JP2002066860A - Ball screw feeder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw feeder capable of enlarging the range of speeds of a moving element without depending on a servomotor or a transmission, and also of enhancing positioning accuracy irrespective of the accuracy of machine elements. SOLUTION: The ball screw feeder comprises a main feed mechanism having a ball screw 12, a nut 13 for threadable engagement with the screw 12, and a servomotor 16 for driving the screw 12 to rotate it, for feeding the moving element 10; and an auxiliary feed mechanism 18 which has an auxiliary servomotor 20 for driving the nut 13 independently of the main servomotor 16 and which rotatably holds the nut 13 while superposing on the screw 12 the rotation of the nut 13 driven by the auxiliary servomotor 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw feeder used for a feed mechanism of a machine tool or the like, and in particular, by adding an auxiliary feed mechanism by a servomotor.
The present invention relates to a ball screw feeder configured to expand a variable range of a feed speed and increase a feed resolution.

[0002]

2. Description of the Related Art In a machine tool, a ball screw feed mechanism is used as a feeder for a moving body such as a table or a spindle head. FIG. 4 is a diagram showing a side surface of a rack cutting machine incorporating a conventional ball screw feed mechanism, and FIG. 5 is a plan view of the rack cutting machine. Reference numeral 30 denotes a cutter table, and 32 denotes a ball screw. In this rack cutting machine, the cutter table 30
The bed 33 is arranged so that it can move linearly while sliding on the sliding surfaces of the guide portions 34a and 34b provided on the bed 33.
It is installed above. The female screw fixing base 35 is a bed 33
And the female screw fixing base 35 includes:
A ball nut 36 screwed into the ball screw 32 is fixed.

[0003] The ball screw 32 is connected via a coupling 37 coaxially with a main shaft 38 to which a cutter 40 for cutting a workpiece W to create rack teeth is mounted. The main shaft 38 is rotatably supported by bearings 39a and 39b in a horizontal posture. The work W is fixed to a jig 41. A worm gear 42 is attached to one end of the main shaft 38, and a worm 44 attached to a rotation shaft of a servomotor 43 is meshed with the worm gear 42.

In such a ball screw feed mechanism of a rack cutting machine, a spindle 38 driven by a servomotor 43 is used.
When the ball screw 32 rotates, the ball nut 3
6, the rotation of the ball screw 32 is converted into a linear motion of the cutter table 30. Therefore, the cutter 40 moves in the axial direction while rotating, and can create rack teeth for the work W.

[0005] In a machine tool, the precision of the feed mechanism is directly linked to the processing precision. Generally, a ball screw always has a pitch error and a straightness error, and in order to improve the accuracy of the feed mechanism, it is necessary to use a highly accurate and highly rigid ball screw. In numerically controlled machine tools, to correct pitch errors and straightness errors in servo motors,
In some cases, a correction pulse is superimposed on a command given to a servomotor.

[0006]

In the case of a feed mechanism using a ball screw mechanism, in order to increase the speed range,
It is necessary to use a servomotor having a wide speed range or use a transmission. In addition, if a highly accurate and highly rigid ball screw is used to ensure accuracy, there is a problem that the cost increases.

In the case of a ball screw feed mechanism applied to the rack cutting machine shown in FIGS.
Because the 0 and the ball screw 32 rotate simultaneously on the same axis,
As in the related art, the pitch error cannot be corrected numerically, and the pitch error of the ball screw 32 appears as a processing error with respect to the workpiece W as it is.

Further, when machining racks with teeth having different pitches, it is necessary to replace the ball screw with a pitch that matches the pitch, and the pitch of the ball screw and the pitch of the tooth to be cut have a one-to-one correspondence. However, there is a problem that teeth having an arbitrary pitch cannot be machined.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, to increase the speed range of a moving body without depending on a servomotor or a transmission, and to position the moving body. It is an object of the present invention to provide a ball screw feeder capable of improving the accuracy without depending on the accuracy of a mechanical element.

It is another object of the present invention to provide a ball screw feeder capable of performing thread cutting and rack cutting at an arbitrary pitch.

[0011]

According to a first aspect of the present invention, a ball screw is driven to rotate by a servomotor, and the nut is screwed to the ball screw. In a ball screw feeder that converts motion, a main feed mechanism for feeding the moving body, comprising a ball screw, a nut screwed to the ball screw, and a main servomotor for rotating the ball screw, An auxiliary feed mechanism having an auxiliary servo motor driven independently of the main servo motor, transmitting the rotation of the auxiliary servo motor to the nut, and superimposing the feed by the rotation of the nut on the feed by the main feed mechanism, It is characterized by consisting of.

