A surface orifice and slot orifice combined frictionless balance cylinder and working method

Abstract

A frictionless balancing cylinder combining surface throttling and slit throttling, and its operating method, are disclosed. The cylinder comprises a front cover, a piston rod, a cylinder body, a piston, and a rear cover. The piston includes an inner piston and an outer piston, with the inner piston nested within the outer piston. The other end of the piston rod is fixed to the inner piston. The outer piston slides in contact with the inner surface of the cylinder body. An axial air supply channel is provided on the end face of the inner piston adjacent to the rear cover. An inner annular groove matching the air supply hole is formed on the inner side of the outer piston. An arc-shaped slit channel is formed on the outer side of the outer piston, located at the bottom of the inner annular groove and communicating with it. An air release groove is formed on the outer side of the outer piston, with an air release hole at the bottom. An annular boss is provided on the outer surface of the outer piston near the air release groove. This invention combines the advantages of surface throttling and slit throttling in high-precision shaft systems, meeting the requirements for high-precision and smooth movement of the vertical axis in ultra-precision machine tools.

Description

Technical Field

[0001] This invention belongs to the field of cylinder technology and relates to a frictionless balanced cylinder with a combination of surface throttling and slit throttling, and its working method. Background Technology

[0002] Ultra-precision machine tools play a vital role in ultra-precision machining and measurement. In recent years, many scholars have conducted research on the vertical axis of ultra-precision machine tools. To ensure high-precision and stable vertical movement of the vertical axis, a suitable balancing system must be designed to counteract the gravity of the moving parts of the vertical axis. Furthermore, the balancing system must minimize friction to avoid affecting machining or measurement accuracy. Therefore, the balancing system plays a crucial role in ensuring the servo control accuracy and machining stability of the ultra-precision vertical axis. Currently, the most common vertical axis balancing systems are mechanical balancing and cylinder balancing.

[0003] Domestic and international scholars have conducted extensive research and achieved numerous results on the dynamic characteristics and operational stability of air bearings, and have also conducted extensive research on frictionless balancing cylinders. Traditional cylinder structures, in order to reduce friction, typically employ methods such as improving the machining and assembly precision of parts, using special low-friction materials, applying lubricating grease, and using diaphragm bladders. These methods only reduce friction through various means, but do not truly achieve frictionlessness. Currently, research on frictionless cylinders often uses air bearings to achieve frictionless performance, requiring the installation of throttles, which increases assembly difficulty and affects operational accuracy. For example, CN116044859A involves a surface-throttling frictionless cylinder, employing a gas static pressure bearing and several small-orifice throttles to achieve throttling and frictionless contact, but this method increases assembly difficulty and affects operational accuracy. CN103016443A involves an air-suspended frictionless cylinder with a pressure relief groove, using a throttling orifice with a throttling plug, which achieves this without affecting the gas film formed on the piston's throttling orifice.

[0004] In summary, there is still relatively little research on dedicated cylinders for the vertical axis gravity balancing system of ultra-precision machine tools. Summary of the Invention

[0005] To overcome existing technologies, this invention provides a frictionless balancing cylinder combining surface throttling and slit throttling, along with its operating method. This cylinder integrates the advantages of surface throttling and slit throttling in high-precision shaft systems, meeting the requirements of high-precision and smooth motion of vertical axes in ultra-precision machine tools. It occupies little space and is simple and reliable to process, assemble, and use.

[0006] A frictionless balanced cylinder combining surface throttling and slit throttling includes a front cover, a piston rod, a cylinder body, a piston, and a rear cover. A cylinder body, sealingly connected to both the front and rear covers, is arranged between them. The piston rod and piston are disposed within the cylinder body, with one end of the piston rod slidably mounted on the front cover. The piston comprises an inner piston and an outer piston, with the inner piston nested within the outer piston. The other end of the piston rod is fixed to the inner piston, and the outer piston slides in contact with the inner surface of the cylinder body. An axial air supply channel is provided on the end face of the inner piston adjacent to the rear cover. The outer piston has an air supply hole that communicates with the air supply channel, but the air supply hole is not connected to the inner cavity of the inner piston. The inner side of the outer piston has an inner annular groove that matches the air supply hole. The outer side of the outer piston has an arc-shaped slit channel that is located at the bottom of the inner annular groove and the two are connected. The inner piston has an air outlet hole on its side. The outer side of the outer piston has a venting groove with a venting hole at the bottom. The venting hole matches the air outlet hole. An annular boss is provided on the outer surface of the outer piston near the venting groove to throttle the gas surface and form a pressure gas film.

