阅读说明：本技术 组合式螺母驱动型液体静压丝杠副、伺服进给系统及方法 (Combined nut-driven hydrostatic lead screw pair, servo feeding system and method ) 是由 冯显英 刘延栋 苏哲 李慧 于 2021-12-08 设计创作，主要内容包括：本发明属于超精密加工领域,公开了一种组合式螺母驱动型液体静压丝杠副、伺服进给系统及方法,其中组合式螺母驱动型液体静压丝杠副包括丝杠和组合式液体静压螺母组件；组合式液体静压螺母组件中除连接支架、第一衬套和第二衬套外均可选用标准件,通过调整连接支架、第一衬套和第二衬套的结构尺寸可以最大限度的适配现有液体静压轴承、液体静压丝杠副和空心电机等实际产品。本发明解决了现有螺母主驱动型液体静压丝杠副技术存在的结构复杂、加工成本高等问题。(The invention belongs to the field of ultra-precision machining and discloses a combined nut-driven hydrostatic lead screw pair, a servo feeding system and a method, wherein the combined nut-driven hydrostatic lead screw pair comprises a lead screw and a combined hydrostatic nut component; except the connecting support, the first lining and the second lining, the combined type hydrostatic nut component can adopt standard parts, and the structure size of the connecting support, the first lining and the second lining can be adjusted to adapt to actual products such as the existing hydrostatic bearing, the hydrostatic lead screw pair and the hollow motor to the maximum extent. The invention solves the problems of complex structure, high processing cost and the like of the existing nut main drive type hydrostatic pressure screw pair technology.)

1. The combined nut-driven hydrostatic lead screw pair is characterized by comprising a lead screw and a combined hydrostatic nut component; the combined type hydrostatic pressure nut component comprises a double-cone hydrostatic pressure bearing, a first bushing, a second bushing, a hollow motor, a connecting bracket, a sealing ring and a hydrostatic pressure lead screw nut;

the hydrostatic pressure screw nut is matched with the screw rod, and a flange is arranged in the middle of the outer ring of the hydrostatic pressure screw nut; one side of the flange plate is connected with the first bushing, and the other side of the flange plate is connected with the second bushing; the double-cone hydrostatic bearing is arranged on the outer ring of the first lining and matched with the first lining; the outer ring of the double-cone hydrostatic bearing is fixed on the connecting support, the outer ring of the double-cone hydrostatic bearing and the first bushing form a closed space, the outer ring of the first bushing is provided with an oil discharge groove, and the oil discharge groove and the inner ring of the double-cone hydrostatic bearing form an oil discharge channel; the second bushing is fixedly connected with the hollow motor rotor; the hollow motor stator is fixedly connected with the connecting bracket.

2. The combination nut driving type hydrostatic lead screw according to claim 1, wherein the first and second bushings are each formed with a circular arc groove on an inner circumferential surface thereof.

3. The combined nut-driven hydrostatic lead screw assembly of claim 1, wherein the second bushing is fixedly connected to a hub of an encoder; the encoder code wheel is fixedly connected with an encoder code wheel shaft sleeve.

4. The combined nut-driven hydrostatic lead screw pair of claim 1, further comprising a reading head bracket, wherein the reading head bracket is fixedly connected with the hollow motor stator through a bolt long hole, and the reading head bracket is fixedly connected with the reading head of the encoder through a mounting hole.

5. A servo feed system comprising a combined nut-driven hydrostatic lead screw pair according to any one of claims 1 to 4.

6. The servo feed system of claim 5, further comprising a servo motor, a first control module, a second control module, an intelligent decision module, a displacement detection device, a distance measuring device, and a table; two ends of the screw rod are connected with a hydrostatic bearing, and the hydrostatic bearing provides support for the screw rod; the servo motor drives the lead screw; the servo motor is controlled by the first control module; the hollow motor is controlled by the second control module; the distance measuring device is arranged in the hydrostatic pressure screw nut and measures the thickness of an oil film between the screw and the nut in real time; the displacement detection device detects the moving position information of the workbench in real time; the distance measuring device and the displacement detecting device are connected with the intelligent decision module, and the intelligent decision module is connected with the first control module and the second control module.

7. The control method of the servo feed system as set forth in claim 6, wherein:

the distance measuring device sends the thickness of an oil film between the screw rod and the nut measured in real time to the intelligent decision module; the displacement detection device sends the position information of the movement of the workbench detected in real time to the intelligent decision module; the intelligent decision system sends the action instruction to the first control module and the second control module according to the signal acquired in real time; the first control module and the second control module control corresponding motor actions; meanwhile, the distance measuring device and the displacement detecting device send the oil film thickness measured in real time and the position information of the movement of the workbench to the intelligent decision module again; the intelligent decision module judges whether the oil film thickness and the position information of the workbench meet set requirements, if so, a stop instruction is sent to the first control module and the second control module, and the corresponding motor does not act any more; if not, continuing to send the action instruction to the first control module and the second control module; the first control module and the second control module control corresponding motor actions until a set requirement is met.

