CN112360838A

CN112360838A - High-frequency-response, high-precision and low-friction digital fluid cylinder

Info

Publication number: CN112360838A
Application number: CN202011169646.4A
Authority: CN
Inventors: 齐潘国; 刘政奇; 赵友军; 杨理昭; 赵丽薇; 郝鹏华; 高明泽; 王顶柱; 沈洋洋
Original assignee: Liaoning Technical University; Xian Coal Mining Machinery Co Ltd
Current assignee: Liaoning Technical University; Xian Coal Mining Machinery Co Ltd
Priority date: 2020-10-28
Filing date: 2020-10-28
Publication date: 2021-02-12
Anticipated expiration: 2040-10-28
Also published as: CN112360838B

Abstract

The invention discloses a high frequency response, high precision and low friction digital fluid cylinder, comprising: the cylinder comprises a cylinder body, a cylinder end cover, a cylinder barrel, a cylinder bottom cover, a piston rod, a static pressure bearing guide sleeve, a ball screw, a feedback nut, a motor, a servo valve block and a dynamic pressure feedback block. One end of the cylinder body is fixedly connected with the cylinder end cover through a bolt, the cylinder barrel is clamped and installed between the other end of the cylinder body and the cylinder bottom cover through a long bolt, one end of the cylinder barrel is communicated with the cylinder body, the other end of the cylinder barrel is communicated with the cylinder bottom cover leakage oil path b, and the cylinder barrel is in static sealing fit with the cylinder bottom cover. According to different performance requirements, the four-side sliding valve core of the servo valve block has two driving modes. For a digital fluid cylinder with high frequency response and high precision, in order to obtain higher open loop gain, a large-diameter valve core is adopted, and an indirect valve core driving type structure is adopted; for digital fluid cylinders that require only low friction, the spool is driven directly by the motor.

Description

High-frequency-response, high-precision and low-friction digital fluid cylinder

Technical Field

The invention relates to a digital fluid cylinder with high frequency response, high precision and low friction, belonging to the technical field of digital hydraulic pressure.

Background

A fluid cylinder is an end effector that performs a linear reciprocating motion by converting pressure energy of a fluid (liquid or gas) into mechanical energy. The traditional fluid cylinder can realize the practical functions of position control, speed control, direction control and the like only by combining with a fluid control valve (a direction valve, a pressure valve, a flow valve, a servo valve and the like), and has the main defects of complex system structure, high price, inconvenient use and maintenance, higher requirement on technical personnel and incapability of directly realizing the control of a digital computer. The digital fluid cylinder is essentially different from the traditional fluid cylinder, is a linear actuator integrating an energy conversion function and a control function, and is far better than the traditional fluid cylinder in a low frequency range, both from the practical function and the control performance.

Existing digital fluid cylinders typically operate in a low frequency range. The digital fluid cylinder has two limiting factors of response frequency, one is limited by a sealing condition, the existing digital fluid cylinders all adopt a non-clearance sealing mode, the friction force at the position of a piston is large, and when the piston moves at a high frequency and a small amplitude, the generated heat cannot be dissipated in time, so that the temperature of a sealing element is increased, and the sealing element is damaged. The other is limited by self structural parameters, the response frequency of the digital fluid cylinder is in direct proportion to the open-loop gain, the improvement of the open-loop gain can be realized by reducing the lead of the lead screw, increasing the lead of the feedback nut and increasing the area gradient of the slide valve, the lead of the lead screw cannot be reduced due to the self structure, the phenomenon of locking can occur when the lead of the feedback nut is too large, the diameter of the valve core can be increased by increasing the area gradient of the slide valve, and further the rotational inertia of the valve core is increased, namely the load rotational inertia of the motor is increased, and the response frequency of the motor is reduced.

The area gradient of the slide valve of the existing digital fluid cylinder is limited by the diameter of the valve core and cannot be made to be large, so that the improvement of the load rigidity of the fluid cylinder is limited, and the load error is large. The existing digital fluid cylinders all adopt a non-clearance sealing mode, the friction force at the piston is large, and the static difference of a system is also large.

In summary, how to combine the characteristics of high frequency response, high precision and low friction of the digital fluid cylinder is an urgent technical problem to be solved in the field of fluid control.

Disclosure of Invention

In view of the above problems, it is an object of the present invention to provide a digital fluid cylinder having high frequency response, high accuracy and low friction characteristics, which employs a structure of hydrostatic bearing, dynamic pressure feedback and indirect drive of a spool valve. In order to achieve the purpose, the invention adopts the following technical scheme:

a high frequency response, high accuracy and low friction digital fluid cylinder comprising: the cylinder comprises a cylinder body, a cylinder end cover, a cylinder barrel, a cylinder bottom cover, a piston rod, a static pressure bearing guide sleeve, a ball screw, a feedback nut, a motor, a servo valve block and a dynamic pressure feedback block. One end of the cylinder body is fixedly connected with the cylinder end cover through a bolt, the cylinder barrel is clamped and installed between the other end of the cylinder body and the cylinder bottom cover through a long bolt, one end of the cylinder barrel is communicated with the cylinder body, the other end of the cylinder barrel is communicated with the cylinder bottom cover leakage oil path b, and the cylinder barrel is in static sealing fit with the cylinder bottom cover. The cylinder bottom cover is communicated with the cylinder end cover through a leakage oil pipe, one end of the leakage oil pipe is communicated with a leakage oil cavity a of the cylinder end cover, the other end of the leakage oil pipe is communicated with a leakage oil path b of the cylinder bottom cover, the leakage oil path b is communicated with the oil tank, and the leakage oil pipe is in static sealing fit with the cylinder end cover and the cylinder bottom cover.

The cylinder body is sleeved on a piston of the piston rod, two sides of the piston rod are respectively sleeved inside the two hydrostatic bearing guide sleeves, and the two hydrostatic bearing guide sleeves are sleeved inside the cylinder body and located at two ends of the cylinder body. The piston of the piston rod is in a symmetrical cone shape and is in clearance sealing fit with the interior of the cylinder body. The static pressure supporting guide sleeve is internally symmetrically tapered and is in clearance sealing fit with the piston rod, and an oil inlet c of the static pressure supporting guide sleeve is connected with a high-pressure oil source.