[0007] Furthermore, two inner annular grooves are formed on the inner surface of the outer piston. Each inner annular groove has three intermittently distributed arc-shaped slit channels. Each inner annular groove is configured to cooperate with the air supply port.

[0008] Furthermore, ball joints are connected to both ends of the piston rod. The ball joint at the rear end of the piston rod is connected to the connecting piston bolt through a fixed ball head nut. The connecting piston bolt is connected to the inner piston. The connecting piston bolt is located at the center of the inner piston. The ball joint at the front end of the piston rod is connected to the fixed ball head bolt through a fixed ball head nut.

[0009] A working method for a frictionless balanced cylinder combining surface throttling and slit throttling is described. High-pressure gas first enters the cylinder body through the air inlet on the side of the rear end cover and the inner hole of the buffer boss. Part of the high-pressure gas entering the cylinder body enters the inner annular groove of the outer piston through the air supply channel and air supply hole inside the inner piston, and then enters the gap between the outer piston and the cylinder body through the arc-shaped slit channel to form a pressure gas film. The other part of the high-pressure gas entering the cylinder body directly enters the gap between the outer piston and the cylinder body from the bottom of the outer side of the outer piston. The high-pressure gas moves upward and encounters the annular boss for surface throttling to form a pressure gas film. Then, it enters the inner piston through the vent hole on the outer piston and the outlet hole on the inner piston, and is discharged after passing through the cylinder body.

[0010] The advantages of this invention compared to the prior art are:

[0011] 1. Existing frictionless cylinder air bearings typically employ orifice throttling, which requires additional throttling devices. The large number of throttling devices increases assembly difficulty and affects operational accuracy. This invention utilizes a combination of surface throttling and slit throttling. Surface throttling involves setting protrusions on the gas film surface for throttling. Since there are no throttling orifices, there is no need to consider reducing the gas film thickness, which can improve stiffness to a certain extent while reducing gas flow rate, making it widely used in precision shaft systems. Slit throttling hydrostatic bearings have continuously distributed air supply points, reducing the adverse effects of diffusion and circumferential flow on bearing characteristics, resulting in higher load-bearing capacity, stiffness, and damping. Furthermore, the absence of air cavities ensures good stability, making it more suitable for high-speed, high-precision, and high-reliability applications. This invention combines the advantages of both surface throttling and slit throttling in high-precision shaft systems.

[0012] 2. Existing frictionless cylinders typically employ dual-path air supply to avoid gas backflow caused by pressure differences within the cylinder due to unidirectional air supply. This places high demands on machining and assembly and consumes a large amount of air. This invention features a venting groove on the piston, located at the bottom. This groove ensures the pressure relief of both the high-pressure gas flowing upwards from the bottom and the high-pressure gas flowing downwards after being throttled by the upper slit, thus preventing gas backflow. Simultaneously, the upper part of the piston uses a slit throttling method, providing linear air supply without a pressure equalization chamber structure. The bearing gas volume ratio is zero, thus preventing air hammer vibration. Furthermore, the bearing's load-bearing capacity and stiffness can be improved by increasing the air supply pressure.

[0013] 3. The combination of slit throttling and surface throttling is achieved by using an interference fit between the inner and outer pistons. The inner piston is equipped with an air supply hole, while the outer piston is equipped with a slit channel, a surface throttling step (annular boss), and an air venting groove. The air supply hole in the inner piston supplies air to the slit channel of the outer piston. The separation of the air supply hole and the slit channel on the inner and outer pistons greatly reduces the difficulty of machining.