8. The control method of the servo feed system as set forth in claim 7, wherein: the construction process of the intelligent decision system is as follows:

step 1, initializing the feeding state of a feeding platform, and setting the micro-feeding speedV _Aim、Initial speed of the screw isV _s、Initial speed of nut motorV _n=V _s-V _AimAnd areV _nLarger than the unavoidable and nonlinear rotary crawling speed of the feeding systemV _c；

Step 2, the feeding platform moves to a first state quantityS(t)；

Step 3, the current state is comparedS(t) Inputting the data into an Actor network, and carrying out strategy selection by the Actor network by using a strategy gradient to obtain a desired actionA(t) (ii) a Adjusting delta according to action commandV _s(t) And deltaV _sn(t)；

Wherein, DeltaV _s(t)∈[－V _small，V _small](ii) a WhereinV _smallAiming at a screw motor when double-drive hydrostatic pressure screw pair double-drive differential ultra-precision feedingV _sThe maximum value of the fine adjustment; deltaV _sn(t) ∈[0,V _max-V _s]，V _maxThe maximum speed which can be reached by a screw motor or a nut motor;

and 4, step 4: feed platform performs actionsA(t) To obtain a prize valueR(S（t）、A（t）) Second state quantity output by the arrival position feedback module and oil film thickness feedbackS(t+1)；

And 5: set data [S(t)，A(t)，R(S(t)，A(t) S (t +1) is stored in an empirical data pool with the sample capacity of N;

step 6: randomly extracting a plurality of sample data from an experience data pool for the training of an Actor network and a Critic network;

and 7: minimizing the loss function L (θ)^Q) Updating Critic network parameter θ^Q；

And 8: updating Actor network parameters by gradient descent methodθ ^μ (ii) a Judging whether the maximum step number or the network convergence is reached, if not, returning to the step (3) to continue circulation; if yes, the process is finished.

Technical Field

The invention belongs to the field of ultra-precision machining, and particularly discloses a combined nut-driven hydrostatic lead screw pair, a servo feeding system and a method.

Background

The ultra-precision machining technology becomes a key technology for development of national defense and high and new technologies, and along with the continuous improvement of the machining precision requirement of high-tech products on parts, the ultra-precision machine tool needs to meet more severe performance indexes. One of the bottlenecks in implementing ultra-precision machining techniques is how to implement precise and uniform micro-feeding control of a tool or a workpiece during machining. The conventional electromechanical transmission system is hardly suitable for micro-feeding of micro-nano-scale resolution due to the influence of a low-speed crawling phenomenon, and the current micro-nano-scale displacement is mostly realized based on the driving of electric, magnetic, thermal, optical, acoustic effect and the like of intelligent materials.

In the prior art documents, patent CN 104714485B: a micro high-precision micro-feeding servo system and a control method thereof provide a high-precision micro-feeding servo system of a double-drive screw pair, which can realize precise micro displacement control in ultra-precision and high-precision machining, but are limited by the defect factors of non-uniformity of balls of the ball screw pair, geometric errors of a raceway spiral, surface roughness of the raceway and the like, and the precision is difficult to achieve nano-scale precision.

Furthermore, patent CN 108788878A: nut-driven hydrostatic screw assembly, and invention patent CN 112077638B: the invention discloses a linear feeding unit of a main driving type screw pair integrated with a hydrostatic nut, and provides a nut main driving type hydrostatic screw pair scheme, wherein the hydrostatic screw pair is supported by a hydrostatic screw nut through a liquid oil film, so that the hydrostatic screw pair has the superior characteristics of low friction, high rigidity, high precision, good damping and the like, although the defects of the invention patent CN104714485B can be solved, the technical implementation schemes provided by the invention patent CN108788878A and the invention patent CN112077638B cannot be realized by using the existing hydrostatic bearing and hydrostatic screw nut products, the hydrostatic bearing and the hydrostatic screw nut used by the hydrostatic bearing and the hydrostatic screw nut are required to be redesigned and processed, the processing technology is complex, and the manufacturing cost and the later-period use and maintenance cost are high.