One end of the piston rod is a driving end, and the other end of the piston rod is a free end. The free end of the piston rod is fixedly connected with the earring through threads and used for pushing an external load. The driving end of the piston rod is fixedly connected with a ball nut through a screw, and the ball nut is sleeved on the screw rod. One end of the ball nut sleeved on the lead screw is a free end, and the other end of the ball nut is a driving end. The screw rod driving end penetrates through the center of the cylinder bottom cover, a screw rod abdicating hole is formed in the center of the piston rod, the free end of the screw rod penetrates through the screw rod abdicating hole, and the screw rod is parallel to the piston rod. And the middle part of the piston rod piston is provided with a leakage oil hole which is communicated with the lead screw abdicating hole on the piston rod. The screw driving end is sleeved with a sealing cover, a bearing, a shaft sleeve and locking nuts, and a screw shaft shoulder is tightly clamped on the sealing cover and is axially fixed through the two locking nuts, so that the screw does not axially move. The sealing cover is sleeved on the screw driving end and tightly clamped on the cylinder bottom cover and the bearing by a screw shaft shoulder, the sealing cover is in static sealing fit with the cylinder bottom cover, and the sealing cover is in dynamic sealing fit with the screw driving end. The ball nut can axially move on the screw rod and drive the screw rod to rotate. And the screw rod driving end is fixedly connected with one end of the feedback nut.

According to different performance requirements, the four-side sliding valve core of the servo valve block has two driving modes. For a digital fluid cylinder with high frequency response and high precision, in order to obtain higher open loop gain, a large-diameter valve core is adopted, and an indirect valve core driving type structure is adopted; for digital fluid cylinders that require only low friction, the spool is driven directly by the motor.

Under the condition of adopting a valve core indirect driving structure, the four-side sliding valve core of the servo valve block is of a split structure, and the motor indirectly drives the valve core to move axially through the transmission shaft. One end of the transmission shaft is connected with the other end of the feedback nut through a thread pair. The other end of the transmission shaft is connected with one end of the coupler through a flat key, and the other end of the coupler is fixedly connected with a motor shaft of the motor. The transmission shaft only rotates along with the motor shaft and has only the freedom of linear sliding relative to the motor shaft. The four-side sliding valve is characterized in that a transmission shaft yielding hole is coaxially formed in the four-side sliding valve core, a bearing yielding hole is coaxially formed in one end of the four-side sliding valve core, the deep groove ball bearing is coaxially arranged in the bearing yielding hole, the transmission shaft is coaxially arranged in the four-side sliding valve core and sleeved in the deep groove ball bearing, and the transmission shaft is in interference fit with an inner ring of the deep groove ball bearing. One end of the four-side sliding valve core, which is provided with the bearing abdicating hole, is fixedly connected with the baffle plate, and the transmission shaft coaxially penetrates through the inside of the baffle plate. The baffle and the shaft shoulder of the transmission shaft clamp the deep groove ball bearing, so that the deep groove ball bearing does not axially displace relative to the four-side sliding valve core.

Under the condition of adopting a valve core direct drive structure, the motor indirectly drives the valve core to move axially. The other end of the feedback nut is connected with one end of the four-side slide valve core in an auxiliary way through threads. The other end of the four-side slide valve core is connected with one end of the coupler through a flat key. The other end of the coupler is fixedly connected with a motor shaft of the motor. The four-side sliding valve core only rotates along with the motor shaft and only has the freedom degree of linear sliding relative to the motor shaft. The four-side sliding valve core is sleeved with a valve sleeve, and the valve sleeve is sleeved inside the servo valve block. The four-side sliding valve core is in clearance sealing fit with the valve sleeve, the valve sleeve is in clearance sealing fit with the inner wall of the servo valve block, and the four-side sliding valve core can axially move back and forth in the valve sleeve to change the opening amount of the throttling opening, so that the throttling opening is opened or closed.

One end of the servo valve block is fixedly connected with the cylinder bottom cover through a bolt, and the other end of the servo valve block is fixedly connected with one end of the motor connecting plate through a screw. The other end of the motor connecting plate is fixedly connected with the motor through a screw. The motor can be a servo motor or a stepping motor. The servo valve block comprises a high-pressure oil inlet P, an oil return port T, a working oil port A and a working oil port B. The high-pressure oil inlet P is communicated with an oil source, and the oil return port T is communicated with an oil tank. And a working oil port A of the servo valve block is fixedly connected with one end of an oil pipe d, and the other end of the oil pipe d is fixedly connected with an oil port e on the dynamic pressure feedback block. And a working oil port B of the servo valve block is fixedly connected with one end of an oil pipe f, and the other end of the oil pipe f is fixedly connected with an oil port g on the dynamic pressure feedback block.

The dynamic pressure feedback block is fixedly connected to the upper end of the cylinder body through a bolt. And an oil path communicated with the oil pipe d on the dynamic pressure feedback block is a first oil path, the first oil path is communicated with a third oil path on the cylinder body, and the third oil path is communicated with a right working cavity of the fluid cylinder, namely a working cavity close to a cylinder end cover. And an oil way communicated with the oil pipe f on the dynamic pressure feedback block is a second oil way, the second oil way is communicated with a fourth oil way on the cylinder body, and the fourth oil way is communicated with a left working cavity of the fluid cylinder, namely the working cavity close to the cylinder barrel.

One end of the dynamic pressure feedback block is provided with a feedback piston abdicating hole, the other end of the dynamic pressure feedback block is provided with a liquid resistance abdicating hole, and the two abdicating holes are communicated with each other. The feedback piston abdicating hole is communicated with the first oil way, the liquid resistance abdicating hole is communicated with the second oil way, and the diameter of the feedback piston abdicating hole is larger than that of the feedback piston liquid resistance abdicating hole. The liquid resistance is sleeved in the liquid resistance abdicating hole. The feedback piston abdicating hole is sleeved with a feedback piston, two centering springs, a positioning shaft sleeve and a dynamic pressure feedback block end cover, and feedback piston rods at two ends of the feedback piston are sleeved inside the two centering springs. And the dynamic pressure feedback block end cover is fixed at one end of the dynamic pressure feedback block through a screw and is in static sealing fit with the inner wall of the abdicating hole of the feedback piston. The dynamic pressure feedback block end cover tightly clamps the positioning shaft sleeve, the feedback piston and the two centering springs on a plane where the two holes of the feedback piston abdicating hole and the liquid resistance abdicating hole are communicated, and the two centering springs are axially fixed. And one end of the positioning shaft sleeve, which is intersected with the first oil way, is provided with four round holes, so that the interior of the positioning shaft sleeve is communicated with the first oil way. The feedback piston can compress the centering spring back and forth to move axially.

The invention has the beneficial effects that: the invention provides a structure adopting static pressure support, dynamic pressure feedback and indirect drive slide valve, which can provide a digital fluid cylinder with high frequency response, high precision and low friction characteristics, also can provide a high-precision digital fluid cylinder, and also can provide a low-friction digital fluid cylinder.

