JPS5996846A - Low vibration motor - Google Patents

Abstract

PURPOSE:To shorten the starting time of a motor by varying the size of an air gap between a rotor and a stator at the starting time and the normally rotating time of an armature, thereby increasing the starting torque. CONSTITUTION:Since a threaded part 12a of a handle nut 12 and a nut 11c are engaged when the handle nut 12 is rotated in one direction, a coupling member 11b moves leftwardly. Accordingly, a stator slide contact member 10 and a stator 9 also move leftwardly. An air gap between the rotor 6 and the stator 9 varies due to the movement of the stator 9. The air gap is reduced to increase the starting torque at the starting time, and the air gap is increased at the normal operation time after the starting, thereby reducing the vibration.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-vibration electric motor used in various devices that require vibration to be suppressed as low as possible.

2. Description of the Related Art Devices such as ultra-precision processing machines and ultra-precision moving tables (for example, moving tables used in LSI pattern printing devices, etc.) are extremely sensitive to vibrations due to their performance. For this reason, the electric motor that drives these devices is usually installed separately from the main body of the device, and the electric motor and the device are connected by a belt or a special vibration-damping joint to transmit power.
This prevents the vibrations of the rotor itself from being transmitted to the device. Under such current circumstances, the problem is how to suppress the vibration of the electric motor itself.

FIG. 1 is a partial sectional view of a conventional electric motor. In the figure, l is the output shaft of the motor, 1a is the load connection end of the output shaft 1, 2 is the rotor fixed to the output shaft 1, 3 is the casing of the motor,
4 is a stator fixed to the casing 3, and 5 is a bearing between the output shaft 1 and the casing 3. The rotor 2 and the stator 4 are arranged to face each other with a gap δ1 interposed therebetween, and the rotor 2 rotates when alternating current is supplied to the stator 4 to generate a rotating magnetic field.

By the way, the following matters are generally considered to be the causes of such vibrations in the electric motor itself.

(1) Dynamic imbalance of the rotor caused by non-uniformity of the material of the rotor 2, etc.

(2) Insufficient rotational accuracy of the bearing 5 of the output shaft l.

(3) 9 Fluctuations in rotational force due to eccentricity of the rotor 2 and stator 4.

(4) Insufficient machining accuracy of each part.

(5) Zero-rotation magnetic field and rotor eccentricity, that is, magnetic imbalance.

Among the above causes of vibration generation, (1) to (4) are mechanical causes. Conventional low-vibration countermeasures are mainly improvements to these problems, and have reduced the amplitude of vibrations to the order of microns (1
, 5 to 3μ). On the other hand, regarding the cause of vibration generation (5), a special electric motor is provided in which the gap δ1 between the rotor 2 and the stator 4 is increased in order to reduce this magnetic imbalance.

However, this special motor has a large air gap δ1, so it is extremely inefficient.For example, compared to a normal motor with an output of 3.7KW, a special motor of the same size has an output of 115~ This decreases to 1/1°, resulting in a severe disadvantage. On the other hand, these disadvantages also give rise to the following disadvantages. That is, in general, in devices such as ultra-precision processing machines and ultra-precision moving tables, the torque required to drive them during operation is extremely small due to the function of the device, and for example, the output torque of an electric motor of 200 to 300 W is sufficient. It is. However, when starting up the device, a considerably large torque is required due to its inertial force, and with the above-mentioned 200-300 W electric motor, it takes an extremely long time to reach a predetermined rotation speed. For example, if a 3.7 KW electric motor is used to drive a certain device, the time required to reach a rotational speed of 2000 r*pem is 5 seconds, while a 200 W electric motor takes about 92 seconds. Since the efficiency of the device is significantly reduced in such a long-time start-up, according to the above example, the low-vibration electric motor must have an output of 3.7 KW. However, a low-vibration electric motor with an output of 3.7 KW has the disadvantage that its occupied volume is several times (5 to 10 times) larger than that of a normal electric motor with the same output. As a result, in conventional low-vibration electric motors in which the air gap δ1 between the rotor 2 and stator 4 is set large, if a low-output motor is used to reduce the occupied volume, it will take a long time to start; If a large output device is used for timed activation, there will be a tradeoff in that the volume occupied will be large just for the activation time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-vibration electric motor which can solve the above-mentioned conventional problems, reduce the starting torque to shorten the starting time, and can be made compact.

In order to achieve this object, the present invention forms the outer diameter of the rotor and the inner diameter of the stator with a predetermined angle of inclination along the output shaft, so that one or both of the rotor and the stator is aligned with the output shaft. It is characterized in that it is movable along the length of the stainer, thereby changing the size of the gap between when the staining machine is started up and when it is in normal operation.

