JPH04244771A - Machine tool spindle driving system employing switching of winding od synchronous motor - Google Patents

Abstract

PURPOSE:To realize spindle driving system for machine tool in which the rotor of a motor is not heated and high speed rotation and low speed heavy cutting are realized without requiring a reduction mechanism. CONSTITUTION:High speed rotation and low speed heavy cutting are realized by driving a spindle through a permanent magnet synchronous motor and switching the ampere turn of a stator winding (switching the excitation between U1-W1, U2-W2 or U3-W3). Since secondary current does not flow through a rotor no copper loss is produced and thereby the rotor is not heated. Consequently, the spindle coupled with the rotor shaft and the rotor shaft are protected against thermal expansion resulting in enhancement of machining accuracy.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle drive system for machine tools.

0002

[Prior Art] Conventionally, in order to drive the main axis of a machine tool,
An induction motor is used. Conventional induction motors that drive the main shaft of machine tools have a low output torque at the base rotation speed (1500 rpm), so a reduction mechanism such as a pulley is used to reduce the output of the motor to drive the main shaft. In machine tools, the load on the spindle varies greatly between cutting and non-cutting, and heavy cutting is performed at low rotation speeds. In particular, when machining a workpiece with a large diameter using a lathe, the main shaft must be driven at a low speed and high torque must be generated in order to bring the circumferential speed of the workpiece to the set cutting speed. Therefore, a reduction mechanism is used to reduce the speed of the electric motor to drive the main shaft at low speed and high torque.

[0003] When the output of the electric motor is reduced using a reduction mechanism to drive the main shaft, vibrations and noise are generated. In particular, if a speed reduction mechanism uses pulleys and a belt, there is a problem in that the belt slides and a speed difference occurs on the main shaft, causing waviness, and if a timing belt is used, there is a problem in that noise is generated.

In order to reduce these vibrations and noises, a method has been considered in which the torque of the main shaft drive motor is electrically increased to directly drive the main shaft without using a speed reduction mechanism. In this case, the base rotation speed is changed by changing the number of turns of the primary winding of the induction motor that drives the main shaft, and by increasing the slippage, the secondary current flowing through the conductor on the rotor side is increased even with the same current, and the output torque is increased. A method is being adopted to increase the That is, when performing low-speed heavy cutting, the number of turns of the primary winding of the induction motor is increased, and the secondary current on the rotor side is increased with the same primary current, thereby increasing the output torque.

[0005]

[Problem to be Solved by the Invention] When the number of turns in the primary winding of an induction motor is increased to increase the secondary current on the rotor side, the copper loss in the rotor increases as the square of the current. This will cause the temperature of the motor shaft to rise. In addition, the winding resistance of the stator also increases due to the increase in the number of windings, and even if the primary current is the same, copper loss increases by the increased resistance, causing a rise in the temperature of the motor. Since the stator windings are stationary, they can be cooled using methods such as liquid cooling, but since the rotor is rotating, similar methods cannot be used, and there is no low-cost and efficient cooling method.

The heat generated by the rotor is transmitted to the motor shaft, which has negative effects such as increasing the temperature of the inner ring of the bearing, reducing the bearing clearance, and accelerating the deterioration of the grease. In particular, the "built-in motor" type, in which the motor shaft is directly fixed to the main shaft,
The heat generated by the rotor reduces the reliability of the bearing and causes thermal expansion (particularly axial displacement) of the spindle, causing dimensional errors in machined products, leading to a decrease in processing accuracy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a main shaft drive system for a machine tool that does not generate heat from the rotor of an electric motor and is capable of high-speed rotation and low-speed heavy cutting without the need for a reduction mechanism.

[0008]

[Means for Solving the Problems] The present invention drives the main shaft of a machine tool with a synchronous motor that generates a magnetic field with a permanent magnet, divides each phase winding of the stator of the synchronous motor into a plurality of parts, and each of the divided A changeover switch is provided to change the connection of each phase winding of the stator of the synchronous motor so that current flows only through the connection of the phase windings or only some of the windings.At low speeds, the ampere turns of the stator windings are increased, and at high speeds, the ampere turns are increased. The above problem was solved by switching the stator winding to reduce the ampere turns to generate high torque at low speeds and to achieve high speed rotation.

[0009]