Drawings

FIG. 1 is a cross-sectional view of a front view of one embodiment of a high frequency response, high accuracy and low friction digital fluid cylinder of the present invention;

FIG. 2 is a three-dimensional isometric view of a high frequency response, high accuracy and low friction digital fluid cylinder of the present invention;

FIG. 3 is an enlarged view of portion C of FIG. 1;

FIG. 4 is an enlarged view of portion D of FIG. 1;

FIG. 5 is an enlarged view of section E of FIG. 1;

FIG. 6 is an enlarged view of portion F of FIG. 1;

FIG. 7 is a schematic structural diagram of a dual interface drive spool for a high frequency response, high accuracy, and low friction digital fluid cylinder in accordance with an embodiment of the present invention;

in the figure, 1-motor, 2-motor connecting plate, 3-servo valve block, 4-coupling, 5-cylinder bottom cover, 6-cylinder barrel, 7-fourth oil path, 8-dynamic pressure feedback block, 9-dynamic pressure feedback block end cover, 10-third oil path, 11-cylinder body, 12-static pressure bearing guide sleeve, 13-lug ring, 14-cylinder end cover, 15-piston rod, 16-leakage oil pipe, 17-valve sleeve, 18-four-side spool, 19-shaft sleeve, 20-locking nut, 21-feedback nut, 22-bearing, 23-ball nut, 24-lead screw, 25-sealing cover, 26-second oil path, 27-hydraulic resistance, 28-feedback piston, 29-centering spring, 30-positioning shaft sleeve, 31-first oil path, 32-baffle, 33-transmission shaft, 34-deep groove ball bearing, 35-left working chamber, 36-right working chamber, P-high pressure oil inlet, T-oil return port, A, B-working oil port, a-a leakage oil cavity of the cylinder end cover, a-a leakage oil way of the cylinder bottom cover, d, f-oil pipes, e, g-dynamic pressure feedback block oil ports.

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 with reference to the following 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. The present invention will be described in further detail with reference to the accompanying drawings.

Example one

As shown in fig. 1 to 6, a digital fluid cylinder with high frequency response, high precision and low friction includes: the device comprises a cylinder body 11, a cylinder end cover 14, a cylinder bottom cover 5, a cylinder barrel 6, a piston rod 15, a static pressure supporting guide sleeve 12, a ball screw, a feedback nut 21, a motor 1, a servo valve block 3, a dynamic pressure feedback block 8 and an indirect drive slide valve structure. One end of the cylinder body 11 is fixedly connected with the cylinder end cover 14 through a bolt, the cylinder barrel 6 is clamped and installed between the other end of the cylinder body 11 and the cylinder bottom cover 14 through a long bolt, one end of the cylinder barrel 6 is communicated with the cylinder body 11, the other end of the cylinder barrel is communicated with the leakage oil path b of the cylinder bottom cover 5, and the cylinder barrel 6 is in static sealing fit with the cylinder bottom cover 5. The cylinder bottom cover 5 is communicated with the cylinder end cover 14 through a leakage oil pipe 16, one end of the leakage oil pipe 16 is communicated with a leakage oil cavity a of the cylinder end cover 14, the other end of the leakage oil pipe is communicated with a leakage oil path b of the cylinder bottom cover 5, the leakage oil path b is communicated with an oil tank, and the leakage oil pipe is in static sealing fit with the cylinder end cover 14 and the cylinder bottom cover 5.

The cylinder body 11 is sleeved on a piston of the piston rod 15, two sides of the piston rod 15 are respectively sleeved inside the two static pressure supporting guide sleeves 12, and the two static pressure supporting guide sleeves 12 are sleeved inside the cylinder body 11 and located at two ends of the cylinder body 11. The piston of the piston rod 15 is symmetrically conical and is in clearance sealing fit with the interior of the cylinder 11. The static pressure supporting guide sleeve 12 is internally symmetrically tapered and is in clearance sealing fit with the piston rod 15, and an oil inlet c of the static pressure supporting guide sleeve 12 is connected with a high-pressure oil source.

One end of the piston rod 15 is a driving end, and the other end is a free end. The free end of the piston rod 15 is fixedly connected with the ear ring 13 through threads and used for pushing an external load. The driving end of the piston rod 15 is fixedly connected with a ball nut 23 through a screw, and the ball nut 23 is sleeved on a screw 24. One end of the lead screw 24 sleeved with the ball nut 23 is a free end, and the other end of the lead screw is a driving end. The driving end of the screw rod 24 penetrates through the center of the cylinder bottom cover 5, a screw rod abdicating hole is formed in the center of the piston rod 15, the free end of the screw rod 24 penetrates through the screw rod abdicating hole, and the screw rod 24 is parallel to the piston rod 15. And the middle part of the piston rod 15 is provided with a leakage oil hole which is communicated with a screw abdicating hole on the piston rod 15. The driving end of the screw 24 is sleeved with a sealing cover 25, a bearing 22, a shaft sleeve 19 and locking nuts 20, and the shaft shoulder of the screw 24 is tightly clamped on the sealing cover 25 and axially fixed through the two locking nuts 20, so that the screw 24 does not axially move. The sealing cover 25 is sleeved on the driving end of the screw rod 24 and is tightly clamped on the cylinder bottom cover 5 and the bearing 22 by the shaft shoulder of the screw rod 24, the sealing cover 25 is in static sealing fit with the cylinder bottom cover 5, and the sealing cover 25 is in dynamic sealing fit with the driving end of the screw rod 24. The ball nut 23 is axially displaceable on the spindle 24 and drives the spindle 24 in rotation. And the driving end of the screw 24 is fixedly connected with one end of the feedback nut 21.

The four-sided spool valve 18 of the servo valve block is driven in two ways according to different performance requirements. For a digital fluid cylinder with high frequency response and high precision, in order to obtain higher open loop gain, a large-diameter valve core is adopted, and an indirect valve core driving type structure is adopted; for digital fluid cylinders requiring only low friction, the spool is driven directly by the motor 1.

Under the condition of adopting a valve core indirect driving structure, the four-side sliding valve core 18 of the servo valve block is of a split structure, and the motor 1 indirectly drives the valve core to move axially through the transmission shaft 33. One end of the transmission shaft 33 is connected with the other end of the feedback nut 21 through a thread pair. The other end of the transmission shaft 33 is connected with one end of the coupler 4 through a flat key, and the other end of the coupler 4 is fixedly connected with a motor shaft of the motor 1. The drive shaft 33 only rotates with the motor shaft and has only a linear sliding freedom with respect to the motor shaft. The four-side sliding valve core 18 is coaxially provided with a transmission shaft 33 abdicating hole, one end of the four-side sliding valve core 18 is coaxially provided with a bearing abdicating hole, the deep groove ball bearing 34 is coaxially arranged in the bearing abdicating hole, the transmission shaft 33 is coaxially arranged in the four-side sliding valve core 18 and sleeved in the deep groove ball bearing 34, and the transmission shaft 33 is in interference fit with the inner ring of the deep groove ball bearing 34. One end of the four-side sliding valve core 18, which is provided with a bearing abdicating hole, is fixedly connected with the baffle 32, and the transmission shaft 33 coaxially penetrates through the inside of the baffle 32. The baffle 32 and the shaft shoulder of the transmission shaft 33 clamp the deep groove ball bearing 34, so that the deep groove ball bearing 34 does not axially displace relative to the four-side slide valve core 18.

