JPH10277932A - Pressing force controlling tail stock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a work from being defectively processed in accuracy because of defective pressing force by a tail stock center. SOLUTION: The current value of a grinding wheel shaft motor 23 is detected by a current meter 70, and the detected current value is converted into digital signals by an A/D converter 69 so as to be inputted into a numerical control device 61. Grinding resistance is operated based on the inputted current value by the numerical control device 61, and a servo motor 55 is thereby driven based on the operated grinding resistance and the stiffness of a work that is stored in advance so as to allow a spring to be pressed, so that the pressing force of a tail stock center 16 is thereby adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tailstock such as a grinding machine capable of adjusting a pressing force.

[0002]

2. Description of the Related Art When processing a workpiece with a grinding machine, it is common to divide the processing step of the workpiece into a rough grinding, a fine grinding, and a fine grinding in order to perform the required precision within a required cycle time. It is a target. In rough grinding, the cutting speed of the grinding wheel is increased to increase the removal amount of the workpiece per unit time to increase the cycle time of grinding.In fine grinding and fine grinding, the cutting speed of the grinding wheel is reduced to reduce The removal amount of the workpiece is reduced to improve the dimensional accuracy and the shape accuracy of the workpiece.

[0003] The pressing force of the tailstock center is adjusted according to the weight of the workpiece and the grinding resistance. Since the grinding resistance in the fine grinding and the fine grinding is much smaller than that in the rough grinding, the same pressure as in the rough grinding is used. When pressure is applied, the workpiece may bend and cause run-out, thereby deteriorating the processing accuracy. For this reason, when it is necessary to machine with high precision, in precision grinding or fine grinding, the pressing force of the center is weakened to prevent the workpiece from oscillating, thereby improving the machining accuracy of the workpiece.

[0004] A tailstock capable of adjusting the pressing force of such a center is disclosed, for example, in Japanese Utility Model Application No. 4-74587. The slide body is movably supported by the tailstock main body, and a ram is fitted to the slide body. A spring is provided behind the ram so as to press the ram. Also,
A fixed member is fixed to the slide body, and the fixed member is supported by a support member, and a nut portion screwed to a screw shaft is fixed to the support member. A gear is fixed to the screw shaft, and this gear meshes with another gear fixed to the NC motor.

[0005] By rotating the NC motor, the slide body is advanced through the gear, the screw shaft, the nut, the support member, and the fixing member. After the slide body advances and the center abuts the center hole of the workpiece and the advance is stopped, the NC motor is further rotated until the set pressing force is generated, and the spring is compressed by the advance of the slide body. . When it is desired to reduce the pressing force at the center, the amount of compression of the spring is reduced by reversing the NC motor and retreating the slide body.

[0006] By thus rotating the NC motor forward and backward, the pressure applied to the center can be freely changed. Then, the pressing force of the center is changed according to the processing steps of rough grinding and fine grinding. In each machining process, the cutting speed of the grindstone and the rotation speed of the workpiece, that is, the spindle, are mainly changed, and the pressing force of the center is changed according to the machining process, that is, the cutting speed of the grindstone and the rotation of the spindle are changed. The pressing force of the center is changed according to the speed.

[0007]

However, the cutting speed of the grindstone and the rotation speed of the spindle vary depending on the machining process, but the conditions such as the grindstone diameter and the sharpness of the grindstone vary irrespective of the machining process. I have. Since the grindstone diameter gradually decreases as the workpiece is machined, the circumferential speed of the grindstone changes when the grindstone shaft drive motor is rotated at the same rotation speed.
Therefore, as the wheel diameter decreases, the rotation speed of the wheel drive motor is changed to maintain a constant wheel peripheral speed.
Since this is a stepwise change, there is a certain difference in the grinding wheel peripheral speed between immediately after the previous change in the rotational speed and immediately before the present change in the rotational speed. Further, the sharpness of the grindstone gradually deteriorates with the increase in the number of processed pieces during the dress interval, so that there is a certain difference in the sharpness of the grindstone between immediately after the previous dress and immediately before the current dress. In addition, the sharpness of the whetstone changes even when the dress conditions such as the dress speed are changed. Therefore, even after the same dress, the sharpness may differ depending on the dress conditions.

