JPH0457655A - Machine tool spindle device with vibration damping function - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a so-called built-in motor type spindle device in which the rotating spindle is composed of a rotor of an electric motor, and particularly to a spindle device of a machine tool having a vibration damping function. Regarding equipment.

[Conventional technology]

A machine tool whose rotating main shaft, on which a machining tool is attached to the tip, is composed of an induction motor rotor is known as a built-in type.

In such a machine tool, vibrations are mainly generated by the electric motor itself and vibrations generated when a processing tool at the tip processes a workpiece.

In general, self-excited vibrations that occur in high-speed rotating motors are caused by rotational unbalance caused by misalignment of the motor's own shaft center of gravity or shaft clearance, or by the driven load connected to the motor (in this case, by the processing tool). This may be caused by processing. Such vibrations greatly affect the performance of machine tools equipped with motors.

As general countermeasures against such vibrations, passive vibration damping mechanisms and active vibration damping mechanisms have been proposed.

As an example of a passive type, an automatic balance mechanism has been proposed in which a ring sealed with liquid or steel balls is attached to the driven shaft. This method absorbs vibrations by utilizing the property that liquid and steel balls are uniformly distributed within the ring due to the centrifugal force generated as the shaft rotates. It is called a passive vibration damping mechanism because it damps the vibrations that occur without suppressing the vibrations themselves.

On the other hand, there is an active vibration damping mechanism that actively suppresses vibrations. For example, in a magnetic bearing that magnetically receives the shaft of a motor, there is a method in which the excitation of the magnetic bearing is actively suppressed in accordance with the shaft rotation and vibrations generated, and a method in which the gap between the air pad and the shaft of an air bearing is controlled. A method of damping vibration by changing dynamic stiffness has been proposed.

However, the above-mentioned vibration damping methods, whether passive or active, focus on the vibration itself and attempt to suppress it.

On the other hand, many proposals have been made to use AC motors such as induction motors and synchronous motors in servo systems, such as AC servo motors to which vector control methods for induction motors are applied. The details of this method will be described later, but basically a current detector detects the current manually applied to the AC servo motor, a speed detector detects the rotation speed, and a position detector detects the rotor position. However, current control, speed control, and position control are performed by feeding these back to each other.

The present invention copes with the overall vibration of a machine tool having a spindle device consisting of a built-in motor by equipping the spindle device of the machine tool with this AC servo motor control system and a motor vibration damping function. It is something to do.

Conventionally, the induction motor of a built-in type machine tool employs vibration damping control using the above-mentioned automatic balance mechanism, and vibration damping control using the motor's servo mechanism is not performed.

When using the induction motor in a built-in type machine tool and servo-controlling the same, conventional servo control devices have the following problems.

FIG. 9 is a block diagram of a conventional AC servo motor control device. In the figure, IM is an induction motor, SS is a rotational position detector, CT is a current detector, PI is a power converter, CA is a current control amplifier, PA is a power amplifier that collectively refers to CA and PI, and CG is a three-phase current command. This is a generation circuit.

The rotational position detector SS is, for example, a rotary encoder, and is an absolute encoder that outputs an absolute phase of zero. It is also possible to output the rotational speed Wr obtained by differentiating the phase.

The power converter PI may convert alternating current to direct current with a built-in converter (not shown), and then convert the direct current to alternating current with a built-in inverter (not shown), and drive the motor with the output of the current control amplifier CA. Motor IM based on the power of the size
supply to.

The current detector CT detects the current flowing through each winding, and feeds back the detected currents iu, iv, iw to the corresponding current control amplifiers CA.

A current control amplifier CA is provided for each phase winding, and adds each detected current iu=iv・iw fed back to the corresponding current command values Iu, Iv, Iw, amplifies the result, and outputs the power converter. Send to PI.

The three-phase current command generation circuit CG generates the current amplitude command I and the slip frequency W of the difference between the slip frequency command ws and the rotational speed wrO.
The current commands IuIv and Iw are generated based on the current commands IuIv and Iw.