According to a second aspect of the present invention, in the first aspect of the present invention, the movable body is a cutter base for feeding a cutter to a work fixed at a fixed position and performing rack cutting. Is characterized in that a main shaft to which a cutter is attached is connected coaxially with the ball screw.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the ball screw feeder according to the present invention will be described below with reference to the accompanying drawings. First Embodiment FIG. 1 shows a ball screw feeder according to a first embodiment of the present invention. In the first embodiment, the ball screw feeder of the present invention is applied to a general feed mechanism of a moving body in a machine tool.

In FIG. 1, reference numeral 10 denotes a moving body. In this embodiment, the moving body 10 is assumed to be a component of a machine tool that moves horizontally. Reference numeral 12 denotes a ball screw, and reference numeral 13 denotes a ball nut screwed into the ball screw 12. In the bed 14, the ball screw 12
It is rotatably supported via bearings 15a and 15b in a horizontal posture. Reference numeral 16 denotes a main servomotor that rotationally drives the ball screw 12, and is directly connected to the ball screw 12 without passing through a transmission. The ball screw 12, the ball nut 13, and the main servomotor 16
The main feed mechanism mechanism for feeding 0 in the axial direction of the ball screw 12 is constituted. In addition, ball nut 1
3 is an auxiliary feed mechanism 18 which will be described later integrally with the moving body 10.
Attached through.

The auxiliary feed mechanism 18 is provided below the moving body 10, and FIG. 2 is a diagram showing the configuration of the auxiliary feed mechanism 18. The auxiliary feed mechanism 18 is provided with the ball nut 1
3 is shared with the main feed mechanism, and the auxiliary servomotor 20 is used.
As a result, the ball nut 13 is driven to rotate, and the feed by the rotation of the ball nut 13 can be superimposed on the feed by the main feed mechanism. In this embodiment, a cylindrical rotating body 21 is integrally fixed to the ball nut 13, and the rotating body 21 is supported by a bearing 22 attached to a lower part of the moving body 10. A gear portion 23 is provided on an outer peripheral portion of the rotating body 21, and the gear portion 23 meshes with a gear 24 attached to an output shaft of the auxiliary servomotor 20.

The ball screw feeder according to the first embodiment is configured as described above. Next, the operation and effects of the device will be described. When the ball screw 12 is rotationally driven by the main servo motor 16 of the main feed mechanism in a state where the auxiliary servo motor 20 of the auxiliary feed mechanism 18 is stopped, the rotation of the ball screw 12 is directly changed to the ball nut 13.
Is converted into a linear motion by the moving object 10 and
The moving object 10 can be sent. Moving object 10 at this time
Is determined by the number of revolutions of the main servomotor 16 and the pitch (lead) of the ball screw 12.

Next, when the auxiliary servomotor 20 of the auxiliary feed mechanism 18 is rotated simultaneously with the main servomotor 16, both the ball screw 12 and the ball nut 13 rotate, so that the feed by the main feed mechanism and the rotation of the ball nut 13 are performed. Is superimposed. That is, when the ball nut 13 is rotated in the same direction as the ball screw 12, the moving speed of the moving body 10 is reduced, and when the ball nut 13 is rotated in the opposite direction, the moving speed of the moving body 10 is increased. Thus, by changing the rotation speed of the auxiliary servomotor 20 without connecting the main servomotor 16 and the ball screw 12 with a reduction gear, the range of the feed speed can be greatly expanded.

In addition, when the speed is reduced by the auxiliary servomotor 20, the feed resolution of the main servomotor 16 is substantially reduced, which is the same as that of the first embodiment. It is possible to further reduce the minimum feed resolution and achieve an improvement in feed accuracy.

If there is a pitch error in the ball screw 12, the rotation of the auxiliary servomotor 20 is controlled to apply a rotation amount corresponding to the pitch error to the ball nut 13, thereby performing complicated control as in the prior art. The correction of the pitch error can be performed without any problem.

Second Embodiment FIG. 3 shows a ball screw feeder according to a second embodiment of the present invention. The ball screw feeder according to the second embodiment is one in which the present invention is applied to the conventional rack cutting machine shown in FIGS. 3, the same components as those in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the ball screw feeder according to the second embodiment of the present invention, the feed mechanism of the cutter table 30 driven by the main servomotor 43 is the main feed mechanism. The ball screw 32 of the main feed mechanism is connected to the main shaft 3 to which a cutter 40 for cutting the work W and creating rack teeth is mounted.
8 and connected via a coupling 37.
A worm gear 42 is attached to one end of the main shaft 38, and a worm 44 attached to the rotation shaft of the main servomotor 43 meshes with the worm gear 42.