[0008] Therefore, if a fixed control of the same center pressing force is performed in the same processing step, when processing a low-rigidity work such as a long object or a hollow object, a large number of workpieces are required. When such a workpiece is machined and the grinding resistance is changed due to a change in the grindstone diameter or the sharpness of the grindstone, there is a problem that the machining accuracy of the workpiece may be deteriorated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. According to the present invention, a tailstock shaft slidably supported by a tailstock main body and a tailstock are provided. A center inserted into the tip of the tailstock shaft to support an object, a spring that presses the tailstock shaft in the axial direction to apply a pressing force to the center, and a compression amount of the spring is changed. In a pressing force control tailstock comprising driving means for adjusting the pressing force of the center, a grinding wheel shaft load detecting means for detecting a load on the grinding wheel shaft, and a grinding wheel shaft load detected by the grinding wheel shaft load detecting means. Control means for calculating the grinding resistance and controlling the driving means so as to change the pressing force of the center according to the calculated grinding resistance and the rigidity of the workpiece stored in advance. It is assumed that.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a table 11 is guided and supported on a bed 10 of a grinding machine by a servo motor (not shown) so as to be movable in the left-right direction (Z-axis direction) of the drawing. A headstock 12 bearing a spindle 13 is arranged on the table 11 and is driven to rotate by a motor 21.

A tailstock 17 is arranged on the table 11 at a position facing the headstock 12, and a center 16 is provided coaxially with a center 22 of the spindle 13. Both ends of the workpiece W are supported by the center 16 of the tailstock and the center 22 of the spindle. The workpiece W has a driving force transmitting member 1 at the left end.
5 is engaged with the engagement pin 14 and is rotated by the motor 21 together with the main shaft 13.

A grindstone table 18 is supported by a servomotor (not shown) so as to be movable in the vertical direction (X-axis direction) behind the table 11 on the bed 10. A grinding wheel 19 is provided with a grinding wheel shaft 2 parallel to the Z-axis direction.
0 and is rotationally driven by a grinding wheel shaft drive motor 23. An ammeter 70 is provided to the grinding wheel shaft drive motor 23.
(Grinding wheel shaft load detecting means) is connected, and the current value detected by the ammeter 70 is input to the numerical controller 61 via the A / D converter 69, and the grinding resistance is calculated. I have.

Next, the detailed structure of the tailstock 17 will be described with reference to FIG. A tailstock shaft 31 is supported on the tailstock main body 30 so as to be slidable in the axial direction. A tapered hole 32 at the tip end of the tailstock shaft 31 has the above-mentioned centerpiece fitted into the center hole of the workpiece W. The press center 16 is inserted.
A spring housing 34 holding a spring 36 is provided in the inner hole 33 of the tailstock 31. A flange 34a is formed at the tip of the spring housing 34.
A flange 34c is formed substantially at the center. Collar 3
A cylindrical portion 34b is formed between the flange portion 4a and the flange portion 34c, and a cylindrical portion 34d is similarly formed behind the flange portion 34c. The flange portion 34c is connected to the tailstock shaft 31 by a bolt (not shown). It is fixed to the rear end face.

The cylindrical portion 34d of the spring housing 34
A stroke ball bearing 38 held by a sleeve 39 is disposed on the outer periphery of the spring housing 34, whereby the spring housing 34 and the sleeve 39 can be relatively moved in the axial direction. A plurality of bolts 40 pass through the sleeve 39 on the same circumference, and the ends of the bolts 40 are screwed to the flange portions 34c of the spring housing 34. The rotation of the sleeve 39 with respect to the spring housing 34 is restricted, It is movable in the axial direction.

A cap 4 is provided on the rear end face of the sleeve 39.
2 is fixed, and a groove 42 a is formed in the front end face of the cap 42. And the tailstock center 16
A predetermined distance is provided between the sleeve 39 and the end face of the cylindrical portion 34d of the spring housing 34 for adjusting the pressing force of the spring housing 34. When the sleeve 39 moves in the axial direction with respect to the spring housing 34, The cylindrical portion 34d of the stroke ball bearing 38 is inserted into the groove 42a.

