Hydrostatic center

Abstract

This invention relates to a hydrostatic center, comprising a bushing and a center shaft inserted within the bushing. The center head of the center shaft extends from the front end of the bushing, and the tail end of the center shaft extends from an end cap fixed to the tail end of the bushing. A bearing oil groove is formed on the outer ring surface of the center shaft within the bushing, and an oil inlet passage is formed on the center shaft connecting the bearing oil grooves to the tail end of the center shaft. A bearing oil cavity is formed between the bearing oil grooves and the inner bore surface of the bushing, allowing the center shaft to be mounted within the bushing using a hydrostatic bearing support. A return oil hole for hydrostatic oil output is provided on the side wall of the bushing. A front oil seal structure is provided between the bushing near the front end and the center shaft, and a tail oil seal structure is provided at the mating part between the end cap and the center shaft. An axial clamping mechanism is provided at the tail end of the center shaft to press the center head against the workpiece. This hydrostatic center has the advantages of high support rigidity, high rotational accuracy, low wear, and good precision durability.

Description

Technical Field

[0001] This invention belongs to the field of workpiece auxiliary support technology for processing or measurement, and relates to movable center structure, and particularly to a hydrostatic center. Background Technology

[0002] Centers are a common auxiliary support structure used on machine tools. They are mainly used for auxiliary clamping and support of long shaft parts (excluding the main spindle), and their rotational accuracy and rigidity have a significant impact on machining quality. Currently, centers are divided into fixed centers and movable centers supported by rolling bearings. Fixed centers have high support accuracy, generally 1-2 μm, but because the contact surface with the workpiece is dry friction, they wear quickly and are prone to accuracy loss. Movable centers use rolling bearings to reduce wear, but the moving parts are in point or line contact, resulting in low rigidity and an accuracy level of generally around 5 μm.

[0003] To address the advantages and disadvantages of existing fixed and movable centers, a high-rigidity, high-precision center structure needs to be designed, which is essential for the machining of high-precision parts. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hydrostatic center with high support stiffness, high rotational accuracy and low wear.

[0005] One of the above-mentioned objectives of the present invention is achieved through the following technical solution:

[0006] A hydrostatic center includes a bushing and a center shaft inserted within the bushing. The center head of the center shaft extends from the front end of the bushing, and the tail end of the center shaft extends from an end cap fixed to the tail end of the bushing. The center shaft is characterized by having a bearing oil groove formed on its outer ring surface within the bushing; an oil inlet passage connecting the bearing oil grooves to the tail end of the center shaft; a bearing oil cavity formed between the bearing oil grooves and the inner bore surface of the bushing, allowing the center shaft to be mounted within the bushing using a hydrostatic bearing support; and a return oil hole for hydrostatic oil output is provided on the side wall of the bushing.

[0007] A front oil seal structure is provided between the outer sleeve near the front end and the center shaft, and a tail oil seal structure is provided at the mating part of the end cover and the center shaft.

[0008] An axial clamping mechanism is provided at the tail end of the center shaft to press the center head against the workpiece.

[0009] Furthermore, a throttle is built into each oil inlet line corresponding to the position of each carrying oil tank, so that the oil flows into the corresponding carrying oil tank through the throttle.

[0010] Furthermore: the bearing oil grooves set on the center shaft are one or more sets symmetrically arranged, and each bearing oil groove is provided with a throttling zone. The throttling zone is provided with an oil inlet hole and connected to the oil inlet passage. The throttling zone of each bearing oil groove is connected to the part outside the throttling zone of another bearing oil groove in the same group through a feedback oil passage built into the center shaft. The feedback oil passage connects the two symmetrically arranged bearing oil grooves to form a hydrostatic circulation oil passage.

[0011] Furthermore: the bearing oil grooves on the center shaft are in two sets, and the two sets of bearing oil grooves are arranged vertically along the axial direction of the center shaft. The upper set of bearing oil grooves and the lower set of bearing oil grooves are staggered in the circumferential direction.

[0012] Furthermore: axial oil return grooves are provided between the two oil grooves of the upper set of bearing oil grooves and between the two oil grooves of the lower set of bearing oil grooves on the outer ring surface of the center shaft; a circumferential oil return groove is provided between the upper and lower sets of bearing oil grooves on the outer ring surface of the center shaft, which communicates with all the axial oil return grooves; when the center shaft is in the axial clamping state, the circumferential oil return groove is aligned and connected with the oil return hole on the shaft sleeve.

[0013] Furthermore: a piston chamber is provided at the tail end of the sleeve, and a piston head is provided at the tail end of the center shaft. The piston head and the piston chamber form a piston engagement. An oil hole is provided on the end cover or the tail end side of the sleeve, and the oil hole communicates with the piston chamber, forming a hydraulic cylinder type axial clamping mechanism that acts on the center shaft.