The invention patent CN104714485B discloses a double-drive high-precision micro-feeding control method for a ball screw pair. However, the hydrostatic lead screw pair and the ball lead screw pair are obviously different in transmission mechanism, a large-stroke ultra-precision micro-feeding system composed of the double-drive hydrostatic lead screw pair is a multivariable, strong-coupling and strong-nonlinearity controlled object, and when ultra-precision machining feeding is carried out, interference factors such as a pitch error and a coaxiality error of the hydrostatic lead screw pair and damping constantly changing in each liquid supporting oil film under different rotating speeds bring great challenges to micro-feeding control feeding of large-stroke and ultra-precision micro-nano-grade resolution. The conventional model-based motion control method has strong dependence on a model, the design process is complex, the advantages of the double-drive hydrostatic lead screw pair in ultra-precision feeding cannot be fully exerted, and particularly, the method has very limited adaptability to unknown processing tasks and model uncertainty and is difficult to cope with complex and variable ultra-precision processing scenes.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the defects of the prior art and provide a combined nut-driven hydrostatic pressure screw pair, a servo feeding system and a method; on one hand, the problems of complex structure, high processing cost and the like of the existing nut main drive type hydrostatic pressure lead screw pair technology are solved; on the other hand, the problems that a mathematical model simplified by the control method of the existing double-drive screw pair differential micro-feeding technology cannot accurately describe the motion characteristics of a large-stroke and high-precision feeding system and the control effect is deteriorated due to various interference factors are solved, and the ultra-precise control of the micro-nano motion servo feeding system is realized.

The invention specifically adopts the following technical scheme to solve the problems:

in a first aspect, the invention provides a combined nut-driven hydrostatic lead screw pair, which comprises a lead screw and a combined hydrostatic nut component; the combined type hydrostatic pressure nut component comprises a double-cone hydrostatic pressure bearing, a first bushing, a second bushing, a hollow motor, a connecting bracket, a sealing ring and a hydrostatic pressure lead screw nut;

the hydrostatic pressure screw nut is matched with the screw rod, and a flange is arranged in the middle of the outer ring of the hydrostatic pressure screw nut; one side of the flange plate is connected with the first bushing, and the other side of the flange plate is connected with the second bushing; the double-cone hydrostatic bearing is arranged on the outer ring of the first lining and matched with the first lining, and a gap is formed between the double-cone hydrostatic bearing and the first lining; the outer ring of the double-cone hydrostatic bearing is fixed on the connecting support, the outer ring of the double-cone hydrostatic bearing and the first bushing form a closed space, the outer ring of the first bushing is provided with an oil discharge groove, and the oil discharge groove and the inner ring of the double-cone hydrostatic bearing form an oil discharge channel; the second bushing is fixedly connected with the hollow motor rotor; the hollow motor stator is fixedly connected with the connecting bracket.

As a further technical scheme, arc grooves are machined on the inner circumferential surfaces of the first bushing and the second bushing.

As a further technical scheme, the second bushing is fixedly connected with a coded disc shaft sleeve of the encoder; the encoder code wheel is fixedly connected with an encoder code wheel shaft sleeve.

As a further technical scheme, the reading head support is fixedly connected with the hollow motor stator through a bolt long hole, and the reading head support is fixedly connected with the reading head of the encoder through a mounting hole.

In a second aspect, the invention further provides a large-stroke high-precision servo feeding system, which comprises the combined nut-driven hydrostatic pressure screw pair; the intelligent decision-making system further comprises a servo motor, a first control module, a second control module, an intelligent decision-making module, a displacement detection device, a distance measuring device and a workbench; two ends of the screw rod are connected with a hydrostatic bearing, and the hydrostatic bearing is supported by a bearing support; the servo motor drives the lead screw; the servo motor is controlled by the first control module; the hollow motor is controlled by the second control module; the distance measuring device is arranged in the hydrostatic pressure screw nut and measures the thickness of an oil film between the screw and the nut in real time; the displacement detection device detects the moving position information of the workbench in real time; the distance measuring device and the displacement detecting device are connected with the intelligent decision module, and the intelligent decision module is connected with the first control module and the second control module.

In a third aspect, the present invention further provides a control method for a large-stroke high-precision servo feeding system, including the following steps:

the distance measuring device sends the thickness of an oil film between the screw rod and the nut measured in real time to the intelligent decision module; the displacement detection device sends the position information of the movement of the workbench detected in real time to the intelligent decision module; the intelligent decision system sends the action instruction to the first control module and the second control module according to the signal acquired in real time; the first control module and the second control module control corresponding motor actions; meanwhile, the distance measuring device and the displacement detecting device send the oil film thickness measured in real time and the position information of the movement of the workbench to the intelligent decision module again; the intelligent decision module judges whether the oil film thickness and the position information of the workbench meet set requirements, if so, a stop instruction is sent to the first control module and the second control module, and the corresponding motor does not act any more; if not, continuing to send the action instruction to the first control module and the second control module; the first control module and the second control module control corresponding motor actions until a set requirement is met.