Hereinafter, the present invention will be explained based on the illustrated embodiments. FIG. 2 is a sectional view of a low-vibration electric motor according to an embodiment of the present invention. In the figure, the same parts as those shown in FIG. 1 are given the same reference numerals. Reference numeral 6 denotes a rotor fixed to the output shaft 1, and its outer diameter is maximum at the right end (in FIG. 2) of the rotor 6 and minimum at the left end. The rate of decrease in the outer diameter from the right end to the left end of the rotor 6 is constant. In FIG. 2, this change in outer diameter is shown as a linear slope. 7 is an end bracket of the electric motor, 8 is a casing fixed to the end bracket 7, and 8a is a water jacket provided on the casing 8 and through which cooling water passes. A stator 9 is installed on the inner surface of the casing 8, facing the rotor 6. The inner diameter of the stator 9 is made to match the outer diameter of the rotor 6, that is, the inner diameter at the right end of the stator 9 is the largest, the inner diameter at the left end is the smallest, and the inner diameter from the right end to the left end is The rate of decrease is the same as the rate of decrease in the outer diameter of the rotor 6. In FIG. 2, this change in inner diameter is shown as a linear slope. The stator 9 is attached to the inner surface of the casing 8 by suitable means, such as a sliding key, so that it can slide only in the axial direction of the output shaft l. A stator sliding member 1o is attached in appropriate numbers to the right end of the stator 9 and contributes to the sliding movement of the stator 9. Each stator sliding member 10
The end portion of the end bracket 7 extends outwardly through the end bracket 7. 1
Reference numeral 1 indicates a stator sliding mechanism, which is housed in a case lla fixed to an end bracket 7 of the electric motor. llb
11c is a rod-shaped or plate-shaped connecting member that connects each end of the stator sliding member 1O, and 11c is a nut attached to the connecting member 11b. A handle 12 is rotatably attached to the case lla, and a threaded portion 12a is formed at the tip of the handle 12. This threaded portion 12a is screwed into a nut 11c of the stator sliding mechanism 11.

In the electric motor having such a configuration, when the handle 12 is rotated in one direction, the threaded portion 12a and the nut 11c are screwed together, so that the connecting member 11b moves, for example, to the left in FIG. 2. Therefore, stator sliding member 10
, the stator 9 also moves to the left. The movement of the stator 9 is parallel to the output axis l. When the handle 12 is rotated in the opposite direction, the stator 9 moves in the opposite direction (to the right). Due to this movement of the stator 9, the gap between the rotor 6 and the stator 9 changes. This change will be explained with reference to FIG.

FIG. 3 is a sectional view of the rotor and stator in the gap portion. When the stator 9 is at the right end position shown by the solid line in FIG. 3, the gap size between the rotor 6 and the stator 9 is δ2. Now, if the handle 12 is rotated in a predetermined direction and the stator 9 is slid in the direction of arrow Since it is parallel to the axis, the gap size δ3 naturally increases. In this way, by rotating the handle 12, the gap between the rotor 6 and the stator 9 can be freely changed within the range of the dimensions δ2 and δ3.

Here, we will consider the effect that the change in the gap size has on the vibration of the motor. Now, assuming that the force that causes the rotor to fluctuate in its diametrical direction, that is, the radial fluctuating force 'kF (Kg), is expressed by the following equation.

F--DL (5000"T"""...(1) However, D: Outer diameter of rotor (cm) L: Length of rotor am) B: Magnetic flux density of air gap (Gauss) Δ: Gap size (μm) δ: Eccentricity between stator and rotor (μm) An example of this radial fluctuating force is calculated for a 0.75KW class electric motor (7t, so each value is an approximate value): F = -HX 10 X 6 X (5ooo)2X-
Stone T middle school 13, 57 (Kp). Since the magnetic flux density of the air gap decreases as the air gap size is increased, it is clear from equation (1) that increasing the air gap size can significantly reduce the shirasial fluctuation force. However, when the gap size is increased, the amount of electric motor protrusion decreases. For the above example, the gap size was increased by 300 μm, and the precision of each part was further improved, Δ = 600 μm,
δ=204m, B=6000X (300/600)”
= 1500 When the value of the radial fluctuation force F is calculated as Gauss, the radial fluctuation force F decreases to approximately 115.

In this way, by increasing the gap size, the radial fluctuation force, that is, the force that causes vibration, can be reduced. However, along with this, the current in the motor stator coil increases, and the heat generation of the stain motor also increases due to a decrease in efficiency, but for the former, the input is reduced in conjunction with the operation of the handle 12. For the latter case, the water jacket 8a can sufficiently prevent heat generation.

In this example, the outer diameter of the rotor and the inner diameter of the stator are increased or decreased at a predetermined ratio, and the stator is made to be able to slide along the output shaft. The starting torque can be increased to shorten the startup time, and during normal operation after the device is started, the vibration can be reduced by increasing the gap size.In the end, the low-vibration electric motor of this example is better than the conventional one. If it has the same exclusive volume as the low-vibration special electric motor, the start-up time can be shortened.
Moreover, if the activation time is the same, the dedicated volume can be reduced and the size can be reduced.

In the above embodiment, the stator is moved, but it goes without saying that the rotor may be moved, or both the stator and rotor may be moved.

As described above, in the present invention, the outer diameter of the rotor and the inner diameter of the stator are increased or decreased at a predetermined ratio, and one or both of the rotor and stator can be moved along the output shaft. The starting torque of the vibration motor can be increased to shorten the starting time, and the motor can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a conventional electric motor, FIG. 2 is a cross-sectional view of a low-vibration electric motor according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view of a rotor and a stator in a gap portion. 1...Output shaft, 6...Rotor, 9...
Group/stator, 10...Stator sliding mechanism, 11.
... Stator sliding mechanism, 11b ... Connection member, 11c ... Nut, 12 ... Handle, 12a ... Threaded part.

Claims (1)

[Claims] an output shaft; a rotor that is attached to the output shaft and whose outer diameter changes at a constant rate along one direction of the output shaft; and a rotor that is attached to the rotor through a gap and whose inner diameter A low-vibration electric motor comprising: a stator that changes at the constant rate along one direction of the output shaft; and means for moving at least one of the rotor and the stator along the output shaft. .