JPH01252337A - Pick feed device for machine tool - Google Patents

Abstract

PURPOSE:To perform a desired pick feed motion only through control of an exciting current and to enable execution of a grinding work under an optimum pick feed, by providing an exciting control means which is adapted to control the exciting current of a magnetic bearing so that the rotor shaft is forward and backward moved in the direction of the rotor shaft in the magnetic bearing. CONSTITUTION:In coarse grinding feed, a pick feed amount responding to the coarse grinding is set. Along with the starting of a pick feed, a lamp signal is fed from a control part 15 to a computing circuit 17 through a D/A converter 19. The exciting currents of electromagnets 6a and 6b on both sides in a thrust magnetic bearing 6 are controlled so that after a rotor shaft 2 is moved backward to a target position through amplifiers 18a and 18b by a control circuit 18, it is returned to its original reference position. Similarly, in a fine grinding feed work, a given pick feed action is also performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a pick feed device for a machine tool.

(Summary of the Invention) According to the present invention, pick feed processing is performed by controlling the excitation current of a magnetic bearing to move a rotor shaft back and forth in the axial direction.

(Prior Art) Conventionally, so-called pick-feed processing has been performed in grinding machines, in which a grinding wheel is reciprocated by a minute amount relative to a workpiece to perform the grinding process in order to improve grinding accuracy.

The reciprocation of the grindstone for this pick-feed operation is performed by a mechanical mechanism. In other words, the whetstone is i! The suspended spindle is reciprocated using an eccentric cam mechanism.

In addition, recently, as machine tools have become more precise in finishing, grinding has been carried out by rotating grindstones at extremely high speeds.

The rotation of the grindstone in this case is achieved by equipping the tip of the rotor shaft with a grindstone, using this rotor shaft as the rotor of the motor, installing a motor stator inside the spindle, and roughly supporting the rotor shaft with a 141 air bearing. It rotates at super high speed.

(Problems to be Solved by the Invention) However, the conventional big feed device of the machine tool described above is a mechanical t! Since it is a groove, there is a problem that the mechanism becomes complicated and large.

Furthermore, since the big feed is performed via the eccentric cam mechanism, it is difficult to arbitrarily set the optimum big feed state depending on the type of workpiece.

(Means for Solving the Problems) The present invention has been made in order to solve the above problems, and its structure includes a spindle having a tool such as a cutter or a grindstone on a rotor shaft that is rotationally driven. In a big feed device of a machine tool that performs processing such as grinding or cutting a workpiece while moving the tool back and forth in the direction of the rotor axis, a magnetic bearing for supporting the rotor shaft, and a magnetic bearing within the shaft bearing are provided. The present invention is characterized by comprising: excitation control means for controlling an excitation current of the magnetic bearing so as to move the rotor shaft back and forth in the rotor axis direction.

(Function) The rotor shaft supported by the magnetic bearing acts to reciprocate in its axial direction by controlling the excitation current of the magnetic bearing.

(Example) Figs. 1 to 3 show a big feed device according to the present invention, and show an example in which the big feed device is applied to a grinding machine.

FIG. 1 is a schematic diagram of the configuration, and 1 in the figure indicates a spindle, and a grinding wheel a is attached to one end of this spindle 1.
A rotor shaft 2 that rotates is horizontally suspended so as to be freely rotatable.

The spindle 1 is placed and fixed on a table (not shown), and this table is moved in the direction of the axis (center) of the rotor shaft 2 by a well-known feeding mechanism consisting of a servo motor 3 and a screw 4 rotated thereby. It is configured to be movable.

The rotor shaft 2 has a disk-shaped plate 5 integrally provided at approximately the center thereof, which is supported by a thrust magnetic bearing 6 provided in the spindle 1 and receives axial force. The left and right ends are equipped with radial magnetic bearings 7.
．． It is pivoted by 9.

Since the mechanisms of the thrust and radial magnetic bearings are well known, their details will be omitted, but these magnetic bearings consist of a plurality of pairs of electromagnets 6a and 6b.

The rotor fitl12 is levitated between 7a, 7b, 8a, and 3b by magnetic force.