FIG. 10 is a wiring diagram of a conventional excitation coil. As shown in the diagram, there are four U-phase Koinope UI, U2U3, U,
are all connected in parallel and connected to the power converter PI. The V-phase and W-phase are also connected in exactly the same way.

Therefore, the current for each phase is detected at once by the current detector CT and fed back to the current control amplifier CA to collectively control the current for each phase.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, measures to suppress vibration itself such as passive vibration damping mechanisms and active vibration damping mechanisms cannot completely relieve the unbalance caused by fluctuations in the slave side load in the passive type. Another problem with the active type is that it makes the damping mechanism extremely complex and expensive.

Also, in the case of an AC servo motor, the control device connects the excitation coils of each phase in parallel as described above and performs collective control.
There is a disadvantage that it is not possible to perform even delicate vibration control (vibration damping).

The purpose of the present invention is to improve the conventional AC servo motor control method and provide a motor vibration damping function in addition to the AC servo control function, thereby increasing the vibration of machine tools with built-in spindle motors. The object of the present invention is to provide a spindle device for a machine tool that can be restrained with precision.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle configuration of the present invention.

The present invention provides a main shaft (8) on which a processing tool (T) is attached to the tip.
A main spindle device of a machine tool, which is integrally configured with a rotor (6) of an electric motor (M), and includes a rotational position detector (SS) that detects the rotational position and rotational speed of the main spindle, and a rotational position detector (SS) that covers the main spindle. A vibration detector (VT) is arranged on the outer wall of the housing (3) and detects vibrations caused by the spindle itself and the processing tool, and a detection signal (
The present invention is characterized by comprising a vibration damping control device (1) that controls the excitation intensity of each phase current (I) supplied to the induction motor by feeding back αθr) and suppresses the vibration.

In the figure, 4.7 is a bearing, and 5 is a stator coil.

The vibration damping control device (1) for a spindle device of the present invention, as shown in the basic configuration in FIG. Based on the vibration (α) detected by the power amplifier (PAI to PAN) connected to each line and the vibration detector (VT) that detects the vibration of the spindle device, the phase (θ) of the current supplied to each phase is determined.
m) and amplitude (m) are set in advance so that vibration of the spindle device is minimized, and the current control method i (C
C), the phase and amplitude input from the current control means, and the rotational position signal (θ'') detected by a rotational position detector (SS) that detects the rotational position and rotational speed of the main shaft. comprising vibration damping modulation means (MC, ~MC,) for supplying modulated each phase current to each power amplifier,
The vibration of the system is controlled to a minimum value by sequentially changing the phase and amplitude of the excitation current supplied to each phase winding for each excitation coil, and moving the changes over time in synchronization with the rotational position signal. It is characterized by the following.

Specifically, according to the present invention, in a spindle device of a machine tool in which a rotary spindle on which a processing tool is mounted at the tip is constituted by a rotor of an electric motor, electric power is provided to supply an amplified current for each phase winding of the electric motor. an amplification means; a current control means for controlling the magnitude and phase of the current supplied to each phase of each power amplification means based on the vibration detected from the housing of the rotating main shaft so that the vibration is as small as possible; and vibration damping modulation means for sequentially supplying modulated phase currents to each of the power amplification means based on the magnitude and phase of the current output from the control means and the rotational position signal of the rotating main shaft. A spindle device for a machine tool having a vibration damping function is provided.

[For production]

In the vibration damping control device for a spindle device of the present invention, in an induction motor or a synchronous motor, the excitation coils, which have conventionally been connected in parallel and controlled collectively, are individually controlled as shown in FIG. Apply the same control to each coil as when connected.

On the other hand, the centrifugal force caused by the misalignment of the centers of gravity of the main shaft, rotor, and processing tool changes its magnitude depending on the motor rotation speed, and is generated in the radial direction while moving at the same rotation speed as the motor rotation speed. At a certain moment and at a certain rotational angle position, the motor's excitation current is controlled to generate an attractive force between the rotor and stator of the same magnitude and opposite direction as the centrifugal force, and to make this attractive force equal to the rotational speed of the motor. When moving at rotational speed, centrifugal force and suction force cancel each other out, eliminating vibrations caused by centrifugal force.