Under the condition of adopting a valve core direct drive structure, the motor 1 indirectly drives the valve core to move axially. The other end of the feedback nut 21 is connected to one end of the four-side spool valve 18 by a screw. The other end of the four-side slide valve core 18 is connected with one end of the coupler 4 through a flat key. The other end of the coupling 4 is fixedly connected with a motor shaft of the motor 1. The four-sided spool valve spool 18 only rotates with the motor shaft and has only linear sliding freedom relative to the motor shaft. The four-side slide valve 18 is sleeved with a valve sleeve 17, and the valve sleeve 17 is sleeved inside the servo valve block. The four-side sliding valve core 18 is in clearance sealing fit with the valve sleeve 17, the valve sleeve 17 is in clearance sealing fit with the inner wall of the servo valve block, and the four-side sliding valve core 18 can axially move back and forth in the valve sleeve 17 to change the opening amount of the throttling opening so as to open or close the throttling opening.

One end of the servo valve block 3 is fixedly connected with the cylinder bottom cover 5 through a bolt, and the other end of the servo valve block is fixedly connected with one end of the motor connecting plate 2 through a screw. The other end of the motor connecting plate 2 is fixedly connected with the motor 1 through a screw. The motor 1 may be a servo motor or a stepping motor. The servo valve block 3 comprises a high-pressure oil inlet P, an oil return port T, a working oil port A and a working oil port B. The high-pressure oil inlet P is communicated with an oil source, and the oil return port T is communicated with an oil tank. And a working oil port A of the servo valve block 3 is fixedly connected with one end of an oil pipe d, and the other end of the oil pipe d is fixedly connected with an oil port e on the dynamic pressure feedback block 8. And a working oil port B of the servo valve block 3 is fixedly connected with one end of an oil pipe f, and the other end of the oil pipe f is fixedly connected with an oil port g on the dynamic pressure feedback block 8.

The dynamic pressure feedback block 8 is fixedly connected to the upper end of the cylinder body through a bolt. The oil path on the dynamic pressure feedback block 8 communicated with the oil pipe d is a first oil path 31, the first oil path 31 is communicated with a third oil path 10 on the cylinder body 11, and the third oil path 10 is communicated with a right working cavity 36 of the fluid cylinder, namely a working cavity close to the cylinder end cover 14. The oil path on the dynamic pressure feedback block 8 communicated with the oil pipe f is a second oil path 26, the second oil path 26 is communicated with a fourth oil path 7 on the cylinder body 11, and the fourth oil path 7 is communicated with a left working cavity 35 of the fluid cylinder, namely, a working cavity close to the cylinder barrel 6.

One end of the dynamic pressure feedback block 8 is provided with a feedback piston abdicating hole, the other end of the dynamic pressure feedback block is provided with a liquid resistance abdicating hole, and the two abdicating holes are communicated with each other. The feedback piston abdicating hole is communicated with the first oil path 31, the liquid resistance abdicating hole is communicated with the second oil path 26, and the diameter of the feedback piston abdicating hole is larger than that of the feedback piston liquid resistance abdicating hole. The liquid resistance 27 is sleeved inside the liquid resistance abdicating hole. The feedback piston abdicating hole is sleeved with a feedback piston 28, two centering springs 29, a positioning shaft sleeve 30 and a dynamic pressure feedback block end cover 9, and feedback piston rods at two ends of the feedback piston 28 are sleeved inside the two centering springs 29. And the dynamic pressure feedback block end cover 9 is fixed at one end of the dynamic pressure feedback block 8 through a screw and is in static sealing fit with the inner wall of the abdicating hole of the feedback piston. The dynamic pressure feedback block end cover 9 tightly clamps the positioning shaft sleeve 30, the feedback piston 28 and the two centering springs 29 on a plane where the two holes of the feedback piston abdicating hole and the liquid resistance abdicating hole are communicated, and axially fixes the two centering springs 29. Four round holes are formed at the intersecting end of the positioning shaft sleeve 30 and the first oil path 31, so that the inside of the positioning shaft sleeve 30 is communicated with the first oil path 31. The feedback piston 28 can compress the centering spring 29 back and forth for axial movement.

The operation of the present invention is described below with reference to the accompanying drawings:

the invention is a digital fluid cylinder with high frequency response, high precision and low friction, when the four-side slide valve core 18 is in the middle position, the piston rod 15 is in the static state, and the feedback piston 28 is also in the middle position due to the action of the centering spring 29. An oil inlet c of a static pressure supporting guide sleeve 12 at two ends of the cylinder body 11 is respectively communicated with a high-pressure oil source in the upper direction, the lower direction, the front direction and the rear direction. And starting to enable the lower surface of the piston rod 15 and the narrow gap of the static pressure supporting guide sleeve 12 to be attached to each other due to the action of gravity and radial load of the piston rod 15, and enabling the lower surface of the piston rod 15 and the inner wall of the cylinder 11 to be attached to each other. High-pressure oil flows into wide gaps of the static pressure supporting guide sleeve 12 from the oil inlet c in four directions, namely up, down, front and back, and then flows to narrow gaps at two ends of the static pressure supporting guide sleeve 12 from the wide gaps and leaks out from the narrow gaps. In the gap, the oil liquid forms radial pressure due to forced flowing, the radial pressure of the lower surface of the piston rod 15 is larger than that of the upper surface, and the piston rod 15 has the tendency of floating upwards. The radial pressure is constantly increased, and when the radial pressure is increased to a certain degree, the oil entering the gap floats the piston rod 15, and then the oil leaks out from the narrow gap. One part of the oil leaked from the narrow gap of the hydrostatic bearing guide sleeve 12 at the left end of the cylinder body 11 flows into the left working chamber 35 of the fluid cylinder, the other part of the oil flows into the cylinder barrel 6, and the oil flowing into the cylinder barrel 6 flows back to the oil tank through the leakage oil path b of the cylinder bottom cover 5. The gap between the surface of the piston rod 15 and the static pressure support guide sleeve 12 is small, a thin oil film is formed, direct contact between metals is eliminated, and a friction-free kinematic pair between the surface of the piston rod 15 and the static pressure support guide sleeve 12 is realized. Because the static pressure supporting guide sleeves 12 at the two ends of the piston rod 15 play a role of static pressure supporting, the whole piston rod 15 is floated, the piston surface of the piston rod 15 is not attached to the inner wall surface of the cylinder body 11, a small gap is formed between the two surfaces to form a thin oil film, and the contact between metals is eliminated, so that a friction-free kinematic pair between the piston surface and the inner wall of the cylinder body 11 is realized. When the radial load on the piston rod 15 changes, the thickness of the thin oil film between the surface of the piston rod 15 and the static pressure support guide sleeve 12 changes, and the radial pressure on the surface of the piston rod 15 also changes, so that the piston rod 15 always floats, and a friction-free kinematic pair between the surface of the piston rod 15 and the static pressure support guide sleeve 12 and a friction-free kinematic pair between the surface of the piston and the inner wall of the cylinder 11 are realized.