As a further technical solution, the construction process of the intelligent decision system is as follows:

step 1, initializing the feeding state of a feeding platform, and setting the micro-feeding speedV _Aim、Initial speed of the screw isV _s、Initial speed of nut motorV _n=V _s-V _AimAnd areV _nLarger than the unavoidable and nonlinear rotary crawling speed of the feeding systemV _c；

Step 2, the feeding platform moves to a first state quantityS(t)；

Step 3, the current state is comparedS(t) Inputting the data into an Actor network, and carrying out strategy selection by the Actor network by using a strategy gradient to obtain a desired actionA(t) (ii) a Adjusting delta according to action commandV _s(t) And deltaV _sn(t)；

Wherein, DeltaV _s(t)∈[－V _small，V _small](ii) a WhereinV _smallAiming at a screw motor when double-drive hydrostatic pressure screw pair double-drive differential ultra-precision feedingV _sThe maximum value of the fine adjustment; deltaV _sn(t) ∈[0,V _max-V _s]，V _maxThe maximum speed which can be reached by a screw motor or a nut motor;

and 4, step 4: feed platform performs actionsA(t) To obtain a prize valueR(S（t）、A（t）) Second state quantity output by the arrival position feedback module and oil film thickness feedbackS(t+1)；

And 5: set data [S(t)，A(t)，R(S(t)，A(t) S (t +1) is stored in an empirical data pool with the sample capacity of N;

step 6: randomly extracting a plurality of sample data from an experience data pool for the training of an Actor network and a Critic network;

and 7: minimizing the loss function L (θ)^Q) Updating Critic network parameter θ^Q；

And 8: updating Actor network parameters by gradient descent methodθ ^μ (ii) a Judging whether the maximum step number or the network convergence is reached, if not, returning to the step (3) to continue circulation; if yes, the process is finished.

The invention has the following beneficial effects:

1. the combined nut-driven hydrostatic lead screw pair provided by the invention is used for the existing liquid

The static pressure lead screw pair and the actual product of the hydrostatic bearing are combined to realize the main drive of the nut of the hydrostatic pressure lead screw pair. Except the connecting support, the first bush and the second bush, standard parts can be selected for use, and the connecting support, the first bush and the second bush can be adjusted in structure size to adapt to actual products such as the existing hydrostatic bearing, the hydrostatic lead screw pair and the hollow motor to the maximum extent. The shapes of the hydrostatic nuts are different due to different throttling modes, and the inner circumferential surfaces of the first bushing and the second bushing are respectively provided with an arc groove. Except for the oil inlet hole and the annular inner groove in the connecting support, an additional oil supply way is not required to be added. The invention overcomes the defect that the original technology needs to re-design the liquid hydrostatic bearing and the liquid hydrostatic lead screw copy, furthest utilizes the existing mature liquid hydrostatic bearing and liquid hydrostatic lead screw pair technology, can effectively ensure the reliability in the normal operation process, greatly reduces the technical difficulty and has lower processing, using and maintaining cost.

2. The invention provides a large-stroke high-precision micro-nano motion servo feeding system and a control method based on deep reinforcement learning. Compared with a conventional motion control method based on a model, the depth reinforcement learning-based double-drive hydrostatic lead screw pair control method is independent of an external environment, is suitable for multivariable, strong-coupling and strong-nonlinear large-stroke high-precision micro-nano motion scenes, and has better robustness.

When the micro high-precision feeding is ensured, the dynamic pressure effect of a liquid oil film in the hydrostatic lead screw pair can be adjusted in real time by increasing or decreasing the rotating speed of the lead screw and the rotating speed of the nut simultaneously, so that various complex external loads of the hydrostatic lead screw pair can be responded, and the feeding precision of the workbench is not influenced by the displacement fluctuation of the lead screw nut.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a control schematic diagram of a micro-nano motion servo feeding system based on depth reinforcement learning;

FIG. 2 is a block diagram of a deep reinforcement learning method based on strategy and evaluation;

FIG. 3 is a schematic diagram of the overall structure of the combined nut-driven hydrostatic lead screw pair;

FIG. 4 is a schematic three-dimensional structure of a bearing inner race bushing;

FIG. 5 is a schematic view of a two-dimensional structure of a bearing inner race bushing;

FIG. 6 is a schematic view of a hollow motor rotor bushing configuration;

FIG. 7 is a schematic view of a reading head support structure;

FIG. 8 is a schematic view of a connecting bracket structure;