In a magnetic bearing, a clearance of about Q, 5 mm is usually provided between the magnetic pole of the electromagnetic member 6 and the outer periphery of the rotor shaft 2 and plate 5. Therefore, − excitation of the pair of electromagnets! i
By adjusting the current, it is possible to bias the rotor shaft 2 toward one of the electromagnets and to support the rotor shaft 2.
The rotor shaft 2 can be moved back and forth in its axial direction.

However, normally, the position of the rotor shaft 2 is detected by a fast position sensor so that the rotor shaft 2 is located approximately in the middle of the clearance, and this detection signal is fed back to adjust the excitation current.

Reference numeral 9 denotes a motor, which acts to rotate the rotor shaft 2 when an induced current flows through it. Therefore, rotor shaft 2
acts as a heptad rotor.

10.11 is a position sensor provided on the left and right sides of the rotor shaft 2, and 12 is a position sensor provided on the other end side of the rotor shaft 2. Among these, the position sensors 10 and 11 are located at the radius of the rotor [NI2 The position in the radial direction is detected, and the position sensor 12 detects the position in the axial (thrust) direction of the rotor shaft 2.

As these position sensors 10 to 12, the position detection sensors previously proposed by the present applicant in Utility Model Application No. 61-61261 can be used.

In the figure, a workpiece is placed and fixed on a support table having a feeding mechanism (not shown).

C in the figure indicates 1ilI1 means, and CPIJ
.

A control unit 151 including a memory, etc.; a position detection circuit 16 that receives a detection signal from the position sensor 12 and detects the axial position of the rotor shaft 2; Arithmetic circuit 17 for calculating so that the rotor shaft 2 is at a predetermined position. A control circuit 18 for controlling the excitation current of the pair of electromagnets 6a and 5b of the magnetic bearing 6 based on the calculation result of the calculation circuit 17. Amplifying circuits 18a and 18b for amplifying the control signal of the control circuit 18, and a control section 15
A D/A converter 19. which provides a ramp wave signal from the D/A converter 19 to the arithmetic circuit 17. A servo motor driver 21 for driving the servo motor 3 via a D/A converter 20 and a counter 23 for inputting a detection signal from an encoder 22 into the control unit 15 to detect table movement ω. It consists of

The control unit 15 controls the grinding work in an integrated manner, and its memory stores the grinding amount of the grindstone a, pick feed conditions, etc. inputted from a setting device (not shown).

Note that FIG. 1 shows a circuit for driving the motor 9, a drive circuit for driving the radial magnetic bearings 7 and 8, or a circuit that controls the radial position of the rotor shaft 2 by receiving signals from position sensors 10 and 11. The circuits and the like are omitted because they are not directly related to the explanation of the present invention.

The operation of this embodiment having the above configuration will be explained with reference to the flow steps ψ-1 to ψ-1 in FIG. 2 and the cut characteristic diagram in FIG. 3.

Now, when the grinding star 1-button (not shown) is pressed to start grinding, the motor 9 is driven by a signal from the control unit 15, and the rotor I[12] rotates.
The servo motor 3 is rotationally driven by the servo driver 21, the table moves to the workpiece b side, and the grinding process is started (step 100).

At the beginning of machining, the servo Tanabata 3 rotates rapidly and the grinding wheel a
rapidly approaches work b (Fig. 3, 81). After the grinding wheel a and the workpiece b come into contact, rough grinding is performed by rotating the rotation of the servo rotor 3 to prevent it from decreasing (step 1).
02 affirmative, FIG. 3 82) The table feed speed and feed amount are detected by inputting a signal from an encoder 22 directly connected to the servo motor 3 to the control unit 15 via the counter 23.

The position sensor 12 detects the contact position between the grindstone a and the workpiece b.
It is done through. That is, the position sensor 12 detects the displacement of the rotor shaft 2 due to contact between the grinding wheel a and the workpiece b.
This is performed by inputting this detection signal to the control section 15 via an A/D converter (not shown).

When the rotor shaft 2 does not perform a big feed operation, the rotor shaft 2 is set so as to be at the intermediate position (reference position) of the clearance within the magnetic bearing, that is, to maintain the Z-axis displacement O as shown in Fig. 3.
The excitation current of the electromagnetic elements E6a and 6b of the thrust magnetic bearing 6 is adjusted. That is, feedback control is performed based on the detected current (or detected voltage) of the position sensor 12 so that the rotor shaft 2 maintains the reference position.