[0014] 4. The piston rod employs a ball joint structure at both ends, facilitating the assembly and adjustment of the piston rod and the vertical shaft connection. This reduces the coaxiality requirements for the piston rod and vertical shaft connection in traditional frictionless cylinders. The double ball joint design also avoids the additional bending moment exerted by the piston rod on the surface throttling and slit throttling combined air bearing between the piston and cylinder, ensuring that it is only subjected to radial loads. Simultaneously, the use of two simple structures—bolts and nuts at the ball joints—ensures a stable connection between the piston and piston rod.

[0015] 5. Polyurethane buffer bosses are provided inside the front and rear covers of the cylinder to prevent large impacts from damaging the piston during piston movement.

[0016] 6. An O-ring seal is used between the rear end cover and the cylinder body to ensure that the high-pressure gas will not leak from the bottom of the cylinder body.

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments: Attached Figure Description

[0018] Figure 1 This is a perspective view of the frictionless balanced cylinder of the present invention, which combines surface throttling and slit throttling.

[0019] Figure 2 This is an exploded view of the frictionless balanced cylinder of the present invention, which combines surface throttling and slit throttling after the cylinder block is removed.

[0020] Figure 3 This is a cross-sectional structural diagram of the present invention;

[0021] Figure 4 This is a perspective view of the piston of the present invention;

[0022] Figure 5 This is a schematic diagram showing that the outer piston of the present invention has an annular boss.

[0023] Figure 6 This is a front sectional view of the piston;

[0024] Figure 7 Another main sectional view of the piston

[0025] Figure 8 This is a schematic diagram of the external piston;

[0026] Figure 9 This is a schematic diagram of an internal piston;

[0027] Figure 10 This is a cross-sectional view of the internal piston;

[0028] Figure 11 For along Figure 10 A cross-sectional view along line AA;

[0029] Figure 12 For along Figure 10 BB line section view;

[0030] Figure 13 This is the front view of the outer piston;

[0031] Figure 14 For along Figure 13 A cross-sectional view of the CC line;

[0032] Figure 15 For along Figure 13 A cross-sectional view of the DD line;

[0033] Figure 16This is a schematic diagram of the gas flow direction according to the present invention;

[0034] Explanation of icon numbers:

[0035] 1. Fixed ball head bolt; 2. Fixed ball head nut; 3. Ball joint; 4. Fixed nut; 5. Front end cap; 6. Buffer boss; 7. Piston rod; 8. Cylinder body; 9. Inner piston; 9-1. Air outlet; 9-2. Air supply channel; 9-3. Air supply hole; 10. Connecting piston bolt; 11. Outer piston; 11-0. Air venting groove; 11-1. Arc-shaped slit channel; 11-2. Inner annular groove; 11-3. Air venting hole; 11-4. Annular boss; 12. O-ring; 13. Universal connector; 14. Rear end cap. Detailed Implementation

[0036] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. Unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art.

[0037] Combination Figures 1-15 Description: A frictionless balanced cylinder combining surface throttling and slit throttling includes a front cover 5, a piston rod 7, a cylinder body 8, a piston, and a rear cover 14. The cylinder body 8 is arranged between the front cover 5 and the rear cover 14 and is sealed to both of them. The piston rod 7 and the piston are arranged inside the cylinder body 8, and one end of the piston rod 7 is slidably mounted on the front cover 5.

[0038] The piston comprises an inner piston 9 and an outer piston 11. The inner piston 9 is nested inside the outer piston 11. The other end of the piston rod 7 is fixed to the inner piston 9. The outer piston 11 slides in contact with the inner surface of the cylinder body 8. An air supply channel 9-2 is axially arranged on the end face of the inner piston 9 adjacent to the rear end cover 14. An air supply hole 9-3 communicating with the air supply channel 9-2 is opened on the side of the inner piston 9. The air supply hole 9-3 is not communicating with the inner cavity of the inner piston 9. An inner annular groove 11-2 that mates with the air supply hole 9-3 is opened on the inner side of the outer piston 11. An arc-shaped slit channel 11-1 is opened on the outer side of the inner piston 11. The arc-shaped slit channel 11-1 is arranged at the bottom of the inner annular groove 11-2 and the two are connected. An exhaust hole 9-1 is opened on the side of the inner piston 9. An exhaust groove 11-0 is opened on the outer side of the outer piston 11. An exhaust hole 11-3 is opened at the bottom of the exhaust groove 11-0. The exhaust hole 11-3 cooperates with the exhaust hole 9-1. An annular boss 11-4 is provided on the outer surface of the outer piston 11 near the exhaust groove 11-0 for gas surface throttling to form a pressure gas film.