FIG. 9 is a schematic view of the construction of the encoder hub;

in the figure: the device comprises a base 1, a servo motor 2, a coupler 3, a hydrostatic bearing support 4, a lead screw 5, a combined hydrostatic nut assembly 6, a hydrostatic bearing support 7, a hydrostatic bearing 8 capable of bearing radial load, a hydrostatic guide rail 9, a displacement detection device 10, a workbench 11, a hydrostatic bearing 12 capable of bearing axial radial load, a motor support 13 and a non-contact distance measuring device 14;

601 a double-cone hydrostatic bearing inner ring, 602 a double-cone hydrostatic bearing outer ring, 603 a bearing inner ring bushing, 604 a hollow motor rotor bushing, 605 a hollow motor rotor, 606 a hollow motor stator, 607 an encoder code disc bushing, 608 an encoder code disc, 609 an encoder reading head, 610 a reading head bracket, 611 a connecting bracket, 612 a sealing ring and 613 a hydrostatic lead screw nut;

6031 bearing inner ring bush outer circumference, 6032 mounting hole, 6033 mounting hole, 6034 oil discharge groove and 6035 arc groove;

6041 mounting hole, 6042 mounting hole, 6043 mounting hole, 6044 arc groove;

6101 bolt long hole, 6102 long hole, 6103 mounting hole, 6111 connecting hole, 6112 mounting hole, 6113 annular groove, 6114 annular oil groove, 6115 oil inlet hole, 6071 taper inner surface.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an", and/or "the" are intended to include the plural forms as well, unless the invention expressly state otherwise, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof;

for convenience of description, the words "up", "down", "left" and "right" in the present invention, if any, merely indicate correspondence with the directions of up, down, left and right of the drawings themselves, and do not limit the structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the invention.

The terms "mounted", "connected", "fixed", and the like in the present invention are to be understood in a broad sense, and may be, for example, fixedly connected, detachably connected, or integrated; the two components can be connected mechanically or electrically, directly or indirectly through an intermediate medium, or connected internally or in an interaction relationship, and the terms used in the present invention should be understood as having specific meanings to those skilled in the art.

The noun explains: the large stroke in the invention means that the whole stroke of the screw rod is more than 100mm and can be expanded to more than 1.5m-2 m. "high precision" means a displacement resolution of about 0.01 μm to 1 nm.

As introduced by the background art, the defects in the prior art are overcome, and in order to solve the technical problems, the invention provides a combined nut-driven hydrostatic pressure screw pair, a servo feeding system and a method; based on the designed combined nut-driven type hydrostatic pressure screw pair, a micro-nano motion servo feeding system is actively explored in the machining process, the self behavior is evaluated according to the micro feeding precision finally output by the feeding system and the thickness of an oil film in the hydrostatic pressure screw pair, the self feeding control strategy is continuously optimized according to the evaluation result, finally, experiences are accumulated in a large number of training processes, learning is carried out step by step until the optimal control strategy suitable for the ultra-precise micro-nano motion servo feeding system is obtained, and micro-nano resolution micro-feeding motion in different ultra-precise machining scenes is achieved.

A mapping relation is established between the micro feed amount and the oil film thickness in the ultra-precise feeding process and the rotating speed of the screw rod and the nut by utilizing a deep neural network, and the rotating speed of the screw rod or the rotating speed of the nut is adjusted in real time based on a deep reinforcement learning algorithm so that the workbench obtains a stable and ultra-high precision feeding speed. The training process of the controller comprises two parts of simulation environment training and entity training: in the simulation training stage, a simplified model of the feeding unit is established based on the hydrostatic transmission principle, and the simplified model is trained by using a deep reinforcement learning algorithm until a controller with good micro-feeding precision in a simulation environment is obtained. In the entity training stage, a deep reinforcement learning algorithm is further used for retraining the trained controller in the simulation environment based on the real feeding environment until the controller achieves the required feeding control effect in the more complex actual feeding process.

In an exemplary embodiment of the present invention, the present embodiment first provides a combined hydrostatic nut assembly 6, as shown in fig. 3, including: the double-cone hydrostatic bearing comprises a double-cone hydrostatic bearing inner ring 601, a double-cone hydrostatic bearing outer ring 602, a bearing inner ring bushing 603, a hollow motor rotor bushing 604, a hollow motor rotor 605, a hollow motor stator 606, an encoder code disc bushing 607, an encoder code disc 608, an encoder reading head 609, a reading head bracket 610, a connecting bracket 611, a sealing ring 612 and a hydrostatic lead screw nut 613, wherein the specific connecting structure is as follows:

the double-cone hydrostatic bearing outer ring 602 is fixed with the connecting bracket 611 through bolts;