[Operation] Even if the excitation current is constant, if the number of windings in each phase of the stator is increased, the base rotation speed can be lowered accordingly, and high torque can be generated even at low speeds. Furthermore, by increasing the excitation current, the generated torque can be increased. That is, by increasing the ampere turns, high torque can be generated even at low speeds. Also, by reducing the ampere turns, high speed rotation can be achieved. Therefore, it is possible to obtain a machine tool that can perform high-speed rotation and low-speed heavy cutting without driving the main shaft using a reduction mechanism. On the other hand, in a synchronous motor that uses a permanent magnet to create a magnetic field, no secondary current flows through the rotor, so heat generation on the rotor side can be kept low, thermal expansion of the motor shaft can be reduced, and the main shaft can be moved without a speed reduction mechanism. Driving directly does not reduce machining accuracy.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of an embodiment of a permanent magnet synchronous motor used in the machine tool main shaft drive system of the present invention, and a stator winding energization switching circuit diagram. In FIG. 1, 1 is a motor housing, and 2 is a liquid cooling pipe line disposed within the motor housing 1. In FIG. A motor shaft 3 is rotatably mounted within the motor housing by a bearing 12 . motor shaft 3
A rotor 6 is fixed to the rotor 6, a stator 4 is arranged around the rotor 6, a stator core 5 of the stator 4, and a rotor 6.
The rotor core 7 is constructed by laminating and bonding silicon steel plates and the like. Further, a rotary plate 11 of a detector for detecting the rotational position, speed, etc. of the motor shaft 3 is fixed to one end of the motor shaft 3, and the detection unit 10 is configured to detect the rotational position, speed, etc. of the motor shaft 3. It has become. As shown in FIG. 2, in the rotor 6, permanent magnets 8 are bonded to the outer periphery of a rotor core 7 so that the polarity changes alternately in the circumferential direction (in the case of FIG. 2, four poles are arranged). A permanent magnet holding tube made of a non-magnetic material (glass binder, stainless steel tape, etc.) is arranged on the outer periphery of the magnet 8. Further, 9 is a coil end of a stator winding wound around the stator core 5, and is connected to input terminals of U, V, and W phases via a changeover switch to be described later.

The configuration of the above-described synchronous motor is the same as that of a conventional permanent magnet synchronous motor, and the only difference is the method of energizing the stator windings.

FIG. 3 is an explanatory diagram illustrating the stator windings and the current supply positions to each winding. In this embodiment, the stator windings for each phase of U, V, and W are divided into three parts, and the input terminals U1, V
1. When power is supplied to W1, all windings UC1 to U
Current flows through C3, VC1 to VC3, WC1 to WC3,
When power is supplied to input terminals U2, V2, W2, two windings UC2, UC3, VC2, VC3, divided into each phase,
Current flows through WC2 and WC3, and input terminals U3, V3, and W
When power is supplied to windings UC3, VC3, and WC3, current flows only through windings UC3, VC3, and WC3, and the number of windings can be changed by energizing the stator windings and switching the effective windings that operate effectively. has been done. As shown in Fig. 1, the effective number of windings of the stator winding is switched by changeover switches S1, S2, and S3, which are composed of non-contact switches such as triacs, so that switching can be performed at high speed. There is. When the changeover switch S1 is turned on, the input terminals U1, V1,
A voltage for each phase is applied to W1, and as described above, all the stator windings of each phase are energized, and the motor is driven with a large number of stator windings. Also, selector switch S2
When turned on, the two windings UC2, UC3, VC2, VC3, which are divided into each phase from the input terminals U2, V2, W2,
Only WC2 and WC3 are energized, and the stator is driven with a small number of windings. Furthermore, selector switch S3
When turned on, winding UC is connected from input terminals U3, V3, W3.
3, only VC3 and WC3 are energized, and the motor is driven with the number of stator windings further reduced.

FIG. 4 is a diagram showing the output characteristics when the current flowing through the stator windings is kept constant and the number of stator windings is changed.
FIG. 5 is a diagram showing the torque characteristics at that time. The number of stator windings when the changeover switch S1 is turned on, that is, the total number of windings, is set to Z1, the number of windings when the changeover switch S2 is turned on is set to Z2, which is 1/2 of the total number of windings Z1, and the changeover switch S3. An example is shown in which the number of windings Z3 when turning on is Z1/4.

The output P of the motor is proportional to the total magnetic flux, the number of stator windings Z, and the excitation frequency up to the base rotation speed, and the total magnetic flux is constant, so the changeover switch S1 is turned on and the number of stator windings is changed to Z1. , the output P rises rapidly in proportion to the rotational speed N and reaches the base rotational speed N1, and the output torque T at this time generates a large torque T1 as shown in FIG. will occur. Furthermore, when the changeover switch S2 is turned on and the effective number of turns of the stator winding is set to Z2, the base rotation speed N2 increases and the output torque T2 decreases, but high-speed rotation is enabled by the increase in the base rotation speed. . Furthermore, when the changeover switch S3 is turned on and the effective number of turns of the stator winding is reduced to Z3, the rise of the output P becomes gradual, the base rotation speed N3 increases, and the output torque T3 of the motor increases.
Although it becomes small as shown in FIG. 5, it enables high-speed rotation.

By switching the number of stator windings in multiple stages in this way, high-speed rotation and low-speed high torque can also be generated.If this electric motor is used to drive the main shaft of a machine tool, high-speed rotation and low-speed heavy cutting can be achieved. enable. Moreover, since no secondary current flows to the rotor side and no copper loss occurs, the rotor does not generate heat due to copper loss.Even if the motor shaft is connected directly to the main shaft, little heat is generated, so the motor shaft has little thermal expansion and does not reduce bearing clearance.
Also, the deterioration of the grease will not be accelerated. moreover,
Even in the case of a "built-in motor" type in which the motor shaft 3 is used as the main shaft, the machining accuracy is improved because the thermal expansion of the motor shaft is small.