Furthermore, when the magnitude of the centrifugal force changes, the magnitude of the suction force is also changed in accordance with the magnitude of the centrifugal force.

In other words, the current applied to the excitation coil is modulated to an excitation intensity that is synchronized with the rotation of the rotor and has a magnitude and phase difference commensurate with the centrifugal force, in a manner that is superimposed on the individual control of each coil described above. As a result, the suction force changes in the circumferential direction, and rotational force is obtained while canceling centrifugal force.

〔Example〕

FIG. 3 is a block diagram of an embodiment of the vibration damping control device used in the spindle device of the present invention. In FIG. 3, the same components as in the prior art are given the same reference numerals. In the figure, VT
is a vibration detector, and PC is an allocation phase and current control means.
The amplitude command generation circuit and MC are a vibration damping modulation circuit.

As described above, the mechanical structure of the induction motor remains the same, but as shown in FIG. 4, the lead wires are simply taken out for each pole of the winding. Therefore, as shown in the figure, the number of current detectors, power converters, current control amplifiers, vibration damping modulation circuits, etc. is equal to the number of poles (four in this embodiment). That is, CT, ~
CT is a current detector, Pl, -Pl is a power converter, C
A 1 to CA t are current control amplifiers, MC, to MC are vibration damping modulation circuits, and four sets are provided. However, it is not necessary to use a power converter that is 4 times as powerful as it is;
Just set up a stand.

In this way, the control device has a structure in which power converters, etc. are connected in parallel as many as the number of poles, and the current command value supplied to these is multiplied by a command value for the purpose of damping vibration (vibration control command value). do.

As will be explained later in FIG. 6, the vibration damping command values for each exciting coil are distributed sinusoidally around 1 in the circumferential direction so that the vibration at the target location is minimized, and the rotation of the rotor is Proceeds with a phase difference. The amplitude coefficient and phase difference of the sine distribution are adjusted by learning control in a short time from the start of rotation, and optimization can be continued even during rotation.

FIG. 5 is a block diagram of an embodiment of the vibration damping modulation circuit of FIG. 3. In FIG. 5, MT is a multiplier, AD is an adder, AMP is an amplifier, and OSC is a sine wave oscillator that oscillates N types of sine waves shown in FIG. 6(C). In this case, the sine wave oscillator ○sc has a damping phase/amplitude command generation circuit PC.
The phase θm and amplitude coefficient m are input from , and the rotational position signal θr detected by the rotational position detector SS is inputted,
Outputs N types of sine waves as shown in the following formula.

5in (θγ+θm+(2π/N)Xi) −ri)
Here, N is the number of excitation coils (N=12 in this example)
and i is an integer from 0 to (N-1).

When the oscillator OSC outputs equation (1) for each set from i=Q to 11, each multiplier MT multiplies the amplitude coefficient m, and the adder AD outputs the current of each phase from the current command generation circuit CG. Command values Iu, Iv.

Jw is added. As a result, for example, the following equation is obtained for the U phase.

Ium = Iu (1+m -5in(θr+θm+(
2π/12) Xl))...(2) Here, u1 is 1=0, Iu2 is 1=3, and Iu.

is i=5, and Ium is 1=9.

Phase (2) and phase W can also be determined in exactly the same manner.

FIGS. 6(a), (b), and (c) are explanatory diagrams of the basic operation of the circuit shown in FIG. In (a), the vibration damping modulation circuit MC receives U from the three-phase current command generation circuit CG.

When receiving three-phase alternating current of V and W phases, Iu+ to IWa are outputted by the specific circuit shown in FIG. 5 based on the rotational position signal θr, phase θm, and amplitude coefficient m.

