JPS6157141B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, in machine tools such as electric discharge machining equipment, hydraulic servo feeding has been mainly used for the main spindle feeding mechanism, in which the tip of the piston rod of a hydraulic cylinder is connected to one end of the main spindle. Generally, a system is used in which a hydraulic servo valve is controlled by a servo control signal according to a gap length between an electrode connected to the other end of the main shaft and a workpiece, and the hydraulic cylinder is driven and controlled. In this case, the piston rod of the hydraulic cylinder reciprocates rapidly or gently in the direction of machining progress depending on the pressure difference and flow rate of the working fluid in the cylinder chamber, but in this case, the piston rod is subjected to a load only in the thrust direction. Therefore, it is considered that there is almost no load component in the radial direction. However, in recent years, as servo motors with extremely large torque-to-inertia ratios have appeared, examples of using the servo motors as a main shaft drive source of electrical discharge machines have increased. When using this servo motor, a feed screw mechanism with excellent rolling properties such as a ball screw is often used to transmit power from the servo motor to the main shaft. This is causing problems. The first problem is that lateral vibration in the radial direction accompanying the rotation of the feed screw is transmitted to the main shaft, which adversely affects the linearity of the movement of the main shaft. This adverse effect seems to be particularly great in the case of a spindle device in which the guide of the spindle is supported in a rolling manner via balls. The second problem is that it is difficult to maintain the accuracy of the entire machine due to the occurrence of abnormal vibrations due to the eccentricity between the axis of the feed screw and the axis of the drive motor, or the generation of frictional heat due to this. There is a point where The situation of the above-mentioned decrease in accuracy is quantitatively shown as follows. In other words, while the servo motor is rotating, the center of the servo motor shaft generally changes due to manufacturing errors in the bearings that support the servo motor shaft.
The deviation from the center of rotation ranges from several μm to several tens of μm. In addition, the eccentricity between the axis of the ball screw used to transmit power from the servo motor to the main shaft and the axis of the servo motor can be several tens of micrometers, and the eccentricity of the entire axis can be reduced to a few micrometers or less. It is extremely difficult to do so. As a result, in electrical discharge machining, etc., the electrode connected to the tip of the spindle, which should originally move only in the direction of the axis of the spindle, moves also in a direction perpendicular to the axis.
Therefore, the machining amount of electric discharge machining is increased more than necessary, leading to an increase in machining time or a decrease in machining accuracy. Of course, countermeasures have been taken to address these problems, such as improving the manufacturing quality of the feed screw, improving the warping of the screw itself, improving the accuracy of the bearing mechanism, and increasing the rigidity of the main shaft. However, these measures have not been able to achieve the intended purpose, and the quality of the feed screw and spindle support mechanism has been increased needlessly, resulting in an increase in price. The present invention was made to solve the above-mentioned problems in conventional machine tools, and relates to an improvement of a spindle device of a machine tool having a spindle feed screw mechanism. The present invention aims to provide a spindle device for electric discharge machines, etc., which has a servo mechanism that can perform extremely precise movement of the spindle with a simple configuration and can also respond at high speed. Embodiments of the present invention will be described below with reference to FIGS. 1 to 4. In FIG. 1, 1 is a servo motor that is a driving source, 2 is a shaft of the servo motor 1, and 3 is fixed to the upper end of a ball screw 4, which is engaged with the shaft 2 of the servo motor with a key or the like (not shown). A connecting portion, 5 is a disk fixed to the connecting portion 3, 5a is a holding plate for fixing the disk 5 to the upper end of the connecting portion 3, 6
is a flange fixed to the upper end of the frame 7, to which the servo motor 1 is attached. 8 is a brake lining attached to the inside of the flange 6, 9 is a non-excitation type electromagnetic brake, and the mounting plate 1
It is attached to the frame 7 via 0. In this braking device, a disc 5 is sandwiched between a brake lining 8 and a pressing pad 11 of an electromagnetic brake 9, and when the brake 9 is not energized, the pad 11 is
is configured to press the disk 5 to suppress its rotation, thereby braking the rotation of the ball screw 4. 12 is a backing plate inserted into the connection part 3 of the ball screw 4, 13 is a ball receiver, and 14 is a ball support part formed inside the upper part of the frame 7. Between the ball support part 14 and the ball receiver 13, a ball 14a is inserted. The thrust bearing 15 is constructed by interposing the two. A nut 16 applies preload to the ball 14a interposed between the ball support part 14 and the ball receiver 13, so that the ball 14a can move somewhat in the radial direction but cannot move in the thrust direction. Therefore, even if the center of rotation of the servo motor 1 and the center of the feed screw do not coincide, and vibration occurs in the radial direction in the rotation of the feed screw, the vibration is absorbed by the thrust bearing 15 and the frame 7 The structure is such that it does not have any impact. In addition, the ball receiver 13 and the ball support part 1
The contact surface (rolling surface) with the ball 14a of No. 4 is subjected to surface hardening treatment. Further, the ball 14a is hardened so that it can sufficiently withstand thrust loads. 15a is a dust-proof cover; 17 is a threaded portion in which a groove for rolling the ball of the ball screw 4 is formed;
18 is a nut that is screwed into the threaded portion 17 via a ball (not shown); 19 is a bearing hardware fixed to the nut 18; 20 is a flange fixed to the upper end of the main shaft 21; The ball 23a is interposed between the ball support part 23, the bearing hardware 19, and the backing plate 22, and the thrust bearing 24
It consists of 25 is the plate 2 for the ball 23a.