In the above embodiment, high-speed rotation and low-speed heavy cutting were made possible by changing the number of stator windings into multiple stages, but it is possible to change the connection method of each stator phase winding without changing the number of stator windings. This enables high-speed rotation and low-speed high torque (low-speed heavy cutting).

FIG. 6 is a switching circuit diagram for one phase (U phase) of the method of switching the connection method of each phase winding of the stator according to the second embodiment of the present invention, and the other phases (V, W) are similarly connected. It has a circuit configuration. When the changeover switch S11 is turned on, the divided stator windings of each phase are connected in parallel as shown in FIG. 7, and when the changeover switch S12 is turned on, some of the windings are connected in parallel as shown in FIG. They are connected in parallel, and other windings are connected in series to the parallel circuit. Furthermore, when the changeover switch S13 is turned on, the windings are connected in series as shown in FIG.

When the same voltage is applied to the windings, when the changeover switch S11 is turned on and the winding connections shown in FIG. Generates low speed and high torque. Furthermore, when the changeover switch S12 is turned on and the connection shown in FIG. 8 is made, the current decreases and medium-speed medium-torque is generated. Further, when the changeover switch S13 is turned on, the current is further reduced, and high speed and low torque is generated.

As described above, high speed rotation and low speed high torque (low speed heavy cutting) can also be achieved by switching the winding connections of each phase of the stator.

[0020] In the above embodiment, an example was shown in which the stator winding was configured with a star connection, but the present invention can be practiced with a similar configuration in the case of a delta connection.

[0021]

[Effects of the Invention] In the present invention, a synchronous motor that creates a magnetic field with a permanent magnet is used as the motor that drives the main shaft, and high-speed rotation and low-speed high torque can be generated by switching the ampere turns of the stator winding. Therefore, by directly driving the spindle with the electric motor without using a speed reduction mechanism, high-speed rotation and low-speed heavy cutting can be achieved. Furthermore, since no secondary current flows to the rotor side, the temperature of the rotor does not rise due to heat generation due to copper loss, and thermal expansion of the motor shaft can be reduced, reducing the bearing clearance of the motor shaft bearing. It is also possible to suppress the deterioration of the grease. In addition, even when used as a "built-in motor" that is directly fixed to the spindle, there is no heat generation due to copper loss in the rotor, so thermal expansion in the axial direction of the spindle is small, and the reliability of the bearing is improved. Accuracy is improved and processing precision can be increased.

Furthermore, if an induction motor is used as the motor for driving the main shaft as in the past, positioning control becomes difficult and C-axis control, which determines the rotational position of the main shaft, becomes difficult, but a synchronous motor simplifies positioning control. , C-axis control can be easily performed. Furthermore, even when controlling a machine tool with a numerical control device, if the main spindle is driven by an induction motor as in the past, a special circuit for driving the main spindle is required, and other control axes such as the feed axis are A different control method had to be adopted, but if the main shaft is driven by a synchronous motor like the other feed axes as in the present invention, the control of the main shaft can be controlled with the control of other feed axes. It can be controlled in the same way, no special circuit is required for spindle control, and control is extremely simple.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a permanent magnet synchronous motor according to an embodiment of the present invention and a stator winding energization switching circuit diagram.

FIG. 2 is a diagram showing the structure of a rotor in the same embodiment.

FIG. 3 is an explanatory diagram illustrating stator windings and energization positions to each winding in the same embodiment.

FIG. 4 is a diagram showing output characteristics in the same example.

FIG. 5 is a diagram showing torque characteristics in the same example.

FIG. 6 is a switching circuit diagram for one phase (U phase) of a method of switching the connection method of each stator phase winding in a second embodiment of the present invention.

FIG. 7 is a diagram showing the winding connection state when the changeover switch S11 is turned on in the second embodiment.

FIG. 8 is a diagram showing the winding connection state when the changeover switch S12 is turned on in the second embodiment.

FIG. 9 is a diagram showing the winding connection state when the changeover switch S13 is turned on in the second embodiment.

[Explanation of symbols]

1 Motor housing 2 Liquid cooling pipe 3 Motor shaft 4 Stator 6 Rotor 8 Permanent magnet

Claims (3)

[Claims] Claim 1: A main shaft of a machine tool is driven by a synchronous motor that generates a magnetic field using a permanent magnet, and a changeover switch is provided to switch the connection of each phase winding of the stator of the synchronous motor, and at low speeds, the ampere turns of the stator winding are switched off. A machine tool spindle drive system that uses a synchronous motor winding switch to increase the ampere turns of the stator winding at high speeds, and to reduce the ampere turns of the stator windings at high speeds, generating high torque at low speeds and achieving high speed rotation. 2. A machine tool spindle drive system by switching windings of a synchronous motor according to claim 1, wherein the ampere turns are changed by switching the number of effective windings of each phase of the stator using the changeover switch. [Claim 3] Each phase winding of the stator is divided into a plurality of parts,
2. The machine tool spindle drive system by switching the windings of a synchronous motor according to claim 1, wherein the ampere turns are changed by switching each of the divided windings to series, parallel, or partially parallel using the changeover switch.