JP3020599U - Hydrostatic nut for machine tool and assembly of this nut and lead screw - Google Patents

Abstract

(57) [Summary] [Purpose] A hydrostatic nut for machine tools that solves problems such as cost, complexity, operating characteristics, local wear, excessive friction, and backlash, and this nut and lead screw. To provide an assembly. [Structure] A metal cylinder having a hole whose both ends are open at the center, at least one helical screw cut on the inner surface of the hole at the center, and attached to all exposed surfaces of the screw. A thick and hard plastic covering, the clearance on the surface of the plastic covering following the shape of the screw is such that it acts as a channel for carrying pressurized fluid when the nut engages with the lead screw. ing.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an assembly of a hydrostatic nut and a lead screw that can move a carriage that supports, for example, a polishing plate. More particularly, the present invention relates to a hydrostatic nut that cooperates with a threaded lead screw, the nut having a channel for receiving pressurized fluid.

[0002]

[Prior art]

 In known grinding machines, a grinding table is rotatably mounted on a tool mount so that a workpiece such as a camshaft can be ground to a predetermined size and shape. The workpiece is held between the headstock and tailstock, and the tool mount with the grinder is moved by the nut and lead screw.

The nut cooperates with a lead screw that is threaded on the inside and threaded on the outside. The nut is secured to the tool mount and the lead screw is driven by a motor located at the end of the lead screw remote from the nut. A numerically controlled motor causes the lead screw to rotate clockwise relative to the nut and vice versa, causing the polishing machine to move linearly relative to the workpiece.

Generally, a carborundum polishing plate having a diameter of 40.6 cm (16 inches) is gradually worn away, and the diameter is reduced by repeating the polishing operation. Over time, the diameter of the polishing machine can reach 8-10 cm (3-4 inches).

In order to compensate for this reduction as the diameter of the grinder gradually decreases, the motor drives the lead screw according to the program to bring the tool mount and the grinder closer to the work piece. As the lead screw approaches, the wear on the lead screw progresses, as does the diameter of the grinding wheel that is reduced by continuous work in the factory.

With the advent of more durable and hard polishing machines made of materials such as CBN (tertiary boron nitride), the reduction in polishing machine diameter became almost negligible. CBN polishing machines are widely used because they can be polished very accurately, require less finishing work, and require less frequent replacement.

[0007]

[Problems to be solved by the device]

 However, using a hard grinding machine such as CBN or diamond increases the wear problem of the lead screw and nut assembly for the tool mount and the grinding machine. Wear is normal when using a conventional grinder, and when the size of the grinder is significantly reduced, the length of the lead screw is also significantly affected.

Conversely, when the diameter of the CBN grinder is reduced slightly, such as by a fraction of 2.5 cm (1 inch), the problem concentrates on the wear of the lead screw. Due to such local wear, damage occurs early. It is not possible to repeatedly and precisely move the tool mount relative to the work piece, and it is not possible to meet the technical requirements for the camshaft or to easily maintain other mechanical movements.

A number of proposals have been made in the past regarding (1) local wear, (2) excessive friction between the contacting metal surfaces of the nut and the lead screw, and (3) backlash due to backlash.

One is to place a precisely sized ball bearing between the contacting threaded surfaces so that the balls circulate from nut to corner. According to this proposal, the problem of excessive friction and backlash is satisfied, but the failure tends to occur early and the control in the moving direction becomes uncontrollable.

Another proposal is for hydrostatic bearings with a thin film of fluid between the threaded surfaces, which also works with nuts and lead screws. In order to avoid metal contact between the helical teeth, it is necessary to distribute the film under pressure from nut to corner.

[0012] To be distributed under pressure, the nut must be accurately formed with pockets, manifolds, channels, and other fluid circuits to deliver the proper amount of fluid into place.

As another proposal, the epoxy agent is injected into the joint portion of the lead screw or the mother die in which the joint portion of the lead screw is duplicated. Epoxy is treated with a special filler that increases strength, lubricity, and wear characteristics, and reduces brittleness.

After curing the mold at room temperature and atmospheric pressure, the mold is removed from the lead screw and left in the nut housing. Then, as the lead screw advances with respect to the nut, the internally threaded nut approximates the shape of the parent screw, but with reduced friction loss and poor alignment.

The use of epoxy agents, such as castable polymer agents, is described in US Pat. No. 4,790,971 (December 13, 1988, licensed to Ross A. Brown et al.) And Description of US Pat. No. 5,152,948 (authorized by Kevin J. Lizenby, October 6, 1992) (both transferred to TranTek, Inc., Traverse, Michigan) It is described in the book.