An electric signal is input to the motor 1, a motor shaft of the motor 1 rotates for a certain angle, the four-side sliding valve core 18 is driven by the coupler 4 to rotate for a certain angle, and due to the effect of the thread pair of the feedback nut 21, the four-side sliding valve core 18 can axially displace, so that a sliding valve throttling opening is opened. Assuming that the four-sided spool valve 18 moves leftward, the spool valve orifice is opened, the oil flows into the servo valve block 3 from the high-pressure oil inlet P, flows out from the working oil port a through the spool valve orifice into the oil pipe d, and then flows into the first oil path 31 of the dynamic pressure feedback block 8 through the oil port e of the dynamic pressure feedback block 8. The oil flowing into the first oil path 31 of the dynamic pressure feedback block 8 is divided into two parts, one part of the oil flows into the third oil path 10 of the cylinder body 11 and then flows into the right working chamber 36 of the fluid cylinder from the third oil path 10, and the piston rod 15 is driven to move leftwards, so that the piston rod 15 retracts. Another part of the oil flows into the positioning sleeve 30 from a circular hole at one end of the positioning sleeve 30, which is intersected with the first oil passage 31, and acts on the right side of the feedback piston 28. When the piston rod 15 retracts leftwards, oil in the left working chamber 35 of the fluid cylinder enters the second oil path 26 on the dynamic pressure feedback block 8 through the fourth oil path 7 on the cylinder body, the oil entering the second oil path 26 is divided into two parts, one part of the oil flows into the oil pipe f from the oil port g on the dynamic pressure feedback block 8, flows into the servo valve block 3 through the working oil port B after flowing out of the oil pipe f, and then flows back to the oil tank from the opened slide valve throttling port through the oil return port T. Another portion of the oil flows through the hydraulic resistance 27 and acts on the left side of the feedback piston 28. The pressure difference acting on the feedback piston 28, i.e. the pressure difference between the left and right working chambers of the fluid cylinder, is greater than the pressure of the left working chamber 35, so the feedback piston 28 moves leftwards to compress the centering spring 29, when the load on the piston rod 15 is not changed, i.e. the pressure difference between the left and right working chambers of the fluid cylinder is stable, the feedback piston 28 has a stable compression amount on the centering spring 29, the pressure difference between the two ends of the hydraulic resistor 27 is zero, oil-free liquid flows through the hydraulic resistor 27, and at this time, the dynamic pressure feedback device does not generate damping action. When the load on the piston rod 15 changes, the load pressure on the feedback piston 28 also changes, the compression amount of the centering spring 29 by the feedback piston 28 changes along with the change of the load pressure, the pressure difference between the two ends of the hydraulic resistance 27 also changes along with the change of the load, so that the oil flows through the hydraulic resistance 27 back and forth, and the dynamic pressure feedback device generates a damping effect. Under the steady state condition, the dynamic pressure feedback device does not generate damping action and does not influence the steady state performance of the fluid cylinder. In the dynamic process, the dynamic pressure feedback device generates an additional damping effect along with the load change, the larger the load pressure change of the left working cavity and the right working cavity of the fluid cylinder is, the larger the damping effect generated by the dynamic pressure feedback device is, and the stability of the digital fluid cylinder is further improved. The digital fluid cylinder adopts the static pressure support device to reduce the friction force at the piston, and the stability of the digital fluid cylinder can be reduced while the friction force is reduced, so that a dynamic pressure feedback device needs to be designed to improve the damping ratio of the system to ensure the stability of the digital fluid cylinder.

When the piston rod 15 retracts leftwards, a small part of high-pressure oil in the right working cavity 36 of the fluid cylinder flows to a narrow gap in the middle of the piston from a wide gap on the right side of the piston rod 15, the oil flowing out of the narrow gap leaks to a leakage oil hole in the middle of the piston through a gap between the piston and the inner wall of the cylinder body 11, the leaked oil flows back to an oil tank through a lead screw abdicating hole in the piston rod 15 and a leakage oil path b on the cylinder bottom cover 5 in sequence, the oil forms radial pressure due to forced flow, and the action of the radial pressure is to separate the surface of the piston from the inner wall of the cylinder body 11. When the piston rod 15 retracts leftwards, a small part of oil in the left working cavity 35 of the fluid cylinder flows to a narrow gap in the middle of the piston from a wide gap on the right side of the piston rod 15, the oil flowing out of the narrow gap leaks to a leakage oil hole in the middle of the piston through a gap between the piston and the inner wall of the cylinder body 11, the leakage oil flows back to an oil tank through a screw rod abdicating hole in the piston rod 15 and a leakage oil path b on the cylinder bottom cover 5 in sequence, the oil forms radial pressure due to forced flow, and the surface of the piston is separated from the inner wall of the cylinder body 11 under the action of the radial pressure. Therefore, when the piston rod 15 is static, the oil source continuously supplies oil, the pressure on the two sides of the piston is equal to half of the oil supply pressure, the symmetrical conical structure at the piston plays a role in static pressure support to float the piston rod 15, and if the oil source stops supplying oil, the pressure on the two sides of the piston is zero, and the symmetrical conical structure at the piston does not play a role in static pressure support. When the piston rod 15 moves leftwards, the conical structures on both sides of the piston rod 15 play a role of static pressure support, and a friction kinematic pair between the surface of the piston and the inner wall of the cylinder body 11 is eliminated.

When the piston rod 15 is retracted leftward, the ball nut 23 follows the piston rod 15 to move axially leftward. The lead screw 24 is axially fixed, the lead screw 24 can rotate for a certain angle due to the action of the thread pair between the ball nut 23 and the lead screw 24, and further the feedback nut 21 is driven to rotate for a certain angle, and the four-side slide valve core 18 is connected with the motor shaft through the coupler 4 and does not rotate due to the action of the thread pair between the four-side slide valve core 18 and the feedback nut 21, so that the four-side slide valve core 18 can generate axial displacement, the slide valve throttling port is closed, the piston rod 15 stops moving, and one process is finished. When the electric signal is continuously input to the motor 1, the piston rod 15 of the fluid cylinder can be continuously moved to the left, and the displacement of the piston rod 15 can be ensured.