as shown in fig. 4 and 5, the side surface of the inner ring 601 of the double-cone hydrostatic bearing is fixedly connected with the inner ring bushing 603 through a mounting hole 6032, the inner circumferential surface of the inner ring 601 of the double-cone hydrostatic bearing is matched with the outer circumferential surface 6031 of the inner ring bushing of the bearing, hydraulic oil in the double-cone hydrostatic bearing flows out through a gap between the inner ring 601 of the double-cone hydrostatic bearing and the outer ring 602 of the double-cone hydrostatic bearing, the end surface of the double-cone hydrostatic bearing far away from the connecting bracket 611 directly discharges the hydraulic oil, the end surface of the double-cone hydrostatic bearing near the connecting bracket 611 firstly discharges the hydraulic oil to a closed space enclosed by the connecting bracket 611, the outer ring 602 of the double-cone hydrostatic bearing and the inner ring bushing 603 of the bearing, and then hydraulic oil is discharged through an oil discharge channel formed by matching the double-cone hydrostatic bearing inner ring 601 with an oil discharge groove 6034 in the bearing inner ring bushing 603. The bearing inner ring bushing 603 is fixedly connected with one side of a flange of the hydrostatic lead screw nut 613 through a mounting hole 6033, as shown in fig. 6, the other side of the flange of the hydrostatic lead screw nut 613 is fixedly connected with the hollow motor rotor bushing 604 through a mounting hole 6041, and the inner circumferential surfaces of the bearing inner ring bushing 603 and the hollow motor rotor bushing 604 are both provided with an arc groove 6035 and an arc groove 6044 so as to be suitable for being sleeved with hydrostatic lead screw nuts with different shapes; the hollow motor rotor bushing 604 is fixedly connected with the hollow motor rotor 605 through a mounting hole 6042, and the hollow motor rotor bushing 604 is fixedly connected with the encoder coded disc shaft sleeve 607 through a mounting hole 6043; the encoder code wheel 608 is fixedly connected with an encoder code wheel shaft sleeve 607; the hollow motor stator 606 is fixedly connected with the connecting bracket 611 through a mounting hole 6112.

As shown in fig. 7, the reading head bracket 610 is fixedly connected with the hollow motor stator 606 through a bolt slot 6101, the reading head bracket 610 is fixedly connected with the encoder reading head 609 through a mounting hole 6103, and the relative position of the encoder reading head 609 and the encoder code wheel 608 can be obtained by respectively adjusting the matching position of the connecting bolt with the bolt slot 6101 and the slot 6102;

as shown in fig. 8, the connecting bracket 611 is fixedly connected to the worktable 11 through a connecting hole 6111;

an annular oil groove 6114 and an oil inlet 6115 are machined in the connecting support 611, the oil inlet 6115 is communicated with the annular oil groove 6114, annular grooves 6113 are machined on two sides of the annular oil groove 6114, and the sealing ring 612 is installed in the annular grooves 6113;

the bearing inner ring bush 603, the hollow motor rotor bush 604 and the hydrostatic lead screw nut 613 are fixedly connected to form an outer circumferential surface, and a gap is reserved between the outer circumferential surface and the inner ring of the connecting bracket 611 and the outer circumferential surface rotates relatively;

the inner circumferential surface of the sealing ring 612 is matched with the circumferential surface formed after the bearing inner ring bushing 603 and the hollow motor rotor bushing 604 are fixedly connected with the hydrostatic lead screw nut 613, the outer circumferential surface of the sealing ring 612 is matched with the annular groove 6113, and when hydraulic oil enters the annular oil groove 6114 through the oil inlet 6115, oil path sealing is realized through the sealing rings 612 on two sides of the annular oil groove 6114;

the hydraulic oil in the annular oil groove 6114 is supplied with oil through an oil inlet on the circumferential surface of the flange of the hydrostatic lead screw nut 613, and finally flows out through the meshing clearance between the two ends of the hydrostatic lead screw nut 613 and the lead screw;

particularly, on the side of the hydrostatic lead screw nut with the encoder code disc 608, the hydraulic oil (as shown in fig. 9) flowing out through the meshing gap between the lead screw 5 and the hydrostatic lead screw nut 613 flows out of the combined hydrostatic nut assembly under the constraint of the conical inner surface 6071 of the encoder code disc sleeve 607, so that the encoder code disc 608 is effectively prevented from being polluted by the flowing hydraulic oil.

Further, based on the above-mentioned combined type hydrostatic nut assembly 6, the present embodiment also provides a combined type hydrostatic nut assembly

The large-stroke high-precision micro-nano motion servo feeding system based on the depth reinforcement learning comprises a DRL intelligent decision-making module, a screw motor control module, a nut motor control module and a feeding platform body module.