2 is a tightening nut for applying preload through the threaded part 19 provided at the lower part of the bearing hardware 19.
Screw into a. In addition, bearing hardware 19, flange 2
0. The ball rolling surface of the backing plate 22 is subjected to a surface hardening treatment, and the balls 23a are further subjected to a quench hardening treatment. In the thrust bearing 24 , like the thrust bearing 15 interposed between the ball screw connection part 3 and the frame 7, the movement of the balls 23a is restricted in the thrust direction, but the balls 23a can move slightly in the radial direction. It is structured like this. Therefore, even if the ball screw 4 experiences some vibration, the vibration is absorbed by the thrust bearing 24 and does not affect the main shaft. Reference numeral 26 denotes a guide pin, which is fixed to the threaded portion 19a of the bearing hardware 19 and is formed and arranged at right angles to the axis of the main shaft 21. FIG. 2 shows a cross section taken along line A-A in FIG. It is composed of The guide plate 28 is fixed to the frame 7 with bolts 29 and has a guide hole 28a, and the guide pin 26 is inserted into the guide hole 28.
It is inserted into the inside of a. As shown in FIG. 2, the guide pin 26 is movable in the Y-axis direction and the axial direction of the main shaft, but movement is restricted in the X-axis direction, and as a result, the bearing hardware 19 is movable in the Y-axis direction and the axial direction. It can only be moved. 3 is a partially enlarged perspective view of FIG. 2, and FIG. 4 is a cross-sectional view of FIG. In FIGS. 2 to 4, reference numeral 101 denotes a long track base fixed at a position opposite to the center of the main shaft on the outer surface of the main shaft 21, and 102 engages with this track base 101 and slides. This is a sliding platform that moves, and grooves 105 are formed in both shoulders of the track platform 101 so as to form left and right pairs along the longitudinal direction. It is used for rolling of the ball 104 of the bearing 103 interposed between the bearing 103 and the bearing 103. Furthermore, inside the sliding table 102, there is a groove 105 of the track table 101.
A rolling groove 106 for the ball 104 is provided facing the ball 104 located in the rolling groove 106.
is supported on the sliding table 102 by a retainer 107. Reference numeral 109 denotes a pressing plate of the retainer 107 fixed to the foot portion 108 of the sliding table 102. Note that the track bases 101 are provided on both sides of the main shaft 21, and the slide bases 102 that engage with these are formed at two locations in the longitudinal direction of the main shaft 21.
We are guiding the movement of Also, as shown in Figure 2,
Sliding base 102 provided on one side of the main shaft 21
is fixed to the frame 7 with bolts 32, and a sliding table 102 provided on the other side is precisely fitted into a guide 30 provided inside the frame 7, and is supported movably in the x-axis direction. With,
It is pressed toward the main shaft 21 by a bolt 33. 34 is a nut for preventing the bolt 33 from loosening. With this configuration, the track platform 101 and the sliding platform 10
2. An appropriate preload is applied to the balls 104, and play and gaps between the track base 101 and the sliding base 102 are eliminated. As a result, the main shaft 21
It becomes possible to precisely guide the vertical movement of the holder without causing backlash or the like. The spindle device according to the present invention is configured as described above. Next, the operation of this spindle device will be explained. When the servo motor 1 is started, the threaded portion 17 connected to the motor 1 rotates. The nut 18 that is screwed into the threaded portion 17 is connected to the guide pin 26 and the guide plate 2.