Assuming that the four-side spool valve 18 moves rightwards, the spool valve throttling opening is opened, the oil flows into the servo valve block 3 from the high-pressure oil inlet P, flows out of the working oil port B through the spool valve throttling opening, enters the oil pipe f, and then flows into the second oil passage 26 on the dynamic pressure feedback block 8 through the oil port g on the dynamic pressure feedback block 8. The oil flowing into the second oil passage 26 of the dynamic pressure feedback block 8 is divided into two parts, and one part of the oil flows into the fourth oil passage 7 of the cylinder body 11 and then flows into the left working chamber 35 of the fluid cylinder from the fourth oil passage 7 to drive the piston rod 15 to move rightwards, so that the piston rod 15 extends out. Another portion of the oil flows through the hydraulic resistance 27 and acts on the left side of the feedback piston 28. When the piston rod 15 extends rightward, the oil in the right working chamber 36 of the fluid cylinder enters the first oil path 31 of the dynamic pressure feedback block 8 through the third oil path 10 of the cylinder 11, the oil entering the first oil path 31 is divided into two parts, one part of the oil flows into the oil pipe d from the oil port e of the dynamic pressure feedback block, and the oil flows out of the oil pipe d, flows into the servo valve block 3 through the working oil port a, and then flows back to the oil tank from the opened throttle port of the slide valve through the oil return port T. Another part of the oil flows into the positioning sleeve 30 from a circular hole at one end of the positioning sleeve 30, which is intersected with the first oil passage 31, and acts on the right side of the feedback piston 28. The pressure difference acting on the feedback piston 28, i.e. the pressure difference between the left and right working chambers of the fluid cylinder, is greater than the pressure of the right working chamber 36, so the feedback piston 28 moves to the right to compress the centering spring 39, when the load on the piston rod 15 does not change, i.e. the pressure difference between the left and right working chambers of the fluid cylinder is stable, the feedback piston 28 has a stable compression amount on the centering spring 29, the pressure difference between the two ends of the hydraulic resistor 27 is zero, oil-free liquid flows through the hydraulic resistor 27, and at this time, the dynamic pressure feedback device does not generate damping action. When the load on the piston rod 1 changes, the load pressure on the feedback piston 28 also changes, the compression amount of the centering spring 29 by the feedback piston 28 changes along with the change of the load pressure, the pressure difference between the two ends of the hydraulic resistance 27 also changes along with the change of the load, so that the oil flows through the hydraulic resistance 27 back and forth, and the dynamic pressure feedback device generates a damping effect. Under the steady state condition, the dynamic pressure feedback device does not generate damping action and does not influence the steady state performance of the fluid cylinder. In the dynamic process, the dynamic pressure feedback device generates an additional damping effect along with the load change, the larger the load pressure change of the left working cavity and the right working cavity of the fluid cylinder is, the larger the damping effect generated by the dynamic pressure feedback device is, and the stability of the digital fluid cylinder is further improved. The digital fluid cylinder adopts the static pressure support device to reduce the friction force at the piston, and the stability of the digital fluid cylinder can be reduced while the friction force is reduced, so that a dynamic pressure feedback device needs to be designed to improve the damping ratio of the system to ensure the stability of the digital fluid cylinder.

When the piston rod 15 stretches out rightwards, a small part of high-pressure oil in the left working cavity 35 of the fluid cylinder flows to a narrow gap in the middle of the piston from a wide gap on the right side of the piston rod piston, the oil flowing out of the narrow gap leaks to a leakage oil hole in the middle of the piston through a gap between the piston and the inner wall of the cylinder body 11, the leakage oil flows back to an oil tank through a lead screw abdicating hole in the piston rod and a leakage oil path b on the cylinder bottom cover 5 in sequence, the oil forms radial pressure due to forced flow, and the action of the radial pressure is to separate the surface of the piston from the inner wall of the cylinder body 11, so. When the piston rod 15 stretches out rightwards, a small part of oil in the right working cavity 36 of the piston rod 15 flows to a narrow gap in the middle of the piston from a wide gap on the right side of the piston rod 15, the oil flowing out of the narrow gap leaks to a leakage oil hole in the middle of the piston through a gap between the piston and the inner wall of the cylinder body 11, the leakage oil flows back to an oil tank through a lead screw abdicating hole in the piston rod 15 and a leakage oil path b on the cylinder bottom cover 5 in sequence, the oil forms radial pressure due to forced flow, and the action of the radial pressure is to separate the surface of the piston from the inner wall of the cylinder body 11. Therefore, when the piston rod 15 is static, the oil source continuously supplies oil, the pressure on the two sides of the piston is equal to half of the oil supply pressure, the symmetrical conical structure at the piston plays a role in static pressure support to float the piston rod 15, and if the oil source stops supplying oil, the pressure on the two sides of the piston is zero, and the symmetrical conical structure at the piston does not play a role in static pressure support. When the piston rod 15 moves to the right, the conical structures on both sides of the piston rod 15 play a role of static pressure support, and a friction kinematic pair between the surface of the piston and the inner wall of the cylinder 11 is eliminated.

When the piston is extended to the right, the ball nut 23 follows the piston rod 15 to move axially to the right. The lead screw 24 is axially fixed, the lead screw 24 can rotate for a certain angle due to the action of the thread pair between the ball nut 23 and the lead screw 24, and further the feedback nut 21 is driven to rotate for a certain angle, and the four-side slide valve core 18 is connected with the motor shaft through the coupler 4 and does not rotate due to the action of the thread pair between the four-side slide valve core 18 and the feedback nut 21, so that the four-side slide valve core 18 can generate axial displacement, the slide valve throttling port is closed, the piston rod 15 stops moving, and one process is finished. When the electric signal is continuously input to the motor 1, the piston rod 15 of the fluid cylinder can be continuously moved to the right, and the displacement of the piston rod 15 can be ensured.

Example two

As shown in fig. 1 to 7, when the motor shaft of the motor 1 receives an electrical signal to rotate, the transmission shaft 33 rotates inside the deep groove ball bearing 34, and due to the effect of the thread pair between the transmission shaft 33 and the feedback nut 21, the transmission shaft 33 moves axially, and further drives the four-side sliding valve core 18 to move axially, so that the throttle of the sliding valve is opened. Because the four-side slide valve core 18 is sleeved outside the deep groove ball bearing 34, the four-side slide valve core 18 only moves axially and does not rotate along with the transmission shaft 33. By adopting the structure of indirectly driving the slide valve, the enlargement of the rotary inertia of the valve core caused by the enlargement of the diameter of the valve core is eliminated, the reduction of the response frequency of the motor 1 caused by the enlargement of the load rotary inertia of the motor 1 is eliminated, the open loop gain of the system can be effectively improved, and the response frequency of the system is improved and the load error of the system is reduced.

