JPH10336952A - Electric servo motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make starting torque small and constant and make a zero point of a linear motion of a ball screw also constant by using angular ball bearings as for bearings for receiving thrust load of a driving shaft which is driven by a rotary motion of the motor and makes a linear motion. SOLUTION: When a nut 18 is tightened, an inner ring of an angular ball bearing 20b is just tightened from right and left and the tightening force does not reach a ball of the bearing, and therefore it does happen that the rotation of the bearing becomes tight. The angular ball bearings 20a, 20b have a taper on an inner side of an outer ring and can receive thrust load as well as radial load. In an electric servo motor of such a structure, starting torque is severalty that of the conventional type, thereby reducing the size of a plumb to be used when a power supply of the motor is lost or of an external closing device constituted of springs. Furthermore, as starting torque is constant in a motor of such a structure, the bearings can be designed and manufactured in parallel with the design and manufacture of the electric servo motor and therefore the time for delivery can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric servomotor used for a flow control device of a water turbine, and more particularly to a bearing for the servomotor.

[0002]

2. Description of the Related Art A conventional electric servomotor has a structure as shown in FIG. That is, the rotating shaft 1a of the electric motor 1 is inserted into the coupling 2, and rotational torque is transmitted to the first reduction gear shaft 3 supported by the bearings 4a and 4b via the coupling key 2a. This rotational torque is transmitted to the bearings 6a, 6 via a second gear 8 meshing with a first gear 5 attached to the first reduction gear shaft 3.
b transmitted to the second reduction gear shaft 7 supported by
The power is transmitted to the ball screw nut 11 via a fourth gear 10 that meshes with a third gear 9 attached to the second reduction gear shaft 7. The rotational torque of the electric motor 1 is converted into a linear motion thrust by the ball screw nut 11 and the ball screw 12 screwed to the nut, and the flow control device of the water turbine is passed through the rod end 13 and the pin 14 attached to the end of the ball screw 12. Thrust is transmitted to The portion of the flow control device that receives the reaction force is the electric servomotor bearing portion, and conventionally uses tapered roller bearings 15a and 15b. That is,
The inner rings of the tapered roller bearings 15a and 15b are fitted to both ends of the main shaft 16 integrated with the ball screw nut 11 and bolts, the outer rings of the tapered roller bearings 15a and 15b are inserted into the inner diameter of the bearing case 17, and the nut 18 is inserted. Tighten,
The rotation stopper 19 prevents the nut 18 from loosening.

[0003]

In the conventional electric servomotor having the above-described structure, the starting torque of the electric motor 1 greatly varies depending on the degree of tightening of the nut 18, and the starting current varies. When the nut 18 is lightly tightened, the starting torque is reduced and the starting current is constant.
By doing so, the backlash increases, that is, play occurs in the tapered roller bearings 15a and 15b, and a difference occurs in the zero point of the linear motion of the ball screw 12.

On the other hand, in order to safely stop the water turbine even when the power of the electric motor 1 is lost, it is necessary to reverse the ball screw 12 by an external force such as a weight or a spring. With an electric servomotor in which the starting torque of the rotating shaft fluctuates and the zero point of the linear motion of the ball screw is not constant, the flow rate adjusting device of the water turbine cannot be operated properly.

Accordingly, an object of the present invention is to provide an electric servomotor in which the starting torque is small and constant, and the zero point of the linear movement of the ball screw is also constant.

[0006]

In order to achieve the above object, an electric servo motor according to the present invention uses an angular ball bearing as a bearing for receiving a thrust load of a linearly driven drive shaft driven by the rotation of the electric motor. And

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. Except for the tapered roller bearings 15a and 15b, the structure from the electric motor 1 to the detent 19 is the same as the conventional one shown in FIG. In the embodiment of the present invention, angular ball bearings 20a and 20b are used instead of the conventional tapered roller bearings 15a and 15b. An adjustment liner 21 for forming a step on the main shaft 16 and adjusting the axial position of the angular contact ball bearing 20b.
And is fixed with a nut 18.

In the electric servo motor having such a configuration, when the nut 18 is tightened, the force is only sufficient to tighten the inner ring of the angular contact ball bearing 20b from the left and right and does not reach the bearing balls, so that the rotation of the bearing is tight. Never be. Angular contact ball bearings are tapered on the inner diameter side of the outer ring and can receive not only radial loads but also thrust loads. In the embodiment of FIG. 1, the rightward thrust load of the main shaft 16 is applied to the angular ball bearing 2.
0a, and a leftward thrust load is received by the angular ball bearing 20b.

The starting torque of the electric servomotor of this embodiment is reduced to a fraction of that of the conventional servomotor, and the external closing device using a weight or a spring when the power of the motor is lost can be reduced. Further, conventionally, the specification of the external closing device is determined after measuring the torque at which the electric servomotor starts to move. Design
It can be manufactured and the delivery time can be shortened.

[0010]

The electric servo motor of the present invention uses an angular ball bearing instead of the conventional tapered roller bearing.
The starting torque is small and constant, and the zero point of the linear movement of the ball screw is also constant.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electric servomotor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional electric servomotor.

[Explanation of symbols]

1. Electric motor, 1a Rotary shaft, 2. Coupling,
2a: coupling key, 3, 7: reduction gear shaft, 4
a, 4b, 6a, 6b ... bearing bearings, 5, 8,
9, 10 ... gear, 11 ... ball screw nut, 12 ...
Ball screw, 13… Rod end, 14… 15a,
15b: tapered roller bearing, 16: main shaft,
17: Bearing case, 18: Nut, 19: Detent, 20a, 20b: Angular contact ball bearing, 21: Adjusting liner.

Claims (1)

[Claims] An electric servomotor for converting a rotary motion of a motor into a linear motion of a drive shaft and driving an external device.
An electric servomotor using an angular ball bearing as a bearing for receiving a thrust load of the drive shaft.