JPH1169703A - Pre-load variable method for bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pre-load variable method for bearing which is freely adjustable for the pre-load by increasing or decreasing a supply current to a motor, in response to the size of the pre-load without providing a hydraulic means. SOLUTION: This method comprises two bearings, respectively bearing a main shaft 1 at both the end portions of a main shaft 1, an outer frame constituted with a frame 7 and a bracket 8, a main shaft 1 supported freely rotatably by this outer frame through the bearings 5, 6, a rotor 2 mounted on the main shaft 1, and stator 3 fixed to a frame 7 via a slight gap facing opposite the rotor 2. In this case, a stator 3 and a rotor 2 have tapered surfaces respectively, and a gap 4 is created between these tapered surfaces, or a deviation δis provided between the center attaching positions of the stator 3 and the rotor 2 in the axial direction, a motor current is adjusted and the magnetic thrust between the stator 3, and the rotor 2 is varied in response to the rotation of the rotor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for varying the preload of a bearing of a spindle unit for smoothing the rotation of a main shaft, especially at a high speed.

[0002]

2. Description of the Related Art In general, for example, a bearing of a spindle unit needs to be appropriately preloaded in the axial direction in order to obtain rotational accuracy and proper rigidity of a main shaft. In order to increase the rigidity, a high preload is required, and when the main shaft is rotated at a high speed, a relatively low preload is required so as not to apply an excessive load to the bearing. Therefore, with the conventional spindle unit, the preload is set low from the beginning to prevent seizure during high-speed rotation, and the preload of the bearing is made variable using hydraulic pressure to prevent seizure during high-speed rotation. And securing the rigidity.

[0003]

However, in the prior art, if the preload is set low from the beginning, machining work on the spindle can be performed at high speed rotation, but the rigidity of the spindle is insufficient at low speed rotation. Then, there was a problem that the actual machining operation could not be performed. The method of making the preload of the bearing variable using hydraulic pressure not only complicates the structure of the spindle unit but also requires a separate hydraulic device.
Here, the present invention provides a method for varying the preload of a bearing that allows the preload to be freely adjusted by increasing or decreasing the current supplied to the motor in accordance with the magnitude of the preload without providing hydraulic means. Aim.

[0004]

According to a first aspect of the present invention, there is provided an apparatus comprising two bearings for rotatably supporting a main shaft at both ends of the main shaft, a frame and a bracket. Outer frame, a main shaft rotatably supported on the outer frame via bearings, a rotor mounted on the main shaft, and fixed to the frame via a slight gap in opposition to the rotor. In a spindle unit including a stator, a gap surface where the stator and the rotor face each other is formed in a tapered shape,
A motor current is adjusted, a magnetic thrust between the stator and the rotor is changed in accordance with the rotation of the rotor, and an arbitrary amount of magnetic thrust is generated in an axial direction of the main shaft. This is a preload variable method.

As described above, according to the present invention, by adjusting the current supplied to the motor to change the magnetic flux density of the stator, the preload of the bearing can be freely varied to an arbitrary value. be able to.

According to a second aspect of the present invention, there is provided a spindle unit including a bearing for rotatably supporting a main shaft, a bracket for fitting the bearing, and a frame for fixing the stator. The center mounting position is shifted, the motor current is adjusted, the magnetic thrust between the stator and the rotor is changed in accordance with the rotation of the rotor, and an arbitrary amount of magnetic thrust is generated in the axial direction of the main shaft. This is a method for varying the preload of a bearing.

Thus, according to the present invention, there is a remarkable effect that a preload proportional to the motor current is applied by displacing the mounting positions of the stator and the rotor. That is, in the present invention, the preload applied to the bearing is generated by using the magnetic thrust generated between the stator and the rotor of the motor to change the magnetic flux on the gap surface. Therefore, rigidity can be secured and high-speed rotation can be performed. In addition, a great effect of not requiring another device such as a hydraulic measure or a new structure is recognized.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. In all the drawings, the same reference numerals represent the same or corresponding members. FIG. 1 is a side sectional view of a spindle unit showing the structure of Embodiment 1 of the present invention.

A load-side bearing 5 and a non-load-side bearing 6 are arranged on both sides of the main spindle (spindle) 1, and are supported in a freely rotatable manner. Each of the bearings 5 and 6 is constituted by an angular bearing, but other bearings can be used. A stator 3 fixed to the frame 7 and a rotor 2 fixed to the main shaft 1 are provided between the bearing 5 on the load side and the bearing 6 on the non-load side, and a gap 4 is provided between the stator 3 and the rotor 2. And the rotor 2 can rotate freely without contacting each other. In the case of FIG. 1, the gap 4 between the stator 3 and the rotor 2 is formed in a tapered shape.