Wherein, the feeding platform body includes: the device comprises a base 1, a servo motor 2, a coupler 3, a hydrostatic bearing support 4, a hydrostatic bearing support 7, a lead screw 5, the combined hydrostatic nut assembly 6, a hydrostatic bearing 8 capable of bearing radial load, a hydrostatic guide rail 9, a displacement detection device 10, a workbench 11, a hydrostatic bearing 12 capable of bearing axial radial load, a motor support 13 and a non-contact distance measuring device 14;

two ends of the base 1 are provided with a hydrostatic bearing support 4 and a hydrostatic bearing support 7, and a hydrostatic bearing 12 capable of bearing axial radial load is arranged on the hydrostatic bearing support 4; a hydrostatic bearing 8 capable of bearing radial load is arranged on the hydrostatic bearing support 7; one end of the screw rod 5 is supported by a hydrostatic bearing 12 capable of bearing the radial load of the shaft, and the other end of the screw rod is supported by a hydrostatic bearing 8 capable of bearing the radial load; the screw 5 is matched with the combined type hydrostatic nut component 6, and the top of the combined type hydrostatic nut component 6 is connected with a slide block of the hydrostatic guide rail 9; a displacement detection device 10 is arranged on the hydrostatic guide rail 9, and a non-contact type distance measuring device 14 is arranged on the combined type hydrostatic nut component 6; one end of the screw 5 is driven by the servo motor 2.

The overall control flow is as follows: after the training of the DRL intelligent decision system is finished, the current required execution action is obtained according to the current oil film thickness of the screw pair and the feeding position of the workbench, the DRL intelligent decision system sends an action instruction to the screw motor controller and the nut motor controller, the two servo motors respectively comprise a three-phase alternating current asynchronous motor, and the servo motors are driven by a three-loop PID control algorithm (a current loop, a speed loop and a position loop) based on signals fed back by a position/speed/current detector of the motors. The movement of the screw motor and the nut motor is controlled and coordinated to enable the hydrostatic pressure screw pair to move and synthesize, so that the dual-drive differential micro-feeding of the workbench is realized.

The non-contact distance measuring device 14 installed in the hydrostatic lead screw nut 613 can measure the thickness of an oil film between the lead screw and the nut in real time, the displacement detection device 10 can detect the position information of the movement of the workbench in real time, and the thickness of the oil film between the hydrostatic lead screw nut 613 and the lead screw 5 and the position information of the workbench are both fed back to the DRL intelligent decision module.

As shown in fig. 2, the decision method and control flow of the DRL intelligent decision module are as follows:

1. establishing a large-stroke high-precision feeding model

The user sets the required feed rate toV _AimThe algorithm initializes the speed of the screw motor toV _sInitial speed of nut motorV _n=V _s-V _AimAnd is andV _nlarger than the unavoidable and nonlinear rotary crawling speed of the feeding systemV _c。

Speed increasing and decreasing amount delta of screw motorV _s(t)∈[－V _small，V _small]，V _smallAiming at a screw motor when double-drive hydrostatic pressure screw pair double-drive differential ultra-precision feedingV _sMaximum value of fine adjustment, synchronous increment and decrement delta of speed of screw motor and nut motorV _sn(t)∈[0,V _max-V _s]，V _maxThe maximum speed that can be achieved by the screw motor or the nut motor.

By dynamic, real-time adjustment of deltaV _s(t) Functional component capable of compensating for speed fluctuation and hydrostatic pressure of screw motor and nut motorThe feeding error of the workbench caused by interference factors such as damping and system vibration and the like enables the workbench to realize ultra-precise feeding finally; because the screw pitch error and the unavoidable pose error of the screw rod and the nut in the operation process in the hydrostatic lead screw pair generate a dynamic pressure effect, the intelligent decision algorithm changes delta in real timeV _snThe size of the screw rod can dynamically adjust the oil film bearing capacity of the hydrostatic screw rod pair so as to cope with various complex external loads of the hydrostatic screw rod pair and ensure that the feeding precision of the workbench is not influenced by the displacement fluctuation of the screw rod nut. The speed of the screw motor and the speed of the nut motor after the adjustment of the intelligent decision algorithm are as follows:

V _S (t+1)=V _S (t)+ ΔV _s (t)+ ΔV _sn (t)

V _Sn (t+1)=V _Sn (t)+ ΔV _sn (t)。

2. modeling as a Markov decision process

(1) The system feed state space is described asS(t)= [h(t), p(t)]By means of the real-time oil film thickness of the hydrostatic screw assembly during operationh(t) Feeding displacement in real time with the feeding tablep(t) As the environmental state, the feeding state of the servo feeding system is expressed.h(t) Need to satisfy 0.2 h ₀≤h(t) ≤0.8h ₀，h ₀For a set axial oil film thickness at no load, and a real-time oil film thicknessh(t) Feeding displacement in real time with the feeding tablep(t) It is necessary to take successive values.