In (b), if there are three phases U, V, and W, and each phase has four sets, there will be 12 excitation coils as shown.

That is, there are 12 excitation coils U, ~U4, ■, ~V49w1~w4.

(C) is an expanded version of (b), with U and V.

It is a figure explaining modulation of W. If the current values of each phase U, V, and W are modulated as shown in the figure to give them strengths and weaknesses (amplitude coefficient m), a strong attractive force X will be generated in the modulated excitation coil even in the same U phase, and the rotor will It is drawn to the side with stronger suction and rotates. However, as it is, the attraction force X is biased in one direction.
It is clear that vibrations are generated.

In the present invention, in order to rotate the suction force, the modulation curve as shown in (C) is moved in synchronization with the rotational position θr detected by the rotational position detector ss or the rotational speed wr obtained by differentiating this. It is in.

On the other hand, vibration of a motor shaft is generally caused by centrifugal force caused by a shift in the center of gravity. Therefore, if suction force is applied in a direction that cancels out this centrifugal force, the force relationship will be canceled out and vibrations should be suppressed. Therefore, in the present invention, as described above, by moving the modulation curve in synchronization with the rotational speed wr and rotating the suction force, the centrifugal force is always canceled out and vibrations are suppressed.

FIG. 7 is a block diagram of an embodiment of the damping phase/amplitude command generation circuit PC shown in FIG. 3.

Here, when determining the phase θm and amplitude coefficient m to be supplied to the vibration damping modulation circuit MC, there are two cases in which the rotational unbalance caused by the misalignment between the center of the shaft and the center of gravity is known in advance; It is divided if it is not clear. In the former case, the phase θm is fixed, and the amplitude coefficient m changes in proportion to the rotational speed wr obtained by differentiating the rotational position signal θr.

In the latter case, for example, there is no room to detect rotational imbalance due to production efficiency, or rotational imbalance is caused by an additional object such as a tool. in this case,
Scan the table with the phase θm in the range of O to 2π and the amplitude coefficient m in the range of 0 to 1 to find the minimum vibration of 6m.
and search m.

This circuit is a circuit that inputs the vibration α of the motor detected by the vibration detector VT, and sends the phase θm and amplitude coefficient m obtained by learning control for the above two cases to the vibration damping modulation circuit MC.

TB is a table storing various combinations of phases θm and amplitude coefficients m, as shown in FIG. 8, and is stored in the ROM. SC is a scanning means for scanning the phase θm and amplitude coefficient m of the table TB, and outputs the phase θm and amplitude coefficient m as the scanning result.

MO and C are mode control circuits, which are means for switching between a mode for determining the optimum 6m and m for the latter case described above by learning control before actual vibration measurement, and a mode for performing actual vibration control. Therefore, when the rotational imbalance is not known, the switch sw,
, sw, are set on the scanning means side (contact a side) to scan the phase θm and amplitude coefficient m of the table in advance, and sequentially give these values to the vibration damping modulation circuit MC, so that the vibration A of the spindle device is the smallest. Find the phase θm and amplitude coefficient m when The obtained 6m and m and vibration A are the holding circuit HOL
is maintained. Note that the vibration A is a value obtained by integrating vibrations at fixed time intervals by the vibration calculation circuit VC.

Next, the switches sw, , sw2 are set to the contact side, and the set phase θm and amplitude coefficient m are applied to the damping modulation circuit MC.
to perform actual vibration control.

On the other hand, if the rotational unbalance becomes large due to some external factor such as a tool change, and the vibration of the spindle device becomes large, the integral value B of the vibration α generated at this time is determined by the vibration calculation circuit VC, and the comparator COM Compare with the minimum value A of vibration determined in advance.

In this case, if the vibration B is smaller, there is no need to change the phase θm and the amplitude coefficient m. However, if vibration B is larger, the mode control circuit MOC switches the switches sw, , sw
, is set to the contact a side, and the table TB is scanned again to find the minimum value of the vibration of this system as described above.

Then, the switch is set to the contact side again to perform vibration control.