Assuming that the four-sided spool valve 18 moves leftward, the spool valve orifice is opened, the oil flows into the servo valve block 3 from the high-pressure oil inlet P, flows out from the working oil port a through the spool valve orifice into the oil pipe d, and then flows into the first oil path 31 of the dynamic pressure feedback block 8 through the oil port e of the dynamic pressure feedback block 8. The oil flowing into the first oil path 31 of the dynamic pressure feedback block 8 is divided into two parts, one part of the oil flows into the third oil path 10 of the cylinder body 11 and then flows into the right working chamber 36 of the fluid cylinder from the third oil path 10, and the piston rod 15 is driven to move leftwards, so that the piston rod 15 retracts. Another part of the oil flows into the positioning sleeve 30 from a circular hole at one end of the positioning sleeve 30, which is intersected with the first oil passage 31, and acts on the right side of the feedback piston 28. When the piston rod 15 retracts leftwards, oil in the left working chamber 35 of the fluid cylinder enters the second oil path 26 on the dynamic pressure feedback block 8 through the fourth oil path 7 on the cylinder body, the oil entering the second oil path 26 is divided into two parts, one part of the oil flows into the oil pipe f from the oil port g on the dynamic pressure feedback block 8, flows into the servo valve block 3 through the working oil port B after flowing out of the oil pipe f, and then flows back to the oil tank from the opened slide valve throttling port through the oil return port T. Another portion of the oil flows through the hydraulic resistance 27 and acts on the left side of the feedback piston 28. The pressure difference acting on the feedback piston 28, i.e. the pressure difference between the left and right working chambers of the fluid cylinder, is greater than the pressure of the left working chamber 35, so the feedback piston 28 moves leftwards to compress the centering spring 29, when the load on the piston rod 15 is not changed, i.e. the pressure difference between the left and right working chambers of the fluid cylinder is stable, the feedback piston 28 has a stable compression amount on the centering spring 29, the pressure difference between the two ends of the hydraulic resistor 27 is zero, oil-free liquid flows through the hydraulic resistor 27, and at this time, the dynamic pressure feedback device does not generate damping action. When the load on the piston rod 15 changes, the load pressure on the feedback piston 28 also changes, the compression amount of the centering spring 29 by the feedback piston 28 changes along with the change of the load pressure, the pressure difference between the two ends of the hydraulic resistance 27 also changes along with the change of the load, so that the oil flows through the hydraulic resistance 27 back and forth, and the dynamic pressure feedback device generates a damping effect. Under the steady state condition, the dynamic pressure feedback device does not generate damping action and does not influence the steady state performance of the fluid cylinder. In the dynamic process, the dynamic pressure feedback device generates an additional damping effect along with the load change, the larger the load pressure change of the left working cavity and the right working cavity of the fluid cylinder is, the larger the damping effect generated by the dynamic pressure feedback device is, and the stability of the digital fluid cylinder is further improved. The digital fluid cylinder adopts the static pressure support device to reduce the friction force at the piston, and the stability of the digital fluid cylinder can be reduced while the friction force is reduced, so that a dynamic pressure feedback device needs to be designed to improve the damping ratio of the system to ensure the stability of the digital fluid cylinder.

When the piston rod 15 is retracted leftward, the ball nut 23 follows the piston rod 15 to move axially leftward. The screw 24 is axially fixed, the screw 24 can rotate for a certain angle due to the action of the thread pair between the ball nut 23 and the screw 24, and further drives the feedback nut 21 to rotate for a certain angle, and the transmission shaft 33 is connected with the motor shaft through the coupler 4 and does not rotate due to the action of the thread pair between the transmission shaft 33 and the feedback nut 21, so that the transmission shaft 33 can generate axial displacement, further the four-side slide valve core 18 is driven to generate axial displacement to close the slide valve throttling opening, the piston rod 15 stops moving, and one process is finished. When the electric signal is continuously input to the motor 1, the piston rod 15 of the fluid cylinder can be continuously moved to the left, and the displacement of the piston rod 15 can be ensured.

When the piston is extended to the right, the ball nut 23 follows the piston rod 15 to move axially to the right. The screw 24 is axially fixed, the screw 24 can rotate for a certain angle due to the action of the thread pair between the ball nut 23 and the screw 24, and further drives the feedback nut 21 to rotate for a certain angle, and the transmission shaft 33 is connected with the motor shaft through the coupler 4 and does not rotate due to the action of the thread pair between the transmission shaft 33 and the feedback nut 21, so that the transmission shaft 33 can generate axial displacement, further the four-side slide valve core 18 is driven to generate axial displacement to close the slide valve throttling opening, the piston rod 15 stops moving, and one process is finished. When the electric signal is continuously input to the motor 1, the piston rod 15 of the fluid cylinder can be continuously moved to the right, and the displacement of the piston rod 15 can be ensured.

The embodiments are not intended to limit the scope of the present invention, and all equivalent implementations or modifications without departing from the scope of the present invention are intended to be included in the scope of the present invention.

Claims

1. A high frequency response, high accuracy and low friction digital fluid cylinder, comprising: the hydraulic cylinder comprises a cylinder body, a cylinder end cover, a cylinder barrel, a cylinder bottom cover, a piston rod, a static pressure bearing guide sleeve, a ball screw, a feedback nut, a motor, a servo valve block and a dynamic pressure feedback block; one end of the cylinder body is fixedly connected with the cylinder end cover through a bolt, the cylinder barrel is clamped and installed between the other end of the cylinder body and the cylinder bottom cover through a long bolt, one end of the cylinder barrel is communicated with the cylinder body, the other end of the cylinder barrel is communicated with a leakage oil path b of the cylinder bottom cover, and the cylinder barrel is in static sealing fit with the cylinder bottom cover; the cylinder bottom cover is communicated with the cylinder end cover through a leakage oil pipe, one end of the leakage oil pipe is communicated with a leakage oil cavity a of the cylinder end cover, the other end of the leakage oil pipe is communicated with a leakage oil path b of the cylinder bottom cover, the leakage oil path b is communicated with the oil tank, and the leakage oil pipe is in static sealing fit with the cylinder end cover and the cylinder bottom cover.

2. The digital fluid cylinder of claim 1, wherein: the cylinder body is sleeved on a piston of the piston rod, two sides of the piston rod are respectively sleeved inside the two hydrostatic bearing guide sleeves, and the two hydrostatic bearing guide sleeves are sleeved inside the cylinder body and positioned at two ends of the cylinder body; the piston of the piston rod is symmetrically conical and is in clearance sealing fit with the interior of the cylinder body; the static pressure supporting guide sleeve is internally symmetrically tapered and is in clearance sealing fit with the piston rod, and an oil inlet c of the static pressure supporting guide sleeve is connected with a high-pressure oil source.