Each of the inventions has problems in cost, complexity, operating characteristics, etc., and the problems such as local wear, excessive friction, and backlash have not been solved.

[0017]

[Means for Solving the Problems]

 The prior proposals to solve the problem have drawbacks, so the preferred features of the known hydrostatic bearings and the epoxy resin and other castable polymers that serve as bearing materials have been replaced with lead screws. We have devised a unique nut that can be easily cast around.

A nut that is cast and that has threads on its inner surface has a channel in the polymer agent that can be cast so that hydrostatic pressure can be continuously applied into the nut. After casting and hardening, the nut is a thin film of fluid and is suitable for use with a lead screw having a spiral thread on its outer surface.

Also disclosed is a unique method of forming a channeled nut in a solid polymeric agent attached to the inner surface. The method is to inject wax or fold the tape onto the outer surface of the lead screw before inserting the epoxy resin into the gap between the outer screw of the mold lead screw and the inner screw. Means are provided along the section.

The wax or tape creates a gap in the exposed surface of the finished mold. When the wax or tape is removed, channels are formed in the solid polymeric material that has adhered to the nut. The nut serves as a mold for the pourable polymer agent and is dimensioned prior to being secured to the hanging portion of the tool mount of the grinder.

As the lead screw advances and retracts through the nut, the nut with the hard polymeric coating on the inner screw moves according to the shape of the screw on the outer face of the lead screw.

The channel is pressurized by the fluid injected into the bore of the nut and the fluid flows within the channel to form a thin film fluid bearing between the cooperating surfaces of the nut and the lead screw. The mold is processed at room temperature and atmospheric pressure.

The cast nut and lead screw assembly is a combination of the ease of making a hard coating with a castable polymer agent, low friction and non-bonding properties, which cooperate with the nut and lead screw. A thin film of fluid is formed between and.

From the description of the accompanying drawings, the person skilled in the art will appreciate other features of the castable nut which can be easily formed and have channels. For example, the channels are reinforced by coated metal spiral screws for long life and precise operation.

This casting technique can be applied to other forms of screws, multiple spiral coils, and the like. Moreover, according to this hydrostatic nut forming method, the nut can be produced at a lower cost than a commercially available ball screw, and complicated and difficult machining is not required.

[0026]

【Example】

 FIG. 1 shows the main elements of the polishing machine 10. A heavy metal base 12 (which may be concrete-filled) is installed on the floor (not shown) of the workplace. The front end of the base 12 is higher than the other parts. The carriage 14 moves orthogonally on the base 12. A turntable 16 is mounted for movement on a carriage 14.

The headstock 18 and tailstock (not shown) are fixed to the rotary table 16 by a dovetail joint 20. The work piece 22 is fixed between the headstock 18 and the tailstock. The work piece 22 is shown as a camshaft.

The sliding surface 24 moves in the longitudinal direction on the upper surface of the base 12, and the tool attachment portion 26 moves on the upper surface of the sliding surface 24. The grinder 28 is fixed to a central shaft 30 near the tip of the tool mounting portion 26, and a motor 32 drives the grinder 28 via an endless belt 34.

The centerline of center axis 30 is aligned with the centerline of workpiece 22. A post 36 depends from the tool mount 26 and a passage 38 extends longitudinally therethrough. Hydrostatic nut 40 is secured within passageway 38. The hydrostatic nut 40 is internally threaded.

The front end of the elongated lead screw 42 extends through the hydrostatic nut 40. The outer surface of the lead screw 42 is threaded. A small motor 44 is attached to the rear end of lead screw 42 with a coupling 46.

A motor 44 drives a lead screw 42 relative to the hydrostatic nut 40 to move the tool mount 26 and grinder 28 relative to the work piece 22. The motor 44 operates in response to a signal from a digital computer control program to calculate the relative position between the polishing machine 28 and the workpiece 22.

The grinder 10 is conventional, but a unique hydrostatic nut 40 is designed to work well. The method of forming the hydrostatic nut 40 is also innovative and differs from known forming methods.

As shown in FIG. 2, the mold 50 is transformed into the hydrostatic nut 40 by a specific operation procedure. The mold 50 includes a metal body having a substantially cylindrical shape, and both ends of the center hole thereof are open.

The smaller holding cap 52 closes one end of the mold 50, and the larger holding cap 54 closes the other end. A hole 56 extends through the retaining cap 52 and the pressure plate 58 can be adjusted within the hole 56 by turning a threaded stud 60.