Note that the holding circuit HOL may be any holding circuit that compares the previous value and the current value and holds the smaller value.

FIG. 8 is an example of a table storing the relationship between θm and m described above, and is stored in the ROM. The horizontal axis is 0 m1, and the vertical axis is the amplitude coefficient m. The range of θm is 0 to 2π, and the range of m is 0 to 1.

All the machining tools T used in the present invention are mounted on the spindle 8 in advance and rotated, and the values of m and θm are registered in the storage means ME (Fig. 3) for each machining tool by the aforementioned learning control. . During actual machining, the damping phase and amplitude command generation circuit PC stores m and θm of the corresponding tool from the storage means ME based on a tool change command from the NC device of the machine tool.
There is also a method of obtaining the value of and immediately sending it to the vibration damping modulation circuits MC, ~MC,. In this way, there is no need to perform learning control every time a tool is replaced, and quick control is possible.

〔Effect of the invention〕

As explained above, according to the present invention, the vibration of the spindle device of a built-in motor type machine tool can be accurately suppressed using electrical means with a simple structure, without adding a mechanical vibration damping device with a complicated structure. can.

In addition, when a machining tool is attached to the spindle or a machining operation is performed, vibration can be suppressed in a short time from the start of rotation, even if there is no prior knowledge of the unbalance of the system and the vibrations caused by it. It is possible to respond quickly even when the load on the device changes.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of the present invention; FIG. 2 is a basic configuration diagram of the vibration damping control device of the present invention; FIG. 3 is a block diagram of an embodiment of the vibration damping control device of the present invention; Excitation coil connection diagram of the present invention; FIG. 5 is a block diagram of an embodiment of the vibration damping modulation circuit of FIG. 3; FIGS. 6(a), (b), and (C) are detailed explanatory diagrams of the present invention; 7 is a block diagram of an embodiment of the damping phase/amplitude command generation circuit of FIG. 3, FIG. 8 is an example of the table of FIG. 7, and FIG. 9 is a block diagram of a conventional control device, and , FIG. 10 is a conventional excitation coil wiring diagram. (Explanation of symbols) IM...Induction motor, CT...Current detector, P
A...Power amplifier, PI...Power converter, CA
...Current control amplifier, MC...Vibration damping modulation circuit, CC
...Current control means, PC...Vibration suppression phase/amplitude command generation circuit, CG...3
Phase current command generation circuit, VT...vibration detector, SS...rotational position detector, ME...storage means, 1... vibration damping control device,
2...Cutting blade, 3...Housing, 4
．． 7...Bearing, 5...Stator, 6...
Rotor, 8...Main shaft, T...Processing tool. U-phase coil Excitation coil wiring diagram of the present invention Fig. 4 Block diagram of an embodiment of a UjJ vibration damping modulation circuit Fig. (b) Episode O

Claims (1)

[Scope of Claims] 1. In a spindle device of a machine tool in which a rotary spindle on which a processing tool is mounted at the tip is constituted by a rotor of an electric motor, power amplification means supplies an amplified current to each phase winding of the electric motor. a current control means for controlling the magnitude and phase of the current supplied to each phase of each of the power amplification means based on the vibration detected from the housing of the rotating main shaft so that the vibration is minimized; and the current control means and vibration damping modulation means for sequentially supplying modulated phase currents to each of the power amplifying means based on the magnitude and phase of the current output from the rotary main shaft and the rotational position signal of the rotating main shaft. A spindle device for machine tools that has a vibration damping function. 2. The current control means controls the magnitude and phase data of the current to be supplied to each phase of each of the power amplification means in order to minimize rotational vibration caused by unbalance of the processing tool mounted on the rotating main shaft. Register it in the storage means in advance,
2. The machine tool having a vibration damping function according to claim 1, wherein the machine tool is configured to read the corresponding current magnitude and phase data from the storage means based on a machining tool exchange command of the machine tool and supply them to each of the power amplification means. main shaft device.