The cylindrical portion 3 of the spring housing 34
An adjusting bolt 41 is arranged in the inner hole of the cap 4d and the outer peripheral screw portion 41a formed on the outer periphery of the adjusting bolt 41 and a screw portion 42b formed on the inner periphery of the cap 42. It has become. A shoulder portion 41d is formed at the front end of the adjustment bolt 41, and a thrust bearing 37 is fitted into the shoulder portion 41d,
The thrust bearing 37 holds the spring 36 between the thrust bearing 37 and the flange 34a of the spring housing 34.

The flange portion 41c of the adjustment bolt 41
A tool insertion hole 41b is formed on the outer periphery, and when a tool (not shown) is inserted into the tool insertion hole 41b and the adjustment bolt 41 is rotated, the rotation of the cap 42 is regulated by the bolt (not shown). The bolt 41 moves forward and backward in the axial direction together with the thrust bearing 37,
The initial compression amount of the spring 36 can be adjusted.

A guide member 4 is provided on the outer periphery of the sleeve 39.
The guide member 43 is guided and moved by a driving means 50. The driving means 50 includes a servomotor 55, a ball screw 45, a gear 4
8, 54. The servo motor 55 is mounted on the rear end face of the motor base 53 mounted on the tailstock main body 30, and an encoder 55a is mounted on the rear end. The output shaft 51 of the servomotor 55 has a key 52
The gear 54 is mounted so as to be able to rotate integrally with the gear 54.
A gear 48 meshes with the gear 54, and the gear 4
8, a ball screw nut 46 is attached via a key 47 so as to be integrally rotatable.
Is screwed with a ball screw 45.

The rotation of the servo motor 55 is transmitted to the ball screw nut 46 via the gears 54 and 48, and the ball screw 45 advances and retreats in the axial direction by the rotation of the ball screw nut 46. A guide member 43 fixed to the rear end of the ball screw 45 is fixed to the outer periphery of the sleeve 39, and is guided by the ball screw 45 moving forward and backward.

As shown in FIG. 1, the control means 60 comprises a numerical control device 61, an input device 66, an output device 67, a drive circuit 6
8. It is composed of an A / D converter 69. The numerical control device 61 includes a CPU 62, a memory 63, and interfaces 64 and 65. The memory 63 stores a correspondence table between the grinding resistance and the center pressing force, a machining program, and the like. The correspondence table between the grinding force and the center pressing force is, for example, such that the center pressing force is a if the grinding force is A to B, and the center pressing force is b if the grinding force is B to C. On the other hand, the center pressing force is set stepwise. In addition, even if the grinding force is the same, it is necessary to change the center pressing force depending on the rigidity of the workpiece. Therefore, the rigidity of the workpiece is divided into a plurality of stages, and each stage of the rigidity corresponds to multiple grinding resistances and the center pressing force. A relation table is stored.

An input device 66 such as a keyboard and an output device 67 such as a CRT are connected to the interface 64, and a drive circuit 68, the encoder 55a and an A / D converter 69 are connected to the interface 65.
The A / D converter 69 is connected to an ammeter 70 for detecting a current value of the grinding wheel drive motor 23.
A / D converter 69 converts an analog signal into a digital signal at the interface 6
5 is input.

The drive circuit 68 is connected to the servomotor 55. The servomotor 55 is driven to rotate by a command from the CPU 62 via the interface 65. This rotation is detected by the encoder 55a and fed back to the numerical controller 61. Thus, the amount of compression of the spring 36 is controlled. When the pressure of the tailstock center 16 is to be changed, the servomotor 55 is further rotated while the center 16 is fitted into the center hole of the workpiece W and the tailstock shaft 31 stops moving forward. Then, the sleeve 39 and the adjustment bolt 41 screwed to the sleeve 39 advance through the gears 54 and 48, the ball screw 45, and the guide member 43. Then, the spring 36 held between the flange 34a of the spring housing 34 and the shoulder 41d of the adjustment bolt 41 is compressed, and the pressing force of the tailstock center 16 is adjusted.