After adjusting the pressure plate 58, the set screw 62 is tightened to fix the stud 60. The retaining cap 54 has an annular body with a flange 64 projecting toward the mold 50. A pressure plate 66 is adapted to move within the flange 64. The movement of the pressure plate 66 is controlled by the central stud 68 and adjusting screws 70,72.

The standard lead screw 74 is fixed in the mold 50 by applying pressure to both ends thereof. The standard lead screw 74 is similar in size and shape to the cross-section of the lead screw 42 that extends through the hydrostatic nut 40, and works with it.

The standard lead screw 74 is precision-machined, has excellent durability, and is repeatedly used for a long period of time, and forms a part of the hydrostatic nut 40. The standard lead screw 74 has a spiral thread on the outer surface. The helical screw is complementary to the screw on the inner wall of the mold 50, as shown in FIG.

A first bead 76 of wax is applied to the first or front side of each thread of the standard lead screw 74. Similarly, a second bead 78 of wax is applied to the second, or rear, side of each thread of standard lead screw 74.

The beads 76, 78 are applied to the threads of the standard lead screw 74 prior to insertion into the cylindrical mold 50. After applying the wax beads 76, 78, the standard lead screw 74 is inserted into the mold 50 and the pressure plates 58, 66 are adjusted inside to secure the standard lead screw 74 in the mold 50.

Prior to inserting the standard lead screw 74 into the mold 50, a surface of the standard lead screw 74 not covered by the bead of wax is coated with a release coating. Epoxy resin or pourable polymer agent 80 enters the gap between the outer teeth of standard lead screw 74 and the complementary inner teeth of mold 50 from inlet 82 of mold 50.

There should be no gaps between complementary teeth at all metal-to-metal contact points. Air is evacuated from the mold 50 through the outlet 84 to remove bubbles. Excess material exits through outlet 84.

The polymer agent is continuously injected into the gap between the screw on the outer surface of the standard lead screw 74 and the screw on the inner surface of the mold 50. The bead of wax 76, 78 adheres to the threads on the outside of the standard lead screw 74 and prevents them from being chemically destructed by the polymer zy 80 or the release coating (not shown) on the standard lead screw 74.

After continuously filling the gap with the polymer agent, the mold 50 is left to stand at room temperature and atmospheric pressure for 12 to 18 hours. The castable polymeric agent 80 cures to a solid. The holding caps 52 and 54 are removed from both ends of the mold 50, and the standard lead screw 74 is removed from the mold 50.

A pre-applied release coating on the standard lead screw 74 prevents the castable polymeric agent 80 from adhering to the standard lead screw 74. It has been found that several castable polymeric agents 80 meet the needs of the mold 50 and the final operating characteristics of the hydrostatic nut 40.

However, one of the most satisfactorily proven epoxies is the commercially available trademark “Moglice” from Devit.

After removing the standard lead screw 74, the mold 50 having the castable polymer agent 80 adhered to the internal threads is machined to the required size and shape.

As shown in FIG. 4, in its final form, the mold 50 becomes a hydrostatic nut 40. When the wax beads 76, 78 are manually removed from the hardened solid agent 80, channels 86, 88 are formed on the exposed surface of the hardened solid agent 80 facing the threads on the outer surface of the lead screw 42. There is.

The wax is dissolved in a suitable solvent and allowed to flow. A hydrostatic nut 40 is then placed in the passage 38 of the post 36 which projects below the tool mount 26, as shown in FIGS.

The front end of the elongated lead screw 42 extends through the hydrostatic nut 40 to move the tool mount 26 and the grinder 28 relative to the workpiece 22.

As shown in FIG. 4, hydrostatic nut 40 works with a portion of lead screw 42. As previously mentioned, removal of the bead of wax 76, 78 results in spiral channels 86, 88 facing each other on the exposed surface of the hardened, castable polymeric agent 80.

The screw of the metal nut structurally supports the channel. Upon delivering fluid from the first inlet 90 to the helical channel 86, the hydrostatic nut 40 floats on a thin film of air with respect to the lead screw 42 as the lead screw 42 advances.

When the fluid is sent from the second introduction portion 92 to the spiral channel 88, the hydrostatic nut 40 causes a thin fluid to flow toward the lead screw 42 as the lead screw 42 retracts from the nut. Floats on the membrane.

The film of fluid cooperating with the formed polymeric agent 80 ensures that the hydrostatic nut 40 operates generally without friction.