In the second embodiment of the present invention, an auxiliary feed mechanism 50 is added to a main feed mechanism of a rack cutting machine.
This auxiliary feed mechanism 50 is incorporated in the female screw base 35.

That is, a cylindrical rotating body 51 is integrally fixed to the ball nut 36 which is shared with the main feed mechanism, and the rotating body 51 is supported by a bearing 52 attached to the female screw base 35. ing. A gear 53 is provided on the outer periphery of the rotating body 51.
Numeral 3 meshes with a gear 54 attached to the output shaft of the auxiliary servomotor 60.

The ball screw feeder according to the second embodiment is configured as described above. Next, the operation and effects of the device will be described.

First, when the main shaft 38 is rotated by the main servo motor 43 of the main feed mechanism with the auxiliary servo motor 60 of the auxiliary feed mechanism 50 stopped, the cutter 40 and the ball screw 32 rotate together with the main shaft 38. The rotation of the ball screw 32 is directly converted into a cutting feed motion of the cutter 40 by the ball nut 36. in this case,
The cutter 40 performs rack processing on the workpiece W at a pitch P of the ball screw 32 per one rotation of the main shaft 38.
Therefore, the pitch P of the ball screw 32 must be equal to the rack pitch Pa. If there is a pitch error in the ball screw 32, it becomes a processing error as it is.

In order to prevent such a processing error, correction of the pitch error by the auxiliary feed mechanism 50 may be performed as follows.

The pitch error of the ball screw 32 is measured in advance. In actual cutting, the main servo motor 4
3 and the auxiliary servo motor 60 are rotated together to perform cutting. Then, the rotation of the auxiliary servomotor 60 may be controlled so that the ball nut 36 rotates by a rotation amount corresponding to a pitch error per rotation of the ball screw 32. As a result, the pitch error correction amount is superimposed on the feed amount of the cutter 40, so that the rack teeth are created on the work W with high accuracy.

By applying the correction by the auxiliary feed mechanism 50 as described above, rack processing at an arbitrary rack pitch using one master ball screw, which cannot be performed by the conventional rack cutting machine shown in FIG. Becomes possible.

If the pitch of the ball screw 32 used as the master ball screw for rack machining is P and the rack pitch of the rack to be machined is Pa, then P-P
Assuming that a is the correction amount by the auxiliary feed mechanism, the ball nut 36 may be rotated by a rotation amount corresponding to the correction amount, and may be superimposed on the feed amount of the cutter 40. This allows the cutter 40 to perform rack processing at the pitch Pa per rotation of the ball screw 32.

[0030]

As is apparent from the above description, according to the present invention, the speed range of the moving body can be expanded without depending on the servomotor or the transmission, and the positioning accuracy of the moving body can be improved. Improvements can be achieved independent of the precision of the mechanical elements.

Further, by applying the ball screw feeder according to the present invention to a rack cutting machine or the like, it becomes possible to cut or thread a rack having an arbitrary pitch using one master ball screw.

[Brief description of the drawings]

FIG. 1 is a partially cutaway side view showing a ball screw feeder according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing an auxiliary feed mechanism of the ball screw feed device.

FIG. 3 is a partially cutaway side view showing a ball screw feeder according to a second embodiment of the present invention.

FIG. 4 is a side view showing a rack cutting machine to which a conventional ball screw feeder is applied.

FIG. 5 is a plan view of the rack cutting machine of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Moving body 12 Ball screw 13 Ball nut 14 Bed 16 Main servo motor 18 Auxiliary feed mechanism 20 Auxiliary servo motor 21 Rotating body 23 Gear part 30 Cutter base 32 Ball screw 35 Female screw base 36 Ball nut 38 Main shaft 40 Cutter 43 Main servo motor 50 Auxiliary feed mechanism 60 Auxiliary servo motor

Claims (2)

[Claims] 1. A ball screw feeder for rotating a ball screw by a servomotor and converting the movement into a linear motion of a moving body by a nut screwed to the ball screw, comprising: a ball screw; and a nut screwed to the ball screw. A main servomotor for rotating and driving the ball screw, a main feed mechanism for feeding the moving body, and an auxiliary servomotor driven independently of the main servomotor; A ball screw feed device, comprising: an auxiliary feed mechanism that transmits rotation to the nut and superimposes feed by rotation of the nut with feed by the main feed mechanism. 2. The moving body according to claim 1, wherein said moving body is a cutter table for feeding a cutter to a workpiece fixed at a fixed position and performing rack cutting, and a main shaft having a cutter mounted thereon is coaxial with said ball screw. The ball screw feeder according to claim 1, wherein the ball screw feeder is connected to the ball screw feeder.