Next, the operation of the pressure control tailstock having the above-described structure will be described with reference to the flowchart of FIG. A correspondence table between a plurality of grinding resistances determined in advance from the weight and rigidity of the workpiece W and the center pressing force is stored in the memory 63 of the numerical controller 61. The workpiece to be ground is designated from now on, and the rotation of the servomotor 55 is controlled via a drive circuit 68 by a command from the CPU 62 to move the center 16 of the tailstock 17 to a specified amount (the length of the workpiece to be ground). (Depending on the above), the workpiece W is fitted into the center hole of the workpiece W, and the workpiece W is supported between the spindle W and the spindle center 22. In this state, the servo motor 55 is further rotated to
And the adjusting bolt 4 screwed to the sleeve 39
1 is advanced to compress the spring 36 and the center 16
Is adjusted to a specified value (depending on the weight and rigidity of the workpiece to be ground).

The workpiece W is rotated by the motor 21, and the grinding wheel 19 is
Is driven to rotate to start grinding. During the grinding, the current value of the grinding wheel drive motor 23 is detected by the ammeter 70. (Step 100) The current value detected by the ammeter 70 is stored in the A / D converter 69.
Is converted from an analog signal to a digital signal and input to the numerical controller 61. The grinding resistance is calculated by the CPU 62 from this current value. (Step 101) Next, from the correspondence table between the grinding resistance calculated by the CPU 62, the current rigidity of the workpiece, the grinding resistance and the center pressing force stored in the memory 63, the optimum grinding for the current workpiece is performed. The pressing force of the tailstock center 16 is determined. (Step 102) The amount of compression of the spring 36 is calculated according to the pressing force of the tailstock center 16 determined by the CPU 62. (Step 103) Then, C is calculated according to the calculated compression amount of the spring 36.
A command is output from the PU 62 and the servo motor 55 is driven to rotate, and the amount of compression of the spring 36 is changed by the advance and retreat of the adjustment bolt 41, so that the pressing force of the tailstock center 16 is changed. (Step 104) In the above-described embodiment, the correspondence table between the grinding force and the center pressing force is set such that the center pressing force is set in a stepwise manner for a certain range of the grinding resistance. The center pressing force may be set continuously.

[0025]

According to the present invention, the grinding resistance is calculated by the control means based on the load on the grinding wheel shaft detected by the grinding wheel shaft load detecting means during the grinding, and the calculated grinding resistance is stored in advance. The spring was compressed by the drive means according to the rigidity of the workpiece, and the pressing force of the center was changed, so the grinding resistance changed due to changes in conditions such as the sharpness of the grinding wheel and the grinding wheel diameter, which were unrelated to the processing process. Even in such a case, the pressing force of the center is adjusted to an optimum value for the grinding resistance, so that even a low-rigidity work such as a long object or a hollow object can be prevented from swaying, and high-precision machining can be performed. .

[Brief description of the drawings]

FIG. 1 is a schematic overall view of a grinding machine provided with a pressure control tailstock according to an embodiment of the present invention.

FIG. 2 is a sectional view of a pressure control tailstock according to the embodiment of the present invention.

FIG. 3 is a flowchart illustrating an operation of changing a center pressing force according to the embodiment of the present invention.

[Explanation of symbols]

13 Spindle 16 Tailstock Center 17 Tailstock 18 Grindstone 19 Grindstone 20 Grindstone Shaft 22 Spindle Center 23 Grindstone Shaft Drive Motor 31 Tailstock 34 Spring Housing 36 Spring 41 Adjustment Bolt 45 Ball Screw 46 Ball Screw Nut 48 Gear 50 Drive Means 54 Gear 55 Servomotor 60 Control means 70 Ammeter (grinding wheel shaft load detecting means)

Claims (1)

[Claims] 1. A tailstock shaft slidably supported by a tailstock body, a center inserted at a tip of the tailstock shaft for supporting a workpiece, and an axial direction of the tailstock shaft. And a driving means for adjusting the pressing force of the center by changing the amount of compression of the spring to apply a pressing force to the center. A grinding wheel shaft load detecting means for detecting, and a grinding resistance is calculated from a grinding wheel shaft load detected by the grinding wheel shaft load detecting means, and the center is calculated according to the calculated grinding resistance and a rigidity of a workpiece stored in advance. Control means for controlling the driving means so as to change the pressing force of the tailstock.