[0014] Furthermore: a fixed shaft end is fitted onto the rear protruding end of the center shaft, and a return spring fitted on the center shaft is press-fitted between the shaft end and the end cover.

[0015] Furthermore: the inner bore of the bushing is composed of a small-diameter inner bore section and a large-diameter inner bore section coaxially located at the tail end of the small-diameter inner bore section; the small-diameter inner bore section cooperates with the bearing oil groove of the center shaft, the large-diameter inner bore section constitutes the piston chamber, and an axial limiting platform is formed between the small-diameter and large-diameter inner bore sections.

[0016] The second objective of this invention is achieved through the following technical solution:

[0017] A machining tool, characterized in that: the machining tool is provided with the above-mentioned hydrostatic center.

[0018] The third objective of this invention is achieved through the following technical solution:

[0019] A testing device, characterized in that: the testing device is provided with the above-mentioned static pressure center.

[0020] The advantages and positive effects of this invention are as follows:

[0021] 1. This hydrostatic center boasts high support stiffness. The center stiffness primarily depends on the stiffness of the center shaft and the bearing support. The stiffness of the hydrostatic bearing can be improved by adjusting the bearing structure and design parameters. The small radial dimension of the hydrostatic bearing allows for a further increase in the diameter of the center shaft. Therefore, the hydrostatic center achieves two goals at once, simultaneously increasing the stiffness of both the center shaft and the bearing, reaching a stiffness up to six times that of a rolling bearing center, achieving the level of a dead-center.

[0022] 2. This hydrostatic center boasts high rotational accuracy: the hydrostatic oil film within the bearing oil chamber has an error-averaging effect, enabling accuracy improvement. The typical error is approximately 1 / 3 to 1 / 5 of the accuracy of the mating parts. This hydrostatic center can achieve rotational accuracy exceeding that of the original part; the rotational accuracy of the machined workpiece can be approximately one level higher than that of the machine tool.

[0023] 3. This hydrostatic center exhibits low wear and excellent precision retention: The rotating components of this center are separated by hydraulic oil, theoretically eliminating the possibility of wear. Practical experience shows that even after ten years of use, machining marks are still visible on the moving surfaces of hydrostatic bearings. Therefore, the precision retention of this hydrostatic center is far superior to that of ordinary dead and live centers. Its rotational accuracy can reach approximately 10 to 20 times that of a fixed center.

[0024] 4. This hydrostatic center is easy to control intelligently, achieving intelligent clamping with optimal clamping force. If the clamping hydraulic cylinder at the tail is controlled by a proportional valve or servo valve, the clamping force can be adjusted in real time according to the cutting conditions of the part, achieving optimal clamping.

[0025] 5. The machining tool using this hydrostatic center can achieve high-precision and high-rigidity clamping and positioning of the workpiece, which is conducive to long-term heavy cutting and precision machining of rotating workpieces.

[0026] 6. Using this hydrostatic center in the testing equipment can improve the positioning accuracy of the workpiece, thereby improving the testing accuracy. The friction of the hydrostatic center is about 1 / 10 of that of the live center, reducing the possibility of creeping when the measured part rotates, thus improving the measurement accuracy. Attached Figure Description

[0027] Figure 1 This is a three-dimensional appearance diagram of the present invention;

[0028] Figure 2 This is a longitudinal sectional view of the present invention;

[0029] Figure 3 yes Figure 2 AA section view;

[0030] Figure 4 This is a schematic diagram of the external appearance of the tip shaft of the present invention;

[0031] Figure 5yes Figure 4 Left view;

[0032] Figure 6 This is a schematic diagram of the structure of the present invention using a small-hole throttle within the top shaft;

[0033] Figure 7 This is a schematic diagram of the structure of the present invention, which uses a capillary throttling device inside the top shaft. Detailed Implementation

[0034] The structure of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that these embodiments are descriptive and not limiting.

[0035] A hydrostatic center includes a sleeve 2 and a center shaft 3 inserted within the sleeve. The sleeve is used to mount the hydraulic center onto the machine tool or equipment. The center shaft cooperates with the sleeve, and the axial movement of the center shaft achieves clamping of the workpiece. The center head 3.1 of the center shaft extends from the front end of the sleeve, and the tail end of the center shaft extends from an end cap 1 fixed to the tail end of the sleeve. Its inventive point is:

[0036] A bearing oil groove is formed on the outer ring surface of the center shaft inside the shaft sleeve. A main oil inlet is provided at the tail end of the center shaft. An oil inlet passage 9 is formed on the center shaft, connecting each bearing oil groove to the tail end of the center shaft. The bearing oil groove and the inner bore surface of the shaft sleeve form a bearing oil cavity 13. By introducing oil, a pressure-bearing oil film is formed in the bearing oil cavity, thereby allowing the center shaft to be installed in the shaft sleeve in a hydrostatic bearing-supported manner. A return oil hole 2.1 for hydrostatic oil output is provided on the side wall of the shaft sleeve.