[0039] This embodiment employs a combined design of surface throttling and slit throttling. Surface throttling involves setting protrusions on the gas film surface for throttling. Since there are no throttling orifices, there is no need to consider the limitation of reducing the gas film thickness, which can improve stiffness to a certain extent while reducing gas flow rate. It is widely used in precision shaft systems. The gas supply points of the slit throttling hydrostatic bearing are continuously distributed, reducing the adverse effects of diffusion and circumferential flow on bearing characteristics, resulting in higher load-bearing capacity, stiffness, and damping; at the same time, there are no gas cavities, leading to good stability.

[0040] In addition, an air relief groove 11-0 is provided on the outer piston 11. The air relief groove 11-0 ensures the pressure relief of high-pressure gas flowing upward from the bottom and high-pressure gas flowing downward after being throttled by the upper slit, thereby avoiding gas backflow. At the same time, the front of the outer piston adopts a slit throttling method, which is a linear gas source and does not contain a pressure equalization chamber structure. The bearing gas volume ratio is zero, so there will be no air hammer vibration. Furthermore, the bearing load-bearing capacity and rigidity can be improved by increasing the supply air pressure. This solution's throttling type balance cylinder has a small overall footprint, is simple to process and assemble, has high precision, and can be conveniently and reliably applied to the high-precision and stable vertical movement of the vertical axis of ultra-precision machine tools.

[0041] Specifically, such as Figure 6 , Figure 7 and Figure 8 As shown, the inner surface of the outer piston 11 has two inner annular grooves 11-2. Each inner annular groove 11-2 has three intermittently distributed arc-shaped slit channels 11-1. Each inner annular groove 11-2 is configured to cooperate with the air supply holes 9-3. Optionally, there are a total of four air supply holes 9-3, with two air supply holes 9-3 corresponding to each inner annular groove 11-2. Optionally, the central angle of each arc-shaped slit channel 11-1 in the circumferential direction is 90 degrees. One side of the annular groove 11-2 is connected to the arc-shaped slit channel 11-1, and the other side is connected to the air supply holes 9-3 on both sides of the air supply channel 9-2 of the inner piston. The outer piston 11 also has two vent holes 11-3. Optionally, there are two vent holes 9-1.

[0042] Specifically, such as Figure 5 As shown, the annular boss 11-4 is disposed on the outer piston 11, away from the arc-shaped slit channel 11-1. The outer piston is provided with a slit throttling channel, an annular boss, and a venting groove. The air supply port in the inner piston supplies air to the slit throttling channel of the outer piston. The separation of the air supply port and the slit throttling channel on the inner and outer pistons greatly reduces the machining difficulty. The annular boss 11-4 disposed here also facilitates the direct use of the high-pressure air supply at the bottom of the piston for surface throttling.

[0043] Specifically, such as Figure 3As shown, buffer bosses 6 are fixed inside the front cover 5 and the rear cover 14 respectively to prevent piston impact. Furthermore, the buffer bosses 6 are made of polyurethane. This design avoids large impacts during piston movement that could damage the piston.

[0044] The air supply port 9-3, air outlet port 9-1, and air discharge port 11-3 are all arranged perpendicular to the axial direction of the cylinder body 8 to ensure stable gas flow.

[0045] Specifically, such as Figure 3 As shown, ball joints 3 are connected to both ends of the piston rod 7. The ball joint 3 at the rear end of the piston rod 7 is connected to the connecting piston bolt 10 via a fixing ball head nut 2. The connecting piston bolt 10 is connected to the inner piston 9, and the connecting piston bolt 10 is located at the center of the inner piston 9. The ball joint 3 at the front end of the piston rod 7 is connected to the fixing ball head bolt 1 via a fixing ball head nut 2. The purpose of this arrangement is to facilitate the assembly and adjustment of the piston rod and the vertical shaft system connector by using a ball joint structure at both ends of the piston rod 7, reducing the coaxiality requirements for the assembly and adjustment of the piston rod and the vertical shaft system connector in traditional frictionless cylinders. The double ball joint design can also avoid the additional bending moment of the surface throttling and slit throttling combined air bearing formed between the piston and the cylinder, so that it is only subjected to radial load. At the same time, the two simple structures of fixing ball head bolt and fixing ball head nut ensure the stable connection between the piston and the piston rod, realizing the connection and fixation with external actuators. The fixing ball head bolt 1 is provided with a threaded boss to facilitate the installation with the vertical shaft system connector.