8 restricts the movement of the frame 7 in the rotational direction and is movable only in the direction of the spindle axis.Furthermore, the track stand 101 fixed to the spindle 21 is prevented from rotating relative to the sliding stand 102 fixed to the frame. Movement in this direction is restricted and the main shaft 21 is fitted so that it can move only in the axial direction, so the main shaft 21 can also only move in the axial direction. Therefore, the nut 18 performs a downward or upward movement due to the forward and reverse rotation of the threaded portion 17 accompanying the forward and reverse operation of the servo motor 1, and the main shaft 21 that is engaged with the nut 18 via the ball support 23 and the ball 23a. moves down or up. As mentioned above, the ball support part 23 to which the main shaft 21 is fixed is engaged with the bearing hardware 19 and the back plate 22 via the balls 23a, and the ball 2
3a is restricted from moving in the thrust direction, but
Since the ball screw 4 can roll somewhat in the radial direction, even if the threaded portion 17 of the ball screw 4 rotates somewhat eccentrically due to manufacturing errors or other reasons, the eccentricity is absorbed by the thrust bearing 24 , so the main shaft 21 rotates slightly eccentrically due to manufacturing errors or other reasons. It is not affected by eccentricity. The ball support portion 14 of the frame 7 also engages with a ball receiver 13 fixed to the ball screw 4 via a ball 14a, and since the ball 14a can roll slightly in the radial direction, the ball screw 4 and the servo motor 1 Even if there is some eccentricity in the connection, the eccentricity is absorbed by the thrust bearing 15 and does not affect the frame 7. Therefore, even if the ball screw 4 causes lateral vibration due to eccentricity, the main shaft 21 that engages with the sliding table 102 fixed to the frame 7 via the track 101 will not be affected by the lateral vibration. You can move up and down without any problems. Note that while the servo motor 1 is starting and rotating, the electromagnetic brake 9 is excited and the pressing pad 11 does not press the disk 5, so the ball screw 4 can rotate freely. However, when the servo motor 1 stops, the electromagnetic brake 9 is energized. Since the excitation is canceled and the pressing pad 11 presses the surface of the disk 5, a braking force acts on the disk 5, and the ball screw 4 becomes unable to rotate. As mentioned above, misalignment of the shaft 2 of the servo motor 1,
Lateral vibration of the ball screw 4 and nut 18 in the radial direction caused by warping or misalignment of the threaded portion 17 of the ball screw 4, or a difference in parallelism between the shaft 2 and the axis of the insertion hole of the shaft 2 of the ball screw 4, etc. No external force acts on the main shaft 21, and the rotation of the ball screw 4 only causes thrust transmission or movement in the thrust direction, and the main shaft 21 is guided with extremely high precision by a guideway 101, a ball 104, and a slider 102. It will be guided by the mechanism. As a result,
The straightness of the movement of the main shaft 21 can be made approximately 1 to 2 microns. Further, vertical runout of the main shaft 21 due to lead error of the ball screw, displacement in the thrust direction due to rotation of the thrust bearing, etc. is generally minute and therefore poses no problem in practice and can be ignored. As shown in FIG. 5, the guide structure of the guide pin 26 is made into a cylinder 40 so as to contact the cylindrical surface of the guide plate 28, and the guide pin 2
6 may be installed. As described above, according to the device of the present invention, it is possible to absorb or restrict the lateral vibration of the feed screw without increasing the accuracy of the feed screw, and maintain the straightness of the spindle motion with high precision. As a result, the main shaft rigidity and the guide mechanism for guiding the main shaft can be easily constructed without increasing the rigidity, and furthermore, the movement component in the perpendicular direction accompanying the main shaft movement is almost eliminated, so the machining volume can be reduced in electrical discharge machining equipment. This results in excellent effects such as reduction in machining time and reduction in machining time. Furthermore, the device of the present invention can be applied not only as a spindle feeding device for electric discharge machining equipment but also as a spindle device for other machine tools.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a sectional view taken along line AA in Fig. 1, Fig. 3 is a partially detailed perspective view of Fig. 2, and Fig. 4 is a schematic diagram of Fig. 3. - Cross-sectional view, FIG. 5 is a diagram showing another example of application. In the figure, 1 is a servo motor, 3 is a ball screw connection, 4 is a ball screw, 7 is a frame, 12
A backing plate, 13 a ball receiver, 14 a ball support part, 15 a thrust bearing, 17 a ball screw thread part, 18 a ball screw nut, 19 a bearing hardware, 21 a main shaft, 23 a ball support part, 2
4 is a thrust bearing, 26 is a guide pin, 2
8 is a guide plate, 28a is a guide hole, 40 is a cylinder, 10
1 is a track base, 102 is a sliding base, and 104 is a ball. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. On the outer surface of the main shaft, which is driven in the axial direction by being screwed into a ball screw connected to the rotating shaft of the servo feed motor, at positions opposite to each other with the center of the main shaft in between. A fixed elongated track is slid onto a slide fixed to the inside of a frame formed on the main shaft with a predetermined gap through a ball, and a nut is screwed onto the ball screw. A guide pin, which is fixed to a bearing hardware fixed to the frame and protrudes through the main shaft in the radial direction, is inserted into a guide hole in a guide plate provided in the frame to restrain movement of the main shaft in the circumferential direction. Particularly, in a main shaft device in which the main shaft is configured to be movable only in the axial direction, the nut part that is screwed into the ball screw is engaged with the main shaft so as to be movable in the radial direction via a thrust bearing, and the ball screw is movable in the radial direction. By engaging the connecting portion of the servo feed motor with the frame so as to be movable in the radial direction via a thrust bearing, vibrations of the ball screw can be prevented from propagating to the main shaft and the frame. A spindle device for a machine tool characterized by the following configuration.