[0037] For a hydrostatic center to operate normally, a throttle valve needs to be installed inside the center shaft. There are two possible methods:

[0038] Method 1: Throttling structure without feedback. Specifically, a throttling device is built into each oil inlet corresponding to a carrying oil tank, allowing the incoming oil to flow into the corresponding carrying oil tank through the throttling device. The throttling device can be a small-hole throttling device 17 or a capillary throttling device 18, etc. See [link to documentation] for the structure of the small-hole throttling device or the capillary throttling device, respectively. Figure 6 and Figure 7 .

[0039] Method 2: Internal clearance feedback type throttling. Specifically: One or more sets of symmetrically arranged bearing oil grooves are provided on the center shaft. Each bearing oil groove has a throttling zone 14, and the throttling zone has an oil inlet hole 15 connected to the oil inlet passage. Each bearing oil groove's throttling zone has a feedback oil hole 16, which is connected to the portion outside the throttling zone of another bearing oil groove in the same group via a feedback oil passage 10 built into the center shaft. The feedback oil passage connects the two symmetrically arranged bearing oil grooves to form a hydrostatic circulation oil passage. Further, preferably, two sets of bearing oil grooves are provided on the center shaft, see [reference]. Figure 4 and Figure 5 Two sets of bearing oil grooves are arranged vertically along the axial direction of the center shaft, with the upper set and the lower set staggered in the circumferential direction. Since the center shaft is typically a slender shaft, this staggered arrangement of the bearing oil grooves facilitates the layout and machining of the bearing oil grooves and internal feedback oil circuits. Furthermore, it ensures the formation of a uniform hydrostatic oil film throughout the circumference, thereby precisely guaranteeing the coaxiality of the center shaft and its outer sleeve. Theoretically, this can achieve a rotational accuracy of 0.1 μm or even higher for the hydrostatic center.

[0040] When adopting the preferred structure of Method 2 above, the preferred scheme for the oil return structure is as follows:

[0041] An axial oil return groove 11 is provided between the two oil grooves of the upper set of bearing oil grooves and between the two oil grooves of the lower set of bearing oil grooves on the outer ring surface of the center shaft. A circumferential oil return groove 12, which communicates with all the axial oil return grooves, is provided between the upper and lower sets of bearing oil grooves on the outer ring surface of the center shaft. When the center shaft is in the axially clamped state, the circumferential oil return groove is aligned and communicates with the oil return hole on the shaft sleeve.

[0042] The above-mentioned oil return structure is reasonably arranged. The specific oil return process is as follows: the oil from the upper set of bearing oil grooves flows into the two upper axial oil return grooves through the gap between the edge of the oil groove and the inner hole of the shaft sleeve. The oil from the lower set of bearing oil grooves flows into the two lower axial oil return grooves through the gap between the edge of the oil groove and the inner hole of the shaft sleeve. The oil flowing into the four axial oil return grooves converges into the circumferential oil return groove and is finally discharged through the oil return hole on the sleeve.

[0043] A front oil seal is installed between the outer sleeve and the center shaft near the front end, and a rear oil seal is installed at the mating point between the end cover and the center shaft. These front and rear oil seals prevent oil entering the bearing oil groove from flowing out from both ends of the center shaft, which is essential for establishing static pressure between the outer sleeve and the center shaft. The front and rear oil seals can be designed using... Figure 2 and Figure 3The structure is achieved by providing sealing ring grooves at the front and rear ends of the center shaft and installing sealing rings in the sealing ring grooves. Other methods can also be used, and are not limited in this invention.

[0044] An axial clamping mechanism is provided at the tail end of the center shaft to press the center head against the workpiece. The axial clamping mechanism can be implemented by adding a separate structure to the tail end of the center shaft, such as by adding a hydraulic cylinder or pneumatic cylinder. Alternatively, the axial clamping mechanism can be implemented by setting a mating structure between the tail end of the center shaft and the tail end of the shaft sleeve. In this invention, the preferred embodiment of the axial clamping mechanism is:

[0045] A piston chamber 7 is located at the tail end of the sleeve, and a piston head 8 is located near the tail end of the center shaft. The piston head can be integrally formed on the center shaft, and the piston head and piston chamber form a piston fit. An oil hole 6 is formed on the end cover or the tail side of the sleeve, which communicates with the piston chamber. The oil hole is connected to the oil supply device through an external oil pipe, forming a hydraulic cylinder-type axial clamping mechanism acting on the center shaft. To simplify the external oil circuit and achieve rapid reset of the center shaft, a shaft end head 4 is fitted onto the rear protruding end of the center shaft, and a reset spring 5 fitted on the center shaft is press-fitted between the shaft end head and the end cover.