[0046] Specifically, the cylinder body 8 and the rear end cover 14 are sealed by an O-ring 12. This design ensures that the introduced high-pressure gas will not leak from the bottom of the cylinder body.

[0047] Furthermore, an air inlet is provided on the side of the rear cover 14, which is connected to the air supply channel 9-2 and the universal connector 13. The purpose of this arrangement is that gas enters the cylinder through the air inlet and finally flows out of the cylinder through the inner hole of the front cover 5.

[0048] Based on any of the foregoing embodiments or combinations thereof, a surface throttling and slit throttling combined frictionless balancing cylinder is further provided, along with a method for operating the surface throttling and slit throttling combined frictionless balancing cylinder. Figures 6-7 , Figures 11-12 , Figure 14 and Figure 16 illustrate( Figure 16 The direction indicated by the middle arrow is the direction of gas flow. Figure 14 Point E in the diagram represents the transition area between the annular boss 11-4 and the remaining surface of the piston. Figure 16The diagram shows the airflow direction and the pressure film formed by surface throttling and slit throttling in the magnified area. F represents a magnified view of the gas gap between the outer piston 11 and the cylinder 8 at the arc-shaped slit channel. G represents a magnified view of the high-pressure gas moving upwards to the gas gap between the annular boss 11-4 and the cylinder 8. H represents a magnified view of the gas gap between the outer piston 11 and the cylinder 8 at the arc-shaped slit channel corresponding to the air supply port 9-3. I represents a magnified view of the gas gap between the annular boss and the piston at the venting groove 11-0. (For ease of understanding of this embodiment)

[0049] High-pressure gas first enters the cylinder body 8 through the air inlet on the side of the rear end cover 14 and the inner hole of the buffer boss 6. Part of the high-pressure gas entering the cylinder body 8 enters the inner annular groove 11-2 (arc-shaped slit channels at F and H) of the outer piston 11 through the air supply channel 9-2 and air supply hole 9-3 inside the inner piston 9, and then enters the gap between the outer piston 11 and the cylinder body 8 through the arc-shaped slit channel 11-1 to form a pressure gas film. The other part of the high-pressure gas entering the cylinder body 8 directly enters the gap between the outer piston 11 and the cylinder body 8 from the bottom of the outer side of the outer piston 11. The high-pressure gas moves upward and encounters the annular boss 11-4 (boss at G and I) for surface throttling to form a pressure gas film. Then it enters the inner piston 9 through the vent hole 11-3 on the outer piston 11 and the outlet hole 9-1 on the inner piston 9, and is discharged after passing through the cylinder body 8.

[0050] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention, and all such modifications or alterations shall still fall within the scope of the present invention.