Other variations will occur to those skilled in the art in view of the preferred embodiments of the present invention. For example, the wax used to form the beads 76, 78 may be beeswax. The tape used for the same purpose may be, for example, a tape for electrical work or a special tough tape such as a duct tape adhered to a helical screw of standard lead screw 74 to form beads 76,78.

When the standard lead screw 74 is removed from the mold 50, the cured polymeric material 80 may strip the wax beads 76, 78. Therefore, only a limited amount of residue must be washed out with solvent or manually removed from the polymeric agent 80.

Further, the hydrostatic nut 40 can be used not only for a cam grinder but also for a combination of a nut and a lead screw 42 for a carriage of another precision machine tool. Accordingly, the appended utility model claims broadly refer to the hydrostatic nut 40 and the combination of the hydrostatic nut 40 and the lead screw 42.

[0057]

[Effect of device]

 Nuts can be made cheaper than commercially available ball screws and do not require complicated and difficult machining.

[Brief description of drawings]

FIG. 1 is a side view of a grinder having a unique hydrostatic nut and lead screw assembly according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a mold and a standard lead screw for forming a hydrostatic nut before injection of a molding agent.

FIG. 3 is an enlarged sectional view of a mold and a standard lead screw for forming a hydrostatic nut after injection of a molding agent.

FIG. 4 is an enlarged cross-sectional view of a hydrostatic nut fixed to a polishing machine that works with a lead screw.

[Explanation of symbols]

 10. . Polishing machine 12. . Base 14. . Carriage 16. . Rotary table 18. . Headstock 20. . Dojo 22. . Workpiece 24. . Sliding surface 26. . Tool mounting part 28. . Polishing machine 30. . Central axis 32. . Motor 36. . Pillar 38. . Passage 40. . Hydrostatic nut 42. . Lead screw 44. . Motor 46. . Coupling 50. . Mold 52, 54. . Retaining cap 56. . Diameter 58. . Pressure plate 60. . Stud 62. . Set screw 64. . Flange 66. . Pressure plate 68. . Stud 70, 72. . Adjustment screw 74. . Standard lead screw 76, 78. . Bead 80. . Polymer agent 82. . Entrance 84. . Exit 86,88. . Channels 90, 92. . Introduction section 34. . Endless belt

Claims (5)

[Scope of utility model registration request] 1. A metal cylinder having a hole at its center, which is open at both ends, b) at least one helical screw cut on the inner surface of the hole at the center, and c) all of the screws. A thick, hard plastic coating adhered to the exposed surface, d) a clearance according to the shape of the screw on the surface of the plastic coating serves as a channel for carrying pressurized fluid when the nut engages with the lead screw. Hydrostatic nuts for machine tools with nuts adapted to function. 2. A) a metal cylindrical body having a hole at both ends which is open at the center, b) at least one spiral screw cut on the inner surface of the hole at the center, and c) a screw of the nut. A solid plastic coating adhered to all exposed surfaces, d) a gap on the exposed side of said coating, e) the elongated body of the lead screw is made of metal and has at least one spiral on its outer surface F) having a thread, f) when the nut and lead screw cooperate, the coating is adapted to prevent metal-to-metal contact between the nut screw and the lead screw thread, and g) the coating. There is a continuous spiral channel between the gap of the material and the outer surface of the helical screw of the lead screw, and h) means for introducing pressurized fluid into the channel through the cylindrical body. And as the lead screw moves relative to the nut, A hydrostatic nut and lead screw assembly for machine tools, wherein the nut is adapted to float on a thin film of fluid. 3. The machine tool is a grinder, and includes a work support tool for supporting a work, a grinder, a tool mounting portion, and a sliding surface for supporting the tool mounting portion, and the grinder passes through the center. Is fixed to the tool mounting part so that it can rotate around the
The nut is fixed to a pillar hanging from the tool mounting portion,
The lead screw penetrates the nut, and a motor attached to the lead screw rotates the lead screw,
3. The hydrostatic nut and lead screw assembly for a machine tool according to claim 2, thereby positioning the tool mount and the grinder with respect to the workpiece support. 4. The hydrostatic nut and lead screw assembly for a machine tool according to claim 3, wherein the workpiece is cylindrical and the grinder is a cam grinder. 5. A machine tool as a base, a work support fixed to the base, a carriage movable with respect to the base, a nut fixed to the carriage, a polishing machine fixed to the carriage, and a carriage. A hydrostatic nut affixed to and a motor driving a lead screw, the lead screw moving relative to the nut, moving the carriage, and moving the carriage and the grinder relative to the workpiece support. 3. A hydrostatic nut and lead screw assembly for a machine tool according to claim 2.