[0046] In the above structure, further: the inner bore of the bushing is composed of a small-diameter inner bore section and a large-diameter inner bore section coaxially disposed at the tail end of the small-diameter inner bore section; the small-diameter inner bore section mates with the bearing oil groove of the center shaft, and the large-diameter inner bore section constitutes the piston chamber, forming an axial limiting platform between the small and large-diameter inner bore sections. The function of the axial limiting platform is to: limit the center shaft in front, preventing the center shaft from sliding out from the front end of the bushing.

[0047] This hydrostatic center is a novel type of live center structure, combining the advantages of existing dead and live centers while overcoming their shortcomings. It achieves a combination of high rigidity, high precision, and high precision retention. Its applications can be expanded to various machine tools, such as grinding machines (vertical or horizontal), lathes, gear processing machines, and measuring equipment. It can be used for axial clamping and positioning of workpieces, and can also be used for radial positioning of workpieces by evenly distributing multiple centers on a ring frame.

[0048] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A hydrostatic center, comprising a bushing and a center shaft inserted within the bushing, wherein the center head of the center shaft extends from the front end of the bushing and the tail end of the center shaft extends from a tail end cap fixed to the tail end of the bushing, characterized in that: A bearing oil groove is formed on the outer ring surface of the center shaft inside the shaft sleeve. An oil inlet passage is formed on the center shaft to connect each bearing oil groove with the tail end of the center shaft. A bearing oil cavity is formed between the bearing oil groove and the inner hole surface of the shaft sleeve, so that the center shaft is installed in the shaft sleeve by means of hydrostatic bearing support. A return oil hole for hydrostatic oil output is provided on the side wall of the shaft sleeve. Two sets of bearing oil grooves are symmetrically arranged on the center shaft. The two sets of bearing oil grooves are arranged vertically along the axial direction of the center shaft. The upper set of bearing oil grooves and the lower set of bearing oil grooves are staggered in the circumferential direction. Each bearing oil groove has a throttling zone with an oil inlet hole and connected to the oil inlet passage. The throttling zone of each bearing oil groove is connected to the part outside the throttling zone of the other bearing oil groove in the same group through a feedback oil passage built into the center shaft. The feedback oil passage connects the two symmetrically arranged bearing oil grooves to form a hydrostatic circulation oil passage. A front oil seal structure is provided between the outer sleeve near the front end and the center shaft, and a tail oil seal structure is provided at the mating part between the tail end and the center shaft. An axial clamping mechanism is provided at the tail end of the center shaft to press the center head against the workpiece; a piston chamber is provided at the tail end of the shaft sleeve, and a piston head is provided near the tail end of the center shaft. The piston head and the piston chamber form a piston fit. An oil hole is provided on the tail end or the side of the tail end of the shaft sleeve. The oil hole communicates with the piston chamber, forming a hydraulic cylinder-type axial clamping mechanism acting on the center shaft; a shaft end is fitted at the rear protruding end of the center shaft, and a return spring fitted on the center shaft is press-fitted between the shaft end and the end cover. An axial oil return groove is provided between the two oil grooves of the upper set of bearing oil grooves and between the two oil grooves of the lower set of bearing oil grooves on the outer ring surface of the center shaft; a circumferential oil return groove is provided between the upper and lower sets of bearing oil grooves on the outer ring surface of the center shaft, which is connected to all the axial oil return grooves; when the center shaft is in the axial clamping state, the circumferential oil return groove is aligned and connected with the oil return hole on the shaft sleeve.

2. The hydrostatic center according to claim 1, characterized in that: The inner bore of the bushing consists of a small-diameter inner bore section and a large-diameter inner bore section coaxially located at the tail end of the small-diameter inner bore section; the small-diameter inner bore section mates with the bearing oil groove of the center shaft, and the large-diameter inner bore section constitutes the piston chamber, with an axial limiting platform formed between the small and large-diameter inner bore sections.

3. A processing machine tool, characterized in that: The machine tool is equipped with a hydrostatic center as described in any one of claims 1-2.

4. A testing device, characterized in that: The testing equipment is equipped with a static pressure tip as described in any one of claims 1-2.

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