(2) The motion space is described asA(t)=[ΔV _s(t), ΔV _sn(t)]。

(3) The large-stroke high-precision servo feeding system is used as an intelligent body and is in an environmental stateS(t) When passing through the decision functionμ(S(t) In motion)Make a selection action in space. Agent performing an actionA(t) Post-reward functionR(S,A) Obtaining a prize valueR(t)。

The reward function setting comprises two parts, namely an oil film thickness constant rule and a high-precision feeding rule, and specifically comprises the following steps:

training based on a deep reinforcement learning algorithm

The intelligent agent adopts DDPG algorithm framework of Actor-Critic framework to train, and the Actor network and the Critic network respectively carry out strategy function trainingμAnd value functionQPerforming function approximation with parameters ofθ ^μ Andθ ^Q . The Actor selects the robot action by strategy learning by using strategy gradient (policy gradient) under the current given environment, and the Critic evaluates the value function by using strategy evaluation (policy evaluation) to generate a signal to evaluate the action of the Actor. And respectively establishing a deep neural network model for the strategy network and the evaluation network, wherein the network consists of a one-dimensional convolutional layer, a full-link layer and an output layer.

DDPG algorithm flow:

(1) initializing an experience playback pool, initializing neural network parameters and setting training times;

(2) actor network based on current stateS(t) According to policyμGenerating actionsμ(S(t) Quote the Uhlenbeck-Ornstein random process as random noiseN _t Post-final execution of actionsA(t)=μ(S(t))+N _t ；

(3) Agent performing an actionA(t) Realization of a pair ofV _s(t) And ΔV _sn(t) And return a prize valueR(t) And new stateS(t+1)；

(4) Actor network state conversion processS(t)，A(t)，R(t)，S(t+1)]Storing the data into an experience playback pool in an array form to be used as a data set of a training network;

(5) random sampling from empirical playback poolsNGroup data is used as minimum batch training data for training an Actor network and a Critic network;

(6) and (3) obtaining a target value of data randomly extracted from an empirical playback pool, wherein the target value of the kth group of data can be expressed as:in the formulaQ'Representing the target network of the critical network,μ'representing the target network of the Actor network.R _k Is as followskThe group sample receives an instant reward, gamma is a discount factor and. Optimization of loss function by Adam algorithm or SGD algorithmL(θ ^Q ) Updating critical network parametersθ ^Q ；

；

(7) Using gradient descent normal landingQActor network parameter is updated in direction of value increaseθ ^μ ；

(8) Actor network parameters are mapped by using running average algorithmθ ^μ And Critic network parametersθ ^Q Update to Actor target network parametersθ ^μ' And Critc target network parametersθ ^Q' ；

Based on servo system utensilThe body structure and the inherent attributes reasonably construct a dual-drive hydrostatic pressure screw pair feeding mathematical model for early-stage algorithm simulation training, and a controller shifts to a servo feeding system entity training after the simulation training obtains a better control effect. After the deep neural network is trained for multiple times until the deep neural network meets the use requirement, even if the workbench is subjected to various complex external loads such as external static load, step load, sinusoidal load and the like, the oil film thickness of the double-drive hydrostatic lead screw pairh(t) Can always andh ₀the consistency is kept, and the nut fluctuation displacement caused by axial load during low-speed ultra-precision feeding of the hydrostatic pressure screw pair is greatly reduced; meanwhile, after multiple times of training are finished, the displacement is fed in real timep(t) Can be displaced from the target p ₀And the consistency is maintained.

The invention provides a large-stroke high-precision micro-nano motion servo feeding system and a control method based on deep reinforcement learning. Compared with a conventional motion control method based on a model, the depth reinforcement learning-based double-drive hydrostatic lead screw pair control method is independent of an external environment, is suitable for multivariable, strong-coupling and strong-nonlinear large-stroke high-precision micro-nano motion scenes, and has better robustness.

When the micro high-precision feeding is ensured, the dynamic pressure effect of a liquid oil film in the hydrostatic lead screw pair can be adjusted in real time by increasing or decreasing the rotating speed of the lead screw and the rotating speed of the nut simultaneously, so that various complex external loads of the hydrostatic lead screw pair can be responded, and the feeding precision of the workbench is not influenced by the displacement fluctuation of the lead screw nut.

In addition, the main driving of the hydrostatic lead screw nut can be realized based on the combination of the existing hydrostatic lead screw pair and the hydrostatic bearing and the scheme provided by the invention, the defect that the main driving of the hydrostatic lead screw nut can be realized only by improving or redesigning the hydrostatic bearing and the hydrostatic lead screw pair body in the prior art is overcome, the technical difficulty can be greatly reduced, and the cost can be saved.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.