(Embodiment 2) FIG. 2 is a side sectional view of a spindle unit showing the structure of Embodiment 2 of the present invention. In this embodiment, the gap 4 between the stator 3 and the rotor 2 has a cylindrical shape but is not tapered and is opposed to each other in parallel as compared with that of FIG. The rotors 2 and the rotor 2 are mounted so that their center positions in the longitudinal direction of the cylindrical shape are not the same but are slightly shifted by [the shift length δ of the center]. Other configurations are the same as those of the first embodiment.

Next, how to apply a preload in the first and second embodiments of the present invention will be described with reference to FIGS. 3 (a) and 3 (b). FIG. 3A shows the case of the structure of FIG. 1, and FIG. 3B shows the case of FIG. In the case FIG. 3 (a), the magnetic attractive force F _G of the stator 3 and the rotor 2 caused by the magnetic flux of the tapered gap 104 is generated perpendicularly to the gap 4. Thereby, the magnetic attraction force F _G can be divided into a magnetic thrust F _A for pulling the rotor 2 in the axial direction and a magnetic radial force F _R. The magnetic thrust F _A is transmitted through the main shaft 1 and acts on the bearing inner ring of the bearing 5 on the load side, and acts as a preload for the front bearing 5. The magnetic radial force F _R has a pair of magnetic poles, and the two directions generated in the corresponding portions are offset by the opposing magnetic radial forces F _R and can be ignored as the characteristics of the motor.

[0012] In case of FIG. 3 (b), since the center of the stator 3 and the rotor 2 are shifted by [delta], the magnetic attraction force F _G of the stator 3 and the rotor 2 caused by the magnetic flux of the gap 4, FIG. 3 ( occurs obliquely as in the case of a), it can be divided into magnetic thrust F _a to pull the magnetic thrust F _R and the rotor 2 of the rotor 2 to the rotational direction in the axial direction. This magnetic thrust F _A is similarly transmitted along the main shaft 1 and acts on the bearing inner ring of the bearing 5 on the load side to act as a preload for the bearing 5 on the load side.

[0013] In both cases of FIGS. 3 (a) and 3 (b), the rigidity of the main shaft 1 is determined by the preload of the bearing 5 of the load side, by changing the magnetic attractive force F _G,
It is possible to make the preload of the bearing variable, that is, to make the rigidity variable. In other words, by changing the magnetic flux density on the gap surface according to the load condition, lowering the magnetic flux density on the gap surface at low load and increasing the magnetic flux density on the gap surface at high load to change the preload of the bearing, Can be adjusted to an appropriate one.

[0014]

As described above, according to the present invention, the preload of the bearing can be varied by adjusting the motor current based on the unique configuration conditions of the stator and the rotor and changing the magnetic flux density of the stator. It is possible to achieve a special effect that it becomes possible. If the rigidity of the spindle is required during machining of the workpiece, the preload can be increased by increasing the magnetic flux density, and the magnetic flux density can be reduced during high-speed rotation to reduce the preload of the bearing to prevent seizure. A noticeable effect is also observed.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a spindle unit according to a first embodiment of the present invention.

FIG. 2 is a side sectional view of a spindle unit according to a second embodiment of the present invention.

FIGS. 3A and 3B show an operation in the first and second embodiments of the present invention, and FIG. 3A is an explanatory diagram showing a vector analysis of generation of a preload in the first embodiment of the present invention; FIG. Explanatory diagram showing vector analysis of generation of preload in Embodiment 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Main shaft 2 Rotor 3 Stator 4 Gap surface 5 Load-side bearing 6 Non-load-side bearing 7 Frame 8 Bracket 9 Center displacement [length δ] F _A Magnetic thrust for pulling rotor 2 in the axial direction F _G Magnetic attraction F _R magnetic radial force [The magnetic poles are formed in pairs and are canceled out at the corresponding parts]

Claims (2)

[Claims] 1. Two bearings rotatably supporting a main shaft at both ends of a main shaft, an outer frame constituted by a frame and a bracket, and a main shaft rotatably supported by the outer frame via bearings. A spindle unit comprising a rotor mounted on the main shaft thereof, and a stator fixed to the frame with a slight gap facing the rotor, wherein a gap surface on which the stator and the rotor face each other is formed. Forming a tapered shape, adjusting the motor current, changing the magnetic thrust between the stator and the rotor in accordance with the rotation of the rotor, and generating an arbitrary amount of magnetic thrust in the axial direction of the main shaft. A method for varying the preload of a bearing, characterized in that: 2. A spindle unit comprising a bearing for rotatably supporting a main shaft, a bracket for fitting the bearing, and a frame for fixing a stator, wherein a displacement is provided at an axial center mounting position between the main shaft of the stator and the rotor. Adjusting the motor current, changing the magnetic thrust between the stator and the rotor in accordance with the rotation of the rotor, and generating an arbitrary amount of magnetic thrust in the axial direction of the main shaft. Variable bearing preload method.