In the rough grinding feed, a big feed amount corresponding to the rough grinding is set (step 104). With the start of the big feed, a ramp wave signal is sent from the control section 15 to the arithmetic circuit 17 via the D/A converter 19 (step 108).
R constant, 110), so that the control circuit 18
electromagnetic 56a so as to return the rotor 1N12 to the target position via a and 18b and then return to the original reference position.
, 6b is controlled (steps 112, 11
4. Figure 3 (a) A).

Similarly, a predetermined big feed operation is performed during fine grinding feed processing (step 102 is negative).

106 affirmation, 104, 108 affirmation, 110, 112.1
14. Figure 3 (a) A2).

After finishing the fine-sharpening, the table is rapidly approached and the process ends (step 116, FIG. 3, 84).

13.Figure 3 (a) A1. A2 is 1 for each feed
Although only the first big feed is shown, this is for convenience of explanation and is arbitrarily performed according to the contents set in advance in the control section 15.

Furthermore, the Z-axis displacement diagrams in FIGS. 3(b) and 3(c) are examples in which a sine wave signal is used instead of the ramp wave signal in step 110. That is, in the same figure (b), the coarse grinding feed B2 has a large amplitude sine wave A3, the fine grinding feed B2 has a small amplitude sine wave A4, and in the same figure (c), the coarse grinding feed B2 has a sine wave A5. A damping sine wave A6 is produced by the fine-tuning feed B3.

In the present embodiment described above, the excitation current of the thrust magnetic bearing of the magnetic bearing is controlled to perform the big feed machining, so any big feed machining can be performed simply by controlling the excitation current. Therefore, grinding can be performed under optimal big feed machining, and grinding accuracy and machining efficiency can be improved.

Furthermore, by effectively performing big feed machining, cutting fluid can easily flow into the machining surface, which has the effect of extending tool life.

Although the above embodiment shows an example of a grinding machine, it can also be used as a cutting machine by attaching a cutter instead of a grinding wheel.Also, in addition to using a grinding wheel, the big feed operation can be set arbitrarily to perform hole drilling. Drilling work can also be carried out.

Furthermore, a position sensor for detecting the position of the plate 5 may be provided in place of the position sensor 12, and the axial direction of the rotor shaft 2 may be detected by this position sensor, or the exciting current of the magnetic bearing (or The big feed operation may be performed by detecting a change in the voltage (voltage) and controlling the excitation current based on this change.

Furthermore, the big feed operation may be performed by detecting changes in current (or voltage) due to changes in the load on the motor 9. In this case, when the current value due to load fluctuation reaches a predetermined value, the workpiece or grindstone (or cutter) may be moved back once and then moved forward again to repeat the grinding (cutting).

In any case, in the present invention, any load detection method may be used as long as the forward movement of the rotor shaft for big feed is performed by controlling the excitation current of the magnetic bearing.

(Effects) In the present invention, the excitation current of the thrust magnetic bearing of the magnetic bearing is controlled to perform big feed processing, so that a desired big feed operation can be performed simply by controlling the excitation current. Therefore, since grinding can be performed under optimal pick feed, machining accuracy and machining efficiency can be improved. Furthermore, since a mechanical pick-feed gate structure is not required, the device can be made smaller and simpler.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of the device of the present invention, and FIG.
The figure is a flowchart of the grinding control operation, and FIG. 3 is a cutting depth characteristic diagram. 1...Spindle 2...Rotor shaft 6...Thrust magnetic bearing 7.8...Radial magnetic bearing 9...Motor 10.11.12...Position sensor 15...Control unit a. ... Grindstone (tool) b... Workpiece C... More than control means

Claims (1)

[Claims] 1. A workpiece in which a spindle having a tool such as a cutter or a grindstone is provided on a rotationally driven rotor shaft, and a workpiece is processed by grinding or cutting while moving the tool back and forth in the direction of the rotor shaft. A pick feed device for a machine includes: a magnetic bearing for pivotally supporting the rotor shaft; and a magnetic bearing for controlling an excitation current of the magnetic bearing so as to move the rotor shaft back and forth in the rotor axis direction within the shaft bearing. A pick feed device for a machine tool, comprising: excitation control means;