hysteresis weighting factor by taking the hysteresis coefficient as a hysteresis weighting factor, and a hysteresis weighting factor is used for the hysteresis coefficient. Further, the calculation of the temperature change rate data is obtained by dividing the temperature data of two adjacent sampling moments by a sampling period after differential operation, and the accumulated work cycle times are the times of complete heating-cooling cycles completed by the shape memory alloy element. Further, the step of judging whether the shape memory alloy element is currently in the heating phase or the cooling phase comprises judging that the shape memory alloy element is in the heating phase when the temperature change rate is larger than zero, judging that the shape memory alloy element is in the cooling phase when the temperature change rate is smaller than zero, judging