3. The digital fluid cylinder of claim 1, wherein: one end of the piston rod is a driving end, and the other end of the piston rod is a free end; the free end of the piston rod is fixedly connected with the earring through threads and used for pushing an external load; the driving end of the piston rod is fixedly connected with a ball nut through a screw, and the ball nut is sleeved on a lead screw; one end of the ball nut sleeved by the lead screw is a free end, and the other end of the ball nut is a driving end; the screw rod driving end penetrates through the center of the cylinder bottom cover, a screw rod abdicating hole is formed in the center of the piston rod, the free end of the screw rod penetrates through the screw rod abdicating hole, and the screw rod is parallel to the piston rod; the middle part of the piston rod piston is provided with a leakage oil hole which is communicated with a screw rod abdicating hole on the piston rod; the screw driving end is sleeved with a sealing cover, a bearing, a shaft sleeve and locking nuts, and a screw shaft shoulder is tightly clamped on the sealing cover and is axially fixed through the two locking nuts, so that the screw does not axially move; the sealing cover is sleeved on the screw rod driving end and is tightly clamped on the cylinder bottom cover and the bearing by a screw rod shaft shoulder, the sealing cover is in static sealing fit with the cylinder bottom cover, and the sealing cover is in dynamic sealing fit with the screw rod driving end; the ball nut can axially move on the screw rod and drives the screw rod to rotate; and the screw rod driving end is fixedly connected with one end of the feedback nut.

4. The digital fluid cylinder of claim 1, wherein: according to different performance requirements, the four-side sliding valve core of the servo valve block is driven in two ways: for a digital fluid cylinder with high frequency response and high precision, in order to obtain higher open loop gain, a large-diameter valve core is adopted, and an indirect valve core driving type structure is adopted; for digital fluid cylinders that require only low friction, the spool is driven directly by the motor.

5. The digital fluid cylinder of claim 4, wherein: under the condition of adopting a valve core indirect drive structure, the four-side sliding valve core of the servo valve block is of a split structure, and the motor indirectly drives the valve core to move axially through a transmission shaft; one end of the transmission shaft is connected with the other end of the feedback nut through a thread pair; the other end of the transmission shaft is connected with one end of a coupler through a flat key, and the other end of the coupler is fixedly connected with a motor shaft of the motor; the transmission shaft only rotates along with the motor shaft and only has the freedom degree of linear sliding relative to the motor shaft; the four-side sliding valve core is coaxially provided with a transmission shaft abdicating hole, one end of the four-side sliding valve core is coaxially provided with a bearing abdicating hole, the deep groove ball bearing is coaxially arranged in the bearing abdicating hole, the transmission shaft is coaxially arranged in the four-side sliding valve core and sleeved in the deep groove ball bearing, and the transmission shaft is in interference fit with the inner ring of the deep groove ball bearing; one end of the four-side sliding valve core, which is provided with the bearing abdicating hole, is fixedly connected with the baffle plate, and the transmission shaft coaxially penetrates through the inside of the baffle plate; the baffle and the shaft shoulder of the transmission shaft clamp the deep groove ball bearing, so that the deep groove ball bearing does not axially displace relative to the four-side sliding valve core.

6. The digital fluid cylinder of claim 5, wherein: under the condition of adopting a valve core direct drive structure, the motor indirectly drives the valve core to axially move; the other end of the feedback nut is in auxiliary connection with one end of the four-side slide valve core through threads; the other end of the four-side slide valve core is connected with one end of the coupler through a flat key; the other end of the coupler is fixedly connected with a motor shaft of the motor; the four-side sliding valve core only rotates along with the motor shaft and only has the degree of freedom of linear sliding relative to the motor shaft; the four-side sliding valve core is sleeved with a valve sleeve which is sleeved inside the servo valve block; the four-side sliding valve core is in clearance sealing fit with the valve sleeve, the valve sleeve is in clearance sealing fit with the inner wall of the servo valve block, and the four-side sliding valve core can axially move back and forth in the valve sleeve to change the opening amount of the throttling opening, so that the throttling opening is opened or closed.

7. The digital fluid cylinder of claim 1, wherein: one end of the servo valve block is fixedly connected with the cylinder bottom cover through a bolt, and the other end of the servo valve block is fixedly connected with one end of the motor connecting plate through a screw; the other end of the motor connecting plate is fixedly connected with a motor through a screw; the motor can be a servo motor or a stepping motor; the servo valve block comprises a high-pressure oil inlet P, an oil return port T, a working oil port A and a working oil port B; the high-pressure oil inlet P is communicated with an oil source, and the oil return port T is communicated with an oil tank; the working oil port A of the servo valve block is fixedly connected with one end of an oil pipe d, and the other end of the oil pipe d is fixedly connected with an oil port e on the dynamic pressure feedback block; and a working oil port B of the servo valve block is fixedly connected with one end of an oil pipe f, and the other end of the oil pipe f is fixedly connected with an oil port g on the dynamic pressure feedback block.

8. The digital fluid cylinder of claim 1, wherein: the dynamic pressure feedback block is fixedly connected to the upper end of the cylinder body through a bolt; the oil passage communicated with the oil pipe d on the dynamic pressure feedback block is a first oil passage which is communicated with a third oil passage on the cylinder body, and the third oil passage is communicated with a right working cavity of the fluid cylinder, namely a working cavity close to the cylinder end cover; and an oil way communicated with the oil pipe f on the dynamic pressure feedback block is a second oil way, the second oil way is communicated with a fourth oil way on the cylinder body, and the fourth oil way is communicated with a left working cavity of the fluid cylinder, namely the working cavity close to the cylinder barrel.

9. The digital fluid cylinder of claim 8, wherein: one end of the dynamic pressure feedback block is provided with a feedback piston abdicating hole, the other end of the dynamic pressure feedback block is provided with a liquid resistance abdicating hole, and the two abdicating holes are communicated with each other; the feedback piston abdicating hole is communicated with the first oil way, the liquid resistance abdicating hole is communicated with the second oil way, and the diameter of the feedback piston abdicating hole is larger than that of the feedback piston liquid resistance abdicating hole; the liquid resistance is sleeved inside the liquid resistance abdicating hole; a feedback piston, two centering springs, a positioning shaft sleeve and a dynamic pressure feedback block end cover are sleeved in the feedback piston abdicating hole, and feedback piston rods at two ends of the feedback piston are sleeved in the two centering springs; the dynamic pressure feedback block end cover is fixed at one end of the dynamic pressure feedback block through a screw and is in static sealing fit with the inner wall of the abdicating hole of the feedback piston; the dynamic pressure feedback block end cover tightly clamps the positioning shaft sleeve, the feedback piston and the two centering springs on a plane where the two holes of the feedback piston abdicating hole and the liquid resistance abdicating hole are communicated, and axially fixes the two centering springs; one end of the positioning shaft sleeve, which is intersected with the first oil way, is provided with four round holes, so that the interior of the positioning shaft sleeve is communicated with the first oil way; the feedback piston can compress the centering spring back and forth to move axially.