Claims

1. A frictionless balanced cylinder combining surface throttling and slit throttling, comprising a front cover (5), a piston rod (7), a cylinder body (8), a piston, and a rear cover (14), wherein a cylinder body (8) is arranged between the front cover (5) and the rear cover (14) and is sealed to both, the piston rod (7) and the piston are arranged inside the cylinder body (8), and one end of the piston rod (7) is slidably disposed on the front cover (5); characterized in that: The piston comprises an inner piston (9) and an outer piston (11). The inner piston (9) is nested inside the outer piston (11). The other end of the piston rod (7) is fixed to the inner piston (9). The outer piston (11) slides in contact with the inner surface of the cylinder (8). An air supply channel (9-2) is provided axially on the end face of the inner piston (9) adjacent to the rear end cover (14). An air supply hole (9-3) communicating with the air supply channel (9-2) is opened on the side of the inner piston (9). The air supply hole (9-3) is not communicating with the inner cavity of the inner piston (9). An inner annular groove (11-2) cooperating with the air supply hole (9-3) is opened on the inner side of the outer piston (11). An arc-shaped slit channel (11-1) is opened on the outer side of the outer piston (11). The arc-shaped slit channel (11-1) is arranged at the bottom of the inner annular groove (11-2) and the two are connected. The front part adopts a slit throttling method, which is a line source gas outlet and does not contain a pressure equalization chamber structure. The bearing gas volume ratio is zero. The inner piston (9) has an outlet hole (9-1) on its side and an exhaust groove (11-0) on its outer side. The exhaust groove (11-0) ensures the pressure relief of the high-pressure gas from the bottom upward and the high-pressure gas after throttling from the upper slit downward, so as to avoid gas backflow. The bottom of the exhaust groove (11-0) has an exhaust hole (11-3), which cooperates with the outlet hole (9-1). An annular boss (11-4) is provided on the outer surface of the outer piston (11) near the exhaust groove (11-0). The annular boss (11-4) is provided on the outer piston (11) away from the arc-shaped slit channel (11-1) to form a pressure gas film by throttling the gas surface.

2. A surface throttling and orifice throttling combined frictionless balanced air cylinder as claimed in claim 1 wherein: The interior of the front cover (5) and the interior of the rear cover (14) are respectively fixed with buffer bosses (6) to prevent piston impact.

3. A surface throttling and orifice throttling combined frictionless balanced air cylinder as claimed in claim 2 wherein: The buffer boss (6) is made of polyurethane.

4. The surface throttling and slot throttling combined frictionless balanced air cylinder of claim 1, wherein: The inner surface of the outer piston (11) has two inner annular grooves (11-2). Each inner annular groove (11-2) has three intermittently distributed arc-shaped slit channels (11-1). Each inner annular groove (11-2) is matched with the air supply port (9-3).

5. The surface throttling and slot throttling combined frictionless balanced air cylinder of claim 1, wherein: The air supply port (9-3), air outlet port (9-1) and air discharge port (11-3) are all arranged perpendicular to the axial direction of the cylinder body (8).

6. The surface throttling and slot throttling combined frictionless balanced air cylinder of claim 1, wherein: The piston rod (7) is connected to ball joints (3) at both ends. The ball joint (3) at the rear end of the piston rod (7) is connected to the connecting piston bolt (10) through the fixing ball head nut (2). The connecting piston bolt (10) is connected to the inner piston (9). The connecting piston bolt (10) is located at the center of the inner piston (9). The ball joint (3) at the front end of the piston rod (7) is connected to the fixing ball head bolt (1) through the fixing ball head nut (2).

7. The surface throttling and slot throttling combined frictionless balanced air cylinder of claim 1, wherein: The cylinder (8) and the rear end cover (14) are sealed by an O-ring (12).

8. The surface throttling and slot throttling combined frictionless balanced air cylinder of claim 1, wherein: An air inlet is provided on the side of the rear cover (14), and the air inlet is connected to the air supply channel (9-2) and the universal connector (13) respectively.

9. A method of operating a surface and slot throttling combined frictionless counterbalance air cylinder according to any one of claims 1-8, characterized by: High-pressure gas first enters the cylinder body (8) through the air inlet on the side of the rear end cover (14) and the inner hole of the buffer boss (6). Part of the high-pressure gas entering the cylinder body (8) enters the inner annular groove (11-2) of the outer piston (11) through the air supply channel (9-2) and air supply hole (9-3) inside the inner piston (9), and then enters the gap between the outer piston (11) and the cylinder body (8) through the arc-shaped slit channel (11-1) to form a pressure gas film. The other part of the high-pressure gas entering the cylinder body (8) directly enters the gap between the outer piston (11) and the cylinder body (8) from the bottom of the outer side of the outer piston (11). The high-pressure gas moves upward and encounters the annular boss (11-4) for surface throttling to form a pressure gas film. Then it enters the inner piston (9) through the vent hole (11-3) on the outer piston (11) and the outlet hole (9-1) on the inner piston (9), and is discharged after passing through the cylinder body (8).

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